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.