BMW 2007 Annual Report Download - page 219

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== 1
Tyres with less roll resistance
are especially fuel-efficient, owing
to reduced strain on tread and
sidewalls.
== 2 – 3
Preparations for flow and circu-
lation testing of the engine com-
partment in the wind tunnel.
Report: A matter of consistency.
This is where the BMW Group’s engineers come in: their electric water pump only switches on when it
is actually needed – and for that it only needs the energy of two bright light bulbs. This technology,
which was driven largely by the BMW Group (and still the only auto manufacturer in the world to use it)
currently saves two percent of fuel in the automobile.
In this way – segment by segment, component by component – the engineers scour all models for
potential economies: engineering minor revolutions such as highly-efficient Brake Energy Regeneration
and the jet-guided direct fuel injection system that result in consumption figures which only used to be
possible for diesel engines; optimising small things such as air flaps which open or close on their own
depending on the engine’s cooling requirements; designing a detachable air conditioning compressor
which only springs into action when it really needs to cool; drastically reducing the roll resistance of
tyres and replacing conventional hydraulic steering with much more economical electric steering. In
the meantime, all of these features are standard in almost all models of the BMW and MINI brands.
Many of them seem so obvious that one has to wonder why they were not implemented long ago. The
reason is that these apparently simple solutions often conceal extremely complex technologies. Just
how complex can be seen from the example of the ASSF.
ASSF stands for Auto Start Stop Function and is the most radical approach to throttling engine
con-
sumption since it cuts off the engine immediately once it is no longer needed. A small number
of
automobile manufacturers tried automatic engine stop functions years ago, but they were quickly
withdrawn from the market because they were too cumbersome, too unreliable, and, as a result,
ineffective. However, engineers at the BMW Group knew from simulations and trial runs that switching
off and restarting the drive train for state-of-the-art injection engines pays off after just a few seconds’
standing time. A red traffic light lasts on average about 20 seconds. That made us realise that there
were huge potential savings to be discovered here, one developer remembers. What we didn’t
realise at the outset was how much work would be involved in successfully harnessing that potential.