Engine start-stop systems are beginning to appear on a wider range of vehicles as carmakers seek to increase fuel economy wherever they can.
In the face of tightening global emissions standards, the savings from shutting down the engine while the car is standing still can be significant in conventional internal-combustion powertrains.
Current systems rely on battery power to keep electrical accessories running, and to restart the engine at the appropriate time.
But General Motors is trying something different with a new start-stop system for Cadillac models.
The system augments battery power with ultracapacitors supplied by Maxwell Technologies, and was developed by global supplier Continental.
It will be standard on 2016 Cadillac ATS and CTS models, excluding the ATS-V and CTS-V performance versions.
2016 Cadillac CTS
Maxwell claims GM is the first manufacturer to employ a system like this on production models.
Ultracapacitors are generally lighter than batteries, and are capable of providing quick bursts of power for the relatively brief periods when cars operate with their engines turned off.
Adding them to a start-stop system can help stabilize the flow of electricity, reducing high currents and repeated cycling that can shorten battery life, Maxwell claims.
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The company also claims this makes for smoother engine restarts.
This is just the latest example of carmakers and suppliers showing interest in more robust start-stop systems as a way to improve fuel economy.
GM created a system for the current-generation Chevrolet Malibu that uses a second 12-volt battery to provide additional electrical power.
2016 Cadillac ATS Sedan
There's considerable speculation that systems like this could grow into a new type of mild-hybrid powertrain for future models.
Bosch recently demonstrated a setup based around a 48-volt electrical system, which it claims could improve fuel efficiency by 15 percent--without a major increase in cost.
The supplier expects roughly 4 million vehicles worldwide to be equipped with this system by 2020.
A123 Systems and Johnson Controls also expect expanded start-stop systems to boost the market for small lithium-ion batteries over the next few years.
None of these systems can propel a car entirely on electricity, but the efficiency benefits of shutting off an internal-combustion engine for longer periods of time could prove worthwhile.