Creep groan of brake systems is a well-known low frequency vibration noise caused by the stick-slip-effect. In this paper, results of a fundamental investigation of creep groan both theoretically and experimentally are shown. A test rig is designed focusing on the investigation of the frictional contact by realizing low damping and small disturbances in the system. Performing experiments with this test rig, limit cycles and bifurcation effects of creep groan can be observed. In terms of modeling, a nonlinear model using the bristle friction law is considered, which includes the Stribeck, stick-slip, and pre-sliding effect. As a result of numerical analysis of this model, trivial solution and stick-slip limit cycle are obtained. Conditions for the existence of the stick-slip limit cycle and the stability of the trivial solution are investigated. There exist three parameter regions at varied brake pressure and driving speed of the test rig. At low speed and high brake pressure, the test rig system has an unstable trivial solution while a stick-slip limit cycle exists. Under this condition, the stick-slip limit cycle is reached for all initial conditions, and creep groan will always occur. At higher speed and lower brake pressure, the system has an asymptotically stable trivial solution while the stable stick-slip limit cycle still exists. In this case, the appearance of the stick-slip limit cycle or the non-vibrating solution depends on the initial conditions. At very high speed and low brake pressure, the system has a stable trivial solution and the stick-slip limit cycle does not exist. In this case, creep groan cannot occur. The experimental results show good agreement, both qualitatively and quantitatively, with the simulation results, and the limits of the three regions can be identified theoretically and experimentally. From these results, it can be concluded that a linearized model in specific operating points may not give the whole picture of creep groan, since creep groan may occur even though the equilibrium position is asymptotically stable. Additionally, the possibility and the limitation of creep groan prediction using linearized friction models, which could be implemented in high dimensional FE models, are discussed in this paper.
Xingwei Xgao, Nils Gräbner, Utz von Wagner, Chair of Mechatronics and Machine Dynamics (MMD), Technische Universität Berlin, Germany.