Tappet Rotation and Friction Reduction in a Center Pivot Rocker Arm Contact

Abstract

The instantaneous tappet rotation velocity and instantaneous friction torque were measured simultaneously for the CVH center pivot rocker arm geometry. The measurements were made in a cam/tappet friction apparatus equipped with a laser reflectance tappet rotation monitor capable of following rapid changes in tappet rotation velocity. The data showed that more rapid tappet rotation resulted in lower friction. The effect was greatest in the region of maximum cam lift. Several tappets were modified to produce higher rotation rates than production tappets. The best results were obtained with tappets incorporating an internal squeeze film bearing to reduce resistance to rotation. The data were analyzed to elucidate the cause for the friction reduction effect. The analysis showed that most important effect was the partial rolling motion between the surfaces, rather than enhancement of the oil film thickness. A model based on that conclusion agreed reasonably well with the experimental data.

Development of valve train rig for assessment of cam/follower tribochemistry

“…The inertia/geometric torque on the other hand have equal positive and negative components during valve opening and closing. Ideally, by taking mean torque values over the cam cycle, the inertia/geometric torque will be effectively cancelled out leaving the friction component [4,31,33]. The average friction torque was obtained by taking an average of the 200 data points obtained for each camshaft cycle.…”

Valvetrain friction and wear: Influence of surface engineering and lubricants

“…The tappet reciprocated in an aluminium bore made out of a production cylinder head. The centre of the cam lobe was at an offset from the centre of the tappet insert to allow tappet rotation and reduce friction torque [13,14]. The cam lobe/insert contact area was lubricated by a jet of lubricant at 100 8C at 30 lb/in 2 .…”