Judged by its individual components, Volt’s 1.4-L four-cylinder combustion engine resembles its nearly identical cousin in the Chevrolet Cruze. It has got an aluminum DOHC head with four valves per cylinder. Its hollow-frame iron cylinder block is a thin-wall casting, making it nearly as light as a comparable aluminum block while retaining iron’s inherent strength and noise-damping qualities.
Derived from GM’s global Family Zero of small-displacement gasoline inline triples and fours, the Volt engine was designed for efficient operation. Its hollow camshafts are manipulated with two-step variable electrohydraulic phasers. Its lubricant is distributed through a variable-displacement flow-control oil pump to reduce parasitics under light load conditions. The thermostat is map-controlled.
There is no starter motor; the car’s generator motor handles that task. And the engine’s undersquare bore/stroke promotes good low-and mid-range combustion efficiency, particularly in turbo versions.
But a closer look, and a drive in the Volt, show this is not a typical Family Zero unit (nor is it turbocharged). It is governed to 4800 rpm, the speed at which the engine typically runs when the Volt’s powertrain management controller calls for the generator to engage.
There are unique control algorithms (Engine Maintenance and Fuel Modes) that start the engine every 45 days and run it for up to 10 min, in case the owner has been driving solely on battery power, to lube the internal surfaces and run the diagnostics. It’s an off-the-shelf engine almost invisibly modified to serve the Volt’s series-hybrid operating mode.
“With our propulsion architecture, the role of this engine is completely different from any other car in the marketplace today, or from what we currently know is coming,” said Pam Fletcher, GM’s Global Chief Engineer, Hybrid and Electric Engineering. She noted that the engine is calibrated to operate “completely differently” than engines in the Cruze or other conventional powertrains.
“We did all of our development around maximum efficiency,” noted Fletcher, who also serves as the chief engineer of GM’s plug-in-hybrid program. “It was a different game than the one we usually play in balancing power and efficiency, because this engine’s really set up to run like a generator.”
The engine’s role in Volt allowed the powertrain development team many degrees of freedom for calibration, as the car’s electricgenerator and traction motors deliver positive and negative torque at a wide speed range. The engine thus does not respond directly to demand from the driver’s right foot as in a conventional vehicle, because you are effectively driving the traction motor, not the ICE.
<snip>
