GM patent for twin-charged high-compression hybrid powertrainEnlarge Photo
The latest General Motors patent underscores how busy the automaker's powertrain engineers have been. The automaker received a patent approval for a high-compression, twin-charged hybrid powertrain in October, AutoGuide reported Wednesday.
And when we say "high compression," we're talking ridiculously high compression.
At the powertrain's core is an internal-combustion engine paired with a low-flow supercharger and a high-flow turbocharger. The supercharger takes care of low-end power, while a turbocharger would spool up after 3,000 rpm. The traditional mechanicals would connect to one or more electric motor or generator, which the patent does not depict. Moving right along to compression ratios, the patent says this powertrain would deliver ratios of 11 to 16:1. That's a higher compression ratio than most car engines.
The patent includes all sorts of intricate details surrounding the powertrain, including new twin-charging methods. GM engineers envision a crankshaft or electric motor to drive the supercharger, while a continuously variable transmission could control the unit's RPM separate from the engine rpm. After 3,000 rpm, the turbocharger would take over, and the system could work sequentially or in tandem fashion. While the description lends itself to be a high-performance hybrid powertrain, the potential for fuel efficiency is also great.
But, how will such a high-compression engine meet federal requirements for legality? GM's patent further describes an extreme Atkinson Cycle that includes a late intake valve to let some of the air-fuel mixture to escape and avoid pre-detonation. To create peak lift, the patent also details two methods: cam-lobe profiling with a variable-ratio rocker arm placed between the valve stem and the cam lobe, or a very interesting solution, an electro-hydraulic actuator. The latter would essentially replace a traditional camshaft.
Although the patent sketches depict an inline-4 engine, the document did note the same powertrain setup could work with additional cylinders. It's possible we may be looking at the foundation of a mid-engine Corvette hybrid's powertrain, or GM's attempt to squeeze every last bit of efficiency from the internal-combustion engine.