Due to the flexibility of the double valve core switching of two oil mouth control ,the two oil mouths respectively take the flow control, pressure control or flow control. We are going to positively introduce two kinds of simple control strategy.
(1) the load direction in the whole process remains the same
As we know, for truck crane, excavator, loader, etc, the load direction of the hydraulic cylinder in the process of the whole work always remain unchanged. The following will take the crane luffing hydraulic cylinder as an example to discuss the double control strategy of the valve core.
Crane luffing cylinder in the working process,its force and the load direction always remain the same.Therefore we can adopt the control strategy of the hydraulic cylinder rod and pressure control, rodless cavity with flow control.
Rodless cavity flow control is used through testing the pressure difference connected to the rodless cavity side valve on both sides and then according to the required inlet flow or outlet flow to calculate the valve core opening size; Rod cavity side uses the pressure control, making this side to maintain a low pressure and makes it more energy saving and efficient.
Since we have adopted in the rodless cavity flow control, therefore, the original controlling balance valve can be replaced by used in control system can be replaced by a hydraulic controlled check valve. It can eliminate the system unstability of the balance valve so as to improve system stability.
(2) the load direction changes in the working process
In this case, you should take "the feeding lateral pressure control, discharging oil lateral flow control".In the hydraulic cylinder rod cavity side pressure control, the rodless cavity side have flow control.
If the load direction remains the same,just because the oil side adopts the flow control, then we can use the bidirectional balance valve hydraulic control one-way valve to replace it so as to improve the stability of the system. Suction side pressure controller can maintain a low pressure.On one hand, it can improve the efficiency of system; on the other hand, the system will not occur air-pocket.
In order to make the working agency of load direction change can be well-controlled, another PI controller will be used to the sucker rod cavity pressure controller.When the load direction changes,the rodless cavity pressure will be decreased; If you still will have the rod chamber to maintain a low pressure.When the load is very big, the hydraulic cylinder will go to the reverse direction. At this point, we can use the added PI controller to monitor the change of the rodless cavity pressure.When the PI controller detected rodless cavity pressure is lower than the set reference, itwill improve the rod chamber pressure controller set pressure so as to guarantee the normal work of the system.
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