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The requirements for emission control, lower fuel consumption and higher engine output have changed the engine valve train system to 4-valve/cylinder and higher cam lift designs, and these changes make the cam/tappet lubrication conditions more severe than before. Under such a working condition, there is a high possibility that cam/tappet surface damages such as scuffing, pitting and wear may occur. Among the damages, the wear of cam/tappet is the most difficult to predict since the wear mechanism still remains unclear. To understand the lubrication condition and therefore, the wear mechanism at the cam/tappet contact, friction was measured with a newly developed apparatus. Measurement results showed that the lubrication condition between cam and tappet is predominantly in the mixed and boundary lubrication conditions.

Recently, exhaust emission has been enforced on diesel engines for the countermeasure of environmental problems. Accordingly, the cylinder pressure in the engine is being increased to improve fuel efficiency, the engine bearings must be used under severe conditions of high specific load. Because the connecting rod bearings, particularly of diesel engines, are used at high specific loads that exceed 100 MPa, elastic deformation of the bearing surface occurs, and the oil film thickness decreases at the edges of the bearing length in the axial direction. This causes the bearings to contact with the crankshaft, thus resulting in the wear of the bearings, which could even result in seizure. The following factors contribute to seizure: bearing materials, bearing shapes, machining methods, and incorrect assembly. Focusing on these factors, this study evaluated the behaviors exhibited by connecting rod bearings in actual engines by using the rig testers.

Thermal loading in pistons of diesel engines installed on commercial vehicles, such as trucks and buses, has been increased dramatically in recent years due to applications of technologies to meet low emission and high power requirements. It causes serious concerns on the reliability and durability of engines and engine components. Control of piston temperatures has become one of the determining factors in a successful engine design. Therefore, design optimization of pistons and cooling oil flow in the lubrication system at the concept design stage has become more and more important. For pistons under higher thermal loading, the adoption of a cooling gallery is a common practice. In this case, the heat flow into the cooling gallery has a significant influence on piston temperatures, similar as that caused by the heat flows from combustion.