Suspension system with axle oscillation circuit

Abstract

A suspension system for a heavy duty crane, excavator or the like is provided with a transverse rear axle and semi-independent suspension by hydraulic cylinders. The cylinders are pivotally attached adjacent the ends of the axle to allow oscillation in a traveling mode simulating a bolster, center pinned type system. The extend sides of the cylinders transfer hydraulic oil through an exchange line to accommodate true oscillation movement. In a working mode, locking valves block the flow of oil between the cylinders to establish a stabilized platform. A hydraulic/pneumatic accumulator communicates with the exchange line in the travel mode for cushioning of the ride. A third locking valve in a bypass return line communicating with the retract sides of the cylinders blocks the oil flow back to the reservoir in the working mode, but upon release by the control circuit is opened to communicate with the reservoir and maintain back pressure to enhance oscillation and prevent cavitation. The set up valve differentially pressurizes the extend and retract sides of the cylinders to select and maintain a desired height during the working and traveling modes. The three locking valves are actuated by an electrical control circuit, which also includes an interrupter switch responsive to the movement of a component of the vehicle, such as a working boom. The support cylinders are mounted outboard of the main frame rails with the center of the axle being free of attachment and a pivotal 4-bar assembly provided to limit lateral movement of the axle. Components of the hydraulic oscillation circuit are mounted in the free space above the center of the axle.