1 Introduction
Figure Q Assembly Drawing of Main Shaft and Oil Seal End Cap
1-Gland; 2-Oil seal; 3-Spindle; 4-Oil seal end cover
On DF4 locomotives, hydrostatic motors are used to drive cooling fans to cool the cooling water system to maintain normal oil and water temperatures, thereby ensuring the normal operation of the diesel engine. In the actual application process, there are often oil leakage failures in the oil seals of hydrostatic motors, which not only waste oil and pollute the environment, but also may cause abnormal operation of cooling fans when the oil leakage is serious, resulting in machine damage and temporary repair, seriously affecting the safety of railway transportation.
The main shaft of the hydrostatic motor adopts a skeleton oil seal axial sealing structure, with the oil seal model of SG65 × ninety × 12. The assembly with the main shaft and oil seal end cover is shown in Figure Q.
2 Fault Analysis
An investigation was conducted on 51 DF4 locomotives in a locomotive depot. The main task of the locomotive is passenger and freight traction. Due to the large gradient fluctuation of the line, many tunnels, and the long working time of the hydrostatic motor under full speed operation, there are also many oil leakage faults in the hydrostatic motor oil seal. A total of 22 cases of oil leakage from the hydrostatic motor oil seal occurred within two years. The main fault locations are as follows:; 12 worn spindles; 9 oil seals cracked; Other pieces. The most dangerous one is oil seal cracking, because there is a large amount of oil leakage after a fault occurs here, and the possibility of mechanical damage is greatest; The second is spindle wear.
3 Analysis of fault causes
(1) The assembly is not standardized, causing damage to the oil seal.
In order to ensure a good sealing effect between the oil seal and the oil seal cap, the installation interference between the oil seal and the oil seal cap is between 0.1 and 0.2 mm. Therefore, the oil seal needs to have a larger force during the installation of the oil seal cap. During actual assembly, due to the lack of a suitable special press fitting tool, workers often use the wooden handle of a screwdriver or other objects to knock the oil seal, or simply use a sharp object to press the oil seal into the oil end cap. This may lead to problems such as deformation of the iron skeleton of the oil seal and slight cracks in the oil seal rubber after assembly. After loading and use, the oil seal may leak or even break.
(2) The hydrostatic motor spindle is worn.
The maximum operating oil pressure of the hydrostatic motor is above 14MPa. To ensure a good oil seal effect, the inner diameter of the oil seal sealing belt is about 3mm smaller than the outer diameter of the main shaft, and a spring is used to clamp it on the main shaft. There is a certain amount of friction when the main shaft rotates and operates. In addition, for cooling fans installed on the hydraulic motor spindle, there is no dynamic balance test device in each locomotive depot. When the fan operates at full speed, it produces a certain deflection force on the hydraulic motor spindle, thereby increasing the aforementioned friction force. Therefore, after long-term use, the main shaft generally has a circumferential groove at the sealing belt, which affects the sealing effect of the oil seal. When the groove reaches a certain depth, it may cause oil leakage from the oil seal.
4 Countermeasures
(1) Use a thickened oil seal end cap. For the failure of oil seal leakage caused by spindle wear, the traditional treatment method is generally to lift the leaking hydrostatic motor from the vehicle, coat or chrome repair the hydrostatic motor spindle, restore its original size, and then put it into use. This method has many inconveniences in field practice. First, the hydrostatic motor on the vehicle only leaks oil from the oil seal. If the hydrostatic motor is lifted down and completely disassembled, it will inevitably cause a waste of manpower and material resources; The second is that chrome plating for repairing the circumferential wear of the main journal of the hydrostatic motor requires a large amount of work and is expensive.
Through observation and analysis, we have made a thickened oil seal end cap and replaced it with the original oil seal end cap. This can adjust the position of the skeleton oil seal on the hydrostatic motor spindle, move the installation position of the oil seal upward, avoid the worn parts of the hydrostatic motor spindle, and make the spindle reused. The thickened oil seal end cap is shown in Figure R. It is only necessary to increase the dimensions of A and B in the oil seal end cap with the drawing number DLT220-00-O1-1 by 3mm.
Figure R Thickened oil seal end cap
(2) Use a special press fitting tool for oil seals. For the failure of oil seal rupture, a special tool can be made, as shown in Figure S. When assembling the oil seal, increase the bearing area when the oil seal is pressed down to prevent damage to the oil seal rubber and the built-in framework.
Figure S Oil seal press fitting tool
By taking the above measures, the failure of oil leakage from the hydrostatic motor oil seal in the locomotive depot has been significantly reduced, the machine damage and temporary repair caused by it have been effectively controlled, and the maintenance cost of the locomotive has been reduced, ensuring driving safety.
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2023-03-25