Mechanism of vibration and noise of spur gears

The causes of spur gear vibration and noise are complex, and there are many sources. It has always been a difficult problem to be solved in the spur gear industry. The unbalance of spur gear will cause the rotation frequency and frequency doubled harmonic vibration of spur gear. When the spur gear transmits load, it will produce alternating load, resulting in the meshing impact of spur gear. When the frequency of exciting force is close to the natural frequency of spur gear, it will cause resonance. The research and analysis show that the main reason for the vibration and noise of spur gears is the excitation of “pitch impulse” and “meshing impulse”.

When a pair of ideal spur gears mesh, the meshing starting point of the driving wheel is near the base circle, and the meshing starting point of the driven wheel is near the tooth top circle. At this time, a large sliding speed is generated. With the continuous rotation of the spur gear, the contact point moves along the meshing line to the vicinity of the pitch line, and the relative sliding speed becomes smaller. When the meshing point crosses the node, the sliding speed changes direction, and the relative sliding speed becomes the largest at the meshing end point. Because of the friction between the tooth surfaces, the relative sliding speed changes the direction at the node, which leads to the change of the direction of the friction and the generation of pulsating force. The fluctuating variation of tooth friction is related to the load transmitted by the tooth, the friction coefficient of the tooth surface and the profile of the tooth. The higher the speed of spur gear, the greater the power transmitted, and the greater the change of pulse force. For an ideal spur gear, the pitch impulse is the main cause of vibration.

However, the ideal spur gear does not exist. The spur gear always produces elastic deformation during operation, and the meshing position of the spur gear deviates from the theoretical position due to manufacturing errors, installation errors and other reasons, resulting in the change of the instantaneous transmission ratio. The speed of the spur gear is no longer constant, and the speed sometimes increases and sometimes decreases, resulting in the impact between the teeth. The impact force at this time is called “meshing impulse”.

In the process of spur gear transmission, the dynamic meshing force is generated due to the time-varying meshing stiffness, transmission error, meshing in and meshing out impact and the change of system input and output torque, resulting in vibration and noise. Dynamic excitation is usually divided into internal excitation generated by time-varying meshing stiffness, meshing error and meshing impact and external excitation generated by input and output load impact. Internal excitation is an important difference between spur gear transmission and other transmission devices. The variation of tooth meshing pairs and the fluctuation of meshing force caused by load deformation will cause the spur gear system to produce vibration and noise even without external excitation.

Studying the stiffness change of spur gear is an important work in spur gear dynamics, and the research is also in-depth. Because the coincidence degree of spur gear meshing is not an integer, the number of teeth participating in meshing also changes alternately, and the meshing deformation of spur gear is also different in the process of meshing in and out, resulting in the change of stiffness from time to time.