Working principle of hydraulic lifting system of dump truck

Hydraulic axle modular trailer system working principle

1. The normal driving state of the car:

At this time, the power take-off (PTO) control valve is in the right position, the power take-off is not connected, the gear pump does not work, and there is no oil flow in the system. The lift cylinder is in the lowest position.

2. The power take-off is connected, and the lift pump works:

When we want to lift the body, we should first combine the power take-off with the lift oil pump. At this time, the power take-off control valve is energized, the spool is moved to the left, and the power take-off control air circuit is connected to connect the power take-off with the lifter. The lift pump shaft is engaged.

The power of the engine is transmitted to the power take-off and the lift oil pump through the gearbox, and the oil pump is rotated at a high speed to generate high-pressure oil. Since the lift valve is in the middle position at this time, the high-pressure oil flows back through the oil passage inside the lift valve. into the fuel tank and filtered through the return oil filter.

3. Lifting state:

When lifting the body, we need to turn the air control valve to the left to the lifting position, connect the system air pressure and the air control valve lifting channel, and the system air pressure flows through the air control valve through the limit valve from the lifting interface into the lift valve.

Act on the cylinder piston, push the piston to the left, and drive the spool to move to the left, connect the oil pump interface with the lifting cylinder interface, and the high-pressure oil enters the cylinder and lifts the cylinder; if the lifting pressure is too large , the bypass relief valve will be opened to prevent the gear pump and pipeline from being damaged due to continuous pressure rise.

4. Falling state:

When the body needs to be lowered, we need to turn the air control valve to the right to the descending position, connect the system air pressure and the air control valve descending channel, and the system air pressure enters the lift valve from the descending interface through the air control valve.

Act on the piston, push the piston to move to the right, and drive the spool to move to the right, connect the lift cylinder interface with the oil return interface, and the high-pressure oil in the cylinder flows back to the oil tank and passes through the oil return filter. filter.

5. Stop status:

Whether we are lifting or descending, we can stop the movement of the cylinder at any time. As long as we turn the air control valve to the stop position.

The compressed air acting on the piston in the lift valve will be discharged from the exhaust port of the air control valve, and then the valve core will return to the middle position under the action of the spring force, cutting off the connection between the oil cylinder interface and other interfaces, and the When the high-pressure oil stops flowing in or out, the cylinder piston is in a stationary state, the so-called intermediate stop state.

6. Limit state:

When the lift cylinder rises to the set lift height, it will touch the limit valve, move the spool of the limit valve to the left, cut off the air path between the system air pressure and the lift valve, and make it act on The compressed air on the piston is exhausted from the exhaust port of the limit valve.

In this way, the valve core will return to the middle position under the action of the spring force, cut off the connection between the lifting cylinder interface and the oil pump interface, and the cylinder will stop rising.

Common fault diagnosis and elimination of hydraulic axles modular trailer lifting system

1. The car can not afford:

The bucket can not afford to be the most common fault in use. We generally follow the three steps of electricity-gas-oil when judging the fault.

Let's talk about electricity first. The power take-off of this system is air-controlled, and an electromagnetic air-controlled valve provides the air source for the power take-off. We can press the power take-off switch in the parking state. If we can hear the "click" action sound of the solenoid valve, and there is a "pop" exhaust sound, it means that the electronic control system is normal.

If you can't hear the above sound, it can basically be judged as an electrical fault. Common faults include blown fuse, short circuit of solenoid valve coil, stuck solenoid valve, etc. The specific maintenance line needs to be checked in detail.

Let's talk about anger. The action energy controlled by this system is provided by compressed air. Under normal circumstances, when the handle on the air control valve is turned to different positions, there will be a "pop" exhaust sound at the exhaust port.

If there is no such sound, we first remove the air inlet of the air control valve and check whether the air pressure of the system is sufficient. If there is no pressure or insufficient pressure, we need to repair the air circuit of the system. The most common fault is that the air pipe is pressed by other components. Dead or frozen in winter.

After the system air pressure fault is eliminated, we remove the air pipe of the lift interface of the air control valve, and then turn the handle to the lifting position to check whether the air is out of the interface. If there is air pressure, it is normal. If there is no air pressure, it means the air control Valve failure. This air control valve can generally only be replaced and cannot be repaired.

Then we will check whether the limit valve is normal. Turn the handle of the air control valve to the lifted position, remove the two air pipe joints of the limit valve respectively, and check whether there is air flow out.

If there is air pressure, it is normal; if there is no air pressure, it means that the limit valve is stuck in the cut-off position. In actual use, the limit valve is rarely damaged, and is generally stuck by rust. Generally, spray a little screw loosening agent on the valve core, which can basically solve the problem.

Finally, we remove the air pipe of the lift port on the lift valve to see if the air pipe is under pressure. If there is pressure, it means that the air circuit is normal, and the fault lies in other parts. If there is no air pressure in the air pipe, it means that this air circuit is blocked and needs to be disassembled and checked.

If there is no problem with the above parts, then the fault may appear in the oil circuit. We first connect the pressure gauge to the pressure measuring hole of the lift valve, then start the engine and combine the power take-off, the pressure of the system should be above 1.8Mpa.

If it is lower than this pressure, it means that the hydraulic oil circuit is faulty. Generally, check whether there is enough hydraulic oil in the oil tank, whether the ball valve is open, whether the low-pressure oil pipe is bent, whether the gear pump is damaged, etc.

If the pressure of the system is normal and the lift cylinder still cannot be lifted, then the fault should be in the lift valve, for example, the valve core is stuck, the opening pressure of the relief valve is too low, the cylinder blows gas, etc., and the lift valve needs to be disassembled and repaired. .

2. The car body does not fall:

The failure of the bucket not falling is generally caused by the air control system, such as damage to the air control valve, blockage or bending of the air pipe, air blow-by of the lift valve cylinder, etc. It is extremely rare that the bucket does not fall due to mechanical failure, such as lifting The cylinder is bent, the lift valve spool is stuck, etc.

3. The lift cylinder rises slowly:

This situation is generally caused by factors such as air leakage or bending of the air pipe, insufficient pressure of the gear pump, and blow-by of the lift valve cylinder.

4. Vibration during the ascent of the lift cylinder:

In most cases, the jitter when the oil cylinder rises is caused by insufficient hydraulic oil. If the gear pump is damaged or the power take-off is damaged and the power transmission is interrupted, this kind of fault will also cause this fault, but it is relatively rare.

5. The lift cylinder descends slowly:

The slow descent of the oil cylinder is generally caused by air leakage or bending of the trachea. After eliminating this factor, we can also adjust the descending speed control valve on the lift valve. This is a hexagonal screw, and screw it inward. To speed up, screw it out to slow down the descent.

6. The lifting cylinder automatically falls:

The automatic falling of the oil cylinder is a very dangerous fault, which seriously threatens the safety of driving and maintenance, and requires us to attach great importance to it. This fault is generally caused by factors such as internal leakage of the lift valve, blow-by gas in the lift valve cylinder, failure of the air control valve, and serious oil leakage from the cylinder.

7. Oil leakage from the upper part of the hydraulic oil tank:

If there is often oil splashing on the upper part of the hydraulic oil tank, we must first check whether the oil return filter element is blocked. If the oil return filter element is seriously blocked, the high-pressure oil of the system will burst and crack the shell of the return oil filter element when it returns to the oil tank. The hydraulic oil will not return to the bottom of the oil tank but splash directly on the upper part, which will cause part of the oil to spray. splashed outside the fuel tank.

In this case, we need to replace the oil return filter element assembly, and install the oil return pipe firmly, so that the hydraulic oil can return directly to the bottom of the oil tank.

8. Oil leakage at each joint of the system:

There are gaskets at the joints of each pipe head of the hydraulic system. These gaskets are disposable and must be replaced after re-installation. When installing, ensure that the sealing surface is clean and flat, without impurities or pits, etc., and tighten it according to the specified torque.

9. Oil leakage of air control valve:

Under normal circumstances, compressed air flows in the air control valve, and there is no oil. However, some vehicles may experience oil leakage from the air control valve during use. After careful inspection and analysis, it was found that it was caused by excessive wear of the lift valve spool.

This is mainly because after the valve core is worn, some oil will enter the cylinder and then be discharged through the air control valve, so the air control valve appears oily.
After discovering this law, the oil leakage of the air control valve has become an important basis for us to judge the wear of the lift valve.