When your vehicle is stopped with the engine idling, the fuel it’s using is effectively wasted.
In that situation, its fuel consumption rate, in terms of litres per hundred kilometres, is infinite. In terms that may be more readily understood, you’re getting zero miles per gallon!
It stands to reason, then, that an effective way to reduce fuel consumption is to reduce idling time. It’s also an effective way to reduce exhaust emissions.
That’s the thought process behind the anti-idling bylaws that have been enacted by several jurisdictions, including Toronto.
More: Why idling is for idiots
Those parallel benefits are also the reasons why one of the common features in hybrid vehicles — and one of the key contributors to their fuel efficiency — is an automatic stop-start system.
Depending on the application and operating conditions, such a system alone can reduce fuel consumption by 2 to 8 per cent.
An auto stop-start system is exactly what its name implies. It automatically shuts off the engine when the car comes to a stop and restarts it when the driver releases the brake or steps on the accelerator.
Most auto stop-start systems require greater battery capacity and a more robust starter motor than is found in a conventional car or truck, which is why they mate well with hybrid technologies.
But they have also been offered on non-hybrid vehicles in Europe for several years.
In fact, more than 30 per cent of all new vehicles sold on the continent are now employing auto stop-start technology, according to the Schaeffler Group, a leading supplier of torque converters for automatic transmissions. Another major supplier, Robert Bosch has projected that the penetration rate will reach 50 per cent by 2013.
So why hasn’t this technology caught on to a greater extent in North America? For one, most of those European applications are in vehicles with manual transmissions, which are not nearly as plentiful in our market.
With a manual transmission, the start-stop cycles can take place when the clutch is disengaged by the driver.
An automatic transmission makes it more difficult to incorporate the technology because the torque converter between the engine and transmission is always engaged.
According to Schaeffler, integrating auto stop-start with automatic transmissions using conventional torque converters could create a delay of up to three seconds in certain situations, such as moving one’s foot from the brake to the accelerator before the vehicle comes to a complete stop.
But technology to overcome that challenge is slowly evolving. Both Schaeffler and Denso, for example, have developed permanently-engaged starter motors that eliminate the need, and the corresponding time lag, to synchronize starter pinion and torque-converter ring gear speeds prior to engagement.
Another issue is that automatic transmissions rely on hydraulic pressure, generated by an engine-driven pump, for their operation. If the engine stops, they lose hydraulic pressure.
Automakers and their suppliers are addressing that issue either by providing either auxiliary electric hydraulic pumps or larger pressure accumulators to keep the transmission functional during short engine shutdowns.
The bottom line is that the technical impediments to adopting auto stop-start systems in vehicles with automatic transmissions are no longer deal-breakers. Solutions are at hand.
But there are other considerations that may slow their adoption.
Mazda, for example, has developed an innovative auto stop-start system, called iStop, which operates without using the starter motor, thus eliminating the need for, and weight penalty of, additional starter and battery capacity, which most other systems require.
But the iStop system will not be offered in North America when the new Mazda3 and CX-5 arrive this fall with other fuel-efficient technologies.
According to a Mazda spokesperson, that’s because North American fuel consumption test procedures and ratings are not designed to accommodate advanced technologies such as auto start-stop systems and therefore don’t fully reflect their fuel-saving benefits. “So that, coupled with the added cost of the system, would make it hard to communicate the real-world benefits to consumers.”
Nevertheless, we will see more widespread availability of auto start-stop systems beyond just hybrid and micro-hybrid applications, such as Buick’s LaCrosse e-Assist.
Porsche already incorporates auto start-stop in both Cayenne and Panamera models and Ford has revealed plans to offer the systems with its EcoBoost engines.
Others will inevitably follow, if for no other reason than competitive pressures will demand it.