Epicycle Gear Apparatus

EPICYCLE GEAR APPARATUS Lab Report No. IST-MECH-MEG-EXP05/00

5.1Introduction

A gear train is two or more gear working together by meshing their teeth and turning each other in a system to generate power and speed. It reduces speed and increases torque. To create large gear ratio, gears are connected together to form gear trains. They often consist of multiple gears in the train. The smaller gears are one-fifth of the size of the larger gear. Electric motors are used with the gear systems to reduce the speed and increase the torque. Electric motor is connected to the driving end of each train and is mounted on the test platform. The output end output end of the gear train is connected to a large magnetic particle brake that is used to measure the output torque.

Simple Gear Train The most common of the gear train is the gear pair connecting parallel shafts. The teeth of this type can be spur, helical or herringbone. The angular velocity is simply the reverse of the tooth ratio. The main limitation of a simple gear train is that the maximum speed change ratio is 10:1. For larger ratio, large size of gear trains is required; this may result in an imbalance of strength and wear capacities of the end gears. The sprockets and chain in the bicycle is an example of simple gear train. When the paddle is pushed, the front gear is turned and that meshes with the links in the chain. The chain moves and meshes with the links in the rear gear that is attached to the rear wheel. This enables the bicycle to move.

Compound Gear Train:For large velocities, compound arrangement is preferred. Two keys are keyed to a single shaft. A double reduction train can be arranged to have its input and output shafts in a line, by choosing equal center distance for gears and pinions.

Epicyclic or Planetary Gear TrainIt is made of few components, a small gear at the center called the sun, several medium sized gears called the planets and a large external gear called the ring gear. The planet gears rolls and revolves about the sun gear and the ring gear rolls on the planet gear. Planetary gear trains have several advantages. They have higher gear ratios. They are popular for automatic transmissions in automobiles. They are also used in bicycles for controlling power of pedaling automatically or manually. They are also used for power train between internal combustion engine and an electric motor.

5.2Theory

Epicyclic gearing or planetary gearing is a gear system consisting of one or more outer gears, or planet gears, revolving about a central, or sun gear. Typically, the planet gears are mounted on a movable arm or carrier which itself may rotate relative to the sun gear. Epicyclic gearing systems also incorporate the use of an outer ring gear or annulus, which meshes with the planet gears.

ME-335L MECHANICS OF MACHINES LAB 2

EPICYCLE GEAR APPARATUS Lab Report No. IST-MECH-MEG-EXP05/00

5.2.1 Gear Ratio

The gear ratio in an epicyclic gearing system is somewhat non-intuitive, particularly because there are several ways in which an input rotation can be converted into an output rotation. The three basic components of the epicyclic gear are:

Sun: The central gear Planet carrier: Holds one or more peripheral planet gears, all of the same size, meshed

with the sun gear Annulus: An outer ring with inward-facing teeth that mesh with the planet gear or gears

In many epicyclic gearing systems, one of these three basic components is held stationary; one of the two remaining components is an input, providing power to the system, while the last component is an output, receiving power from the system. The ratio of input rotation to output rotation is dependent upon the number of teeth in each gear, and upon which component is held stationary.

In our case the annulus is held stationary and the sun gear is used as the input, the planet carrier will be the output. The gear ratio in this case will be

1 / (1+Na/Ns) 1.1

This is the lowest gear ratio attainable with an epicyclic gear train. This type of gearing is sometimes used in tractors and construction equipment to provide high torque to the drive wheels.

5.2.2 Data Sheet

Gear Type Teeth on Gear

Sun Driving 20

Planet Driven 16

Annulus Fixed 52

ME-335L MECHANICS OF MACHINES LAB 3