FOUR-WHEEL STEERING MECHANISM DESIGN FOR UNMANNED ELECTRIC SHUTTLE BUS

FOUR-WHEEL STEERING MECHANISM DESIGN FOR UNMANNED ELECTRIC SHUTTLE BUS

A four-wheel steering mechanism is proposed for an unmanned electric bus with identical driving characteristics in the forward and backward directions. The target steering parameters are defined with reference to existing vehicles, related theories, and vehicle design regulations. The basic layouts of the steering and suspension systems are first defined, with the hard points of the steering system positioned such that the desired wheel alignment is maintained throughout the entire travel range of the suspension system without interference. The lengths and position points of the steering linkages are adjusted according to mechanism geometry theory and Ackermann steering theory to ensure that the turning radius and Ackermann steering ratio meet the target values for both forward and backward movements of the vehicle. The validity of the proposed suspension and steering design is confirmed by comparing the wheel alignment parameters obtained in Adams/View full-vehicle simulations with those obtained from CAD simulations. The validated CAE model is then used to evaluate the steering performance in turning radius and steady-state cornering maneuvers using various values of the front-to-rear wheel steering angle ratio. Overall, the results confirm that the proposed design satisfies the requirement for a consistent handling performance when traveling in the forward and backward directions and reduces the road width requirement by up to 12.4% compared to a two-wheel steering design.