Search Results

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%.

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.

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).

A method of fatigue life prediction of spot welded joint under multi-axial loads has been developed by fatigue life estimation working groups in the committee on fatigue strength and structural reliability of JSAE. This method is based on the concept of nominal structural stress ( σ ns) proposed by Radaj and Rupp, and improved so that D value is not involved in stress calculation. The result of fatigue life estimation of actual vehicle with nominal structural stress which was calculated through newly developed method had very good correlation with the result of multi-axial loads fatigue test carried out with test piece including high strength steel.

Various prediction methods have been proposed for evaluating the fatigue life of welded joints by combining finite element analysis (FEA) with an experimental database. However, to obtain more universal and accurate fatigue life predictions, it is necessary to have criteria for making integrated evaluations of the fatigue strength of welded joints. This paper presents a study that focuses on the local cyclic plastic zone size (ω*) as the criterion of fatigue strength and investigates its validity. The definition of ω* was given by the relationship between the stress state at the notch tip and the elastic strain which was defined along the strain-life fatigue curve (ε - N diagram) of a base metal. As a result of using ω*, it was found that an integrated fatigue life prediction was possible to a certain extent for notch and arc-welded joint specimens.

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)*.

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.

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.

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.

Ceramic materials such as silicon nitride and sialon are known for their excellent wear-resistance and scuffing-resistance even under high contact pressure and poor lubrication1. However, ceramic materials, which have excellent sliding properties, are not widely adopted for valve train components, at present. A main reason for this is their high cost. A ceramic cam follower, newly developed by utilizing the direct brazing technology, has the following features and can be produced at the lowest cost: (1) Parts are only three. -A thin ceramic disc, a steel body, and an active brazing foil. (2) No grinding is necessary after brazing. -A crowning at the cam sliding surface is formed by the difference of the thermal expansion coefficients between silicon nitride and steel. (3) No hardening is necessary after brazing. -The steel body is hardened by the heat treatment of brazing.

This paper describes the development of an inexpensive ceramic cam follower that uses a silicon nitride material and is more wear and scuff resistant than the sinter alloy cam follower. A thin ceramic disk is directly brazed on a steel cam follower body without using any stress-relief materials which makes the grinding for crowning unnecessary, reducing the production cost. We performed a material screening test using an abrasion tester to determine the optimum type of silicon nitride and the optimum surface roughness. Engine endurance tests proved its excellent wear and scuff resistance. Consequently, it has been adopted in the 1993 series production engines as the first ceramic cam follower.

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.

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.

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.

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.

Injection process simulation methods were developed for both the unit injector (UI) system and the pump-line nozzle (PLN) system consisting of an in-line injection pump, fuel line, and nozzle. Simulation results agreed well with measured ones. With regard to the shape of injection rate and the peak injection pressure change at various engine speeds, the injection characteristics of the UI system are better than those of the PLN system. Simulation results showed that similar injection characteristics can also be obtained with the PLN system by using a concave cam with a carefully designed cam profile for a sleeve-controlled in-line injection pump and by changing the prestroke according to the operating conditions. Engine test results demonstrated the possibility of improving the trade-off between NOx and fuel consumption by shaping the injection rate. The shape of injection rate plays an important role in diesel combustion(1,2)*, affecting exhaust emissions and also combustion noise.