In the design of industrial machinery, gear transmission is the most important part of gear reducer and the main form of system power transmission. Therefore, as the main role of mechanical transmission, gear plays an important role in the whole mechanical system. However, the previous evaluation of gear transmission performance only focused on transmission efficiency, stability, reliability and so on, ignoring the noise of gear transmission. With the improvement of people's requirements for the performance and quality of mechanical equipment, there is also a high demand for the working environment, which makes the noise problem of reducer gear transmission stand out and become an urgent problem to be solved in mechanical transmission.
Mechanism of noise generation in gear transmission
1 System transmission error
In gear transmission, the composition of an integral mechanical system is often complex. As a complex transmission system, the complete gearbox will produce dozens of natural frequencies in the process of force transformation, so the vibration forms are various. In physics, we know that sound is produced by vibration, and any system transmission will produce vibration. In system transmission, the vibration is caused by system error, which is the main cause of vibration.
2 Gear transmission error
The main cause of noise in gear transmission is involute error or adjacent pitch error between gears. The vibration amplitude and frequency in gear transmission are the main factors to measure the gear noise, which is of great significance in noise research. However, the mechanical response of gear system is very complex in practical research, so the natural frequency of the system can be changed by adjusting the excitation. In a word, the gear transmission error is a disturbance factor acting on the gear and the whole system, which makes it respond, thus generating noise that propagates outward through the air.
Cause analysis of noise of gear reducer in mechanical transmission
1.Parametric factor
Gear precision
Gear precision is an important measure of its design and machining quality. High-precision gears run smoothly in the process of mechanical transmission and produce less noise. However, in the actual design and machining of gear teeth, for economic reasons, in order to reduce the cost, designers often choose low-precision gear grades to the maximum extent while meeting the basic strength requirements, so they ignore the precision grades, and low precision becomes the main factor of gear noise and backlash, resulting in increased noise.
Gear width
In the allowable design range of gear transmission, the tooth width of driven gear should be increased as much as possible, so that the contact area can be increased, which can not only improve the load-bearing capacity of gear, but also improve the stability of gear tooth transmission, reduce vibration and achieve the purpose of noise reduction.
Reducing the pitch in an appropriate range can increase the number of gear teeth meshing and the degree of gear teeth overlap, thus reducing the deflection of meshing gears, improving the transmission efficiency and reducing the generation of noise. In addition, the smaller pressure angle can increase the contact angle and transverse coincidence degree of the gear, which makes the transmission stable, reduces the noise and improves the transmission accuracy.
2 Accuracy factor
Accuracy of meshing smoothness
The working stability accuracy of gears refers to the requirement of changing the instantaneous speed ratio of gears in gear transmission. The rotation angle error will occur many times when the gear rotates once, and the change of instantaneous transmission ratio will make the gear collide many times to form vibration, which will make the gear generate noise in the transmission process.
Gear contact accuracy
The size of gear contact spot is the main index to evaluate the gear contact accuracy. If the contact spot is too small, the noise of gear transmission will increase. The low contact accuracy of gear is due to the influence of tooth orientation error on the transverse contact area of gear teeth, while both the base pitch deviation and tooth profile error will have an impact on the transverse contact area of gear teeth.
Gear motion accuracy
The motion accuracy of gears mainly represents the accuracy of motion transmission, that is, the maximum limit of rotation angle error of gears after meshing for one cycle. The accumulated error between teeth of gear ring radial runout in one rotation of gear will produce low frequency noise, especially when the accumulated error between teeth gradually increases, it will cause impact during gear meshing, which will lead to the change of angular velocity and make the noise increase significantly.
3 Assembly factors
The axial assembly clearance of gear is too small
If the burr of the gear is not removed in time before assembly, the sliding joint surface between the end face of the gear and the front and rear end covers will be damaged in the meshing process, which will reduce the motion accuracy of the gear and produce noise.
Influence of sundries
Due to the entry of sundries in the gearbox, the wear between gear teeth is intensified, and the smoothness of the gear during rotation is reduced, which not only reduces the transmission efficiency of the gear, but also increases the noise.
3 Noise reduction measures of gear reducer in mechanical transmission
1 Reasonable optimization of gear parameters
Properly increase the spiral angle of the driving gear
Because when the spiral angle increases, the gear overlap will also increase, which will greatly reduce the noise. Then, when the spiral angle is too large, the operability of gear machining and installation will become worse, and the installation accuracy is very high. If the accuracy is not reached, the actual coincidence degree will become smaller, and the noise reduction effect will be worse than when the spiral angle is small, so it is necessary to choose the appropriate spiral angle.
Improve gear accuracy
With the improvement of gear precision, the surface roughness of gear teeth will be greatly improved, thus improving the motion precision of gear and effectively reducing noise.
2 Reasonable selection of tooth surface hardness and gear backlash
Through experiments, it can be concluded that the noise is usually low when the side clearance of the module gear is less than 0.04 mm. Therefore, the noise can be reduced by appropriately reducing the gear backlash within the range permitted by the design. In addition, under the condition of the same material and precision, the noise of the soft tooth surface is 1.5-6dB lower than that of the hard tooth surface, and when the hardness of the driving gear is 2-3HBC higher than that of the driven gear, the noise can be effectively reduced.
3 Carry out special treatment on the tooth surface
When the strength design of gears allows, high damping cast iron or some non-metallic materials can be used for gear processing, and the tooth surfaces can also be treated by coating non-metallic materials. Because the materials with good plasticity and toughness can reduce the meshing impulse and pitch line impact, the noise can be effectively reduced by reducing vibration and impact.
4 Improve gear lubrication conditions
The proper lubrication method and lubricating oil should be selected according to the peripheral speed of the gear, which can effectively reduce the noise. Therefore, according to the difference of speed reducer and working conditions, the proper lubrication method and lubricant should be selected. In addition, for the reducer working in high temperature environment, lubrication by oil pool alone will not meet the lubrication requirements, so lubrication should be combined with circulating oil lubrication.
5 Reasonable design of gearbox body structure
In the design process of reducer gearbox box, reasonable box structure can increase the tightness of gear transmission box and make it have good noise reduction effect. Therefore, when designing gears, the closed structure should be adopted as much as possible. At the same time, the vibration damping device should be installed at the junction of the box body, and the reducer should be installed on the fixed seat or support. All these methods can effectively reduce the noise. In addition, in the case of high requirements for reducer noise, a damping material layer, such as foam plastic, can be arranged on the surface of the box to reduce the reducer noise.
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