Systematic Experimental Creep Groan Characterization Using a Suspension and Brake Test Rig

Vehicle road tests are meaningful for investigations of creep groan noise. However, problems in reproducing experiments and partly subjective evaluations may lead to imprecise conclusions. This work proposes an experimental test and evaluation procedure which provides a precise and objective assessment of creep groan. It is based on systematic corner test rig experiments and an innovative characterization method. The exemplary setup under investigation consisted of a complete front wheel suspension and brake system including all relevant components. The wheel has been driven by the test rig’s drum against a brake torque. The main parameters within a test matrix were brake pressure and drum velocity. Both have been varied stepwise to scan the relevant operating range of the automobile corner system for potential creep groan noise. Additionally, the experiments were extended to high brake pressures, where creep groan cannot be observed under road test conditions. The measurements with creep groan showed vibration characteristics of a non-linear stick-slip effect, particularly at high brake pressures. A novel method to detect and evaluate creep groan events within a large number of systematic measurements has been developed and tested. It uses the characteristic patterns of acceleration signals which are analyzed in the frequency domain. The main evaluation results are displayed collectively in multi-dimensional maps. Such Creep Groan Maps (CGM) show vibration intensity levels and relevant frequencies in dependence of brake pressure and drum velocity. An overall Creep Groan Index (CGI) scores the groaning tendency of a whole setup by a single number. Its calculation is based on the acceleration signals across the observed test matrix as well. CGM and CGI both allow a simple and objective comparison of different mechanical and/or tribological setups as well as parameter influence studies.