When gears work, especially at high loads and speeds, the noise and vibration caused by the rotation of the gears is considered a big problem. However, since noise problems tend to happen due to several causes in combination, it is very difficult to identify the cause. The following are ways to reduce noise and these points should be considered in the design stage of gear systems.
- Use High-Precision Gears
Reduce the pitch error, tooth profile error, runout error and lead error. Grind teeth to improve the accuracy as well as the surface finish.
- Use a Better Surface Finish on Gears
Grinding, lapping and honing the tooth surface, or running in gears in oil for a period of time can also improve the smoothness of tooth surface and reduce the noise.
- Ensure a Correct Tooth Contact
Crowning and end relief can prevent edge contact. Proper tooth profile modification is also effective. Eliminate impact on tooth surface.
- Have a Proper Amount of Backlash
A smaller backlash will help produce a pulsating transmission. A bigger backlash, in general, causes less problems.
- Increase the Transverse Contact Ratio
A bigger contact ratio lowers the noise. Decreasing the pressure angle and/or increasing the tooth depth can produce a larger contact ratio.
- Increase the Overlap Ratio
Enlarging the overlap ratio will reduce the noise. Because of this relationship, a helical gear is quieter than the spur gear and a spiral bevel gear is quieter than the straight bevel gear.
- Eliminate Interference on the Tooth Profile
Chamfer the corner of the top land, or modify the tooth profile for smooth meshing. Smooth meshing without interfering makes low noise.
- Use Gears that have Smaller Teeth
Adopt gears with a smaller module and a larger number of gear teeth.
- Use High-Rigidity Gears
Increasing facewidth can give a higher rigidity that will help in reducing noise. Reinforce housing and shafts to increase rigidity.
- Use Resin Materials
Plastic gears will be quiet in light load and low speed operation. Care should be taken to decrease backlash, caused from enlargement by absorption at elevated temperatures.
- Use High Vibration Damping Material
Cast iron gears have lower noise than steel gears. Use of gears with the hub made of cast iron is also effective.
- Apply Suitable Lubrication
Lubricate gears sufficiently to keep the lubricant film on the surface, under hydrodynamic lubrication. Highviscosity lubricant will have the tendency to reduce the noise.
- Lower Load and Speed
Lowering rotational speed and load as far as possible will reduce gear noise.
- Use Gears that have No Dents
Gears which have dents on the tooth surface or the tip make cyclic, abnormal sounds.
- Avoid too much thinning of the Web
Lightened gears with a thin web thickness make high-frequency noises. Care should be taken.
Related article – The gear noise
When it comes to a high power and high-speed gears such the ones that transmit power of a motor or engine, the gear noise or vibration often becomes a problem. However, the countermeasure for the noise is not easy since the gear noise usually occurs from multiple various factors. In this part, examples of gear noise and countermeasures are explained.
The gear noise can be divided broadly into two, depending on where the noise occurs. First is the one that occurs from the gear itself, and second is from peripheral components such as gearboxes.
When noise is from the gear itself, it can be from the friction when teeth mesh. Though it depends on the conditions such as the number of rotation, the frequency of sound is relatively low for the most cases. In this kind of case, first thing to check is the accuracy of a gear. If the accuracy of the basic gear shape is low such as a pitch error and tooth shape error, it can cause noise and vibration since teeth don’t mesh by theory. Also, even when the accuracy of a gear was high and shape was theoretically correct, the tooth bearing could be uneven when a gear shaft is warped from the pressure on a gear. In this kind of situation, the noise can be reduced by adjusting the tooth bearing with improvement of the rigidity of a shaft or treatment like crowning.
The smooth meshing of teeth can be an important factor to limit noise and vibration from a gear. The countermeasures are using profile shifted gears to prevent interference and having a reasonable backlash, lubricating a gear, and making the tooth flank smooth by reducing the roughness of it. Particularly for the smoothness of a tooth flank, plastic gears are highly effective, but one needs to be careful because it is sensitive to the humidity and temperature compared to metal gears.
Among peripheral components of a gear, a gearbox is often the cause of noise. In many cases, noise occurs when vibration from a gear transmits to a gearbox, making it vibrate sympathetically. The frequency of sound is most likely to be high compared to the noise from the friction of teeth. For the countermeasures, one can improve the rigidity of a gearbox or use cast iron that has high vibration damping factor for a gear, gear boss, and gearbox. Other effective methods are enhancing the front gear contact ratio by reducing the reduction ratio of a gear and improving the overlapping meshing ratio with a helical gear. The countermeasures for the noise from a gear are also effective as it is caused by vibration from a gear.