A View from Kevin Bullis
Teardown Reveals the Remarkable Complexity of Chevrolet's Volt
A look inside the car reveals just how complicated it is.
A recent tear down of the Chevrolet Volt reveals the surprising complexity of this extended range electric vehicle. UBM Tech Insights took apart the car’s battery and charging system to identify the components of each, and it’s making at least some of its results, including photos, available for free here.
It’s been clear for a long time that the Volt is a complicated car. GM prefers to call it “advanced.” To a skeptic, all that complexity means there are more ways for something to go wrong.
The Volt is an electric vehicle in the sense that it’s powered by an electric motor almost all the time. But it also has a gas-powered engine for extending the car’s range.
In fact, the Volt has two electric motors. One serves primarily as a generator—it’s attached to the gas engine and generates electricity that either recharges the battery or powers the car’s main electric motor.
A complex transmission system also allows the gas engine to connect directly to the wheels. The new teardown looks at the electronics used to control this system. The charging and power distribution system is complex, having over 10 million lines of code and 100 microcontrollers.
Another complication is the fact that the main motor also generates electricity when recovering energy from braking. An inverter system (which includes inverters, rectifiers, converters, and microcontrollers) has two-way AC power connections to the main motor and the generator, which it allow it to deliver power to the motors or to accept power from the motors when they’re acting as generators.
The inverter system’s DC connections send power to the battery, and receive power from it. The inverter system also directs DC power to an oil pump in the transmission. Several communications hookups monitor things such as the Volt’s two electric motors, the speed of the gas engine, and signals from the ignition.
The home charger system—which connects to a cord you can plug into an ordinary outlet—is tucked in under the fender, below one of the headlights. It has its own liquid cooling system, with coolant and a pump to circulate it.
In the trunk, a fan-cooled module converts the high voltage (nearly 360 volt) power from the battery to 12 to 14 volt DC power to run the systems powered by a belt-driven alternator in a conventional car.
The car’s lithium ion battery pack is also complex. It consists of 288 cells, 288 voltage sensors, dozens of temperature sensors, a cooling and heating system, and 12 electronic control modules within the battery pack—including about 30 individual microchips, and one control module for the whole pack. These systems are designed in part to balance out differences between the cells that can increase as the cells age—which could increase the life of the battery pack by about 10 percent, according to UBM.
UBM has also done an analysis of what it calls the car’s “infotainment system,” which includes displays to help drivers drive more efficiently.
So what does this all mean for vehicle reliability? It’s probably too early to provide good comparisons to other vehicles, since the car has been on the road in limited numbers and for less than two years. For those interested in what Volt owners have experienced so far (and there have been problems, as with any vehicle) a good source is this owners forum (not GM’s official site).