Abstract: The brake groan vehicle road test is carried out under the starting condition of conventional flat road and downhill and transient dynamic characteristics of brake groan are analyzed. The key factors tests of brake groan are designed to study influences of powertrain, brake assembly and suspension assembly on brake groan. The research shows that the vehicle brake groan includes two typical modes of motion, one is the shock vibration with short duration and wide frequency band, and has no definite limit cycle. The other is the periodic harmonic wave vibration with long duration and multiple frequency characteristics, which belongs to a typical stick-slip vibration and has a clear limit cycle. Braking pressure is the key trigger conditions for brake groan. When the braking pressure drops to a specific range with a large slope, the first groan motion mode tends to be triggerred. On the other hand, it is easy to trigger the periodic harmonic vibrations. Vehicle powertrain drive force and engine speed fluctuation are the key factors affecting brake groan. Reasonable design of engine enrichment control strategy from low temperature to normal temperature and starting powertrain control strategy can effectively suppress brake groan. Brake dynamic and static friction coefficient difference is an important factor of brake groan. The connection stiffness between brake backplate and anchor and the mass of brake caliper are also the key factors. Through the design of brake assembly structure parameters to change the vibration mode of the brake when groan occurs, to improve the bow effect of suspension in brake, which provide new ideas for the control of brake groan.

Key words: brake, brake groan, experimental research, key factors, stick-slip motion