Mechanical Gear Systems and Transmission Ratios

Gear Speed and Transmission Ratio Calculations

For Gears 2 and 3, the speed calculation is: Nm x Zm = Ns x Zs. The transmission ratio for gears is defined as: Zm / Zs = Nm / Ns.

For chain transmission, the formula remains: Nm x Zm = Ns x Zs.

Fundamental Gear Characteristics

Gears are mechanical elements designed to transmit turning movements. There are two main characteristics of gears:

• The fundamental characteristic is the number of teeth it has, which is represented by the letter Z.
• The other characteristic is the rotational speed, represented by the letter N, which is measured in RPM (revolutions per minute).

Gear Sizes and Rotational Speed

If two gears have a different number of teeth, and the output gear is larger than the motor gear, it will turn slower. If two gears have the same number of teeth, they won't change the rotational speed and they will turn at the same time.

In a couple of gears, the motor gear always pushes while the output gear receives the movement. The bar where the gears are mounted is called the shaft.

Types of Gears and Shaft Configurations

Depending on their shape, there are two main types of gears:

• Cylindrical gears: These have a cylinder shape and transmit movement between parallel shafts.
• Conical gears: These have a truncated cone shape and transmit movement between perpendicular shafts.

Straight vs. Helical Gear Teeth

The difference between a gear with straight teeth and one with helical teeth is that straight teeth follow straight lines. Helical teeth have curved teeth, and they are quieter than gears with straight teeth.

Idler and Compound Gear Mechanisms

An idler gear is a mechanism formed by more than two gears. It serves to reverse the rotational direction and is useful if you want to maintain the same rotational speed.

The characteristics of a gear speed multiplier mechanism are: the motor gear is bigger than the output gear; the output gear rotates faster but carries out less force.

A compound gear consists of two gears of different sizes that are joined, moving the force at the same speed; they serve to reduce the speed of the motor.

Advantages and Disadvantages of Gear Systems

When gears transmit movement accurately, it means the gears rotate at the same time.

Advantages: They transmit movement accurately because they cannot slide, which is very useful in certain machines.

Disadvantages: In the case of sudden engine starts, the gear teeth can break.

The Importance of Lubrication in Gear Machines

The functions of the lubricant in gear machines are:

• To reduce friction, thereby increasing mechanical efficiency.
• To reduce the noise generated when the gears turn.
• To reduce the wear of the teeth, increasing the useful life of the gears.