In order to improve the performance and reliability of internal combustion engines the past experimental or analytical studies conducted by the author and the collaborators as follows on the tribotechnology for the valve train cam & follower and lubricants in the engines have been reviewed to consider the design concepts still important in the future. Firstly, the changes of friction characteristics with the material, the surface roughness or the oil supply method were examined by measuring the friction force of the cam and slipper follower specimens with an original cam follower test rig. Secondly the friction characteristics of the cam and roller tappet was examined by measuring the forces acting onto the tappet body with an original test rig as large as the practical OHV train mechanism. And, the effect to reduce the friction was examined for the surface finishing of the cam lobe or the bearing type to support the roller follower. Thirdly the changes of the friction and scuffing characteristics with the blend of additives like ZnDTP and MoDTC in low viscosity base oils were examined to ascertain the best blend of additives as the high SAPS lubricant. Also, the friction and the wear under the lubrication with the test oil contaminated with diesel soot kinds were measured with the cam and slipper follower test rig. Additionally, the friction and the wear under the lubrication with the low SAPS lubricant with or without the soot contamination were measured to examine the friction and wear characteristics and/or the effect for the compatibility of the test oil with DLC coating or other surface modification like a mirror face finish.
Variable Valve Actuation System (VVA) enables to change valve lift characteristics, such as lift amount, duration, opening timing, and closing timing. VVA was adapted to automotive engines in 1980’s, for improvement of driving performance and thermal efficiency. With environment issue, VVA was applied to reduce exhaust emission and CO2, and VVA has been widely installed. VVA has been developed in not only actuation mechanism, but also tribotechnology. This paper summarizes VVA, such as oscillating cam type, hydraulic lost-motion type, cam switching type, and cam phaser type, and explains tribological characteristics which support them.
Roller follower application for rocker-arms is quite popular technology for recent efficient engine to reduce friction loss of the valve train. However the roller rocker has several unique issues about tribological problems, such as camshaft pitting, bearing shaft wear, and so on. Mechanism of those failure and measures are explained in this paper.
The timing chain is generally used for the camshaft drive for passenger vehicle engine because of high durability and compact package. However the chain elongation during the usage causes reduction in engine performance and rise in noise level. Therefore it is very important to design the chain specification by considering the chain load and engine oil lubrication condition.
The present study describes effects of the surface finishing condition by cutting on tribological properties of an aluminum cast alloy AC8A containing segregated silicon (Si) phase. The testing surface was finished with various cutting speeds with a mono crystalline diamond tool tip having large lake face angle using a CNC machining center. It was found that the exposed Si particle frequently removed from the surface at lower cutting speeds. The tribological properties were evaluated with a ball-on-disc type testing apparatus mated with 3 chromium alloy steel (SUJ2) balls with a flat contacting surface in lubricated condition. Results showed that the friction coefficient decreased with the increase in the Si particle removal rate. To clarify effects of Si particle removal on the tribological properties, an aluminum alloy without Si particle (A2017) was conducted. As results, small dimples formed by Si particle removal acted as entrapment of the wear debris, then the friction coefficient decreased and stabilized. Therefore, it was concluded that the surface finish using sharp diamond cutter at a low cutting speed was effective means to improve the tribological properties of the aluminum cast alloy.
We have characterized the adsorption and desorption behavior of a sulfur-type extreme-pressure (EP) agent at an aluminum-based substrate/dodecane interface by means of quartz crystal microbalance with dissipation monitoring (QCM-D) technique. We have also analyzed the surface composition of an aluminum plate, followed by thermal treatment of the adsorption film. The EP agent used in this study was synthesized from oleic acid and has a double-chain structure with two carboxylic acid headgroups. The QCM-D results suggested that the EP agent formed a monolayer film on the aluminum-based substrate. In addition, the adsorption film still remained on the substrate even after rinsing by the solvent. After thermal treatment of the adsorption film, the EP agent yielded a decomposed product on the aluminum plate. Ball-on-plate type friction measurements suggested that this product reduced significantly a dynamic friction coefficient. On the basis of these results, we suggest that it is important to see the adsorption and desorption behavior as well as the reactivity in order to understand the friction reducing mechanism of the sulfur-type EP agent on the aluminum plate.