Abstract
This paper presents a control algorithm for semi-active suspensions to reduce the braking distance of passenger cars. Active dampers are being controlled and used to influence the vertical dynamics during ABS-controlled full braking. In today´s series cars the active dampers are switched to a passive damping - generally hard damping - during ABSbraking. Several approaches to reduce vertical dynamic tire forces are known, implemented and some of them tested in non-braking situations (refer to Yi (1), Valásek (2), Nouillant (3), and Hedrick (4)).
The approach presented in this paper makes use of a switching control logic, called MiniMax control. It gets its name from the fact that it changes only from soft to hard damping and vice versa. The control algorithm includes two modules: One that reduces the peak values of dynamic wheel load and another one that reacts on the slip of each wheel by interacting with the ABS. Both control algorithms are implemented in a compact class passenger car. Simulations with a quarter- and a 2D-car model have been undertaken as well as tests on a 4-post-test rig, driving tests with defined excitations (like defined obstacles) and test drives on a real road with a braking machine.
It could be shown that it is possible to reduce the braking distance by affecting on the vertical dynamics of a passenger car in general. The amount of reduction depends on the height profile of the chosen testing track and on the initial velocity. On a road with an unevenness like a regular German autobahn it was possible to reduce the braking distance by 1.5 % compared to the best passive damping.
Keywords:Semi-active Suspension, Active Damper, Braking Distance, ABS, Test Drives On Real Roads