1992-02-01

Comparative Friction Assessment of Different Valve-Train Types Using the FLARE (Friction and Lubrication Analysis) Code 920491

A mathematical model for tribological analysis of different automotive- valve-train configurations has been developed as a part of the FLARE (Friction and Lubrication Analysis of Reciprocating Engines) package. The model is based on an in-depth kinematic analysis and on a rigid-body dynamic analysis, including dynamic analysis of the valve spring. Lubricant film thickness, contact pressures, and frictional power loss are predicted. A mixed-lubrication model is used to determine the friction force at the cam-follower interface. In addition, lifter rotation is modeled to predict its effect on frictional power loss. Detailed results are presented for a pushrod valve train. Also, this paper compares frictional power loss for five different valve train types. They are: direct-acting overhead cam, pushrod, end-pivoted finger follower, center-pivoted finger follower, and cam-in-head. The valve trains are made equivalent by keeping the valve lift and the no-follow speed the same. In addition, all other valve train parameters were kept the same with a few exceptions. From this study, it appears that the direct acting valve train has the lowest frictional power loss. The two finger follower valve trains viz., the end-pivoted and the center-pivoted are among those with the highest power loss. The system features of FLARE make a comparative study such as the one presented here very convenient.

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