Electric Assist Gives Buick's LaCrosse 37 MPG

As gas prices go up, so does purchase consideration for more fuel-efficient cars.  And the new 2012 Buick LaCrosse with eAssist, a sedan that comfortably seats five adults, delivers highway fuel economy on par with subcompacts like the Mini Cooper.

LaCrosse with eAssist, which goes on sale this summer, uses a variety of technological advances and body enhancements to deliver estimated segment-leading fuel economy of 37 mpg on the highway and 25 mpg in city driving without sacrificing passenger comfort. The fuel economy ratings await EPA certification.

Not only is the luxury sedan expected to be more fuel efficient than competitors like the Acura TL, Lexus ES350 and Lincoln MKS, it also expects to beat smaller hybrids, including the Lincoln MKZ Hybrid, Toyota Camry Hybrid and Lexus HS Hybrid on the highway, while offering more rear leg room than any of them.

LaCrosse is the first in its segment with a four-cylinder, six-speed powertrain, the first with HiPer Strut suspension for improved ride and handling, and is now has the new standard eAssist technology.

Program engineers improved the fuel economy of the outgoing four-cylinder, six-speed 2011 model by 25 percent by implementing a number of improvements.  Chief among them was the introduction of the electric assist (eAssist) system that is mated to a 2.4L Ecotec direct injection four-cylinder engine and a next-generation six-speed automatic transmission.

The eAssist system uses a 115-volt lithium-ion battery system and 15-kilowatt electric motor-generator to enable regenerative braking, which takes place anytime the driver is off the throttle. Regenerative braking provides up to 15 kW of electricity to charge the battery to power all of the vehicle's electrical systems with recaptured energy instead of fuel, which dramatically reduces the need to load the engine with the generator.

The system uses power stored in the battery to provide 15 hp of electric power assistance in various driving scenarios, delivering more than three times the power provided by the previous-generation belt-alternator-starter system.

"The additional 15 hp provided by electric assist allowed us to lower LaCrosse's gear ratio without sacrificing reserve acceleration and performance," said Steve Poulos, global chief engineer of the eAssist system. "For example, when climbing the grade of an overpass, a normal vehicle will downshift and lose some fuel efficiency, but LaCrosse with eAssist maintains gear for improved performance and increased efficiency."

EAssist also enables LaCrosse's Ecotec engine to shut down fuel delivery in certain deceleration conditions, which saves additional fuel. While in fuel shut-off mode, the motor-generator unit continues spinning along with the engine to provide immediate and smooth take-off power when the driver presses on the accelerator. Then, as the vehicle comes to a stop, the motor-generator unit spins the engine, bringing it to a smooth stop -- properly positioned for a smooth restart.

"All Buick automatics do some deceleration fuel cutoff when the driver is not on the accelerator," said Daryl Wilson, LaCrosse lead development engineer. "But eAssist allowed us to take the decel fuel cutoff all the way down to zero speed, which resulted in a significant fuel economy increase."

Program engineers also improved LaCrosse's underbody aerodynamics by strategically placing underbody aero panels. Tires were optimized for performance and fuel economy, and electronically controlled shutters in the lower grille close at higher speeds to push more air over the vehicle, which increases aerodynamic efficiency to enhance fuel economy and engine warm-up. All of these technologies increase the effectiveness of the eAssist system's regenerative braking capability, while also improving the vehicle's efficiency while driving.

LaCrosse with eAssist includes an ECO gauge on the instrument panel that continuously responds to driving behavior, helping the driver attain maximum efficiency. It also features a hill-assist system that captures brake pressure to help the driver more comfortably accelerate from a stop on a moderate or steep grade. It does this by greatly reducing the tendency of the vehicle to roll backward with the engine in shut-down mode. 

"All of these improvements deliver significant fuel-efficiency gains Buick customers will appreciate," DiSalle said. "With eAssist, Buick customers don't have to trade a premium driving experience for efficiency."

The eAssist system also comes to Buick Regal in late 2011.