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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.

Properties of engine bearings were investigated with different bearing materials and different HTHS viscosity oils by means of both an engine test and a rig test. The rig test well simulated the bearing wear which occurred in the engine test. Lead-bronze bearings with lead-tin-indium overlay gave the least amount of wear in operating under high speed and heavy load conditions even with low HTHS viscosity oil. Aluminum bearings without overlay gave good wear resistance in the case of no seizure occurrence. The wear amount of bearings were well correlated with HTHS viscosity, not with kinematic viscosity.

Heavily-loaded engine bearings in recent years have frequently utilized aluminum-tin-silicon alloy which does not require overlay. It has been found that some special fatigue damage may occur in these aluminum alloys under certain heavy-load application. A microscopic examination of such fatigue revealed a structural change inside the aluminum alloy. In this paper such fatigue phenomenon was studied in detail and reproduction tests were carried out on the bearing test machines. As a result, we have developed a new high-strength aluminum alloy which can prevent such fatigue damage.

The recent trend toward the compact and light-weight construction of automotive engines with high power output has been imposing higher requirements of fatigue strength, anti-seizure property and conformability on bearings. In order to meet these requirements, the authors analyzed the property of each layer of multi-layer Al-Si-Sn bearings and investigated its influence on bearing performance. Improvement was achieved as to the bearing alloy and the intermediate bonding layer based on the results of the investigation. As a result, this newly improved bearing has been concluded to provide better fatigue strength than conventional bearings. It has thus become possible to apply it as a bearing for the recent engines used under harsh conditions.

A sintered aluminum-lead alloy of the bimetal type was manufactured in Japan (1977), and has been widely used in main and crankpin bearings for automobile engines. However, the recent trend of automobile engines toward high power output, light-weight and compact construction increases the bearing load. As a result, the margin of fatigue strength of the conventional sintered aluminum-lead alloy has been diminishing. In this paper, a new method of manufacturing bearing material by the hot extrusion process is reported. The new method makes it possible to produce the optimum lead grain distribution and strong adhesion between powder particles. The new manufacturing method produces the aluminum-lead bearing material which has 30% or more increase in fatigue strength over the conventional sintered aluminum-lead bearing material.

The diffusion phenomena of tin and indium which are contained in the lead-base overlay of 3-layer copper-lead alloy bearings were studied. Easier diffusion of tin compared with indium decreases the corrosion resistance of the overlay, and the tin reacts with the underlayer to form brittle Ni-Sn or Cu-Sn intermetallic compound, resulting in weak bonding strength. Addition of copper into Pb-In overlay markedly restrains the diffusion of indium and therefore stabilizes the characteristics of corrosion resistance, bonding strength and mechanical properties for a long period. Cavitation tests, seizure tests and bearing fatigue tests were conducted on Pb-In-Cu overlay to study the feasibility of its application to actual engine bearings.

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.

The recent trend toward the compact and light-weight construction of diesel engines with high power output has been imposing higher requirements of fatigue strength and antiseizure characteristics on bearings. In order to meet these requirements, the authors developed a new bearing alloy of higher fatigue strength for use in heavy load engines, through the analysis of the Al-Zn-Si alloy which has high corrosion resistance. Experimental results of this new alloy to study its physical properties and bearing performances indicate that it can be applied to bearings in diesel engines which operate in harsh conditions.

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.

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.

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.

Recently, there has been a tendency of high power and high speed in automotive engines. In addition they have been also required high reliability. And engine bearings have been required to be advanced in wear resistance as well as seizure resistance. Therefore, copper-lead alloy bearings with overlay, which have better seizure resistance, have been widely used for high speed engines up to the present. But it becomes very important for them to advance the overlay wear resistance. In this paper, the composite overlay is mainly researched to improve wear resistance regarding kind of hard particles and their amounts in the overlay.

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.

The possibility of predicting engine bearing durability by elastohydrodynamic lubrication (EHL) calculations was investigated with the aim of being able to improve durability efficiently without conducting numerous confirmation tests. This study focused on the connecting rod big-end bearing of an automotive engine. The mechanisms of wear and fatigue, which determine bearing durability, were estimated by comparing the results of EHL analysis and experimental data. This comparison showed the possibility of predicting the wear amount and the occurrence of fatigue by calculation.

The advent of high-performance, compact, and lightweight engines in recent years brings forth a tendency to increase the load for engine bearings and demands on producing even higher levels of durability and reliability in bearing products against fatigue, seizure, wear, and corrosion. Based on the perspective of extending the bearing life, the authors have studied the problems that are encountered with the current three layer copper-lead alloy bearings after their overlay has worn out. Then, we studied the issues of lowered seizure resistance that results from the exposure of the nickel barrier, and of deficient corrosion resistance that results from the exposure of the bearing alloy. In order to improve upon these areas, we focused on diffusion phenomenon of overlay elements without the nickel barrier and also studied the feasibility of creating engine bearings whose alloy composition has been partially modified.

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.

Engine bearings today are operating under very harsh conditions. Consequently, a wear propagates for a short time and a fatigue sometimes occurs on the bearings. In present study, on the rig test machine, the operating conditions of engine bearing were simulated to reproduce the bearing damage. The bearing wear was measured until the fatigue crack occurred. The bearing wear increased at the edges of the bearing length and the crack also was observed near the edges. The experimental results were compared to the calculated results based on the elastohydrodynamic lubrication (EHL) theory. The correlations between the bearing damage and the bearing performances by the theoretical analysis were investigated.