US3410089A

US3410089A - Fluid operated device

Info

Publication number: US3410089A
Application number: US621511A
Authority: US
Inventors: Joseph D Snitgen
Original assignee: Individual
Current assignee: Individual
Priority date: 1967-03-08
Filing date: 1967-03-08
Publication date: 1968-11-12
Anticipated expiration: 1985-11-12
Also published as: GB1184531A

Description

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.J. D. SNITGEN Filed March 8, 1967 FLUID OPERATED DEVI CE \QNx Nm Nov. 12, 1968 United States ABSTRACT OF THE DISCLOSURE This application discloses a fluid operated device for applying force to a workpiece through a force applying member that is first moved at a relatively rapid rate of speed toward the workpiece and which it is capable of applying a relatively low force against the workpiece, and which subsequently and automatically upon encountering the workpiece moves at a substantially slower rate but applies a substantially higher force. The device is comprised of a first fluid motor having a piston that is actuated by air pressure. This piston is connected to a substantially smaller piston of a hydraulic pump to displace fluid from a pumping chamber into a second fluid motor chamber for moving a piston of a second fluid motor that is connected to the force applying member and which has a substantially greater area than the pump piston. A spring biased connection is provided between the pump piston and the piston of the second fluid motor for simultaneous movement of the piston of the first fluid motor, the piston of the fluid pump and the piston of the second fluid motor upon the initial introduction of the air pressure to the first fluid motor. This effects the rapid movement of the force applying means to a first position. When this first position is reached and the workpiece is engaged, the spring yields causing the displacement of fluid from the fluid pump to the second fluid motor to effect a substantial force amplification.

Background of the invention This invention relates to a fluid operated device and more particularly to an improved fluid operated device that is adapted to apply an intensified force against a workpiece.

In many instances a force applying element is brought into engagement with a workpiece and subsequently exerts a force against the workpiece. For example, in a punch press the punch engages and pierces a workpiece, in a spot welding apparatus one or both of the welding electrodes engage and apply pressure against a workpiece, and so on. Other examples include devices for locking, holding, clamping or pinching workpieces, jacks, or any other devices utilizing a power cylinder wherein it is desired to apply a relatively small force when encountering a relatively small resistance and a considerably higher force when the resistance increases. With each type of apparatus, it is desirable to have the workpiece engaging element move rapidly into its initial engagement with the workpiece. It is, however, necessary in many instances to apply a considerable force against the workpiece once it is engaged. It is diflicult to achieve these high forces as well as the rapid movement without extremely high power requirements or without extremely complicated or large machinery or without damaging the workpiece by engaging it at tOo high a speed with too high a force.

It is, therefore, a principal object of this invention to provide a fully self-contained relatively compact and simple force magnifying or intensifying device.

It is another object of this invention to provide a fluid operated device having a force applying member that is rapidly moved into engagement with a workpiece and which subsequently exerts a substantial force against the atent O 3,416,689 Patented Nov. 12, 1968 workpiece. A related object concerns the provision of such a device also having a powered return stroke.

Summary of the invention A fluid operated device embodying this invention is particularly adapted to apply force to a workpiece. The device includes a first fluid motor composed of first and second members supported for relative movement in a first direction under the influence of a fluid force. A fluid pump composed of third and fourth members supported for relative movement in a first direction and adapted to displace fluid upon this relative movement is associated with the first fluid motor. A second fluid motor com prised of fifth and sixth members supported for relative movement in a first direction upon the exertion of a fluid pressure thereto is adapted to receive the fluid transferred from the fluid pump upon relative movement of its members in the first direction through fluid passage means. The second fluid motor and fluid pump are proportioned to effect substantially less relative movement between motor members upon the fluid transfer through the fluid passage means than the relative movement occurring between the pump members for a force amplification between the fluid pump and the second fluid motor. Means operatively connect the first and third members for simultaneous movement and means operatively connect the fourth and fifth members for simultaneous movement. Force applying means are operatively connected to the fifth member for its movement upon movement of the fifth member to apply force against a workpiece. Coupling means operatively connect the first member to the fifth member for simultaneous movement of the first, third, fourth and fifth members upon the introduction of fluid to the first fluid motor and until the force applying means reaches a first position for effecting rapid movement of the force applying means to this first position. The coupling means is effective to provide for relative movement between the third and fourth members upon the force applying means reaching its first position for displacing fluid from the fluid pump to the second fluid rnotor for movement of the force applying means from the first position to a second position at a substantially lower rate and wherein the force applying means is capable of transmitting a substantially greater force to the workpiece than the force generated during the movement of the force applying means to the first position.

Brief description 0 the drawings FIGURES 1 and 2 are cross sectional views taken along the longitudinal axis of a fluid operated device embodying this invention and showing the components in two different positions. FIGURE 1 shows the components before a workpiece is engaged, and FIGURE 2 shows the components subsequent to the engagement with the workpiece.

FIGURE 3 is a cross sectional view taken along the line 3-3 of FIGURE 1.

FIGURE 4 is an enlarged view of the encircled area in FIGURE 1.

In the drawings the reference numeral 11 illustrates a fluid operated, force applying device embodying this invention. The device 11 includes a force applying member, indicated generally by the reference numeral 12, which is adapted to engage and apply a force against a workpiece (not shown). The member 12 may carry a punch, other forming tool or may comprise a welding electrode for spot welding. Other uses for this device will suggest themselves to those skilled in the art.

The force applying device 11 is comprised of a sup porting housing 13 which with internal components defines a first fluid motor, indicated generally by the reference numeral 14; a fluid pump, indicated generally by the reference numeral 15; and a second fluid motor, indicated generally "by the reference numeral 16. In addition, a fluid reservoir 17 is provided for the pump 15 and for the second fluid motor 16 which are hydraulically interconnected in a manner that will become more apparent as this description proceeds.

Thesupporting housing 13 is comprised of a first tubular cylindrical member '18 defining a cylindrical bore 19. The tubular member 18 is closed at one end of the cylindrical bore 19 by an end closure member 21 in any suitable manner. At the other end of the bore 19, the tubular member 18 is telescoped around a reduced diameter portion 22 of a generally cylindrical housing member 23. This end of the tubular member 18 is axially aflixed to the housing member 23 by means of a plurality of circumferentially spaced, socket headed bolts or studs 24. A fluid-tight seal is provided between the members 18 and 23 by an O-ring seal 25 that is received within a circumferential groove 26 formed in the housing member portion 22 and which sealingly engages the bore 19. The housing member 23, end closure 21 and member 18 define a first fluid cavity 27 which forms a part of a fluid motor 14. A generally cup-shaped piston 28 is supported within the fluid cavity 27. The piston 28 is formed with a circumferential groove in which an O-ring seal 29 is positioned to provide a fluid-tight seal between the bore 19 and piston 28 whereby the latter divides the fluid cavity 27 into two variable volume fluid chambers thus completing the first fluid motor 14.

A tapped opening 32 is formed in the closure member 21 for receipt of a fitting 33 for introduction of fluid under pressure, for example compressed air or hydraulic fluid under pressure, to the fluid cavity 27. For purposes of this description compressed air is used. During the advanced stroke pressurized air is introduced on one side of the piston 28 by means of a fluid passage 34 formed at the terminus of the tapped opening 32, and on the retract stroke the passage 34 is vented to the atmosphere. The portion of the cavity 27 on the other side of the piston 28 is vented to the atmosphere during the advance stroke or exposed to a source of fluid pressure during the retract stroke by means of an axially extending, fluid passage 35 formed in the housing member 23. The passage 35 intersects a tapped opening 37 into which a fitting 38 is threaded. A conventional four-way valve (not shown) may be used to vent and pressurize the respective cavities, as Will become more apparent as this description proceeds.

The closure member 21 may be formed with a cylindrical extension 41 in which an axially extending fluid passage 42 is formed. The fluid passage 42 terminates in the outer face of the extension 41 at a tapped opening 43 which may be used as an alternative location for the introduction of air in lieu of opening 32. If not used opening 43 may be closed by a plug 44.

The piston 28 is formed with a concentric cylindrical bore 46 in which one end of an elongated piston rod 47 is .aflixed by means of a set screw 48. The elongated piston rod 47 has a chamfered end portion 49 that is received within an axially extending bore 51 formed in an extension of the force applying member 12. The piston rod end portion 49 acts as a piston and coacts with the bore 51 to form the fluid pump 15. The piston rod end 49' is formed with a circumferential groove 52 (FIG- URE 4) in which a resilient O-ring 53 is received. The O-ring 53 bears against a cylindrical member 54, which is preferably formed from Teflon or some other antifriction material and urges'it into engagement with bore 51 to form a fluid-tight, low friction seal. A back-up O-ring seal 55 is received in a groove in the piston rod 47 at a location spaced from the end 49. The seal 55 engages a cylindrical bore 56 in an enlarged cylindrical portion 57 of the force applying member 12. The seal 55 may be of 4 the same type as shown in FIGURE 4 or may be of a conventional O-ring type.

The enlarged portion 57 of the force applying member 12 acts as a piston and is slidably received in a cylindrical bore 61 extending axially through one end of the housing member 23. The piston portion 57 has a circumferential groove 62 in which an O-ring seal 63 is received. The piston portion 57 and bore 61 form the second fluid motor 16 and define spaced variable volume fluid cavities 64 and 65.

A cylindrical housing member 66, which also forms a portion of the housing 13, is telescopically received upon a second cylindrical extension of the housing member 23 and is fixed thereto by circumferentially spaced socket headed bolts or studs 67. An O-ring seal 68 is received in a groove 69 of this housing extension and sealingly engages a bore 71 defined by the housing member 66 to effect a fluid-tight seal.

The outer end of the tubular housing member 66 is closed by a. closure plug 72 in which a cylindrical bore 73 is formed. The outer end of the force applying member 12 is piloted or slidingly supported in the bore 73. An O-ring seal 74 is received in a circumferential groove 75 formed in the outer end of the force applying member 12 to sealingly engage the bore 73. The closure member 72 is axially fixed to the housing member 66 by circumferentially spaced studs or socket headed bolts 76.

An outer edge of the closure member 72, indicated generally by the reference numeral 77, snugly engages the adjacent portion of the force applying member 12 and may act as a scraper during reciprocation of the force applying member 12 to remove any foreign matter that tends to accumulate thereon, such as Weld splatter which will accumulate if the force applying member functions in a welding electrode. To assist in this cleaning action, a wiper ring 78 is received in a groove 79 formed in the closure member 72 adjacent the edge 77.

The housing members 66 and 23 and closure member 72 coact to define the fluid reservoir 17. This reservoir is annular and encircles the force applying member 12. This reservoir not only accommodates for changing volumes of fluid used by the device as it is cycled, as will become more apparent, but also serves as a source of makeup fluid to replace that lost through normal leakage. As a consequence devices of the present type are fully self-contained and may be operated for long periods of time Without ever requiring additional fluid. To prevent the entrainment of air in the reservoir 17, a floating annular piston 81 is received on a cylindrical extension 82 of the closed member 72. The piston 81 has a cylindrical bore 83 in which an O-ring seal 84 is carried to sealingly engage the extension 82. A second O-ring seal 85 at the outer periphery of the piston 81 sealingly engages the bore 71 thus precluding leakage from the reservoir 17 past the piston 81. The back side of the piston is vented to atmosphere through normal leakage.

A plurality of circumferentially spaced coil springs 86 are received in bores 87 and 88 formed in the piston 81 and' closure member 72, respectively. The springs 86 urge the piston 81 in a direction which tends to decrease the volume of the reservoir 17. One or more circumferentially spaced, radially extending openings 89 are formed at the inner end of the extension 82 and pro vide a fluid connection between the reservoir 17 and the fluid cavity 65.

The fluid pump 15 is maintained in fluid registry with the cavity 64 of the fluid motor 16 by means of a plurality of fluid passages formed at circumferentially spaced locations in the force applying member 12 (FIGURE 3). The fluid passages 95 extend from the bore 51 into the cavity 64 through the enlarged piston portion 57. The passages 95 terminate adjacent a reduced diameter cylindrical portion 96 of the force applying member 12 on the inner end of the piston portion 57. The portion 96 is slidably received in a bore 97 formed in the housing member 23 and is sealingly engaged by an O-ring seal 98 received in a circumferential groove 99 formed in the member 23.

A plurality of radially extending passages 101 extend through the force applying member 12 adjacent the outer end of the piston portion 57. Under some circumstances, as will become more apparent as this description proceeds, the passages 101 are closed by the piston end portion 49 of the piston rod 47. Preferably the passages 101 have a total flow area equal to the flow area of the passages 95.

One end of the cylindrical extension 96 of the force applying member 12 is formed with an axially extending bore 102 coaxial with the piston rod 47 and extending around the latter. An enlarged diameter portion 103 of the piston rod 47 is received in the bore 102. The outer end of the extension 96 is threaded, as at 104, to receive a cap-shaped stop member 105 having a bore 106 through which one end of the piston rod 47 extends. A coil spring 107 encircles the piston rod 47 and is compressed between its enlarged diameter portion 103 and a shoulder 108 formed at the base of the bore 102. The spring 107 normally urges the piston rod enlarged diameter portion 103 into engagement with the stop member 105 (FIGURE 1).

Operation The sequence of operation of the force applying device 11 will be described assuming that the force applying member 12 is a welding electrode for a spot welding device. It is to be understood, however, that the device is capable of use in other embodiments and that different sequences of operations may be employed. When the force applying member 12 functions as a welding electrode, it is preferred to preclude its rotation with respect to the supporting housing assembly 13 and for this purpose a pin 111 is inserted in a bore 112 formed in the housing member 23. The pin 111 extends into an elongated keyway 113 formed in the force applying member 12 to preclude rotation during its reciprocation. The force applying member 12 may then be connected to any suitable source of electrical current so that it may function as a spot Welding electrode.

FIGURE 1 illustrates the force applying device 11 as it appears before the work engaging end of the force applying member 12 is brought into engagement with the piece to be welded. In this position, the piston 28 is at the extreme right hand side of the cavity 27 and the coil spring 107 has urged the force applying member 12 to its extreme right hand position wherein the cavity 64 of the second fluid motor 16 has substantially little or no volume. In this position, fluid from the reservoir 17 can flow through the passage 89 into the cavity 65 as a result of the force exerted by the spring biased piston 81. Fluid will also fill the passages 101 and the bore 51 of the fluid pump so that the bore 51 and cavity will be completely filled with fluid.

When the device 11 is to be actuated, air under pressure is admitted to the first fluid motor 14 through the fitting 33. At the same time, the volume of the cavity 27 on the other side of the piston 28 is exposed to the atmosphere by means of the valve which cooperates with the fitting 38. Hence, the fluid pressure applied to one side of the piston 28 will cause it to move to the left within the bore 19. The precompression on the coil spring 107 is chosen so that the air pressure acting upon the piston 28 will not cause the spring 107 to yield until the force applying member 12 engages some resistance. Hence, the force applying member 12 will be moved to the left simultaneous with movement of the piston 28 during the initial stage of operation.

The piston 28, which as has been noted, is directly coupled to the piston rod 47, will tend to cause the piston rod end 49 to move into the bore 51. However, since the force applying member 12 is also moving in the same direction and at the same rate of speed, there will be substantially no displacement of fluid from the fluid pump 15. The volume of the fluid cavity 64 is, however, increased during this initial movement since the piston portion 57 of the force applying member 12 moves with respect to the supporting housing 13. This results in a decrease in volume of the cavity 65 and an increase in volume of the cavity 64 Since the cross sectional areas of the cavities 64 and 65 are the same and the piston portion 57 is common to these cavities, fluid will merely flow from the cavity 65 to the cavity 64 through first the ports 101, then the bore 51 and finally through the passages 95. As has been noted, the ports 101 and passages havesubstantially the same cross sectional area, hence, there will be substantially no restriction to flow. This described initial phase of movement of the force applying member 12 is accomplished at a relatively high rate of speed since there is substantially no force amplification during this initial movement.

When the end of the force applying member 12 contacts a workpiece, there will be very little force amplification exerted upon the workpiece. Such initial force amplification will be proportional to the ratio of the area of the piston 28 to the area of the force applying element 12 that contacts the workpiece. Assuming that the workpiece is supported in a relatively unyielding manner, a resistance to further movement of the force applying element 12 is created as soon as the workpiece is engaged. This resistance to further movement eventually will overcome the action of the coil spring 107 and the previous coupling between the piston rod 47 and force applying member 12 efiected by the spring 107 will now yield and permit relative movement between the piston rod 47 and force applying member 12( FIGURE 2). During the initial relative movement, the piston rod end 47 will move toward the ports 101 and tend to displace fiuid from the cavity defined by the bore 51. This initial displacement of fluid will drive fiuid through the ports 101 into the cavity 65 and into the reservoir 17 through the port 89. This will cause the piston 81 to be displaced slightly to the left against the action of the coil springs 86.

Continued movement of the piston rod end 49 will bring it into registry with the ports 101 cutting off further flow of fluid to the cavity 65- and reservoir 17 from the bore 51. Member 54 prevents abrasion of O-ring 53 by the ends of bores 101. As the relative movement continues, created by the continued application of fluid pressure on the piston 28, the piston rod end 49 will displace fluid from the fluid pump 15 into the cavity 64 of the fluid motor 16 through the passages 95. Inasmuch as the exposed area of the piston portion 57 of the force applying member 12 is greater than the area of the piston rod end 49, there will be a fluid amplification in the fluid force exerted upon the force applying member 12 by the fluid motor 16. This force amplification is achieved because of the noted difference in areas and results in a substantially lesser movement of the force applying member 12 than the movement of the piston 28. A considerably higher force is exerted, however, upon the workpiece by the force applying member 12 during this stage of operation. As the force applying member 12 moves relative to the housing assembly 13 during this movement, the volume of the fluid chamber 65 will be decreased. The fluid displaced from the chamber 65 cannot, however, flow into the chamber 64 since the ports 101 have been closed by the piston rod end 49. The fluid thus displaced from the chamber 65 is, however, transferred into the fluid reservoir 17 through the ports 89. This necessitates an increase in the volume of the reservoir 17 which is accomplished by displacement of the piston 81 against the action of the coil springs 86.

When the desired degree of pressure is exerted upon the workpiece current is passed through the force applying member 12 or an electrode aflixed thereto to effect the spot weld. After the spot weld has been effected, the fitting 33 is vented to the atmosphere and air under pressure is introduced to the chamber 27 on the opposite side of the piston 28 by exposing the fitting 38 to air pressure. The piston 23 then is forced to the right within the bore 19. This relieves the compression upon the spring 167 and the piston rod 47 can also follow the movement of the piston 28 in this direction. This permits fluid to return to the bore 51 from the fluid cavity 64 by means of the passages 95. Hence, the piston 28 and piston rod 47 will again move to the position shown in FIGURE 1 and the force applying element 12- will be retracted at a rapid rate. During this movement, fluid is transferred from the fluid cavity 64 to the fluid cavity 65 via passages 96 and ports 101. The fluid previously displaced into the reservoir 17 can then return into the cavity 65 and bore 51.

The action of the spring biased piston 31 within the reservoir 17 will insure that the pump 15 and motor 16 are maintained filled with hydraulic fluid. In addition any leakage which may occur can be taken up from the reservoir 17 so as to reduce the necessity for refilling.

It should be readily apparent that the disclosed device is highly effective in permitting rapid movement of the work engaging element 12 toward the workpiece. When the workpiece is engaged, continued movement will occur at a substantially slower rate but with a very large force amplification. In one exemplary embodiment of the invention, the piston 28 has an effective area of 2.405 square inches, the piston rod end 49 has .an effective area of 0.062 square inch, and the effective area of the piston portion 57 of the force applying member 12 is 0.475 square inch. The spring 197 has a preload of about 42 pounds and a force of 48 pounds is required to deflect this spring to a point where ports 101 are closed. These factors will result in the force applying member 12 ultimately applying a force of about 1200 pounds to the workpiece when a line pressure of 80 p.s.i. is applied to the piston 28. Other ratios may be obtained by merely varying the areas of one or more of the several pistons. Generally speaking, spring 107 should be preloaded to a degree in which the force necessary to cause it to further compress is slightly greater than the force necessary to overcome friction of the various parts as the electrode or tool, as the case may be, is advanced toward the workpiece. This permits the force applying member to advance all the way to the workpiece while the device is in the relatively rapid or first stage mode of operation, whereby upon encountering the workpiece the device may shift to the second stage high force mode of operation.

It is to be understood that various modifications are possible in the mode of operation without departing from the spirit and scope of the invention and that various other changes and modifications will suggest themselves to those skilled in the art. Such changes in the mode of operation and in the structure as may suggest themselves to those skilled in the art are within the scope of the invention, as defined by the appended claims.

What is claimed is:

1. A fluid operated device for applying a force to a workpiece or the like comprising a first fluid motor comprised of first and second members supported for relative movement in a first direction under the influence of a fluid force exerted thereupon, afluid pump comprised of third and fourth members supported for relative movement in a first direction and adapted to displace fluid from said fluid pump upon relative movement in their said first direction, a second fluid motor comprised of fifth and sixth members supported for relative movement in a first direction upon the exertion of a fluid pressure thereto, fluid passage means interconnecting said fluid pump and said second fluid motor for fluid transfer from said fluid pump upon relative movement of said third and fourth members in their said first direction to said second fluid motor for effecting relative movement between said fifth and said sixth members in their said first direction, said fluid pump and said second fluid motor being proportioned to effect substantially less relative movement between said fifth and said sixth members upon said fluid transfer through said fluid passage means than the relative movement occuring between said third and said fourth members for a fluid force amplification between said fluid pump and said second fluid motor, means operably connecting said first and said third members for simultaneous movement, means operably connecting said fourth and said fifth members for simultaneous movement, force applying means operatively connected to said fifth member for movement upon movement of said fifth member to apply a force to a workpiece upon movement thereof, and coupling means operatively connecting said first member to said fifth member for simultaneous movement of said first, third, fourth and fifth members upon the introduction of fluid to said first fluid motor and until said force applying means reaches a first position for effecting rapid movement of said force applying means to said first position, said coupling means being effective to provide for relative movement between said third and fourth members upon said force applying means reaching said first position for displacing fluid from said fluid pump to said second fluid motor for movement of said force applying means from said first position to a second position at a substantially lower rate and wherein said force applying means is capable of transmitting a substantially greater force to a workpiece than the force generated during the movement of said force applying means to said first position.

2. A fluid operated device as set forth in claim 1 wherein the coupling means includes biasing spring means effective to transmit motion from the third member to the fourth member until the force applying means encounters an object to creat suflicient force for yielding of said spring means, the yield of said spring means providing for relative movement between said third and fourth members.

3. A fluid operated device as set forth in claim 1 wherein the fifth and sixth members define axially spaced, variable volume fluid chambers and further including second fluid passage means interconnecting said fluid pump with one of said chambers, the first named fluid passage means interconnecting said fluid pump with the other of said chambers, and means for precluding flow through said second fluid passage means when said third and fourth members move relative to each other more than a predetermined amount.

4. A fluid operated device as set forth in claim 3 further including fluid reservoir means in direct fluid communication with the one chamber of the second fluid motor, and means for maintaining the fluid in said reservoir under a predetermined pressure to preclude the entrainment of air therein and to take up any loss of fluid from said fluid pump and said second fluid motor.

5. A- fluid operated device as set forth in claim 4 further including means for introducing air under pressure to the first fluid motor for effecting relative movement between the first and second members, said second fluid motor, said fluid pump and said reservoir being filled with a liquid.

6. A fluid operated device as set forth in claim 4 wherein the fluid operated device includes housing means defining a first cylinder which comprises the second member, the first member comprising a first piston supported for reciprocation within said first cylinder, the third member comprising a second piston aflixed for movement with said first piston, the fourth member comprising a second cylinder in which said second piston is supported for reciprocation, the fifth member comprising means defining a third piston integrally connected to said second cylinder, the sixth member comprising a third cylinder reciprocally supporting said third piston, said third cylinder being defined by said housing at a point axially spaced from said first cylinder.

7. A fluid operated device for applying force to a workpiece or the like comprising housing means defining a first cylinder bore opening through One end of said housing means and means defining first and second fluid closures at opposite ends of said first cylinder bore, a first piston supported for reciprocation within said first cylinder bore, means for introducing air under pressure into said first cylinder bor on opposite sides of said first piston for reciprocating said first piston within said first cylinder bore, a force applying member supported for reciprocation within said housing means and having a projecting end adapted to engage a workpiece, means defining a second cylinder bore in said force applying member concentric with said first cylinder bore, a second piston supported for reciprocation within said second cylinder bore, means for aflixing said second piston to said first piston for simultaneous reciprocation of said first and second pistons, biasing means interposed between said second piston and said force applying member for establishing a yieldable driving connection between said second piston and said force applying member, means in said housing means defining a third cylinder bore, means fixed to said force applying member defining a third piston supported for reciprocation within said third cylinder bore, the effective area of said third piston being substantially greater than the effective area of said second piston, first fluid passage means extending through said force applying member from said second cylinder bore to said third cylinder bore on one side of said third piston, second fluid passage means formed in said force applying member and extending from said second cylinder bore to said third cylinder bore on the other side of said third piston, and a liquid substantially filling said second cylinder bore, said third cylinder bore and said first and said second fluid passage means, said biasing means being effective to transmit movement of said first and said second pistons into movement of said force applying member in the same direction and at the same speed upon the application of fluid pressure to said first piston and until the resistance to movement of said force applying member exceeds a predetermined value, said biasing means being effective to yield upon the exertion of such a predetermined resistance to movement of said force applying member for relative movement of said second piston and said force applying member for displacing a fluid from said second cylinder bore into said third cylinder bore on said one side of said third piston through said first fluid passage means, said second piston precluding fluid flow from said second cylinder bore to said third cylinder bore on said other side of said third piston through said second fluid passage means upon a predetermined relative movement between said second piston and said force applying member for generating a force amplification upon said force applying member by the fluid displaced from said second cylinder bore after said predetermined relative movement.

8. A fluid operated device :as set forth in claim 7 wherein the closure means for one end of the first cylinder bore defines the third cylinder bore and further ineluding a tubular member sealingly engaged at on end with said closure means and extending away therefrom, means defining a closure for the other end of said tubular member, said last named closure means having an inwardly extending tubular portion for piloting said force applying member, said tubular extension and said tubular member defining an annular fluid reservoir, third fluid passage means extending through said tubular extension from said fluid reservoir to said third cylinder bore on the other side of the third piston, and a spring biasedannular piston received within said annular fluid reservoir for displacing fluid from said reservoir to said third cylinder bore through said third fluid passage means.

9. A fluid operated device :as set forth in claim 7 wherein the force applying member has a cylindrical portion extending into the first cylinder bore through the closure means at one end thereof, the second piston having a portion extending through said cylindrical portion, said cylindrical portion of said force applying member defining an annular cavity around said second piston and in which an enlarged portion of said second piston is positioned, said biasing means comprising coil spring means positioned within said annular cavity and reacting against said enlarged portion of said second piston at one of its ends and against said force applying member at its other end.

10. A fluid operated device as set forth in claim 9 wherein the closure means for one end of the first cylinder bore defines the third cylinder bore and further including a tubular member sealingly engaged at one end with said closure means and extending away therefrom, means defining a closure for the other end of said tubular member, said last named closure means having an inwardly extending tubular portion for piloting said force applying member, said tubular extension and said tubular member defining an annular fluid reservoir, third fluid passage means extending through said tubular extension from said fluid reservoir to said third cylinder bore on the other side of the third piston, and a spring biased annular piston received within said annular fluid reservoir for displacing fluid .from said reservoir to said third cylinder bore through said third fluid passage means.

References Cited UNITED STATES PATENTS 3,266,415 8/1966 Palmer -52 XR 3,276,206 10/1966 Calkins 60545 EDGAR W. GEOGH'EGAN, Primary Examiner.