Application of Proportional Solenoid in Cartridge Solenoid Valve

The traditional cartridge solenoid valve is a kind of switch solenoid valve, which is often used to control the direction of the fluid under the on and off two states. When power is connected, the electromagnetic force generated by the solenoid coil separates the valve core from the seat, the oil inlet and control inlet is connected, and the hydraulic actuator begins to work. When the power is cut off, the electromagnetic force disappears, the valve core resets under the action of spring force, the oil return port is connected with the control port, and the hydraulic actuator stops working.

Generally speaking, the traditional cartridge solenoid valve is reliable in operation, easy to connect with computer, and has good anti-interference. However, the operating noise of it is big, and when the valve is started up or shut down, the impact phenomenon is prominent. With the rapid development of modern hydraulic technology, some foreign companies have carried out the research work of on/off proportional cartridge solenoid valve and made great achievements. The on/off proportional cartridge solenoid valve is a new type of cartridge solenoid valve which integrates the pilot valve with the main valve core and utilizes the characteristic of the proportional solenoid. We’ll cover it briefly in the following content.

The Structure and Working Principle of Cartridge Solenoid Valve

This valve is a two-stage control cartridge solenoid valve. Its pilot valve is a two-way solenoid valve and its main valve core is a three-way cartridge valve. The opening of the main valve core is determined by the pilot solenoid valve. Just as the picture shown below, when the pilot valve is powered on, this solenoid valve will work in the left position and the main oil pressure A will act on this valve through the damping hole R1. At this time, the main oil pressure will be cut off by the electromagnetic force which is generated by the solenoid coil. With the increase of the hydraulic oil quantity, the main oil pressure will increase at the lower end of the main valve core, making the main valve core overcome the spring force. At this point, the main oil pressure A will communicate with the control oil pressure C, and the hydraulic actuator works.No matter the main oil pressure increases or decreases, the main valve core will reach a new balance point under the action of electromagnetic force. Its working principle is similar to the pilot pressure reducing valve. When the power of the pilot valve is cut off, this solenoid valve will work in the right position, the electromagnetic force disappears and the main valve core will be reset under the action of spring force. The oil port B and oil port C will be connected to make the oil pressure flow back to the oil tank through the small hole. The main oil pressure will flow back to the oil tank through the damping holes R1 and R2.

Characteristics of Proportional Solenoid

The solenoid is a kind of electromagnetic attractive force which depends on the electromagnetic system. Its basic characteristics can be expressed as the relation between electromagnetic force F and travel x of the armature during its movement, namely, F=f(x). This relation is called the attraction characteristic of the solenoid.

In the motion course of the solenoid, the mechanical load and resistance should be overcome. For ordinary solenoids, the electromagnetic force is required to be greater than the load counterforce. For proportional solenoids, the armature is in a balanced state between the electromagnetic force and the load counterforce. The position of it depends on the strength of the electrical signal and it can stay anywhere between the two limit positions.

Different spring stiffness has different effects on the electromagnetic force. When we use the proportional solenoid, choosing a spring with high stiffness can make the system more stable. But the larger the spring’s stiffness, the larger the current needed to produce the electromagnetic force. It will cause heat problems. In addition, the proportional solenoid can be divided into force output type and position output type according to the matching with load and the spring stiffness. The force output type takes the output electromagnetic thrust as the main purpose and the position output type takes the output certain displacement as the main purpose. The electromagnetic force of proportional solenoid moves up and down according to the different input current and maintains the balance with spring force at all times. With the improvement of hydraulic control technology, the proportional solenoid will play an increasingly important role.

Compared with the traditional on/off solenoid valve, the cartridge solenoid valve adopts proportional solenoid to keep the valve opening in a certain position and realize the proportional control function of the on/off solenoid valve. It can be used in an automatic transmission clutch control system and be widely used in small flow control system.