Analysis of the hydraulic control structure and characteristics of several typical governors

Each product serves a different purpose. You can ask. Hangzhou Libei Electro-Hydraulic Technology Co., Ltd., located in Zhejiang Province Overseas High-level Talent Innovation Park, is a high-tech enterprise in the development of hydraulic and electronic control components and the integrated design, manufacturing, commissioning and maintenance of electro-hydraulic control systems.

The main products include digital proportional amplifiers, proportional solenoids, industrial hydraulic controllers, construction machinery controllers, proportional valves, servo valves, multi-way valves, pump automatic test benches, etc., while providing professional mechanical and electro-hydraulic control system solutions and components, as well as integrated design and manufacturing, commissioning and maintenance services of various industrial electro-hydraulic control systems, and sales of German brand hydraulic components.

With the development of computer technology and control engineering, the main components (motor conversion device, main pressure distribution valve, accident pressure distribution valve, mechanical manual device, etc.) that constitute the mechanical hydraulic part of the digital electro-hydraulic governor are developing in the direction of modularization and structure, focusing on structural reliability and redundancy. In this paper, several typical redundant control structures are formed according to the combination of different control modes, and the characteristics of each structure are analyzed. The issue of coordination with the emergency shutdown of the cylindrical valve after the configuration of the accident pressure distribution valve was discussed.

1. Volume throttling speed regulation.

Volume throttling speed regulation, energy loss is small, fuel tank size is small, but the cooling conditions are poor, in order to change the displacement adjustment speed of the pump or motor, in order to control it quickly, the closed oil circuit of volume speed regulation is mostly adopted, and the speed regulation circuit is divided into two types: open circuit and closed circuit.

2. Throttle speed regulation.

The open oil circuit of throttling speed regulation has fast response speed. Generally speaking, at present, the open circuit is mostly used to adjust the speed. The open circuit structure is simple, which can realize the work of one pump (hydraulic pump) and multiple machines (actuators), cooling and compensating for oil leakage, low efficiency, and good oil pressure cooling conditions.

3. Volume speed regulation and sensitive control.

Oil circuit circulation type, air and dirt are not easy to intrude, although the efficiency is low, the flow rate of inflow or outflow of actuators is changed by the flow control valve, and air and dirt are easy to intrude. Due to the control performance, the structure is more complex, in order to achieve high efficiency to reduce energy loss, and at the same time, the flow rate of the variable pump is adapted to the flow rate through the flow control valve, forming a closed annular circuit, and the open oil circuit of throttling speed regulation is mostly adopted.

At present, there are three main speed regulation methods in the hydraulic system: (1) throttling speed regulation, using a quantitative pump to supply oil, and changing the flow flow into and out of the actuator by the flow control valve to adjust the speed, this kind of system is called valve control system.

2) Volumetric speed regulation, using variable pump or variable motor to change the displacement adjustment speed of the pump or motor. This type of system is called a pump control system.

3) Volumetric throttling speed regulation, using pressure feedback variable pump oil supply, by the flow control valve to change the flow into or out of the actuator flow, and then adjust the speed, and at the same time make the flow of the variable pump and the flow through the flow control valve adapt.

As far as the oil circuit circulation type is concerned, the speed regulating circuit is divided into two types: open circuit and closed circuit. In the open circuit, the pump sucks oil from the oil tank and delivers the pressure oil to the actuator, which discharges the oil directly back to the mailbox; In a closed oil circuit, the oil inlet of the hydraulic pump is directly connected to the oil outlet of the actuator without passing through the mailbox, forming a closed annular circuit. The open circuit structure is simple, which can realize the work of one pump (hydraulic pump) and multiple machines (actuators), and the hydraulic cooling conditions are good, but the size of the oil tank is large, and air and dirt are easy to invade.

The closed oil circuit is compact in structure, the size of the mailbox is small, it is generally a pump and a machine, because it is a closed annular oil circuit, the air and dirt are not easy to invade, but the cooling conditions are poor, and the auxiliary pump is needed to change the oil to cool and compensate for the oil leakage, so the structure is more complex. In practical application, due to the high heat generation and low efficiency, the open circuit is mostly used for throttling speed regulation. The volumetric speed regulation efficiency is high, the heat generation is also less, and the closed circuit is mostly used.

As far as the control performance is concerned, the closed oil circuit of volumetric speed regulation is slow due to the variable speed regulation of the pump or motor, including a large volume, especially the need to rebuild the pressure when starting or reversing. In contrast, the open oil circuit with throttling speed regulation is correspondingly fast and sensitively controlled.

Due to the above characteristics, in practical application, the hydraulic equipment below the small and medium power, because the power is small, although the efficiency is low, but the energy loss is still small, in order to achieve its agile control, the structure is simple, and the open oil circuit of throttling speed regulation is mostly adopted. For hydraulic equipment above medium power, in order to achieve high efficiency and reduce energy loss, the closed oil circuit with volumetric speed regulation is mostly used. In general, the manufacturing cost of both systems is similar for the same power.

As mentioned earlier, the advantages of the two circuits are simple structure, sensitive control, and easy use and maintenance. The disadvantage is that the pump and the actuator cannot be strictly matched with the power due to the speed regulation of the throttle valve, so the efficiency is low and the heat generation is large. Generally, it is only used in occasions where the power is not high.

Structural features of rigid feedback hydraulic governor.

As shown in Figure 7-4, it is a hydraulic governor with a rigid feedback system. Except that the upper end A of the lever AC is not mounted on a fixed hinge but is connected to the piston rod of servo piston 3, its structure is basically the same as that of the pure Zen hydraulic adjuster with no feedback described above. This change results in the following changes in the relationship between the sensing element, the hydraulic amplification element, and the oil quantity regulating mechanism.

The working principle of a rigid feedback hydraulic governor.

When the load is reduced, the engine speed increases, and the flying hammer flies outward, driving the speed lever 1 to move to the right. At this time, the servo piston 3 has not yet acted, so the upper end point A of the feedback rod AC is temporarily used as a fixed point. The lever AC rotates counterclockwise around A, drives the slide valve 6 to move to the right, opens the control hole, and the high-pressure oil enters the right chamber of the power cylinder, and the left chamber communicates with the low-pressure oil circuit.

In this way, the high-pressure oil pushes the servo piston 8 to drive the fuel injection pump adjusting lever 5 to move to the left, and the root gear trouser leather reduces the oil supply according to the new load.

When the servo piston moves to the left, the lever AC swings to the left around point C, and drives the slide valve 6 connected with point B to move to the left, so that the slide valve moves in the opposite direction. Prevent excessive reduction in oil supply. Row difference, a lever device that can have an opposite effect on the movement of the slide valve when the servo piston is moving, is called a rigid feedback system.

After the adjustment process, the spool valve returns to the equilibrium position, closes the control oil hole, and cuts off the servo cylinder oil circuit. At this time, the servo piston stops moving, the fuel injection pump adjustment lever moves to a new equilibrium position, and the engine works under the corresponding new load. Therefore, the governor has different stable speeds according to the different loads of the engine.

Because the oil supply needs to be changed when the engine load changes, the position of point A varies with the load. Point B, which is connected to the spool valve, should be in an equilibrium position under any stable operating conditions, regardless of the load. Therefore, the position of point C must change accordingly with point A, resulting in a change in velocity.

For example, when the load is reduced, when the spool valve 6 returns to the original position in the middle after the speed regulation process is completed, the servo piston 3 is in the position of reducing the oil supply, so that point A is to the left and point C is to the right. Because point C is to the right, spring 7 is further compressed, and only when it runs at a higher speed, the centrifugal force of the flying weight can be balanced with the spring pressure. This indicates that after stable operation at reduced load, the diesel engine rotates slightly higher than before.

Similarly, when the load increases, the speed of the diesel engine is slightly lower than the original after stable operation. The hydraulic governor with rigid feedback can ensure stable working characteristics during speed regulation. However, after the load change, the speed of the diesel engine changes, and the stable differential speed 2 cannot be zero.

1. Oil inlet throttle speed regulation circuit: after the hydraulic cylinder is activated, the piston rod moves slowly, and the piston rod movement speed can be observed to increase gradually by increasing the flow area; In the process of operation, it can be seen that the piston rod moves fast and slow, which is due to the fact that there is a throttle valve at the oil inlet to limit the flow, and there is no back pressure valve at the oil return port, so the movement stability is poor; Usually at the beginning of start-up, because there is a throttle valve in series at the oil inlet, so the starting impact is small; In addition, the excess oil is overflowed, so the work efficiency is low. In this circuit, the movement speed of the working parts fluctuates with the increase or decrease of the external load, and it is difficult to obtain the accurate speed, so it is suitable for light load or load change little, and the speed is not high.

2.Return throttle speed control circuit: the throttle valve is in the oil return circuit, so this circuit is mostly used in hydraulic systems with small power, but large load changes and high motion stability requirements, such as grinding and fine boring combined machine tools.

3. Bypass throttle speed regulation circuit: Different from the speed regulation method of the first two circuits, its throttle valve and actuator are connected in parallel, the larger the throttle valve opens, the slower the piston rod runs. This circuit is suitable for high-speed and high-power occasions with small load changes and low requirements for motion stability, such as the main drive system of the bull head planer, and sometimes it can also be used in the case where the feed rate is automatically reduced with the increase of load.

The hydraulic control system of the automatic transmission should be designed according to its characteristics, with higher performance and more effective transmission, so as to make the operation convenient, the start is smooth, the ride comfort is good, the fuel economy is high, and the safety and reliability are reliable. Hydraulically operated, its structure consists of (1) oil pump The hydraulic pump is the pressure of the hydraulic control system of the automatic transmission**. Hydraulic pumps are usually installed in front of the automatic transmission and are driven by torque converter pump wheels.

The structure of the internal gear pump, when the engine is running, the pinion and the internal gear rotate in the same direction, the volume of the lower chamber continues to increase, forming a vacuum and absorbing oil, and the volume of the upper chamber is constantly decreasing, and the hydraulic oil is pumped out (2) the hydraulic torque converter control device, the function of the hydraulic torque converter control device is to draw out the high-temperature oil in the torque converter to be cooled, and then pressurized back to the torque converter for compensation. The torque converter control device is composed of pressure regulating valve, lock-out signal valve, lock-up relay valve (also known as lock-up relay valve) and corresponding oil circuits. The work of the latching clutch in the torque converter is controlled by a lock-up signal valve and a lock-up relay valve.

The pressure of the speed regulator is applied above the spool of the locking signal valve, and the oil circuit of the overdrive shift valve is communicated below.

A commonly used speed regulation method for hydraulic systems.

1.Throttling speed regulation This speed regulation method is suitable for hydraulic systems consisting of a dosing pump and a dosing element.

2.Volumetric speed regulation is achieved by changing the oil supply of the variable pump or changing the displacement of the hydraulic motor.

3.Volumetric throttling speed regulation The variable pump is used to supply oil, and the flow rate flowing in or out of the actuator is changed through the throttle valve or speed regulating valve to achieve speed regulation.

The speed control circuit should generally meet the following basic requirements:

1.It can sensitively realize stepless speed regulation in the maximum and minimum speed range required by the working parts;

2.When the load changes, the adjusted speed will not change, or only change within the allowable range;

3.The power loss should be small to save energy and reduce the heat generation of the system;

4.Strive for simple structure, safe and reliable.

1, Inverter, 2 Variable Pump, 3, Proportional Valve, 4 Speed Regulating Valve 5 Throttle Valve.

Speed regulation is mainly to regulate the flow rate, such as a shut-off valve.