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. The ancillary
drive system typically contributes up to 8% of the total engine
friction level, so improvements in this system can make a real
difference to engine efficiency, fuel consumption and CO₂
emissions.
Mahle has undertaken a series of rig tests, based on a 2.5-liter
gasoline engine, but built to a minimum friction level of hardware.
Using motored drive torques, the losses associated with different
alternator drive concepts was investigated: - Standard 150A
alternator, - Reduced capacity 120A alternator, - Reduced capacity
120A alternator driven by a dual speed gearbox, and - Reduced
capacity 120A alternator driven by a twin-belt dual ratio
pulley.
The engine test configuration enabled the friction sensitivity
to be considered in respect of oil temperature, belt tension, belt
temperature and alternator loading, as well as the hardware changes
considered.
The twin-belt concept demonstrated a friction improvement
capability, whereas changing the effective alternator ratio by
means of a dual speed gearbox demonstrated a detriment. The use of
a twin-belt system could offer the opportunity to reduce the
overall FEAD system losses as well as potentially enabling smaller
alternators to be specified. Cost and packaging issues permitting,
this could reduce the parasitic losses associated with an
alternator drive system.
With a twin-belt arrangement, the test engine demonstrated an
improvement in net parasitic losses of between 300W and 400W, at an
engine speed of 5000 RPM and alternator loading of 60A. For the
same test conditions, a dual speed gearbox would need to be
operating at an efficiency above approximately 80% to avoid a net
worsening in parasitic losses, whilst the measured efficiency of
the test unit was approximately 60%.
This paper considers the approach to the testing, the test
results obtained and some further discussion.