Investigation on cam–follower lubricated contacts

Abstract

The cam-follower contact is one of the most complex lubricated non-conformal contact due to its continuous variation of load, speed and geometry. Investigations on new design quantities such as geometry, materials and coatings are important for a reduction of friction losses and wear problems. The complexity of the phenomena occurring in the camshaft systems make experimental verifications very important. In this work, an already existing versatile experimental apparatus for investigation of nonconformal lubricated contacts, able to measure film thickness using the optical interference method and friction force trough a load cell, has been modified in order to tests cam-follower contacts. Some test have been carried out for investigating the behaviour of some fundamental components of the rig. A theoretical/numerical simulations has been performed to investigate the dynamic behaviour of the system and in order to provide important indications for the interpretation of the experimental results. The programme has been also an important support for the design and of a new apparatus specifically addressed to the cam-follower contact and with increased potentialities capable of more detailed measurement of film thickness and contact forces. The apparatus is able to reproduce a cam-follower mechanism that uses a rocker as a link device between the cam follower set and the valve.

Low viscosity engine oils: Study of wear effects and oil key parameters in a heavy duty engine fleet test

“…The technical developments in valve trains, e.g. the overhead camshaft (OHC), has made the lubrication of this tribological contact a difficult issue [28]- [30]. The relative distance and the contact morphology present specific characteristics which results in a less important role of lubricant viscosity [31] .…”

Numerical simulation of the effects of coating on thermal elastohydrodynamic lubrication in cam/tappet contact

“…The calculation process yields the tappet acceleration and displacement and the contact force as outputs. The acceleration and displacement values are entered into equations (22) to (25) 17 to calculate the entrainment velocity u s , the equivalent contact radius R C , and the velocities u a and u b of the contact points on the cam and tappet, respectively. Figure 5 shows the variations in the tappet displacement, the contact force, the entrainment velocity, the velocities of both surfaces and the slide-to-roll ratio during a cam event cycle from a valve opening angle of 0 to a closing angle of 164 .…”

“…Wang et al showed that a depth of 3.15 times the Hertzian half-contact width is sufficient to ensure a zero temperature gradient, 18,36 and this conclusion was utilized for the substrates in this study. Analyzing equation (25), the conclusion u a 50 can be easily obtained, and when u b 50, the boundary conditions are as follows…”

Analytic and numerical results of a disc cam bending with a roller follower

“…Data acquisition technique through signal processing approach was used to measure the contact load [17,18]. Macro sensors were attached to the cam and the follower.…”