Relief valve is an important pressure control element in servo hydraulic system, and also one of the main noise sources in hydraulic system. Based on the survey data, in addition to the hydraulic pump's biggest noise source is the overflow valve, the noise is not only directly endanger the person's mood, health and environment, and influence the reliability of the hydraulic system work, shorten the service life of itself or other hydraulic components, reduce product reliability, and even lead to servo energy function failure. At present, many relief valve products have put forward the requirement of noise index. Therefore, the vibration and noise of relief valve are studied, and the dynamic characteristics and noise are analyzed
It is of great significance to find ways to reduce and eliminate noise in relation.
Hydraulic system noise is divided into mechanical noise and fluid noise. Mechanical noise is mainly caused by the vibration of mechanical components. The fluid noise is caused by pressure flow pulsation, cavitation and cavitation erosion, vortex movement, high and low pressure mutation, fluid friction and other reasons. For the relief valve, mechanical noise is mainly caused by self-excited oscillation of the mass-spring system of the pilot valve or the main valve, mainly including the following two situations:
1. Self-excited vibration noise
The spool of the relief valve is supported on the spring. When the quality of the spring (including the elasticity of the oil) and the damping hole of the relief valve and the relevant parameters matched with the load exceed the stable critical value, the spool will produce continuous self-excited vibration and abnormal noise because of the disturbance of other parts. The vibration is related to the shape and size of the pilot valve and the main valve of the relief valve. The machining accuracy of the pilot valve, the main valve and the seat will also affect the occurrence of such noise. The higher the oil temperature, the lower the oil viscosity
The more likely it is to happen. General pilot valve close to the opening pressure is the most easy to vibration, and bring the corresponding vibration of the main valve.
Resonant noise
The resonant noise is the result of high harmonic resonance between the spring mass system of relief valve and pressure pulsation of hydraulic pump. This resonance sometimes causes the spool to hit the seat, producing a strong noise. This paper mainly analyzes the dynamic characteristics and modal characteristics of a certain type of relief valve from the perspective of stability, especially its stability problem; Then the valve noise spectrum analysis, and finally find out the dynamic characteristics of the internal relationship between the noise.
Preliminary study on noise reduction
Generally according to experience when the relief valve is found to scream, first of all, you can consider setting the muffler or muffler screw to change its natural frequency, followed by the way to reduce the volume of the pilot spool before the chamber. The AMESim simulation analysis shows that the gain margin of the relief valve is small. In order to improve its stability, the method of increasing the inlet damping effect is adopted to reduce the system stiffness, so as to try to reduce the natural frequency and noise.
Starting from the dynamic stability of relief valve, the modal analysis of frequency characteristics is used to find out the natural frequency of the more complex relief valve model, and combined with the noise test to study its spectrum characteristics. By optimizing the stability margin of relief valve, the natural frequency is reduced, so as to achieve the goal of reducing noise. It has been verified by the test that adding an oil inlet sleeve in the front chamber of the main valve can improve the damping effect of the inlet of the main valve and basically eliminate the frequency noise of about 1000Hz. It should be pointed out that there are many factors causing the noise of the relief valve, and it is not enough to analyze the stability and frequency spectrum only through the simplified mathematical model, and the related factors of the hydraulic system should be fully considered. Such as working pressure and flow of equipment, oil viscosity, cleanliness, oil temperature, oil return circuit is normal and other factors.
