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Vehicle model plays an important role during the development process of a new car chassis. There are 2 different ways to set up the vehicle mathematics model, one is set up based on understanding the system mechanism and the other is based on system identification technique. In this paper, the transfer functions of the vehicle at 100 km/h, including yaw rate to the steering angle and lateral acceleration to the steering angle, were identified. And then the transfer functions under other forward speed were derived through studying two degrees of freedom vehicle model equation. At last the identified model at different speed was used to analysis the stability of closed loop system from the classical control theory viewpoint.

The results of a research programme involving a three pronged approach to vehicle handling - involving a series of experimental measurements, subjective assessments and modelling predictions (1) - were presented at FISITA 98 in Paris. From the analysis of this extensive range of results it was concluded that although some significant areas of correlation e.g. transient step steer responses, were identified, there was still some way to go before the confidence levels such as those associated with aircraft practice could be achieved. Consequently, a subset of the results - in particular those associated with the results frequency response measurements - have been analysed using a technique proposed originally in 1990 at Mitsubishi (2). This approach is called the “Four Parameter Evaluation Method” and uses a rhombus pattern graph to plot out steady state yaw velocity gain, natural frequency of yaw velocity, damping of yaw velocity response and phase delay at 1 Hz lateral acceleration.

The conflicting suspension requirements of vehicles which are designed for both on and off-road operation are examined. The example vehicle used throughout the calculations is a six-wheel truck of 24 tonne GVW and is based on an existing crash tender design. Using the Vehicle Dynamics Analysis Software (VDAS) package, the ride and handling behaviour of the truck is analysed for two versions of the vehicle; one with three axles suspended on leaf springs with a bogie arrangement at the rear, and another with independent wheel suspension throughout. The overall conclusion drawn is that axle designs have significant advantages for off-road vehicle applications; they maintain good ground clearance, they are based on inexpensive, well proven technology and, with attention to detail design, offer vehicle dynamic performance comparable with independent designs.

Previous work by the authors on fully active control systems is extended to model semi-active systems which (a) can only dissipate energy and (b) involve some restrictions in their response characteristics. Various control laws are studied but the one which turns out to be of most interest includes the “wheelbase preview” effect, i.e. it takes advantage of the information that the rear input is a delayed version of that at the front wheel. For example, the semi-active system which includes this feedforward information is better overall than a fully active system which assumes uncorrelated inputs at the wheels.