Gear transmission has the advantages of constant instantaneous transmission ratio, stable and reliable operation, long service life and high efficiency. It is the most extensive mechanical transmission in modern machinery. This paper mainly discusses the meshing transmission and its characteristics of involute gears.
For example, a pair of involute gears of the external meshing drive, the driving wheel 1 pushes the driven theory 2 to rotate. Point B is the starting point of the meshing point, point B is the end point of the meshing point, and N and N are the inner common cutting points of the two gear base circles, respectively. We know that the meshing point has four lines (the common normal of the meshing point, the meshing line, the inner common tangent of the two base circles, and the positive pressure line of action). The actual trajectory of a pair of gear teeth meshing points is the actual meshing line and is the theoretical meshing line. N and N are the extreme positions of B and B, respectively. The intersection C of the NN and the connected heart OO is a node.
For example, when two teeth are engaged at any point K, the linear velocities are V and V, respectively, and the directions are perpendicular to OK and OK, respectively. Therefore, since the two tooth profiles are in contact at point K, it can be seen that V and V are in the NN direction. The partial speeds must be equal, otherwise the two tooth profiles will be embedded or separated from each other. Therefore, the sub-speed in the NN direction can be obtained as a constant value, and it can be considered that the pair of teeth has its meshing point moving at a constant speed from point B to point B along the line. The transmission ratio ignores the friction at the contact, the force acting on the driving wheel is, T is the torque on the driving wheel, the instantaneous gear ratio of the two gears is constant and the transmitted torque is constant, and the positive pressure and direction of action It is unchanged, thus ensuring the smoothness of the transmission.
V and V are not equal in the direction perpendicular to the NN direction, that is, in the direction along the tooth surface (only the two speeds coincide when the node C is meshed), so that relative sliding occurs along the tooth surface direction. Since the sliding speed is substituted, the relationship between the relative sliding speed V of the tooth surface and the position x of the meshing point K at the meshing line is obtained. It is apparent that there is no relative slip when engaged at node C, and there is relative slip when engaged outside the node. It is far away from the position of the node C, and the relative sliding speed is relatively large. The sliding speed on both sides of the node C is opposite, but the acceleration of the sliding is the same, which is a constant value. Under the action of the driving force, the sliding is inevitable. Causes wear of the gears.
It is discussed above that when the two teeth are engaged at any point K, when the linear speeds V and V of the two points at the K point do not coincide, the relative sliding along the tooth surface direction causes the tooth surface to wear.
In the state, when the meshing point K is between BC (ie, above the node C), the relative sliding speed V is positive, that is, the dividing speed of V on the tooth surface is greater than that of the V driven wheel 2 relative to the driving wheel 1 The face direction is upward, and thus the driven wheel 2 is subjected to downward friction.
Similarly, the meshing point K is between CB, and the relative sliding direction is changed, so that the driven wheel 2 receives an upward frictional force.
When the gear tooth material is soft and the load is large, the tooth surface material will be plastically deformed along the frictional force direction, for example, the groove is formed at the pitch line of the driving gear tooth surface, and the rib is formed at the pitch line of the driven gear tooth surface. The tooth surface is broken, thereby affecting the normal meshing of the gear. At the position of the pitch line, the sliding speed of the two opposing gears is small, and it is not easy to form an oil film. Improve the hardness of the tooth surface and use a high viscosity lubricant to prevent or reduce the plastic deformation of the tooth surface.
The two gears mesh, when engaged at the node, there is no relative slip, and outside the node there is relative slip. The farther away from the location of the node, the greater the relative sliding speed. The sliding speeds on both sides of the node are opposite, but the acceleration of the sliding is the same, which is a constant value. This relative sliding speed causes plastic deformation of the tooth surface, improves the hardness of the tooth surface, and uses a high viscosity lubricating oil to prevent or reduce plastic deformation of the tooth surface.
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