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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Smaller gear is known as pinion and larger mating gear is called gear. Hypoid gears are widely used in many power trains to transfer power between two non-intersecting crossed axes. Nominal pressure angle is given by: An efficient method of achieving high reduction ratios in minimum space is the use of planetary gearing. As contact moves towards or away from pitch point, sliding occurs.
Higher entraining velocity increase “spin losses”. Too much or too less lubricant is harmful for gear operation.

In such trains as shown in Fig. Therefore, contact stress is. Using AGMA pitting equation formula, determine the maximum contact stress. Rolling and sliding in gears: But for home npteo, we use N-N gear pair, where rate of heat generation is relatively low. This means mild wear is bound to occur in gear operations. By using parameters shown in Table 6. Concept of involute profile. Due hear sliding, power loss occurs and transmission efficiency decreases. So N-S is prefferable. 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.
Normal load on tooth.
Epicyclic gear train nptel pdf merge
In practice, sliding comes along rolling action. Composite roughness depends on gear manufaturing process as given in Table 6. Pressure angle at base circle is zero. Ideally, rolling gears are required. This favorable behavior is utilized by intentionally creating protective surface coating.
Helical gearing, in which the teeth are cut at an angle with the axis of rotation, tdains developed after spur gearing and has the advantages that has the smoother action and tends to be quieter Fig. Gear life depends on effective lubrication, which can be quatified by minimum film thickness to R compositeas shown in Fig.
Usually, following two types of lubrication mechanisms are commonly used for gear lubrication.

Maximum contact pressure at the contact point between two cylinders is given by:. These dimensions are determined on the basis of tooth stresses, which are imposed by the transmitted tooth load.
Sliding at point I. In this topic, we shall discuss about the geometry of gears and then consider three different aspects of gearing namely elastohydrodynamic lubrication, nptfl contact phenomena, and wear of gears. Helical crossed axis gears.
Epicyclic gear train nptel pdf merge | sijthre
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. Properly designed gear-sets should never fail but must be expected to eventually fail by wear of one of surface. Torque is calculated from the horsepower transmitted and the speed of rotating component in question.
By adding teeth of the proper shape on disk, power can be transmitted without slip at uniform rate.
The internal gears eliminates the use of an idler gear, where it is necessary to have two parallel shafts rotate in the same direction. Typical gear pair having high sliding is shown in Fig. Inadequate lubrication may also be a source of excessive heat and wear.
With increase in pitch line velocity, lubricant used should be less viscous in order to min. Sliding action in spur gears.
In normal atmospheric conditions, all engineering metallic surfaces are primarily coated with some adsorbed gas Fig. For rolling action, tangential velocities at point of contact must be equal to make sliding zero. Gear surface with adsorbed gases. Higher value of T tgains cause scuffing failure of gears.
It is interesting to note that coefficient of friction is variable and it depends on operating conditions. This happens at pitch point.



























