Brake Judder - Analysis of the Excitation and Transmission Mechanism within the Coupled System Brake, Chassis and Steering System 2005-01-3916
The prevention of any brake noise or brake-induced body vibrations is a key development target firmly integrated in the car development process. Emphasis is placed here on disc brake judder that is attributable to thickness variations in the disc. These deviations from the ideal plane surface can be caused either by wear and corrosion or by thermal stresses (changes within the microstructure of the disc material). They are termed “cold judder” and “thermal judder” respectively.
During braking, possible vibration excitation passes through a wide frequency band due to the coupling between the judder frequency and the wheel rotational speed, and thus, resonant frequencies of many vehicle components can be excited. This includes wheel suspension components and the steering column.
In this paper, it is reported on extensive investigations into the topic of “cold judder”. Both, complex vehicle measurements on a roller dynamometer and optimised simulation calculations have been carried out with the goal of describing excitation and the transmission mechanism within the car. Thermography and a distance-measuring technique were used to measure the thermo-mechanical response of the brake disc and its deformation under controlled braking conditions. At the same time, the vibration response of the coupled brake, chassis and steering system was detected by using acceleration sensors and a multi-channel data acquisition system.
In the time-synchronous analysis of the measured data, the correlation between brake disc deformation, induced vibrations and resonances in various car components is described. These findings form the basis for a comparison of the numerical computer simulation with the measurement results from the test bed and allow validation and optimisation of the calculation model.
The numerical calculations and simulation result in an improved understanding of the various influencing variables on cold brake judder. Regarding steering wheel rotary vibrations caused by brake judder, critical influencing variables can be identified and rated in order to derive effective methods for reducing these vibrations and also to build system configurations that generally are less sensitive to brake judder.