The use of three-way globe directional valve control technology the oil inlet and outlet control of the traditional reversing valve is carried out through a spool, and the corresponding relationship between the two ports has been determined as early as the design and processing of the spool, and it is impossible to modify it in the process of use. so that the flow or pressure through the two ports can not be controlled independently and do not affect each other.
With the decrease of the cost of microprocessor controller and sensor components and the continuous improvement of control technology, double spool control technology has been applied in the field of construction machinery.
In order to meet the functional requirements of hydraulic system for Chinese construction machinery products.
1. The defects of the traditional single-core reversing valve the hydraulic system composed of the traditional single-core reversing valve is difficult to reasonably solve the contradiction between the following functions and control: (1) in order to improve the stability of the hydraulic system, reduce the impact of load changes on speed, either sacrifice some of the functions we want to achieve, or add additional hydraulic components, such as speed regulating valve, pressure control valve, etc., by increasing damping.
Improve the speed stiffness of the system to improve the stability of the system.
However, the increase of components will reduce the efficiency and waste energy; it will also reduce the availability of the whole system and increase the cost.
(2) due to the particularity of the reversing structure, users must purchase corresponding hydraulic components when realizing a certain function, and construction machinery manufacturers will design corresponding functions according to different end-user requirements. This will cause manufacturers to purchase similar, multi-specification hydraulic control components to meet the needs of different functional requirements, which is not conducive to product generalization and product management, and will greatly increase product costs.
(3) since the hydraulic oil in and out of the actuator is controlled by a valve spool, it is impossible to control the pressure on both sides of the actuator alone.
Therefore, the back pressure of the oil outlet side acts on the opposite direction of the movement of the actuator, and with the increase of the back pressure of the oil outlet side, in order to ensure the movement of the quality actuator, the oil inlet side pressure must be increased.
This will increase the function consumed by the hydraulic system, low efficiency and increase heat.
In the hydraulic system with double spool technology, because the position and control mode of the valve core in and out of the oil side valve are independent and independent of each other, so through the different combination of the control modes of the two spools, the use of software programming can solve the problems that can not be solved by the traditional single valve system, and at the same time can easily realize the functions that are difficult to be realized in the traditional hydraulic system.
2. Two basic control strategies of double-core directional valve due to the flexibility of double-core reversing and two-port control, the two ports can adopt flow control, pressure control or flow pressure control respectively.
Positive introduction of two simple control strategies.
(1) the load direction remains unchanged throughout the working process. We know that for truck cranes, excavators, loaders, etc., the load direction of the hydraulic cylinder remains the same throughout the working process.
Taking the luffing hydraulic cylinder of the crane as an example, the control strategy of double spool is discussed.
The luffing cylinder of the crane is subjected to force during the working process, and the load direction remains unchanged all the time, so we can adopt the control strategy of pressure control with rod control and flow control without rod cavity.
The non-rod cavity flow control is to detect the pressure difference between the front and back sides of the valve connected to the rod-less cavity side, and then calculate the opening size of the valve core according to the required inflow or outflow flow; the rod cavity side uses pressure control to maintain a low pressure on the side, making it more energy-saving and efficient.
Because we use flow control in the rodless cavity, the balance valve used in the original control system can be replaced by a hydraulic control one-way valve.
This can eliminate the system instability caused by the balance valve, thus improving the stability of the system.
(2) the load direction changes during the working process. In this case, the pressure control on the inlet side and the flow control on the outlet side are adopted, the pressure control is used on the rod cavity side of the hydraulic cylinder, and the flow control is on the rod cavity side of the hydraulic cylinder.
If the direction of the load remains unchanged, because the flow control is adopted on the oil outlet side, we can replace the two-way balancing valve with a hydraulic one-way valve to improve the stability of the system.
The inlet side uses a pressure controller to maintain a low reference pressure, on the one hand, to improve the efficiency of the system, on the other hand, so that the system does not have cavitation.
In order to control the working mechanism with changing load direction, another PI controller will be applied to the pressure controller with rod cavity, when the load direction is changed, the pressure of the rod cavity will be reduced; if the rod cavity will still maintain a very low pressure, when the load is heavy, 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-free cavity. When the PI controller detects that the pressure of the rod-free cavity is lower than the set reference value, it will increase the pressure set by the rod cavity pressure controller, so as to ensure the normal operation of the system.
