Hydro-electrical priority valve and speed control circuit

Abstract

The invention is concerned with an improvement in a hydrostatic auxiliary front wheel drive system for a vehicle which comprises a hydraulic implement pump, a hydraulic implement powered by the pump and motors drivingly connected to a front wheel shaft rotatable in a forward or a reverse direction, the motors being powered via motor conduits by the pump. The improvement of the invention comprises an electrical switch operating responsive to hydraulic pressure developed by the implement pump, the electrical switch a including biasing spring preventing switching thereof into a closed circuit position until the hydraulic pressure reaches a predetermined value and forcing the switch into an unswitched open circuit position when the hydraulic pressure drops below the predetermined value. Also part of the improvement is a valve in the motor conduits providing a pump hydraulic pressure shut-off mode, a forward direction mode leading to forward motion of the vehicle, and a reverse direction mode leading to reverse motion of the vehicle, the valve being constrained in the shut-off mode until the electrical switch switches into said closed circuit position. The improvement yet further comprises directional selection valves for selecting a respective one of the forward direction mode and the reverse direction mode when the switch is switched into the closed circuit position.

Dependencies are inferred from the claim text.