Troubleshooting of the hydraulic steering system of ZL40B loader

Abstract

Based on the discussion of the working principle of the hydraulic steering system of the loader, the performance detection and adjustment of the system as well as the troubleshooting are proposed.

Key words

Troubleshooting the working principle of the loader steering system

The ZL40B loader produced by Liuzhou Construction Machinery Co., Ltd. is a new generation of loader imitating the American Caterpillar. Its hydraulic steering system adopts a flow amplification system, which is composed of a pilot oil circuit and a main oil circuit. The so-called "flow amplification" refers to the fact that through the fully hydraulic steering gear and flow amplification valve, the flow variation in the pilot oil circuit can be ensured to have a certain proportion with the flow variation entering the steering cylinder in the main oil circuit, achieving the purpose of controlling high pressure and large flow with low pressure and small flow, ensuring smooth and easy operation for the driver, full utilization of system power, and significantly improved reliability.

1 Working Principle

As shown in the figure, in the steering hydraulic system, the oil is diverted from the main oil circuit and then depressified through the pressure reducing valve 6 to serve as the power source for the pilot oil circuit, ensuring that the oil pressure in the pilot oil circuit does not exceed 2.5Mpa.

Hydraulic principle of steering system

1. Steering cylinder 2. Flow amplification valve 3. Oil filter 4. Radiator 5. Steering pump (BG2080) 6. Pressure reducing valve 7. Fully hydraulic steering gear

When the steering wheel is not turned, the two oil outlets of the steering gear 7 are closed, and the main valve stem of the flow amplification valve 2 remains in the neutral position under the action of the reset spring. The oil passage between the steering pump 5 and the steering cylinder 1 is cut off, and the main oil passage is unloaded back to the oil tank through the flow amplification valve. When the steering wheel is turned, the oil discharged by the steering gear 7 is directly proportional to the rotation Angle of the steering wheel. The pilot oil enters the flow amplification valve to work, controlling the displacement of the main valve stem through the metering small hole on the main valve stem, that is, controlling the size of the opening, thereby controlling the flow volume entering the steering cylinder 1. Due to the pressure compensation adopted by the flow amplification valve 2, the pressure difference between the inlet and outlet is basically a constant value. Therefore, the flow entering the steering cylinder 1 is independent of the load and only related to the size of the opening on the main valve stem. After the steering stops, the oil pressure at one end of the main valve stem tends to balance. Under the action of the reset spring, the main valve stem returns to the middle position, thereby cutting off the main oil circuit to the cylinder.

2 System Adjustment

2.1 Steering time adjustment

Place the loader on a flat road surface and quickly turn in place without load. If the time difference between turning left and right exceeds 0.3 seconds, adjust it according to the following steps:

1) Remove the end cover of the flow amplification valve (there are three types of spring adjustment gaskets inside: 0.25mm, 0.12mm, and 1.2mm);

2) Adding adjustment gaskets can reduce the right turn time and increase the left turn time, while reducing the adjustment gaskets has the opposite result.

Adding or removing two 0.25mm adjusting gaskets can change the steering time by 0.1 seconds.

4) After adjustment, install the end cover.

If the entire steering time is slow, a 1.2mm adjustment gasket can be added following the same steps. Adding one adjustment gasket can reduce the steering time by 0.1S.

2.2 Safety valve Pressure adjustment

The steps for adjusting the pressure of the safety valve are as follows

1) Install the bumper to prevent the front and rear frames from rotating relatively.

2) Unscrew the plug of the flow amplification valve and install the pressure gauge (with a range of 25 mpa).

3) Start the engine and let it idle at high speed;

4) Turn the steering wheel until the safety valve opens. At this point, the pressure gauge should indicate 12± 0.3Mpa.

5) If the pressure is incorrect, the plug of the flow rate amplification valve can be unscrewed, and an adjusting gasket of 0.25mm can be added or removed. Adding one more gasket can increase the safety valve by 3.4pa.

After adjustment, remove the pressure gauge, screw on the plug and take off the safety rod.

3 Troubleshooting

3.1 The steering of the loader is difficult

1) Inspection. Is the oil temperature too low? Whether the pilot oil circuit is blocked; Whether the connection of the pilot oil circuit pipe is correct; Is the pressure of the steering pump too low? Check if the bolts of the full hydraulic steering metering motor are tightened too much.

2) Troubleshooting. Work after the hydraulic oil is heated up. Clean the pilot oil circuit and connect the pilot pipeline as specified. Adjust the pressure of the relief valve as required; Tighten the bolts of the hydraulic steering metering motor part according to the specified values.

3.1.1 It is difficult for the loader to rotate in the reverse direction.

1) Inspection. The spherical check valve in the shut-off valve is clogged.

2) Troubleshooting. Clean the shut-off valve.

3.1.2 The loader can still rotate in the direction behind its head

1) Inspection. Whether the position of the shut-off valve and the impact block is aligned; Is the spherical one-way valve in the shut-off valve malfunctioning? Check if there is a problem with the pilot oil circuit relief valve.

2) Troubleshooting. Adjust the position of the collision block; Inspect or replace the spherical check valve; Inspect and repair the pilot oil circuit relief valve.

3.2 The loader's steering is not smooth

1) Inspection. The flow control valve operates insensitively.

2) Therefore, it is excluded. Inspect or replace the flow control valve.

3.2.1 The loader turns slowly both left and right

1) Inspection. Whether the spring adjustment of the flow control valve is correct; Is the flow rate of the steering pump sufficient? Check whether the valve stem of the flow amplification valve has moved in place.

2) Troubleshooting. Adjust the gasket of the flow valve as per regulations. Inspect or replace the steering pump; Adjust the pressure of the pilot oil circuit or replace the spring of the pressure reducing valve.

3.2.2 The loader turns fast on one side and slow on the other

1) Inspection. The number of adjusting gaskets at both ends of the flow amplification valve is incorrect.

2) Troubleshooting. Adjust the flow amplification valve stem adjustment gasket as per the regulations.

3.2.3 When the steering resistance is low, the steering is normal; when the resistance is high, the steering is slow (the same for both left and right steering).

1) Inspection. Is the internal leakage of the main relief valve seat too large? Whether the internal leakage of the spherical judgment valve is too large; The clearance between the flow valve stem and the hole is too large.

2) Troubleshooting. Inspect and repair the valve seat or replace the sealing ring; Inspect and repair the spherical judgment valve or replace the sealing ring; Inspect or replace the flow control valve.

3.2.4 When the steering resistance is low, the steering is normal; when the resistance is high, one side is normal and the other side is slow

1) Inspection. One end of the spherical judgment valve has less internal leakage and the other end has more internal leakage.

2) Troubleshooting. Inspect or replace the spherical judgment valve, or replace the sealing ring.

3.3 When turning the direction, the loader does not turn

1) Inspection. Whether the flow control valve operates; The pilot relief valve is leaking oil. There is internal leakage in the main oil circuit relief valve.

2) Troubleshooting. Inspect or replace the flow control valve; Inspect and repair the pilot oil circuit relief valve; Inspect and repair the main oil circuit relief valve.

3.4 When the driver is not operating, the loader will turn by itself

1) Inspection. Whether the valve stem of the flow amplification valve returns to the middle position; Is the fixing screw of the flow amplification valve tightened too much? Is the screw on the end cover of the flow amplification valve too tight? Is the clearance between the valve stem and the hole of the flow amplification valve too large?

2) Troubleshooting. Inspect and repair the reset spring of the flow amplification valve. Loosen the fixing screws or end cover screws; Inspect or replace the valve stem.

3.5 When the driver is not operating, the steering wheel rotates by itself

1) Inspection. The valve sleeve of the fully hydraulic steering gear may get stuck. The spring plates of the fully hydraulic steering gear may break.

2) Troubleshooting. Clean the foreign objects inside the full hydraulic steering gear valve; Replace the spring plate.

3.6 The steering pump makes a lot of noise and the piston movement of the steering cylinder is slow

1) Inspection. There may be air in the steering oil circuit. Is the flow rate of the steering pump insufficient due to severe wear? The viscosity of the hydraulic oil might be incorrect. The hydraulic oil might be insufficient. Is the adjustment pressure of the main oil circuit overflow valve too low? Is the leakage in the steering cylinder too large?

2) Troubleshooting. Strengthen the sealing of the oil suction joint; Inspect or replace the steering pump; Replace the hydraulic oil as per regulations; Replenish the hydraulic oil as prescribed; Adjust the pressure of the relief valve as required; Inspect and repair the steering cylinder or replace the seals.