Abstract
Modern project management for brake development requires the exchange of reliable results from different sources and different locations. The ISO TC22/SWG2 - Brake Lining Committee established a task force to address the issue of test variability in brake performance testing. The overall goal was to provide guidelines on how to reduce variability and how to improve correlation between dynamometer and vehicle test results. This collaborative study used the ISO 26867 Friction Behavior Assessment for Automotive Brake Systems test procedure (1). Future efforts of the ISO task force will address NVH and vehicle-level tests.
This paper presents the findings from phases one to three of this effort:
- Measurement of variability level in friction coefficient from five brake dynamometers (with different designs, vintage, and test locations)
- Assessment of differences in the test and dynamometer setup, test execution, and test interpretation
- Description of potential root-causes of the friction coefficient repeatability (within-lab) and reproducibility (between-labs) levels observed during phase 1
- Proposals to reduce the overall test variability from improving the dynamometer setup, the test procedure, and the test execution based on results from the Design of Experiments (DOE) study
The analysis provided the effects and interactions of the DOE factors and their influence on variability of friction coefficient during different types of brake applications. This analysis allows the identification of most critical types of brake tests. The proposed changes to the ISO test procedures also apply to other dynamometer tests commonly used by the industry, including wear and Noise, Vibration, and Harshness (NVH) testing.
KEYWORDS – brake testing, dynamometer, variability, friction, performance, repeatability, reproducibility