The control of the inlet and outlet of traditional directional valves is carried out through a single valve core. The corresponding relationship between the two oil ports has been determined during the design and processing of the valve core, and cannot be modified during use. As a result, the flow or pressure through the two oil ports cannot be independently controlled and do not affect each other.

With the decrease in the cost of microprocessor controllers and sensor components, and the continuous improvement of control technology, the dual valve core control technology has been applied in the field of engineering machinery.

1. Defects of traditional single spool directional valves

The hydraulic system composed of traditional single spool directional valves is difficult to reasonably solve the contradiction between the following functions and control:

(1) In order to improve system stability during the design of hydraulic systems, the manufacturer of quick connectors reduces the impact of load changes on speed. They either sacrifice some of the functions we want to achieve or add additional hydraulic components, such as speed control valves and pressure control valves, to improve system stability by increasing damping and increasing system speed stiffness. However, the addition of such components will reduce efficiency and waste energy; It will also reduce the reliability of the entire system and increase costs.

(2) Due to the unique nature of the reversing structure, users must purchase corresponding hydraulic components when implementing a certain function. In addition, construction machinery manufacturers will design corresponding functions according to different user requirements, which will cause manufacturers to purchase similar and multi specification hydraulic control components to meet different functional requirements, which is not conducive to product generalization and product management, and will greatly increase product costs.

(3) Due to the fact that the hydraulic oil in and out of the actuator is controlled through a valve core, it is impossible to control the pressure on both sides of the actuator separately. Therefore, the back pressure on the outlet side acts in the opposite direction of the actuator's movement. As the back pressure on the outlet side increases, in order to ensure the movement of the actuator, it is necessary to increase the inlet side pressure. This will increase the functionality consumed by the hydraulic system, resulting in low efficiency and increased heating.

The hydraulic system adopts dual valve core technology. Due to the independent position and control method of the valve core at the inlet and outlet of the actuator, the quick connector manufacturer can easily solve the problems that traditional single valve systems cannot solve by combining different control methods of the two valve cores and using software programming. At the same time, it can also easily achieve functions that are difficult to achieve in traditional hydraulic systems.

2. The two basic control strategies of a dual spool directional valve are based on the flexibility of the dual spool directional control with two oil ports. The two oil ports can be respectively controlled by flow control, pressure control, or flow pressure control. Positively introduce two simple control strategies.

(1) The load direction remains unchanged throughout the entire working process

We know that for truck cranes, excavators, loaders, etc., the load direction of their hydraulic cylinders remains unchanged throughout the entire working process. The following is an example to explore the control strategy of dual valve core using the crane variable amplitude hydraulic cylinder.

During the working process, the force and load direction of the crane's variable amplitude cylinder remain unchanged. Therefore, we can adopt a control strategy of hydraulic cylinder with rod control using pressure control and non rod cavity using flow control.

Rod less cavity flow control is achieved by detecting the pressure difference between the front and rear sides of the valve connected to the rod less cavity side, and then calculating the size of the valve core opening based on the required inflow or outflow flow rate; The pressure control is used on the cavity side of the rod to maintain a low pressure value, making it more energy-efficient and efficient.

Due to the use of flow control in the rodless chamber, the balance valve used in the original control system by the quick coupling manufacturer can be replaced by a hydraulic one-way valve. This can eliminate system instability caused by the balance valve, thereby improving system stability.

(2) The direction of the load changes during operation

In this case, "inlet side pressure control and outlet side flow control" are adopted, with pressure control on the side with rod chamber in the hydraulic cylinder and flow control on the side without rod chamber.

If the load direction remains unchanged, due to the flow control adopted on the oil outlet side, we can replace the bidirectional balance valve with a hydraulic controlled one-way valve to improve the stability of the system. A pressure controller is used on the oil inlet side to maintain a lower reference pressure, which improves system efficiency and prevents cavitation.