US2577981A - Hydraulic motor control - Google Patents

Description

Dec. 11, 1951 T. F. STACY HYDRAULIC MOTOR CONTROL Filed May 15, 1945 2 SHEETS -SHEET l INVE TOR.

92. MQMM a i forfleys Dec. 11,1951 TRQACY 2,577,981

HYDRAULIC MOTOR CONTROL 62%Zorwegs Patented Dec. 11, 195i HYDRAULIC MOTOR CONTROL 7 Thomas F. Stacy, Piqua, Ohio, assignor to The French Oil Mill Machinery Company, Piqua,

Ohio

Application May 15, 1945, serial lid 593,851

11 Claims. (01. s 52) This invention relates to hydraulic motors,

such as hydraulic presses, and particularly to the control of the hydraulic circuits by which the working member or ram of the motor is operated in a selected manner.

An object of the invention is to provide an improved control for a hydraulic motor, with which the activity of the working member of the motor may be controlled manually or automatically; with which a fast closing or initial movement of the working member may be obtained, and then automatically a slower movement for the remainder of the advance; with which the advance travel of the working member may be terminated manually, in response to pressure, or position reached by the working member, and which will be relatively simple, dependable, sensitive, compact and inexpensive.

Another object of the invention is to provide an improved control for a hydraulic motor; with which the working member of the motor may be held in its retracted position by a definite pressure which is sufiicient to prevent drifting or gradual movement of the working member away from retracted position; which will not place an undue load upon the pump, and which will have adequate safety protection against damage to the apparatus in case some control should fail to operate.

Further objects and advantages will be apparent from the following description of one embodiment of the invention, and the novel features will be particularly pointed out hereinafter in connection with the appended claims.

In the accompanying drawings:

Fig. l is a schematic diagram of a control system applied to a hydraulic motor, such as'used in a hydraulic press, of the type where the ram or motor moves vertically, and descending'during its'advance movement;

Fig. 2 is a diagram of the main control or reversing valve, with its valve element in the position which it occupies during the initial advance of the ram when the press is closing rapidly;

Fig. 3 is a similar diagram, but with the valve element in the position occupied after the ram travel has been slowed down for'the actual. work such as a pressing or drawing movement;

Fig. 4 is a similar diagram with the valve element in the position which it occupies at the end of an advance of the working member but before reversal has occurred; and

Fig. 5 is a side elevation of part of a press illustratingsome of the controls operated by the ram.

In the illustrated embodiment of the invention, and referring first to Figs. 1 and 5, a hy-.

draulic motor is incorporated in a hydraulic press of the type havinga vertically disposedcylinder I open at its lower end, and with a ram or working member 2 reciprocating in the cylinder and depending through the open lower end thereof. The usual packing gland 3 at the open lower end of'the cylinder I' provides a sliding, tight connection with the'ram or working'member 2.

The ram 2 is provided with a head 4 which fits and slides along the side walls ofthe interior of the cylinder I, with a retracting chamber 5 between the head 4 and the packing gland 3, and an advancing chamber 6 at the opposite face of the head 4.

The cylinder lhas the usual prefill checklvalve 7 which is spring pressed into closed position, but which may be'opened by the action of piston 8 operating in a pilot cylinder 9. The valve 1 has an open port I0 connectedto'the reservoir (not shown) which is frequently disposed at the top of the press, so that when the piston head '4 descends, the suction will draw operating liquid from the reservoir through the prefill valve into the advancing chamber until the descending ram encounters resistance. The valve 1' also serves as a rapid release for the fluid from the advancing chamber while the ram is being retracted, but this is' common in hydraulic presses. j 5

Fluid under pressure for the operation'of the ramorhydraulic motor is obtained from a suitable. pump ll which is driven by a motor in any suitable manner. The" pump is preferably cone tinuously driven, and is shown as of the variable delivery type with a compensator control"! 2. The pump is connected by a pipe to the reservoir (not shown) and at its "delivery side is connected by 'a pipe [4 to a main control or reversing valve 15 having a reciprocating valve element IS. The pipe M has, in series therein, a pressure relief check valve I! which opens to pass fluid from the pumptothe valve l5, but automatically closes to prevent reverse flow toward thepump. Also connected to the pipe I4 is a. pressure relief or unloading valve [8 which when open connects-the pipe E4 to a branch pipe 19 leading to the reservoir, so as to by-pass all or part of the fluid delivered by the pump back to the reservoir. ,f,

' The reversing valve [5 has a port 20 to which the pipe [4 is connected, and arranged along the chamber of the valve l5, but on opposite sides ofthe port 20 are, ports 2| and 22 which are connected by pipes 23 and 24 to the advancing chain- 3 ber 6 and retracting chamber respectively. Further along the valve |5 are exhaust ports and 26 which lead to the reservoir. The valve element I5 is provided with spaced lands 21 and 28 which control the fluid flow through the valve. One end of the valve I5 is provided with a chamber 29 in which a land 30 reciprocates, and a helical compression spring 3| is 'compressed'be tween the land 30 and the end of the housing of the valve |5, so as to resiliently urge the valve element l8 downwardly in Fig. 1. At the opposite end of the housing of the valve I5 is a cylinder 32' in which reciprocates a piston 33 that has a stem engaging against the land 28 or which can be coupled thereto. The cylinder 32 opens into a larger cylinder 34 having a reciprocating piston 35 which abuts against a stem 38 "depending K-in Fig. 1) from the piston 33. tween the pistons 33 and 35 is connected by a pipe 31 to the chamber of a pilot control valve 38, and a pipe 38 alsoconnectsth'e valv'efl38to the pipe M at a zone between the pump and "the check valve H. The valve 38 has a reciprocating valve element 40 with spaced lands 41, 42, and 43 all of the same size, so that the valve element is balanced against internal pressures. By reason of such balancing, the'valve element 48 will remain in any of the different positions into which it may be moved, unless outside forces are applied thereto.

One end of the housing of the valve 38 is closed, which in the example illustrated, is'the end in which the land 4| re'ciprocates, to form a chamber 45. This chamber is connected by a pipe 46 to the discharge side of a pressure relief valve 41; the other side of which is connected by a pipe 48 to the pipe 23. When the pressure in the pipe 23 exceeds the pressure for which the pressure relief valve 41 is set, that valve will open and pass fluid from the pipe 23 to pipe and thence into the chamber 45 of valve 38 where the resultant pressure on the land 4| forces the valve element 40 to the right into the position shown in 'full lines in Fig. 1. The pipe has a bleed port 49 so that when the valve '41 is closed, the pressure in the chamber 45rnay be released. The valve element 40, at the end opposite the chamber 45, is coupled to a valve stem 58 that extends outside of the housing and carries an armature 5| in a position to be magnetically operated upon by. either of two solenoids 52 and 53. When solenoid 52 is energized, it will movethe armature 5| to the left in Fig. 1 and shift the valve element 48 to the left, whereas when solenoid 53 is energized, it will move the valve element 48'int'o the full line position shown in Fig. 1.

A line wire L is connected to one end of each of the solenoids 52 and 53. Line wire L is connected through a manually operated, normally open starting switch 54 to the other end of the solenoid 52, and through a normally open stop switch 55 to the other end of the solenoid 53. Thus by closing either switch 54 or 55, the solenoids 52 and 53 may be energized to cause movement of the valve element 40 in either direetion'. depending upon which of the switches .54 and 55 is operated. An auxiliary, normally open switch 56 is connected by wires 51 and 58111 parallel across the switch 55, so that when the switch '56 is closed, it will also energize solenoid '53 in the same manner that the solenoid isenergized'when switch 55 is closed.

When the valve element '40 is in the righthand position shown in Fig. 1, the land 42 is'disposed between the openings into the chamber 'or The chamber bevalve 38, of the pipes 31 and 39, which prevents the passage of fluid from pipe 39 to pipe 31. At the same time the land 4| is to the left of an exhaust port 59, leading to the reservoir, and this vents the pipe 31. The land 43 is also at the same time somewhat to the right of port 53, into which pipe 39 opens. When valve element 40 is in its right-handposition. shown in Fig. 1, escape of fluid from the space between lands 42 and 43 is blocked and n0 fluid flows in pipe 39.

When the valve element 40 of the pilot valve 38 is moved to the left, such as when it is moved by energization of the solenoid 52, the land 42 will move to the left of the port opening into pipe 31 to connect the pipes 31 and 39 and interrupt flow from pipe 31 to the port 58. This delivers fluid from the pump to the pipe 31 and thence to the chamber between the pistons 33 and 35 in the valve l5. The fluid pressure in that chamber forces piston 33 upwardly in Fig. 1 against the action of the spring 3| until the valve element has the position shown in Fig. 2, which is the position in which it causes a fast advance movement of the ram 2.

Since the valve element 40 of the pilot valve is balanced against internal pressures, it will remain in whichever of the two positions it is moved into by the solenoids 52 and 53. When moved into the left-hand position in Fig. l, where it connects the pump to the chamber between pistons 33 and 35, it will not only cause the valve element Hi to be moved endwise against action of spring 3| into the position shown in Fig. 2, but also yieldingly hold it in that position by fluid pressure. This fluid pressure is obtained by a spring on the top of the check of valve l1. When this valve element |5 is in the position shown in Fig. 2, the land will be between the ports 2| and '25, and land 28' will be between the ports 22 and 28. This valve element thus connects the pump directly to the pipe 23 so that the fluid from the pump will be delivered to the advancing chamber 6. The ram will drop by gravity at a high rate of speed, and the fluid displaced by the piston head 4 from the chamber 5 will be expelled through pipe 24 and will pass beneath the land 28 in Fig. 1 to -exhaust port 26.

As the ram 2 advances, the preflll valve 1 will open, due to suction, but as soon as the ram encounters resistance, valve 1 will close, due to spring action, and the continued delivery of fluid to the chamber 5 through the pipe 23 from the pump will cause continued advance of the ram, but at a slower rate than that occurring when the prefill valve 1 was fully open. At an intermediate point before the same encounters resistance, it may be desired to have the speed of advance of the ram 2" also controlled, which is usually just before the press closes, or the work of the press begins. To obtain this result, the valve'elementlfi of the main control valve element I5 is moved'endwise (which would be downw'ar'dly in Fig. 1) into the position shown in Fig. 3. This Fig. Spo'sition may be considered one intermediate position which the valve element l6 may occupy, and which may be also identified as the slow-down or pressing position of the valve element.

In this position of the valve element It (see Fig. 3), the land 21 is still between the ports 2| and 25, but the land 28 has moved entirely across the port 22 to which the pipe 24 is connected, so that further escape of fluid from the retracting chamber 5 through the valve I5 is prevented. A pressure relief valve 61 is connected between the pipes 23' and 24 and opens to pass fluid-from;

the pipe 24 to the pipe 23 when the pressure in the pipe 24 exceeds that in pipe 23 bya selected amount for which the valve is set. The fluid expelled from the chamber 5 during theadvance of the ram after escape through valve I5 is prevented, passes through valve-8|, pipe 23, and then to the advancing chamber 6.: The ram'2 will therefore continue to advance at a slow speed as determined by the capacity of the pump discharging into advancing chamber 6 of cylinder I. This increased back pressure on the piston head 4 prevents jumping of the piston in case the resistance to the advance should'suddenly decrease, and it also partly balances the pressure on opposite sides of the packing or piston rings on piston head t so that leakage past the head willbe decreased, during the pressure or working stroke of the press.

The valve element i6 is moved into this first intermediate position for this purpose, either manually or under manual control, or in response to some operative condition of the press, such as when the press reaches a selected position in its advance, usually just before the real work of the press or ram starts. In the illustrated'example of the invention, the ram 2 carries a platen 62 (Fig. 5) with a cam 63 thereon, and this cam at the desired position in the advance of the ram engages a roller 64 on an arm 65 which is secured to a valve rod 66 in any of a plurality of different positions therealong. This valve rod extends vertically and is rockably mounted in bearings 81. At its upper end, the valve rod 66 carries an arm- 68 which is pivoted by a pin 69 (Fig. l to one end of a link i0,the other end of the link being pivoted by a pin II to the outer end of the valve element Hi. When arm 65 is rocked by the cam 63, this will rock arm 68 andmove the valve element l6 downwardly in Fig.1 from the fast advance position shown in Fig.2, into the intermediate position shown in Fig. 3. The cam 63 will holdv the arm 65 in that position during continued advance of the ram 2. In moving the valve element 18 into this intermediate position, the ram will overcome the fluid pressure which yieldingly holds the valve element in its upper position in Fig. 1.

The platen or ram also carries another cam '12, Fig. 5, which when the ram reaches a desired position in its travel, engages and operates an arm 13 also secured to, but adjustable'along valve rod 66. This further rocks arm 68 until it engages and operates theswitch 56 to close a circuit through the solenoid 53. The resulting energization of solenoid 5 3 pulls the valve element 40 of the pilot control valve back into the full line position shown in Fig. 1, which releases the pressure holding the valve element H3 in the intermediate position, whereupon the spring 31 moves the valve element [8 further in the same direction or toward the opposite end of its valve housing, but since the pressure in the chamber 34 jcorresponds to that in pipe 23, the piston 35 will stop the valve element [8 in another intermediate position shown in Fig. 4, until the pressure. in pipe 23 has fallen. sufficiently so that it can be overcome by the pressure of the spring 3|. The spring 3! then moves the valve element into the position shown in Fig. l, which is the reversing position.

This other intermediate position is shown clearly in Fig. 4, and it will be noted that when the valve element It is in this second inter-,

therport 2i andthe land 28 Will'still', cover-the:

port 22. The fluid will then be trapped inthere;-

tracting chamber 5, but fluid in the advancingchamber 6 may escape through port 2| around 5 the edge of land 21 to exhaust port 25,-and .the

fluid. delivered by the pump to the portcan also-pass around the edge of the land .21 to the ex-= haust port 25. a i I J When the valve element is moved into? itsfull. reverse position shown in full lines in-Fig. 1, the land 21 will be between ports 20 and 2i and land 28 will uncover port 22 and cover exhaust port 26. The fluid from the pump will then be delivered to the pipe 24 and through it to there tracting chamber 5- where it causes an elevation or retraction of the ram 2. The fluid expelled from the advancing chamber'fi during retraction of ram 2, will escape'partly through pipe 23 and valve l5 to port leading to the reservoir, and partly through pre-flll valve I directly to' the reservoir.

A pipe 14 connects the prefill pilot chamber 9 to the pipe 24, so that during the retracting operation, the pressure of the retracting chamber 5 will also be impressed on the chamber 9 which forces the prefill valve 1 open as soon as the" pressure in the chamber 6 has fallen sufliciently, and thereafter fluid may escape from the advancing chamber 6 largely through the 'preflll valve back to the reservoir which provides a much faster return movement of the ram 2 than would be possible if all of the fluid from chamber 6 had to escape through the main reversing valve. i

When the platen reaches a selected position in its return movement, which would be the de' sired end of the return movement,- another carn 15 on the platen or ram 2 engages a roller 16 on an arm 11 carried by another valverod 78. This,

rod I8 is rockably mounted in suitable bearings on the frame of the press, and at its upper end this rod 18 carries an arm 19 which engages and operates a valve element (Fig. 1) of a valve: 8|. This valve 8| is normally urged into a closed position by a helical compression spring 82 which is compressed between the valve element and the closed end of the housing of the valve 8|. The valve element 80 has spaced lands 83 and 84 so as to have a balanced interior pressure, and the space between the lands opens into a pipe 85 which is connected to a vent 86 of the pressure relief or unloading valve 18. The valve [8 is of a type known in the trade as a hydrocon valve which is obtainable in the open-market, and one example of such a valve is illustrated in U. S. Patent No. 2,043,453.

Valves of this type, such as I 8, have a valve element 8'! which normally engages with a seat, and. the pipe l4 opens into the valve chamber above the seat. The stem of the valve element 81 car 60 r1es a piston 88 which reciprocates vertically in'. the chamber of the valve housing, and this piston has a restricted vent 89 between its opposite faces.

The upper end of the valve chamber above the piston 86 is connected to the control vent 86.

This 'vent 88 normally opens through a spring. seated, ball check valve 90 to a vent port 9| leading to the reservoir. This ball check valve is ieldingly urged into closed position against its seat by a small compression spring, the degree 70 of compression of which may be varied or adju sted, or otherwise predetermined. A compression spring 92, urges the valve element 81 into. closed position on its-seat, and the valve stem 8'1v has a port 93 extending endwise therewith from.

7 end toend to take care ofthe oil displaced above th -ste'm whn the-steam-opens andcloses. vent" is also connected to the pipe 85,-it will be obvious that fluid from the vent: may escape either through the ball'check valve '90 or through the pipe 85. 1 h pipe'"94. leads-from the valve 81' to a=pressure relief valve. 95 of any suitable type which may be adjusted to open at any selected pressure, and in this example this valve 95 shouldbe-set to open at a relatively low pressure, or one'lower than that for which the valve 80 is set to open. When the .valve element 80 of valve BI is re-" leased, the spring 82 will operate thevalve element" into a position to place the land 83 between the openings into the pipes 85 and 94, which. disconnects these pipes. r In such a case the-pressure relief valve 95 will be ineffective, and valve I8 will open only in response to a pressurewhlchis suflicient to unseat or open the ball valve element 90. When the valve'element 80 is, i

When thepressure has reached a value highenough to openball check valve Sill, the, pressure above'the piston 88 will be relieved. Vent- 89 is smaller than vent 86, and therefore pressure above the piston 88 will be relieved faster than it can be built up. This creates a differential of pressure on the piston 88 causing it to open.

When piston 88 opens, the pressure in the line- I4, of course, will be relieved, which will cause'the ball check valve 90 to close,,and pressure building up through the vent 89 willthen balance-on each sid'eofthe piston 88, andthe spring 92 will then again seat the valve 81. Pressure will again build up and the valve will open. Actually the;

dampened action of the piston 88 causes'the valve element 81 to come to rest at a position where it will maintain the required pressure accordingto thesetting of the spring on the ball checkvalve- 90. When the valve 8| is open and connects pipes 85 and 94, then the valve I8 will open according to the lower pressure setting of the relief valve 95; When valve 8i is closed, then valve I8 opens:

only in response to the pressure for which ballclieckvalve 9011s set. V H

When the ram is approaching its desired r e trac'ted position'and hasopene'd the valve 8I,-thisconnects the low pressure relief valve 95 to the vent 88, and as a result the valve [8 will open'at a relatively low pressure, and maintain in' pipe I4 that relatively low pressure which caused the opening of valve 95. Thiisth'e pump will continue to exert this relatively low'pres'sure in the retracting chamber and hold the rain' retracted under that'pressure', whichis'sufiicient to prevent advance or descent of theram'througli fluid leakageyweight or'otherforce, The p ess will be held in this idle positionuntila" downward movement is initiated: v

Toenable amanual operation of themain re versingvalve I5, the valve rod 66 has fixedmere-- on an arm 99 (Fig. 5) to which ahandle IIiiiis' pivoted by pin IUI. The rod 66 also carries a' spring clip I02 which releasably engages the handle I08 when the handle is swun gfi'nto the dash-line position shown in Fig. 5-. When'the handle is in'this dash-line positio'n 'it 'is out of the: way, and the rod may be-rockd bythe-cams crane-n; When manual operation of 'the ro verslng 'valve' is desired} the-handle I00 can'be pulled-forwardly into the'fullline position, and thenby rockingor-moving it sidewise, it will cause the valverod68 to be rocked, which will move the valve element I6' upwardly in Fig. 1 and dausean advance or descent'of the ram 2. This descent will continue only so long as the handle I'IIIiisheld in its rocked position, and when this I handle is released-spring 3| will return the valve element iii to its reversed position shown in full lines in Fig.1. If the operator allows the handle Hill to return only partly to the idle positiom-the valve element I6 may be stopped in either of the positions shown in Figs. 3 and 4 to cause a slow advance-of the ram, or to stop movement of the ram and hold it-in that position without'reversal'.

.In;' the operation; of the illustrated control system, the press will be idle while the control parts are in the :position in Fig. 1, because the cam on the-platen or ram has rocked the arm I]. shaft 18 and arm I9 to push the valve BI into the open position that connects the control valve or device 95 to the vent 88 of the unloading valve I8.

1 The reversing valve element I6 is in the full line position shown'in Fig. 1, so that fluid from the pump will be delivered to the retracting chamber 5to hold the ram or working member 2 elevated. To initiate anadvance movement of the ram or working member,- the operator closes the switch 54 to'energize solenoid 52, and this causes movement, of the pilot valve element to the left in Fig, 1 toconnect the pipes 31 and 39. This causes fluid to be delivered between the pistons 33 and 35 of: valve I5,and that pressure forces the valve element I6gupwardly in Fig. 1 into the position shown in Fig. 2. The valve element iii, in that position, connects-the pump to the advancing chamber 6, and releases fluid from the retracting chamber 5 through the valve I5 to the reservoir.

The rain 2 will then descend or advance rapidly under the action of gravity, and the prefill valve I automatically opens by suction to allow this rapid advance. At the beginning of this descent,

1 the caml5 releases arm 11 and thus causes release of the valve element of valve 8|, which disconnects the pressure relief valve from the vent of the unloading valve I8. At a desired intermediate position in the descent of the ram Mth'e cam 63, on the platen or ram, engages androcks arm 65, which moves the valve element I6. i'nto'the position shown in Fig 3, and auyor the operating fluid thereafter displaced from, the retracting chamber 5 will be forced through thepressure relief valve 8| into pipe 23 and then'into the chamber 6.

Aftertlie ram has encountered a suflicient resistance, that is, hasexerted a pressure which is a ma'xim'umdesire'd, the pressure in the advancing chamber 8,'which is communicated through the pipe, 48 to the pressure relief valve 41, will open that valve and pass through pipe 46 to the cylinder 45 in the pilot valve 38. This will move the valve element 40 promptly and quickly to the right, in Fig. 1, which disconnects the pipes 31 and 39'and vents the pipe 31. The spring 3i then urges the valve'element I6 toward the position shown in Fig. 1, but the pressurein the pipe 23, which was transmitted'through pipe 48 to the chamber34 in the reversing valve, forced the piston 35 upwardly i'ntothe' position shown in Figs. 3 and 4, where it prevents movement of the valve element I6 beyond the-second in'termediateposition shown in Fig. 4. The valve element IS in that second inter m'ediate positionreleasesthe pressure in' the advencingchamber, closes theretra'cting chamber,

and by-passes the delivery from the pump, but as soon as the pressure falls in pipe 23, the spring 3| will overcome the pressure in chamber 34 and automatically will continue the movement of the valve el ment is into the full reversing position, shown in Fig. 1. The ram 2 will then be elevated to a selected retracted position at the end of which it again operates valve 8| to decrease the pressure in the retracting chamber, but which holds the ram 2 in its upper position under a balancing pressure.

If the pressure in the advancing chamber 6 does not build up enough to open the valve 47 before the cam 12, that moves with the ram, engages and rocks arm 13 further in the same direction as was caused by cam 63, then the valve rod 66 will be rocked further and will positively move the valve element l6 into the position shown in Fig. 4, and also close the switch 56. The valve element It, when in the Fig. 4 position, stops further advance of the ram and releases the pressure in the advancing chamber, and the closing of the switch 56 causes the sole- "noid 53 to be energized, and the latter will move the valve element 40 of the pilot valve 38 into the position shown in Fig. 1, which disconnects the pipes 31 and 39 and releases the pressure holding the valve element It in the Fig. 4 position. Spring 3| then continues the movement of the valve element l6 into the Fig. 1 position,

and this automatically causes the ram 2 to be retracted, as explained above.

It will be understood, of course, that the pressure exerted by the ram or platen on the valve rod 66 is suflicient to move valve element it against the fluid pressure exerted against the end of piston 33. This fluid pressure, which is made effective by the pilot valve 38, thus yieldingly holds the valve element IS in its upper position in Fig. 1, where it causes an advance or descent of the ram. The descent of the ram 2 may be stopped and reversed at any position of its advance by merely operating the switch 55.

It will be understood that various changes in the details, materials and arrangements of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.

I claim:

1. In an operating system for a hydraulic mo tor of the type having a working member, ad-

vancing and retracting chambers for operating said member, a pump, and connections between the pump and chambers for controlling the movements of said member, that improvement which comprises a reversing valve in said connections for connecting said pump alternately to said chambers and having a movable valve element, a pilot valve, fluid operated means controlled by said pilot valve for moving said valve element 'into a position in which it connects said pump 'to said advancing chamber and releases fluid from said retracting chamber, and holds it yieldably in said position by fluid pressure, means yieldingly urging said valve element in the opposite direction into another position in which it connects said pump to said retracting chamber and releases fluid from said advancing chamber,

hydraulic means responsive to fluid pressure in said advancing chamber-for blocking movement of said valve element in said opposite direction beyond an intermediate position in which it closes 10 said retracting chamber and releases fluid from said advancing chamber, and means operated by said member in a selected position in its advance caused by pressure in the advancing chamber, for moving said valve element against the force of said fluid operated means into said intermediate position.

2. In an operating system for a hydraulic motor of the type having a working member, advancing and retracting chambers for operating said member, a pump, and connections between the pump and chambers for controlling the movements of said member, that improvement which comprises a reversing valve in said connections for connecting said pump alternately to said chambers and having a valve element movable between four positions in one of which it connects the pump to the the advancing chamber and releases fluid from the retracting chamber, in another position of which it connects the pump to said retracting chamber and releases fluid-from the advancing chamber, in one intermediate position of which nearest said one position it connects the pump'to the advancing chamber and prevents the release therethrough to exhaust of fluid from said retracting chamber, and in a second intermediate position of which it prevents release of fluid therethrough to exhaust from the retracting chamber and releases fluid from said advancing chamber, fluid actuated means for moving said valve element into said one position in which the pump is connected to the advancing chamber to cause an advance of said working member, and holding it yieldingly in that position by fluid pressure, means yieldingly urging said valve element from said one position through said intermediate positions into said another position in which it connects the pump to the retracting chamber, hydraulic means responsive to fluid pressure in said advancing chamber for temporarily blocking movement of said valve element towards said other position beyond said second intermediate position, while pressure in said advancing chamber exceeds a predetermined pressure and releasing said valve element at other times, and means operated by said working member in a selected zone of its advance caused by pressure in the advancing chamber for moving said valve element against the force'of said fluid actuated means into said one intermediate position, and preventing its return to said one position during further advance of said working member.

3. In an operatin system for a hydraulic motor of'the type having a working member, advancing and retracting chambers for operating said member, a pump, and connections between the pump and chambers for controlling the movements of said member; that improvement which comprises a reversing valve in said connections for connecting said pump alternately to said chambers and hav n a valve element movable between two endpositions through an intermediate position, in one; end position of which it -con connecting the pump to the advancing chamber and preventing release therethrough to exhaust of fluid from said retracting chamber, a pressure relief valve connectedtbetween said chambers and passing fluid therethrough in a direction from termediate positionibut weaker than said fluid actuated means, and means operated by said working member while in a selected zone of its advance caused by pressure in the advancing chamber, for moving said valve element against the force' of said' fluid. actuated means into said intermediate position and preventing its return to said. one position during further advance of said working member in said zone, whereby fluid from said retracting.- chamber will then be, forced through said pressure relief valve into. said advancing chamber.

4. In an operating system for a hydraulicmotor of the type having advancing and retracting chambers, a working member reciprocated by pressure differences in said chambers, a pump, and connections between the pump and chamber for controlling the movements of said member, that improvement which comprises a reversing valve'in said connections; and having a valve-element which, by its movement between two positions, connects said pump alternately to said chambers and releases therethrough fluid from the other chamber, and havinga'n' intermediate position in which it connects said pump to said advancing chamber and prevents release therethrou'gh of fluid from said retracting chamber, means yieldingly urgin said valve element into the position in which it connects the pump to the retractingchamber, means yieldingly holding said valve element in the position in which-it connecte the pump to the advancing chamber with release of fluid from said retracting chamber, a pressure relief valveconnected between said chambers and passing fluid from said retracting chamber to said advancingchamber when the fluid pressure per unit area in the retracting chamber exceeds that in the advancing chamber by a selected amount, and means operated by said workin member for moving said valve element into said intermediate position during a selected zone of movement of said member.

5. In an operating system for a hydraulic motor of the type having advancing and retractin chambers, a working member'reciprocated by pressure differences in said chambers, a pump,

and connections between the pump and chambers for controlling the movements of said member, that improvement which comprises a reversing valve in said connections, and having a valve element which, by its movement between two positions, connects said pump alternately to said chambers and releases therethrough fluid from the other chamber, and having-an intermediate position in which it connects said pump to said advancin chamber and prevent'srelease there- .5

through of fluid from said retracting chamber, means yieldingly urging said valve element into the position in which it connects the pump to the retracting chamber, means yieldingly'holding said valve element in the position in which it connects the pump to the advancing chamber with release of fluid from said retracting chamber, a

' pressure relief valve connected between said chambers and passing fluid from said retracting chamber to said advancin chamber when the fluid pressure, per. unit, area in the retractin chamber exceeds that in the advancing chamber by a selected amount, and means responsive t'oa predetermined: operativecondition of said motor for moving said valve element into said intermediate position during a seiectedzone of m0,v.,ement of-said member,

6. In an operating; system for a hydraulic motor of the type having advancing and retracting chambers, a working member reciprocated by pressure differences in said chambers, a, pump, and connections between the pump and: chamber for controlling the movements of said member, that improvement which comprises a reversing valve in said connections, and having, a valve element which, by its movement between two positions, connects said pump alternately to said chambers and releases therethrough fluid from the other chamber, and having an intermediate position in whichitprevents release therethrough of fluid from said retracting chamber and releases thcrethrough fluid from said advancing chamber, means yieldingly urging saidvalve element into the position in which it connects the pump to the retracting chamber, means yieldingly holding said valve element in the position in which it connects the pump to the advancing chamber with the release of fluid from saidretracting chamber, and means operated by said working member at a selected intermediate position in its advance movement for positively moving said valve element into said intermediate position.

7,. In an operating systemitor a hydraulic motor of the type having advancing and retracting chambers, a working member reciprocated by pressure differences in said chambers, a pump, and connections between the pump. and chamber for controlling the movements of said member, that improvement which comprises a reversing valve in said connections, and having a valve element which, by its movement between two positions, connects said pump alternately to said chambers and releases therethrough fluid from the other chamber, and having an intermediate position in which it connects said, pump to said advancing chamber and prevents release therethrough of fluid from said retracting chamber, means yieldingly urging said valve element into the position in which, it connects the. pump to the retracting chamber, means yieldingly holding said valve element in the position in which it connects the pumpvv to, the advancing chamber with, release of fluidirom said retracting chamber, a pressure relief valve connected between said chambers and passing fluid from, said re- 1 tracting chamber to said advancing, chamber when the fluid pressure per unit area in the retracting chamber exceeds thatin the advancing chamber by a selected amount, and means operated by said working member when it reaches a selected. position in its advance; for. releasing said. valve element fromthe actionof said yielding; holding means, whereby said, urging means may move said valve element. into the position in which it connects the pump to the retracting chamber and releases therethrough fluid from said advancing chamber.

8. In an operating system for a hydraulic motor of the type having advancing and retracting chambers, a working; member, :reciprocated by pressure differences; in said chambers, a. pump, and connections between the. pumpandchamher for controlling the movements of :said member, that improvement which comprises a reversing '13 valveln said connections, and having a valve element which, by its movement between two positions, connects said pump alternately to said chambers and releases therethrough fluid from the other chamber, a pressure relief valve connected to the connection from the pump to said reversing valve, and when open, discharging fluid from the pump to exhaust, means associated with said pressure relief valve for causin'git to open at a selected, relatively low pressure, means for making said last named means effective and inefiective, and additional means associatedwith said pressure relief valve for normally causing said pressure relief valve to open at a selected, relatively high pressure.

9. In an operating system for ahydraulic motor of the type having advancing and retracting chambers, a working member reciprocated by pressure differences in said chambers, a pump, and connections between the pump and chamber for controlling the movements of said member, that improvement which comprises a reversing valve in said connections, and having a valve element which, by its movement between two positions, connects said pump alternatelyto said chambers and releases therethrough fluid from the other chamber, a pressure relief valve connected to the connection from the pump to said reversing valve, and when open, discharging fluid from the pump to exhaust, means associated with said pressure relief valve for causing it to open at a selected, relatively low pressure, means for making said last named means effective and ineffective, and means rendered effective by said working member at a selected end position in its retracting movement, for operating said control means to place the pressure relief valve under they control of said relatively low pressure control.

10. In an operating system for a hydraulic motor of the type having advancing and retracting chambers, a working member reciprocated by pressure differences in said chambers, a pump,

and connections between the pump and chamber for controlling the movements of said member,

that improvement which comprises a reversing valve in said connections, and having a valve element which, by its movement between two positions, connects said pump alternately to said chambers and releases therethrough fluid from r the other chamber, a pressure relief valve connected to the connection from the pump to said reversing valve, and when open, discharging fluid from the pump to exhaust, a control device associated with said pressure relief valve for causing operation of said pressure relief valve at a relatively low pressure, an additional control device also associated with said pressure relief valve for causing operation of said pressure relief valve at a relatively higher pressure, a device for normally removing the pressure relief valve from the control of said first mentioned control device, but operable to place the relief valve under control of said first mentioned control device, and means operated by the working member at a selected end position in its retracting movement for operating said device that places the pressure relief valve under the control of said first mentioned control device, whereby the working member will be held and retracted by said relatively low pressure.

11. In an operating system for a hydraulic motor of the type having advancing and retracting chambers, a working member reciprocated by pressure differences in said chambers, a pump,

connecting means between the pump and chambers for delivering fluid from the pump alternately to said chambers, and means for controlling selectively such delivery of fluid from the pump to said chambers, that improvement which comprises a valve connected to the pressure side of the pump for lay-passing delivery from the pump, control devices associated with crating said nullifying means to place said valve under the control of said low pressure control device, whereby when the working member reaches said selected position, said valve will open and by-pass suflicient fluid from the pump to maintain said selected low pressure in the chamber to which the pump is then delivering f uid.

12. In an operating system for a hydraulic motor of the type having advancing and retracting chambers, a working member reciprocated by pressure difierences in said chambers, a pump, connecting means between the pump and chambers for delivering fluid from the pump alternately to said chambers, and means for controlling selectively such delivery of fluid from the pump to said chambers, that improvement which comprises a valve connected to the pressure side to operate at a relatively low pressure, and, the

other being set to operate at a relatively higher pressure, and means normally preventing control of the valve by said control device set for the relatively low pressure and operated by the working member at a selected end position in its movement thereof to place the valve under the control of said control device set for the relatively low pressure.

13. In an operating system for a hydraulic motor of the type having advancing and retracting chambers, a working member reciprocated by pressure differences in said chambers, a pump, connecting means between the pump and chambers for delivering fluid from the pump alternately to said chambers, and means for controlling selectively such delivery of fluid from the pump to said chambers, that improvement which comprises a pressure relief valve connected to the delivery side of said pump, and when opened, bypassing fluid from the pump away from said chambers, said valve having two control vents, either of which, when opened, will cause opening of the valve, a control device with each vent, one set to open when the pressure in the vent reaches a relatively low pressure, and the other when a relatively higher pressure is reached, a normally closed auxiliary valve in the vent connection to the control device set for the relatively low pressure, and means responsive to movement of the working member for opening said auxiliary valve when said working member reaches a selected end position in one of its movements.

14. In an operating system for a hydraulic motor of the type having advancing and retract- .ingchambers, a working member ;reciprocated shy pressure'difierences in said chambers, a pump for delivering operating fluid under pressure, and connections between the pump and chambers for selectively controlling the delivery of operating fluid from said pump tosaid chambers and thereby controlling the direction of means effective to cause delivery of fluid at .a

pressure that will hold said member retracted.

15. In an operating system for a hydraulic motor of the type having advancing and retract.- ,ihgchambers, a working member reciprocated by ,pressure difierences in said chambers, a pump for delivering operating fluid under pressure, and connections between the pump and chambers for selectively controlling the delivery of operating fluid from said pump to said chambers and thereby controlling the direction of movement of said member, that improvement which comprises means for controlling the maximum pressure of fluid delivered by said pump to said retracting chamber, and ,means effective when said member reaches a desired end position in its return movement for causing the pressure of fluid delivered to said retracting chamber to fall to a point where it will sustain the weight of the work- .ing member and hold it retracted, and place a vminimum practical load on said pump.

16. In an operating system for a hydraulic motor of the type having advancing and retracting chambers, a working member reciprocated by pressure differences in said chambers, a pump for delivering operating fluid under pressure, and connections between the pump and chambers for thereby controlling the direction of movement qprl es, means controlle by saidzmember an renderedseflective when said member reaches a desired end position in its return movement for causing a decrease in the pressure of the fluid delivered by the pump to that which will sustain the weight. of said member and hold it re- ..tracted, and place a minimum load on said punm.

17.In,an operating system for a hydraulic motorflot the type having advancing and, .retracting chambers, a working member reciprocated by pressure difierences in said chambers, .a pump for delivering operating fluid under prusure, and connectionsbetween the pump and chambers for selectivelyucontrolling the delivery of. operating fluidfrom said pump to said chambers and. thereby controlling the direction of movement of said member, that improvement which comprises an element operated by said member when said member reaches a selected end position in its return travel, and means coritrolled by said. member and rendered efiective by said operation of said member to reduce the pressure of the fluid-delivered by said pump to-said retracting chamber to a pressure which will hold said member in retracted position and place a minimum load'on said pump.

THOMAS F. STACY.

REFERENCES CITED The following references are of record in'tho fileof this patent:

UNITED STATES PATENTS Number Name Date 2,157,240 Keel May 9, .1939 2,192,778 Stacy Mar. 5, 1940 2,218,818 Harrington Oct. 22, 1940 2,240,898 Wiedmann May 6, 1941 2,277,640 Harrington Mar. 24, 1942 2,303,946 Miller Dec. 1, 1942 2,320,759 Stacy June 1, 1943 "2,324,697 Harrington July 20, 1943 2,351,872 Parker June 20, 1944 2,367,241 Stacy Jan. 16, 1945 2,385,119 Welte Sept. 18, 1946

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