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A driving simulator capable of duplicating the critical sensations incurred during a spin, or when a driver is engaged in drift cornering, was constructed by Mitsubishi Heavy Industries, Ltd., and Hiromichi Nozaki of Kogakuin University. Specifically, the simulator allows independent movement along three degrees of freedom and is capable of exhibiting extreme yaw and lateral acceleration behaviors. Utilizing this simulator, the control characteristics of drift cornering have become better understood. For example, after a J-turn behavior experiment involving yaw angle velocity at the moment when the drivers attention transitions to resuming straight ahead driving, it is now understood that there are major changes in driver behavior in circumstances when simulator motions are turned off, when only lateral acceleration motion is applied, when only yaw motion is applied, and when combined motions (yaw + lateral acceleration) are applied.

In this research, we examine the three controls inside-outside wheel braking force and driving force, camber angle, and the derivative steering assistance to determine how angle differences affect cornering performance and controllability. This is accomplished by comparing body slip angle area differences in a closed loop examination of the grip to drift area using a driving simulator. The results show that inside-outside wheel braking force and driving force control in the area just before critical cornering occurs has a significant effect on vehicle stability. We also clarified that controlling the camber angle enhances grip-cornering force, and confirmed that the sideslip limit could be improved in the vicinity of the critical cornering area. Additionally, when the counter steer response was improved by the use of derivative steering assistance control in the drift area exceeding the critical cornering limit, corrective steering became easier.

A new steering method to improve control during cornering is examined using a driving simulator, and the following findings were obtained. During cornering, there is a danger that it is not possible to finish curving is course out by the only differentiation steering. However, the driver can easily maintain a drift in the drift area when assisted by differentiation steering, and the behavior of the return to a straight course becomes stable. Therefore, since a remarkable effect was expected by controlling the steering method corresponding to the running condition, an examination experiment was performed. The shapes of the waves of initial steering at start up differ according to the running condition, and as a result, initial steering of the steering wheel is a two-step motion in J-turn running. In contrast, smooth steering proceeds without steps in the lane change running.

In the cornering performance of a formula car, turning is performed at a considerably high level. However, few studies have investigated the control of the camber angle. Therefore, a mechanism that swings to the negative camber side of the suspension in cornering was examined in the present study. A swinging suspension member structure was assumed when a lateral force acted on the tires, and the momentary rotation center of the swing suspension member was controlled so that the direction of the swing would be to the negative camber side. As a result, compliance of the negative camber was achieved. The layout of a preferable mechanism was first determined by geometrical analysis. The negative camber angle obtained with this mechanism changes according to the length of the link for the fixation of the swing suspension member, the installation position, and the angle. The specifications for achieving a proper compliance negative camber were then clarified.

The relation of the front wheel steering angle to the steering wheel angle in electric vehicles is changing due to the “steer-by-wire” method, which is based on an electric signal. With this method, excellent maneuverability is possible in various driving situations. Therefore, this steer control method technique is considered in this study. It was clarified that steer-bywire requires an improvement in the control stability in emergency maneuvers and the delay of counter steering in drift cornering without causing a sense of driver incompatibility. (Here, the sense of incompatibility was defined as feeling by which the harmony between the steer intention of the driver and the vehicle movement was lost.) (Here, the drift cornering shows cornering done in the area with counter steering where the rear wheel exceeded the maximum cornering force.) One control stability method is Proportional Derivative (PD) steering assistance, which is dependent on the anticipated driving situations.

A drift-turn experiment to assess the influence of differences in steering wheel gear ratios was undertaken using a driving simulator. It is relatively easy to maintain control of a commercial vehicle if the tire is in contact with the road surface and the steering wheel gear ratio is 15.0:1 to 18.0:1. Conversely, in the event of a change in traction such as the rear wheel meeting a drift area, a steering wheel gear ratio of 7.5:1 to 9.0:1 is required to maintain control of the vehicle, even when the vehicle became unstable. Moreover, the stability of the vehicle deteriorates in drift running if the steering gear ratio is reduced too much. That is, the steering gear ratio in which the drift angle is maintained most easily is in the range 7.5∼9.0. And, a drift performance evaluation index D n=x was determined and was found to agree with the subjective ratings. Thus, evaluating drift control for drift cornering using the drift performance evaluation index was assumed to be effective.

In this study, we focus on “camber angle control” and “derivative steering assistance” using “steer-by-wire” as maneuverability and stability improvement techniques that are appropriate for the electric vehicle (EV) era. Movements that produce a negative camber angle generate camber thrust, and vehicle motion performance improvements extend from the fact that the tire side force is increased by the camber thrust effect. In our experimental vehicle, a proportional steering angle system was used to create negative camber angle control via an electromagnetic actuator that allowed us to confirm improvements to both the effectiveness and stability of steering control in restricted cornering areas. More specifically, we determined that it is possible to improve critical cornering performance by executing ground negative camber angle control in proportion to the steering angle.

It has been reported that steering systems with derivative terms have a heightened lateral acceleration and yaw rate response in the normal driving range. However, in ranges where the lateral acceleration is high, the cornering force of the front wheels decreases and hence becomes less effective. Therefore, we applied traction control for the inner and outer wheels based on the steering angle velocity to improve the steering effectiveness at high lateral accelerations. An experiment using a driving simulator showed that the vehicle's yaw rate response improved for a double lane change to avoid a hazard; this improves hazard avoidance performance. Regarding improved vehicle control in the cornering margins, traction control for the inner and outer wheels is being developed further, and much research and development has been reported. However, in the total skid margin, where few margin remains in the forward and reverse drive forces on the tires, spinout is unavoidable.

In recent years, the conversion of vehicles to electric power has been accelerating, and if a full conversion to electric power is achieved, further advancements in vehicle kinematic control technology are expected. Therefore, it is thought that kinematic performance in the critical cornering range could be further improved by significantly controlling not only the steering angle but also the camber angle of the tires through the use of electromagnetic actuators. This research focused on a method of ground negative camber angle control that is proportional to the steering angle as a technique to improve maneuverability and stability to support the new era of electric vehicles, and the effectiveness thereof was clarified. As a result, it was found that in the critical cornering range as well, camber angle control can control both the yaw moment and lateral acceleration at the turning limit.