GM working on a new disc brake to eliminate brake squeal

Article by Christian Andrei, on January 3, 2012

General Motors engineers wanted to eliminate the screeching sound produced by brakes. They are now developing a quieter brake technology that would put an end to the source of frustration for many car owners and automotive technicians who want to find a solution for the noise from this otherwise normally functioning brake.

To absorb the vibrations and keep it quiet, this GM-patented design called the Coulomb friction-damped disc brake that features a thin ring of metal embedded in the brake rotor.

It is named after Charles-Augustin de Coulomb, the 18th century physicist who came up with the friction-based damping mechanism. GM will use this quieter brake technology with a corrosion resistant brake technology on over 80% of GM’s U.S. vehicles by model year 2016. This may save customers over $400 in over 10 years.

GM engineers are testing the quieter brake but it’s likely to be offered on several of its cars and trucks within two to three years. What makes the Coulomb damped brake more remarkable is that it enables the brake to just do its job, according to Jim Webster, GM engineering technical expert for rotors. Due to friction in the brakes, they produce a significant amount of noise when the pads are pressed against the flat face of the rotor to slow or stop the vehicle.

The noise from older brakes could mean that the braker pads are now thinner and thus have to be replaced. However, the noise produced by new brakes is usually repulsive, but doesn’t necessarily mean that there is something mechanically wrong with the system. To minimize such noises in current brake systems, sound-absorbing materials are installed in the brake pads, but could also cause the pads to wear down faster.

On the other hand, the Coulomb damped brake takes care of this unpleasant sound by going straight to the rotor, the largest noise source in the brake system. However, it is difficult to soften the noise from the rotor since this component has large unconstrained areas that are free to vibrate. Thus, to create the new brake, engineers at GM created a proprietary manufacturing process that inserts a metal ring into the rotor. This metal ring insert is wrapped in a special coating to prevent it from melding to the rest of the rotor during casting – thereby enabling the insert to remain free to absorb vibrations and to act as a dampener.

Jim Schroth, a group manager in GM’s manufacturing systems research lab, remarked that the Coulomb damped brake creates a bell that doesn’t ring. This bell is gagged by having the special insert absorb the vibrations in the rotor. This innovation should significantly reduce the number of customer complaints -- in the short-run – over unwanted noise. Nevertheless, the Coulomb damped brake could still provide alerts through electronic sensors when the brake pads are worn and have to be replaced.

Press Release

GM Engineers Quiet Brake Squeal

For car owners and automotive technicians alike, brake squeal is a source of frustration. It’s best described as that screeching sound created by what may otherwise be a normally functioning brake. General Motors engineers are developing new technology that could practically eliminate the age-old problem.

The GM-patented design uses a thin ring of metal embedded in the brake rotor to absorb vibrations and mute the squeal. The design is called a Coulomb friction-damped disc brake after the friction-based damping mechanism associated with 18th century physicist Charles-Augustin de Coulomb.

The quieter brake technology comes atop a previously announced corrosion resistant brake technology that will be featured on more than 80 percent of GM’s U.S. vehicles by model year 2016 and could save customers more than $400 over 10 years.

The quieter brake is still being tested by GM engineers but is expected to be available on some cars and trucks within two to three years. The beauty of the Coulomb damped brake is that it allows the brake to simply do its job, said Jim Webster, GM engineering technical expert for rotors.

“When we design brakes, our goal is to make them an extension of the driver,” Webster said. “When the brake pedal is applied, the customer shouldn't have to worry about unwanted noises. The car should just stop or slow down within the distance that’s expected. The Coulomb damped brake allows the brake to perform quietly as a seamless part of the automobile.”

Automotive engineers have been dealing with brake squeal for 100 years. By nature, brakes are a major source of friction, which makes them a potentially significant source of noise. The unwanted noise in a brake is usually created when the brake pads are pressed against the flat face of the rotor to slow or stop the vehicle. The friction of the two surfaces leads to vibrations and noise.
With older brakes, the noise can be an indicator that the pads are getting thin and need to be replaced. But in many cases, especially with new brakes, the squeal is unpleasant but not an indicator of anything mechanically wrong with the system making them unsafe. In current brake systems, noises are minimized primarily through sound-absorbing materials in the brake pads, which can significantly reduce brake squeal but can wear down quickly.

The Coulomb damped brake attacks the problem from the largest noise-generating part of the brake system – the rotor. The rotor, though, is difficult to muffle because it has large unconstrained areas that are free to vibrate. In order to create the new brake, GM engineers developed a proprietary manufacturing process that sandwiches a metal ring inside the rotor.

A special coating for the insert prevents it from melding to the rest of the rotor during casting. This allows the insert to remain free to absorb vibrations and serve as a dampener. It’s like putting an object against a ringing bell.

“The Coulomb damped brake essentially creates a bell that doesn’t want to ring,” said Jim Schroth, a group manager in GM’s manufacturing systems research lab. “By absorbing the vibrations in the rotor with the special insert, we’re silencing the bell.”

In the short-run, the Coulomb damped brake could dramatically reduce the number of customer complaints with unwanted noise on otherwise normally operating brakes. The Coulomb damped brake would still alert drivers, possibly through electronic sensors, when the brake pads are worn and need to be replaced.

In the long-run, the Coulomb damped brake opens new opportunities for brake design. Future brake systems could use materials with even higher coefficients of friction, meaning stronger grips, because the Coulomb damped brake can eliminate the higher potential for squeal.

“The Coulomb damped brake creates new possibilities because we don’t have to worry as much about unwanted noise,” Webster said. “It could allow us to create smaller, lighter brake systems that provide even more stopping force than the larger brake systems in some automobiles today.”

GM’s advances in brake technology also include a recent effort to eliminate rotor rust, double the life of the component and save consumers hundreds of dollars over the life of their vehicle.

Topics: gm, technology

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