US3727521A

US3727521A - Rotary pump with displacement control

Info

Publication number: US3727521A
Application number: US00133278A
Authority: US
Inventors: R Reynolds
Original assignee: Sundstrand Corp
Current assignee: Sundstrand Corp
Priority date: 1971-04-12
Filing date: 1971-04-12
Publication date: 1973-04-17
Anticipated expiration: 1990-04-17
Also published as: DE2217891A1; FR2132869B1; JPS5520072B1; FR2132869A1; GB1363990A

Abstract

An axial piston pump including a rotary cylinder block with reciprocable pistons controlled by an adjustable swashplate for varying displacement as the cylinder block rotates against a valve plate, together with a control port in the valve plate for supplying fluid under pressure to the pumping pistons for controlling the position of the swashplate and therefore the displacement through the medium of the pumping pistons rather than separate control means.

Description

United States Patent 91 Reynolds [45] Apr. 17, 1973 I I RQTARY PUMP WITH FOREIGN PATENTS OR APPLICATIONS DISPLACEMENT CONTROL 463,045 4/1951 Italy ..91/505 [75] Inventor: Richard W. Reynolds, Rockford, Ill. [73] Assignee: Sundstrand Corporation Rockford Primary Examiner-William Fresh m Assistant ExaminerRichard E. Gluck Att0rneyHofgren, Wegner, Allen, Stellman & Mc-

22 Filed: Apr. 12, 1971 Cord Appl, No.: 133,278

[52] US. Cl. ..91/475, 91/505, 417/222 [51] Int. Cl ..F0lb 1/00, FOlb 3/00, F04b H26 [58] Field of Search ..91/505, 506, 487, 91/475, 6.5, 599; 417/222 [56] References Cited UNITED STATES PATENTS 3,190,232 6/1965 Budzich ..417/222 3,199,461 8/1965 Wolf 91/506 X 3,230,894 H1966 Badenoch et al. ..9l/6.5 X

[57] ABSTRACT An axial piston pump including a rotary cylinder block with reciprocable pistons controlled by an adjustable swashplate for varying displacement as the cylinder block rotates against a valve plate, together with a control port in the valve plate for supplying fluid under pressure to the pumping pistons for controlling the position of the swashplate and therefore the displacement through the medium of the pumping pistons rather than separate control means.

13 Claims, 2 Drawing Figures PATENTEB APR 1 7 I975 INVENTOR- RICHARD W. REYNOLDS {964%, M a fl/M'w- M mba awkw- ATTORNEYS.

ROTARY PUMP WITH DISPLACEMENT CONTROL BACKGROUND OF THE INVENTION Rotary hydraulic fluid translating devices such as pumps and motors are commonplace in the art and comprise both axial piston devices and radial devices involving pistons or vanes. In general, an axial piston device, for example, may include a housing comprised of two or more housing portions suitably joined, a cylinder block rotatable in the housing with axially disposed pistons reciprocable in fluid chambers under control of a cam or swashplate as the cylinder block rotates against a valve plate having inlet and outlet ports communicable serially with the fluid chambers. It is also common practice to provide for variable displacement of such hydraulic units by pivotally mounting the swashplate for adjustment about an axis generally transverse to the cylinder block axis in a manner to vary the stroke of the pistons. Frequently, automatic controls are desirable in variable displacement hydraulic units. Controls may include a constant biasing means acting on the displacement varying member in a manner to urge it into stroke or out of stroke, and a variable bias control may be applicable in opposition to the constant bias in order to overbalance or underbalance the latter selectively in a manner to vary displacement according to some desired principle. In particular, in axial piston pumps, for example, a constant pressure control may utilize a spring biasing force urging the swashplate into stroke, and a piston and cylinder device for urging the swashplate out of stroke under control of a valve responsive to discharge pressure in a manner effective to maintain constant discharge pressure.

In devices of the character described, the control piston and cylinder device and the linkages associated with it often require precise manufacture and often are fragile so that the control becomes a critical factor in the unit controlling both the cost of manufacture and the durability. Further, in order to conduct control pressure from the pump outlet to the control valve, and the control piston and cylinder device, the porting must pass through one or more joints at the juncture of housing members which gives rise to potential leakage problems.

SUMMARY OF THE INVENTION The present invention has for its general object a simplification of control means in variable displacement hydraulic units by utilizing the main pistons to control displacement.

More particularly, the variable displacement cam controlling the stroke of the pistons is subjected to a displacement varying force by application of control fluid to the main pistons, thereby eliminating the need for a separate control piston and cylinder device of expensive and fragile construction.

In a preferred embodiment illustrated herein, the principles of the invention are demonstrated in connection with an axial piston pump with a cam or swashplate mounted for pivotal adjustment about an axis generally transverse to the axis of the rotary cylinder block. As the cylinder block rotates, axial pistons are reciprocated by the swashplate at one end of the cylinder block, while the piston chambers successively communicate with inlet and outlet ports in a valve plate at the opposite end of the cylinder block. In order to control the pivotal adjustment of the swashplate, the valve plate includes a control port located between the inlet and outlet ports and adapted to supply control fluid successively to the pistons as they pass the control port, thereby to apply a force for varying the angle of the swashplate.

In the control shown, the swashplate is biased in a stroke increasing direction and the control port is utilized to supply fluid for biasing the swashplate in a stroke reducing direction. Fluid is supplied to the control port under control of a valve responsive to outlet pressure and adapted to function in a way to control the swashplate to maintain the outlet pressure constant. Preferably, the control port is centrally located between the outlet port and the inlet port and spaced from each by an amount approximately equal the length of each cylinder block port so that the control port is always in communication with one of the cylinder ports, and the size of the control port is such that it primarily communicates with only one cylinder port.

As illustrated herein, the inlet and outlet ports in the valve plate have a greater length at one side of the swashplate pivot axis in order to utilize the pumping pistons to urge the swashplate into stroke. However, other means may be used for urging the swashplate into stroke.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic illustration of a pump together with control circuit embodying the principles of the present invention; and

FIG. 2 is a sectional view taken at about the line 22 in FIG. 1, showing the arrangement of the control port in the valve plate.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT Referring now to the drawings in more detail, the invention is illustrated in connection with a pump generally designated 10 which may be of the type described in US Pat. Nos. 3,366,072 and 3,366,968, if desired, but the invention is not limited to use with such pump constructions. In FIG. I, the pump is illustrated diagrammatically as including a rotatable cylinder block appropriately mounted in bearings as at 12 for rotation about a longitudinal central axis 13. The cylinder block is formed with an annular series of axially disposed fluid chambers 15 arranged around the axis of rotation and each including a reciprocable piston as at 17. In order to control reciprocation of the pistons on rotation of the cylinder block, there is an adjustable cam or swashplate 18 mounted for pivotal movement about an axis 19 transverse to cylinder block axis 13. To facilitate pivotal adjustment, the swashplate is formed with one or more arcuate bearing surfaces as at 20 supported on roller bearings 21 in an arcuately curved bearing race 22. In the pump shown, there are seven fluid chambers 15 with pistons 17, but there may be other numbers.

In the preferred construction illustrated, the face of the swashplate 18 at 25 supports an annular bearing ring 26. The bearing ring includes a plurality of sockets for universally receiving the spherical ends 28 of a plurality of piston rods 29 having opposite spherical ends 30 universally mounted in the pistons 17 respectively. Attached to the bearing ring 26 is a timing member 32 which allows limited pivotal movement of the connecting rods 29 but essentially maintains the rods generally perpendicular to the bearing ring so that as the cylinder block rotates, the bearing ring rotates with the block. The timing member 32 is piloted on a spherically shaped member 34 appropriately mounted on the cylinder block 1 1, all as described in more detail in the aforementioned U. S. Pat. Nos. 3,366,072 and 3,366,968.

At the opposite end of the cylinder block from the swashplate 18, the cylinder block rotates against the face of a stationary valve plate 36 appropriately mounted in a suitable housing with the remaining pump structure and including ports for supplying fluid to and from the pump chambers through cylinder ports 37 which lead from the chambers 15 to the end of the cylinder block. As seen in FIG. 2, the port plate 36 includes an arcuate inlet port 38 and a similarly shaped arcuate outlet port 39 symmetrically disposed in the plate at opposite sides of a piston dead center axis 40 which extends generally transverse to the cylinder block axis and transverse to the swashplate pivot axis and lies in the plane passing through the angular positions where the pistons reach opposite ends of their strokes.

In operation of the pump as described thus far, it will be understood that when the swashplate 18 is pivoted as shown in FIG. 1, the pistons 17 reciprocate as the cylinder block is rotated, and if inlet fluid at low pressure is supplied to the arcuate inlet port 38, it is admitted to the passing cylinder ports 37 as the pistons are withdrawn from the cylinders 15. As the cylinder ports 37 pass the high pressure discharge port 39, the pistons are forced into the cylinders and fluid is pumped out of the discharge port under pressure. The displacement of the unit, that is, the volume of fluid displaced on each revolution of the cylinder block, may be varied by pivoting the swashplate 18 to increase or decrease the angle of the swashplate relative to the end of the cylinder block. If the face of the swashplate is parallel to the end of the cylinder block, the pistons will not reciprocate and the displacement is zero.

In the construction as illustrated, the swashplate 18 is mounted to pivot about an axis (19) which is transverse to the cylinder block axis and which intersects the cylinder block axis perpendicular thereto and perpendicular to a timing axis coincident with the piston dead center axis 40 and centrally disposed between the inlet and

outlet ports

38 and 39. The swashplate is biased in a stroke increasing direction by arrangement of the

arcuate ports

38 and 39 with a greater length above the pivot axis 19 than below, so that the pumping pistons exposed to high pressure in the port 39 exert a greater force on the swashplate above the axis 19 than below the axis 19. By such an arrangement, the swashplate is normally biased into stroke by use of the main pumping pistons without other additional structure, as a result of which the pump is simplified, the cost is reduced, and life is prolonged. If desired, other means may be employed separately or in combination with the arrangement described for purposes of biasing the swashplate into stroke. For example, the swashplate pivot axis 19 may be lowered from the transverse center line through the port plate, and such arrangement will have the effect of increasing the length of the arcuate port 39 above the pivot axis in a way such that the pumping pistons exert a stroke increasing influence on the swashplate. As another example, the swashplate may be urged in a stroke increasing direction through the medium ofa suitable spring mechanism applying a constant bias along the lines of that illustrated in the aforementioned U. S. Pat. Nos. 3,366,072 and 3,366,968.

In order to apply a force to the swashplate in a stroke decreasing direction, to oppose the stroke increasing force and control the swashplate angle selectively, the present invention contemplates application of a control force through the medium of the main pumping pistons by subjecting the latter to control fluid under pressure. For such purposes, the port plate 36 is formed with a control port 42 located in the path of the cylinder ports 37 and located centrally between the end 39a of the outlet port 39 and the beginning 38a of the inlet port 38. As viewed in FIG. 2, when the device is employed as apump, the cylinder block rotates counterclockwise in the direction of the arrow 43. Thus, it will be seen that as a pump cylinder 15 passes the control port 42, the piston 17 therein may be subjected to control fluid under pressure to apply a stroke decreasing force. Preferably, the control port is spaced from the adjacent ends of the

ports

38 and 39 by an amount equal to the length of cylinder ports 37 so that one port 37 is substantially always exposed to control fluid under pressure and only one at a time is exposed. The use of the main pumping pistons for biasing the swashplate in a stroke reducing direction simplifies the pump construction in avoiding the need for additional separate control means which traditionally has required precise construction involving substantial expense and limited life. Use of the main pumping pistons takes advantage of pump parts which are normally constructed for heavy duty performance.

In the circuit illustrated in FIG. 1, a supply of fluid under pressure to the control port 42 is controlled by a constant pressure control valve as at which may be of the type described in US. Pat. No. 3,465,680 if desired. In order to provide for maintaining the pump at a zero stroke or substantially reduced stroke near zero, the circuit may include a solenoid depressurization valve as at 51 which may be of the type described in U. S. Pat. No. 3,563,675.

As shown in FIG. 1, the pump outlet port 39 communicates with a discharge conduit 53, and branch conduit 54 communicates discharge pressure to the constant pressure control valve 50. The latter includes a valve member 55 having enlarged lands 56 and 57 with a reduced stem portion 58 therebetween. The end of the valve member 55 is formed with a large disc 59 which provides a spring seat for a coil spring 61 in a spring chamber 62 where the spring is grounded at the end of the chamber. The valve 50 includes a port 66 normally closed by land 56 and a port 67 normally closed by land 57 when the spring 61 biases the valve member toward the left as viewed in FIG. 1. The

ports

66 and 67 communicate with a passage 68 leading to the control port 42. When the valve member 55 is positioned as illustrated, the reduced stem portion 58 is aligned with a drain port 69.

In operation, the swashplate is normally biased into stroke as described above so that on rotation of the cylinder block, the pump delivers fluid under pressure to the discharge conduit 53. The valve 50 senses discharge pressure through the conduit 54, and when the pressure rises unduly, the valve stem 55 is moved to the right against the bias of spring 61, admitting fluid under pressure past the land 57 to the port 67 and the control port 42 to reduce pump displacement. In order to damp the action of the pressure responsive valve as described in U. S. Pat. No. 3,465,680, movement of the valve member 55 toward the right also communicates port 66 with drain port 69 through the reduced stem portion 58 in a way to reduce the effect of the correction called for by the pressure response of the valve. When the discharge pressure is reduced appropriately as a result of the reduction of the swashplate angle, the spring 61 is again effective to move the valve member toward the left where the pressure passage 64 is disconnected from the control port 42, and the stroke may be increased. In this manner, constant pressure may be maintained in the discharge conduit 53.

The depressurization valve 51 includes a valve stem 70 with a reduced stern portion 71 between

enlarged portions

72 and 73. The valve member is normally positioned as illustrated in FIG. 1 so that the enlarged portion 72 blocks a high pressure passage 54a and communicates a control port 74 with a drain port 75 leading to a conduit 76 which in turn connects with an inlet conduit 77 leading to the pump inlet port 38. When it is desired to take the pump out of stroke, the valve stem 70 may be moved to the right as viewed in FIG. 1 by means such as a selectively energizable solenoid to a position where the drain port 75 is blocked by the enlarged stem portion 73, and the pressure port 54a is communicated with the control port 74 through the reduced stem portion 71. At that time, discharge pressure is supplied to both sides of the control land 57 in the constant pressure valve and the valve functions only to deliver discharge pressure to the control port 42, without the capability of connecting the latter to drain, so that the effect is to apply a constant bias to the swashplate in a stroke reducing direction. The latter operation is described in detail in the aforementioned U. S. Pat. No. 3,563,675.

It will be appreciated that the control of displacement through the medium of one of the main pistons in the hydraulic unit represents a great simplification in contrast to provision of separate control mechanisms. While the invention has been illustrated in connection with an axial piston swashplate pump, it should be understood that the principles of the invention are also applicable to other hydraulic units such as radial piston and vane units. Also, while the inlet port 38 and the outlet port 39 have been illustrated as symmetrical relative to the piston dead center plane 40 and the timing axis coincident therewith, it is conventional practice to shorten the beginning of the outlet port at 39b in order to precompress the fluid in each cylinder by piston movement before exposure to the high pressure port 39, and such construction may be utilized herein.

In the port plate illustrated in FIG. 2, with the control port 42 located at top dead center in the piston dead center plane, where the pistons begin the intake stroke, there may be some tendency to lose some of the effect of the control pressure due to the intake stroke enlarging the fluid chamber, but in actual practice in a unit of the type described, it has been found that the inertia of the system is such that the control port is substantially always under pressure without significant suction effect. However, if desired, in order to ensure pressure effect in the control port 42, the latter may be indexed a few degrees clockwise, so that the port is entirely located at the side of the piston dead center plane where the pistons are cammed in a direction reducing the volume of the fluid chambers. In such event, the end of discharge port 39 may be shortened at 39a and the beginning of inlet port 38 may be lengthened at 3811 so that the control port is centrally disposed between the port ends and spaced therefrom by an amount approximately corresponding to the length of cylinder ports 37.

Iclaim:

l. A rotary fluid translating apparatus, comprising, a rotary cylinder block having a plurality of fluid chambers angularly spaced around the axis of rotation of the block, a plurality of pistons reciprocable in the fluid chambers, a cam disposed relative to the cylinder block for causing reciprocation of the pistons as the cylinder block rotates, means mounting the cam for adjustment to vary the stroke of the pistons, means biasing the cam in one direction, a port plate adjacent the cylinder block having inlet and outlet ports, ports in the cylinder block communicating the fluid chambers successively with the inlet and outlet ports as the cylinder block rotates, a control port in the port plate for supplying fluid under pressure successively to the fluid chambers as the cylinder block rotates to apply a force through the pistons to the cam in opposition to the biasing means for controlling the position of the. cam, and selectively operable means for supplying control fluid under pressure to the control port.

2. A rotary fluid translating apparatus as defined in claim 1, including selectively operable valve means for controlling the supply of control fluid to the control port.

3. A rotary fluid translating apparatus as defined in claim 1, including means biasing the cam in a direction to cause the pistons to stroke when the cylinder block rotates, and means locating the control port to supply fluid under pressure to the pistons while positioned to bias the cam in a stroke reducing direction.

4. A rotary fluid translating apparatus as defined in claim 3, including valve means responsive to outlet pressure for controlling the supply of control fluid to the control port.

5. An axial piston pump, comprising, a rotatable cylinder block having an annular series of axially disposed fluid chambers spaced around the axis of the cylinder block, piston means reciprocable in the fluid chambers and projecting from one end of the cylinder block, a cam disposed adjacent said one end of the cylinder block for causing reciprocation of the piston means as the cylinder block rotates, a valve plate engaging the other end of the cylinder block, inlet and outlet ports in the valve plate for admitting low pressure fluid and exhausting high pressure fluid, ports in the end of the cylinder block communicating the chambers successively with the inlet and outlet ports as the cylinder block rotates, means mounting the cam for pivotal adjustment to vary the stroking of the piston means as the cylinder block rotates, means biasing the cam in a direction to increase stroking of the piston means, and a control port in the valve plate between the outlet port and the inlet port for successive communication with the chambers as the block rotates to supply control fluid to successive piston means to bias the cam in a stroke reducing direction.

6. A pump as defined in claim including conduit means for supplying control fluid under pressure to the control port, and selectively operable valve means in the conduit means for controlling the flow of control fluid to the control port.

7. A pump as defined in claim 6 wherein the valve means is responsive to increase in outlet pressure to reduce displacement.

8. An axial piston pump, comprising, a rotatable cylinder block having an annular series of fluid chambers spaced around the axis of the cylinder block, piston means reciprocable in the fluid chambers, a swashplate disposed adjacent one end of the cylinder block for causing reciprocation of the pistons as the cylinder block rotates, means mounting the swashplate for pivotal adjustment about an axis generally transverse to the axis of the cylinder block to vary the stroke the cylinder block, arcuate inlet and outlet ports in the valve plate at opposite sides ofa piston dead center axis generally transverse to the cylinder block axis and the swashplate pivot axis for admitting and exhausting fluid, ports in the end of the cylinder block communicating the chambers successively with the inlet and outlet ports as the cylinder block rotates, said arcuate inlet and outlet ports including a greater length at one side of the swashplate pivot axis so that the swashplate is biased by the pistons in a direction to increase piston stroke, and a control port in the valve plate between the outlet port and the inlet port at the other side of the swashplate pivot axis for successive communication with the chambers as the block rotates to supply control fluid to successive pistons to bias the swashplate in a stroke reducing direction.

9. A pump as defined in claim 8 wherein the control port is located centrally between adjacent ends of the outlet port and inlet port.

10. A pump as defined in claim 9 wherein the space of the pistons, a valve plate engaging the other end of between the control port and each of the inlet and outlet ports corresponds to the length of each cylinder port.

11. An axial piston pump, comprising, a rotatable cylinder block having an annular series of axially disposed fluid chambers spaced around the axis of the cylinder block, piston means reciprocable in the fluid chambers and projecting from one end of the cylinder block, a swashplate disposed adjacent said one end of the cylinder block for causing reciprocation of the piston means as the cylinder block rotates, a valve plate engaging the other end of the cylinder block, arcuate inlet and outlet ports in the valve plate for admitting and exhausting fluid, ports in the end of the cylinder block communicating the chambers successively with the inlet and outlet ports as the cylinder block rotates, means mounting the swashplate for pivotal movement about an axis generally transverse to the axis of rotation of the cylinder block, means biasing the swashplate in a direction to cause stroking of the piston means as the cylinder block rotates, a control port in the valve plate between the inlet and outlet ports for successive communication with the chambers as the block rotates, conduit means for supplying control fluid to the control port to supply fluid to successive pistons as the cylinder block rotates thereby to bias the swashplate in a stroke reducing direction, and valve means controlling the supply of control fluid to the control port responsive to outlet pressure so that increases in outlet pressure reduce displacement and constant outlet pressure is maintained.

12. A pump as defined in claim 11 wherein the inlet and outlet ports are symmetrically disposed at opposite sides of a piston dead center axis generally transverse to the cylinder block axis and the swashplate pivot axis and include a greater length at one side of the swashplate pivot axis opposite from the control port so that the pistons bias the swashplate in a stroke increasing direction.

13. A pump as defined in claim 12 wherein the control port is centrally located between adjacent ends of the outlet port and inlet port and spaced therefrom by an amount corresponding to the length of each cylinder port.

Claims

1. A rotary fluid translating apparatus, comprising, a rotary cylinder block having a plurality of fluid chambers angularly spaced around the axis of rotation of the block, a plurality of pistons reciprocable in the fluid chambers, a cam disposed relative to the cylinder block for causing reciprocation of the pistons as the cylinder block rotates, means mounting the cam for adjustment to vary the stroke of the pistons, means biasing the cam in one direction, a port plate adjacent the cylinder block having inlet and outlet ports, ports in the cylinder block communicating the fluid chambers successively with the inlet and outlet ports as the cylinder block rotates, a control port in the port plate for supplying fluid under pressure successively to the fluid chambers as the cylinder block rotates to apply a force through the pistons to the cam in opposition to the biasing means for controlling the position of the cam, and selectively operable means for supplying control fluid under pressure to the control port.

6. A pump as defined in claim 5 including conduit means for supplying control fluid under pressure to the control port, and selectively operable valve means in the conduit means for controlling the flow of control fluid to the control port.

8. An axial piston pump, comprising, a rotatable cylinder block having an annular series of fluid chambers spaced around the axis of the cylinder block, piston means reciprocable in the fluid chambers, a swashplate disposed adjacent one end of the cylinder block for causing reciprocation of the pistons as the cylinder block rotates, means mounting the swashplate for pivotal adjustment about an axis generally transverse to the axis of the cylinder block to vary the stroke of the pistons, a valve plate engaging the other end of the cylinder block, arcuate inlet and outlet ports in the valve plate at opposite sides of a piston dead center axis generally transverse to the cylinder block axis and the swashplate pivot axis for admitting and exhausting fluid, ports in the end of the cylinder block communicating the chambers successively with the inlet and outlet ports as the cylinder block rotates, said arcuate inlet and outlet ports including a greater length at one side of the swashplate pivot axis so that the swashplate is biased by the pistons in a direction to increase piston stroke, and a control port in the valve plate between the outlet port and the inlet port at the other side of the swashplate pivot axis for successive communication with the chambers as the block rotates to supply control fluid to successive pistons to bias the swashplate in a stroke reducing direction.

10. A pump as defined in claim 9 wherein the space between the control port and each of the inlet and outlet ports corresponds to the length of each cylinder port.