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GM introducing 2012 LaCrosse with new eAssist “light electrification” system as standard

Powertrain of the 2012 LaCrosse with eAssist. Click to enlarge.

GM is unveiling the 2012 Buick LaCrosse with eAssist—incorporating its second-generation belt-alternator-starter (BAS) hybrid technology—which increases fuel economy by 25% compared to the four-cylinder/six-speed powertrain in the 2011 LaCrosse. The eAssist “light electrification” system supports highway fuel economy of 37 mpg US (6.36 L/100km) and 25 mpg (9.41 L/100km) city, and becomes the standard powertrain on LaCrosse starting next summer.

Mated to a 2.4L Ecotec direct injection four-cylinder engine and next-generation six-speed automatic transmission, the eAssist system incorporates a 115V (0.5 kWh, 15 kW peak power) Li-ion battery and 15 kW, 110 lb-ft (150 N·m) electric motor-generator to recapture braking energy, to provide electrical boost in various driving scenarios, and to optimize engine and transmission operation. The eAssist system:

  • Delivers regenerative braking, which provides up to 15 kW of electricity to charge the battery;
  • Provides up to 11 kW (15 hp) of electric power assistance during acceleration;
  • Automatic engine shut-off when the vehicle is stopped
  • Aggressive fuel cut-off during deceleration down to zero vehicle speed, enabled by the torque smoothing provided by the motor-generator unit; and
  • Intelligent charge/discharge of the high-voltage battery.
“The battery system is designed to provide power assistance to the internal combustion engine, rather than storing energy for all-electric propulsion. It’s really an extension of the conventional internal combustion engine, not a replacement for it.”
—Steve Poulos

Buick LaCrosse with eAssist technology also features improved underbody aerodynamics and tires optimized for performance and fuel economy, as well as active control of front-end airflow that improves aerodynamics and engine warm-up. 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. All of these technologies increase 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, enabling the driver to drive with 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.

eAssist. While the eAssist system shares the same basic belt-alternator-starter configuration of previous BAS designs, it delivers more than three times the power and is much more capable than the previous-generation BAS system.

The eAssist system is more than just the next-generation BAS system. The ability to integrate regenerative braking with the latest lithium-ion battery technology creates a system that delivers significant fuel-efficiency gains that customers will enjoy. Being able to provide electric boost to the powertrain system during heavy acceleration and grade driving enables the LaCrosse transmission to operate more efficiently, while the added functionality of engine start-stop and fuel shut-off during deceleration provides added fuel savings.

—Steve Poulos, global chief engineer of the eAssist system

The eAssist system’s 115V air-cooled lithium-ion battery bolsters the 2.4L Ecotec four-cylinder engine with approximately 11 kW (15 horsepower) of electric power assist during heavy acceleration and 15 kW of regenerative braking power. That compares with only 2 kW of power assist and 5 kW of regenerative power on the previous BAS system. The greater power capability enables greater energy capture during regenerative braking for improved fuel economy.

The system also enables the 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.

The eAssist power pack contains the lithium-ion battery pack, the integrated power inverter and 12V power supply. It is located in a compartment between the rear seat and trunk, and weighs 65 pounds (29 kg). It still allows rear access to the trunk via the split-folding rear seat. Trunk space is slightly reduced when compared with 2011 models with the four-cylinder/six-speed powertrain, but still offers 10.9 cubic feet (307 liters) of storage. An electric fan cools the power pack, drawing air from a vent located in the package tray, behind the rear seat. The fans are designed to be quiet from the cabin.

The eAssist system’s electric motor-generator is mounted to the engine in place of the alternator to provide both motor assist and electric-generating functions through a new engine belt-drive system. The motor-generator is a high-performance, compact induction motor that is liquid-cooled for increased performance and efficiency.

Next-generation six-speed. The eAssist system works with LaCrosse’s direct injected 2.4L Ecotec four-cylinder and next-generation six-speed automatic powertrain combination. In the LaCrosse with eAssist, the engine is rated at approximately 180 horsepower (134 kW) and the next-generation Hydra-Matic 6T40 offers features designed to enhance powertrain efficiency.

Significant internal transmission changes to clutch controls and hardware provide reduced spin losses while improving shift response and time. The added electric power provided by the eAssist system allows for higher gearing to improve steady state efficiency without impacting acceleration performance or driveability. The system’s capability of providing some electric assistance at cruising speeds allows the driver to accelerate lightly or ascend mild grades without the transmission downshifting.

An auxiliary, electric-driven transmission oil pump is added to the 6T40, which keeps the transmission primed and the fluid flowing when the engine shuts down at a stop. That keeps the transmission ready to perform when the driver accelerates.

It’s a very integrated powertrain system, with no compromises in driving performance, shift quality or ride and handling. We believe this combination points to the future of vehicles powered primarily by an internal combustion engine.

—Daryl Wilson, LaCrosse lead development engineer



GM introducing 2012 LaCrosse with new eAssist “light electrification” system as STANDARD, as in, you have no other choice except a different vehicle altogether. As in, you have no choice, if you want the LaCrosse, but to pay the $10,000 premium for eAssist. Will you get $10,000 in fuel savings over the life of the vehicle? Probably NOT.


$10,000??? Where did you get that number? That would seem to be rather high. The lithium battery is only .5kWh which couldn't cost more tha $250-$300 in volume today so I will be interesting to see what the price differential from the 2011 to 2012 model is.

I would be surprised to see more than a $1,000 difference in price. That would still take a few years to save on gasoline, but not impossible to get there.


Easy to save over $10K. Gas @ $3.00 (increases 10% per year) drive 15,000 miles/year, old MPG 24, new MPG 40. After 10 years savings = $11,953.07 Of course your savings will very, just play with the numbers. But more important is you've save 2,500 gallons of gas which is the direction we all should be going.

The motor-generator is a high-performance, compact induction motor
No brushes and no rare-earth metals.

Suck it, China!


This is very good.
25% improvement for little cost, which will reduce as the technology becomes better understood and more widely rolled out.

Over time, they will be able to improve the efficiency improvement while keeping the cost down.
It is much better that 1M people get 37 mpg cars than 100,000 get 50mpg cars, hence low cost, widely applied light hybridization reduces fuel usage more than expensive full hybridization.


I agree but one has to keep Jevon's paradox in the back of the mind. That's why I'm for a bit of market intervention: higher gasoline taxes and then using those taxes to subsidize vehicles with hybrid technologies


I think your numbers look right for the cost component.


Will it be available with the 2.0 or 1.4 turbos?


Vehicle electrification can be done one mini step at a time to progressively reduce fuel consumption. That's one example of a low cost step that could be applied almost across the board to reduce fuel consumption by up to 25%. Why not do it now?

As batteries are mass produced in large quantities and their price come down, the next step could be taken to further reduce fuel consumption by up to another 20%/25%% with larger capacity batteries and another e-motor.

Extended e-range PHEVs and BEVs could follow with the third step or generation.

Each mini step should not take more than 4 to 6 years.

Reducing fuel consumption by 20% to 25% every 4 to 6 years could solve liquid fuel shortages and importation for many countries by 2020/2025.


2011 Buick LaCrosse
CX $26,495 2.4L I4 182HP 19/30 mpg

Comparing 19/30 mpg to this 25/37 mpg, it seems like an improvement, if the price is right. I can not see a lot of regenerative capture with 0.5 kWh of batteries, but we will see what the market says.


Another mini step could be done with improved performance, smaller, thinner, variable flux, in wheel or rear/front wheel e-motors using less rare earth. Those motors are being developed in Japan (Toyota ++) and will be more suited to electrified vehicles because they will maintain a more stable efficiency under variable loads, which is not the case on most existing e-motors.

Eventually, lighter 4 in-wheel improved e-motors will allow 4-wheel steering + 4WD and would liberate valuable cab space for more batteries, passengers, cargo etc. Overall drive train efficiency will be maximized by better controlling power to front and rear wheels.

Advanced EVs are in their infancy. By 2020/2030 we will have more efficient, longer range, lower cost, much lighter EVs.

Interesting decades ahead.

Nick Lyons

RE price:

GM press release states, "...about $30,000 (exact pricing has not yet been set)..."

So it appears they are upping the base price by ~$3K and making e-assist standard. Not clear if this comparison is pure apples-to-apples, based on other features included, etc.


BAS has been offered as a more cost effective solution, we will see if the market thinks so. It could be a good match up of torque and horsepower with the 6 speed transmission. They will have to let the car magazines take a turn at the wheel to see.

Stan Peterson

Engineer Poet,

I like that you noticed that no rare earths, are needed or used. The right way to "sell", light, micro-hybrids, is to simply include them as standard equipment, like they have done with the Lacross.

Perhaps this whole approach will spread across GM. With EPA numbers of 25 and 37 that is awfully close to meeting the 36.5 mpg CAFE,which uses a different scale. And this is for a heavily optioned, (higher weight), upscale, mid-size car, too.

I still think unlike you, in the long run it is best to keep fuel costs a low a possible, to make everybody's products more inexpensive that have embedded Transportation costs.

I'd much rather do that, than pouring it down a rat hole rewarding do-nothing politicians and bureaucrats, whose only product is more regulations and more mischief.


In comparing the 2011 19/30 mpg rating to the 2012 25/37 mpg rating I'm wondering why this eAssist doesn't improve the numbers more during city driving[where you have a lot of stop&go] and less during highway driving[which is mostly steadystate].

What this tells me is that they are getting more out of the aerodynamics than the eAssist.


The BAS+ is only 11 kw on a car weighing more than 4000 pounds. A Honda Civic hybrid is 20 kw on a car that weighs less than 3000 pounds. Even though they both have start/stop and regenerative braking, the Buick is a lot of weight to launch from a stop.

2011 Honda Civic Hybrid
Standard Engine 1.3L I4
Fuel Economy Cty/Hwy 40/43

2011 Honda Civic Sedan
Standard Engine 1.8L I4
Fuel Economy Cty/Hwy 25/36

What is says to me is that the BAS+ does not do much at all. The start/stop, off the line and regenerative energy recovery are the major gas savers around town.

paul in hampden

SJC..... You seem to contradict yourself. You say BAS+ does not do much at all yet you show that it is giving a car that is 1000lbs heavier slightly better MPG as a Honda Civic. I think that is pretty good!


I was wondering in the same line as ai_vin why aould there be such a similar gain in both city and highway driving.

For city driving cycles,acceleration, deceleration and the stop and go, this kind of BAS based "light electrification" with regenerative braking should bring immediate benefits. No surprises here.

For highway driving cycles, with a nearly constant engine speed, this upgrade seem quite 'too good to be true'.

How can the get this extra 7 mpg (30->37mpg) out of the already efficient NA DI 2.4L ecotec? Even though the compression ratio of 11.2:1 allowed by the DI is quite high (for regular gas) it was already so in 2009/2010.

Would this be related to the substitution of the fuel enrichment in the upreving the engine by the 'electrical help' and the agressive fuel shut-off when in the standard test cycle ?


No contradiction, Honda gets 50% better mileage around town and Buick gets 25% better. Honda chose light weight and more motor and battery power and got better results. I would say the contradiction was at Buick.

As I said, most of the city gains were from start/stop and maybe some regenerative braking energy capture. The Honda has better statistics because of a down sized engine and better use of the battery and motor accelerating a much lighter car. The Buick motor can not do much to launch the car because the motor is too weak and the car too heavy. That is certainly a contradiction in goals and results.


Nothing in the news on the air-conditioning system. It really needs to be electric and run off the HV battery, or else the engine cannot shut down during stops when the climate control is running.

Highway mileage is mostly a factor of aerodynamics and engine efficiency. I'd believe 37 MPG from this car.


The .5kWh is plenty for the regen braking. The LeCross weighs in at 3829lbs so going from 60mph->0 only regens .175kWh (about .155kWh after mechanical and aero losses).

The average stop is about 4 seconds so that is a rate of 141kW. The regen system only takes about 15kW so that is 10.6% of the braking...and the rest is left to the traditional brakes.

So those numbers work out pretty well.

As for the hwy mpg improvements...I think Engineer Poet nailed that one. Aero and general engine efficency improvements. The city improvements come from the regen braking.


The 2010 has 182hp @ 6700rpm, and 172ft-lbs torque @ 4900rpm, apparently the 2012 version has approximately the same hp but perhaps much higher low end torque due to the electric motor. The high compression ratio and reduced hp of the ICE suggest that they may have atkinsonized it.


Correction, from the pdf posted by Nick Lyons:

Maximum electric motor torque (electric assist)
79 lb.-ft. / 107 Nm @ 1,000 rpm

Maximum electric motor power(electric assist)
15 hp / 11.2 kW @ 1,000-2,200 rpm

The power and torque ratings for the ICE remain the same as the 2010 version.. Thus the electric motor brings up the low end torque higher than the V6 powered LaCrosse.

This BAS + would be great in the Equinox


The highway numbers look good, ai-vin has it right the BAS+ does little or nothing on the highway, so it seems to be mostly the six speed transmission and streamlining.

My point is the city numbers, they could have gone with the 2.0 turbo and BAS+ or just a 2.0 and BAS+. They chose the cheapest route and I think the performance will not be all that good.


You save the most oil/emissions per kWh of battery capacity by spreading it to as many cars as possible. It would be better to have the ~24kWh of battery capacity in an EV as 20 hybrids.

Although I would like to see how it works in the Eco Cruze, should hit 45 hwy 35 city sort of numbers.

Need to add an electric heat pump and a plug so you can top up the battery and preheat the cab / engine.

Do we assume it uses the same batteries as the volt?


The car does not have 15 kW of braking energy, it is an 11 kW motor and it may not produce that much as an inductive alternator in a 45 mph to zero stop. Even if it does, it is hard to put 11 kW into 0.5 kWh of batteries. It would depend on State of Charge so maybe they run them at half capacity. The city mileage gains come mostly from start/stop, you get zero miles per gallon at a stop light with the engine idling.

We don't know what this model weighs after the motor, controller and battery weight. If they can only capture 5% of the braking energy, that is not a lot. It is there as a marketing tool, but it does little to improve mileage. It has been said in HEVs with 1 kWh of batteries and larger motor/alternators that only 10% of the mileage improvement in the city is due to regenerative braking.

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