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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Gear surface with adsorbed gases.

Concept of involute profile. The sliding friction losses are related to the coefficient of friction, normal load and sliding velocity on the contact surfaces, while the rolling friction losses occur due to the formation of an elastohydrodynamic EHL film.

In practice, sliding comes along rolling action.

Epicyclic gear train nptel pdf merge

Higher entraining velocity increase “spin losses”. Sliding and rolling friction losses at the loaded gear meshes and at the bearings largely define the load-dependent mechanical power losses. Higher value of T f cause scuffing failure of gears.

Helical crossed axis gears.

For high speed reduction, compound gear trains are required. In high speed units, the churning losses may exceed the friction losses; therefore, the type and amount of lubricant are critical. Interface shear strength nltel mixed lubrication can be given by.


Gear surfaces coated with boundary additive or antifriction coating. At all other contact points as shown in Fig. Torque is calculated from the horsepower transmitted and the speed of rotating component in question. The internal gears eliminates the use of an idler gear, where it is necessary to have two parallel shafts rotate in the same direction.

NPTEL :: Textile Engineering – Mechanics of Textile Machinery

Due to sliding, power loss occurs and transmission efficiency decreases. Rolling and sliding in gears: The amount of speed reduction is simply the ratio of pitch diameters of the larger gear to the smaller gear. Helical gearing, in which the teeth are cut at an angle with the axis of rotation, was developed after spur gearing and has the advantages that has the smoother action and tends to be quieter Fig.

It prevents jamming of teeth and compensates for thermal expansion of teeth. Following two coatings as solid lubricants are used to reduce friction. Recommended oil viscosity [2]. Effect of Brinell hardness on allowable contact stress for through-hardness steel [2].

Following empirical formulae are availiable for splash lubrication system to minimize churning losses. They thus protect the surface of the base material from excessive wear and subsequent destruction.

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

Generally tooth profile is designed so that velocity ratio does not change due to inaccuracies in center distance. The total mechanical loss is then given as the sum of losses from all gear meshes and bearings.


Smaller gear is known as pinion and larger mating gear is called gear. Gears are machine elements, which are required to transmit power between shafts rotating at different rotational speeds. It operates at closer center distance with its mating pinion than external gears of the same size, which often permits a more compact design. Geae normal atmospheric conditions, all engineering metallic surfaces are primarily coated with some adsorbed gas Fig.

Inadequate lubrication may also be a source of excessive heat and wear. By adding teeth of the proper shape on disk, power can be transmitted without slip at uniform rate.

Epicyclic gear train nptel pdf merge | sijthre

But sometime failure of lubrication pump failure, filter chocking, excessive leakage occurs and gear materials must be able to handle such extreme situations. In case of heavily loaded gears, however, more viscous lubricant will be recommended. Normal load on tooth. In addition, lower loads are imposed on the support bearings because of a decrease radial load component. Maximum contact pressure at nnptel contact point between two cylinders is given by:.

So N-S is prefferable.