Oil film behavior under minute vibrating conditions in EHL point contacts

Maruyama, Taisuke; Saitoh, Tohru

doi:10.1016/j.triboint.2009.11.004

Cited by 26 publications

(23 citation statements)

References 11 publications

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“…Various methods have been proposed for the above objectives (8). Especially, optical interferometry has been used as accurate methods for measuring the oil film thickness in EHD contacts (9)(10)(11)(12)(13)(14)(15)(16)(17). For example, Johnston et al (10) showed that the thickness of molecularly thin films (i.e., several nanometers) could be measured by applying a silica spacer layer on a glass disc.…”

Section: Introductionmentioning

confidence: 99%

In Situ Quantification of Oil Film Formation and Breakdown in EHD Contacts

Maruyama¹,

Nakano

2018

Tribology Transactions

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A measurement method using electrical impedance has been developed for simultaneous quantifications of the thickness (h) and breakdown ratio (a) of oil films in elastohydrodynamic (EHD) contacts. First, based on simplified geometrical and electrical models of EHD contacts, theoretical expressions of h and a were derived as explicit functions of the measured electrical impedance by using the Lambert function. Then, to verify the proposed measurement principle, oil film thickness measurements were conducted by using the electrical method together with the optical interferometry method in a ball-on-disc-type apparatus, which utilized the lubricated contact between a steel ball and a glass disc with a transparent conductive layer (i.e., an indium tin oxide layer). As a result, it was confirmed that the measured h-values obtained by the electrical method agreed well with those obtained by the optical method, under various test conditions with changing the entrainment speed, slide-to-roll ratio, normal load, and viscosity. Besides, it was also confirmed that the measured a-values obtained by the electrical method showed consistent correlations with the film parameter and the friction coefficient. It is hoped that the developed electrical method will be applied to practical metal-to-metal contacts (e.g., the contacts in practical ball bearings) to understand invisible behaviors of oil films in EHD contacts.

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Section: Introductionmentioning

confidence: 99%

In Situ Quantification of Oil Film Formation and Breakdown in EHD Contacts

Maruyama¹,

Nakano

2018

Tribology Transactions

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“…With small oscillation amplitudes (x/2b < 1.5), mixed friction prevails in the contact. 34 The most common wear phenomena under oscillating movements are false brinelling and fretting corrosion. False brinelling was mentioned in the literature as early as 1937.…”

Section: Wearmentioning

confidence: 99%

“…Maruyama et al investigated the effect of oils and greases in oscillating applications with the aid of model experiments. 34,44,45 The experiments showed that the frequency had The number of oscillation cycles has a significant effect on the extent of the wear. The greater the number of oscillation cycles that occur, the higher the probability that wear sets in.…”

Section: Effect Of the Wind Turbine Controllermentioning

confidence: 99%

Effect of load reduction mechanisms on loads and blade bearing movements of wind turbines

et al. 2019

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The power control of wind turbines is usually realized via a change in the pitch angle of the rotor blades. Pitching facilitates the exact control of the turbines and the reliable deceleration of the rotor when required. Pitch movements can moreover be used for load control. One of these methods is called individual pitch control (IPC). IPC controls the blades individually and brings about a significant reduction in the fatigue loads and extreme loads placed on the structural components, while at the same time reducing the yield of the turbine only slightly. The lower loads reduce material costs, and thus, the cost of energy (CoE) is reduced, despite the slight reduction in yield. The method is nevertheless not used everywhere since the additional movement cycles put the rotor blade bearings in particular under stress. Special attention must be paid to small amplitude oscillating movements, which carry a high risk of inducing surface damage in the rolling contacts of the blade bearings. This paper uses a cycle analysis of the IWT7.5-164 reference turbine to illustrate the differences in the movement patterns of wind turbine blade bearings with and without IPC. Moreover, model calculations with single contacts are used to show which of the movement patterns carries a risk of inducing surface damage. The use of IPC leads to the expected load reduction at the blade root. In current literature, IPC is usually assumed to have a negative influence on the life expectancy of blade bearings, but the findings of this study contradict this. The summed blade bearing movement is increased, although the number of very small pitch angles occurring is reduced. This reduction reduces the risk of wear in the blade bearings.

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“…There have been various studies conducted on conventional methods of monitoring lubrication conditions in EHD contacts [6]. Optical interferometry [7][8][9][10][11][12][13][14] is widely used as it is well suited for measuring the oil film thickness in EHD contacts with high accuracy. Johnston et al [7] developed the optical method which measured molecularly thin films (i.e., several nm) with high accuracy by applying a SiO 2 spacer layer on a glass disc.…”

Section: Introductionmentioning

confidence: 99%

“…Johnston et al [7] developed the optical method which measured molecularly thin films (i.e., several nm) with high accuracy by applying a SiO 2 spacer layer on a glass disc. The optical method also allows for detailed understanding of oil film distribution in EHD contacts; thus, it has been applied to measure the oil film thickness under non-steady states [8][9][10][11], abnormal film shapes [12,13], or temporal change in the thickness of adsorbed films [14]. However, the material must transmit light for the optical method to work, which means that lubrication conditions of practical bearings cannot be visualized.…”

Section: Introductionmentioning

confidence: 99%

Lubrication Condition Monitoring of Practical Ball Bearings by Electrical Impedance Method

2019

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In this study, the electrical impedance method was developed to monitor the thickness and breakdown ratio of oil films in elliptical elastohydrodynamic (EHD) contacts of practical ball bearings. First, it is theoretically shown that the oil film thickness and breakdown ratio can be simultaneously measured from the complex impedance generated when a sinusoidal voltage is applied to elliptical contacts. Subsequently, lubrication conditions of practical ball bearings were monitored at an ambient temperature to verify the measurement accuracy of the developed method. The oil film thickness in the low-speed range was consistent with the theoretical value calculated by Hamrock-Dowson equation. However, in the high-speed range, the oil film was thinner than the theoretical value considered an ambient temperature. In this high-speed range, the results of both the outer ring temperature and bearing torque revealed that the viscous shear heating and starvation were occurring simultaneously, thus supporting that the measured thickness would be thinner than the theoretical value. Besides, the developed method can also measure the breakdown ratio, confirming that it increases in the lowspeed range where the bearing torque increases. That is, it indicates that not only the oil film thickness but also the breakdown ratio can be evaluated quantitatively.

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Oil film behavior under minute vibrating conditions in EHL point contacts

Cited by 26 publications

References 11 publications

In Situ Quantification of Oil Film Formation and Breakdown in EHD Contacts

In Situ Quantification of Oil Film Formation and Breakdown in EHD Contacts

Effect of load reduction mechanisms on loads and blade bearing movements of wind turbines

Lubrication Condition Monitoring of Practical Ball Bearings by Electrical Impedance Method

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