The eAssist system may have entered production less than a year ago, but General Motors is clearly making a big bet on the mild hybrid system to help its Buick brand meet rising fuel economy regulations.

First offered on the base 2.4-liter engine in the 2012 Buick Lacrosse, the eAssist system was optional on the smaller 2012 Buick Regal.

Now, for 2013, that formerly optional 2.4-liter engine with eAssist becomes the base engine in the 2013 Regal--there's no more regular direct-injected 2.4-liter engine.

The new base engine takes the 2013 Regal's EPA fuel efficiency ratings to 25 mpg city, 36 mpg highway, for a combined 29-mpg rating--the same as the ratings for the larger Lacrosse with the same engine.

That improves on the previous year's base Regal, with the direct-injected 2.4-liter four, which was rated at 19 mpg city, 31 mpg highway, for a combined rating of 23 mpg.

(There's also a turbocharged 2.0-liter four, offered in a 240-hp version in the Regal Turbo and a 270-hp output in the Regal GS. Both are rated at 22 mpg.)

The 2013 Regal joins the Lacrosse and the 2013 Chevrolet Malibu Eco, which launched earlier this year, as the three mid-size and large sedans in GM's lineup thus far that use the mild hybrid system to boost EPA fuel-efficiency ratings.

2012 Buick Regal prototype touchscreen interface

2012 Buick Regal prototype touchscreen interface

Despite a rocky start five years ago for the first generation of its system, General Motors is convinced that eAssist offers a cost-effective way to improve the fuel efficiency of its mid-size and larger sedans.

As a mild hybrid, the eAssist system cannot move the car solely on electric power from a standstill--unlike the full hybrid system in a Toyota Prius, for instance.

But the smaller 0.5-kilowatt-hour lithium-ion battery pack, mounted in the trunk, and the combined alternator-starter--which acts as an electric motor and generator as well--recapture energy that would have been wasted in braking and feed it back as torque that supplements that provided by the engine.

With GM's six-speed automatic transmission, the added torque from the electric motor can avert many transmission downshifts, keeping the engine running more slowly and fuel efficiently.

2012 Buick Regal with eAssist

2012 Buick Regal with eAssist

After the car comes to a stop and switches off the engine, the motor-generator acts as a starter to restart the engine as soon as the driver starts to lift off the brake pedal.

GM seems likely to fit the eAssist system to other vehicles in its lineup in future model years.

Candidates might include the all-new 2014 Chevrolet Impala, built on the same platform as the larger Buick Lacrosse, and perhaps some of its compact crossovers as well.

GM has said in the past that it could build as many as 100,000 vehicles a year fitted with the eAssist system.

Buick hasn't yet released pricing for the 2013 Regal; the eAssist package is priced as a $2,000 option for the 2012 Regal, which started at $27,940.


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