REXROTH servo valve R901096781 4WS2EM10

REXROTH servo valve R901096781 4WS2EM10Generally speaking, the main valve of an electro-hydraulic directional valve is a slide valve structure similar to a directional valve, except that the valve core is not driven by an electromagnet, but by the hydraulic pressure output from the pre stage valve. This is similar to an electro-hydraulic directional valve, except that the pre stage valve of the electro-hydraulic directional valve is an electromagnetic directional valve, while the pre stage valve of the servo valve is a nozzle baffle valve or jet pipe valve with good dynamic characteristics.

That is to say, the main valve of the servo valve is controlled by the output pressure of the pre stage valve, and the pressure of the pre stage valve comes from the inlet p of the servo valve. If the pressure at port p is insufficient, the pre stage valve cannot output enough pressure to push the main valve core to move.

And we know that when the load is zero, if the four-way slide valve opens, the pressure at port p=pressure at port t+valve loss (ignoring other pressure losses on the oil circuit). If the pressure loss at the valve port is small and the pressure at port t is zero, then the pressure at port p is not enough to supply the pre stage valve to push the main valve core, and the entire servo valve fails. So the valve port of the servo valve is made too small, even when the valve port is fully open, there must be a certain pressure loss to maintain the normal operation of the pre stage valve.

Servo valves actually have many disadvantages, such as high energy consumption and waste, easy failure, poor anti pollution ability, high price, etc. The only benefit is that their dynamic performance is the highest among all hydraulic valves. With this advantage, servo valves have to be used in many situations that require high dynamic characteristics, such as servo control of aircraft rockets, turbine speed regulation, and so on. Those with lower dynamic requirements are basically dominated by proportional valves.

Generally speaking, servo systems seem to be closed-loop control, while proportional valves are often used for open-loop control; Secondly, there are many types of proportional valves, such as proportional pressure and flow control valves, which are more flexible in control than servos. From their internal structure, servo valves are mostly zero covered, while proportional valves have a certain dead zone, low control accuracy, and slow response. But from the perspective of development trends, especially in the aspect of proportional flow control valves and servo valves, the performance difference between the two is gradually narrowing. In addition, the cost of proportional valves is much lower than that of servo valves, and their anti pollution ability is also strong!

There is no strict regulation on the difference between servo valves and proportional valves, as the performance of proportional valves is gradually improving and approaching that of servo valves. Therefore, in recent years, proportional servo valves have emerged.

The difference between proportional valves and servo valves mainly lies in the following points:

1. The driving device is different. The driving device of the proportional valve is a proportional electromagnet; The driving device of the servo valve is a force motor or a torque motor;

2. Different performance parameters. Due to different characteristics such as hysteresis loop, median dead zone, bandwidth, and filtering accuracy, the application scenarios are different. Servo valves and servo proportional valves are mainly used in closed-loop control systems, while other structures of proportional valves are mainly used in open-loop control systems and closed-loop speed control systems;

2.1 The servo valve has no dead zone in the center position, while the proportional valve has a dead zone in the center position;

2.2 The frequency response (response frequency) of servo valves is higher, up to around 200Hz, while proportional valves generally have a maximum frequency of several tens of Hz;

2.3 Servo valves have higher requirements for hydraulic oil, which needs to be filtered to prevent blockage. Proportional valves have lower requirements;

3. The valve core structure and machining accuracy are different. The proportional valve adopts a valve core+valve body structure, with the valve body serving as the valve sleeve. Servo valves and servo proportional valves adopt a structure of valve core and valve sleeve.

4. The median functional types are different. Proportional directional valves have a neutral function similar to ordinary directional valves, while servo valves only have an O-type neutral function (E-type of Rexroth products).

5. The rated pressure drop of valves varies.

REXROTH servo valve R901096781 4WS2EM10, while the performance of proportional servo valve is between servo valve and proportional valve.

Proportional directional valve is a type of proportional valve used to control flow and direction. ---Electric proportional valve

Automatic control can be divided into intermittent control and continuous control. Intermittent control refers to switch control. In pneumatic control systems, on-off directional valves with lower operating frequencies are used to control the on/off of the pneumatic circuit. Adjust the required pressure with a pressure reducing valve and adjust the required flow rate with a throttle valve. This traditional pneumatic control system requires multiple pressure reducing valves, throttle valves, and directional valves in order to have multiple output forces and multiple motion speeds. In this way, not only do the components need to be numerous, the cost is high, and the system is complex, but many components also require manual adjustment in advance. Electric proportional valve control belongs to continuous control, which is characterized by the output quantity changing with the input quantity, and there is a certain proportional relationship between the output quantity and the input quantity. Proportional control can be divided into open-loop control and closed-loop control.

　　REXROTH servo valvestructural principle

As the input signal increases, the supply solenoid valve pilot valve 1 changes direction, while the exhaust solenoid pilot valve 7 is in the reset state. The supply pressure enters the pilot chamber 5 through valve 1 from the SUP port, and the pilot chamber pressure rises. The air pressure acts on the top of diaphragm 2, and the supply valve core 4 connected to diaphragm 2 opens, while the exhaust valve core 3 closes, generating output pressure. This output pressure is fed back to control circuit 8 through pressure sensor 6. Here, a quick comparison correction is made with the target value until the output pressure is proportional to the input signal, thereby obtaining a change in output pressure proportional to the change in input signal. Due to the absence of a nozzle baffle mechanism, the valve is insensitive to impurities and has high reliability.

characteristic

1) It can achieve infinite adjustment of pressure and speed, avoiding the impact phenomenon when the normally open switch air valve changes direction.

2) Can achieve remote control and program control.

3) Compared with intermittent control, the system is simplified and the components are greatly reduced.

4) Compared with hydraulic proportional valves, they have smaller volume, lighter weight, simpler structure, and lower cost, but their response speed is much slower than hydraulic systems and they are also more sensitive to load changes.

5) Low power consumption, minimal heat generation, and low noise.

6) No fire, no pollution to the environment. Less affected by temperature changes.