Overview of Two Basic Control Strategies of Double Spool Directional Valve

The oil inlet and outlet ports of the traditional directional valve are controlled by a spool. The corresponding relationship between the two oil ports has been determined during the design and processing of the spool, and it is impossible to modify it during use, so that the flow rate through the two ports Or the pressure cannot be controlled independently and does 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-spool control technologyConstruction machineryThe field is applied. Utronics in the United Kingdom has developed a double-spool multi-way directional valve with its own technology and patent advantages, which has been widely used in excavators, trucks, loaders, backhoe loaders and other products of JCB, Deere, DAWOO, CASE and other companies .To adapt to Chinese engineeringmechanicalThe product has functional requirements for the hydraulic system. With the continuous improvement of stability and automation control, Utronics products have entered the Chinese market in due course. The prototypes of Xiagong (5t) loaders and Zhanyang (8t) excavators have been commissioned and entered the test phase.

1. Defects of traditional single spool directional valve

The hydraulic system composed of the traditional single-spool directional valve is difficult to reasonably solve the contradictions between the following functions and controls:

(1) In the hydraulic system design, in order to improve the stability of the system and reduce the impact of load changes on the speed, we must either sacrifice some of the functions we want to achieve, or add additional hydraulic components, such as speed control valves, pressure control valves, etc., by increasing damping , Improve system speed stiffness to improve system stability. However, the increase 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 particularity of the reversing structure, users must purchase corresponding hydraulic components when realizing a certain function. In addition, construction machinery manufacturers will design corresponding functions according to the requirements of different end users, which will cause manufacturers to purchase Hydraulic control components of the same type and multiple specifications to meet the needs of different functional requirements are 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 spool, it is impossible to control the pressure on both sides of the actuator separately. Therefore, the back pressure on the oil outlet side acts on the opposite direction of the movement of the actuator. As the back pressure on the oil outlet side increases, the oil inlet side pressure must be increased to ensure the quality of the movement of the actuator. This will increase the consumption of functions of the hydraulic system, low efficiency, and increase heat generation.

The hydraulic system adopts double spool technology. Since the valve spool position and control mode of the oil inlet and outlet side of the actuator are independent and do not affect each other, through the different combinations of the two spool control methods, the use of software programming can solve the traditional The single valve system cannot solve the problem, and at the same time, it can easily realize the functions that are difficult to achieve in the traditional hydraulic system.