Deflection reduction module for boom hoist cylinder of mobile crane

Abstract

A mobile crane comprises a vehicle chassis mounted on balloon tires, a crane boom pivotally mounted on the chassis, and a double-acting boom hoist cylinder connected between the chassis and the boom for raising and lowering the boom. As the mobile crane traverses rough terrain or accelerates or decelerates, its mass causes the chassis to deflect (bounce or porpoise) relative to the terrain. A deflection reduction system, which presupposes that the boom is unrestrained and free to pivot (deflect) relative to the chassis, comprises a deflection reduction module mechanically mounted on the outside of the boom hoist cylinder and selectively operable valves for hydraulically connecting the module thereto. The module comprises a gas barrel containing compressed gas, a gas piston slidably mounted therein, a hydraulic fluid barrel axially aligned with the gas barrel, a hydraulic fluid piston (of smaller area than the gas piston) slidably mounted therein and connected to the gas piston, and a helical compression spring in the gas barrel for biasing the pistons in the same direction as the compressed gas. Operation of a first solenoid valve mounted on the outside of the boom hoist cylinder isolates the double-acting boom hoist cylinder and interconnects its opposite ends in a closed circuit. Simultaneous operation of a second solenoid valve mounted on the outside of the module connects the closed circuit to a fluid inlet/outlet port in the hydraulic fluid barrel. As a result, boom deflection causes hydraulic fluid flow into and out of the hydraulic fluid barrel. The resulting reaction of the spring and the compressed gas reduces deflection of the chassis.