Brake squeal is one of the most challenging problems that car manufacturers have today. It occurs as a result of the vibration of the brake components such as brake disc and brake pads and therefore it disturbs the driver and passengers. Furthermore, because of its complex nature it is hard to completely understand the causes of it. One of the causes that is understood at the moment is that it happens due to the dynamic instability of the system and noise and vibration generated during brake. During this event, rotor is the primary source of the noise and its flat surface is what radiates it. Noise is generated on it because it rubs with the brake pad, and when coefficient friction increases, it creates higher squeal noise.
Some of the strategies that are currently being used to minimize brake squeal are increasing rotor damping; changing the rotor fins with long and short fins, and alternating to induce phase difference so the vibrations are not coupled; using organic material dust or rubber filler in the brake pad or combining two or more abrasive materials with different hardness; using graphite lubricants, and/or reducing the tendency of the brake pad to absorb water as it increases the coefficient of friction. Another method is to use dither – a high-frequency disturbance to minimize the effects of frictional forces.
There has been several different physical testing techniques to verify brake squeal. These are lase vibrometer ODS (operational deflection shape), accelerometer and holographic interferometry. These techniques are effective up to a certain point, however, CAE tools give manufacturers a deeper insight and an ability to do many more tests for one product. Acoustic simulation tools also make it less expensive by reducing the number of physical prototypes that are needed.
To learn more about how acoustic simulation helps brake squeal, read our white paper.