Monday, 10/12/2018 | 2:32 UTC+8

How Engine Auto Start/Stop System Works


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Fuel-saving idle-stop technology explained, and a few myths dispelled

Automatic idle-stop is an increasing popular technology installed in a wide-range of new vehicles. Simply put, the system switches off the engine as the car comes to a stop and starts it again when you want to set off (by releasing the clutch or brake, depending on transmission type).

It’s a feature designed to reduce the amount of fuel wasted while a vehicle would otherwise be idling and, depending on the type of engine and time spent at idle, is claimed to reduce combined-cycle fuel consumption by as much as eight per cent.

Since 2010 idle-stop has become a commonly used feature in most European and Japanese cars. Australian, American and Korean models have been slower to adopt the technology, though it’s anticipated we’ll soon see all manufacturers fit idle-stop across their passenger vehicle ranges.

Idle-stop systems vary in the way they operate depending on the manufacturer in question. In most scenarios the engine uses sensors to establish when the car is stationary and switches off the ignition, relying on either road-speed input, pressure on the brake pedal, or a combination of the pair. In manual models, the system may take input from the clutch pedal (with the gearbox in neutral) instead of the brake.

Once the driver has released the brake, or begins to release the clutch in a manual, the engine automatically restarts. In most cars the starter motor is employed to start the engine, just as it would when you turn the key. Some idle-stop systems are claimed to have the engine running within 400 milliseconds of the start request.

However, some models, like those from Mazda and some diesel engines, use engine compression to begin the combustion process. It’s claimed to be not only quicker than starter motor-type systems, but saves the obvious strain on the starter motor, its solenoid, the ring-gear, battery and electrical system.

In fact, you shouldn’t fear that idle-stop will impact your car’s function in any significant way. The system is designed for repeated use with bolstered versions of the aforementioned components installed to match demand, although some argue that shutting down a turbocharged engine immediately after extended high-speed use could shorten the turbo’s lifespan.

Idle-stop is also carefully calibrated to operate only when the engine is at its optimal operating temperature (to prevent stalling and reduce engine wear) and to not engage when the engine is required to provide high-demand auxiliary power, such as when the electrical system is at capacity or the air-conditioning is required.

Idle-stop is also smart enough to know if its own repeated use is discharging the battery and will not operate until the battery has sufficiently recharged.


Auto start/stop, Idle stop indicator. Google Image, BMW

However, in spite of all the investment made to ensure idle-stop systems operate smoothly, there are times when its timing just doesn’t suit the scenario.

You might be pausing momentarily before darting across a busy roundabout, or trying to dash across a fast-moving highway. In these instances a momentary interruption to your car’s motive power can be at best disconcerting or at worst downright dangerous.

Fortunately (and there are a few exceptions), most idle-stop systems are designed to anticipate ‘pauses’ such as these and won’t engage until the vehicle is at rest. Similarly, most reignite very quickly, meaning any chance of an interruption long enough to cause an incident is unlikely.

But if you’re still not convinced, there’s always the option of a manual override, which can be selected by the driver at any time while the car is running and will not be overridden by the vehicle until the engine is switched off and on again manually by the driver. Your owner’s manual will help you find the button or switch in your particular car as at this stage there is no standardised symbol or methodology.

In short, idle-stop is designed to save fuel and money, without impacting day-to-day driving or vehicular wear and tear. Far smarter people than us have made sure the technology will work as intended for many years.

And with its fuel economy gains – especially in city traffic – far outweighing any perceived inconvenience, idle-stop is a technology that’s worth embracing when you consider your next new car.


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