Reasons for Reducer Design and Countermeasures

1. Gear precision grade inside the reducer

Design Gear reducer At times, designers tend to consider economic factors and, as much as possible, select gear precision grades that are economically viable, often overlooking the fact that precision grades serve as indicators of gear noise and backlash. The American Gear Manufacturers Association, through extensive gear research, has determined that gears with higher precision grades generate significantly less noise than those with lower precision grades. Therefore, whenever conditions permit, it is advisable to increase the precision grade of gears as much as possible—this not only reduces transmission errors but also helps minimize noise.

2. Internal gear width of the reducer

When the transmission space of the gearbox permits, increasing the gear width can reduce the unit load under constant torque. This, in turn, decreases tooth deflection and reduces noise excitation, thereby lowering transmission noise. Research conducted by German scholar H. Opaz indicates that, at constant torque, a smaller tooth width results in a steeper slope on the noise curve compared to a larger tooth width. At the same time, increasing the gear width also enhances the gear’s load-carrying capacity, boosting the gearbox’s maximum allowable torque.

3. Tooth pitch and pressure angle of the internal gears in the gearbox

A small tooth pitch ensures that more teeth are in simultaneous contact, increasing gear overlap, reducing the deflection of individual gears, lowering transmission noise, and improving transmission accuracy. A smaller pressure angle results in larger gear contact angles and transverse overlap ratios, thereby leading to lower operating noise and higher precision.

4. Selection of Gear Shift Coefficient for Internal Gears in the Reducer

Proper and rational selection of the modification coefficients not only helps to adjust the center distance, avoid undercutting of gear teeth, ensure compliance with concentricity requirements, improve the transmission performance of gears, enhance their load-carrying capacity, and extend their service life, but also effectively controls side clearance, temperature rise, and noise. In closed gear drives, for gears with hardened tooth surfaces (hardness ≥350 HBS), the primary failure mode is fatigue fracture at the tooth root. Such gear drive designs are typically based on bending fatigue strength; when selecting modification coefficients, it is essential to ensure that meshing gear teeth have equal bending strengths. For gears with softened tooth surfaces (hardness <350 HBS), the primary failure mode is pitting fatigue. Such gear drive designs are generally based on contact fatigue strength; when selecting modification coefficients, it is crucial to maximize both contact fatigue strength and fatigue life. The limiting conditions for the rational selection of modification coefficients include:

① Ensure that the gear being cut does not experience undercutting;

② To ensure smooth gear transmission, the overlap ratio must be greater than 1; generally, it should be greater than 1.2.

③ Ensure that the tooth tops have a certain thickness;

④ When a pair of gears is in mesh and the involute curve at the tip of one gear tooth comes into contact with the transition curve at the root of the other gear tooth, since the transition curve is not an involute, the common normal to the two tooth profiles at the point of contact cannot pass through a fixed pitch point. This results in a variation in the transmission ratio and may even cause the two gears to jam and become immobile. Such “transition-curve interference” must be avoided when selecting the modification coefficients.

5. Gear profile modification (edge trimming and root filleting) and chamfering of gear tooth tops inside the gearbox.

The tooth profile at the tooth tip is cut to have a slightly convex shape compared to the ideal involute curve. When the gear tooth surface undergoes deformation due to external forces, this design helps prevent interference with mating gears, reduces noise, and extends the service life of the gears. It’s important to avoid over-machining; excessive machining would increase tooth profile errors, adversely affecting gear meshing performance.

6. Analysis of Gear Noise Radiation Characteristics

When selecting gears with different structural configurations, a sound radiation model is established for each specific structure and subjected to dynamic analysis to perform a preliminary assessment of noise generated by the gear transmission system. This allows us to meet the diverse requirements of users—such as the intended application environment, whether the equipment will be operated unattended, whether it will be located in an urban area, whether there are specific requirements for above-ground or underground structures, whether noise protection measures are needed, or whether no special requirements apply at all.

7. Operating speed of the reducer's power source

Experiments conducted on gear reducers under different rotational speed conditions show that as the input rotational speed of the reducer increases, the noise level also rises.

8. Gearbox housing structure type

Experimental studies have shown that using a cylindrical housing is beneficial for vibration damping. Under otherwise identical conditions, the noise level of a cylindrical housing is, on average, 5 dB lower than that of other types of housings. Resonance tests conducted on gearbox housings can identify resonance locations; by adding appropriate stiffening ribs (plates) at these locations, the rigidity of the housing can be enhanced, vibrations reduced, and noise levels lowered. In multi-stage transmissions, it is essential to minimize variations in the instantaneous transmission ratio as much as possible, thereby ensuring smooth operation with minimal impact, vibration, and noise.

Manufacturing Causes and Countermeasures

1. Influence of gear errors inside the reducer

In the gear manufacturing process, tooth profile error, base pitch deviation, helix angle error, and radial runout error of the gear ring are the primary sources of transmission noise in planetary reducers. They also represent critical factors affecting the transmission efficiency of planetary reducers. Below, we will briefly explain the effects of tooth profile error and helix angle error. Gears with small tooth profile errors and low tooth surface roughness produce noise that is 10 dB lower than that of conventional gears under the same test conditions. Gears with small pitch errors exhibit a noise level that is 6 to 12 dB lower than that of conventional gears under the same test conditions. However, if pitch errors are present, the influence of load on gear noise will be reduced. Tooth alignment errors will cause the transmission power to be transmitted not across the entire tooth width, but rather shifting the contact zone toward either the leading or trailing end of the tooth. This localized increase in stress leads to greater tooth deflection, thereby raising the noise level. However, under high loads, tooth deformation can partially compensate for these tooth alignment errors.

2. Assembly concentricity and dynamic balancing

Misalignment during assembly will lead to imbalance in the shaft system, and since the gear teeth engage unevenly—loose on one side and tight on the other—it will further exacerbate noise. Imbalance during the assembly of high-precision gear transmissions can severely affect the accuracy of the transmission system.

3. Hardness of internal gears in the reducer

With the advancement of hard-tooth surface technology for gears, their characteristics—such as high load-carrying capacity, compact size, light weight, and high transmission accuracy—have led to increasingly broad application fields. However, the carburizing and quenching process used to achieve a hard tooth surface causes gear deformation, resulting in increased gear transmission noise and shortened service life. To reduce noise, it is necessary to perform precision finishing on the tooth surfaces. Currently, in addition to the traditional grinding method, a new hard-tooth-surface scraping technique has been developed. By modifying the tooth top and root profiles or by slightly reducing the tooth profiles of both the driving and driven gears, this method minimizes the impact during gear meshing and disengagement, thereby reducing... Gear transmission noise.

4. Verification of Reducer System Specifications

The machining accuracy of components prior to assembly, as well as the component selection methods (such as full interchangeability, group selection, and individual selection), will affect the precision level of the system after assembly. Moreover, these factors also influence the noise level of the system. Therefore, it is crucial to verify (or calibrate) all system performance indicators after assembly, especially with regard to controlling system noise.

Installation Reasons and Countermeasures

1. Vibration reduction and blocking measures

When installing a gearbox, it is essential to avoid resonance between the gearbox housing and its foundation supports and connecting components, as resonance can generate noise. Inside the gearbox, one or more gears often resonate within certain speed ranges. Aside from design-related factors, this resonance is frequently caused by failing to conduct no-load tests during installation to identify resonant frequencies and subsequently implement appropriate vibration-damping or isolation measures. For gearboxes that have stringent requirements for low transmission noise and vibration, it is advisable to select base materials with high toughness and high damping properties to minimize noise and vibration generation.

2. Adjustment of component geometric accuracy

Since the geometric accuracy during installation failed to meet the requirements specified in the standards, resonance occurred in the reducer's components, resulting in noise. This issue is directly related to improving the installation process, enhancing tooling, and ensuring the overall competence of assembly personnel.

3. Loose components

During installation, looseness in certain components—such as the bearing preload mechanism and shaft alignment mechanisms—can lead to inaccurate system positioning, abnormal gear meshing, shaft movement, and consequently, vibration and noise. To address these issues, it is essential to start with the design structure itself and strive to ensure stable connections among all mechanisms by employing a variety of connection methods.

4. Damage to transmission components

During installation, improper handling can damage transmission components, leading to inaccurate system motion or motion instability. High-speed moving parts, when damaged, may experience oil-film vibration. Human-induced dynamic imbalance in moving parts can also generate vibrations and noise. All these factors must be carefully noted and avoided as much as possible during the installation process. For damaged components that cannot be repaired, they must be replaced to ensure the system maintains a stable noise level.

Reasons for Use and Maintenance, as well as Countermeasures

Although proper use and maintenance of gear reducers cannot reduce the system’s noise level or guarantee transmission accuracy, they can prevent deterioration of performance indicators and extend the service life.

1. Internal cleaning

Cleaning the internal components of the gearbox is a fundamental requirement for ensuring its proper operation. Any ingress of impurities or contaminants can affect and damage the transmission system, leading to noise generation.

2. Operating temperature

Ensure the reducer operates at a normal temperature to prevent component deformation caused by excessive temperature rise, guarantee proper gear meshing, and thereby avoid increased noise levels.

3. Timely lubrication and proper use of lubricants

Both improper lubrication and incorrect use of lubricants can cause immeasurable damage to gear reducers. At high speeds, friction between gear teeth generates significant amounts of thermal energy; if lubrication is inadequate, this can lead to tooth damage, compromise precision, and increase noise levels. During design, it is essential to provide appropriate clearances between gear pairs—specifically, the clearance between the non-working surfaces of meshing teeth—to accommodate thermal deformation and to allow for the storage of lubricant. Proper selection and application of lubricants can ensure safe and efficient system operation, slow down the deterioration process, and stabilize noise levels.

4. Proper Use of Gear Reducers

Proper use of the gearbox can minimize damage to components and ensure a stable noise level. Gear reducer Noise increases as the load increases; therefore, it should be used within the normal load range.

5. Regular maintenance and servicing

Regular maintenance (including oil changes, replacement of worn parts, tightening of loose fasteners, removal of internal debris, adjustment of component clearances to standard specifications, and verification of various geometric accuracies) can enhance the reducer’s ability to resist degradation in noise levels and maintain a stable operational condition.

Conclusion

Gearbox transmission noise control is a systematic engineering endeavor that encompasses the entire lifecycle of the transmission system—from its design and manufacturing to installation, operation, maintenance, and eventual replacement. It places numerous demands not only on designers and manufacturers but also on those responsible for installation, operation, maintenance, and servicing. If any of these stages fails to be effectively controlled, gear transmission noise control will inevitably become ineffective.