Autonomous engine stop-start systems, designed to save fuel by turning off a car’s engine when at a standstill, are increasing in popularity, especially in Europe, where fuel prices are often double what they are here. In many cases, the addition of an engine stop-start system can net fuel savings in the range of 5-10 percent.

The limiting factor for their widespread use so far has been that they are mostly available with manual transmissions only (not including hybrid vehicles). This trend is starting to change, however. Early last year, German transmission specialist ZF showed off a new eight-speed automatic designed with engine stop-start capability and soon after that Audi launched a version of its dual clutch equipped A3 hatcback overseas with an engine stop-start system

now automotive parts supplier Bosch has developed its own engine stop-start system that can be used reliably in automatics.

In vehicles featuring automatic transmission, the start-stop function is especially easy to use. The driver only has to step on the brake pedal, and as soon as the car has stopped the engine stops automatically--and it starts again when the brake pedal is released.

The challenge for engineers was to make the start process faster and more dynamic, as the time for declutching, changing gear, and re-engaging the clutch done in manuals is not available in an automatic vehicle. To solve this challenge, Bosch engineers adjusted the electric starter motor and pinion-engaging mechanism, as well as the injection system and control software.

The good news is that Bosch has been working closely with the major automakers to develop the system, trialing it in vehicles like the Volkswagen Passat, dual clutch equipped Porsche Panameras, the Audi A8 and the Fiat 500 minicar fitted with automated manual transmissions.

No word yet on which U.S.-delivered models will feature the new Bosch developed system.

[Bosch]