AGM Stop-Start

Auto-start-stop explained

What is stop-start technology?

Stop-start is a system on most modern cars that cuts the engine when the car is stationary, in order to reduce fuel consumption and emissions. The engine starts again when the clutch is engaged or the brake is released, or when the driver is ready to move again.

The system uses a computer to detect when the car is stationary or the car is out of gear, at which point it halts fuel delivery and spark to the engine. The ignition starts again when the car begins moving or the clutch is pressed.

The process happens automatically, but drivers can choose whether the system is active or disabled by pushing their car’s stop-start button; a capital A with an arrow circling clockwise.

A conventional electric starter motor works by engaging a small pinion gear with a large ‘ring’ gear fitted around the outside of the engine flywheel.

The latest stop-start technology looks much the same but the motors are more powerful, faster acting and more robust. Some are designated ‘TS’ for ‘tandem solenoid’ and designed to cope more smoothly with scenarios where the engine is about to stop and then the driver accelerates again.

Such a moment may come when the driver has decided to stop, but for whatever reason has a change of mind, such as when the traffic moves off unexpectedly.

At that moment the engine might be ‘committed’ to stopping but is still spinning, so to avoid crunching, one solenoid fires up the starter motor to synchronise its speed with the engine before the second smoothly engages the gear.

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