In this article, Dahlan hydraulic editorial to introduce the working principle and structure of variable vane pump, that is, the working principle and structure of single-acting vane pump.
1, single-acting vane pump working principle
The working principle of single-acting vane pump is shown in Figure 1 below. Similar to double-acting vane pump, the main structure of single-acting vane pump consists of rotor 1, stator 2, vane 3 and end cap. However, the stator's working surface for the cylindrical inner surface, and the stator and rotor set between the eccentric distance, when the rotor rotates, due to the centrifugal force of the vane, so that the vane is close to the inner wall of the stator, so that, in the stator, the rotor, the vane and the two sides of the oil distribution disk between the formation of a number of sealed workspace. When the rotor rotates in the direction shown in the figure (counterclockwise), in the right part of the stator cavity, the blades should gradually extend, and the working space between the blades will gradually increase, forming the condition of oil suction, and when it rotates to the left side of the oil cavity, the blades are gradually pressed by the inner wall of the stator into the grooves, and the sealing space is gradually narrowed down, forming the condition of oil pressure, and the oil will be pressed from the pressurized oil port.
There is a section of oil sealing area between the oil suction chamber and the oil pressure chamber, which separates the oil suction chamber and the oil pressure chamber. The rotor of this vane pump rotates every week, and each sealing space completes the oil suction and oil pressure only once, so it is called single-acting vane pump. The rotor keeps rotating, and the pump continuously carries out the working cycle of oil suction and oil pressure.
2, single-acting vane pump features and applications
Compared with double-acting vane pump, single-acting vane pump has the following characteristics.
(1) pump flow can be adjusted. Change the size of the eccentric distance between the stator and turn to change the magnitude of the change in the sealing volume, thus changing the displacement and flow of the pump.
(2) Suction and pressure oil circuit can be reversed. When the rotor and stator eccentric direction is reversed, the direction of suction and pressure of the external oil circuit is also opposite, so the direction of suction and pressure oil circuit can be realized.
(3) Radial force imbalance of the rotor. Due to the eccentric mounting structure of the stator and rotor, the rotor of the oil pump will be subjected to unbalanced radial force, so this type of pump is generally used only for low-pressure variable applications. Single-acting vane pumps are mostly low-pressure variable pumps, and their maximum working pressure is generally 7MPa.
3, pressure-limiting variable vane pump working principle
Pressure-limiting variable vane pump is a single-acting vane pump, by changing the eccentricity between the stator and rotor e, it can change the output flow of the pump.
The working principle of the limited-pressure variable pump is shown in Figure 2, the rotor's rotary center is fixed, while the stator sleeve is movable and adjustable relative to the eccentric installation of the rotor, the right side of the stator sleeve is set up with a feedback cylinder 6 and piston 4, the left side of the set up with a regulator spring 9 and a regulator screw 10, and the action of the feedback cylinder is derived from the pump's pressure oil port, so that the pump is in normal operation, the stator in the feedback pressure of the exit oil and the the interaction of the regulating spring 9 is in a relatively balanced position.
The operating principle of this pump can be roughly analyzed in the following four cases.
(1) When the pump has just begun to work and the outlet pressure of the pump has not yet been established, or when the external load is small and the oil pressure of the system is very low, and the force on the piston 4 is not sufficient to overcome the force of the regulating spring 9, the stator 2 is in the right-most position under the action of the regulating spring 9, i.e., the pump is in the state of maximum eccentricity and maximum output flow.
(2) When the outlet pressure of the pump reaches the working pressure p, under the action of the system pressure, the piston 4 overcomes the force of the regulating spring g and pushes the stator sleeve to the left, so that the stator 2 is in a certain relatively balanced working position under the joint action of the piston 4 and the regulating spring 9, and the eccentricity of the stator and the output flow rate are both in a relatively balanced state.
(3) When the external load changes, caused by the system pressure changes will lead to corresponding changes in the pump's oil supply adjustment: when the external load increases caused by the system pressure rises, the stator 2 will move to the left under the action of the piston 4, resulting in a reduction of the eccentricity, the flow rate decreases, the hydraulic actuating elements of the movement of the speed is slowed down accordingly; when the external load decreases, the stator will cause the stator to move to the right, and the movement of the speed will be accelerated accordingly.
(4) When the outlet pressure of the pump due to system overload or overload and exceeds the maximum limit pressure pB regulated by the regulating spring 9 and regulating screw 10, the regulating spring 9 will be in the state of maximum compression, the piston 4 will be pressed to the stator 2 to the leftmost position, at this time, the eccentricity of the stator is zero (or close to zero), the pump will stop the outward supply of oil, which prevents the outlet pressure from continuing to rise, and plays a role in safety protection .
Because the maximum output pressure of this pump can be controlled by the regulator spring 9 and regulator screw 10, so it is called a pressure-limiting pump. Because the feedback control of this pump is applied to the outside of the stator sleeve, it is also called an external feedback pressure-limiting pump.
4,Operating characteristics of pressure-limiting variable vane pumps
The working characteristic curve of pressure-limiting variable vane pump is shown in Figure 3. When the working pressure p is less than the pre-adjusted minimum pressure, the hydraulic force can not overcome the force of the spring 9, then the eccentricity of the stator to maintain the maximum, the output flow rate of the pump qA will maintain the maximum value, but also due to the increase in oil supply pressure will make the pump leakage flow rate q1 also increased, so the actual output flow rate of the pump q is slightly reduced, such as the working curve of the figure 3 in the AB section shown.
When the working pressure p exceeds the minimum limit pressure, the hydraulic force is greater than the force of the spring 9, at this time, the spring 9 began to compress, the stator to the direction of the eccentricity of the decrease in the direction of the pump's output flow rate decreases, the higher the pressure, the greater the amount of spring compression, the greater the amount of eccentricity of the smaller, the smaller the output flow rate. In the spring 9 effective elastic deformation range, the flow rate and the relationship between the system working pressure is basically a characteristic curve BC section shown in the linear change rule.
Adjust the regulating screw 10 can change the highest regulating pressure pB size, then the characteristic curve of the BC section will be shifted around; and change the stiffness of the regulating spring can change the slope of the BC section, the spring is more "soft", the steeper the BC section.
5, the application of limited pressure variable vane pumps
Pressure-limiting variable vane pump structure is complex, large contour size, relative movement of more parts, leakage is larger, while the rotor shaft to withstand a large unbalanced radial fluid pressure, noise is also larger, volumetric efficiency and mechanical efficiency are not as high as the quantitative vane pump. From the other side, under the working pressure conditions of the pump, it can automatically adjust the flow rate according to the external load and pressure fluctuations, saving energy, reducing the heating of the oil, the mechanical action and changes in the external load with a certain degree of adaptive adjustment.
The pressure-limiting variable vane pump is a more suitable power source for those hydraulic drives that want to realize the fast movement of the empty stroke and the slow feeding of the working stroke (slow movement). Generally speaking, the fast stroke requires a fast moving speed and a large working flow rate, while the load pressure is low, which corresponds to the beginning section of AB of the characteristic curve; while the working feeding requires a higher pressure, while the moving speed is low, and the flow rate required is reduced, which corresponds to the BC section of the characteristic curve. This corresponds to the BC section of the characteristic curve. Therefore, these pumps are particularly suitable for medium and low pressure systems where the actuator is required to have fast, slow and holding pressure phases, which contributes to saving energy and simplifying the circuits.