Duncan Dowson: Pioneer of elastohydrodynamic lubrication of gears

The paper briefly reviews Duncan Dowson's ground-breaking contribution to the theory of elastohydrodynamic lubrication in relation to the understanding of lubrication of gear tooth contacts. His early work with Higginson on numerical modelling of elastohydrodynamic lubrication finally explained how gears can operate successfully, and avoid wear, due to the generation of a stiff, protective oil film. The resulting minimum film thickness equation stands as a reliable reference formula for calculations in gear design standards. The paper includes examples of how elastohydrodynamic lubrication theory has been developed by the present authors and their co-workers, and applied to aid the design of engineering components such as worm gears, thrust rims and profile-modified helical gears. Also included is its extension to include the important effects of surface roughness at the asperity level (micro-elastohydrodynamic lubrication) and its relevance to the current, troublesome problem of micropitting.

Design and Analysis of 2-Stage Gearbox for ATV Applications

The main objective of this project is to design and develop a 2-Stage- Reduction gearbox for all terrain vehicles application. Gearbox is a mechanical unit consisting of series of gears within a housing (casing) or a simple gear train. It is the main component of the powertrain system as it provides speed and torque conversions from the Engine or CVT to the wheels. The gears inside of gearbox can be any one of a number of different types of the gear that are available in the market i.e., from spur gears to worm gears and planetary gears as well. In this report the gearbox is made from a helical gear train. This report focuses on selection of overall reduction ratio of the gearbox, material selection, selection of gear dimensions, selection of shaft dimension, design of key and bearing selection from SKF bearing catalogue. The bending and wear strengths are calculated to determine factor of safety and later, Finite element analysis is performed to validate the results. Keywords: Geartrain, Shaft Design, SKF Bearings, Solidworks, FEA

Wear simulation of worm gears based on an energetic approach

Wear phenomena in worm gears are dependent on the size of the gears. Whereas larger gears are mainly affected by fatigue wear, abrasive wear is predominant in smaller gears. In this context a simulation model for abrasive wear of worm gears was developed, which is based on an energetic wear equation. This approach associates wear with solid friction energy occurring in the tooth contact. The physically-based wear simulation model includes a tooth contact analysis and tribological calculation to determine the local solid tooth friction and wear. The calculation is iterated with the modified tooth flank geometry of the worn worm wheel, in order to consider the influence of wear on the tooth contact. Experimental results on worm gears are used to determine the wear model parameter and to validate the model. A simulative study for a wide range of worm gear geometries was conducted to investigate the influence of geometry and operating conditions on abrasive wear.

Scuffing load capacity calculation of worm gears

Worm gears with wheels of harder materials, such as cast iron or steel, are often prone to the damage type scuffing, which can cause a sudden and rapid failure of the gear box. Contact temperature is a suitable criterion to determine the scuffing safety for other types of gears. However, for worm gears, a scuffing load capacity calculation is not available at the moment. This paper presents a numerical temperature simulation for worm gears that considers transient multidimensional heat transfer and local frictional loading due to the contact. Based on the results of this simulation, this paper derives a simplified calculation of worm gear contact temperatures. The calculation only contains input parameters that are already part of current standards. Its result, the contact temperature of worm gears, can be used to rate the scuffing load capacity.

Investigation of the influence of the process of gear honing by diamond worm honing tools on the roughness factor of gear wheels

In the presented article, a new method of finishing is considered in more detail - gear honing of cylindrical gears. Analysis of literature sources shows that the most problematic technological operation is the finishing of gear wheels and gear honing in particular. The difference between the traditional honing of cylindrical gears with disc abrasive honing and the new method of processing with diamond worm honing is shown. The main advantage of this method is that it can be implemented on milling machines. New tools are proposed - diamond worm gears and the technology of their manufacture is described. The modes of processing cylindrical gears with various diamond worm gears are given and the processing method itself is described. The gear wheels that were processed are used in hydraulic pumps and in hydraulic motors. Roughness parameters Rmax (total height of profile), Rz (irregularity height at 10 points), Rq (root mean square deviation of the assessed profile), which correspond to the Ukrainian and European DSTU ISO 4287 standard, were used as a criterion for assessing the quality of gear processing: 2012. As you know, the strength, wear resistance, durability and other parameters depend on the roughness of the working surfaces of the teeth of the gear wheels. Roughness affects the wear of contact surfaces and noise during operation when running in gears, as well as at the time of their starting. The surfaces were compared before and after treatment. Distribution curves were plotted to visualize the experimental data. When using the new processing method, the correction of defects of the previous processing methods is shown. Based on the results of the studies carried out, it can be concluded that the roughness parameters Rmax, Rz, Rq improve on average by 1.5-2 times. This method can be recommended for the finishing of cylindrical gears, as effective and not requiring new equipment, replacing the traditional methods of honing gears, which can be implemented without significant costs at most Ukrainian enterprises.

Calculation of the Digital Prototype for Modification of the Initial Straight Profile to the Form of the Tooth-Cutting Tool’s Producing Surface

Spatial helical gears, worm gears with a cylindrical worm, globoid gears, etc., are widely used in most of modern engineering products [1-3; 37; 42]. Cylindrical worm gears are actively used in the creation of metalworking equipment (push mechanisms of rolling mills, presses, etc.), in lifting and transport machines, in drives and kinematic chains of various machine tool equipment where high kinematic accuracy is required (dividing machine tools, adjustment mechanisms), etc. In a worm gear a cylindrical worm or its cylindrical helical surface can be cut by various technological methods [49-51], but no matter how the shaping of the worm gear elements’ working surfaces is carried out, the worm wheel is cut with a gear cutting tool, whose producing surface coincides with the worm thread’s lateral surface [19; 22; 23]. In this regard, the working surface of the cylindrical worm wheel’s tooth, even with a non-orthogonal arrangement of axes, is an envelope of a one-parameter family of surfaces that gives a linear contact, which presence makes it possible to transfer a large load using a worm gear. For high-quality manufacturing of worm gears, it is necessary to design and manufacture a productive gear cutting tool - an accurate worm cutter, whose shaping (working) surface must be identical to the profiled worm’s shaping (working) surface [24-27; 54]. One of the most important tasks in the implementation of worm gearing is the problem of jamming of the cylindrical worm and the worm wheel’ contacting surfaces. This problem is excluded by relieving the contacting surfaces’ profile along the contact line. Considering that any violations of contacting surfaces’ geometric parameters affect the change in their geometric characteristics, the tasks of accurately determining the adjustment parameters of the technological equipment, used for shaping the worm and worm wheel, enter into in the foreground of the worm gearing elements production. In modern conditions of plant and equipment obsolescence, and in particular, of gear cutting machines used for worm gears manufacture, these machines physical wear, implies an inevitable decrease in the accuracy of their kinematic chains. Therefore, in order to maintain the produced gears’ quality at a sufficiently high level, it is necessary to use deliberate modification of contacting surfaces when calculating the worm gearing’s geometric parameters; such modification reduces the worm gear sensitivity to manufacturing and mounting errors of its elements [28-31].

Worm gear wear and coefficient of efficiency during their running-in period

The process of worm gear wear is considered. The reasons for the change in the coefficient of efficiency of worm gears during the running-in period are analyzed. Keywords: worm gear, line of engagement, contact surfaces, involute worm, velocity vector, friction coefficient. [email protected]