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.

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.

Misalignment is one of the most common challenges that the normal operation of journal bearings faces. This type of problem may be the result of a wide range of reasons, such as bearing wear, shaft deformation, and errors related to the manufacturing and installation process. The main undesirable consequences of the misalignment, such as pressure rise and lubricant film reduction, are concentrated on the bearing edges. Therefore, chamfering the bearing edges reduces such misalignment-related drawbacks. This work presents a novel numerical solution to the problem of finite-length journal bearing considering edge chamfering. This solution involves the determination of the levels of lubricant layer thickness and pressure distribution in addition to the journal trajectory under impact load with the related stability limits. The finite difference method is used in this solution, and the equations of motion are also solved numerically using the Runge–Kutta method. The Results of this novel analysis show that chamfering the bearing edges increases the film thickness and reduces pressure spikes associated with the system operation under the case of 3D misalignment. Furthermore, the chamfered bearing shows a wide stability range under impact loads, where the normal bearing is unstable as the critical speed increases by 26.98%, which has positive consequences on the journal’s trajectory.