One of the major concerns of brake NVH is Brake judder coming from Brake Torque Variation (BTV). This is a vibration that occurs during braking and can be felt by the driver through the steering, brake pedal or vehicle body. This can create a feeling of discomfort for the vehicle occupants.

One of the main contributors to BTV is Disc Thickness Variation (DTV), and this relationship is well known in the industry. Current literature focus has mainly been on the sensitivity due to caliper design and pad characteristics. However, this paper introduces a new sensitivity factor, attributed to piston bore machining quality. Specifically, this paper shows BTV sensitivity due to built-up edge; an accumulation of material onto the tool tip which is separated from the chip, and creates surface anomalies which cannot always be captured by normal surface roughness measurements. This paper highlights the importance to ensure good machining quality as well as inspection methods to confirm the presence of built up edge in the piston bore.

Patrick Kane, Senior Engineer, Toyota Motor Europe; Mr. Yusuke Kinoshita, Toyota Motor Europe; Mr. Pavlos Ioannidis, Toyota Motor Europe