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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.

Approximately 200,000 units of Hino J-series diesel engine were produced for 7 years. The J-series engines had a reputation all over the world for their performance, reliability, lightweight, and installation ability. They are composed of 4, 6 cylinders engines and unique 5-cylinder engine J07C. In 2002, newly modified J-series engines, which met the Japan 2001 noise emission regulations, were developed and J07C-TI, 5-cylinder TI engine, equipped with a common-rail fuel injection system was added in the J-series. Common-rail fuel injection system was equipped in order to achieve the emission targets in the future as well as to meet the current emission regulations. Achieving higher injection pressure level through the all engine speed, include excess low speed, was effective in reduction of PM emissions and in increasing of low engine speed torque drastically.

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.

In order to meet the strict exhaust emission legislation and customer's requirements of high power, heavy-duty diesel engines have to have a higher peak firing pressure and higher thermal load recently. It causes serious influence on the reliability and durability of the engines and engine parts, pistons in particular. The pistons for the next generation heavy-duty diesel engines are required to withstand more than 20 MPa of the peak firing pressure and higher thermal load, productivity of course. Nodular cast iron (NCI) pistons are one of the answers that could satisfy the requirements mentioned above. It is well known that NCI pistons have a lot of advantages but not popular. The difficulty of the casting technology and the quality control are the major reasons. Hino P11C engine has adopted it and kept it under mass production since 1991 and approx.20000 units of total production volume without any troubles.

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.

Wear of valve train components has increasingly become a problem in engine durability and reliability these days, due to the many design changes to meet the requirements of emission legislation and high performance of automotive engines. To minimize friction and the possibility of severe wear at the cam/tappet interface, the analysis at the design stage of tribological behavior of the cam/tappet pair is important and has become an important feature in valve train design. This paper describes the development of a valve train friction and lubrication analysis model and its application in a cam/tappet wear study. The model is based on established technology including kinematic and dynamic analyses, prediction of Hertzian stress of both line and elliptical contacts, the elastohydrodynamic lubrication (EHL) theory a mixed-friction model which separately predicts hydrodynamic and boundary friction and estimation of the average surface temperature using the flash temperature concept.