Proposed Test Method for Brake Pad Lining Robustness in Cold Conditions 2024-01-5049

With globalization, vehicles are sold across the world throughout different markets and their automotive brake systems must function across a range of environmental conditions. Currently, there is no current standardized test that analyzes brake pads’ robustness against severe cold and humid environmental conditions. The purpose of this proposed test method is to validate brake system performance under severe cold conditions, comparing the results with ambient conditions to evaluate varying lining materials’ functional robustness. The goal of this paper is to aid in setting a standardized process and procedure for the testing of automotive brakes’ environmental robustness.

Seven candidate friction materials were selected for analysis. The friction materials are kept confidential. Design of experiment (DOE) techniques were used to create a full-factorial test plan that covered all combinations of parameters. The test script involves brake applications at 5, 10, 15, and 20 bar, at both ambient/non-humid and cold/humid conditions. Each brake application collects the stop time and coefficient of friction (COF) values throughout the stop. Failure modes are subjectively long braking times and failed brakes.

The test results verify that brake pad effectiveness is dependent on friction lining, braking pressure, and environmental conditions. Other than at the lowest tested braking pressure, the COFs appear to be consistent across the tested braking pressures. Each material was evaluated for robustness against cold conditions by calculating their signal-to-noise (S/N) ratio, a common method used during design for six sigma (DFSS) robust optimization analysis. The braking time S/N is calculated using smaller the better (STB) analysis, whereas the COF S/N is calculated using the larger the better (LTB) analysis. Using the S/N ratio, it can easily be determined which brake pad friction lining material is the most robust against environmental conditions.

Friction designation A was consistently calculated to be the most robust friction material against the cold environmental conditions. All friction linings had extended stopping times in cold conditions when compared to ambient conditions. In some cases, the lining materials reached critical failure in severe cold environments. Additionally, the collected friction values gave insight into potential extreme pad wear rates.