This year's recently concluded L.A. Auto Show was all about green, from the Kia Optima Hybrid to the Toyota Rav4 EV to GM’s 2012 Buick LaCrosse with eAssist. What’s that last one, you ask? How is this Buick a green machine?
"eAssist is similar in principle to the belt-alternator-starter (BAS) first used on the 2007 Saturn Vue Green Line," explained Steve Poulos, eAssist global chief engineer.
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For those who don't remember the Saturn Vue Green Line Hybrid, it ranks as one of the least successful forays into the hybrid market. GM didn’t sell many of these mild hybrids, and a painful recall harmed the reputation of the system.
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But now GM is back with a new and improved version. A belt-alternator-starter system combines the function the alternator and starter motor into one multi-talented device, which hangs off the engine looking somewhat like an enormous alternator. (An alternator is the underhood component responsible for recharging a vehicle's battery and supplying electricity to the vehicle whenever it's running.) The BAS is connected to the crankshaft of the engine by a substantial drive belt, kind of like a conventional accessory belt on steroids.
In the eAssist system, this combined alternator/starter is an AC induction motor that is capable of multiple functions. It can generate electricity just like an alternator -- or for recharging the Buick's Hitachi 65-pound lithium ion battery array. It can also be used to start the engine. And unlike in the previous generation, it can actually propel the vehicle by itself in certain limited conditions.
New Application For Buick
In the 2012 Buick LaCrosse, the BAS is attached to 2.4-liter four-cylinder engine and six-speed automatic transmission. The engine and transmission are designed to enable regenerative braking and battery charging during coasting or while braking.
GM says that the BAS system adds 15 horsepower and 79 lb-ft of torque, which increases the fuel economy by 25-percent. So the 2012 LaCrosse with eAssist should be rated at 25 mpg city and 37 mpg highway -- solid numbers for well-equipped, comfortable mid-size sedan.
eAssist enhances mileage by "assisting" the gasoline engine with its work, and by making start/stop functionality possible. This is important because when the engine shuts off it stops consuming fuel entirely, for instance, while waiting at a red light. The eAssist system can then supply electricity to the vehicle accessories for up to two minutes. When the engine is cued to automatically re-start, the BAS delivers torque through its belt directly to the engine's crankshaft. This spins the engine back up to operating speed before the ignition fires to make the re-start smoother. The BAS then supplies torque assist as needed when the driver accelerates.
"Hybrid batteries provide power for longer durations. Our system is designed to charge and discharge in bursts so we don't need more capacity," explained GM's Polous.
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Not A Hybrid? Really?
None of GM’s auto show literature described eAssist as a mild-hybrid or a hybrid system of any sort. It’s curious that the percentage bump in fuel efficiency for the LaCrosse with eAssist is just a tad below the improvement in GM’s full hybrid system used in the Chevy Tahoe and Cadillac Escalade. In other words, eAssist is delivering an economy boost nearly equal to GM's much more sophisticated and complicated dual-mode hybrid system.
As for how it compares to other contemporary fuel-saving technologies, eAssist is less complex than a full hybrid such as the Toyota Prius or Ford Fusion. These vehicles have large batteries and powerful electric motors that can propel these vehicles for miles on nothing but electrons. Their fuel economy gains are much greater -- a 50 percent improvement, in the case of the Ford Fusion Hybrid.
However, eAssist is more complex than the start/stop technology used in the 2011 Porsche Panamera and Cayenne or the Mazda iStop (currently for sale in Japan and across Europe). Neither the German or Japanese options allow for any electric assist to the gasoline engine. These systems save fuel strictly by allowing the engine to shut down while the vehicle is idle in normal traffic.
eAssist more closely resembles the functionality offered by the Honda Insight hybrid and BMW’s ActiveHybrid 7. These hybrids use modestly sized electric motors located between the engine and transmission. Like eAssist, these electric motors do provide assist as well as start/stop, so they save fuel in two ways.
A Modular Design
We asked Poulos why GM dusted off its old BAS technology instead of going the same way as Honda and BMW. "We were already familiar with BAS and had learned so much about a simple, cost-effective system that added economy," he said. “There are challenges with adding an integrated motor into transmissions. Particularly in a front-wheel-drive application, packaging becomes an issue because it (the electric motor) adds length.”
So GM didn't want to invent something new when they already had something in house that worked and could be made better. Another benefit is that GM's BAS is also modular, meaning that it could be used on other vehicles and even other powertrains, such as smaller four-cylinder engines or larger V6 engines. The new BAS operates at three times the voltage of the old system and produces more than three times the power (11kW compared to less than 3kW).
When the 2012 LaCrosse goes on sale in the late spring of 2011, Buick will offer customers two engine choices for an identical MRSP: An eAssist 2.4-liter four-cylinder or a 3.6-liter V6. The 3.6-liter V-6 engine option cost $1,370 on the 2011 LaCrosse, so expect a base price starting around $28,000 for an eAssist LaCrosse.
But regardless which engine you select, hybrid badges won't be included. GM says one of the lessons it learned earlier this decade is that when customers see a hybrid badge, they assume the vehicle should deliver Toyota Prius mileage (think 50 mpg). The Green Line vehicles that Saturn offered, as well as the Chevrolet Malibu Hybrid (2008-09) were widely avoided because they didn't deliver the mileage the public expected from a hybrid.So it seems that GM is avoiding the issue by not calling the eAssist what it is, a mild-hybrid. Regardless, the technology promises significant fuel economy gains for a modest price increase. As for how the system actually works on the road, we'll let you know once we drive one.