This paper investigates the windage power loss generated by helical gears rotating in pure air. A... more This paper investigates the windage power loss generated by helical gears rotating in pure air. A three-dimensional approach using computational fluid dynamics (CFD) code which has been validated for spur gear is adapted here in order to consider helix angle. The numerical approach is at first validated with the power losses measured in similar conditions. The influence of both width and helix angle values on the expelled volumetric flow rate and the windage losses are studied. Considering these observations, a correlation which is based on a classical approach used in turbomachinery is proposed.
A thermo-mechanical model of a splash lubricated one-stage gear unit is presented. This system co... more A thermo-mechanical model of a splash lubricated one-stage gear unit is presented. This system corresponds to a first step towards the design of a hybrid vehicle gearbox which can operate up to 40,000 rpm on its primary shaft. The numerical model is based on the thermal network method and takes into account power losses due to tooth friction, rolling elements bearings and oil churning. Some calculations underline that oil churning causes a high amount of power loss. A simple method to reduce this source of power losses is presented, and its influence on the gear unit efficiency and its thermal capacity is quantified.
ABSTRACT The purpose of this study is to investigate the various fluid flow regimes generated by ... more ABSTRACT The purpose of this study is to investigate the various fluid flow regimes generated by a pinion running partly immersed in an oil bath and the corresponding churning power losses. In a series of papers, the authors have established several loss formulae whose validity depends on two different flow regimes characterized via a critical Reynolds number. Based on some new measurements for transient operating conditions, it has been found that the separation in two regimes may be not accurate enough for wide-faced gears and high temperatures. An extended formulation is therefore proposed which, apart from viscous forces, introduces the influence of centrifugal effects. The corresponding results agree well with the experimental measurements from a number of gears and operating conditions (speed, temperature). Finally, the link between churning and windage losses is examined and it is concluded that the physical mechanisms are different thus making it difficult to establish a general correlation between the two phenomena. In particular, it is shown that tooth geometry is of secondary importance on churning whereas, the air-lubricant circulation being different for spur and helical gears, it substantially impacts windage.
Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, Jan 29, 2013
An original formulation for tooth friction power losses in internal gears including the influence... more An original formulation for tooth friction power losses in internal gears including the influence of tooth profile modifications is presented. For unmodified gears, the results agree well with the classic formulae in the literature thus validating the proposed approach. The contributions of profile modifications on internal gear efficiency are compared to that on external gears and the formulation is extended to planetary gears. Finally, the role of profile relief on planetary gear efficiency is pointed out and commented upon.
Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, Mar 19, 2014
The aim of this study is to develop a thermal modeling of a grease lubricated rolling bearing in ... more The aim of this study is to develop a thermal modeling of a grease lubricated rolling bearing in order to analyze the heat evacuated through its solid parts and the lubricant. The system under consideration in this study is a clutch thrust bearing and more precisely a sealed single row angular contact ball bearing. To analyze heat transfer inside the bearing, two models have been developed using the thermal network method. These models have been compared to measurements performed on a specific test rig. As some heat transfers appear to be negligible, in the end a simplified model is proposed.
In order to use electric motors which run up to 40,000 rpm in future automotive applications, thi... more In order to use electric motors which run up to 40,000 rpm in future automotive applications, this study aims to experimentally investigate if splash lubrication technique is worth considering for high-speed gears, i.e., for tangential gear speed up to 60 m/s. To this end, a specific test rig has been used to operate a single spur or helical gear in various operating conditions (lubricant, oil sump volume, temperature, etc.). Churning loss is measured and, as the fraction of air in the lubricant (namely, oil aeration) can be influential on this source of dissipation, a specific sensor is also employed for online monitoring of oil sump aeration. By inserting some moveable walls in the gearbox, it is demonstrated that churning losses and oil aeration can be significantly reduced by mounting these flanges at an appropriate distance to the gear lateral faces. Based on dimensional analysis, an engineering criterion is proposed to properly choose the clearance between the tested gear and the flanges.
Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, Jan 16, 2009
It is generally accepted that the total power loss in gears can be decomposed into contributions ... more It is generally accepted that the total power loss in gears can be decomposed into contributions of friction between the teeth, lubrication (churning and/or jet lubrication that could induce gas—oil trapping in inter-tooth spaces), and gear windage effects. For low- to medium-speed transmissions, tooth friction is recognized as the main source of dissipation for gears and can significantly influence the temperature equilibrium of a gearbox. In this article, a model to predict power losses due to tooth friction combined with a thermal network to describe the temperature distribution in a geared transmission are presented. The numerical results compare favourably with experimental measurements from a gear test rig.
Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, Jan 16, 2012
A thermal model of a back-to-back gear test rig relying on a network approach is presented in whi... more A thermal model of a back-to-back gear test rig relying on a network approach is presented in which the predictions of temperatures and power losses are coupled. The numerical findings are in good agreement with the measurements for transient regimes on a FZG test rig and it is demonstrated that the proposed simulation is reliable. A number of results are presented which illustrate the influence of the pinion and gear immersion depths. It is found that, in certain conditions, the classic isothermal method for estimating integral temperatures is questionable because the actual bulk temperature can substantially deviate from that of the oil sump. The practical consequences in terms of scuffing capacity are emphasised.
HAL (Le Centre pour la Communication Scientifique Directe), May 17, 2015
Scuffing is defined in the literature as "gross damage characterized by the formation of local we... more Scuffing is defined in the literature as "gross damage characterized by the formation of local welds between the sliding surfaces" [1]. This localized damage suddenly appears when the frictional heat generated at the contact induces a critical temperature increase. Numerous studies were conducted in order to establish a scuffing criterion. Some of them focus on the power dissipation inside the contact (product of the sliding speed and the load) [2] some others compare the minimum film thickness of lubricant separating the surfaces to the surface roughness [3,4]. In 1937 Blok introduced a thermal scuffing criterion [5]: each combination of base-stock lubricant and material has a characteristic scuffing temperature. The present study proposes a thermal model based on correlations between experimental tests performed on a twin-disc machine and numerical studies using the thermal network methodology in order to better understand scuffing.
Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, Oct 26, 2021
Accurate modelling of friction coefficient is of primary importance in efficiency, vibration and ... more Accurate modelling of friction coefficient is of primary importance in efficiency, vibration and failure analyses of enclosed gear drives. After showing the influence of surface/lubricant interactions on friction, the authors used a semi-empirical model which can take all these aspects into account. Lubricant is modelled as an Eyring–Reynolds fluid and rough surfaces are described with two parameters via a stochastic approach. A specific two-disc machine is used to perform series of friction measurements on smooth and rough discs. Smooth discs allow to operate under full film lubrication and to measure a reference shear stress of lubricant, whereas rough discs reproduce gear tooth roughness and generate a representative value of friction on asperities. The purpose of this present paper is to describe calculations of this physical-based friction coefficient model and to present the experimental process. On the basis of new results, the impact of a surface finishing process is assessed as well as the consequence of calculating friction coefficient based on oil injection instead of local bulk temperature.
HAL (Le Centre pour la Communication Scientifique Directe), May 5, 2013
In high speed roller bearings, the drag force due to the oil-air mixture present in the bearing c... more In high speed roller bearings, the drag force due to the oil-air mixture present in the bearing cavitythat is acting against the roller movementis usually computed with a two-dimensional model of flow around a cylinder of infinite length. However rollers are of finite length, and the flow is perturbed by the two free ends, the surrounding rings, the cage and other rolling elements. In this article, the Computational Fluid Dynamics (CFD) method is employed to analyze first the flow around one finite-length circular cylinder with two free ends in an open space. Then the model is changed to one finite cylinder and then several in-line circular cylinders sandwiched by two flat walls, which represents a simplified approach. The results indicate that both the flow pattern around the cylinder and its drag coefficient are modified in comparison with the two-dimensional model. Finally a relationship between the drag coefficient and the Reynolds number suitable for circular cylinder in roller bearings is proposed.
HAL (Le Centre pour la Communication Scientifique Directe), Aug 24, 2015
Un modèle thermo mécanique d'un banc FZG est développé. Le modèle numérique se base sur la méthod... more Un modèle thermo mécanique d'un banc FZG est développé. Le modèle numérique se base sur la méthode des réseaux thermiques et prend en compte les pertes de puissance dues aux dentures, aux roulements et au brassage du bain d'huile. Des mesures soulignent que les bagues des roulements présentent un gradient de température significatif. Pour expliquer ce gradient, deux modèles de roulement sont proposés et comparés aux mesures. Leur influence sur le comportement thermique global de la transmission mécanique est discutée et analysée.
This paper investigates the windage power loss generated by helical gears rotating in pure air. A... more This paper investigates the windage power loss generated by helical gears rotating in pure air. A three-dimensional approach using computational fluid dynamics (CFD) code which has been validated for spur gear is adapted here in order to consider helix angle. The numerical approach is at first validated with the power losses measured in similar conditions. The influence of both width and helix angle values on the expelled volumetric flow rate and the windage losses are studied. Considering these observations, a correlation which is based on a classical approach used in turbomachinery is proposed.
A thermo-mechanical model of a splash lubricated one-stage gear unit is presented. This system co... more A thermo-mechanical model of a splash lubricated one-stage gear unit is presented. This system corresponds to a first step towards the design of a hybrid vehicle gearbox which can operate up to 40,000 rpm on its primary shaft. The numerical model is based on the thermal network method and takes into account power losses due to tooth friction, rolling elements bearings and oil churning. Some calculations underline that oil churning causes a high amount of power loss. A simple method to reduce this source of power losses is presented, and its influence on the gear unit efficiency and its thermal capacity is quantified.
ABSTRACT The purpose of this study is to investigate the various fluid flow regimes generated by ... more ABSTRACT The purpose of this study is to investigate the various fluid flow regimes generated by a pinion running partly immersed in an oil bath and the corresponding churning power losses. In a series of papers, the authors have established several loss formulae whose validity depends on two different flow regimes characterized via a critical Reynolds number. Based on some new measurements for transient operating conditions, it has been found that the separation in two regimes may be not accurate enough for wide-faced gears and high temperatures. An extended formulation is therefore proposed which, apart from viscous forces, introduces the influence of centrifugal effects. The corresponding results agree well with the experimental measurements from a number of gears and operating conditions (speed, temperature). Finally, the link between churning and windage losses is examined and it is concluded that the physical mechanisms are different thus making it difficult to establish a general correlation between the two phenomena. In particular, it is shown that tooth geometry is of secondary importance on churning whereas, the air-lubricant circulation being different for spur and helical gears, it substantially impacts windage.
Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, Jan 29, 2013
An original formulation for tooth friction power losses in internal gears including the influence... more An original formulation for tooth friction power losses in internal gears including the influence of tooth profile modifications is presented. For unmodified gears, the results agree well with the classic formulae in the literature thus validating the proposed approach. The contributions of profile modifications on internal gear efficiency are compared to that on external gears and the formulation is extended to planetary gears. Finally, the role of profile relief on planetary gear efficiency is pointed out and commented upon.
Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, Mar 19, 2014
The aim of this study is to develop a thermal modeling of a grease lubricated rolling bearing in ... more The aim of this study is to develop a thermal modeling of a grease lubricated rolling bearing in order to analyze the heat evacuated through its solid parts and the lubricant. The system under consideration in this study is a clutch thrust bearing and more precisely a sealed single row angular contact ball bearing. To analyze heat transfer inside the bearing, two models have been developed using the thermal network method. These models have been compared to measurements performed on a specific test rig. As some heat transfers appear to be negligible, in the end a simplified model is proposed.
In order to use electric motors which run up to 40,000 rpm in future automotive applications, thi... more In order to use electric motors which run up to 40,000 rpm in future automotive applications, this study aims to experimentally investigate if splash lubrication technique is worth considering for high-speed gears, i.e., for tangential gear speed up to 60 m/s. To this end, a specific test rig has been used to operate a single spur or helical gear in various operating conditions (lubricant, oil sump volume, temperature, etc.). Churning loss is measured and, as the fraction of air in the lubricant (namely, oil aeration) can be influential on this source of dissipation, a specific sensor is also employed for online monitoring of oil sump aeration. By inserting some moveable walls in the gearbox, it is demonstrated that churning losses and oil aeration can be significantly reduced by mounting these flanges at an appropriate distance to the gear lateral faces. Based on dimensional analysis, an engineering criterion is proposed to properly choose the clearance between the tested gear and the flanges.
Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, Jan 16, 2009
It is generally accepted that the total power loss in gears can be decomposed into contributions ... more It is generally accepted that the total power loss in gears can be decomposed into contributions of friction between the teeth, lubrication (churning and/or jet lubrication that could induce gas—oil trapping in inter-tooth spaces), and gear windage effects. For low- to medium-speed transmissions, tooth friction is recognized as the main source of dissipation for gears and can significantly influence the temperature equilibrium of a gearbox. In this article, a model to predict power losses due to tooth friction combined with a thermal network to describe the temperature distribution in a geared transmission are presented. The numerical results compare favourably with experimental measurements from a gear test rig.
Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, Jan 16, 2012
A thermal model of a back-to-back gear test rig relying on a network approach is presented in whi... more A thermal model of a back-to-back gear test rig relying on a network approach is presented in which the predictions of temperatures and power losses are coupled. The numerical findings are in good agreement with the measurements for transient regimes on a FZG test rig and it is demonstrated that the proposed simulation is reliable. A number of results are presented which illustrate the influence of the pinion and gear immersion depths. It is found that, in certain conditions, the classic isothermal method for estimating integral temperatures is questionable because the actual bulk temperature can substantially deviate from that of the oil sump. The practical consequences in terms of scuffing capacity are emphasised.
HAL (Le Centre pour la Communication Scientifique Directe), May 17, 2015
Scuffing is defined in the literature as "gross damage characterized by the formation of local we... more Scuffing is defined in the literature as "gross damage characterized by the formation of local welds between the sliding surfaces" [1]. This localized damage suddenly appears when the frictional heat generated at the contact induces a critical temperature increase. Numerous studies were conducted in order to establish a scuffing criterion. Some of them focus on the power dissipation inside the contact (product of the sliding speed and the load) [2] some others compare the minimum film thickness of lubricant separating the surfaces to the surface roughness [3,4]. In 1937 Blok introduced a thermal scuffing criterion [5]: each combination of base-stock lubricant and material has a characteristic scuffing temperature. The present study proposes a thermal model based on correlations between experimental tests performed on a twin-disc machine and numerical studies using the thermal network methodology in order to better understand scuffing.
Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology, Oct 26, 2021
Accurate modelling of friction coefficient is of primary importance in efficiency, vibration and ... more Accurate modelling of friction coefficient is of primary importance in efficiency, vibration and failure analyses of enclosed gear drives. After showing the influence of surface/lubricant interactions on friction, the authors used a semi-empirical model which can take all these aspects into account. Lubricant is modelled as an Eyring–Reynolds fluid and rough surfaces are described with two parameters via a stochastic approach. A specific two-disc machine is used to perform series of friction measurements on smooth and rough discs. Smooth discs allow to operate under full film lubrication and to measure a reference shear stress of lubricant, whereas rough discs reproduce gear tooth roughness and generate a representative value of friction on asperities. The purpose of this present paper is to describe calculations of this physical-based friction coefficient model and to present the experimental process. On the basis of new results, the impact of a surface finishing process is assessed as well as the consequence of calculating friction coefficient based on oil injection instead of local bulk temperature.
HAL (Le Centre pour la Communication Scientifique Directe), May 5, 2013
In high speed roller bearings, the drag force due to the oil-air mixture present in the bearing c... more In high speed roller bearings, the drag force due to the oil-air mixture present in the bearing cavitythat is acting against the roller movementis usually computed with a two-dimensional model of flow around a cylinder of infinite length. However rollers are of finite length, and the flow is perturbed by the two free ends, the surrounding rings, the cage and other rolling elements. In this article, the Computational Fluid Dynamics (CFD) method is employed to analyze first the flow around one finite-length circular cylinder with two free ends in an open space. Then the model is changed to one finite cylinder and then several in-line circular cylinders sandwiched by two flat walls, which represents a simplified approach. The results indicate that both the flow pattern around the cylinder and its drag coefficient are modified in comparison with the two-dimensional model. Finally a relationship between the drag coefficient and the Reynolds number suitable for circular cylinder in roller bearings is proposed.
HAL (Le Centre pour la Communication Scientifique Directe), Aug 24, 2015
Un modèle thermo mécanique d'un banc FZG est développé. Le modèle numérique se base sur la méthod... more Un modèle thermo mécanique d'un banc FZG est développé. Le modèle numérique se base sur la méthode des réseaux thermiques et prend en compte les pertes de puissance dues aux dentures, aux roulements et au brassage du bain d'huile. Des mesures soulignent que les bagues des roulements présentent un gradient de température significatif. Pour expliquer ce gradient, deux modèles de roulement sont proposés et comparés aux mesures. Leur influence sur le comportement thermique global de la transmission mécanique est discutée et analysée.
Uploads
Papers by Fabrice Ville