Caterpillar Inc.

Joseph P Reilly

John C Endsley

C Nickolas Goloff

William F Guse, Jr

Known all wheel steer arrangements use standard spool-type valves which are inherently subject to leakage that results in the front and rear wheels getting out of synchronization due to the leakage. In the subject invention, a hydraulic system has front and rear pairs of steerable wheels respectively interconnected by front and rear fluid actuated mechanisms. A steering valve delivers pressurized fluid to the front fluid actuated mechanism for steering of only the front pair of wheels and to both the front and rear fluid actuated mechanisms to steer the front and rear pairs of wheels simultaneously but in opposite directions. Furthermore, a rear steer valve mechanism is provided to independently direct pressurized fluid to the rear fluid actuated mechanism to steer the rear pair of wheels independent of the front pair of wheels. A normally open pilot operated poppet valve and a pair of normally closed pilot operated poppet valves are utilized to provide control for the various modes of operation and to provide separation of the fluid between the front and rear fluid actuated mechanisms when they are being operated independently. By utilizing pilot operated poppet valves, the leakage thereacross is substantially reduced and the synchronization between the front and rear pair of wheels is generally maintained.

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Oak Park, IL, United States of America

Joseph P Reilly