Torque Output Improvement for S-cam Drum Brakes using DOE Methods (per ASTM E1169-07) and the SAE J2115-06 Inertia Dynamometer Test Procedure

This paper presents three main topics which proved useful during the systematic resolution and testing program to confirm the ability of the proposed friction material to conform to the performance requirements indicated on the TP-121D [1] dynamometer test. Initially, the paper presents some commonalities and differences between the vehicle FMVSS 121[2], the dynamometer TP-121D and the SAE J2115-06 [3] test protocols. The second part of the paper elaborates on the implementation of the methodology established on the ASTM E1169-07 [4]. This standard relies on Design of Experiments (DOE) methods to assess the robustness of a given test method when testing on the extreme values allowed for key test conditions. The DOE used a three-factor, two-level, fractional factorial design to investigate the influence of (a) cooling air speed, (b) brake power as the combination of test inertia and deceleration settings, and (c) brake adjustment method. This experiment allows the quantification of their effects on brake retardation, maximum brake pressures, brake stroke, and cycle times among others. The third and last section presents the test results and the net effects from each factor; with the brake adjustment being the most significant among the three factors investigated. These test results demonstrate the ruggedness (sensitivity) of torque output to the brake adjustment method used, making a difference between complying or not to the inertia dynamometer output requirements. This highlights the need to revise the SAE J2115-06 procedure to reflect industry practices for brake adjustment and to provide a harmonized method to control the test conditions.