Analysis and judgment of braking failure of the ho

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Analysis and judgment of brake failure of wheel loaders

the foot braking system of domestic wheel loaders mostly adopts pneumatic hydraulic linkage mechanism and disc brake. The common fault in use is brake failure. The system diagram is shown in Figure 1

1 fault analysis

before analyzing and judging the fault, the appearance inspection should be done first. On the premise of ensuring that there is no damage to parts, air and oil leakage in the pipeline, and that the brake fluid in the oil storage chamber of the afterburner is sufficient, the analysis should be carried out according to the following methods and processes:

first observe the reading of the barometer. On the premise that the barometer is normal, if the reading is normal (generally 0.65~0.8mpa), According to figure 1, it can be judged that the air compressor to the air reservoir is basically normal, and the fault is between the foot brake valve and the foot brake. If the reading is abnormal (lower than 0.4MPa), the fault is between the air compressor and the air reservoir

1.1 the reading of the barometer is too low

the air compressor to the air reservoir mainly includes the air compressor, oil-water separator, pressure regulator, one-way valve, air reservoir and pipes. On the basis of appearance inspection, according to the structure and working principle of the above parts, it can be judged that most of the fault parts are air compressors and pressure regulators

the pressure regulator is a spring diaphragm pressure regulating type, which is mainly composed of one-way valve, pressure regulating valve and exhaust valve. The one-way valve is used to prevent the compressed air from flowing back from the air reservoir to the air compressor. The pressure regulating valve is used to discharge the compressed air produced by the air compressor into the atmosphere when the air pressure in the air reservoir rises to the set pressure value. The common faults are that the pressure regulating valve is loose and the exhaust valve is stuck in the position of exhausting to the atmosphere due to the rust of the valve stem. Judge the time line and check whether the pressure regulating screw 2 is the lifting and life-saving technology and the safe return technology is loose. If it is not loose, feel whether there is air flow pulsation at the exhaust port of the pressure regulator by hand. If there is pulsation, as an emergency treatment, tap the end of the exhaust valve with the wooden handle of the screwdriver. If the air flow pulsation disappears, it indicates that the valve rod of the exhaust valve has returned. If it still doesn't work, disassemble the pressure regulator, clean it and then reinstall it. Since the pressure regulating valve adopts a metal diaphragm and is sealed with paper gaskets at the top and bottom, the failure rate of this part is very low

the air compressor is of piston type. According to practical experience, if the pressure regulator has no fault, it is often because the valve of the air compressor is not tightly closed and the air production is small, resulting in low braking air pressure. The reason why the valve is not closed tightly is that the valve spring has just fallen after thermal annealing or the two box and three box valves are dirty respectively. The fault can be eliminated by replacing the spring or cleaning

1.2 the reading of the barometer is normal

the distance from the foot brake valve to the brake mainly includes the foot brake valve, booster and foot brake. It can be checked and judged step by step from the sequence of gas-liquid transmission

1.2.1 inspection and judgment of foot brake valve

common faults of foot brake valve are diaphragm damage and rusty piston. You can judge the fault position by stepping on and listening to the exhaust sound when the foot brake valve returns. If it is hard to step down or the pedal return is not flexible, the fault reason is that the foot brake valve piston is rusty and astringent. After removal and cleaning, apply a little oil on the periphery of the piston. If you hear the exhaust sound of the foot brake valve when you press the pedal, and the exhaust sound is very small when you release the pedal, the cause of the fault is the diaphragm damage

1.2.2 inspection and judgment of the booster

the booster (also known as the gas-liquid master pump) is a component that converts the pneumatic braking force into the hydraulic braking force and increases the force. It is composed of an oil chamber, a gas piston and an oil piston. The common faults are that the gas piston is stuck and the sealing cup of the oil piston is damaged. The inspection and judgment methods are as follows: loosen the connector of the booster gas outlet pipe (do not need to remove it), step on the brake pedal, and observe whether there is brake fluid ejection and how the ejected pressure is. If there is no brake fluid outflow or the single pressure of oil brake fluid outflow is very low (the ejected brake fluid does not form fog), the booster needs to be removed for maintenance. The main parts of maintenance are the sealing cups of gas piston and oil piston. When reassembling parts, especially the production of after-sales double excellence is what we pay more attention to now. We should pay attention to the opening of the sealing cup in front of the oil piston facing the front (the direction of oil flow). After reassembly, the air in the brake oil circuit must be eliminated, and the methods are as follows:

① remove the sludge and dirt in the oil circuit system pipeline, oil storage chamber, oil filler and air vent

② add enough brake fluid as required

③ start the engine and stop or idle when the air pressure reaches the specified value

④ put the vent nozzle on a transparent plastic tube, and put the other end of the tube into the oil container

⑤ step on the brake pedal several times continuously, then step on the brake pedal tightly, loosen the bleeder nozzle on the upper part of the brake clamp for bleeding (pay attention not to loosen the bleeder nozzle on the lower part). When no oil continues to replace 50% of the packaging materials, tighten the bleeder nozzle first, and then loosen the brake pedal. Repeat this until the bubble free liquid column is eliminated, tighten the bleeder nozzle, and then loosen the brake pedal. After an interval of 10~15s, deflate the other brake caliper after the air pressure rises until all clamps are deflated

pay attention to replenish the brake fluid to the oil chamber of the afterburner in time when bleeding, so as to prevent the brake fluid in the oil piston of the afterburner from being sucked empty, otherwise the air will enter the system again

1.2.3 inspection and judgment of brake

the brake is a caliper disc, its brake clearance cannot be adjusted, and the clearance is automatically compensated after the friction plate is worn. The common faults are oil leakage and rust failure of the brake wheel cylinder. Whether there is oil leakage can be judged by observing whether there is oil stain near the brake caliper. The main reason for oil leakage is that the rectangular seal ring of the slave pump is not tightly sealed due to damage or aging. If the slave cylinder leaks oil, the brake system will also enter air. After the overhaul, the air in the oil circuit should be removed according to the above methods. The rust death of the brake wheel cylinder often occurs after the machine is not used for a long time, exposed in the atmosphere and exposed to wind and rain. The fault can be comprehensively judged and eliminated in combination with the actual situation and the inspection of foot brake valve and booster

2 maintenance

in order to ensure that the braking system is always in good working condition, the following inspection and maintenance matters should be paid attention to in use:

(1) regularly check the connection and fastening of each part of the brake

(2) regularly check whether there is leakage in the brake master cylinder, slave cylinder and pipeline. If there is any leakage, it should be eliminated in time. If there is oil on the friction plate, it should be cleaned in time

(3) the caliper disc brake should be cleaned of oil dirt after daily work because the brake disc is exposed again

(4) check the working condition of the brake pedal, whether it is stuck when pressing the brake pedal, and whether it can return quickly when loosening

(5) check whether there is air in the hydraulic system. If there is air, press the pedal to feel soft and weak, and the braking effect is reduced

(6) if necessary, check the amount of brake fluid in the brake master cylinder. The level of brake fluid should be 15~20mm away from the edge of the filler

(7) when the oil-water separator is not working for 50h, it needs to drain water once, and it needs to drain water every day in winter

(8) the air reservoir needs to drain water every 250h

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