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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.

This paper describes the experimental studies of turbocharged and intercooled diesel engines with particular emphasis on combustion characteristics following increase of boost pressure. Through these studies, it has become possible to determine the optimum air quantity for minimizing fuel consumption at each engine speed range under the restrictive conditions of NOx emission, exhaust smoke and maximum cylinder pressure. Discussed also is the lack of air quantity in the low engine speed range of high-boost turbocharged diesel engines. Various turbocharging systems to improve air quantity in this speed range are introduced herein. Practically the engine performance of conventional turbocharging, waste gate control turbocharging and variable geometry turbocharging are discussed from the viewpoint of torque recovery in the low engine speed range.

For the 1990's diesel engines, particulate control has been an important problem. The purpose of this paper is to discuss emission control needs for heavy duty diesel truck engines for the 1990's. This paper will focus on the factors such as fuel injection pressure and fuel properties which most affect particulate emission. The characteristics of diesel spray in the atmosphere and also actual combustion of a turbocharged and charge-cooled H.D. D.I diesel engine were studied as a function of injection pressure ranging from 50 to 150 MPa. Experimental results show that high pressure injection improves the atomization and air entrainment. Though Bosch smoke level, fuel consumption and combustion period decreased with the rise of injection pressure, particulate emission in EPA transient test cycle did not decrease dut to an increase of SOF.

Hino has developed new J-series medium-duty diesel engines for trucks and buses. The new J-series comprises four, five and six-cylinder engines with the same cylinder bore and stroke and with both naturally aspirated and charge air cooled. Both output and torque have been enhanced along with fuel efficiency in an engine that is lighter and more compact than ever and reaches new heights of durability and reliability. J-series engine features a 4-valve system and OHC valve train design, which achieved an uniform combustion by a centered nozzle and combustion chamber design. This decreases the maximum combustion temperature and hence improved the NOx,smoke and PM emissions. And a reduced pumping loss results in improving the fuel consumption. J-series engines thus meet the Japanese 1994 emission regulations. Another feature is a fully electronically controlled common-rail fuel injection system, which is equipped in a specified engine of naturally aspirated 6 cylinder.

Diesel particulate trap systems are one of the effective means for the control of particulate emission from diesel vehicles. Hino has been researching and developing various diesel particulate trap systems for city buses. This paper describes two of the systems. One uses a wall flow filter equipped with an electric heater and a sensing device for particulate loading for the purpose of filter regeneration. Another makes use of a special filter named “Cross Flow Filter” with an epoch-making regeneration method called “Reverse Jet Cleaning”, by which it becomes possible to separate the part for particulate burning from the filter. Both systems roughly have come to satisfy the functions of trap systems for city buses, but their durability and reliability for city buses are not yet sufficient.

Fuel injection timing retardation for reducing exhaust emission of direct injection diesel engines prolongs the period to complete cold starting. Engine speed at this period varies through some accelerating and faltering stages. The speed variation and relating combustion characteristics was investigated through the measurement of cylinder pressure for each cylinder as well as the dynamic fuel injection timing and instantaneous engine speed. An improvement of cold start was shown by application of afterheat of a sheathed type glow plug and an electronic fuel injection timing control device.

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.