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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.

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.

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

Austempered ductile iron (ADI) is a material having excellent mechanical properties and damping capacity. However practical mass production of ADI gears has not been possible due to ADI's poor machinability and distortion during the austempering heat treatment. With a new process method of carrying out hobbing before austempering when the material is in its soft condition, then austempering it and lastly, conducting the shave finishing process, we have diminished the above defects and developed practical ADI gears. These new gears generate less noise than ordinary nitrocarburized steel gears and are superior in pitting resistance.

This paper describes the calculative verification of the effect of the right-and-left torque vectoring system in various types of drivetrain, namely, the front wheels only, the rear wheels only, and both front and rear wheels in FWD, RWD, and AWD vehicles. The effect is evaluated by calculating the vehicle dynamics limit; maximum acceleration and cornering ability. The right-and-left vectoring torque, which is needed for expanding the vehicle dynamics limit, is also calculated. And finally, the paper evaluates the suitable wheels for which the system should be applied in each drivetrain. The application to the front wheels is more effective for FWD vehicles. On the other hand, the application to the rear wheels is more effective for RWD and AWD vehicles.

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.

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.

The 4M5 series of four-cylinder, in-line, direct-injection diesel engines has been released by Mitsubishi Motors Corporation for light and medium-duty trucks and buses. Featuring an updated structure and reflecting the employment of state-of-the-art technology in the design of every component, the new engine series offers high reliability and compact dimensions. Moreover, the new series well meets contemporary demands for high performance, low noise, and clean combustion.

The gasoline direct injection engine starts significantly faster than a conventional engine. Fuel can be injected into the cylinder during the compression stroke at the same time of cranking start. When the spark plug ignites the mixture at the end of compression stroke, the engine has its first combustion, that is, the first combustion occurs within 0.2 sec after the start of cranking. This unique characteristic of quick startability has realized a idle stop system, which enables drivers to operate the vehicle in a natural manner.

As the global environmental protection becomes the world consensus recently, the regulations of the fuel consumption and the exhaust gas have large effects on the performance and the fundamental structure of commercial vehicles. Especially the technology concerning "fluid" and "heat" has a close relationship with those issues. Owing to above circumstances, commercial vehicles such as large trucks and buses are forced to be designed near the limit of allowance. Furthermore, a rapid design is another requirement. However, though significant number of variations, i.e., cab configuration, wheel base, rear body configuration, engine specification, etc., are prepared, it is impossible to improve the performance of all those combinations by experiments which cost a lot. Accordingly, the quantitative prediction using computer will become indispensable at the beginning term of new car development.

A characteristic mechanism of in-cylinder combustion is “time-domain mixing” which mixes up unburned gas, products in the different stages of combustion process, and burned gas, by “eddy”, a flow component with its scales of several to 10 mm. It seems to play a role in completing the combustion. Now that direct injection is a central engine technology, a keyword to combustion control is “freedom of mixing”, that is, no restriction on mixture formation, realized by direct injection. Various kinds of combustion control technologies utilizing it, have been presented. After combustion control for a premixed leanburn gasoline engine, and a direct injection gasoline engine, was achieved by turbulence control, and mixing control, respectively, the next target of combustion control will be ignition control. It will be possible, by controlling some boundary condition on combustion and fuel chemistry. Time-domain mixing and freedom of mixing will support it.

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 stratified-charge lean-burn engine is newly developed for the purpose of energy saving and carbon dioxide reduction to minimize the global warming. The engine, named MVV(Mitsubishi Vertical Vortex)engine, is based on the unique vertical vortex technology which realizes stable combustion even with lean mixture without any additional device. And it also has another feature of “all range air-to-fuel ratio feedback control system” utilizing linear air-to-fuel ratio sensor. This paper describes various technologies developed in this engine.

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.

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.