Testing Mazda's Smart Idle Stop System
Testing Mazda’s Smart Idle Stop System. Click image to enlarge

Story and photos by Norm Mort

Hiroshima, Japan – Well, it might have been the shortest test drive ever (about .05 kms with a maximum time allowed being three minutes!), but it did provide me with an opportunity to test Mazda’s new SISS (Smart Idle Stop System). And the system works and works well. While having your engine shutting down when you come to a full start is not news to drivers of hybrids, the method of restarting your engine once the light goes green is unique to Mazda.

Mazda has found that cutting the engine to stop the idling reduces fuel consumption by about 10%. And, whereas a conventional idle stop system uses an electric motor to restart the engine, Mazda’s SISS injects fuel directly into the engine’s cylinders while the engine is stationary and ignites the fuel to create a downward piston force that serves to re-start the engine. This system not only saves fuel every time you have to stop, but also restarts the engine more quickly and quietly than a conventional idle-stop system.

For the engine to be restarted, sensors relay information on which piston should be fired. It is not always the first piston, but this is most often the case. The compression-stroke piston and expansion-stroke piston are stopped in positions that create the right balance of air volumes. SISS effects precise control over the piston positions during engine shutdown.

During the automatic restart, the cylinders for combustion are indexed and fired from the stored piston positions at the time of engine shutdown. Even at extremely low rpm, cylinders are continuously selected for ignition, and the engine quickly picks up to idle speed. Certainly in my brief stop and start tests there was never any hesitation, sudden jerk, or lag in accelerating away from a full stop. You simply touched the accelerator pedal and the SISS went into effect. Initially the restart by compression alone starts the engine in reverse to produce compression. The SISS system can also monitor the condition of your battery. A weak battery results in the threshold valve starting the motor to maintain the air conditioning system on hot days. No photos could be taken of the interior of the SISS test vehicle as due to the fact certain panels and switches had been removed. This truly was a test vehicle.

The SISS technology will be introduced in 2009 in Japan and worldwide markets will be individually considered later. Certainly the Canadian journalists present all gave SISS a thumbs-up and felt both Canadian consumers and cities would benefit from the innovative system.

Program Manager Kenichiro Saruwatari, who introduced the system to us earlier in a presentation, also noted SISS was compatible with both manual and automatic transmissions. My test vehicle was fitted with an automatic transmission.

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