1、 Causes of noise:

When the oil pump is meshed with the gear, the two parts of the oil pump are not connected with each other. When its capacity changes from large to small, the trapped hydraulic oil is squeezed, and the pressure speed increases, which is far higher than the output pressure of the gear oil pump (the trapped liquid is forced out from the leakable gap), so that the shaft and the shaft bear a considerable impact load, causing vibration and noise; When the trapped oil volume changes from small to large, a local vacuum is formed to separate the dissolved gas in the oil, resulting in cavitation, vibration and noise.

2、 Noise reduction strategy:

1. The external meshing hydraulic gear pump is mainly to open "unloading groove" on the internal parts such as the shaft sleeve (or inverted plate). The principle of slotting is to ensure that the high and low pressure cavities in the gear oil pump are not communicated with each other, and try to make the trapped oil volume communicate with the high pressure cavity or low pressure cavity, so as to partially remove the trapped oil phenomenon, so as to reduce the noise and vibration.

2. Increase the volumetric efficiency of the gear oil pump, reduce the internal leakage of the gear oil pump, so as to reduce the flow and pressure pulsation of the pump, so as to achieve the purpose of reducing noise. That is to say, the overall 8-shaped shaft sleeve with higher accuracy is selected inside the pump, and the axial automatic compensation structure is used to reduce the leakage in the end face and increase the volumetric efficiency of the pump. At the same time, the layout of "riveting groove" of shaft sleeve is improved, and the asymmetric load relief groove is adopted to reduce the noise caused by trapped oil.

3. The internal gear structure of conjugate curve is used to reduce oil trapping. For example, the profile of the external gear of an internal gear pump uses a straight line, while the profile of the internal gear is a conjugate line of the straight line. The geometric shape of this pair of gear profiles determines that the change of trapped oil volume is small. At the same time, because the pressure oil is led out from the bottom hole between the teeth of the internal gear, there is basically no trapped oil area during the operation, so the gear pair transmission is quite stable without impact, and the flow rate of the pump is low The pressure pulsation is very small, and the inlet area of the oil suction chamber is large, and the oil suction is sufficient, which will not cause cavitation phenomenon. Therefore, the noise of this kind of pump is very low, which can be reduced to 55 ~ 65dB, and has a good application prospect.