The stop bucked here
Hybrid cars, by design, shut off the gas engine when they’re stopped, which is a neatish way to save a little more fuel. But there’s nothing about the technique that demands hybrid technology:
It’s available from a number of automakers in the European and Japanese markets. Mazda claims nearly half of its Mazda3 compacts and Biante minivans sold in Japan are ordered with the $500 option, as consumers seek out fuel economy improvement without the cost of a full hybrid system. So, why doesn’t Mazda sell idle-stop equipped cars in the US? According to the company, though Japanese fuel economy tests show stop-start improving efficiency by seven to nine percent “the EPA city-mode test cycle includes only one complete vehicle stop, so stop-start technology registers only a 0.1- or 0.2-mpg improvement.” And who would pay $500 for that?
Having burned up rather a lot of starters in my day, I looked askance at this idea, but Mazda’s restart system doesn’t involve the starter at all:
Conventional idling stop systems restart a vehicle’s engine with an electric motor using exactly the same process as when the engine is started normally. Mazda’s SISS, on the other hand, restarts the engine through combustion. Mazda’s system initiates engine restart by injecting fuel directly into the cylinder while the engine is stopped, and igniting it to generate downward piston force.
In order to restart the engine by combustion, the pistons must be stopped at exactly the correct position to create the right balance of air volume in each cylinder. The Smart Idle Stop System provides precise control over the piston positions during engine shutdown to accomplish this. The SISS indexes each cylinder and initiates fuel injection before the engine begins to rotate. This enables the engine to be restarted in just 0.35 seconds, roughly half the time of a conventional electric motor idling stop system.
One drawback: this apparently wouldn’t work on Mazda’s Wankel rotary engines, which don’t have cylinders but which need all the help they can get to save fuel.
On the other hand, the 3 at the moment doesn’t offer any particular fuel-economy advantages over its C-segment competition (Corolla, Civic, Focus), which suggests that the system might be worthwhile if they can get the price down a little.
