HOW IT WORKS Stop/start
Cut it out
Mystified by the list of the features on the spec sheets of modern cars? Driving gets behind the jargon to explain what they all do, starting with start-stop technology
Car manufacturers, as part of their attempts to make cars more fuel-efficient and emit less carbon dioxide, have introduced a number of new technologies in recent years. Many of these features, such as regenerative braking, are invisible to the driver, their magic being conducted out of sight and, for the most part, out of mind. However, one feature that drivers will be aware of, especially in
urban driving situations, is the stop-start system. A start-stop system (or stop-start) system, based on a combination of engine, brake, and battery management, automatically shuts down and restarts an engine in an attempt to reduce the amount of time the engine is at idle in static traffic. As soon as the driver depresses the clutch pedal, the system automatically restarts the engine – in most cases, the engine fires up instantaneously. There are three main components of a start-stop system: the
internal combustion engine, an electric starter/generator and a battery. The energy is transferred between those working parts in that order, in both directions, depending on what the car is doing at any one time. When the engine is working to move the car and the brakes are about to be engaged, a start-stop system uses what is known as regenerative braking, where the rotational energy from the wheels turns the electric generator, creating electricity. The generator then sends that electricity to the battery, where it is stored for when it is needed. Then, when the brakes are applied, the generator shuts off the engine. When the driver is ready to set off again, s/he merely squeezes the accelerator pedal, which starts the engine again by taking the energy previously stored up in the battery and running it through an electric starter. The system feels odd when you first drive a car fitted with it,
as you start to think you must have stalled the engine. However, you quickly become accustomed to it and within the first hour of driving, it feels absolutely normal and you don’t even think about it.
It is, in fact a welcome addition to modern cars because during
the time the engine is switched off, the car isn’t consuming fuel or emitting CO2. Estimates of how much fuel is saved range from 5 to 10%, depending on how much of its life in spends in urban or metropolitan driving conditions. The comfort of the car’s cabin isn’t compromised, either.
The function is not activated, for example, until the engine has reached the ideal running temperature or if the air conditioning unit (when fitted) hasn’t had a chance to bring the cabin to the chosen temperature, if the battery isn’t adequately charged or if the driver moves the steering wheel. If necessary for comfort or safety, the control unit will also automatically restart the engine if, for example, the vehicle begins to roll, the battery charge falls too low or condensation forms on the windscreen. The system also recognises the difference between a temporary stop and the end
of a journey and it won’t restart the engine if driver’s seatbelt is undone, or if the door is open. The system can also be completely deactivated by pressing a button. If you’re considering buying a new car, this is one piece of
modern technology that you should seriously consider being on the ‘must-have’ list of features. With fuel prices rising in the way they are, even a 5% improvement in fuel economy could add up to a serious saving.
April / May 2011 | driving
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