Stop-start engine technology is designed to reduce fuel use particularly in heavy traffic where manufacturers claim it is able to improve fuel economy by as much as 10 per cent.
It shuts off the engine when the car comes to a complete stop and starts it again when the brake is released and the accelerator pressed.
If a car with a conventional starting system was continuously started and stopped, it would soon have issues. To make it work reliably, car makers have rethought how the mechanicals are laid out. Items that once needed the engine running in order to operate, such as air-conditioning and gearbox and power steering hydraulics, have been redesigned to use electric motors instead.
Battery charging was a big hurdle – a car that is restarting every few hundred metres in traffic could soon drain the battery. To cope with this, cars with stop-start technology generally have a larger-capacity battery and more sophisticated multi-stage charging systems.
In addition to this, most of these engines are designed so that they start within one turn of the crankshaft. Some have gone even further by making sure they always stop with the pistons in the same place, which means the starter motor isn’t used much at all.