Reducing Braking Distance by Control of Semi-Active Suspension

Inhaltsangabe:Abstract:
This thesis presents a control algorithm for semi-active suspensions to reduce the braking distance of passenger cars. Active shock absorbers are controlled and used to influence the vertical dynamics during ABS-controlled full braking. In today’s series cars the active shock absorbers are switched to a passive damping - usually hard damping - during ABS-braking. Several approaches to reduce oscillations of vertical dynamic tire forces are known, implemented and some of them tested in non-braking situations (refer to Yi, Valàšek, and Nouillant).
The approach presented in this paper goes a step further by connecting the vertical with the longitudinal dynamics. To influence the vertical dynamics a switching control logic, called MiniMax-controller, is used. It is named after the fact that it changes only from soft to hard damping and vice versa. A control quantity was identified that connects the vertical dynamics with the longitudinal dynamics: the integral of dynamic wheel load. The control algorithm is implemented in a compact class passenger car. Simulations with a quarter-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, using a braking machine for reproducibility reasons.
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 elevation profile of the chosen testing track and on the initial velocity. On a road with an unevenness comparable to the one that is found on a typical German Autobahn, a reduction of typically 1-2%, compared to the best passive damping, was achieved. Inhaltsverzeichnis:Table of Contents:
List of Abbreviationsix
List of Symbols and Indicesx
Abstractxv
1.Introduction1
1.1Classification of Suspension Systems1
1.2State of the Art3
1.3Research Objectives11
1.4Methodology12
2.Fundamentals of Vehicle Dynamics14
2.1Coordinate Systems14
2.2The Braking Process16
2.2.1The Quality of a Braking Process23
2.2.2Parameters that Influence the Braking Distance24
2.3Possibilities to Influence the Braking Force26
2.3.1Influence via Braking Torque-ABS30
2.3.2Influence via Wheel Load-Active Shock Absorbers34
2.4Conclusions35
3.Tools and Research Environment36
3.1Active Shock-Absorbers36
3.2Testing Vehicle38
3.2.1Testing Vehicle […]