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The objective of this study was to develop a test method for heavy-duty HEVs using a hardware-in-the-loop simulator (HILS) to enhance the type-approval-test method. To achieve our objective, HILS systems for series and parallel HEVs were actually constructed to verify calculation accuracy. Comparison of calculated and measured data (vehicle speed, motor/generator power, rechargeable energy storage system power/voltage/current/state of charge, and fuel economy) revealed them to be in good agreement. Calculation error for fuel economy was less than 2%.

In complying with a customer demand for improving low-speed maneuverability of commercial vehicles in narrow streets, a medium-duty truck with a mechanical linkage type four-wheel steering system with a hydraulic assist and a steering lock device is developed. A mode select gearbox allows a driver to select one of three rear-wheel steering modes; 2WS, same-phase 4WS, and opposite-phase 4WS. The steering lock device is locked during 2WS operation for preventing rear-wheel steering. An electronic control system is applied for easier mode selection, synchronization of locking and unlocking the steering lock device with a mode select operation, and vehicle speed limitation during 4WS operation. We made efforts particularly to suppress vehicle yaw motion when the vehicle is running in the same-phase 4WS mode. Several innovative new mechanisms are incorporated on this vehicle. This paper deals with these mechanisms and these functions.

Because of smaller ratios of tread to height of gravitational center, longer wheel-bases, and larger moment of inertia, vehicle roll is the most important characteristics governing truck controllability and stability. And longer wheel-bases result in a reduction in vehicle body torsional stiffness. Hence, the influence of vehicle body torsional stiffness on vehicle roll characteristics is investigated. We carried out a simulation analysis and vehicle test on medium-duty trucks, in studying the vehicle frequency response characteristics by changing vehicle design parameters. The results show that a reduction in body torsional stiffness increases the steady state gain of the front roll angle without affecting the yaw and lateral characteristics of vehicle motion. Accordingly, even if body torsional stiffness is unavoidably lowered, reducing the front roll angle by increasing the roll stiffness of the front suspension can maintain appropriate vehicle controllability and stability.

Biodiesel Fuel (BDF) Research Work Group works on identifying technological issues on the use of high biodiesel blends (over 5 mass%) in conventional diesel vehicles under the Japan Auto-Oil Program started in 2007. The Work Group conducts an analytical study on the issues to develop measures to be taken by fuel products and vehicle manufacturers, and to produce new technological findings that could contribute to the study of its introduction in Japan, including establishment of a national fuel quality standard covering high biodiesel blends. For evaluation of the impacts of high biodiesel blends on performance of diesel particulate filter system, a wide variety of biodiesel blendstocks were prepared, ranging from some kinds of fatty acid methyl esters (FAME) to another type of BDF such as hydrotreated biodiesel (HBD). Evaluation was mainly conducted on blend levels of 20% and 50%, but also conducted on 10% blends and neat FAME in some tests.

In Biodiesel Fuel Research Working Group(WG) of Japan Auto-Oil Program(JATOP), some impacts of high biodiesel blends have been investigated from the viewpoints of fuel properties, stability, emissions, exhaust aftertreatment systems, cold driveability, mixing in engine oils, durability/reliability and so on. In the impact on exhaust emissions, the impact of high biodiesel blends into diesel fuel on diesel emissions was evaluated. The wide variety of biodiesel blendstock, which included not only some kinds of fatty acid methyl esters(FAME) but also hydrofined biodiesel(HBD) and Fischer-Tropsch diesel fuel(FTD), were selected to evaluate. The main blend level evaluated was 5, 10 and 20% and the higher blend level over 20% was also evaluated in some tests. The main advanced technologies for exhaust aftertreatment systems were diesel particulate filter(DPF), Urea selective catalytic reduction (Urea-SCR) and the combination of DPF and NOx storage reduction catalyst(NSR).

Nissan Diesel Motor Co.,LTD have developed a new turbocharged diesel engine with a variable nozzle turbocharger for the purpose of solving the contradictory problems of mobility and fuel economy, while meeting the 1990 Japanese emission standards. The heavy-duty trucks equipped with this new turbocharged engine have been released in the market recently. The variable nozzle turbocharger capable of maintaining sufficient turbine efficiency over the broad range of engine operating band was jointly developed with Allied Signal, Garrett Automotive Group in United States of America.It's control method, a stepless boost pressure feedback control system, was newly developed in order to make the most effective use of the turbocharger.

We studied the use of SiC porous material for diesel particulate filters. Crystallities of SiC grow into hexagonal plates during sintering,but their sizes have not been controllable yet. We developed a production process that makes the average pore diameter as desired in limiting the pore size distribution to a narrow range. Diesel particulate filters made of SiC greatly reduce pressure loss even when a large quantity of particulates accumulates as compared with conventional wall-flow type filter of cordierite of the same size. This enables particulate filter to be made smaller. The good thermal conductivity of SiC allows fast regeneration without a temperature spike, but its large coefficient of thermal expansion causes heat cracks during rig tests and engine bench tests. The rig tests showed that the heat cracking problem can be solved if the length and diameter are below a certain threshold for each.

The characteristics of a new diesel particulate filter material made of SiC were studied through engine tests in varying material properties, such as average pore diameter, and wall thickness. Compared to a conventional cordierite filter of the same size, particulate trapping efficiency is almost the same, and the pressure loss and the deterioration of fuel consumption can be reduced to about half with the optimum material properties. If the same pressure loss is allowed, the filter size can be reduced by 30%. Its good thermal conductivity prevents local temperature increases, which doubles the permissible amount of trapped particulates. As heat crack problems occurred in integral-type filters due to the high thermal expansion of SiC, a split-type filter having 49 filter segments with a square section was developed.

This study establishes the feasibility of improving the motion characteristics of commercial vehicles by applying rear axle steering. A model-matching control algorithm for rear axle steering was used to achieve the desired yaw rate response to steering action. Simulations with a two-degree-of-freedom model evaluated the effectiveness of the control method. Results of vehicle tests on an experimental medium-duty truck with rear axle steering proved that this control method can improve vehicle yaw response. However, the simulation results did not well represent the vehicle test results, because the simulation model was too simple. Adding the roll effect to the model reduced the discrepancy between the simulation and vehicle test results.

In Japan there is currently a strong social demand for exhaust emissions reduction from heavy-duty diesel engines. Therefore, new Long-Term Regulation will come into effect in October 2005, setting the NOx standard at 2.0 g/kWh and the PM standard at 0.027 g/kWh. At the same time, customers always demand exceptional fuel economy from heavy-duty commercial vehicles. A urea-based Selective Catalytic Reduction (SCR) system was developed to satisfy both these demands, and will be introduced in the fall of 2004. The operating conditions of vehicles in Japan are different from those in the US and Europe. Basically, average vehicle speeds are significantly lower. To improve the low temperature SCR performance, an oxidation catalyst was located upstream of the SCR, and an additional oxidation catalyst was located downstream of the SCR for emergency NH3 slip. The muffler size with all three catalysts was similar to a conventional muffler.

To analyze truck ride comfort, the authors developed a relatively simple simulation model in 16 degree-of-freedom. As a result of studying important truck structural features, such as friction of leaf springs, bending stiffness of a frame, etc., calculation results of a transfer function response analysis agreed fairly well with measured data. As means for ensuring better ride comfort, NISSAN DIESEL developed a floating cab suspension system. To optimize the specification of the system, we utilized this analytical method effectively.

A simulation technique has been developed for describing the synchronization mechanism of a transmission for heavy-duty trucks, to clarify why and how abnormal (two-stage) shift reaction force while upshifting occurs sometimes. It is hard to analyze this phenomenon with a conventional experimental approach because the synchronizer mechanism is complex and synchronization performs in a short time. Hence, the movement and contact force of the synchronizer components are simulated with an analytical model using ADAMS. According to the simulation results, the abnormal shift reaction force occurs during the meshing process of both splines of the sleeve and clutch gear, its cause is a backward movement of the sleeve. The relative relationship between a sleeve movement force at the contact point of both spline chamfers and clutch gear rotational force influences the phenomenon, and it can be reduced by tuning the friction force on the chamfer surfaces.