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Mo-free 1.6-GPa bolt was developed for a Variable Compression Turbo (VC-Turbo) engine, which is environment friendly and improves fuel efficiency and output. Mo contributes to the improvement of delayed fracture resistance; therefore, the main objective is to achieve both high strength and delayed fracture resistance. Therefore, Si is added to the developed steel to achieve high strength and delayed fracture resistance. The delayed fracture tests were performed employing the Hc/He method. Hc is the limit of the diffusible hydrogen content without causing a delayed fracture under tightening, and He is the diffusible hydrogen content entering under a hydrogen-charging condition equivalent to the actual environment. The delayed fracture resistance is compared between the developed steel and the SCM440 utilized for 1.2-GPa class bolt as a representative of the current high-strength bolts.

In recent years, the removal of lead (Pb), which is an environmentally hazardous material often used in bearings for automotive engines, has been continuously promoted. Bismuth (Bi) is attracting attention as a substitute for lead, and it is currently being used mainly for passenger cars and trucks as a lead replacement. However, lead has not been replaced for motorcycles where the bearings are exposed to high temperatures at high rotation speeds, and trucks and generators where high loading capacity, long lifetime and good corrosion resistance are required. It has been difficult to achieve both high load and corrosion resistant for a bearing overlay material. The purpose of this development is to improve the corrosion resistance and fatigue resistance of bismuth overlay by developing a bismuth- antimony alloy overlay in which antimony (Sb) is added to the bismuth matrix.

The size and weight of the traction inverter needs to be reduced to ensure a sufficient cruising range of an electric vehicle. To this end, one approach involves changing materials of the inverter case from aluminum to resin. However, the resin in use of inverter case causes technical issues in terms of collision performance, electromagnetic compatibility (EMC), and cooling performance because of the difference in the material properties between the resin and the conventionally used aluminum. By solving the abovementioned issues, a resin water jacket case (hereinafter, resin water jacket) was successfully adopted with inverters designed for next-generation electric powertrain in mass production models for the first time. The resin-based structure had advantages to reduce the weight of the inverter case by ~35% and decrease the number of parts to ~3/5, compared to that for the conventional cases.

Nissan’s variable compression turbo (VC-Turbo) engine has a multilink mechanism that continuously adjusts the top and bottom dead centers of the piston to change the compression ratio and achieve both fuel economy and high power performance. Increasing the exhaust gas recirculation (EGR) rate is an effective way to further reduce the fuel consumption, although this increases the exhaust gas condensation in the cylinder bores, causing a more corrosive environment. When the EGR rate is increased in a VC-Turbo engine, the combined effect of piston sliding and exhaust gas condensation at the top dead center accelerates the corrosive wear of the thermal spray coating. Stainless steel coating is used to improve the corrosion resistance, but the adhesion strength between the coating and the cylinder bores is reduced.

Engine oil with viscosity lower than 0W-16 has been needed for improving fuel efficiency in the Japanese market. However, lower viscosity oil generally has negative aspects with regard to oil consumption and anti-wear performance. The technical challenges are to reduce viscosity while keeping anti-wear performance and volatility level the same as 0W-20 oil. They have been solved in developing a new engine oil by focusing on the molybdenum dithiocarbamate friction modifier and base oil properties. This paper describes the new oil that supports good fuel efficiency while reliably maintaining other necessary performance attributes.

In order to improve the accuracy of the coil temperature prediction, detailed fundamental experiments have been conducted on thermal resistances that are caused by the void air gap and contact surfaces. The thermal resistance of the coil around the air gap can be calculated by an air gap distance and air heat conductivity. Contact surface thermal resistance between the core and the housing was constant regardless of the press-fitting state in this experiment. Prediction accuracy of the coil temperature is improved by including the heat resistance characteristics that is obtained by the basic experiment to conjugate heat transfer analysis model.

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.

The number of vehicles with engines using idling stop systems and hybrid systems to improve fuel consumption has recently been increasing. However, with such systems the frequent starts and stops of the engine, where the oil film between the bearings and shaft is squeezed out and direct contact between the components is more likely, can result in increased wear of the engine bearings, particularly in the main bearing. Bearings with resin overlays have been shown to display superior resistance to wear from such start-stop cycles. Moreover, cast iron shafts without quenching treatment have also been used in engines for cost reduction. Because the cast shaft has low hardness and unstable surface graphite after abrasive finishing, increase in the wear amount cannot be suppressed by conventional resin overlay in comparison with steel shaft. Therefore, the resin overlay with improved wear resistance achieved by adding hard particles was developed.

A low viscosity API SN 0W-16 engine oil was developed to achieve a 0.5% improvement in fuel efficiency over the current GF-5/API SN 0W-20 oil. Oil consumption and engine wear are the main roadblocks to the development of low viscosity engine oils. However, optimization of the base oil and additives successfully prevent oil consumption and wear. First, it was confirmed in engine tests that NOACK volatility is still an effective indicator of oil consumption even for a low viscosity grade like 0W-16. As a result of base oil volatility control, the newly developed oil achieves the same level of oil consumption as the current GF-5/API SN 0W-20 oil. Second, it was found that the base oil viscosity and molybdenum dithiocarbamate (MoDTC) had a significant effect on chain wear in rig testing that simulated silent chain wear. For the same base oil viscosity, the new oil maintains the same oil film thickness under high surface pressure.

With increased awareness of environmental issues and regulations, developments for recent automotive engines are progressing towards engines with low fuel consumption. Due to these changes, automotive engine bearings are increasingly used in harsher environments, with higher loading and corresponding wear. From this background, resin overlays, where solid lubricant is dispersed in a resin binder, are being developed. Resin overlays show excellent sliding properties under boundary lubrication conditions, and are known to have superior wear and fatigue resistance compared with conventional aluminium based bearings. However, while conventional resin overlay bearings display excellent sliding properties, they tend to have inferior seizure resistance compared to Al-Sn-Si alloy bearings. In this study, by optimizing the strength of the resin overlay layer with addition of calcium carbonate particles, a resin overlay with equal wear resistance but improved seizure resistance was developed.

Recently, automotive engines have been operating under harsh conditions of high-power, low viscosity oil and increase of start-stop (e.g. idling stop). In plain bearing used within engine, as oil film thickness decreases, the frequency of direct contacts on the sliding surfaces between the shaft and the bearing are gradually increasing. In fact, the plain bearings for engines would tend to be used under mixed lubrication and the contacts of the surface roughness asperities sometimes occur between the shaft and the bearing. As a result, the bearing wear on the sliding surfaces is accelerated by the contacts of the roughness asperities. In order to predict the bearing performance exactly, it is very important to understand the change progress of the geometric shape of sliding surfaces caused by the wear.

This paper describes the motor and inverter of Nissan's newly developed parallel hybrid system for rear-wheel-drive hybrid vehicles. The new system incorporates a high-power lithium-ion battery and a one-motor-two-clutch powertrain to achieve both highly responsive acceleration and better fuel economy. As the main components of the hybrid system, both the motor and the inverter have been developed and are manufactured in house to attain high power density for providing responsive acceleration, a quiet EV drive mode and improved fuel economy. Because the motor is located between the engine and the transmission, it had to be shortened to stay within the length allowed for the powertrain. The rotary position sensor and clutch actuator are located inside the rotor to meet the size requirement. High-density winding of square-shaped wire and a small power distribution busbar also contribute to the compact configuration.

Research is under way on an engine system [1] that achieves a variable compression ratio using a multiple-link mechanism between the crankshaft and pistons for the dual purpose of improving fuel economy and power output. At present, there is no database that allows direct judgment of the feasibility of the specific sliding parts in this mechanism. In this paper, the feasibility was examined by making a comparison with the sliding characteristics and material properties of conventional engine parts, for which databases exist, and using evaluation parameters based on mixed elasto-hydrodynamic (EHD) lubrication calculations. In addition, the innovations made to the mixed EHD calculation method used in this study to facilitate calculations under various lubrication conditions are also explained, including the treatment of surface roughness, wear progress and stiffness around the bearings.

The life of automotive transmission gears today is often governed by pitting fatigue life. Being able to predict pitting fatigue life accurately is a crucial issue. Pitting fatigue life is substantially influenced by surface hardness and tooth surface geometry. For that reason, this study examined a new method of predicting pitting fatigue life that takes into account changes in these factors over time. This method makes it possible to predict the pitting fatigue life of automotive transmission gears under a wide range of evaluation conditions with markedly better accuracy than conventional methods used previously.

In a previous study, we developed and validated a new driving posture focused on biomechanical loads for physical fatigue reduction in static long-term sitting. In this study, the posture was evaluated in dynamic long-term driving condition by qualitative and quantitative measurements. The results showed physical fatigue of the new posture was halved in comparison with the one of the conventional posture in same car by subjective evaluations. Physiological indices had same tendency with subjective evaluations. From the results, we extracted seven physiological indices as good measures of physical fatigue while driving. Therefore, fatigue reduction of the new posture was qualitatively validated by physiological measurements.

As the recent engines are designed for higher performance, piston pin bushing used for small end of connecting rod must endure higher dynamic load and oil temperature conditions. Therefore, the bushing is required higher wear resistance and anti-corrosion. And it is also expected to develop the bushing without lead due to environmental concerns. In this report, lead free copper based bushing alloy was studied. At first, in order to keep the anti-seizure property without lead, we studied the effects of hard particles added into copper based alloy. Second, we evaluated the effect of addition of hard particles on wear resistance and anti-corrosion.

Resin-based overlays as lead-free bearing materials for automobile engines are experimentally studied using tribology testing apparatus and an engine bench test rig. A resin overlay newly proposed is composed of Polybenzimidazole (PBI) as the base resin and solid lubricant Molybdenum disulfide (MoS2) as an additive. PBI has high temperature performance and good adhesion and physical strength under higher temperatures. Consequently, a PBI-based overlay has good sliding properties in terms of wear resistance and fatigue resistance. The resin overlay shows applicability to automobile engine bearings which are used under high loads.

Fatigue resulting from long-term driving can be classified into physical and mental fatigue. Physical fatigue seems to be mainly caused by driving posture. The purpose of this study is to develop a new driving posture for reduction of causal factors of physical fatigue, that is, biomechanical loads caused by the posture. In this paper, driving posture was optimized by subjective optimizations of seat contours and biomechanical analysis considering necessary conditions for driving operations and forward view. The new driving posture was tested by subjective evaluations and pelvic movement measurements. It was found that the new posture reduced physical fatigue dramatically.

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.

Recent engine bearings are operating under severe conditions to support such engine requirements as lower fuel consumption, longer life and protection of global environment. On Al-Sn-Si alloy bearings, it has some issue that fatigue may occur on the bearing alloy under severe condition such as in automotive diesel engines. Higher strength of alloy, which allows the fatigue resistance, can be obtained by solid solution treatment at higher temperature in general. But at the same time it makes intermetallic compounds with less bonding strength between intermediate layer and steel backing. A new bearing without lead has been developed by applying the heat treatment of bimetal and adequate intermediate layer for the process, consequently concluded to have the higher fatigue strength, with usual property on Al-Sn-Si alloy bearings.