Effect of lubricant chemistry on the performance of end pivoted roller follower valve train Muhammad Khurram, Riaz Ahmad Mufti n , Rehan Zahid, Naqash Afzal, Muhammad Usman Bhutta, Mushtaq Khan School of Mechanical and Manufacturing Engineering, National University of Sciences and Technology, H-12 Islamabad, Pakistan article info Article history: Received 26 August 2014 Received in revised form 14 October 2014 Accepted 27 October 2014 Keywords: End pivoted roller follower Roller slip Giant magneto resistive sensor abstract Real production engine employing end pivoted roller follower valve train has been instrumented to investigate the effects of engine operating conditions, lubricant rheology and chemistry on the sliding of rollers. The experimental results showed that due to shear drag it was not necessary for roller rotational speed to increase with camshaft speed. The lubricant viscosity played a key role in the roller slip at lower temperatures however at higher oil temperatures negative slip was also observed indicating that component inertia and internal friction have a role to play in roller slip. The results also clearly showed the impact of viscosity improvers on roller slip. The experimental setup, test procedure and results are presented in this research work. & 2014 Elsevier Ltd. All rights reserved. 1. Introduction In automotive industry, demands of lower fuel consumption, reduced emissions, higher power output, longer service intervals and improved life cycle have become extremely important market drivers. In order to meet these requirements, several design changes and advanced technologies are being pursed in internal combustion engines. The compact engine design and enhanced power output have resulted in higher loadings at the engine main tribological components. On the other hand, resurgence of interest to assess the fuel efficient lubricants in the industry has led to the introduction of low viscosity lubricants to reduce the shear friction at component level. High contact loading coupled with the use of low viscosity lubricants have raised concerns about the dur- ability and reliability of engine components particularly in the valve train area. Engine valve train is one of the most complicated tribological mechanisms in the engine which often operate in severe operating conditions due to continuous variations in the contact loading, higher operating temperatures and varying nature of cam geome- trical profile affecting the lubricant entrainment velocity and thus the lubrication mode. In addition, engine valve train has witnessed numerous design changes over the years to improve performance in the form of higher spring stiffness, multi valves system, variable valve and cam timing. These design factors along with the use of low viscosity lubricant have pushed the valve train mechanism to operate in much harsh operating conditions than before. In automotive sector, there is a wide spread use of end pivoted roller follower valve train (Fig. 1) in the modern passenger automobiles due to their improved power output, better fuel economy, compact cylinder head and smoother valve operation. Many researchers [1–3] have reported substantial reduction in the power loss by using the roller followers instead of sliding tappets. The improved lubrication condition at cam/roller contact due to roller rotation was recognized by Jonmin and Taylor [4]. In roller follower valve train, roller rotation plays an important role to reduce the friction, wear and minimizes the chances of fatigue failure by even distribution of wear. It also improves the lubrica- tion at cam/roller interface and influences the valve train power loss significantly. However, sliding of mating surfaces of cam and roller operating under marginal lubrication condition can lead to wear of surfaces [5,6]. Miyamura [7] and Cheng et al. [8] in their research analyzed the wear problem in the roller follower mechanism. Gecim [9] identified the shortening of roller fatigue life under low specific film thickness values. Hence, in order to minimize the possibility of roller slip and severe wear at cam/roller interface and to understand the effects of engine operating conditions and impact of lubricant chemistry and rheology on the sliding of rollers, it becomes essential to carry out the cam/roller studies on real production engines under realistic environment. Moreover, the available mathematical mod- els may not foresee all the aspects of the environment in which the parts have to operate actually thus elaborated testing based on efficient and reliable experimental investigation is often required as a complement to these models for their validation. Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/triboint Tribology International http://dx.doi.org/10.1016/j.triboint.2014.10.021 0301-679X/& 2014 Elsevier Ltd. All rights reserved. n Corresponding author. E-mail address: riazmufti@smme.nust.edu.pk (R.A. Mufti). Please cite this article as: Khurram M, et al. Effect of lubricant chemistry on the performance of end pivoted roller follower valve train. Tribology International (2014), http://dx.doi.org/10.1016/j.triboint.2014.10.021i Tribology International ∎ (∎∎∎∎) ∎∎∎–∎∎∎