NO MORE NOISY BRAKES

ASEE Prism, Sep 2004 by Grose, Thomas K

MECHANICS

CONSUMERS MAKE a lot of noise about squealing brakes. Though brakes that squeak pose no safety risk, they're an annoyance and they cost automakers $100 million a year in warranty work. It's a "perceived problem with the quality of the car," says Kenneth A. Cunefare, a mechanical engineer and acoustics researcher at Georgia Tech who has devised a possible, low-cost solution to the problem. Brakes squeal when their pads touch the rotors at low speeds. That results in a vibration that creates high-pitched squeals. Fixes such as putting in damping materials and replacing the pads often don't work, or don't last. Cunefare's solution is a piezoceramic actuator that slots into the brake piston. It's made from stacks of piezoelectric materials that expand or contract when an electric current passes through the layers. Every time the brakes are applied, the actuator injects a burst of a "dithering" frequency to the pads, which suppresses the squeal. Test devices haven't been affected by brake wear, or extremes in temperature, or humidity. The test model costs $130, but Cunefare thinks mass production would get that figure down to around $30. A small price to pay for a bit of motoring peace and quiet.-TG