A pumping system includes a first variable displacement pump having a first inlet and a first outlet. The first outlet is fluidically connected to a system outlet. A first actuator is mechanically coupled to a first displacement mechanism of the first variable displacement pump A second variable displacement pump includes a second inlet and a second outlet. The second outlet is fluidically connected to the system outlet. The pumping system also includes a second actuator mechanically coupled to a second displacement mechanism of the second variable displacement pump. An electrohydraulic servo valve is hydraulically connected to the first and second actuators. An electronic engine controller is in communication with the electrohydraulic servo valve and is configured to send electrical current to the electrohydraulic servo valve to drive the first actuator and the second actuator.

A pump control system, comprising: a motor (12) configured to drive a pump (14); a pressure relief valve (22) in fluid communication with the pump (14); a torque control valve (32) connected to a swashplate of the pump (14) and in fluid communication with the pressure relief valve (22); a swashplate angle sensor (36) connected to the swashplate (34); and a computer (40) connected to the swashplate angle sensor (36) and the pressure relief valve (22) wherein the computer (40) controls the pressure relief valve (22) based upon swashplate displacement to achieve maximum system pressure. The corresponding method of controlling is also disclosed.

A working vehicle provided with a fixed-capacity hydraulic pump driven by power from an engine and a working hydraulic actuator driven by working oil pumped from the fixed-capacity hydraulic pump is a rotary working vehicle which is provided with an electromagnetic relief valve for modifying the pressure of working oil from the fixed-capacity hydraulic pump, and the rotary working vehicle is such that if the actual number of revolutions (N) of the engine is reduced by a set number of revolutions (Ns) as the load on the engine increases, then the electromagnetic relief valve operates in accordance with the deviation (e) between the actual number of revolutions (N) of the engine and the specified number of revolutions (Ns), and the pressure of the working oil from the fixed-capacity hydraulic pump is modified.

A working vehicle provided with a fixed-capacity hydraulic pump driven by power from an engine and a working hydraulic actuator driven by working oil pumped from the fixed-capacity hydraulic pump is a rotary working vehicle which is provided with an electromagnetic relief valve for modifying the pressure of working oil from the fixed-capacity hydraulic pump, and the rotary working vehicle is such that if the actual number of revolutions (N) of the engine is reduced by a set number of revolutions (Ns) as the load on the engine increases, then the electromagnetic relief valve operates in accordance with the deviation (e) between the actual number of revolutions (N) of the engine and the specified number of revolutions (Ns), and the pressure of the working oil from the fixed-capacity hydraulic pump is modified.

In an embodiment, a variable flow pump may include a swashplate rotatably driven by a driveshaft. The swashplate may be movable between a first and second tilt angle relative to the driveshaft. A piston pump may be reciprocatingly driven by the swashplate based upon, at least in part, the tilt angle of the swashplate. An actuator piston may be moveable between a first and second position based upon, at least in part, a downstream backpressure of a fluid pumped by the piston pump. An actuator assembly may be moveable between a first and second position based upon, at least in part, the position of the actuator piston. The actuator assembly may include a swashplate driver configured urge the swashplate between the first and second tilt angles, and a biasing driver configured to apply a force urging the swashplate into contact with the swashplate driver.

In the hydraulic pump according to the present invention, a straight path among the paths, through which the fluid flows within the hydraulic pump, and a connection point on the straight path are formed to have curvatures, so that it is possible to prevent stress from being concentrated to the connection point, thereby improving durability, and it is possible to manufacture the hydraulic pump by forming a casting shape with a curvature in advance, thereby decreasing additional machining and decreasing costs of a product.

A servo piston assembly having a servo piston body mounted within a servo piston cylinder. A pair of bushings are mounted within each end of the servo piston body. An elongated bore extends through the servo piston body and receives a guide rod that extends out of the servo piston body and is received within the servo piston cylinder.

An axial piston pump may comprise a valve plate assembly including a plurality of valve plates rotatably disposed adjacent to each other and configured to control the flow of fluid between a piston chamber and inlet and outlet port passages. The piston pump may also comprise a swashplate arrangement that is capable of being angled in two different directions to be used in combination with the valve plate assembly. A fixed displacement axial piston pump may also comprise the valve plate assembly disclosed herein in which pressure transitions are facilitated in the same fashion, but without the variable of changing swashplate angles which control pump flow.

A double-headed piston type swash plate compressor includes a rotation shaft, a housing, a swash plate, two cylinder bores, a double-headed piston, and two shoes. The double-headed piston includes two shoe holders, a neck, two heads, and two coupling portions. At least one of the two coupling portions includes a load receiving portion. The load receiving portion is configured to receive bending load that is applied from the swash plate to the double-headed piston and acts toward an inner side in the radial direction. The load receiving portion is separated from the wall surface of the cylinder bore when load applied to the double-headed piston is less than a specific threshold value. The load receiving portion abuts against the inner wall of the cylinder bore and receives the bending load when the load applied to the double-headed piston is greater than the specific threshold value.

A double-headed piston type swash plate compressor includes a rotation shaft, a housing, a swash plate, two cylinder bores, a double-headed piston, and two shoes. The double-headed piston includes two shoe holders, a neck, two heads, and two coupling portions. At least one of the two coupling portions includes a load receiving portion. The load receiving portion is configured to receive bending load that is applied from the swash plate to the double-headed piston and acts toward an inner side in the radial direction. The load receiving portion is separated from the wall surface of the cylinder bore when load applied to the double-headed piston is less than a specific threshold value. The load receiving portion abuts against the inner wall of the cylinder bore and receives the bending load when the load applied to the double-headed piston is greater than the specific threshold value.