HYDROSTATISK DRIVANORDNING FOR KRANAR O D MED ANORDNING FOR ATT FOREKOMMA RYCK VID START MED HENGANDE LAST

摘要

A fluid pressure drive system for rotating a lifting device such as a winch includes a fluid motor having a drive shaft adapted to be connected to the winch which is engaged by a brake which may be actuated to stop the shaft by biasing means such as a spring. The fluid motor is driven by a pump which has a fluid pressure discharge connected to the motor which is also connected through a line to an accumulator. During pump operation the accumulator is charged with the pump operating pressure through a one way valve so that the accumulator stores the operating pressure during the operation of the motor to move the winch. The brake is released by forcing a fluid piston against the force of its biasing means to a releasing direction under the influence of actuating pressure which is supplied from a separate actuating pressure source. The actuating pressure source is connected through a control valve to a throttle and to a fluid pressure cylinder in which the fluid pressure piston which actuates the brake is movable. When the brake is applied the control valve is set so that the cylinder is vented to the atmosphere so that the biasing means may press the piston into an operative or brake engagement position. When the pump driving the fluid motor which operates the winch is stopped the control member is actuated to provide an actuating pressure connection through the throttle and to the control cylinder but also to a release valve for the accumulator pressure which is first connected to the line connected between the pump discharge and the motor to insure that the motor is held under operating pressure. The throttle in the line between the valve control and the brake control cylinder is set to regulate the pressure to the brake control cylinder in order that the brake may be released only after the accumulator pressure is communicated to the drive motor in order to insure that the drive motor is not subjected to the immediate loading of the winch would would cause a rapid unwinding of the winch.