{"84351":{"#nid":"84351","#data":{"type":"news","title":"Stop the Noise: Active Control System Could Halt Squealing Brakes in Cars, Trucks and Buses","body":[{"value":"\u003Cp\u003ENow, acoustics researchers at the Georgia Institute of Technology have developed a solution that could stop the problem of noisy brakes once and for all.\n\u003C\/p\u003E\n\u003Cp\u003EIn disc brakes, squeal can occur when the brake pads contact the rotor while the vehicle is moving at low speeds, setting up a vibration that manifests itself as an annoying high-pitched squeal.  The noise doesn\u0027t affect brake operation, but the problem - which occurs in cars, trucks and buses - leads to needless replacement of brake pads and the addition of shims, damping materials and other parts designed to stop the noise.   \n\u003C\/p\u003E\n\u003Cp\u003E\u0022A squealing brake still works, and from an engineering perspective, there is no safety problem when the brakes are squealing,\u0022 said Kenneth Cunefare, an acoustics researcher in Georgia Tech\u0027s School of Mechanical Engineering.  \u0022But it\u0027s a perceived problem with the quality of the vehicle.  If you\u0027ve bought a new luxury car, you don\u0027t want the brakes to squeal.  So manufacturers must spend money on warranty repairs that shouldn\u0027t be necessary.\u0022\n\u003C\/p\u003E\n\u003Cp\u003EAutomotive engineers have learned many tricks for designing quiet braking systems, but despite their best efforts, squeal still appears unpredictably.  Designers have proposed feedback control systems that would detect the noise and then generate out-of-phase vibrations to counter the specific frequency of the squeal.  Because of the complexity and cost, such systems haven\u0027t been implemented.\n\u003C\/p\u003E\n\u003Cp\u003EBy contrast, the Georgia Tech system would use a simple piezoceramic actuator mounted inside the brake piston to apply bursts of a \u0022dithering\u0022 frequency to the backing plate of the inside brake pad, suppressing the vibrations that cause squeal.  This active control would work despite temperature and humidity changes - and normal brake system wear - all of which can change the squeal frequency.\n\u003C\/p\u003E\n\u003Cp\u003EThe system would be connected to vehicle brake light switches, turned on whenever the brakes were applied.  \n\u003C\/p\u003E\n\u003Cp\u003E\u0022Compared to feedback control, our dither system would be much simpler,\u0022 Cunefare said.  \u0022It would be an open loop control system in which we won\u0027t need to detect the presence of squeal.  All we would need to know is that the brakes have been applied.\u0022\n\u003C\/p\u003E\n\u003Cp\u003EWithout the need for detectors or logic systems to determine the proper control frequency, the Georgia Tech system could be much simpler, with fewer components.  The piezoceramic stacks that Cunefare is now testing cost $130 each today, but he estimates high-volume production should reduce that to around $30 each - and perhaps even to a few dollars each.  A single frequency generator and power electronics system could serve a vehicle\u0027s entire braking system, though an actuator would be required for each brake piston.\n\u003C\/p\u003E\n\u003Cp\u003EIn extensive laboratory testing using a dynamometer and acoustic measuring equipment, the system has been able to control brake squeal under a variety of different conditions.  Next, Cunefare and his collaborators would like to field-test the system under real vehicle operating conditions.\n\u003C\/p\u003E\n\u003Cp\u003E\u0022In terms of understanding the design constraints, we are pretty far along with this,\u0022 he said.  \u0022We know the temperature changes we\u0027ll have to survive, and we know the forces that we\u0027ll have to generate.\u0022\n\u003C\/p\u003E","summary":null,"format":"limited_html"}],"field_subtitle":"","field_summary":[{"value":"Squealing brakes cost auto manufacturers several hundred million dollars a year in warranty repairs and are among consumers\u0027 top 20 vehicle complaints - even in luxury cars.","format":"limited_html"}],"field_summary_sentence":"","uid":"27304","created_gmt":"2003-06-16 00:00:00","changed_gmt":"2016-10-08 03:03:41","author":"Matthew Nagel","boilerplate_text":"","field_publication":"","field_article_url":"","dateline":{"date":"2003-06-16T00:00:00-04:00","iso_date":"2003-06-16T00:00:00-04:00","tz":"America\/New_York"},"extras":[],"related_links":[{"url":"http:\/\/gtresearchnews.gatech.edu\/newsrelease\/brakesqueal.htm","title":"A simpler system"}],"groups":[{"id":"1188","name":"Research Horizons"}],"categories":[],"keywords":[],"core_research_areas":[],"news_room_topics":[],"event_categories":[],"invited_audience":[],"affiliations":[],"classification":[],"areas_of_expertise":[],"news_and_recent_appearances":[],"phone":[],"contact":[{"value":"\u003Cstrong\u003E \u003C\/strong\u003E\u003Cbr \/\u003E\u003Ca href=\u0022http:\/\/www.gatech.edu\/contact\/index.html?id=\u0022\u003EContact  \u003C\/a\u003E","format":"limited_html"}],"email":[],"slides":[],"orientation":[],"userdata":""}}}