Electric vehicle (EV) and hybrid electric vehicle (HEV) technologies are on a roll. Major automotive manufacturers around the world have unveiled or are on the verge of unveiling many such cars for the market, as all of these companies are eager to adopt the technology.
That’s not surprising, given governmental regulations and incentives. There’s also the need to reduce pollutants as well as our dependence on oil. And, the mass market is ready for a car that fits into the average consumer’s already squeezed budget.
Most experts say that such an inexpensive EV or HEV won’t be easy to achieve in the short term, though. Plus, no one knows how the current electric grid infrastructure will handle a significant increase in automotive batteries that require daily recharging. And, today’s most advanced battery technologies are still quite costly.
Most projections for HEVs put their price tag around $40,000 to $50,000, which is too high for mass-market appeal. Some numbers bandied about for EV end-user prices are over $100,000. Much of this is due to high battery pack costs, which are projected to range anywhere from several thousand dollars to well over $10,000 each (see “Battery Challenges For Electric Vehicles”).
A study by Carnegie Mellon University published by Energy Policy points out that HEVs like the Chevy Volt from General Motors (GM) will not save enough on gas to cover the higher purchasing cost of the car. The study’s authors conclude that the only way the Volt will save car owners energy costs over the vehicle’s lifetime would be for both gasoline and electricity costs to drop substantially from present levels, which is unlikely to happen.
Still, GM is putting its muscle behind the Chevy Volt, a plug-in series HEV slated for market introduction this year. Its internal combustion engine (ICE) is engaged to generate power for its electric-drive motor and its battery pack, not to power the wheels. In a parallel hybrid vehicle, the electric motor is connected directly to the car’s ICE flywheel, allowing the clutchless powertrain to capture torque from both the electric motor and the ICE.
Besides GM, other major automakers are actively pursuing more energy-efficient HEV and EV technologies. One of the most notable HEVs is the Ford Fusion, which was introduced to the market last year. The Fusion can be driven at speeds up to 47 mph from solely its nickel-metal-hydride (NiMH) battery. After that, its gas-powered ICE kicks in. The popular Toyota Prius automatically starts its gas ICE at 25 mph.
A MILD HYBRID FORM
In a typical HEV system, a gasoline-powered high-efficiency ICE works with a rechargeable battery (Fig. 1) to power the car. The ICE’s output is also fed to a planetary gear power-split device, which in turn feeds an ac synchronous generator. The battery’s output is fed to a high-voltage dc-ac inverter. The inverter also accepts the generator’s output and feeds a permanent-magnet ac motor. A circuit controls the power.
To satisfy legislative efficiency and environmental requirements, automakers are grappling with many different forms of relatively inexpensive HEV technologies. One such form that may soon take off rapidly is the belt alternator starter (BAS) system. Many call it a “mild” hybrid technology, though pure hybrid enthusiasts may cringe at this naming convention. A BAS system is considered a relatively low-cost approach to HEV technology that can provide some meaningful benefits.
General Motors is an advocate of BAS systems, which offer additional fuel savings and fewer tailpipe emissions at a slightly higher cost. Fuel savings of 5% to 10% are possible, mostly for city driving. Currently, most BAS systems are limited to being used with engines of about 3 liters and six cylinders or less. However, such engines are expected to see rapid growth in the next few years, making the adoption of BAS systems easier.
In a BAS system (Fig. 2), an electric motor replaces the conventional belt-driven alternator and starter. When the engine is running, the electric motor acts as a generator and charges a separate 36-V battery. When the engine has to be started, the motor starts its torque via the accessory belt for cranking. The BAS system can perform engine stop/start, electromechanical launch assist, regenerative braking, high-power generation, and other functions without the need for large changes in a car’s design.
The actual implementation of the BAS system depends on the performance level sought in the car in terms of motor/generator efficiency and output-power capability. Some BAS systems, which might not include a starter motor, will have heavier loads while starting an engine, particularly in very cold weather. In general, BAS systems improve fuel economy by 10% to 15% (mostly in city driving) over conventional gas-powered ICE cars.
Although they provide only about half the benefit of a full HEV, BAS systems only cost automakers 15% to 20% more and don’t require significant engine-compartment and chassis modifications. Vehicles equipped with BAS systems don’t provide much of a benefit for highway driving, though. Nevertheless, their relative simplicity is causing a lot of optimism among automotive system designers.
“Within the next five to 10 years, every car will have a BAS system, because it will provide a lot of benefit for very little added cost and complexity,” says Ted Bohn, an electrical engineer at the Argonne National Laboratory’s Center for Transportation Research.