Range extender

This article is about the vehicle. For devices that extend wireless networks, seewireless repeater.

"EREV" redirects here. For the novel by Eli Schechtman, seeErev.

A prototypeAC Propulsion tzeroelectric carwith an external range-extender or genset trailer, 1999

Arange extenderis a fuel-basedauxiliary power unit(APU) that extends the range of abattery electric vehicleby driving anelectric generatorthat charges the vehicle's battery. This arrangement is known as aseries hybriddrivetrain. The most commonly used range extenders areinternal combustion engines,butfuel-cellsor other engine types can be used.

Range extender vehicles are also referred to asextended-range electric vehicles(EREV),range-extended electric vehicles(REEV), andrange-extended battery-electric vehicle(BEVx) by theCalifornia Air Resources Board(CARB).

Many range extender vehicles, including theChevrolet Voltand theBMW i3,are able to charge their batteries from the grid as well as from the range extender, and therefore are a type ofplug-in hybrid electric vehicle(PHEV).Historically PHEV,HEVandMHEVwere primarily powered by combustion (bigger engine and fuel tank with smaller battery and electric motor(s)). While EREV are the opposite.

Motivation

The key function of the range extender is to increase the vehicle's range. Range autonomy is one of the main barriers for the commercial success of electric vehicles, and extending the vehicle's range when the battery is depleted helps alleviaterange anxiety.

A range extending vehicle design can also reduce the consumption of the range extending fuel (such as gasoline) by using the primary fuel (such as battery power), while still maintaining the driving range of a single fuel vehicle powered by a range extending fuel such as gasoline. The range extending fuel is generally considered to be less environmentally and economically friendly to use than the primary fuel source, so the vehicle control system gives preference to using the primary fuel if it's available. However, due to range limitations with the primary fuel source, the range extending fuel allows the vehicle to get many of the cost and environmental benefits of the primary fuel, while maintaining the full driving range of the range extending fuel source.That said, the benefits (cost, carbon emissions) derived from using a vehicle with a range extender ultimately depend on how the vehicle is driven, and in particular how often the range extender is used.

As an example, cars such as theBMW i3with optional range extender and theChevrolet Voltare equipped with sufficiently large batteries to drive 80–160 km (50–100 miles), which is enough for many trips but not sufficient to drive long distances. As such, the driver may use battery power for commuting and daily driving, but still be able to drive fromNew YorktoBoston(about 320 km, 200 miles) by using the auxiliary gasoline internal combustion engine, without stopping frequently to charge the battery (which can take hours). The vehicle owner therefore accrues the benefits of using cheaper and lesscarbon-intensiveelectric power for most driving, while maintaining the ability to embark on longer trips with the same vehicle.

When a range extender uses conventional fuels they can re-fuel at regularfuel stations,which provides them with a similar driving range to conventional automobiles.

As an REEV is only propelled by the electric motor it can do away with the weight and cost associated with the gearboxtransmissionsystem typically used in internal combustion engine cars. Further, as the range extender does not need to increase or decrease output in line with the power needs of the vehicle (this task is handled by the electric motor) the range extender can be sized to satisfy the vehicle's average power requirement rather than its peak power requirement (such as when accelerating). The range extender can also operate much closer to its most efficientrotational speed.These design features allow an REEV to convert fossil fuel energy to electric power and vehicle motion relatively efficiently.

Generations

• The first generation range extenders are off the shelfinternal combustion engines.
• The second generation consists of piston engines with new designs from scratch for fairly constant load in series hybrids. They include thewankel engines,rotary combustion enginesandfree piston engines.
• The third generation aremicro turbinesandfuel cellsthat work at constant load.

CARB regulation

According to 2012 Amendments to the Zero Emission Vehicle Regulations adopted in March 2012 by the California Air Resources Board (CARB), a range-extended battery-electric vehicle, designated as BEVx, should comply, among others, with the following criteria:

• The vehicle must have a ratedall-electric rangeof at least 120 km (75 miles). This is higher than the 80 km (50 miles) required of azero-emission vehicle;
• Theauxiliary power unit(APU) must provide range less than or equal to battery range;
• The APU must not be capable of switching on until the battery charge has beendepleted;
• The vehicle must meetsuper ultra low emission vehicle(SULEV) requirements; and
• The APU and all associated fuel systems must comply with zeroevaporative emissionsrequirements.

Applications

Range extenders are commonly used inmarine(autonomous underwater vehicle),aircraftand Generator/Utility,automotiveandhybrid electric vehicleapplications.

Automotive

Chevrolet Volt

TheChevrolet Voltis aseriesplug-in hybridreferred by General Motors as "an electric car with extended range."

General Motorsdescribes theChevrolet Voltas anelectric vehicleequipped with a 16 kWh battery plus a "range extending" gasoline poweredinternal combustion engine (ICE)as agensetand therefore dubbed the Volt an "Extended Range Electric Vehicle" or E-REV.In a January 2011 interview, the Chevy Volt's Global Chief Engineer, Pamela Fletcher, referred to the Volt as "an electric car with extended range."The Volt operates as a purely electric car for the first 40–80 km (25–50 miles) incharge-depletingmode. When the battery capacity drops below a pre-established threshold from full charge, the vehicle enters charge-sustaining mode, and the Volt's control system will select the most optimally efficient drive mode to improve performance and boost high-speed efficiency.

According to General Motors' real time tally of the distance driven by Volt owners in North America, by mid June 2014 they had accumulated more than 800 million all-electric km (500 million miles). GM also reported that Volt owners driving is more than 63% in all-electric mode. Volt owners who charge regularly typically drive more than 1,560 km (970 miles) between fill-ups and visit the gasoline station less than once a month.A similar report, issued by GM in August 2016, reported that Volt owners have accumulated almost 2.4 billion km (1.5 billion miles) driven in EV mode, representing 60% of their total distance traveled.

BMW i3

An optional range-extender is available for theBMW i3,which allows the car to qualify as arange-extended battery-electric vehicle(BEVx) according to theCalifornia Air Resources Boardregulations.

TheBMW i3all-electric car with at least 22 kWh battery capacity offers an optional gasoline-powered range extenderAPU.The range extender is the same 647 cc two-cylinder gasoline engine used in theBMW C650 GTscooter with a 9 L (2.0 imp gal; 2.4 US gal) fuel tank. The US model originally had its tank electronically limited to a smaller 7 L capacity.The range extender engages when the battery level drops to 6%. It generates electricity to extend the range from 130–160 km (80–100 miles) to 240–300 km (150–190 miles)Performance in range-extending mode may be more limited than when it is running on battery power, as BMW designed the range extender as a backup to enable reaching a recharging location.

According to BMW, at the beginning of the i3 release, the use of range-extender was much more than the carmaker expected, more than 60%. Over time it has decreased significantly, with some people almost never using it, and by 2016 it is being regularly used in fewer than 5% of i3s.

The range-extender option costs an additionalUS$3,850in the United States,an additional€4,710(~US$6,300) in France,and€4,490(~US$6,000) in the Netherlands.

The range-extender option of the BMW i3 was designed to meet the CARB regulation for an auxiliary power unit (APU) called REx. According to rules CARB adopted in March 2012, the 2014 BMW i3 with a REx unit fitted will be the first car to qualify as a range-extended battery-electric vehicle or "BEVx." CARB describes this type of electric vehicle as "a relatively high-electric range battery-electric vehicle (BEV) to which an APU is added." The APU, which maintains battery charge at about 6% after the pack has been depleted in normal use, is strictly limited in the additional range it can provide.

Other examples

The discontinuedFisker Karmais an extended-range electric vehicle.

Other range-extended electric vehicles include the discontinuedCadillac ELRand the discontinuedFisker Karma.In June 2016, Nissan announced it will introduce a compact range extender car in Japan before March 2017. The series plug-in hybrid will use a new hybrid system, dubbed e-Power, which debuted with the Nissan Gripzconceptcrossover showcased at the 2015Frankfurt Auto Show.The technology, without the plug-in ability, had been deployed to theNissan Note e-PowerandNissan Kicks e-Power.

TheLEVC TXLondon taxi was launched in 2017 and features a 33 kWh battery that is charged by a 1.5-litre gasoline engine.

TheLi Auto Oneis a large SUV which combines a 41-kWh battery with a small 1.2-litre gasoline engine.

This approach has also been used for heavy vehicles, such asWrightbus'sGemini 2andNew Routemasterbuses.

Hydrogen fuel cells have also been used as a range extender forbattery electric buses,allowing them to have greater range.For example, theMercedes-Benz eCitarohas a range of 280 kilometres (170 mi) as a battery electric model, with the eCitarofuel cell bushaving a range of 400 kilometres (250 mi) thanks to a 60kW Toyota fuel cell that recharges the battery.

Ford has patents for a bed mounted gasoline-powered generator for their fully electric pickups.Rivian has patents for bed mounted additional batteries for increased range.Rivian electric trucks can charge each other for extended range.

Unmanned aerial vehicles

The 2010 Wolverine 3 program included an ICE range extender for itsunmanned aerial vehicle.

Powertrain

Schematic classification of alternative powertrains

A range-extended electric vehicle uses aseries hybriddrivetrain.

See also

• Hybrid vehicle drivetrain
• Microturbines
• List of hybrid and plug-in hybrid vehicles
• Diesel–electric powertrain