Cadillac Converj Concept (top); Chevrolet Volt. Click image to enlarge
By Jim Kerr
Will the vehicle of your future be an E-REV? GM is betting so, having invested more than a billion dollars in research and development to bring E-REV (Extended Range Electric Vehicle) vehicles to market. The 2011 Chevrolet Volt will be the first GM E-REV and others are sure to follow shortly.
The E-REV design is different from conventional hybrids. Hybrids use a combination of two power sources in combination to move the vehicle. Some start out using electric propulsion and the gas engine assists; others start out with gas propulsion and add electric assist – but both designs use a combination of the two systems to move the vehicle.
The E-REV design uses only an electric motor to move the vehicle, but there is a gas engine on board. It is used only as a generator to keep the battery pack charged if necessary.
Pure electric vehicles have one major drawback: their range is limited. Battery technology is rapidly improving but it is still difficult to produce a practical vehicle with a range of more than a couple hundred kilometres. Even then, a vehicle with that range uses a lot of its energy and space just hauling batteries around. One of the disadvantages of driving an electric vehicle is “Range Anxiety”. Drivers must always keep the battery state of charge in mind while they are driving or they may run out of power away from where the vehicle can be recharged. You can’t simply have someone bring you a can of “electricity” like they would bring a can of gas to a conventional vehicle.
E-REV vehicles do away with Range Anxiety. The Volt powertrain operates on electric power supplied by a T-shaped lithium ion battery pack located in the centre floor tunnel of the vehicle. With over 220 cells in the battery pack, the Volt will have a range of over 40 miles (65 km) on an initial charge. This is less than the majority of daily commutes, but if a driver needs to travel further, the vehicle switches to extended range mode and the onboard gasoline engine automatically starts up to charge the depleted battery pack. This provides a range of hundreds of kilometres, but the vehicle is still propelled solely by the electric motor.
Sophisticated electronic controls optimize the vehicle’s electrical current flow. It can deliver 273 lb-ft torque from the 16 kilowatt-hour battery pack, which could provide acceleration similar to a turbocharged four-cylinder engine or a larger displacement V6 engine. It can also provide 120 kilowatts of power for a short time (150 horsepower), which gives the vehicle a top speed of 160 km/h. Battery cell temperatures and voltages are monitored to maintain the optimum charge and power is recaptured during deceleration and braking by converting the vehicle’s motion back into electrical energy through the electric motor.
Another feature of the E-REV design is that the vehicle can be plugged in to charge the battery. It takes less than three hours to recharge the battery at 240 volts or about eight hours from a 120-volt outlet. For drivers who mostly drive shorter commutes, this means the gasoline engine may seldom operate. GM estimates that it would cost about 80 cents of electricity to charge the batteries fully for a 65-km drive. With electricity at 10 cents per kilowatt-hour, they estimate the energy cost per kilometre would be about one sixth of a conventional gasoline vehicle. This could save drivers who drive an average of 65 km a day about 2081 litres of gasoline annually compared to a typical compact economy car, and use less than half the gasoline compared to a plug-in hybrid vehicle.
Zero emissions from the electric motor, power and economy are all key features of E-REV vehicles. At the 2009 North American International Auto Show, GM presented a concept car, the Cadillac Converj, also based on the Volt E-REV powertrain, showing that future vehicles can be stylish, luxurious and economical. Driving our future automobiles may be a lot of fun.