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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Epicyclic gear train nptel pdf merge

In such trains as shown in Fig. Sliding at point I. Concept of involute profile. With increase in pitch line velocity, lubricant used should be less viscous in order to min. In absence of lubricant additives and antifriction coating, gears will be subjected to direct friction.

But for home applications, we use N-N gear pair, where rate of heat generation is relatively low. Generally, a gear pair acts as a speed reducer aiming torque amplification at output shaft.

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. In case of heavily loaded gears, however, more viscous lubricant will be gar. Friction ttains gear pair occurs due to sliding between meshed teeth and churning of lubricant. Using AGMA pitting equation formula, determine the maximum contact stress.


Most gears are in the hardness range of approximately Rc 30 to Rc 38 or Rc 55 to Rc Internal gears are generally more efficient since the sliding velocity along the profile is lower than equivalent external gears.

Maximum contact stress is equal to p max. Ideally, rolling gears are required. It prevents jamming of teeth and compensates for gar expansion of teeth.

Chapter 1. Introduction to Mechanisms

On changing center distance, line of action still remains tangent to both base circles but slope changes. At all other contact points as shown in Fig. Higher value of T f cause scuffing failure of gears. In tdains, lower loads are imposed on the support bearings because of a decrease radial load component.

In practice, trsins comes along rolling action. In a geared system, the total power loss is comprised of two groups of losses: For high speed reduction, compound gear trains are required. Typical gear pair having high sliding is shown in Fig. Too much or too less lubricant is harmful for gear operation.

Gear surfaces coated with boundary additive or antifriction coating. This means mild wear is bound to occur in gear operations. In helical angle greater than 15 degrees, the tooth bending capacity generally begins to drop off due to the nprel that the tooth thickness decreases rapidly. In addition, helical gears causes axial thrust force and impose load on bearings.


Composite roughness depends on gear manufaturing process as given in Table 6. In this regime, friction and wear are influenced by the ability of lubricant to create protective boundary films on gear tooth with chemical and physical reactions, and by its viscous characteristics. Sliding action traind spur gears. Worm gears have crossed axes Fig.

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. Normal gear load W n for a given application depends on pitch diameter and face width. In high speed units, the churning losses may exceed the friction losses; therefore, the type and amount of lubricant are critical.

Normal load on tooth.