Eaton Char-Lynn Motor – Aero Engine: Development Direction
The domestic engine life has finally reached half of the US engine: a key breakthrough in key technologies

  The Eaton Char-lynn Motor says – At present, the development direction of aero engines is a large thrust-to-weight ratio, high reliability and long life, and the performance and service life of aero-engine spindle bearings are one of the “key” factors determining engine reliability. In China, the development of turbofan 10 Taihang engine successfully realized the span of domestic engine from vortex jet to turbofan, from medium thrust to large thrust. However, in the process of developing Taihang engine, the reliability of engine spindle bearing occurred many times. As a result of the problem, engine researchers began to realize that “bearing life and reliability” has become a “bottleneck” problem that restricts the development of high-performance engines in China. At present, there is no publicly available information on the life of the Taihang engine spindle. However, the information on the remanufacturing of the AL-31 shows that the bearing life of the bearings produced in China is only 500 to 600 hours, that is, the bearings need to be replaced when the engine is first turned over. According to foreign data reports, the engine bearing life developed by the German FAG, Sweden SKF and other advanced bearing companies has reached more than 10,000 hours, and can be repaired according to the situation after the end of life, further extending the life. The gap between China’s bearings and foreign advanced levels is enormous.

  The latest military standards for China’s engines stipulate that all turbofans, turboshafts, and turbojet engines must be interrupted by lubricating oil for half an hour. The engine still continues to work normally to meet the test, and the engine oil is completely damaged. The aircraft is still in need of safe return. This standard has high requirements. It is said that a large bypass ratio turbofan developed in China is in accordance with this standard. In the case of the oil interruption test, in order to pass the test without 30% of the maximum thrust, the two subjects are caused by the lubrication. Engine damage, impact and loss are huge. It can be seen from the above information that the main bearing of the military aviation engine is the core heavy-duty part, and the long-term work is in the severe working condition of high-speed (14,500 rpm) heavy load (not less than 5 tons), and the injection lubrication mode is adopted in the structural design. This will lead to problems such as insufficient lubrication of the engine oil during the over-design conditions of the fighter aircraft, poor oil film establishment, etc., causing major accidents in bearing failure, which is also a difficult problem for the AL31 engine.

  Since AL-31 and Taihang are already stereotyped products, it is costly to adopt a new type of spindle design. It is an effective technical way to improve bearing life through surface engineering technology without changing the bearing material and structural design. Since diamond is the hardest material among all natural materials, and has a low coefficient of thermal expansion and a very low coefficient of friction, it is natural to think that if the bearing moving parts are coated with a diamond film, the life and performance of the bearing will be Greatly improved, but the current production of diamond film needs to be carried out under high temperature and high pressure, and the steel used for the bearing has a low tempering temperature. At high temperature, the performance of the coated bearing body is greatly reduced, which is not worth the loss. Researchers at the Golden Wheel Company, a subsidiary of the China Agricultural Machinery Institute, have recently developed a device that can perform diamond-like coating on steel surfaces below 200 °C, resulting in a significant increase in bearing performance.

  According to public information, when the main bearing of the turbofan 10 is used as the test object, the simulated engine has 50 combat takeoffs, and each combat takeoff time is 1 hour (including 35 minutes of cruise state, 15 minutes of afterburning state, 0 minutes of slow train). State), after 50 hours of continuous operation, the diamond-coated diamond bearing has no visible wear, while the active uncoated bearing has never completed 8 hours of continuous operation. This also means that the life of the main bearing of China’s aero-engines has increased by at least 6 times, reaching 3,000 hours, almost the same life as the Taihang engine, reaching half the life of the same engine of the US.

  In the most noteless oil-free lubrication 30-minute operation test, since the Taihang engine design has passed this standard, both the coated bearing and the uncoated bearing have been successfully completed, but the active uncoated bearing assembly is seriously damaged after the experiment. It must be replaced, and the coated bearing is almost undamaged and can be tested. It is worth mentioning that the life of the coated bearing is far more than 3,000 hours, just because the product is to be used for other tests, but not for the destructive life test, but it is also sufficient to meet the requirements of the bearing and the Taihang engine.