The traditional valve inlet and outlet control through a spool to carry out, the two oil mouth to listen to the opening of the corresponding relationship as early as the spool design and processing has been determined, in the use of the process is not possible to modify, so that through the two oil mouth flow or pressure can not be independent control, without impact
With the decrease of the cost of the micro-processing controller and the sensor, the control technology is perfected, which makes the double spool control technology be applied in the field of construction machinery.
1, the traditional single valve core reversing valve defects
The traditional hydraulic system composed of single valve core reversing valve is difficult to solve the contradiction between the following functions and control: (1) hydraulic system design in order to improve system stability, reduce the load change on the speed of the impact, or sacrifice part of the function we want to achieve, or to add additional hydraulic components, such as speed control valve, pressure valve and so on, by increasing damping, improve system speed stiffness to improve system stability.
However, the increase of the components will reduce the efficiency, waste of energy, but also to reduce the reliability of the entire system and increase costs. (2) Because of the particularity of the commutation structure, enable the user to achieve a certain function must purchase the corresponding hydraulic components, coupled with the construction machinery manufacturers in accordance with the requirements of different end-users to design the corresponding functions, which will cause manufacturers to purchase similar, more specifications of hydraulic control components to meet the needs of different functional requirements,
Not conducive to product generalization and product management, but also greatly improve product costs. (3) It is impossible to control the pressure on both sides of the actuator independently because the actuator is controlled by a spool. Therefore, the oil side back pressure acts on the opposite direction of the actuator movement, as the oil side back pressure rises, for the durability of the actuator movement, must improve the oil inlet side pressure.
This will make the hydraulic system to consume more functions, low efficiency, increased fever.
The hydraulic system with double spool technology is independent of valve core position and control mode of inlet and outlet of the actuator. Each other, so through the two valve core control mode of different combinations, the use of software programming can be a good solution to the traditional single valve system can not solve the problem, but also easy to realize the traditional hydraulic system is difficult to achieve the function.
2. Two basic control strategies of double spool directional valve Due to the flexibility of two-valve-core commutation control, the two oil ports can be controlled by flow control, pressure control or flow pressure respectively.
Two simple control strategies are presented in front.
(1) The load direction remains unchanged throughout the work process. We know that for truck cranes, excavators, loaders and so on, its hydraulic cylinder throughout the operation of the load direction has remained unchanged.
The following is an example of a crane variable-amplitude hydraulic cylinder to discuss the control strategy of the double spool.
Crane luffing Cylinder In the work process of its force, the load direction has remained unchanged, so we can take the hydraulic cylinder rod control pressure control, no rod cavity flow control strategy.
The flow control of the rod-free cavity is detected by detecting the pressure difference between the sides of the side valve of the rod-free cavity. According to the required inflow or outflow of the amount of flow to calculate the opening size of the valve core, the rod cavity side using pressure control, so that the side to maintain a low value of pressure, so that more energy-saving, efficient. Since we use flow control in the rod-free cavity, the balance valve used in the original control system can be replaced by a liquid-controlled one-way valve.
In this way, the system instability caused by the balance valve can be eliminated, thereby improving the system stability.
(2) The load direction changes during the working process
In this case, take the "oil side pressure control, oil side flow control", in the hydraulic cylinder with rod cavity side pressure control, no rod cavity side has flow control. If the load direction does not change, because the oil side has taken the flow control, we may use the two-way balance valve to replace with the liquid control one-way valve, thus enhances the system stability.
The pressure controller is used to maintain a lower reference pressure, on the one hand, improve the system efficiency, on the other hand, the system does not occur cavitation. In order to make the load direction change of the working mechanism can be well controlled, another PI controller will be applied to the pressure controller with a rod cavity, and when the load direction is changed, the pressure of the rod cavity will be reduced, if the rod cavity is still maintained a very low pressure, when the load is very large, the hydraulic cylinder will move in the opposite direction. At this time, we can use the increased PI controller to monitor the change of the pressure of the rod cavity, when the PI Controller detects that the bar cavity pressure is lower than the set reference value, the pressure of the rod cavity pressure controller will be increased, thus ensuring the normal operation of the system.