Effect of front-wheel drive or rear-wheel drive on the limit handling behaviour of passenger vehicles

Abstract

A seven-degree-of-freedom four-wheeled vehicle-handling model was developed for the purpose of investigating differences in the behaviours of front-wheel drive (FWD) and rear-wheel drive (RWD) vehicles. The handling treatments of the two cases have been studied on horizontal, sloping, and low-friction roads by applying step steer angle inputs. The difference between the behaviours of two layouts on a horizontal road was found to be small; it became pronounced on low-friction roads and severe on sloping roads. On horizontal roads, both layouts showed understeering behaviours up to the limit lateral accelerations. On sloping roads, however, the RWD vehicle tended to oversteer whereas the FWD vehicle remained in an understeering mode. The variation in the parameters showed that increasing the velocity or slope and decreasing the friction coefficient reveals the differences in the behaviours of the two layouts. A small perturbation technique was also applied to the model and the resulting linearized equations were used to obtain the modal frequencies at different trims. Considerable differences were noticed in the disturbed behaviours of the two cases, including unit step responses.