US2962970A

US2962970A - Pump

Info

Publication number: US2962970A
Application number: US664095A
Authority: US
Inventors: Francis E Norlin
Original assignee: Borg Warner Corp
Current assignee: Borg Warner Corp
Priority date: 1957-06-06
Filing date: 1957-06-06
Publication date: 1960-12-06
Anticipated expiration: 1977-12-06

Description

F. E. NORLIN PUMP 4 Sheets-Sheet l Filed June 6, 1957 b. Nm @Mn www kw .om um ww wm n w wk v N mN\\ WW QM' w .w

F. E. NORLIN Dec. 6, 1960 PUMP 4 Sheets-Sheet 2 Filed Junel 6, 1957 Filed June 6, 1957 F. E. NORLIN PUMP 4 Sheets-Sheet 5 F. E. NORLIN PUMP 4 Sheets-Sheet 4 Filed June 6, 1957 m R 7&7 7///// /////A///////f-m//4 clS mw wh A V w /mb//Q Nm. Mb v\ /M/ l fr /u Nm. ww

United States Patent PUMP Francis E. Norlin, Chesterland, Ohio, assignor to Borg- Warner Corporation, Chicago, Ill., a corporation of Illinois Filed June 6, 1957, Ser. No. 664,095

12 Claims. (Cl. 10S-37) This invention relates to pumps in which a plurality of pump cylinders are arranged in circular series parallel to each other and to the axis of the drive shaft, each of the cylinders having disposed therein a piston or a plunger actuated by a cam or swash plate fixed on the shaft.

The pump forming the su-bject matter of this invention is provided with means to vary the displacement thereof, such means including means responsive to the discharge pressure of the uid from the cylinders, and the pump is formed provided with means allowing a selection of a particular maximum discharge pressure therefrom. Such means are desirable in pumps which are constantly running, as for example, those used in aircraft installations and where the Vdisplacement requirements vary from a maximum to a zero value. The structure forming the subject matter of the instant application includes a variance of the means for accomplishing the desired results described yand claimed in copending applications, Serial No. 573,543, iiled March 23, 1956, entitled Variable Displacement Hydraulic Pump, and Serial No. 598,718, filed Iuly 18, 1956, entitled Pump Therefore, the prim-ary object of this invention is the provision of an improved variable displacement pump of the type incorporating a plurality of circularly arranged cylinders having pistons therein actuated by means of a cam or swash plate.

More particularly, the subject pump includes pistons, each having -an open-ended cavity therein in which is disposed a valve means adapted to seat and close the open end of the piston cavity together with means for varying the position of closing the open end of the piston cavity by means of the valve during the piston discharge stroke to thereby effectively vary the effective discharge stroke of the piston and the displacement of the pump, the latter means including a pilot valve responsive to pump discharge pressure. The piston valve means of the subject pump includes a valve proper adapted to close the open end of the piston cavity and at least one axially extending portion received in the piston Vcavity and having a slot therein adjacent the end o-pposite from the valve proper. The means for varying the eltective discharge stroke of the pistons incorporates a member which may take the form of a substantially circular plate or a spider having a plurality of fingers, both of which are mounted for limited axial and oscillatory movement relative to the axis of the pump, which member cooperates with the aforementioned slots, so as to vary the relative seating position of the valve proper on the piston during its stroke. The circular plate or spider is moved axially by means of an associated piston responsive to a pressure related to the pump discharge pressure and the limits of its axial movement are such to provide full and zero displacement, respectively. When in its zero displacement position, the plate or spider is prevented from oscillating by its engagement with a stop means, but in its full or partial displacement positions, it is free to oscillate relative to the pump axis.

Still another object of this invention is the provision of an improved swash plate pump having a plurality of pisice tons reciprocated within cylinders so as to each have a suction stroke and a discharge stroke, valve means associated with each of the pistons, and a circular plate or spider mounted for limited axial and oscillatory movement relative to the pump axis cooperating with the piston valve structure to vary the seating and unseating of the piston valve and therefore the displacement of the pump.

Another and still further object of this invention is the provision of ian improved swash plate variable displacement pump including acircular plate or spider responsive to a iluid pressure related to the discharge pressure of the pump to vary the displacement thereof.

In one form of this invention, the piston valve comprises a valve proper, a connected axially extending portion and a second, separate, portion, the latter two portions being received in the piston cavity and being interconnected in such a manner as to provide a lost-motion connection therebetween, thereby relieving adverse forces tending to damage or destroy the valve. Inthis embodiment, the second portion is provided with the slot to receive a p0rtion of the plate or spider and it is resiliently urged toward the connected portion.

Therefore, another object of this invention is the provision of an improved swash plate open-ended piston pump having valve means associated with the pistons to close the open end thereof, each valve means comprising a valve proper, a connectedportion and a second portion interconnected with the connectedportion with a lost-motion connection, and meansto vary the position during a piston stroke where the valve means closes the open end of a piston.

These and other objects and features of this invention will be apparent from the following specification when taken with the accompanying drawings, wherein the same reference numbers are used to referto like parts and in which- Figure 1 is a partial, sectional view showing one embodiment of the pump of this invention wherein a circular plate is employed for varying the position of seating a valve on the open end of a piston;

Figure 2 is an enlarged, partial, sectional view showing the pump structure of Figure 1 in more detail;

Figure 3 is yan enlarged, partial, sectional view of the pilot valve structure of Figures l and 2;

Figure 4 is a partial, sectional view of another embodiment of this invention wherein the piston valve is provided with a lost-motion connection;

Figure 5 is a view taken on line 5 5 of Figure 4;

Figure 6 is a view taken on line 6-6 of Figure 4; and

Figure 7 is a partial, sectional View of another embodiment of this invention wherein a spider is used instead of the circular plate, as in Figures l to 6.

Referring now to the drawings, there is illustrated a pump, generally indicated at 10, having a housing comprising a body 11 and a cover 12. The cover has an inlet connection 13 and an outlet connection 14 which take the form of tapped ports into which suction and discharge pipes or hoses (not shown), vmay be affixed. The body and cover are maintained in their illustrated abutting position by means such as bolts (no-t shown).

A cylinder assembly is clamped between a shoulder 15 in the body and a shoulder 16 in the cover, and the cylinder assembly is composed of a cylinder barrel block 17 and a guide block 18. The blocks 17 and 18 annular in form and define with the cover an inlet chamber 19 which communicates with the inlet port 13 by way of a passage 20 formed in the cover 12. The cylinder barrel block 17 defines with the cover 12 a discharge chamber 21 which communicates with the outlet port 14 by way of a passage 22 formed in the cover.

The guide block 18 is restrained from any tendency to rotate by means of a retainer element 23 having an enlarged portion threadably received in an internally threaded boss-like portion of the body and extending within a cavity in the block (see Figure 1). The retainer member 23 is provided with a central bore 24 which is in alignment with a bore 25 in the block member. The function of the bores 24 and 25 will be later described. However, it is obvious that the internally screw threaded portion of the body boss may receive a suitably threaded hose or pipe.

The cylinder barrel block 17 is bored through to form a plurality of radially arranged cylinders 26, and the block 1'! is formed to define with the block 18 inlet passages 27 which communicate with the cylinders 26. The usual number of cylinders in a pump of this type is nine (9). The guide block 18 is bored through as at 28, the guide bores being of the same diameter and in alignment with the cylinders 26. Each cylinder 26 has a discharge valve 29 associated therewith which is seated by a coiled compression spring 30 against the outer face of the cylinder barrel block 17. The discharge valves are guided in pockets 31 formed in the cover, and the valves 29 are disposed within the discharge chamber 21, as illustrated.

A piston or plunger 32 is slidably received in each of the cylinders 26 and extends through the guide bore 28 and the block member 18, terminating in an enlarged shoulder portion 33 located in a cavity 34 within the body 11 and behind the block 18. Each piston 32 is provided with a cavity 35 open at the end thereof adjacent the associated discharge valve 29, and a cylindrically elongated inlet port 36 in communication with the inlet passage 27 when the piston is in its suction position.

A swash plate or cam 37 disposed within the cavity is provided for reciprocating the pistons or plungers between the full suction and full discharge positions. The cam is suitably journalled in a conventional manner needing no further description.

Each piston 32 is provided with a substantially hemisperical cavity in its enlarged portion to receive a complementary shaped bearing shoe 38 having a flat surface which bears against the cam. An annular retainer member 39 is fixedly positioned in the body and is also provided with hemispherical cavities to receive complementary shaped bearing shoes 40 having fiat surfaces engaging the opposite side of the cam from the bearing shoes. The pistons 32 are retracted by means of a piston return plate 41 having fork portions engageable with the enlarged portions of the pistons, and the return plate is provided with a hemispherical cavity disposed over a complementary shaped end portion 42 of a pilot valve retainer member 43 which is received in a central bore 44 in the guide block 18. The end portion 42 of the pilot valve retainer member 43 maintains the piston return plate 41 in its proper operating position.

A valve member, generally indicated at 45, having a frusto-conical portion 46 adapted to seat on a correspondingly shaped surface portion of the piston is provided in each of the embodiments for closing the open end of each piston during at least a portion of the pressure or discharge stroke of the piston. The valve members 45 of the embodiments illustrated in Figures l, 2 and 7 are provided with an axially extending cylindrical portion 47 having a diameter substantially equal to that of the cavity 35 and spaced slots 48 (not shown in Figures l and 7) adjacent the portion 46 for the passage of liuid therethrough when the valve 45 is unseated. The valve members 45 are slotted as at 49 adjacent their ends removed from the portions 46 and the slots 49 may be shaped as illustrated in Figure 6, for purposes to be described. The valve member 45 of the embodiment illustrated in Figures 4, and 6 is provided with an axially extending cylindrical portion 50 of the same diameter as the cavity 35, one end of which is cut to form a hook-like portion 51 to cooperate with a complementary shaped hook-like portion 52 on a cylindrical member 53 formed with the slot 49 therein -(see Figures 5 and 6 also). The portion 50 is provided with the spaced slots 48. The portion 51 and 52 provide a lost-motion connection therebetween, and the member 53 is resiliently urged toward the valve member 45, of which it forms a part, by means of a coiled compression spring 54 received in the cavity 35. By varying the position, relative to the cylinder 26, in which the valve 45 closes the open end of the piston 32, as by seating on the frusto-conical surface, the effective discharge stroke of the piston will be varied, and such variation will thereby vary the displacement of the pump.

In order to vary the position at which a valve 32 seats on the frusto-conical surface of each piston, means in the form of a substantially circular plate 55 (Figures l, 2 and 4) or a spider 56 having a plurality of rod-like fingers 57, one for each piston (Figure 7), is provided which has a portion or a finger, which ever the case may be, extending through the slot 49 in each valve. The circular plate 55 or the spider 56 is axially movable between certain limits corresponding to zero and full pump displacement and is mounted for limited oscillatory motion, the limits of such axial movement and oscillatory motion being determined by abutments formed on the block members 17 and 18, as illustrated. A plate or spider is provided with an enlarged hub portion 58 having an internal cylindrical curved surface 59 therethrough received on an external complementary-shaped surface 60 of a support member 61, the support member 61 being also supported for axial movement. The support member 61 is supported for such axial movement on a cylindrical extension 62 of an annular plate or spider piston 63 disposed within a cavity 64 in the guide block 18, and defining with the cavity 64 a chamber 65 which will be referred to as the plate or spider piston chamber. It should be noted here that the passage 25 previously described communicates with the plate or spider piston chamber 65, as illustrated.

The spider in the Figure 7 embodiment is resiliently urged towards the left by means of coiled compression springs 66 received in suitable cavities in the spider piston 63, while in the other embodiments, no resilient means urging the plates to the left are employed. A retainer member or retainer portion 67 is slidably received around the cylindrical extension 62 of the plate or spider piston, and a coiled compression spring 68, hereinafter referred to as a plate or spider return spring, is received between the retainer member or portion 67 and a closure member 69 (see Figures l and 2) received in the cover 12. It will be noted that the retainer member 67 in the Figure 7 embodiment is provided with a guide surface 70 for the hub 5S of the spider 56. The closure member 69 is provided with a reduced cylindrical extending portion 71 to support the reduced cylindrical portion 62 of the plate or spider piston 63 in telescopic arrangement.

The pilot valve retainer 43 received in the bore 44 also includes a portion received Within the plate or spider piston 63. The retainer member 43 (see especially Figure 3) is provided with open ended concentric communicating

bores

72 and 73, one being of smaller diameter than the other as illustrated, and is drilled as at 74 to form a communication between the outer periphery thereof and the bore 73. The retainer member 43 is also provided with a reduced groove portion 75 defining with the plate or spider piston 63 and the bore 44, a chamber 76 for a later to be described purpose.

The chamber 76 is in communication with the plate or spider piston chamber 65, as illustrated. The retainer member 43 is also provided with bores or openings 77 and 78 providing communication between the cavity 72 and the chamber 76.

A pilot valve 79 is slidably received within the cavity 72 and is provided with an open ended cavity 80, a first reduced portion 81, a groove 82, a second reduced portion 83 and a third reduced portion 84, the latter reduced portions defining a shoulder 85. A pilot valve sleeve 86 is disposed within the cavity surrounding the third reduced portion 84 of the pilot valve and is afxedly retained` in position by means of a fastening element 87. The sliding movement of the pilot valve is limited by the shoulder 85 engaging the pilot valve sleeve 86 in one direction and the end of the pilot valve engaging the shoulder formed by the intersection of the

bores

72 and 73 in the other direction. The pilot valve is bored, as at 88 to provide communication between the groove 82, and the bore 80, and the second reduced portion 83 together with a part of the third reduced portion 84 and the pilot valve sleeve 86, dene with the bore 72 a pilot ring pressure chamber 89.

A pin member 90 is disposed within the cavity 80 at one end and within a cavity in a cup-like spring retainer member 91 at its other end. The spring retainer member 91 is elongated and has annular portions slidably engageable with the interior of the cylindrical member 62 extending from the plate or spider piston 63. A coiled compression spring 92, hereinafter referred to as a pilot valve spring, is disposed within the cup-like spring retainer member 91 at one end, and at its other end is supported by means of a portion extending from a block of an adjusting screw 93 threadably received in the closure member 69, as illustrated. The adjusting screw 93 extends to a position outside the cover 12 and is provided with a slot to receive a screw driver to adjust the position of the screw member and thereby the loading of the spring 92. The spring resiliently urges the pilot valve 79 to the right through the pin member 9i). An acorn nut is threadably received over the adjusting screw to prevent damage thereto. Openings 94 and 95 are provided in the portion 62 and in the retainer 91 for the passage of uid therethrough as will be explained later.

The guide block 18 is providedk with an annular chamber 96 in communication with the openings 74, and is also provided with an annularly disposed passage 97 communicating at one end with the chamber 96 and at the other end with a passage 98 formed in the cylinder barrel block 17, the latter passage communicating with the discharge chamber 21 for the passage of discharge lluid to the chamber 96. An air lock release valve, generally indicated at 99 is provided and is identical to that described and claimed in the aforementioned copending application Serial No. 573,543. Since the air lock valve forms no part of this invention, further description is unnecessary.

As in pumps of the type, suitable O-ring sealing means may be provided where necessary or desirable.

The following description sets forth the operation of the pump and this operation will be described with reference to one of the plurality of pistons, it being understood that the operation of all pistons is the same.

Assuming the drive shaft is rotating, it will be apparent that the cam or swash plate 42 will be rotating and the pistons 32 will be reciprocated within the cylinders 2S between their suction positions and their discharge positions. Fluid from a suitable source will flow to the inlet 13, into the passage 20 and into the chamber 19 filling the entire chamber. From the chamber 19 the fluid will ow through the passage 27, and when the piston is in its suction position, through the openings 36 into the cavity 35 of the piston. The uid within the piston cavity exerts a force on the piston valve 45 causing it to unseat and move away from the end of the piston 32 so that fluid will flow around the valve 45 and into the cylinder 28 in advance of the piston, the liuid being retained therein by means of the seated discharge valve 29. The movement of the valve 45 away from the piston 32 will cause the plate 55 or the spider 56, as the case may be, to oscillate as indicated by the drawings, since the plate or spider is freely mounted for this movement. As is obvious, on the discharge stroke of the piston the fluid within the chamber will be compressed causing the valve 45 to close.

As the piston 32 moves to the left in its discharge stroke, compressing the uid trapped within the cylinder 28, the discharge valve 29 will be unseated from the end of the block 17, so that the fluid under pressure will flow into the discharge chamber 2,1, through the discharge passage 22 and out the outlet 14. This high pressure uid will exert a force on the valve 45 causing it to seat on the piston 32 and, also, causing the spider or plate to oscillate. The lost-motion connection in the Figure 4 embodiment relieves the plate 55 from the shock of the iiuid acting on the valve 45, thereby insuring a quieter operation and longer life to the pump 10. At the same time liuid pressure is being discharged out the outlet 1-4, high pressure fluid from the discharge chamber 21 will ow through the passage 98, through the passage 97 and into the chamber 96. The uid in the chamber 96 will flow through the openings 74 and into the bore 73 where it contacts and acts upon one end of the spooltype pilot valve 79.

When the pressure in the bore 73 becomes sufficiently high, or, in other words, the discharge pressure becomes sufliciently high, so that the force on the end of the pilot valve 79 overbalances the spring 92, the pilot valve 79 moves to the left, as illustrated in the drawings, and compresses the pilot valve spring 92. The pilot valve spring 92 may be adjusted by means of the screw-threaded, slotted member 93 to a load which will allow the pilot valve 79 to reach a position providing a bleed between the reduced portion 81 and the opening 78 at a predetermined outlet pressure. At this point a slight increase in outlet pressure will allow the ow of fluid in the reduced portion S1 to bleed into the plate or spider piston chamber 65 through the opening 78. When the pilot valve 79 is positioned to provide the bleed of uid to the chamber 65, the groove 82 is blocked by the interior of the bore 72. Pressure will build up in the plate or spider piston chamber 65 sufficient to overcome the plate or spider return spring 63, and the iiuid thus acting on the piston 63 will start moving the plate 55 or spider 56 to the left, as illustrated in the drawings.

After the plate 55 or spider 56 has moved a short distance a portion thereof contacts the slot 49 in the piston valve 45 and forces the valve 45 to open for part of the pressure stroke. This allows Huid in the piston cavity 35 to bypass back to inlet, and also prevents pressure in the piston cavity from building up until the piston 32 has reached a point in its travel toward its discharge position where it picks up the valve 45 and pulls the valve 45 away from the plate 55 or spider 56.

A slight decrease in outlet or discharge pressure Will allow the pilot valve 79 to move toward its position illustrated in Figure 3 and thereby shut off the outlet flow to the chamber 65, and will allow uid trapped in the chamber 65 to bleed out through the passage 78, into the groove 82, through the passage 88, through the bore and to the chamber 19 through the aforementioned openings in the cup-like retainer member 91 and openings 94 in the cylindrical portion 62. The plate or spider return spring 63 will then start returning the plate or spider to its illustrated position, which will allow the piston valve 45 to close off sooner, thereby increasing the effective piston stroke, which in turn increases the displacement of the pump.

A steady, partial flow demand will cause the pilot valve 79 to assume a position in which pilot valve leakage or bleed into the spider or plate piston chamber 65 will equal pilot valve leakage out of the piston chamber 65 back to the inlet cavity 19 through the groove 82, passage 88 and bore 80, thus holding the plate or spider in a constant partial ow position. Since the pilot valve 79 travels only a few thousandths of an inch in the bore 72 to bleed ow into and out of the plate or spider chamber 65, the pilot valve spring load increase due to this travel is very slight. Also, since the pilot valve 79 assumes, the same position for any partial flow demand, the load on the spring 92 is the same, and

therefore, the outlet pressure Will be the same. Thus, there would be no pressure differential between maximum pressure at full flow and at zero flow. But, there must be a pressure change in order to control the location of the plate or spider, and this pressure change, also called the pressure differential, has been built into the pilot valve. Thus, a cutoff slope or angle is provided on a pressure versus flow curve, which corresponds to the pressure differential.

To provide the pressure differential is the function of the pilot ring pressure chamber 89. As will be obvious, when lluid flows to the chamber 65, there will also be a ow to the chamber 89 through the opening 77. When the chamber 89 is under pressure, it balances out part of the outlet pressure which contacts the end of the pilot valve 79. The pressure in the chamber increases as the plate or spider axially moves towards zero displacement position (the axial limit of the plate or spider movement to the left, as illustrated) due to the increasing plate return spring load. As the pressure increases in the pilot ring pressure chamber 89, the outlet pressure of the pump must increase to overcome this pressure and this creates the pressure differential between full and zero ow.

Thus, the pilot ring pressure chamber 89 hydraulically applies the spring rate of the plate or spider return spring 92 to the pilot valve 79. During partial displacements of the pump, the plate or spider return spring load varies with the axial position of the plate or spider. As the plate or spider return spring load varies, the pressure in the plate or spider piston chamber 65 and in the pilot ring chamber S9 varies. Since the pilot ring chamber 89 applies this pressure to the pilot valve 79 against outlet or discharge pressure the outlet pressure must vary to maintain the pilot valve 79 in balance. Therefore, a definite link has been established between the axial location of the plate or spider and outlet pressure, and since the axial location of the plate or spider establishes the correct displacement, it can be said that outlet pressure establishes the correct displacement.

Without this pilot ring chamber 89 the valve 79 would crack at a set pressure and close off at a set pressure regardless of the axial location of the plate or spider. This is so because the plate or spider can move axially from the full displacement position (as illustrated) to the zero displacement position (the limit of their movement to the left) without increasing the load of the pilot valve spring 92. Therefore, there would be no change in outlet pressure whether ythe pump be in, for example, 75% displacement, 50% displacement or zero displacement. If there were no change in outlet pressure there would be no means of stopping the plate or spider at any desired axial location, and as a result, the plate or spider would hunt back and forth, resulting in undesirable chatter.

It is also possible in the instant pump to provide for zero ow by connecting a low pressure source of uid to the passages 24 and 25, so that the low pressure fluid will act upon the piston 63 and axially move the plate or Spider to its zero llow position, which corresponds to the left-host position of the plate or spider, as when the plate or spider is urged against the left hand stop portion of the housing and wherein there will be no oscillatory movement thereof.

While this invention has been described in connection with certain specific embodiments thereof, it is to be understood that this is by way of illustration and not by way of limitation and the scope of this invention is defined solely by the appended claims which should be construed as broadly as the prior art will permit.

I claim:

l. In a pump of the type in which a plurality of cylinders are arranged in circular series with their cylinder axes paral el, the combination of a housing provided with an inlet and an outlet; means defining a circular series of cylinder bores within said housing in communication with said inlet and said outlet; a plurality of pistons, each received in a cylinder bore for reciprocation therein so as to have a suction stroke and a discharge stroke; a rotary drive shaft; a cam carried by said drive shaft for reciprocating said pistons; an open-ended cavity in each of said pistons; valve means carried by each piston and effective to close the open end of said cavity for at least a portion of the discharge stroke; and means operatively interconnected with said valve means to vary the position at which said valve means becomes effective to thereby vary the displacement of said pump, said means including pilot valve means in communication with said outlet and movable in response to pump discharge pressure above a predetermined value, said pilot valve means providing a pressure related to said pump discharge pressure, and means mounted for limited axial and oscillatory movement relative to the axis of the pump and engaging said valve means, said last-named means being moved axially in response to said pressure related to pump discharge pressure to thereby vary the displacement of said pump in accordance with the related pressure.

2. A pump of the type recited in claim l, wherein said means mounted for limited axial and oscillatory movement relative to the axis of the pump comprises a substantially circular plate.

3. A pump of the type recited in claim l, wherein said means mounted for limited axial and oscillatory movement relative to the axis of the pump comprises a plurality of finger-like elements each individual to a valve means.

4. A pump of the type recited in claim l, wherein said valve means comprises a valve proper adapted to close the open end of said cavity and a connected axially extending portion slidably received in said cavity, said last-named portion having a slot therein to receive a portion of said means mounted for limited axial and oscillatory movement relative to the axis of the pump.

5. A pump of the type recited in claim l, wherein said valve means comprises a valve proper adapted to close the open end of said cavity, a rst integral axially extending portion and a second axially extending portion, said first and second portions being so constructed and arranged to interlock and provide a lost motion connection therebetween, said second portion having a slot therein to receive a portion of said means mounted for limited axial and oscillatory movement relative to the axis of the pump.

6. A pump as recited in claim 5, wherein there is provided resilient means received in said cavity and engaging said second portion to urge said second portion into close proximity to said first portion.

7. In a pump of the type having a plurality of circularly arranged parallel pistons reciprocated within cylindrical bores by means of a cam or swash plate so as to each have a suction and a discharge stroke; the improvement comprising, an open-ended cavity in each piston, means to vary the effective discharge stroke of each piston, said means comprising a valve having a valve proper and an axially extending portion received in each piston, said valve proper being adapted to seat on the open end thereof to close said open end, a fluid motor, means adapted to engage said axially extending portion and adapted to seat and unseat each valve during its strokes, said last-named means including a member mounted for limited axial and oscillatory movement relative to the axis of the pump and adapted to engage said axially extending portions of said valves, said last-named means being interconnected with said motor and axially moved thereby, and means connecting said uid motor to a source of Huid pressure so as to be responsive thereto whereby said member is axially moved in response to said iiuid pressure to thereby be effective to vary the positions at which said valves seat to vary the displacement of said pump in accordance with the value of said uid pressure.

8. A pump of the type recited in claim 7, wherein said means mounted for limited axial and oscillatory movement relative to the axis of the pump comprises a substantially circular plate.

9. A pump of the type recited in claim 7, wherein said means mounted for limited axial and oscillatory movement relative to the axis of the pump comprises a plurality of finger-like elements each individual to a valve means.

10. A pump of the type recited in claim 7, wherein said valve means comprises a valve proper adapted to close the open end of said cavity and a connected axially extending portion slidably received in said cavity, said last-named portion having a slot therein to receive a portion of said means mounted for limited axial and oscillatory movement relative to the axis of the pump.

11. A pump of the type recited in claim 7, wherein said valve means comprises a valve proper adapted to close the open end of said cavity, a rst integral axially extending portion and a second axially extending portion, said rst and second portions being so constructed and arranged to interlock and provide a lost-motion connec tion therebetween, said second portion having a slot therein to receive a portion of said means mounted for limited axial and oscillatory movement relative to the axis of the pump.

12. A pump of the type recited in claim 11, wherein there is provided resilient means received in said cavity and engaging said second portion to urge said second portion into close proximity to said first portion.

References Cited in the file of this patent UNITED STATES PATENTS 2,385,784 Baker Oct. 2, 1945 2,664,047 Huber Dec. 29, 1953 2,778,314 Sivers Jan. 22, 1957 2,848,954 Budzich Aug. 26, 1958 FOREIGN PATENTS 1,125,458 France July 16, 1956