1) How do you identify a planetary gear? A gear whose axis itself is revolving is called a planetary gear. In some epicyclic gear trains, we may find two or more. described a number of gear applications, typical ones are shown in Figs. used in high speed and high load application in all types of trains and a wide range. The velocity ratio of an epicyclic gear train is determined by the following methods: (a) Tabulation method; (b) Formula method; and (c) Instant centre method or.
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Recommended oil viscosity . In manufacturing point of view also, external gears are simpler than internal gears. The limit on velocity ratio depends on gear pair for example:. Hypoid gears are widely used in many power trains to transfer power between two non-intersecting crossed axes. By using parameters shown in Table 6. There is no limit to the speed reduction ratio that can be achieved using vear but larger ratio must be obtained using multi-stage reduction.
In case of heavily loaded gears, however, more viscous lubricant will be recommended. So N-S is prefferable. Gear surface with adsorbed gases.
The lower pressure angle has the advantage of smoother and quieter tooth action because of larger profile traind ratio. Generally tooth profile is designed so that velocity ratio does not change due to inaccuracies in center distance. In this regime, friction and wear are influenced by the ability of lubricant to create protective boundary films on gear tooth with chemical and physical reactions, and by its viscous characteristics.
In a geared system, the total power loss is comprised of two groups of losses: Effect of Brinell hardness on allowable contact stress for through-hardness steel . This is hypothetical situation which occurs rarely in extreme conditions.
NPTEL Phase II :: Tribology
Usually, following two types of lubrication mechanisms are commonly used for gear lubrication. An efficient notel of achieving high reduction ratios in minimum space is the use of planetary gearing. This happens at pitch point. It is interseting to note that even spur gears experience sliding ,as depicted in Fig.
NPTEL :: Textile Engineering – Mechanics of Textile Machinery
It is interesting to note that oil sample collected after 3 hours of operating gear at rpm no load conition show wear Fig. In such trains as shown in Fig. Normal gear load W n for a given application depends on pitch diameter and face width. Worm gears have geat axes Fig. Typical gear pair having high sliding is shown in Fig.
Gesr thus protect the surface of the base material from excessive wear and subsequent destruction. Inadequate lubrication may also be a source of excessive heat and wear. Following empirical formulae are availiable for splash lubrication system to minimize churning losses. Due to sliding, power loss occurs and transmission efficiency decreases.
Nnptel AGMA pitting equation formula, determine the maximum contact stress. Too much or too less lubricant is harmful for gear operation.
In absence of lubricant additives and antifriction coating, gears will be subjected to direct friction. With involute profile of gears, only one contact position experiences pure rolling.
But sometime failure of lubrication pump failure, filter chocking, excessive leakage occurs and gear materials must be able to handle such extreme situations.
In helical angle greater than 15 degrees, the tooth bending capacity generally begins to drop off due to the fact that the tooth thickness decreases rapidly. Helical crossed axis gears.
Helical crossed axes Fig. Q v vs geometric tolerance. To estimate the working life of gears, it is essential to analyze the destructive forces at work, and tains of the ability of chosen gear materials to withstand those forces. Gears are machine elements, which gsar required to transmit power between shafts rotating at different rotational speeds.
Tooth curves of the mating teeth need to be tangent to each other as shown in Fig.
Epicyclic gear train nptel pdf merge
As contact moves towards or away from pitch point, sliding occurs. In addition, helical gears causes axial thrust force and impose load on bearings. Friction between gear pair tranis due to sliding between meshed teeth and churning of lubricant.
In practice, sliding comes along rolling action. Their most common and highest-volume applications can be found in npetl and rear axles of rear-wheel-drive or all-wheel-drive vehicles.
Friction losses can be divided into two major categories: Higher entraining velocity increase “spin losses”. Rolling and sliding in gears: Surface failure of gear tooth occurs due to very high local contact stresses.