What is the benefit of vehicle stop-start systems

With increasing restrictions on vehicle emissions, manufacturers are having to come up with more ways of lowering emission outputs.

Stop-start systems on vehicles are one way manufacturers are achieving this.

Stop-start systems serve two main purposes – to reduce fuel consumption and lower CO2 emissions.

The system works by switching off the engine when you have come to a stop and then restarting it when you go to move off.

By not having the engine idling while you are sitting still, fuel is saved and emissions reduced. Manufacturers claim about a 5–8% fuel saving.

Like many technologies, each manufacturer has its own way of doing things and stop-start is no exception.

Some utilise a conventional-looking, though substantially up-rated, starting system while at the other end of the spectrum is a belt-driven combined starter/alternator unit.

Hybrid models typically use a traction motor/generator for engine start.

Similarly, the vehicle’s electrical system can resemble a conventional system, incorporate an extra battery for starting or even a high-tech super-capacitor just to run the starter.

Most systems provide a switch that allows the driver to disable the function if desired.

Stop-start systems operate within defined parameters which will, to some degree, vary from maker to maker.

Generally, though, the system will not operate unless the vehicle is stationary, the engine is at operating temperature, the battery has a certain level of charge and the cabin temperature is within a certain range.

Gearshift, brake pedal, handbrake lever position and, for manual vehicles, clutch pedal position are also factors in the system’s operation.

Stop-start operation is generally inhibited if there is high electrical load, as would be the case with a discharged battery, or when there is high demand on the heater or airconditioner.