Improvements to car/caravan handling and high speed stability through computer simulation

It is well known that car/caravan combination systems can be unstable at high speed. This study addresses the problem of high speed in stability through simulation using a twenty four degree of freedom computer model and experimental testing of an instrumented car and caravan. The mathematical model developed for this study included the effect of tyre nonlinear behaviour, axle lateral load transfer and compliance at the tow-ball in a dynamic model. The model accounted for roll, pitch, yaw, bounce, lateral and longitudinal degrees of freedom for both the car and caravan. Using an adjustable frame built on to a standard, single axle chassis, the effect of caravan mass and inertia on lateral directional stability was measured experimentally. Having obtained good correlation between simulation and experiment, the destabilising effect of caravan design parameters such as mass, inertia, centre of gravity height, secondary suspension rate and damping, wheel track and axle longitudinal position were investigated through simulation. It was found that caravan mass, yaw inertia, axle longitudinal position and tow-ball load were the most important parameters to influence stability. The car/caravan combination system stability was less sensitive to changes in secondary suspension parameters and other inertial properties, although handling characteristics such as roll steer and roll over capacity were affected.