US3183849A - Variable displacement pump - Google Patents

Description

May 18, 1965 R. E. RAYMOND VARIABLE DISPLACEMENT PUMP Filed May l0, 1962 4 Sheets--SheeI l ATTORNEYS May'lS, 1965 R. E. RAYMOND VARIABLE DISPLACEMENT PUMP 4 Sheets-Sheet. 2

Filed May l0, 1962 m fwu.,

ATTORNEYS INVENTOR ROBERT E. RAYMOND Q NO May 18, 1965 R. E. RAYMOND VARIABLE DISPLACEMENT PUMP 4 Sheets-Sheet 5 Filed May l0, 1962 INVENTOR ROBERT E. RAYMOND ATTORNEYS May 18 1955 R. E` RAYMOND 3,183,849

VARIABLE DISPLACEMENT PUMP Filed May' l0, 1962 4 Sheets-Sheet 4 ROBERT E. RAYMOND ATTORNEYS United States Patent O 3,133,849 VARIABLE DEPLACEMENT PUMP Robert E. Raymond, Zanesville, Ohio, assigner to Hydro-Kinetics, Inc., Zanesville, hio Filed May 10, 1962, Ser. No. 187,325 8 Claims. (Cl. 10S-173) This invention relates generally to hydraulic machines and particularly to a novel piston type variable displacement pump.

In general, the pump of the present invention comprises a housing and cylinder barrel that support a plurality of axially disposed cylinders including side walls provided with intake ports and a plurality of pumping pistons mounted for axial reciprocating movement in the cylinders. The housing further supports an axially shiftable cam in driving engagement with said pistons and means for moving the cam and pistons to various axial positions whereby the effective stroke of the pistons, relative to the lixed position intake ports is increased or decreased to vary the displacement and volumetric delivery of the pump.

As another aspect of the present invention the pump includes two oppositely acting annular piston and cylinder means mounted in the housing means which comprise hydraulic means for axially moving and positioning the previously mentioned cam and pumping pistons relative to the intake ports.

As another aspet of the present invention the pump includes two oppositely acting springs mounted in the housing means which serve to constantly bias the pumping pistons towards the cam and which constantly bias the cam and pumping pistons towards the position .of minimum piston stroke.

As another aspect of the present invention, the pump including novel apparatus for transferring oil from a removable cylinder barrel to the pump housing which apparatus includes novel pressure biased hollow outlet members movably mounted in the pump housing and in sliding sealed engagement with the cylinder barrel.

As another aspect of the present invention, the pump includes novel mounting means for supporting a removable cylinder barrel in the pump housing, said mounting means being in the form of longitudinally extending rail bearings that not only absorb piston side thrust but, in addition, absorb torque and serve as keys against barrel rotation.

As another aspect of the present invention, the pump includes novel means for transferring piston thrust reaction forces to the pump housing in the form of a plurality of reaction plugs which serve to isolate the cylinder barrel pulsating piston forces.

As another aspect of the present invention, the pump includes a plurality of reaction plugs which are selfaligning since they freely engage the pump housing at any location dictated by the aligned position of the cylinder barrel on its longitudinally extending rail bearings. This eliminates costly alignment problems.

As another aspect of the present invention, the pump includes a plurality of reaction plugs that not only serve to transfer individual piston reactionforces to the pump housing but also serve the additional function of housing outlet check valve assemblies.

As another aspect of the present invention, the pump includes a novel variable displacement control spring arrangement whereby a single control spring is utilized to bias the pumping pistons against the driving cam. The same control spring also serves to bias the previously mentioned reaction plugs against the pump housing.

As another aspect of the present invention, the pump comprises a novel piston return apparatus that forces the "ice piston to follow a driving cam. This apparatus includes a yoke that engages each piston, a yoke reaction plug mounted in the cylinder barrel, and a yoke reaction spring for biasing the plug and yoke against the pistons. This eliminates the need for individual piston return springs and permits a more compact apparatus.

As another aspect of the present invention, the pump comprises a novel composite piston shoe construction formed of nylon or the like surrounded by a steel casing, the latter being crimped around a ball shaped base on the piston. This shoe construction serves the dual function of preventing the nylon shoe portion from splitting and retaining the shoe on the piston. This results in a piston shoe with sufficient compression strength and a low coefficient of friction. Moreover, the shoe is self-aligning and accommodates foreign materials without abrading the driving cam.

As another aspect of the present invention, the pump includes a novel control apparatus that automatically meters a control flow of oil to the previously mentioned annular piston that shifts the driving cam. The control apparatus is adapted to automatically vary the effective stroke of the pistons responsive to variations in the outlet pressure to the load whereby oil is delivered to the load at substantially constant pressure.

As another aspect of the present invention, the control l apparatus mentioned in the previous paragraph can readily be removed and other control apparatus substituted' therefor to establish other desired conditions at the load other than the substantially constant pressure conditions provided by the control apparatus discussed in the previous paragraph.

As another aspect of the present invention, the pump is modified to include a novel shock relief apparatus for the variable displacement control mechanism which apparatus is responsive to the excessive rates of change of pressure and to excessive flow rates. This shock control apparatus comprises a modified pressure biased holloW outlet member that includes a shock detection plate provided with an orice of sufficient size to accommodate higher rates of flows encountered during shock conditions.

As another aspect of the present invention, one modication of the pump includes an annular cam driving cylinder that extends circumferentially around the casing of the pump and includes an intake opening for a relatively hot flow of control oil and an outlet passage, on the opposite side of the casing means, for releasing the control How to the exterior of the casing means. This annular cylinder and passage arrangement not only serves to cool the relatively hot control flow of oil by passing it circumferentially around the outer regions of the casing, in heat exchange relationship with the environment, but also provides built in means for delivering the control ow from a control mechanism mounted on the top of the casing means to a subplate mount on the bottom of the casing means from where the control flow can be conveniently returned to an external reservoir.

As still another aspect of the present invention, the pump includes a removable cylinder barrel provided with an integrally moulded annular manifold that functions in a novel manner to collect the outlet oil from the cylinders and transfer it to the pump housing.

Further objects and advantages of the present invention will -be apparent from the following description, reference being had to the accompanying drawings wherein a preferred form of embodiment of the invention is clearly shown.

In the drawings:

FIG. l is a side sectional view of a variable displacement pump constructed in accordance with the present 3l invention, the section being taken along the plane 1 1 of FIG. 2;

FIG. 2 is an end sectional view of the pump of FIG. 1, the section being taken along the line 2 2 of FIG. 1;

FIG. 3 is a second end sectional view of the pump of FIG. 1, the section being taken along the line 3 3 of FIG. 1;

FIG. 4 is a third end sectional view of the pump of FIG. 1, the section being taken along line 4 4 of FIG. l;

FIG. 5 is a fourth end sectional view of the pump of FIG. 1, the section being taken along the line 5 5 of FIG. 1;

FIG. 6 is a top elevational view, partially in section, of the pump of FIG. 1, the section being taken along the line 6 6 of FIG. 1; and

FIG. 7 is a partial top sectional View showing one of the studs that mounts the cylinder barrel in the casing means of the pump, the section being taken along the line 7 7 of FIG. 4.

Referring in detail to the drawings, a variable displacement pump constructed in accordance with the present invention is illustrated in FIGS. 1 and 6 and comprises a housing means indicated generally at 22 and a rear housing portion indicated generally at 24. The two casing portions are joined together at the central portion of the pump'by a plurality of studs 26 seen in FIG. 6.

A drive shaft 28 is mounted in the forward end of the housing means by a tapered roller bearing assemblies 30 and 32 which assemblies are pressed into recesses 34 and 36.

An oil seal 38 is pressed into a recess 40 in the housing and includes an annular resilient element 42 that wipes the periphery of drive shaft 28.

As seen in FIG. 1 the inner end of drive shaft 28 slidably carries cam indicated generally at 44 which includes a female spline 46 that slideably receives a male spline 48 on shaft 28 for preventing rotation of cam 44 relative to shaft 28. The shaft 28 is retained against axial movement by a nut 52 and a shoulder 53 that engage the inner races of bearing assemblies 30 and 32.

With continued reference to FIG. 1, cam 44 includes an inclined surface 54 which engages a plurality of nylon shoes 56, the latter including sockets 58 which form pivotal ball joints with ball-shaped ends 60 formed on a plurality of pumping pistons 62.

Each of the nylon shoes 56 is surrounded by a metal casing 64 that is crimped around an annular upper nylon bearing portion 65. Each metal casing 64 also includes an inwardly extended annular protrusion 66 that snaps into an annular recess 68 formed in the base of the nylon shoe portion.

With reference to FIGS. 1 and 7, a cylinder barrel indicated generally at 70 is removably mounted within the casing means by means of a plurality of barrel mounting studs 72 having threads screwed into threaded holes 73 circumferentially spaced around the rear end of cylinder barrel 70. Lock washers 76 are provided in the counter sinks 74 between the heads of studs 72 and the rear wall of casing portion 24.

The barrel mounting studs 72 not only absorb piston side thrust reaction imposed on the cylinder barrel, but, in addition, function as keys against cylinder barrel rotation and thereby serve to absorb torque.

Pistons 62 are disposed in respective barrel cylinders 78 which receive low pressure oil or hydraulic fluid via intake 80 in base 82, passage 84 in front housing portion 22, the inner chamber 86 within the housing and the intake ports for each cylinder, two of which are seen at 8S and 88A in FIG. 1.

Intake port SS-A is shown with its respective piston 62 at the bottom of a stroke at which position the piston has uncovered intake port 88-A and drawn fluid into its cylinder. Intake port 88, however, is closed since its respective piston is at the top of its stroke.

As seen in FIGS. 1 and 3, each of the cylinders 78 includes a respective reaction plug, indicated generally at 90, in free self-aligning engagement with the inner end surface 92 of rear housing portion 24.

Each reaction plug 98 is provided with a central bore 94 that carries an outlet ball check valve 96 which is freely retained in bore 94 by a threaded plug 98.

Each threaded plug 98 includes a seat portion 100 and a longitudinal passage 102, the latter communicating with a radial passage 103 and an annular passage 104 formed in the outer wall of reaction plug 90.

With continued reference to FIG. l, the bore 94 in each reaction plug includes a valve stop 106 andy a compression spring 108 which serve to limit the stroke of the ball and bias it towards a closed position.

Pressurized oil from cylinders 78 is discharged to the exterior of the pump, in a unique manner, through a pressure biased outlet member 110 which includes a central passage 112 that communicates with high pressure discharge passage 114 that in turn leads to an outlet hole 116 formed in base 82.

As seen in FIG. 1, outlet member 110 includes a foot portion provided with a surface 118 that is in sealed er1- gagement with a longitudinally extending surface 126 formed in the outer wall of cylinder barrel 70.

With continued reference to FIGS. 1 and 2, pressure biased outlet member 110 includes a piston surface 124 that causes the pressurized hydraulic iluid in passage 112 to bias the surface 118 on outlet member 110 downwardly into sealed engagement with longitudinally extending surface 120 on barrel 7u.

A spring 126 augments the biasing force of the high pressure oil on piston surface 124 and also serves to retain surface 118 inV sealed engagement with surface 120 at low pressures and at the outset of operation.

The outer peripheral surface of outlet member 110 is provided with an annular seal 128 and a threaded plug 129 is screwed into the hole forming passage 112 and includes an inner prOtrusion that forms a retainer for the end of spring 126.

With reference to FIGS. 1 and 4, pressurized oil from the pumping cylinders 78 is released from longitudinal passages 102 in reaction plugs 90 via a plurality of small radially extending passages 103, FIG. 4, annular recesses 104, an annular manifold 134, cylinder barrel outlet port 122, radial passage 112 through outlet member 110, passage 114, and base outlet hole 116 to the load.

Pressurized oil is also released to a variable displacement hydraulic control unit indicated generally at by a second pressure biased outlet member 110-A, FIGS. l and 2, which is identical to outlet member 110 previously described. It will be noted that outlet member 11u-A includes a base surface 136 that is hydraulically biased into sealed engagement with a longitudinally extending surface 138 formed in the outer wall of cylinder barrel 70. Outlet member 11G-A is biased downwardly against longitudinally extending surface 138 by a force exerted on piston surface 124 by pressurized oil in a passage 140.

Referring to FIG. 1 the displacement is varied by shifting caml 44 which is hydraulically accomplished by a cam driving piston and cylinder means indicated generally at 145. The rear housing portion 24 and an annular cam driving piston 147 form an annular cam driving cylinder 149 that receives a pressurized flow of control oil from a flow control apparatus 13S later to be described in detail herein.

The cam 44 is biased towards the rear of the housing by a cam return spring 151 and by an annular reaction piston and cylinder means 153. The spring 151 is interposed between a spring mounting recess 155 and an axially shiftable cam mount indicated generally at 161.

Cam mount 161 is keyed against rotation by a pin 258 mounted by press fit in a hole in front housing portion 22 with the inner end of the pin extended into a longitudinal slot 256 in the periphery of cam mount 161.

With reference to FIGS. 1 and 3, cam mount 161 includes an annular reaction piston portion 163 that is slideably mounted in an annular reaction cylinder 165 formed by front housing portion 22 and annular reaction piston portion 163.

Pressurized oil is delivered to cam reaction cylinder 165 via annular manifold 134, radial passage 112, outlet passage 114, and intersecting drilled holes 167 and 169.

In view of the above it will be understood that cam mount 161 and cam 44 are constantly biased toward the cam driving piston and cylinder 149 by both the spring 151 and the reaction piston and cylinder means 153. The annular area of the driving piston 147 is, however, suciently greater than the annular area of the reaction piston 163 whereby the control flow of Oil at manifold pressure exerts suficient force to shift cam mount 161 against the combined force of reaction piston and cylinder means 153 and cam return spring 151.

It should be pointed out that reaction piston and cylinder means 153 permit the use of a relatively light cam return spring 151 under operating loads, the spring being required to return the pumping pistons to the maximum effective stroke position under low pressure starting conditions.

As seen in FIG. 1, a tapered roller bearing 171 is carried by cam mount 161 and includes a bore 173 that receives a shank portion 175 of bearing 171.

Referring particularly to FIGS. 1 and 6, pressurized oil is delivered through the control apparatus 135 to the cam driving piston and cylinder means 146 via passage 140, passage 144, orifice 147, spool cylinder 148, radial passage 138 in spool housing 151, lateral passage 154 in control block 156, longitudinal passage 158 in control block 156, vertical passage 160 in control block 156, and passage 162 in the pump housing which connects to cam driving cylinder 149.

Cam driving cylinder 149 is continuously drained back to tank via passage 181, small control orifice 232, FIGS. l and 2, passage 183, and outlet port 185 which is connected to a line back to tank.

Referring particularly to FIGS. 1, 4 and 6, a stationary spool housing 151 is mounted in control block 156' and carries a longitudinally shiftable spool member 164 that is normally biased towards a closed position by a spring 166, the latter being contained in a spring housing 168 that is threaded into control block 156 at a threaded hole 170. Compression spring 166 is selectively compressed or released by manipulating a control knob 172 that includes a shank 174 in threaded engagement with spring housing 168 at a threaded hole 176. As seen in FIG. 1, a radial passage 178 extends through control block 156 and rear housing portion 24 to provide a drain back to tank for any hydraulic fluid that may leak between the outer surface of control spool 164 and the inner surface of spool cylinder 148.

Control block 156 is mounted on housing 20 by means of a plurality of studs 192 as seen in FIG. 6. It will be understood that other types of control apparatus and various types of load conditions, can be readily mounted on `the pump merely by unscrewing the studs and replacing control block 156 with a modified version.

The pumping pistons 62 are returned and biased against cam 44 in a novel manner, by means of a single centrally disposed piston return rod 194, FIG. l, which includes aspherical foot portion 196 that ts into socket 198 formed in a nylon piston return yoke 202. Yoke 202 includes a plurality of circumferentially spaced sockets 204 that receive the previously described crimped casing p0rtions 64 of thepiston shoes 62 to the rear sides of piston foot casings and in turn receives force from piston return rod 194 via the pivot joint formed by foot portion 196 and socket 198.

A compression spring 210 is disposed between a shoulder 214 on the rear end of piston return rod 194, a shoulder 212 on a spring retainer plug 216 which in turn bears against the front side of spider 143. Spider 143 is restrained from rearward movement by retaining rings 220 formed on the ends of reaction plugs 90. It should be pointed out that reaction plugs are fitted loosely into respective holes 222 in spider 143 and are in free engagement with the inner surface 92 of the housing whereby the plugs are self-aligning with respect to pump cylinders 78.

The ends of passages 154 and 158 in control block 156 are closed by threaded plugs 224 and 225 respectively.

The pump may include a shock relief feature that is provided by adding a shock detection plate 25,2 provided with a relatively small orifice 254 to pressure biased outlet member liti-A. During normal operating conditions orifice 254 is large enough to handle the control flow and outlet member remains pressure biased downwardly Vinto sealed engagement with surface 138 due t-o the outlet pressure exerted on piston surface 124.

During shock conditions, however, the high rates of flow exceed the capacity of orifice 254 .and develop large forces across shock detector plate 252 in a direction that lifts outlet member 110-A away from surface 138 on the cylinder barrel. When outlet member 11G-A separates from the cylinder barrel, the high volumetric shock flow passes between member 110-A and surface 138 and into the low pressure zone of the housing. When the shock condition subsides spring 126 and the unbalanced hydraulic force on outlet member 11o-A return it immediately into sealed engagement with surface 138 on the cylinder barrel.

In operation, when the pump is driven by a prime mover cam 44 reciprocates pistons 62 which, on the suction stroke, draw oil into the cylinders 78 via inlet passage 84, chamber 86 formed by housing 20, and intake ports 88.

On the compression stroke pistons 62 deliver oil from cylinders 78 to outlet port 116 via passages 102 in plugs 98, check valves 96, radial passages 103, annular grooves 104, manifold 134, passage 112 in hollow outlet member 110, outlet port 116 connected to the load.

Some of the pressurized oil in manifold 134 is delivered to variable displacement control apparatus 135 for shifting cam driving piston yand cylinder 146 in the manner previously described.

A constant pressure at the load is obtained by arranging spool 164 to open only when a predetermined selected load pressure is exceeded. Control knob 172 is adjusted to compress spool control spring 166 so as to bias spool 164 with the proper force to permit its opening when the predetermined selected operating pressure is exceeded. When the pressure at the load rises above the operating pressure oil from the manifold passes through passage 144 and orifice 147 to spool cylinder 148. The increased pressure in the spool cylinder overcomes the preset control force exerted by spool control spring 166 whereby spool 164 is shifted to the left, as viewed in FIG. l, and oil is released through radial passages in spool housing 151 and thence through the previously described passages to the cam driving cylinder 146. This shifts annular cam driving pist-on 147 and cam mount 161 to the right, as viewed in FIG. l, whereby pumping pistons 62 are moved to the right relative to intake ports 88. This decreases the effective strokes of the pistons since the intake ports 88 are closed later in the return stroke of the piston whereby a smaller charge of oil is translated, With less oil being pumped per piston compression stroke the pressure is automatically cut back and when the pressure drops to the preselected control pressure the biasing force exerted by spool control spring 166 shifts spool 164 to the right, as viewed in FIG. l,

f whereby the spool closes radial ports 130 and the flow and passage 226, previously described, reaction piston and cylinder means 153 yand spring 151 shift the cam mount 161 and cam 44'towards the left, as viewed in FIG. 1, and thereby shift the pumping pistons to the left to provide a longer effective stroke for each piston. When this occurs, more oil is delivered to the load per piston stroke. It will, therefore, be understood that the reaction piston and cylinder means 153 and spring 151 constantly biases the pump apparatus towards a higher pressure producing configuration. As soon as the predetermined desired load pressure is exceeded, however, the previously described pressure producing action of spool 164 occurs.

In view of the above, it will be understood that the pump operates with spool 164 in a threshold configuration relative to radial passages 130. The moment the manifold pressure exceeds the predetermined pressure desired at the load, spool 164 departs from its threshold piston and opens to release oil to cam driving cylinder 149. Conversely, the moment the manifold pressure drops below the predetermined value desired at the load spool 164 maintains radial passages 130 closed whereby oil can drain from cam driving cylinder 149 and permits the cam mount to -drive the pistons to the left, as viewed in FIG. 1. This increases the volumetric delivery of oil per piston stroke whereby the pressure at the load is returned to the predetermined value.

While the form of embodiment of the present invention as herein disclosed constitutes a preferred form, it is to be understood that other forms might be adopted, all coming within the scope of the claims which follow.

I claim:

1. In a hydraulic machine the combination of housing means including a plurality of axially disposed pumping cylinders having side walls provided with intake ports and a reaction cylinder communicating with a source of pressurized fluid; piston driving means including a cam axially moveably mounted in said housing means; a plurality of pumping pistons disposed in said pumping cylinders and in driven engagement with said cam; a cam return spring operative between said cam and said housing means in one axial direction; an annular reaction piston in said reaction cylinder for moving said cam in said one axial direction in opposition to reaction forces exerted by said pumping pistons on said cam, yoke means engaging said pumping pistons; and a pumping piston return spring operative between said yoke and sai-d housing means in the other axial direction.

2. In a hydraulic machine the combination of housing means including a plurality of axially disposed pumping cylinders having side walls provided with intake ports and a reaction cylinder communicating with a source of pressurized uid; piston driving means including a cam axially movealbly mounted in said housing means; a plurality of pumping pistons disposed in said cylinders and in driven engagement with said cam; an annular reaction piston in said reaction cylinder in force transmitting relationship with said cam in one axial direction; and an annular cam driving piston and cylinder in said housing means in force transmitting relationship with said cam in the other axial direction, the pressurized area of said annular reaction piston being greater than the combined areas of said pumping pistons.

3. In a hydraulic machine the combination of housing tmeans including a cam driving cylinder; a cylinder barrel removeably mounted in said housing means and including a plurality of axially disposed pumping cylinders having side walls provided with intake ports; piston driving means including a cam axially moveably mounted in said housing means; a plurality of pumping pistons disposed in said cylinders and in driven engagement with said cam; cam return means constantly urging said cam means in one axial direction; an annular cam driving piston mounted for reciprocating movement in said cam driving cylinder in surrounding relationship with said cylinder barrel for shifting said cam in fthe other axial direction in' opposition to the force exerted by said cam return means; and piston return means conlstantly urging said pistons into engagement with said cam.

4. In a hydraulic machine the combination of housing means including a plurality of axially pumping cylinders having side walls provided with intake ports; piston driving means including a cam axially moveably mounted in said housing means; a plurality of pumping pistons disposed in said cylinders and in driven engagement with said cam; cam return means including a piston and cylinder communicating with a source of pressurized fluid for constantly urging said cam means in one axial direction in opposition to reaction forces exerted by said pumping pistons on said cam; cam driving means including a piston and cylinder communicating with a source of pressurized uid for shifting said cam in the other axial direction in opposition to the force exerted by said cam return means; yoke means including peripheral portions engaging foot portions of said pistons and a central spherical socket portion; a yoke driving member axially shiftably mounted in said housing means and including a `second spherical socket portion; a ball in said two socket portions; and a compression spring between said yoke driving member and said housing means.

5. In a hydraulic machine the combination of housing means; a removable cylinder barrel mounted in said housing means and including a plurality of axially disposed pumping cylinders having iside walls provided with intake ports and outlet ports, an annular manifold connecting said outlet ports, and a manifold outlet passage including a manifold outlet port in an outer wall surface of said barrel; an annular shock relief member radially shiftably mounted in said housing means and including a radially disposed iow outlet passage and an inner end engaging said outer wall surface of said cylinder barrel in surrounding relationship with said manifold outlet port; a compression spring between said shock relief member and said housing means for releasably urging isaid inner end against said outer wall surface; piston driving means including a cam axially moveably mounted in said housing means; a plurality of pumping pistons disposed in said cylinders and in driven engagement with said cam; cam return means constantly urging said cam means in one axial direction; cam driving means for shifting said cam in the other axial direction in opposition to the force exerted by said cam return means; and pumping piston return means constantly urging said pistons into engagement with said cam.

6. In a hydraulic machine the combination of housing means; a cylinder barrel mounted in said housing means and including a plurality of axially disposed pumping cylinders having side walls provided with intake ports; a plurality of reaction pins disposed in said pumping cylinders and including free ends engaging an end of said housing means; piston driving means including a cam axially moveably mounted in said housing means; a plurality of pumping pistons disposed in said cylinders and in driven engagementV with said cam; cam return means including a reaction piston and cylinder in force transmitting relationship with said cam for shifting said cam in one axial direction; cam driving means for shifting said cam in the other axial direction in opposition to the force exerted by said cam return means; and pumping piston return means constantly urging said pumping pistons into engagement with saidV cam.

7. In a hydraulic machine the combination of housing mean-s including an axially disposed pumping piston and cylinder and a piston force reaction cylinder communicating with a source of pressurized uid; and a cam mount axially shiftably mounted in said housing means and including a reaction piston portion disposed in said reaction cylinder for biasing said cam mount towards said pumping piston in opposition to reaction forces exerted by said pumping piston.

8. In a hydraulic machine the combination of housing Q l@ Vmeans including a cam driving cylinder and a piston 2,578,561 12/51 Lagardelle 103--173 X force reaction cylinder, said cylinders communicating 2,672,095 3/.54 Lucien etal. 103-173 with pressurized uid source means; a rotatalble cam 2,672,819 3/54 Widmer 103--173 axially shiftably mounted in said housing means be- 2,684,630 7/54 Widmer etal. 103-173 tween said two cylinders; a reaction piston in said re- 5 2,732,805 1/56 Lucien 103--173 `action cylinder; and a driving piston in said driving 2,733,666 2/56 Poulos 10.3-162 cylinder, said driving piston having a greater pressurized 2,945,444 7/ 60 Leissner 103173 X area than said reaction piston. 2,990,781 7/61 Tuck etal 103-173 X 3,087,432 4/63 Budzich 103-173 References Cited by the Examiner 10 F UNITED STATES PATENTS 556 384 7/29ORCEIGN PATENTS 1,710,567 4/29 Carey 10s-162 91072 12/58 Nlfyrds 1,817,063 8/31 Carrie et a1. 10s-lf2 2,169,456 8/39 Wahlmark 15 LAURENCE V. EFNER, Primary Examzner. 2,369,134 2/45 Cameron 103-173 JOSEPH H. BRANSON, JR., Examiner.

Claims (1)

1. IN A HYDRAULIC MACHINE THE COMBINATION OF HOUSING MEANS INCLUDING A PLURALITY OF AXIALLY DISPOSED PUMPING CYLINDERS HAVING SIDE WALLS PROVIDED WITH INTAKE PORTS AND A REACTION CLYINDER COMMUNICATING WITH A SOURCE OF PRESSURIZED FLUID; PISTON DRIVING MEANS INCLUDING A CAM AXIALLY MOVEABLY MOUNTED IN SAID HOUSING MEANS; A PLURALITY OF PUMPING PISTONS DISPOSED IN SAID PUMPING CYLINDERS AND IN DRIVEN ENGAGEMENT WITH SAID CAM; A CAM RETURN SPRING OPERATIVE BETWEEN SAID CAM AND SAID HOUSING MEANS IN ONE AXIAL DIRECTION; AN ANNULAR REACTION PISTON IN SAID REACTION CYLINDER FOR MOVING SAID CAM IN SAID ONE AXIAL DIRECTION IN OPPOSITION TO REACTION FORCES EXERTED BY SAID PUMPING PISTONS ON SAID CAM, YOKE MEANS ENGAGING SAID PUMPING PISTONS; AND A

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