Study on reducing the noise of tractor gears

Tractor is a kind of strong noise source, which not only pollutes the environment, but also endangers the driver’s health. Working under strong noise for a long time will damage driver’s hearing and reduce driver’s working efficiency. The working environment of tractor is complex, including road transportation and field operation. During the operation, the load changes greatly, and the factors affecting the noise are complex. The engine noise and chassis noise are the main factors that affect the tractor noise. The chassis noise mainly comes from gear noise. The following mainly describes the mechanism of tractor gear noise and the measures to reduce it.

The gear is the main noise source of the gearbox because of the vibration caused by the gear meshing. There are many reasons and influencing factors for the vibration of the gear during the transmission of power, such as the design parameters of the gear: accuracy, load, circumferential speed, modification coefficient, side clearance of the gear pair, overlapping coefficient, tooth profile modification, tooth surface roughness, modulus, number of teeth, pressure angle, tooth surface width, meshing angle, etc.

The tooth surface roughness directly affects the friction coefficient of relative sliding between tooth surfaces, especially when the lubrication is poor or the quality of lubricating oil is poor, the coarser the tooth surface is, the greater the friction coefficient is, directly affects the change of normal force on the tooth surface, and makes a very unpleasant scream when running at high speed. The influence of tooth surface roughness on noise is also related to the speed and load of the gear. When the rotating speed is greater than 800 R / min and the load is greater than 200 nm, the influence of tooth surface roughness on noise increases with the increase of speed and load.

The influence of gear pair side clearance and its variation on noise is especially manifested in light load, large torque change, high-speed working condition, alternating change of positive and negative working surfaces of gear during acceleration and deceleration, large side clearance of gear pair will cause knocking, and the variation of side clearance is the comprehensive reflection of gear accuracy, which directly affects the unevenness of gear operation.

According to the calculation formula of Professor G.N i e m a n, the noise level is directly proportional to (1-tg β / 2). The larger the helix angle is (no more than 40 °), or the wider the tooth width is, the larger the overlap coefficient is, so the noise is reduced. But the influence of helix angle and tooth width on noise is limited. This effect is also related to the load. When the load is large, the larger the helix angle is, the smaller the noise level is.

Small tooth width is easy to cause axial vibration and noise. The tooth width is inversely proportional to the bending deformation of the tooth. If the tooth width is doubled, the bending deformation of the tooth can be reduced by half in theory. In the case of insufficient stiffness, increasing the tooth width is beneficial to reduce the noise.

When the teeth enter the meshing and disengaging area, the impact and noise will be produced due to the fluctuation of the angular velocity caused by the tooth error and the load deformation. After the top and root of the teeth are modified and the tooth direction is modified, the meshing performance of the teeth will be effectively improved and the noise of the gears will be reduced.

The impact in gear transmission will produce noise. Reducing the impact in gear transmission is an effective way to reduce the noise. The use of gear modification can effectively reduce the impact of gear transmission and control the noise of gear transmission.

Sometimes the effect of gear modification is better than that of improving gear accuracy. Improving the gear accuracy can reduce the gear transmission error and noise, but it will cause the gear tooth deformation and transmission error when the load is large, and the noise will increase with the load. This phenomenon can be effectively improved by gear modification. Gear tooth modification is one of the ways to reduce gear noise.

The high-grade gear pair should first meet the noise index, then meet the requirements of strength and life. The greater the speed and load of the same gear, the greater the noise. The noise changes linearly with the speed and the load.