Geneva '08: GM announces new second-generation mild hybrid system

Click to enlarge

In mid-2006, General Motors released their first mainstream hybrid vehicle with first Saturn Vue Green Line. Prior to that the company had offered a mild hybrid system in the Silverado pickup but since that was really only offered in limited volumes to fleet and commercial buyers, we'll skip that one. The system in the Vue was dubbed the GM Hybrid system but it's more commonly called the belted-alternator-starter (BAS) system. Since the first Vue, the BAS system has been added to the Saturn Aura and Chevy Malibu as well as the redesigned 2008 Vue.

Last fall at the Frankfurt Motor Show GM showed a concept Opel Corsa with an updated version of the BAS system. At the time GM declined to give any details of the system other than the fact it had a lithium ion battery. At the Geneva Motor Show today, GM Chairman Rick Wagoner is announcing that the next-generation GM Hybrid system will go into production in 2010. More importantly, the upgrades to the system will make it more suitable for a much larger range of applications and production of the system will be increased dramatically. Learn more about the second generation of GM's mild hybrid system after the jump.

[Source: General Motors]

The BAS system has been criticized by many since it's debut for it's limited gains in fuel efficiency compared to hybrids from Toyota, Honda and Ford. In some applications that criticism has been pretty valid, with the Saturn Aura hybrid only picking up 2mpg over the conventional four-cylinder model. The new Vue on the other hand gets a 27 percent bump in mileage going from the base four cylinder to the hybrid. The one advantage that the system has had over competitors is cost. The price premium for the BAS system is typically only about $1,600-1,700.

The GM Hybrid system is actually pretty straightforward and requires relatively little in the way of changes to the base vehicle. The heart of the system is the motor/generator. The standard alternator is replaced by a unit that looks very similar but has the capability to provide extra drive assist to the engine. To do that GM had to develop a belt drive system with two idler tensioners to allow the motor to drive the engine as well as the other way around.

Normally the forces acting the drive belt only act on one side of the belt as the engine pulley pulls the belt to drive the alternator. The other side of the drive belt would be slack as the engine pulley can't push on a rubber belt. The idler takes up this slack. If the motor is driving the engine, it's pulling on the normally slack side and the reverse side would go slack requiring a second idler pulley.

All of this allows the motor/generator to provide automatic start/stop capability, motor the engine along with fuel shutoff during coast down, provide electrical power boost under acceleration and regenerative braking. Electrical energy for the current generation of the system is stored in a 36V nickel metal hydride battery. The 5kW capacity of the motor/generator and 36V output of the battery limits the application capability of the system which is why it's only available with the 2.4L four cylinder in three applications.

When GM showed the updated system in the Corsa last fall, it was paired up with a 1.3L turbodiesel. When the new system launches two years from now it will have the capability to be used with many more drivetrains, including diesels and flex-fuel engines. That's because an all-new motor generator using different technology will provide three times the power of the current unit while fitting into roughly the same package size. During a pre-show backgrounder, GM officials declined to say exactly what the nature of the new motor design was. GM also declined to get specific about the output of the new motor although 15kW is a good estimate and would put it at the same range as the mild hybrid system being developed by Mercedes-Benz and BMW.

The same basic drive system will be retained although it is upgraded to handle the extra power. Of course a more powerful motor and generator needs more electrons and place to store them. For a system that's intended to be applied globally to a wide range of vehicles and engines, a nickel battery won't cut it.

The new system switches over to a lithium ion power battery. Again GM was short on details, but they did give us some tantalizing hints. While Stephen Poulos, chief engineer for the hybrid system declined to reveal exactly what the battery voltage would be, it will be more than the 36V of the current system and less than the 300V used in the Two-Mode system. Somewhere around 100V seems to be a good bet.

The new pack will be 24 percent smaller in volume than the current NiMH unit. It will weigh forty percent less and have thirty-three percent more power. The smaller more powerful battery will give GM better packaging flexibility helping to make the system more adaptable to other applications.

The control software for the current system is completely different from the two-mode system. While developing the two-mode, GM engineers made the software architecture scalable and flexible so that it could be used with different hybrid applications. That includes the mild hybrid which will now use the same software base.

The low power capability of the current system means that it's not practical for use on bigger vehicles. The increased power output and energy storage of the new version makes it suitable for use with almost every mainstream application GM has. During the presentation Poulos provided an application example that started with the 3.6L V-6 that GM uses in numerous applications including the Lambda platform crossovers. That engine produces around 260hp depending on the application.

As an alternative, Poulos showed a turbocharged 2.4L four cylinder that matched the torque curve of the V-6 above 3,000rpm but was lacking at the lower regions where most drivers spend most of their time. With the next-gen mild hybrid system providing a torque assist at lower engine speeds in combination with the turbo four, the overall curve matched or exceeded the larger engine. While the current Two-Mode hybrid apparently doesn't fit in the Lambda engine compartment, this system definitely would. While matching performance, the turbo hybrid combination is smaller, lighter and more efficient.

While GM was undeniably reticent about getting too specific more than two years ahead of the production launch, they expect the new system to deliver a 15-20 percent boost in fuel economy compared to a similarly powerful conventional system. They also declined to say which vehicles would get the system, although the current vehicles are an obvious start.

However, the fact that they chose to announce the system in Geneva is a clear system that they intend to offer this system in every market they operate in. The system will be compatible with both front and rear wheel drive systems, so it seems likely that we'll see the new hybrid on rear drive cars like the Pontiac G8 and Chevy Camaro. While hybrids haven't been particularly in Europe to date, the coming of CO 2 limits in Europe will require companies like GM to go beyond the diesels they currently offer.

GM also declined to say how the manufacturing cost compares between the current and next gen systems. They did say that they expect the customer cost to be similar to the current system and it will be profitable quickly as volumes climb. No one would say on the record how high they expect volumes to go, but all indications are that 100,000 per year is strictly a jumping off point.

Share This Photo X