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MetroMPG 12-21-2007 10:41 AM

Article: Idle stops just got smarter
If you haven't yet heard of Mazda's take on idle-stop, this is worth a read.

"Mazda says the system will reduce fuel consumption in the normal city cycle by 10 per cent, more in heavy traffic — an incredible saving."


At Mazda's research and development centre in Hiroshima, engineers had a different idea. Why go to the added expense, weight and complexity of that powerful electric motor, space-robbing battery pack and gigs of computing power if the same result can be achieved using existing parts and pieces? So they came up with SISS — Smart Idle Stop System.

SISS starts with a thoroughly conventional four-cylinder engine with direct injection. The process starts when the vehicle comes to a stop and remains there for a predetermined period of time, say a second or two, as would be the case in heavy traffic or at a stop sign.

The engine control module makes sure all four pistons stop half-way between top and bottom dead-centre and stores the position of each in memory. Both the compression and expansion stroke pistons are stopped in the right position to balance air volume.

When the signal is received to start the engine — from a sensor on the brake or accelerator — a shot of fuel is injected into the combustion cylinder, and the spark plug in that cylinder fired.

The resultant explosion forces the piston down, pushing the engine backward slightly. That motion forces another piston upward and into the regular compression mode, where everything reverts to normal operation, the fuel is injected and ignited and piston pushed down and the crankshaft turned etc., starting the engine in the forward direction — without the starter.


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

diamondlarry 12-21-2007 01:29 PM

That sounds very cool! It also sounds similar to something my uncle was telling me about 25-30 years ago. He said that GM(?) was experimenting with a car that would not have a starter but instead would start the car as in the above. I think he said that there was a small motor that could be used to spin the engine over to get a reference point in case of 12V failure/replacement.

brucepick 12-21-2007 02:09 PM

I did read about that somewhere.
Really cool idea.
Hope they license it to all the makers.

At least in the past, that was the Japanese way - one maker would develop a concept, and would license it to most or all of the big Japanese players. Here, we fight over stuff like that and are just as likely to ditch our best new concepts and crush them. I can't believe how stupid we are sometimes. Sometimes???

newtonsfirstlaw 12-21-2007 08:58 PM

That's a brilliant idea, but sounds difficult to retrofit. Am I wrong?

MetroMPG 12-21-2007 09:06 PM

You are not wrong. That would be hard to DIY.

Lucky for us, all cars are already equipped from the factory with basic idle-stop systems:

newtonsfirstlaw 12-21-2007 09:30 PM


Originally Posted by MetroMPG (Post 2802)

Yes, I call my car a "manual hybrid" sometimes.

MetroMPG 12-21-2007 09:33 PM


Originally Posted by diamondlarry (Post 2747)
I think he said that there was a small motor that could be used to spin the engine over to get a reference point in case of 12V failure/replacement.

You'd also need the 12v starter if the car's been sitting a while - don't you need compression for this to work? I was under the impression that compression "leaks down" when an engine's been off for a while. Not an issue for idle-stop/restart, but I don't know that the Mazda approach would start a motor that's been off overnight, for example.

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