Patent ID: 8636082

Claim:
A pile driver comprising: a leader having a bottom and a top; a press-in winch which lowers an operation unit towards the bottom of the leader, the press-in winch having a brake with a drum; and an elevation winch which elevates the operation unit towards the top of the leader, the elevation winch having a brake with a drum; wherein a hydraulic circuit of the press-in winch and a hydraulic circuit of the elevation winch are respectively provided with a torque changing solenoid valve which switches the torque of each winch to previously set low torque compared to high torque for winding and a brake release solenoid valve which releases the brake of each winch, wherein high torque is a fully-engaged state and low torque is a semi-engaging state in which the respective drum will be held but move in response to an opposing winch in high torque; and an electric circuit having a switching switch to operate each solenoid valve is provided so that the electric circuit respectively sets the torque changing solenoid valve of the press-in winch into a low torque state, the brake release solenoid valve thereof into a brake release state, the torque changing solenoid valve of the elevation winch into a high torque state, and the brake release solenoid valve thereof into a brake state, when the switching switch is switched to an operation unit elevating position; and respectively sets the torque changing solenoid valve of the press-in winch into a high torque state, the brake release solenoid valve thereof into a brake state, the torque changing solenoid valve of the elevation winch into a low torque state, and the brake release solenoid valve thereof into a brake release state, when the switching switch is switched to an operation unit lowering position.