Based on the objective of reducing vibration and noise of helical gears, taking the helical gear pair of a reduction gearbox of an electric vehicle as an example, a systematic numerical simulation analysis and experimental study were carried out on the influence of helical gear parameters (such as helix angle, pressure angle, tooth width, etc.) and helical gear modification technology (such as different tooth profile modification shapes, large and small gear selection, tooth profile tooth direction selection, etc.) on its meshing performance, dynamic characteristics, and acoustic characteristics, A novel process for determining the optimal profile modification scheme of helical gears is proposed, and some valuable results are obtained. The main research conclusions are as follows:
(1) Properly increasing the pressure angle of helical gear is beneficial to improve the transmission efficiency of gear pair, Hertz contact stress and timely change the meshing stiffness, but it will increase the transmission error; Proper helix angle can reduce the transmission error of helical gear pair and Hertz contact stress to timely change the meshing force, but the larger the helix angle, the greater the time-varying meshing stiffness and the lower the transmission efficiency of the gear pair; Properly increasing the gear tooth width can reduce the time-varying meshing force of helical gear under low speed working condition (2000r/min), but the larger the tooth width is, the greater the time-varying meshing stiffness is; The tooth side clearance has no effect on the time-varying meshing stiffness of the helical gear, but the smaller the tooth side clearance, the smaller the meshing force, generally 0.05mm.
(2) The tooth profile modification is mainly to reduce the Hertz contact stress on the tooth surface of the gear, that is, to increase the strength (life) of the helical gear, but also to reduce the transmission error; Tooth alignment modification is mainly to reduce the transmission error, that is, to reduce the internal dynamic excitation of the gear, but also to reduce the Hertz contact stress.
(3) Comparing the multi-body dynamics and acoustic numerical simulation results of the linear modification optimization scheme of the long tooth profile, the broken arc modification optimization scheme of the long tooth profile and the drum modification optimization scheme of the pinion tooth profile for the helical gear pair of an electric vehicle reducer, it is found that although the time-varying meshing force of the helical gear of each scheme does not decrease or even increase under the high-speed working condition, the noise power level is lower than that before the modification, Therefore, it is considered that the vibration and noise of helical gear under high-speed working condition (10000r/min) may mainly depend on the stiffness excitation (time-varying meshing stiffness) and error excitation (transmission error).
(4) Taking the helical gear pair as an example, from the point of view of vibration reduction and noise reduction, it is suggested that both large and small gears should be shaped at the same time; If you only want to reduce the transmission error of the helical gear and improve the strength of the gear teeth, you can only modify the large gear, but it is recommended to modify the large and small gears at the same time, and you need to consider the possibility of complex modification (for example, only for the large gear long tooth profile tooth top arc 3 μ M+tooth drum 3 μ M shape modification, the transmission error decreases by about 8.2%, and the Hertz contact stress decreases by about 3.6%); In addition, in addition to the drum profile modification, the effect of vibration reduction, noise reduction and life increase only for the pinion profile modification is not good.
(5) In the secondary optimization modification scheme (linear, involute, circular arc, broken arc) of all the long tooth profiles of the helical gear pair, the linear effect is the best in terms of reducing the helical gear error excitation and improving the gear tooth strength (the transmission error decreases by about 17.6%, and the Hertz contact stress decreases by about 6.6%); In terms of reducing the time-varying meshing force and time-varying meshing stiffness of helical gears, the effect of circular arc and involute is better (the time-varying meshing force reduces 123.41N, 1606.187N, 2492.734N and 122.687N, 1540.64N and 2348.992N respectively under low, medium and high speed conditions, and the time-varying meshing stiffness decreases by 14.3% and 14.1% respectively); In terms of the overall noise reduction effect, the effect of arc and involute is better (the average sound power in the full frequency domain is reduced by 5.2 dBA, 1.6 dBA, 2.8 dBA and 4 dBA, 2.1 dBA and 2.9 dBA respectively under low, medium and high speed conditions).
(6) In all the modification schemes of the helical gear pair of an electric vehicle gearbox optimized by transmission error, Hertz contact stress, time-varying meshing force and time-varying meshing stiffness, the drum shape of tooth profile (simultaneous modification of large and small gears) has the best effect of vibration reduction and noise reduction (the average sound power in the full frequency domain has decreased by 8.4 dBA, 1.7 dBA and 3 dBA respectively under low, medium and high speed conditions), And because the overall noise reduction effect of the optimization scheme of tooth profile drum (only for large gears) is close to that of multiple quadratic optimization modification schemes, the optimization modification of tooth profile drum only for large gears can be used in engineering practice due to production cost considerations. In addition, the selection of the modified helical gear is extremely important for the drum profile modification method. If the main purpose is to reduce the stiffness excitation of the helical gear pair, it is recommended that the large and small gears be modified at the same time (the time-varying meshing stiffness decreases by about 16.3%); If the objective is to reduce the time-varying meshing force of the helical gear pair, it is recommended to only modify the large gear (the time-varying meshing force has decreased by 425.59N, 5174.793N and 5925.515N respectively under low speed, medium speed and high speed conditions); If you simply want to reduce the error excitation of helical gear and improve the strength of gear teeth, you can only modify the pinion (the transmission error decreases by about 16.3%, and the Hertz contact stress decreases by about 13.8%), but it is not recommended (the high frequency noise (4978.5Hz~8525Hz) sound power value under low speed conditions increases significantly).
(7) It is not rigorous for many studies to evaluate whether the meshing noise of helical gears has been improved based on the transmission error value of gears before and after modification. From the simulation results, the vibration noise of the helical gear will be reduced only if the main dynamic excitation such as time-varying meshing stiffness, time-varying meshing force and transmission error are reduced simultaneously through the modification, and the tooth shape is appropriate.
(8) Do not blindly modify the helical gear by experience (for example, the large and small gears adopted by a subsidiary product of the helical gear of an enterprise also have a tooth profile of 25 μ M and tooth drum 25 μ M compound modification scheme), otherwise, it will only increase the production cost, increase the vibration noise of the helical gear pair and shorten its service life.