Abstract
KEYWORDS – hot judder, hot spots, brake torque variation, dynamometer, order analysis, thermal increase
ABSTRACT
Hot judder is brake-induced vibration, which is mainly caused by thermal deformations of brake disc. It is typically perceived by the driver as minor to severe steering wheel oscillation, brake pedal pulsation, whole car body vibrations as well as low-frequency noises during braking. In the last decades, hot judder tests were predominantly carried out at inertia dynamometers and manifold hot judder orders were observed. However, only a few vehicle tests were executed, and there is no direct comparison with dynamometer tests up to now. Considering the different constraints of wheel brakes as well as the different hydraulic layouts of the braking system, whether inertia dynamometer test can represent the real hot judder situation in a vehicle is still unknown.
In order to investigate the potential different hot judder behaviors between dynamometer test and vehicle test, one front brake and one rear brake with two different pads are separately tested at brake dynamometer and through vehicle tests by means of road tests and chassis dynamometer tests. Hot judder behaviors in these tests are then compared with defined criteria: thermal increases of Brake Torque Variation (BTV) and Brake Pressure Variation (BPV), overall order behaviors and dominant orders of BTV. Significant discrepancies are found in the different tests. However, hot judder seems to be generally more likely to happen at brake dynamometer. Brake dynamometer test is still appropriate for preventing the occurrence of hot judder in the vehicle. This study provides a reference regarding hot judder detection for the brake manufactures.