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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.

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.

Wireless Power Transfer (WPT) promises automated and highly efficient charging of electric and plug-in-hybrid vehicles. As commercial development proceeds forward, the technical challenges of efficiency, interoperability, interference and safety are a primary focus for this industry. The SAE Vehicle Wireless Power and Alignment Taskforce published the Recommended Practice J2954 to help harmonize the first phase of high-power WPT technology development. SAE J2954 uses a performance-based approach to standardizing WPT by specifying ground and vehicle assembly coils to be used in a test stand (per Z-class) to validate performance, interoperability and safety. The main goal of this SAE J2954 bench testing campaign was to prove interoperability between WPT systems utilizing different coil magnetic topologies. This type of testing had not been done before on such a scale with real automaker and supplier systems.

A CVT variator chain system is superior in transmission efficiency to a belt system because of its lower internal friction. However, a chain produces more noise than a belt due to the long pitch length of contact between the pulleys and rocker pins. This study focuses on optimization of the pitch sequence for reducing chain noise. The previous pitch sequence was suitably combined of links of different lengths to improve noise dispersibility for reducing chain noise. First, the object function was defined as the reduction of the peak level of 1st-order chain noise combined with a well-balanced the levels on the low and high frequency sides. Interior background noise consisting of road noise and wind noise have the characteristic that they increase as the frequency decreases.

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.

The new Jatco CVT8 High Torque (CVT8 HT) was developed for use on front-wheel-drive vehicles fitted with a large displacement engine. The development objectives set for this new CVT with a high torque capacity were outstanding fuel economy, size and weight reductions. To achieve those targets, a high torque capacity CVT chain was newly developed in cooperation with LuK GmbH & Co. KG. This article describes the efforts undertaken to develop increasing torque capacity.

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.

This study examined methods of machining a microsurface texture on the surface of the rolling elements of a toroidal continuously variable transmission (CVT) for improving the traction coefficient. The microsurface texture of the toroidal surfaces consists of tiny circumferential grooves (referred to here as micro grooves) and a mirror-like surface finish similar to the rolling surface of bearings. Hard turning with a cubic boron nitride (cBN) cutting tool, grinding with a cBN wheel and micro forming were applied to machine the micro grooves. The results made clear the practical potential of each method. A micro forming device was also developed for use in actual production. A mirror-like surface finish and micro crowning of the convex portions of the microsurface texture were simultaneously executed by superfinishing them with a fine-grained elastic superfinishing stone.

Building a toroidal continuously variable transmission (CVT) with multiple power rollers arranged in parallel is an effective way to improve its torque capacity. However, that requires a method for synchronizing the operation of all of the power rollers. This paper describes a method of synchronizing the four power rollers in a toroidal CVT that we have researched and developed. It also presents the results of an analysis of the cause of power roller vibration, which was a serious issue encountered in the development process, and describes an effective method for preventing it. The methods described here achieve sufficient synchronization performance for practical use of the toroidal CVT on production vehicles.

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.

In Europe and the U.S., fracture split connecting rods are used in many types of current engines. This process can eliminate the machining of crankshaft end and eliminate the dowel pin for positioning. The most important key for fracture split connecting rods is a reduction in the plastic deformation during the fracture splitting process. For this reason, sinter-forged materials and pearlitic steels (C70S6) are used for fracture split connecting rods because of their low ductility. Such types of steel, however, are inferior to the hot forged microalloyed steels typically used as connecting rod material in Japan in terms of buckling strength and machinability although they are easier to fracture split. On the other hand, the conventional microalloyed steels used for connecting rods in Japan are not suitable for fracture splitting. The reason is that these steels have too much ductility and associated plastic deformation for fracture splitting.

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.

This paper describes the improvement made to the high rigidity power-roller support structure in a dual-cavity half-toroidal CVT to further increase torque capacity. As a result of re-analyzing the function and parts composition of the previous structure, a high rigidity power-roller support structure, which permits power roller movement only in the horizontal direction, has been adopted. This structure enables the thrust and radial stiffness of the power-roller support to be substantially improved over the previous structure.

This paper describes a newly developed steel composition and surface modification methods for improving the rolling contact fatigue strength of parts used in transmission systems, especially continuously variable transmissions (CVTs) to increase their torque capacity. The mechanisms of two types of typical rolling contact fatigue phenomenon in case hardening steel were examined with the aim of improving rolling contact fatigue strength. One concerned white etching constituents (WEC) and the other one concerned peculiar microstructural changes caused by hydrogen originating from decomposition of the lubrication oil as a result of repeated rolling contact stress cycles. The rolling contact fatigue strength limit due to WEC has been improved markedly by dispersing fine M23C6 alloy carbides in the martensite matrix at the subsurface layer of parts.