With the cost reduction of microprocessor controller and sensor components and the continuous improvement of control technology, double spool control technology has been applied in the field of construction machinery. Utronics Company of the United Kingdom has developed a double spool multi-way reversing valve with its own technical and patent advantages, which has been widely used in excavators, trucks, loaders and backhoe loaders of JCB, Deere, DAWOO, CASE and other companies. So as to meet that functional requirement of China's construction machinery products on the hydraulic system. With the continuous improvement of stability and automation control, Youtuo's products entered the China market in time, and the prototype debugging of Xiamen Industrial (5t) loader and Zhanyang (8t) excavator has been initially completed and entered the experimental stage.
1. Defects of traditional single spool reversing valve
The traditional hydraulic system composed of single spool reversing valve is difficult to reasonably solve the contradiction between the following functions and control:
(1) In the design of hydraulic system, in order to improve the stability of the system and reduce the influence of load change on speed, we either sacrifice some functions we want to realize or add additional hydraulic components, such as speed control valve and pressure control valve, to improve the stability of the system by increasing the damping and speed stiffness of the system. However, the increase of such components will reduce efficiency and waste energy; It will also reduce the feasibility of the whole system and increase the cost.
(2) Due to the particularity of the reversing structure, users must purchase corresponding hydraulic components when realizing a certain function, and construction machinery manufacturers will design corresponding functions according to different end-user requirements, which causes manufacturers to purchase similar and multi-specification hydraulic control components to meet different functional requirements, which is not conducive to product generalization and product management, and will greatly increase product costs.
(3) Because the hydraulic oil in and out of the actuator is controlled by a spool, it is impossible to independently control the pressure on both sides of the actuator. Therefore, the back pressure on the oil outlet side acts in the opposite direction of the actuator movement. As the back pressure on the oil outlet side increases, the pressure on the oil inlet side must be increased to ensure the movement of the actuator. This will increase the functions consumed by the hydraulic system, reduce the efficiency and increase the heat.
In the hydraulic system with dual spool technology, because the position and control mode of the actuator in and out of the oil side valve port are independent and do not affect each other, through the different combinations of the two spool control modes, the problems that can not be solved by the traditional single valve system can be well solved by software programming, and at the same time, the functions that can not be realized by the traditional hydraulic system can be easily realized.
2. Two basic control strategies of double spool reversing valve.
Because of the flexibility of the control of the two ports of the double-core commutation, the two ports can adopt flow control, pressure control or flow pressure control respectively. Actively introduce two simple control strategies.
(1) The load direction remains unchanged during the whole working process.
We know that for truck cranes, excavators, loaders, etc. The load direction of its hydraulic cylinder remains unchanged during the whole working process. Taking the luffing hydraulic cylinder of crane as an example, the control strategy of double spool is discussed.
During the working process of the luffing cylinder of crane, its stress and load direction always remain unchanged, so the control strategy of hydraulic cylinder with rod control and without rod cavity flow control can be adopted.
The flow control of rodless cavity is to detect the pressure difference between the front and back sides of the valve connected to the rodless cavity side, and then calculate the opening of the valve core according to the required inflow or outflow flow; Pressure control is adopted at the side of the cavity with rod, which keeps the side at low pressure and is more energy-saving and efficient.
Because we adopted flow control in the rodless cavity, the balance valve used in the original control system can be replaced by hydraulic control one-way valve. This can eliminate the system instability caused by the balance valve, thus improving the system stability.
(2) The load direction changes during the working process.
In this case, "oil inlet pressure control, oil outlet flow control" is adopted, and the hydraulic cylinder has rod cavity side pressure control and no rod cavity side flow control.
If the load direction is unchanged, because the oil outlet side adopts flow control, we can use hydraulic control one-way valve instead of two-way balance valve, thus improving the stability of the system. On the oil inlet side, a pressure controller is used to maintain a low reference pressure, which on the one hand improves the efficiency of the system, and on the other hand prevents cavitation in the system.
In order to control the working mechanism with changing load direction well, another PI controller is applied to the rod cavity pressure controller. When the load direction changes, the pressure of rodless cavity will decrease. If there is still a rod cavity to maintain low pressure, the hydraulic cylinder will move in the opposite direction when the load is heavy. At this point, we can use the added PI controller to monitor the change of rodless cavity pressure. When the PI controller detects that the rodless cavity pressure is lower than the set reference value, it will increase the pressure set by the rodless cavity pressure controller, thus ensuring the normal operation of the system.
3. Ultramicro hydraulic control system
Ultronics is an electro-hydraulic technology company integrating design, research and development and manufacturing. Its hydraulic control system adopts CAN bus communication and double spool control technology. Through the joint control of the two valve cores, various controls of the actuator can be realized, thus improving the stability of the system and reducing energy consumption. At the same time, it can make the system simpler, reduce costs and speed up product development, which traditional electronic systems can't do.
The hardware of Ultronics control system is generally composed of joystick, ECU, regulating valve, double spool hydraulic valve group and external sensor or switch, and they communicate with each other through CAN bus. Hydraulic valve group is the intersection of electronic control system and hydraulic system, and another important part of the system is software.
The handle is in photoelectric non-contact form, and can be equipped with at most 4 proportional outputs or 2 proportional outputs and at most 5 switches. There are proportional and self-locking switches to choose from. Its protection level has reached IP67. The delay characteristics, output curve and dead zone of the handle can be modified by special software JoyVal.
The power supply voltage of ECU is 12V and 24V, and it has 25 and 50 interfaces, providing analog and digital input and output interfaces. At the same time, ECU also provides CAN interface, so that the system can receive sensors or control signals or connect with other systems. All application programs required for system control are stored in ECU, which can convert other devices and signals (such as sensor detection signals and engine control system information). ) from the handle or connected to the ECU, it is converted into instructions for the action of each valve core.
The key of Ultronics control system lies in its unique dual spool control technology. Each valve has two valve cores, which is equivalent to changing a three-position four-way valve into a combination of two three-position three-way valves. According to the control logic, the two valve cores can be controlled independently or in pairs, both working oil ports have pressure sensors, and each valve core has position sensors. Through the closed-loop control of the sensing signal, the pressure or flow of two kinds of hydraulic oil can be controlled separately, and the control accuracy is high.
Each valve has two complete mixed-signal ASIC (Analog Application Specific Integrated Circuits) and a RISC (Reduced Instruction Processor). These controllers provide excitation and compensation for sensors, and provide power for controlling transmission equipment, valve core control software and CAN bus communication. The control strategy and specific parameters of the spool action can be set or modified by the user according to the requirements of the controlled actuator. After the control valve receives the instruction, its embedded processor runs the valve core action control software to realize the setting function, and the function coordination among multiple valves is completed by ECU, thus realizing the complex system functions. This hierarchical control mode makes the application of the system very flexible, and it is easy to build a complex control system.
The functional diversity of Ultronics control system is realized by application software, and the control software is written in a targeted way. Ultronics control system can realize many functions. Efforts made by advanced models such as crawler excavators, wheel excavators and loaders in terms of operating comfort, operating efficiency, operating cost consumption, fault diagnosis and environmental protection. For example, adaptive control of engine state and hydraulic system, specific operating functions, etc. Can be achieved by using Ultronics system.
In a word, through CAN bus communication, unique dual spool structure, application of pressure and displacement sensors, closed-loop control technology of pressure or flow, and electro-hydraulic control system of Ultronics, the control system of construction machinery will cause revolutionary changes in many aspects, such as functional diversity, flexibility, low cost performance, control concept, maintenance mode and so on.
Classification of directional control valves
In practical application, according to different needs, directional control valves can be divided into several categories:
(1) According to the flow direction of gas in the pipeline, if gas is allowed to flow in only one direction, such valves are called one-way control valves, such as one-way valves and shuttle valves. Control valves that can change the direction of gas flow are called directional valves, such as commonly used 2way2port, 2way3port, 2way5port, 3way5port, etc.
(2) According to the control mode, it can be divided into electromagnetic valve, mechanical valve, pneumatic valve and manual valve. Among them, the electromagnetic valve can be divided into single and double electric control valves; Mechanical valves can be divided into ball valves and roller valves. Pneumatic valves can also be divided into single pneumatic valves and double pneumatic valves; Manual valves can be divided into manual valves and bottom valves.
(3) According to the working principle, it can be divided into direct-acting valve and pilot valve. Direct-acting valve is a valve that directly realizes the reversing requirements through manpower, electromagnetic force and aerodynamic force; The pilot valve consists of a pilot head and a valve body, and the piston with the pilot head drives the valve stem in the valve body to realize commutation.
(4) According to the working position of the reversing valve rod, the valve can be divided into two-way valve and three-way valve.
(5) According to the number of air holes on the valve, it can be divided into 2-hole, 3-hole and 5-hole valves.
Ordinary check valve (check valve or check valve)
Function: only oil is allowed to flow forward, but not backward.
Classification: straight-through, right-angle
Structure: valve body, valve core cone, steel ball type, spring, etc.
Working principle: when the liquid flows in from the oil inlet, A →B B b.
When the liquid flows in from the oil outlet, a→ b.
Opening pressure: 0.04-0. 1 MPa.
Making back pressure valve: PK = 0.2-0.6 MPa 3.
Hydraulic control check valve
Function: forward circulation, reverse controlled circulation
Structure: common one-way valve+hydraulic control device
K is blocked by pressure oil, A → B
principle of operation
K through pressure oil, A → B
Structural characteristics: B→ A, PB = P, very high.
∴ The back pressure of the spring cavity is very high, and the valve core can be pushed open only when pk is very high, which affects the reliability.
Therefore, the following measures can be taken.
1) Use the pilot valve to release the pressure in advance.
2) Use the oil return from the external outlet to reduce the back pressure.
Usage: Hydraulic control one-way valve has good anti-sealing performance.
∴ Usually used for pressure maintaining, locking and balancing circuits.
Shuttle valve, double pressure valve and quick exhaust valve.
1) shuttle valve
2) Double pressure valve
3) quick exhaust valve No.2 reversing valve
Function: change the relative working position of the valve core in the valve body, so that the oil port of the valve body is connected or disconnected, thus
Control the reversing or start-stop of the actuator.
Classification of reversing valves
According to the structural form, it is divided into slide valve reversing valve, seat valve reversing valve and rotary valve reversing valve.
Slide valve reversing valve
Structure and working principle of (1) reversing valve
Valve body: cylindrical hole with multi-stage undercut groove.
structure
Valve core: a cylinder with multiple circular grooves.
Classification:
two
According to the working position
four
Bidirectional access is divided according to the number of paths.
Four-way (excluding control oil and oil spill)
Wu Tong
Magnetic exchange valve
Hydraulic reversing valve
According to the control mode, it is divided into
Motor reversing valve
hand-operated direction valve
Graphic symbol meaning:
1 digit-represented by squares, and several numbers are several squares.
2 Pass-↑ No Pass-┴, ┬ How many intersections do arrows and intercept symbols have with a square?
One point is several levels.
3 Oil ports have a fixed orientation and meaning, P- oil inlet (lower left) and T- oil return port (lower right).
A.B—— working oil ports (left and right) connected with the actuator.
Four springs -W, M, drawn on both sides of the square.
Two-position valve, one controlled by spring.
5 Normal position