SAE International Brake Dynamometer Test Variability Part 2- Description of the Influencing Factors 2011-01-2374

The ISO TC22/SWG2 - Brake Lining Committee established a task force to determine and analyze root causes for variability during dynamometer brake performance testing. SAE paper 2010-01-1697 "Brake Dynamometer Test Variability - Analysis of Root Causes" [ 1 ] presents the findings from the phases 1 and 2 of the "Test Variability Project." The task force was created to address the issue of test variability and to establish possible ways to improve test-to-test and lab-to-lab correlation. This paper presents the findings from phase 3 of this effort-description of factors influencing test variability based on DOE study. This phase concentrated on both qualitative and quantitative description of the factors influencing friction coefficient measurements during dynamometer testing. The Design of Experiments investigated factors regarding: brake cooling , environmental conditions during testing, kinetic energy level , pad soak prior to testing, location of control temperature , caliper drag condition, and number of snubs in the burnish section. The paper describes a methodology used to select the levels for the factors used during the study, and possible ranges of factor variations encountered during actual testing. The ranking of factors by their importance to reduce test variability is determined based on the effect on variation of the friction coefficient metrics (and other metrics related to test execution) defined on the ISO 26867 test procedure [ 2 ]. The findings and conclusions, even though are specific to the boundary conditions and the brake configuration used for this DOE study, are useful for further refinement of existing test procedures, laboratory test equipment, test results evaluation, and testing conditions with the primary aim of reducing test-to-test and lab-to-lab variability during regular testing activities.