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%.
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.
Now, Audi has announced that its A3 with a S tronic dual-clutch transmission is now available with an engine stop-start system. The only models so far with this feature are the highly-efficient 1.6-liter TDI and 1.4-liter TFSI.
The start-stop system turns the engine off as soon as the vehicle comes to a stop; the engine stays off as long as the driver depresses the brake pedal. As soon as the driver removes their foot from the brake pedal, start-stop turns the engine back on--quietly, conveniently and quickly.
According to Audi, the 1.6-liter TDI with the S tronic and engine stop-start system achieves a fuel economy of 56 mpg while the 1.4-liter TFSI gets 44 mpg.
Also standard in both A3 models is an on-board energy-recovery system. During braking and coasting phases, this intelligently controls the alternator to recover energy, which is temporarily stored in the battery. This energy is then fed back into the electrical system during acceleration--thus reducing the load on the alternator.
First sales will start this November.