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Oil film thickness is one of the most important issues for optimization of bearing design. A technique has been developed to measure oil film thickness by noting the change in capacitance between the shaft and a thin-film electrode of several micrometers thickness formed on the surface of a bearing. The authors applied this technique to the main journals of an automobile engine and measured the oil film thickness up to maximum speed and full load. The oil film thickness became thinner with increased engine load, and then turned thicker with increased engine speed.

Fuel efficiency improvement measures are focusing on both cold and hot conditions to help reduce CO2 emissions. Recent technological trends for improving fuel economy such as hybrid vehicles (HVs), engine start and stop systems, and variable valve systems feature expanded use of low-temperature engine operation regions. Under cold conditions (oil temperature: approximately 30°C), fuel consumption is roughly 20% greater than under hot conditions (80°C). The main cause of the increased friction under cold conditions is increased oil viscosity. This research used the motoring slipping method to measure the effect of an improved crankshaft bearing, which accounts for a high proportion of friction under cold conditions. First, the effect of clearance was investigated. Although increasing the clearance helped to decrease friction due to the oil wedge effect, greater oil leakage reduced the oil film temperature increase generated by the friction.

Aluminum alloy bearing with overlay, which was developed for automotive engine bearing material, has both advantages of conventional aluminum bearing and copper-lead bearing with overlay. This new bearing consists of four(4) layers of tin overlay, nickel intermediate layer, aluminum alloy lining and back steel. This paper reports that seizure, fatigue and wear resistance are improved in order to prevent nickel exposure which may easily seize on the entire sliding surface from the interface structure between the overlay and aluminum alloy and maintain low tin-nickel compound creation which is prepared by the intermediate layer due to heat from the overlay plating bath; which is also examined.

Oil pump down sizing is one of the effective method to improve engine friction loss. Reducing the required amount of lubricating engine oil can be achieved by the application of a new crankshaft bearing with an eccentric oil groove. By adopting a bearing with an eccentric groove, we found the well balanced specification which can keep the necessary amount of oil to the crankshaft pin and reduce leaking oil from crankshaft main journal. Measuring oil amount distribution in engine running condition simultaneously and checking capability of eliminating contamination analytically have achieved.

High tin and aluminum alloy bearings can seize easily when used with nodular cast iron shafts. The authors have investigated the process of seizure between such nodular cast iron shafts and high tin and aluminum alloy bearings, and found that the seizures are normally caused by a combination of burrs around the graphite at the surface of the nodular cast iron shafts and abrasive aluminum debris adhering to the shaft. In an attempt to remove the burrs and abrasive aluminum debris, the authors dispersed hard particles in the alloy bearings. The new alloy used has a chemical composition of Al Si 3, Sn 10 and Pb 1.5 and, as a result bearings formed from it do not require a lead-based overlay. This arrangement provides much higher seizure resistance than overlayed copper and lead alloy bearings when used with nodular cast iron shafts. The bearings made with this alloy can be used in all engines with nodular cast iron shafts without any problems whatsoever.

Cu-Pb alloy bearings were collected from diesel engines actually operated in the United States and Japan, and a study was made of the damage to bearing overlays and linings. Results indicated exposure of compound layers produced by the diffusion of overlay components due to the complete removal of overlay from large segments of the bearing inner surface. There were many bearings in which the Pb had been last from the Cu-Pb alloy. Based on the above results, experiments were conducted in which a tester was used to recreate the damage conditions of the overlay and the lining. Then, based on observation and the results of regenerative tests, it was concluded that high temperatures and lubricating oil used over a long period had a great impact on damage.

With increased engine output and lower fuel consumption, the operating conditions for engine bearings are becoming more rigorous. With this trend, bearing damage caused by geometric defects in journals occurs. In this paper, the hourglass, barrel and double-barrel shaped journals have been investigated as representative defects in axial geometry. Employing calculations based on the hydrodynamic lubrication theory and experiment, the effects of these axial geometries on bearing performance have been investigated. It was found that the deterioration of precision of these journals invites reduction of oil film thickness and a rise in oil film pressure, and seriously affects seizure and fatigue resistance.

Engine friction reduction is an effective means to improve fuel consumption. Fluid friction reduction of main bearing is examined for engine friction reduction in cold condition. As one of the examinations, it was focused on low temperature of lubricating oil in the early stage during engine cold start. In hydrodynamic lubrication, the oil film temperature is maintained by balance between heat generation and heat transfer. The heat generation is generated by shear of lubricating oil. The factors of the heat transfer, the following elements are considered as follows, A) The heat transfer to a crank shaft, B) The heat transfer to a bearing, C) The heat transfer by convection. If the heat generation is constant, oil film temperature is increased by reduction of heat transfer. It is considered that the reduction of oil leakage and reduction of the heat transfer by convection is equivalent.

In recent years, engines equipped with idle reduction system for fuel saving have been increased in Europe and Japan. Because of the start-stop frequency increase, correspondingly crankshaft and engine bearing contacts also increase. The friction between shaft and bearing is significant to reduce fuel consumption, and besides it, engine bearing wear tends to increase. Therefore, lower friction with small wear engine bearings are expected. In this paper, new developed engine bearing with solid lubricant overlay and its frictional and wear properties are reported (1). As experimental result, a bearing with MoS2 solid lubricant contained polyamide-imide resin coated overlay proved 40% less coefficient of friction, 25% less starting torque and 65% less bearing wear against conventional aluminum alloy bimetal bearing without overlay under close to the start-stop lubrication conditions by testers. Also diesel engine bench test proved less FMEP.