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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For high speed reduction, compound gear trains are required. Tooth curves of the mating teeth need to be tangent to each other as shown in Fig. In high speed units, the churning losses may exceed the friction losses; therefore, the type and amount of lubricant are critical.

Chapter 1. Introduction to Mechanisms

Insufficient backlash is sometimes the cause of excessive heat and wear. Typical gear pair having high sliding is shown in Fig. 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.

For rolling action, tangential velocities at point of traijs must be equal to make sliding zero. Generally, a gear pair acts as a speed reducer aiming torque amplification at output shaft. The internal gears eliminates the use of an idler gear, where it is necessary to have two parallel shafts rotate in the same direction.

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With increase in pitch line velocity, lubricant used should be less viscous in order to min. Normal gear load W n for a given application depends on pitch diameter and face width.

With involute profile of gears, only one contact position experiences pure rolling. An efficient method of achieving high reduction ratios in minimum space is the use of planetary gearing.

Epicyclic gear train nptel pdf merge

The total mechanical loss is then given as the sum of losses from all gear meshes and bearings. Loss due to load and loss due to speed. Usually, following two types of lubrication mechanisms are commonly used for gear lubrication. 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.

Most gears are in the hardness range of approximately Rc 30 to Rc 38 or Rc 55 to Rc It is interesting to note that oil sample collected after 3 hours of operating gear at rpm no load conition show wear Fig.

Epicyclic gear train nptel pdf merge | sijthre

To design gear, we need to estimate W n Fig. It is interesting to note that coefficient of friction is variable and it depends on operating conditions. Interface shear strength in mixed lubrication can be given by. In a geared system, the nptep power loss is comprised of two groups of losses: Inadequate lubrication may also be a source of excessive heat and wear.


This means mild wear is bound to occur in gear operations. Composite roughness depends on gear manufaturing process as given in Table 6.

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. This happens at pitch point. Properly designed rtains should never fail traisn must be expected to eventually fail by wear of one of surface.

Typical values of gear efficiencies are listed in Table 6. It prevents jamming of teeth and compensates for thermal expansion of teeth. Torque is calculated from the horsepower transmitted and the speed of rotating component in question.

Gear surfaces coated with boundary additive or antifriction coating. Recommended oil viscosity [2]. Concept of involute profile.