eAssist technology extends Malibu ECO driving range to 550 miles
The photo shows the General Motors (NYSE: GM) display of eAssist™ at the SAE 2011 World Congress in Detroit. This is considered a mild form of vehicle electrification when compared to the Chevrolet Volt and other full hybrids.
Originally introduced for the Buick, the eAssist technology for the Malibu ECO is basically the same stop-start system. The Malibu ECO combines it with a 180-hp (134-kW) direct-injected 2.4-L Ecotec four, 6T40 6-speed automatic transaxle, Hitachi-supplied 115-V air-cooled lithium-ion battery pack, and belt-driven motor/generator.
According to Chevrolet media sources as well as an article by EV.SAE.org, the system is capable of producing approximately 11 kW (15 hp) of electric power assist during hard acceleration and 15 kW (20 hp) of regenerative braking power.
The liquid-cooled, induction-type motor/generator unit delivers 79 lb·ft (107 N·m) and provides electric-only operation at very low speeds. For the record, the motor/generator is supplied by Continental, a major supplier to the auto industry with a design center located north of Detroit..
The battery pack for the system has a total package mass of 65 lb (29 kg); and is located in the trunk behind the rear seat. It includes an integrated power inverter along with a 12-Volt power supply. The pack has a peak power density of 518 W/kg.
According to Steve Poulos, System Chief Engineer quoted by the EV.SAE.org article, the battery has a working state-of-charge (SOC) window of approximately 20%.
And like other lithium-ion battery systems, this one requires cooling; but instead of a liquid, a small electric fan draws air from the cabin.
The electrified power system, as it is called in some engineering circles, enables the internal-combustion engine to literally shut down fuel delivery in certain deceleration conditions. The eAssist is thus officially deemed by engineers as a mild hybrid technology.
Used in the Chevrolet Malibu Eco, the drive function is reported to be transparent; in other words, the driver does not realize that the vehicle is operating with an electric power boost at all. The biggest difference between the Malibu Eco and the standard Malibu, though, will definitely be the silence from the engine compartment when the vehicle is sitting at a stop light.
The Malibu Eco will excel in highway mileage when compared to the Toyota Camry and Nissan Altima hybrid at 35 mpg, and the Ford Fusion hybrid at 36 mpg. Chevy expects 38 mpg highway. However, those vehicles are considered full hybrids which perform best for city mileage, at 31 mpg and 41 mpg, respectively, whereby the Malibu ECO is rated well below at 26 mpg. The reason for this difference centers on the design choice of the final drive ratio.
As with the Buick LaCrosse, the eAssist for the Malibu ECO enables a numerically lower final drive ratio. GM engineers claim it gives the Malibu ECO up to 550 mi (885 km) in range with the 15.8-gal (60-L) fuel tank.
A hill-assist feature captures brake system pressure to help keep the car stationary when eAssist’s start-stop function is activated on a moderate or steep grade. This enables the driver to accelerate more smoothly from a stop.
In addition, both Malibu and ECO feature active grille shutters, where it automatically closes airflow through the lower front intake opening according to engine cooling demand. This is similar to the system used on the Chevy Cruze and the Buick LaCrosse,
The electromechanical shutter is opened or closed based on engine coolant temperature and vehicle road speed. For example, the shutters open when the car is traveling up a hill, pulling a trailer, or in hot city driving; they close at highway speeds when engine cooling is required less.
When closed totally, the shutter system enhances aero performance by redirecting airflow around the front of the vehicle and down the sides, rather than through it. This, too, increases gasoline mileage.
Adding the eAssist™ to the Malibu is a welcomed surprise. However, one has to wonder when GM and others will bring lower cost to these high tech ideas. For example, high-energy capacitors called ultra-capacitors have greater storage capacity as well as a much faster charging capability, and at a much lower price than small lithium-ion batteries. In addition, these ulta-capacitors enable faster rates of discharge as well as recharging, which enhances regenerative braking further.
It may take that kind of technology to make a mild hybrid competitive with the big boy hybrids, and maybe bring the costs down so the masses can afford it.
About the Author: After 39 years in the auto industry as a design engineer, Frank Sherosky now trades stocks and futures, and writes articles, books and ebooks via authorfrank.com, but may be contacted here by email: FrankS@TorqueNews.com
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