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The mechanical loss reduction of the bearing reduces the fuel consumption of the engine, which can help realize a sustainable society. Thus, a bearing friction reduction technique has been studied. There have been many studies related to friction-reduction techniques for mixing and boundary lubrication. However, there are few studies on hydrodynamic lubrication, and the main methods have been related to changing the low-viscosity oil and bearing size. In driving passenger cars in urban areas, the lubricant condition of the engine bearings is largely dependent on hydrodynamic lubrication. Therefore, the power loss under this operating condition cannot be ignored. In this study, the reduction of the friction loss under hydrodynamic lubrication was focused. A method for reducing the shear resistance of oil was examined and its effect was confirmed through experiments and calculations.

Recent automotive engine developments have made great progress in protecting the global environment and in meeting exhaust gas regulations and fuel economy regulations. As a result, engine bearings tend to be used under severe conditions such as higher specific load onto the bearings and with low viscosity of lubricating oil. Aluminum alloy bearings are widely adopted as main bearings and connecting rod bearings in gasoline and diesel engines for passenger cars, and generally Al-Sn-Si alloy bearings without an additional overlay are used. Although these Al-Sn-Si alloy bearings have good anti-seizure properties and excellent running-in-properties, their material strength under high temperature conditions is not sufficient because of the low melting point of Sn phase contained in the alloy, and they could potentially result in damage to the bearing as seizure and fatigue under these conditions. In such cases, Cu-Pb-Sn alloy bearings with lead-based overlay are usually applied.

The number of vehicles with engines using idling stop systems and hybrid systems to improve fuel consumption has recently been increasing. With idling stop systems the engine is switched off when waiting at city traffic lights or stopping on the road, suppressing the fuel usage which leads to improved fuel consumption. 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 to occur, can result in increased wear of the engine bearings. As a countermeasure, recent engine bearings can have thin coatings based on polymeric resin material (polymer overlays) applied to the bearing surface, which are known to have good bearing properties such as wear resistance and low friction characteristics.

In order to determine the seizure limit of the main bearings of passenger vehicles under actual operating conditions, evaluations were conducted in environments containing noise factors (Various factors which designer cannot adjust and which make function vary were defined as noise factors in this paper.) [1,2] It was shown that noise factors have an effect on seizure limit performance in relation to performance under ideal test conditions (test conditions in which no noise is present). In relation to oil properties, the results showed that a reduction in viscosity as a result of dilution affected seizure limit performance. In relation to the shape of the sliding sections of the test shaft, seizure limit performance declined in a shaft in which the central section was swollen (“convex shaft” below).

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. These operating conditions require bearings with both conformability and fatigue resistance. From the above background, various aluminum alloy bearings have previously been developed, including materials with solid solution treatment to improve their properties, and alloys which can be used with or without an overlay [1, 2, 3]. These materials are known to have good conformability and fatigue resistance. However, while conventional Al-Sn-Si alloy bearings display excellent sliding properties, due to the unceasing trend for engine downsizing, more conformability is required.

Foreign particles remaining in an engine cause bearing trouble on rare occasions. It is required to promptly and effectively discharge foreign particles from the bearing clearance space to improve reliability of the engine. In this paper, the bearing configuration of at the parting line between upper and lower bearings which are capable of discharging foreign particles are experimentally studied. Tests were conducted for fundamental visualization of oil flow and particles. As a result, the behavior of the particles in the bearing clearance space and the effects of the bearing configurations were well demonstrated. In the bench test using an actual engine, the bearing configuration with grooves at the parting line of the bearing demonstrated the effectiveness to prevent bearing damage caused by foreign particles. The influence of the bearing configurations on oil flow rate was confirmed not to increase the flow rate.