Created on:2021-09-06 10:32

Construction machinery_ Hydraulic system principle of D375A-2 bulldozer working mechanism

Construction machinery_ Hydraulic system principle of D375A-2 bulldozer working mechanism

D375A-2 bulldozer is a large bulldozer successively introduced by a company from Komatsu company of Japan since 1991. Its engine power is 525 HP and the vehicle design is advanced. It represents the development achievements of international construction machinery in the 1990s. As the main equipment of the company, it undertakes the daily production of mining area, the implementation of key projects, the expansion of projects, etc. its quality is good or bad, It is related to the completion of the task of 63 million tons of annual mining and stripping. After more than ten years of use of the machine, many stubborn diseases have appeared in the hydraulic system, such as too fast and too high oil temperature rise, slow or even no lifting of the blade, which seriously affects the working efficiency of the equipment and makes the system invalid due to long-term high temperature. Through years of hard research, these problems have finally been solved.

Working mechanism hydraulic system principle

The hydraulic system principle of D375A-2 bulldozer working mechanism is shown in Figure P.

P.jpg

① The hydraulic system of the working mechanism consists of two hydraulic pumps. The theoretical displacement of the large pump is 2731l / min, the theoretical displacement of the small pump is 1321l / min, and the maximum working pressure in the working system is 21MPa. The system consists of four valve blocks, and each valve block contains several valves, which are composed as follows.

a. The blade lifting valve block is composed of blade lifting valve, main valve, shuttle valve, etc.

b. The main overflow valve block (Figure q) is composed of slide valve, main overflow valve and throttle valve.

Q.jpg

c. The scarifier low pressure valve block is composed of overflow valve, blade tilt control valve, scarifier tilt control valve, scarifier lift control valve, shuttle valve, etc.

d. The high-pressure valve block of the scarifier is composed of the scarifier tilt control valve, the scarifier lift control valve, etc. There is also a pair of piston valves on the piston of the blade lift hydraulic cylinder (Figure R).

The actuating elements of the hydraulic system are hydraulic cylinders, which are blade lifting hydraulic cylinders (2), blade tilt hydraulic cylinders (1), Ripper lifting hydraulic cylinders (2) and Ripper tilt hydraulic cylinders (2).

② The functions of each valve are shown in Figure P. blade lifting valve 3 is a manual valve that controls the flow direction of oil to realize the telescopic movement of piston rod in lifting cylinder. Flow control valve 4 is a hydraulic control valve that controls the amount of oil to blade lift hydraulic cylinder, Ripper lift hydraulic cylinder and Ripper tilt hydraulic cylinder. When the hydraulic cylinder needs to move slowly, flow control valve 4 allows more oil to flow back to the oil tank; When the hydraulic cylinder needs to move quickly, flow control valve 4 allows more oil to flow to the hydraulic cylinder. Spool 7 is a hydraulic control valve that controls the control oil of flow control valve 4 so that the control oil of flow control valve 4 is either feedback oil from shuttle valve 19 or feedback oil from shuttle valve 20. Main relief valve 5 controls the maximum pressure of the control oil of flow control valve 4. Blade tilt control valve 15 is a manual valve that controls the flow direction of oil to realize the telescopic movement of the piston rod in the blade tilt hydraulic cylinder. Scarifier tilt control valve 16 is a manual valve, which controls the flow direction of oil to realize the movement of scarifier tilt control valve; Ripper lifting control valve 17 is a manual valve, which controls the flow direction of oil to realize the movement of Ripper lifting control valve. The Ripper lifting valve 13 is a hydraulic control valve, which controls the flow direction of the oil to realize the telescopic movement of the piston rod in the Ripper lifting hydraulic cylinder; The scarifier tilt valve 14 is a hydraulic control valve that controls the flow direction of oil to realize the telescopic movement of the piston rod in the scarifier tilt hydraulic cylinder. There is also a piston valve in the blade lifting cylinder, which can drain the oil of the hydraulic pump when the piston reaches the end of the stroke, so as to reduce the oil pressure and oil pressure impact. Throttle valve 6 is actually a very narrow oil passage, which makes the pressure difference when the oil flows through it, so as to make the pressure at both ends of the valve core of flow control valve 4 unequal, generate thrust, make the end core move, and the oil pressure here is directly proportional to the flow.

③ Oil flow

a. There are two load feedback oil circuits. The feedback oil circuit works through shuttle valve 19, slide valve 7 and throttle valve 6 to the left side of flow control valve 4 to control the lifting speed of the blade; The feedback oil circuit II reaches the left side of flow control valve 4 through shuttle valve 20, slide valve 7 and throttle valve 6 to control the lifting (tilting) speed of Ripper.

b. The flow of oil to the blade lift hydraulic cylinder. The oil from the hydraulic pump passes through flow control valve 4 to blade lift valve 3. Blade lift valve 3 opens and the oil enters the blade lift hydraulic cylinder. If the blade lifting valve 3 is fully opened and the pressure loss is the smallest, the flow of feedback oil flowing through shuttle valve 19 is the largest. After flowing through throttle valve 6, the flow is also the largest and the pressure is also the largest, so that the left oil pressure of the control oil of flow control valve 4 is equal to the right oil pressure, the valve core does not move, flow control valve 4 allows more oil to flow to the hydraulic cylinder, and the hydraulic cylinder realizes rapid movement.

c. The flow of oil to the blade tilt hydraulic cylinder. The oil from the hydraulic pump passes through blade tilt control valve 15. When the valve opens, the oil enters the blade tilt hydraulic cylinder.

d. The flow of oil to the Ripper lift cylinder. The oil of the hydraulic pump reaches both ends of the lifting valve 13 through the Ripper lifting control valve 17, pushes the valve core to open the lifting valve 13 and enters the Ripper lifting hydraulic cylinder. If the Ripper lifting control valve 17 is fully opened and the pressure loss is the smallest, the flow of feedback oil flowing through shuttle valve 20 is the largest, and the flow and pressure are the largest after flowing through throttle valve 6, so that the left oil pressure of the control oil of flow control valve 4 is equal to the right oil pressure, the valve core does not move, flow control valve 4 allows more oil to flow to the hydraulic cylinder, and the hydraulic cylinder realizes rapid movement.

e. The flow of oil to the Ripper tilt cylinder. The oil from the hydraulic pump passes through the scarifier tilt control valve 16 to both ends of the tilt valve 14, pushes the valve core to open the tilt valve 14 and enters the scarifier lifting hydraulic cylinder. If the scarifier tilt control valve 16 is fully opened and the pressure loss is the smallest, the flow of feedback oil flowing through shuttle valve 20 is the largest, and the flow and pressure are the largest after flowing through throttle valve 6, so that the left oil pressure of the control oil of flow control valve 4 is equal to the right oil pressure, the valve core does not move, flow control valve 4 allows more oil to flow to the hydraulic cylinder, and the hydraulic cylinder realizes rapid movement.

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