Practical explanation of proportional servo technology hydraulic valve

The hydraulic valve represented by proportional servo is the neuron of hydraulic system, which is indispensable for the precise and accurate control of actuator (such as position, force, speed, etc.). It is helpful to design and optimize the control system and make the hydraulic drive system more energy-saving, more accurate and more economical.

In the "practical explanation of proportional servo technology hydraulic valve (1)", through the analysis of two cases, it is shared with you that before choosing the appropriate proportional servo valve, it is necessary to determine which control mode to choose: position control, flow control or pressure control.

Position control (position closed-loop control) is widely used and can reflect the typical / standard selection specification. Therefore, in this paper, after the shared control strategy is determined as position control, the first step of choosing the appropriate proportional servo valve is to determine the size of the hydraulic valve diameter and the corresponding specifications.

Different from the same on-off valve, due to the design of throttle side of proportional servo valve core, there are different flow options for hydraulic valves of the same specification and model under the same pressure difference under the same input signal. On the other hand, under the same input signal, hydraulic valves of different specifications and models will have the same flow under the same pressure difference.

It is difficult to select the flow rate. Generally speaking, there are several principles for flow selection

1. Known through the flow, calculate the pressure difference, determine the valve core specification

The pressure difference between the two sides of the hydraulic valve is not determined by human, but by the flow through the valve and the flow capacity of the valve.

The 220 flow and 325 flow spool in ng25 diameter are suitable for this condition. When 220 flow spool is selected, the opening of valve core is 92%, and that of 325 flow spool is 78%.

2. According to the separation rate of valve core displacement, the size of valve core should be small rather than large

If the spool with two different nominal flow rates can meet the requirements, the spool with smaller flow rate is usually selected. If 220l / min and 350L / min of the two kinds of spool, 92% of the opening of the first spool can meet the design requirements, and the remaining 8% of the spool displacement is useless. The opening of the second kind of spool is 78%, and the remaining 22% of the spool displacement is useless. The 220l / min spool has higher resolution to the input signal.

3. Improve the working efficiency, the same diameter of the valve core flow specification selected large not small.

Under the same flow rate, the valve core with large flow rate has small pressure loss and low energy loss, and the working efficiency of hydraulic system is higher.

4. Increase the response time of the valve core, the hydraulic valve diameter should be small or not large.

For the same type of hydraulic valve, the response of small-diameter hydraulic valve is faster than that of large-diameter hydraulic valve. In many applications, two small-diameter hydraulic valves are used instead of large-diameter hydraulic valve. For example, in metallurgical AGC application, two ng16 servo valves are used instead of ng25 hydraulic valves. The following figure also uses two ng6 hydraulic valves as pilot valves instead of ng10 pilot valves to improve dynamic characteristics.

Hard to understand? For example, when the decoration smashes the wall, the large area smashes the wall certainly uses the sledgehammer. Hit a big piece, can improve efficiency. But what about the final stitching? Small hammers are needed naturally, and large hammers can easily damage the walls. In the final positioning process, it is just like a seam smashing the wall. If the flow rate is too large, it is easy to cause overshoot, which will cause the cylinder to vibrate back and forth.