Supplemental steering control for a differential steer machine

Abstract

A supplemental steering control is provided for use in a machine that is normally steered by a differential steer mechanism. A second source of pressurized fluid and an independently controlled brake actuator mechanism function to control steering in the event a first source of pressurized fluid fails. By interconnecting the fluid ports of a fluid actuated steer motor when the first source of pressurized fluid fails, the fluid actuated motor is permitted to freely rotate. A single steering control valve is used to control steering during normal use and also during supplemental steering. The independently controlled brake actuator mechanism is connected to the steering control valve and acts to selectively direct pressurized fluid from the second source of pressurized fluid to respective ones of first and second fluid actuated brake mechanisms. Since the fluid operated steer motor is free to rotate, braking of one of the output drives slows its rotation relative to the other output drive thus causing the machine to turn in the desired direction. The subject supplemental steering control uses a common steering control valve and permits the use of existing service/parking brakes to provide the needed steering of the machine in the event the first source of pressurized fluid fails.