Documents disponibles écrits par cet auteur

Optimization of groove geometry for thrust air bearing to maximize bearing stiffness / Hiromu Hashimoto in Transactions of the ASME . Journal of tribology, Vol. 130 n°3 (Juillet 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 130 n°3 (Juillet 2008) . - 11 p. Titre : Optimization of groove geometry for thrust air bearing to maximize bearing stiffness Type de document : texte imprimé Auteurs : Hiromu Hashimoto, Auteur ; Masayuki Ochiai, Auteur Année de publication : 2008 Article en page(s) : 11 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Bearings  Film  thickness  Geometry  Stiffness  Optimization  Design  Springs Résumé : Hydrodynamic gas film bearings are widely used for very-high-speed, lightly loaded rotating machinery. In the design of hydrodynamic gas film bearings, it is of cardinal importance to enhance the stiffness of gas films to minimize vibration due to external excitations. Among various types of hydrodynamic gas film thrust bearings, grooved bearings have an advantage of high stiffness and load-carrying capacity, but the stiffness of the bearings strongly depends on groove geometry. Therefore, when the groove geometry is suitably designed, it is expected to considerably improve the stability characteristics of the bearings. However, conventional bearing geometries are based on a fixed logarithmic spiral curve, and there is no literature on how to effectively change the groove geometry to drastically improve the bearing characteristics. In this paper, the entirely new optimum design methodology, in which the groove geometry can be flexibly changed by using the spline function, is presented to maximize the stiffness of gas films for grooved thrust bearings. The effectiveness of the methodology is experimentally verified. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleID=1468053 [article] Optimization of groove geometry for thrust air bearing to maximize bearing stiffness [texte imprimé] / Hiromu Hashimoto, Auteur ; Masayuki Ochiai, Auteur . - 2008 . - 11 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 130 n°3 (Juillet 2008) . - 11 p. Mots-clés : Bearings  Film  thickness  Geometry  Stiffness  Optimization  Design  Springs Résumé : Hydrodynamic gas film bearings are widely used for very-high-speed, lightly loaded rotating machinery. In the design of hydrodynamic gas film bearings, it is of cardinal importance to enhance the stiffness of gas films to minimize vibration due to external excitations. Among various types of hydrodynamic gas film thrust bearings, grooved bearings have an advantage of high stiffness and load-carrying capacity, but the stiffness of the bearings strongly depends on groove geometry. Therefore, when the groove geometry is suitably designed, it is expected to considerably improve the stability characteristics of the bearings. However, conventional bearing geometries are based on a fixed logarithmic spiral curve, and there is no literature on how to effectively change the groove geometry to drastically improve the bearing characteristics. In this paper, the entirely new optimum design methodology, in which the groove geometry can be flexibly changed by using the spline function, is presented to maximize the stiffness of gas films for grooved thrust bearings. The effectiveness of the methodology is experimentally verified. En ligne : http://tribology.asmedigitalcollection.asme.org/article.aspx?articleID=1468053

Robust optimum design of fluid dynamic bearing for hard disk drive spindle motors / Hiromu Hashimoto in Transactions of the ASME . Journal of tribology, Vol. 134 N° 04 (Octobre 2012) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 134 N° 04 (Octobre 2012) . - 11 p. Titre : Robust optimum design of fluid dynamic bearing for hard disk drive spindle motors Type de document : texte imprimé Auteurs : Hiromu Hashimoto, Auteur ; Masayuki Ochiai, Auteur ; Yuta Sunami, Auteur Année de publication : 2012 Article en page(s) : 11 p. Note générale : tribology Langues : Anglais (eng) Mots-clés : robust  optimum  design;  fluid  dynamic  bearings;  hard  disk  drives;  dimensional  tolerances;  spindle  motors Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : This paper describes the robust optimum design considering dimensional tolerances for fluid dynamic bearings (FDBs) of 2.5 in. hard disk drives (HDDs). Recently, 2.5 in. HDDs are widely used for mobile devices such as laptops, video cameras, and car navigation systems. Therefore, in mobile devices, high durability toward external vibrations is essential for high HDD performance. On the other hand, FDBs for HDD spindle motors are generally manufactured by mass production processes which will eventually require reduction of production costs. Consequently, the FDBs are demanded to be easily manufactured and expected to have an insensitive design with low variability of bearing characteristics due to manufacturing errors. In this paper, first, the vibration model of the spindle motor is constructed, and then the vibration experiment was carried out in order to verify the appropriateness of the vibration model. Second, the bearing characteristics are calculated considering dimensional tolerance using optimum design combined with the statistical method in which the dimensional tolerance is assumed to distribute according to the Gaussian distribution. The bearing characteristics are estimated by expectation and standard deviation. Finally, the results of this robust optimum design compared with ones of optimum design neglecting tolerance, and the validity of this technique, were clarified. It was found from the results that the tolerances of radial clearance and groove depth are important factors to be considered to reduce the variability of the amplitude and friction torque. In addition, the variability of the amplitude strongly depends on the groove depth. DEWEY : 621.5 ISSN : 0742-4787 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JOTRE9000134000004 [...] [article] Robust optimum design of fluid dynamic bearing for hard disk drive spindle motors [texte imprimé] / Hiromu Hashimoto, Auteur ; Masayuki Ochiai, Auteur ; Yuta Sunami, Auteur . - 2012 . - 11 p. tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 134 N° 04 (Octobre 2012) . - 11 p. Mots-clés : robust  optimum  design;  fluid  dynamic  bearings;  hard  disk  drives;  dimensional  tolerances;  spindle  motors Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : This paper describes the robust optimum design considering dimensional tolerances for fluid dynamic bearings (FDBs) of 2.5 in. hard disk drives (HDDs). Recently, 2.5 in. HDDs are widely used for mobile devices such as laptops, video cameras, and car navigation systems. Therefore, in mobile devices, high durability toward external vibrations is essential for high HDD performance. On the other hand, FDBs for HDD spindle motors are generally manufactured by mass production processes which will eventually require reduction of production costs. Consequently, the FDBs are demanded to be easily manufactured and expected to have an insensitive design with low variability of bearing characteristics due to manufacturing errors. In this paper, first, the vibration model of the spindle motor is constructed, and then the vibration experiment was carried out in order to verify the appropriateness of the vibration model. Second, the bearing characteristics are calculated considering dimensional tolerance using optimum design combined with the statistical method in which the dimensional tolerance is assumed to distribute according to the Gaussian distribution. The bearing characteristics are estimated by expectation and standard deviation. Finally, the results of this robust optimum design compared with ones of optimum design neglecting tolerance, and the validity of this technique, were clarified. It was found from the results that the tolerances of radial clearance and groove depth are important factors to be considered to reduce the variability of the amplitude and friction torque. In addition, the variability of the amplitude strongly depends on the groove depth. DEWEY : 621.5 ISSN : 0742-4787 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JOTRE9000134000004 [...]

Stabilization method for small-bore journal bearings utilizing starved lubrication / Hiromu Hashimoto in Transactions of the ASME . Journal of tribology, Vol. 132 N° 1 (Janvier 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 132 N° 1 (Janvier 2010) . - 07 p. Titre : Stabilization method for small-bore journal bearings utilizing starved lubrication Type de document : texte imprimé Auteurs : Hiromu Hashimoto, Auteur ; Masayuki Ochiai, Auteur Année de publication : 2010 Article en page(s) : 07 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Flow  control  Lubricating  oils  Lubrication  Machine  bearings  Mechanical  stability Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : This paper describes the stabilization method for small-bore circular journal bearings using starved lubrication. First, we describe the experimental examination to confirm the effect of supply oil conditions on stability of circular journal bearing by using a high-speed test rig. Then, the theoretical model considering the effect of amount of supply oil is discussed. Journal center trajectories are calculated by nonlinear motion analysis under various conditions. The theoretical results agree well with the experimental ones for three types of supply oil conditions and the mechanism of the stabilization by using the starved lubrication for small-bore journal bearings is clarified. Moreover, we suggest a supply oil control mechanism to stabilize the journal bearing using starved lubrication. Finally, the effectiveness of the proposed control mechanism on stability for high-speed small-bore journal bearings is verified experimentally. DEWEY : 621.5 ISSN : 0742-4787 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JOTRE900013 [...] [article] Stabilization method for small-bore journal bearings utilizing starved lubrication [texte imprimé] / Hiromu Hashimoto, Auteur ; Masayuki Ochiai, Auteur . - 2010 . - 07 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 132 N° 1 (Janvier 2010) . - 07 p. Mots-clés : Flow  control  Lubricating  oils  Lubrication  Machine  bearings  Mechanical  stability Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : This paper describes the stabilization method for small-bore circular journal bearings using starved lubrication. First, we describe the experimental examination to confirm the effect of supply oil conditions on stability of circular journal bearing by using a high-speed test rig. Then, the theoretical model considering the effect of amount of supply oil is discussed. Journal center trajectories are calculated by nonlinear motion analysis under various conditions. The theoretical results agree well with the experimental ones for three types of supply oil conditions and the mechanism of the stabilization by using the starved lubrication for small-bore journal bearings is clarified. Moreover, we suggest a supply oil control mechanism to stabilize the journal bearing using starved lubrication. Finally, the effectiveness of the proposed control mechanism on stability for high-speed small-bore journal bearings is verified experimentally. DEWEY : 621.5 ISSN : 0742-4787 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JOTRE900013 [...]

Theoretical modeling for microgrooved journal bearings under mixed lubrication / Katsuhiro Ashihara in Transactions of the ASME . Journal of tribology, Vol. 132 N° 4 (Octobre 2010) 

Public ISBD [article]  in Transactions of the ASME . Journal of tribology > Vol. 132 N° 4 (Octobre 2010) . - 16 p. Titre : Theoretical modeling for microgrooved journal bearings under mixed lubrication Type de document : texte imprimé Auteurs : Katsuhiro Ashihara, Auteur ; Hiromu Hashimoto, Auteur Année de publication : 2011 Article en page(s) : 16 p. Note générale : Tribology Langues : Anglais (eng) Mots-clés : Elastic  deformation  Friction  Lubrication  Machine  bearings Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : In designing of engine bearings for automobiles, we need to establish a mixed lubrication model that considers the solid-to-solid contact between journal surfaces and bearing surfaces with microgroove. However, as far as we know, there is no literature treating such problems. This paper describes theoretical modeling for microgrooved bearings under the mixed lubrication conditions with experimental verifications and prediction of performance in the actual engine bearings. In this modeling, a sectional shape of the microgrooved bearing was approximated to be a circular sectional shape. Contact pressure between the journal surfaces and the bearing surfaces with microgroove was calculated using the Hertzian contact model and the effects of elastic deformation of bearing surface due to hydrodynamic and contact pressures were considered. A numerical calculation model was developed to predict bearing performance under the mixed lubrication condition in microgrooved journal bearings. Oil film thickness distributions, hydrodynamic and contact pressure distributions, and real contact area between the journal surfaces and the bearing surfaces with microgroove were obtained simultaneously by the theoretical model. Moreover, friction coefficients under mixed lubrication conditions were determined by the theoretical model and the calculated results were compared with experimental results using test rig. The calculated results successfully agreed with the experimental results and the applicability of the model was verified. Moreover, the model was applied to predict the performance of engine bearings. In the numerical results, real contact area occurred relative widely under low-speed conditions when engine was started but friction loss was not excessive because of low shearing velocity. On the other hand, under high-speed engine conditions, the friction loss was large in spite of narrow real contact area because of high shearing velocity. Under both low-speed and high-speed conditions, the real contacts will occur severely at the edge of the bearing in the axial direction and at the bearing angles from 50 deg to 110 deg in circumferential direction. In addition, an appropriate design of the microgrooved bearing was examined under mixed lubrication conditions. In the design of the microgrooves, a cooling effect and an enough amount of oil flow to the contact area are needed. As the results from parametric studies using present theoretical model, an influence of the depth of the microgroove was the largest on the cooling effect and the enough amount of oil flow. In the case of typical operation condition, it was found that 1.0 µm of the groove depth was the most appropriate. DEWEY : 621.5 ISSN : 0742-4787 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JOTRE900013 [...] [article] Theoretical modeling for microgrooved journal bearings under mixed lubrication [texte imprimé] / Katsuhiro Ashihara, Auteur ; Hiromu Hashimoto, Auteur . - 2011 . - 16 p. Tribology Langues : Anglais (eng) in Transactions of the ASME . Journal of tribology > Vol. 132 N° 4 (Octobre 2010) . - 16 p. Mots-clés : Elastic  deformation  Friction  Lubrication  Machine  bearings Index. décimale : 621.5 Energie pneumatique. Machinerie et outils. Réfrigération Résumé : In designing of engine bearings for automobiles, we need to establish a mixed lubrication model that considers the solid-to-solid contact between journal surfaces and bearing surfaces with microgroove. However, as far as we know, there is no literature treating such problems. This paper describes theoretical modeling for microgrooved bearings under the mixed lubrication conditions with experimental verifications and prediction of performance in the actual engine bearings. In this modeling, a sectional shape of the microgrooved bearing was approximated to be a circular sectional shape. Contact pressure between the journal surfaces and the bearing surfaces with microgroove was calculated using the Hertzian contact model and the effects of elastic deformation of bearing surface due to hydrodynamic and contact pressures were considered. A numerical calculation model was developed to predict bearing performance under the mixed lubrication condition in microgrooved journal bearings. Oil film thickness distributions, hydrodynamic and contact pressure distributions, and real contact area between the journal surfaces and the bearing surfaces with microgroove were obtained simultaneously by the theoretical model. Moreover, friction coefficients under mixed lubrication conditions were determined by the theoretical model and the calculated results were compared with experimental results using test rig. The calculated results successfully agreed with the experimental results and the applicability of the model was verified. Moreover, the model was applied to predict the performance of engine bearings. In the numerical results, real contact area occurred relative widely under low-speed conditions when engine was started but friction loss was not excessive because of low shearing velocity. On the other hand, under high-speed engine conditions, the friction loss was large in spite of narrow real contact area because of high shearing velocity. Under both low-speed and high-speed conditions, the real contacts will occur severely at the edge of the bearing in the axial direction and at the bearing angles from 50 deg to 110 deg in circumferential direction. In addition, an appropriate design of the microgrooved bearing was examined under mixed lubrication conditions. In the design of the microgrooves, a cooling effect and an enough amount of oil flow to the contact area are needed. As the results from parametric studies using present theoretical model, an influence of the depth of the microgroove was the largest on the cooling effect and the enough amount of oil flow. In the case of typical operation condition, it was found that 1.0 µm of the groove depth was the most appropriate. DEWEY : 621.5 ISSN : 0742-4787 En ligne : http://scitation.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JOTRE900013 [...]