Go to school on the Chevrolet Bolt’s clever Drive Unit
When you look at the Chevrolet Bolt’s Drive Unit, it’s immediately clear that simplicity plays a vital role in a drivetrain’s efficiency. The “Drive Unit” is Chevy-speak for the compact motor and gear set that replaces a traditional engine and transmission in the Bolt EV. A V-8 engine alone uses 100+ moving components, but the Bolt’s entire powertrain uses fewer than five gears to transmit power from the rotor, the electric motor’s only spinning part, to the wheels.
In this video, Weber State University Professor John D. Kelly breaks down the Bolt’s drivetrain into its core components, allowing us to understand the system from the inside out.
For the sake of simplicity, Kelly’s presentation eliminates the charging, battery, cooling, and power-control systems of the General’s pint-sized EV. His approach allows us to peek at several clever packaging tricks that an EV powertrain allows—for instance, an intermediate CV axle passing through the center of the motor on the same axis as the motor itself. This arrangement keeps the Drive Unit incredibly compact.
The traditional front-wheel-drive transmission/transverse engine combination uses several gear sets, including those in the final drive and differential assemblies, a setup that wastes space compared to the solution Chevrolet employs in the Bolt. The EV’s gear set is good for a 7.0518:1 final drive ratio, while the motor is capable of a tick over 8800 rpm. From there, the 201-horse motor churns out 265 lb-ft of torque directly to the wheels with no further disruption via a transmission, torque converter, or clutch. Imagine how low the center of gravity could be if this system could tuck between the frame rails of a Radical or an MR2.
Kelly also breaks down the entire electrical system into its individual components, starting with the Power Distribution and Accessory Power Modules that break down the battery’s 400VDC power into its various uses. These two modules control convert the battery’s DC power to three-phase AC for the brushless motor and step down it to 12VDC to power all of the interior components. Both the Power Distribution and the Accessory Power Module rely on the Onboard Charger Module to orchestrate charging, whether you’re home on 240VAC or at a 400VDC fast-charger that’s essentially jacked straight into the battery.
Understanding these components will give you a better idea of what’s under the hood of the next Bolt you see
Even if you’re not a self-proclaimed Bolt fanatic, this video is well worth a watch; Chevrolet’s upcoming crate motors share many of their parts with the Bolt’s powertrain.