First, gear design.
1, gear type and material
(1) gear type:
From the point of view of stable transmission and low noise, helical cylindrical gears have more tooth pairs in contact at the same time, and the change of meshing comprehensive stiffness is relatively stable. Therefore, the vibration noise may be lower than that of the same spur gear, sometimes as low as about 12dB. For herringbone gears, due to strict centering, small errors or uneven wear may affect the load sharing and transmission stability of herringbone gears. Therefore, among cylindrical gears, helical cylindrical gear is the best gear type to reduce noise. From 1969- 1987, A.Y.Atfia, a professor at Ain-Shams University in Cairo, Egypt, conducted experiments on single-arc gears and double-arc gears. He compared the noise of these three gears under different loads and speeds. The research shows that among these three gears, involute helical gear has the lowest noise and is least affected by the transmitted load and running speed, followed by single-arc gear and double-arc gear.
(2) Gear material
The material of the gear. Heat treatment and lubrication methods will affect the system noise. Generally speaking, noise can be reduced by using materials with good attenuation performance, but materials with good attenuation performance are not strong enough to be used in any occasion. For example, phenolic resin and nylon can only be used to make light gears for sewing machines and other light industrial machinery. In order to reduce noise, the tooth surface of bearing steel gear can be sulphurized or copper plated. The purpose of tooth surface sulphurization is to reduce the friction coefficient of tooth surface. Copper is plated on the tooth surface of turbine gear to improve the contact accuracy of gear. Heat treatment of gears will also affect noise. For example, after quenching, the attenuation performance of gears will become worse, and the noise will increase by 3-4dB, so gears with low requirements on strength and wear performance do not need to be quenched. As for the influence of lubricating oil and refueling method, it is generally believed that with the increase of oil quantity and oil viscosity, the noise decreases, because lubricating oil has damping effect, which can prevent the meshing tooth surfaces from contacting directly. When oil bath lubrication is used, the gear noise is different due to different oil levels, that is, different gear boxes have different optimal oil levels.
2. Geometric parameters of gears
(1) modulus
When a large load is transmitted, the dynamic excitation of gear meshing is mainly caused by the bending deformation of gear teeth, and the bending stiffness of gear teeth is proportional to the modulus, so increasing the modulus can reduce the dynamic excitation of gear teeth and thus reduce the noise. But when the transfer load is small or empty, the situation is different. At this time, the influence of gear tooth error will be much greater than gear tooth deformation, so the influence of modulus on noise should be considered from the perspective of gear dry machining error. For example, the pitch error △P can be obtained by the following formula: △P=C 1 +C2M+C3 (1).
Where do—— refers to the pitch diameter of the gear.
M modulus
Calculation of C3 C2 c 1- correlation constant
Tooth profile error △f can be calculated by the following formula:
△f=C4M+C5 (2)
Where C4 and C5 are related constants.
From (1)(2), it can be seen that the above two errors are directly related to the modulus, the modulus is large, the tooth profile error is large, and the noise is also large. Therefore, when the transmission load is small or no-load, the modulus should be as small as possible when the gear strength allows.
(2) Number of teeth
If the modulus is constant, the gear diameter and gear surface area will change with the change of the number of teeth, so the noise will change with the change of gear noise radiation area. Generally speaking, noise is mainly determined by the radiation area of noise rather than the energy of vibration source. According to the acoustic principle, if the gear is regarded as a circular plate, the acoustic power WR radiated into the air can be calculated as follows: WR = 0.06 PWR/πC3(6+0.85 RP)xF(3).
Where: f-effective value of exciting force changing according to sine law.
R—— Diameter of circular plate
O-area density
P- air density
ω-angular frequency
C constant
According to Equation (3), with the increase of the diameter of the circular plate, the noise will increase sharply. Therefore, when designing gears, the gear diameter should be reduced as much as possible. In addition, from equations (1) and (2), it can be seen that the pitch error is related to the gear diameter, while the tooth profile error has nothing to do with the diameter, so reducing the diameter will not increase the difficulty of realizing the gear machining accuracy.
(3) Because of the different energy attenuation, the change of tooth width causes the change of noise. Therefore, the wide tooth gear has good attenuation performance and low noise.
(4) coincidence degree
Increasing the coincidence degree can reduce the noise of gear transmission. First of all, increasing the coincidence degree can reduce the load of a single pair of gear teeth, thus reducing the load impact of meshing and meshing and reducing the gear noise. Secondly, with the increase of the number of contact teeth, the transmission error of a single pair of gear teeth is balanced, thus reducing the dynamic excitation of gear teeth. In addition, almost all the gear tooth parameters that affect the gear noise are actually due to their influence on the coincidence degree. For example, for a cylindrical gear with a coincidence degree of 1-3, the pressure angle of the gear is reduced, the modulus is reduced, and the height of the tooth tip is slightly increased, all because the coincidence degree is improved and the gear noise is reduced. Of course, the reduction of pressure angle increases the flexibility of gear teeth, reduces the dynamic excitation, and is beneficial to the reduction of noise.
(5) Spiral Angle Because the helical gear gradually enters the meshing from one end of the tooth, the meshing impact is small and the noise is low. Generally speaking, with the increase of spiral angle, the coincidence degree increases and the noise decreases. However, the noise reduction effect is smaller when the spiral angle is larger than that of the spiral angle. This is because it is difficult to process and install when the spiral angle is large, which affects the actual coincidence degree.
(6) Tooth modification, reshaping and displacement In the actual working state of the gear, the deformation of the gear teeth, the transmission shaft and the box will cause interference and impact when the gear teeth are engaged and disengaged, resulting in strong vibration and noise. Therefore, the meshing deformation can be compensated by means of modification, shaping and displacement, so as to achieve the purpose of vibration and noise reduction.
Second, the gear processing
The machining accuracy of (1) gear has an important influence on the noise of gear system. Generally speaking, improving machining accuracy is helpful to reduce the noise of gear system. However, improving the machining accuracy is limited by the machining cost. The higher the initial machining accuracy, the less obvious the noise reduction effect of improving the accuracy.
Among the tooth errors of a single gear, the tooth profile error has the greatest influence on noise. When the tooth profile error is large, the gear noise is large, but the relationship between them is not simple linear. Because the size of noise depends not only on the size of tooth profile error, but also on the shape of tooth profile. Experiments show that a slightly drum-shaped tooth profile is beneficial to reduce noise.
Generally speaking, if the backlash is too small, the noise will increase sharply, and if the backlash is slightly larger, it will have little effect on the noise.
(2) Processing method
There are many ways to process gears. Generally speaking, there is no fixed relationship between machining method and gear noise, because it is also affected by machining technology. Usually, different machining methods will produce different tooth surface roughness, and improving tooth surface roughness is beneficial to reduce noise.
Third, the gear train and gearbox.
1, the structure of the gear body has an important influence on the noise of the gear system.
First of all, under the dynamic excitation force of gear teeth, the wheel as an elastic body will vibrate and radiate noise. Secondly, the dynamic exciting force acting on the gear teeth will be transmitted to the transmission shaft through the gear body, and then to the bearing and the box body. Furthermore, the structure of the wheel body will also affect the transmission error in the process of gear meshing, and then affect the dynamic excitation force. Therefore, noise can be reduced from two aspects: reducing the noise radiation of the gear body and reducing the vibration transmission of the gear body.
(1) Reduce the noise radiation of the gear body.
Generally speaking, besides the energy of vibration source, noise is mainly determined by radiation area. Therefore, reducing the surface area of gear can reduce the radiation area of noise, thus reducing the radiation noise. In addition, the shape of the gear is also related to noise, for example, the thicker the gear blank, the smaller the noise.
(2) reduce the transmission of vibration of the gear body
In this regard, we can adopt some composite structures, or fill damping materials in the middle of the gear body to increase the damping effect of the gear, thus reducing the transmission of vibration and noise.
2. Shafting structure.
Through the design of shafting, the phase relationship of meshing excitation in multi-stage gear transmission can be controlled, which can prevent the deflection of transmission shaft and reduce noise.
3. Box structure.
Gear box is a typical elastic structural system, which produces vibration and radiated noise under the dynamic load of bearings. Therefore, reasonable design of the structure and vibration characteristics of the box will help to reduce the noise of the gear system. For example, in the design, the minimum vibration of the thin wall of the box is the goal, and the constraints are frequency constraints, stress constraints and geometric constraints, so as to minimize the vibration of the box wall under dynamic excitation and achieve the purpose of reducing noise radiation. In addition, in the structural design of the box, we should pay attention to make the structural connection between the bearing bracket and the box fulcrum have enough rigidity to reduce the vibration of the system. For large-area thin walls, stiffeners should be set to reduce the amplitude of vibration and noise.