Mechanical noise is the noise caused by the collision, friction, impact and vibration of mechanical parts during operation.When a pair of gears mesh, due to the inevitable existence of varying degrees of errors in tooth pitch, tooth shape, tooth direction, etc., coupled with changes in external loads, meshing impact will occur during operation and an emission corresponding to the gear meshing frequency will occur. Noise, friction sound will also occur due to relative sliding between the tooth surfaces.Gears are the basic parts in engine transmission. Reducing gear noise is very necessary to control engine noise. So what measures should be taken during the manufacturing process?
So what is the mechanism of gear noise?In what form is the noise generated?
1. Pulsating impact of meshing gear nodes
During the transmission process of a pair of involute gears, the trajectory of the contact points of each pair of gear teeth always runs continuously on the meshing line, as shown in Figure 1.O; is the driven gear driven by the driving gear 02 in the direction shown in the figure. The two teeth of this pair of gears start to contact at point A and disengage at point C. Point B is the tangent point of the pitch circles of the two gears, and NN is its meshing line].Gear 1 rotates clockwise around the axis O at an angular speed W. Gear 2 is driven by gear 1 to rotate counterclockwise around the axis O2 at an angular speed W. During the transmission process, the relative sliding speed between the tooth profiles on the entire meshing line of the gear pair will change accordingly. The relative sliding speed changes with different meshing point positions. Among them, the relative sliding speed of the meshing start point A and the end point C is the maximum. The relative sliding speed is zero at the tangent point of the pitch circle (i.e. point B). At the same time, the direction of the relative sliding speed is also at B. point begins to change. Since there is relative sliding on the meshing tooth surface, sliding friction will inevitably occur. When the relative sliding speed changes direction at point B, the direction of the friction force also begins to change. Due to the change in the magnitude and direction of the friction force, resulting in A pulsating impact of force occurs on the node, which is called node pulsation. Its size and duration are proportional to the transmission force when the gear meshes, the friction coefficient between the gear teeth and the relative sliding speed of the rotation speed.It can be seen that when the transmission power of the gear is greater, the speed is higher, and the surface roughness of the gear is worse, the node pulsation impact will be greater. Due to this pulsation impact, the gear will vibrate and be accompanied by friction sound, so for For a pair of 'ideal' gears, assuming there is no pulsating torque on the transmission shaft, the pulsating impact it generates during the meshing process is unavoidable, which will cause vibration and noise in the transmission gear.
2. Gear meshing impact
During the meshing process of a pair of gears, since the gears will inevitably undergo a certain degree of elastic deformation, whenever one gear tooth meshes, the load on the originally meshed gear teeth will be relatively reduced, and they will immediately The deformation is restored toward the load position, thereby giving the gear body a tangential acceleration. Coupled with the bending deformation of the original meshed gear teeth under load, the newly meshed teeth cannot obtain smooth contact with the theoretical tooth profile and collide, forming a so-called 'Meshing impact force', under the action of this excitation force, the gear will also excite circumferential vibration, radial vibration, and axial vibration of the gear, thereby generating noise and spreading through air and solid media.Therefore, the pulsating impulse and meshing impulse generated during the gear meshing process cause a pair of transmission gears to vibrate, thereby radiating noise.
