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In the heavy-duty commercial vehicle market in Japan, particularly in the segment of dump trucks and tractors, naturally aspirated engines maintain a dominant market share because of their superior torque characteristics in the low speed range. In order to meet the ever increasing needs for higher speeds of transportation, better fuel economy and higher reliability, and the needs for increasingly strict exhaust emission regulations, Mitsubishi Motors Corporation (MMC) has developed the 8M20, a 20 liter V8 diesel engine. The '92 model series of “THE GREAT”, MMC's main heavy-duty trucks, has featured this new and powerful engine and has been in the market place since October, 1991. The 8M20 is a naturally aspirated engine that provides an output of 294kW/2200rpm, complying with the current Japanese exhaust emission regulations.

A trap system has been developed that collects particulate using two small filters and regenerates alternately by electric heaters. This system contains a new idea in detection of the amount of particulate accumulation in the filters. The system counts the amount using a particulate accumulation rate map which is a function of the engine load and speed. In vehicle test with this trap system, the particulate collection efficiency and the regeneration efficiency were proved to be high enough for practical use. The test results also showed that the shutdown performance of the route switch valve greatly influenced the regeneration efficiency.

Mud adhesion to the rear surfaces of trucks, vans and buses causes troublesome results such as aesthetic degradation, hindered rear view and laborious washing. To raise the product value of trucks and buses, it is important to develop effective measures for suppressing such mud adhesion. In this research the authors first clarified the mechanism of mud adhesion through flow visualization tests. Then, wind tunnel tests were performed to predict the effects of various countermeasures, and prospective ones were put under actual driving tests to verify their effects. The following measures were found effective in suppressing mud adhesion. (1) Aerodynamic improvement by attaching corner vanes to the upper and side edges of the rear surface. (2) Blocking road splash with a slanted plate under the truck and close to the base.

To improve vehicle startability and transient response of turbocharged diesel trucks, their phenomena have been investigated and analyzed in detail and various supercharging systems have been developed and installed on a truck for comparison of their characteristics. The systems considered were ceramic, variable geometry, variable entry,and air-assisted turbochargers and a combined supercharging system. The variable entry turbocharger has two turbine scrolls with different nozzle areas and two switching valves to get three different turbine flow capacities. The combined supercharging system consists of a mechanical supercharger and a turbocharger. These are linked in series. Both work in a low engine speed range, and the turbocharger only works in middle and high engine speed ranges. Among these systems, the combined supercharging system is the best for improving both vehicle startability and transient response of a truck.

This paper describes the method to improve the energy absorption characteristics during the vehicle frontal collision. The method is to control the collapse phases of the members constituting the vehicle body and to increase collapse force of a member. This phase-control can be accomplished by superimposing the crest of the collapse force curve, which one member causes, on the trough of any other members'. The bulkheads installed in the members are useful. to control the phase and to increase the collapse force. Numerical analysis and experiment of a vehicle collision show that the control leads to the improvement of energy absorption characteristics and load transmission efficiency.

Structural attenuation of a running diesel engine measured by a new technique showed a constant value regardless of engine speeds. It was verified by this result that structural attenuation is a physical quantity unique to the structure of each engine and, therefore, a good indicator for evaluation of low noise engine structure. In addition, a hydraulic excitation test rig was devised to measure structural attenuation directly and to make effective use of it for noise reduction. Based on the accurate measurements by the excitation test rig, modal analysis and system simulation were conducted for implementation of countermeasures against noise.

In order to design a well-balanced truck frame, optimization of not only the stiffness of the entire body and stress of each member, but also the internal force of each member is necessary, including the effect of a rear body mounted on the frame. This paper proposes a new parameter, “torsional stiffness share rate,” that directly correlates the contribution of member torsional stiffness to frame torsional stiffness with the internal force of the members as to torsion of the truck frame. The merits of the torsional stiffness share rate are shown in comparison with the strain energy share rate and the stiffness contribution rate. The results of experimental and FEM analyses of the torsional stiffness share rate are also presented.

During next decade, automotive engineers will take up unprecedented challenges to meet a variety of technical demands on passenger cars. While performance, refinement and reliability will continue to be major technical goals of passenger cars, reducing their impact on the environment not only in urban areas but also on the global basis will become an increasingly urgent issue. In addition, the need for energy and resources saving will necessitate development of more fuel efficient cars, exploitation of alternative energy and recycled materials. In this paper, the authors will review various alternative engines as candidates to satisfy the above demands. The authors will also discuss various alternative transportation energy sources such as alcoholic fuels, natural gas, hydrogen and electricity. Finally the trends of future passenger car engine design will be discussed.

Optimization of the clutch torsional characteristics is one of the effective methods to reduce the idling rattle noise. Many researches on th.s problem have been reported, but only few of them give sufficient consideration to the drag torque applied to the clutch disc during engine idling. This paper pays attention to the drag torque and discusses the mechanism of idling rattle noise by using vehicle testing, bench test with rotating torsional exciter and computer simulation. Reauction of Idling

This paper presents the results of acoustic analyses of light duty truck cabs by actual vehicle testing and by numerical analysis utilizing the boundary element method (BEM). In the resonance mode analysis using BEM, by taking into account the vibration characteristics of cab panels, the presence of the modes other than the purely acoustic cavity resonance modes were confirmed. The contribution of the panel vibrations to booming noise that occurs in actual light duty trucks was analyzed. BEM analysis showed that some of the panel vibration had a negative contribution to booming noise. In other words, decreasing vibration in such a section was shown to increase sound pressure. The results of the BEM analysis match well with actual test results. It has thus been demonstrated that BEM is an effective method for analyzing truck interior noise reduction.

A fuel control method to reduce the harmful exhaust gas from SI engines is proposed. As is well known, both the amplitude and the frequency of the limit cycle in a conventional air-fuel ratio control system are determined uniquely by parameters in the system. And this limits our making full use of the oxygen storage effect of TWC. A simple model of TWC reaction revealed the relationship between maximum conversion efficiency and both the amplitude and the frequency in a air fuel control system. It also revealed that TWC conversion efficiency attained to maximum levels when both the amplitude and the frequency of the limit cycle are selected so as to make full use of the oxygen storage effect of TWC. In order to achieve this, it is necessary to vary both the amplitude and the frequency arbitrarily.

A flexible fuel vehicle (FFV) was evaluated through various tests for its potential as an alternative to the conventional gasoline vehicle. This paper presents the systems incorporated in the FFV and the test results. 50,000 mile emission durability tests were also performed and the potential of the FFV as a “Low Emission Vehicle” was assessed. As the result of extensive engineering work, we successfully developed a Galant FFV which exhibits very good durability and reliability. The emission control system which we have developed demonstrated that the vehicle has a good potential to comply with the California formaldehyde emission standard of 15 mg/mile. However, due to the large portion of unburnt methanol in the tail-pipe emissions, FFVs will have more difficulty than gasoline vehicles in meeting non-methane organic gas (NMOG) standards applicable to “Low Emission Vehicles”.

In order to meet increasing demands for safety and comfort in a vehicle compartment, automatic adjustment of seat, mirrors, steering wheel has been developed. The multiplex wiring system was constructed for the automatic adjustment of the cockpit elements to drivers preferred positions or to physique-matched settings based on ergonomic data. This paper describes the construction of the multiplex system and functions of automatic adjustment of the cockpit elements for comfortable driving position and better visibility.

Beta Ti alloy valve spring retainers are newly developed for use in mass produced automobiles for the first time. Ti alloy valve spring retainers vith a weight saving of 42%, compared to steel retainers, have reduced the inertial weight of the valve train components by 6%. And this weight reduction has the benefit of increasing the upper limit of the engine speed, which improves the engine performance. Ti alloy valve spring retainers are cold forged by the conventional fabrication facilities for steel retainers, using Ti-22V-4Al (the beta Ti alloy) which possesses excellent cold workability in a solution treated condition. Oxygen surface hardening is applied to protect Ti alloy valve spring retainers from wear damage. In addition, aging treatment and shot blasting are performed to improve strength and stiffness of valve retainers.

When truck tires have a deformation such as radial runout, flat spot, and abnormal wear as a result of panic braking, they affect vehicle vibration in the form of displacement input whose spectrum involves higher order terms of tire revolution. While a truck has vibration modes of frame bending as well as pitching and unsprung-mass viberation in the input frequency range, the tire displacement input induces vehicle vibration as a combination of these modes. Results of calculations and experiments of a 4x2 medium-duty truck are analyzed and an example of means for improving ride comfort is described in this paper.

Protection of the Earth's environment by means of energy saving and cleaning up of air pollution on a global scale is one of the most important subjects in the world today. Because of this, the requirements for better fuel economy and cleaner exhaust emissions of internal combustion engines have been getting stronger, and, in particular, simultaneous reduction in nitrogen oxides (NOx) and particulate matter (PM) from heavy-duty diesel engines (HDDEs) without degrading fuel economy has become a major subject. Mitsubishi Motors Corporation (MM) has been selling diesel-powered heavy-duty trucks in the U.S. market since 1985 and has agressively carried out development work for meeting the 1991 model year exhaust emission standards.

A new prototype oxygen storage componented oxygen sensor has been developed which shows significant emission reductions of a 3-way catalyst system. This sensor is composed of ceria, as an oxygen storage component and supported pellets as a buffer layer surrounding the protective coating of the sensor element. This sensor offers a more rapid response than conventional ones under lean and rich fuel mixture excursions, which is caused by CO or O2 electrode poisoning.

To meet the increasingly strong demand for high-speed transportation, better fuel economy, higher reliability and the social requirements for more strict Japanese regulations against exhaust and noise emissions, Mitsubishi Motors Corporation has recently developed the 6D40T1 in-line 6-cylinder, 12.0-liter turbocharged and intercooled diesel engine for heavy-duty trucks. This engine meets the 1989 Japanese exhaust emission regulations and has an output of 258 kW. To achieve both fuel economy and good drivability, Mitsubishi's original, electronically-controlled fuel injection system was adopted. The so-called prestroke-controlled fuel injection pump is capable of flexible and precise control of both fuel injection rate and timing. The basic structure of the 6D40T1 was designed with high rigidity to permit high cylinder pressures. In addition, to reduce friction and heat losses, a 4-valve design, roller cam followers with needle roller bearings, and shortened exhaust ports were adopted.

This paper describes a control strategy for autonomous vehicles in an intelligent vehicle/highway system. The control concept aims at the compatibility of passenger riding comfort and vehicle controllability. The main subject of this paper is lateral control of vehicles. In order to analyze riding comfort, we have experimented on the lateral riding comfort during a lane change. It was found that the riding comfort is mainly related to the jerk more than the acceleration, and that the trajectory pattern is important. According to the experimental results, a motion control system was designed. We found through the computer simulation and the experiment with an autonomous test vehicle that comfortable ride is realized along with system stability. Lastly, in order to apply this strategy to the longitudinal direction, we have experimented on the longitudinal acceleration with the test vehicle. The results shows that the same strategy is applicable to the longitudinal direction.

Three zone mixture preparation model, assuming that fuel and air are distributed in three separate zones, fuel air and mixture zone, was proposed. Air Utilization Efficiency derived from the model was used to evaluate the mixing nonuniformity. Effect of the large scale nonisotropic turbulence downstream of the dimple or edge in the intake port of MPI engine on the convective mass transfer from fuel film was clarified by the proposed nondimensional index, Local Sherwood Number. It was found that when the fuel is injected toward the wall where large scale turbulence exists, almost all of the fuel is seeded in the air passing the region at the beginning of the intake process, resulting in the time-resolved nonuniformity of the mixture strength at the intake valve. Using the Air Utilization Efficiency, it was elucidated that time-resolved mixing nonuniformity at intake valves induces spatially nonuniform fuel/air distribution in the cylinder.