In the quest to improve fuel economy and reduce emissions to meet government regulations, global automakers have developed several powertrain options. Electrification is a strategy used by automakers to shift the vehicle from mechanical to electrical power. This move results in more efficient vehicles by the elimination of mechanical and idling losses.
Automakers have developed various levels of electrification to choose from to provide the most efficient vehicles possible. Here is a look at the various electrification options being employed today, up to and including the fully-electric, zero-emissions category.
Micro hybrid: simple in design, widely efficient, effective
A micro hybrid starts with a standard internal combustion engine (ICE), but substitutes the standard alternator with a 12-volt belt-driven starter generator. The engine stops running when the vehicle is braked at idle, such as when at a traffic signal, but restarts instantaneously (<400 milliseconds) as soon as the driver releases the brake pedal.
Micro hybrid technology offers automakers a low-cost (about $200 U.S.), easily-adaptable way to improve fuel efficiency (usually 2-6%) and reduce CO2 emissions by about 5%. It’s estimated that as much as 17.2% of vehicle inefficiency (fuel consumption, exhaust) comes from engine idling.
Today 90% of vehicles produced in Europe have this simple stop/start feature. The Audi A4 is an excellent application of micro hybrid technology, and it’s estimated that by 2020 more than 50% of vehicles produced globally will have micro hybrid technology, while still relying on ever higher fuel efficient ICE propulsion. In the U.S., Ford is betting heavily on micro hybrid by making the feature standard beginning with its top-selling F-150 Eco-Boost pick-up trucks.
Mild hybrid: why 48 (volts) is great
Combining the micro hybrid start/stop system with electrical power regenerative braking and a 48-volt electrical system (versus the standard 12 volts) advances powertrain technology to mild hybrid architecture. Here, as with the micro hybrid system, the IC engine stops when at idle, and while coasting, disconnecting itself from the transmission.
Meanwhile, the 48-volt battery can partially power the vehicle, while also powering its other electronic components. In addition, the mild hybrid’s starter generator converts the vehicle’s kinetic energy into electrical energy during braking and deceleration, and the system, incorporating the starter generator and ICE, boosts engine torque and power. This enables automakers to match a 48-volt system with smaller displacement engines. For some automakers, it could mean downsizing its families of V8 and V6 engines to just one family of more-efficient four-cylinder engines.
Mild hybrid technology provides automakers a very attractive cost-to-benefit strategy, with the ability to achieve a significant 10-11% reduction in CO2 emissions at a cost of between $1,000-$1,200 per vehicle. When compared with full hybrid systems, mild hybrids offer 50% of the CO2 reduction for approximately 30% of the cost of a full hybrid system.
The 48-volt system offers additional advantages to automakers as they continue to add more electrical and electronic features to vehicles, including additional passenger climate control options, heated windshields, and vehicle connectivity to communication, diagnostic, and entertainment packages
Full, plug-in hybrid systems face cost-benefit challenge
A full hybrid vehicle, such as the iconic Toyota Prius, shares the same powertrain components as the previously-referenced mild hybrid, but has a larger battery system and an electric motor and generator. The vehicle can propel itself in full electric mode with the assistance of the generator, in tandem with the ICE, or simply the ICE itself.
And, like the micro hybrid and mild hybrid, a full hybrid system has engine start/stop in idle mode and while coasting.
A variation of the full hybrid is the plug-in hybrid, which shares all the same components, with the addition of an electrical outlet, which can be used to charge the vehicle when not in use. Now a feature on newer Toyota Prius models, the plug-in feature provides the opportunity for the vehicle to operate in full electric mode more often.
Vehicles equipped with a full or plug-in hybrid system can achieve CO2 reduction of 18-22% over a conventional ICE. However, such a reduction comes at a considerable cost – on average, $3,200-$3,600 per vehicle. Because of this, automakers are expected to embrace more fully the mild hybrid-48-volt strategy instead.
Range extended technology may only be short term
Cars such as the Chevrolet Volt and the BMW i3 are examples of range extended vehicles (REX), which are just one step away from being considered a fully-electric vehicle. A high-capacity battery powers the electric motors which drive the wheels. Vehicles of this configuration have a small gasoline-powered ICE/generator, which engages and charges the battery as it drains to give the vehicle a few extra miles of range, with the intent of getting the vehicle to the next charging station. In the case of the BMW i3, that amounts to about 80 extra miles; for the Chevrolet Volt, its range extender unit buys its owner an extra 260 miles.
In fully-electric mode, a REX can be labeled a zero CO2 emissions vehicle, but that technology comes with a high cost. It’s considered by OEMs the most expensive option between a full/plug-in hybrid and a full-battery electric vehicle. It’s expected that OEMs will steer clear of producing REX vehicles as battery technology improves, and electric-powered driving ranges are extended.
The industry disruption: battery electric vehicles
A truly zero-emissions vehicle, battery electric vehicles (BEVs) use large-capacity batteries and electric motors to power the wheels. When depleted, the batteries are recharged off the grid from a wall socket or at a dedicated charging station. With no carbon fuel-powered generating system onboard, BEVs are considered “all-electric” vehicles.
The hurdles ahead for growth in this technology include battery costs, limited driving range and the lack of a reliable charging infrastructure.
Except for a handful of dedicated manufacturers (e.g., Tesla Motors, Faraday Futures) major North American automakers interest in BEVs has been slow to develop, with currently less than 1% of all vehicles produced globally being all-electric. However, due to the increasing regulatory pressure, specifically in Europe and China, BEV market share is forecasted to grow to more than 14% of the total global vehicle production over the next ten years.