Hydraulic system for controlling an attachment to a work machine such as thumb attachment used on an excavator

Abstract

A hydraulic control circuit for controlling the operation of an attachment or tool associated with a particular work machine wherein such circuit includes an actuator for controlling the operation of the attachment or tool, a control valve operable to control fluid flow to the actuator, a fluid path communicating the control valve with the actuator, and a pilot signal control device positioned in communication with both the control valve and a pilot pressure source and having a signal port in communication with the actuator for sensing the pressure associated therewith, the control device being responsive to the pressure associated with the actuator and being operable for sending a control signal to the control valve when a pressure condition in the actuator reaches a predetermined value, the control signal actuating the control valve so as to at least partially close such valve and maintain an operative pressure on the attachment actuator while, at the same time, decreasing the fluid flow through the control valve. Appropriate pressure reducing valves regulate fluid pressure to the attachment actuator, and regulate the control signal pressure to maintain a predetermined pressure differential between the signal ports of the control valve. This circuit configuration allows the remaining system pressure to be maintained above the maximum allowable attachment actuator pressure to operate other devices and/or functions associated with the work machine.