Active Four Wheel Brake Proportioning for Improved Performance and Safety 2008-01-1224
A vehicle undergoing longitudinal or lateral accelerations experiences load transfer, dynamically changing the normal load carried by each tire. Conventional braking systems are designed only to work adequately over a large range of conditions, but often ignore the dynamic state of the tire's normal load. Fortunately, new developments in braking system hardware give designers more control over the application of braking pressures. By identifying the tires that carry increased normal load, and biasing the braking system toward those tires, total braking force can be increased.
The purpose of this research is to investigate advantages of open-loop load transfer based active brake pressure distribution. By estimating the tractive ability of the tires as a function of measurable vehicle conditions, brake pressure can be applied in proportions appropriate for the current dynamic state of the vehicle, referred to as Active Brake Proportioning (ABP). The result is increased braking ability before the onset of tire lockup (or ABS activation).
In the paper, a mathematical model to predict normal load at each tire is developed, and incorporated into a high fidelity vehicle model. Brake pressure is distributed according to the predicted loads. A series of simulations are conducted using the model to investigate stopping distances under various conditions, vehicle stability during extreme obstacle avoidance maneuvers, and impact on driver steer effort. The results show that ABP can potentially provide significant benefits for both performance and safety.