Two-Stage Variable Compression Ratio with Eccentric Piston Pin and Exploitation of Crank Train Forces

By variation of the compression ratio the fuel consumption of high boosted gasoline engines can be reduced, due to operating with higher compression ratios at low load compared to an engine with fixed compression ratio. The two-stage VCR-system enables a high share of fuel saving potential relative to full variable systems.

Considering a low cost manufacturability and a beneficial integratability into common engine architectures the length-adjustable conrod using an eccentric piston pin in the small eye has proved as the best concept. The adjustment is performed by a combination of gas and mass forces.

This article describes the design of such a two-stage VCR-system as well as the functional testing under motored and fired engine operating conditions.