Development of a Measurement Technology in Order to Determine the Dynamic Behavior of a Two-Stage Variable Connecting Rod

Variation of the geometric compression ratio in gasoline combustion engines during engine operation enables potential for decreasing fuel consumption as well as emissions. One way to achieve a variable geometric compression ratio (VCR) is the application of a connecting rod with a variable effective length between its large end and its small end. Such a system consists of a connecting rod body with an eccentrically supported piston pin and a linkage which is supported hydraulically. Therefore, the connecting rod evolves from a solid part to a complex assembly of mechanical and hydraulic parts.

In order to deploy this system in the most efficient way, an understanding of the physics and the dynamic behavior of the VCR connecting rod is necessary. This includes the mechanical subsystem as well as the hydraulic subsystem. This paper describes the experimental examination of a two stage variable connecting rod. For that purpose a measurement technology which acquires all relevant operating parameters of the connecting rod is developed and integrated into a VCR connecting rod. This specially prepared connecting rod is mounted into a complete engine. On a friction test rig experiments in stationary operating points as well as in switching operation are performed while the operating parameters are acquired with respect to crank angle. The acquired data is discussed and its plausibility is validated on the basis of the qualitative behavior of the measured variables.