US2943574A - Pump - Google Patents

Description

F. E. NORLIN July 5, 1960 PUMP Filed May 28, 1957 United States Patent C).fi

PUMP

Francis E. Norlin, Chesterland, Ohio, assignor to Borg- `Warner Corporation, Chicago, Ill., a corporation of Filed May 28, 1957, Ser. No. 662,030

2 Claims. (Cl. 103-37) 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 xed on the shaft.

The pump forming the subject matter of this invention is provided with means to vary the displacement thereof, such means including means responsive to the discharge pressureV of the fluid 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 displacement 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 and claimed in oopending applications, Serial No. 573,543, iiled March 23, 1956, entitled Variable Displacement Hydraulic Pump and Serial No. 598,718, tiled July 18, 1956, entitled Pump Therefore, the primary 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 mean 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 eiectively vary the eiective 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, a retainer sleeve having a slot therein adjacent one end, and an axially extending stem. Resilient means are disposed to cooperate with the stem and the retainer sleeve to urge the valve proper to its seated position. The means for varying the effective discharge stroke of the pistons incorporates a substantially circular plate mounted for limited axial movement which engages the slots in the retainer sleeve, so as to vary the loading on the resilient means, and by its axial movement, changes the relative position of the Valve proper and its seat on the piston. The circular plate is moved by means of an associated piston movable in response to a pressure related to the pump discharge pressure, the limits of movement being such to provide full and zero displacement of the pump.

Still another object of this invention is the provision of ran improved swash plate pump having a plurality of pistons reciprocated within cylinders so as to eachV have asuction stroke and a discharge stroke, valve means able circular plate'cooperating with the piston structure #2,943,574 Patented July 5, 1960 ICC to vary the seating and unseating of the valve and therefore the displacement of the pump.

Another and still further object of this invention is the provision of an improved swash plate variable displacement pump including a circular plate movable axially in response to a fluid pressure related to the discharge pressure of the pump to vary the displacement thereof.

These and other objects and features of this invention will be apparent from the following specification when taken with the accompanying drawings, in which the single igure of the drawing is a partial sectional view of a pump constructed in accordance with the invention.

Referring now to the drawing, 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), may be atlixed. The body 11 and cover 12 are connected by means such as bolts or the like (not shown).

A cylinder assembly is clamped between a shoulder 15 in `the cover 12' and a shoulder 16 in the body 11, and the cylinder assembly is composed of a cylinder barrel block -17 and a guide block 18. The blocks 17 and 18 are annular in form and define with the cover 12 an inlet chamber 19 which communicates with the inlet port P13 by way of a passage 20 formed in the cover 12. The cylinder barrel block 17 deiines 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 12.

The cylinder barrel block 17 is bored through to form a plurality of radially arranged cylinders 23, and the block 17 is formed to define with the block 18 inlet passages 24 communicating with the cylinders 23. The usual number of cylinders in a pump of this` type is nine (9). The guide block \18 is bored through as at 25, the guide block bores being of the same diameter and in alignment with the cylinders. Each cylinder 23 has a discharge valve 26 associated therewith seated by means cf a coiled compression spring Z7 against the outer face of the cylinder barrel block 17. The discharge valves are guided in pockets 28 formed in the cover 12, and they are disposed within the discharge chamber 21, as illustrated.

A piston or plunger 29 is slidably received in each of the cylinders 23 and extends through the coextensive guide block bore 25 and the block member 18 terminating in an enlarged portion located in a cavity 30` within the body 11 and behind the block 18. Each piston 29 is provided with -a cavity 31 open at the end thereof adjacent the lassociated disch-arge valve 26, an axially elongated inlet port 32 in communication with the inlet passage 24 when the piston is in its full displacement position as illustrated in the drawing.

A conventional swash plate lor cam (not shown) disposed within the cavity 30y is provided for reciprocating the pistons or lplunger-s 29 between their suction and discharge positions.

Each piston is provided with a substantially hemispherical `cavity 33 in its enlarged portion to receive a complementary-shaped bearing shoe 34 having a iiat surface (not shown) which bears against the cam or swash plate. 'The pistons are retracted in a conventional manner by means of a piston return plate (not shown) having fork portions engageable with the enlarged portions of the pistons 29, and the return plate is received over an end portion 35 of a pilot valve retainer member 36, the latter being received in a central bore 37 in the guide block 18. The end portion 35 of the pilot valve retainer member 36 maintains the piston return plate in its proper operating positions.

Avalve 38 having a partial frusto-conical valve proper 39 adapted to seat on a correspondingly shaped surface portion of the piston 29 is provided for closing the open end of each piston during ,at least a portion of the pressure or discharge stroke of the piston. The valve 38 is provided with an axially extending stem 40 having an enlarged end 41 taking the form of an annular collar. The stem 40 is slidably supported within the piston by means of a retainer `sleeve 42 having axially extending spaced portions 43 terminating in a cylindrical portion 44 having `a slot 45 therein. A coiled compression spring 46 vsurrounds the stem and is disposed between the collar 41 and the retainer sleeve 42 to resiliently urge the valve proper 39 to its seated position. By varying the position, relative to the cylinder, at which the valve proper closes the open end of the piston 29, 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 the valve proper 39 seats on each .piston 29, a substantially circular plate 47 is provided having a peripheral portion extending through the elongated slot 32 in each piston 29 to a position wherein it engages the slot 45 in the retainer sleeve 42. The circular plate 47 is axially movable between certain limits corresponding to zero and full pump displacement, the limits being defined by stop means48 and 49, taking the form of annular projections on the blocks 17 and 18, respectively. The plate 47 is axially moved between the stop means 48 and 49 by a fluid motor, indicated vgenerally by the reference `letter M, which is hereinafter described. The plate `47 is supported on a cylindrical extension V50 of an-annular plate piston 51 of the motor M disposed within a cavity 52 in the'guide block `18, and defining with the cavity 52 a chamber 53 referred to as the plate-piston chamber.

The circular plate is resiliently urged towards the .left against a cylindrical, 'anged spring retainer 54 abutting a shoulder in-the extension t) by means of coiled compression springs 55 received in suitable bores vin the plate piston 51. A coiled compression spring 56, hereinafter referred to as a plate return spring, is received between the retainer 54 and a closure and retainer member 57 received in the cover 12. The member 57 is provided with a reduced cylindrical -extending portion to support the extension 50 of the plate piston 51 in telescopic, sliding arrangement. Y

The pilot valve retainer 36 received in the bore 37 also, as illustrated, extends within the plate piston and isprovided with open-ended concentric communicating bores 58 and 59, one being of smaller diameter than the other. The retainer 36 is `drilled as at 60 to form a communication .between the outer pe-ripheries thereof and the bore 59, and is also provided with an elongated groove 61 delining with the plate piston and the bore 37, a chamber 62 for a later to be `described purpose. The chamber 62, due to the position of the retainer 36 is in communication with the plate piston chamber 53, and the retainer 36 is provided with bores or openings 63 and 64 providing communication between the bore 58 and the chamber 62.

A pilot valve 65 is slidably received within the cavity 5S and is provided with an open-ended bore 66, a first reduced portion 67, a-groove 68, a second reduced portion 69 `and a third reduced portion 70, the latter two reduced portions'deiining a shoulder at their juncture. A pilot valve sleeve 71 is disposed within the bore 58 surrounding the third reduced portion 70 of the pilot valve 65 and is affixedly retained in position byv means Of a fastening element '72. The slidingvmovement of the pilot valve V65 is limited by the shoulder formed by the junc- -ture of the reduced portions 69 and 70 -engaging the pilot valve sleeve 71 in one direction Vand the end of the pilot valve engaging the shoulder formed by the intersection of the bores 58-and 59 -in the other direction. The pilot valve 65 is bored, as at 73 to provide communication between the groove 68 and the bore 66, and the second reduced portion 69 together with a part of the third reduced portion 70` and the pilot valve sleeve 71, define with the bore 58 a pilot ring pressure chamber 74.

A pin is disposed within the bore 66 at one end and within a cavity 76 in a cup-like spring retainer 77 at its other end. The sprin'g'retainer 77 is elongated and has annular portions slidably engageable with the interior of the cylindrical extension 50 of the plate piston 51. A coiled compression spring 78, hereinafter referred to as a pilot Valve spring, is disposed within the spring retainer 77 at one end and at its other end is supported `by a portion extending from an adjusting screw 79 threadably received in the member 57. The adjusting screw extends to a position outside the cover, 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 78 which resiliently urges the pilot valve 65 to the right through Athe pin 75. An acorn nut 80 is threadably received over the adjusting screw to prevent damage thereto. Openings v81, 82 are provided in the extension 50 and in the retainer 77 for the passage of fluid therethrough, as will be .explained later.

The guide block 18 is provided with an annular chamber 83 in communication with the openings 60, and is also provided with an annularly disposed passage `84 communicating at one end With the chamber 83 and at the other end with a passage 85 formed in the cylinder barrel block 17, the latter passage communicating with the discharge chamber 21 fo'r the passage of discharge fluid to the chamber 83. An air lock release valve, generally indicated at 86 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 this 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 ofall pistons is the same.

Assuming the cam or swash plate to be rotating, the pistons 29 will be axially reciprocated within the cylinders 23 between their suctio'n and 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 Huid will ow through the passage 24 and into the cavity 31 in the piston. During a suction stroke, uid Within the piston cavity 31 will exert a force on the valve proper 39 causing it to unseat when the spring 46 becomes overbalanced and moves away from the end of the piston, so that uid will flow around the valve proper and into the cylinder 23-in advance of the piston. On the discharge stroke of the piston the iluid within the cylinder 23 will be compressed causing the valve proper to seat and close the piston.

As the piston 29 moves to the left in its discharge stroke, compressing the fluid trapped within the cylinder 23, the discharge valve 26 will be unseated from the end o'f the block 17, so that the fluid under pressure will ow into the discharge chamber 21, through the discharge passage 22 and out the outlet 14. At the same time, high pressure fluid from the discharge chamber 21 will flow through the passage 85, through the passage 84 and into the chamber 83. The uid in the chamber 83 will ow through the openings 60 and into the bore 59 where it may act on one end of the spool-type pilot valve 65.

When the pressure in the bore 59 becomes suciently high, or, ,in other words, the discharge pressure becomes sufficiently high, so that the force on the end of the pilot valve 65 overbalances the spring 78, the pilot valve 65 will move to the left, as illustrated in the drawing, and willcompress the pilot Vvalve spring 78. The pilot .valvl spring 78 may be adjusted by means of the screwthreaded, slotted member 79 to a load which will allow the pilot valve 65 to reach a position providing a bleed between the reduced portion 67 and the opening 64 at a predetermined outlet or discharge pressure. When this bleed occurs, a slight increase in outlet pressure will allow the iiowof iiuid in the reduced portion 67 to' bleed into the plate piston chamber 53 throughthe openings 64. It will be noted that when the iiow to the chamber 53 occurs the groove 68 is blocked by the interior of the bore 58. Pressure will build up inthe plate piston chamber 53 suflicient to overcdne'the plate return spring 56, and the fluid thus acting on theplate piston 53 will start moving the plate piston 51 and the plate 47 to the left, as illustrated in the drawing, andto a lower displacement position.

After the plate 47 has moved a short distance the portion thereof in contact with the piston valve sleeve retainer 43 moves the retainer to the left, contacting valve 39 and holds valve proper 39 open for part of the pressure stroke. This action allows iiuid in the cylinder 23 to bypass back to inlet and also prevents pressure in the cylinder 23 from building up until the piston 38 has reached a point in its travel toward its discharge position where it picks up the valve proper and pulls the valve proper with it during its further travel.

When the plate 47 has moved to its limit to the left, the displacement of the pump will be at or very near to a zero value. The sleeve retainer 43 will also reach its limit to the left, so that the left terminal end of the sleeve 43 will abut the valve proper 39 outside the piston 29, thereby holding the valve proper 39 unseated during substantially the entire discharge stroke of the piston. The valve proper 39 will seat near the end o'f the discharge stroke, so as to maintain the pressure at a substantially constant value. Under this condition of operation, the spring 46 will be at or near to its free length, i.e., will not be compressed, and therefore, Will not exert a force tending to seat the valve proper 39.

A slight decrease in outlet or discharge pressure will allow the pilot valve 65 to move toward its position illustrated and thereby shut off the outlet ilow to the chamber 53, and will allow fluid trapped in the chamber 53 to bleed out through the passage 64, into the groove 68, through the passage 73, through the bore 66, and to the chamber 19 through the aforementioned openings 82 in the retainer member 77 and openings 81 in the cylindrical portion 50. The plate return spring S6 will then start returning the plate 47 to its illustrated position, which Will allow the piston valve 38 to close oif sooner by moving the sleeve retainer 43 to the right, thereby increasing the eective piston stroke, which in turn increases the displacement of the pump.

A steady, partial flow demand will cause the pilot valve `65 to assume a position in which pilot valve leakage or bleed into the plate piston chamber 53 will equal pilot valve leakage out of the piston chamber back to the inlet cavity 19 through the groove 68, passage 73 and bore 66, thus holding the plate 47 in a constant partial ow position. Since the pilot valve 65 travels only a few thousandths of an inch in the bore to bleed ilow into and out of the plate chamber 53, the pilot valve spring load increase due to this travel is very slight. Also, since the pilot valve 65 assumes the same position for any partial ilow demand, the load on the spring 78 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 47, and this pressure change, also called the pressure differential, has been built into the pilot valve.` Thus, a cut-off slope or angle is provided on a pressure versus ow curve, which corresponds to the pressure diierential.

To provide the pressure diierential is the function of the pilot ring `pressure chamber 74. As will be obvious, when fluid flows to the chamber 53, there will also be la flow tothe chamber 74, through the opening 63 and into the chamber 62. When the chamber 74 is under pressure, it balances out part of the outlet pressure which contacts the end of the pilot valve 65. The pressure in the chamber 74 increases as the plate 47 moves towards zero displacement position (the limit of the plate movement to the left, as illustrated) due to the increasing plate return spring load. As the pressure increases in the pilot ring pressure chamber 74, 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 74 hydraulically applies the spring rate of the plate return spring 56 to the pilot valve 65. During partial displacements of the pump, the plate return spring load varies with the position of the plate 47. As the plate return spring load varies the pressure in the plate piston chamber 53 and in the pilot ring chamber 74 varies. Since the pilot ring chamber 74 applies this pressure to the pilot valve 65 against outlet or discharge pressure, the outlet pressure must 'vary to maintain the pilot valve 65 in balance. Therefore, a definite link has been established between the location of the plate 47 and outlet pressure, and since the location of the plate 47 establishes the correct displacement, it can be said that outlet pressure establishes the correct displacement.

Without this pilot ring chamber 74, the valve 65 would crack at a set pressure and close ot at a set pressure regardless of the location of the plate 47. This is true because the plate 47 can move from the full displacement position (as illustrated) to the zero displacement position (the limit of its movement to the left) without increasing the load of the pilot valve spring 78. Therefore, there would be no change in outlet pressure whether the 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 47 at any desired location, and as a result, the plate would hunt back and forth, Iresulting in undesirable chatter.

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:

1. In a pump of the type having a plurality of circularly arranged parallel pistons reciprocated within cylindrical bores by means of a 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, a stem for said valve, an axially movable sleeve disposed in each piston and surrounding said valve stem, stop means on said stem axially `disposed and spaced `from said valve, resilient means disposed between said sleeve and said stop means, a fluid motor having an axially movable piston, means adapted to vary the loading of said resilient means to thereby seat and unseat each valve during its stroke, said last-named means including a substantially circular plate operatively associated with said motor piston and engaging said sleeve, and means connecting said fluid motor to `a source of uid pressure so as to be responsive thereto, said elective stroke varying means being effective to vary the displacement of said pump.

2. In a pump of the type having 4a plurality of circularly arranged parallel pistons reciprocated within cylindrical bores `by means of a 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 veach pjistomgsaid means comprising a valve, a stem for .said ylvalve, an axially movable sleeve disposedineach ;pi ston and -surrounding said valve stem, stop means on said stem axially disposed and spaced from said valve, ,resilient means'disposed between-said sleeve and said ,St0p1means, a slot in said sleeve, a uid motor 4including fan axially movable piston, means including 'an axially movable -circular plate engaging said slot -adaptedfto vary ,the loading of said resilient means yto thereby seat and unseat each valve during its stroke, said last-named means being operatively associated with said'motor piston, valve means connected to pump discharge pressure and being so constructed and arranged to provide a pressure related it'o pump discharge pressure, means connecting said Amotor 8 piston to :said related pressureso ias tomove said piston and therefore said plate when the related ,pressure is above `a predetermined `-value, said effective stroke varying means -being veffective to vary the displacement ,of said pump.

References ACited in the le of this patent :UNITED STATES 'PATENTS n, s s@

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