Rear drive inching control for a four wheel drive vehicle

Abstract

An inching system for use in a vehicle for performing work which permits the vehicle to be moved at reduced speeds while maintaining sufficient engine speed, and therefore, sufficient hydraulic fluid flow and pressure for actuating the work-performing apparatus. The inching system includes a control valve for controlling the amount of hydraulic fluid which a forward-reverse valve is able to direct to the rear drive means, an orifice through which hydraulic fluid flows from a source of hydraulic fluid to the control valve to restrict the flow of fluid to a level below that of the flow to the work-performing apparatus, and a variable inching valve for metering hydraulic fluid from the control valve so that fluid pressure available to the forward-reverse valve, and in turn, to the rear drive means, is progressively reduced. A pedal is provided in the cab of the vehicle to selectively actuate the variable inching valve to effect inching control. Depression of the pedal initially disconnects the front drive means so that only the rear drive means is operative, then opens the variable inching valve to progressively drain fluid from the control valve, then finally brakes the vehicle.