Abstract: An apparatus for controlling a variable displacement type hydraulic pump including an engine as a driving power source is disclosed. The subject invention detects the number of revolutions of the engine and the pressure of hydraulic oil delivered from the hydraulic pump, and sets a pump absorption torque characteristic which decreases in relation to the number of revolutions of the engine. The inclination angle of a swash plate in the pump is detected with reference to the pump absorption torque characteristic and the pressure of hydraulic oil delivered from the pump, and the swash plate in the pump can be controlled so as to assure its inclination angle; the number of revolutions of the engine can be reduced without the absorption torque of the hydraulic pump exceeding the allowable torque of the engine. When the controlled apparatus is utilized, the number of revolutions of the engine can be optimally reduced and fuel consumption cost reduced correspondingly.

Abstract: A fluid operated pump displacement control system is provided wherein a self pressure is defined as a first control signal, and characterized in that an arbitrary switchable second control signal different from the first control signal is added to the first control signal, and a displacement is adapted to be switched to a displacement corresponding to a value of the second control signal as added to the first control signal. Further, a fluid operated pump displacement control system is provided comprising a control circuit connected to respective displacement control devices of variable displacement pumps and adapted to be operated by discharge pressure fluid from a discrete control pump.

Abstract: A retarder brake automatic control system capable of causing a vehicle to run downhill at a speed set by a speed setter, in which a vehicle speed is automatically controlled by means of a microcomputer. The microcomputer includes a fault detector which detects abnormality in factors for safety running of the vehicle, and controls a retarder brake so as to cause the vehicle to run at an appropriate speed in accordance with the output of the fault detector.