Planetary gearbox: device, principle of operation, operation and repair

2024 Author: Erin Ralphs | [email protected]. Last modified: 2024-02-19 11:42

Planetary gears are among the most complex gear boxes. With a small size, the design is characterized by high functionality, which explains its widespread use in technological machines, bicycles and caterpillar vehicles. To date, the planetary gearbox has several design versions, but the basic principles of operation of its modifications remain the same.

Unit device

The basis of the design is formed by only three functional parts with one axis of rotation. They are represented by a carrier and two toothed central wheels. The device also provides for an extensive group of auxiliary links in the form of a set of single-format gears, crown gears and bearings. From this we can conclude that the planetary gearbox is a mechanism from the family of gears."boxes", but with a fundamental difference. It consists in the conditional independence of the angular velocities of each of the main links. Now it is worth familiarizing yourself with the elements of the aggregate in more detail:

• Carrier is the basis and an obligatory part of any planetary system, including those with differential connection. This is a lever mechanism, which is a spatial fork, the axis of which is aligned with the common axis of the transmission. In this case, the gear axles with satellites rotate around it in the planes of the central wheels.
• Gear wheels. First of all, it is necessary to separate the groups of large central and small central wheels of this type. In the first case, we are talking about large wheels with internal teeth - this system is called the epicycle. As for the small gears with teeth, they are distinguished by the outer arrangement of the teeth - also called the sun gear.
• Satellites. The wheel group of a planetary gearbox (less often a single gear), the elements of which necessarily have external teeth. Satellites are located in the coupling with both groups of central wheels. Depending on the functionality and power of the equipment, the number of satellites can vary from 2 to 6, but 3 segments are most often used, since in this case there is no need for additional balancing devices.

Principles of operation of planetary gearboxes

Transmission change depends on the configuration of the placement of functional units. The value will have the mobility of the element and the direction of the torque. One of the three components (carrier,satellites, sun gear) is fixed in a fixed position, and the other two rotate. To block the elements of the planetary gearbox, the principle of operation of the mechanism provides for the connection of a system of band brakes and clutches. Unless there are brakes and lock-up clutches in differential devices with bevel gears.

The downshift can be activated in two ways. In the first version, the following principle is implemented: the epicycle stops, against which the working moment from the power unit is transferred to the base of the sun gear and removed from the carrier. As a result, the intensity of rotation of the shaft will decrease, and the sun gear will increase in frequency of operation. In an alternative scheme, the sun gear of the device is blocked, and the rotation is transferred from the carrier to the epicycle. The result is similar, but with a slight difference. The fact is that the gear ratio in this working model will tend to unity.

In the process of upshifting, several working models can also be implemented, and for the same planetary gearbox. The principle of operation in the simplest scheme is as follows: the epicycle is blocked, and the moment of rotation is transferred from the central sun gear and transmitted to the satellites and carrier. In this mode, the mechanism works as a step-up gearbox. In another configuration, the gear will be blocked and the torque will be transferred from the ring gear to the carrier. Also, the principle of operation is similar to the first option, but there is a difference in the frequency of rotation. When reverse gear is engaged, torquetorsion will be removed from the epicycle and will be transmitted to the sun gear. In this case, the carrier must be in a stationary state.

Workflow Features

The fundamental difference between planetary mechanisms and other types of gearboxes is the already mentioned independence of working elements, which is formulated as two degrees of freedom. This means that due to the differential dependence, to calculate the angular velocity of one component of the system, it is necessary to take into account the speeds of the other two gear units. In comparison, other gear transmissions assume a linear relationship between the elements in determining the angular velocity. In other words, the angular velocities of the planetary "box" can change at the output, regardless of the dynamic performance at the input. With fixed and stationary gears, it becomes possible to summarize and distribute power flows.

In the simplest mechanisms, there are two degrees of freedom of gear links, but the operation of complex systems can also provide for the presence of three degrees. To do this, the mechanism must have at least four functional links, which will be in differential connection with each other. Another thing is that such a configuration will actually be inefficient due to low performance, so in practice, applications and transmissions with four links retain two degrees of freedom.

Simple and complex planetary gears

One of the signs of the division of planetary mechanisms into simple andcomplex - this is the number of working links. Moreover, we are talking only about the main nodes, and groups of satellites are not taken into account. A simple system usually has three links, although all seven are allowed by kinematics. As an example of such a system, we can cite sets of single and double gears, as well as paired interlocking groups of gears.

There are many more main links in complex mechanisms than in simple ones. They provide at least one carrier, but there can be more than three central wheels. Moreover, the principle of operation of the planetary gearbox allows the use of several simple units even within one complex system. For example, a four-link model can have up to three simple nodes, and a five-link model can have up to six. However, the complete independence of simple planetary systems within the framework of complex devices is out of the question. The fact is that several such mechanisms are more likely to have one common carrier.

Mechanism controls

While maintaining several degrees of freedom, the device can be used as the main self-sufficient functionality. But if a model with one leading and one driven link is selected (reducer mode), then it will be necessary to set certain speeds for them. For this, the control elements of the planetary gearbox are used. The principle of their operation is the redistribution of speeds due to the friction clutch and brakes. Extra degrees of freedom are removed, and the main free nodes become reference.

Frictions are responsible for connecting two free links orone link (also free) with an external power supply. Both configurations of clutches in blocking conditions provide the controlled links with a certain angular velocity, and not zero. By design, such elements are multi-plate clutches, but sometimes there are also conventional clutches for transmitting torque.

As for the brake, its task in the control infrastructure of the planetary gearbox is to connect the free links to the gear case. This element, under blocking conditions, endows the free links with zero angular velocity. According to the technical device, such brakes are similar to clutches, but in the simplest versions - single-disk, shoe and tape.

Application of the planetary gear

For the first time this unit was used in the Ford T car in the form of a two-speed gearbox with a foot shift principle and band brakes. In the future, the device went through many transformations, and today the Japanese Prius planetary gearbox can be called the latest version of mechanisms of this type. The principle of operation of this unit is to distribute energy between the power plant (which can be hybrid) and the wheels. During operation, the engine stops, after which the energy is sent to the generator, as a result of which the wheels begin to move.

In this case, the system can be not only the functionality of a gearbox alone. Today, this device is used in gearboxes, differentials, in complexkinematic diagrams of industrial equipment, in drive systems of special equipment and aircraft. Advanced auto giants are also mastering the principles of operation of the mechanism in combination with electromagnetic and electromechanical drives. The same Prius planetary gearbox has been successfully used in hybrid electric vehicles. There is no gearbox itself in the traditional sense in such designs, but there is a semblance of a variator without step shifting - a complex of planetary gears that sets the wheels in motion and receives energy from the engine performs this function.

Planetary Bicycle Gearbox

In the traditional sense, there is no gearbox in cycling transport provided with planetary mechanisms. These are hubs with the same sun gear, which is rigidly attached to the rear wheels on their axle. Also, a carrier is used for fixation, which determines the direction of movement of the satellites and does not allow them to disperse and interlock with each other. And the most important element of the planetary "box" of the bicycle is represented by an epicyclic gear, the rotation of which occurs due to the torsion of the pedals. When the gear is changed, the hub actuator (splined drive) changes the dynamics of the carrier, which gives the effect of adjusting the speed.

That is, we can again conclude that the planetary model works as a gearbox. In this system, the epicycle performs the function of a driven link in the chain, the sun gear remains stationary, and the carrier closes on the housing. AtIn this case, the working schemes of simple and multi-speed bushings will be the same. The only slight difference is that each node of the planetary system has its own strictly defined indicators of gear ratios.

Operational process

The main measure in the operation of this mechanism by the user is to maintain the planetary gear set in optimal working condition. This is achieved through periodic cleaning of the elements and, most importantly, through lubrication. What should be lubricated in the planetary box? Mainly sliding bearings of the reducer. Oil is directed from the crankshaft into the cavity of the gear shaft, filling the cavities of the satellites with gears. Further, depending on the design, technical lubricant enters the gear bearings through the pins and radial holes. For maximum distribution of oil along the length of the bearings, a flat is sometimes made on the outside of the trunnion.

Gearings are lubricated either by dipping the wheel teeth in a liquid bath, or by directing oil into the hitch area through special nozzles. That is, jet lubrication or dip lubrication is realized. But the most effective way is the spread of oil mist, which is used in relation to the elements of engagement and bearings. This method of lubrication is implemented by spraying from a special spray gun.

As for the lubricant itself, unalloyed petroleum oils are recommended for planetary gears. For example, general-purpose industrial formulations are suitable for use. For high speedmechanisms, it is desirable to use special turbine and aviation facilities.

Faults and repair mechanism

The most common symptom of a planetary gear failure is the presence of vibrations in the box area. Drivers also note extraneous noises, shocks and twitches. The presence of certain symptoms depends on the nature of the malfunction, for which there may be several reasons:

• Mechanism overheating.
• Aggressive driving style with heavy braking and acceleration.
• Lack of oil, low level or insufficient quality.
• Insufficient warm-up of the transmission before driving.
• Slippage on ice.
• Car hitting snow or mud.
• Wear of planetary gear elements.

To repair a planetary gearbox, you need to know the specific cause of its failure. For this, the mechanism is disassembled. Usually the box is bolted inside the drive shaft. It is necessary to remove the speed brackets from one of the sides (depending on the design) and then unscrew the bolt through the hole in the drive shaft. Next, the element is cleaned or replaced. Typically, these are metal swarf contamination, broken teeth, worn axles and gears.

Conclusion

Planetary mechanisms differ in the complexity of the device, which has its pros and cons. The first one is the balanceserviced elements with a relatively accurate distribution of forces. This factor allows the development of modestly sized gearshift units, which allow for an optimized layout. In the case of the “planetary” of a bicycle, ergonomic advantages are also noted, including the ability to switch in a standing position. When driving around the city, this is a particularly useful quality, since you have to change speed modes quite often. If we talk about the shortcomings of planetary systems, then with large gear ratios they are still characterized by modest performance. Also, the system requires precise assembly, since the slightest deviations increase the risk of the same wear of parts.