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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With increase in pitch line velocity, lubricant used should be less viscous in order to min.

Epicyclic gear train nptel pdf merge | sijthre

Sliding action in spur gears. Ideally, rolling gears are required. Surface failure of gear tooth occurs due to very high local contact stresses.

Maximum contact pressure at the contact point between two cylinders is given by:. Recommended oil viscosity [2].

They thus protect the surface of the base material from excessive wear and subsequent destruction. If sufficient backlash has not been provided to take care of the differential thermal expansion, the teeth will bind, with disastrous results. Effect of Brinell hardness on allowable contact stress for through-hardness steel [2]. So N-S is prefferable. Gears traisn machine elements, which are required to transmit power between shafts rotating at different rotational speeds.


Often gears are treated as pitch cylinder, which roll together without slip as shown in Fig. Nnptel, following two types of lubrication mechanisms are commonly used for gear lubrication. To estimate the working life of gears, it is essential to analyze the destructive forces at work, and knowledge of the ability of chosen gear materials to withstand those forces. There is no limit to the speed reduction ratio that can be achieved using gearing; but larger ratio must be obtained using multi-stage reduction.

By using parameters shown in Table 6. Composite roughness depends on gear manufaturing process as given in Table 6. In simple gear mesh, a maximum ratio in order of 7: This is hypothetical situation which occurs rarely in extreme conditions. With involute profile of gears, only one contact position experiences pure rolling. In absence of lubricant additives and antifriction coating, gears will be subjected to direct friction.

Tooth curves of the mating teeth need to be tangent to each other as shown in Fig. Using AGMA pitting equation formula, determine the maximum contact stress. By adding teeth of the proper shape on disk, power can be transmitted without slip ntel uniform rate.

Epicyclic gear train nptel pdf merge

For high speed reduction, compound gear trains are required. As contact moves towards or away from pitch point, sliding occurs. Helical crossed axes Fig. Gear life depends on effective lubrication, which can be quatified by minimum film thickness to R compositeas shown in Fig. Hypoid gears are widely used in many power trains to ttrains power between two non-intersecting crossed axes. These types of geometrics are known as external gears. For high speed reduction, two stage or three stage construction are preferred, otherwise gear wheel size increases, which increases the gearbox size.


Properly designed gear-sets should never fail but must be expected to eventually fail by wear of one of surface. Bore diameter of pinion is 17 mm, and bore nptell of gear is 20 mm. This friction process is aided by the presence of small quantities npteo lubricant, at the point of friction.

Long service life, free from wear problems depends on lubrication system; its gesr to keep gear cool, and to deliver lubricant free from hard particles filter with 5 micron rating.

At all other contact points as shown in Fig. 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.