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Mazda’s New Smart Idling Stop System for Direct-Injection Spark-Ignition Engines

Conventional idle-stop systems save fuel by automatically shutting down the engine when the driver brings the vehicle to a halt (at traffic lights, for example) and automatically restarting the engine when the driver subsequently wishes to pull away.

Mazda is displaying a new form of an idle-stop system for direct-injection spark-ignition engines that uses combustion and the reverse operation of the engine as a restart trigger rather than an electric motor.

Called the Smart Idling Stop System, it injects fuel directly into a cylinder while the engine is stationary and ignites the fuel to create downward piston force that serves to start the engine. Mazda claims that the Smart Idling Stop System is more energy-efficient than an electric motor restart, and also restarts the engine more quickly and quietly than a conventional idle-stop system.

Direct-injection technology makes it possible for fuel to be supplied directly to the engine’s cylinders while the engine is stationary and then ignited to turn the engine over.


The three stages of the Smart Idling Stop System operation. The stages correspond to the numbered descriptions to the right. Click to enlarge.

However, since the cylinders soon return to atmospheric pressure when the engine stops, a special technique is needed to achieve enough expansion energy to restart the engine. The Smart Idling Stop System operates as follows:

  1. The system injects a small amount of fuel into the cylinder whose piston is part-way through its compression stroke and ignites it, causing the engine to run slightly in reverse.

  2. The system then injects fuel into the cylinder that has begun to undergo compression owing to the engine’s reverse operation.

  3. Finally, the system ignites the latterly injected fuel, causing powerful expansion that drives the engine in the forward direction, thereby starting the engine.

For this to work, the compression-stroke piston and expansion-stroke piston must be stopped in positions that create the right balance of air volumes. Consequently, the Smart Idling Stop System effects precise control over the piston positions during engine shutdown.


Kiril Petrov

Hi, I am a student at Imperial College London and am currently doing a literature research on the topic of "Impact of engine cut-out (idle-stop) operation on emissions and engine life".
Could anyone guide me where I could find some more data on the topic.

Thank you.
Kiril ([email protected])

from: gilles sancereau

Voici le réel concurrent de la couronne de démarreur!


Hello,I am a student.
I am interested in your study about Smart Idling Stop, but I have some questions such as precise control over the piston positions.
Could anyone guide me where I could find some more data on MAZDA Smart Idling Stop? If you can give me some advices, I will appreciate you sincerely.
Thanks you again.
my email:[email protected]


Hi, i'm also an engineering student doing a literature research about stop & start system for cars and i'm looking for information about it.
Could anyone give me some help?
Thanks a lot
[[email protected]]

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