The three main factors traditionally used to measure the performance of a gearbox are load capacity, fatigue life, and operating accuracy, often neglecting transmission noise. With the successive promulgation of ISO14000 and ISO18000 standards, the importance of controlling the transmission noise of reducers has become increasingly evident. Industrial development and demand have stricter requirements for the transmission error of reducers, and the requirements for noise control are also becoming higher and higher.

At present, the factors that contribute to the formation of gearbox noise can be roughly analyzed from several aspects such as the design, manufacturing, installation, and maintenance of internal and external meshing gears.

Design reasons and countermeasures

1. Accuracy level of internal gears in the reducer

When designing a gearbox, designers often consider economic factors and determine the gear accuracy level as economically as possible, ignoring the fact that accuracy level is a marker of gear noise and backlash. The American Gear Manufacturers Association has determined through extensive gear research that high-precision gears produce much less noise than low precision gears. Therefore, if conditions permit, the accuracy level of gears should be improved as much as possible, which can reduce transmission errors and noise.

2. Width of internal gears in the reducer

When the transmission space of the reducer allows, increasing the gear width can reduce the unit load under constant torque. Reduce gear tooth deflection, decrease noise excitation, and thus reduce transmission noise. The research by H Oppertz in Germany shows that when the torque is constant, the noise curve gradient is higher for small tooth widths than for large tooth widths. Simultaneously increasing the width of the gear can also increase its load-bearing capacity and improve the bearing torque of the gearbox.

3. The tooth pitch and pressure angle of the internal gears of the reducer

A small tooth pitch can ensure that more teeth are in contact at the same time, increase gear overlap, reduce individual gear deflection, lower transmission noise, and improve transmission accuracy. The smaller pressure angle results in lower operating noise and higher accuracy due to the larger gear contact angle and lateral overlap ratio.

4. Selection of internal gear displacement coefficient for reducer

Correctly and reasonably selecting the displacement coefficient can not only adjust the center distance, avoid gear root cutting, ensure the satisfaction of concentric conditions, improve the transmission performance and load-bearing capacity of gears, and extend the service life of gears, but also effectively control backlash, temperature rise, and noise. In closed gear transmission, the main failure mode of gears with hard tooth surfaces (hardness: 350HBS) is root fatigue fracture. This gear transmission design is generally based on bending fatigue strength. When selecting the displacement coefficient, it should be ensured that the meshing teeth have equal bending strength. For gears with soft tooth surfaces (hardness # lt; 350HBS), the main failure mode is fatigue pitting corrosion. This type of gear transmission design is generally based on contact fatigue strength. When selecting the displacement coefficient, it should be ensured to maximize the contact fatigue strength and fatigue life as much as possible.

The limiting conditions for the reasonable selection of displacement coefficients are:

(1) Ensure that the gear being cut does not undergo root cutting;

(2) To ensure the smoothness of gear transmission, the coincidence degree must be greater than 1, and generally requires greater than 1.2;

(3) Ensure that the tooth tip has a certain thickness;

(4) When a pair of gears are engaged for transmission, if the involute curve at the top of one tooth contacts the transition curve at the root of the other tooth, since the transition curve is not involute, the common normal of the two tooth profiles at the contact point cannot pass through a fixed node, causing a change in transmission ratio and possibly causing the two wheels to get stuck. This "transition curve interference" must be avoided when selecting the displacement coefficient.

5. Gear profile trimming (trimming edges and roots) and tooth top chamfering inside the reducer

Cut the tooth profile of the tooth tip into a slightly convex shape compared to the correct involute curve. When the gear tooth surface is deformed by external forces, it can avoid interference with the gears that mesh with it, reduce noise, and extend the service life of the gears. Be careful not to make excessive adjustments, as excessive adjustments increase tooth profile errors and have a negative impact on meshing.

6. Analysis of Gear Sound Radiation Characteristics

When selecting gears with different structural forms, establish sound radiation models for their specific structures, conduct dynamic analysis, and pre evaluate the noise of the gear transmission system. In order to meet the different requirements of users (such as the location of use, whether there is unmanned operation, whether it is within the urban area, whether there are specific requirements for above ground and underground buildings, whether there is noise protection, or no other specific requirements).

7. Operating speed of gearbox power source

According to experiments on gearboxes under different speed conditions, it is shown that as the input speed of the gearbox increases, the noise will also increase.

8. Structural form of gearbox body

Experimental studies have shown that using a cylindrical box is beneficial for shock absorption. Under the same conditions, the average noise level of a cylindrical box is 5dB lower than other types of boxes. Conducting resonance testing on the gearbox body, identifying the resonance location, and adding appropriate reinforcement bars (plates) can improve the stiffness of the gearbox body, reduce its vibration, and achieve noise reduction. When using multi-stage transmission, it is required to minimize the change in instantaneous transmission ratio to ensure smooth transmission, minimal impact and vibration, and low noise.

Manufacturing reasons and countermeasures

1. The influence of internal gear errors in the reducer

The main errors that cause transmission noise in planetary gearboxes are tooth profile errors, pitch deviations, tooth orientation errors, and radial runout errors in the gear manufacturing process. It is also a problem point in controlling the transmission efficiency of planetary gearboxes. Now let's give a brief explanation of tooth profile error and tooth alignment error.

Gears with small tooth profile errors and small tooth surface roughness have a noise reduction of 10dB compared to ordinary gears under the same test conditions. Gears with small pitch errors have a noise level 6-12dB lower than ordinary gears under the same test conditions. But if there is a tooth pitch error, the impact of load on gear noise will be reduced.

Tooth alignment error will result in transmission power not being transmitted across the entire tooth width, and the contact area turning towards this or that end face of the teeth will experience increased tooth deflection due to local stress, leading to an increase in noise level. But at high loads, tooth deformation can partially compensate for tooth alignment errors.

2. Assembly concentricity and dynamic balance

Assembly misalignment will cause imbalance in the operation of the shaft system, and due to the loose and tight meshing of the teeth, it will jointly lead to increased noise. The imbalance during the assembly of high-precision gear transmission will seriously affect the accuracy of the transmission system.

3. Internal tooth surface hardness of reducer

With the development of gear hard tooth surface technology, its characteristics of high load-bearing capacity, small size, light weight, and high transmission accuracy have made its application fields increasingly widespread. However, the use of carburizing and hardening to obtain a hard tooth surface causes deformation of the gear, resulting in increased transmission noise and shortened lifespan. To reduce noise, it is necessary to perform precision machining on the tooth surface. At present, in addition to the traditional grinding method, a hard tooth surface scraping method has been developed, which reduces gear meshing and meshing impact by correcting the tooth top and root, or reducing the tooth profile of both the driving and driven wheels, thereby reducing gear transmission noise.

4. Calibration of reducer system indicators

The machining accuracy of components before assembly and the selection method of components (complete interchangeability, grouping selection, single piece selection, etc.) will affect the accuracy level of the system after assembly, and its noise level is also within the affected range. Therefore, it is crucial to verify (or calibrate) various indicators of the system after assembly to control system noise.

Installation reasons and countermeasures

1. Vibration reduction and blocking measures

When installing the gearbox, efforts should be made to avoid resonance and noise between the machine body, foundation support, and connecting components. One or several gears inside the gearbox often resonate within certain speed ranges. Apart from design reasons, the resonance location may not have been identified during installation without conducting a test. And taking corresponding vibration reduction or blocking measures is directly related. Some reducers that require low transmission noise and vibration should use high toughness and high damping base materials to reduce the occurrence of noise and vibration.

2. Geometric accuracy adjustment of components

Due to the geometric accuracy not meeting the standard requirements during installation, resonance occurred in the gearbox components, resulting in noise. This should be directly related to improving the installation process, increasing tooling, and ensuring the overall quality of assembly personnel.

3. Loose components

Due to the loosening of individual components during installation (such as bearing pre tensioning mechanism, shaft positioning mechanism, etc.), the system positioning is inaccurate, abnormal position meshing occurs, shaft movement occurs, and vibration and noise are generated. This series needs to start from the design structure, try to ensure the stable connection of each mechanism, and adopt multiple connection methods.

4. Damage to transmission components

Improper operation during installation can damage transmission components, resulting in inaccurate or unstable system movement; High speed moving parts experience oil film vibration due to damage; Artificially causing dynamic imbalance of moving parts; Both generate vibration and noise. These reasons must be taken into account and avoided as much as possible during the installation process. Damaged components that cannot be repaired must be replaced to ensure a stable noise level in the system.

Reasons and Countermeasures for Use and Maintenance

The correct use and maintenance of the reducer cannot reduce the system noise level and ensure transmission accuracy, but it can prevent its indicators from deteriorating and increase its service life.

1. Internal cleaning

The cleanliness of the internal components of the gearbox is a basic condition for its normal operation. Any impurities or dirt entering will affect and damage the transmission system, leading to the generation of noise.

2. Working temperature

Ensure the normal working temperature of the reducer, avoid deformation of components due to excessive temperature rise, ensure normal gear meshing, and thus prevent the increase of noise.

3. Timely lubrication and correct use of oil products

Unreasonable lubrication and incorrect use of lubricating grease will cause immeasurable damage to the gearbox. At high speeds, the friction between gear teeth generates a large amount of heat energy. Improper lubrication can cause damage to gear teeth, affect accuracy, and increase noise. During design, it is required that the gear pair has appropriate clearance (clearance between non working surfaces of meshing teeth to compensate for thermal deformation and storage of lubricating grease). The correct use and selection of lubricating grease can ensure the safe and effective operation of the system, delay the deterioration trend, and stabilize the noise level.

4. Correct use of gearbox

Proper use of the gearbox can minimize damage and deterioration of components, ensuring a stable noise level. The noise of the gearbox will increase with the increase of load, so it should be used within the normal load range.

5. Regular maintenance and upkeep

Regular maintenance (changing oil, replacing worn parts, loosening fasteners, removing internal debris, adjusting clearances between components to standard values, verifying geometric accuracy, etc.) can improve the ability of the gearbox to resist noise level degradation and maintain stable use.

The control of gearbox transmission noise is a systematic engineering that involves the entire process of designing, manufacturing, installing, using, maintaining, and updating the transmission system (gears, housings, connectors, bearings, etc.). It not only puts forward many requirements for designers, manufacturers, but also for installation, use, maintenance, and maintainers. If any of the above links are not effectively controlled, the control of gear transmission noise will be considered ineffective.