Brake noise : A study in multi-tonal brake squeal

Sammanfattning: Brake squeal is a major problem for the vehicle industry due to recla-mations and quality perception of vehicles, as well as the unpredictability of its occurrence. This report investigates the physical reasons behind a multi-tonal brake squeal generated in a motorcycle disc brake. It also covers why previous remedies to eliminate the noise has had an e↵ect, as well as trying to find a stable cost-e↵ective solution to the problem. The brake components are studied using numerical simulations as well as experimental analysis, the accuracy of which is investigated by analyzing a simple beam and compar-ing the results to analytical calculations. By performing a FEM-simulation of the di↵erent subsystems, the multi-tonal sound was tracked down to the ABS tone wheel, e.a. the sensory ring that is used for wheel speed mea-surements. By simulating the modes with altered tone wheel thickness, the modal pattern remains the same albeit reduced in frequency. A character-istic dimension between the tone wheels mounting points where found, as the frequency where these bending modes between the mounting points oc-curred closely correlated with the frequency content of the measured noise. A thinner tone wheel was then manufactured and field tested, these test results shows a reduction in frequency for the multi-tonal sound, thus the indications from the simulation is confirmed. Furthermore, an investigation in to brake disc properties is carried out in order to explain the reason why discs with altered geometry lacks the squealing problems of the original disc. This is done by a simulation of the sound propagation efficiency of the discs out-of-plane surfaces as well as an experimental study of the insertion loss from the friction surface between the brake disc and the brake pads to the tone wheel. The report ends with suggestions of design changes that can help combat the current issues, as well as problems of the same nature that might arise in future brake designs