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.
An infinitely variable transmission (IVT) is a system that allows for a continuous (nondiscrete) variation (including zero) in transmission ratio between two rotating elements. In this paper, a novel ratcheting-type IVT mechanism is presented and its geometrical design and kinematic analysis are studied in details. The proposed system contains two identical units. Each unit includes a cam with a follower, oscillatory slotted links pivoted at a shaft that can be moved vertically by a hydraulic ram (alterable transmission ratio), and a grooved wheel with an actuating rod. The input rotational motion is converted through each unit to an oscillatory angular motion of controlled amplitude. This resulting motion is rectified using a ratchet to get a unidirectional output rotational motion. Therefore, the system output motion will have a different velocity and acceleration than those of the system input. The kinematic analysis revealed that the transmission ratio can be varied continuously in a range from zero to infinity. The analysis also showed that, for particular transmission ratios, the system gives uniform output (angular velocity and acceleration) for a corresponding uniform input.
Experimental and theoretical analyses are reported to study the heat generation and partition in an elastohydrodynamic rolling/sliding point contact. Heat is generated within the lubricant in the Hertzian region by shearing and compression of the oil film. This heat is essentially conducted to the contacting surfaces as the amount convected from the Hertzian zone by the lubricant can be neglected due to the very low lubricant mass flowrate.A two-disk test rig was used for the experimental tests using crowned, superfinished 76.2 mm diameter disks fixed on parallel shafts. Each disk was fitted with six thermocouples in two rows of three located 3 mm and 6 mm below the surface to measure the temperature distribution of the disks during the tests. In addition, the disks were insulated on both plane sides by ceramic washers to minimise heat transfer to the surroundings over those surfaces.A numerical model was developed to calculate the circumferential mean disk temperature distribution in the outer 6 mm annular ring using the inner row of thermocouples to provide a boundary condition. The model was used to predict the temperature distribution for given values of the fraction of the total heat entering the fast disk, b, and the heat transfer coefficient, h, for the disk running surfaces.Minimisation of error between predicted and experimentally measured temperatures at the thermocouple positions, together with consideration of the physical relationship between fast and slow shaft heat transfer coefficients led to the conclusion that b lies in the range 0.71 to 0.77 for the experiments reported in the paper and that approximately 75% of the frictional heat dissipated within the lubricant film flows
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