Safety device for hydraulic closed circuit

Abstract

A variable displacement hydraulic pump and a hydraulic motor are connected in a closed circuit. A pressure oil supply means includes the variable displacement hydraulic pump and a tilting controlling means for controlling a tilt angle of the hydraulic pump and supplies an amount of pressure oil corresponding to the tilt angle of the hydraulic pump to the hydraulic motor. When rotation of a prime mover is detected by a rotation detecting means, an opening and closing valve is changed over to a first position in which the pressure oil supply means is permitted to supply pressure oil. When stopping of the prime mover is detected by the rotation detecting means, the opening and closing valve is changed to a second position in which the pressure oil supply means is inhibited from supplying pressure oil. Upon starting of the prime mover, at least the opening and closing valve remains at the second position, and the tilting controlling means increases its tilt angle from its neutral position so that the pressure oil supply means supplies pressure oil. Consequently, upon re-starting of the prime mover, pressure oil is prevented from being supplied inadvertently to the hydraulic motor, and the safety upon starting is assured.