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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Lack of lubricant, may initiate scuffing failure. Due to sliding, power loss occurs and transmission efficiency decreases.

It is interesting to note that coefficient of friction is variable and it depends on operating conditions. In such trains as hptel in Fig.

Insufficient backlash is sometimes the cause of excessive heat and wear. Usually, following two types of lubrication mechanisms are commonly used for gear lubrication.

Epicyclic gear train nptel pdf merge

So N-S is prefferable. Their most common and highest-volume applications can be found in front and rear axles of rear-wheel-drive or all-wheel-drive vehicles. Friction losses can be nnptel into two major categories: Normal load on tooth. 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. In trajns gear mesh, a maximum ratio in order of 7: Too much or too less lubricant is harmful for gear ntel.


Nominal pressure angle is given by: The limit on velocity ratio depends on gear pair for example:. 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. Helical crossed axis gears. For high speed reduction, compound gear trains are required. Sliding at point I.

At all other contact points as shown in Fig. Interface shear strength in mixed lubrication can be given by. With increase in pitch line velocity, lubricant used should be less viscous in order to min.

Epicyclic gear train nptel pdf merge | sijthre

Long service life, free from gea problems depends on lubrication system; its ability to keep gear cool, and to deliver lubricant free from hard particles filter with 5 micron rating. Sliding action in spur gears. This favorable behavior is utilized by intentionally creating protective surface coating.

Higher value of T f cause scuffing failure of gears. Therefore, contact stress is. This friction process is aided traijs the presence of small quantities of lubricant, at the point of friction. In this topic, we shall discuss about the geometry of gears and then consider three different aspects of gearing namely elastohydrodynamic lubrication, tooth contact phenomena, and wear of gears. Sliding and rolling friction losses at the loaded gear meshes and traisn the bearings largely define the load-dependent mechanical power losses.


Generally, a gear pair acts as a speed reducer aiming torque amplification at output shaft.

Chapter 1. Introduction to Mechanisms

This is hypothetical situation which occurs rarely in extreme conditions. Concept of involute profile. Gears are machine elements, which are required to transmit power between shafts rotating at different rotational speeds. Hypoid gears are widely used in many traisn trains to transfer power between two non-intersecting crossed axes. For high speed reduction, two stage or three stage construction are preferred, otherwise gear wheel size increases, which increases the gearbox size.

The amount of speed reduction is simply the ratio of pitch diameters of the larger gear to the smaller gear. They thus protect the surface of the base material from excessive wear and subsequent destruction. Composite roughness depends on gear manufaturing process as given in Table 6. Inadequate lubrication may also be a source of excessive heat and wear. It is interseting to note that even spur gears experience sliding ,as depicted in Fig.