Kabushiki Kaisha Komatsu Seisakusho

Shoichiro Inatomi

Mitsuru Arai

Hideyori Sato

A hydraulic circuit is disclosed for driving a bidirectional hydraulic motor from a pump via a hand operated directional control valve, as for propelling an earthmover or actuating an implement assembly thereon. For mitigating an abrupt pressure rise as when the motor is set into or out of rotation, the circuit has a pair of oppositely directed dual pressure relief valves connected in parallel with each other between a pair of main lines extending between motor and directional control valve. Each dual pressure relief valve is normally conditioned to pass at a predetermined lower pressure the pressurized fluid from one of the main lines and to pass at a predetermined higher pressure the pressurized fluid from the other main line. When pilot operated from a timing valve responsive to a pressure differential between the main lines, that one of the relief valves which has been bleeding off the pressurized fluid at the low pressure is closed, with the result that the pressurized fluid is then released at the high pressure through the other relief valve, thereby causing two stepwise pressure rises for the reduction of a shock. The invention proposes the provision of a variable resistor between the timing valve and each main line for variably delaying the pilot actuation of the relief valves by the timing valve.

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Yokohama, Japan

Shoichiro Inatomi