Liebherr excavator hydraulic control system has many types, mainly include load induction control system, positive flow control system, limit power control system and other three categories, each control system has its advantages applicable to the market and the applicable era. Take the Liebherr R926C excavator as an example to introduce the positive flow control system that is still used in the market.
Positive flow control system
The Liebherr R926C excavator positive flow control system consists of a main pump 1, a main pump regulator 2, a joystick 3, a logic valve block 4, a multi-way valve 5, a hydraulic cylinder 6, a main relief valve 7, and a central control Modules and other components, as shown in Figure 1.
Figure 1 Principle of positive flow control system
1. Work main pump 2. Main pump regulator 3. Joystick
4. Logic valve block 5. Multi-way valve
6. Hydraulic cylinder 7. Main relief valve
When the joystick 3 is pulled, its output pilot control oil (control signal) first reaches the logic valve block 4 and is controlled by the logic valve block 4 and simultaneously outputs two control oils: One control oil reaches the main pump regulator 2, In order to adjust the output flow of the working main pump 1, the pressure value of the hydraulic output of the way is controlled by the detecting sensor in the main pump regulator 2, the central control module and the like, and the corresponding solenoid valve is adjusted to make the output of the working main pump 1 work. The flow rate is proportional to the control pressure of the joystick 3; the other control oil reaches the multi-way valve 5 and directly pushes the corresponding valve core of the multi-way valve 5 so that the multi-way valve 5 corresponds to the movement amount of the valve body and the control pressure of the joystick. Proportional, so that the work unit hydraulic cylinder to obtain the required flow.
It can be seen that the Liebherr R926C excavator positive flow control system is characterized by the pilot pressure oil not only controlling the multi-way valve 5, but also used to adjust the displacement of the working main pump 1 so that the displacement of the working main pump 1 is Multi-valve 5 spool opening is proportional. Since the displacement of the working main pump 1 can be controlled in real time, it can be supplied on demand. The sensor signal point of the positive flow control system is located at the front end of the multi-way valve 5. The pressure signal is sent to the multi-way valve 5 and the working main pump 1 at the same time, so that the two actions can be synchronized. In simple terms, the positive flow control is to manually control the displacement of the main pump 1 according to the needs of the working device.
2. Main pump flow regulation principle
In the Liebherr R926C excavator positive flow control system, the two working main pumps 1 are adjusted by a combination of flow regulation (SD) and total power regulation (SL). The total power regulation is through the setting of the engine speed operation mode. The main pump regulator 2 is controlled under the function of the central control module 9. When the total working power reaches the specified limit value, the two working main pumps 1 are adjusted. The working pump flow control principle is shown in FIG. 2.
Figure 2 working master pump flow control schematic
1. Work main pump 2. Main pump regulator 3. Joystick
4. Logic valve block 5. Multi-way valve
6, 7. Flow control solenoid valve 8. Pressure sensor
9. Central control module
When the joystick 3 is pulled, its output pilot control oil (control signal) first reaches the logic valve block 4 and is controlled by the logic valve block 4 and simultaneously outputs two control oils: One control oil directly pushes the multiple valve 5 corresponding valve In the core, the corresponding valve of the multi-way valve 5 is moved in direct proportion to the control pressure of the joystick, so that the hydraulic cylinder of the working device obtains the required flow; the other control oil is transmitted to the front end of the flow control electromagnetic valve 6, 7. The electrical signal from the central control module 9 is output in proportion to control the main pump regulator 2, so that the main working pump 1 outputs the corresponding flow according to the demand.
The electric signals of the flow control solenoid valves 6, 7 come from the pressure sensor 8. After the pressure sensor 8 detects the pilot control oil pressure from the logic valve block 4, the pilot control oil pressure signal is converted into an electric signal and transmitted to the central control module 9. The central control module 9 outputs electrical signals after processing to control the flow control solenoid valve (6, 7), and the flow control solenoid valve (6, 7) outputs the corresponding control oil to regulate the main pump regulator 2, In turn, the output of the work pump 1 is controlled.
3. Positive flow control system advantages and disadvantages
(1) Advantages
The control signal of the sensitive working main pump is collected in the logic valve block at the front of the multi-way valve, that is, the detected pilot pressure output from the joystick is sent to the multiple control valve and the hydraulic pump at the same time, so that both can be Synchronous action, so the positive flow control system is very responsive.
High control accuracy The positive flow control system has small flow fluctuations, good operability, high work efficiency, and good reliability.
The sensor signal of the fuel positive flow system is saved from the pilot control oil pressure and is not affected by other aspects. The system return pressure is the back pressure, only about 0.5MPa, the system energy loss is small, the excavator can save fuel.
(2) Disadvantages
The higher manufacturing cost of the positive flow system requires an additional large number of proportional solenoid valves, sensors, logic valves consisting of shuttle valves, and a central control module that can be optimally controlled, thereby increasing manufacturing costs.
Higher technical difficulty The positive flow control system solves problems such as control accuracy, reliability, work efficiency, and operator's hand touch. Therefore, its technical difficulty is high, and some manufacturers cannot fully grasp this technology.
