G.M. Claims Remedy for Squealing Brakes

By Paul Stenquist on December 21, 2011

At one time or another, most motorists register the fingers-on-chalkboard sound of squealing brakes coming from their cars. So unnerving is the sound that it can cause drivers to erroneously assume that their brakes may be on the verge of failure. On Wednesday, General Motors announced that it was working on a brake assembly that might prevent the cacophony.

Brake squeal can indicate worn pads: the parts that push against the brake rotor to create the friction that stops the car. But even newly serviced brakes that otherwise work well can scream mercilessly at every application of the pedal. Automobile mechanics, to placate angry customers, may have to redo work that was done correctly.

The demon is vibration, the same physical effect that causes a bell to ring when it's struck by a clapper. In the case of the brake assembly, the pads serve as clapper and the brake rotor as the bell. When the pedal is applied, the pads and rotor collide, causing both to vibrate. Mechanics and car manufacturers have attempted a variety of fixes to prevent that vibration, including clips intended to hold the pads more securely, silicone compounds applied to the back of the pads, beveling the edges of the pads and more esoteric remedies.

G.M.'s solution is a thin ring of metal built into the brake rotor. The ring touches the rotor but is not melded to it, so it absorbs vibration. G.M. compares the effect to placing an object against a ringing bell: the sound is quelled.

The concept is based on a damping mechanism developed by Charles-Augustin de Coulomb, a French engineer and physicist active in the 18th century. G.M. magnanimously calls its design a Coulomb friction-damped disc brake.

"The Coulomb damped brake essentially creates a bell that doesn't want to ring," said Jim Schroth, a G.M. group manager, in a media release. "By absorbing the vibrations in the rotor with the special insert, we're silencing the bell."

The hushed braking system is being tested by G.M. engineers and is expected to be available on some cars and trucks within two to three years.