Sun gear – a real planetary system workhorse

What is this?

Sun gear is a fixed element of the planetary system that is responsible for the drive transmission. The number of travel final drive sun gears is slightly diversified and depends of the hub construction. Most often, we distinguish the reduction sets of the first, second and third order, which determine the number of sun gears.

Sun gear is placed on the first-order disc. If the planetary gear has three rows of satellites, there are two sun gears in the system. If there are two rows, only one sun gear is included.

In planetary gears, the drive is given through interlocking gears. To imagine the operation of such a gear in a travel final drive, it is enough to compare it to the solar system. The sun and the planets that are circling around it (moreover, hence the name “planetary system”). In our system the sun will be ofcourse the motor shaft, while the gears will be planets circling around it. The sun gear propels them.

How to avoid damage?

Very rarely, the hydromotor fails itself – most often the satellite transmission system or any part of it breaks down. Sun gears are also damaged. Why? The sun gear, compared to planetary gear, is in contact with all the elements of a given row of satellites. This is because it is responsible for putting them in motion (has a high rotational speed). Thus, it is significantly exposed to greater damage.

Of course, the damage is also related to the state of oils and greases. If there is not enough in the planetary gear, the working gears will simply wear off. There is a high probability that their detached elements will fall into the center of planetary gearbox and damage it.

Therefore, we advise you to constantly check the oil and grease level. This is a recipe for preventing many potential damages.

Of course, gears are not immortal and often wear away (especially due to their contact with the planetary gears and high speed, which we mentioned a bit higher). You will be informed about the necessity of replacing them by a characteristic rasp or crack.

Another symptom of damage is the situation when the travel motor is clearly working but the drive from the engine is not transmitted to the excavator track. Probably the part responsible for transferring the drive between particular satelites rows has failed.