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In the Japanese heavy duty truck market, demands of improved fuel economy and lighter vehicles to increase load capacity, and further improvements in emissions are constantly increasing. To satisfy these requirements, basically a smaller sized and higher boosted diesel engine is effective, because such an engine has a compact size and light weight, and shows improved fuel consumption due to a relatively lower frictional loss. On the basis of this concept Hino introduced the original EP100 in 1981 as the first Japanese turbocharged and air to air charge-cooled engine. Since then Hino has made many efforts to improve the engines and develop new technologies.

Hino Motors, Ltd. has added to its line of charge-cooled engines for heavy duty trucks a higher power version which is called EP100-II. To meet the recent customers' demands for rapid transportation with better fuel economy, this engine was developed on the uprating program for the original EP100 which was introduced in 1981 as the first Japanese turbo-charged and air to air chrge-cooled engine. EP100-II has the same displacement as the original EP100, 8.8 liters, and is an in-line six cylinder engine with 228kW (310PS)/2,100rpm (JIS) output that provides the world's utmost level specific output of 25.8 kW (35.1PS)/ liter. Also this engine achieved a maximum BMEP of 16.8 bar/1,300 rpm and best BSFC of 199 gr/kWh at 1,500 rpm. This paper describes the advanced technology for increasing horsepower and improving fuel consumption such as the so-called multi harmonized inertia charging system, the electronically controlled waste gate valve of turbocharger.

This paper presents technical solutions and a development process to accomplish not only superior fuel economy but also excellent driveability with a turbocharged diesel engine for heavy duty trucks. For better fuel economy, one of the basic considerations is how to decrease the friction losses of the engine itself while keeping the required horsepower and torque characteristics. A high boost turbocharged small engine offers this possibility, but it has serious disadvantages such as inferior low speed torque, poorer accelerating response, insufficient engine braking performance, and finally not always so good fuel consumption in the engine operating range away from the matching point between engine and turbocharger. These are not acceptable in complicated traffic conditions like those in Japan - a mixture of mountainous and hilly roads, city road with numerous traffic signals, and freeways.