US2847938A - Hydraulic pump - Google Patents

Description

J. T. GoNDl-:K

HYDRAULIC PUMP Aug. 19, '195s Filed Deo'. 1, 1955 4 Sheets-Sheet 1 R Q Nw mm ,mw

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- HYDRAULIC PUMP Filed Deo. l, 1955 4.7Sheets-Sheet 2 ATTORNEY Aug. 19, 1958 J. T. GoNDl-:K

HYDRAULIC PUMP I Aug. 19, 1958 J. T. GoNDEK HYDRAULIC PUMP 4 Sheets-Sheet 4 Filed Dec. 1. 1955 INVENTOR John 7.' onae/r Y @ed m a@ ATTORNEY nited States Patent Oliice 2,847,938 Patented Aug. 19, 1958 HYDRAULIC lUMP John T. Gondek, Minneapolis, Minn.

Application December 1, 1955, Serial No. 550,388

Claims. (Cl. 10S-3) This invention relates to an improvement in fluid or hydraulic pump and deals particularly with an apparatus commonly known as a swash plate type pump. Pumps of this type include a rotating cylinder barrel which supports a series of pistons in angularly spaced relation about a common axis. Pistons are provided in these cylinders which are moved in an axial direction by engagement with a swash plate.

An object of the present invention resides in the provision of a swash plate ytype pump having a simple and effective means of varying the volume of tluid pumped. ln swash plate type pumps of usual construction the swash plates are tiltable so that the surface of the swash plate may vary from a plane normal to the axis of rotation of the cylinder barrel to a position at a substantial angle to a normal position. With pumps of this type some sort of tting must be provided between the pistons and the swash plate to compensate for the Varying angularity of the swash plate. Due to the high pressure which is normally found in pumps of this type considerable difficulty is experienced in these connections between the pistons and the swash plate. An object of the present invention lies in the provision of a pump of the general type described but which is provided with a swash plate which remains at a constant angle to a plane normal to the axis of rotation. The volume of the pump is controlled by rotating the swash plate relative to the valve plate to render the pumping action of the pistons inelective during predetermined periods of rotation of the cylinder barrel.

A feature of the present invention resides in the provision of a pump of a swash plate type which is provided with cylinders having bearing ends thereupon which are arranged on planes at an angle from a plane normal to the axis of each piston which is equal to the angularity of the swash plate with respect to a plane `normal to the axis of rotation of the cylinder barrel. As a result the pistons may at all times bear snugly against the swash plate by rotation of the pistons in their cylinders in the cylinder barrel.

Pumps of the type in question usually employ a valve plate through which fluid is forced and through which the uid entering the cylinders is drawn. Normally each piston draws in fluid through approximately one-half the rotation of the cylinder barrel and forces lluid from the cylinder during the other half of rotation of the cylinder barrel. A similar type of valve plate is employed in the present construction. However, due to the fact that the swash plate may be rotated, the pistons may be arranged to pump into each port a time equal or an amount of uid equal to that employed to draw fluid out of the port. In a similar manner any adjustment between a full pumping operation and a zero pumping operation may be readily obtained by merely rotating the swash plate relative to the valve plate.

A feature of the present invention resides in the provision of a means of balancing the pressure exerted by the pistons against the swash plate. Each of the pistons includes in its closed end a recessed area which communicates with the interior of the hollow piston. As a result the pressure of the lluid within the piston is communicated to this recessed area which acts against the closed end of the piston. By properly proportioning the size of the recessed area to the size of the hollow piston much of the force which would normally be exerted by the hollow piston against the swash plate can be effectively counterbalanced.

A further feature of the present invention resides in the provision of a means of counterbalancing the force against the swash plate so that this plate may be readily rotated when desired to vary the pump output. Arcuate grooves are provided in the body of the pump housing at the end thereof against which the swash plate bears. These arcuate grooves are of similar shape and are opposed to the arcuate grooves in the Valve plate which provide a means of ingress and egress of the fluid to the various cylinders during the rotation of the cylinder barrel. The arcuate grooves in the end of the pump body against which the swash plate engages are connected to the similar arcuate grooves in the valve plate so that a similar pressure exists at both ends of the housing. As a result the force against the swash plate is at least partially balanced by the fluid pressure at the opposite end of the pump housing.

A further feature of the present invention resides .in the provision of a simple and effective means of lubricating the pistons so that they can operate readily in their cylinders. Longitudinal grooves are provided in the pistons alternate of which communicate with the opposite ends of the piston. As a result the grooves communicating with one end of the piston are subject to pressure at that end of the cylinder while the grooves communicating with the opposite end of each piston are subject to the pressure within the housing and externally of the cylinder barrel. Rotation of the pistons about their axes causes a thin lilm of oil to be spread upon the inner surface of each cylinder during reciprocation and rotation of the piston.

A further feature of the present invention resides in the particular arrangement of arcuate grooves in the valve plate. As the pump is reversible two arcuate grooves are provided one of which is connected to one port and the other of which is connected to the other, Either port may serve as the inlet port while the other serves as the outlet port. The arcuate grooves are spaced apart a distance substantially equal to the width of the cylinder inlet in the cylinder barrel. A pocket is provided between the adjacent ends of the groove, this pocket being normally filled with oil. Vlf the cylinder is under compression at the time the cylinder inlet passes this pocket, the Huid in the pocket compresses suiliciently to permit continued compression of the cylinder as the inlet passes from one arcuate groove to the other.

A further feature of the present invention resides in the provision of a closed circuit pumping sytem which includes a variable capacity swash plate type pump having in association therewith a super-charging pump which is connected to the first mentioned pump in a manner to hold the pistons against the swash plate, and to replenish any fluid which leaves the closed circuit system due to leakage or due to variations in volume of the closed circuit system. For example, if the closed circuit system is used to reciprocate a piston type driven apparatus having a piston rod on one side only, the uid which is pumped into one end of the driven cylinder must be greater than what is forced from the opposite end of the cylinder due to the displacement of the piston rod. In an event of this type the super-charging pump acts to replenish the oil and to mix with the iluid in the closed circuit system thus producing a definite cooling elect on the fluid in the closed circuit system. The super-charged pump also replenishes any fluids used for lubricating the cylinder walls and the surfaces of the swash plate and of the valve plate.

A further feature of the present invention resides in the provision of a pump which incorporates in its housing a pair f check` valves which function automatically to control the ilow of fluid to the cylinders depending upon the position of adjustment of the swash plate. When the` swash plate is rotated beyond a predetermined angularity, the check value in the port leading to one arcuate valve closes and the check valve leading to the opposite arcuate groove in the valve plate opens to reverse the flow of fluid through the pump.

A further feature of the present invention resides in the provision of a pump housing incorporating a shuttle valve which is controlled by the fluid being pumped from the pump due to the action of the super charging pump to permit excess lluid not needed to overcome leakage to escape, and also to carry away the hot oil.

These and other objects and novel features of my invention will be more clearly and fully set forth in the following specification and claims.

In the drawings forming a part of the specification:

Figure 1 is a longitudinal and sectional View through the swash plate pump showing the general construction thereof;

Figure 2 is a cross sectional view through the pump, the position of the section being indicated by the line 2 2 of Figure 1;

Figure 3 is a sectional view through a portion of the pump housing, the position of the section being indicated by the line 3 3 of Figure 1;

Figure 4 is a cross sectional view through the pump, the position of the section being indicated by the line 4 4 of Figure l;

Figure 5 is diagrammatic view showing the manner in which the fluid ows through the system;

Figure 6 is a cross sectional view of the pump, the position of the section being indicated by the line 6 6 of Figure l.

F luid pump construction The fluid pump includes a generally cylindrical housing having a central portion 10 which is hollow in form and which is closed at opposite ends by end members 11 and 12. These end members 11 and 12 are secured to the central portion by cap screws such as 13 and 14 respectively. A drive shaft 15 extends through the end plate 11 and is supported by an antifriction bearing 16 mounted in an axial recess 17 in this end plate 11. The bearing 16 is held in place by a bearing cap 19 having a peripheral ange 26 which is bolted or otherwise secured to the end plate 11 by cap screws 21 or other suitable means. A nut 22 is threaded upon the shaft 15 and forces a locking ring 23 against the inner face of the bearing 16, this locking ring 23 serving to hold the inner bearing race from rotation relative to the shaft 15 and also holding the nut 22 from unthreading once it is in place. A seal 24 encircles the shaft 15 within the bearing cap 19 to prevent the leakage of iluid from the pump housing.

A snap ring 25 is interposed between the inner race of the bearing 16 and a shoulder 26 on the drive shaft 15 to hold the bearing from longitudinal movement upon the shaft. A sleeve 27 freely encircles the shaft 15 inwardly from the shoulder 26 and is rotatively supported between and within bearing rings 29 and 30. This sleeve 27 is provided with angularly spaced external teeth 31 which are engageable with cooperable teeth 32 on a transversely arranged gear rack 33. As is illustrated in Figure 4 of the drawings the rack 33 is mounted in a cylindrical bore 34 extending transversely of the end plate 11, the bore 34 being closed at one end by a closure plate 35 held in place by cap screws 36 or other suitable means. The other end of the rack 33 may be reduced in diameter 4 as indicated at 37 and extends through the opposite side of the closure plate 11, suitable seals 39 being provided to prevent the leakage of fluid from the pump housing. As is evident from Figure 4, longitudinal movement of the rack 33 may rotate the externally tooth sleeve 27 in either direction.

A swash plate 40 bears against the inner surface of the end plate 11 encircling the drive shaft 15. This swash plate 40 is provided with internal teeth as indicated at 41 which engage the external teeth 42 on the sleeve 27. ln other words, the swash plate 40 is Splined to the sleeve 27 so that it can move in an axial direction but rotates in unison with the sleeve.

A ring 43 of suitably hardened material is supported internally of the central portion 10 of the pump housing and has one edge preferably recessed into a circular groove 44 in the end plate 11. A roller bearing 45 is provided inwardly of the ring 43 and between this ring andthe exterior o-f the swash plate 40. This roller bearing 45 rotatably supports the swash plate so that it may be readily rotated within the pump housing.

As is evident from Figure l of the drawings, the swash plate 40 is provided with an outer surface 46 which is on a plane normal to the axis of rotation of the shaft 15. The opposite surface 47 of this swash plate is on an angle relative to the plane normal to the axis of rotation of the shaft 15 and the degree of angularity of this surface 47 determines the length of stroke of the pump pistons which will be later described in detail.

A valve plate 49 bears against the opposite end plate 12 and this valve plate is preferably pinned or otherwise held from rotation with respect to the end plate 12 by suitable pins 50 or other suitable means. This valve plate 49 is preferably provided with arcuate grooves 51 and 52 as is best illustrated in Figure 6 of the drawings. The arcuate groove 51 is connected by a port 53 to an inlet or outlet 54 leading from the pump housing. The arcuate groove 52 is similarly connected by a port 55 to a port 56 leading from the pump housing. The ports 55 and 56 are usually on diametrically opposite sides of the pump axis.

As is also shown on Figure 6 of the drawings the arcuate grooves 51 and 52 terminate in spaced relation, the distance between these grooves being approximately equal to the width of the openings in the ends of the pistons as will later be described. In other words as each piston moves out of contact with one groove, the opposite edge of the piston is in contact with the other groove. However as there is a substantially line to line engagement between the grooves and the piston openings, pockets 57 are provided in the valve plate 49 between the ends of the grooves 51 and 52. These pockets 57 normally contain oil or other fluid which can be compressed to some extent when sufficient pressure is provided. In the event the pistons are under compression when passing over the pockets 57, the fluid within these pockets can compress sufficiently to permit continued and unimpaircd rotation of the pistons.

The valve plate 49 is held to the closure plate 12 by a bolt or cap screw 59 extending axially into this end plate 12 and through a central aperture in a valve plate 49. The valve plate is designed to t snugly against the end plate 12. Circular grooves 60 and 61 are provided in the end plate 12 outwardly and inwardly of the ports 53 and 55. Pressure on opposite sides of the valve plate 49 is equalized by passages 62 and 63 leading from the grooves 60 and 61 through the valve plate to grooves 64 and 65 respectively on the inner surface of the valve plate 49 in opposed relation to the grooves 60 and 61.

A second bearing ring 66 is provided within the central portion 10 of the housing and a roller bearing 67 is provided inwardly in the ring 66. This roller bearing 67 supports the rotating cylinder barrel 69 for rotation about the axis of the shaft 15 and in unison therewith. The cylinder barrel 69 is provided with an end plate 70 which bears against the valve plate 49 in sliding contact therewith. This cylinder barrel 69 is provided with a hollow interior bore 71 which encircles the extremity of the drive shaft 15. The shaft is provided with an externally splined enlargement 72 which cooperates with the internal spline 73 of the cylinder barrel 69 to cause rotation of the cylinder barrel with the drive shaft. A spring 74- has one end encircling a shaft projection 75 on the drive shaft and has its opposite end bearing against an inwardly extending flange 76 forming a part of the cylinder barrel end 70. This spring 76 holds the cylinder barrel against the valve plate 49 and in substantial surface contact therewith.

Fluid leakage between the rotating cylinder barrel 69 and a xed valve plate 49 produces a force acting against the end 70 of the cylinder barrel tending to cause free rotations of this member. The grooves 65 are connected with radially extending grooves 77 to the interior of the bore '71 of the cylinder barrel while similar grooves 79 permit the escape 0f iluid under pressure in the grooves 60 and 64 to the exterior of the cylinder barrel. A bleed passage 80 is provided through the central portion 10 of the housing and communicates with the tank or reservoir which will be later described so that this portion of the housing is not subjected to the high pressures of the actual pumping cylinders.

The cylinder barrel 69 is provided with a series of angularly spaced cylinders 01, these cylinders usually being uneven in number. The cylinders 81 are arranged with parallel axes and are equally spaced about the center of rotation. Pistons 82 are slideably and rotatably supported in each of the cylinders 81. One of these pistons has been omitted from the uppermost cylinder in Figure 2 of the drawings in order to show the shape of the port 53. It should be understood however that similar pistons are provided in each of the cylinders.

Each of the pistons' 82 comprises a hollow sleeve like body 83 having an enlarged bearing end 84 at one end thereof. The opposite end of each piston is open. The piston heads 84 are arranged on a plane which is angularly related to a plane normal to the axis of each piston. The degree of angularity of the piston heads corresponds with the angularity of the surface 47 of the swash plate i0 so that these heads are in contact with the surface 47 of the swash plate during rotation of the cylinder barrel. The head 84 of each piston is provided with a central recess 85 which communicates with the interior of the piston 82 by a passage S6. The follow area 85 is of slightly smaller dimensions than the effective area of the opposite or open end of the piston. As iluid under pressure may enter the hollowed areas 85 of the pistons, a pressure is exerted against the head ends 84 of the pistons which is somewhat smaller than the pressure exerted upon the opposite ends thereof. This equalization of pressure on opposite sides of the head ends of the pistons materially decreases the pressure which the pistons exert on the swash plate thereby materially decreasing the force necessary to rotate the cylinder barrel during the operation of the pump.

The pistons 82 are provided on their exterior surface with a series of angularly spaced elongated grooves 87 extending to a point near the bearing end 84 of these pistons. A second series of grooves 89 are provided in the exterior surfaces of the pistons 82. communicating with the open ends of these pistons. The grooves 89 alternate with the grooves 87 and the ends of these grooves preferably overlap to some extent. Thus while none ofthe grooves extend throughout the length of the pistons or are of suiicient length to permit fluid to ilow completely throughout the length of the pistons, these grooves permit a distribution of fluid to the walls of the cylinders 81 to lubricate these cylinder walls and permit easy reciprocation and rotation of the pistons 82.

As is also indicated in Figure l of the drawings, the end plate 11 is provided in its inner surface with a ring shaped groove comprising arcuate sections 90 and 91 which are similar in shape and which are opposed to the grooves 51 and 52 of the valve plate 49. A passage 92 leads from the port 53 through the housing of the pump to communicate with the arcuate groove 90. A similar passage 93A extends from the port 55 through the pump housing to the arcuate groove 91. The grooves 90 and 91 are of proper Width to provide a balancing force against the swash plate 40 to considerably diminish the force required to rotate this swash plate. In other words fluid under' pressure is communicated to the area between the swash plate 40 and the end plate 11 to more or less equalize the pressure between the valve plate and the cylinder barrel 69. Circular grooves 94 and 95 which are outwardly and inwardly of the arcuate grooves 90 and 91 may be connected by suitable means to the bleed line such as 80 to prevent the loss of Huid under pressure.

The bearing rings 43 and 66 are held in properly spaced relation within the pump housing by a spacing member 96. A second spacing member 97 is interposed between the ring 66 and a shoulder 99 in the interior of the pump housing to hold the rings and bearings in proper spaced relationship.

The pump also incorporates a check valve and a shuttle valve which are actually a part of the fluid system. However as they are actually embodied in the pump housing, they will be described in conjunction with the pump structure.

An inlet passage 100 extends transversely through the end plate 12 and communicates with two opposed passages 101 and 102 leading in opposite directions. Valve seats 103 and 104 are provided between these passages 101 and 102 and enlargements 105 and 106 of these passages. Thimble like check valves 107 and 109 are normally engaged against the seats 103 and 104. Springs 110 and 111 are interposed between the valves 107 and 109 and plugs 112 and 113 threaded into the passage enlargements 105 and 106. Passages are provided between the enlarged diameter portions 105 and 106 and the arcuate grooves 51 and 52 respectively of the valve plate 49. As the sectional view of Figure 3 is directed toward the end of the closure plate 12, these passages would not normally be visible in Figure 3. However, a general position of these passages is indicated in dotted outline at 114 and 115 so that the construction may be more readily understood.

An outlet port 116' communicates with two branches 117 and 119 communicating with ' annular chambers 120 and 121 and circling the body of a shuttle valve 122. The shuttle valve 122 is slideably supported in a cylindrical bore 123 in the end plate 12, which cylindrical bore is closed at its ends by suitable end plugs 125 and 126. The shuttle valve 122 is provided with hollow outer ends 127 and 129 having inlet passages 130 and 131, respectively, and outlet passages 132 and 133, respectively. The outlet passages 132 and 133 communicate with annular chambers 134 and 135 which communicate with the arcuate grooves 51 and 52 of the valve plate 49. The passages extending between the annular chambers and the arcuate grooves would not normally be Visible in Figure 3 of the drawings but to simplify the description, such connections are shown in dotted outline at 136 and 137, respectively.

When in the position illustrated the arcuate groove 52 is connected through a passage 137 to the annular chamber 135. This annular chamber 135 is connected through the passages 131, 133 and the hollow interior of the valve with the annular chamber 121. The annular chamber 121 is connected through the branch passage 119 to the outlet port 116. In this position of the valve, the passage is out of registration with the annular chamber 120 so that a branch passage 117 is closed.

is connected through the passage 136 to the annular chamber 134 which in turn is connected through the passages 132 and 13@ and the hollow interior 127 of the shuttle valve with the annular chamber 121). This in turn is connected with the branch 117 leading to the outlet port 116.

The fluid system The fluid system is illustrated diagrammatically in Figure of the drawings. A typical fluid system embodying the pump is illustrated in this iigure. Numerals which have previously been used to designate parts of the pump have been employed in Figure 5 wherever these numerals are applicable. The check valves 187 and 109 have been shown in a simplified form in this figure.

In the particular arrangement illustrated in Figure 5 the port 54 is connected by a suitable conduit 139 to one end of a cylinder 140 including a piston llil which is to be reciprocated by fluid pressure. The opposite end of the cylinder 140 is connected by a suitable conduit 142 to the port 56 of the pump. As the pump is driven, fluid is drawn from the conduit 142 and into the port 56. The fluid is pumped under pressure through the port 54 and into the conduit 139 leading to the cylinder 14) so as to move the piston 141 downwardly as illustrated in this figure.

Fluid is also drawn upwardly from the reservoir tank 143 through the conduit 14d by the super-charging pump 145. This fluid is forced through the intake port 10d past the check valve 109 and through the passage 115 communicating with the arcuate groove 52 in the valve plate 49. This fluid acts to replenish the oil in the system and also acts to mingle with the fluid being circulated by the pump to have a cooling effect thereon. The excess uid pumped into the groove 52 extends through the lower portion of the shuttle valve 122 and through the outlet branch 119 in outlet port 116 which is connected to a pressure relief valve 146. The outlet of this valve is connected by a conduit 147 with the reservoir tank 143.

When the piston 141 reaches the limit of its downward movement, suitable means either manual or automatically controlled are provided to move the gear rack 33 longitudinally. This acts to rotate the sleeve 27 in a manner to rotate the swash plate i0 through a desired angle of rotation. If the pump is operating at maximum volume the swash plate will be rotated through an angle of 180 degrees.

Rotation of the swash plate i0 acts to reverse the pump ing action of the pump and the port 5d now forms the inlet and port 56 forms the outlet. As a result the check valve 109 will close and the check valve 107 will open. This permits the uid from the super-charging pump 145 to ow into the arcuate groove 51 and permits the excessive uid to tiow into the annular chamber' 134. The shuttle valve 122 reverses in position and the excessive pressure is communicated through the hollow end 127 of the shuttle valve to the outlet branch 116 leading to the outlet port 116 communicating with the relief valve 146. This uid communicates through conduit 147 to the reservoir tank 143.

Operation of t/ze apparatus The operation of the pump is believed obvious from the foregoing description. As the cylinder barrel rotates with the drive shaft uid is pumped from each successive cylinder into one of the arcuate grooves 51 or 52. if the swash plate 40 is in the position illustrated in Figure l of the drawings, each piston successively will pump during approximately one-quarter of a revolution into the arcuate groove 51 and then during the following quarter revolution into the arcuate groove 52. Similarly, each piston will draw fluid from the arcuate groove 52 during approximately one-quarter revolution and then draw fluid from the arcuate groove 51 during the next quarter revolution. As a result, the fluid will circulate but will not act to move the piston 141.

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If the swash plate ll0 is rotated approximately 90 degrees in one direction the full movement of the pistons 82 will act to force Huid through the outlet port 54 through the arcuate groove 51 and the inlet 56 will be simultaneously connected through the arcuate groove 52 to the cylinders in a manner to draw fluid from the inlet 56 throughout substantially 180 degrees of rotation of the pump. In other words, when in this position the pump will operate to its maximum effect to force liuid in one direction.

If the swash plate MB is rotated approximately degrees in the opposite direction from the position shown in Figure l of the drawings, fluid will be forced to a maximum extent through the port 56 and will enter with maximum effect through the port 54 and into the pump. The uid is actually forced into the cylinders by the super-charging pump. Because of this fact, the pistons are at all times held against the swash plate under some pressure even during the intake portion of the cycle.

In intermediate positions of the swash plate, intermediate effects will be obtained. In other words, the pumping action will continue partially in both arcuate segments 51 and 52 of the valve plate, partially overcoming the pumping pressure and decreasing the volume of iluid being pumped. Stated otherwise, in intermediate positions of the swash plate, some of the pistons are motoring and taking oil from the ports while others are pumping into these same ports. This can be effected while the pump is travelling at a constant rate of speed and without changing the angularity of the swash plate. The forces against the various parts are hydraulically balanced and therefore friction is reduced to a very low value. The circulation of fluid under pressure from the super-charging pump tends to cool the fluid of the main circulating system and to replenish any Huid which leaks past the pistons or through the same in the operation of the pump.

Certain variations can be made from the construction described. For example, while the construction disclosed is somewhat simpler, similar results may be obtained by holding the swash plate stationary and rotating the valve plate. It should also be understood that lthe device may be used as a fluid motor as well as a pump.

In accordance with the patent statutes, I have described the principles of construction and operation of my swash plate type pump, and while I have endeavored to set forth the best embodiment thereof, I desire to have it understood that obvious changes may be made within the scope of the following claims without departing from the spirit of my invention.

I claim:

l. A fluid pumping system including a pump housing, a rotatable cylinder barrel supported in said housing, a series of pistons slideably and rotatably supported by said barrel., a swash plate having a surface against which said pistons engage during rotation of said barrel, a valve plate engageable with the end of the cylinder barrel opposite the swash plate, a pair of spaced arcuate ports in said valve plate, said barrel including open ended angularly spaced cylinders supporting said pistons, the ends of the cylinders communicating with said arcuate ports during rotation of said barrel, a fluid reservoir, a Super charge pump connected to said reservoir, passages between said pump and said arcuate ports including check valves therein, said pump providing pressure tending to hold said pistons against said swash plate, passages leading from said arcuate ports, a relief valve in said last named passages, said relief valve including a connection to said reservoir, valve means in said last named passages, said last named valve means opening the passage from one arcuate port to said relief valve and closing the other, and including a closed circuit uid system connected between said arcuate ports.

2. A pump including a housing, a cylinder barrel rotatable within said housing having parallel angularly spaced cylinders therein, a rotatably supported swash plate axially aligned with said barrel in said housing and having a surface on a plane at an acute angle to a plane normal to the axis of the barrel, pistons in said cylinders and projecting therefrom, said pistons being slidably and rotatably supported in said cylinders, fixed angularly arranged bearing ends on said pistons in surface icontact with said swash plate, said pistons rotating in their cylinders as said barrel rotates, a valve plate supported at the end of said barrel opposite that from which said pistons project, said valve plate having a pair of arcuate grooves therein, angularly spaced passages in said barrel communicating with said cylinders and communicable with said arcuate grooves upon rotation of said barrel, the ends of Said arcuate grooves being spaced apart a `distance greater than the angular Width of said passa-ges, said valve plate having closed pockets therein extending partially therethrough between the ends of said arcuate grooves communicable With each said passage as it travels from registry with one arcuate slot to registry with the other, a pinion rotatable with said swash plate, and a rack engaging said pinion for rotating said lswash plate and holding it in adjusted relation.

3. A pump including a housing, a cylinder barrel rotatably supported in said housing having parallel angularly spaced cylinders therein, a swash plate axially aligned with said barrel and having a surface on a plane at an acute angle to a plane normal to the axis of the barrel pistons in said cylinders and projecting there from one end thereof, heads on said pistons engageable against said swash plate, a valve plate engageable with the other end of said barrel, said other end of said barrel having angularly spaced passages therethrough communicating with said cylinders, arcuate grooves in said valve plate alternately communicating with said passages during rotation of said barrel, said housing including a port communicating with each of said arcuate grooves, one of said ports acting as an inlet port while the other acts as an -outlet port, and means rotatably supporting said swash plate relative to said valve plate for rotation substantially through one hundred and eighty degrees, means engaging said one plate for rotating the same and holding it in adjusted position, whereby the pistons may pump fluid from either of said arcuate grooves into the other, and whereby the volume of uid pumped may be varied from no output to maximum output.

4. The structure of claim 3 and in which the ends of said arcuate grooves are spaced apart a distance greater than the angular width of said passages, and in which the valve plate includes closed pockets traversed by said passages during rotation of said barrel.

5. A pump including a housing, a cylinder barrel rospaced cylinders therein, a swash plate axially aligned with said barrel in said housing and having a surface on a plane at an acute angle to a plane normal to the axis of the barrel, pistons in said cylinders and projecting therefrom, said pistons being slidably and rotatably supported in said cylinders, fixed angularly arranged bearing ends on said pistons in surface contact with said swash plate, said pistons rotating in their cylinders as said barrel rotates, a valve plate supported at the end of said barrel opposite that from which said pistons project, longitudinally extending angularly spaced grooves in the outer surfaces of said pistons communicating with the ends of said piston opposite said projecting ends but terminating short of said projecting ends thereof, and intermediate longitudinally extending grooves in the outer surfaces of said pistons terminating short of said opposite ends thereof but extending substantially to the projecting ends thereof, the ends of said grooves overlapping near the longitudinal center of said pistons, said valve plate having a pair of arcuate grooves therein, angularly spaced passages in said barrel communicating with said cylinders and communicable with said arcuate lgrooves upon rotation of said barrel, the ends of said arcuate grooves being spaced apart a distance greater than the angular width of said passages, said valve plate having closed pockets therein extending partially therethrough between the ends of said arcuate grooves communicable with `each said passage as it travels from registry with one arcuate slot to registry with the other.

References Cited in the le of this patent UNITED STATES PATENTS 2,300,009 Rose Oct. 27, 1942 2,364,301 MacNeil Dec. 5, 1944 2,421,846 Neuland .Tune 10, 1947 2,428,809 Parilla et al. Oct. 14, 1947 2,449,297 Hoier Sept. 14, 1948 2,617,360 Barker Nov. 11, 1952 2,642,809 Born et al. June 23, 1953 2,661,695 Ferris Dec. 8, 1953 2,661,701 Ferris Dec. 8, 1953 2,711,724 Jenny Iune 28, 1955 2,741,188 Wemhoner Apr. 10, 1956 2,749,844 Weisenbach June 12, 1956 2,757,612 Shaw Aug. 7, 1956 FOREIGN PATENTS 549,323 Great Britain Nov. 16, 1942 897,198

France Aug. 11, 1943

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