True crab steering apparatus

摘要

A mobile lift having extendable axes that is capable of switching between front-wheel steer, rear-wheel steer, all-wheel steer, and crab steer without resulting in undesirable tire scrubbing or unfavorable steering geometry. One embodiment provides a mobile personnel lift having a chassis supported by steerable front and rear wheel sets. The steerable wheel sets are mounted on axles that are extendable and retractable. A double-acting hydraulic cylinder is pivotally coupled between each steerable wheel and its corresponding axle for turning the wheel. A microprocessor controls the flow of hydraulic fluid to the hydraulic cylinders. Sensors positioned adjacent to each wheel measure the angular position of each wheel relative to the chassis, and transmit this information to the microprocessor to synchronize the wheels as required to provide the optimum steering geometry for the selected mode.