On The Topic of EVs and Hybrids: The Chevrolet Volt

On The Topic of EVs and Hybrids: The Chevrolet Volt


11 October, 2010

GM touted the Volt at their electric savior. We were told that the volt would get 230 MPG and would be a plug-in extended range electric vehicle (See MSU’s EcoCAR for an example of a plug-in EREV). Everybody loved the idea and everybody supported GM in their endeavor. Clearly interest in this new generation of high-efficiency vehicles was there.

Unfortunately, the path to market has changed the Volt considerably. After some real-world testing by Popular Mechanics, a few things became clear.

First of all, the vehicle’s all-electric range was nowhere near great enough to award 230 MPG. Before these tests, GM announced that the all-electric range will be closer to 20 – 50 miles. From the tests, the average range was found to be about 33 miles. Fuel economy was found to be about 32 MPG city and 36 MPG highway. This is far shorter than the 230 MPG claimed. Of course, the caveat was that the fuel economy was calculated after the battery was depleted. While not very far, 33 miles is still greater than the commute of 75% of the population. I travel roughly 2 miles daily, so I could possibly go half a week to a week without having to recharge the car. In my situation, I would get, after 70 miles (assuming the battery depletes at the 33 mile mark), my fuel economy would be about 70 MPG. Still not 230 MPG, but better than the 21 MPG I get from my Sable.

But more importantly, Volt engineers announced that the gasoline engine would actually power the wheels directly like in a conventional car. No longer can the Volt be considered an EV, but is now classified as a hybrid. Edmunds called GM out over Twitter. We were lied to.

Honestly, through the course of development, designs change. Rather than saying we were lied to, I’d rather say we were misinformed by GM PR. The original concept of the Volt was for it to be a EREV. Many concepts don’t make it the market without changes. While the reasons behind why the change in the drive change may not be understood yet, it’s not unreasonable that these kinds of changes were made.

The old design of the Volt was that the electric drive-train was independent of the charging source. This is what an EREV is. It’s an electric car with a non-electric power source to charge the batteries when the batteries are depleted. And this is what I see future vehicles becoming. This design allows the car to run on gasoline, diesel, natural gas, propane, hydrogen, or any other fuel source without too much modification to the overall workings of the vehicle. Classifying an EREV as an EV is correct, however, the term electric vehicle is too broad. It’s better classified as a hybrid.

So why has the Volt always been, technically, a hybrid? The basics on the classification of a hybrid is that the vehicle uses two sources of power to drive the wheels. There are three distinct types of hybrids and two classifications of hybrids.

Parallel hybrids can simultaneously power the wheels with both the internal combustion engine and the electric motor. The distinct feature of a parallel hybrid is that the engine and the motor are not connected directly, though, some hybrids will have a motor inserted between the engine and transmission. This configuration is still technically parallel because the electric motor does not receive electricity due to the engine. The battery is recharged by the engine through regenerative braking and, in cases where the electric motor is not in between the engine and transmission, through the electric motor itself from the movement of the vehicle. Parallel hybrids are particularity efficient at higher, highway speeds.

Series hybrids convert power from the engine directly into electricity. The electricity generated is used to charge the battery pack and can directly power the electric motors. In this case, the electric motors can drive the wheels using two different power sources. Most diesel electric trains are series hybrids. This type of hybrid is starting to gain some popularity in passenger cars, but still doesn’t have the market penetration that parallel hybrids have. One of the biggest factors is that series hybrids are more efficient at lower, city speeds.

Finally, series-parallel hybrids take the best of both-worlds. Alternately, they can be called two-mode hybrids, referencing to the two modes in which they can power the wheels, though series-parallel hybrids are becoming more complicated and can have more than two-modes. These hybrids take the best of both worlds and can disable and enable certain parts of the power train to utilize the most efficient mode for the speed at which the vehicle is moving. The Toyota Prius is one big example. At lower speeds, the computer will disable the mechanical link between the engine and the wheels so that the electric motor is doing more of the work. The engine is only used to power the electric motor. As the vehicle goes faster, the computer will switch the vehicle to a parallel configuration so that the engine powers the wheels at higher speeds.

All three types can be plug-in or self-charging. This is fairly self-explanatory, and the intricacies of self-charging hybrid electric vehicles vary between companies and models.

Aside from the types of hybrids and the ways they are charged and can sustain charge, hybrids are either full (strong) hybrids or mild (weak) hybrids. Full hybrids can use both sources independently from each other or blend the two together. On the other hand, mild hybrids cannot rely on only one source of power. A lot of hybrid crossovers and SUVs tend to be mild hybrids because the electric motors are unable to efficiently propel the vehicles forward on their own. Because of this, many mild hybrids are parallel or series-parallel because of the need for the internal combustion engine to power the wheels.

The Volt uses some non-electric power source (in the current production model, a gasoline engine) to charge the batteries and to power the electric motors. By definition, even with the plug-in and electric only features, the Volt is still a series hybrid. And even though now it’s confirmed that the engine can drive the wheels directly, the Volt is still a hybrid, and was always a hybrid. The behavior of the Volt can now be described as a series-parallel hybrid instead of just a series hybrid since the car can go from a series to a parallel configuration.

So sorry to bust the bubble, but the Volt is still an EV, but it is also still a hybrid. Just as much as a Suburban Hybrid can be called an EV, the Volt is an EV. Just as much as the Nissan LEAF is an EV, the Volt is an EV.