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This paper describes method which experimentally reproduces the most prevalent bearing fatigue failure modes experienced in ball and roller bearing applications. Generally, bearing fatigue life is divided into two groups. One is a surface-originating type of fatigue. The other is a subsurface-originating type of fatigue. The mechanism of each type of fatigue has been studied. Bearing materials were developed for long-life based on the study of the mechanism of fatigue. However, the condition of the evaluation method, or life test, may be different from the actual application conditions. For instance, the subsurface-originating type of fatigue is tested under extremely heavy loads. The surface-originating type of fatigue is tested with severely contaminated lubrication. There is the possibility that the evaluation methods do not simulate the failure modes that are actually present in the field.

As for the polyamide (nylon) resins, i.e., nylon 6, nylon 66, nylon 46 and so on, when they are reinforced by glass fibers (GF), their static mechanical strength and heat distortion temperature increase considerably, and many faults of them are improved. However, when repeating stress is applied to a GF-reinforced nylon, the interface stress concentration between nylon and GF is easily to happen and so, depending upon working condition, the damage phenomenon similar to fatigue flaking is often observed for the GF-reinforced nylon by the reason of the insufficiency of interface strength between nylon and GF. In this study, thus, it mainly focused on the improvement of the fatigue property of GF-reinforced nylon. Actually, we compounded of nylon 66 and GF the fiber diameter of which was smaller than conventional GF, and investigated the mechanical and physical properties of the nylon 66 / GF composite we prepared.

This paper investigates and describes the fatigue mechanism in bearings for automotive alternators. We have analyzed the peculiar microstructure change found in these bearings. We have also investigated the effects of grease properties, vibration, and elastic deformation of the outer ring. By analyzing the bearings used in actual engine tests and grease tests for fundamental characteristics, we were able to conclude that the fatigue causes were two-fold: load amplification caused by resonance and high bending stresses caused by elastic deformation of the outer ring. As a practical result, we were able to adopt a newly formulated grease which decreased the vibration level and the peak rolling element load. This led to the development of longer life bearings for automotive alternators.

The belt-type continuous variable transmission (b-CVT) consists of a simple structure that transmits power by using a steel push belt in combination with a pulley. One important factor that leads to the deterioration of rolling bearing life is influence of additives in the special traction oil (CVT fluid). CVT fluid is mixed various additives to increase friction coefficient with the aim of maximizing sliding performance between the metal belt and pulley surface areas. In order to restrain heat generation due to friction driving between the metal belt and the pulleys, and to minimize churning resistance of the gears in the unit, viscous resistance of CVT fluid is designated at a lower class than that of gear lubrication oil used in manual transmissions. As a result, formation of an oil film is impeded throughout the bearing interior, creating harsher operating conditions that those found in conventional transmissions.

Bearings used in electrical engine-driven accessories, such as alternators and air conditioner (A/C) compressor pulleys, generate flaking related to non-metallic inclusions of unusual microstructure (white structure flaking), which occurs at one-tenth to one-twentieth of the calculated bearing life. In this paper, we will describe our investigation of the mechanism of white structure flaking, and report on how we achieved extended service life of engine-driven accessory bearings by implementing an evaluation of white structure flaking based on the discovered mechanism. We verified that the tribochemical reaction of grease, and statistic electricity generated by friction between the drive belt and pulley were the main culprits of white structure flaking. White structure flaking was further augmented by hydrogen invading the bearing steel, which further impaired bearing life.

Lubricant contamination is a frequent hazard to bearing life in automotive transmissions. The “Sealed Clean” bearing concept uses dynamic, rubber seals to exclude significant contamination from transmission bearings. However there is often insufficient space in a roller bearing application to accommodate seals. HTF steel specifications and processing were developed for such applications. Debris within a rotating bearing will create indentations in the raceway. Contact stress is concentrated at the indentation edges and fatigue damage is accelerated. A indentation's diameter and edge radius determine the stress concentration between the ball and raceway. The HTF steel specification and tightly controlled heat treatment processing have been developed to provide long life despite the contamination hazard. Testing confirms the effectiveness of the new material.

Regarding tapered roller bearings used on pinion shafts in differential gearboxes, it has been observed that some cases of bearing failure, like flaking or seizure, occurred much earlier than expected. As to the cause of this kind of failure, it has been clarified that on the shaft system supported by a pair of tapered roller bearings, the actual bearing load, including the preload of the bearings, fluctuates not only under the dynamic state but also under the static state because of the temperature distribution around the bearings. This fluctuation of the actual bearing load and preload greatly affects rolling fatigue life, seizure performance and the stiffness of the shaft support system. This paper discusses optimal design concepts for improving the rolling fatigue life, frictional torque, rigidity and seizure performance of a pair of tapered roller bearings. The design concepts are based on analysis results of the dynamic preload situation under actual operating conditions.