Created on：2021-08-28 09:59

Fault diagnosis and maintenance of marine hydraulic equipment_ Analysis and influence of zero bias and zero drift of electro-hydraulic servo system

Fault diagnosis and maintenance of marine hydraulic equipment_ Analysis and influence of zero bias and zero drift of electro-hydraulic servo system

(1) Test on the influence of the covering amount of square hole of valve core and valve sleeve on the zero deviation and zero drift of servo valve

The influence of the covering amount of the square hole of the valve core and valve sleeve on the zero deviation and zero drift of the servo valve shall be tested by measuring and grinding method. Firstly, measure the square hole and square hole spacing of the valve sleeve on the universal tool microscope, accurate to 0.001mm, and then measure the size and spacing of the two working shoulders of the valve core on the universal tool microscope. Finally, calculate the axial grinding amount of the valve core by using the symmetry method, grind and measure step by step, and accurately control the covering amount of the valve core and the square hole of the valve sleeve. Fig. f is the schematic diagram of measuring and grinding the square hole cover of valve core and valve sleeve. When the fit clearance between the valve core and the valve sleeve is 0.005mm, the influence of the cover amount of the flow channel between the valve core and the valve sleeve on the zero position of the valve is shown in the table below. The data show that near the zero opening, when the cover amount of the valve core to the flow channel of the valve sleeve is slightly negative, the change of the zero current value of the steering gear is the smallest.

Test data of influence of cover amount of flow channel between valve core and valve sleeve of servo hydraulic actuator on its zero position

 Single side covering amount of flow channel between valve core and valve sleeve / mm 舵机零位电流值的变化（3min）/mA A:0.050, B:0.051, C:0.050, D:0.049 +170～-150 A:0.030, B:0.029, C:0.031, D:0.029 +100～-90 A:0.009, B:0.010, C:0.010, D:0.010 +30～-30 A:0.001, B:0.001, C:0.000, D:0.002 +5～-4 A:-0.006,B:-0.007,C:-0.006,D:-0.006 +2～-1 A:-0.020,B:-0.019,C:-0.020,D:-0.021 +10～-10

(2) Analysis

When it is a negative opening and in the zero position, the valve core moves slightly, but the output of the servo valve is still zero, its performance is characterized by large dead zone, insensitivity, poor zero recovery and instability of the servo valve; The servo valve is near the zero opening. When the opening is slightly positive, the servo valve is at the zero position. At this time, a small amount of oil passes through the throttle. When the oil supply pressure is constant, the valve core will produce a dynamic balance position relative to the valve sleeve under the action of oil leakage from the throttle. As long as the oil pressure remains unchanged, this dynamic balance point will not be easily changed, Reflected in the electro-hydraulic servo valve, the zero position remains basically stable; When the servo valve is positive opening and large, the power loss is large, and there are more oil leakage at the throttle, which will cause vibration. Through repeated research and practice, it is found that when the fit gap between the valve core and the valve sleeve is 0.004 ~ 0.006mm, the best covering amount of the square hole between the valve core and the valve sleeve is about -0.006mm on one side.

(3) Influence of torque motor on zero bias and zero drift of electro-hydraulic servo valve

The stability of torque motor directly affects the zero bias and zero drift of electro-hydraulic servo valve. Generally, the hysteresis of torque motor is large, and the zero bias and zero drift of its electro-hydraulic servo valve are relatively large. In production practice, we found that the symmetry of the torque motor is poor during assembly, and the zero position of its electro-hydraulic servo valve is unstable, and the zero deviation and zero drift are quite large. Therefore, when the torque motor is matched with the slide valve, the mechanical symmetry of its assembly is very important.

(4) Influence of oil on zero drift of electro-hydraulic servo valve

The electro-hydraulic servo system has high requirements for the cleanliness of the oil used, which is generally required to reach moog2. At present, phosphate fire-resistant oil is widely used in electro-hydraulic servo system. It is a kind of synthetic oil, which is easy to deteriorate in the process of use, mainly manifested in the increase of pollution particle size. With the increase of pollution particle size, that is, after the oil becomes dirty, when the electro-hydraulic servo valve works, the friction generated by the valve core in the valve sleeve increases, larger electrical signals are required to drive the valve core to move, and the zero drift range of the electro-hydraulic servo valve becomes larger. Therefore, the oil used in the electro-hydraulic servo system should be checked regularly, and the filtering equipment should be set in the system to ensure the quality of the oil.

The change of oil temperature and pressure will also affect the zero drift of electro-hydraulic servo system. When the oil temperature and pressure used in the electro-hydraulic servo system change, the dynamic balance relative to the original zero position of the electro-hydraulic servo valve is destroyed until the new dynamic balance is reached, which is manifested in the offset of the zero position of the electro-hydraulic servo valve, which is difficult to eliminate.

(5) Influence of ambient temperature on zero bias and zero drift of electro-hydraulic servo valve

In the low temperature environment, the oil used by the electro-hydraulic servo system will become very viscous, which directly increases the friction of the valve core moving in the valve sleeve when the electro-hydraulic servo valve works, resulting in the large zero deviation and zero drift of the electro-hydraulic servo system. In addition, in the low-temperature environment, the valve core and valve sleeve of the electro-hydraulic servo valve will shrink cold. However, due to the thin wall near the square hole flow channel of the valve sleeve, it is easier to shrink relative to the shoulder of the valve core. At this time, the valve core of the spool valve with negative opening covers the square hole flow channel of the valve sleeve more, and the dead zone during operation is also larger, which is directly manifested as unstable zero position, zero deviation The zero drift range is larger. Therefore, the spool valve of electro-hydraulic servo valve used in low temperature environment should adopt positive opening.

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