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Journal Article

Oil Flow Simulation Based on CFD for Reducing Agitation Torque of Ball Bearings

Agitation torque associated with oil lubricant is one important factor of torque loss in bearings under sufficient lubricating conditions. So far, efforts on reducing agitation torque were taken mostly by means of conventional experimental trials. Aiming for speedy, low-cost development, a calculation program for predicting the amount of agitation torque and oil distribution tendency in rolling bearings has been developed using computational fluid dynamics (CFD) analysis. At first, since rolling bearings are axially symmetric, sector models of bearings were adopted. To verify the method, torque losses and oil quantities in ordinary-sized bearings have been measured. Calculated values based on sector models are qualitatively in good agreement with measured results. The difference between the absolute values of measured and calculated torque may be caused by the difference between the vertical model used in CFD analysis and the horizontal torque-testing rig used in measurement.
Technical Paper

Research Work for the Improvement of the Durability of Glass Fiber-Reinforced Nylon 66 by Modifying the Glass Fiber Diameter

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.
Technical Paper

A New Method for Studying Surface-Initiated Bearing Failure

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.
Technical Paper

Research Work for Clarifying the Mechanism of White Structure Flaking and Extending the Life of Bearings

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.
Technical Paper

Development of Long Life Pulley-Supporting Bearing for Belt-CVT

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.
Technical Paper

Optimum Strength Design of Hub Bearings for the Full Float Rear Wheel (Dual-Wheel)

Bearing load for full float rear wheel has been determined by simple geometric calculation. In order to achieve an optimum strength design, we measured bearing load while a vehicle was running and compared it to the calculated one. As a result of the comparison, several differences were found between collected data and calculated values. We quantitatively investigated items that cause the differences. Considering those causes, we developed a simple way to estimate the bearing load and a design procedure for optimum bearing design.
Technical Paper

Development of a New Life Equation for Ball and Roller Bearings

The conventional rolling bearing life equation (1), which is based on the theory of Lundberg and Palmgren, has a problem in that it does not match the actual bearing life in all operating conditions. For instance, while the actual life of a bearing under clean lubrication is 20 times longer than the calculated life, actual life under contaminated lubrication is as low as one-tenth of the calculated life. To solve this problem, the following life equation (Eq. 1: Advanced Bearing Life Equation) was developed with the aNSK life modification factor: The new aNSK factor is based on data from bearing life aNSK tests involving over 450 roller bearings and over 550 ball bearings under a variety of operating conditions. The new life equation with the aNSK factor showed a satisfactory fit between calculated life and actual life.
Technical Paper

Analysis of Fluctuations in Bearing Preload and Optimal Design of Tapered Roller Bearings for Pinion Shaft Support in Differential Gearboxes

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.
Technical Paper

Multi-Disc Viscous Auto-Tensioner for Timing Belts

This paper describes the construction, characteristics and capabilities of a compact automatic tensioner for timing belts that was recently developed by NSK. This auto-tensioner differs from conventional ones having separate actuators. By incorporating the damping mechanism inside the bearing, a compact size nearly equal to that of fixed type tensioners was achieved. The damper is a multi-disc viscous type that uses high viscosity silicone oil.
Technical Paper

A Finite Element Method Analysis of Heavy Duty Axle Bearing Loads

Pinion bearing loads of a heavy duty rear truck axle were determined by Finite Element Method Analysis (FEM). The results were compared with measured loads. This report describes the method used to measure bearing loads, the FEM model used, and the comparison of the results.
Technical Paper

Rolling Bearing Analysis Codes “BRAIN” - The Estimation of Rolling Bearing Performance for an Automotive Application

A computer program package named “BRAIN” has been developed to simulate the kinematics and the performance of rolling bearings under various running conditions. The calculation time necessary for running BRAIN software on a PC is very short. Various outputs can be obtained using BRAIN such as running torque, roller skew angle, roller slippage, and PV values. Several experiments have been conducted to confirm the validity of BRAIN. The running torque of a four point contact ball bearing and that of a tapered roller bearing were measured. In addition, the skew of the roller in a needle bearing was measured. These experimental results were compared with the calculation results. The experiments and the calculations showed good agreement.
Technical Paper

Fighting Debris: Increasing Life with HTF Bearings for Transmissions

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.
Technical Paper

Long Life Bearings for Automotive Alternator Applications

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.