US3173377A - Hydraulic pumps - Google Patents

Description

March 16, 1965 Filed March 11, 1963 D. E. LEE

HYDRAULIC PUMPS 2 Sheets-Sheet 2 e is) gram.

United States Patent "cc 3,173,377 HYDRAULIC PUMPS Denis Ernest Lee, Birmingham, England, assignor to Joseph Lucas (Industries) Limited, Birmingham, England Filed Mar. 11, 1963, Ser. No. 264,111 Claims priority, application Great Britain, Mar. 22, 1962, 10,988/ 62 3 Claims. (Cl. 103-462) This invention relates to variable stroke hydraulic pumps of the kind wherein the stroke control of the pump is biased towards a position of maximum stroke, and comprising a servo-cylinder containing a piston for moving the stroke control towards a position of minimum stroke, and an axially movable and spring-loaded valve member for controlling the admission of pump output pressure to the servo-cylinder, said valve member being arranged to be subjected to the output pressure of the pump, and the arrangement being such that when pump output pressure exceeds a predetermined value the valve member will be moved to a position to admit fluid to the servo-cylinder and thereby reduce the stroke of the pump, whereas when the pump output pressure falls the valve member will move to a position to permit the servocylinder to exhaust.

The object of the invention is to provide such a pump in a convenient form.

According to the invention a pump of the kind specified comprises an annular piston surrounding the valve member adjacent an abutment thereon, said piston being contained in a cylindrical chamber, and an attendant controllable valve through which the chamber can be placed in communication with the pump output, the arrangement being such that when the attendant controllable valve is opened with the pump in operation, the combined efiect of the pump output pressure acting on both the piston and the valve member will move the latter against its spring to a position to admit fluid to the servo-cylinder even when the pump output pressure is below said predetermined value.

In the accompanying drawings FIGURE 1 is a sectional side view of an example of the invention, and FIGURE 2 is a fragmentary plan of FIGURE 1.

Referring to the drawings there is provided a housing 3 having an inlet 4 and outlet 5 at one end. Within the housing is supported a rotatable spindle 6 one end of which extends from the end of the housing remote from the inlet and outlet, and is adapted for connection to a source of power whereby it can be rotated. Also within the housing there is formed on the spindle 6 a rotary body 7 in which are formed a plurality of parallel, angularly spaced and annularly arranged bores S in which respectively is a plurality of plungers 9. Each plunger 9 extends at one end from its bore 8 and is provided with a shoe 10 which is held in contact with an angularly adjustable swash plate 11 by a spring 12 acting on the plunger.

The swash plate 11 which is of annular form, is pivotally mounted in the housing about a transverse pin 13 offset from the axis of rotation of the spindle 6, and is angularly adjustable about this pin by movement of a fluid actuated piston 14 in a servo-cylinder 15 formed in the body part.

The opposite end of the body 7 is in contact with a valve plate 16 in which are formed a pair of arcuate ports 17, 18 which are in communication with the inlet 4 and outlet 5 respectively, and the arrangement is such that as the body rotates the plungers 9 will be reciprocated by their interaction with the swash plate 11 thereby drawing fluid from the inlet 4 into the bores and discharging the fluid from the bores in turn to the outlet 5.

3,173,377 Patented Mar. 16, 1965 In the end of the housing remote from the swash plate is a stepped cylindrical bore 19 which is co-axial with the spindle 6. In the bore is engaged a cylindrical spool 20 having a stepped head 20 at its end adjacent the pump body 7 whilst between the latter and the head 2% is a coiled compression spring 21 which serves both to load the spool axially away from the body and also to transmit rotation from the body to the spool.

Freely surrounding the spool 20 adjacent the head is an annular piston 22 which is accommodated within the wider portion of the bore 19 hereinafter termed the chamber 19. Moreover, acting between the piston 22 and the step of the head is a second and relatively lighter coiled compression spring 23. Furthermore the piston 22 can, as will be described, bear against the head 20 the latter then acting as an abutment.

The end of the bore 19 remote from the body is connected through a passage 24 to the pump outlet 5. Thus the delivery pressure of the pump is caused to act on the spool in opposition to the spring 21. Moreover, in the wall of the bore are two axially spaced ports 25, 26 both of which are connected through a passage 27 to the servocylinder 15, and a spill port 28 connected to a source through a passage 29 of low pressure such as the interior of the housing 3 which in use is flooded. Furthermore, the spool incorporates a neck 20* which registers with the spill port 28 and the port 25 when the spool has been moved axially to its one limit position by the spring 21. In this position the servo-cylinder 15 can exhaust and the port 26 is covered by the spool. However, when the delivery pressure of the pump exceeds a predetermined value it will move the spool axially against the spring 21 to a position to uncover the port 26 and cover the port 25. As a result pump delivery pressure is admitted to the servo-cylinder 15 to move the swash plate 11 towards a position of minimum obliquity against its natural tendency to assume a position of maximum obliquity. During such movement of the spool the piston 22 remains stationary and the spring 23 assists movement.

The passage 24 is also connected through a valve 30 (operable by a solenoid 31) to the annular space within the chamber 19* between the piston and the step. When the valve 30 is opened, pump delivery pressure acts on the piston as well as the spool, with the result that the piston is urged into contact with the head 20 and the spool is moved to uncover the port 26 by a much smaller pump delivery pressure, as the piston is of far greater area than the spool.

A pump as above described may be used in a vehicle transmission comprising an engine driven swash plate type pump for supplying motive fluid to a hydraulic motor for driving the vehicle wheels. In such a transmission it is advantageous that the pump should be at minimum stroke whilst starting the engine, and to achieve this ad-- vantage the solenoid 31 may be energised whilst start-- ing the engine.

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

1. Hydraulic pumping apparatus comprising in combination, a variable stroke hydraulic pump including a hollow body part, an inlet and an outlet defined in the body part, a stroke control mounted within the body part, means biasing the stroke control towards a position to permit the pump to partake of its maximum stroke, a fluid pressure operable piston mounted in a first cylinder within the body part for moving said stroke control in a direction to reduce the stroke of the pump, valve means comprising an axially movable valve member slidable within a second cylinder within the body part, resilient means for urging the valve member towards one end of the second cylinder, passage means connecting said sec- 0nd cylinder with the outlet so that the valve member will be subjected to the pressure at the outlet and will be moved thereby against the action of said resilient means, further passage means connecting said first and second cylinder so that when the valve member is moved against the action of said resilient means, as the pressure at the outlet attains a predetermined value, fluid under pressure will be admitted to said first cylinder to move the piston and the stroke control to reduce the output of the pump, a third cylinder in the body part, a further pisiton slidable in said third cylinder, an abutment on the valve member against which the further piston can bear, extra passage means interconnecting said third cylinder :and said outlet, and valve means mounted in said extra passage means for controlling the'flow of liquid to said third cylinder whereby, when said valve means is open to permit theflow of fluid'through said extra passage means, the valve member will be moved, to permit fluid pressure to act against said piston, at a value of output pressure lower than said predetermined value.

2. Hydraulic pumping apparatus comprising in combination a variable stroke hydraulic pump including a hollow body part, apump rotor mounted within the body part, said rotor being arranged to be rotated, an inlet and an outlet defined in the body part, a stroke control mounted Within the body part, means biasing the stroke control towards a position to permit the pump to partake of its maximum stroke, a fluid pressure operable piston mounted in a first cylinder within the body part for moving said stroke control in a direction to reduce the stroke of the pump, valve means comprising an axially movable valve member slidable within a second cylinder within the body part, a spring for urging the valve member towards one end of the second cylinder, said spring serving to interconnect the rotor and the valve member so that as the rotor rotates the valve member will be rotated, passage means connecting said second cylinder with the outlet so that the valve member Will be subjected to the pressure at the outlet, and will be moved thereby against the'action ofsaid spring, further passage means connecting said first and second cylinder so that when the valve member is moved against the action of said spring, as the pressure at the outlet attains a predetermined value, fluid under pressure will be admitted to said first cylinder to move the piston and thestroke control to reduce the output of the pump, a third cylinder in the body part, a further piston slidable in said third cylinder, an abutment on the valve member against which the further piston can bear, extra passage means interconnecting said third cylinder and said outlet, and valve means mounted in said extra passage means for controlling the How of liquid to said third cylinder whereby, when said valve means is open to permit the fiow of fluid through said extra passage means, the valve member Will be moved, to permit fluid pressure to act against said piston, at a value of output pressure lower than said predetermined value.

3. Hydraulic apparatus as claimed in claim 2 including a solenoid for controlling said valve means.

7/45 Snader et a1. "103-162 X 8/58 Keel 103-l62 LAURENCE v. EFNER, Primary Examiner.

Claims (1)

1. HYDRAULIC PUMPING APPARATUS COMPRISING IN COMBINATION, A VARIABLE STROKE HYDRAULIC PUMP INCLUDING A HOLLOW BODY PART, AN INLET AND AN OUTLET DEFINED IN THE BODY PART, A STROKE CONTROL MOUNTED WITHIN THE BODY PART, MEANS BIASING THE STROKE CONTROL TOWARDS A POSITION TO PERMIT THE PUMP TO PARTAKE OF ITS MAXIMUM STROKE, A FLUID PRESSURE OPERABLE PISTON MOUNTED IN A FIRST CYLINDER WITHIN THE BODY PART FOR MOVING SAID STROKE CONTROL IN A DIRECTION TO REDUCE THE STROKE OF THE PUMP, VALVE MEANS COMPRISING AN AXIALLY MOVABLE VALVE MEMBER SLIDABLE WITHIN A SECOND CYLINDER WITHIN THE BODY PART, RESILIENT MEANS FOR URGING THE VALVE MEMBER TOWARDS ONE END OF THE SECOND CYLINDER, PASSAGE MEANS CONNECTING SAID SECOND CYLINDER WITH THE OUTLET SO THAT THE VALVE MEMBER WILL BE SUBJECTED TO THE PRESSURE AT THE OUTLET AND WILL BE MOVED THEREBY AGAINST THE ACTION OF SAID RESILIENT MEANS, FURTHER PASSAGE MEANS CONNECTING SAID FIRST AND SECOND CYLINDER SO THAT WHEN THE VALVE MEMBER IS MOVED AGAINST THE ACTION OF SAID RESILIENT MEANS, AS THE PRESSURE AT THE OUTLET ATTAINS A PREDETERMINED VALUE, FLUID UNDER PRESSURE WILL BE ADMITTED TO SAID FIRST CYLINDER TO MOVE THE PISTON AND THE STROKE CONTROL TO REDUCE THE OUTPUT OF THE PUMP, A THIRD CYLINDER IN THE BODY PART, A FURTHER PISTON SLIDABLE IN SAID THIRD CYLINDER, AN ABUTMENT ON THE VALVE MEMBER AGAINST WHICH THE FURTHER PISTON CAN BEAR, EXTRA PASSAGE MEANS INTERCONNECTING SAID THIRD CYLINDER AND SAID OUTPUT, AND VALVE MEANS MOUNTED IN SAID EXTRA PASSAGE MEANS FOR CONTROLLING THE FLOW OF LIQUID TO SAID THIRD CYLINDER WHEREBY, WHEN SAID VALVE MEANS IS OPEN TO PERMIT THE FLOW OF FLUID THROUGH SAID EXTRA PASSAGE MEANS, THE VALVE MEMBER WILL BE MOVED, TO PERMIT FLUID PRESSURE TO ACT AGAINST SAID PISTON, AT A VALVE OF OUTPUT PRESSURE LOWER THAN SAID PREDETERMINED VALUE.

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