Effect of Valvetrain Components Misalignment on Valve and Guide Interactions in Automotive Engines

摘要

Strict requirements for fuel economy and emissions are the main drivers for recent automotive engine downsizing and an increase of boosting technologies. For high power density engines, among other design challenges, valve and guide interactions are very important. Undesirable contact interactions may lead to poor fuel economy, engine noise, valve stem to valve guide seizure, and in a severe case, engine failure. In this paper, the valve stem and valve guide contact behavior is investigated using computational models for the camshaft drive in push and pull directions under several misalignment conditions for an engine with roller finger follower (RFF) valvetrain and overhead cam configuration. An engine assembly analysis with the appropriate assembly and thermal boundary conditions are first carried out using the finite element solver ABAQUS. Hot assembly displacements results for the exhaust valves, the guides, the valve seats and the cylinder head from the static analysis are then used as the boundary conditions for subsequent dynamic simulations of the valvetrain motion. A single RFF valvetrain is modeled using the elasto-hydrodynamically coupled multibody systems program FIRST by IST. A tolerance study is conducted to identify few key valvetrain misalignment conditions used in the simulations. The computational results show that at the given scale the influences on wear initiation at the bottom of the guide are very similar for the push and pull directions for the case with no misalignments, although the affected regions in the circumference of the guide differ. The results also show that the horizontal RFF misalignment with respect to the plane of RFF motion and with the drive in push direction has the most significant effect on wear initiation at the bottom of the guide. These results can be further processed for wear simulation for the valve guide. Simulation results for misalignments indicate that the wear pattern may vary significantly under various misalignment conditions.