Claims
- 1. A fluid power apparatus for delivering a liquid working fluid at an outlet, said fluid delivered at varying flow rates and pressures, power for said apparatus provided by a motor having a power output rating, said apparatus adapted to adjust said flow rate and said pressure at said outlet to avoid exceeding the power output rating of said motor means, said apparatus comprising;
- a variable volume piston pump driven by said motor, said pump including an inlet in communication with a supply of said working fluid, an outlet, and a swash plate, said swash plate having a variable angle, the volume of fluid flow delivered from said outlet proportional to said angle, said pump further including a servo piston in operative connection with said swash plate for varying the angle of said swash plate;
- a cam in operative connection with said swash plate, said cam moveable responsive to the angle thereof between a first position and a second position, said pump delivering a maximum fluid flow when said cam is in the first position and a minimum fluid flow when said cam is in a second position;
- a compensation valve portion, said compensation valve portion including a CV inlet in fluid communication with the outlet of the pump, and a CV outlet, said compensation valve portion further including a first CV passage in fluid communication with said servo piston of said pump, said compensation valve portion further including an outlet flow passage for delivery fluid from said CV outlet to said pump outlet; said compensation valve portion further including a pressure-responsive valve for delivering fluid from said CV inlet to said first CV passage responsive to a differential pressure between said CV inlet and said CV outlet; and
- a load-limiting control in operative connection with said cam and said CV outlet for controlling fluid pressure at said CV outlet above a cracking pressure, said fluid control variable with the position of said cam, and at a minimum restriction when said cam is in the first position and a maximum restriction when said cam is in the second position;
- whereby when said cam is in said first position and the cracking pressure is exceeded, fluid flows from said CV outlet, and the differential pressure between said CV inlet and said CV outlet enables fluid to be delivered to said servo piston changing the angle of said swash plate and moving said cam toward said second position, whereby said flow rate from said CV outlet is reduced and said flow is maintained at a reduced rate until a maximum relief pressure of the compensating valve portion is exceeded.
- 2. The apparatus according to claim 1 wherein said load limiting control includes:
- a low flow setting adjustment comprising a control valve which is at a minimum restriction when the cam is in the first position and a maximum restriction when the cam is in the second position, and operatively engaged by said cam, and a high-flow cut-off comprising a cut-off valve having a preset cracking pressure.
- 3. The apparatus as in claim 2, wherein said low flow control includes means for manually adjusting the metering of flow through the control valve, and said high-flow cut-off includes means for manually adjusting the cracking pressure of the cut-off valve.
- 4. The apparatus as in claim 2, wherein said low flow control valve comprises:
- a sleeve retained in a passage fluidly connected to the CV outlet and the high-flow cut-off valve, and a spool closely slideably received in said sleeve, said spool being in operative engagement with said cam and moveable longitudinally within the sleeve thereby, the relative positioning of said sleeve with respect to said spool metering the fluid through the low flow control valve.
- 5. The apparatus as in claim 4, wherein said low flow control valve includes means for manually adjusting the metering of flow through the control valve.
- 6. The apparatus as in claim 2, wherein said high-flow cut-off valve comprises:
- a flow passage interconnecting the low flow control valve and ambient;
- a body adapted for blocking said flow passage; and biasing means for biasing said blocking body in abutting relation of said flow passage.
- 7. The apparatus as in claim 6, wherein said high-flow cut-off valve includes means for manually adjusting the biasing force of the blocking body.
- 8. A system for limiting the load on a variable displacement rotating piston pump, said pump having a moveable swash plate, said system including a pressure compensating valve including an outlet, the flow of said pump being controlled responsive to a control pressure at said outlet; an improvement comprising:
- load control means for controlling the low-flow setting of the pump and for adjusting the point at which the pump transitions from high-flow to low-flow, said load control means in fluid communication with said outlet of said compensator valve and in operative connection with said swash plate;
- wherein when said swash plate is at a minimum angle said load control means has maximum restriction of flow from the outlet and when said swash plate is at a minimum angle said load control means has a minimum restriction of the flow from the outlet.
- 9. The system according to claim 8 wherein said swash plate is connected in said pump to a pin and said pin is in operative connection with a cam, said load control means in engagement with said cam.
RELATED CASE
The present application claims priority to U.S. Provisional Application Ser. No. 60/064,293; filed Nov. 5, 1997.
US Referenced Citations (9)