Start-stop system

A vehicle start-stop system or stop-start system (also known as S&S, micro hybrid, or micro hybrid electric vehicle (μHEV))^[1] automatically shuts down and restarts the internal combustion engine to reduce the amount of time the engine spends idling, thereby reducing fuel consumption and emissions. This is most advantageous for vehicles that spend significant amounts of time waiting at traffic lights or frequently come to a stop in traffic jams. Start-stop technology may become more common with more stringent government fuel economy and emissions regulations.^[2] This feature is present in hybrid electric vehicles, but has also appeared in vehicles that lack a hybrid electric powertrain. For non-electric vehicles, fuel economy gains from this technology are typically in the range of 3–10%, potentially as high as 12%.^[3] In the United States, according to the Department of Energy, idling wastes more than 6 billion U.S. gallons (23 billion liters; 5.0 billion imperial gallons) of fuel per year.^[4]

In a manual transmission vehicle, stop-start is activated by stopping the car, shifting the gear to neutral, and releasing the clutch. The engine will not stop if the car is moving, even if the aforementioned steps are followed (this is not true for all cars). The engine restarts when the clutch is pressed prior to selecting a gear to move the car. The engine may also restart if there is a demand for power from, for example, the air conditioning system.

Since automobile accessories like compressors and water pumps have typically been designed to run on a serpentine belt on the engine, those systems must be redesigned to function properly when the engine is turned off. Typically, an electric motor is used to power these devices instead. In vehicles where the air conditioner compressor still runs from the drive belt, some drivers turn on the air conditioner as an improvised way to disable start-stop. In the Mazda 3, a supercapacitor is used to power the air conditioner and other accessories as part of the i-ELOOP system; the air conditioner and fans are lowered significantly to minimum settings when the engine is off. With the air conditioning and fan at maximum settings, the supercapacitor will be drained in five seconds, and the engine will automatically turn on.^[5][6][7]

This technology has also been used on Honda scooters in Asian markets for the last decade.^[8] Honda's PCX 125 cc model was released in 2010 with this technology for the European market, though its North American model does not feature it.^[9]