US2642809A

US2642809A - Hydraulic apparatus

Info

Publication number: US2642809A
Application number: US647872A
Authority: US
Inventors: Ellis H Born; Leroy E Bonnette
Original assignee: Denison Engineering Co
Current assignee: Denison Engineering Co
Priority date: 1946-02-15
Filing date: 1946-02-15
Publication date: 1953-06-23
Anticipated expiration: 1970-06-23

Description

June 23, 1953 a H. BORN EIAL HYDRAULIC APPARATUS 4 Sheets-Sheet 1 /INVENTORS Ellis H.B0m

Filed Feb. 15, 1946 June 23, 1953 a H. BORN ETAL 2,642,809

HYDRAULIC APPARATUS 7 Filed Feb. 15, 1946 dramas-Sheet 3 F1e.6 FIG-5. 51, 52

A 56 A 51. 52 I /A H IL IVE NTOR I Ellis I-LIBorn B Leroy E.Bo11nett6 m mm u 3 Hm am 3 5 w. 2w 2 e 4 Sheets-Sheet 4 Filed Feb. 15, 1946 INVENTORS Ellis H.B0rn L eroy E Bonnetuc Patented June 23, 1953 HYDRAULIC APPARATUS Ellis H. Born, Columbus, and Leroy E. Bonnette, Delaware, Ohio, assignors' to The Denison En, gineering Company, Columbus, Ohio Application February 15, 1946, Serial No. 647,872

11 Claims. (C1. 103162) This invention relates to hydraulic apparatus. It is particularly directed to fluid pressure energy translating devices which may be employed to generate or utilize high fluid pressures.

One form of such devices includes a plurality of piston receiving cylinders which are alternately connected with ports containing fluids at different pressures. tween the cylinders and the ports in the operation of such prior devices, a shock occurs as they are brought into communication, which shock produces an objectionable noise and thus detracts from the desirability of the device. The shock or jar thus produced is also detrimental to the mechanism of the unit since it causes premature wear and other deterioration thereof.

It is an object of the present invention to produce a fluid pressure energy translatingdevicein the operation of which such shocks or Jars will be eliminated with the consequent avoidance of the objectionable noise. Previous attempts have been made to secure the object desired herein, but such attempts have been unsuccessful for various reasons, among which were the complications of the proposed apparatus and the selection of unsound principles. shock and noise can be eliminated by causing the pressure in the cylinders to increase or decrease to substantially equal the pressure in the valve port approached thereby, and to provide means which will prevent the pressure in the cylinders, after it has become equal to the valve port pressure, from exceeding the same whereby the pressures in the cylinders and ports will substantially conform to one another when registration between these elements is effected.

Due to the difference in pressures bea It has-been discovered that the controlled flow of fluid into and out of the cylin ders in the barrel, the device having valveecontaining passages which are operative to effect an equalization of the pressure in the cylinders and ports in the valve member prior to the registration thereof.

A still further object is to provide a fluid pres- I i sure energy translating device of the type mentioned in the preceding paragraph in which the valves in the passages are exposed to the fluid pressure in either the cylinder or the port, depending upon which port is being considered, to

control the direction of flow through the passages,

and a piston-containing cylinder barrel movable 1 relative to the two former members to effect a valve-controlled flow of fluid into and out of the cylinders in the barrel, the valve member and cam member being so related that the pistons will be moved, between periods of communication of the cylinders with either of the ports in the valve member, by the cam member in a direction to cause the fluid pressure in the cylinders to rise or Another object of this invention is to provide a a fluid pressure energy translating device having a relatively movable cylinder 'barrel and portcontaining valve member in sliding engagement therewith, the cylinders in the barrel consecutively registering with the ports in said valve member, the device having means for moving the .pistons in the cylinders to effect a flow of fluid into the cylinders from one valve port and out of the cylinders to another valve port, and forming the device with auxiliary ports and passages whereby the cylinders may communicate with the tive to the two former members to effect a valve- 5 fall toward the pressure in the port being approached, the device having valved passages by means of which the pressure in the cylinders is prevented from changing excessively from that in the port being approached. a I ,An object of the invention also is to provide a fluid pressure energy translating device having a ported valve member, a cam member and a pistoncontaining cylinder barrel movable relative to the two former members to effect a valve controlled flow offluid into and out of-the cylinders in the barrel, the relation between the valve and cam members being such that the pistons will be moved into the cylinders, asthe latter approach the high pressure port and before registration therewith,

a distance sufficient to raise the fluid pressure to I and to maintain such communication until the cylinder and port are in actual registration.

A more specific object is to provide a fluid pressure energy translating device having a valve plate and a cylinder barrel movable relative thereto in sliding engagement to control communication between cylinders in the barrel and the port in the valve plate, the valve plate being provided with auxiliary ports between the adjoining ends of the ports therein and passages connecting these auxiliary ports with either of the other ports, the passages receiving check valves to limit the direction of fluid flow therethrough, the valve in the passage in communication with the high pressure port being such as to prevent fluid flow from the pressure port to the auxiliary port and cylinders, while the valve in the passage communicating with the low pressure port serving to preclude fluid flow from the cylinders to such port.

An object of the invention also is to provide a fluid pump of the axial piston type which has a port plate and a cylinder barrel in sliding engagement and a cam member for moving piston means in the cylinder barrel; to index the port plate relative to the cam member so that the pistons will move into the cylinder far enough before the registration of the cylinder with the high pressure port to increase the fluid pressure in i the cylinders to the maximum pressure capacity of the pump and to provide valved passage means operative to establish communication between the cylinders and the high pressure ports before registration thereof when the pressure in the cylinders reaches that in the high pressure port, thus the pressure in the cylinders and high pres sure ports will be equalized before registration whether the pressure in the latter is at the maximum of the pump or at a lesser pressure.

A still further object of the invention is to provide a fluid pressure energy translating device capable of operation either as a fluid pump or motor operable in either clockwise or counterclockwise direction and having means for equalizing fluid pressures between ports containing fluid under pressure and cylinders containing fluid at different pressures prior to registration thereof whereby undue shock and noise will be avoided in the operation of the device.

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. 1 is a partial vertical longitudinal sectional view taken through a pump formed inaccordance with the present invention;

Fig. 2 is a detail vertical transverse sectional view taken on the plane indicated by the line 11-11 of Fig. 1;

Fig. 3 is a diagrammatic view illustrating the relationship of various parts of the pump at a particular stage of operation thereof, the view including a development of the cam track traversed by the piston bearing shoes;

Fig. 4 is a diagrammatic view of a slightly modified form of the invention designed for operation both as a fluid pump and motor either of which is capable of operation in either direction and in which fluid pressures are equalized between the cylinders and a port approached thereby;

is disposed in bearing engagement with a showing such relations when the device operates in a counterclockwise direction;

Figs. 7 and 8 are similar views of difierent portions of the cam track traversed by the pistons when the device is functioning as a fluid pump, Fig. 7 showing the relation of the cam and port plate when the device is driven in a counterclockwise direction and Fig. 8 showing suchrelation when the device is driven in a clockwise direction.

Fig. 9 is a diagrammatic view of the port plate and the means for indexing the same showing the port plate in the position occupied in Fig. 7;

Fig. 10 is a similar view showing the port plate indexed as in Fig. 8; and

Fig. 11 is a vertical transverse sectional view taken through a modified form of fluid pressure energy translating device in which the cam memher is indexed instead of the port plate; in this form of the invention, the port plate may be stationarily located or it may also be made adjustable as in a previously illustrated modification.

In carrying out this invention, a device of the type shown in Fig. 1 may be employed. The device illustrated has been designed for use as either a fluid pump or motor of the axial piston type, the invention, however, being adaptable to both pumps and motors of the radial piston type designed for operation in either direction of rotation. The device shown in Fig. 1 includes a hollow body is which is closed at one end by a head II and at the opposite end by a cover l2 to define a chamber i3. The chamber I3 receives the operating-mechanism of the device which mechanism comprises a'valve plate H which may be either adjustably or stationarily mounted on the head H, a cam i5 carried in spaced relationfrom'the plate M by the cover 12 and a rotor mechanism indicated generally by the numeral 5 5, this rotor mechanism being disposed for rotation between the valve plate l4 and the cam 15. Rotary motion is imparted to the mechanism if) by a shaft l7 journaled in the head H and projecting into the chamber H3. The inner end of the shaft i! is keyed by a splined connection it to a cylinder barrel [9 which has one end in sliding engagement with the valve plate [4. In the present illustration, the opposite end of the cylinder barrel an annular skirt 20 projecting therefrom which skirt suitably finished portion of the body Such a skirt and the reasons therefor are disclosed in the copending application of Ellis H. Born, Se-

rial No. 575,864, filed February 2, 1945, now Patent No. 2,608,159.

Cylinder barrel i9 is formed with series of axially extending cylinders 25 which terminate at their inner ends in ports opening to the surface of the cylinder barrel in en'" 'e the port plate. These cylinders slidably receive piston members 23 used to effect the move ment of fluid into and out of the cylinders. Reciprocatory movement of the pistons in the cylinders is governed by the cam member I? through a sliding engagement tl' rebctwecn, friction being reduced to a minimum by the provision of sliding shoes 2i and ball and socket connections 25 thereof with the pistons. These shoes 24 are held in sliding contact with the cam plate 15 by a perforated disc 25'and a spring pressed plunger 21. the latter being received by a ferrule 23 inserted in the inner end of the shaft ll. Spring 29, disposed between the inner end of the ferrule 28 and the plunger 21, tends to urge the latter towardthe cam plate -I5. Since the plunger 21 engages a socket in disc 26 which in turn engages flanges on the shoes 24, the latter will be held in sliding contact with the face of the cam member. Due to the inclination of such face the pistons will move into and outof the cylinders in the cylinder barrel as the rotor mechanism is revolved. From Fig. 1 which is a verti'cal sectional view through the device, itwill be noted that cam I is so disposed that the points thereon in the path of movement of the shoes closest to and farthest away from the valve plate will be disposed in a vertical plane, indicated by the dotted line A-B in Fig. 2, passingthrough the axis of rotation of a shaft [1. I p p j I As illustrated in Fig. 2, one form of the invene tion has the valve plate It indexed or rotated in the direction of rotation of the cylinderbarrel, so that at the instant each cylinder ceases to communicate with the inlet port 30, itwill occupy the top dead center position indicated by dotted lines in Fig. 2, in the pump. The port plate is also so made that the sealing portion or land 3| between the inlet and

outlet ports

30 and 32 will be of a length sufiicient to permit the pressure in the cylinders to be increased by the movement of the pistons into the cylinders to the maximum pressure for which the device has been designed before the cylinder registers with the outlet port 32. When the pump is, in operation at such maximum capacity, the pressure in the cylinders as they register with the outlet port 32 will be equalto that in such port and no shock or noise will occur. In the event, however,'the pump is change the pressures in the cylinders will be higher than the pressure in the outlet port immediately prior to registration therebetween, and

when registration occurs a shock and consequent noise will be produced. This objectionable operation is avoided in the present invention by forming the port plate with an auxiliary port 33 in the land 3! between the inlet and outlet ports, This auxiliary port 33 is connected by a passage. 34

with the outlet port which passage contains a spring pressed ball check valve 35as illustrated in Fig. 3. Port 33 is so located that immediately upon the termination of communication between the inlet port 30 and each cylinder, the latter will communicate with the ort 33 and remain in com- .munication therewith until the cylinder registers with the outlet port 32. r

The valve 35 is arranged in the passage in ,such manner'that fluid flow from the port 32 to .the port 33 will be precluded.- Due'to such an arrangement, communication between the cylin- :ders and the outlet ports 32'will be established only when the pressure in the cylinder reaches that in the outlet port which communication will will occur when the cylinders register with the cylinder port pressure-Will not appreciably exoperated at lower pressures with no further are provided as at and 55, respectively, with symmetrically located auxiliary ports connected This passage is intersected by then be maintained until the cylinder registers It will thus be seen'that with the ports 5| and 52. connection with the passage 51, the passage is ceed the outlet port pressure toinitiate flow between the cylinder and theoutlet port in the operation of the device. 'j

' Shock and noise which might occur when the cylinders are open to the inlet port after traveling over the lower cutofi may be similarly avoided by providing a second auxiliary port 36 in th valve plate at the land 31. nected with the inlet port 30 by a passage 38 which passage also contains a spring pressed check valve 40.

port 36. Immediately upon reaching bottom dead center position when the pressure in the cylinders is at a minimum, they will communicate with the ports 36 and as the cylinders move 'on toward the inlet port 30 and the pistons are moved outwardly by the cam, fluid may flow through the passage 38 to relieve any suction occurring in the cylinders. The pressure therein will thus be equal to the inlet port pressure when the cylinders register with such ports. Figs. 4 to 10, inclusive, diagrammatically illustrate 'a, slightly modified form of the invention which is adapted to serve either as a fluid pump or motor, each being capable of clockwise or counterclockwise rotation, the fluid pressure being automatically equalized between the cylinders and certain of the pressure ports, to avoid shock and noise. In Fig. 4 a port plate 50 is diagrammatically illustrated, this port plate being provided with means for automatically indexing the same-in either counterclockwise or clockwisedirection, the indexing being controlled by the fluid pressure in one orthe other of the ports in the port plate. The plate 50 includes spaced arcuate ports 5| and 52 separated by upper and

lower cutoff sections

53 and 54. These cutofi sections by a passage 51. another passage 58 connected at opposite ends Adjacent the port of enlarged to slidably receive a piston valve 60 which serves to connect the passage 51 with one or the other of the ports 5| and 52. The piston valve 60 responds to fluid pressure in one or the other of ports 5] and 52 to establish communication between theport containing the higher pressure and the passage 51. This pressure is prevented from reaching the auxiliary ports at 55 and 56, by spring pressedcheck valves 6] and 62 disposed in the passage 5'! between the points of connection thereof with the passage 58 and the auxiliary ports. c

The port plate 59 is provided with a laterally projecting arm 63 disposed for engagement by a disposed for movement in the

cylinders

61 and 68.

A pair of passages 10 and H extend from the ports 5| and 52, respectively, to the outer ends of the

piston chambers

61 and 68, respectively.

Figs. 5 and 6 show developed views of the cam track at thehigh point thereof, i. e.) the point This port con The valve 40 is arranged to permit, flow only from the inlet port to the auxiliary atxvarious stages of movement along ,the .cam track, the lower cutofi section of the valve plate andthe. relation thereof to the high point of thecam track. In Fig. the cylinder barrel is rotating in a clockwise direction while in Fig. 6 it is rotating in a counterclockwise direction. It has been found that when the device is operated as a fluid motor, it is necessary that the port plate or the cam plate be indexed relative to the other. When the port plate is indexed, it is moved in a direction reverse to that of the direction of rotation of the cylinder barrel; if the cam plate is moved, it is adjusted in the direction of rotation of the cylinder barrel. When the device is used as a pump, however, the port plate must be indexed in the direction of rotation of the cylinder barrel while the cam plate, if adjusted, must be moved in the opposite direction. In the modification of the invention shown in Figs. 4 to 10, inclusive, two auxiliary ports are provided, one in each cutoff portion of the valve plate. When the device is operated as a fluid motor, the auxiliary port in the lower cutoff portion is effective to neutralize the pressure in the cylinders with the pressure in the high pressure port prior to registration thereof with the high pressure port, whether the device rotates in a counterclockwise or clockwise direction. When the device is operated as a pump, the auxiliary port in the upper cutoff portion of the port plate is utilized to efiect this operation. By providing the fluid pressure operated piston valve 60, the proper auxiliary port may be connected with the high pressure port andisolated from the low pressure port.

The device is purely automatic in its operation. From Figs. 4, 5 and 6, it will be seen that when the device functions as a. fluid motor and fluid under pressure is supplied to the port 5|, the cylinder barrel will be revolved in a clockwise direction. At this time pressure from the port 5| will flow through the passagelO to the closed end of the piston cylinder 61. This fluid pressure will operate upon piston 55 moving the same outwardly of the piston cylinder 61. to the engagement of the piston 65 with the projection 63, the port plate will be indexed in a counterclockwise direction, that is, in a direction opposed to that taken by the cylinder barrel.

The lower auxiliary port at 55 will therefore move to the right as shown in Fig. 5 of the vertical plane AB passing through the longitudinal axis of the cylinder barrel or the axis of rotation of the pump, in which plane the point of the cam nearest to the port plate is located as above described.

From Fig. 5, it will be apparent that as the cylinders move beyond the exhaust port 52 and communication therebetween is interrupted by the cut-off portion, the pistons will move along the cam track and continue to be forced into the cylinders, causing the fluid therein to be compressed. As soon as a cylinder discontinues communication with the exhaust port, it will register with the auxiliary port 55 and when the pressure in this cylinder builds up to that in the inlet or pressure port 5|, a further increase in pressure will be prevented since any increase in pressure will be dissipated through the auxiliary port 56 and

passages

51 and 58 to the high pressure port. This pressure dissipation will take place when the pressure in the cylinder reaches the outlet port pressure whether the latter pressure is at the maximum for which the device has been designed or at a lower pressure,

Due

If it is desired to operate the fluid motor in a counterclockwise direction, fluid will be supplied under pressure to the port 52. This pressure will enter the cylinders communicating with this port and cause the cylinder barrel to rotate in the desired direction. Some of the pressure will also flow through passage 1| to the closed end of the piston cylinder 68. This pressure will operate on piston 66 to move the same toward the left when viewed as in Fig. 4 causing the port plate to index in a clockwise direction. This movement of the port plate will place the auxiliary port on the left side of the vertical plane AB passing through the axis of rotation of the device as shown in Fig. 6 in which position the pressure equalizing operation will be substantially the same as when the parts were in the position shown in Fig. 5 except that the pressure in the cylinders will be equalized with the high pressure in the port 52 since piston valve will have been moved to the left to connect port 52 with the auxiliary ports.

When the device is operated as a hydraulic pump the auxiliary port at the upper cutofl portion is effective to equalize the fluid pressure in the cylinder and in the high pressure port. Figs. 7 and 9 show the relative positions of the port and cam plates when the device is operated as a fluid pump and rotated in a counterclockwise direction. Figs. 8 and 10 show the relation when the cylinder barrel is rotating in a clockwise direction. In the first two figures, that is, Figs. 7 and 9, fluid is admitted through the port 52 and discharged through the port 5|. This discharge of fluid causes a pressure to build up in port 5| which pressure is transmitted through line 10 to the closed end of the piston cylinder 61. This pressure reacts on piston 66 causing the port plate to be indexed in the direction of rotation of the cylinder barrel. When the port plate is indexed in this direction, the piston cylinders will communicate with the the auxiliary port 55 in the upper cutoff portion of the port plate when the pistons are at the point on the cam track most remote from the port plate. As the cam track is traversed by the pistons, the pressure will build up in the cylinder barrel as in the first form of the invention described and when this pressure starts to exceed that in the outlet or high pressure port 5|, 2. flow of fluid from the cylinder through the auxiliary port 55 and passages 5! and 58 to the hi h pressure port 5| will take place. The pressure in the cylinders will thus be prevented from exceeding that in the outlet port whether the outlet port pressure is as high as the device has been designed to develop or not. The opera tion, when the pump is rotated in a reverse or clockwise direction, as illustrated in Figs. 8 and 10 is substantially identical except the port plate is indexed in a clockwise direction and port 5| serves as the inlet port while port 52 is employed as the outlet port. The high pressure will thus exist in the port 52 and will engage the right end of piston valve 60 causing the same to move to the left end of its chamber and connect port 55 with port 52.

From the foregoing it will be apparent that a mechanism has been designed which will operate both as a fluid motor and as a fluid pump and in which the fluid pressure in the piston cylinders is automatically equalized with that in the pressure port toward which the cylinders are moving. The mechanism is characterized by its simplicity, the minimum requirements of service, and positain the same resultj 9 tive action. I It should be borne in mind that, although provisionfhas been made injthe present illustration for indexing 'the'port plate, it is mere lyn'ecessary to secure relative rotary movement between the port plate and the cam plate.

It should be obvious, therefore, that instead of indexing'the port plate, the cam "plate '15 could be pivotally supported and provided with hydraulic cylinders 12 and pistons 13, as illustrated in Fig. 11, to effect movement thereof relative tothe port plate It should also be obvious that although the invention has been shown and described asapplied to an axial piston pump or motor, the principles are applicablealso to other types of fluid energy translating devices'such', for example,

"as radial pistonpumps' and motors in which similar conditions of operation are encountered.

When the cam plate is adjusted, as in the form of the invention illustrated in Fig. 11, the port plate may be symmetrically arranged and positively secured to its support or it may also be in- I dexed if deemed advisable; [It will be necessary 'in' such a device to index thecam plate in a reverse direction from that in which the port plate 'isindexe'd in the previously discussed form to ob- While the invention has been illustrated in diagrammatic form only, it should be obvious that many modifications may be made inthe application of the idea to a practical device without departing from the spirit and scope of the invention.

We claim:' I T '1. An axial'piston type fluid pressure energy translating device comprising a cylinder barrel having a plurality of cylinders; a'port plate having spaced inlet and outlet ports, said port plate being disposed in relatively rotatable sliding engagement with said cylinder barrel; piston means in the cylinder barrel; cam plate means imparting reciprocatory movement to said piston means,

said cam and port plates being so related that 4' said outlet port to said auxiliary port. v

2. An axial piston type fluid pressure energy translating device comprising a cylinder barrel having a plurality of cylinders; a port plate having spaced inlet and outletrports, said port plate being disposed inrelatively rotatable sliding engagement with said cylinder barrelg-piston means in the cylinder barrel; camplate means imparting reciprocatory movement to said piston means,

' said cam and port plates being so related that the pistons move into the cylinders, prior to registra- -.tion thereof with saidoutlet port the distance requiredto raise the fluid pressure in the cylinders above that in the outlet port; an auxiliary port in saidlport platein the space between said inleti and outlet ports, "communicationbetween said cylinders and said auxiliary port commencing prior to and continuing until their registration with said outlet port; passage means connecting said outlet port to prevent fluid flow from said outlet port to said auxiliary port.

3. In a fluid pressure energy translating device, a cylinder barrel disposed for rotation about its longitudinal axis and having a plurality of cylinders; a valve plate in sliding engagement with one end of said cylinder barrel,said plate having'spaced inlet and outlet ports with which the cylinders alternately register upon rotation of said barrel; piston means disposed for reciprocation in said cylinders; an additional port pro- .vided in said valve plate between adjacent ends of said inlet and outlet ports; passage means connecting said additional port and said inlet and outlet ports} valve means responsive to pressure in either said inlet or outlet port to obstruct communication between the other port and said additional port; and check valve means in said passage means, said check valve means permitting fluid flow from said additional port to the other ports and preventing reverse flow. 4. In a fluid pressure energy translating device, a cylinder barrel'disposed for rotationabout its longitudinal axis and having a plurality of cylinders;,a valve plate in sliding engagement with one end of said cylinder barrel, said plate having spaced inlet and outlet ports with which the cylinders alternately register upon rotation of said barrel; piston means disposed for reciprocation in said cylinders; an additional port provided in said valve plate between adjacent ends of said inlet and outlet ports; passage means connecting said additional port and said inlet and outlet ports; valve means responsive to pressure in either said inlet or outlet port to obstruct communication between the other port and said additional port; and fluid pressur operated motor means responsive to pressure differentials between said inlet and outlet ports to move said valve plate relative to said cylinder barrel about the axis of rotation thereof. a a

5. In a fluid pressure energy translating device, a cylinder barrel mounted for rotation about an axis and having aplurality, of cylinders; a plurality of pistons disposed for reciprocation in the cylinder barrel; an inclined cam member disposed at one end of the cylinder barrel and operative to cause the reciprocation of said pistons; a valve plate disposed in sliding engagement with the opposite end of said cylinder barrel, said valve plate having spaced inlet and outlet ports alternately communicating with the cylinders in said barrel upon rotation thereof; additional ports in i inlet and outlet ports; passage means connecting said additional ports with one of the other ports; and motor means responsive to pressure differentials existing between said inlet and outlet ports to cause relative movement between said cam member and valve plate about the axis of rotation of said cylinder barrel.

6. In a fluid pressure energy translating device, a cylinder barrel mounted for rotation about an axis and having a plurality of cylinders; a plurality of pistons disposed for reciprocation in said cylinder barrel; a valve plate disposed in sliding engagement with said cylinder barrel, said barrel having ports leading to the cylinders therein, said plate having spaced inlet and outlet ports alternately communicating with the cylinder ports upon rotation of the cylinder barrel, the spacing j between said inlet and outlet ports being at least said auxiliary port and said outlet port; and valve 1 means in said passage governed by pressure in twice the length of a cylinder port; an additional port in said valve plate in the space between said inlet and outlet ports; a passage establishing communication between said additional port and one of the other ports in said valveplate, said additional port being so located that a cylinder r l 1 port will communicate therewith and with'the port connected thereto simultaneously; and check valve means in said passage for preventing fluid flow from the port connected with said additional port to such additional port.

7. An axial piston pump comprising a body having main inlet and pressure ports; a cylinder barrel rotatable relative to said body and having a plurality of cylinders; a plurality of pistonsd1sposed for movement in the cylinders in said barrel; means for moving said pistons into said cylinders as the latter approach said pressure port and out of said cylinders as they approcah said inlet port; a rotary valve operated in timed relation with said pistons, said valve including a port for each cylinder positioned in one end of the barrel and controlling communication between each cylinder and the main inlet and pressure ports; a set of valved passages in the body providing communication between each cylinder and the main port approached thereby durmg operation of said rotary valve, the valve in said set of passages being yieldably closed and preventing communication between the cylinders and ports approached until the pressure in the cylinders difiers from the pressure in the main port approached only in an amount suflicient to overcome the force tending to hold the valves in the passages closed.

8. A fluid pressure energy translating device comprising a body having main inlet and outlet ports; a cylinder barrel rotatable relative to said body and having a plurality of cylinders; a plurality of pistons disposed for movementun the cylinders in said barrel; a rotary valve operated in timed relation with said pistons, said valve 1ncluding a port for each cylinder positioned in one end of the barrel and controlling communication between each cylinder and the main inlet and outlet ports; a set of passages in the body providing communication between each cylinder and the main port approached thereby; and spring pressed valves in said passages, the valve in the passage connected with the high pressure port permitting fluid flow only toward said port and the valve in the passage connected with the low pressure port permitting fluid flow only from said ort. p 9. A fluid pressure energy translating device comprising a body having main inlet and outlet ports; a cylinder barrel rotatable relative to said body and having a plurality of cylinders; a plurality of pistons disposed for movement in the cylinders in said barrel; a rotary valve operated in timed relation with said pistons, sa d valve including a port for each cylinder positioned in one end of the barrel and controlling communication between each cylinder and the main nlet and outlet ports; passages in the body providing communication between each cylinder and the main port approached thereby prior to registration therewith, and valve means in said passages, said valve means being operative to permit fluid flow from the cylinders to the high pressure port approached thereby only when the pressure in the cylinder exceeds that in the port and from the low pressure port to the cylinders approaching the same only when the pressure in the cylinders is less than that in the low pressure port. 10. A fluid pressure energy translating device comprising a body having spaced inlet and outlet 7 ports; a cylinder barrel having cylinder ports 1'0- 12 tatable relative to said body, said barrel having a plurality of cylinders and a plurality oi cylinder ports to alternately provide communication between the cylinders and said inlet and outlet ports; a plurality of pistons disposed formovement in the cylinders in said barrel; cam means for imparting reciprocatory movement to said pistons, said cam means being so disposed relative to said inlet and outlet ports that movement of each piston inwardly in the respective cylinder therefor will commence immediately uponthe interruption of communication between such cylinder and said inlet port; an additional port in the body between said inlet port and said outlet port; a passage in said body connecting said outlet port and said additional port to establishcommunb cation between said cylinder ports and said outlet prior to registration with said outlet port, said additional port being spaced from said outlet port a distance substantially equal to the length of a cylinder port; and a check valve in said passage to prevent fluid flow from said outlet port to said cylinder ports.

11. A fluid pressure energy translating device comprising a body having spaced inlet and outlet ports; a barrel rotatable relative to said body, said barrel having a plurality of cylinders and a plurality of cylinder ports to alternately provide communication between the cylinders and said inlet and outlet ports; a plurality of pistons disposed for movement in the cylinders in said barrel; cam means for imparting reciprocatory movement to said pistons said cam means being so disposed relative to said inlet port andsaid outlet port that movement of eachrpiston inwardly in the respective cylinderitherefor will commence immediately upon the interruption of communication between such cylinder and said inlet port; an additional port in said body between said inlet port and said outlet port, said additional port being so spaced from said outlet ort that each cylinder .port will communicate continuously therewith during the movement of the respective piston into such cylinder prior to the registration of the cylinder port with said outletport; a passage connecting saidoutlet port and said additional port to establish communication between said cylinder ports and said outlet prior to the registration of the cylinder port with said outlet port; and a check valve in said passage to prevent fluid flow from said outlet port to said cylinder ports.

ELLIS H. BORN.

LEROY E. BONNETTE.

ReferencesCited in the flle of this patent UNITED STATES PATENTS Number Name Date 924,787 Janney June 15, 1909 1,081,810 'Carey Dec. 16, 1913 2,032,079 Benedek Feb. 25,1936 2,288,768 Zimmermann July 7, 1942 2,299,234 Snader Oct. 20, 1942 2,407,013 Ifield Sept, 3, 1946 2,418,123 Joy Apr. 1, 1947 FOREIGN PATENTS Number Country Date 285,468 Germany 1915 442,450 Great Britain Feb. 10, 1936 506,684 Great Britain 1939