Gear Trains

Definitions

A gear train is a set or system of gears arranged to transfer rotational torque from one part of a mechanical system to another, with some gear ratio performing a mechanical advantage.

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.

Key Facts

Types of Gear Trains

·         Simple Train - three or more wheels connected in series.

·         Compound Train - an intermediate shaft carries two wheels connected in series.

The Structure of an Epicyclic gear - The Sun wheel, the planet wheels, the Annulus and the Spider.

Analysing epicyclic gear trains Three methods:

·         Tabular Method.

·         The Relative Velocity Method.

·         The Determination Of Torques.

One of the most common uses of Gear Trains is in the gear boxes of cars. In the simplest form, the crash gear box, a collection of spur gears were arranged to give different ratios of input to output speed and in the case of the reverse gear, change the direction of the output rotation.

The modern synchromesh gearbox is a development working on very similar principles.

Another, and in many ways more interesting type of train uses epicyclic gears. Many modern cars use a small epicyclic in the starter motor but much larger and more complicated versions have been used as the main gearbox. Before the 1939 - 1945 war the Daimler Car Company used a "pre-selector" Wilson box.

In more recent years these were fitted to London Transport Buses and they were also to be found in some British Army armoured wheeled vehicles. The gear box, which is driven through a fluid fly wheel, allows the driver to pre-select the next gear to be used and then to make a very rapid change at the right moment. This ability is useful in heavy urban traffic and when driving across uneven country.