Large car stop/start stumbling block

High torque engines and automatic transmissions are the default choice for prestige-car buyers. It's certainly the one combination available to buyers of sports-oriented Mercedes-AMG models.

With society's concerns about global warming and peak oil production escalating, products of this ilk would appear to be the most logical application of auto-stop/start. A feature that switches off the engine in traffic to save fuel and then restarts it immediately with a prod of the accelerator, would seem a ‘must have’ for a brand like AMG.

However, it a fuel saving strategy that's technically difficult to apply to many large cars, suggests one of the German performance car maker's senior engineers, Alexander Weber.

"First of all, it's a matter of integrating it with automatic transmission," Weber told the Carsales network during our visit to AMG’s Affalterbach HQ tthis week.

"We have at least 600Nm on the 63 [AMG's M159 6.2-litre engine]. There is absolutely no manual transmission that can bear such an amount... [And] If you look at companies already offering start/stop, they only offer it with manual-shifted cars. You need a pressure-storage device for automatic transmissions, so we are also working on that. As soon as it's out, we will offer it.

The wider use of dual-clutch automated manual transmissions could be one answer. If the problem proves to be too challenging, however, other technological developments may overtake it.

"We will be introducing an electric drive on the SLS," said Weber. "but there is a compromise... we have to bridge the gap between emotion and emission."

For the present, Weber seems content that AMG is moving in the right direction, at least. He cites the international launch for the E 63, during which a journalist succeeded in using just 9.4L/100km of fuel over a section of road.

Once again, the trick to reducing fuel consumption seems to rest in the purview of the driver as much as with the engineers.

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