CA2019336C - Structure to form a load-bearing air cushion for a vehicle - Google Patents
Structure to form a load-bearing air cushion for a vehicle Download PDFInfo
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- CA2019336C CA2019336C CA 2019336 CA2019336A CA2019336C CA 2019336 C CA2019336 C CA 2019336C CA 2019336 CA2019336 CA 2019336 CA 2019336 A CA2019336 A CA 2019336A CA 2019336 C CA2019336 C CA 2019336C
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Abstract
In an air cushion load transport vehicle, an annular sealing assembly comprising an annular inflatable hanger on the underside of a load-bearing base and an annular sealing means on the underside of the hanger confines a load-supporting air cushion that is continuously supplied with compressed air during operation, Stability is promoted by a number of design features in the inflatable hanger, the annular sealing means, the flexible connection between them and the load support structure. These include means for automatically closing off flow through hanger damping eyelets during initial hanger pressurization together with means to keep the eyelets open at all operating hanger heights. Additional covered ports are provided in the outer hanger wall positioned to automatically vent if the hanger is over-inflated thereby avoiding dyanmic instability.
A check valve is incorporated into the device to prevent damage from inadvertantly inflating the hanger before the cushion is pressurized. Finally, critical relation ships between key design parameters and seal materials are defined which avoid dynamic instability of the air cushion load-bearing vehicle during operation.
A check valve is incorporated into the device to prevent damage from inadvertantly inflating the hanger before the cushion is pressurized. Finally, critical relation ships between key design parameters and seal materials are defined which avoid dynamic instability of the air cushion load-bearing vehicle during operation.
Description
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CROSS REI'ERENCE TO PREVIOUSLY ISSUED PATENT
CROSS REI'ERENCE TO PREVIOUSLY ISSUED PATENT
3 This application describes and claims a number of 4 improvements over.my previously issued patent Ser. No.
5 951360 titled "Structure to Form a Load-bearing hir 6 Cushion For a Vehicle" which issued on ~TUly 16, 1974..
7 .
BACfCGROUND OF THE INVENTION
11 'lhe cross-referenced issued patent discloses various 12 embodiments of a load-bearing air cushion device in which an 13 annular sealing assembly for confining an air cushion comprises 14 an annular hanger which inflates downwardly from a load-bearing 15 base together with a flexible resiliently yieldable annular 16 sealing means which projects downward from the annular hang er 17 into close proximity to the ground or support surface along 18 which the vehicle travels.
19 In the application of this technology to the design 20 'of practical air cushion vehicles, it was found that certain 21 combinations of design parameters are critical and must fall 22 within well defined ranges to avoid dynamic instability of the 23 loaded vehicle. Also it was found that operational advantages ' 24 accrue from separately inflating the seal hang er and the lifting 25 cushion. However, the ratio of pressures in these two components 26 must fall within defined limits. If the inflation pressure in 27 the seal hanger is too low compared to pressure in the lifting 28 cushion, the hang er will tend to collapse allowing the loaded 29 vehicle to settle to the floor. On the other hand, if the hang er 30 inflation pressure is too high the vehicle will experience dynamic 31 instability which increases in severity as this pressure is in-32 creased.
33 It is a primary objective of this invention to define and 34 claim the useful wor)ci.ng ranges of critical design parameters 35 required to avoid dynamic instability of tlu s type air cushion 36 vehicle. Structure is also described and claimed which prevents ~~i~~ ~~
1 inadvertant over-pressurization of the seal hanger at all loads 2 carried by the air cushion vehicle.
3 Another objective of this invention is to provide a 4 sealing assembly comprising an annular inflatable hang er with an annular sealing means dependent therefrom in which the annular 6 sealing means is made of relatively soft resiliently deformable 7 material of substantial vertical dimension and yet does not ex-8 pand outward radially under pressure inside the confined air 9 cushion even when this pressure is substantially greater than pressures attained with previous designs.
3 This invention relates to improvements in air or 4 fluid cushion load bearing and transport devices in which each.
5 lifting cushion is contained under the load by an encompassing 6 seal assembly comprising an upper inflatable element in combina-7 tion with a lower flexible non-inflatable element. The upper in-8 flatable element comprises a seal "hanger" made from concentric 9 opposite-facing truncated cones of fluid-tight flexible material.
11 'lhe cross-referenced issued patent discloses various 12 embodiments of a load-bearing air cushion device in which an 13 annular sealing assembly for confining an air cushion comprises 14 an annular hanger which inflates downwardly from a load-bearing 15 base together with a flexible resiliently yieldable annular 16 sealing means which projects downward from the annular hang er 17 into close proximity to the ground or support surface along 18 which the vehicle travels.
19 In the application of this technology to the design 20 'of practical air cushion vehicles, it was found that certain 21 combinations of design parameters are critical and must fall 22 within well defined ranges to avoid dynamic instability of the 23 loaded vehicle. Also it was found that operational advantages ' 24 accrue from separately inflating the seal hang er and the lifting 25 cushion. However, the ratio of pressures in these two components 26 must fall within defined limits. If the inflation pressure in 27 the seal hanger is too low compared to pressure in the lifting 28 cushion, the hang er will tend to collapse allowing the loaded 29 vehicle to settle to the floor. On the other hand, if the hang er 30 inflation pressure is too high the vehicle will experience dynamic 31 instability which increases in severity as this pressure is in-32 creased.
33 It is a primary objective of this invention to define and 34 claim the useful wor)ci.ng ranges of critical design parameters 35 required to avoid dynamic instability of tlu s type air cushion 36 vehicle. Structure is also described and claimed which prevents ~~i~~ ~~
1 inadvertant over-pressurization of the seal hanger at all loads 2 carried by the air cushion vehicle.
3 Another objective of this invention is to provide a 4 sealing assembly comprising an annular inflatable hang er with an annular sealing means dependent therefrom in which the annular 6 sealing means is made of relatively soft resiliently deformable 7 material of substantial vertical dimension and yet does not ex-8 pand outward radially under pressure inside the confined air 9 cushion even when this pressure is substantially greater than pressures attained with previous designs.
3 This invention relates to improvements in air or 4 fluid cushion load bearing and transport devices in which each.
5 lifting cushion is contained under the load by an encompassing 6 seal assembly comprising an upper inflatable element in combina-7 tion with a lower flexible non-inflatable element. The upper in-8 flatable element comprises a seal "hanger" made from concentric 9 opposite-facing truncated cones of fluid-tight flexible material.
10 The innermost and outermost peripheral edges of these truncated 11 cones are mounted in fluid-tight manner to underside structure 12 of the load bearing device. The intermediate adjacent peripheral 13 edges of the two truncated cones are attached in fluid-tight man-14 ner to a cloth ring which in turn is attached, preferably by bond-15 ing, to a rigid flat structural ring. The lower flexible non-16 inflatable seal assembly comprises a lowermost flat flexible 17 wear ring with its inner and outer edges preferably chamfered.
18 This wear ring can be made of a variety of alternate materials to 19 provide an efficient fluid seal when operated over various floor 20 surfaces. However, for most common operating surfaces such as 21 smooth concrete for example, the preferred construction of this 22 wear ring is elastomeric material faced with low-friction plastic.
23 The remainder of the lower seal element is comprised of flat ten-24 sion rings with sponge elastomer spacer rings interposed between 25 them. The uppermost sponge rings are preferably of lesser density 26 and stiffness than the lowermost rings. The lowermost flat ten-27 sion ring is attached in fluid-tight manner to the aforementioned 28 seal ring. The uppermost flat tension ring is attached in fluid-29 tight manner to the outer region of a flat ring of fluid-tight 30 flexible material. The inner region of this flat ring is then 31 attached in fluid-tight manner to the underside of the aforemen-32 tinned rigid flat structural ring. The regiori of the flat flex-33 ible ring which lies between these two concentric areas of attach-34 ment is preferably formed of "slack" material to allow the lower 35 element of the seal assembly to flex both vertically and angularly 36 relative to the flat structural ring.
2~~~~~C
1 In an sir cushion device constructed as described 2 above, operating experience has demonstrated that certain re-3 lationships between design parameters of the seal assembly are 4 critical for avoidance of dynamic instability during operation.
5 For example, the ratio of innermost and outermost radii of the 6 inflatable seal hanger must fall within. a well-defined rang a 7 for stability. Similarly, there is a critical range in the 8 ratio of height of the truncated cons which comprise the in-9 flatable hanger compared to the overall radial width of the 10 hanger. In the lower non-inflatable seal assembly there is a 11 critical ratio between the radial width and vertical height of 12 the sponge elastomer spacer rings. There is also a critical 13 ratio between the density (and therefore stiffness) of the upper 14 elastomer spacer rings compared to the lower rings. During opera-15 tion, there is also a critical ratio between the seal inflation 16 pressure and lifting cushion pressure. To prevent over-pressuri-17 zing the seal hanger and exceeding this ratio, an automatically 18 opening port is provided in the outer flexible wall of the seal 19 hanger. Damping ports which are also located in the outer hanger 20 wall have auxiliary devices in this invention to automatically 21 close them off during initial inflation of the seal hanger and 22 to insure that they do not close at other times when their damp-23 ing effect is required.
24 The seal hanger is inflated separately frcm the lifting 25 cushion in this invention. During operation it is necessary that 26 pressure inside the lifting cushion exceed pressure inside the 27 seal hanger. This requires that the lifting cushion be inflated 28 during start up prior to inflating the seal hanger. However, 29 since seal inflation is under control of the operator, it is possi-30 ble to inadvertantly inflate the seal before pressurizing the 31 lifting cushion. If this is done, the seal hanger attachment 32 could separate from the base structure around its innermost 33 periphery.. To prevent this, the invention includes a check valve 34 mounted on the outer wall of the center support structure. This 35 valve allows air or fluid to pass freely from the seal hanger 36 into the lifting cushion if seal pressure exceeds cushion pressure ~1,.~ !~99('.
v E ;J c~ e~ iD
1 but prevents flow from the lifting cushion into the hanger if 2 cushion pressure exceeds hanger pressure.
7 In the drawings which are to be regarded as merely 8 illustrative:
9 FIG. 1 is a diametric cross-sectional view of a single 10 air caster critical dimensions shown.
with 11 FIG. 2 is a partial plan view of the air caster of 12 Figure l withternal details of the cylindrical structural in 13 base shown shed outlines.
by da 14 FIG. 3 is a partial underside view of the air caster 15 showing meansattaching the air caster to adjacent of structure 16 and also showinga check valve mounted in the outer cylindrical 17 wall of the ctural base.
stru 18 FIG. 4 is a flat pattern for a conical seal hanger wall 19 showing its truction from truncated angular segments.
cons 20 FIG. 5 is a perspective view of the hanger wall in 21 Figure 4 showingthe truncated conical form it takes after edges 22 of all segmentsare attached together.
23 FIG. 6 is a perspective view of a hanger assembly with' 24 two types omatic valves mounted in the outer of aut flexible wall 25 of the hang er .
26 FIG. 7 is a partial plan view of the hanger assembly in 27 Figure 6 showinga preferred method of assembly for the parts.
28 FIG. 8 is an enlarged fragmentary view of one of the 29 radial overlapped joints of Figure 7.
30 FIG. 9 is a cross-sectional view of a hanger and seal 31 assembly showingcritical dimensions and means for increasing 32 strength of parts to contain elevated pressures the inside the 33 hanger and air cushion.
the 26~~336 3 This invention relates to improvements in air cushion 4 lifting and transport vehicles. Such vehicles are typically sup-s ported by one or more devices known variously as "air casters"
6 or "air bearing s". These can actually be energized by any work-? ing fluid including either liquids or gases. However, for con-8 venience throughout this description, the invention will be refer-9 red to as an "air caster".
10 As shown in Figures 1 and 2 a single air caster has a 11 planar structural base plate 1 with a closed hollow cylindrical 12 support structure 2 centered on its underside. This support 13 structure is lifted clear of the floor when the air caster is 14 energized but it is capable of supporting the dead weight of the 15 load whenever the air caster is de-energized and is at rest.
16 The air caster also has a sealing assembly to confine a fluid 17 cushion under the vehicle. This sealing assembly includes an 18 annular hanger projecting from the base means and annular struct-19 ure below the hanger and cooperative therewith to enclose the 20 lifting air cushion.
21 The seal hang er is made of flexible sheet material and 22 is inflatable to .urge the annular seal structure away from the 23 base of the air caster. The hanger when inflated has an outer 24 annular flexible sheet wall 3 extending from the underside of 25 the planar base plate radially inward to the annular seal struct-26 ure to oppose lateral displacement of the seal structure in one 27 respect relative to the base. The hanger also has an inner an-28 nular flexible sheet wall 4 extending from the cylindrical part 29 of the base radially outward to the seal structure to oppose 30 lateral displacement of the seal structure in the opposite re-31 spect relative to the base.
32 The outer attachment of the inflatable seal hanger to 33 the planar base structure is at radius "R" as shown in Figure 1.
34 The inner attachment of the inflatable seal hanger to the cylin-35 drical part of the base is at radius "r". To prevent dynamic 36 oscillation or bounce of the loaded air caster, tests have 20~0'~~~
1 shown that the ratio of these two radii must be r 5 0.6 R
2 Construction of the inflatable seal hanger is shoian in 3 Figures 4,5,6 and 7. Figure 4 is a flat pattern for one seal 4 hanger cone showing how it is assembled from truncated angular 5 segments of coated woven fabric overlapped at their radial 6 edges and attached together in an airtight manner. To provide 7 uniform radial strength of the hanger around its entire periphery, 8 the threads of each angular segment are oriented parallel to the 9 radial center line of the segment as shown. Figure 5 is a per-10 spective view of the hanger of Figure 4 showing the truncated 11 conical form it takes after edges of all segments are attached 12 tog ether. Figure 6 is a perspective view of a complete hanger 13 assembly. This assembly consists of outer cone 3 and inner cone 14 4 positioned concentric to each other and attached around their 15 intermediate adjacent edges to the concentrically central region 16 of a flat cloth ring 5. Ring 5 in turn is attached, preferably 17 by bonding, to the top surface of rigid ring-shaped plate 6 to 18 complete the assembly. Figure 7 is a plan view of the inflatable 19 hanger assembly showing the segments of the hanger attached to 20 each other and to flat cloth ring 5 by stitching. and bonding.
21 Figure 8 shows an enlarged detail view of the stitching. If 22 stitching is used in this manner, the stitches must be sealed to 23 prevent leakag a of air through the needle holes. However, stitch-24 ing and sealing can be avoided if the hanger parts are vulcanized 25 together.
26 Figure 9 is a diametric cross-sectional view of the 27 hanger and plate assembly of Figure 6 with a reinforced seal assem-28 bly mounted to the underside of rigid ring-shaped plate 6. As 29 shown, outer hanger cone 3 and inner hanger cone 4 have vertical 30 height "h", the outer radius of the outer cone is "R" and the 31 inner radius of the inner cone is "r". Test experience with this 32 type air caster has demonstrated: that to prevent dynamic oscilla-33 tion or bounce of the loaded air caster, the ratio of cone height 34 to overall hang er width must be h ~ 0.6 (R-r) 35 As a further consequence of the hanger cone geometry specified 36 above it is also true that height of inner cone 4 must be related 201~~3G
1 to its innermost radius "r" by the ratio 1~ 5 0.4 r 2 Similarly, height of outer cone 3 must be related to its outer-3 most radius "R" by the ratio h_ 5 0.2 R
4 When the seal hanger is inflated, pressure-induced 5 stresses are greater in the outer cone 3 than they are in inner 6 cone 4. This is the natural result of the annular geometry of 7 the seal hanger. Therefore, to-increase load capacity of a given 8 size air caster, it is desirable to make the strength of the outer 9 cone greater than the strength of the inner cone. This can be 10 done by using heavier material in the outer cone than in the 11 inner cone. However, due to strength limitations of commercially 12 available materials, it may be preferablw to use additional lay-13 ers of material in the outer cone. This can be done by nesting 14 identical outer truncated cones 3, 3a and 3b together as indicated 15 by the dashed lines in Figure 9. These dashed lines show that 16 two additional outer cones have been added to give the outer hang er 17 wall the strength of three layers. Although these multiple layers 18 could be bonded or vulcanized to each other over their surface 19 area, this is not recommended because the stiffening of the hanger 20 which results can cause dynamic instability of the operating air 21 caster. It is preferable to attach the multiple cone layers to 22 each other only along their innermost and outermost circumferen-23 tial edges. When multiple outer hang er cones are nested tog ether 24 it is also desirable to circumferentially stagger them relative 25 to each other so their radial overlapped joints are equally spaced 26 around the hang er like the spokes of a wheel to promote uniform 27 radial strength of the hanger around its entire periphery.
28 With the hanger geometry specified above it follows that 29 the circumferential edg a of smallest diameter of the inner hanger 30 cone is the inner circumferential edg a of the hanger and the cir-31 cumferential edg a of largest diameter of the outer hang er cone 32 is the outer circumferential edg a of the hang er. As shown in Fig-33 ure 1, the inner circumferential edg a of the hanger is attached 34 to the vertical wall of the hollow cylindrical portion of the 35 structural base 2. To avoid dynamic instability of the loaded 36 air caster, tests have shown that it is advantageous to maximize 1 enclosed volume of the seal hanger and minimize enclosed volume 2 of the lifting air cushion. To contribute to this objecti~re, 3 the cylindrical portion of the base 2 projects downward into the'.
4 lifting cushion cavity, thereby displacing volume from the lifting 5 cushion. Furthermore, this cylindrical structure is hollow as 6 shown and its inner volume is in communication with the interior 7 of the seal hanger through passages 7. Therefore, the volume of 8 cylindrical structure 2 is effectively. added to volume of the seal 9 hanger and subtracted from volume of the lifting cushion. Volume 10 enclosed by the seal hanger is further increased by attaching the 11 innermost marginal edge of the hang er to the cylindrical wall of 12 the base as close to the bottom edge of the wall as possible.
13 This is shown in Figure 1 where the inner hanger is attached to the 14 cylindrical base around its entire periphery over a vertical height 15 "B".
16 As shown in Figure 1, an integral circumferential struct-17 oral ridge 8 projects downward from the underside of planar base 18 structure 1. This ridge is preferably circular in plan view. The 19 outer edg a of outer hanger wall 3 is attached in airtight manner, 20 preferably by bonding, to the outer vertical surface of ridge 8.
21 Ridge 8 is concentrically encompassed by structural guard ring 9 22 which is circular in plan view and is of larger diameter than 23 ridge 8. Guard ring 9 is preferably of slightly less vertical ' 24 height than cylindrical base structure 2. Therefore, when the air 25 caster is at rest the load is supported by cylindrical structure 2 26 with the lower edge of guard ring 9 not quite touching the floor.
27 Guard ring 9 is fitted with a number of inward-facing horizontal 28 tabs equally spaced around its inner periphery. Each of these 29 tabs has a hole drilled through it to fit over an attaching screw 30 11. Each of these screws projects through planar base structure 1 31 and is flush mounted thereto so the screw head does not protrude 32 above the top surface of base 1. A nut 12 on each attaching screw 33 11 bears against the underside of each tab 10 to secure guard ring 34 9 against the underside of base 1. Typically from eight to twelve 35 attaching screws are used to attach the outer guard ring to the 36 base of the air caster. However, additional flush head screws are to 1 installed in the annular space between ridge 8 and guard ring 9.
2 These are typically spaced approximately 1z inches apart and are 3 equally spaced circumferentially between tabs 10. No nuts are 4 required on these intermediate screws. A fillet of suitable 5 sealing material 13 is applied around the outer periphery of 6 guard ring 9 where its upper edge bears against the underside of 7 base 1. The air caster is plaC~d inverted on a level surface 8 with its seal assembly facing upward.and the annular cavity be-g tween ridg a 8 and guard ring 9 is filled with rigid-setting 10 plastic. This plastic material 14 unites the seal hanger, the 11 structural base and the guard ring into one integral structural 12 assembly after the plastic flows around the attaching screws and 13 hardens.
14 The air caster shown in Figure 1 has a structural base 15 to receive loads and a seal assembly to confine a fluid cushion 16 under the load. This seal assembly includes an annular inflatable 17 hanger projecting from the base, a rigid ring-shaped plate mounted 18 to the inflatable hang er and resiliently deformable annular seal-19 ing means mounted to the underside of the ring-shaped plate and 20 projecting downward therefrom to close proximity to the floor 21 over which the air caster operates. Tests have established that 22 with the geometry specified, to avoid dynamic instability of the 23 loaded air caster, annular sealing means 15 must be centered con=
24 centrically relative to the inflatable hanger. Therefore, if the 25 inner radius of the inflatable hang er is "r" and its outer radius 26 is "R" the mean radius of annular sealing means 15 must equal 27 R+r as shown in Figure 1.
28 Annular sealing means 15 consists of a lowermost wear 29 ring 16 backed up by a lamination of flexible flat tension rings 30 separated by elastomeric sponge spacer rings. The flat tension 31 rings and the elastomeric spacer rings have identical radial width 32 "d" as shown in Figure 1. Using the elastomeric materials speci-33 fied, this radial width combined with vertical height "c" of the 34 individual elastomeric rings determines vertical stiffness or 35 spring rate of the annular sealing assembly 15. This spring rate 36 in turn affects the dynamic characteristics of the loaded air 20~.9~36 1 caster. Tests have shown that for the geometry and materials 2 specified, radial width "d" of the annular sealing means must 3 be substantially less than radial width of the inflatable seal 4 hanger (R-r) and must be related thereto by the following ratio 5 0.25 < d < 0.35 (R-r) 6 In the configuration shown in Figure 1, the annular 7 sealing means has three flat flexible tension rings separated 8 by two relatively thick elastomeric sponge rings. The purpose 9 of these flat tension rings is to prevent radial expansion of 10 the seal assembly as a result of fluid pressure inside the lifting 11 cushion. A similar annular seal assembly is shown in Figure 9 12 except that it is designed to withstand greater fluid pressure 13 inside the lifting cushion. In that configuration the seal 14 assembly is strengthened by using five tension rings instead of 15 three.
16 As shown in Figure 1 the ring-shaped elastomeric members 17 of seal ring assembly 15 are relatively thick having vertical 18 height or thickness "c". To provide the proper spring rate of 19 the seal ring assembly, vertical height "c" of each ring-shaped 20 resiliently deformable member and radial width "d" of each said 21 member must have the ratio 0.40 < c < 0.50 a 22 Lowermost wear strip 16 of the annular seal assembly is 23 made of resilient abrasion-resistant material. The outer edge of 24 this wear strip is set back radially from the outer edg a of the 25 remainder of the seal ring assembly to minimize noise created by 26 air escaping under the wear strip. Both outer and inner edges of 27 this wear strip are chamfered as shown to facilitate passage over 28 small imperfections in the floor surface. The material used for 29 this wear strip can be matched to the characteristics of the floor 30 or ground surface over which the air caster operates. For operat-31 ion over smooth impervious surfaces, the wear strip may be made of 32 elastomeric material coated on its underside surface with a low 33 friction wear resistant plastic. By contrast, for operation 34 over rough or porous surfaces the wear strip may be made of felt-35 like material. The wear strip may be permanently attached to 36 the lowermost flat tension ring of the seal ring assembly, or 2~~.9~3G
1 alternatively, it may be attached by releasable pressure-sensitive 2 adhesive means for easy replacement whenever it becomes worn or 3 d amag ed .
4 As shown in Figure 1, annular seal assembly 16 consists 5 of an upper resiliently defbrmable ring having density pl and a 6 lower resiliently deformable ring having density p2, these rings 7 being separated by a flat flexible tension ring. The upper ring 8 is substantially softer than the lower ring to cause the seal to 9 accomodate to any local rise in the floor surface primarily by 10 compression of the upper ring. In the preferred embodiment of 11 the invention, the upper resilient ring having density pl is -12 molded of MIL-C-3133 SCO11 soft open cell natural sponge rubber.
13 The lower resilient ring having density p2 is molded of MIL-R-6130 14 type II soft closed cell neoprene sponge. These elastomer sponge 15 rings are typically molded in heated aluminum molds which produce 16 an airtight flexible skin over their entire outer surfaces. This 17 skin prevents radial air loss through the sponge material. Tests 18 have shown that optimum dynamic characteristics will be attained 19 if density of the upper ring pl and density of the lower ring p2 20 have the ratio _pl ~ _2 p2 3 21 Figure 9 shows a modified form of the annular seal 15a 22 which is designed to withstand increased pressure inside the , 23 fluid cushion. This seal assembly employs five flat tension rings 24 instead of three and four elastomeric spacer rings instead of two.
25 To maintain the overall height of the seal assembly unchanged, 26 each of the elastomeric rings in~Figure 9 is half the height of 27 each elastomeric ring in Figure 1. To maintain dynamic character-28 istics unchanged, the two upper elastomeric rings in Figure 9 both 29 have density pl and their combined vertical height is "c" which is 30 identical to vertical height of the single upper elastomeric ring 32 in Figure 1. Similarly, the two lower elastomeric ring s in Fig-33 ure 9 both have density p2 and their combined vertical height is 34 "c" which is identical to vertical height of the single lower 35 elastomeric ring in Fig ure.l. For the seal configuration shown I in Figure 9, overall height "c" of each pair of rings having the 2 same density and radial width "d" of the seal assembly must have 3 the ratio 0.4 < c < 0.5 a 4 The air caster shown in Fig ure 1 has a structural base 5 to receive loads and a seal assembly to confine a fluid cushion 6 under the load. This seal assembly includes an annular inflatable 7 hang er 3,4 projecting from the base, a rigid ring-shaped plate 6 8 mounted to the inflatable hanger and. resiliently deformable 9 annular sealing means 15 mounted to the underside of the ring-10 shaped plate and projecting downward therefrom to close proximity 11 to the ground surface over which the air caster operates. The 12 resiliently deformable annular sealing means is flexibly mounted 13 to the underside of the ring-shaped plate by a ring-shaped flexible, 14 fluid-tight sheet 17 which is attached in fluid-tight manner over 15 radial width "d" to the top surface of annular sealing means 15 16 around its outer circumferential margin and is attached in fluid-17 tight manner to rigid ring-shaped plate 6 over radial width "A"
18 around its inner circumferential margin. The intermediate circum-19 ferential portion of the ring-shaped sheet is slack to permit 20 the annular sealing means to tilt locally relative to the rigid 21 ring-shaped plate.
22 Operating experience with the type air caster described 23 has demonstrated that vertical spacing of rigid ring-shaped plate 24 6 below planar base structure 1 during operation is dependent on 25 the ratio of hanger pressure "PH" to cushion pressure "P~".
26 This vertical spacing is designated "e" in Figure 1. Pressurized 27 air or fluid is supplied to the lifting cushion through a gate 28 valve 18 which is typically controlled by the operator of the 29 air caster. This flotation air or fluid is supplied to the 30 lifting cushion through orifice 19 as shown. This air or fluid 31 is trapped inside the lifting cushion by surrounding seal assembly 32 15 where it develops cushion pressure "PC". Note that the under-33 side of cylindrical base structure 2 is preferably supplied with 34 radial grooves 20 to facilitate rapid dispersal of flotation air 35 or fluid throughout the cushion cavity even when base 2 is at 36 rest on a flat f7.oor. These radial grooves are shown in profile 1 cross-section in Figure 1 and in plan view in the underside view 2 of Figure 3. When flotation air or fluid is supplied to the air 3 caster, cushion pressure will continue to build up until the 4 mathematical product of cushion pressure times cushion area 5 equals the magnitude of the load. Flotation air or fluid will 6 then begin to flow radially outward between the lower face of 7 seal ring 16 and the floor. This thin film eliminates friction 8 between the seal and the floor allowing the loaded air caster to 9 be moved easily in any direction.
10 The seal hanger is pressurized by opening pressure 11 regulating valve 21. This valve, which is shown schematically 12 in Figure 1, is normally under the control of the operator and 13 supplies air or fluid to the seal hanger through orifice 22.
14 Note that orifice 22 is shown entering the hollow central portion 15 of base 2 but, as indicated by arrows 7, this space is in communi-16 cation with the seal hanger. Therefore, both the interior of cen-17 tral structure 2 and the hanger operate at the same pressure "PH".
18 Pressure regulating valve 21 is preferably a precision type valve 19 to provide accurate control over hanger inflation height "e" by 20 adjusting hanger pressure "PH". Also, opposite-pointing arrows 21 in the symbol for valve 21 indicate that it is preferably a 22 "relieving" type valve. Such a relieving pressure regulating 23 valve allows back-flow through the valve whenever pressure down-' 24 stream of the valve exceeds the desired valve output pressure.
25 Since the seal hanger and lifting cushion are inflated separately 26 in this air caster, it is possible for the operator to inadvertantly 27 over-inflate the seal hanger. If this occurs, the loaded air caster 28 will begin a vertical bouncing motion which becomes progressively 29 more severe as seal hanger pressure is increased. It is therefore 30 desirable to provide means in the air caster for automatically 31 preventing over-inflation of the seal hang er thereby avoiding 32 the dynamic instability which would result.
33 Operating experience has demonstrated that the optimum 34 hanger inflation height "e" is virtually independent of load 35 carried by the air caster. Therefore, avoidance of dynamic in-36 stability entails control of hanger inflation height "e" so it 1 cannot exceed a specified maximum level. As shown in Figure 6, 2 this can be accomplished by placing at least one port 23 in.ou';.er 3 flexible sheet wall 3 of the seal hanger. To prevent air from 4 rushing out of this port during initial inflation of the hanger 5 the port is preferably covered by a flexible sheet of fluid-tight 6 elastomeric material 24. This sheet is rectangular and is attached 7 to the outer surface of hanger sheet wall 3 only near its outer S ends leaving its central portion which covers port 23 unattached.
9 Attachment of sheet 24 to hang er wall 3 is therefore confined to 10 the areas of sheet 24 outboard of the dotted lines in Figure 6.
11 This construction is shown in detail in Figure 7 where sheet 24 12 of radial width "F" is attached to the outer -surface of hanger 13 wall 3 only over circumferential length "E" near each of its ends.
14 As shown in Figures 7 and 9, port 23 in outer hanger wall 3 is 15 positioned radially so that it will normally be pressed down 16 against the top surface of ring 6 thereby closing off the port 17 whenever the hanger is pressurized. However, as hanger pressure 18 increases causing hanger inflation height "e" to increase, hanger 19 wall 3 peels away from the upper surface of ring 6. When the 20 hanger wall peels away far enough to lift port 23 out of contact 21 with ring 6, hanger inflation air will begin to escape to atmos-22 phere through port 23 passing freely between the unattached central 23 portion of sheet 29 and the outer face of hanger wall 3. This 24 automatic loss of hang er inflation air will prevent further in-25 crease of pressure inside the hanger and stabilizes inflation 26 height "e" at a level below which dynamic instability would 27 occur. It is desirable for this automatic pressure limiting to 28 occur even if the operator should attPlnpt to further increase 29 hanger pressure by further opening valve 21. This is accomplished 30 by making the cumulative leaKage area of all ports 23 greater than 31 the area of orifice 22 which adtttits inflation air into the hang er.
32 To insure that hanger inflation air will not leaK out 33 through port 23 during initial inflation of the hang er, port 23 34 can be pressed against the top surface of plate 6 and sealed off 35 by a block of elastomeric sponge material 25 (in Figure 1) which 36 is mounted to the inside surface of base 1 positioned immediately 2~a.~~3~
7 above port 23. When the hanger is deflated and the air caster 2 is at rest, ring 6 presses port 23 against block 25 thereby 3 sealing the port and preventing air flow therethrough until the 4 hang er is pressurized and begins to inflate.
5 Operating experience with this type air caster has 6 demonstrated that the ratio of hanger pressure "PH" to cushion 7 pressure "P~" is critical for the avoidance of dynamic instability 8 of the loaded air caster. Typically; air casters of this type 9 will be stable whenever PH < ? P~ . Furthermore, hanger in-10 flation height "e" and hang er pressure "PH" are also related 11 with greater hanger pressure producing greater hanger inflation 12 height. Therefore, with the seal geometry specified, this type l3 air caster will be stable provided a < 1 (R-r) where "R" is 14 outer hanger radius and "r" is inner hanger radius as shown in 15 Figure 1. Maximum hanger inflation height "e" is governed by 16 the radial position of port 23 relative to the outer edge of 17 flat ring-shaped. plate 6. If port 23 is located radially outboard 18 toward the edge of ring 6 it will begin to pass air at a lower in-19 flation height than if it is located radially inboard. Therefore, 20 it is a feature of this invention to radially position port 23 21 relative to the outer edge of ring 6 so that the relationships 22 specified above are satisfied.
23 The cross-referenced issued patent discloses small fixed 24 diameter bleed holes or eyelets in the outer flexible wall of the 25 inflatable seal hanger. These eyelets allow air to bleed from 26 the interior of the hanger to atmosphere during operation to pro-27 vid-e dynamic damping of hanger pressure pulsations. As stated in 28 the patent, these bleed eyelets are preferably located in the 29 lower portion of the hanger so they are closed by pressing against 30 the flat rigid ring-shaped plate during initial buildup of hanger 31 inflation pressure and remain closed until the hanger expands to 32 its desired operating height. However,. subsequent operating experi-33 ence has demonstrated that positive means of sealing off these 34 bleed eyelets is desirable during initial pressurization of the 35 hanger. On the other hand, once the hanger begins to inflate, 36 other means must insure that the bleed eyelets cannot close at 2a1~~3~
1 any operating height of the hanger. These apparently conflicting 2 requirements are satisfied by the design features described below.
3 Figure 6 is a perspective view of the inflatable seal 4 hanger showing one small diameter bleed eyelet 26 located in the 5 outer flexible hanger wall. This bleed eyelet is also shown in 6 the plan view of Figure 7 and the cross-sectional view of Figure 9.
7 As shown in the figures, ribbed material 27 is mounted to the top 8 surface of the flat rigid ring-shaped plate 6 facing the bleed 9 eyelet. Therefore, when the inflatable hanger is pressurized to 10 press the outer wall of the hanger 3 tightly against the flat 11 ring-shaped plate, air continues to flow through the bleed eyelet 12 finding its way to atmosphere through the radial grooves of the 13 ribbed material. Therefore, addition of this ribbed material 14 makes the damping action of the eyelet effective at all operating 15 heights of the air caster. To close off flow thro~h the bleed 16 eyelet during initial hanger pressurization, an elastomeric sponge 17 block 25 is mounted inside the hanger on the underside surface of 18 of base 1. This block is positioned immediately above bleed 19 eyelet 26 to press against the eyelet and seal off flow there-20 through when the inflatable hanger is collapsed. Then as soon as 21 the hang er is pressurized and begins to inflate, the elastomeric 22 block is lifted clear of the bleed eyelet allowing air to flow 23 through it at all operating heights of the hanger.
24 Ideally the operator initially opens gate valve 18 to 25 admit flotation air into the lifting cushion of the air caster 26 and then opens pressure regulator valve 21 to pressurize the seal 27 hanger. If the valves are opened in this sequence, inner flexible 28 wall 4 of the seal hanger balloons upward as shown in Figure 1.
29 However, since cushion and seal hanger are separately inflated, 30 it is possible to inadvertantly inflate them in reverse order. If 31 the seal hanger is pressurized first with no pressure inside the 32 lifting cushion, it is possible to damage the air caster by causing 33 inner wall 4 of the hanger to balloon downward. This will tend to 34 peel the inner flexible wall of the seal hanger away from its 35 attachment to the cylindrical base structure. It is an object of 36 this invention to make operation foolproof by preventing this.
2~~~3~G
1 This is accomplished by placing at least one radial port 28 in 2 the outer wall of hollow cylindrical structure 2. This port is 3 positioned between the circumferential attachment of inner seal 4 hanger wall 4 to the wall of cylindrical structure 2 and the 5 bottom edge of the cylindrical structure. This port is shown in 6 profile cross-section in Figure 1 and is shown in planview cross-? section in Figure 3. When the air caster is operated properly, 8 lifting cushion pressure "P~" is always greater than hanger in-9 flation pressure "PH". Therefore, means must be provided to pre-10 vent flow through radial port 28 whenever P~ > PH, However, to 11 prevent reverse operation, it is necessary to allow flow through 12 port 28 whenever P~ < pH . Therefore, the port must function as 13 a check valve to allow flow in the outward radial direction but 14 block flow in the inward direction. This is accomplished by 15 placing a flexible sheet of fluid-tight elastomeric material 29 16 over the port on the outside of cylindrical structure 2. This 17 sheet has vertical height "B" when installed as shown in Figure 1.
18 It is attached to the outer face of the cylindrical wall, by bonding 19 for example, only over its outer portions in the regions designated 20 to be of circumferential width "D" in Figure 3. The central region 21 of sheet 29 which covers over port 28 is therefore left unattached.
22 When flotation air attempts to flow outward through port 28 it can 23 pass freely between sheet 29 and the cylindrical wall to escape 24 into the lifting cushion. On the other hand if cushion pressure 25 "P~" exceeds hanger pressure "PH", sheet 29 is pressed firmly 26 against the outer face of the cylindrical wall by cushion pressure 27 and radially inward flow through port 28 is automatically blocked.
28 In the event the operator attempts to pressurize the seal hanger 29 before pressurizing the lifting cushion, it is impera~.ive that all 30 radial ports 28 be capable of venting seal inflation air at least 31 as rapidly as it can be supplied through hang er inflation port 22.
32 This is assured by making the cumulative effective area of all 33 ports 28 larger than the area of hanger inflation port 22.
34 An air caster like that described is typically mounted 35 to the flat underside of cooperative load bearing structure.
36 Such structure may be a flat-bottomed platform or pallet for example.
?~i~~36 1 The load bearing platform or pallet typically includes integral 2 supply manifolds to bring air or fluid to orifice 19 for intro-3 duction into the lifting cushion and to orifice 22 for intro-4 duction into the seal hanger. G ate valve 18 and pressure regula-5 for valve 21 may be mounted on the load bearing platform or pallet;
6 or alternatively, they may be installed at a remote location and 7 be connected to the manifolds of the load bearing structure by 8 flexible hose. In any event, orifices 19 and 22 typically match 9 up to similar orifices on the underside of the load bearing plat-10 form or pallet with flexible elastomeric gaskets surrounding each 11 orifice sandwiched between the air caster and the load bearing 12 structure to provide a fluid-tight interface for transfer of air 13 or fluid between the two.
14 Holes 30 equally spaced around the outer periphery of 15 planar air caster base structure 1 accept attaching bolts or screws 16 for mounting the air cater to cooperative load bearing structure.
17 Operating experience has demonstrated, however, that it is also 18 desirable to have at least one attaching screw located near the 19 center orifice 19. This compresses the gaskets between the parts 20 to prevent leakage past the gaskets which surround the two orifices.
21 To accomodate a central attaching screw, an axial passage 31 is 22 provided which surrounds orifice 19 and passes downward through 23 the center of cylindrical base structure 2. This passage admits 24 flotation air or fluid to the lifting cushion. This axial passage 25 is typically of larger cross-sectional area than orifice 19. A1-26 though this axial passage is integral with the lifting cushion as 27 shown in Figure 1, it is isolated from the interior of cylindrical 28 base structure 2 and the interior of the inflatable seal hanger.
29 The marginal area of axial passage 31 surrounding, orifice 19 pro-30 vides space for one or more attaching screws immediately outboard 31 of orifice 19. However, space limitations, particularly on small 32 size air casters, make it preferable to provide an annex 31a to 33 axial passag a 31. This annex is shown in profile cross-section 34 in Figure 1 and in planview in Figure 2. As shown, this annex is 35 an integral part of the axial passage and the lifting cushion but 36 it provides an enlarged area for mounting an attaching screw or 2Q~~~3~
1 bolt. Port 32 through base structure of the air caster can accept 2 an attaching bolt or screw 33 as shown in Figure 3.
_2m
2~~~~~C
1 In an sir cushion device constructed as described 2 above, operating experience has demonstrated that certain re-3 lationships between design parameters of the seal assembly are 4 critical for avoidance of dynamic instability during operation.
5 For example, the ratio of innermost and outermost radii of the 6 inflatable seal hanger must fall within. a well-defined rang a 7 for stability. Similarly, there is a critical range in the 8 ratio of height of the truncated cons which comprise the in-9 flatable hanger compared to the overall radial width of the 10 hanger. In the lower non-inflatable seal assembly there is a 11 critical ratio between the radial width and vertical height of 12 the sponge elastomer spacer rings. There is also a critical 13 ratio between the density (and therefore stiffness) of the upper 14 elastomer spacer rings compared to the lower rings. During opera-15 tion, there is also a critical ratio between the seal inflation 16 pressure and lifting cushion pressure. To prevent over-pressuri-17 zing the seal hanger and exceeding this ratio, an automatically 18 opening port is provided in the outer flexible wall of the seal 19 hanger. Damping ports which are also located in the outer hanger 20 wall have auxiliary devices in this invention to automatically 21 close them off during initial inflation of the seal hanger and 22 to insure that they do not close at other times when their damp-23 ing effect is required.
24 The seal hanger is inflated separately frcm the lifting 25 cushion in this invention. During operation it is necessary that 26 pressure inside the lifting cushion exceed pressure inside the 27 seal hanger. This requires that the lifting cushion be inflated 28 during start up prior to inflating the seal hanger. However, 29 since seal inflation is under control of the operator, it is possi-30 ble to inadvertantly inflate the seal before pressurizing the 31 lifting cushion. If this is done, the seal hanger attachment 32 could separate from the base structure around its innermost 33 periphery.. To prevent this, the invention includes a check valve 34 mounted on the outer wall of the center support structure. This 35 valve allows air or fluid to pass freely from the seal hanger 36 into the lifting cushion if seal pressure exceeds cushion pressure ~1,.~ !~99('.
v E ;J c~ e~ iD
1 but prevents flow from the lifting cushion into the hanger if 2 cushion pressure exceeds hanger pressure.
7 In the drawings which are to be regarded as merely 8 illustrative:
9 FIG. 1 is a diametric cross-sectional view of a single 10 air caster critical dimensions shown.
with 11 FIG. 2 is a partial plan view of the air caster of 12 Figure l withternal details of the cylindrical structural in 13 base shown shed outlines.
by da 14 FIG. 3 is a partial underside view of the air caster 15 showing meansattaching the air caster to adjacent of structure 16 and also showinga check valve mounted in the outer cylindrical 17 wall of the ctural base.
stru 18 FIG. 4 is a flat pattern for a conical seal hanger wall 19 showing its truction from truncated angular segments.
cons 20 FIG. 5 is a perspective view of the hanger wall in 21 Figure 4 showingthe truncated conical form it takes after edges 22 of all segmentsare attached together.
23 FIG. 6 is a perspective view of a hanger assembly with' 24 two types omatic valves mounted in the outer of aut flexible wall 25 of the hang er .
26 FIG. 7 is a partial plan view of the hanger assembly in 27 Figure 6 showinga preferred method of assembly for the parts.
28 FIG. 8 is an enlarged fragmentary view of one of the 29 radial overlapped joints of Figure 7.
30 FIG. 9 is a cross-sectional view of a hanger and seal 31 assembly showingcritical dimensions and means for increasing 32 strength of parts to contain elevated pressures the inside the 33 hanger and air cushion.
the 26~~336 3 This invention relates to improvements in air cushion 4 lifting and transport vehicles. Such vehicles are typically sup-s ported by one or more devices known variously as "air casters"
6 or "air bearing s". These can actually be energized by any work-? ing fluid including either liquids or gases. However, for con-8 venience throughout this description, the invention will be refer-9 red to as an "air caster".
10 As shown in Figures 1 and 2 a single air caster has a 11 planar structural base plate 1 with a closed hollow cylindrical 12 support structure 2 centered on its underside. This support 13 structure is lifted clear of the floor when the air caster is 14 energized but it is capable of supporting the dead weight of the 15 load whenever the air caster is de-energized and is at rest.
16 The air caster also has a sealing assembly to confine a fluid 17 cushion under the vehicle. This sealing assembly includes an 18 annular hanger projecting from the base means and annular struct-19 ure below the hanger and cooperative therewith to enclose the 20 lifting air cushion.
21 The seal hang er is made of flexible sheet material and 22 is inflatable to .urge the annular seal structure away from the 23 base of the air caster. The hanger when inflated has an outer 24 annular flexible sheet wall 3 extending from the underside of 25 the planar base plate radially inward to the annular seal struct-26 ure to oppose lateral displacement of the seal structure in one 27 respect relative to the base. The hanger also has an inner an-28 nular flexible sheet wall 4 extending from the cylindrical part 29 of the base radially outward to the seal structure to oppose 30 lateral displacement of the seal structure in the opposite re-31 spect relative to the base.
32 The outer attachment of the inflatable seal hanger to 33 the planar base structure is at radius "R" as shown in Figure 1.
34 The inner attachment of the inflatable seal hanger to the cylin-35 drical part of the base is at radius "r". To prevent dynamic 36 oscillation or bounce of the loaded air caster, tests have 20~0'~~~
1 shown that the ratio of these two radii must be r 5 0.6 R
2 Construction of the inflatable seal hanger is shoian in 3 Figures 4,5,6 and 7. Figure 4 is a flat pattern for one seal 4 hanger cone showing how it is assembled from truncated angular 5 segments of coated woven fabric overlapped at their radial 6 edges and attached together in an airtight manner. To provide 7 uniform radial strength of the hanger around its entire periphery, 8 the threads of each angular segment are oriented parallel to the 9 radial center line of the segment as shown. Figure 5 is a per-10 spective view of the hanger of Figure 4 showing the truncated 11 conical form it takes after edges of all segments are attached 12 tog ether. Figure 6 is a perspective view of a complete hanger 13 assembly. This assembly consists of outer cone 3 and inner cone 14 4 positioned concentric to each other and attached around their 15 intermediate adjacent edges to the concentrically central region 16 of a flat cloth ring 5. Ring 5 in turn is attached, preferably 17 by bonding, to the top surface of rigid ring-shaped plate 6 to 18 complete the assembly. Figure 7 is a plan view of the inflatable 19 hanger assembly showing the segments of the hanger attached to 20 each other and to flat cloth ring 5 by stitching. and bonding.
21 Figure 8 shows an enlarged detail view of the stitching. If 22 stitching is used in this manner, the stitches must be sealed to 23 prevent leakag a of air through the needle holes. However, stitch-24 ing and sealing can be avoided if the hanger parts are vulcanized 25 together.
26 Figure 9 is a diametric cross-sectional view of the 27 hanger and plate assembly of Figure 6 with a reinforced seal assem-28 bly mounted to the underside of rigid ring-shaped plate 6. As 29 shown, outer hanger cone 3 and inner hanger cone 4 have vertical 30 height "h", the outer radius of the outer cone is "R" and the 31 inner radius of the inner cone is "r". Test experience with this 32 type air caster has demonstrated: that to prevent dynamic oscilla-33 tion or bounce of the loaded air caster, the ratio of cone height 34 to overall hang er width must be h ~ 0.6 (R-r) 35 As a further consequence of the hanger cone geometry specified 36 above it is also true that height of inner cone 4 must be related 201~~3G
1 to its innermost radius "r" by the ratio 1~ 5 0.4 r 2 Similarly, height of outer cone 3 must be related to its outer-3 most radius "R" by the ratio h_ 5 0.2 R
4 When the seal hanger is inflated, pressure-induced 5 stresses are greater in the outer cone 3 than they are in inner 6 cone 4. This is the natural result of the annular geometry of 7 the seal hanger. Therefore, to-increase load capacity of a given 8 size air caster, it is desirable to make the strength of the outer 9 cone greater than the strength of the inner cone. This can be 10 done by using heavier material in the outer cone than in the 11 inner cone. However, due to strength limitations of commercially 12 available materials, it may be preferablw to use additional lay-13 ers of material in the outer cone. This can be done by nesting 14 identical outer truncated cones 3, 3a and 3b together as indicated 15 by the dashed lines in Figure 9. These dashed lines show that 16 two additional outer cones have been added to give the outer hang er 17 wall the strength of three layers. Although these multiple layers 18 could be bonded or vulcanized to each other over their surface 19 area, this is not recommended because the stiffening of the hanger 20 which results can cause dynamic instability of the operating air 21 caster. It is preferable to attach the multiple cone layers to 22 each other only along their innermost and outermost circumferen-23 tial edges. When multiple outer hang er cones are nested tog ether 24 it is also desirable to circumferentially stagger them relative 25 to each other so their radial overlapped joints are equally spaced 26 around the hang er like the spokes of a wheel to promote uniform 27 radial strength of the hanger around its entire periphery.
28 With the hanger geometry specified above it follows that 29 the circumferential edg a of smallest diameter of the inner hanger 30 cone is the inner circumferential edg a of the hanger and the cir-31 cumferential edg a of largest diameter of the outer hang er cone 32 is the outer circumferential edg a of the hang er. As shown in Fig-33 ure 1, the inner circumferential edg a of the hanger is attached 34 to the vertical wall of the hollow cylindrical portion of the 35 structural base 2. To avoid dynamic instability of the loaded 36 air caster, tests have shown that it is advantageous to maximize 1 enclosed volume of the seal hanger and minimize enclosed volume 2 of the lifting air cushion. To contribute to this objecti~re, 3 the cylindrical portion of the base 2 projects downward into the'.
4 lifting cushion cavity, thereby displacing volume from the lifting 5 cushion. Furthermore, this cylindrical structure is hollow as 6 shown and its inner volume is in communication with the interior 7 of the seal hanger through passages 7. Therefore, the volume of 8 cylindrical structure 2 is effectively. added to volume of the seal 9 hanger and subtracted from volume of the lifting cushion. Volume 10 enclosed by the seal hanger is further increased by attaching the 11 innermost marginal edge of the hang er to the cylindrical wall of 12 the base as close to the bottom edge of the wall as possible.
13 This is shown in Figure 1 where the inner hanger is attached to the 14 cylindrical base around its entire periphery over a vertical height 15 "B".
16 As shown in Figure 1, an integral circumferential struct-17 oral ridge 8 projects downward from the underside of planar base 18 structure 1. This ridge is preferably circular in plan view. The 19 outer edg a of outer hanger wall 3 is attached in airtight manner, 20 preferably by bonding, to the outer vertical surface of ridge 8.
21 Ridge 8 is concentrically encompassed by structural guard ring 9 22 which is circular in plan view and is of larger diameter than 23 ridge 8. Guard ring 9 is preferably of slightly less vertical ' 24 height than cylindrical base structure 2. Therefore, when the air 25 caster is at rest the load is supported by cylindrical structure 2 26 with the lower edge of guard ring 9 not quite touching the floor.
27 Guard ring 9 is fitted with a number of inward-facing horizontal 28 tabs equally spaced around its inner periphery. Each of these 29 tabs has a hole drilled through it to fit over an attaching screw 30 11. Each of these screws projects through planar base structure 1 31 and is flush mounted thereto so the screw head does not protrude 32 above the top surface of base 1. A nut 12 on each attaching screw 33 11 bears against the underside of each tab 10 to secure guard ring 34 9 against the underside of base 1. Typically from eight to twelve 35 attaching screws are used to attach the outer guard ring to the 36 base of the air caster. However, additional flush head screws are to 1 installed in the annular space between ridge 8 and guard ring 9.
2 These are typically spaced approximately 1z inches apart and are 3 equally spaced circumferentially between tabs 10. No nuts are 4 required on these intermediate screws. A fillet of suitable 5 sealing material 13 is applied around the outer periphery of 6 guard ring 9 where its upper edge bears against the underside of 7 base 1. The air caster is plaC~d inverted on a level surface 8 with its seal assembly facing upward.and the annular cavity be-g tween ridg a 8 and guard ring 9 is filled with rigid-setting 10 plastic. This plastic material 14 unites the seal hanger, the 11 structural base and the guard ring into one integral structural 12 assembly after the plastic flows around the attaching screws and 13 hardens.
14 The air caster shown in Figure 1 has a structural base 15 to receive loads and a seal assembly to confine a fluid cushion 16 under the load. This seal assembly includes an annular inflatable 17 hanger projecting from the base, a rigid ring-shaped plate mounted 18 to the inflatable hang er and resiliently deformable annular seal-19 ing means mounted to the underside of the ring-shaped plate and 20 projecting downward therefrom to close proximity to the floor 21 over which the air caster operates. Tests have established that 22 with the geometry specified, to avoid dynamic instability of the 23 loaded air caster, annular sealing means 15 must be centered con=
24 centrically relative to the inflatable hanger. Therefore, if the 25 inner radius of the inflatable hang er is "r" and its outer radius 26 is "R" the mean radius of annular sealing means 15 must equal 27 R+r as shown in Figure 1.
28 Annular sealing means 15 consists of a lowermost wear 29 ring 16 backed up by a lamination of flexible flat tension rings 30 separated by elastomeric sponge spacer rings. The flat tension 31 rings and the elastomeric spacer rings have identical radial width 32 "d" as shown in Figure 1. Using the elastomeric materials speci-33 fied, this radial width combined with vertical height "c" of the 34 individual elastomeric rings determines vertical stiffness or 35 spring rate of the annular sealing assembly 15. This spring rate 36 in turn affects the dynamic characteristics of the loaded air 20~.9~36 1 caster. Tests have shown that for the geometry and materials 2 specified, radial width "d" of the annular sealing means must 3 be substantially less than radial width of the inflatable seal 4 hanger (R-r) and must be related thereto by the following ratio 5 0.25 < d < 0.35 (R-r) 6 In the configuration shown in Figure 1, the annular 7 sealing means has three flat flexible tension rings separated 8 by two relatively thick elastomeric sponge rings. The purpose 9 of these flat tension rings is to prevent radial expansion of 10 the seal assembly as a result of fluid pressure inside the lifting 11 cushion. A similar annular seal assembly is shown in Figure 9 12 except that it is designed to withstand greater fluid pressure 13 inside the lifting cushion. In that configuration the seal 14 assembly is strengthened by using five tension rings instead of 15 three.
16 As shown in Figure 1 the ring-shaped elastomeric members 17 of seal ring assembly 15 are relatively thick having vertical 18 height or thickness "c". To provide the proper spring rate of 19 the seal ring assembly, vertical height "c" of each ring-shaped 20 resiliently deformable member and radial width "d" of each said 21 member must have the ratio 0.40 < c < 0.50 a 22 Lowermost wear strip 16 of the annular seal assembly is 23 made of resilient abrasion-resistant material. The outer edge of 24 this wear strip is set back radially from the outer edg a of the 25 remainder of the seal ring assembly to minimize noise created by 26 air escaping under the wear strip. Both outer and inner edges of 27 this wear strip are chamfered as shown to facilitate passage over 28 small imperfections in the floor surface. The material used for 29 this wear strip can be matched to the characteristics of the floor 30 or ground surface over which the air caster operates. For operat-31 ion over smooth impervious surfaces, the wear strip may be made of 32 elastomeric material coated on its underside surface with a low 33 friction wear resistant plastic. By contrast, for operation 34 over rough or porous surfaces the wear strip may be made of felt-35 like material. The wear strip may be permanently attached to 36 the lowermost flat tension ring of the seal ring assembly, or 2~~.9~3G
1 alternatively, it may be attached by releasable pressure-sensitive 2 adhesive means for easy replacement whenever it becomes worn or 3 d amag ed .
4 As shown in Figure 1, annular seal assembly 16 consists 5 of an upper resiliently defbrmable ring having density pl and a 6 lower resiliently deformable ring having density p2, these rings 7 being separated by a flat flexible tension ring. The upper ring 8 is substantially softer than the lower ring to cause the seal to 9 accomodate to any local rise in the floor surface primarily by 10 compression of the upper ring. In the preferred embodiment of 11 the invention, the upper resilient ring having density pl is -12 molded of MIL-C-3133 SCO11 soft open cell natural sponge rubber.
13 The lower resilient ring having density p2 is molded of MIL-R-6130 14 type II soft closed cell neoprene sponge. These elastomer sponge 15 rings are typically molded in heated aluminum molds which produce 16 an airtight flexible skin over their entire outer surfaces. This 17 skin prevents radial air loss through the sponge material. Tests 18 have shown that optimum dynamic characteristics will be attained 19 if density of the upper ring pl and density of the lower ring p2 20 have the ratio _pl ~ _2 p2 3 21 Figure 9 shows a modified form of the annular seal 15a 22 which is designed to withstand increased pressure inside the , 23 fluid cushion. This seal assembly employs five flat tension rings 24 instead of three and four elastomeric spacer rings instead of two.
25 To maintain the overall height of the seal assembly unchanged, 26 each of the elastomeric rings in~Figure 9 is half the height of 27 each elastomeric ring in Figure 1. To maintain dynamic character-28 istics unchanged, the two upper elastomeric rings in Figure 9 both 29 have density pl and their combined vertical height is "c" which is 30 identical to vertical height of the single upper elastomeric ring 32 in Figure 1. Similarly, the two lower elastomeric ring s in Fig-33 ure 9 both have density p2 and their combined vertical height is 34 "c" which is identical to vertical height of the single lower 35 elastomeric ring in Fig ure.l. For the seal configuration shown I in Figure 9, overall height "c" of each pair of rings having the 2 same density and radial width "d" of the seal assembly must have 3 the ratio 0.4 < c < 0.5 a 4 The air caster shown in Fig ure 1 has a structural base 5 to receive loads and a seal assembly to confine a fluid cushion 6 under the load. This seal assembly includes an annular inflatable 7 hang er 3,4 projecting from the base, a rigid ring-shaped plate 6 8 mounted to the inflatable hanger and. resiliently deformable 9 annular sealing means 15 mounted to the underside of the ring-10 shaped plate and projecting downward therefrom to close proximity 11 to the ground surface over which the air caster operates. The 12 resiliently deformable annular sealing means is flexibly mounted 13 to the underside of the ring-shaped plate by a ring-shaped flexible, 14 fluid-tight sheet 17 which is attached in fluid-tight manner over 15 radial width "d" to the top surface of annular sealing means 15 16 around its outer circumferential margin and is attached in fluid-17 tight manner to rigid ring-shaped plate 6 over radial width "A"
18 around its inner circumferential margin. The intermediate circum-19 ferential portion of the ring-shaped sheet is slack to permit 20 the annular sealing means to tilt locally relative to the rigid 21 ring-shaped plate.
22 Operating experience with the type air caster described 23 has demonstrated that vertical spacing of rigid ring-shaped plate 24 6 below planar base structure 1 during operation is dependent on 25 the ratio of hanger pressure "PH" to cushion pressure "P~".
26 This vertical spacing is designated "e" in Figure 1. Pressurized 27 air or fluid is supplied to the lifting cushion through a gate 28 valve 18 which is typically controlled by the operator of the 29 air caster. This flotation air or fluid is supplied to the 30 lifting cushion through orifice 19 as shown. This air or fluid 31 is trapped inside the lifting cushion by surrounding seal assembly 32 15 where it develops cushion pressure "PC". Note that the under-33 side of cylindrical base structure 2 is preferably supplied with 34 radial grooves 20 to facilitate rapid dispersal of flotation air 35 or fluid throughout the cushion cavity even when base 2 is at 36 rest on a flat f7.oor. These radial grooves are shown in profile 1 cross-section in Figure 1 and in plan view in the underside view 2 of Figure 3. When flotation air or fluid is supplied to the air 3 caster, cushion pressure will continue to build up until the 4 mathematical product of cushion pressure times cushion area 5 equals the magnitude of the load. Flotation air or fluid will 6 then begin to flow radially outward between the lower face of 7 seal ring 16 and the floor. This thin film eliminates friction 8 between the seal and the floor allowing the loaded air caster to 9 be moved easily in any direction.
10 The seal hanger is pressurized by opening pressure 11 regulating valve 21. This valve, which is shown schematically 12 in Figure 1, is normally under the control of the operator and 13 supplies air or fluid to the seal hanger through orifice 22.
14 Note that orifice 22 is shown entering the hollow central portion 15 of base 2 but, as indicated by arrows 7, this space is in communi-16 cation with the seal hanger. Therefore, both the interior of cen-17 tral structure 2 and the hanger operate at the same pressure "PH".
18 Pressure regulating valve 21 is preferably a precision type valve 19 to provide accurate control over hanger inflation height "e" by 20 adjusting hanger pressure "PH". Also, opposite-pointing arrows 21 in the symbol for valve 21 indicate that it is preferably a 22 "relieving" type valve. Such a relieving pressure regulating 23 valve allows back-flow through the valve whenever pressure down-' 24 stream of the valve exceeds the desired valve output pressure.
25 Since the seal hanger and lifting cushion are inflated separately 26 in this air caster, it is possible for the operator to inadvertantly 27 over-inflate the seal hanger. If this occurs, the loaded air caster 28 will begin a vertical bouncing motion which becomes progressively 29 more severe as seal hanger pressure is increased. It is therefore 30 desirable to provide means in the air caster for automatically 31 preventing over-inflation of the seal hang er thereby avoiding 32 the dynamic instability which would result.
33 Operating experience has demonstrated that the optimum 34 hanger inflation height "e" is virtually independent of load 35 carried by the air caster. Therefore, avoidance of dynamic in-36 stability entails control of hanger inflation height "e" so it 1 cannot exceed a specified maximum level. As shown in Figure 6, 2 this can be accomplished by placing at least one port 23 in.ou';.er 3 flexible sheet wall 3 of the seal hanger. To prevent air from 4 rushing out of this port during initial inflation of the hanger 5 the port is preferably covered by a flexible sheet of fluid-tight 6 elastomeric material 24. This sheet is rectangular and is attached 7 to the outer surface of hanger sheet wall 3 only near its outer S ends leaving its central portion which covers port 23 unattached.
9 Attachment of sheet 24 to hang er wall 3 is therefore confined to 10 the areas of sheet 24 outboard of the dotted lines in Figure 6.
11 This construction is shown in detail in Figure 7 where sheet 24 12 of radial width "F" is attached to the outer -surface of hanger 13 wall 3 only over circumferential length "E" near each of its ends.
14 As shown in Figures 7 and 9, port 23 in outer hanger wall 3 is 15 positioned radially so that it will normally be pressed down 16 against the top surface of ring 6 thereby closing off the port 17 whenever the hanger is pressurized. However, as hanger pressure 18 increases causing hanger inflation height "e" to increase, hanger 19 wall 3 peels away from the upper surface of ring 6. When the 20 hanger wall peels away far enough to lift port 23 out of contact 21 with ring 6, hanger inflation air will begin to escape to atmos-22 phere through port 23 passing freely between the unattached central 23 portion of sheet 29 and the outer face of hanger wall 3. This 24 automatic loss of hang er inflation air will prevent further in-25 crease of pressure inside the hanger and stabilizes inflation 26 height "e" at a level below which dynamic instability would 27 occur. It is desirable for this automatic pressure limiting to 28 occur even if the operator should attPlnpt to further increase 29 hanger pressure by further opening valve 21. This is accomplished 30 by making the cumulative leaKage area of all ports 23 greater than 31 the area of orifice 22 which adtttits inflation air into the hang er.
32 To insure that hanger inflation air will not leaK out 33 through port 23 during initial inflation of the hang er, port 23 34 can be pressed against the top surface of plate 6 and sealed off 35 by a block of elastomeric sponge material 25 (in Figure 1) which 36 is mounted to the inside surface of base 1 positioned immediately 2~a.~~3~
7 above port 23. When the hanger is deflated and the air caster 2 is at rest, ring 6 presses port 23 against block 25 thereby 3 sealing the port and preventing air flow therethrough until the 4 hang er is pressurized and begins to inflate.
5 Operating experience with this type air caster has 6 demonstrated that the ratio of hanger pressure "PH" to cushion 7 pressure "P~" is critical for the avoidance of dynamic instability 8 of the loaded air caster. Typically; air casters of this type 9 will be stable whenever PH < ? P~ . Furthermore, hanger in-10 flation height "e" and hang er pressure "PH" are also related 11 with greater hanger pressure producing greater hanger inflation 12 height. Therefore, with the seal geometry specified, this type l3 air caster will be stable provided a < 1 (R-r) where "R" is 14 outer hanger radius and "r" is inner hanger radius as shown in 15 Figure 1. Maximum hanger inflation height "e" is governed by 16 the radial position of port 23 relative to the outer edge of 17 flat ring-shaped. plate 6. If port 23 is located radially outboard 18 toward the edge of ring 6 it will begin to pass air at a lower in-19 flation height than if it is located radially inboard. Therefore, 20 it is a feature of this invention to radially position port 23 21 relative to the outer edge of ring 6 so that the relationships 22 specified above are satisfied.
23 The cross-referenced issued patent discloses small fixed 24 diameter bleed holes or eyelets in the outer flexible wall of the 25 inflatable seal hanger. These eyelets allow air to bleed from 26 the interior of the hanger to atmosphere during operation to pro-27 vid-e dynamic damping of hanger pressure pulsations. As stated in 28 the patent, these bleed eyelets are preferably located in the 29 lower portion of the hanger so they are closed by pressing against 30 the flat rigid ring-shaped plate during initial buildup of hanger 31 inflation pressure and remain closed until the hanger expands to 32 its desired operating height. However,. subsequent operating experi-33 ence has demonstrated that positive means of sealing off these 34 bleed eyelets is desirable during initial pressurization of the 35 hanger. On the other hand, once the hanger begins to inflate, 36 other means must insure that the bleed eyelets cannot close at 2a1~~3~
1 any operating height of the hanger. These apparently conflicting 2 requirements are satisfied by the design features described below.
3 Figure 6 is a perspective view of the inflatable seal 4 hanger showing one small diameter bleed eyelet 26 located in the 5 outer flexible hanger wall. This bleed eyelet is also shown in 6 the plan view of Figure 7 and the cross-sectional view of Figure 9.
7 As shown in the figures, ribbed material 27 is mounted to the top 8 surface of the flat rigid ring-shaped plate 6 facing the bleed 9 eyelet. Therefore, when the inflatable hanger is pressurized to 10 press the outer wall of the hanger 3 tightly against the flat 11 ring-shaped plate, air continues to flow through the bleed eyelet 12 finding its way to atmosphere through the radial grooves of the 13 ribbed material. Therefore, addition of this ribbed material 14 makes the damping action of the eyelet effective at all operating 15 heights of the air caster. To close off flow thro~h the bleed 16 eyelet during initial hanger pressurization, an elastomeric sponge 17 block 25 is mounted inside the hanger on the underside surface of 18 of base 1. This block is positioned immediately above bleed 19 eyelet 26 to press against the eyelet and seal off flow there-20 through when the inflatable hanger is collapsed. Then as soon as 21 the hang er is pressurized and begins to inflate, the elastomeric 22 block is lifted clear of the bleed eyelet allowing air to flow 23 through it at all operating heights of the hanger.
24 Ideally the operator initially opens gate valve 18 to 25 admit flotation air into the lifting cushion of the air caster 26 and then opens pressure regulator valve 21 to pressurize the seal 27 hanger. If the valves are opened in this sequence, inner flexible 28 wall 4 of the seal hanger balloons upward as shown in Figure 1.
29 However, since cushion and seal hanger are separately inflated, 30 it is possible to inadvertantly inflate them in reverse order. If 31 the seal hanger is pressurized first with no pressure inside the 32 lifting cushion, it is possible to damage the air caster by causing 33 inner wall 4 of the hanger to balloon downward. This will tend to 34 peel the inner flexible wall of the seal hanger away from its 35 attachment to the cylindrical base structure. It is an object of 36 this invention to make operation foolproof by preventing this.
2~~~3~G
1 This is accomplished by placing at least one radial port 28 in 2 the outer wall of hollow cylindrical structure 2. This port is 3 positioned between the circumferential attachment of inner seal 4 hanger wall 4 to the wall of cylindrical structure 2 and the 5 bottom edge of the cylindrical structure. This port is shown in 6 profile cross-section in Figure 1 and is shown in planview cross-? section in Figure 3. When the air caster is operated properly, 8 lifting cushion pressure "P~" is always greater than hanger in-9 flation pressure "PH". Therefore, means must be provided to pre-10 vent flow through radial port 28 whenever P~ > PH, However, to 11 prevent reverse operation, it is necessary to allow flow through 12 port 28 whenever P~ < pH . Therefore, the port must function as 13 a check valve to allow flow in the outward radial direction but 14 block flow in the inward direction. This is accomplished by 15 placing a flexible sheet of fluid-tight elastomeric material 29 16 over the port on the outside of cylindrical structure 2. This 17 sheet has vertical height "B" when installed as shown in Figure 1.
18 It is attached to the outer face of the cylindrical wall, by bonding 19 for example, only over its outer portions in the regions designated 20 to be of circumferential width "D" in Figure 3. The central region 21 of sheet 29 which covers over port 28 is therefore left unattached.
22 When flotation air attempts to flow outward through port 28 it can 23 pass freely between sheet 29 and the cylindrical wall to escape 24 into the lifting cushion. On the other hand if cushion pressure 25 "P~" exceeds hanger pressure "PH", sheet 29 is pressed firmly 26 against the outer face of the cylindrical wall by cushion pressure 27 and radially inward flow through port 28 is automatically blocked.
28 In the event the operator attempts to pressurize the seal hanger 29 before pressurizing the lifting cushion, it is impera~.ive that all 30 radial ports 28 be capable of venting seal inflation air at least 31 as rapidly as it can be supplied through hang er inflation port 22.
32 This is assured by making the cumulative effective area of all 33 ports 28 larger than the area of hanger inflation port 22.
34 An air caster like that described is typically mounted 35 to the flat underside of cooperative load bearing structure.
36 Such structure may be a flat-bottomed platform or pallet for example.
?~i~~36 1 The load bearing platform or pallet typically includes integral 2 supply manifolds to bring air or fluid to orifice 19 for intro-3 duction into the lifting cushion and to orifice 22 for intro-4 duction into the seal hanger. G ate valve 18 and pressure regula-5 for valve 21 may be mounted on the load bearing platform or pallet;
6 or alternatively, they may be installed at a remote location and 7 be connected to the manifolds of the load bearing structure by 8 flexible hose. In any event, orifices 19 and 22 typically match 9 up to similar orifices on the underside of the load bearing plat-10 form or pallet with flexible elastomeric gaskets surrounding each 11 orifice sandwiched between the air caster and the load bearing 12 structure to provide a fluid-tight interface for transfer of air 13 or fluid between the two.
14 Holes 30 equally spaced around the outer periphery of 15 planar air caster base structure 1 accept attaching bolts or screws 16 for mounting the air cater to cooperative load bearing structure.
17 Operating experience has demonstrated, however, that it is also 18 desirable to have at least one attaching screw located near the 19 center orifice 19. This compresses the gaskets between the parts 20 to prevent leakage past the gaskets which surround the two orifices.
21 To accomodate a central attaching screw, an axial passage 31 is 22 provided which surrounds orifice 19 and passes downward through 23 the center of cylindrical base structure 2. This passage admits 24 flotation air or fluid to the lifting cushion. This axial passage 25 is typically of larger cross-sectional area than orifice 19. A1-26 though this axial passage is integral with the lifting cushion as 27 shown in Figure 1, it is isolated from the interior of cylindrical 28 base structure 2 and the interior of the inflatable seal hanger.
29 The marginal area of axial passage 31 surrounding, orifice 19 pro-30 vides space for one or more attaching screws immediately outboard 31 of orifice 19. However, space limitations, particularly on small 32 size air casters, make it preferable to provide an annex 31a to 33 axial passag a 31. This annex is shown in profile cross-section 34 in Figure 1 and in planview in Figure 2. As shown, this annex is 35 an integral part of the axial passage and the lifting cushion but 36 it provides an enlarged area for mounting an attaching screw or 2Q~~~3~
1 bolt. Port 32 through base structure of the air caster can accept 2 an attaching bolt or screw 33 as shown in Figure 3.
_2m
Claims (42)
1. In a fluid cushion device comprising:
base means to receive loads, and at least one sealing assembly to confine a fluid cushion, said sealing assembly including an annular hanger projecting from the base means and annular structure below the hanger and cooperative therewith to enclose the fluid cushion, said hanger made of flexible sheet material and inflatable for vertical resilient deformability to yieldingly urge said annular structure away from the base means, the hanger when inflated having an outer annular flexible sheet wall extending from the base means radially inwardly to the annular structure to act under tension to oppose lateral displacement of the annular structure in one respect relative to the base means, and having an inner annular flexible sheet wall extending from the base means radially outwardly to the annular structure to oppose lateral displacement of the annular structure in the opposite respect relative to the base means.
attachment of said outer annular flexible sheet wall to said base means being at radius "R" and attachment of said inner annular flexible sheet wall to said base means being at radius "r" with the ratio ~ ~ 0.6
base means to receive loads, and at least one sealing assembly to confine a fluid cushion, said sealing assembly including an annular hanger projecting from the base means and annular structure below the hanger and cooperative therewith to enclose the fluid cushion, said hanger made of flexible sheet material and inflatable for vertical resilient deformability to yieldingly urge said annular structure away from the base means, the hanger when inflated having an outer annular flexible sheet wall extending from the base means radially inwardly to the annular structure to act under tension to oppose lateral displacement of the annular structure in one respect relative to the base means, and having an inner annular flexible sheet wall extending from the base means radially outwardly to the annular structure to oppose lateral displacement of the annular structure in the opposite respect relative to the base means.
attachment of said outer annular flexible sheet wall to said base means being at radius "R" and attachment of said inner annular flexible sheet wall to said base means being at radius "r" with the ratio ~ ~ 0.6
2. A combination as set forth in Claim 1 in which the inner and outer flexible sheet-walls of said inflatable hanger comprise truncated cones with height "h" such that
3. An inflatable seal hang er as described in Claim 1 having an outer annular flexible sheet wall and an inner annular flexible sheet wall. each comprising at least one truncated cone;
the height of said inner wall cone "h" related to its innermost radius "r" by -the ratio ~ ~ 0.4 and the height of said outer wall cone "h" related to its outermost radius "R" by the ratio ~ ~ 0.2
the height of said inner wall cone "h" related to its innermost radius "r" by -the ratio ~ ~ 0.4 and the height of said outer wall cone "h" related to its outermost radius "R" by the ratio ~ ~ 0.2
4. An inflatable hanger as described in Claim 3 in which the two conical annular flexible sheet walls are mounted concentrically with their contiguous edges attached to a common ring-shaped sheet which is attached to one surface of a rigid ring-shaped plate.
5. A combination as set forth in Claim 4 in which each conical annular flexible sheet wall is made of radial segments of woven fabric in which threads of each segment are oriented parallel to the radial center line of the segment, and said fabric is coated with flexible fluidtight sealing material.
6. A combination as set forth in Claim 4 in which the sheet material of the inner and outer flexible sheet walls comprises truncated cones, the circumferential edge of smallest diameter of the inner cone being the inner circumferential edge of the hanger and circumferential edge of largest diameter of the outer cone being the outer circumferential edge of the hanger.
7. An inflatable hanger as described in Claim 3 in which said outer annular flexible sheet wall consists of multiple truncated cones nested together to give the outer wall greater strength than the inner wall.
8. A multi-layer hang er wall as described in Claim 7 wherein said nested truncated cones are staggered in azimuth relative to each other equally spacing their overlapped joints around the periphery of the hanger.
9. An inflatable hang er as described in Claim 6 in which the inner circumferential edge of the hanger is attached to the wall of the cylindrical base at a level spaced below the planar portion of the base to increase the effective volume enclosed by the hanger envelope.
10. An inflatable hang er as described in Claim 6 in which the outer circumferential edge of the hanger is attached to an annular structural ridge tin the underside of the planar portion of the structural base, said hang er encompassed by an annular guard means fixedly mounted to the underside of the planar portion of the base to protect the inflatable hanger, said guard means comprising a cylindrical structural ring with vertical height less than height of the cylindrical base structure, said annular guard attached by a number of equally spaced flush-head screws projecting through the planar portion of the base into an annular space between said hanger and said guard ring, said annular space also filled with rigid-setting plastic material to units the hanger, the base and the guard ring into one integral structural assembly.
11. In a fluid cushion device comprising:
base means to receive loads, and at least one sealing assembly to confine a fluid cushion, said sealing assembly including an annular inflatable hanger projecting from the base means and annular structure below the hanger and cooperative therewith to enclose the fluid cushion, said annular structure including resiliently deformable annular sealing means projecting downward to close proximity to the ground surface under the device, said annular sealing means centered concentrically on said inflatable hanger.
base means to receive loads, and at least one sealing assembly to confine a fluid cushion, said sealing assembly including an annular inflatable hanger projecting from the base means and annular structure below the hanger and cooperative therewith to enclose the fluid cushion, said annular structure including resiliently deformable annular sealing means projecting downward to close proximity to the ground surface under the device, said annular sealing means centered concentrically on said inflatable hanger.
12, Resiliently deformable annular sealing means as described in Claim 11 having radial width "d" substantially less than radial width (R-r) of the inflatable hanger and related thereto by the ratio
13. A combination as set forth in Claim 11 in which said annular sealing means comprises a stack of substantially ring-shaped resiliently deformable members; and in which at least one flexible ring-shaped sheet is interposed between two of said members to act under hoop tension to oppose radially outward expansion of the annular sealing jeans due to fluid pressure inside the lifting cushion.
14. A combination as set forth in Claim 13 in which a resiliently flexible wear strip is removably attached to the underside of the lowest member of the stack.
15. A combination as set forth in Claim 14 in which a flexible abrasion-resistant wear strip is mounted on the under-side of the stack; and in which a ring-shaped reinforcement sheet is interposed between the lowermost ring-shaped member of the stack and said wear strip.
16. A combination as seat forth in Claim 13 in which the ring-shaped members of the stack include relatively thick members made of resiliently deformable cellular elastomer, radial dimensions of said deformable members and said ring-shaped members being essentially identical, vertical height "c" of each ring-shaped resiliently deformable member and radial width "d" of each said member having the ratio 0.40 < c < 0.50 d
17. A combination as set forth in Claim 16 which includes at least one ring-shaped sheet in hoop tension between two of the relatively thick members of the stack.
18. A combination as set forth in Claim 11 which includes a wear strip of resilient abrasion-resistant material mounted to the underside of the annular sealing means, said wear strip being set back radially from the outer edge a of the annular sealing means around its circumference to minimize noise created by escaping air under the wear strip.
19. A combination as set forth in Claim 18 in which the wear strip is made at least largely of elastomeric material.
20. A combination as set forth in Claim 19 in which the underside of the wear strip is coated with a low friction wear-resistant plastic.
21. A combination asset forth in Claim 18 in which said wear strip is constructed of felt-like fabric:
22. A combination as set forth in Claim 18 in which the wear strip is releasably mounted by pressure-sensitive adhesive means.
23. A Combination as set forth in Claim 18 in which the wear strip is chamfered along its outer circumferential edge.
24. A combination as yet forth in Claim 18 in which the wear strip is chamfered along its inner circumferential edge.
25. A combination as set forth in Claim 11 in which an upper annular portion of said sealing means is resiliently deformable and is substantially softer than the lower annular portion of the sealing means to cause the sealing means to accomodate itself to a local rise in the underlying ground surface primarily by compression of said annular portion, the relatively thick part of said upper annular portion consisting of MTL-C-3133 SCO11 soft open cell natural rubber sponge, the relatively thick part of said lower annular portion consisting of MIL-R-6130 type II soft closed cell neoprene sponge, density of the upper annular part "p1" and density of the lower annular part "p2" having the ratio
26. A combination as set forth in Claim 25 wherein said upper annular portion of said sealing means having overall height "c" consists of multiple relatively thick ring-shaped members with flexible ring-shaped sheets interposed between them, said lower annular portion of said sealing means having overall height "c" consists of multiple relatively thick ring-shaped members with flexible ring-shaped sheets interposed between them, overall vertical height "c" of each said annular portion and radial width "d" of each said member having the ratio
27. A combination as set forth in Claim 25 in which said annular sealing means comprises a stack of relatively thick, substantially ring-shaped resilient deformable members alternating with ring-shaped sheets acting under hoop tension to oppose radially outward expansion of the annular sealing means, one of said sheet members being the uppermost member of the stack.
28. A combination as set forth in Claim 26 in which a flexible abrasion-resistant wear strip is mounted on the underside of the stack; and in which a ring-shaped reinforcement sheet is interposed between the lowermost ring-shaped member of the stack and said wear strip.
29. In a fluid cushion device comprising:
base means to receive loads, and at least one sealing assembly to confine a fluid cushion, said sealing assembly including an annular inflatable hanger projecting from the base means and annular structure below the hanger and cooperative therewith to enclose the fluid cushion, said annular structure including a rigid ring-shaped plate attached to the underside of the hanger, said annular structure further including resiliently deformable annular sealing means projecting downward from the ring-shaped plate to close proximity to the ground surface under the device, said resiliently deformable annular sealing means flexibly mounted to the underside of the ring-shaped plate by a ring-shaped flexible, fluid-tight sheet which is attached in fluid-tight manner around its outer circumferential margin to the annular.
sealing means and is attached in fluid-tight manner around its inner circumferential margin to the rigid plate, the intermediate circumferential portion of the ring-shaped sheet being slack to permit the annular sealing means to tilt locally relative to the rigid ring-shaped plate.
base means to receive loads, and at least one sealing assembly to confine a fluid cushion, said sealing assembly including an annular inflatable hanger projecting from the base means and annular structure below the hanger and cooperative therewith to enclose the fluid cushion, said annular structure including a rigid ring-shaped plate attached to the underside of the hanger, said annular structure further including resiliently deformable annular sealing means projecting downward from the ring-shaped plate to close proximity to the ground surface under the device, said resiliently deformable annular sealing means flexibly mounted to the underside of the ring-shaped plate by a ring-shaped flexible, fluid-tight sheet which is attached in fluid-tight manner around its outer circumferential margin to the annular.
sealing means and is attached in fluid-tight manner around its inner circumferential margin to the rigid plate, the intermediate circumferential portion of the ring-shaped sheet being slack to permit the annular sealing means to tilt locally relative to the rigid ring-shaped plate.
30. In a fluid cushion device comprising:
base means to receive loads, and at least one sealing assembly to confine a fluid cushion, said sealing assembly including an annular hanger projecting from the base means and annular structure below the hanger and cooperative therewith to enclose the fluid cushion, said hanger being made of flexible sheet material and being inflatable for vertical resilient deformability to yieldingly urge said annular structure away from the base means, said annular structure being of less radial dimension than the hanger and being positioned within an annular area defined by the hanger, the hanger when inflated having an outer annular flexible sheet wall extending from the base means radially inwardly to the annular structure, said annular structure including a rigid-ring-shaped plate attached at its central circumferential region to the underside of the hanger, automatically throttling valve means to bleed fluid from the seal hanger to atmosphere comprising at least one port in the outer flexible wall of the hanger positioned radially inboard of the outer edge of said rigid ring-shaped plate so it lies against the plate to be closed off by the plate when the hanger is partially inflated and to open when the hanger wall peels away from the plate as the hanger becomes fully inflated.
base means to receive loads, and at least one sealing assembly to confine a fluid cushion, said sealing assembly including an annular hanger projecting from the base means and annular structure below the hanger and cooperative therewith to enclose the fluid cushion, said hanger being made of flexible sheet material and being inflatable for vertical resilient deformability to yieldingly urge said annular structure away from the base means, said annular structure being of less radial dimension than the hanger and being positioned within an annular area defined by the hanger, the hanger when inflated having an outer annular flexible sheet wall extending from the base means radially inwardly to the annular structure, said annular structure including a rigid-ring-shaped plate attached at its central circumferential region to the underside of the hanger, automatically throttling valve means to bleed fluid from the seal hanger to atmosphere comprising at least one port in the outer flexible wall of the hanger positioned radially inboard of the outer edge of said rigid ring-shaped plate so it lies against the plate to be closed off by the plate when the hanger is partially inflated and to open when the hanger wall peels away from the plate as the hanger becomes fully inflated.
31. Throttling valve means as described in Claim 30 wherein said port is covered over by a sheet of flexible fluid-tight elastomeric material attached to the outer surface of the flexible hanger wall on opposite sides of said port.
32. At least one port in the outer wall of the hanger as described in Claim 30, the effective leakage area of all such ports being greater than the area of the port which admits fluid into the hanger envelope.
33. A block of resiliently deformable elastomeric sponge positioned opposite each port described in Claim 30 and mounted to the structural base inside the hanger envelope to press said port against the rigid ring-shaped plate of the annular seal assembly whenever the hanger envelope is deflated thereby blocking fluid flow therethrough during initial hanger inflation.
34. At least one port in the outer flexible wall of the seal hanger as described in Claim 30, each said port positioned radially inboard of the outer edge of said rigid ring-shaped plate to pass fluid through the port as the hanger peels away from the plate during inflation whenever the ratio where "P H "
is fluid pressure inside the hanger envelope and "P C" is pressure inside the lifting cushion.
is fluid pressure inside the hanger envelope and "P C" is pressure inside the lifting cushion.
35. At least one port in the outer flexible wall of the seal hanger as described in Claim 30, each said port positioned radially inboard of the outer edge of said rigid ring-shaped plate to pass fluid through the port as the hanger peels away from the plate during inflation whenever the ratio where "e"
is vertical separation between the rigid ring-shaped plate and the structural base during operation and (R-r) is radial width of the hanger envelope.
is vertical separation between the rigid ring-shaped plate and the structural base during operation and (R-r) is radial width of the hanger envelope.
36. In a fluid cushion device comprising:
base means to receive loads, and at least one sealing assembly to confine a fluid cushion, said sealing assembly including an annular inflatable hanger projecting from the base means and annular seal structure below the hanger and cooperative therewith to enclose the fluid cushion, said annular seal structure being of less radial dimension than the hanger and being positioned within an annular area defined by the hanger, said annular structure including a rigid ring shaped plate attached at its central circumferential region to the underside of the hanger, at least one damping eyelet in the flexible outer wall of said hanger positioned radially inboard of the outer edge of said rigid ring-shaped plate, ribbed material mounted onto the rigid ring-shaped plate facing said eyelet with its ribs parallel to the radial direction, a block of resiliently deformable elastomeric sponge mounted onto the structural base inside the hanger envelope facing said eyelet, said ribbed material allowing fluid to flow through the eyelet at all inflation heights of the seal hanger except when the eyelet is pressed against said sponge block.
base means to receive loads, and at least one sealing assembly to confine a fluid cushion, said sealing assembly including an annular inflatable hanger projecting from the base means and annular seal structure below the hanger and cooperative therewith to enclose the fluid cushion, said annular seal structure being of less radial dimension than the hanger and being positioned within an annular area defined by the hanger, said annular structure including a rigid ring shaped plate attached at its central circumferential region to the underside of the hanger, at least one damping eyelet in the flexible outer wall of said hanger positioned radially inboard of the outer edge of said rigid ring-shaped plate, ribbed material mounted onto the rigid ring-shaped plate facing said eyelet with its ribs parallel to the radial direction, a block of resiliently deformable elastomeric sponge mounted onto the structural base inside the hanger envelope facing said eyelet, said ribbed material allowing fluid to flow through the eyelet at all inflation heights of the seal hanger except when the eyelet is pressed against said sponge block.
37. A combination as set forth in Claim 36 in which the means to inflate the seal hanger comprises an adjustable pressure regulating valve operable to maintain a selected pressure inside the hanger envelope.
38. An adjustable pressure regulating valve as described in Claim 37 which is a "relieving" type valve to allow back flow through the valve if hanger pressure exceeds pre-set valve outlet pressure.
39. In a fluid cushion device comprising:
base means to receive loads, and at least one sealing assembly to confine a fluid cushion, said sealing assembly including an annular inflatable hanger projecting from the base means and annular seal structure below the hanger and cooperative therewith to enclose the fluid cushion, said base means including a hollow cylindrical chamber, said hanger encompassing the chamber and being in fluid communication with the chamber for fluid flow between the chamber and the hanger, at least one port in the outer wall of said cylindrical chamber positioned between the attachment of the inner hanger envelope to said wall and the lower edge of said wall, said port covered over by a sheet of flexible fluid-tight elastomeric material attached to the outer surface of the cylindrical wall on opposite sides of said port, said combination allowing fluid to pass through the port whenever chamber pressure exceeds pressure in the surrounding fluid cushion but blocking fluid flow therethrough whenever cushion pressure exceeds chamber pressure.
base means to receive loads, and at least one sealing assembly to confine a fluid cushion, said sealing assembly including an annular inflatable hanger projecting from the base means and annular seal structure below the hanger and cooperative therewith to enclose the fluid cushion, said base means including a hollow cylindrical chamber, said hanger encompassing the chamber and being in fluid communication with the chamber for fluid flow between the chamber and the hanger, at least one port in the outer wall of said cylindrical chamber positioned between the attachment of the inner hanger envelope to said wall and the lower edge of said wall, said port covered over by a sheet of flexible fluid-tight elastomeric material attached to the outer surface of the cylindrical wall on opposite sides of said port, said combination allowing fluid to pass through the port whenever chamber pressure exceeds pressure in the surrounding fluid cushion but blocking fluid flow therethrough whenever cushion pressure exceeds chamber pressure.
40. At least one port in the outer wall of a hollow cylindrical chamber as described in Claim 39, the effective leakage area of all. such ports being greater than the area of the port which admits fluid into the chamber.
41. In a fluid cushion device comprising:
base means to receive loads, and at least one sealing assembly to confine a fluid cushion, said sealing assembly including an annular inflatable hanger projecting from the base means and annular seal structure below the hanger and cooperative therewith to enclose the fluid cushion, said base means including an axial passage through the base means to supply pressurized fluid to the lifting cushion, said passage being of larger cross-sectional area than the port which admits pressurized fluid into said passage.
base means to receive loads, and at least one sealing assembly to confine a fluid cushion, said sealing assembly including an annular inflatable hanger projecting from the base means and annular seal structure below the hanger and cooperative therewith to enclose the fluid cushion, said base means including an axial passage through the base means to supply pressurized fluid to the lifting cushion, said passage being of larger cross-sectional area than the port which admits pressurized fluid into said passage.
42. A fluid passage as described in Claim 41 which includes an annex in said passage providing space adjacent to said port to accomodate attaching means for securing the base to cooperative load bearing structure.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2019336 CA2019336C (en) | 1990-06-20 | 1990-06-20 | Structure to form a load-bearing air cushion for a vehicle |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2019336 CA2019336C (en) | 1990-06-20 | 1990-06-20 | Structure to form a load-bearing air cushion for a vehicle |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2019336A1 CA2019336A1 (en) | 1991-12-20 |
| CA2019336C true CA2019336C (en) | 2000-04-25 |
Family
ID=4145274
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2019336 Expired - Fee Related CA2019336C (en) | 1990-06-20 | 1990-06-20 | Structure to form a load-bearing air cushion for a vehicle |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2019336C (en) |
-
1990
- 1990-06-20 CA CA 2019336 patent/CA2019336C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| CA2019336A1 (en) | 1991-12-20 |
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