The Performance of One-Way Clutch in a Cam-Based Infinitely Variable Transmission

Continuously variable transmission is the system which provides a step-less change in transmission ratio between two rotating shafts. When it can provide zero ratio, it is known as infinitely variable transmission (IVT). These systems are mainly classified into two categories; traction and non-traction types. In the traction type, the power is transmitted by friction force that develops between the active elements in the mechanism, while in the non-traction systems, the power is transmitted via direct contact. A very common type of non-traction IVT is the cam-based system. In this type, the rotating motion of the input element is converted to oscillatory motion with continuously variable amplitude. Eventually, the oscillatory motion is rectified to one-way rotational motion by means of a one-way clutch (rectifier). The rectifier is considered an essential element in the IVT system, as it is subjected to an extreme dynamical condition. In this study, the performance of one-way clutches (rectifiers) in a cam-based IVT is presented. The IVT system under consideration is a combination of two identical units and in each one, a rectifier is fitted at the output shaft. It is required that this rectifier is able to efficiently transmit the power during its engagement. It should also generate minimal power loss during disengagements, when aggressive relative motion is presented between its parts. It has been found that the operation of the one-way clutch is mainly determined by the designed cam profile. For this study, the profile is a combination of constant speed and trapezoidal forms. It was also concluded that the value of the selected transmission ratio controls the amount of fluctuation in the acceleration, velocity and displacement and hence, the energy lost due to slippage of the clutches

Dynamics and lubrication analyses of scotch yoke mechanism

In this paper the contact problem of a scotch yoke mechanism has been investigated in details under the elastohydrodynamic lubrication regime and line contact model is used in the analyses. The non-Newtonian oil behavior of the lubricant and the variation of the load and the surface velocities throughout the operating cycles are considered in the analyses. The results reveal that the variation of these values makes the contact problem (depending on the position in the operating cycle) to operate under lightly and heavily loaded conditions. Under these conditions, extremely thin levels of film thickness have been predicted

The transient effects of profile modification on elastohydrodynamic oil films in helical gears

This article presents the results of a transient elastohydrodynamic analysis of the conditions at the contact of two pairs of helical gears operating with different gear ratios. The effects of the variation in contact geometry, kinematics, and tooth loading during the meshing cycle are taken into account together with both tip relief and axial crowning profile modifications. The results are compared with analyses under corresponding steady-state conditions for both point contact and equivalent line contact models. The comparisons show that, away from the ends of the contact lines, steady-state conditions can be used effectively to assess the film-forming capabilities of the gears. Conditions at the end of the contact lines are found to be more adverse with significant transient squeeze film effects. The form of tip relief profile adopted is shown to be highly influential in determining the peak contact pressures and thinnest oil films within the contacts. These conditions are experienced at all axial positions on the tooth flanks at the locations of the start of tip relief profile modifications. If the tip relief profile introduces a slope discontinuity to the gear profile, this can cause a significant stress concentration and very poor film-forming behavior

Lubrication analyses of cam and flat-faced follower

The principal factors that affect the characteristics of contact problem between cam and follower vary enormously during the operating cycle of this mechanism. This includes radius of curvature, surface velocities and applied load. It has been found over the last decades that the mechanism operates under an extremely thin film of lubricant. Any practical improvement in the level of film thickness that separates the contacted surfaces represents an essential step towards a satisfactory design of the system. In this paper a detailed numerical study is presented for the cam and follower (flat-faced) lubrication including the effect of introducing an axial modification (parabolic shape) of the cam depth on the levels of film thickness and pressure distribution. This is achieved based on a point contact model for a cam and flat-faced follower system. The results reveal that the cam form of modification has considerable consequences on the level of predicted film thickness and pressure distribution as well as surface deformation

Numerical analysis of cam and follower based on the interactive design approach

The contact between the cam and follower is considered as one of the most complicated problems from the lubrication point of view. The contact in this elastohydrodynamic lubrication (EHL) problem undergoes extreme variation conditions of different parameters. These include the load variation, geometry at the contact point and sliding speed. This paper presents an EHL solution for the contact problem between cam and chamfered follower (originally flat faced). The model of solution is point contact in order to accurately simulate the chamfering of the follower. The solution of Reynolds equation considers the non- Newtonian oil behavior in the calculation of the flow factors. The interactive design approach used in this paper focused mainly on the effect of chamfer as well as the other general parameters of the mechanism. The results revealed that chamfering of the follower in the axial direction has considerable effects on the performance of the mechanism. The linear modification causes significant rise in the maximum pressure and extreme thinning in the film thickness

An Investigation on the Teeth Crowning Effects on the Transient EHL Performance of Large-Scale Wind Turbine Spur Gears

Crowning is applied to wind turbine gears, including spur gears, to ensure adequate stress distribution and contact localization in wind turbine main gearbox gears to improve the gear performance in the presence of misalignments. Each gear tooth is crowned along the face width using a parabolic curve that graduates from a maximum height at the edges and vanishes at the center of the tooth flank. This crowning transfers the elastohydrodynamic contact problem from a line to a point contact case where the surface curvatures and pressure gradient are considered in both directions of the solution space. A wide range of longitudinal crowning heights is considered in this analysis under heavily loaded teeth for typical large-scale wind turbine gears. Furthermore, the variation in the velocities is considered in the analysis. The full transient elastohydrodynamic point contact solution considers the non-Newtonian oil behavior, where the numerical solution is based on the finite difference method. This work is focused on the evaluation of the effectiveness of teeth’s longitudinal crowning in terms of the consequences on the resulting pressure distribution and the corresponding film thickness. The modification of the tooth flank significantly elevates the film thickness levels over the zones close to the tooth edges without a significant increase in the pressure values. Moreover, the zone close to the tooth edges from both sides, where the pressure is expected to drop to the ambient pressure, is extended as a result of the flank modification

Minimizing misalignment effects in finite length journal bearings

This paper focuses on a method to reduce the detrimental effects that occur due to the misalignment in journal bearings by approaching it with the more complete model of a finite length bearing. Such a drawback is quite common in industrial applications, and it is generally accepted that misalignment causes a significant thinning in the film thickness in the area that is close to the bearing edges. Therefore, removing a certain volume of material from the inner surface of the bearing (bushing) over a distance that is at the bearing edges provides an additional clearance to compensate for the clearance reduction that is due to misalignment. A numerical solution that is used in this work is based on the finite difference method where the Reynolds boundary conditions are considered in the solution scheme, thereby, using an iterative procedure to identify the cavitation zone. A three-dimensional misalignment model is incorporated in the solution in order to provide a more realistic presentation of the deviations and errors that there are in comparison with the ideal aligned case. It has been found in the present work that the edge modification increases the thickness of the lubricant layer considerably and reduces the pressure spikes that are associated with the presence of misalignment. The suggested design also reduces the coefficient of friction in comparison with that of the misaligned case. Furthermore, this method helps in reducing the asymmetry of the hydrodynamic pressure field that results from the misalignment. This method enables the operation of journal bearings over a wider range of misalignment levels without sacrificing the load-carrying capacity of the bearing by maintaining a relatively thicker layer of lubricant at the critical positions that are not so due to the effects of misalignment.This paper focuses on a method to reduce the detrimental effects that occur due to the misalignment in journal bearings by approaching it with the more complete model of a finite length bearing. Such a drawback is quite common in industrial applications, and it is generally accepted that misalignment causes a significant thinning in the film thickness in the area that is close to the bearing edges. Therefore, removing a certain volume of material from the inner surface of the bearing (bushing) over a distance that is at the bearing edges provides an additional clearance to compensate for the clearance reduction that is due to misalignment. A numerical solution that is used in this work is based on the finite difference method where the Reynolds boundary conditions are considered in the solution scheme, thereby, using an iterative procedure to identify the cavitation zone. A three-dimensional misalignment model is incorporated in the solution in order to provide a more realistic presentation of the deviations and errors that there are in comparison with the ideal aligned case. It has been found in the present work that the edge modification increases the thickness of the lubricant layer considerably and reduces the pressure spikes that are associated with the presence of misalignment. The suggested design also reduces the coefficient of friction in comparison with that of the misaligned case. Furthermore, this method helps in reducing the asymmetry of the hydrodynamic pressure field that results from the misalignment. This method enables the operation of journal bearings over a wider range of misalignment levels without sacrificing the load-carrying capacity of the bearing by maintaining a relatively thicker layer of lubricant at the critical positions that are not so due to the effects of misalignment

Effect of Chamfer Form and Parameters on the Characteristics of Finite Length Journal Bearing under Impact Load

Journal bearings in typical applications are subjected to misalignment due to several causes, such as shaft deformation under load and errors related to the installation and manufacturing processes. Misalignment has well-known severe negative consequences on the performance of the bearings. This paper deals with the bearing chamfer to reduce these consequences of misalignment, and two forms of bearing edge modification are considered in the analysis. These forms are linear and curved chamfering of the bearing edges, where the height of the chamfer in the circumferential direction and the length of the modification in the longitudinal direction are considered as geo- metrical design parameters. The investigation includes a numerical solution of the hydrodynamic lubrication problem of finite length journal bearing, considering 3D misalignment cases using the finite difference method. This includes the assessment of the chamfer forms and their effects on the bearing performance in terms of the main bearing design parameters. Furthermore, the stability of the chamfered bearings is also investigated under impact load. Results showed that both chamfer forms are beneficial for a certain limit of the design parameters in reducing the maximum pressure and coefficient of friction and in elevating the film thickness levels, extending the range of misalignment in which the journal bearing can operate safely. In addition, the chamfered bearings in both forms showed more stability range in terms of the critical speed and shaft center trajectories under impact load. The bearings with the curved chamfer, where the slope is continuous at the start of modification, showed more uniform film thickness levels, and their shaft center trajectories were closer to the perfectly aligned bearing in the stable operating range of the system

Effect of Chamfer Form and Parameters on the Characteristics of Finite Length Journal Bearing under Impact Load

Journal bearings in typical applications are subjected to misalignment due to several causes, such as shaft deformation under load and errors related to the installation and manufacturing processes. Misalignment has well-known severe negative consequences on the performance of the bearings. This paper deals with the bearing chamfer to reduce these consequences of misalignment, and two forms of bearing edge modification are considered in the analysis. These forms are linear and curved chamfering of the bearing edges, where the height of the chamfer in the circumferential direction and the length of the modification in the longitudinal direction are considered as geometrical design parameters. The investigation includes a numerical solution of the hydrodynamic lubrication problem of finite length journal bearing, considering 3D misalignment cases using the finite difference method. This includes the assessment of the chamfer forms and their effects on the bearing performance in terms of the main bearing design parameters. Furthermore, the stability of the chamfered bearings is also investigated under impact load. Results showed that both chamfer forms are beneficial for a certain limit of the design parameters in reducing the maximum pressure and coefficient of friction and in elevating the film thickness levels, extending the range of misalignment in which the journal bearing can operate safely. In addition, the chamfered bearings in both forms showed more stability range in terms of the critical speed and shaft center trajectories under impact load. The bearings with the curved chamfer, where the slope is continuous at the start of modification, showed more uniform film thickness levels, and their shaft center trajectories were closer to the perfectly aligned bearing in the stable operating range of the system