(Dr. Kenneth Cunefare, advisor)
"Active Control of Automotive Disc Brake Rotor Squeal Using Dither"
Automotive disc brake squeal is believed to be due to the resonant vibration of components of the brake system enhanced by a feedback loop between the brake pads and rotor. The exact causes of brake system vibration have been in debate for many years, but in general, an in-plane disturbance between the brake pads and the rotor induces a brake system vibration. The brake system vibration creates an out-of-plane acoustic disturbance, which radiates into the passenger cabin.
Brake noise and vibration has long been a problem, but as consumers have demanded quieter and more comfortable automobiles, automotive manufacturers have put more effort into better understanding the problem. Advancement in computer technology has enabled engineers to better detect and process complex information about the brake system to develop noise control systems. Active control has been shown to be useful in controlling brake squeal, but this research took active control one step further in eliminating and even preventing brake squeal from occurring, using dither.
This Masters Thesis research first examined the acoustic and vibration characteristics of disc brake squeal. The results from the vibration analysis showed the squeal emanated from the brake system as a rotor mode. This squeal was able to be eliminated and most importantly, prevented from occurring using a harmonic vibration, with a frequency higher than the squeal frequency, generated from a stack of piezoelectric elements placed in the caliper piston of the brake system. The control signal used to create the harmonic vibration is commonly referred to as a dither control signal. The resulting control vibration was not heard from the brake system if an ultrasonic control signal was activated. This gives rise to a possible active control system integrated into the brake system of automobiles to prevent squeal once a braking application is detected.