Hydraulic system for a towed implement

摘要

A hydraulic rockshaft control circuit which includes a three-way valve that normally operates the rockshaft is connected to the lift cylinder on a trailing implement. A hitch lock valve connected to the rockshaft control valve maintains the rockshaft in a preselected position regardless of changes in pressure at the valve output. The extend side of the lift cylinder is connected to the control valve output so that the tractor hitch control is used to operate the trailing implement cylinder. To overcome the inability of the three-way valve to positively retract the trailing implement cylinder, a reducing/relieving valve is connected to the retract side of the cylinder and is adjusted to provide just enough pressure to retract the cylinder and raise the implement wheels from ground contact when the extend side is connected to return pressure. A position feedback system on the implement is connected to the hitch control unit (HCU) on the tractor. When the HCU senses a feedback signal from the implement, the HCU control mode changes from rockshaft control to trailing implement control wherein implement position is set and maintained in a manner similar to that for the conventional rockshaft control. A voltage readout from the feedback signal provides a visual indication of implement position.