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The research described in this paper aimed to study the cornering resistance and dissipation power on the tire contact patch, and to develop an efficient direct yaw moment control (DYC) during acceleration and deceleration while turning. A previously reported method [1], which formulates the cornering resistance in steady-state cornering, was extended to so-called quasi steady-state cornering that includes acceleration and deceleration while turning. Simulations revealed that the direct yaw moment reduces the dissipation power due to the load shift between the front and rear wheels. In addition, the optimum direct yaw moment cancels out the understeer augmented by acceleration. In contrast, anti-direct yaw moment optimizes the dissipation power during decelerating to maximize kinetic energy recovery. The optimization method proved that the optimum direct yaw moment can be achieved by equalizing the slip vectors of all the wheels.

Steer-by-wire is a system that can independently control steering-wheel torque and vehicle-wheel steering angle. The object of this research was to realize a vehicle that can be driven according to driver's intention in any situation, such as in a crosswind, and rutted road surface. Using a steer-by-wire system, disturbance torque from the vehicle-wheels is not transmitted to the driver, signifying that the steering-wheel angle always indicates driver intention. Also, since unexpected feelings by active steering controls are reduced, feedback controls for the target vehicle behavior are easily realized. This research achieved good characteristics from steering-wheel angle to lateral acceleration by studying response characteristics using a vehicle equipped to measure lateral acceleration feedback.

Improvement of vehicle dynamics in limit cornering have been studied. Simulations and tests have verified that vehicle stability and course trace performance in limit cornering have been improved by active brake control of each wheel. The controler manages vehicle yaw moment utilizing difference braking force between left and right wheels, and vehicle deceleration utilizing sum of braking forces of all wheels.

This paper presents a new method for estimating the ambiguous change in a 4WS control system using a failure detection filter. This filter is designed to discriminate ambiguous failure modes in the control system by processing output errors between sensors and an observer. The result of the experiments using a 4WS vehicle revealed that the filter can estimate the failures of the sensors and the actuator with high accuracy. The effects of a lateral wind and other disturbances on the filter were also clarified.

Active control systems pertaining to handling and stability have been systematically analyzed and tested. While the tires maintain adhesion the most effective system is steer angle control. A new 4WS strategy utilizing steering wheel angle feedforward and yaw velocity feedback functions is found to minimize the effect of external disturbances as well as to optimize steering response. When the limits of tire adhesion are approached other control systems must be adopted. Experimental methods of controlling the distribution of the driving/braking force and roll stiffness, based upon yaw velocity model following strategy, indicate a high potential for improving cornering performance.