Abstract: A flushing valve system suitable for use in a closed circuit hydrostatic transmission including a variable displacement hydraulic pump, a hydraulic actuator and two main lines. The flushing valve system includes poppet valves mounted in passages for respectively communicating the main lines with a fluid tank, passages mounting throttles for causing the pressure in the main lines to act on pressure chambers to keep poppets of the poppet valves from moving to an open position, and a change-over valve responsive to the pressure differential between the main lines to communicate the pressure chamber of the poppet valve connected to the main line on the lower pressure side with the fluid tank. The poppet valve connected to the main line on the lower pressure side opens when a predetermined pressure level is exceeded by the pressure in the main line, to thereby allow working fluid in the main line to be drained to the fluid tank.

Abstract: A control system for a hydrostatic power transmission having a variable displacement hydraulic pump (2) and a hydraulic actuator (3) connected in a closed or semi-closed circuit, wherein the displacement of the pump or the delivery thereby is adjustable in accordance with a manipulated variable of an operating lever (13). A control unit of the system (16) is operative to calculate a hydraulic pump displacement command (X) on the basis of a manipulated variable signal (X.sub.

Abstract: A hydraulic drive system including a main line, a variable displacement hydraulic pump and another main line connected to a single rod cylinder in a closed hydraulic circuit, and a flushing valve having a first switching position in which one main line is communicated with a low pressure line and a second switching position in which the other main line is communicated with the low pressure line. The flushing valve is operative to maintain at least one of the two main lines in communication with the low pressure line at all times while moving from one switching position to the other switching position, to keep a lock-up phenomenon from taking place in the closed hydraulic circuit. The system further includes a pressure generating device for generating between the two main lines a pressure differential necessary for effecting switching of the flushing valve.

Abstract: A circuit pressure control system for a hydrostatic power transmission having a variable-displacement hydraulic pump driven by a prime mover, a hydraulic actuator for actuating a load and a displacement adjusting mechanism for the hydraulic pump. The hydraulic pump and actuator are connected together in closed or semi-closed circuit, and the displacement adjusting mechanism is actuated by a signal indicative of the operating lever manipulated variable and a signal indicative of the actual displacement of the hydraulic pump to control the speed of the hydraulic actuator.

Abstract: An automatic neutral point detecting system for a hydraulic pump equipped with a displacement varying device capable of shifting both in a (+) direction and in a (-) direction and connected to at least one hydraulic actuator to form a hydraulic circuit to drive the hydraulic actuator. The system includes pressure sensors for sensing the port pressures of the hydraulic pump, a shifting detector for detecting the shifting of the displacement varying device, a closing device for closing the hydraulic circuit and blocking the flow of a hydraulic fluid, a start switch for giving a command to start detection of the neutral point of the hydraulic pump, and a control unit for detecting the neutral point of the hydraulic pump.

Abstract: A failure detection system for a hydraulic pump (1) having a displacement volume varying device (1a) and connected to at least one hydraulic actuator (4) to constitute a hydraulic circuit for driving the hydraulic actuator. The system includes means (7a, 7b) for sensing the discharge pressure of the pump, means (6) for detecting the value of shifting of the displacement volume varying device, means (5, 24) for closing the hydraulic circuit to block the flow of a hydraulic fluid through the circuit, starting means (9) for giving a command to start checking on the pump to see if it is normally functioning, and a control unit (2, 23, 28, 29) for performing checking on the pump to see if it is normally functioning. The control unit includes means (S-5, S-5') responsive to the command given by the starting means for giving a command to activate the closing means, data collecting means (S-11) for causing the displacement volume varying device to shift based on information (P.sub.a, P.sub.

Abstract: A control method and a control system for a hydrostatic drive system including a variable displacement hydraulic pump and a hydraulic actuator connected together to form a closed hydraulic fluid circuit. When the flow rate of the hydraulic pump is increased, the rate of change in the tilt of the hydraulic pump is controlled so that the discharge pressure does not exceed a first set of preset values with respect to the flow rate of the pump, meanwhile when the flow rate of the pump is reduced, the rate of change in the tilt of the hydraulic pump is controlled so that the suction pressure does not exceed a second set of preset values with respect to the flow rate of the pump.

Abstract: A control method of a system for generating hydraulic power, the system including an internal combustion engine controlled by fuel injection from a fuel injection pump, and a plurality of hydraulic pumps of the variable displacement type. An engine speed deviation is obtained by calculating a difference between a target engine speed set by a manipulated variable of an accelerator for the internal combustion engine and an output engine speed of the engine. The engine speed deviation is converted into a pump control coefficient which is in a functional relation with this deviation. A calculation is performed with the converted value and an externally manipulated variable for inclination of a swash plate of the hydraulic pump, and the calculated value is supplied to a regulator of the hydraulic pump as a target value for inclination of the swash plate thereof to thereby control the inclination angle of the swash plate of the hydraulic pump.

Abstract: A drive system for construction machinery in which hydraulic circuit is provided with a plurality of variable-displacement hydraulic pumps and a plurality of hydraulic actuators, each pump being connected in closed circuit to one or a plurality of the actuators via a solenoid-operated valve or valves to drive a movable member or members connected to the actuator or respective actuators when pressurized fluid is supplied to the actuator or actuators from the pump. At least one of the selected hydraulic actuators is further connected in closed circuit through a solenoid-operated valve to at least one of the hydraulic pumps other than the hydraulic pump which is connected in closed circuit to the hydraulic actuator. The hydraulic circuit means is controlled such that timing for switching the solenoid-operated valves is controlled in conjunction with the operation of the pump so as to absorb the shock which would otherwise be produced when each actuator is rendered operative and inoperative.