|GM’s Belt Alternator Starter Hybrid in the Vue. Click to enlarge.|
General Motors announced that it will launch its Belt Alternator Starter (BAS) mild hybrid system starting in mid-2006 with the Saturn Vue Green Line.
The BAS system, which most recently appeared on the Chevy S3X diesel-hybrid prototype shown at the Paris Motor Show (earlier post), was originally announced late in 2003, and targeted for deployment first on the Saturn, then followed by the Malibu.
The BAS hybrid is one of three different hybrid systems that GM plans to introduce on up to 12 models. In addition to the BAS systems, GM offers a different version of a mild hybrid system (Flywheel Alternator Starter) on its Silverado and Sierra pickups, and is developing an all-new two-mode full hybrid system with DaimlerChrysler (earlier post).
Although initially sold only in six states, the Silverado/Sierra hybrids will expand nationwide beginning with the 2006 model year.
The two-mode system, designed to be deployable in a variety of applications, will appear first in GM’s new Chevrolet Tahoe and GMC Yukon full-size SUVs in 2007. The system is based on GM’s diesel-electric hybrid propulsion system for transit buses.
The Belt Alternator Starter system—a motor/generator with power electronics mated to the engine—basically provides stop-start functionality and regenerative braking with occasional motive assistance.
The BAS system enables early fuel cutoff to the engine during deceleration and shuts off the engine at “idle”. Regenerative braking and optimized charging combined with an energy storage system further enhance fuel economy while maintaining all vehicle accessories and passenger comfort systems during the periods when the engine is temporarily shut off.
The belt alternator starter hybrid also will provide an electric motor boost during acceleration when needed—some 110 lb-ft (150 Nm) of auto-start torque. During a wide-open throttle or aggressive passing maneuver, the system improves vehicle launch and acceleration feel by assisting the engine to achieve maximum power.
The BAS system is simple and flexible—able, according to GM, to be applied to multiple engines with minimal changes to the engine or transmission.
The best design is uncomplicated and easy to implement. This simple, elegant hybrid architecture makes it possible to implement globally on a broad spectrum of vehicle applications at an attractive price.—Larry Nitz, executive director of GM’s hybrid program
The belt alternator starter hybrid consists of six major components:
The electric motor/generator unit.
Engine coolant-cooled power electronics that control the motor/generator unit and provide 12-volt vehicle accessory power.
A 42V nickel metal hydride (NiMH) hybrid battery pack capable of delivering and receiving more than 10 kW of peak power
An engine control module that includes sophisticated Hybrid Supervisory Software to manage both engine and hybrid system operation.
A new engine accessory drive with dual tensioner assembly and aramid cord belt that enables reliable transfer of both motoring and generating torque.
The hybrid-enabled 4T45-E electronically controlled overdrive transaxle that includes an auxiliary oil pump and unique hybrid controls to ensure seamless hybrid operation.
GM’s belt alternator starter hybrid operates in motoring or generating mode.
In the motoring mode, the belt alternator starter hybrid is used to restart quickly the engine upon brake pedal release and to provide momentary acceleration assist as needed. Vehicle accessory power (12V) is also generated in this mode.
In the generating mode, the BAS hybrid system provides both 12V vehicle accessory power and power to recharge the hybrid battery.
In the Saturn Vue Green Line, the system will be mated with GM’s 2.4-liter variable valve timing (VVT) Ecotec engine and Hydra-Matic 4T45-E electronically controlled overdrive transaxle.
GM is not yet announcing fuel economy numbers or pricing for the Vue hybrid.
However, earlier projections on the BAS systems indicate a range of improvement of around 10%–12%. Since the current Saturn Vue with a 2.2-liter engine delivers about 24 mpg US combined, the BAS system—depending upon whatever other enhancements GM might make—probably will increase combined fuel economy for the small SUV to the upper 20s, with the greatest improvement, clearly, in city driving.
GM seems to be trying to strike a compromise between functionality (fuel efficiency), price and their projections of consumer demand.
We want to provide consumers a choice that will be in harmony with their budget, vehicle expectations and fuel economy needs. The belt alternator starter hybrid will offer consumers the combination of an affordable price and a good fuel economy improvement over the base vehicle.—Tom Stephens, group vice president, GM Powertrain