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Technical Paper

The Development of Second Generation Ceramic Turbocharger Rotor - Further Improvements in Reliability

Nissan has developed a second generation ceramic turbocharger rotor which provides greater reliability and higher performance than a conventional ceramic rotor. The new rotor is made of silicon nitride, which has demonstrated sufficient strength in vehicle applications. The bonding technique for joining the ceramic rotor to the metal shaft has been confirmed through experimentation to have sufficient reliability. The second generation rotor is featured by the low stress design and higher dynamic strength, and two factors contribute to its higher reliability. The rotor shape was optimized on the basis of results obtained in two analyses of particle impact resistance and applied combined stress. Test results show that the reliability of the second generation rotor have been substantially improved over those of the conventional rotor now being used on production vehicles.
Technical Paper

Swirl Controlled 4-Valve Engine Improves in Combustion under Lean Air-Fuel Ratio

Since a 4-valve engine is less flexible in the design and location of the intake ports as compared with a conventional 2-valve engine, there are some difficulties in strengthening the air motion, including swirl and turbulence, in order to achieve stable combustion under lean mixture operation. This study examined air motion imporvements of 4-valve engine that result in a stable combustion with a lean mixture. These improvements are brought about by the installation of a swirl control valve in each intake port. The results of this study have clarified that the lean stable limit was extended from an air-fuel ratio of 21.5 to 26.3 under a partial load, by optimizing the location and diameter of aperture of the swirl control valve.
Technical Paper

Study on Miniaturization of an Air-Cooled Inverter Integrated with Motor

This paper reports about a trial for miniaturization of an air-cooled inverter integrated with motor, which is realized by reduction of the total volume of smoothing capacitor. An integrated system prototype was constructed with a disk-shaped inverter positioned at the rear end of the motor. We examined the possibility of using a ceramic capacitor, which features a higher heat-resistance temperature, lower internal resistance and higher capacity density than a film capacitor. At the same level of capacitance, the volume of a ceramic capacitor is less than one-half that of a film capacitor, enabling the size of the smoothing capacitor to be reduced to approximately one-fifth that of the currently used device. A suitable circuit configuration and physical layout of distributed smoothing capacitors and corresponding power device modules are proposed and demonstrated.
Journal Article

Silicon Carbide Inverter for EV/HEV Application featuring a Low Thermal Resistance Module and a Noise Reduction Structure

This paper presents the technologies incorporated in an electric vehicle (EV)/hybrid electric vehicle (HEV) inverter built with power semiconductors of silicon carbide (SiC) metal-oxide-semiconductor field-effect transistors (MOSFETs) instead of conventional silicon (Si) insulated gate bipolar transistors (IGBTs). A SiC inverter prototype of 2.9 L in size for driving an 80-kW motor was fabricated and evaluated on a motor test bench. The SiC inverter prototype attained average efficiency of 98.5% in the Worldwide harmonized Light-duty Test Cycle (WLTC) driving mode. The two main technologies achieved with this SiC inverter prototype are described. The first one is a new direct-cooled power module with a thick copper (Cu) heat spreader located under the semiconductors that improves thermal resistance by 34% compared with a conventional direct-cooled power module.
Technical Paper

Optimization of the Heat Flow Distribution in the Engine Compartment

The use of higher output engines and more auxiliary units is resulting in greater heat generation in the engine compartment. At the same time, design trends and demands for improved aerodynamic performance are diminishing the cooling air flow rate. These two sets of factors are making the thermal environment in the engine compartment more severe. In this work, heat flow in the engine compartment was investigated by numerical analysis and flow visualization, and flow control devices were devised for optimizing the temperature distribution. This paper discusses the heat flow optimization techniques and presents the results obtained in experiments with an actual vehicle.
Technical Paper

Improvement of Practical Electric Consumption by Drag Reducing under Cross Wind

Reducing vehicle fuel consumption has become one of the most important issues in recent years in connection with environmental concerns such as global warming. Therefore, in the vehicle development process, attention has been focused on reducing aerodynamic drag as a way of improving fuel economy. When considering environmental issues, the development of vehicle aerodynamics must take into account real-world driving conditions. A crosswind is one of the representative conditions. It is well known that drag changes in a crosswind compared with a condition without a crosswind, and that the change depends on the vehicle shape. It is generally considered that the influence of a crosswind is relatively small since drag accounts for a small proportion of the total running resistance. However, for electric vehicles, the energy loss of the drive train is smaller than that of an internal combustion engine (ICE) vehicle.
Technical Paper

Improvement in Pitting Resistance of Transmission Gears by Plasma Carburizing Process

The application of both high strength gear steels and shot peening technology has succeeded in strengthening automotive transmission gears. This technology, though, improves mainly the fatigue strength at the tooth root, but not the pitting property at the tooth face. Therefore, demand has moved to the development of new gear steels with good pitting resistance. In order to improve pitting resistance, the authors studied super carburizing which is characterized by carbide dispersion in the case, especially processed with a plasma carburizing furnace. Firstly, the influence of the carburizing temperature and carburizing period on the carbide morphology was investigated and the optimum carburizing conditions were determined. Secondly, the fatigue strength and pitting resistance was evaluated using carbide dispersed specimens.
Technical Paper

High Performance Differential Gear

Excellent fuel economy and high performance have been urgent in Japanese automobile industries. With increasing engine power, many of the power train components have to withstand higher loads. Differential pinion gear being one of those highly stressed parts, excellent fatigue and shock resistance have been demanded. At first the fundamental study on the fatigue and impact crack behavior of carburized components was studied and the new grade composed of 0.18%C-0.7%Mn-1.0%Cr-0.4%Mo was alloy designed. Furthermore, Si and P is reduced less than 0.15 and 0.015%, respectively aiming at the reduction of intergranular oxidation and improved case toughness. The differential gear assembly test has proved that the new grade shows three times as high impact strength as that of conventional steel, SCM418, and almost the same as that of SNCM420 containing 1.8%Ni.
Technical Paper

Exhaust Noise Abatement with Porous Sintered Metal Silencer

The exhaust system is often one of the main sources of vehicle noise. A new type of exhaust silencer made of porous sintered aluminum and installed at the end of the exhaust tube considerably reduces this noise, with no rise in back pressure. The mechanism of noise abatement is analyzed utilizing fluid dynamic analysis techniques. It is concluded that noise reduction results mainly from the fluid dynamic effects arising from the gas permeability of the material. Among these effects are the boundary layer control effect of the inner flow, flattening of the velocity profile, heat dispersion effect, decrease in turbulence of flow, smoothing of exhaust pulsation, contraction of the mixing region, and the resulting large decrease in the volume of the noise source. In regard to acoustical effect, the sintered metal can be thought of as Helmholtz resonators. The change in the end condition as an acoustic tube also reduces the peak level of acoustic resonance.
Technical Paper

Evaluation of an Open-grill Vehicle Aerodynamics Simulation Method Considering Dirty CAD Geometries

In open-grille vehicle aerodynamics simulation using computational fluid dynamics, in addition to basic flow characteristics, such as turbulent flow with a Reynolds number of several million on the bluff body, it is important to accurately estimate the cooling air flow introduced from the front opening. It is therefore necessary to reproduce the detailed geometry of the entire vehicle including the engine bay as precisely as possible. However, there is a problem of generating a good-quality calculation grid with a small workload. It usually takes several days to a week for the pretreatment process to make the geometry data ‘clean’ or ‘watertight’. The authors proposed a computational method for complex geometries with a hierarchical Cartesian grid and a topology-independent immersed boundary method with dummy cells that discretize the geometry on a cell-by-cell basis and can set an imaginary point arbitrarily.
Technical Paper

Engine Application of a Battery Voltage-Driven DI Fuel Injection System

Every fuel injection system for DI gasoline engines has a DC-DC converter to provide high, stabile voltage for opening the injector valve more quickly. A current control circuit for holding the valve open is also needed, as well as a large-capacity capacitor for pilot injection. Since these components occupy considerable space, an injector drive unit separate from the ECU must be used. Thus, there has been a need for a fuel injection system that can inject a small volume of fuel without requiring high voltage. To meet that need, we have developed a dual coil injector and an opening coil current control system. An investigation was also made of all the factors related to the dynamic range of the injector, including static flow rate, fuel pressure, battery voltage and harness resistance. Both efforts have led to the adoption of a battery voltage-driven fuel injector.
Technical Paper

Development of the Aerodynamics of the New Nissan Murano

The new Murano was developed with special emphasis on improving aerodynamics in order to achieve fuel economy superior to that of competitor models. This paper describes the measures developed to attain a drag coefficient (CD) that is overwhelmingly lower than that of other similar models. Special attention was paid to optimizing the rear end shape so as to minimize rear end drag, which contributes markedly to the CD of sport utility vehicles (SUVs). A lower grille shutter was adopted from the early stage of the development process. When open, the shutter allows sufficient inward airflow to ensure satisfactory engine cooling; when closed, the blocked airflow is actively directed upward over the body. The final rear end shape was tuned so as to obtain the maximum aerodynamic benefit from this airflow. In addition, a large front spoiler was adopted to suppress airflow toward the underbody as much as possible.
Technical Paper

Development of an Electric Concept Vehicle with a Super Quick Charging System

Recent environmental concerns such as atmospheric pollution and energy conservation have intensified the need to develop pollution-free, energy-efficient vehicles. One such solution is the electric automobile which draws its power from rechargeable batteries. There are few vehicles on the road today because present batteries can store very little energy compared with that of a tank of gasoline. To obtain adequate range, this concept vehicle adopts a new battery which can be recharged to 40% of capacity in six minutes. This super quick charging system makes it possible to recharge the batteries at an electric recharging station just as gasoline-powered vehicles are refilled at service stations. The electric concept vehicle also has improved aerodynamics, reduced rolling resistance and a lighter curb weight, which help to assure adequate range.
Technical Paper

Development of a Wear Resistant Aluminum Alloy for Automotive Components

Hypereutectic Al-Si alloy 390, containing large amounts of hard silicon particles, has mainly been used for wear-resistant alloy applications. In the case of hypereutectic Al-Si alloys, the primary silicon particle size and distribution must be controlled to obtain stable wear resistance. The service life of furnaces and molds is shortened by the high melting and casting temperatures required for controlling primary silicon. Furthermore, machinability is degraded by large primary silicon particles. To overcome these problems, a new wear-resistant Al-Si alloy has been developed which provides good castability and machinability. This alloy also has wear resistance and mechanical properties similar to those of the 390 alloy. Specifically, the problems regarding castability and machinability were solved by decreasing the silicon content of the 390 alloy, but that also reduced wear resistance.
Technical Paper

Development of a Prediction Method for Passenger Vehicle Aerodynamic Lift using CFD

Increasing expectations for stability at high speed call for the improvement of cars' aerodynamic performance, in particular lift reduction. However, due to styling constraints, traditional spoilers must be avoided and replaced by other solutions like underfloor components. Flow simulation is expected to be a useful tool for lift prediction, but the conventional models used so far did not represent complex geometry details such as the engine compartment and underfloor, and accuracy was insufficient. In the present study, a full vehicle simulation model, including the engine compartment and underfloor details, was used. Other improvements were also made such as optimization of the computational grid and the setting of boundary conditions for reproducing wind tunnel experiments or actual driving, making it possible to predict lift variations due to vehicle geometry changes.
Technical Paper

Development of a New-Generation High-Performance 4.5-liter V8 Nissan Engine

This paper describes a new 4.5-liter V8 engine, VH45DE, which was developed for use in the INFINITI Q45 sporty luxury sedan that was released in the U.S. and Japanese markets in November 1989. The many V8 engines in use around the world can be broadly devided into two categories. One category is characterized by ample torque at low engine speed and relatively large engine displacement. The other category is characterized by enhanced performance at relatively high engine speeds. The VH45DE engine is a new-generation V8 powerplant that delivers smooth power output at top-end speed and also generates ample torque at low engine speed to maintain good idle stability, and accomplishes it all with the smallest possible displacement. Development efforts were focused on two main goals. The first was to achieve efficient intake air charging. This has been accomplished the intake air resonant point at a relatively high engine speed through appropriate intake branch and collector tuning.
Technical Paper

Development of a High-Performance TiA1 Exhaust Valve

A new high-performance and lightweight TiA1 intermetallic compound exhaust valve has been developed. The TiA1 valve can improve power output and fuel economy by contributing higher engine speeds and a reduction in valvetrain friction. It was achieved by developing a Ti-33.5A1-0.5Si-1Nb-0.5Cr (mass%) intermetallic compound, a precision casting method for TiA1 that provides a low-cost, high-quality process, and a plasma carburizing technique for assuring good wear resistance on the valve stem end, stem and face.
Technical Paper

Development of Plastic Region Tightening 1.6-GPa Ultra-High Strength Bolt with High Delayed Fracture Resistance

A new variable compression turbo (VC-Turbo) engine, which has a multi-link system for controlling the compression ratio from 8:1 to 14:1, requires high axial force for fastening the multi-links because of high input loads and the downsizing requirement. Therefore, it was necessary to develop a 1.6-GPa tensile strength bolt with plastic region tightening. One of the biggest technical concerns is delayed fracture. In this study, quenched and tempered alloy steels were chosen for the 1.6-GPa tensile strength bolt.
Technical Paper

Development of Pitting Resistant Steel for Transmission Gears

It was found that pitting resistance of gears is strongly influenced by resistance to temper softening of carburized steel. The investigation about the influence of chemical compositions on hardness after tempering revealed that silicon, chromium and molybdenum are effective elements to improve resistance to temper softening and pitting resistance. Considering the production of gears, molybdenum is unfavorable because it increases hardness of normalized or annealed condition. Developed new steel contains about 0.5 mass% of silicon and 2.7 mass% chromium. The new steel has excellent pitting resistance and wear resistance. Fatigue and impact strength are equivalent to conventional carburized steels. Cold-formability and machinability of the new steel are adequate for manufacturing gears because of its ordinary hardness before carburizing. The new steel has already been put to practical use in automatic transmission gears. Application test results are also reported.
Technical Paper

Development of Improved Metal-Supported Catalyst

A compact, high-performance and durable metal-supported catalyst has been developed by using the properties of the metal support effectively. The advantages of the metal-surpported catalyst against the ceramic-supported one are higher geometrical surface area, higher heat conductivity and thinner wall thickness. Higher geometlical surface area and higher heat conductivity lead to higher conversion efficiency after durability test and it allows reduction in catalyst volume. And the thinner wall thickness lowers gas flow resistance. But also, the metal-supported catalyst has the disadvantage of larger heat expansion and it requires special structure and material.