Single cam tribometer for evaluating tribological parameters and tribochemistry of DLC coated valve train follower

Abstract

In engine valve train systems, due to the sliding–rolling motion at the cam/follower interface, mixed and boundary lubrications dominate. It is in this regime that the effects of the lubricant chemistry at the molecular scale prevail over lubricant rheology effects in determining the friction and wear performance. The precise evaluation of friction and wear on the contact surfaces is essential to understand the tribochemistry of modern lubricant formulations and modern coating technologies. In the literature, a range of experimental tribometers have been used to simulate the tribology and tribochemistry of the cam/follower interface, leading to valuable information on the lubrication of this system. However, conventional tribometers such as pin on plate (PoP), pin on disc and disc on disc are not precise simulators due to their steady load operating conditions. This study looks into the opportunity of using the single cam tribometer (SCT) for better simulation of tribology and tribochemistry of engine valve train systems. The friction, wear and surface chemistry characteristics of a-C:15H (diamond like carbon) coated shims in contact with a chilled Cr cast iron cam lubricated using model oils have been evaluated using the SCT. Single cam test results are discussed in relation to the results obtained from a reciprocating PoP tribometer.

Keywords:

• DLC
• PAO
• Additives
• Tribofilm
• Friction
• Wear

The authors would like to thank Mr R. Cellier for setting up the test rig, Mr S. Terry for interfacing the torque sensor with NI modules and LabView programming and Dr Y. Yan for his time and assistance given on Raman spectroscopy. Mr Adrian Eagles has also contributed greatly on Talysurf measurements.