Abstract To investigate the effect of the inlet starvation severity on the flash temperature, which dictates the scuffing failure, a thermal mixed elastohydrodynamic lubrication model is developed for line contacts operating under the starved lubrication condition. The scuffing failure of high speed gearing applications is commonly associated with the very high sliding condition occurring in the vicinity of either the root or the tip, where the shear thinning effect that decreases the lubrication film thickness and increases the contact pressure is significant. Utilizing a generalized Newtonian Reynolds equation, the lubricant viscosity dependence on the shear rate, as well as on the pressure and temperature, is incorporated for the proper and accurate modeling of the tribological behavior under the high sliding condition. A film fraction parameter is employed in the Reynolds equation to include the starvation and cavitation description, eliminating the need for the measured or assumed meniscus location in the inlet zone. Considering different operating and surface roughness conditions, a parametric study is performed to show an asymptotic relationship between the flash temperature and the inlet starvation severity.

An analysis for operating characteristics of piston lubrication system is performed based on the numerical model in the area of fluid-structure interaction. A numerical model with an integration of elastohydrodynamics and multi-flexible-body dynamics (MFBD) is developed to analyze lubrication characteristics such as oil film thickness and pressure. In particular, elastic deformation of components in piston lubrication system through modal reduction method is reflected on elastohydrodynamic analysis. The oil film pressure evaluated from elastohydrodynamic analysis is used as external force to calculate the elastic deformation of flexible bodies in multi-flexible-body dynamics (MFBD) again. A series of process proposed in this study is available for the analysis of realistic elastohydrodynamic lubrication phenomenon. Moreover, asperity contact effect is also implemented. Finally, a numerical example for the piston lubrication system is also demonstrated.

This study investigates the role of the tribo-dynamic behavior in the contact fatigue crack nucleation for spur gears. To describe this fatigue phenomenon, a six-degree-of-freedom (DOF) lumped parameter dynamics formulation is coupled with a set of mixed elastohydrodynamic lubrication (EHL) governing equations. The former provides the dynamic tooth force to the EHL analysis, and the latter yields the gear mesh damping as well as the friction excitations that are required in the gear dynamics simulation. The converged tribo-dynamic surface normal pressure and tangential shear are then used to determine the multi-axial stress fields using the potential theory based closed-form stress formulation for half space. Lastly, the stress means and amplitudes are implemented in a multi-axial fatigue criterion to assess the fatigue damage.

Elastohydrodynamic lubrication phenomenon in spiral bevel gears was modeled in this study. The coefficient of friction calculated from the elastohydrodynamic (EHL) lubrication model is time varying. Friction is expected to have a greater impact on the spiral bevel gears than on any other right angled geared system due to the reversal of the contact area over a full tooth-to-tooth engagement cycle. The coefficient of friction formulated from an EHL model of spiral bevel gears depends upon lubricant properties, mesh forces and rotational speeds of the pinion and gear. Hence in this present study, a full elastohydrodynamic lubrication model was used to calculate the coefficient of friction in spiral bevel gears. The geometric and kinematic input data required for the EHL simulations were obtained from tooth contact analysis. Full numerical elastohydrodynamic lubrication simulations were carried out using the asymmetric integrated control volume (AICV) algorithm to compute the contact pressures and the coefficient of friction. The elastic deformations on the gear contact surfaces were calculated by circular convolution using a Fourier transform technique. The computed pressures, film thickness and the effective viscosity were used to calculate the time varying coefficient of friction for the spiral bevel gears. Parametric studies were conducted by varying the speed, torque applied, lubricant properties, temperature and slide to roll ratio to identify their impact on the time varying coefficient of friction.

In this work, the impact of the surface micro-dimple arrays on the frictional behavior under the mixed elastohydrodynamic lubrication condition is examined, considering a point contact problem. The interested geometric parameters of the micro-dimple arrays include the dimple center distance and the dimple depth. To quantify the influence of these parameters on the friction coefficient, a computational approach is implemented. In addition, different surface texture combinations, namely micro-dimpled and polished surface versus polished surface, polished surface versus polished surface and ground surface versus ground surface, are compared to determine any advantage or disadvantage of micro-dimpled surfaces on the aspect of the friction performance under the typical gearing application operating conditions.

This study proposes a formulation for the description of the gear mesh mechanical power loss under the thermal tribodynamic condition. A six degree-of-freedom motion equation set that models the vibratory motions of a general spur gear pair is coupled with the governing equations for the description of the gear thermal mixed elastohydrodynamic lubrication to include the interactions between the gear dynamics and gear tribology disciplines in the modeling of the gear mesh mechanical power loss. The important role of the gear thermal tribo-dynamics in power loss is demonstrated by comparing the predictions of the proposed model to those under the thermal quasi-static condition, and the iso-thermal tribo-dynamic condition, respectively.

A three dimensional non-linear vibration model of tapered roller bearings was developed based on an in-house dynamic bearing model (DBM), which simulates the motion of bearing components and their interactions using Hertzian contact, traction, and hydrodynamic/ elastohydrodynamic lubrication models. The vibration model can simulate bearings with distributed and localized geometrical imperfections on their cup raceways, cone raceways, and roller bodies. This paper focuses on the influence of localized cup raceway imperfections on bearing vibration. Three levels of localized defects were intentionally created on cup raceways and quantified using a surface profile gauge. The quantified defects on actual test bearings were used as inputs to the vibration model. The corresponding test bearings were evaluated with a high-precision bearing vibration test machine. Two different bearing designs were used in the study. The simulation and test data were analyzed and compared, and it was found that the simulation results agreed well with the test data.

Differential hypoid gears play an important role on the Noise, Vibration and Harshness (NVH) signature of vehicles. Additionally, friction developed between their teeth flanks under extreme loading conditions adds another source of power loss in the drivetrain which can mitigate vibrational energy. The paper considers the coupling between dynamics and analytical tribology to study dynamic response of hypoid gear pairs with lateral motion of support shafts also included in the analysis framework. Friction of teeth flank pairs is assumed to follow elastohydrodynamic lubrication under elliptical point contact geometry with lubricant film behavior conforming to Non-Newtonian thermal shear, also with surface asperity interactions. Tooth Contact Analysis (TCA) has been used to obtain the input data required for the investigation. The dynamic behavior and efficiency of a differential hypoid gear pair under realistic operating conditions is determined. The proposed tribo-dynamic framework provides a useful platform to conduct an extensive series of parametric studies.

This paper presents a model to predict the crack formation fatigue lives of spur gear contacts operating under mixed lubrication conditions where surface roughnesses introduce intermittent metal-to-metal contacts and severe stress concentrations. The proposed model consists of several submodels including (i) a gear load distribution model to determine the normal tooth force distribution along the tooth profile, incorporating any profile modifications and manufacturing deviations, (ii) a mixed elastohydrodynamic lubrication model customized to handle transient contact conditions of gears, (iii) a stress formulation that assumes the plane strain condition to compute the transient elastic stress fields on and below the tooth surface induced by the mixed lubrication surface pressure and shear stress distributions, and (iv) a multi-axial fatigue model to predict the crack nucleation life distribution. The proposed spur gear fatigue model is used to simulate the contacts of gear pairs having different surface roughness amplitudes. The predictions are compared to the measured gear fatigue Stress-Life data for each surface condition to assess the model accuracy in predicting the crack nucleation fatigue lives as well as the location of the critical failure sites.

The experimental knowledge about medium lubricated journal bearings (e.g. diesel-oil lubricated sliding bearings in fuel-injection systems) is far too small in order to confirm the different hypotheses of the actual simulation models. The study of such components implicates very restrictive requirements on security against explosion, exact measurement of the friction torque and so on. A new test bench design to meet these requirements is presented, allowing a system-conform study of the components. For a high resolution of the temperature repartition in the smearing gap, thin film sensors, which have allowed the verifications experiments in the field of the Elastohydrodynamic-lubrication (EHL) are being enhanced. Beside a higher wear resistance, a reduction of the sensor size is an important requirement for the new sensor generation, allowing the resolution of local phenomena in the mixed lubrication. For the electrical isolation and wear protection of the new sensors developed at the Institute of Product Development of the University of Karlsruhe (TH) (IPEK), diamond like carbon (DLC) coatings are used. For the fulfillment of the requirements on the size of the sensors, a new concept of micro thermocouples is presented.

The paper presents results obtained using a transient analysis technique for point contact elastohydrodynamic lubrication (EHL) problems based on a formulation that couples the elastic and hydrodynamic equations. Results are presented for transverse ground surfaces in elliptical point contact that show severe film thinning at the transverse limits of the contact area. This thinning is caused by transverse leakage of the lubricant from the contact in the remaining deep valley features. A comparison is also made between the point contact results on the entrainment centre line and the equivalent line contact analysis.

The paper describes the application of a full non-Newtonian, thermal elastohydrodynamic lubrication (EHL) model for the prediction of film thickness and viscous traction force in a special high speed rolling traction rig. The primary objective of the work was to identify a suitable lubricant rheological model that would describe the behavior of practical EHL traction drive contacts over their operating range. Experiments were carried out on a special rolling contact rig at temperatures of 60, 90 and 120°C and contact loads giving maximum Hertzian pressures of 1, 2 and 3 GPa. Entrainment speeds of up to 18 m/s were investigated. Corresponding modelling work was carried out using lubricant physical properties obtained for the traction fluid Santotrac 50. Viscosity data for this lubricant were available from the work of Bair and Winer, but a degree of extrapolation was required to this data to cover the range of the experiments. In view of the crucial importance of viscosity/pressure behavior in the prediction of traction attention was therefore focused upon the lower contact loads for which reliable viscosity/pressure data are available. A best-fit exercise was then carried out to establish an appropriate rheological model to account for shear thinning of the lubricant. Different non-Newtonian relationships were investigated including those of Johnson and Tevaarwerk, Bair and Winer, and a model which combined the features of both of these. The most encouraging agreement between experiment and theory over the range of temperatures and speeds considered was obtained with the Johnson and Tevaarwerk (Eyring) model.

In this study, a methodology for prediction of mechanical efficiency of helical gear pairs is proposed. It combines a gear load distribution model with a friction coefficient computation model. The load distribution model is used to provide contact pressures and other contact parameters to the friction coefficient model. Two different approaches are used for the computation of the friction coefficient. The first approach employs a number of published empirical friction coefficient formulae that were typically obtained through twin-disk tests. The second approach uses a rough-surface, thermal elastohydrodynamic lubrication (EHL) model. A simplified, smooth-surface version of the EHL-based model is also proposed. The friction coefficient distributions along the tooth contact surfaces are then used to calculate the friction forces that yield the instantaneous mechanical efficiency loss of the gear pair at a given mesh angle. The model is used to study the influence of a number of design, lubricant and surface related parameters as well as load and speed on the mechanical efficiency of helical gear pairs.