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A robust control method applied to a DC-motor the actuator of a steering system installed on a radio-controlled multiloader truck is developed Requirements for the control system are robustness and stability against disturbances and change in plant characteristics, and rapid and accurate response to steering commands To comply with these requirements, we applied a robust model matching (RMM) control method to the steering actuator Results of simulation analyses and a hardware-in-the-loop simulation show the effectiveness of this control method

A diesel particulate filter (DPF) for city buses was developed that combines a SiC filter and a full-flow type burner for regeneration. Filter crack problems were averted by suppressing the peak temperature inside the filter to under 900°C. This was done by setting the maximum tolerable amount of collected particulate mass before regeneration at 50 g and controlling the burner so as to increase the regeneration gas temperature slowly up to a set value. This DPF was retrofitted to a Tokyo metropolitan bus to conduct a field test. The field test has been under way for half a year without any trouble or deterioration of system performance. THE DIESEL PARTICULATE FILTER (DPF) receives much recognition as an effective tool for reducing diesel particulates. However, its practical applications are still quite limited, because to date its durability remains immature.

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.

A heavy-duty, naturally aspirated diesel engine was converted into a turbocharged, aftercooled, compressed natural gas engine. Engine test results show that excess air ratio and ignition timing strongly affect NOx and THC emissions. Leaning the air-fuel mixture reduces NOx emission, but it increases THC emission and combustion becomes unstable above a certain excess air ratio. Retarding the ignition timing reduces both the NOx and THC emissions. Dual-plug ignition improves brake thermal efficiency. The NOx emission level can be reduced to meet the Japanese long-term emission regulation limit for heavy-duty gasoline engines with a sufficient safety margin by appropriately selecting the air-fuel ratio and ignition timing so as to keep the THC emission level below the regulation limit without using any after-treatment. The engine full torque characteristics were almost the same as the base engine throughout the engine speed range, while the maximum exhaust gas temperature was lower.

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.

The effects of fuel properties on diesel engine exhaust emission characteristics are investigated using eleven kinds of fuel with varying levels of sulfur and aromatic contents. Exhaust emissions from three engines are measured over the new Japanese 13-mode cycle as well as the U.S. transient test procedure. Engine test results show that reducing the fuel sulfur content decreases particulate levels. This effect is more pronounced for engines that emit more SOF. Enriching the aromatic content with dicyclic and other polycyclic compounds increases particulate, NOx, CO, and THC emissions. This particulate increase is due to the increase of SOF. Accordingly, low sulfur fuel should be produced without increasing the aromatic content, otherwise the SOF increase will offset the particulate reduction effect of the low sulfur fuel.

Several types of oxidation catalyst material are tested in repeated particulate emission measurements over the US HDD transient test procedure. Particulates are effectively reduced in the initial stage of the measurements. However, particulates tend to increase when repeating the measurements. This is believed to be caused by sulfate adsorption on the catalyst surfaces. Hence, oxidation catalysts are tested after stabilizing surface adsorption. Test results show that an oxidation catalyst which forms more sulfates is not effective in reducing particulates because the sulfate increase offsets the SOF reduction effect. An effective catalyst for particulate reduction is developed by suppressing sulfate formation.

The injection nozzle inclination angle affects the flow characteristics in nozzle holes. Stroboscopic photographs of instantaneous spray plumes show that the length of each spray plume is different. Test results show that the fuel quantities injected from the holes are remarkably less when the nozzle hole spray angle relative to the injection nozzle axis is smaller compared with others with the same hole diameter. Hence, the authors analyzed the flow characteristics in injection nozzles using a computational fluid dynamic technique. Calculation results show good qualitative agreement with experimental results. INJECTION NOZZLES are normally installed in a two-valve cylinder head with an inclination angle. As shown in Fig. 1, the spray angle of each nozzle hole is different in order to maintain the same impingement height against the piston cavity for each spray.

To improve the low-speed followability of semi-trailers, a control method has been developed for trailer-wheel steering. The basic concept of the control method is to steer the wheels so that the trailer rear end follows the tractor front end. Computational simulation results show that the control method minimizes the swept path of the tractor and trailer combination without causing any rear end overhang swing problems. To evaluate the effectiveness of the control method, the approximately one twelfth scale model vehicles of the tractor and semitrailer were produced. Tests on the articulated model vehicles show that better low speed follwabilty improvement is expected with path-following control compared with other trailer wheel steering control methods.

This paper studies the feasibility of improving vehicle ride comfort and vehicle dynamics by applying mechanically controlled hydropneumatic suspension to a medium-duty truck. Both front and rear suspensions consist of hydraulic cylinders, small gas accumulators and leaf springs. Hydraulic pressure In the cylinder is controlled by a hydraulic pressure difference between diagonally located hydraulic cylinders. Vehicle test results show that this suspension system reduces vertical vibration in the frequency range of 3 to 10 Hz, the pitch motion during braking, and the roll angle during a steady turn, when compared those the conventional suspension system. However, due to a response lag in the hydraulic control system, this system causes an unfavorable vehicle motion when there is a rapid steering operation, such as an abrupt lane change.

Soot accumulation in diesel engine crankcase is the dominant factor which governs engine oil drain interval. So, efficient soot elimination from crankcase oil can be a practical way to achieve drain interval extension. Combination of high performance oil filter and low soot dispersancy oil results in an effective measure to trap soot efficiently. In this paper, the behavior of newly developed high performance diesel engine oil having low soot dispersancy is reported. Prior to oil development, an evaluation method of soot dispersancy in oil was elaborated. Based on relative viscosity defined as ratio of soot containing oil viscosity to soot eliminated oil viscosity, dispersancy parameter was determined. Oil dispersancy evaluated on this parameter agreed with the results obtained from particle size analyzer. Secondly, a method to obtain oil filter soot trap rate to total soot contaminated into crankcase (trap rate) was established.

Analysis results of used oils sampled from many engines operating in the field show that the most critical factor governing the limits of oil use is insoluble fraction concentration in oil. Hence, the authors developed a new oil and by-pass oil filter to increase soot trapping efficiency, so as to extend oil change interval. Soot trapping efficiency could be improved from 30% to more than 80% using a bigger oil filter with fine mesh and a newly developed low soot dispersancy oil. Engine lubrication performance of the new oil was compared to that of standard and commercial long-drain oils by conducting 300-hour endurance tests on an 11.7 liter direct injection, turbocharged and aftercooled diesel engine at rated output. Test results proved superior engine lubrication performance of the new oil. THE INTERVAL between lubricating oil changes for diesel engines is twenty to forty thousand kilometers, depending on engine manufacturers' recommendations (1)*.

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.

A reduction in vehicle weight sometimes results in a reduction in truck body torsional stiffness. Hence, the authors investigate the influence of vehicle body torsional stiffness on vehicle controllability and stability. A simulation analysis and vehicle test are carried out on a medium-duty truck, and the frequency response characteristics of the vehicle are studied by changing vehicle design parameters. The results show that a reduction in body torsional stiffness does not affect the yaw and lateral characteristics of vehicle motion, but increases the steady state gain of the front roll angle. Accordingly, even if body torsional stiffness is unavoidably lowered, appropriate controllability and stability can be maintained by increasing the roll stiffness of the front suspension, thereby reducing the front roll angle.

This paper describes a preliminary study of the role of computational fluid dynamics in analyzing the aerodynamic characteristics of a heavy-duty truck body. Among truck related aerodynamic problems, we selected the soil problem on the vehicle side surfaces as the analysis subject. Because of computer capacity limitations, a half-truck-cab model with a tire and mud guard are used and created by using the multi-block transformation technique. The flow around the cab is simulated by directly integrating the Navier-Stokes equations, approximated by finite-difference equations. Calculated results on the flaw structures around the vehicle body surface where it becomes dirty under wet weather conditions provide some useful information in the search for understanding of soil problems.

Evaporative cooling was applied to a heavy duty diesel engine to investigate the feasibility of this cooling method. Engine test results showed the following benefits of this cooling method: Reduction of the size of theradiator and cooling fan is feasible. The maximum temperature of the combustion chamber wall did not increase, though the coolant temperature rose by 20°C. The fuel consumption could be reduced especially at partial load. Engine warm-up performance was significantly improved. An oil cooler rig test was also conducted to investigate the heat transfer characteristics of the oil cooler with evaporative cooling.

Gear tooth characteristics that minimize noise excitation are identified, and a new “Maximum-Conjugacy” tooth form is described that employs these characteristics to reduce gear noise excitation to approximately 15% of that of conventional gearing. Kinematic action, relative torque capacity, and comparative manufacturing costs are discussed. Noise reductions obtained from employing the new gearing in the timing train of a small diesel engine are evaluated for the full range of engine speeds.

An acceleration mode in measuring vehicle pass-by noise was simulated on an engine test bed in an anechoic room. The accelerated running noise of various types of diesel engines was measured and compared with the steady running noise. The measurement results show that naturally aspirated DI engines become noisier at acceleration, while IDI engines change only slightly. In turbocharged DI engines, the response lag of the turbo charger causes an especially big noise level difference immediately after acceleration start. This paper deals also with the mechanisms of higher level of accelerated running noise in DI engines.