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In the last article in this series we dealt with the methods of applying grease to anti‐friction bearings. In this article we deal with application of lubricating oils.

This study aims to numerically investigate the multi-phase flow and thermal physics inside gearboxes, which is critical to the theoretical analysis of energy transfer.

To explore the churning power losses, a three-dimensional numerical model of the gearbox is built using the RNG k–e turbulence model and three alternative moving mesh strategies (i.e. the dynamic mesh [DM], sliding mesh and immersion solid methods). The influence of the rotational speed on the transient flow field, including the oil distribution, velocity and pressure distribution and the churning losses, is obtained. Finally, the time-dependent thermo-fluid state of the gearbox is predicted.

The findings show that the global DM method is preferable for determining the flow structures and power losses. The rotational speed exerts a significant effect on the oil flow and the wheel accounts for most of the churning losses. Based on the instantaneous temperature distribution, the asymmetric configuration leads to the initial bias of the high-temperature region towards the pinion. Additionally, the heat convection efficiency of the tooth tip is slightly higher than that of the tooth root.

An in-depth understanding of the flow dynamics inside the gearbox is essential for its optimisation to decrease the power and enhance heat dissipation during operation.

This paper aims to propose a numerical method to calculate the convective heat transfer coefficient of spiral bevel gears under the condition of splash lubrication and to reveal the lubrication and temperature characteristics between the gears and the oil-air two-phase flow.

Based on computational fluid dynamics, the multiple reference frames (MRF) method was used to simulate the rotational characteristics of gears and the motions of their surrounding fluid. The lubrication and temperature characteristics of gears were studied by combining the MRF method with the volume of the fluid multiphase flow model.

The convective heat transfer coefficient can be improved by increasing the rotational speed and the oil immersion depth. Moreover, the temperature of the tooth surface having a large convective heat transfer coefficient is also found to be low. A large convection heat transfer coefficient could lead to a good cooling effect.

This method can be used to obtain the convective heat transfer coefficient values at different meshing positions, different radii and different tooth surface positions. It also can provide research methods for improving the cooling effect of gears under the condition of splash lubrication.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-07-2020-0233/

THIS series of articles is mainly directed towards enclosed gears, but since there is a very large quantity of open gearing that deserves better lubrication attention than it receives, a few words concerning methods of applying gear oils in these cases will not be out of place.

HISTORICAL. THE story of textile manufacture and the development of machinery designed to increase the production of yarns and cloths is an absorbing history. Although from the earliest times man has been master of the art of spinning and weaving, yet it is only during the last 200 years that any form of mechanisation has entered the industry.

The lubrication of the high-speed reducer of an electric vehicle is investigated. The specific contents include visualization of the flow field inside reducer, lubrication evaluation of bearings and efficiency experiment.

The flow field inside reducer at five working conditions: straight, uphill, downhill, left lean and right lean is simulated by smoothed particle hydrodynamics (SPH). According to the instantaneous number of particles through bearings, the lubrication states of bearings are evaluated. The test platform is set up to measure the efficiency of the reducer.

The flow field inside the reducer is obtained, the lubrication of bearings needs to be improved, the efficiency of the electric vehicle reducer meets the requirement.

The SPH method is used to simulate lubrication instead of using the traditional grid-based finite volume method. A novel method to evaluate the lubrication of bearings is proposed. The method and conclusions can guide electric vehicle reducer design.

Part One in this series appeared in our January issue and dealt with fundamental factors and properties required by gear lubricants. Part Two in our February issue covered the lubrication of worm gear units. The next part will give details of gear manufacturers' recommendations and their formulae for arriving at the most suitable oil viscosity for lubrication of their respective gear units. Future parts will include full details of the causes and elimination of gear wear, fracture and breakdowns caused by incorrect lubrication or application of lubricants, and of course those troubles frequently and erroneously blamed on to the lubricant.

The major steel works of the world have been the foremost industries to recognise the importance of correct lubrication. Whilst we appreciate their foresight and good sense and are particularly observant of the impetus that they have given to the subject of applied lubrication, we must not lose sight of the fact that this advancement in lubrication has been forced upon them since it is correct to state that no modern rolling mill could possibly attain anything like its present output unless the lubrication of its mill roll bearings was adequately catered for by modern lubricating equipment.

A series of articles dealing, in as simple a way as possible, with the basic facts of lubrication, lubricants, their selection and prescription, specification, application, and testing. This series is primarily intended for students, engineering personnel who may be unfamiliar with certain aspects and others who, one way or another, are interested in this important subject.

A STUDY of the published literature on I.C. engine lubrication during the last ten years leads one to the conclusion that we are in a state of crisis, with no final solution for many of the problems involved. One reason for this may be due to over specialisation. The automobile engineer, for example, knows little of the intricate problems involved in refining and blending lubricating oils. At a meeting in the U.S.A. recently, a well known technical expert, describing his tests, said that he first used a “Medium Refined Straight Mineral Oil”. This he later replaced by a “Highly Refined Straight Mineral Oil”. Next he selected a “High Viscosity Index Straight Mineral Oil” and ended by using a “Heavy Duty Oil”, apparently believing that he moved always in the direction of oils of higher quality.