Vehicle Integration Factors Affecting Brake Caliper Drag

Disc brakes operate with very close proximity of the brake pads and the brake rotor, with as little as a tenth of a millimeter of movement of the pads required to bring them into full contact with the rotor to generate braking torque. It is usual for a disc brake to operate with some amount of residual drag in the fully released state, signifying constant contact between the pads and the rotor. With this contact, every miniscule movement of the rotor pushes against the brake pads and changes the forces between them. Sustained loads on the brake corner, and maneuvers such as cornering, can both produce rotor movement relative to the caliper, which can push it steadily against one or both of the brake pads. This can greatly increase the residual force in the caliper, and increase drag. This dependence of drag behavior on the movement of the brake rotor creates some vehicle-dependent behavior. Major factors affecting rotor movement include wheel bearing stiffness, wheel radius, vehicle mass and mass distribution, and brake corner geometry. The present work studies two vehicle-integration dependent mechanisms which can affect brake drag. The first involves rotor movement due to sustained tire/wheel loading conditions and brake corner geometry, and is examined through a case study involving two vehicles. The second involves rotor movement due to cornering loads. In both cases, rotor movement is related to brake drag by component dynamometer measurements of brake drag versus small axial movements of the rotor.