Analysis and improvement of inner leakage of hydraulic motor in antenna pedestal of an airborne radar

The pedestal of an airborne radar adopts hydraulic motor as driving element. The parts of this motor are of high precision and difficult to be machined. It is very harmful to mass production. Through internal leakage test and statistical analysis, the structure design of hydraulic motor is improved.

1. motor working principle and processing difficulties

As shown in figure 23-8, the hydraulic motor for motor blade structure, working angle range + 130 degrees, a front cover, back cover, casing, shaft, sealing device, blade and the output shaft are made into a whole, the blade and the shell as a whole, the front and the back cover is arranged in the needle bearing supporting the output shaft the work, blade cavity into two cavities, one person when the pressure oil cavity, the cavity volume increases, the blade rotation, another cavity volume decrease for discharge of oil. When the pressure oil reverses, the blade reverses. A sealing structure is adopted between the fixed blade and the shaft, the moving blade and the shell, the blade and the front and rear covers, the circumferential direction of the shaft and the shell and the front and the back cover by adopting a O shape sealing ring + a retaining ring.

As shown in figure 23-8, the hydraulic motor shaft and the rotor blades, and the blades are shell as a whole, the processing difficulties are mainly concentrated in the shaft and the housing two parts in order to ensure internal leakage of soil, index, the parts of the form and position accuracy requirements for general 0.002~0.003, high precision is the inevitable requirement of the clearance seal is. One of the difficulties in processing. The overall structural form leads to an increase in the irregular shape of the outer surface of the shell and the outer surface of the shaft. With the same accuracy, it is more difficult to process irregular shapes.

2. internal leakage of hydraulic motor

The leakage point of the hydraulic motor mainly consists of four parts (Figure 23-9), the radial clearance at the big and small round arc, and the two axial clearance. From the angle of division formed gap, the radial clearance is mainly composed of three parts: the amount of the reserved clearance pattern; the deformation under the action of high pressure oil casing and shaft; the leaf of the motor shaft by the unbalanced radial force, the gap will cause changes in the radial clearance.

There are mainly two parts in the axial clearance: the clearance amount in the drawing; the front and back of the front and rear cover become arc surface, and the maximum deformation is near the shaft. Suppose the center of the motor is 0 degrees, the counterclockwise angle is positive, and the clockwise angle is negative. After the leakage test of the hydraulic motor, the location is not exceed the standard, generally in the range of 90 degrees beyond the soil. A great deal of statistics show that when the angle of turn is from -130 degrees to +130 degrees, the inner leakage of the motor is gradually reduced when the P1 oil port is a high pressure oil port. When the oil outlet is a high pressure oil port, the inner leakage of the motor gradually increases. In fact, the measured leakage characteristics can be approximately represented by figure 23-10. Take P1 oil port as a high pressure oil inlet as an example.

In the process from -130 to +130 degrees degrees in the high pressure chamber and from small to large, and the rotation angle alpha is proportional to the force of the front and the back cover has also been a linear increase in the elastic range, increase the linear deformation before and after the cover, the axial gap also increased linearly, the leakage characteristics as shown in figure 23-10. On the shaft, the process to 0 degrees in -130 degrees, the radial force increases gradually, the deflection of the F1 axis (alpha) gradually become larger, large and small arc surface radial gap change caused by the process; to +130 degrees in 0 degrees, the radial force decreases and the deflection of the F2 axis (alpha) gradually, large and small arc surface radial gap change caused by the. The influence of high pressure oil to the direction of the axis of the radial clearance: the assumption that the needle gap size and circular arc Delta, the change of radial clearance values at the corner and. Relation formula:. In the same position, the radial clearance of the big and small round arc changes the same, so the size and direction of the unbalanced radial force cause the radial gap to change:

It can be seen that the radial gap is the largest at -130 degrees, and the radial gap is minimum at +130 degrees, and the leakage characteristic is approximately shown in figure 23-11.

Thus, the effect of the high pressure oil on the axial clearance is opposite to the measured result, while the radial force's influence on the radial clearance coincides with the measured results. In the same position, such as -130 degrees, P1 oil port is high pressure oil port, the internal leakage is large, excessive standard often occurs in such a position, P1 oil port is low pressure oil port, the leakage is very small. It can be concluded that the influence of radial force on radial clearance is the main factor of internal leakage.

3. structural design improvement

According to the above analysis, the main influencing factors of the inner leakage are determined. The amount of swing of the needle gap and the deformation of the shaft under the radial force are not conducive to sealing, and the inner leakage is larger. To this end, a sealing structure is used at the radial gap (Figure 23-12). A scheme of the sealing strip for radial seal; scheme two: the leaves of a chip seal structure (Figure 23-13), by the action of high pressure oil to keep the blade always contact the shell arc surface, specific structure needs further design and test.

4. feasibility of sealing with sealing strip

The rubber material of the sealing strip is made of 45713 chloroprene rubber (SXS108-77) and is wrapped with polytetrafluoroethylene film. The structure form is identical with the other dynamic sealing rings of the antenna base.

The raw liquid press motor requires dynamic friction torque <5N.m, and the increase of the sealing strip still meets the requirement. As for the internal seal, in order to reduce the amount of leakage, the pre compression can be designed to be very small, close to 7% of the minimum requirements; the process of existing full fluorine, can minimize friction, after a preliminary calculation, the friction torque increase is about 0.5N.m, so the friction torque will not exceed the original motor requirements.

The seal life can draw the conclusion through the comparison, the line speed is 1.28 times of the antenna seat rotating hinge dynamic sealing ring line speed, O ring using the speed range of 0.005~0.3m/s, the line speed is about 0.05m/s, in the middle section, and the pre compression only rotating hinge half. When the roughness of the contact surface is the same, the wear of the seal depends mainly on the pressure and coefficient of friction, so the life of the sealing strip must be higher than that of the rotating hinge.

5. test verification

In the test piece, the sealing strip is added, and the inside leakage of the whole corner range is even. The indexes of the improved hydraulic motor can still meet the original requirements. Therefore, analysis and improvement have been verified. The rubber seal, and the radial clearance size tolerance and tolerance can be generally lower, the shaft, shell has interchangeability, reduce processing costs, improve product yield, more suitable for mass production.