Brake Dynamometer Test Variability - Analysis of Root Causes

Jaroslaw Grochowicz; Karl-Heinz Wollenweber; Carlos Agudelo; Harald Abendroth

doi:10.4271/2010-01-1697

Modern project management including brake testing includes the exchange of reliable results from different sources and different locations. The ISO TC22/SWG2-Brake Lining Committee established a task force led by Ford Motor Co. to determine and analyze root causes for variability during dynamometer 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 accuracy study used the ISO 26867 Friction behavior assessment for automotive brake systems. Future efforts of the ISO task force will address NVH and vehicle-level tests.

This paper corresponds to the first two phases of the project regarding performance brake dynamometer testing and presents results, findings and conclusions regarding repeatability (within-lab) and reproducibility (between-labs) from different laboratories and different brake dynamometers. The new EKB 3008 data exchange format was used by participating facilities to share test results using spreadsheet applications, help automate the evaluations, and simplify the different comparisons performed for this project. This on one of the first practical applications for the EKB 3008 format with several software platforms involved.

In order to minimize variations caused by test parts, components (brake discs, brake pads, calipers and vehicle knuckles) were carefully selected, prepared, and measured prior to testing. Special attention was given to: test procedure implementation, critical braking and testing conditions, dynamometer setup and controls, data collection, data processing and test evaluation routines. Statistical analysis (Minitab® and ISO Statistical Methods) were used to separate variability caused by test parts and caused by the test setup. Based on the findings, the paper presents guidelines for improving repeatability (within-lab) and reproducibility (between-labs) during regular testing activities.

Compared to vehicle testing, variability root-cause investigation using brake dynamometers is more efficient (less sources of variation and less use of testing and engineering resources) and under more controlled conditions. Findings from this variability study will support future improvement efforts for several laboratory and vehicle performance and NVH test procedure and techniques.

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Brake Dynamometer Test Variability - Analysis of Root Causes 2010-01-1697

SAE MOBILUS