1. Shortcomings of the traditional single valve core of the reversing valve
The hydraulic system composed by the traditional single valve core of reversing valve is hard to deal the contradiction between the following functions and control:
(1) when describing the hydraulic system, in order to progress the system stability and reduce the influence that load changing has on its speed, we can devote some functions that we want to put into end, or add the rated hydraulic components, such as speed control valve, pressure control valve, etc., after adding damping, the progress system will speed stiffness to improve the system stability. But adding this element will decline the power, laying waste to power; and it will also decline the feasibility of the whole system and add cost.
(2) because of the particularity of the reversing layout, making users using the corresponding hydraulic components in a particular function and with engineering machinery manufacturers will describe the corresponding function according to different users' needs, which will make the manufacturers to buy the same kind, more standard hydraulic control components to satisfied the needs of different function demand, which is bad for product generalization and management and greatly increase the cost.
(3) because the performance of inlet and outlet of hydraulic oil is controlled by a valve core.It is impossible to control the performance of both sides pressure alone. Thus, out of the back pressure of oil side acts on the performance of the organization movement in the opposite direction, and then the oil side back pressure increases, and guarantee the quality of performance of the organization of sport, it is necessary to progress the oil side pressure. This makes the function of the hydraulic system cost be added with low power and more heat.
Choose the hydraulic system with double valve core skills, because the performance of the valve core position and control method of the inlet and outlet of the oil side valve is independent and the combination of different control methods of the valve core, using the software programming can dispose of the problem that the traditional single valve system can't dispose.It can also easily finish the function that the traditional hydraulic system cannot reach.
2, Two kinds of basic control strategy of the double valve core of the reversing valve
Because the flexibility of the double valve core reversing two oil mouths control , two oil mouth do not adopt the flow control, pressure control or flow control. We are going to positively analyse these two kinds of brief control strategy.
(1) the load direction stay the same in the whole operation process
We know that the truck crane, excavator, loader, ect, their load direction remain the same during the operation process of the hydraulic cylinder. The following will discuss the double valve core control strategy of the crane luffing hydraulic cylinder as an example.
The crane luffing cylinder in operation process always has the same direction, so we can adopt the pressure control, rodless cavity with control flow control strategy of the hydraulic cylinder.
Rodless cavity flow control after testing connects to the rodless cavity side valve before and after the pressure difference on both sides,and then according to the required inlet flow or outlet flow to calculate the valve core openings intrusive;The rod cavity side selects the pressure control, and keep the side to maintain at a low pressure, making it more energy saving and efficient.
Because we choose the flow control of the rodless cavity, thus the balancing valve of the original control system can be replaced by a hydraulic controlled single valve. It can eliminate the unstability of the balance valve system is not stable, and then improve the system's stability.
(2) the load direction change in the operation process
In this case, adopt "Inlet oil side pressure control, outlet oil side flow manipulation", use the pressure control at the hydraulic cylinder rod chamber, and the rodless cavity side uses the flow control.
If the load direction remains the same, just because the oil side adopted the flow control, we can use the hydraulic control one-way valve to replace the two-way balancing valve , and then improve system's stability. Suction side uses the pressure control valve to maintain at a low reference pressure, on the one hand, it can improve the system power, on the other hand, the system does not occur air pockets.
In order to make the operation of the load direction changes can be well-controlled, the other a PI controller will be applied to the pressure control valve with rod cavity.When the load direction changes, the rodless cavity pressure will be decreased; If the rod cavity can still remain at a low pressure, when the load is very big, the hydraulic cylinder to the reverse direction. At this moment we can add the PI control implement supervision and rodless cavity pressure changes, when PI control device detected rodless cavity pressure is lower than the refer to the value set, it will progress the set pressure of the rod cavity pressure controller, and guaranteeing the normal operation of system.
3¡¢Ultronics Hydraulic control system
Ultronics Co., Ltd is a company that combines drawing, research and producing electronic hydraulic skills. The CAN bus communication is used in the hydraulic control system, double control valve core skills, through the combination of the two core control, many kinds of control CAN be completed on the performance of the organization and to improve system's stability, declining the power loss, and also it can make the system more simple and save cost, speed up the product development. These cannot be achieved by the traditional electronic system.
The hardware of the Ultronics controlling system is usually composed of the operating handle, the electronic control unit ECU hydraulic valve, regulating valve, double valve core group and external sensor or switch, etc, with the CAN bus communication, hydraulic valve group for the intersection of the electric control system and hydraulic system is another important component of some software.
Handle for the photoelectric touch method, it can take up to four share outputs or two share outputs and at most five switches. The switch has share type selection and self-locking type. The protection grade reaches at the IP67. Handle the time delay characteristic, output curve and dead zones can be modified by special software JoyVal.
Electronic control unit ECU two kinds of power supply voltage 12 v and 24 v£¬ 25 and 50 road two interfaces, supplying to imitation and digital input and output interface, with the electronic control unit also CAN supply the letter interface, enables the system to accept the sensor control signal or connect with other system. Stored in the ECU control everything you need to use the system procedures, the procedures used to come from the handle or other equipment and cohesion on the ECU of signals (such as sensor signal, the engine control system information, etc.), they are converted into the valve core after disposal.
The key to the Ultronics control system is its common double valve core control skills, each valve has two valve cores, equivalent to change a three four-way valve into the combination of two three three-way valve, two valve cores can be controlled alone, it also can be controlled in pairs according to the control logic, and two oil mouths each has a pressure sensor and each valve core has a position sensor, after the sensing signal of the closed-loop control, it can control the pressure or flow of the two-way hydraulic oil separately with very high control precision.Through different combinations ,you can get lots of control plans to satisfy the system requirements.
Every piece of valve has two intact set good mixed signal ASIC (application-specific integrated circuit for imitation) and a RISC (reduced instruction disposal). The manipulation of the device to the sensor supply encourages and counter, power supply for manipulation of the transmission device, the supply valve core and CAN bus communication control software. Valve core moves control strategy and detailed parameters can be performed by the user according to the accused demand element set or correction. Control valve to accept to the command, the embedded type disposer can the valve core moves has set the function of control software, the completion of the function of harmony between multiple valve is composed of ECU, then the system function is mixed without order. The use of this kind of hierarchical control method makes the system have a very good flexibility, easy to build a messy control system together.
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