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Driving a Chevy Volt Test Mule.

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GM recently announced that the 2011 Chevrolet Volt could score 230 mpg in the EPA city fuel economy cycle and well into the triple digits for combined driving. Though the final EPA test methodology for vehicles that will plug into the electric grid has yet to be finalized, 230 mpg is GM's best guess estimate given the EPA's current criteria for plug-in hybrids and extended range electric vehicles.

chevy volt, chevy volt test muleTest Mule.

The numbers game GM is playing here is only accurate if you drive the exact distance that the EPA will use in the test. Drive beyond that and the Volt's fuel economy will begin to drop with every additional mile you drive. Once the battery reaches a 30-percent state of charge and the gasoline engine fires to provide electricity, the Volt will deliver approximately 50 mpg and fuel economy will gradually go down until the car is recharged. If you drive less than the Volt's 40-mile electric range, however, GM's revolutionary car won't use a drop of gasoline, so gasoline mileage isn't even a factor.

We recently had the opportunity to drive the latest Chevy Volt test mule around GM's Warren, Michigan Tech Lab compound. The current Volt mules are based on the European Chevy Cruze sedan. GM's Global Delta II platform due to replace the Chevy Cobalt in North America in the 2011 model year, and is very close in size and weight to the Volt, making it more suitable as a test mule than the first generation Chevy Malibu mules.

At this stage of testing, the Volt mules are operating strictly in the battery supplied electric mode. Integration of the gasoline generator should happen in the next phase of testing. Still, the driving experience is representative of how the Volt will drive because unlike hybrids that most consumers are familiar with, the Volt is propelled solely by electric drive. GM's Voltec powertrain utilizes the gasoline engine purely as a means to generate electricity, not to directly propel the car.

chevy volt test drivePre-Production Volt.

Like other electric drive vehicles, power delivery is smooth and positive. Without an internal combustion engine running, noise, vibration, and harshness levels are easier to manage. Since the Cruze has a different body structure than the production Volt and the test mules aren't as polished as a production product, there was no way to gauge just how quiet the Volt will be. We expect that it will be very pleasing to drive. Once the gas engine fires to make electricity, dynamics will change, but the transition should be manageable since the engine will generally run at a constant rpm and not cycle on and off as much as a hybrid.

One of GM's performance targets for the Volt is a 0-60 time of 8.5 seconds. That's reasonably quick and our experience in the test mule indicates that eight and a half seconds is a very realistic number. Power delivery is different than with internal combustion power. Electric motors provide maximum torque from a dead stop and have the capability to spin at very high rpm. That immediate torque launches the Volt with a smooth authority. Traction control is handled by the powertrain's computer, minimizing wheel spin. GM is tuning the Volt to achieve a good balance of overall performance and range. Extracting more performance from the Volt will reduce electric range.

The Volt's electric motor produces 149 horsepower and drives the front wheels through a single speed transmission. Since electric motors have a wide rpm range and produce generous torque at very slow speeds, there is no need to step the power through a variety of gear ratios in the transmission. The shifter offers two settings for forward motion, the normal drive position and, by pulling the lever rearward to what would normally be low, the driver can select more aggressive regenerative braking when their foot backs off the accelerator. This is handy for city driving to maximize electric power production and reduce the need for brake application. If you drive efficiently and look ahead to time lights and stops, electric range will be enhanced.

Chevy Volt Test Mule InteriorInterior View.

The heart of any electric vehicle is the battery. Volt uses GM's proven "T" battery configuration that runs down the center tunnel of the car and T's out to each side below the rear seat area. This battery is about one half the size and one-third the weight (375 pounds) of the battery that supplied power to the EV-1, and will be assembled in Michigan utilizing cells supplied by LG Chem. The advanced Lithium-ion pack has a potential power output of 16 kWh. To enhance battery life, the Volt won't use all the potential power on hand. By cycling between a maximum 80-percent change and minimum 30-percent charge, GM is confident the Volt battery pack will easily deliver a 100,000-plus mile life. It can be charged in six to seven hours from a 110-volt household outlet, or two to three hours when plugged into 240 volts.

The Chevy Volt marks a new era in the evolution of the automobile. Once the engineers learn what they can from the Cruze-based mules, they will move on to hand-build prototypes of the Volt for the next phase of testing. We'll try to wrangle some wheel time and let you know how they perform.



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