Planetary gear hydraulics: all about the operation and applications
Planetary gear units are all about enabling efficient transmission of power within working machines. These gearboxes can be connected both directly and indirectly to an electric motor or hydraulic motor. Their use is widespread in many industries, including mechanical engineering, chemical and plastics processing, food production, construction, mining, agriculture and forestry, transportation and lifting equipment, shipbuilding, and wind turbines.
Functionality of the planetary gear
A planetary gear is an epicyclic gear consisting of a central sun gear, several planet gears and a ring gear. The gears are arranged so that the planet wheels roll on the sun wheel and rotate around their own axis at the same time. The ring gear encloses the planetary gears and thus forms the outer shell of the gear unit.
The sun gear is driven by the drive motor and transmits torque to the planet gears. By the movement of the planet wheels around the sun wheel and around its own axis, the torque is transmitted to the ring gear.
The planetary gear allows to increase the torque and decrease the speed. The transmission ratio can be changed by the number of teeth. By adding additional gear stages, the transmission ratio can also be increased. Depending on the application, different planetary gear configurations can be used.
One advantage of the planetary gear is its high efficiency. Due to the arrangement of the gears and the low friction, a large part of the energy used is converted into kinetic energy. In addition, the planetary gearhead is very compact and can be used in various applications.
In this gear simulator, the operation of a planetary gear is visually represented.
Structure of the planetary gear
The planetary gear consists of several components that work together to transmit torque and increase the gear ratio. The main components are:
- Sun wheel
- Planet wheels
- Ring gear
- Planetary gear carrier
- If necessary, hydraulically released multi-disc brake
The sun wheel is located in the center of the housing and is driven by a hydraulic motor. It has external teeth that mesh with the internal teeth of the planet gears. The planet gears are smaller than the sun gear and move freely on rotational axes attached to the planet gear carrier. The planetary gear carrier is usually connected to the output shaft.
The ring gear is the outer gear and has internal teeth that mesh with the external teeth of the planet gears. It is usually permanently mounted in the housing and forms the frame for the planetary gear.
The planetary gears are arranged so that they roll on the sun gear and at the same time roll on the ring gear. This transmits the torque. Different gear ratios can be achieved by changing the gearing and by using several planetary stages.
Applications of the planetary gear in hydraulics
In hydraulics, the planetary gear is a proven precision gear used in many applications. Here are some examples:
- Construction machinery: Planetary gearboxes are used in construction machinery such as excavators, cranes and concrete pumps to increase the torque of the hydraulic motor. Typical applications include wheel or chain drives (using wheel hub gearboxes), planetary gearboxes for earth drilling equipment, asphalt pavers, etc.
- Agricultural technology: In agricultural machinery such as tractors and combine harvesters, planetary gear units are also used to increase the torque of a hydraulic drive. Typical applications for planetary gearboxes in agricultural machinery are wheel drives, cone log splitters, timber harvesters, etc.
- Marine technologyIn maritime applications, planetary gear units are used for power transmission in winches, loading cranes, rudder systems, cargo hatches, etc.
- Industry: Planetary gear units are used in many industrial applications, such as presses, rolling mills, wind turbines and conveyors. Here they ensure precise control of movements and high positioning accuracy.
Another advantage of planetary gear units in hydraulics is their compact design, which allows space-saving integration into machines and systems. They are also characterized by their high efficiency, which contributes to efficient and energy-optimized operation. Multi-stage planetary gear units are capable of transmitting torques of up to 2.4 million newton meters!
Overall, the planetary gearbox is an indispensable component in hydraulics that works reliably and precisely and plays an important role in many applications.
Advantages and disadvantages of the planetary gear
The planetary gearhead is a popular choice in many applications because of the many advantages it offers. Some of the main advantages are:
- Compact design: Planetary gear units are coaxial gear units and therefore very compact in diameter and take up little radial space compared to spur gear units.
- High efficiency: The planetary gear has a high efficiency, which means that it loses little energy in the form of heat.
- Low backlash: Planetary gearheads have low backlash, which means they are very precise and provide high (positioning) accuracy.
- High torque transmission: The planetary gearhead can transmit very high torque and is therefore very popular in many applications.
- Planetary gear units can be combined with hydraulically released multi-disc brakes and thus also transmit high holding torques.
- Wheel hub gearboxes are a special type of planetary gearbox that are already designed with corresponding wheel mounts and are therefore suitable for traction drives.
Although the planetary gear offers many advantages, there are also some disadvantages that should be considered:
- Complexity: The design of the planetary gearbox is relatively complex, which can make it difficult to manufacture and maintain.
- Cost: Planetary gearheads are usually more expensive than other types of gearheads due to their complex design and high accuracy.
Despite these drawbacks, the planetary gearhead is a popular choice in many industries due to its many advantages and applications.
Assembly, maintenance and servicing of the planetary gear unit
Regular maintenance and servicing of the planetary gearbox is of great importance to maintain its performance and service life. Here are some important points to consider when maintaining the planetary gearbox:
- Always use gear oil according to the manufacturer’s recommendation. Neither motors nor hydraulic oil are suitable for planetary gearboxes.
- Regularly check the oil level and change the gear oil according to the manufacturer’s recommendations.
- Observe the mounting positions specified by the manufacturer (horizontal or vertical). Please check whether an expansion tank may be necessary.
- Regularly check the seals and replace them if necessary.
- When servicing the gearboxes, check the gears for wear and damage. The same applies to the bearings, replace them if necessary.
- Check the holding brake plates and replace them if necessary.
It is also important that the maintenance of the planetary gearbox is performed by professionals who have the necessary knowledge and experience to properly maintain and repair the gearbox. Improper maintenance can cause serious damage to the gearbox, which may require expensive repairs or even replacement of the entire gearbox.
Maintenance of the planetary gearbox should be carried out at regular intervals to ensure that the gearbox functions optimally and has a long service life. It is also important to monitor the planetary gearbox during operation for signs of problems such as unusual noise or vibration. If such signs appear, the gearbox should be serviced immediately to prevent further damage.