Working principle of vane pump
f. Wear of blade and stator inner surface and Countermeasures Due to the large gradient of vector diameter variation on the inner surface of the stator of double acting vane pump, the blade in the oil suction section is required to have greater radial acceleration to ensure that its outer end is not empty. However, due to the influence of motion friction, the centrifugal force of the blade itself is often unable to meet the requirements, so this kind of pump usually makes the bottom of the blade groove connect with the pump through the annular groove on the valve plate It is connected with the oil pressure chamber of the pump. As shown in Fig. 3-6, the annular groove a is connected with the oil pressure area through the groove (dotted line) on the back of the valve plate. The position of the annular groove corresponds to the bottom of the blade groove of the rotor, so as to introduce high-pressure oil into the bottom of all blade grooves. With the help of hydraulic pressure, the blades located in the oil suction area can quickly extend.
For the pump with higher working pressure, the hydraulic force at the top and bottom of the blade in the pressure area can be basically balanced. However, the hydraulic pressure at the bottom of the blade slot in the oil absorption section is significantly higher than the force required to extend the blade, resulting in the excessive contact stress between the blade and the inner surface of the stator in this section, which increases the friction resistance, decreases the mechanical efficiency, and intensifies the wear of the contact surface (especially near the end of the oil absorption section). In severe cases, the blade will be damaged due to too much tangential resistance at the end The extension of the disc was broken. Therefore, for high-pressure double acting vane pump, it is necessary to compensate the external thrust acting on the bottom of the vane (generally, it is not necessary for medium and low pressure pump).
When the blade is in the oil absorption area, the external thrust F of the pressure oil at the bottom of the blade is 0
Where P -- oil pressure at blade root;
A -- effective compression area of blade root.
There are two kinds of compensation principles for the external thrust acting on the bottom of the blade: one is to try to reduce the pressure P at the bottom of the blade groove in the oil absorption area to a reasonable value; the other is to use a special blade structure to reduce the effective pressure area a at the bottom of the blade. The internal spring force can also be used to replace the hydraulic pressure to extrapolate the blade. The specific measures are as follows.
i. Figure h shows a vane pump with a set value reducing valve and a floating port plate. The pressure reducing valve 6 attached to the pump reduces the pressure in the pressure chamber of the pump and then leads it to the bottom of the blade groove in the oil suction area, so as to reduce the force of the blade 2 on the stator 1. It is possible for this method to reach the optimal thrust value. But the pressure reducing valve is not only complex and expensive, but also consumes part of the output flow, resulting in the reduction of the volumetric efficiency of the pump; and the simple throttling groove is difficult to fully meet the requirements of pressure distribution, so it has been rarely used at present.
II. Special blade structure is adopted. The commonly used special blade structures are double blade structure, twin blade structure, stepped blade structure, etc.
Fig. I shows a double blade structure. Two blades 2 are made into fillet inclined planes at the top and overlapped in opposite directions. The triangular chamber 4 formed by the top of two small blades and the slideway is connected with the blade groove bottom 6 through the groove 5 on the overlapped surface. The pressure in the oil discharge chamber connected with the blade groove bottom is introduced into this chamber, thus forming an incomplete unloading static pressure between the blade top and the slideway Bearing. The advantage of this method is that it has the compensation effect proportional to the working pressure, and the leakage is further reduced due to the formation of two sealing lines on the slide surface at the top of the blade. The disadvantage is that it is difficult to ensure the strength of the blade; the force generated by the high-pressure oil between the blade overlap surfaces will be greater than the pressing force of the oil between the blade and the rotor groove, and the opening force generated by the difference will aggravate the wear of the blade and the rotor groove. This structure is more suitable for large size vane pump.
The structure of the vanes is shown in Fig. J. in the slot of the rotor blades, there are vanes 7 and vanes 3 which are separated in the middle. The vanes can slide freely. The pressure balance hole 6 on the rotor 1 equalizes the hydraulic pressure at the head and bottom of the mother blade. The pressure oil pressure of the pump passes through the port plate and the rotor slot to the middle pressure chamber 5 between the daughter and mother blades. If the centrifugal force and inertia force are not considered, the thrust of the blade acting on the stator is
The structure of the stepped blade is shown in Fig. K. the blade is divided into a stepped shape along the thickness direction. The blade groove on the rotor is also made into a corresponding shape. The middle oil cavity between them is connected with the pressure oil through the groove on the valve plate. The pressure balance oil passage on the rotor leads the oil pressure at the top of the blade to the bottom of the blade. Similar to the structure of the mother and son blades, throttling damping is set before the pressure oil is introduced into the middle oil chamber to keep enough pressure in the chamber when the blade retracts inward to ensure that the blade is close to the inner surface of the stator. The shape of blade groove with this kind of structure is complex, and its processability is poor.
III. spring pressure as shown in Fig. L, several compression springs (cylindrical spring or swallow spring) are preset at the bottom of the rotor slot to help the blade extend outward. When the slot bottom is connected with the in-phase flow distribution window, the compression force of the blade end on the slideway only depends on the pump speed and the vector diameter of the contact position, and has nothing to do with the working pressure. The advantage of this structure is that the movement of the blade will not affect the instantaneous displacement of the pump. The disadvantage is that it is necessary to drill holes at the bottom of the rotor slot, which has an adverse effect on the strength, and it is often difficult to meet the requirements of spring fatigue strength.