US2383093A - Fluid pressure generating means - Google Patents

Description

Aug. 21, 1945. G. A. WAHLMARK FLUID PRESSURE GENERATING MEANS Filed Sept. 15 1941 3 Sheets-Sheet l as b INVENTOR.

A. WAHLMARK 2,383,093

FLUID PRESSURE GENERATING MEANS Filed Sept. 15, 1941 3 Sheets-Sheet 2 INVENTOR.

Aug. 21, 1945. G. A. WAHLMARK FLUID PRESSURE GENERATING MEANS Filed Sept. 15, 1941 3 Sheets-Sheet 3 wmw Gil/7227,62)" Q4 Patented Aug. 21,1945

FLUID PRESSURE GENERATING MEANS Gunnar A. Wahlmark, Rockford, Ill., asslgnor to Sundstrand Machine Tool (20., Rockford, 111., a

corporation of Illinois Application September 15, 1941, Serial No. 410,861

Claims.

The invention relates generally to a fluid pressure generating means and more particularly to a pumping unit of the Wobbler type.

One object of the invention is to provide a pumping unit of new and improved construction.

Another object is to provide a pumping unit of the wobbler type having new and improved mean governing the Wobbler to determine the displacement of the unit.

Another object is to provide a pumping unit of the Wobbler type having a control means governing the position of the Wobbler to determine the rate of fluid discharge and means for placing a constant pre-load on the control means.

Other objects and advantages will become apparent from the following detailed description taken in connection with the accompanying drawings, in which:

Fig. l is a longitudinal central sectional view of a pumping unit embodying the features of this invention. A portion of the casing at the right end of the figure is illustrated projecting forwardly of the exact central section in order to illustrate a passage.

Fig. la is a detail view taken along line la-la of Fig. 1.

Fig. 2 is a view partially in section and partially in elevation taken approximately along the line 2-2 of Fig. 1.

Fig. 3 is a transverse sectional view taken along the line 3-3 of Fig. 1 and looking in the direction of the arrows.

Fig. 4 is a fragmentary view partially in plan elevation and partially in horizontal diametrical section.

Fig. 5 is a fragmentary sectional view taken ap proximately along the lines 5-5 of Figs. 1 and 2.

Fig. 6 is a fragmentary sectional view taken approximately along the line 6-6 of Fig. 1.

While the invention is susceptible of various modifications and alternative constructions, it is shown in the drawings and will hereinafter be described in a preferred embodiment. It is not intended, however, that the invention is to be limited thereby to the specific construction disclosed, but it is intended to cover all modifications and alternative constructions falling within the spirit and scope of the invention as defined in the appended claims.

The pumping unit comprises a casing, generally designated 5, composed of a hollow housing member having near one end a radially outwardly projecting annular flange l for attachment to a motor or other support (not shown) and a radially inwardly projecting annular flange 8. Non-rotatably received in the housing member 6 at the end opposite the flange 8 is a cylinder block ii provided with a radially outwardly extending I annular flange ill. Mounted over the outer end of the cylinder block 9 is an end closure l l secured to the housing member 8 through the medium of a phirality of bolts I2 projecting through the end closure, the flange Id andinto the housing member 5. The inner face of the end closure ii is provided with a circular recess it which with the end face of the cylinder block t forms a valve chamber housing valve means more particularly described hereinafter.

The cylinder block t is formed with a plurality of parallel, longitudinally extending and annularly arranged cylinders it opening at their left end, as viewed in Fig. 1, to the valve chamber it through an annular series of ports it, and at the other end opening without restriction to the interlor of the housing member ii. Reciprocable in each cylinder it is a piston l t adapted in all positions to extend partially from the cylinder block for engagement by an actuating means, generally designated ll. Extending axially of the cylinder block is a stepped bore having a first portion l8 opening outwardly through the right hand end of the cylinder block, as viewed in Fig. l, a second portion it of slightly smaller diameter so as to form an annular shoulder 20, a third portion M of still smaller diameter so as to form an annular shoulder 22, and a portion 23 of still smaller diameter forming a shoulder M. Extending longitudinally of the casing with its inner end projecting through the valve chamber it into a recess 25 in the end closure l l, and with its outer end projecting outwardly of the casing for connection with a motor, is a shaft 26. Near its inner end, the shaft is journaled in a roller bearing 21 seated in the portion H of the stepped bore, while near its outer end the shaft is surrounded by a s eeve is formed with a radially projecting flange 29. Mounted in the housing member 6 adjacent the flange 8 is an annular ring 30, generally L-sh'aped in cross section,,and between the ring and the sleeve 28 there is interposed a roller bearing 3! while between the ring and the flange 29 there is interposed a roller bearing 32, respectively supporting the shaft radially and against end thrust.

The end closure H (see Figs. 2 and 4) has opening through the end thereof two large threaded ports 35 and 36. The port 35 opens to an arcuate recess 31, which in turn communicates with the outer portion or the chamber l3 through a plurality of oblong ports 38 (see Figs. 3 and 4) The port 36, through a passage 39, opens to an annular chamber 40, which in turn communi-- cates with the chamber 13 by a narrow annular port 41 concentric with the shaft 26 and disposed intermediate the center and the periphery of the chamber. 1

order to control the flow of fluid between the ports 35 and 36, and the ports l of the cylinders 14, there is interposed in the chamber 13 a wheel-like or spoked valve 42 such as more particularly disclosed and claimed in my Patent No. 2,190,812, dated February 20, 1940. This valve is mounted eccentrically with respect to the shaft 26, and to that end such eccentric mounting is here obtained by the employment of an eccentric cam 43 (Fig. 1a) non-rotatably secured on the end of the shaft 26 by means such as a pin 44. To more effectively seal the inner periphery of the valve against leakage of fluid,- there is interposed between the valve and the eccentric member 43 a pair of annular rings 45, and interposed between the rings are a p urality of small compression springs 46 urging the rings apart so as to cause them to complete an effective seal against the end faces of the end closure II and the cylinder block 9 to provide effective seals.

Incorporated in the end closure H are high pressure relief valve means, generally designated 50 and 5|, one for each of the passages between the ports 35 and 36 and the valve chamber l3. The valves ar so arranged that fluid which is relieved from a high pressure passage is returned t the other passage, which will then be at low pressure. To that end there is fitted into a bore 52 (see Fig. 1), extending between the annular chamber 40 and the arcuate recess 31, a nipple 53 having a central bore 54 and providing an annular valve seat 55 disposed in the recess 31. Cooperating with this annular valve seat is a disk valve 56 urged toward seated position by a strong compression spring 51. This compression spring (bears at its other end in a cap screw 58 threaded into the'end closure I I s that the spring 51 may be adjusted to permit discharge from the annular recess 40 to the arcuate recess 31 only at certain desired high pressure. From the arcuate recess 31 there leads a passage 59 which is connected to a chamber 60 for the valve means 51 through the bore 6| of a nipple 62 similar to the nipple 53. This nipple provides an annular valve seat 63 disposed Within th chamber 60, and cooperating with the valve seat is a disk valve 64 urged to seated position by a strong compression Spring 65. This spring, like the spring 51, is seated in a cap screw 66 threaded into the end closure Ii 7 so as to adjust the valve means to open only at certain desired high pressures in the recess 31. The chamber 6|] is, as best seen in Fig. 3, connected by a passage 61 directly to the port 36.

The actuating means 11 here takes the form of a wobbler composed of an inner annular member 1U pivotally mounted on the shaft 26 by means of a pin 11 and an outer annular ring member 12. This ring member 12 is rotatable relative to the inner member 10, and to that end there is interposed between the members and 12 a ball 'bearing 13 to take the side thrust and a roller bearing 14 to take the end thrust. The member 12 is, of course, disposed to engage the projecting ends of the pistons 16, and to that end the ends of the: pistons, as well as the surface of the member 12 contacted thereby, are rounded. Herein the curvature given to the ends of the pistons and to the surface of the member 12 is such that the moment arms of the forward (in Fig. 1 upper) half of the wobbler will have such proportion with respect to the moment arms of the rearward (in Fig. 1 lower) half of the wobbler as to tend to cause the reaction of the pistons on the wobbler to restore the same to neutral or no-stroke position.

Unique control means are herein provided for governing the position of the wobbler. This control means permits of a pre-loading of the wobbler and enables slight increase in pump displacement to be automatic to compensate for increased working pressures. Moreover, this control means in conjunction with certain valve means, presently to be disclosed, but more particularly disclosed and claimed in my copending application Serial No. 410,860, filed of even date herewith, permits of adjustment of the wobbler by a force of constant value regardless of the pressure at which the pump may be working at any particular time. Comprising this control means is a cylindrical control member or cam 11 slidable longitudinally in the portion IQ of the stepped bore in the cylinder block 9 so as to be concentric of the shaft 26 and particularly of the wobbler I1. At its right hand end, as viewed in Fig. 1, the control cam 11 is enlarged to form a piston 18 slidable in the portion H! of the stepped bore. At its extreme right hand end, the control cam 11 is provided with an end edge 11' disposed in a plane at right angles to the shaft 26 and adapted to bear against the.

outer member 12 of the wobbler to determine the angular adjustment of the wobbler. The piston portion 18 of the control cam 11 in cooperation with the annular shoulder 20 forms a hydraulic means which, as presently will become apparent, is utilized to place the wobbler under a, pre-load of a predetermined constant pressure.

The control cam 11 may be shifted longitudinally to determine the angular position of the wobbler H by a variety of means. Herein this means is shown as hydraulic and comprises a casing member secured to the housing member 6 by suitable means, such as bolts 81, to a base surface 82 formed on the top of the housing member 6 for that purpose. Extending longitudinally of the casing member 80 is a bore 83 forming a cylinder in which is reciprocable a piston 84. The ends of the bore 33 are closed by caps 85 and 66 threaded thereinto with the cap 86 having threadedly projecting therethrough an adjusting screw 81 against which the piston is adapted to abut to determine the limit of its movement in that direction. A cap screw 68 is mounted over the outwardly projecting end of the screw 81. Fluid under pressure may be supplied to either end of the cylinder through ports 89 and 90 by and under the control of suitable means not herein shown.

Reciprocatory movement of the piston 84 is transmitted to the control cam 11 through a lever 33 extending through registering openings 94 and 95 formed in the members 80 and 6, respectively. The lever 93 is pivotally mounted intermediate its ends on a shaft 96 iournaled in ears 91 depending from the casing member 80 and extending into the opening 95 in the housing member 6. At its upper end, the lever 93 is somewhat rounded and projects into an appropriate socket 99 formed in the piston 84 for that purpose. The lower end of the lever 93 is adapted to engage the control cam 11 which, however, instead of being formed with a socket, is formed with an elongated slot 99 into which the end of the lever projects. The slot is So disposed that the lever is capable of shifting the control cam in a direction to adjust the Wobbler toward nostroke position, but permits movement of the control cam in that same direction independently of the lever 03. trol cam 11 to the right, as viewed in Fig. 1, under the influence of the piston 34 is determined by the adjustment of the screw 81 or by the control cam itself when the control cam has shifted the wobbler to its absolute zero or nostroke position, determined by full 360 engagement of the end of the control cam with the member I2. Maximum stroke position of the Wobbler is determined by abutment of the control cam with the shoulder 22, the piston 84, as best seen in Fig. 1, being arranged to still have some clearance when the control cam is in this position so that this maximum stroke position is definitely determined by the control cam. Shift of the Wobbler from one side to the other of its neutral position to obtain reversal of operation of the pump is obtained by means operating independently of the control cam TI. Herein this means also is hydraulic and comprises an annular piston I03 fixedly secured on the shaft 26 by means such as a pin I04. Cooperating with the piston. is a cylinder I05 having a narrow extension I06 slidable in a groove I'I formed in the periphery of the shaft for that purpose. Extending radially from the extension I06 is an arm I08 received in a suitable socket I03 formed in the inner member I0 of the wobbler.

Operating fluid is supplied to opposite ends of the cylinder I through passages formed in the shaft 26. To that end, the shaft is formed with an axial bore III terminating at one end in a portion II2 of slightly reduced diameter. Inserted into the bore is a tube II3 fitting snugly into the bore III at its left hand end, but rednced throughout the major portion of its length to the diameter of the reduced portion II2 of the bore and projecting into the reduced portion II2 so as to define with the bore I I I an annular passage. This annular passage is by a radial passage II4 connected to the left hand end of the cylinder at a point immediately adjacent the piston I03. A similar radial passage II5 opens to the right hand end of the cylinder I05 immediately adjacent the piston I03 and communi cates at its inner end with the interior of the tube H3. At its left hand end the annular passage formed by the bore III and the tube H3 is connected by a radial passage II6 to an annular groove i ii formed internally of a sleeve or bushing tilt fixedly retained by a pin II9 in the reduced portion 23 of the stepped bore in the cylinder block. Spaced from the groove III is a similar groove I20 connected by a passage I2I to the interior of the tube H3. Control fluid is supplied to the grooves I I? and I20 by and under the control of suitable means not completely shown herein, but which is fully disclosed and claimed in my copending application Serial No. 410,860, filed of even date herewith. Reference is made to that application for more complete disclosure. The extreme left hand end of the bore I II is, of course, suitably plugged to close the passage formed by the interior of the tube.

Make-up fluid for the pump and control fluid are supplied by a make-up pump, generally designated I25. This pump is of the rotary gear element type disclosed and claimed in my Patent No. 2,132,813, dated October 11, 1938, and comprises generally an inner gear element I26 fixed on the shaft 26 to be driven thereby, an outer gear I21 mounted eccentrically withrespect to The extent of shift of theconthe inner element, and a crescent shaped dividing member I28. The elements operate in a chamber formed by the outer end face of the housing member 3 and an end closure I23 secured by bolts I30 to the housing member 6. Fluid is drawn into the pump through an intake passage I3I formed in the housing member 3 which leads to an enlarged recess I32 forming the intake port for the pump. A similar enlarged recess I33 forms the discharge port for the pump and leading from this recess is a make-up and control fluid supply passage I34. This passage, as best seen in Figs. 1 and 4, is formed as a bore extending longitudinally of the housing member 6 to.

one side of the opening- 35 formed therein, thence through the flange I0 of the cylinder block and the end closure II (see Fig. 6) where it discharges through a port I35 to the extreme upper end of a bore I36 formed in the end closure II.

Closing the upper end of the bore is a cap I40 formed with a raised boss I4I to provide an annular space to which the port I35 opens. Mounted in the bore I36 are valve means acting to govern the pressure of the control fluid supplied by the pump I25. These valve means include a piston valve I42 reciprocable in the bore I36. A light compression spring I43 bears at one end against the valve I42 and at the other end bears against a sleeve I44 disposed in the lower end or the bore I36. The valve is designed to maintain approximately lbs. per square inch under normal operating conditions. The sleeve may be retained in position by a pin I45. The valve I42 is in the nature of a by-pass relief valve and governs a port I46 opening to the bore at a point spaced inwardly from the port I35 and communicates by means including a passage I4I with a tank or reservoir (not shown). The passage I41 opens to the opening 05 in the housing member 6, whence the fluid discharged from the passage I41 flows to the interior of the casing and thence back to the tank through a port I40 formed in the bottom of the housing member 6.

In addition to the spring I43 the valve I42 is urged toward its normal closed position, that is, in abutment with the raised boss I4 I'and with the port I46 covered, by a plunger I5I which is subjected to the working pressure of the pumping unit. This plunger is reciprocably mounted in a bore I52 in the sleeve I44 and projects out of the end 01' the sleeve into abutment with the inner face of the end of the valve I42. In order that this plunger may act on the valve I 42 regardless of the direction of discharge of the pumping unit, it is formed at its inner end with a reduced portion I53 so as to provide an annular shoulder I54 constituting a first area on which pressure fluid may act to urge the plunger outwardly of the sleeve. The reduced portion of the plunger I53 reciprocates in a smaller sleeve I55 mounted in the bore I52. The end of this reduced portion I53 constitutes a second area upon which pressure fluid may act to shift the plunger outwardly. These pressure areas are made equal so that fluid under the same pressure will have thesame effect on either. Opening to the space between the shoulder I54 and the end of the sleeve I55 is a passage I56 which communicates at the other end with the outer periphery of the valve chamber I3, while the end of the reduced portion I53 is subjected to the pressure of the fluid in the annular recess through the medium of a passage I51. Thus it will be seen that as the working pressure at which the pump unit is operating increases the valve I42 will open the port I46 only at increased pressure, and thus will raise the pressure of the control fluid supplied by the pump I25.

Valve means, generally designated I60 is provided to maintain the supply of make-up fluid and fluid for pre-loading the control cam 11 at a constant pressure regardless of variation produced by the valve I42, Accordingly, there is formed in the end closure II parallelwith the bore I36 a bore I6I which again is closed at its outer end by a cap I62 having on its inner face a raised boss I63. Reciprocable in the bore is a valve I64 of the cylinder type having lands I65 and I66 separated by a groove I61. The land I66 also has opening longitudinally therethrough a plurality of passages I68. The valve is urged toward abutment with the boss I63 by means of a compression spring I69 operable to maintain a certain desired pressure, herein approximately one hundred pounds per square inch.

Opening to the bore so as to be controlled by the valve I64 is a port I1I which is by a passage I12 connected to the bore I36 at the annular space provided by the boss I4I, so as at all times to be supplied with fluid by the pump I25. This port I1I is so positioned relative to the land I66 of the valve I64 that it is open when the valve abuts the boss I63, but is progressively closed to reduce the fluid supply to the bore I6I as the pressure of the fluid acting on the end of the piston I64 forces the piston downwardly (Fig. 1) against the action of the spring I69. Opening to the bore I6I opposite the boss I63, so as to be constantly open, is a passage I13 (see Fig. 2) leading to a bore I14 extending parallel with the bore I6I.

From the bore I14 a diagonal passage I15 (Fig. 5) leads to a horizontal bore I16 intersecting a bore I11, and opening at one end to a bore I18 similar to and parallel with the bore I11. Interposed in each of the bores is a cylindrical screen or strainer I19. The bore I11 communicates with the annular recess 40, while the bore I18 communicates with the arcuate recess 31, all as best seen in Fig. 5. Disposed in each bore is a check valve I80 urged to seated position by a light compression spring I8I, and so disposed as to permit flow of fluid from the bore I16 toward the recesses but to prevent reverse flow. A diagonal passage I84 leads from the inner end of the valve bore I6I t0 the recess 25 in the inner face of the end closure I I.

This constant pressure fluid provided by the reducing valve means I60 is also supplied to preload the control cam 11, and is additionally supplied to the valve bore I36 inwardly of the valve I42 so as to act on the valve in a manner to maintain the port I46 closed. The passages or conduits for supplying the fluid to these places include a diagonal bore I85 (Fig. 6) leading from the bore I14 to the bore I36 inwardly of the valve I42 and a passage I86 leading from the opposite side of the bore I36 flrst diagonally upwardly and rearwardly in the end closure II (see Fig. 1), thence downwardly, longitudinally, forwardly, and again downwardly through the cylinder block 9 to the space between the shoulder and piston 18.

It is intended that the cylinder I05 will be supplied with control fluid generated by the pump I and at the pressure of such control fluid as determined by the valve I42. Such control fluid is to be constantly supplied to one end or the other of the cylinder I05 and thus will hold the wobbler against the control cam 11, the pressure area of the piston and cylinder being such that the device will hold the wobbler against the end of the control cam in opposition to the action of the pistons on the wobbler tending to restore the same to neutral or no-stroke position. It will be seen that with this arrangement an increase in the working pressure of the pumping unit will, through the control pressure governin valve means, increase the pressure acting on the cylinder I05 to increase the angle of the wobbler and thus increase the displacement of the pumping unit. This increase in pressure acting on the cylinder I05 is sufficient to overcome the pre load pressure and the reaction of the pistons on the wobbler and thus, merely by taking up the play inherent in the mechanism, increase the angular position of the wobbler lust enough to compensate for the increased leakage which takes place at such higher working pressures. As the working pressure increases the metal parts which carry the thrust stretch or compress, as the case may be, and cause the pivot H of the wobbler to move slightly to the right (Fig, 1). This permits the control to increase the pump stroke and compensate for the increased leakage at higher pressures. It is to be borne in mind that the increase in stroke here mentioned is extremely small, in the order of a few thousandths of an inch. With the construction shown, the end edge 11 of the control cam is actually the fulcrum for the tilting of the wobbler, and since this edge is effective for both directions of pump discharge the increased stroke with increased working pressure is obtained for both directions of pump discharge. In practice pumps of this type with absolutely constant output are thus possible. In fact, pumps of this type can even compensate for leakage in a fluid motor connected thereto, as well, so as to obtain constant motor speed regardless of variations in working pressure. Moreover, with this arrangement the increase of the pressure of the control fluid compensates for the increased reaction of the pistons at the higher working pressures to tend to return the wobbler to neutral or no-stroke position, so that the pressure of the ring member 12 against the end edge 11' of the control cam is of constant value regardless of the working pressure. This makes possible adjustment of the wobbler by the application of a force of constant value regardless of the working pressure of the pumping unit. The arrangement further makes possible the employment of a low pressure control and make-up fluid for normal conditions of operation.

I claim as my invention:

1. In a fluid device, a casing, a cylinder block having a plurality of annularly arranged cylinders therein, a piston reciprocable in each cylinder and projecting at one end therefrom, a shaft -rotatably mounted concentrically of said cylinders, a wobbler on said shaft operatively engaging said pistons, said wobbler being adjustably mounted to vary the stroke of said pistons, and control means governing the adjustment of said wobbler including hydraulic means for placing a pre-load on said wobbler biasing the same toward no-stroke position including an annular ders therein, a piston reciprocable in each cylinder and projecting at one end therefrom, a shaft rotatably mounted concentrically of said cylinders, a Wobbler on said shaft operatively engaging said pistons, said wobbler being adjustabiy mounted to vary the stroke of said pistons, and control means governing the adjustment of said wobbler including hydraulic means for placing a pre-load on said wobbler biasing the same toward no-stroke position comprising a stepped bore concentric with said shaft and providing an annular shoulder and an annular member slidable in said bore and having a piston portion disposed opposite said annular shoulder, said member having an end edge disposed in a plane perpendicular to said shaft and adapted to engage said wobbler.

3. In a fluid device, a casing, a cylinder block having a plurality of annularly arranged cylinders therein, a piston reciprocable in each cylinder and projecting at one end therefrom, a shaft rotatably mounted concentrically of said cylinders, a wobbler on said shaft operatively engaging said pistons, said wobbler being adjustably mounted to vary the stroke of said pistons, and control means governing the adjustment of said wobbler including hydraulic means for placing a pre-load on said wobbler biasing. the same toward no-stroke position including an annular piston member concentric with said shaft and movable longitudinally thereof, said member having an end edge disposed in a plane perpendicular to said shaft and adapted to engage said wobbler, and means operable to engage said piston member and shift the same to adjust said wobbler toward no-strokeposition.

and shift the same to adjust said wobbler toward no-stroke position.

6. In a fluid device, acasing. a cylinder block having a plurality of cylinders therein, a piston reciprocable in each cylinder and projecting at one end therefrom, a rotatable shaft, means on the shaft operatively engaging said pistons, said means being adjustable to vary the stroke of said pistons and the direction of operation of the device, and control means governing the adjustment of said piston engaging means comprising means for determining the stroke of said pistons I urging said piston engaging means toward nostroke position including means operable to place a bias of constant force on said piston engaging means urging it toward no-stroke position, and means governing the direction of operation of the device urging said piston engaging means toward increased stroke of said pistons in op sition to the first mentioned control means.

7. In a fluid device, a casing, a cylinder block having a plurality of annularly arranged cylinders therein, a piston reciprocable in each cylinder and projecting at one end therefrom, a shaft rotatably mounted concentrically of said cylinders, a wobbler on said shaft operatively engaging said pistons, said wobbler being adjustably mounted to vary the stroke of said pistons and the direction of operation of the device, and control means for the wobbler comprising a first hydraulic means including an annular member concentric with said shaft and said wobbler and operatively engaging said wobbler to determine the length of stroke of said pistons, said piston and cylinder means when supplied with fluid I being operable to provide a pre-load biasing the 4. In a fluid device, a casing, a cylinder block rotatably mounted concentrically of said cylin-- ders, a wobbler on said shaft operatively engaging said pistons, said wobbler being adjustabiy mounted to vary the stroke of said pistons, and control means governing the adjustment of said wobbler including hydraulic means for placing a pre-load on said wobbler biasing the same toward no-stroke position including an annular piston member concentric with said shaft and movable longitudinally thereof, said member having an end edge disposed in a plane perpendicular to said shaft and adapted to engage said wobbler, and means operable to engage said piston member and shift the same to adjust said wobbler toward no-stroke position, said last mentioned means having a one-way connection with said pistonmember.

5. In a fluid device, a casing, a cylinder block having a plurality of annularly arranged cylinders therein, a piston reciprocable in each cylinder and projecting at one end therefrom, a shaft rotatably mounted concentrically of said cylinders, a wobbler on said shaft operatively engaging said pistons, said wobbler being adjustabiy mounted to vary thestroke the said pistons, and

lic means operable to engage said pistonmember wobbler toward no-stroke position, a second hydraulic means operable to adjust said wobbler from one side of its neutral to the other side, said second hydraulic means when supplied with operating fluid urging said wobbler in a direction to increase the stroke of said pistons in opposition to the piston of said first hydraulic means,

'and a third hydraulic means having a member engaging said piston of said first hydraulic means and operable when supplied with fluid under pressure :to determine the adjustment of said wobbler.

8. In a fluid device, a casing, a cylinder block having a plurality of annularly arranged cylinders therein, a piston reciprocable in each cylinder and projecting at one end therefrom, a shaft rotatably mounted concentrically of said cylinders, a wobbler on said shaft operatively engaging said pistons, said wobbler being pivotally mounted on said shaft to vary the stroke of said pistons and the direction of operation of the device, and control means for the wobbler comprising hydraulic means operable to swing said wobbler about its pivot in either direction away from its neutral position, an annular member concentric with said shaft and said wobbler providing an end edge operatively engaging said wobbler radially outwardly of its pivot and on the same face as said pistons to determine the length of stroke of said pistons and means constantly urging said member in a direction to preload said wobbler; the end edge of said annular member constituting a fulcrum about which said entire wobbler pivots under yield of the parts with increases in the working pressure in said cylinders to increase slightly'the stroke of said pistons to compensate for increased leakage.

9. In a fluid device, a casing, a cylinder block having a plurality of annularly arranged cylinders therein, a piston reciprocable in each cylinder and projecting at one end therefrom, a shaft rotatably mounted concentrically of said cylinders, a Wobbler on said shaft operatively engaging said pistons, said Wobbler being adjustably mounted to vary the stroke of said pistons and the direction of operation of the device, and control means for the wobbler comprising means operable to urge said wobbler in either direction away from its neutral position to determine the direction of operation of the device, and means engaged by said Wobbler on either side of neutral and constantly opposing shift of said wobbler from neutral determining the length of stroke of said pistons, said last mentioned means constituting a fulcrum aboutiwhich said entire wobbler pivots under increases in the working pressure in said cylinders to increase slightly the stroke of said pistons to compensate .for increased leakage.

10. In a fluid device, a casing, a cylinder block having a plurality of cylinders therein, a piston reciprocable in each cylinder and projecting at one end therefrom, a rotatable shaft, means on the shaft operatively engaging said pistons, said means being adjustable to vary the stroke of said pistons and the direction of operation of the device, and control means governing the adjustment of said piston engaging means com-- prising means operable to adjust said first mentioned means to determine the direction of fluid discharge from the device, and means engaged by said first mentioned means in either direction of operation of the device and constantly opposing an increase in piston stroke gauging the length of stroke of said pistons for determining the displacement of the device, said first mentioned means and its mounting yielding under increases in the working pressure in said cylinders to increase slightly the stroke of said pistons.

GUNNAR A. WAHLMARK.

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