In the process of gear transmission, there is a deviation between the actual base pitch and the theoretical pitch due to the manufacturing error of the gear and the load deformation of the gear tooth, which is called the basal pitch error (as shown in Fig. 1). The meshing of two gears with pitch error will form a “composite pitch error”, and its expression is shown in the formula
Among them, Δ FP and Δ FG are the base pitch errors of main and driven wheels respectively.
Due to the existence of the error of synthetic base pitch, the meshing point near the meshing point deviates from the theoretical meshing position when the gear enters into meshing, which makes the tooth pair enter into meshing ahead of time. At this time, the sudden change of transmission ratio causes the normal speed difference between the two gears at the meshing position near the meshing point, thus forming the meshing impact force; similarly, when the gear withdraws from meshing, the meshing point near the meshing point deviates from the meshing position, forming the meshing out impact force. Meshing impact and meshing out impact are called meshing impact. The meshing impact force is one of the important excitation factors for the vibration and noise of gear transmission system. The formation mechanism of meshing impact is shown in Fig. 2.
As shown in Figure 2, the actual engagement point a ‘deviates from the theoretical engagement point a’ when the gear enters the meshing due to theerror and the gear load deformation. At this time, the driving wheel base section PB1 is smaller than the driven wheel base section PB2, which causes the gear transmission ratio to change suddenly and the speed of the driven wheel rises sharply. At this time, the normal speed of the driven wheel at the actual engagement point is greater than that of the driving wheel, resulting in the velocity difference and impact speed, thus forming the instantaneous “engagement interference” between the driving gear root and the driven gear top.
Similarly, when the gear is out of engagement, the base pitch PB1 of the driving wheel is larger than that of the driven gear PB2 due to the existence of the meshing composite pitch error, which results in the change of gear transmission ratio and the sudden increase of driving wheel speed. At this time, the normal speed of the driving wheel at the actual engagement point is greater than that of the driving wheel, resulting in the velocity difference, resulting in the “meshing out interference” between the top of the driving gear and the root of the driven gear.
The formation mechanism of meshing impact and meshing out impact are the same, but the impact of meshing impact on the vibration characteristics of gear system is significantly higher than that of meshing out impact, so only the impact of meshing impact on the vibration characteristics of gear system is considered.