Quantification of Brake Pad Rattle Noise – Correlating Accelerometer Measurements with Subjective Ratings

Of the many types of brake noise, pad rattle is a significant source of customer dissatisfaction and warranty costs. During brake development pad rattle noise is assessed on rough surface tracks of various types. Typically, subjective ratings are used by evaluators to rate the noise on a scale of 1 to 10. Since subjective ratings are used, often different evaluators rate the same brake's pad rattle noise with differing ratings. This ambiguity represents a problem in determining at what level a brake's pad rattle performance is acceptable or unacceptable for the field.

The aim of this paper is to demonstrate a correlation between subjective ratings of brake pad rattle noise and accelerometer measurements taken on the pads. A selection of front calipers was evaluated for pad rattle noise over a test track. Subjective ratings were collected from the driver together with accelerometer data from the outer pad measured during test. The accelerometer data was analysed with the subjective ratings to assess correlation between acceleration levels of the outer pad and subjective ratings. Initial results demonstrated limited correlation between filtered pad acceleration data and subjective ratings and some difficulty was encountered when discriminating between cases with low levels of pad rattle. Further testing was conducted measuring acceleration of both the inner and outer pads for cases where a large range of subjective ratings were made. The sum of filtered acceleration data measured on the inner and outer pads was found to better correlate with subjective ratings of rattle noise.