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Recently further improvements of fuel economy and performance of truck diesel engines are required in the market. At the same time, countermeasures for exhaust emissions are requested as a clean air activity. So the improvement of performance and the reduction of emission are keysubjects today. As a countermeasure for both problems, the reduction of friction is effective. The authors took notice of the pumping loss, and analyzed the pumping loss at the gas exchange process and improved the performance by a multi valve intake & exhaust system. Particularly the multi valve system is effective on a higher boost and/or smaller sized engine because of its larger air and gas flow through the relatively small passage. And the reduction of the fuel rate resulted in better reliability with regard to thermal load and exhaust temperature.

In heavy duty vehicles, a higher boost and/or smaller sized diesel engine is quite effective in achieving fuel economy. However, this causes an increase of pumping loss due to increased intake air and exhaust gas flow of the engine at high load and high speed conditions. It also causes a relatively poorer torque at low speed conditions due to a lack of boosted air. The authors investigated the pumping loss and volumetric efficiency of a high boosted turbocharged diesel engine and analyzed the effects of the turbocharger, inertia charging and the valve opening areas. An optimization of small geometry turbine housing was obtained for the improvement of both low speed torque and fuel economy. The effects of inertia charging were ascertained from the relation between engine valve timing and the amplitude and phase of intake air pulsation. Increasing the intake and exhaust valve opening area improved fuel consumption by reducing pumping loss.

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.