Brake Dynamometer Squeal Noise Test Procedure for Regenerative Systems
The SAE J3211 procedure applies to brake squeal evaluation using single-ended inertia dynamometers for friction couples used on vehicles with regenerative braking systems. This RP applies to squeal noise occurrences for on-road passenger cars and light trucks with a gross vehicle weight rating of 4536 kg or below.
The procedure incorporates aspects related to (a) minimum inertia dynamometer capabilties, (b) fixture requirements and setup, and (c) test sequences with emphasis on brake temperatures, brake pressure profiles, and strategies to represent brake blending.
Rationale: Foundation brakes used on hybrid and electric vehicles with regenerative braking tend to have lower average operating temperatures, compared to vehicles using internal combustion engines. Besides, the intervention of the foundation brakes during vehicle deceleration is a function of the blending technology and the capabilities of the propulsion system. Some vehicles can achieve a high percentile of decelerations during regular vehicle use using only the regenerative system and minimal foundation brake intervention. Lastly, the lack of engine noise, a high percentage of hybrid and electric vehicles operating in cold weather, and some electric vehicles with high-performance capabilities, demand a new approach to measure and characterize brake squeal. This Recommended Practice addresses multiple aspects of brake squeal for regenerative braking systems by (a) focusing on lower operating brake temperatures also induced by more extended periods between wheel brake events, (b) addressing brake fade for high-performance applications, and (c) defining test sequences and brake profiles more applicable to regenerative braking systems.