Coupled Dynamic Simulation of Two Stage Variable Compression Ratio (VCR) Connecting Rod Using Virtual Dynamics
Published January 9, 2019 by SAE International in United States
Annotation of this paper is available
The fuel consumption of combustion engines requires continuous reduction to meet future CO2 fleet targets. The progression of emission legislations shifted the focus on PN and NOX emissions in real world driving scenarios (RDE). Recently, the monitoring of CO emissions puts high load fuel enrichment for component protection into focus and a ban on enrichment is widely expected. Hence, gasoline engine technologies, which enable Lambda 1 operation in the entire engine map are specifically promoted. Variable Compression Ratio (VCR) attacks all these topics already at the combustion process. In addition to the well-known CO2 capability, VCR also enables enlargement of the lambda 1 operation in gasoline engines as well as reduced NOX emissions in diesel engines. The basic principle of developed VCR solution is to change the effective length of the connecting rod (and thereby the compression ratio) in two stages by several millimeters. Basically, the VCR connecting rod consists of a mechanical and hydraulic system which is fed with oil by the connecting rod bearing. All functional elements to realize the variability such as an eccentric, lever, support rods, check valves and shift valve are integrated into the connecting rod. The system works without “external” energy supply but uses mass- and gas forces - acting on the piston pin - to vary its length. In order to analyze and optimize the system dynamics, a highly sophisticated simulation approach based on coupled simulations of the mechanical and the hydraulic subsystem of the VCR connecting rod. The co-simulation is carried out in time domain using the commercial software Virtual Dynamics for the elastic multi body simulations and GT-Suite for 1D fluid simulations. In this article the coupled 3D-multi body simulation/1D-hydraulic co-simulation as used to optimize the VCR connecting rod performance are presented.