The Effect of Controllable Suspension Settings On the ABS Braking Performance of An Off-Road Vehicle On Rough Terrain.

The value of anti-lock braking systems (ABS), to improve the safety of passenger vehicles on roads, have long been recognised to such an extent that all new passenger and commercial road vehicles in some countries must be equipped with ABS due to legislation requirements. Although ABS does not always ensure the shortest possible stopping distance, it enables reliable stopping whilst maintaining stability and steering control.

The present study investigates the effect of ABS brakes, combined with a controllable suspension system, on the stopping distance of an off-road vehicle on smooth as well as very rough but hard roads (e.g. Belgian paving). The alterable suspension system consists of a 4-state semi-active suspension system (4S₄) that enables spring settings on each wheel to be set between two discrete settings (hard and soft), as well as damping to be set between high and low damping.  A multi-body vehicle model, developed in commercial software, IPG CarMaker, contains the parameterisation of the vehicle under investigation with corresponding sub-systems, the software realization of the alterable suspension system and ABS, which operates the real hydraulic brake system. A driver model, also realized in IPG CarMaker, and the real brake system are coupled by means of a brake robot, also represented as the hardware component. The tyre-road interaction is simulated with an experimentally parameterized Pacejka 2002 tyre model and a digital model of a real road profile.

Results indicate that there is little difference in stopping distances on smooth roads, either with operating ABS or without it. The different combinations of spring and damper settings have a small but noticeable effect. On the rough terrain, differences are more pronounced and significantly influenced by changing the damping and stiffness properties of the suspension. ABS essentially deteriorates braking distances from 70 km/h by up to 20 m compared to braking without ABS. The effects of different spring and dampers settings are also very pronounced in that suspension settings alone can result in stopping distance differences of up to 14m.