Integrated Layout of the Friction Reduced Piston Group

17. October 2014 | Engineering Service

To improve fuel economy and performance in combustion engines, optimization of the FMEP level can be very important. Since up to 30 percent of the engine FMEP is related to the piston group, this area of the motor offers a high potential for optimization. During the development process, the basis for a friction-optimized engine must be already defined at the concept phase. For this reason, the combination of appropriate development tools with respect to both testing and simulation is one of the most efficient ways to realize a friction-optimized engine.

Powerful simulation tool

FEV offers advanced tools for both testing (PIFFO-system) and simulation of the piston group friction. FEV‘s „Virtual Engine“ includes an MBS simulation tool that utilizes a full 3D model of the piston group components. This model incorporates 3D flexibility of the rings, a gas blow-by model, a 3D contact model for the piston ring in the groove, a 3D ring-liner contact model that includes hydrodynamic as well as a dry contact components, a model for the oil film on the liner, and a wear model for the liner and rings. Detailed modeling of the piston group is not a stand-alone functionality but a model refinement of the MBS engine model.

Validated prediction and analysis

The simulation model allows validated predictions of the ring friction and the ring dynamics in the groove. The contributions of the piston skirt and rings to the total friction force can be individually resolved and can be separated into hydrodynamic- and a dry-friction components for use in further investigations.

Trend data from the measured signals can be reproduced with minimal effort associated with fine-tuning of the input parameters. Present simulation results suggest that the influence of the axial ring transition does not significantly affect friction. The current 3D MBS model, which features a typical simulation time of about one hour per engine cycle, therefore, represents a particular benefit with regard to layout and optimization of the piston group for optimized friction behavior.

Piston group friction force over crank angle over at full load (1,000 rpm)

Piston group friction force over crank angle
at full load (1,000 rpm)

 

Piston group friction force over crank angle over at full load (2,000 rpm)

Piston group friction force over crank angle
at full load (2,000 rpm)

 

Axial displacement of the top compression ring for two pressure load cases at 2,000 rpm at three positions (A, B, C) over the ring circumference

Axial displacement of the top compression ring for two pressure load cases at 2,000 rpm at three positions (A, B, C) over the ring circumference

 

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