• Abhi Shejul

Gears and Transmission - Part 3

What are the different types of gear assemblies?


Law of Gearing

The common normal at the point of contact between a pair of teeth must always pass through the pitch point for all mating gear positions, according to the law of gearing. The design of the gear profile is based on this law. This is a must for the two gears to function properly.


The angular velocity between two mating gears always remains constant.

Therefore, from the Law of gearing we can derive the relationship as:

where w is angular velocity of gear, n is the gear speed, d is the pitch diameter of the gear,

T is number of teeth on the gear.


How do gears work together? How are these gearing law and gear ratio applied in a gear assembly?



 

Effect of gear ratio on speed:

The configuration is known as reduction gear drive when the number of gears on the output shaft is more than the number of gears on the input shaft. The speed of output shaft will be les than the input shaft.


The output shaft will have a higher speed than the input shaft if the configuration is reversed, i.e. the number of gears on the output shaft is less than the number of gears on the input shaft.


The best example to understand this is the automotive gear box. For lower speeds, we must drive in the low gears (1st or 2nd gear) but as the speed increases we shift to higher gears.


Gear trains are created when two or more gears are made to interfere with each other in order to transmit power from one shaft to another. In a vehicle, power is transferred from engine to the wheels through the gearbox.

A gear assembly with two or more gears is commonly referred to as a Gear Train!
 

Types of gear train:

There are generally four types of gear trains.

  • Simple Gear Train

  • Compound Gear Trains

  • Reverted gear Trains

  • Epicyclic Gear Trains

Simple Gear Trains:

A simple gear train is made up of single gear connected to each shaft, one linked to the drive shaft (input) and the other to the driven shaft (output). The motion of the driver gear and the motion of the driven gear will always be in the opposing directions for a simple two geared train.

In a multi geared simple gear train, the gear which is not connected to drive shaft of driven shaft is called as idler.


Where n is the speed of the respective gear.


Compound Gear Trains:

In a compound gear train, the intermediate gear is a compounded gear i.e. there will be more than one gear on the intermediate axil/shaft. The co-axially connected gears will rotate with same speed, but will have different outputs.

Where n is the speed of the respective gear.


Reverted Gear Trains:

The compound gear train where the input and output gears are on the same axis is know as reverted gear train. The input and output shafts are aligned on the same axis, and they rotate at different speeds. This type of assembly is optimal for compact spaces.

Where n is the speed of the respective gear.


Epicyclic Gear Trains:

One of the most complex and widely used gear train assembly is the Epicyclic gear train. An epicyclic gear train (also known as a planetary gearset) is made up of two gears with the center of one rotating around the center of the other. A carrier connects the two gears' centers and turns the planet and sun gears' pitch circles so that they roll without slipping. An epicycloid curve is traced by a point on the planet gear's pitch circle. The solar gear is fixed in this simplified example, while the planetary gears rotate around it.


Check the below video to understand the functioning of an planetary gearset.


 

How is torque affected by the gear arrangement?

The torque produced at the output shaft is Gear Ratio times the torque produced at the input shaft.

For example, a gear system having a gear ratio of 1.5 is having input torque of 100 N-m.

 

Summary:

  • The angular velocity between two mating gears always remains constant.

  • A gear assembly with two or more gears is commonly referred to as a Gear Train.

  • Different types of gear trains have different application.

  • Epicyclic gear train is one of the complex gear assemblies. It is used in watch and even in automatic transmissions in vehicles.

 

That is all for gear trains. Please let us know which gear train you found interesting in the comments. Follow Mech n Flow for more amazing content ahead!

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