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First Drive: 2010 Mazda3 i-Stop

By Evan McCausland

Photography by Evan McCausland

Is the internal combustion engine dead? The number of firms around the globe sinking capital into advancing electric drive technologies, battery chemistry, and other alternative propulsion systems might suggest the internal combustion engine has finally reached its swansong, but Mazda begs to differ. Although the Japanese automaker has tinkered with a number of advanced propulsion systems over the past decade, it feels there's plenty of life left in conventional, fuel-burning engines, albeit not without a little help from new technologies.

The company's wide-reaching SkyActiv program promises to refine engines and transmissions alike in the pursuit of improved fuel economy and reduced emissions, but the company has another (and arguably simpler) card up its sleeve: the i-Stop start/stop system. Although i-Stop isn't offered in North America, we recently had a chance to sample a Japanese-spec Mazda3 so equipped.

Look Ma, No Belt Alternator Starter

In this day and age, a start/stop system isn't exactly revolutionary technology, but i-Stop is a relatively new addition to Mazda's powertrain portfolio. The system was first introduced in Japanese-market Mazda3 and Biante minivans in late 2008, before being rolled out into models destined for European and Australian markets. Mazda's system does, however, break from most other start/stop systems in one notable way: while most use a belt-driven starter/alternator to restart the engine, i-Stop accomplishes this same feat via direct fuel injection.

Mazda's i-Stop system is fitted to the company's 151-horsepower, direct-injection 2.0-liter I-4. When a driver brings the vehicle to a stop, the engine computer analyzes a number of different factors (manual transmission cars, for instance, need to be shifted into neutral). Once it determines that the vehicle has come to a halt, the computer manipulates both the throttle and alternator to shut off the engine, and then aligns each piston at the center of its stroke. When it's time to restart the engine, fuel is injected into a single cylinder and ignited, allowing the crankshaft to begin revolving before the starter motor completes the process.

An unusual approach, perhaps, but it does have its merits. Not only does this save Mazda the cost of designing and installing a belt alternator/starter system, it also improves the response time for restart. According to the company, i-Stop can restart the engine in under four-tenths of a second, roughly half that of conventional belt-alternator-starter systems.

The Art of Start/Stop

On paper, triggering i-Stop to shut off the engine should have been as simple as coming to a halt, but the system is occasionally fickle in the real world. Mazda notes certain conditions, including low engine temperatures or high accessory loads (i.e. running the air conditioning at its highest settings) will preempt engine shutdown, but even in best-case scenarios, i-Stop exhibits a few quirks.

To prevent shutting the engine down during short or rolling stops, engineers have tuned i-Stop to activate once the car has come to a complete stop. As a result, drivers will need to be resting for quite some time with a steady, firm foot on the brake pedal. I-Stop's quick start-up is a boon when trying to drive in aggressive, fast-moving traffic patterns, but its tuning is a bit too aggressive. Any movement on the brake pedal, including wiggling a big toe, tricks the computer into thinking the driver is ready to go and fires the engine up once again.

Mazda claims the i-Stop system can increase fuel economy by up to ten percent, but such sizable improvements will only be noted if the car is extensively driven in stop-and-go traffic. In highway cycles or commutes with infrequent stops, including the route we put the Mazda3 through over the course of a weekend, i-Stop fails to return any notable fuel economy averages.

The i-Start of Something?

This dilemma is precisely why we haven't yet seen i-Stop in any North American Mazda to date. Jeremy Barnes, communications director for Mazda North America, tells us the company is quite keen on bringing the system to North America (especially Canada, where some providences have anti-idling regulations), but the problem comes when trying to illustrate the benefit to the consumer.

The touted ten-percent figure is based upon Japan's 10-15 fuel economy test cycle, which incorporates multiple lengthy stops. The EPA's city cycle test regiment, however, incorporates only one full stop. In that case, Barnes says i-Stop will only improve the Mazda3's EPA rating by one-tenth of one percent. Couple that meager improvement with the added cost of the system (estimated to be roughly $500-600) and it's easy to see why many American consumers would avoid taking the plunge.

Barnes notes Mazda's first priority is to introduce the SkyActive technologies across its global portfolio, but suggests introducing i-Stop in additional vehicles -- even those bound for North America -- could be the next step in improving fuel economy and paving the way for hybrid drivetrains further down the line. No precise timetable was given, but unless the EPA decides to alter its city cycle test methodology, expect i-Stop's American introduction to be part of Mazda's long-term solution, not a short-term fix.