Towards the Active Suppression of Disc Brake Squeal

This work is concerned with disc brake squeal that is widely accepted as a friction-induced self-excited vibration of the brake assembly. The present thesis aims to investigate the possibility of active disc brake squeal suppression using a method of varying the leading and trailing piston pressures in a multi-piston opposed brake caliper. This thesis describes the development of a new prototype four-piston brake caliper, a two-channel brake actuation system and an advanced control system, which is capable of varying the leading/trailing pressure ratio (LTPR) when squeal is detected. This causes the centre of pressure (CoP) position at the pad/disc interface to move, which leads to new dynamic parameters of the brake system and thereby to different squeal propensity. The control system maintains the overall brake torque to a constant value, so the variation of the LTPR on the brake performance is minimised. Other novel approaches described in the thesis include a new three-dimensional analytical model of the brake pad, which was used to predict the CoP position in both circumferential and radial directions for a given LTPR. A reduced finite-element model of the current brake setup was also developed to predict positions of the CoP and unstable modes of vibration for varying LTPR. Using low-cost piezoresistive force sensors, a new embedded brake pad sensor was designed that can determine the current position of the CoP during a braking event. The new brake pad sensor along with the new 3D analytical model served as indicators of the current CoP position during brake tests. Experiments using the current disc brake setup showed that by varying the LTPR, thereby changing the CoP position, the squeal occurrence can be controlled. It was shown that the new squeal control system operating in an automatic mode reduced the squeal occurrence significantly for a given duty cycle.