Electro hydraulic proportional control system for

2022-08-22
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The "ZL50G robotic loader" project of the national "863" plan jointly undertaken by XCMG group and Jilin University of technology has passed the acceptance organized by the Ministry of science and technology. The main technical achievement of the project "working device electro-hydraulic proportional control system" adopts the pulse width modulation electro-hydraulic proportional control module with independent intellectual property rights, and realizes the electro-hydraulic proportional control of the loader working device through computer control technology, which greatly improves the control performance of the loader, reduces the labor intensity of the operator, and has the international advanced level

1 requirements of the working device control system

the working device of the loader uses the hydraulic system to control the expansion and contraction of the boom and bucket hydraulic cylinder, and realizes digging, loading and other operations through the actuator. The design of the hydraulic system is the key of the whole system. A good hydraulic system must meet the following requirements: safe and reliable work, flexible operation, small operating force and stable operation

the development of the hydraulic control system of the working device of the loader has mainly gone through three stages. 1. Precautions for the use of the mortar tensile testing machine: the change-over valve spool is directly controlled manually by the joystick, and the main change-over valve is hydraulically controlled by the manual pilot proportional reducing valve. Later, it has developed into the current advanced electro-hydraulic proportional control technology under the control of the computer, and its control performance and degree of automation are gradually improved

2 main functions and technical parameters

this system mainly generates digital electrical signals by operating the control handle to control the output pressure of the electro-hydraulic proportional pilot valve, so as to control the position of the spool of the main reversing valve and realize the control of the working speed of the working hydraulic cylinder. Because the computer control module can realize the electronic positioning of the working device, and has the logic control functions of memory, automatic return and automatic leveling, the loader has certain characteristics of "intelligent robot", which reduces the physical labor of the operator and improves the reliability and maneuverability of the whole machine during operation

the main control process is shown in Figure 1

Figure 1 control flow chart of boom and bucket hydraulic cylinder

main technical parameters:

control handle angle (.) ± 30

control handle operating force (n) <3

control handle output pulse frequency (kHz)

control handle output pulse duty cycle (%) 10 ~ 90

control module output pulse duty cycle (%) 20 ~ 80

system pressure (MPA) 16

pilot control system pressure (MPA) 3. O

pilot control system input flow (lmin) 30

control system voltage (V) DC 24

maximum current of electrohydraulic proportional pilot valve(MA) 800

3 system composition and working principle

3.1 system composition

the basic composition of the electro-hydraulic proportional control system of the working device is shown in Figure 2, and the hydraulic system is shown in Figure 3

Figure 2 composition of the system

Figure 3 Schematic diagram of hydraulic system of working device

the main components of the system include: electric control operating handle, computer control module, electro-hydraulic proportional pilot valve, main reversing valve, hydraulic pump and working hydraulic cylinder

3.2 working principle of hydraulic system

working device the electro-hydraulic proportional control system is supplied by two hydraulic pumps, and the main pump is cbaa2100, which is used to control the movement of boom and bucket hydraulic cylinders; The pilot pump is cbaa0016, which is used to control the electro-hydraulic proportional pilot valve, and then control the displacement of the main reversing spool, so as to control the working speed of the boom and bucket hydraulic cylinders. The oil of the pilot pump is first reduced to the control pressure required by the pilot control system through the pressure reducing valve, and then enters the safety locking valve of the control oil circuit. The safety locking valve is set to prevent misoperation. It is a two position two solenoid directional valve created by polar racing. When the operator places the control switch in the "off" position, the electromagnet is in the power-off state. At this time, any operation of the operating handle will not make the working device act. When the control switch is placed in the "on" position, control the oil to enter the electrohydraulic proportional pilot valve, and control the electrohydraulic proportional pilot valve through the operating handle to complete the action of the working device

3.2.1 boom rise

pull the operating handle to move backward. At this time, the electrical signal output by the position sensor of the handle enters the proportional electromagnet of the electrohydraulic proportional pilot pressure reducing valve. The pressure signal output by the pilot pressure reducing valve is proportional to the input electrical signal, that is, the greater the angle of the handle, the greater the output electrical signal. The greater the output pressure of the electro-hydraulic proportional pilot pressure reducing valve, the greater the displacement of the control main reversing valve spool, the greater the flow through the main reversing valve, and the faster the boom rises. When the operating handle is pulled to the limit position, the limit electromagnet in the handle is energized, the handle is pulled in at the limit position, and the boom rises at the maximum speed. When it rises to the position limited by the upper limit switch of the boom, the computer control module controls the limit electromagnet of the operating handle to cut off power, the handle automatically returns to the middle position, and the boom can be maintained at the limited position. In the process of boom rising, if the boom needs to stop at a certain position, it is necessary to return the joystick to the middle position

3.2.2 boom lowering

the joystick moves forward. At this time, the position sensor in the joystick sends out a control signal opposite to that when the boom rises, and the proportional electromagnet that controls the boom lowering works. The electro-hydraulic proportional reducing valve outputs the corresponding control pressure to control the downward movement of the main reversing valve core and the boom lowering. When the operating handle is pushed to the limit position, the limit electromagnet in the handle is energized, the handle is pulled in at the limit position, and the boom drops at the maximum speed. When the boom drops to the position limited by the limit sensor, the computer control module controls the electromagnet of the handle to power off, and the handle returns to the middle position. At this time, the boom stops at the limited position. If you need to stop at any position during this process, pull the handle back to the middle position

3.2.3 boom floating

push the handle to the boom floating working condition. At this time, the handle position sensor sends a floating working signal to the controller. The controller places the electro-hydraulic proportional pilot reducing valve in the maximum pressure output state, and the output pressure controls the two position three-way valve in the pilot valve group in the lower working condition. The hydraulic control check valve in the main valve is in the reverse conduction condition. The upper and lower chambers of the boom hydraulic cylinder are connected through the one-way valve, and the boom is in the floating working condition at this time. When the floating work stops, pull the handle to the middle position and the floating work ends

3.2.4 bucket loading

pull the bucket control handle backward, and the position sensor in the handle outputs an electrical signal that is proportional to it through the control module to control the electro-hydraulic proportional pilot valve, so as to control the bucket control valve in the main reversing valve, make the bucket hydraulic cylinder move, and complete the loading action. When the handle is pulled to the maximum position, the limit electromagnetic iron in the handle is energized, the handle is sucked in when it is at the limit position, and the bucket flips upward at the maximum speed. When turning to the maximum position, the limit sensor sends a signal, the computer control module controls the limit electromagnet of the handle to cut off power, and the handle automatically returns to the middle position. At this time, the bucket stops at the limit position. Similarly, the driver can also manually control the handle to return to the middle position to make the bucket stay at any position

3.2.5 bucket unloading

pull the bucket control handle in the opposite direction, and its control process is as described above

3.3 working principle of electric control system

3.3.1 control handle

working device control handle is the input signal in the system. With the change of handle position, the corresponding electrical signal is output. The computer control module amplifies the signal and drives the corresponding proportional electromagnet, so as to control the electro-hydraulic proportional reducing valve to output the corresponding control pressure and control the displacement of the valve core of the main reversing valve

3.3.2 computer control module

the main functions of the computer control module are: to receive and control the electrical signals input by the handle, to control the action of the boom and bucket s, to receive the boom and bucket limit input signals, and to set the ideal position of the boom and bucket; Control the locking electromagnet of the working device and the electromagnet of the limit position of the handle; Data exchange with the central electronic control module is used to diagnose the fault of the control system of the working device. The control relationship of the electric control system is shown in Figure 4

Figure 4 control relationship of the electric control system

the electric control system of the working device is composed of the position sensor of the operating handle of the working device, the boom position sensor, the control switch, the travel switch, the locking electromagnet, the proportional electromagnet of the electrohydraulic pilot valve and the controller of the working device. The controller receives and outputs signals through cables, and exchanges data with monitoring system and driving system through communication lines

3.3.2.1 input signal

(a) boom command position sensor: installed on the boom operating handle, the electrical signal it sends represents the position of the shuffle weighting handle in the battery industry. The controller interprets the signal as the command signal of the boom movement direction and speed

(b) bucket command position sensor: installed on the bucket operating handle, its electrical signal represents the position 1 of the handle and the host position. The controller interprets the signal as a command signal for the direction and speed of bucket movement

(c) safety locking switch of working device: it is a two position switch, and the two positions represent that the working device is locked and unlocked respectively, which is selected by the driver. When the switch is in the locked position, the joystick and hydraulic valve do not work

(d) bucket positioning switch: indicates the preset bucket digging angle

(E) boom positioning setting switch: it is an automatic reset switch. When the boom position sensor continuously measures the position of the boom, this switch can be used to set the upper limit position of the boom at any position above the boom middle position, and the lower limit position of the boom can also be set at any position below the boom middle position. These two positions are used in automatic positioning control

(f) boom floating command switch: sends boom floating command signal, which is interlocked with the maximum forward position of boom operating handle

3.3.2.2 output signal

(a) control the bucket loading electro-hydraulic proportional electromagnet: control the bucket to flip backward

(b) control the bucket unloading electro-hydraulic proportional electromagnet: control the bucket to flip forward

(c) control boom rising electro-hydraulic proportional electromagnet: control boom rising

(d) control boom lowering electro-hydraulic proportional electromagnet: control boom lowering

(E) boom handle front locking electromagnet: when the boom handle is pushed forward to the maximum position, the solenoid coil generates electromagnetic force through current to keep the handle in the maximum forward position. At this time, the boom drops continuously. When the preset lower limit position is reached, the signal is automatically cut off and the handle automatically returns to the middle position

(f) boom handle rear position locking electromagnet: when the boom operating handle is pulled backward to the maximum position, the electromagnetic coil generates electromagnetic force through current to keep the handle in the maximum position backward. At this time, the boom rises continuously. When the preset upper limit position is reached, the signal is automatically cut off and the handle automatically returns to the middle position

(g) bucket handle rear position locking electromagnet: when the bucket operating handle is pulled backward to the maximum position, the electromagnetic coil generates electromagnetic force through current to keep the handle in the rear maximum position. At this time, the bucket flips backward continuously. When the preset digging angle is reached, the signal is automatically cut off and the handle automatically returns to the middle position

3.3.2.3 input and output data

through the data communication line, the working device control system and monitoring system and the transmission control system

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