Chevrolet Volt

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Chevrolet Volt
Chevrolet Volt Concept
Chevrolet Volt Concept (as shown in the North American International Auto Show of 2009)
ManufacturerGeneral Motors
Also calledHolden Volt
AssemblyUnited Kingdom
United States[1]
ClassCompact car
Body style(s)4-door liftback
LayoutFront engine, front-wheel drive
PlatformDelta II / E-Flex
Engine(s)111 kW (150 hp) electric motor[2]
1.4 L 4-cylinder for powering 53 kW generator[3]
Wheelbase105.7 in (2,680 mm)[2]
Length177 in (4,500 mm)[2]
Width70.8 in (1,800 mm)
Height56.3 in (1,430 mm)
Fuel capacityunknown[4] + 16 kWh nominal, 8.8 kWh usable
Electric range40 miles (64.4 km) (on the EPA‎ city cycle using battery only, much more using on-board gasoline-powered 53 kW generator)

The Chevrolet Volt is a plug-in series hybrid vehicle to be produced by General Motors, expected to be launched as a 2011 model with production currently slated to begin in 2010.[5] The Volt's propulsion system will be based on GM's new E-Flex platform.

Unlike current commercially available hybrids, the actual propulsion of the Volt is accomplished by the electric motor, as the internal combustion engine (ICE) is not mechanically connected to the wheels. With fully charged batteries, this electric power will initially be sourced exclusively from its on-board lithium-ion batteries for up to 40 miles (64 km), a distance capable of satisfying the daily commute of 75% of Americans,[6] which averages around 33 miles (53 km).[7]

After 40 miles (64 km), the range of the Volt will need to be extended through the use of a small 4-cylinder ICE which drives a 53 kW generator. The electrical power from the generator is then sent to either the electric motor or the batteries, depending on the state of charge (SOC) of the battery pack and the power demanded at the wheels. The distribution is controlled by the electronic control unit (ECU) of the vehicle. This effectively extends the Volt's potential range to as much as 640 miles (1,030 km) on a single tank of fuel[8] (which could be potentially extended for longer trips through conventional refueling).[9][10]

The Volt's 16 kWh lithium-ion battery pack can also be fully charged (technically ~85% SOC) by plugging the car into a 120-240VAC residential electrical outlet using the provided SAE J1772[11] compliant charging cord. No external charging station will be required.[12]

Since the current Society of Automotive Engineers (SAE) definition of a hybrid vehicle states the vehicle shall have "two or more energy storage systems both of which must provide propulsion power, either together or independently",[13]the company has avoided the use of the term "hybrid" when describing its non-conforming E-Flex designs. Instead GM has described the Volt as an electric vehicle equipped with a "range extending" gasoline powered internal combustion engine (ICE) as a genset and therefore dubbed an "Extended Range Electric Vehicle"[14] or EREV.[14][15][8] However, the combination of an internal combustion engine and electric motors in such a configuration is most often referred to as a series hybrid.


Concept vehicle

The Volt concept vehicle has four doors with a rear liftgate, and is capable of carrying four passengers. This is a significant change in design when compared to the General Motors EV1 of the 1990s, which only seated two to reduce weight. The top speed has also been increased on the Volt, from the electronically limited 80 miles per hour (130 km/h) to 120 miles per hour (190 km/h). The battery pack size has also been reduced, from about 300 L in volume in the EV1, to just 100 L in the Volt.

Production model

On September 16, 2008 General Motors first publicly displayed the production design model of the Chevrolet Volt that differed greatly in design from the original concept car. Citing necessary aerodynamic changes needed to extend the Volt's initial full-charge range, the Volt uses GM's new "Delta II" platform, shared by the planned 2010 Chevrolet Cruze and the 2011 Saab 9-3.[2][16]

Electromechanical design timeline

GM executives report that battery technology will have a large impact in determining the success of the car.[17][18]

To help spur battery research, GM selected two companies to provide advanced lithium-ion battery packs: Compact Power, which uses manganese oxide based cells made by its parent company, LG Chemical, and Continental Automotive Systems, which uses nanophosphate based cylindrical cells made by A123Systems.[19][20] However, on August 9, 2007, GM established a more close-knit relationship with A123Systems so that the two companies could co-develop a Volt-specific battery cell.[21] This cell was later unveiled at the EVS23 industry convention in Anaheim, CA.[22] Work with CPI has continued at a rapid pace, and in late 2007 CPI delivered two fully-functional prototype battery packs to GM's testing facilities. On January 31, 2008, A123 and Continental delivered their first prototype to GM's European test facilities. GM announced on January 12, 2009 that it would use the LG Chem batteries for the production model. [23]

GM expects ten years of life out of the batteries. As of early 2008, they had started extensive battery testing and planned to have 10-year battery results in two years. Batteries were placed in the Chevrolet Malibu for further real-world testing.[24]

In April 2008, GM Vice Chairman Bob Lutz said that the first battery test mule was now running with a lithium-ion battery pack.[25] By that summer, GM confirmed that a non-turbocharged, 1.4 liter 4-cylinder engine would be used as the range extender, and that the intention is to build it in Flint, Michigan.[26] A thermovoltaic solar power roof, allowing the owner to charge the battery by leaving the vehicle in sunlight, will be offered as an optional feature.[27] Andrew Farah, the car's chief engineer, states that the project remains on-track to hit the 2010 deadline saying "at this point, there’s nothing standing in our way of continuing to do what we said we’re going to do."[28]

In early September 2008, leaked photos of the production version of the Chevrolet Volt, along with various members of its development team, were shown on Autoblog.[29] Significant changes from the original design concept, as indicated by the leaked photos, were met with mixed reviews. On September 16. 2008 General Motors officially revealed the production version of the Volt.[2]


The 2007 Chevrolet Volt concept vehicle that appeared in the North American International Auto Show[30] introduced the E-Flex[31] drive system, which is an attempt to standardize many components of possible future electrically-propelled vehicles, and to allow multiple interchangeable electricity-generating systems. The initial design as envisioned in the Volt combines an electric motor and 16 kWh (58 MJ) lithium-ion battery plug-in system[32] with a small engine (1.4 liter) powered by gasoline linked to a 53 kW (71 hp) generator. The vehicle is propelled by an electric motor with a peak output of 120 kW (160 hp). Ordinarily, the vehicle would be charged while at home overnight. According to General Motors a full charge will take approximately 8-hours from a standard North American 120 V, 15 A household outlet and less than 3 hours if using a standard 240VAC outlet.[2]Charge times will be less if the battery is not fully depleted when charging commences.

Since the electrical drivetrain is not affected by the method used to charge its batteries, several options could be available for an engine. The original prototype specifications for the Volt indicated a turbo-charged 1.0 litre 4cyl engine would be used.[33] However the initial production configuration currently specified by GM indicates the use of a naturally aspirated 1.4-liter 4-cyl gasoline engine. It will be a flex-fuel internal combustion engine capable of running gasoline or E85 (85% ethanol, 15% gasoline) or any blend of those fuels. Fuel would be supplied from a "saddle" tank 45 litres (12 US gal) in size.

This general layout is considered a plug-in series hybrid design since mechanical power initially drives the generator, which in turn either charges the battery pack or provides power to the electric motor. While the ICE has an electrical connection with the electric motor and hence the wheels, it does not have any mechanical linkage to the wheels (unlike current hybrid vehicles such as the Toyota Prius), and can run at necessary speeds for optimizing fuel consumption, reduced emissions and charge rate efficiency.

GM plans to station charge the lithium-ion battery to a state-of-charge (SOC) range of approx 85%. Then once the battery depletes to a precise low set-point (<25%) the on-board ICE powered generator will recharge the battery to an upper set-point above the 30% SOC level.[13][34]

GM has decided on a new descriptive terminology to distinguish it from traditional hybrids. They are calling the Volt an E-REV, for extended-range electric vehicle.[35] This is in part justified since there is no mechanical linkage between the gasoline engine and the wheels. The design is conceptually similar to a modern electromotive locomotive, with a generator, an electric motor, and regenerative braking, with the addition of a storage battery.

Production and sales

In July 2007, General Motors stated that it would have the Volt on the U.S. market in 2010,[36] and in early June 2008, they confirmed that production had been approved, with a target of getting the Volt into showrooms by the end of 2010.[37] Following the conclusion of the 2007 UAW-GM contract talks, assembly of the Volt was assigned to Detroit/Hamtramck Assembly.[38] Initially the gasoline engine will be imported from GM's Opel engine plant in Aspern, Austria.[39] Early estimates, from GM staff, were of initial annual production of 60,000 units,[40] but these claims have been scaled back to a planned 10,000 units, as of May 2008,[41] with a ramp up to 60,000 units in the second year.[42]

At the British International Motor Show in July 2008, GM stated that they were considering building all of the Volts for the European market, branded Chevrolet, Opel and Vauxhall, at their Vauxhall plant in Ellesmere Port in the United Kingdom.[1] In August 2008 GM stated that the Volt would be available for sale in Europe in 2011.[43] In late January 2009, GM Europe announced that its version of the Volt, the Opel Ampera, will be unveiled at the Geneva Auto Show in March.[44]

At the Sydney Motor Show in October 2008, Holden stated that the Volt would be available in Australia by 2012 for "more than $30,000". [45]


In the U.S. market, the price of the Volt is expected to be around US$40K[46][47] with government approved subsidies bringing the price to around $32.5K. Initially, the GM vice president wanted it at about US$30K.[48]

The indicated price for the UK market is GBP£20K.[1]

Anticipated U.S. Federal Tax Subsidies

In the United States, and based on its current battery power density, the Volt will reportedly qualify for a $7,500 tax credit.[49]


Fuel efficiency

For trips less than about 40 miles (64 km) per charging cycle, the Volt will not use any onboard gas, so assigning a fuel consumption value which only referred to onboard fuel might not be appropriate. Once the Volt's battery has discharged to its lower limit set-point, the Volt's range-extending gasoline engine is expected to get from approximately 50 mpg-US (4.7 L/100 km; 60 mpg-imp) to as much as 150 mpg-US (1.6 L/100 km; 180 mpg-imp) depending on its run-time duty cycles. This is because once the battery has been recharged to an upper limit set-point (by the engine driven 53 kW onboard generator), the internal combustion engine will again shut off. Therefore the variables that contribute to the specific duty cycle periods of the internal combustion engine run-times, will need to be factored in to the Volt's final fuel economy rating as determined by the EPA.[50]


It has been reported that GM has decided to work exclusively with Compact Power Incorporated (CPI), a Detroit-based unit of South Korea’s LG Chem, to provide the battery systems for the first production version of the Volt.[51][52][53][54] The cells will be produced in Korea and subsequently shipped to the United States, where the battery packs will be assembled at a purpose-built facility in Michigan owned and operated by GM.[55]

The anticipated energy capacity of the Volt's 375 lb (170 kg) 220-cell lithium-ion battery pack is estimated at 16 kWh,[2] but is only charged to 85% full when charged up, and is discharged to 30% SoC approximately, before the engine cuts in and maintains the charge at around this level. When the vehicle is plugged into a charger the battery SoC is restored to 85%. Hence the battery has an effective capacity in use of 8.8 kWh.

The weight of the battery pack in the Volt which finally comes to market will reportedly be approximately 375 lb (170 kg),[56] primarily because the Volt will use lithium-ion (Li-ion) batteries while the EV1 used heavier lead-acid and nickel metal hydride (NiMH) batteries. Li-ion batteries are expected to become cheaper to manufacture, once economies of scale take effect.[57]

Regulated emissions impact

Tailpipe emissions

It is anticipated that the Chevrolet Volt will be granted a California Air Resources Board (CARB) classification as an Advanced Technology Partial zero-emissions vehicle (AT-PZEV) Assuming a fully charged battery, the Volt will use no gasoline and produce no tailpipe emissions for up to 40 miles (64 km) of initial daily driving.[2] However, after 40 miles (64 km), the state-of-charge (SOC) of the HV battery will be depleted and the internal combustion engine (ICE) will startup to commence power generation.[58]During this period, using typical closed-loop fueling and exhaust after treatment (i.e. catalytic converter) the tail-pipe exhaust emissions will be similar to other 4-cyl low displacement gasoline-powered automobile..[59] However, once a sufficient battery state-of-charge has been achieved, the ICE will again turn OFF,[2] returning to a zero emissions state. This ON:OFF ICE cycling behavior results in the reduction of Initial Trip Starts and therefore a reduction in total tailpipe emissions per distance travelled.[2]


EPA testing

As of September 2008, General Motors was reportedly in disagreement with the United States Environmental Protection Agency regarding how the Volt should be tested to determine its official fuel economy rating. The EPA reportedly wants to alter the method of testing currently used for all other hybrid vehicles. If tested with the same EPA tests used by other hybrids, the Volt's ability to use the energy stored in the batteries would result in it achieving a fuel economy rating of over 100 mpg, which would make the Volt the first mass-produced automobile to achieve such a rating.[60]

General Motors believes that although the Volt is an entirely new type of vehicle, it suggests that altering the current EPA hybrid testing methods to suit a single vehicle entry would be unfair and would not recognize the fact that the car can travel an estimated 40 miles (64 km) on battery power alone before the gasoline powered engine has to be started to commence recharging its battery pack.[61]

CAFE impact

In a response to the U.S. National Highway Traffic Safety Administration's (NHTSA) proposed targets for Corporate Average Fuel Economy (CAFE), GM indicated that the potentially limited production numbers of the Volt will mean it will have little influence on its CAFE results during the 2011-2015 timeframe."[62]

Battery charging emissions

One article describes a claim by General Motors that operating the Volt for a year, results in a possible reduction of about 4.4 metric tonnes in CO2 emissions as compared to a typical U.S. car.[63] However, unless the Volt uses wholly green energy sources for charging, the generation of electricity to station-charge its batteries will, depending on the energy source, result in the emission of varying levels of combustion by-products including the greenhouse gas CO2 directly from the generating power station.[64]

In locations such as Ontario, where there is a high level of constant electric generation due to a high mix of nuclear power generation and large-scale hydro-electric power generation, much of the power goes to "waste" in off-peak times as generation exceeds the baseload due to the impracticality of scaling back the output of a CANDU reactor or hydro-electric plant on an hour-by-hour basis. In Ontario, baseload demand varies between 12000 and 15000 MW depending on season[65], however the total generation by nuclear and hydroelectric plants (when all are in operation) accounts for over 19000 MW.[66] In this jurisdiction and other similar ones, electric vehicles which are charged during off-peak times result in zero additional pollution.

The University of California, Davis calculated that, generally, plug-in cars that are charged using electricity from the local grid will emit notably less CO2 overall than the use of cars powered from on-board, oil-based fuel, if a significant proportion of that electricity is generated from nuclear power and renewable sources such as hydro-electric (45% in California, for example).[67]

UK based Auto Express magazine claims to have calculated that the generation of electricity for charging the batteries in the Volt resulted in emissions equivalent to 124.2 g/km of CO2 for electric-only trips (those not involving the use of any on board fuel), based on government figures for the average CO2 emissions from power stations. No calculations are shown in the article, so the veracity of this claim cannot be evaluated. According to Auto Express, this is more CO2 than the BMW 118d produces.[68]

A study by the American Council for an Energy Efficient Economy (ACEEE) predicts that, on average, a typical plug-in hybrid electric vehicle is expected to achieve about a 15% reduction in net CO2 emissions compared to the driver of a regular hybrid, based on the 2005 distribution of power sources feeding the U.S. electrical grid. The ACEEE study also predicts that in areas where less than 80% of grid-power comes from coal-burning power plants, local net CO2 emissions will decrease, but points out that these numbers are first order estimates and are not conclusive.[69]

In Australia, where 85% of electricity nationally is produced using black and brown coal [70], with most of the remainder produced using hydro and natural gas, the greenhouse emission factors vary between states, and is 1.22 kg-CO2e/kWh [71] in Victoria, 0.890 kg-CO2e/kWh in New South Wales, and 0.120 kg-CO2e/kWh in Tasmania. Assuming a charge requires 8.8 kWh[72], allowing 40 miles (64 km) of travel without petrol, the greenhouse intensities are 167 g-CO2e/km for Victoria, 122 g-CO2e/km for NSW, and 16 g-CO2e/km for Tasmania. Electricity consumers can elect to purchase green power at a higher cost, but with significantly lower emissions. For comparative purposes using the same methodology, that is, measuring only the direct emissions from the burning of the fuel, and ignoring fuel procurement/production/delivery [73], the Toyota Prius tank-to-wheel greenhouse intensity in units of g-CO2 (CO2e information not available) in Australia is 115 g/km (5.1 l/100km combined cycle),[74] Toyota Yaris 1.3 manual is 141 g/km (6.0 l/100km combined cycle), and the BMW 120d is 162 g/km (6.1 l/100km combined cycle)[75]. It should be noted that this comparison is not the standard method used by government agencies for comparing the emissions of two vehicles, where the tank-to-wheel only is used; in this case, the Volt would be emission-free for the 40-mile all-electric range (AER). The above comparison does not include the full fuel cycle for either vehicle, known as a well-to-wheel analysis, and so the numbers may be slightly misleading.

See also


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External links