Created on:2021-10-19 10:25

Locomotive equipment_ Fault analysis and treatment of locomotive hydrostatic system

Locomotive equipment_ Fault analysis and treatment of locomotive hydrostatic system

(1) Cause analysis

① The temperature control valve fails. According to the working principle of the hydrostatic system, the temperature control valve plays a role in regulating the pressure oil flow to the hydrostatic motor in the hydrostatic system. When the temperature of diesel oil and water reaches a certain value, the thermostatic element in the temperature control valve acts to push the slide valve to gradually close the bypass oil circuit. In this way, the pressure oil flowing through the hydrostatic motor gradually increases, so that the motor gradually reaches full speed.

Failure of the temperature control valve will cause some or all of the hydrostatic oil to flow back to the oil tank from the bypass pipeline of the temperature control valve, resulting in the fan speed not reaching the specified value or the fan does not rotate. After analysis, the main causes of temperature control valve failure are as follows.

a. Improper fit clearance between the slide valve and the valve body or dirt makes the slide valve jam.

b. If the temperature sensing element fails, the push rod cannot act accordingly with the change of oil and water temperature.

c. The stroke of the slide valve fails to meet the specified requirements, and its maximum stroke is less than 7.5mm, resulting in that the slide valve cannot be fully closed at the maximum temperature of oil and water (water temperature 82 ℃± 2 ℃, oil temperature 65 ℃± 2 ℃).

d. The starting temperature of the temperature control valve is higher than the specified starting temperature, so that when the oil and water temperature is within a certain temperature value within the specified range, the fan speed can not reach the corresponding rated speed.

② Safety valve failure locomotive safety valve (see Figure b) is different from ordinary safety valve, and its opening pressure is not a fixed value. If the locomotive safety valve fails, its opening pressure will be lower than the working pressure of the high-pressure oil circuit, and the oil return channel should not be opened, so that the oil circuit cannot establish normal oil pressure, and the fan speed cannot reach its rated speed. The main reasons for its failure are as follows.

B.jpg

a. The opening pressure of the cone valve can be changed by adjusting the screw. If the adjustment is improper and the set opening pressure is lower than the normal working pressure in the high-pressure oil circuit, the cone valve is pushed away from the cone valve body, the oil pressure in chamber C decreases rapidly, and the slide valve overcomes its spring force to open chambers a and B under the action of high-pressure oil, resulting in the failure of the safety valve.

b. The cone valve is subject to the combined action of the spring restoring force of the cone valve, the spring restoring force of the shock absorber and the return oil pressure in the D cavity. These three forces must be overcome when it is pushed away from the valve body. The higher the speed of the diesel engine, the higher the oil pressure in the D chamber, the greater the force that the cone valve is pushed away from the cone valve body, and the opening pressure of the safety valve increases with the increase of the speed of the diesel engine. When the oil pipe breaks or the oil pipe joint leaks oil, the oil pressure cannot be established in chamber D. at this time, the opening pressure of the safety valve is much lower than the normal opening pressure, resulting in the failure of the safety valve.

c. After the inner hole of the damping plug is blocked by foreign matters, resulting in no oil in chamber C, the pressure on both sides of the slide valve cannot be balanced. Under the action of high-pressure oil, chambers a and B are opened, resulting in the failure of the safety valve.

d. The slide valve is stuck, so that the safety valve is always open.

e. The pilot valve is stuck, so that the cone valve always leaves the cone valve body, resulting in the failure of the safety valve.

③ Hydrostatic pump failure DF4B locomotive adopts ZB732 hydrostatic pump. When the main shaft of the hydrostatic pump rotates, the pressing plate connected with the main shaft rotates, and the seven ball joint connecting rods connected with the pressing plate also rotate, so that the position of the plunger changes along the circumference to produce oil suction and oil discharge. The low speed or non rotation of fan caused by static fault is caused by insufficient pump oil pressure of hydrostatic pump. The main causes of this fault are as follows.

a. The hydrostatic pump oil seal leaks oil, and the hydraulic oil in the pump flows into the gearbox, resulting in the lack of oil in the hydrostatic system and the establishment of normal oil pressure.

b. The contact surface between the hydraulic cylinder block and the oil distribution plate is seriously strained, resulting in poor sealing performance and insufficient oil pressure of the hydrostatic pump.

c. The hole of the hydraulic cylinder of the hydrostatic pump is strained, so that the matching clearance between the plunger and the hydraulic cylinder does not meet the requirements.

d. The spindle spring is broken, and the surface of the hydraulic cylinder block and the oil distribution plate cannot fit closely.

e. Some hydrostatic pumps can control the clearance between the hydraulic cylinder block and the oil distribution plate by adjusting the gasket. During assembly, if the thickness of the adjusting gasket is not enough, the clearance between the hydraulic cylinder block and the oil distribution plate will be greater than the specified value (0.015 ~ 0.025mm). In this way, some hydraulic oil does not enter the plug hole of the hydraulic cylinder block, but directly enters the return pipe of the hydrostatic pump, which reduces the oil volume of the pump and causes insufficient pump oil pressure.

④ The internal structure of ZM732 hydrostatic motor and ZB732 hydrostatic pump used in DF4B locomotive is exactly the same. The common faults are as follows.

a. The motor bearing is burned and the resistance increases when the fan rotates, resulting in inflexible fan rotation.

b. The bearings in the front pump body are installed reversely, and the motor main shaft and the bearing inner ring move upward under the action of high-pressure oil, resulting in excessive clearance between the hydraulic cylinder block and the oil distribution plate. The high-pressure part in the pipeline can not establish sufficient pressure, and the motor can not be affected by the high-pressure effect of hydraulic oil, resulting in non rotation or low speed of the fan.

c. The hole in the plunger or hydraulic cylinder of the hydrostatic motor is strained, so that the matching clearance does not meet the requirements, which will affect the normal oil absorption and drainage of the plunger.

d. The surface of the hydraulic cylinder block is seriously strained, resulting in that the surface of the hydraulic cylinder block and the oil distribution plate cannot fit closely.

(2) Treatment method

The common faults of hydrostatic system are finally reflected in the non rotation of fan or abnormal speed. When dealing with the fault, the cause shall be accurately judged, and the following steps shall be taken for inspection and treatment.

① Before starting up, check whether the oil level of the hydrostatic oil tank connected to the hydrostatic pump is normal. If there is oil overflow from the opening of the transmission dipstick, it can be judged that the oil seal of the hydrostatic pump leaks, resulting in oil channeling, and the normal oil pressure cannot be established in the high-pressure oil circuit, affecting the speed of the fan; If the oil level is normal, turn the fan by hand. If the rotation is not flexible, it can be judged that the hydrostatic motor is faulty. Then conduct corresponding maintenance according to the fault phenomenon, replace the skeleton oil seal of the hydrostatic pump or repair the hydrostatic motor.

② Check that everything is normal before starting the machine, and then check the heat engine. When the oil and water temperature reaches the maximum value (water temperature 82 ℃, soil 2 ℃, oil temperature 65 ℃ ± 2 ℃), manually adjust the screw at the maximum speed of the diesel engine to make the temperature control valve fully closed (if it cannot be adjusted manually, it indicates that the slide valve is stuck). If the fan speed is normal, it can be judged that the temperature sensing element of the temperature control valve has failed; If the fan speed is abnormal, when there is no obvious temperature difference between the oil return pipe and the oil inlet pipe of the temperature control valve, it can be judged that the clearance between the slide valve and the valve body of the temperature control valve is too large or strained. Replace the temperature control valve.

③ After judging and determining that the temperature control valve is normal, keep the speed of the diesel engine at the highest level, and use a hand to model the oil return pipe and oil inlet pipe of the safety valve. If there is no obvious temperature difference, it can be judged as failure of the safety valve or failure of the hydrostatic pump. In order to reduce the inspection workload, the safety valve can be removed and tested on the test bench. If the test results do not meet the requirements, it indicates that the safety valve is invalid and can be replaced; If the test is normal, the hydrostatic motor is faulty and must be replaced.

④ If the temperature control valve and hydrostatic motor are normal, the diesel engine speed can be maintained at the highest level; If the fan speed is still low, it can be judged that the outlet pressure of the hydrostatic pump is not enough, and the high-pressure oil circuit cannot establish normal pressure, resulting in low fan speed. After replacing the hydrostatic pump, the fan speed will return to normal.

⑤ When checking a hydrostatic pump or motor, it is best to test its volumetric efficiency. Because the clearance between the plunger connecting rod group and the corresponding cylinder block is too large, its leakage must be large, so the volumetric efficiency is reduced. When the volumetric efficiency of the hydrostatic pump or motor is lower than the specified value, it must be repaired or replaced.

⑥ After changing the single oil seal of hydrostatic pump and motor to double oil seal, the leakage has been basically eliminated, which can make the fan in good operation.

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