US3179061A

US3179061A - Variable displacement pump control

Info

Publication number: US3179061A
Application number: US175201A
Authority: US
Inventors: Budzich Tadeusz
Original assignee: Weatherhead Co
Current assignee: Weatherhead Co
Priority date: 1962-02-23
Filing date: 1962-02-23
Publication date: 1965-04-20
Anticipated expiration: 1982-04-20
Also published as: GB981845A; DE1453697A1; CH407751A; ES284953A1; CH405935A; GB981844A; DE1453696A1

Description

April 20, 1965 'r. auozaba-l 3,179,061

VARIABLE DISPLACEMENT PUMP CONTROL film men. 23. 1962 4 Sheets-Sheet 1 INVENTOR. 74 05052 BuDZ/CH 4 ITOIP/VWS April 20, 1965 1-. BUDZICH VARIABLE DISPLACEMENT PUMP CONTROL 4 Sheets Sheet 2 Filed Feb. 23. 1962 INVENTOR. 7A0U5Z 300 21c H April 1965 "r. BUDZICH 3,1 $9,061

VARIABLE DISPLACEMENT PUMP commm Filed Feb. 23. 1962 4 Sheets-Sheet a INVENTOR. 740F052 BUDZ/CH April 20, 1965 Filed Feb. 23. 1962 T. BUDZICH 3,179,061

VARIABLE DISPLACEMENT PUMP ,COfiTROL 4 Sheets-Sheet 4 INVEN TOR. 74 05052 5002/01 BY E/(HEX MS'NE'N/V Y: FA me lms ro/v A770 A/EYS United States Patent 3 179 061 VARIABLE DISPLACEMENT PUMP CONTROL Tadeusz Budzich, Shaker Heights, Ohio, assignor to The vvfegglierhead Company, Cleveland, Ohio, a corporation 0 o Filed Feb. 23, 1962, Ser. No. 175,201 Claims. (Cl. 103-173) This invention relates generally to hydraulic pumps and more particularly to controls for regulating the displacement of variable positive displacement pumps.

It is a primary object of this invention to provide a variable displacement pump having a displacement controlling member which is movable by a fluid motor controlled by a valve which can be operated remotely by manual movement, in which movement of the valving member requires a force which is variable in proportion to the position of the displacement controlling member to give the operator a feel for the controlled position.

It is another object of this invention to provide a variable displacement pump having a displacement controlling member movable by a fluid motoroperated through a manual control valve by the outlet fluid pressure, in which the operation of the control is independent of variation in the outlet pressure level. i

It is another object of this invention to provide a variable displacement pump having a control va ve for a fluid motor for shifting a displacement controlling member in which the control valve is operable with a minimum of applied force through a minimum distance of movement for rapid response under manual control.

It is still another object of this invention to provide a control valve for a fluid motor for shifting the displacement controlling member in a variable displacement pump, in which the control valve includes a valve spool whose motion and position is controlled by opposing variable forces including a variable spring bias tending to shift the valve spool in one direction and applied through remote control by the operator and an opposing or counterbalancing force proportional tothe control pressure in the fluid motor actuating thedisplacement controlling member and in which the control pressure is variable in proportion to the position of this displacement controlling member. i

. The invention is shown as applied to a modified pump of the type disclosed in this inventors co-pending applications, Serial No. 825,005, filed July 6, 1959, now Patent No. 3,090,312 reissued as Patent No. 25,553 and Serial No. 88,142, filed February 9, 1961, now Patent No. 3,087,- 432. The pump includes a hollow pump housing containing a cylinder block mounted for axially sliding movement within the housing. The cylinder block contains a plurality of axially extending cylinder bores, each containing a piston which is reciprocated through a Wobble plate drive assembly. Inlet ports are formed in the cylinder block opening into the cylinder bores intermediate the ends, and the ends of the cylinder bores opposite the pumping pistons contain floating reaction pistons which make sealing contact with check valve assemblies in an end housing which collects the outletfluid. The effective output displacement of the pump depends upon the position of the inlet port relative to the pumping piston stroke since the point at which the piston blocks off the inlet port determines the start of the effective pumping stroke of the piston. Thus the axial sliding movement of the cylinder block is employed to vary the effective output displacement of the pump between zero and maximum volume.

The control for the shifting of the cylinder block in cludes a fluid pressure motor located axially within the cylinder block assembly and connected to the control valve mounted on the outside of the pump housing. The control valve includes a valve spool and ports connected to the outlet pressure from the pump and drain as well as to the control pressure in the fluid motor for shifting the cylinder block. The position of the valve spool is determined by balancing forces consisting of a variable spring bias applied by an external control tending to shift the spool in one direction. This force is counter-balanced by the control pressure acting on the other end of the pilot valve spool and opposing the adjustable spring bias. The cylinder block is biased to the maximum displacement position by means of a compression spring, and since the force of this spring will increase as the cylinder block is shifted toward the minimum displacement posi tion, the control pressure wtihin the fluid motor is there- 'fore proportional to the force of the cylinder block spring, since all pumping forces are absorbed on the reaction pistons and do not affect the cylinder block. Therefore, since the control pressure will increase as the cylinder block moves toward the minimum displacement position, the counter-balancing control pressure force on the pilot valve spool varies in proportion to the cylinder block position, and an increasing force must be applied by increasing compression of the spring bias on the pilot valve spool and order to decrease the displacement of the pump.

Further features and advantages of this invention will EQadflyappear tothose skilled in the art upon a more complete understanding of the preferred embodiment of the invention as shown in the accompanying drawings and described in the following detailed description.

In the drawings:

FIG. 1 is a longitudinal cross-sectional view through a pump incorporating the present invention;

FIG. 2 is an endelevational view of the pump;

FIG. 3 is an enlarged fragmentary cross-sectional view taken along line 3-3 of FIG. 2 and showing details of the control valve;

-FIG. 4 is an enlarged fragmentary cross-sectional view taken on line 4-4 of FIG. 2;

FIG. 5 is an enlarged fragmentary detail view taken along line 5-5 of FIG. 2 showing the external connection for the control valve; and

FIG. 6 is an enlarged fragmentary cross-sectional view taken along line 6-6 of FIG. 2 and showing details of the pressure compensated valve.

Referring now to FIG. 1 in greater detail, the pump includes a pump housing 10 defining a fluid chamber 11 therein. The pump housing 10 is formed with an interna cylindrical end portion 12 within which is fitted an outlet housing 13. Outlet housing 13 abuts against an internal flange 14 on the pump housing 10 and is held in place by means of set screws 15 (see FIG. 4). An -0-ring seal 16 is provided around the'periphery of outlet housing 13 to prevent leakage at this point. The pump housing 10 is provided with an inlet opening 18 on its side wall for connection to a fluid reservoir to insure that the pump chamber 11 is 'filled with fluid at all times.

The other end of pump housing 19 is-closed ofi" by means of a drive housing 21) secured to the pump housing by fastening means such as cap screws (not shown). Drive housing 20 is provided with an axial bore 21 there through and supports a bearing member 24. A drive member 25 is journaled by the bearing member 24 and has axially extending shank 26 extending outward through bore 21 to engage an oil seal 27 carried by the drive housing to prevent leakage of fluid out of the housing. The drive member 25 is rotatably driven through'a drive shaft 29 which fits within a bore 3% in the drive member 25 to make a driving connection through the splined connection indicated at 31. It is understood that the drive shaft 29 is rotatably driven by a suitable prime mover for operating the pump.

On its inner end, drive member 25 is provided with an inclined face 33 and a hub portion 34 projecting normal to the inclined face 33. A bearing member 36 is mounted on the inclined-face 33 and hub 34 to rotatably journal the wobble plate 38. To prevent the wobble plate 38 from rotating with respect to the pump housing 11) a stud 39 projects radially from the outer periphery of wobble plate 38, and at its outer end, rotatably journals a bearing block 40 which is fitted within a longitudinal guide channel 41 secured within the pump housing. Thus, the wobble plate 38 will not rotate with drive member 25, but will oscillate with a sinusoidal motion as the drive member 2 is rotated by the drive shaft 2%.

A web member 44 is mounted transversely within the interior of pump housing 10 a spaced distance from the wobble plate 38. Web member 44 is fixedly .secured in place by means of a pair of snap ring 45 and 46 and serves as a support for various portions of the pump as will be described in greater detail hereinafter.

A cylinder block 51) is slidably journaled Within the end portion 12 intermediate the outlet housing 13 and web member 44. Cylinder block 50 is mounted for free axial sliding movement between the outlet housing 13 and the web member 44 is prevented from rotating within the pump housing by a set or guide screw 51 (see FIG. 4) mounted on the pump housing wall. Set screw 51 has 'a tip portion. 53 which extends into a longitudinal guide slot 52 formed along the outer periphery of cylinder block 5t) to positively prevent rotation of the cylinder block regardless of its longitudinal position. 7

The cylinder block 5% is provided with a plurality 0 cylinder bores 55 spaced equidistantly around the central axis and extending from end to end through the cylinder block. Since each of the cylinder bores and its associated V pumping mechanism is the same, only one cylinder bore has been shown in the drawings and described in greater detail hereinafter. To admit fluid from chamber 11 into the cylinder bores, theeylinder blockstlf has an outer fill- 7 ing slot or port 57 formed on the outer periphery of the cylinder block intermediate its ends and opening into the cylinder bore 55 on the outer side. An inner filling slot or port 58 opens into the cylinder bore 55 on the inner side opposite the outer port 57 and is connected to an axial bore 60 opening into the pump housing chamber 11 on the side of the cylinder block adjacent the web member 44.

A pumping piston or plunger 62 is fitted within the end of the cylinder bore 55 adjacent web member 44 and has a head portion 63 adjacent the ports 57 and 58 when the piston is in the'retracted position. Piston 62 has a tubular skirt portion 64 which extends through a suitable opening in the web member 44 toward the wobble plate 37. A compression spring 66 is fitted around this tubular skirt portion 64 and abuts at one end against the web member 44. The other end of spring 66 abuts against a spring retainer 67 carried onthe outer end of tubular skirt portion 62. In order to reciprocate the piston 62, a piston rod 69 is located within the tubular skirt portion 64 and has a ball end portion 70 which rests against a socket on the under side of head portion 63. The other end of piston rod 69 has another ball portion 71 fitted within a cup-like recess '73 on the exposed face of the wobble plate 38. Thus, rotation of the drive member 25 and the consequent oscillation of the wobble plate 38 will 7 cause the pistons 62 to oscillate with a sinusoidal motion with a positive return to the retracted position being provided by the action of compression spring 66.

Within the other end of cylinder bore 55 is slidably fitted a reaction piston '75 having an axial bore 76 extending from end to end therethrough. The outlet housing 13 is provided with a recess or bore 78 in axial alignment with reaction piston '75, and within this recess is mounted a port member 79 having an axial bore 80 in alignment with the axial bore '76 and the reaction piston. A short compression spring 82 is fitted around the end of reaction piston to abut at one end against. a snap ring 83 secured to the reaction piston and at the other end against a retainer plate 84 secured to the outlet housing 13 by suitable screws indicated at 85. Compression spring 82 serves to bias the reaction piston 75 into sealing engagement against the end of port member 79 while permitting a certain amount of transverse movement between them to compensate for possible misalignment. Within recess 78, a check valve plate 8'7 is fitted over the other end of port member bore to make sealing contact therewith under the bias of compression spring 88. The other end of compression spring 88 is fitted within a cage 8? held in place by a plug 90 which closes oil? the outer end of recess 78. A passage $2 is provided in the outlet housing to conduct fluid from the recess 78 into an outlet chamber 93 centrally located on the outlet housing and having a threaded portion 94 to receive a suitable coupling or pipe fitting for connection to the hydraulic circuit operated by the pump.

When the pump is operating atmaximum output volume, the cylinder block is in the position shown in FIG. 1 adjacent the web member 44. The cylinder block is normally maintained in this position by the bias ofan axially located compression spring 97 which abuts at one end in the recess 8 formed in the end of .cylinder block 50 and at the other end is fitted over a'boss 99 formed on the interior of outlet housing 13.

In order to reduce the effective output volume of the pump, a fluid motor assembly 100 is provided to shift the cylinder block 50 toward the outlet housing 13 against the biasing force of the compression spring 97. Fluid motor assembly 100 includes a piston member 101 secured in a centrally located aperture 102m the cylinder block 56. Piston member 101 is secured against axial movement by flange 103 and snap ring 104. The piston member 101 has an end or head portion 106 which is slidably received within an axial bore 108 in cylinder member 167. The cylinder member 107 is mounted within an axial bore 111 in the central boss portion of the web member 144. A shoulder 113 and snap ring 114 serve to secure the cylinder member 107 against axial movement with respect to the web member 44 and boss 110.

A floating piston 116 is fitted within the cylinder bore 108 and is provided with a projection 118 to space the piston 116 away from the end wall 119 of the cylinder member. The space surrounding the projection 113 forms a first expansible chamber fluid motor 121. On the other side of the floating piston 116 there is a longer projection 123, which abuts against the end of the piston head 166 to space the latter away from the end wall 119 and thereby define a limiting position to the cylinder block under the bias of the compression spring 97. The space surrounding the projection 123 forms a second expansible chamber fluid motor 124 which is sealed off from the other chamber 121by means of the floating piston 116.

Fluid is admitted to chamber 121 by means of a radial port 127 in the wall of cylinder member 107. Port 127 on the outside connects with longitudinal groove 126 formed .in the outer periphery of cylinder member 107 in axial alignment with a radial passage 128 in the web member 44. In like manner, chamber 124 is connected through a radial port 131 through a groove 130 on the outer periphery of cylinder member. 107, and groove 130 is in radial registration with a radial passage 132 formed in a web member 44 substantially diametrically opposite the other radial passage 128. It will therefore be seen that by selectively controlling the admission and exhaust of fluid through the radial passages 128 and 132, the amount of fluid within the

chambers

121 and 124, respectively, may be controlled to thereby control the axial position of the cylinder block 50.

The control valve for varying the effective output displacement of the pump by controlling the flow of fluid to and from motor chamber 121 is indicated generally at 150 and is shown in detail in FIGS. 3 and'5. Control valve 158 includes a valve housing 151 secured on a boss 148 on the external surface of pump housing by suitable cap screws 149. Valve housing 151 has an axial bore 152 in which is slidably journaled a valve spool 155. The valve spool 155 has a pair of annular grooves 156 and 158 which define a land portion 157 between them. At one end, valve spool 155 has an outer land 159 sealing off axial bore 152 outward of groove 156. At the other end, the valve spool has a guide land 161 outward of the other groove 158, and flats 162 are provided on land 161 to allow fluid flow past the land.

A transversely extending control pressure bore 164 is formed in the valve housing 151 and extends across the axial bore 152 adjacent the land 157. To permit fluid flow between both sides of bore 164, the land 157 is provided with an annular groove 165 at its mid portion. Outlet pressure is admitted to axial bore 152 adjacent groove 166 by a pressure passage 167. Pressure passage 167 extends radially to bore 148 where it is connected to a passage 168 formed in the wall of pump housing 10. Further connection is made through a fitting arrangement 171) to connect the passage 168 to a radial passage 171 formed in the outlet housing 13 and opening into the output chamber 93. Thus, passage 167 serves to admit fluid at full outlet pressure at all times to the groove 156 on valve spool 155.

A drain passage 173 is providedin valve housing 151 and opens into axial bore 152 adjacent the other groove 158. Drain passage 173 connects with another drain passage 174 formed in the pump housing wall 10 and opening into the pump chamber 11. Further connection between the control valve 150 and the pump is made by a connecting tube 146 which extends atone end into a counterbore in the control pressure bore 164 and at the other end inwardly through the pump housing wall 10 into a counterbore within the web member-44 where it 7 connects to the'radial passage 128 leading into chamber 121.

At the end of. valve spool 155 having land 159, there is fitted a spring abutment 177 Within a chamber 178 formed in the valve housing. A compression spring 1'79 is mounted within chamber 178 to abut at its one end against spring abutment 177 and at its other end against a piston 180 slidably mounted within bore portion 181 of chamber 178. Chamber 178 is connected by a suitable passage (not shown) to drain passage 173 to prevent possible buildup of fluid pressure within chamber 178' as a result of leakage past the outer land 159.

By virtue of the connectionthrough spring 179, movement of the piston 180 along bore 181 provides a variable biasing force on the valve spool 155. To provide means for moving the piston 180, a control arrangement is provided as shown in FIG. 5 The valve housing 151 is provided on its outer periphery with a forked boss 183 which supports a pivot pin 184 on which is journaled one end of a lever 186 which extends transversely across the opening of bore 181. At its other end, lever 186 is provided with a suitable connection to a control rod 187 for rotating the lever about pivot pin 184. Adjacent its mid point, lever 186 is provided with a longitudinal slot 189 in which is located a roller 190 journaled on a pivot pin 191 carried in the lever 186. Thus movement of the control rod 187 will cause movement of the roller 190 to contact the piston 180 and shift the axial position of piston 180 along bore 181. To limit outward movement of the roller 190 and piston 180, lever 186 is provided with a projecting lug 193 adjacent pivot pin 184. A stop screw 194 is threadedly engaged in lug 193 and held in place by lock nut 195. By virtue of engagement between the end of stop screw 194 and the outer surface 196 of valve housing 151, rotation of the lever 186 is limited to define an outermost position of piston 180.

At the other end of valve housing 151, land 161 on valve spool projects into a counterbore 198 which opens into a larger counterbore 199. Counterbore 199 is closed oil. by a cap 200 held in place by suitable cap screws 201. Cap 200 is provided with an axial extension 202 which extends into counterbore 198 to make sealing contact therewith. The chamber within counterbore 198 is thus sealed off from counterbore 199 and connected by means of flats 162 on land 161 to the drain passage 173. Counterbore 199 is connected through the passage 286 to the control pressure bore 164 so that at all times it is subjected to the control pressure within chamber 121. The extension 202 has an axial bore 203 in which is slidably journaled a small piston 204. A radial passage 205 extends through the walls of extension 282 to connect bore 203 to the conunterbore 199. Thus piston 284 which abuts against the end of valve spool 155 is at all times subjected to the control pressure within chamber 121, and this control pressure thus acts as a biasing force on valve spool 155 to oppose the biasing force of compression spring 179.

From the above description it will be seen that the position of the valve spool 155 depends upon the balance of forces between the control pressure in chamber 121 acting on piston 204 and the biasing force of compression spring 179 as determined by the position of piston 180. Since the fiuid pressure within chamber 121 is directly propor tional to the force exerted on the cylinder block by the spring 97, the control pressure within chamber 121 varies with the position of the cylinder block with an increasing pressure at cylinder block positions corresponding to decreased pump output displacement. When piston is shifted inward to compress spring 179, the increased biasing force on the valve spool 155 shifts it toward end cap 200 and fluid at outlet pressure in groove 156 is connected to control pressure bore 164 and hence to the chamber 121. This increased pressure causes the piston 116 to move and shift the cylinder block 50 to a reduced output displacement position. Because of the increased force of spring 97 as the cylinder block is moved in this di-" rection, the control pressure within chamber will increase until it reachesa level where the biasing force of spring 179 is counterbalanced and the valve spool 155 moves back into the neutral position in which the land 157 isolates the control passage bore 164 from both of the adjacent grooves 156 and 158. Conversely, a decrease in the biasing force of compression spring 179 will allow the valve spool to shift in theother direction to connect the control pressure bore 164 through groove 158 to the drain passages 173 and 174. This allows fluid to flow out of chamber 121 and allows the cylinder block to move toward a greater output displacement position until the decreased control pressure in the new position allows the spring 1'79 to shift the valve spool 155 back to the neutral position.

Since the control pressure within chamber 121 required to shift the cylinder block 50 is relatively low compared to the outlet pressure in chamber 93, normal operation of the pump will produce an outlet pressure exceeding the maximum pressure level in chamber 121 and therefore be suificiently high to shift the cylinder block Silaccording to the position of the piston 126 Since in the balanced position, the outlet pressure is not connected to the chamber 121, and the outlet pressure produces no ubalanced forces on valve spool 155, control valve 15% operates independently of the outlet pressure. Furthermore, since the control pressure is relatively low and the effective area of piston 204 relatively small, the counterbalancing force on valve spool 155 is relatively small and compression spring179 can be made quite light. There fore, only a relatively light force need be applied through the control rod 187 for operation of control valve 1545. Furthermore, since the valve spool 155 always returns to the neutral position when theposition of the cylinder block th is stabilized, and since the compression spring 179 may have a relatively high spring rate, the range of movement of piston 180 needed for the full range of movement'of cylinder block 5% can be much less than the actual length of movement of the cylinder block 50. Thus, not only is the force required for operating the control valve small, but the distance through which the applied force moves is also small, thereby providing a very sensitive and responsive control valve for controlling the output displacement of the pump.

As shown in FIG. 1, the pump may also be provided with a separate manually adjustible stop for positively limiting the maximum output displacement of the pump independently of the operation of control valve The pump housing ltiis provided with a bore or guide 229 in which a slide 268 is slidably journaled for longitudinal movement parallel to the axis of the pump. The position of slide 2% is adjusted by a screw 21% which is rotated by an external hand wheel 211. A transversely projecting pin 212 is secured in slide 2% and extends radially inward toward the axis of the pump for engagement against an abutment portion 213 formed on cylinder block 59. Thus the pin 212 positively engages the cylinder block 54) through contact with abutment 213 to limit movement of the cylinder block 5i) toward the maximum output displacement under the action of compression spring 2'7. By

shifting the position of slide and pin 212, this limitirig position can be varied and the maximum output volume of the pump can be adjusted to any level less than that determined by the full stroke of the pumping pistons.

The pump is also provided with a pressure compensated valve adapted to limit the maximum outlet pressure of the pump by shifting the position of the cylinder block Ell to reduce the output displacement Whenever the outlet pressure exceeds a predetermined level. The pressure cornpensated valve indicated generally at 22% and shown in detail in FIG. 6, is adapted to control the admission of fluid from the pump outlet chamber )3 to the other motor chamber 124 in fluid motor assembly 1%. The pressure "compensated valve 226 includes a valve housing 221 mounted on a boss 222 formed on the exterior of pump housing 1t opposite the control valve 15d. Valve housing 221 has an axial bore 224 therein'to slidably receive a valve spool 225. The valve spool 225 has a pair of

annular grooves

227 and 228 whichdefine a valving land 229 between them. At the one end, valve spool 225 is providedwith alongitudinal flat 231, and at this end the axial bore 224 is closed oil by means of a suitable plug 232. The other end 234 of valve spool 225 projects into an enlarged bore 235 in valve housing 221 where it receives a spring abutment assembly 236. A helical compression spring 258 is located within the enlarged bore 235 and abuts at the one end against spring abutment 236 on valve spool 225 and at the otherend against an adjustable abutment 239 which is threadably secured in the outer end of enlarged bore 235 and fixed in place by suitable lock nut 24%.

The

valve spool grooves

227 and 228 together with the land 229cooperate with an arrangment of ports to control the flow of fluid through the valve. Accordingly, a

control pressure port 243 opens into the axial bore 224' opposite the land 229 and it is substantially the same width as land 22950 that the latter is able to block off port 243 only when it is in exact alignment with the port. An outlet pressure port 244 opens into axial bore 224 opposite the one annular groove 22?; and end portion 231, while a drain port 245 opens into axial bore 224 opposite groove 227. A passage 247 extends from the control pressure port 243 to the enlarged bore 235 so the fluid in the latter is always at the control pressure. The control pressure port 243 is connected by a tube 24-2 which extends to the wall of pump housing 15) and into the web member 44 to connect with-the radial passage 132. A drain passage 251 also extends to the wall of pump housing it) to connect the drain port 245 to the pump housing chamber 11. Pressure is delivered to the outlet pressure port 24 by means of a radial passage 253 which extends through the wall of pump housing it} where it connects with an axial passage 254. In turn, axial passage 25 extends axially within pump housing 1% to a connecting angle fitting 255 which is also connected through a radial passage 257 in the outlet housing 13 to the outlet chamber 93.

It willtherefore be seen that the axial position of the valve spool 225 and hence the valving action of pressure compensated valve 220 will depend upon the balance of forces acting on the opposite ends 231 and 234 of the valve spool. The one end 231 is always exposed to the outlet pressure communicated through port 244 and this pressure tends to bias the valve spool 225 in a direction to bring the groove 22% into alignment with the control pressure port 243 and thereby allow the outletpressure from port 24-4 to be communicated through the tube 49 and passage 132 to the chamber 124 in fluid motor assembly 1.00. This pressure force is opposed by the combined force of the compression spring 238 acting against the spring abutment 23d and the control pressure within enlarged bore 235 acting on the cross-sectional area of the valve spool. Since the control'pressure is relatively low, it will be seen that the compression spring 238 provides most of the force opposing the outlet pressure acting on the other end of the valve spool; The force of the compression spring 233 may therefore be regulated by the threaded adjustment of the abutment 239 so as to limit the maximum outlet pressure of the pump.

When the outlet pressure is below the maximum level determined by the position of threaded abutment 239, compression spring 238 shifts the valve spool 225 so that the control pressure port 243 is in communication with groove 2217 and hence with the drain port 245. Therefore, the motor chamber 124 will be connected with'drain so that any fluid therein will be exhausted and the piston head 1% will be in an abutting engagement with the projection 123 including piston 116. Increasing outlet pressure at port 244- acts on the end'231 of valve spool 225 tending to shift the latter toward the left as seen in FIG. 6 to compress the spring 238. The limiting maximum pressure is determined when the land 22% is shifted intoa position where the control pressure port 244 is connected with the groove 228 to allow the relatively high outlet pressure to enter the control port 243 and pass in the aforesaid manner into the motor chamber 124. When this pressure level is reached, the high pressure fluid from the outlet port acts on both the floating piston 116 and the piston head 1%. Since the floating piston 116 is free to move within the bore 168, the high pressure outlet fluid will tend to force the floating piston toward the end wall 119 and thereby raise the control pressure within chamber 121. This increase in pressure in chamber 121 tends to shift the valve spool of control valve 151 in a direction to permit the fluid within chamber 121 to drain 'into the pump housing chamber 11 and thereby allow the floating piston 116 to come to rest in engagement with end wall 119.

At the same time, the force of the outlet pressure fluid within chamber 124 acts on the piston head 106 to shift the cylinder block 50 toward the outlet housing 13 against the force of spring 97 and thereby reduce the outlet displacement of the pump regardless of the position of the cylinder block 50 as previously determined by the manual control of valve 150. Thus the pressure compensated valve 220 always acts to override the operation of the manual control valve 150 to positively prevent a build up of fluid pressure in the outlet chamber 93 above the level determined by the position of the threaded abutment 239. As soon as the outlet pressure drops below this level, the spring 238 will overcome the outlet pressure force acting on the other end'of valve spool 225 to shift the latter into a position where the fluid Within chamber 124 will be connected through groove 227 to the drain port 245 and drain into the pump housing chamber 11 through drain passage 251. Whenever this happens, the pressure Within the other motor chamber 121 will drop to the original level and thereby operate the manual valve 150 to admit fluid into chamber 121 and thereby allow the cylinder block 50 to return under the action of spring 97 to the original position where the pressure in chamber 121 balances the biasing force of thecontrol spring 179'. It will therefore be seen that as soon as a high pressure condition has been overcome by relief in the external circuit of the pump, the output displacement of the pump will rise immediately from the low position required by the pressure compensated valve 220 to the setting determined by the control valve 150 and remain at this level until changed by action of either the external control valve 150 or a reoccurrence of excessive pressure acting on the pressure compensated valve 220.

While the preferred embodiment of the invention has been shown and described in detail, it is understood that this invention can take many other forms and embodiments, and that such forms and embodiments as may occur to those skilled in the art may be resorted to without departing from the scope of the invention as defined in the following claims.

What is claimed is:

1. A variable displacement pump having a pump housing and a pumping mechanism within said housing, said pumping mechanism including a movable member for varying the effective displacement of the pump and a fluid motor for shifting said movable member in one direction, spring means biasing said movable member in the other direction, a control valve for controlling the flow of fluid to and from said fluid motor, said control valve including a control valve housing, a bore in said control valve housing, a valve spool axially slidable in said bore, port means cooperable with said valve spool whereby movement of said valve spool in one direction connects said fluid motor to said pump outlet and movement of said valve spool in the other direction connects said fluid motor to drain, control means to apply a variable springbias tending to shift said valve spool in one of said directions, and fluid pressure means responsive under static conditions solely topressure in said fluid motor to bias said valve spool in the other of said directions to counterbalance said spring bias.

2. A variable displacement pump having a pump housing and a pumping mechanism within said housing, said pumping mechanism including a movable member for varying the effective displacement of the pump and a fluid motor for shifting said movable member in one direction, spring means biasing said movable member in the other direction, a control valve for controlling the flowof fluid to and from said fluid motor, said control valve including a control valve housing, a longitudinal bore in said control valve housing, a valve spool axially slidable in said bore, port means in said control valve housing cooperable with said valve spool whereby movement of said valve spool in one direction connects said fluid motor to said pump outlet and movement of said valve spool in the other direction connects said fluid motor to drain, control means to apply a variable spring bias tending to shift said valve spool in one of said directions, and piston means operable under static conditions solely by fluid pressure in said fluid motor to bias said valve spool in the other of said directions to counterbalance said spring bias, said piston means having a cross-sectional area less than the cross-sectional area of said valve spool.

3. A variable displacement pump comprising a pump housing having a fluid chamber therein, an outlet on said pump housing and an inlet to said fluid chamber, a cylinder block slidably mounted within said pump housing for movement along a longitudinal axis, said cylinder block having a plurality of cylinder bores extending longitudinally therein, a pumping piston in one end of each of said cylinder bores, drive means to reciprocate said pumping pistons, a tubular reaction piston in the other end of each of said cylinder bores, check valve means interconnecting said reaction pistons and said outlet, inlet port means on said cylinder block opening into each of said cylinder bores intermediate the pumping piston and the reaction piston, spring means biasing said cylinder block toward said pumping pistons, a fluid motor adapted to shift said cylinder block toward said reaction pistons to oppose said spring means, and a control valve for controlling the flow of fluid to and from said fluid motor, said control valve including a control valve housing on said pump housing, a bore in said control valve housing, a valve spool axially slidable in said bore, port means cooperable with said valve spool whereby movement of said valve spool in one direction connects-said fluid motor to said pump outlet and movement of said valve spool in the other direction connects said fluid motor to said fluid chamber, control means to apply a variable spring bias tending to shift said valve spool in said one direction, and fluid pressure means responsive to pressure in said fluid motor to bias said valve spool in said other direction.

4. A variable displament pump comprising a pump housing having a fluid chamber therein, an outlet on said for movement along a longitudinal axis, said cylinder block having a plurality of cylinder bores extending lon gitudinally therein, a pumping piston in one end of each of said cylinder bores, drive means to reciprocate said pumping pistons, a tubular reaction piston in the other end of each of said cylinder bores, check valve means interconnecting said reaction pistons and said outlet, inlet port means on said cylinder block opening into each of said cylinder bores intermediate the pumping piston and the reaction piston, spring means biasing said cylinder block toward said pumping pistons, a fluid motor adapted to shift said cylinder block toward said reaction pistons to oppose said spring means, and a control valve for controlling the flow of fluid to and from said fluid motor, said control valve including a control valve housing secured to said pump housing, a bore in said control valve housing, a valve spool axially slidable in said bore, port means cooperable with valve spool whereby movement of said valve spool in one direction connects said fluid motor to said pump outlet and movement of said valve spool in the other direction connects said fluid motor to said fluid chamber, manual control means to apply a variable spring bias tending to shift said valve spool in said one direction, and a piston and cylinder motor operable by fluid pressure in said fluid motor to shift said 'valve spool in said other direction, said piston and cylincross-sec- 1 l fluid motor for shifting said movable member, spring means biasing said movable member in opposition to said fluid motor, a control valve for controlling the flow of fluid to and from said fluid motor, said control valve including a control valve housing secured to said pump housing, a first bore in said control valve housing, a valve spool axially slidable in said first bore, a first port opening into said first bore and connected to the pump outlet, a second port opening into said first bore and con nected to said fluid motor, a third port opening into said bore and connected to said fluid chamber, a land on said valve spool adapted to close off said second-port, a first groove on said valve spool adjacent said land opposite said first port, a second groove on said valve spool adjacent said land opposite said third port, an enlarged counterbore in said control valve housing coaxial with said first bore adjacent one end of said valve spool, a first piston slidable in said counterbore, control spring means within said counterbore abutting at one end against said first piston and at the other end against said one end of said valve spool, manual control means to move said first piston axially within said counterbore, a second bore in said control valve housing having a diameter less than that of said first bore, atsecond piston slidable in said second bore and engageable with the outer 'end of said valve spool, and passage means in said control valve housing interconnecting said second port and said second bore whereby said second piston biases said valve spool against adapted to connect said second-fluid-motorto' said pump outlet and to drain, said second control valve including a valve spool axially shiftable in one direction to interconnect the second fluid motor With said pump outlet and shirtable in the other direction to connect said second fluid motor to drain, manual control means for applying a variable spring bias tending to shift said valve-spool in said one direction, and fluid pressure means operable by the pressure in said second fluid motor to shift said valve spool in said other direction.

8. A variable displacement pump having a pump hous- 7 ing and a pumping mechanism withinsaid pump houssaid control spring means with a' force proportional to the fluid pressure in said fluid motor.

means biasing said cylinder block toward the maximum output displacement position, a first expansible chamber fluid motor coaxial with said longitudinal axis and adapted to shift said cylinder block against the bias of said spring means, a first control valve adapted to connect said first fluid motor to said pump outlet and to drain, said first control valve being operable When the pump outlet pressure exceeds a predetermined level to admit fluid pressure into said first fluid motor to reduce the effective output displacement of the pump, a second fluid motor coaxial with said longitudinal axis and adapted to shift said cylinder block against the bias of said spring means, a second control valve'adapted to connect said second fluid motor to said pump outlet and to drain, said second control valve including a valving member shiftable in one direction to interconnect said second fluid motor with said pump outlet and shiftable in the other direction to connect said second fluid motor to drain, and manual con biasing said cylinder block toward the maximum output displacement position, a first expansible chamber fluid rnotor coaxial with said longitudinal axis and adapted to shift said cylinder block against the bias of said spring, a first control valve adapted to connect said first fluid motor to said pump outlet and to drain, said first control valve being operable when the pump outlet pressure exceeds a predetermined level to admit fluid pressure into said first fluid motor to reduce the eflfective output displacement of the pump, a second fluid motor coaxial with said longitudinal axis and adapted to shift said cylinder block against the bias of said spring means, a second control valve ing, said pumping mechanism including a cylinder block axially slidable along a longitudinal axis to vary the effective output displacement of said pump, said cylinder block having a plurality of axially extending cylinders arranged equidistantly about said longitudinal axis, fluid motor means for shifting said cylinder block in one direction, means biasing said cylinder block in the other direction, saidfluid motor means comprising a cylinder coaxial With said longitudinal axis, closure means to seal one end of said cylinder, first piston means slidably received in the other end of said cylinder whereby relative movement of *said first piston means and said cylinder shifts said cylinder block relative to said pump housing, a second piston slidably received in said cylinder inter-mediate said closure means and said first piston to define a first motor chamber adjacent said first piston means and a second motor chamber adjacent said closure means, first control valve means adapted to control the flow of fluid to and from said first motor chamber, and second control valve means adapted to controlthe flow of fluid to and from said second motor chamber.

9. A variable displacement pump having a pump housingdefining a fluid chamber therein, an inlet to said fluid chamber, an outlet on said pump housing, pumping mechanism within said pump housing adapted to pump fluid from said fluid chamber to said outlet, said purnping mechanism including a cylinder block axially slidable along a longitudinal axis for varying the effective-output, displacement of the pump, fluid motor means for shifting said cylinder block in one direction, spring means biasing said cylinder block in the other direction, said fluid motor means comprising a cylinder coaxial with said longitudinal axis, closure means to seal one end of said cylinder, first piston means slidably received in the other end of said cylinder and operatively engaging said cylinder block whereby relative movement of said first piston means and said cylinder shifts said cylinder block relative to said pump housing to vary the output of the pump, a second piston slidably received in said cylinder intermediate said closure means and said first piston means to define a first motor chamber adjacent said first piston means and a second motor chamber adjacent saidclosure means, first control 'valve means operable responsive to the pressure in said outlet to selectively connect one of said motor chambers to said outlet and to drain, and second control valve means adapted to selectively connect the other motor chamber to said outlet and to drain.

10. A variable displacement pump comprising a pump housing defining a fluid chamber therein, an inlet to said chamber, an outlet on said pump housing, a cylinder block slidably mounted for axial movement along a longitudian axis within said pump housing, a plurality of axially said housing coaxial with said longitudinal axis, closure means to seal one end of said cylinder, first piston means slidably received in the other end of said cylinder and operatively connected to said cylinder block whereby relative movement between said first piston means and said cylinder shifts said cylinder block relative to said pump housing, a second piston slidably received in said cylinder intermediate said closure means and said first piston means to define a first motor chamber adjacent said piston means and a second motor chamber adjacent said closure means, first control valve means operable responsive to fluid pressure in said outlet-to selectively connect said first motor chamber to said outlet and to said fluid chamber, and second control valve means adapted to selectively connect said second motor chamber to said outlet and to said fluid chamber.

References Cited by the Examiner UNITED STATES PATENTS Webb 91-433 X Tucker et al 10338 X Widmer et a1. 103-473 Welborn et al 251-76 Setka 251-76 Norlin l03173 Tuck et a1 103-173 Hyler et al. 91433 X Great Britain.

15 LAURENCE v. EFNER, Primary Examiner.

JOSEPH H. BRANSON, JR., Examiner.

Claims

1. A VARIABLE DISPLACEMENT PUMP HAVING A PUMP HOUSING AND A PUMPING MECHANISM WITHIN SAID HOUSING, SAID PUMPING MECHANISM INCLUDING A MOVABLE MEMBER FOR VARYING THE EFFECTIVE DISPLACEMENT OF THE PUMP AND A FLUID MOTOR FOR SHIFTIONG SAID MOVABLE MEMBER IN ONE DIRECTION, SPRING MEANS BIASING SAID MOVABLE MEMBER IN THE OTHER DIRECTION, A CONTROL VALVE FOR CONTROLLING THE FLOW OF FLUID TO AND FROM SAID FLUID MOTOR, SAID CONTROL VALVE INCLUDING A CONTROL VALVE HOUSING, A BORE IN SAID CONTROL VALVE HOUSING, A VALVE SPOOL AXIALLY SLIDABLE IN SAID BORE, PORT MEANS COOPERABLE WITH SAID VALVE SPOOL WHEREBY MOVEMENT OF SAID VALVE SPOOL IN ONE DIRECTION CONNECTS SAID FLUID MOTOR TO SAID PUMP OUTLET AND MOVEMENT OF SAID VALVE SPOOL IN THE OTHER DIRECTION CONNECTS SAID FLUID MOTOR TO DRAIN, CONTROL MEANS TO APPLY A VARIABLE SPRING BIAS TENDING TO SHIFT SAID VALVE SPOOL IN ONE OF SAID DIRECTIONS AND FLUID PRESSURE MEANS RESPONSIVE UNDER STATIC CONDITIONS SOLELY TO PRESSURE IN SAID FLUID MOTOR TO BIAS SAID VALVE SPOOL IN THE OTHER OF SAID DIRECTIONS TO COUNTERBALANCE SAID SPRING BIAS.