기어의 종류 1 - 평행축 기어

Let's take a look at the different types of gears.

What is a gear?

A gear is a mechanical component shaped like a toothed wheel that transmits rotational force or power to a rotating shaft.
They can be broadly classified as follows.

Among these, we will focus on gears with parallel shafts.

"Parallel shafts" refers to shafts that are arranged parallel to each other.

In this configuration, a gear where the teeth are arranged in a straight line parallel to the axis is called a spur gear.

The advantages of spur gears include ease of machining, high efficiency due to their simple structure, and a high degree of design freedom.
However, because the contact area between the gears is small, they cannot be used in applications requiring high torque.

This is where helical gears come into play.

In helical gears, the teeth are cut diagonally to increase the contact area compared to conventional spur gears. This allows for the transmission of higher torque.
Additionally, because the teeth do not engage all at once but gradually mesh, operation becomes smoother and quieter.
However, this design led to increased machining costs and generated thrust forces in the axial direction, resulting in torsional stress.

The double helical gear, also known as the herringbone gear, was developed to address these issues.

Both double helical gears and herringbone gears are designed with a bidirectional structure to counteract axial thrust.
Double helical gears incorporate a gap in the middle to improve machinability during the manufacturing process and reduce costs, while herringbone gears offer spatial advantages.

Now let’s look at another type of parallel-axis gear: the internal gear, which operates with its teeth on the inside rather than the outside.
The structure consists of an inner pinion gear and an outer ring gear.

The word "pinion" derives from the Old French word "pignon," which itself comes from the Latin "pinna" (feather). You can simply think of it as a small gear!

The characteristics of internal gears are that they take up little space and rotate in the same direction without changing direction.
They are widely used in reducers and pumps, and this structure is applied to the outer part of the planetary gears, which will be discussed later.

A rack-and-pinion gear is a structure that combines a rack gear with the pinion gear described earlier.
Unlike other parallel-axis gears, it converts rotational force into linear motion.

They are used in sliders and automotive steering systems. Since they have a spur gear structure, they may sometimes adopt helical or herringbone configurations if torque becomes insufficient later on.