Lubrication and frictional analysis of cam–roller follower mechanisms

Abstract

In this work, a full numerical solution to the cam-roller follower-lubricated contact is provided. The general framework of this model is based on a model describing the kinematics, a finite length line contact isothermal-EHL model for the cam-roller contact and a semi-analytical lubrication model for the roller-pin bearing. These models are interlinked via an improved roller-pin friction model. For the numerical study, a cam-roller follower pair, as part of the fuel injection system in Diesel engines, was analyzed. The results, including the evolution of power losses, minimum film thickness and maximum pressures, are compared with analytical solutions corresponding to infinite line contact models. The main findings of this work are that for accurate prediction of crucial performance indicators such as minimum film thickness, maximum pressure and power losses a finite length line contact analysis is necessary due to non-typical EHL characteristics of the pressure and film thickness distributions. Furthermore, due to the high contact forces associated with cam-roller pairs as part of fuel injection units, rolling friction is the dominant power loss contributor as roller slippage appears to be negligible. Finally, the influence of the different roller axial surface profiles on minimum film thickness, maximum pressure and power loss is shown to be significant. In fact, due to larger contact area, the maximum pressure can be reduced and the minimum film thickness can be increased significantly, however, at the cost of higher power losses.

Lubrication Analyses of Cam and Flat-Faced Follower

“…To avoid dynamic problems in the cam-follower mechanism, the cam profile should be designed carefully for achieving smooth velocity, acceleration and jerk during operation. Alakhramsing et al [17] for example, considered different roller axial profiles in order to study their effects on crucial performance indicators around the nose region. It was found that minimum film thickness and maximum pressure values can be improved significantly, however, at the cost of higher power losses.…”

“…In their study, systematic analyses were presented for the effects of roller crowning and edge geometries in additional to lubricant rheology. More recently, Alakhramsing et al [17][18][19] investigated in detail the contact problem of the cam-follower mechanism in which friction and mixed EHL analyses were considered.…”

Contact Force Measurements in Cam and Follower Lubricated Contacts

“…For the sake of completeness, it is worth mentioning some studies on the cam-roller follower mechanisms reported in Alakhramsing et al (2018aAlakhramsing et al ( , 2018bAlakhramsing et al ( , 2019. A full numerical solution of line contact isothermal-EHL model for the cam-roller contact combined with a semi-analytical lubrication model for the roller-pin bearing were used in Alakhramsing et al (2018b). Frictional forces were also evaluated.…”

The influence of stick–slip transitions in mixed-friction predictions of heavily loaded cam–roller contacts

“…Convergence is achieved according to user-specified tolerances. For specific numerical details pertaining to the weak finite element formulation of the governing equations and mesh element size distribution, see Habchi et al 23 and Alakhramsing et al 36 as only the main features are recalled here.…”

“…The variation of reduced radius of curvature R, contact force F, and cam surface velocity U c as a function of the cam rotational velocity is depicted in Figure 10(a). The trend of F as a function of cam rotational velocity is extracted from a worst-case scenario mapping of cam rotational speed versus the pumping load on the valve train mechanism (see Alakhramsing et al 36 for more details on this).…”