US3339489A - Hydraulic pumps - Google Patents

Description

D. F. MOWBRAY HYDRAULIC PUMPS Sgpt. '5, 1967 Filed May 25, 1965 United States Patent O 3,339,489 HYDRAULIC PUMPS Dorian Farrer Mowbray, Solihull, England, assignor to Joseph Lucas (Industries) Limited, Birmingham, England Filed May 25, 1965, Ser. No. 458,531 3 Claims. (Cl. 103-38) ABSTRACT OF THE DISCLOSURE This invention relates to hydraulic pumps of the kind comprising a body in which is mounted a rotor, the rotor having a plurality of angularly spaced bores in which are disposed respective plungers, an inlet passage and an outlet passage for hydraulic fluid in the body, an angularly adjustable swash plate mounted in the body, against which ends of the plungers, extending from the bores, abut, means for rotating the rotor so that the plungers are moved in the bores by contact of their ends with the swash plate, and a servo mechanism for varying theangle of the swash plate in accordance with the pressure of fluid in the outlet passage.

The object of the present invention is to provide an hydraulic pump of the kind specified, in a convenient form.

According to the present invention, an hydraulic pump of the kind specified is characterised by a servo mechanism comprising a piston in a cylinder, the cylinder at one side of the piston being in communication with the outlet passage from the pump, a spring acting between the opposite side of the piston and a further piston in the cylinder, and a valve, the position of which is dependent upon pressure conditions in the pump outlet passage, said valve being arranged to control the supply of fluid to, or the escape of fluid from the end of the cylinder adjacent to the side of said further piston remote from the spring.

A specific example of the invention will now be described with reference to the accompanying drawings, the single figure of which shows an hydraulic pump in crosssection and incorporating the present invention.

In this example the hydraulic pump has a hollow body in which is mounted for rotation a rotor 11 having a plurality of angularly spaced bores containing respective plungers 12. The ends of the plungers 12 protrude from the rotor 11 and abut against an angularly adjustable and non-rotatable swash plate 13. A driving shaft 14 is connected to the rotor 11 and as the rotor rotates, fluid is admitted to those bores in the rotor 11 in which the plungers 12 are moving outwardly and fluid is pumped out of those bores in which the plungers 12 are moving inwardly, through respective inlet and outlet passages 15 and 16 in the body. I

The inlet passage 15 includes a chamber containing a boost pump 17 of the impeller type, this pump being driven by the driving shaft 14 through gears 18, 19. The outlet passage 16 includes a non-return valve 20 and the inlet and outlet passages 15 and 16 are connected through a passage 21 containing an adjustable relief valve 22 oper ative in the event of excessive pressure conditions in the outlet passage 16.

Connected to the swash plate 13 for moving it angularly to vary the strokes of the plungers 12, is a servo mechanism comprising a rod 23 carrying at its end remote from the swash plate 13, a servo piston 24 slidable in a cylinder 25, this cylinder, at its end through which the rod 23 extends, being in communication with the pump outlet passage 16 through an intermediate chamber 26. This intermediate chamber includes a flow-restricting orifice 27, through which fluid is constrained to pass from the outlet passage 16 to the cylinder 25, and also a spring loaded non-return valve 28 through which fluid can only pass from the cylinder 25 to the outlet passage 16. With this arrangement, response of the servo piston to increasing pressure in the outlet passage is retarded whilst substantially unrestricted response to decreasing outlet pressure can take place when the differential pressure across the non-return valve 28 has been exceeded. This tends to minimise movement of the piston 24 in response to relatively small pressure fluctuations.

On the opposite side of the servo piston 24 from the end of the cylinder 25 in communication with the outlet passage, is a compression spring 29 which, at its other end, abuts against a further piston 30 slidable in the cylinder 25. The end of the cylinder at the side of the piston 30 remote from the spring is in communication with a passage 31 leading to a spool valve 32.

This valve is mounted in a bore in the body 10 and is rotatable by means of a coaxial cup-shaped and axially adjustable member 32 which is driven through gearing 34 from the driving shaft 14 of the pump. Transmission of the drive between the spool valve 32 and the cup-shaped member 33 is by means of an intervening compression spring 35. Axial adjustment of the cup-shaped member 33 determines the spring pressure exerted on the spool valve 32, the opposite end of which is in communication with the output passage 16 of the pump through a passage 36. Adjustment thus determines the pressure in the outlet passage 16 at which the spool valve 32 can move. From the bore in which the spool valve 32 is disposed is a passage 37 axially spaced from the passage 31, which communicates with the inlet passage 15. Opposite ends of the bore for the spool valve 32 communicate through a passage 38 in the body 10.

When the pump is running at a steady rate, the pressure in the outlet passage 16 is at a predetermined value, dependent upon the adjusted position of the cup-shaped member 33. In this condition, the spool valve 32, which has three lands, is so positioned that the central land closes access to the passage 31 to the appropriate end of the cylinder 25 of the servo mechanism. The two spaces between the three lands of the spool valve 32 are respectively in communication with the passages 37 and 38 and thus with the outlet passage 16 in one case, and the space nearest to the cup-shaped member 33 being in communication with the outlet passage 16 through the passage 38.

In the event of a decrease in pressure in the outlet passage 16, due, for example, to a demand for fluid by a machine to which the pump supplies fluid, the fluid at the end of the servo mechanism cylinder 25 which is in communication with the outlet passage 16 escapes when the pressure diiference across the non-return valve 28 exceeds the rating of its spring. The compression spring 29 of the servo mechanism moves the servo piston 24in a direction to increase the inclination of the swash plate 13 thus increasing the strokes of the plungers 12 in the rotor 11 and increasing the supply of fluid to the machine. On the other hand, if the pressure increases in the pump outlet passage 16 the servo piston 24 is moved against the spring 29 to decrease the strokes of the plungers 12 in the rotor 11.

In order that the response of the servo mechanism to changes in pressure shall, as far as possible, be independent of variation in load upon the servo mechanism compression spring 29, the further piston 30, against which this spring 29 acts, is capable of being moved in the following manner. During initial movement of the servo piston 24 against the spring 29, the passage 31 to the opposite end of the cylinder 25 is closed and the fluid which is trapped in this end prevents movement of the further piston 30.

However, changes in pressure in the outlet passage 16 are also felt at the end of the spool valve 32, causing it to move. An increase in the pressure at the outlet passage 16 result in exhausting of the cylinder 25 to the inlet passage 15 of the pump, through the passages 31 and 37, the inlet passage 15 being, of course at a lower pressure than the outlet passage, thus permitting movement of the further piston 30 to relieve the compressive load on the spring 29. Furthermore, a decrease in the pressure at the outlet passage 16 results in movement of the further piston 30 in the same direction as the servo piston 24, thus again bringing the compressive load on the spring 29 approximately to its original value, before movement of the servo piston.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

1. An hydraulic pump comprising a body, a rotor mounted within the body,'the rotor having a plurality of angularly spaced bores, plungers disposed in the bores respectively, the body having an inlet and an outlet for hydraulic fluid, an angularly adjustable swash plate mounted in the body against which the ends of the plungers abut, means for rotating the rotor so that as the plungers reciprocate by contact with the swash plate, liquid is pumped between the inlet and the outlet and a piston and cylinder type servo mechanism for varying the angle of the swash plate in accordance with the pressure in the outlet, the cylinder at one side of the piston being in communication with the outlet from the pump, a spring acting between the opposite side of the piston and a further piston in the cylinder, and a valve, the position of which is dependent upon pressure conditions in the pump outlet, said valve being arranged to control fiow of fluid to or from the end of the cylinder adjacent to the side of said further piston remote from the spring.

2. An hydraulic pump according to claim 1 in which the valve is in the form of a spool at one end of which, in use, the pressure in the pump outlet is exerted, the valve being biased against the action of said pressure, and passage means being provided for permitting entry or escape of fluid to or from said end of the cylinder adjacent to the side of the further piston remote from the spring, in accordance with variations in pressure in the pump outlet.

3. An hydraulic pump according to claim 1 in which the cylinder portion which is in communication with the outlet of the pump is in communication through a passage which includes a flow restricting portion and a non-return valve, the latter being arranged only to permit of flow of fluid from the cylinder to the pump outlet, this flow occurring when the pressure drop across the non-return valve exceeds a predetermined value.

References Cited UNITED STATES PATENTS 2,114,443 4/1938 Foisy 103-162 2,523,214 9/1950 Ifield 103-38 X 2,713,312 7/1955 Shaw et al 103162 3,213,805 10/1965 Cooper et al 103l62 DONLEY J. STOCKING, Primary Examiner.

W. L. FREEH, Assistant Examiner.

Claims (1)

1. AN HYDRAULIC PUMP COMPRISING A BODY, A ROTOR MOUNTED WITHIN THE BODY, THE ROTOR HAVING A PLURALITY OF ANGULARLY SPACED BORES, PLUNGERS DISPOSED IN THE BORES RESPECTIVELY, THE BODY HAVING AN INLET AND AN OUTLET FOR HYDRAULIC FLUID, AN ANGULARLY ADJUSTABLE SWASH PLATE MOUNTED IN THE BODY AGAINST WHICH THE ENDS OF THE PLUNGERS ABUT, MEANS FOR ROTATING THE ROTOR SO THAT AS THE PLUNGERS RECIPROCATE BY CONTACT WITH THE SWASH PLATE, LIQUID IS PUMPED BETWEEN THE INLET AND THE OUTLET AND A PISTON AND CYLINDER TYPE SERVO MECHANISM FOR VARYING THE ANGLE OF THE SWASH PLATE IN ACCORDANCE WITH THE PRESSURE IN THE OUTLET, THE CYLINDER AT ONE SIDE OF THE PISTON BEING IN COMMUNICATION WITH THE OUTLET FROM THE PUMP, A SPRING ACTING BETWEEN THE OPPOSITE SIDE OF THE PISTON AND A FURTHER PISTON IN THE CYLINDER, AND A VALVE, THE POSITION OF WHICH

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