A RESEARCH ON STEERING WHEEL CONTROL STRATEGY AS A MAN-MACHINE INTERFACE FOR A STEER-BY-WIRE VEHICLE

摘要

Present steering systems are the parallel link type, wherein the independent right and left axles of the front wheel are supported by the suspension, and the knuckle arms are connected by the tie-rods. The steering wheel is used for the interface with the driver. Disturbance from the road is suppressed and steering wheel torque is reduced because the reduction ratio is enlarged by use of a steering wheel. Furthermore, power steering systems such as the rack-and-pinion type and ball-screw type began to be mass-produced since 1926. However, intelligent steering function having integrated control with other chassis and drive systems is required in addition to independent steering systems. The Steer By Wire (SBW) system has been developed as a steering system that achieves this function. Since the operation of the steering gear is electronically controlled in the SBW system, it is possible for safe and comfortable vehicle motion control to be automated. Since there is no mechanical linkage between the steering wheel and steering gear in a SBW system, it is easy to avoid interference between the steering system and driver operating active front steering control, which was difficult with a conventional steering system. It has been confirmed in a full braking test on a μ-split road that the stabilization performance of the vehicle by the SBW system is better than that of other practical active stability control systems using the distribution of driving and braking force. (1)(2) In conventional steering systems, the amount of steering wheel torque and its value or continuousness has been focused on steering design technique to improve the usability of steering systems equipped with a steering wheel. Therefore, steering wheel torque and steering wheel angle in operation of the steering wheel have not been designed taking into account the driver’s characteristics because it is a precondition that reactive torque from the road surface is transmitted to the driver through the mechanical linkage in conventional steering system. On the other hand, since there is no mechanical linkage between the steering wheel and steering gear in SBW, the degree of freedom of the design rises greatly. In a conventional steering system, the torque characteristic and manoeuvrability have been influenced by elements such as suspension geometry and road surface conditions, which are not related to the steering system. In SBW, it is possible that fine manoeuvrability and torque characteristics can be applied to the driver by controlling information appropriately. The feasibility of intelligent usability in SBW different from in the conventional system was studied. The relation between various elements concerning the vehicle and its relation with the driver, such as between the driver and vehicle behavior, should be clarified. A steering system as a man-machine interface that feeds back the physical characteristics of the vehicle and environmental characteristics of the road to the driver more linearly was researched.