Application of Dual Valve Core Control in Hydraulic Multi way Directional Valve

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. Utronics, a British company, has developed a dual spool multi way directional valve using its own technology and patent advantages. It has been widely used in excavators, trucks, loaders, and excavator loaders from companies such as JCB, Deere, DAWOO, CASE, etc. To meet the functional requirements of hydraulic systems for Chinese construction machinery products. With the continuous improvement of stability and automation control, Utronics’ products have timely entered the Chinese market. The prototype debugging of Xiamen Engineering (5t) loader and Zhanyang (8t) excavator has been preliminarily completed and entered the experimental stage.
The hydraulic system composed of traditional single spool directional valves is difficult to reasonably solve the contradiction between the following functions and control:
When designing a hydraulic system, in order to improve system stability and reduce the impact of load changes on speed, we 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 scalability 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 end user requirements. This 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 using dual valve core technology, due to the independent position and control method of the valve core at the inlet and outlet of the actuator, does not affect each other. By combining different control methods of the two valve cores, software programming can effectively solve problems that traditional single valve systems cannot solve, and can also easily achieve functions that are difficult to achieve in traditional hydraulic systems.
2. Two basic control strategies for dual spool directional valves
Due to the flexibility of dual valve core reversing and dual oil port control, the two oil ports can be respectively controlled by flow control, pressure control, or flow pressure control. Positively introduce two simple control strategies.
() 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 heads 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 can be replaced by a hydraulic controlled 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.
In order to effectively control the working mechanism with changes in load direction, another PI controller will be applied to the pressure controller with a rod cavity. When the load direction changes, the pressure of the rod cavity will decrease; If there is still a rod chamber that maintains a very low pressure, when the load is high, the hydraulic stamping anodized golden aluminum cylinder will move in the opposite direction. At this point, we can use the added PI controller to monitor the changes in the pressure of the rodless cavity. When the PI controller detects that the pressure of the rodless cavity is lower than the set reference value, it will increase the pressure set by the rodless cavity pressure controller to ensure the normal operation of the system.
3. Ultronics hydraulic control system
Ultronics is an electronic hydraulic technology company that integrates design, research, and manufacturing. Its hydraulic control system adopts CAN bus communication and dual valve core control technology. Through the combination control of two valve cores, various controls of the actuator can be achieved to improve system stability, reduce energy consumption, and also make the system simpler, reduce costs, and accelerate product development speed, which traditional electronic systems cannot achieve.
The hardware of the Ultronics control system is generally composed of a joystick, an electronic control unit ECU, a regulating valve, a dual spool hydraulic valve group, and external sensors or switches. Communication is achieved through CAN bus between them. The hydraulic valve group serves as the intersection point between the electronic control system and the hydraulic system, and another important component of the system is software.
The handle is in a photoelectric non-contact form and can have up to 4 proportional outputs or 2 proportional outputs and up to 5 switches. There are proportional and self-locking switches available for selection. Its protection level has reached IP67. The delay characteristics, output curve, and dead zone of the handle can be modified through dedicated software JoyVal.
The electronic control unit ECU has two types of supply voltages: 2V and 24V, with 25 and 50 interfaces, providing analog and digital input and output interfaces. At the same time, the electronic control unit also provides a CAN signal interface, allowing the system to receive sensor or control signals or connect with other systems. The ECU stores all the application programs required for system control. This application program can convert signals from the handle or other devices and signals connected to the ECU (such as sensor detection signals, engine control system information, etc.) into instructions for the action of each valve core after processing.
The key to the Ultraonics control system lies in its unique dual valve core control technology. Each valve has two valve cores, which is equivalent to transforming a three position four way valve into a combination of two three position three way valves. The two valve cores can be controlled separately or in pairs based on control logic. Additionally, both working oil ports have pressure sensors, and each valve core has a position sensor, By closed-loop control of sensing signals, the pressure or flow rate of two hydraulic oils can be controlled separately, with high control accuracy. Through different combinations, many control schemes can be obtained to meet the needs of the system.
Each valve has two fully configured mixed signal ASICs (Analog Specific Integrated Circuit) and one RISC (Reduced Instruction Processor). These controllers provide excitation and compensation to sensors, power to control transmission devices, valve core control software, and CAN bus communication. The valve core action control strategy and specific parameters can be set or modified by the user according to the requirements of the controlled executing component. After the control valve receives instructions, its embedded processor runs the valve core action control software to achieve the set function. The functional coordination between multiple valves is completed by the ECU, thus achieving complex system functions. This hierarchical control method provides great flexibility in the application of the system, while making it easy to construct complex control systems.
The diversity of Ultronics control system functions is achieved through application software and targeted programming of control software. The functions that the Ultronics control system can achieve are extremely extensive. The efforts made by advanced models such as tracked excavators, wheeled excavators, and loaders in terms of operational comfort, work efficiency, work cost consumption, fault diagnosis, environmental protection, etc., such as adaptive control of engine status and hydraulic systems, specific job functions, etc., can be achieved using Ultratronics systems.
In summary, the application of CAN bus communication, unique dual valve core structure and pressure, displacement sensors, and closed-loop control technology for pressure or flow, as well as Ultronics’ electronic hydraulic control system, will trigger one-time changes in the diversity of functions, flexibility in implementation, low cost-effectiveness, control concepts, maintenance modes, and many other aspects of the engineering machinery control system.