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Historically the high speed diesel engine for commercial vehicles has been developed along with its combustion system in compliance with political and economical changes. After the 1970's, stricter exhaust emission regulations and fuel economy requirements induced combustion developments and application of turbocharged and inter cooled engines. From the late 1980's, high pressure fuel injection has been investigated and recognized as an essential tool for lowering emissions especially of particulate matter. Although turbulence effects on both in-cylinder air motion and during the combustion process are quite effective, they show different phenomena in conventional and advanced high pressure fuel injection systems. In the 1990's, multiple injection with high pressure has been attempted for further reduction of NOx and particulate matter.

In Japan, about 5.6 billion tons of freight are transported annually and 90% of this figure is supported by trucks. Among them, the heavy vehicles of GVW 20ton are employed as one of the main means of such transportation and they are produced about 40,000 units annually. For these trucks, over 80 types of diesel engines have been developed during the past 20 years. Today, there are more than 30 domestic types. The engine displacement ranges from 8.8 to 18.0 liters and the maximum output spreads from 270hp (199kW) to 380hp (280kW). The naturally aspiration type occupies 70% and the turbocharged or turbo-intercooled type takes the remaining portion. The authors present the design concept and the technical background which are involved in the above-mentioned engines. They also describe the technology which concerns combustion, gas exchange, construction, electronic control, etc. and the ‘total power system’ (some simultaneously managing system) formulated to realize such engines.

The electric power steering (EPS) is increasing its number since there are many advantages compared to hydraulic power steering. The EPS saves fuel and eliminates hydraulic fluid. Also, it is more suitable to the cooperation control with the other vehicle components. The EPS is now expanding to the heavier vehicle with the advance in the power electronics. In order to meet customer's needs, such as down-sizing, lower failure rate and lower price, we have developed the new motor control unit (MCU) for the EPS. The motor and the electric control unit (ECU) were integrated for the better installation. We adopted new technologies of redundant 2-drive design for more safe EPS. “2-drive Motor Control technology” which consists of dual winding, two torque sensors and two inverter drive units. In our developed MCU, even if there is a failure in one of the drive unit, the assistance of the EPS can be maintained with the other drive unit.