GM Figured a Way to Make Its Longitudinal Variable-Compression Engine Easier to Service
Packaging the compression system
GM has filed multiple patents on applying variable-compression technology to automobile engines. A filing first spotted by CarMoses focuses on fitting the system into a longitudinal engine and improving service access.
The company has explored a variable-compression ratio for about a decade. Nissan already sells a variable-compression engine, the VC-Turbo, but it is designed for transverse front- and all-wheel-drive applications.
How the mechanism works
In an earlier filing, GM placed the control shaft above the crankshaft. A connecting-rod linkage, including a center link and control rod, connects the crankshaft assembly to that shaft.
A phaser changes the control shaft’s rotational timing relative to the crankshaft. That movement controls piston travel and varies compression from approximately 7:1 to 11:1.
Access and potential benefits
GM says the bolts joining the mechanism could be reached from below the engine, likely after removing the oil pan. Locating the control shaft above the crankshaft also leaves space underneath for engine mounts, steering equipment or four-wheel-drive components.
The design permits conventional lubrication of the connecting rods. GM says that feature, combined with a two-piece center link, could make the engine easier to service and less prone to bearing-related problems.
Key points
- A GM patent application describes a longitudinal variable-compression engine with improved service access.
- The system varies compression from approximately 7:1 to 11:1.
- Bolts may be accessible from below, likely with the oil pan removed.
- GM says conventional connecting-rod lubrication could help reduce bearing-related problems.