Control for four-wheel individual steering and four-wheel driven electronic vehicle

An indoor four-wheel individual steering and driving vehicle with full electronics was built for evaluation of the system's ability and the performance in practical use. Mechanical parts such as the connecting rod and the differential gear are not provided for this vehicle. From trial operation, the characteristics fully performed as in design, but some problems originating from the design concept were disclosed. Rotating radius (R) of the vehicle was taken for the steering command parameter, but it was found to not be an appropriate parameter for driving operation. The reasons are as follows: 1) R has a much different sense of driving conformability for the driver, because it does not refer to the running direction, but to the rotating radius of crosswise direction. 2) Sensitivity of each wheel steering angle versus R differs over double figures in the full range of R. 3) R changed from plus to minus and also vice versa in most practical situations around straight-go operation. For these reasons, the steering command parameter was changed from R to alpha, where alpha is the angle between the vehicle lengthwise direction and the moving direction. The steering control algorithm using alpha has been proven to solve the three above-mentioned problems. (C) 2005 Wiley Periodicals, Inc.