Electro-hydraulic pump control system

#This invention relates to an electro-hydraulic pump control system for controlling displacement of a pump. More particularly, the invention is directed to a method and system for electro-hydraulic pump control that utilizes pump characteristics determined from an operation of the pump.

#A pump having a variable displacement capability is well known in the industry to drive an implement or a hydrostatic motor. In an open-loop hydraulic system, a variable displacement pump is used to drive an implement, such as a cylinder or a hydraulic motor, and the fluid pressure from the pump to the implement is controlled by varying the displacement of the variable displacement pump. In a closed-loop hydrostatic system, similarly, a variable displacement pump is used to drive a hydrostatic motor in the forward or reverse direction, and the speed of the hydrostatic motor is controlled by varying the displacement of the pump.

#A variable displacement pump generally includes a drive shaft, a rotatable cylinder barrel having multiple piston bores, and pistons held against a tiltable swashplate biased by a centering spring. When the swashplate is tilted relative to the longitudinal axis of the drive shaft, the pistons reciprocate within the piston bores to produce a pumping action. Each piston bore is subject to intake and discharge pressures during each revolution of the cylinder barrel. As the piston bores sweep pass the top and bottom center positions, a swivel force is generated on the swashplate as a result of the reciprocating pistons and pressure carryover within the piston bores. Some hydrostatic pumps have eliminated the actuator and/or cut-off valves by controlling swivel forces and actuator pressure. In order to accurately control the pump displacement, however, it may be necessary to provide a closed logic on the pump displacement and/or pressure, which increases manufacturing cost and reduces reliability.

#The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description, serve to explain the principles of the invention.

#FIG. 1A illustrates a schematic and diagrammatic representation of an electro-hydraulic pump control system according to one embodiment of the present invention;

#FIG. 1B is an enlarged view of a portion of the electro-hydraulic pump control system of FIG. 1A;

#Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

#FIG. 1 illustrates one embodiment of the pump control arrangement for controlling displacement of a variable displacement pump coupled to a load 12, such as implement devices including cylinder pistons, hydraulic motors, or for example, other implement devices apparent to one skilled in the art. Open loop system 10 for driving implement devices 12 includes a variable displacement pump 14 and a pump control system 16 for controlling displacement of the pump 14. The pump 14 is fluidly connected to the implement devices 12 via a supply conduit 22 and an implement control valve 24 for driving the implement devices 12. The pump 14 is driven by a motor, such as an engine, via a drive train 11, and receives fluid from a reservoir 18. The pump 14 has a pressure outlet port 20 connected to the supply conduit 22, and can vary its displacement between minimum and maximum displacement positions. By changing the displacement, the pump 14 can provide necessary fluid pressure to the implement devices 12.

#In an exemplary embodiment, the pump 14 also has a pump speed sensor 13 that can measure the speed of the pump 14. The speed of the pump 14 can be measured by monitoring the drive train 11 or by any other method known to those having ordinary skill in the art. In addition, the pump 14 may have a pump pressure sensor 15 for measuring fluid pressure at the outlet port 20. Similarly, the implement 12 may have a load pressure sensor 17 that can monitor fluid pressure at the implement 12.