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International audience; In this paper a computational fluid dynamics (CFD) code is applied to three-dimensional simulations of windage power loss generated by spur gears rotating in air. Emphasis is placed on the simplification which can be made in the numerical approach in order to gain cost and time needed for reaching a converged solution when using both fine mesh and important angular velocity. It appears that the similarity of the flows which are observed in the vicinity of both gear and disk sides is helpful. It is finally possible to compute the flow pattern near the teeth without simulating the contribution of the sides when appropriate boundary conditions are applied at the inlet of a truncated computational domain. The predictions of windage power losses using this original method are satisfying.

International audience; The collaborative robot (cobot) is a technology contributing to the industrial revolution Industry 4.0. Indeed, cobots’ flexibility and their easy-to-use solutions fill a gap with traditional robots to robotize manufacturing of products with low volume and high mix profiles. Parts needed to manufacture a product must first be presented to the cobot, so that afterwards it can perform operations such as assembly. The paper classifies the current part presenters. Then, a methodology is proposed to select the best presenter based on the characteristics of the parts and the workstation. To be aligned with markets requiring a high mix of products frequently renewed, the development times for part presenter design and for cobot programming are new data to select the best presenter. Indeed, at every part redesign, the part presenter changes and the cobot is reprogrammed. These two times are depreciated based on the lifespan quantity of the part. Lifespan quantity is the number of the same parts, which are dropped-off on the part presenter during the part’s lifespan, i.e. until its redesign. A concrete industrial use case is explained to test the methodology. Results conclude that a tray pattern is the best part presenter, except for parts with low lifespan quantity. Lifespan quantity of the part appears to be a significant parameter when deciding the best part presenter.

International audience; This article deals with the Windage Power Losses (WPL) of pinion-gear pairs rotating in air. The WPL of several disks, spur and helical gears have been measured using a dedicated test rig developed from a WPL measurement system initially used for one single pinion or disk. In practice, several gears are in mesh and the windage losses for coupled pinion-gear systems need to be addressed. It is experimentally confirmed that, although some couplings can be identified between two rotating gears, the total WPL can be estimated as the sum of that of each individual member.

International audience; Gear unit condition monitoring is a key factor for mechanical system reliability management. When they are subjected to failure, gears and bearings may generate excessive vibration, debris and heat. Vibratory, acoustic or debris analyses are proven approaches to perform condition monitoring. An alternative to those methods is to use temperature as a condition indicator to detect gearbox failure.The review focuses on condition monitoring studies which use this thermal approach. According to the failure type and the measurement method, it exists a distinction whether it is contact (e.g. thermocouple) or non-contact temperature sensor (e.g. thermography). Capabilities and limitations of this approach are discussed. It is shown that the use of temperature for condition monitoring has a clear potential as an alternative to vibratory or acoustic health monitoring.

This paper deals with recent experimental and numerical research in the possible reduction of windage power losses (WPL). It is accepted that these load-independent losses become prominent over other sources in mechanical transmissions with peripheral speeds above 100 m/s as is the case in energy production, aeronautics and electric vehicles. So far, the majority of the experiments and models deal with WPL evaluation for one single rotating pinion. The unique test rig designed at INSA Lyon makes it possible to measure both the WPL of a single pinion or a non-meshing pinion-gear pair. A number of comparisons between experimental and numerical results are presented and commented upon. It is shown, that the gear environment changes the airflow and, in depending on the cases, it can either reduce or increase WPL. Finally, the influence of pinion-gear couplings on WPL is discussed as well as the interest of shrouds and deflectors.

The objective of this work is to study the improvement of the tribological properties of low alloy steel using a duplex treatment of low pressure carburizing and the deposition of a Cr–(WC–Co) coating by dual RF magnetron sputtering. The treatments result in a 500 μm thick carburized layer and a sputtered coating thickness of ~ 2 μm. Tribological tests were made with a ball-on-disk tribometer under dry conditions with low load and low speed. The worn surfaces of the disk, the wear counterpart, and resulting debris were analyzed by X-ray diffraction, optical microscopy, optical profilometry, and a scanning electron microscope equipped with an energy-dispersive X-ray spectrometer. The wear performance of the samples was evaluated in terms of wear rates and friction coefficients during the sliding processes against two different counterparts. Experimental results have shown that sliding wear, of the investigated duplex treated low alloy steels, is strongly dependent on the counterface materials. Under testing conditions, the overall wear performance of a Cr–WC coating (Cr/W ratio of 1.12:1) deposited onto the surface of a carburized low alloy steel (0.61 wt.% C; HV = 654 ± 5) can be recommended as the best. The duplex-treated samples suffered severe, concentrated wear when against alumina. This wear is characterized by a combination of delamination, mild abrasion and oxidative wear. However, the wear mechanism seems to be oxidative and adhesive when against WC balls.

International audience; In rolling contact fatigue (RCF), failure mechanisms are known to be very sensitive to material microstructure. Yet, among the different numerical models developed to predict the RCF life, few models use a microstructure representation. A granular cohesive finite element model has been developed to simulate progressive damage of a structure subject to RCF and to investigate failure initiation mechanisms. This paper focuses on the implementation of crystal elasticity in the model. The numerical analysis of a representative volume element (RVE) validates the use of cubic elasticity to represent crystal behavior. The influence of the RVE size and the influence of boundary conditions applied on the RVE are evaluated in the finite element approximation framework. As regards the implementation of cubic elasticity in the RCF model, the generation of stress singularities at triple junctions is first highlighted. Then the average value of the intergranular shear stress is proved to be mesh size independent and therefore can be used as damage criterion. Finally, the influence of crystal elasticity on micro-cracks distribution is presented.

International audience; 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 highly 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.

International audience; Churning losses are a complex phenomenon which generates significant power losses when considering splash lubrication of gear units. However, only few works deal with bevel gears dipped lubrication losses. The objective of this study is to provide a wide variety of experimental tests on churning losses, especially getting interested in geometry of spiral bevel gears influence. A specific test rig was used in order to study a single spiral bevel gear partially immersed in an oil bath. Experiments have been conducted for several operating conditions in terms of speeds, lubricants, temperatures and gear geometries to study their impact on splash lubrication power losses. These experimental results are compared with the predictions from various literature sources. As the results did not agree well with the predictions for all operating conditions, an extended equation derived from previous works is introduced to estimate churning losses of bevel gears.

International audience; This study aims to experimentally investigate churning power losses generated by a planetary gear set which is splash lubricated. To this end, a specific test rig has been used to operate a planetary gear train under unloaded conditions in various configurations within a range of the planet-carrier rotational speed. Churning loss is isolated from the measured drag torque and the effects of several parameters (rotational speed, temperature, oil sump level, planet number…) on this source of dissipation are quantified. Beyond the influence of speed or oil level, it is concluded that the number of planets is of primary importance on churning power losses. Moreover, a first assumption is made concerning the oil sump behavior regarding the experiments: an oil ring is created explaining the evolution of the churning losses measured. In addition, this study compares the churning phenomenon occurring in cylindrical gear trains with the one observed during the experiments. It is shown that the approach used for conventional gear trains cannot be used for epicyclic ones: in planetary gear sets the centrifugal effects are predominant whereas the gravity forces have a larger influence on the free surface flows which occur in cylindrical gear sets.

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.

In Rolling Contact Fatigue (RCF), understanding initiation and propagation failure mechanisms remains a challenge. A cohesive Finite Element model has been developed to investigate microstructure role on initiation mechanisms. The approach consists in modelling the Grain Boundary (GB) progressive damage (from initial undamaged state to failure). In this paper, numerical singularities at triple junctions are highlighted and cohesive stiffness values (for undamaged and fully damaged GB) are defined. Preliminary results underscore the influence of damage application: a linear relation between cohesive stiffness and damage is not suitable to simulate progressive damage.

This paper presents an original method to investigate the power losses distribution into a planetary gear unit. A thermal model, which allows the estimation of power losses linked to the temperature distribution, is established. This model is used to analyse some experimental results obtained on a specific test rig. For the planetary gear set studied here, it is demonstrated that load-independent power losses are mainly due to hydrodynamic power losses generated in planets bearings and that gears windage effects are negligible.

International audience; X38CrMoV5-1 steel is a typical tool steel commonly used in forging and plastic moulding industry for production of ejectors, slides, dies, etc. In plastics moulding a lot of these parts sustain relative movement. Because of this, some seizing or micro-welding may appear, especially when lubrication is not used. For many years, the different types of protective coatings were developed to avoid such problems. Most of the obtained solutions relate to the manufacturing of low friction coatings obtained by different nitriding processes and by CVD or PVD methods. In this article, the friction coefficients and the wear resistances of TiC+a-C:H protective coatings manufactured on X38CrMoV5-1 steel samples by using PVD technology are studied. The investigations are based on tribometer tests in different temperature conditions. The process of deposition of PVD coatings was realized by using multisource, hybrid factory-scale equipment of type URM 079. This equipment allows for deposition of coatings by a physical method. The tribological tests were performed using a precision high temperature tribometer under ambient and high temperature conditions with a steel and corundum balls as a counter-samples. In this paper, the results of these tribological tests are presented. It is shown that the measured friction coefficient of steel samples with PVD coatings is significantly lower than the friction coefficient of uncoated steel. It is also shown that X38CrMoV5-1 steel samples with manufactured TiC+a-C:H coatings are characterized by a very low friction coefficient and high wear resistance.

In this article the friction coefficients and the wear resistances of MoS2TiW protective coatings manufactured on X38CrMoV5-1 steel samples by using PVD technology are studied. The investi- gations based on tribometer tests which were carried out in different temperature conditions. The process of deposition of PVD coatings was realized by using multisource, hybrid factory- scale equipment of type URM 079. This equipment allows for deposition of coatings by the phys- ical method. The tribological tests were performed using a precision high temperature tribome- ter under ambient and high temperature conditions with a steel and corundum balls as coun- ter-samples. In this paper the results of these tribological tests are presented. It is shown that the measured friction coefficient of steel samples with PVD coatings is significantly lower than the friction coefficient of uncoated steel. It is also shown that X38CrMoV5-1 steel samples with manufactured MoS2TiW coatings are characterized by very low friction coefficient and high wear resistance.

International audience; This paper investigates the windage power losses generated by spur gears rotating in pure air by using a computational fluid dynamics (CFD) code. The three-dimensional simulations are at first validated comparing CFD predictions with the power losses measured in similar conditions from other investigations. The volumetric flow rate which is expelled by the teeth is then analysed, and a correlation which is based on a classical approach used in turbomachinery is finally proposed which makes it possible to estimate windage losses for spur gears. It was observed that this latter approach seems satisfying since the formulation of the volumetric flow rate which is employed in the model is appropriate to each gear.

International audience; In order to investigate the oil projected by gears rotating in an oil bath, a test rig has been set up in which the quantity of lubricant splashed at several locations on the casing walls can be measured. An oblong-shaped window of variable size is connected to a tank for flow measurements and the system can be placed at several locations. A series of formulae have been deduced using Dimensional Analysis which can predict the lubricant flow rate generated by one spur gear or one disk at various places on the casing. These results have been experimentally validated over a wide range of operating conditions (rotational speed, geometry, immersion depth, etc.).

International audience; 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.

International audience; 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.

International audience; It is currently assumed that churning losses can be described by using only two physical parameters representative of the lubricant properties, i.e., density and viscosity. To verify this hypothesis, a number of transient measurements were carried out on a specific gear test rig over a range of oil temperatures. It appears that, for high temperatures and/or high rotational speeds, the drag torque can suddenly increase with an increasing Reynolds number. Extensive on-line lubricant aeration measurements were conducted showing that this particular behaviour can be related to churning losses when the fraction of air in the lubricant reaches a certain threshold. In order to quantify the influence of oil sump aeration on churning losses, a simplified original model, based on surface tension and lubricant aeration is proposed. This study shows clearly that density and viscosity are not sufficient to estimate churning losses under some specific operating conditions and emphasises the need to account for other physical properties of the lubricant.

International audience; In this paper, a computational fluid dynamics (CFD) code is applied to two- and three-dimensional simulations of windage power loss (WPL) generated by spur gears rotating in air. Emphasis is placed on the various meshes associated with the Finite Volume Method (FVM) and on the choice of turbulence model. Comparing CFD predictions with the power losses measured on a specific test rig, it is shown that the fluid ejection in the radial direction must be included in order to reproduce the experimental evidence. The relative importance of the losses generated by the gear front and rear faces along with those due to the teeth is discussed. The volumetric flow rate expelled by the teeth is analysed and the influence of flanges is highlighted.

International audience; 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.