Real-Driving Residual-Drag-Torque of Disc Brakes

Residual drag torque of disc brakes is caused by unintended contacts between brake-disc and -pads when the brake is not applied. Brake drag opposes the current efforts for BEV range improvement as well as prospective restrictions for brake dust emission. Since every unnecessary friction contact dissipates kinetic energy and emits additional particles. State of the art for brake-drag-analysis is based on component level measurement primarily performed on brake dynamometers. Tough under real driving conditions in-vehicle the brake is exposed to different and additional influencing factors like wheel forces known to potentially affecting drag torque significantly. Therefore, using component-test results to forecast brake drag behavior in-vehicle on the road is to some degree uncertain, evoking the provocative question: Is drag optimization, on brake dynamometer effective or maybe even overengineered for in-vehicle use? A related comprehensive answer is currently prevented by a lack of appropriate brake drag measurement data in-vehicle. In this light the following research first defines the requirements for in-vehicle brake drag measurement under real driving conditions. Based on a categorization and assessment of existing measurement technology as well as related patents, an approach using 3-axis piezo-force-sensors is identified and subsequently implemented. After evaluating sufficient functionality on the brake dynamometer, a vehicle is equipped with the measurement system at each (fixed caliper) brake. According to the RDE-categorization real-driving tests are performed on urban, rural and highway-road-sections and additionally on the roller dyno. The results point out certain differences (theoretical presumed in literature) between component- and in-vehicle brake drag behavior motivating further investigation to expand the understanding under real driving conditions.