The hydraulic servo system of dump truck consists of three parts: power part and executive part (lifting hydraulic cylinder). The power part mainly includes the hydraulic pump and the transmission machine connecting the two<br>Construction. The control part is used to control the lifting hydraulic cylinder to realize the car roll. It has three actions: lifting, holding and lowering. The working principle is as follows:<br>1) Lifting<br>When the reversing valve 6 is in the middle position, the reversing valve is normally closed and the hydraulic cylinder is in the contraction state. When the dump truck tilts, first drive the hydraulic pump 9, and then the pressure oil of the hydraulic pump passes through the<br>Check valve 2, oil filter 3, change-over valve 6, return to the oil tank, the carriage does not move, it is the idle start of the hydraulic pump. If the right solenoid coil of the solenoid valve is energized, the pressure oil output by the hydraulic pump will be<br>Direction valve 2, four-way valve 6, bridge two-way synchronous valve 8, enter hydraulic cylinder 9, jack up the car and tilt the goods. If the system pressure exceeds a certain value during lifting, safety valve 5 will be hit<br>Open and overflow to keep the hydraulic system pressure below the regulated pressure. When the car is tilted to the limit position, the lifting cylinder will touch the limit switch, which will cause the electromagnetic coil to lose power and the output of the hydraulic pump<br>The ground pressure oil flows back to the oil tank 4 through the four-way valve 6, and the position with the largest lifting angle at the lifting mechanism.<br>Twenty-four<br>2) Descent<br>When the cargo is poured out, the carriage needs to be lowered. First, turn off the hydraulic pump to power on the left solenoid coil of solenoid reversing valve 6. The control oil of the reversing valve is discharged to the main oil tank. The lifting cylinder is operated by gravity in the carriage<br>Use it to lower and return the car.<br>3.4 selection of operation mode of hydraulic lifting mechanism<br>(1) Mechanically operated<br>The mechanical control type has the advantages of good reliability, strong universality and convenient maintenance, but it has many members and complicated arrangement. This kind of operation mode is not suitable for the reversible cab.<br>(2) Hydraulically operated<br>Depending on the oil pressure established by the manual valve to close or open the lifting direction control valve, the lifting and lowering of the car can be realized, and the valve can stop working by cutting off the power. It's easy to control remotely<br>The control and operation are reliable, but the response is slow.<br>(3) Pneumatically operated<br>Depending on the compressed air in the air tank of the car, the pneumatic hydraulic reversing valve is operated by controlling the air valve, and the direction of the oil circuit is controlled to realize the lifting, lowering and middle stop of the car. The system is easy to operate and work<br>It is suitable for medium and heavy dump trucks because of its complete structure and advanced structure.<br>Because the operation of dump truck is not frequent and the sequence of action is random, it belongs to engineering operation, and it is often controlled by manual multiple directional valve. If the control force is large, manual servo control can be used. according to<br>Characteristics of dump truck, the dump truck adopts manual hydraulic servo control<br>After the operation mode is selected, the appropriate hydraulic directional control valve can be selected, which is usually a three position four-way valve. The valve selection is based on the rated working pressure and flow of the hydraulic system<br>It shall adapt to the selected operation mode.<br>
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