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By EWAN
KENNEDY
16 November 2009
The phrase ‘stop-start’ is one we find ourselves using
quite a lot when road testing new-design engines these days.
Basically it refers to an engine that automatically stops when the
car comes to a standstill, then restarts when it's ready to move
off again. Thus reducing fuel usage and exhaust emissions.
It works well in the petrol-electric hybrids, because they have a
huge electric motor and a large battery to get the petrol engine
up and running again. But you pay a lot of extra money to buy a
hybrid.
The stop-start concept is also being trailed in conventional
vehicles. In recent weeks we have seen stop-start in special
economy versions of models from BMW and the smart car company.
There are drawbacks. There's no doubt that stop-start is fitted
because in both cars there's a slight tremble as the engine shuts
down and the restart is even more obvious.
Arguably these are good results in the early days of this new
technology, and will be improved as the engineers come to grips
with it. But the average driver and passenger are likely to find
the effect irritating. To the extent that in the smart fortwo we
actually switched the stop-start off at times. We were then losing
the environmental benefits of stop-start and that worried us.
Another hassle in stop-start systems is that a heavy-duty starter
motor and, probably, a larger battery need to be installed. That's
because in congested cities the starter may be asked to operate on
hundreds of occasions every day, instead of the usual four to six
times.
Now Mazda has come up with an elegantly system solution to the
disadvantages of stop-start. We spent some time at the recent
Tokyo Motor Show talking to one of the senior directors of the
company, Nobuhiro Hayama, about the engineering side of the
upcoming Mazda i-stop system.
The basic principle is simple. Instead of the pistons in the
engine coming to rest wherever they happen to be when the car
stops, sensors make the engine stop rotating when one of the
pistons is in the most favourable position for a restart. When the
driver lifts their foot off the brake pedal a tiny amount of fuel
is injected into the cylinder and an ignition spark is created at
just the right time. Thus the engine restarts without requiring
the use of the starter motor.
Mazda claims it is running again after a third of a second, which
is about half the time taken by current stop-start setups. And
that it starts so smoothly the occupants will be unaware of
what’s happening. We look forward to road testing these
new-generation Mazda engines to feel and hear just what they are
like.
Fuel savings may be as high as 15 per cent if the vehicle is being
used in crowded areas, with C02 emissions being trimmed by about
the same amount.
The new-generation Mazda engine also contains other significant
new design ideas and isn't expected to go into production until
2011 or 2012. Australia is one of the countries where early
imports are anticipated.
© Copyright
Marque Publishing Company
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