Measurement and control of brake pedal feel quality in automobile manufacturing

Abstract

Customer perception of brake pedal feel quality, as related to the perception of the brake pedal feeling soft or mushy, depends on both the customer's subjective judgment of quality and the actual build quality of the brake system. This project analyzed the different factors contributing to the soft brake condition using a fishbone diagram. A low cost tool to objectively measure brake pedal feel was developed and tested. Using this tool we found a negative linear correlation between residual air in the brake system and brake pedal feel. Even in the worst-case, a residual air level of 0.9 mL or greater is required before the brake pedal force drops 10%. The air evacuation step in the brake fluid filling process was investigated by the addition of a vacuum accumulator tank, and we found the air evacuation to depend on the brake system cross-sectional area (i.e. tube diameter) and not on the vacuum pressure. Organizational process issues were analyzed, and we found that greater cross-functional communication and collaboration are needed between manufacturing and external groups such as design and marketing.