Search Results

In complying with a customer demand for improving low-speed maneuverability of commercial vehicles in narrow streets, a medium-duty truck with a mechanical linkage type four-wheel steering system with a hydraulic assist and a steering lock device is developed. A mode select gearbox allows a driver to select one of three rear-wheel steering modes; 2WS, same-phase 4WS, and opposite-phase 4WS. The steering lock device is locked during 2WS operation for preventing rear-wheel steering. An electronic control system is applied for easier mode selection, synchronization of locking and unlocking the steering lock device with a mode select operation, and vehicle speed limitation during 4WS operation. We made efforts particularly to suppress vehicle yaw motion when the vehicle is running in the same-phase 4WS mode. Several innovative new mechanisms are incorporated on this vehicle. This paper deals with these mechanisms and these functions.

Because of smaller ratios of tread to height of gravitational center, longer wheel-bases, and larger moment of inertia, vehicle roll is the most important characteristics governing truck controllability and stability. And longer wheel-bases result in a reduction in vehicle body torsional stiffness. Hence, the influence of vehicle body torsional stiffness on vehicle roll characteristics is investigated. We carried out a simulation analysis and vehicle test on medium-duty trucks, in studying the vehicle frequency response characteristics by changing vehicle design parameters. The results show that a reduction in body torsional stiffness increases the steady state gain of the front roll angle without affecting the yaw and lateral characteristics of vehicle motion. Accordingly, even if body torsional stiffness is unavoidably lowered, reducing the front roll angle by increasing the roll stiffness of the front suspension can maintain appropriate vehicle controllability and stability.

This study establishes the feasibility of improving the motion characteristics of commercial vehicles by applying rear axle steering. A model-matching control algorithm for rear axle steering was used to achieve the desired yaw rate response to steering action. Simulations with a two-degree-of-freedom model evaluated the effectiveness of the control method. Results of vehicle tests on an experimental medium-duty truck with rear axle steering proved that this control method can improve vehicle yaw response. However, the simulation results did not well represent the vehicle test results, because the simulation model was too simple. Adding the roll effect to the model reduced the discrepancy between the simulation and vehicle test results.