In the design of reducer, gear transmission, as the main power transmission and deceleration device, is widely used in the field of mechanical industry. But with the increasing demand of noise control for reducer, the control of gear transmission noise is an important part of production quality control in the design and manufacture of modern reducer. This paper analyzes the noise generating mechanism in gear transmission, studies the causes of noise formation in mechanical transmission of gear reducer, and then puts forward corresponding noise reduction measures and treatment methods according to the causes of noise generation, which provides scientific theoretical basis for noise reduction.

In the design of industrial machinery, gear transmission is the most important part of gear reducer and the main form of power transmission of the system. Therefore, gear as the main role of mechanical transmission plays a pivotal role in the whole mechanical system. However, the previous evaluation of gear transmission performance only focuses on the transmission efficiency, stability, reliability and other aspects, The noise of gear transmission is ignored. With the improvement of the performance and quality of mechanical equipment, there are also high requirements for the working environment, which makes the noise problem of gear transmission of reducer prominent, which becomes an urgent problem in mechanical transmission.

Noise generation mechanism in gear transmission

1 system transmission error

In gear transmission, the composition of a whole mechanical system is often more complex. As a complex transmission system, the complete gearbox will produce as many as dozens of natural frequencies during the transformation of various forms of force, so the vibration forms are various. In physics we know that sound is produced by vibration, and any system drive will produce vibration. In the system transmission, vibration is caused by system error, and system error is the main reason for vibration.

2 gear transmission error

The main reason for noise in gear transmission is involute error or the error of adjacent pitch between gears. The vibration amplitude and frequency of gear transmission are the main factors to measure the noise of gear, which is of great significance in the study of noise. But in the actual research, the mechanical response of gear system is very complex, so the natural frequency of the system can be changed by adjusting the excitation. In a word, the gear transmission error is the disturbance factor acting on the gear and the whole system and making it respond, thus generating noise which propagates outward through the air.

Analysis of the noise cause of gear reducer in mechanical transmission

1 Parameter factors

Gear accuracy

Gear precision is an important measure of design and processing quality. High precision gear runs smoothly and stably in the process of mechanical transmission, resulting in less noise. But in the actual gear design and processing, for economic reasons, in order to reduce the cost, designers often choose the low precision gear class to the maximum extent to meet the basic strength requirements. Therefore, the accuracy level is ignored, low precision becomes the main factor of noise and side gap of gear, which causes noise increase.

Gear width

In the allowable design range of gear transmission, the width of driven gear teeth can be increased as much as possible, which can increase the contact area, not only improve the load bearing capacity of gear, but also improve the stability of gear transmission, reduce vibration and achieve the purpose of noise reduction.

Pitch and pressure angle

Reducing the gear pitch in a proper range can increase the number of teeth engagement and increase the overlap degree of the teeth, thus reducing the deflection of the meshing gear, improving the transmission efficiency and reducing the noise generation. In addition, the smaller pressure angle can increase the contact angle and transverse coincidence degree of gear, make the transmission stable, reduce noise and improve the transmission accuracy.

2. Accuracy factors

Accuracy of meshing stability

The working stability accuracy of gear refers to the requirement of the change of gear instantaneous speed ratio in gear transmission. The angular error occurs many times when the gear is rotating for one week. The change of instantaneous transmission ratio in the process of gear mesh will cause the gears to impact and form vibration many times, which makes the gears generate noise during the transmission process.

Gear contact accuracy

The contact spot size of gear is the main index to evaluate the accuracy of gear contact. Too small contact spot will cause the increase of gear transmission noise. The low contact accuracy of gear is that the tooth direction error affects the lateral contact area of the tooth, and the pitch deviation and the tooth shape error will affect the tooth transverse contact area.

Gear motion accuracy

The accuracy of gear motion mainly represents the accuracy of motion transmission, that is, the maximum limit of the angular error of the gear after one period of engagement. The accumulated error of gear ring runout in the gear rotation will produce low frequency noise, especially when the cumulative error between teeth increases gradually, it will cause impact when the gear is engaged, which will cause the change of angular speed and make the noise increase significantly.

3 assembly factors

The axial assembly clearance of gear is too small

If the gear is not deburring before assembly, it will cause the sliding joint surface between the gear end face and the front and rear end cover to cause the joint surface damage during the engagement, and reduce the gear motion accuracy and generate noise.

Influence of sundries

The gear box is more worn between gears due to the entry of sundries. The flatness of gear decreases during the rotation process, which not only reduces the transmission efficiency of gear, but also increases the noise.

Noise reduction measures of gear reducer in mechanical transmission

The reasonable optimization of the parameters of 1 gear

Increase the spiral angle of driving gear properly

Because when the helix angle increases, the coincidence degree of gear will increase, which will make the noise greatly reduced. Then, when the screw angle is too large, it will lead to the poor machining and installation operability of gear. The installation accuracy is required to be high. If the accuracy is not reached, the actual coincidence degree will be reduced, and the noise reduction effect is worse than that of the spiral angle, so the appropriate spiral angle should be selected.

Increase the width of the driven gear tooth surface

The proper increase of tooth width will increase the meshing degree of the teeth, thus enhancing the transmission stability of the gear teeth. So the larger the tooth width of the gear, the better its stability and the better the noise reduction effect.

Improve gear accuracy

The improvement of gear precision will greatly improve the surface roughness of the gear, thus improving the motion accuracy of the gear and effectively reducing the noise.

2. Reasonable selection of tooth surface hardness and gear side clearance

The conclusion can be drawn by experiments that the noise is lower when the side clearance of modular gear is less than 0.04mm. Therefore, the noise can be reduced by properly reducing the backlash of the gear within the allowable range of design. In addition, under the same material and accuracy, the soft tooth surface noise is 1.5-6db lower than that of hard tooth surface. When the hardness of active gear is 2-3hbc higher than that of driven gear, C can effectively reduce the noise.

3 special treatment of tooth surface

When the gear strength design allows, the gear processing can be made of high damping cast iron or some non-metallic materials, or the tooth surface can be coated with non-metallic materials. Because the material with good plasticity and toughness can reduce the impact of gear engagement force and joint line, and by reducing vibration and impact, it can effectively reduce noise.

4 improve gear lubrication conditions

The gear lubrication should choose the proper lubrication method and lubricating oil according to the gear circumference speed, so that the noise can be effectively reduced. Therefore, according to the difference of reducer and working conditions, the proper lubrication method and lubricant are selected. In addition, for the reducer working in high temperature environment, lubrication through oil pool will not meet the requirements. Therefore, it is necessary to combine the lubrication of circulating oil and other methods.

5. Design the gearbox box structure reasonably

In the process of gearbox design, reasonable box structure can increase the sealing property of gearbox, and make it have good noise reduction effect. Therefore, the gear design should adopt the closed structure as much as possible, and the vibration damper should be installed at the joint of the box, and the reducer should be installed on the fixed seat or support. These methods can effectively reduce the noise. In addition, when the noise requirements of the reducer are relatively high, the damping material layer, such as foam plastics, can be set on the surface of the box to reduce the noise of the reducer.