A lightning rod for controversies, contradictions and conservation.
The Chevy Volt…and Its Role in Policing
By: John Bellah and PFM Staff
Introduced for 2011, the Chevy Volt is an Electric Vehicle. It uses a lithium ion battery to power the electric drive motors. However, the Volt is also an Extended Range Hybrid. It uses a gasoline engine to power a generator that produces electricity for those same electric drive motors. Except for the rarest situation, the Volt is strictly driven by electricity, either from the main battery or from the generator.
What separates the Volt from other plug-in electric vehicles is the over 300-mile range made possible by the back-up gas engine. In Normal (battery-only) mode, the Volt will go 35 and 38 miles on a fully charged battery. Heads-up: That 38 miles goes by faster than you might think!
If the travel is longer than this, the gas engine starts and produces electricity from the engine’s generator. This electricity then powers the Volt, and not the gas engine. The gas engine extends the driving range by about 325 miles. Combining the battery-supplied electricity and the gas engine / generator-supplied electricity, the Volt has a driving range of more than 350 miles.
The Volt blurs the line with definitions of what a plug-in hybrid means. The Volt is not a plug-in battery electric vehicle, since it has a gas engine that can operate a generator to produce electricity to drive the car and produce energy to charge the main battery. The Volt is not a gas-electric hybrid because the gas engine does not typically propel the Volt. The best description for the Volt is an Extended-Range Electric Vehicle, E-REV.
The Volt has two electric motors combined into the electric drive. One is a 111 kW drive motor; the other is a 55 kW generator motor. The electric drive is rated at 149 hp. The gasoline engine is the same 84 hp, 1.4L I4 used in other GM vehicles like the Sonic and Cruze.
The Volt is a four-passenger, front-wheel-drive, Compact sedan. The Chevy Volt is built on the same Delta II compact platform as the Chevy Cruze. The Volt is small but still comfortable for all but the larger officers. (The duty belt may or may not be compatible with the front seat.) In fact, once the novelty of the huge electro-mechanical engineering accomplishment wears off, once the novelty of plug-in electric cords wears off, think of the Volt as a Cruze.
The Volt changes peoples’ minds about electric cars because it is so normal to drive. It “feels” like a conventional sedan. Since electric motors operate at maximum torque immediately, the Volt is very responsive, even perky. Electric motors produce their maximum torque instantly. Gas engines have to rev up to produce their maximum torque. The instant max torque from the electric-powered Volt makes it very responsive to drive. Step on the accelerator pedal, and the Volt GOES.
With a zero to 60 mph time of 10 seconds, the Volt is only about a second slower than the Ford CVPI. The Volt has a top speed of 100 mph. The two-lane road passing ability is just fine. At 45 mpg, step on the pedal and go. The Volt easily cruises at 75 mph. The overall acceleration is very good. The overall handling is excellent, the Volt is quite sporty. The brakes are outstanding.
Four Driving Modes
The Volt has four driver-selectable driving modes – Normal, Mountain, Sport and Hold. Normal is the default mode. With each key start, the Volt is set to Normal mode. In Normal mode, the Volt will start operating on the main lithium-ion battery pack. It will remain powered only by the main battery until it reaches the minimum charge, which is 30 percent State of Charge (SOC). Then the gas engine will start, which provides electricity to the drive motors.
In Mountain mode, the gas engine provides all the electricity to the drive motors. In Mountain mode, the gas engine also provides electricity to recharge the main battery pack. Mountain mode charges the battery up to a half charge, and then maintains that half charge. Think of Mountain mode as a trickle charge. More on the Mountain mode later.
In Sport mode, the Volt is much more responsive at extremely low speeds, like zero to 30 mph. Above this urban speed, Sport mode doesn’t add any more throttle response than Normal mode. The slightly faster zero to 60 mph time in Sport mode compared to Normal mode is due only to the Sport mode’s faster zero to 30 mph time.
In Sport mode, a different calibration is used to modify the pedal map or pedal request to the operating system. It does not change any of the drive unit characteristics, i.e., it does not keep the Volt in the 111 kWh motor-only, locked ring gear condition; it does not mechanically change the two electric motors or three clutch packs to improve responsiveness. It does, however, modify the request to the system, making the request more aggressive.
In Hold mode, the main battery is disconnected and the Volt runs on the gas engine. It is like Mountain mode, except the battery is not charged in Hold mode. The battery remains at whatever State of Charge it was when Hold was activated. For example, in Hold mode the Volt will hold a fully charged level, or a half charged level (whatever) until the driver switches out of Hold mode. More on the Hold mode later.
Run Out of Battery…and Gas
Once you deplete the battery and begin to run on gas, keep the 9.3-gallon tank in mind. The Volt may average 35-plus mpg, and that will give you the same range as a 20-gallon tank in a sedan that gets 16 mpg. However, the total fuel situation aboard the Volt is not as obvious as looking at your old gas gauge. With information overload from the Driver Information Center, once you deplete the battery, start looking for a gas station.
What if you run the battery down to the preset minimum level, so the Volt switches to the gas engine…and you run out of gas? The Volt propulsion battery has a reserve amount of electric power. The acceleration will be reduced, but the Volt will move for three to four miles.
Just the opposite. What if you never run the battery to the minimum and never actually use any gasoline? The Volt uses an internal Fuel Maintenance Mode, which activates the gas engine to burn at least a little gas. This automatically kicks in if you have been in electric mode (only) so long, there is a risk of the gasoline growing state, or the alcohol separating from the gasoline on E10 pump gas. So the Volt uses the gas in the tank before it grows stale, even if the Volt is only ever operated in Normal (Electric Mode).
Low-Gear Regenerative Braking
The Volt uses regenerative braking each time the vehicle gradually slows down. Almost undetectable by the driver, regenerative braking in Drive (D) charges the main battery pack. The Volt can also be driven with the shift lever in Low (L) position. The use of Low produces much more aggressive regenerative braking than in Drive. Consider using Low in heavy stop-and-go traffic and when traveling or coasting downhill.
The use of Low involves such aggressive regenerative braking that almost no use of the brakes is required. And the Volt can be driven in Low instead of Drive indefinitely. Of course, that assumes the driver and passenger can put up with the very aggressive regenerative braking.
The use of Low in suburban, urban or heavily urban traffic produces a lot of battery charging. In fact, Low produced so much electric power from regenerative braking that we drove 39 miles in Normal mode (battery-only) when the propulsion battery gauge and electric range estimated displayed an initial reading of 31 miles. That extra 8 miles of battery-only driving came from the battery being recharged by regenerative braking.
Noise-Vibration-Harshness – Not!
The Voltec electric drive system consists of two electric motors, three clutches, and a planetary gear set made up of a planetary sun gear, planetary ring gear and planetary carrier. With all these clutch engagements and disengagements and all the gear set locking and locking, you will never notice it. The entire powertrain and drivetrain is smooth and silent. It is noise-free, vibration-free, harshness-free. Transitions between all four major electric vehicle (battery) and extended range (gasoline) modes are instantaneous and surge-free.
Your only sense that anything whatsoever is going on may be in Mountain mode, and only when the battery is depleted or less than half charged, and only when you are at a stop or driving at very low speeds. Under that one situation, the Volt is working hard to catch up. Otherwise, the Volt is very quiet. The seamless and transparent transition from battery power to all the varieties of gas-engine support is an amazing engineering accomplishment.
Is There a Plug-in Around Here?
The charging screen on the instrument panel shows the time to fully charge the battery using either 120-volt household current or 240-volt industrial current. However, even the 120-volt mode has two versions: 8-amp and 12-amp. On a completely depleted battery, the 120-volt, 8-amp setting has a recharge time of 16 hours. The 120-volt, 12-amp current shortens this to about 10 hours. Face the reality that you may not be at the home base long enough to fully charge the battery with 120 volts. These are best case and will be longer in cooler or colder weather.
You may find the Volt to be “high maintenance,” not in terms of service and repair but instead for your constant search for an electrical outlet. And not just a two-way, polarity-biased outlet. Oh, no. You need a genuine three-way plug. Officers may indeed feel like a slave to that electric cord…a modern-day ball and chain. The novelty of driving the Volt can wear off quickly as officers of all rank go about their job. One of the officers who drove the Volt home – on day one – forgot to plug it in overnight.
The 240-volt, 20-amp charging time is a mere four hours. For all practical purposes, if you get a Volt, get a 240V charging station. For information on a 240V charging station, go to the “home charging” website. A 240 V charging station is a must-have.
Heads-up! You know about all those E85-capable vehicles that never use a drop of E85, right? The EPAct “box was checked” but ethanol is never used, right? Same with the Volt. Check to be sure the electric vehicle is actually driven in Normal, EV-battery mode when it is used. Be sure the apparent need to plug it in for hours – at every opportunity – doesn’t become so much of a hassle that they just run the Volt on the gas engine (Extended Range) the whole time.
And Isn’t It Ironic
Some of the controversies around the Volt come from some clear contradictions. For example, the Volt works the best where the least gas is used anyhow. Driving a few miles out and then driving a few miles back doesn’t really use a lot of gas in the first place. Again, that 35-mile battery range may go fast.
The 120-volt charge from household current is simply not enough. The Volt must be parked at the home base for 16 hours. That is not going to fit many agency, business or family schedules. An expensive 240-volt charging system must be factored into the purchase price. Heads-up! The cost of the Volt to a retail customer includes a $7,500 tax credit. Since municipalities do not pay taxes, this $7,500 credit does not apply to police department purchase. While dealers set the pricing, the Volt has an MSRP of $39,145. The Volt is an expensive way to meet a green initiative.
The Volt is the in the running for the “ultimate” green vehicle, right? You would naturally assume the Volt is E85 FlexFuel capable, right? After all, E85 is the greenest of the somewhat available fuels. No, the Volt is not E85-compatible. Nor is the Volt supposed to be fueled with E10 gasohol, i.e., Regular Unleaded.
The irony is the Volt requires Premium fuel (91 octane or more). Premium is required to allow the tiny engine to use more ignition timing with higher compression ratios for maximum output. Premium is $0.20 to $0.40 per gallon more expensive than Regular. An E85 FlexFuel version was planned for the 2013 model year, but it didn’t happen.
“We drove 1,000 miles and used no gasoline at all.” “We drove 1,000 miles and used 30 gallons of gasoline.” More than any other vehicle on the road, the fuel economy you get depends on the number of miles between battery charging, your informed use of Hold, Sport and Mountain modes, the exact driving terrain, and the ambient temperature.
Black & Gold and Green
Police officers with the Purdue University (Indiana) Police Department put about 150 miles on the Volt over a four-day period. It was driven on routine admin and investigative tasks by six different officers, from detectives to Chief John Cox. As much as possible, it was used as any other admin vehicle, including taken home at night, driven to meetings on campus, etc.
“Driving the Volt dispelled many misconceptions of electric vehicles...very responsive and nimble,” Lt. John Moore said.
Purdue University has two 240-volt charging stations donated by General Electric. When these were not in use by the faculty and staff, 240 volts was used to charge the Volt. Otherwise, 120-volt household current was used.
When the Volt returned to the police department, it was plugged into the 120-volt outlet for a trickle charge. However, even at the higher 12-amp setting, the 120-volt charge took so long to almost make the few hours of trickle charge not worth the effort.
“The charge time on 120-volt is an issue. Perhaps an adaptor that would accept two 120-volt inputs could be developed,” Capt. Eric Chin offered.
The detectives and senior police admin filled out a questionnaire based on their time with the Volt. For room in the front seat, either in plain clothes or in full uniform, the Volt was rated a 6.7 (where 1 is too small and 10 is very roomy). This ranged from 4 to 8.
Not enough legroom and not enough headroom were cited by a few. However, the area noted by almost all as needing more room was the hip room. That is a significant issue since most reviewers were in plain clothes, i.e., without a full duty belt.
Ratings for the room in the rear seat were predictable. It averaged 2.0 out of 10 with four of the six officers giving the minimum score of 1. The rear seat of the Volt has virtually no legroom, period. Whether an admin police sedan needs a rear seat at all is the question. No one other than a child will fit in the rear seat.
How easy or difficult was it to enter and exit the front seat of the Volt? With 10 as very easy, the Volt got a 6.8, ranging from 4 to 9. Some of the rating depended on the physical size of the officer, of course. However, the lowest score came from an officer in full uniform. Either the car is simply too small or the front seat adjustment (back-forth, up-down) is not enough. The Volt, after all, is a Compact sedan.
Visibility? How well can you see out of the Volt? The Volt is at its best in heavily urban, stop-and-go scenarios. By definition, this means crowded situations. So, can the driver see all those cars and people? With a 10 as easy to see everything, the Volt got an 8.3, ranging from 5 to 10. (The majority were 8, 9 or 10.) The one area that needs better visibility? The rear.
In terms of performance, the Volt got a 9.2 out of 10 for acceleration, a 9.2 out of 10 for brakes, and a 9.3 out of 10 for steering and handling. “The overall performance of the Volt changed a lot of minds about electric cars,” Capt. Eric Chin said. “This is a great innovation.”
The operating range? The Volt is an electric car. Depending on ambient temperature, it has a fully charged, driving range in normal use of around 38 miles. Is that enough? With 10 being plenty in this campus environment, the Volt was rated 5.8. Except for the rear seat room, this was the lowest average score of the evaluation. It was also the one with the widest range of opinions: literally from 1 to 10.
Just like the general public’s polarized opinion on the Volt itself, the driving range of the Volt was rated as either “not enough” or “plenty.” If 38 miles is not enough, and a 5.8 out of 10 certainly indicates it is not enough, how much battery-only range is enough? The consensus is 50 miles. During the four-day, 150-mile evaluation, the PUPD averaged 109 mpg.
“I am impressed with the responsiveness of the electric motor. The issue is the price,” Chief John Cox stated.
Mountain and Hold Modes
By switching to Mountain mode, the driver manually activates the gas engine. The gas engine then provides electricity to the drive motors, and also provides electricity to charge the main battery. The original purpose for Mountain mode was to charge the main battery enough to drive 60 mph up a 5 percent grade without loss of speed. You will need the half charged battery that comes from Mountain mode and remain in Mountain mode.
Of course, Mountain mode is something you use ahead of time, i.e., charge the depleted battery before the need! However, you can use Mountain mode anytime you want to charge the battery to half level. That will produce 15 to 18 miles of battery-only driving once you switch it to Normal mode.
So, why mess around with plugging in the Volt to charge the battery? Why not run it in Mountain mode all the time? Two reasons. First, the Mounting mode produces electricity in the most expensive and least efficient way. Second, the Mountain mode only charges the battery half way, or maintains the battery at about half-charge (45 percent State of Charge). To fully charge the battery, you have to plug it in. To reduce the rate of capacity degradation, the fully charged battery is limited to an 85 percent SOC. The fully depleted battery is limited to a 30 percent SOC.
Instead of using Mountain mode to charge the battery for specific times when battery propulsion is the most efficient, use the Hold mode. Driving with the gas engine to power the propulsion motor in Hold uses less gas than driving in Mountain mode. In Mountain mode, the gas engine has to power both the propulsion motor and the generator to recharge the battery.
One way to use the battery for city driving involves Mountain mode. Change from Normal mode to Mountain mode when the remaining battery capacity is equal to the amount of city miles coming up. When you change from highway driving to city driving, change back to Normal mode for battery-only operation. Remember now, the Volt uses more gas in Mountain mode than in battery-depleted Normal mode, so max overall efficiency is a balancing act for the green enthusiast.
In Mountain mode, the system is working to a high-voltage battery state of charge. The resultant generator rpm might be higher. The generator speed is a function of many factors including the high-voltage battery starting point, vehicle pedal request, current ambient conditions, and road grade. It is not simply an increase in gas engine rpm compared to Normal mode.
The most significant change for the 2013 model year is the addition of the Hold mode. The Hold mode allows drivers to decide exactly when they will use the battery-only, i.e., when to use the Volt in the most fuel-energy efficient way. When the battery is depleted, the Volt gets better gas mileage on the highway (40 mpg) than in the city (35 mpg). So it makes sense to do as much fully electric driving as possible in the city, and as little fully electric driving as possible on the highway.
The Hold mode is a big deal for drivers who mix highway and city driving. The electric motors are most efficient in suburban, urban and heavily urbanized driving. Not so much in highway and rural driving. With a mix of city and highway driving, Hold allows the driver to isolate the main battery. In Hold mode, the gas engine powers the generator motor to drive the Volt. The battery is not used at all.
Here is how Hold pays off. The Volt is fully charged overnight. Start the inbound commute from the suburbs with a drive into the city. Put the Volt in Hold mode as you drive at higher speeds the first few miles. Change back to Normal mode (battery-only) for the slower, stop-and-go driving. Start the outbound commute in the default, Normal mode (battery-only).
Using only the battery in slower traffic, get as far as the battery will last under the conditions that battery-only is the most energy efficient. Depending on a number of conditions, the gasoline-produced electricity may only be needed for a few minutes during the entire travel. When the gas-engine is activated, it will be under driving conditions that are better suited to gas generated electricity, where battery only operation is less energy efficient.
Miles Per Gallon Equivalent and Energy Costs
What is MPGe? Miles per gallon gasoline equivalent (MPGe or MPGge) is an attempt to put alternative energy sources in perspective with gasoline. It is a way to compare the energy consumption of alt fuel (CNG, LPG) vehicles, plug-in battery electric vehicles and plug-in hybrid electric vehicles and hydrogen vehicles with the fuel economy of gasoline and diesel powered vehicles.
One gallon of gasoline is equivalent to 33.7 kilowatt hours (kWh) of electricity. However, most people cannot relate to kilowatt hours per mile as a measure of “fuel economy” in their vehicles. So the EPA and NHTSA jointly developed miles per gallon equivalent (MPGe) as a common fuel economy unit of measure.
With the Volt, it is impossible to cite fuel economy estimates that have any real world meaning. The EPA eventually adopted a dual economy estimate and had to use a miles per gallon “equivalent” (MPGe) rating. It is all very complicated, conditional and confusing. Their 98 MPGe (combined city/highway electricity) and 37 MPG (combined city/highway, gasoline-only) are totally meaningless.
During our two weeks with the Volt, we averaged 24 mpg, 34 mpg, 39 mpg, 44 mpg, 58 mpg, 98 mpg, 109 mpg and 250 mpg depending on a bunch of different factors. Every single mileage number is true and real. Every number is a fully documented experience. To be more helpful, we put 1,600 miles on the Volt and had a grand average of 43 mpg.
This particular 2013 Volt came from the GM press fleet and had a total of 2,700 miles on the odometer. The Volt keeps track of “Lifetime” fuel economy. That lifetime average was 58 mpg as driven under the widest possible variety of conditions and scenarios. So, what kind of gas mileage do you get from the Volt? A reasonable number is 58 mpg.
Electricity is Not Free, Not Green
The Volt is a study in contradictions for at least two aspects of electricity. First, electricity is not free. It does a lot for the money, but it is certainly not free. Driven strictly by the battery, with no electricity from the gas engine, the Volt costs about $0.02 per mile ($0.10 per kWh). Compare this to a comparable, conventional gasoline powered vehicle that costs about $0.12 per mile ($3.60 per gallon). Charging the Volt’s battery once per day from empty to full costs about $1.50, the cost of a bottle of water.
So, while in electric operation, the Volt costs one-sixth what a gas powered compact would cost. However, every time the Volt’s gas engine starts up, the cost of operation goes up sharply. Remember, the Volt can get as little as 24 mpg (Mountain mode, depleted battery.)
Second, electricity is not green. In the fine print, even the EPA is careful to point out their greenhouse gas and smog ratings are tailpipe only. Their disclaimer on the window sticker reads “producing and distributing fuel and electricity also create emissions.”
In the U.S., 45 percent of electricity is produced by burning coal. That is certainly not considered green. Another 20 percent of the electricity is produced by nuclear. Nuclear power is also arguably not green. Both nuclear and coal are excellent, low-cost methods of producing electricity. However, be intellectually honest about the Volt. Justify the use of the Volt on full-disclosure economic and environments facts, and not on naïve, tree-hugging emotion.
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Inside the Electo-Mechanic Marvel
The Voltec drive system used in the Volt is the same basic electric motor and planetary gearset as used in the Chevy Equinox (hydrogen) Fuel Cell vehicle. The Voltec electric drive system consists of two electric motors, three clutches and a planetary gear set. The gear set is made up of a planetary sun gear, planetary ring gear and planetary carrier. Electric motors drive the Volt, not the gasoline engine. One is the bigger, more powerful primary traction motor, chiefly powered by the lithium-ion battery pack. The other is the smaller, less powerful generator motor, chiefly powered by the gas engine.
Most battery electric vehicles use a single motor with a fixed reduction gear. The reduction gear steps down the electric motor to synchronize with the wheel speed. Instead of a fixed gear, the Volt uses a planetary gear set.
The efficiency of any electric motor drops off as it approaches its maximum rotational speed. The use of two different motors in the Volt (and a planetary gear set) reduces the combined rotational speed of the electric motors. That increases efficiency, reduces battery drain at highway speeds, and that alone adds battery-only range at highway speeds.
Two of the three clutches are used to either lock the ring gear of the planetary gear set, or connect the ring gear to the generator motor, depending on the mode the Volt is in. The third clutch connects the gas engine to the generator motor. This is the key to the Volt’s unique extended range ability.
One Motor, Electric Vehicle Driving, Low Speed
The Voltec drive has four different ways to operate. The first is single motor, low speed, electric vehicle (battery-only) driving. In this mode, at low speeds, the primary traction motor gets power from electrical power only from the main battery. The ring gear is locked. The generator motor is isolated from both the gas engine and the gear set. The more powerful 111 kWh motor and the locked (fixed) ring gear produces very snappy off-the-line acceleration.
Two Motor, Electric Vehicle Driving, High Speed
The second way of operating is with two motors at higher speeds, i.e., above 50 mph. As the speed of the Volt increases, the ring gear is unlocked and coupled to the 54 kWh generator motor. This allows both the primary traction motor and the secondary generator motor to provide a blended power source, while the planetary gear lowers the motor rotation speed of each, keeping the electrical efficiency high. In two motor, EV driving, the electricity to power the main traction motor and the electricity to power the secondary generator motor all comes from the lithium battery via the inverter.
One Motor, Extended Range Driving, Low Speed
Once the battery has been depleted to its minimal level, the gas engine starts and is clutch-coupled to the secondary generator motor. However, the generator motor doesn’t drive the Volt, the generator just provides electricity to the main traction motor via the inverter. At low speeds, with the battery depleted, the generator-powered main traction motor propels the Volt. This is in the default setting of Normal mode.
In the driver-selected Mountain mode, the generator will provide electricity via the inverter to the main traction motor. The generator will also provide electricity via the inverter to the lithium-ion battery pack. If the battery pack is less than 45 percent SOC, and Mountain mode is engaged, the generator will charge the battery up to 45 percent SOC and then maintain it there. Mountain mode will not fully charge the battery pack. The only way to do that, the most efficient way, is to plug in the Volt.
Two Motor, Extended Range Driving, High Speed
The blended, two-motor, planetary gear set-engaged method used in high-speed electric vehicle driving is also used in extended range (gas engine) high-speed driving. In this case, however, the electricity to operate the main traction motor and the secondary generator motor comes from the gas engine-powered generator.
Remember those three clutches? During high speed, Extended Range driving, the clutch that locks the ring gear to the planetary gear is engaged, the clutch that locks the ring gear to the generator motor, and the clutch that locks the gas engine to the generator motor is engaged. By following the long path of clutches and gears, you can see the best kept secret of the Volt. Yes, it is a technicality, however, in two-motor, extended range, high-speed operation, the gasoline engine is (gasp) actually, physically connected to the final drive gearing and axle.
Under this one condition, the Volt is not a purely electric vehicle. GM is quick to point out that the engine alone cannot propel the Volt unless the traction motor is also powered. In order for any planetary gear set to transmit torque, two of the three main components (ring gear, sun gear, planet carrier) must be driven. Or one must be locked with third providing the output. With the Volt, in this situation, the traction motor provides torque to the sun gear and only that allows propulsion. So the debate among purists rages on. We are going with the definition that the Volt is an Extended-Range Electric Vehicle (E-REV).
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Fire Hazard Myth
In June 2011, the NHTSA performed a 20 mph side-pole-impact crash test on the Volt. This side impact test involved a vehicle rollover as part of the test. The Volt achieved a five-star rating for the front-seat side crash; a five-star rating for the rear-seat side crash, and a five-star rating for the rollover after crash. Three weeks later, this Volt caught fire and was virtually destroyed. The main battery was the source of the fire.
What made the worldwide news was the fact that the Volt, sitting in a parking lot, caught fire. Few news reports mentioned that the car had sustained a 20 mph side pole crash. Fewer still mentioned that the Volt was rollover tested after the side crash.
The clear impression from the news reports was the Volt, just sitting in your garage and not even plugged in, could suddenly catch fire. Controversy sells in news reporting. About 250 of 12,000 Volt owners were frightened into requesting a loaner vehicle or selling their Volt back to GM. Here is the rest of the story.
Both General Motors and NHTSA independently repeated the tests to find the conditions that caused the battery leakage. The cause of the fire was a piece of the vehicle piercing the side of the battery, causing a leak. The leak alone did not cause the fire. After the side impact and subsequent leak, the Volt was put through a roll as part of the NHTSA rollover testing.
The rollover test involves rolling the vehicle on its far side, holding that for five minutes, on its top with a five-minute hold, and then on the near side for five minutes. When the Volt was upside down, the battery fluid dripped onto a circuit board on the top of the battery pack. This slowly short circuited the fully charged battery, causing a fire three weeks after the crash and rollover.
GM strengthened the parts of the Volt to further protect the battery in the event of a severe side crash. They also added a sensor to monitor battery fluid levels and added a tamper-resistant bracket to prevent overfilling the battery coolant reservoir.
GM and NHTSA then conducted side crash-rollover tests on five Volts. There was no battery damage and no fluid leaks on these upgraded Volts. NHTSA said GM’s changes were sufficient and closed their inquiry with the statement, “...based on available data, NHTSA does not believe the Chevy Volt or other electric vehicles pose a greater risk of fire than gasoline powered vehicles.” By the way, the fire would not have occurred if the GM protocol for deactivating the battery after any crash had been followed by NHTSA. First responders take note!
While the Volt is a Compact sedan, it is clearly among the safest, the most crashworthy. The Volt has eight airbags including dual-side knee airbags. It has an overall vehicle score (frontal, side, rollover) of five-star safety rating.