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15/11/2009
By EWAN KENNEDY
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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. |
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