Concerns over greenhouse gas emissions are driving governments
and the automotive industry to seek out ways of reducing vehicle
CO₂ emissions. Engine friction reduction is one means of reducing
CO₂ emissions, through fuel consumption improvements. Of the
different systems within the engine, the camshaft timing drive can
contribute around 5 to 10% of the overall engine friction. It is
therefore a system that can benefit from careful optimization.
MAHLE has undertaken a motored friction-testing program on a
2.2-liter turbocharged diesel engine with the following different
types of camshaft timing drive: - Chain drive with hydraulic
tensioner. This is the standard configuration for this engine. -
Chain drive with friction tensioner. - Wet belt drive. - Dry belt
drive.
Testing was conducted to allow the differences in friction
between the different drive configurations to be calculated, by
comparing each camshaft drive against the standard chain drive
system. Using the frictional differences as a basis, the changes in
fuel consumption from the standard configuration were predicted for
a drive cycle. Changes in CO₂ emissions were then calculated.
Experimental uncertainty levels were assessed during the analysis
of the results.
This paper considers the approach to the testing, the testing
process and the test results.
