Pumps with servo-type actuation for cheek plate unloading

Abstract

The pressure acting on a pressure loaded cheek plate in a pump is selectively vented by a servo valve actuated by the buildup of pressure in the pump outlet caused by normal parasitic losses in a downstream hydraulic flow circuit. Since it may be desirable to actuate the servo valve by the pressure drop across an orifice in the outlet line or by a suitable orifice in the pump return to pump, both embodiments are disclosed as exemplary means for achieving the premises of this design.

What we claim as our invention: .[.1. The method of flow control in a rotary pump which comprises the steps of 
     
        the pump flow output..]. .[.5.  In a pump as defined in claim 4, said means forming an orifice forming said orifice in the return line of the pump and through which spent fluid is directed on the return line side of the pump..]. .[.6. In a pump as defined in claim 4, said means forming an orifice forming said orifice in the outlet line of the pump through which fluid discharged by the pump is directed before proceeding to a motoring means..]. .[.7. In a fluid pump as defined in claim 4, said servo valve comprising a spool valve having a tapered spool movable in a bore having lands and recesses,   spring means initially loading said spool in one direction,   said spool controlling the venting passage by gradually opening the passage due to the tapered configuration,   thereby to produce an axial movement of the cheek plate but through a significantly lesser distance than the corresponding movement of the spool to maintain a flow level corresponding to a servo ratio effect in the flow regulation of the pump..]. .[.8. In a pump as defined in claim 4 and further characterized by means forming a metering passage from a source of pump generated pressure to said static cavity, and means forming a   
     
     
        metering orifice for said metering passage..]. 9. In combination, a pump having housing means forming a pumping chamber having inlet and outlet portions,   rotary fluid displacement means in said pumping chamber for moving the fluid at increased pressure from the inlet to the outlet portions,   a cheek plate adjacent said pumping chamber having a sealing face for sealing the inlet and outlet portions during operation of the pump,   means including said housing forming a static pressure control chamber behind said cheek plate and having an orificed metering passage to load said cheek plate with fluid at pump-generated pressure, .Iadd.   a seal between said cheek plate and said housing blocking flow into said cavity except through said orificed metering passage, .Iaddend.   means including said housing forming a pumping circuit including an outlet line and a return line for said pump receiving said spent fluid returned to the pump,   means forming an orifice in said pumping circuit,   and a servo valve controlling a venting passage in said housing venting said pressure control chamber to a zone at lower pressure and having actuating means responsive to the pressure drop across said orifice,   thereby valving the cheek plate in servo ratio proportion with the servo valve and directly by-passing the outlet portions of the pump to the inlet portions adjacent the sealing face of the cheek plate to modulate pump   
     
     
        flow output. 10. A pump as defined in claim 9 wherein said orifice is formed in said return line and through which spent fluid is directed on 
     
     
        the return line side of the pump. 11. A pump as defined in claim 9 wherein said orifice is formed in the outlet line of the pump and through which fluid discharged by the pump is directed before proceeding to a point of 
     
     
        utilization. 12. The invention of claim 9 and further characterized by a hollow dowel pin extending through said cheek plate and into said housing means and forming a passage extending therethrough communicating at one end with said pressure control chamber,   said servo valve controlling said passage at the other end of said passage in said dowel pin for selectively venting the pressure control chamber to a zone of reduced pressure, whereupon unloading of the cheek plate will by-pass the outlet portion to the inlet portions directly across the   
     
     
        sealing face of the cheek plate. 13. In a pump having an axial row of parts including a cam ring forming a pumping chamber and an end plate formed with a sealing face adjacent the cam ring and means forming a pressure control chamber behind the end plate, the improvement of hollow dowel pin means extending through the axial row of parts and having formed therein a venting passage communicating at one end with the pressure control chamber,   orifice means for sensing a pressure gradient in the pump, and a servo valve in the pump responsive to changes in the pressure gradient controlling the other end of the venting passage to a zone of reduced pressure,   thereby to selectively unload the end plate for by-passing the outlet portions of the pump directly to the inlet portions of the pump adjacent   
     
     
        the sealing face. 14. In a pump having a return line, a valve in said return line having a tapered spool movable in a valve bore having lands and recesses,   spring means initially loading said spool in one direction,   means forming an orifice in said return line through which fluid in the return line is directed, said spool being movable as a function of the pressure drop across said orifice,   and by-pass means comprising a pressure-loaded end plate having a sealing face forming one wall of a pumping chamber and having a motive surface loaded by fluid at pump-generated pressure,   a venting passage for venting the pressure acting on said motive surface,   said valve controlling said venting passage by gradually opening the passage due to the tapered surface, thereby to trigger a movement of the end plate to directly by-pass the outlet portions of the pump to the inlet portions thereof,     said valve moving a significantly greater distance than said end plate to maintain a flow level, thereby to provide a servo ratio effect in the flow control regulation of     
     
     
        said pump. 15. In a pump, .Iadd.a housing, .Iaddend.   a cam ring .Iadd.in said housing .Iaddend.forming a pumping chamber for a fluid displacement means operable in said pumping chamber,   a cheek plate for sealing against said cam ring, thereby to seal the pumping chamber,   .[.means including.]. .Iadd.said housing and .Iaddend.said cheek plate forming a static chamber receiving fluid at pump-generated pressure and whereby said cheek plate is pressure-loaded against said cam ring,   and venting means for said chamber including a venting passage and a servo valve in control of said venting passage and forming the master valve of a control system wherein the cheek plate forms a slave valve, .Iadd.   means for sealing said static chamber against fluid flow except for said venting means and said fluid receiving means in said static chamber including a seal between said housing and said cheek plate, .Iaddend.   orifice means externally of said static chamber in the pumping circuit of the pump for developing a pressure gradient independently of the pressure in said static chamber upon buildup of pressure in the pump outlet caused by normal parasitic losses in a downstream hydraulic flow circuit,   and means for actuating said servo valve as a function of the pressure drop across said orifice means, thereby to vent said chamber to unload the cheek plate .Iadd.resulting in movement of said cheek plate relative to said housing and modulation of     
     
     
        .Iaddend..[.and modulate.]. pump flow output. 16. In a pump as defined in claim 15, said servo valve being actuated by pressure drop across an orifice formed in the outlet line of the pump and through which fluid at 
     
     
        pump-generated pressure is directed. 17. In a pump as defined in claim 15, said servo valve being actuated by pressure drop across an orifice formed in the return line of the pump and through which spent fluid is directed 
     
     
        on the return line side of the pump. 18. In a pump as defined in claim 15, housing means and reservoir means successively outwardly adjacent said cam ring, and openings in said housing means forming conduits for flow from the reservoir and being disposed so that the fast by-pass over the cam ring from the plate lift inducts out from the reservoir to accomplish 
     
     
        super-charge. 19. The method of flow control in a pump which comprises the steps of pressure loading a cheek plate with fluid at pump-generated pressure to form a seal between the inlet and outlet portions of the pump,   directing the fluid discharged by the pump at pump-generated pressure to a point of utilization and returning the spent fluid to the pump,   sensing a pressure gradient on opposite sides of an orifice, selectively venting the pressure acting on the cheek plate by using a servo valve,   and actuating the servo valve in accordance with the changing pressure drop through the orifice occurring with varying pump speed,   thereby to unload the cheek plate and allowing the outlet portions of the pump to by-pass directly to the inlet portions thereof at the cheek plate, said method being further characterized by actuating the servo valve by   
     
     
        the pressure drop across an orifice in the pump return line. 20. In a pump having a pressure-loaded cheek plate sealing the respective inlet and outlet portions of a pumping chamber containing fluid displacement means, the improvement of a servo valve for venting the pressure acting on the cheek plate,   means forming an orifice in the return line of the pump and through which spent fluid is directed on the return line side of the pump,   and means for referencing the servo valve to the pressure drop across said orifice,   whereby upon loading the cheek plate the outlet portions of the pump will   
     
     
        be by-passed directly to the inlet portions thereof. 21. In combination, a pump having housing means forming a pumping chamber having inlet and outlet portions,   rotary fluid displacement means in said pumping chamber for moving the fluid at increased pressure from the inlet to the outlet portions,   a cheek plate adjacent said pumping chamber having a sealing face for sealing the inlet and outlet portions during operation of the pump,   means including said housing forming a pressure control chamber behind said cheek plate to load said cheek plate with fluid at pump-generated pressure,   means including said housing forming a return line for said pump receiving spent fluid returned to the pump,   means forming an orifice in said return line and through which spent fluid is directed on the return line side of the pump,   and a servo valve controlling a passage in said housing venting said pressure control chamber to a zone at lower pressure in response to the pressure drop across said orifice, thereby unloading the cheek plate and directly by-passing the outlet portions of the pump to the inlet portions adjacent the sealing face of the cheek plate. .Iadd.22. In a pump having a nonrotatable axially movable pressure-loaded cheek plate sealing the respective inlet and outlet portions in a pump containing rotary fluid displacement means, the improvement of     means forming a static cavity behind said cheek plate,   means forming a venting passage from the static cavity to a zone at a reduced pressure,   pumping circuit means forming a pump outlet and a pump return for placing the pump in a pumping circuit,   means forming a flow control orifice in said pumping circuit means,   a servo valve for controlling said venting passage and thus venting the pressure in said static cavity acting on the cheek plate,   whereby the cheek plate will act as a slave and the servo valve will act as the master to establish a servo ratio effect,   and means for referencing the servo valve to the pressure drop across said orifice, whereupon unloading the cheek plate the outlet portions of the pump will be by-passed directly to the inlet portions thereof to modulate the pump flow output,   said means forming an orifice forming said orifice in the return line of the pump and through which spent fluid is directed on the return line side of the pump. .Iaddend. .Iadd.23. In a pump having a nonrotatable axially movable pressure-loaded cheek plate sealing the respective inlet and outlet portions in a pump containing rotary fluid displacement means, the improvement of   means forming a static cavity behind said cheek plate,   means forming a venting passage from the static cavity to a zone at a reduced pressure,   pumping circuit means forming a pump output and a pump return for placing the pump in a pumping circuit,   means forming a flow control orifice in said pumping circuit means,   a servo valve for controlling said venting passage and thus venting the pressure in said static cavity acting on the cheek plate,   whereby the cheek plate will act as a slave and the servo valve will act as the master to establish a servo ratio effect,   and means for referencing the servo valve to the pressure drop across said orifice, whereupon unloading the cheek plate the outlet portions of the pump will be by-passed directly to the inlet portions thereof to modulate the pump flow output,   said servo valve comprising a spool valve having a tapered spool movable in a bore having lands and recesses,   spring means initially loading said spool in one direction, said spool controlling the venting passage by gradually opening the passage due to the tapered configuration,     thereby to produce an axial movement of the cheek plate but through a significantly lesser distance than the corresponding movement of the spool to maintain a flow level corresponding to a servo ratio effect in the flow   
     
     
        regulation of the pump. .Iaddend..Iadd.24.  In a pump having a nonrotatable axially movable pressure-loaded cheek plate sealing the respective inlet and outlet portions in a pump containing rotary fluid displacement means, the improvement of means forming a static cavity behind said cheek plate,   means forming a venting passage from the static cavity to a zone at a reduced pressure,   pumping circuit means forming a pump output and a pump return for placing the pump in a pumping circuit,   means forming a flow control orifice in said pumping circuit means,   a servo valve for controlling said venting passage and thus venting the pressure in said static cavity acting on the cheek plate,   whereby the cheek plate will act as a slave and the servo valve will act as the master to establish a servo ratio effect,   means for referencing the servo valve to the pressure drop across said orifice, whereupon unloading the cheek plate the outlet portions of the pump will be by-passed directly to the inlet portions thereof to modulate the pump flow output,   means forming a metering passage from a source of pump generated pressure to said static cavity,   and means forming a metering orifice for said metering passage. .Iaddend.   
     
     
        .Iadd.25.  A pump for supplying fluid to a system comprising, a housing having an inlet and an outlet, said housing defining a pumping chamber,   pumping means in said chamber operable to pump fluid from said inlet to said outlet, said pumping means including pumping elements which define a series of pumping pockets which expand and contract to effect pumping of fluid,   a cheek plate having one axial side adjacent to and facing said pumping means and being supported in said housing, said cheek plate having a sealing position blocking fluid communication between said pockets and being axially movable therefrom to enable fluid to flow directly between said pockets and by-pass the system,   spring means for biasing said cheek plate into said sealing position,   said housing at least in part defining a cavity on the other axial side of said cheek plate,   a fluid passage for directing a flow of fluid from said outlet into said cavity for urging with said spring  means said cheek plate into said sealing position,   a seal between said cheek plate and said housing blocking flow into said cavity except through said fluid passage, an orifice in said outlet and through which fluid flows to the system,   valve means for venting the fluid pressure in said cavity to enable said cheek plate to move away from said pumping means, said valve means including a movable valve member having surfaces acted upon by fluid pressures on opposite sides of said orifice and which is movable to control the pressure in said cavity to control the position of said cheek plate and thereby control the flow of fluid to the system. .Iaddend..Iadd.26. A pump as defined in claim 25 wherein said valve means comprises a valve spool movable to vent said cavity to said inlet to enable said cheek plate to move axially away from said pumping means and wherein said orifice is defined by a surface portion carried by said valve spool and a surface portion carried by said housing. .Iaddend..Iadd.27. A pump as defined in claim 25 wherein said valve means comprises a valve spool having at least two axially spaced lands, a first land cooperating with a first port communicating with said cavity and which when moved past said first port creates a fluid flow from said cavity through said port past said land, and a second land for at least temporarily blocking communication between the pump outlet and pump inlet. .Iaddend..Iadd.28. A pump as defined in claim 27 wherein said valve spool is located in axial alignment with said orifice, and said valve spool has a projection extending therefrom, said orifice being defined in part by the outer surface of said projection, said projection having a passage therethrough for communicating the system pressure on one side of said orifice to one portion of the valve spool while outlet pressure on the other side of said orifice acts on another portion of said valve spool. .Iaddend. .Iadd.29. A pump as defined in claim 28 wherein said cheek plate is nonrotatable and said fluid passage for directing flow into said cavity comprises a passage through said cheek plate and which passage has an orifice therein.