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A block-on-ring friction and wear testing machine (LFW-1) was used as a test method for making fundamental evaluations of the effect of the Belt-Drive Continuously Variable Transmission(B-CVT) fluid on the friction coefficient between the belt and pulleys. The results confirmed that this method can simulate the friction phenomena between the belt and pulleys of an actual transmission. The mechanism whereby ZDDP and some Ca detergents improve the torque capacity of a B-CVT was also investigated along with the effect of the deterioration of these additives on the friction coefficient. It was found that these additives form a film, 80-90 nm in thickness, on the sliding surface, which is effective in increasing the friction coefficient. The friction coefficient declined with increasing additive deterioration. The results of a 31P-NMR analysis indicated that the decline closely correlated with the amount of ZDDP in the B-CVT fluid.

Cold forging has been applied to form a component of the constant velocity joint. This part, slide joint housing, is made of JIS S48C (SAE 1048) high carbon steel. As it has been very difficult to form this part by cold forging, it has been formed by hot forging up until now. Success was obtained in forming this part by cold forging through improving the chemical composition of S48C high carbon steel and tool design, determining the optimum condition for heat treating the slug, and using a TiC coated punch. Since this slide joint housing, which is nearly net shape, was able to be formed through this cold forging technique, material saving was improved about 40% and machining time was reduced much in comparison with hot forging. Manufacturing cost can be greatly reduced through this cold forging which has been developed.

The demands on valve seat insert materials, in terms of providing greater wear-resistance at higher temperatures, enhanced machinability and using non-environmentally hazardous materials at a reasonably low cost have intensified in recent years. Due therefore to these strong demands in the market, research was made into the possibility of producing a new valve seat insert material. As a result a high speed steel based new improved material was developed, which satisfies the necessary required demands and the evaluation trials, using actual gasoline engine endurance tests, were found to be very successful.

Generally, cobalt-contained sintered materials have mainly been applied for exhaust valve seat inserts (VSI). However, there is a trend to restrict the use of cobalt as well as lead environmental law, and cobalt is expensive. To solve these problems, a new exhaust VSI on the assumption of being cobalt and lead free, applicable for conventional engines, having good machinability, and with a reduced cost was developed. The new exhaust VSI is a material dispersed with two types of hard particles, Fe-Cr-C and Fe-Mo-Si, in the matrix of an Fe-3.5mass%Mo at the ratio of 15 mass % and 10 mass % respectively.

Diesel engines have attracted more attention in recent years as one means of reducing carbon dioxide (CO2) emissions from motor vehicles. One of the major issues for diesel engines is exhaust emissions performance. Diesel engines also face various difficulties in providing the driving force demanded by the driver because of their greater inertia than that of gasoline engines. Meanwhile, continuously variable transmissions (CVTs) have been popularized as gearboxes that execute ratio changes continuously without generating shift shock. The aim of this research is to achieve higher levels of drivability and exhaust emissions performance by mating a CVT to a diesel engine and making maximum use of the continuous ratio change capability. An integrated engine-CVT control algorithm that can freely set the driving force and also the engine operating conditions for generating that driving force has been developed through this study.

The key-points in the diffusion bonding technique of green compacts during sintering, are the material compositions, which should be chosen according to their dimensional change during sintering, and the fitting clearance, which should be maintained in the range of press fit. Applying this technique, we have developed sinter-diffusion bonded idler sprockets for automotive engines by comfirming the bonding strength and torsional fatigue strength. And we also have developed a nondestructive analysis method for assuring the joint strength of idler sprockets in the mass production.

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.

A new belt-drive continuously variable Transmission (B-CVT) was introduced into the Japanese market in September 1997 by Nissan Motor Co., Ltd. It transmits a maximum torque of 196 Nm and represents a major breakthrough of the torque limit transmitted by B-CVTs, thus opening a new epoch for the automatic transmission. The major features of the CVT are transmission of high torque between a steel belt and pulleys, electronic control of high hydraulic-pressure to pulleys and a torque converter with an electronically controlled lockup clutch engaging at low vehicle speeds. A CVT fluid formulated for this CVT was designed to optimize these features and this paper describes the performance of the CVT fluid in lab-scale tests and an endurance test of the CVT unit. In order to realize high torque transmission between a steel belt and pulleys, high friction between metal/metal contacts is required with normal wear.

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.

Internal combustion engines experience severe valve train wear and the reduction of valve seat and seat insert wear has been a long-standing issue. In this work, worn valve seats and inserts were examined to obtain a fundamental understanding of the wear mechanisms and the results were applied in developing new valve seat insert materials. The new exhaust valve insert material for gasoline engines is a sintered alloy steel containing Co-base hard particles, with lead infiltrated only for inserts used in unleaded gasoline engines. The new intake valve insert material for gasoline engines is a high-Mo sintered steel, obtained through transient liquid phase sintering and with copper precipitated uniformly. This material can be used for both leaded and unleaded gasoline engines. Valve and valve seat insert wear has long been an issue of concern to engine designers and manufacturers.

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.

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.

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.

JIS SCM440M (SAE4140H), heat treated to the strength level of 120 to 140 kgf/mm2(171 to 199 ksi) -ISO 12.9 class-, is currently used for cylinder head bolts of Japanese passenger cars. Lower alloy steels, such as SAE 1541 for example, have not been substituted for JIS SCM440H so far because of their high susceptibility to delayed fracture. Daido Steel has tackled this problem and succeeded in applying the lower alloy SAE 1541 steel to 12.9 class cylinder head bolts by enhancing the resistance to delayed fracture by reducing impurities, especially sulphur. In this paper mechanical properties and delayed fracture characteristics of SAE 1541-ULS (Ultra Low Sulphur) steel are reported. 1541-ULS (S<0.005%, S+P< 0.020%) shows outstanding resistance to delayed fracture compared to conventional steel. Furthermore, the amount of MnS inclusions decreases remarkably in ULS steel, which results in high toughness.

We succeeded in developing a parallel hybrid electric vehicle (HEV) with a fuel efficiency in the 10-15 mode more than double that of existing vehicles of the same class of driving performance. A prominent feature of this HEV system is the belt-drive continuously variable transmission (CVT) with built-in traction motor and powder clutch. Adopting a more efficient configuration proved effective in minimizing cost increases and loss of space utility and offered the same reliability provided by existing vehicles. This paper discusses the functional design aspects of the parallel HEV system, which holds great promise for viable mass production.

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.

This paper describes the results of an investigation into the controllability of a traction-drive type half toroidal CVT, built with traction-drive elements. One feature of this CVT is that it provides better power transmission efficiency at its rolling contact points than other traction-drive CVTs developed previously. Another feature is that ratio changes can be effected with only a slight power input. A third feature is that it does not require any special hydraulic system to engage the contact points of rolling elements because it is designed to generate engaging force spontaneously in proportion to the torque input. The first half of the paper presents an analysis of the shifting mechanism. The characteristics of ratio changes effected by slight displacements of the power rollers were analyzed theoretically. A simplified CVT model was then examined experimentally and found to provide good response characteristics.

This paper presents a method for obtaining a large-capacity, high-efficiency continuously variable transmission (CVT). In designing a dual-cavity half toroidal CVT, it is essential to balance the load forces of each cavity. The axial position of the inner output disks has an important effect on the load forces. Several dual-cavity layouts designed to maintain the necessary balance are discussed, and an optimum layout is proposed that meets three required conditions. One is that the inner output disks should be supported by a wall separating the cavities. The second is that the outer input disks should have identical rotational phases. The third is that a single loading cam should produce all the contact forces. Tests of the proposed layout indicate that it provides good synchronization of all power rollers.

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.

Lock-up operation of an automatic transmission is known as one good method of improving fuel economy. However, locking up the transmission at low vehicle speeds can often cause undesirable vibration or booming noise. Slip control of the lock-up clutch can resolve these problems, but the speed difference of the lock-up clutch needs to be controlled at a certain value. This control system has to overcome large changes in the parameters of the lock-up system at low vehicle speeds and also changes with regard to the speed ratio in a continuously variable transmission (CVT). In this study, this complex non-linear system has been modeled as a first-order linear parameter varying (LPV) system. A robust control algorithm was applied taking various disturbances into account to design a new slip lock-up control system.