Air disc brakes — a technology whose time may finally have come
In the 1940s, British novelist Nevil Shute, who was also a respected aircraft designer/engineer, wrote The Breaking Wave, one of his two dozen or so novels. That title popped into mind — with a twist — as we reviewed some of the new technology presented at the recent SAE International Truck & Bus Meeting & Exposition in Portland, Ore.
What came to mind was “A Wave of Brakes,” as authors presented technical papers on brake developments, demonstrators showed new brake hardware, and panelists discussed the implications of braking.
Much of the attention was devoted to air disc brakes for heavy-duty vehicles, a technology widely accepted for many years in Europe and whose time seems finally to have come in the North American market. For example:
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Bendix Commercial Vehicle Systems announced it is beginning fleet testing of its North American air disc brake, the Bendix ADB 225, for 22.5-in. wheel applications. Its mono block caliper design makes the brake more compact, enabling it to fit North American truck wheel-ends. Features include internal automatic brake adjustment, integrated pad and rotor wear sensing diagnostics, and braking efficiency that results in a stopping distance 30-35% shorter than required.
Both the ADB 225 brake, now slated for production in 2003, and the “splined disc” air disc brake technology described in the “Nuts & Bolts” section of this issue, are developments of the joint venture of Bendix and its German partner Knorr-Bremse.
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Haldex Brake Systems, whose air disc brakes are marketed in the U.S. by Dana Corp., will offer a dual-disc air disc brake in which the rotors slide in and out and the pads remain stationary, a design said to reduce rotor cracking. The company also noted that it is beginning production in Europe of an electronically controlled trailer-brake system for the European market. Its higher-powered processor will provide control capabilities for additional vehicle functions.
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NewTech Group International, a Quebec-based braking system developer and manufacturer, exhibited heavy-duty air disc brakes featuring its “full contact” design. Essentially, the NewTech brake consists of two annular brake pads — an “outboard” pad and an “inboard” pad. When the brakes are applied, these pads grip the entire surface of the rotor, thereby distributing pressure over the full 360° surface of the rotor. Benefits are said to include less overheating, reduced noise and vibration, and improved braking performance.
The company is currently adapting its “full contact” design for a single-disc air disc brake that will fit the Renault Magnum 480 (Class 8) truck. Road testing is scheduled to begin shortly.
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Drum brakes came in for a share of the SAE spotlight as engineers for ArvinMeritor and Freightliner presented a paper on the CamLaster brake, which they referred to as “one of the first new drum brake designs in over 20 years.” Freightliner has an exclusive agreement with ArvinMeritor to market the CamLaster, which combines features of wedge and S-cam brakes: a high-efficiency expander mechanism, fixed cam and leading-trailing sliding shoes. The shoes slide down an inclined ramp on a cam to evenly contact the drum. Better pressure distribution and lower peak pressures result in longer lining life.
In fleet tests, a West Coast fleet averaged 403,190 miles with only 46% of the wearable lining used. A fleet in the Southeast averaged 381,934 miles wearing only 39% of the lining. No adjustments were required.
