Transmission error belongs to error excitation, which is an important factor affecting the vibration and noise of meshing helical gear pair, but not the only factor. The actual process of helical gear transmission is not a simple interaction of a pair of helical gears, but a multi-body movement of shafts, bearings, shells and other components assembled together. Therefore, based on the preliminary optimization modification scheme of a helical gear pair obtained in Chapter 3, this chapter uses the Motion module of LMS Virtual Lab software, based on the high reliability torsional vibration method, to truly simulate the actual working conditions of the helical gear pair of the gearbox (comprehensively considering the nonlinear factors such as gear backlash, time-varying meshing stiffness, meshing damping, bearing stiffness, system damping, etc.) The time-varying meshing force and time-varying meshing stiffness of the rear meshing helical gear pair are deeply analyzed, which lays the foundation for the subsequent acoustic simulation.
The multi-body dynamics simulation was carried out for all the modification schemes of helical gear pair of an electric vehicle gearbox optimized by transmission error and Hertz contact stress. By comparing the time-varying meshing force and time-varying meshing stiffness of the front and rear gears modified by different optimization modification schemes, the modification schemes with smaller internal dynamic excitation of the helical gear were further selected, and at the same time, the helix angle, backlash The influence of helical gear parameters such as pressure angle on time-varying meshing force and time-varying meshing stiffness. The conclusions are as follows:
(1) The appropriate helix angle can significantly reduce the time-varying meshing force of helical gears, make the meshing smooth (the curve is relatively smooth), and reduce the meshing impact, but the larger the helix angle, the greater the time-varying meshing stiffness; Large pressure angle is beneficial to reduce the time-varying meshing stiffness of helical gears; Therefore, small helix angle and large pressure angle should be selected on the premise of meeting the use requirements and small time-varying meshing force.
(2) The backlash has no effect on the time-varying meshing stiffness of helical gear, but the smaller the backlash is, the smaller the time-varying meshing force of helical gear is at low speed (2000r/min), generally 0.05mm; The tooth width of the helical gear only affects the time-varying meshing force of the gear at low speed (2000r/min), that is, increasing the tooth width can reduce the time-varying meshing force, but the larger the tooth width is, the greater the time-varying meshing stiffness is. Therefore, if the requirements for the use of helical gear pairs at low speed are not strict, smaller tooth width can be selected to obtain better vibration and noise performance of helical gear pairs at medium and high speeds.
(3) From the point of view of reducing the time-varying meshing force and time-varying meshing stiffness of helical gears, in all the modification schemes of helical gear pair of an electric vehicle reducer optimized by transmission error and Hertz contact stress, the top of long tooth profile (linear, broken line arc), the crown of tooth profile (only for pinion) The composite optimization modification of tooth profile and tooth direction of big gear (long tooth profile tooth top involute+tooth direction drum, long tooth profile tooth top circular arc+tooth direction drum, long tooth profile tooth top broken line circular arc+tooth direction drum) has poor effect, while the long tooth profile tooth top (circular arc, involute) and tooth profile drum (big and small gears, only for big gears) have good effect.
(4) For the drum modification of tooth profile, the selection of modified helical gears is extremely important. If the main purpose is to reduce the stiffness excitation of helical gear pair, it is recommended to modify the big and small gears at the same time; If the goal is to reduce the time-varying meshing force of helical gear pair, it is recommended that only the big gear or the small gear be modified at the same time. In addition, it is not recommended that only the pinion be modified because the drum shaped optimization modification of the driving gear (pinion) profile can only slightly reduce the stiffness excitation.
(5) Because only the composite optimization modification of the big gear of the helical gear pair can only slightly reduce the stiffness excitation, it cannot effectively improve the meshing impact between the helical gear pairs. Therefore, on the premise that the optimization scheme of single modification mode can achieve the goal of helical gear modification, the composite modification of tooth profile and tooth direction is not recommended considering the processing cost.