Why supercharger is the most vulnerable assembly on Cummins engine?
Because the rated working speed of the supercharger is more than 130,000 rpm, and it is at the outlet of the exhaust manifold, the temperature is extremely high (above 800°C), and the inlet and exhaust pressure is also large, high temperature, high pressure and high speed. Therefore, the requirements for lubrication, cooling and sealing of the supercharger are relatively high.
In order to ensure the service life of the supercharger, it is necessary to ensure the lubrication and cooling of the turbocharger floating bearing. At the same time, in use, it is required to:
a. The engine should idle for 3-5 minutes after starting. Do not add load immediately to ensure good lubrication of the supercharger. The main reason is that the supercharger is located at the top of the engine. If the supercharger starts to run at high speed immediately after the engine starts, it will cause the oil pressure to fail to rise in time to supply oil to the supercharger, resulting in oil shortage damage of the supercharger, and even burning out the whole supercharger.
b. Idle time should not be too long, generally not more than 10 minutes. If the idle time is too long, it will easily cause oil leakage at the compressor end.
c. Do not turn off the engine immediately before stopping. It should be idling for 3-5 minutes to reduce the speed of the supercharger and the temperature of the exhaust system to prevent heat recovery—oil coking—bearing burning and other faults. Frequent incorrect use can damage the supercharger.
d. Long-term unused engines (generally more than 7 days), or engines with new superchargers, should be filled with oil at the inlet of the supercharger before use, otherwise the life may be reduced or the supercharger may be damaged due to poor lubrication.
e. Regularly check whether the connection parts are loose, leaking, oil leakage, and whether the return pipe is unobstructed, if any, should be removed timely.
f. Keep the air filter clean and regularly replace it as required.
g. Regularly change the oil and oil filter.
h. Regularly check the radial axial clearance of the turbocharger shaft. The axial clearance should not be more than 0.15 mm. The radial clearance is: the clearance between the impeller and the pressure shell should not be less than 0.10 mm. Otherwise, it should be repaired by professionals to avoid loss.
Why is the new supercharger often short life after the supercharger on the engine is damaged?
a. The lubricating oil is not clean.
b. There are impurities in the oil passage.
c. There are foreign bodies in the intake and exhaust pipes.
Diagnosis and treatment
a. Check that the lubricating oil is clean. Because the speed of supercharger is very high, the matching precision between bearings is also very high, if the lubricating oil is not clean, the shaft of the new supercharger will be damaged quickly, so it is very important to replace the lubricating oil and oil filter at the same time.
b. If the lubricating oil and oil filter are replaced when the turbocharger is replaced, the service life of the supercharger is still very short. It is caused by too much impurities in the oil passage. The oil passage needs to be cleaned. Refer to the following cleaning methods:
1. Remove the broken supercharger and drain the oil when the engine is hot.
2. Add a certain amount of mixed oil (30% oil + 70% diesel oil).
3. Plug the inlet pipe of the supercharger into the return pipe or seal the outlet of the inlet pipe.
4. Start the engine, stop after 1 to 2 minutes of idle speed, and release the mixed oil (if it is dirty, it is best to clean twice). The above work is carried out in the hot car.
5. Clean or replace supercharger inlet pipe, clean oil pan, and replace oil filter and air filter.
6. Install a new supercharger and pre-lubricate the oil at the inlet of the supercharger, then put it into the oil pipe, fill the filter with oil and install it, and finally install other pipes.
7. Start the engine, idle for 3 to 5 minutes, and then speed up to check if there is any oil leakage and air leakage.