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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The lower pressure angle has the advantage of smoother and quieter tooth action because of larger profile contact ratio. Friction losses can be divided into two major categories: On changing center distance, line of action still remains tangent to both base circles but slope geae.
Higher entraining velocity increase “spin losses”.
Epicyclic gear train nptel pdf merge
Tooth curves of the mating teeth need to be tangent to each other as shown in Fig. Most gears are in the hardness range of approximately Rc 30 to Rc 38 or Rc 55 to Rc The tooth load is simply the torque on a given gear divided by the gear pitch radius.
In case nptrl heavily loaded gears, however, more viscous lubricant will be recommended.
It is interesting to note that oil sample rrains after 3 hours of operating gear at rpm no load conition show wear Fig. These dimensions are determined on the basis of tooth stresses, which are imposed by the transmitted tooth load.
Epicyclic gear train nptel pdf merge | sijthre
Long service life, free from wear npteo depends on lubrication system; its ability to keep gear cool, and to deliver lubricant free from hard particles filter with 5 micron rating. Often gears are treated as pitch cylinder, which roll together without slip as shown in Fig. This is hypothetical situation which occurs rarely in extreme conditions.
Gears are machine elements, which are required to transmit power between shafts rotating at different rotational speeds. Torque is calculated from the horsepower transmitted and the speed of rotating component in question. Sliding at point I. Lack of lubricant, may initiate scuffing failure. The amount of speed reduction is simply the ratio of pitch diameters of the larger gear to the smaller gear.
Inadequate lubrication may also be a source of excessive heat and wear. Q v vs geometric tolerance. In manufacturing point of view also, external gears are simpler than internal gears.
In a geared system, the total power loss is comprised of two groups of losses: In such trains as shown in Fig. Usually, 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. Recommended oil viscosity .
Friction between gear pair occurs due to sliding between meshed teeth and churning of lubricant. In this regime, friction and wear are influenced by the ability of lubricant to create protective boundary films on gear nptdl with chemical and physical reactions, and by its viscous characteristics. Helical crossed axis gears.
Typical values of gear efficiencies are listed in Table 6. If sufficient backlash has not been provided to take care of the differential thermal expansion, the teeth will bind, with disastrous results. Following empirical formulae are availiable for splash lubrication system to minimize churning losses. Smaller gear is known as pinion and larger mating gear is called gear. It prevents jamming of teeth and compensates for thermal expansion of teeth. Generally, a gear pair acts as a speed reducer aiming torque amplification at geae shaft.
Surface failure of gear tooth occurs due to very nptep local contact stresses. Internal gears are generally more efficient since the sliding velocity along the profile is lower than equivalent external gears. 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. Interface shear strength in mixed lubrication can be given by. Following two coatings as solid lubricants are used to reduce friction.
Helical crossed axes Fig.