Planetary Gears and Final Drive Motors

The ultimate drive motor of an excavator is a hydraulic motor with a planetary gear set that decelerates and multiplies the torque. We will discuss the planetary gear sets and their components as well as their working methods. In the following article we will provide some The ultimate transmission example from reality, and then discuss how to maintain the gearbox.

Low Speed, High Torque Motors.

Most of the hydraulic motors used for propel motors are low-speed, high-torque (LSHT) motors. Speed and torque are related by power:

Power = Speed x Torque

 That means if we want to increase torque for a given horsepower, we need to reduce speed:

Torque = Power / Speed

Hence the term “low-speed, high-torque.”  One way of reducing speed involves the use of planetary gears. They provide speed reduction which results in torque multiplication.  And they do this all in a compact package when compared to gear and pinion speed reducers, and that means they have excellent torque density.  Below you can see a planetary gear system from a final drive motor.

Planetary Gear Systems.

In the gear hub of the final reducer, there are generally two sets of planetary gears that rotate around the sun gear.

  They also mesh with the fixed gear ring. As shown in the figure above, the planetary gear set above is fixed together by a planetary carrier. As shown in the figure, all three gears are divided into equal distances from each other. In the center is where the sun gear meshes and provides input to the system.