|Regal with eAssist. Click to enlarge.|
GM is applying its eAssist mild hybrid system to the 2012 Regal, making it the second Buick model after LaCrosse to feature the second-generation light electrification technology (earlier post), which is GM’s current default mild hybrid system for electrification applications of 20 kW power or less.
The system uses a 115V, 0.5 kWh lithium-ion battery system built with Hitachi power-optimized cells (earlier post), an electric induction motor-generator and regenerative braking capability to improve fuel economy.
Somewhere around 20 kW, you start to act like a full hybrid...you start adding clutches, motors, your cost goes up. We have solutions for strong hybrid solutions. If we stay under 20 kW and keep a direct drive we think [eAssist] is the most cost-effective.
We’ve done a comparison with a flywheel motor. There are packaging constraints, it forces the motor into a certain geometry. It might be marginally more efficient than a belt-driven system, but it’s more expensive. It made more sense [for us] to stay with a BAS (belt-alternator-starter) type system. We have a lot of history with it. For this power level, we think this is the right solution for GM, and we continue to develop it beyond this level introduced today.—Steve Poulos, GM Chief Engineer for Mild Hybrid and Battery Electric Powertrains
|GM’s Pete Savagian is scheduled to give a talk on the eAssist powertrain at the SAE 2011 Hybrid Vehicle Technologies Symposium this Wednesday in Anaheim, Ca.|
The eAssist system’s 115V air-cooled lithium-ion battery (15 kW peak) bolsters the 2.4L Ecotec four-cylinder engine with approximately 11 kW (15 hp) of electric power assist during heavy acceleration and 15 kW of regenerative braking power. The system also enables the Ecotec engine to shut down fuel delivery in certain deceleration conditions, which saves additional fuel. Total pack weight of is 29kg, giving the pack a peak power density of 517 W/kg.
The battery was designed from the outset some time ago for this type of application...it evolved for this application, really for transient-type maneuvers. It doesn’t want to run electrically for a long period of time, it’s cranked up for power. It’s not a derivative of an electric car battery, it’s customized for this type of application.
GM is trying to lead in this area, trying to lead in a foundational approach as well as on the high end with the Volt. I think that from a volume standpoint what we have created is something that has high bandwidth potential. The Epsilon platform has many variants sold in many parts of the world.—Steve Poulos
The pack has a working state of charge (SOC) window of about 20%, Poulos said, with the ability to go above and beyond.
The Regal with eAssist uses the same power cube—engine, transmission and eAssist pack—used in the LaCrosse, said Poulos. LaCrosse and Regal are sister vehicle from a platform standpoint, being built on the global Epsilon platform, he said.
In the Regal, eAssist improves overall fuel economy by 25% over the 2011 four-cylinder/six-speed powertrain. Estimated fuel economy is 26 mpg city and 37 mpg on the highway (pending EPA certification).
Regal with eAssist option goes on sale this fall. It joins an expanding lineup that also includes 2.4L and 2.0L Turbo (with manual transmission) models, as well as the upcoming Regal GS. In addition to the packages offered in other Regal models, Regal with eAssist offers unique features including:
- Lightweight 17-inch alloy wheels and tires with lower rolling resistance;
- A driver-selectable, fuel economy-optimizing mode for the air conditioning system, which enables more frequent and longer-duration engine stop periods;
- An ECO gauge on the instrument panel that continuously responds to driving behavior, enabling the driver to drive with greater efficiency; and
- A powerflow readout in the 7-inch infotainment screen, which shows the flow of energy through the electric assist system, such as battery charging from regeneration and electric power directed to the engine.
Mated to Regal’s 2.4L Ecotec direct injection four-cylinder engine and next-generation six-speed automatic transmission, the eAssist system uses power stored in the battery to provide needed electrical boost in various driving scenarios, optimizing engine and transmission operation. A 115V lithium-ion battery and latest-generation 15-kW induction motor-generator unit help increase fuel economy through:
- Regenerative braking, which provides up to 15 kW of electricity to charge the battery;
- Providing 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 induction motor-generator unit;
- Intelligent charge/discharge of the high-voltage battery.
Regal with eAssist technology also features improved underbody aerodynamics and tires optimized for performance and fuel economy. 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.
While in fuel shut-off mode, the induction 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 induction motor-generator unit spins the engine, bringing it to a smooth stop—properly positioned for a smooth restart.
|The trunk of the Regal w/ eAssist still offers cargo passthrough. Click to enlarge.|
The eAssist power pack contains the lithium-ion battery pack, the integrated power inverter and 12V power supply and is compactly packaged in a compartment between the rear seat and trunk. Even with the pack, the Regal still offers a cargo passthrough, Poulos noted (see photo right).
Trunk space is slightly reduced when compared with 2011 models with the four-cylinder/six-speed powertrain, but still offers 11.1 cubic feet (314 liters) of storage. A quiet electric fan cools the power pack, drawing air from a vent located in the package tray, behind the rear seat.
The eAssist system’s electric induction motor-generator is mounted to the engine in place of the alternator to provide both motor assist and electric-generating functions through a unique engine belt-drive system. The induction motor-generator is a high-performance, compact induction motor that is liquid-cooled for increased performance and efficiency.
The eAssist system works with Regal’s direct-injected 2.4L Ecotec four-cylinder and next-generation six-speed automatic powertrain combination. In the Regal with eAssist, the engine is rated at 182 horsepower (136 kW) and the next-generation Hydra-Matic 6T40 further enhances 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 ability to provide 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.