US3059475A - Power element having novel forcetransmitting plug - Google Patents

Description

Oct. 23, 1962 s. VERNET ETAL 3,059,475

POWER ELEMENT HAVING NOVEL FORCE-TRANSMITTING PLUG Filed May 9, 1956 IN VEN TOPS 5 5 VERNET By G: ASA/(4M4 5mm 0mm, [av/s t M645 4 TTORNEVS This invention relates to a power element operable by pressure change in a pressure-producing material. The pressure-producing material may be a contained thermally expansible material as for example disclosed in United States Patent No. 2,259,846, or the pressure-producing material may be a pressure fluid introduced from a remote source as illustrated in FIG. 3 of United States Patent No. 2,534,497.

Power elements of the above discussed type usually include a housing for the pressure-producing material, and a piston slidably mounted in the housing. Pressure change in the pressure-producing material causes the piston to move rectilinearly into and out of the housing. Necessary multiplication of the linear piston movement relative to that of the pressure-producing material is effected by providing a body or plug of force-transmitting material in a tapering chamber between the pressure-producing material and piston.

Objects of the present invention are to provide a power element of the above-mentioned type wherein:

1) The plug of force-transmitting material is a low friction, non-sticking, pliable material having the ability to easily reshape itself in accordance with such changes in the contour of its housing as occur during movement of the power element piston; thereby offering minimum resistance to piston movement and permitting formation of the power element as a comparatively small, low cost device,

(2) The plug reshaping characteristic is obtained without any such liquidity or fluidity a would cause the plug material to extrude or flow into the clearance spacebetween the piston and its housing; thereby enabling the power element to retain its calibration over a large number of cycles,

(3) The plug retains its reshaping and lack of fiuidity characteristics over a wide range of temperatures, as for example between minus 80 F. and 500 F.

Other objects of this invention will appear in the following description and appended claims, reference being had to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in the several views.

In the drawing FIG. 1 is a sectional view of a power element constructed according to the present invention.

Before explaining the present invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practiced or carried out in various ways. Also, it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

In the drawing there is shown a power element 1 including a housing 2, a body or pellet of wax or other thermally-expansible, pressure-producing material 3, a movable wall or piston 4, a corrugated stainless steel diaphragm 5, and a body of pliable force-transmitting material 6. A disc 7 of polytetrafluoroethylene is positioned between material 6 and piston 4 in order to prevent material 6 from extruding into the clearance space 9 between piston 4 and its bore 8. A spring (not shown) is pro- 3,059,475 Patented Oct. 23', 1962 vided for returning piston 4 to its illustrated position during pressure decrease in material 3.

Force-transmitting material 6 consists of discrete resinous particles dispersed in a flowa'ble polysiloxane. Preferably the discrete resinous particles are formed of poly tetrafluoroethylene, polymonochlorottifluoroethylene or nylon. The polysiloxane preferably includes a major pro portion of dimethyl polysiloxane and a minor proportion of diphenyl polysiloxane. The discrete resinous particles preferably comprise between and by volume of the force-transmitting material with the remainder being the polysiloxane. Some pliability advantages may be obtained by operating with volume percentages of resinous particles above 90% but the polysiloxane tends I to flow into clearance space 9 when the volume percentage of the resinous particles is below 75%.

The molecular weight of the flowable polysiloxane is preferably such as to obtain polysiloxane viscosities above 1000 centistokes at 25 C. Preferably the polysiloxane viscosity is about 2,000,000 centistokes at 25 C. Below polysiloxane viscosities of 1000 centistokes the polysiloxane is so fluid as to leak into clearance space 9. Polysiloxane having a viscosity of 2,000,000 centistokes is very slowly flowa'ble, i.e. if a lump of it were placed on a table it would require several hours to lose its lump shape.

Preferably force-transmitting material 6 is compounded the resinous particles with the polysiloxane and solvent,

and thereafter drive oh the solvent at a temperature between 300 F. and 400 F. The resulting mixture of discrete resinous particles and fiowable polysiloxane is admirably suited for use as a pliable force-transmitting material in the FIG. 1 power element.

In operation of the FIG. 1 power element atemperature increase in ambient atmosphere 10 causes material 3 to expand so as to exert an upward pressure against corrugated diaphragm 5. Diaphragm 5 thereby is flexed upwardly so as to push material 6 upwardly into cylindrical bore 8 and move piston 4 in the arrow 11 direction against the action of its return spring (not shown).

It will be noted that piston 4 is quite small in diameter, and conical surface 12 (which confines material 6) converges quite rapidly, i.e. the angle 13 which it makes with diaphragm 5 is fairly small. Also a considerable diaphragm area is exposed to material 6. These factors, coupled with the pliable character of material 6 enable pellet 3 to be formed large enough to produce a considerable movement of material 6 into bore 8 and a correspondingly long linear movement of piston 4 in the arrow 11 direction. Because of the considerable movement of force-transmitting material 6 into bore 8 material 6 undergoes a considerable amount of reshaping. In the past there have been employed as force-transmitting materials various types of deformable materials such as Ameripol, andneoprene. These deformable materials were however not flowable and could not undergo the deformation taking place in the FIG. 1 construction without exerting considerable pressures against the walls of housing 2. Such pressures (particularly those exerted against the wall formed by bore 8) offered considerable resistance to return movement of piston 4 and therefore necessitated the use of fairly heavy return springs if piston 4 was to keep pace time wise with the condition of atmosphere 10 during temperature decrease. Such heavy return springs exert considerable forces against the power clement walls, and the power element walls must therefore be relatively thick in order to withstand the forces. The power element housings are usually constructed of high cost brass, and it is therefore economically desirable to limit the amount of housing material; however, as indicated above, this has heretofore not been possible. An

the present invention includes discrete resinous particles dispersed in a ilowable polysiloxane. The discrete character of the resinous particles, coupled with the coating of polysiloxane around each particle, enables the individual resinous particles to easily change position with respect to one another without sintering into a solid immovable mass at the high temperatures (sometimes above 400 F.) to which the power element may be subjected.

The polysiloxane employed in the present invention has a comparatively flat viscosity curve when plotted against temperature; i.e. the viscosity at 150 F. is almost the same as at 400 F. Also the polysiloX-ane does not tend to decompose at the higher temperatures. As a result the polysiloxane does not tend to flow into clearance space 9 at the higher temperatures or solidify at the lower temperatures. Because of this characteristic of the polysiloxane the power element can .be employed in ambient atmospheres undergoing large temperature changes, as for examplein aircraft applications.

The pliable or reshaping characteristics of material 6 are not obtained at the expense of increased fluidity or tendency to flow into clearance space 9. 'Thus, by

utilizing 'a material containing only 25% by volume of" flowable polysiloxane and employing a polysiloxane haw ing a viscosity above 1000 centistokes it is possible toprevcnt leakage of material 6 into clearance space 9 and still retain the desired pliability. When the power element is to be used only in the higher temperature ranges (300 F. to 400 F.) the volume percent of the polysilox'ane may be advantageously reduced to approximately 10% or less since the pliability characteristic contributed by the polysiloxane is enhanced by slightly lowered viscosity characteristics. The discrete resinous particles (particularly when polytetrafluoroethylene is employed as the resinous material) contribute lubricating and non-sticking characteristics to material 6, and thereby enable the material to move into and out of bore 8 without sticking or clinging to the housing interior surfaces.

We claim:

1. In a power element," the combination comprising a housing structure defining a guideway and a flaring passageway extending therefrom; a piston reciprocably fitting said passageway; and a plug body of pliable force-transmitting material within the flaring passageway in operative engagement with the piston; said force-transmitting material comprising discrete solid resinous particles dispersed in and coated by a fiowable organic polysiloxane, said discrete particles occupying between 75% and 90% of the plug body volume, the arrangement of the resinous particles dispersed in the flowable polysiloxane serving to isolate the resinous particles from one another so as to permit said particles to easily shift relative to one other in response to pressure development on the plug body.

2. The combination of claim 1 wherein the polysiloxane includes a major proportion of dirnethyl polysiloxane and I a minor proportion of diphenyl polysiloxane.

3. The combination of claim 1 wherein the viscosity of the polysiloxane at 25 C. is above 1000 ccntistokes.

4. The combination of claim 1 wherein the discrete particles are selected from the group consisting of polytetrafluoroethylene, polymonochlorotiifluoroethylene, and nylon.

5. The combination of claim 1 wherein the discrete particles are formed of polytetrafluoroethylene.

6. The combination of claim 1 wherein the discrete particles are formed of polymonochlorotrifiuoroethylene.

7. The combination of claim 1 wherein the discrete particles are formed of nylon.

8. The combination of claim 1 wherein the fiowable polysiloxane comprises about 20% of the plug material volume.

9. The combination of claim 1 wherein the viscosity of the polysiloxane at 25 C. is between 1000 centistokes and 2,000,000 centistokes.

References Cited in the tile of this patent UNITED STATES PATENTS FOREIGN PATENTS 702,868 France Apr. 18, 1931

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