Development of bevel gear and transmission system

Relevant statistical analysis shows that the development difficulty of bevel gear and transmission system accounts for 9% ~ 13.5% of the development difficulty of aeroengine, and the failure rate is higher than this proportion. Among them, the tooth profile of central bevel gear is more complex and the development will be more difficult. At the same time, the faults also continue. The turbojet seven series engine developed in China in the early stage has been tested in the factory and used in flight from 1969 to 1986. The central bevel gear has failed many times. Especially from February 1985 to March 1986, four second-class accidents were caused in a year, which seriously threatened the production and use of the engine.

When a certain aero-engine developed by AVIC 608 carries out the low cycle fatigue test of the whole machine on the whole machine test bench according to the requirements of the model specification, when the test reaches the 469th cycle, the engine speed drops suddenly and stops quickly. Before the engine stops, all performance parameters, working parameters and equipment of the test bench are normal. After the disassembly and inspection of the engine, it is found that the bevel gear in the central transmission gearbox is broken in the circumferential direction along the root of the spoke plate. From this fault, it can be found that all parameters of the engine are stable and unchanged before the failure of the central bevel gear, and the fault is sudden and unpredictable.

When the core engine of an aeroengine pre researched by China Gas Turbine Research Institute was tested on the high altitude platform, when the core engine was running at 93% of the converted speed, the engine vibration suddenly increased sharply, accompanied by abnormal noise, and then emergency shutdown. When the engine was disassembled and inspected after stepping down, it was found that the wheel body of the driven bevel gear of the central drive of the accessory gearbox was broken and the driving bevel gear was worn and deformed.

After the fault occurred, the engine was disassembled and inspected. It was found that 11 teeth of the central driven bevel gear were broken (40 teeth in total), and the silver coating on the gear tooth surface was worn and peeled to varying degrees. The driving bevel gear is relatively complete without fracture and block falling. However, the gear teeth are seriously worn, rolled or even gnawed. After failure, the appearance of the central driving bevel gear teeth is shown in Figure 1. The appearance of the failed central bevel gear (left driving bevel gear and right driven bevel gear).

The spectrum diagram at different times from stable operation at 93% speed to shutdown before fault is shown in Figure 2. It can be seen from the figure that the spectrum diagram at the measuring point of the accessory gearbox 72s to 10s before the engine emergency shutdown is relatively clean, while the spectrum diagram from 10s to 2S before the engine emergency shutdown increasingly presents a comb like spectrum diagram, which is a typical spectrum diagram of engine failure. The fundamental frequency value is small, and the high frequency doubling vibration is large. The frequency doubling (more than 3 times is obvious) in the spectrum is rich and higher than the fundamental frequency value.

Serious accidents caused by frequent bevel gear faults are a profound and painful lesson for those engaged in Aeroengine Research, manufacturing and maintenance. Due to the sudden and difficult detection of gear faults, the structural rationality, strength and process requirements of aeroengine central bevel gear should be guaranteed at the beginning of design and manufacture. Higher requirements are put forward for the design of central bevel gear, which can not be careless. In order to ensure the safe and reliable operation of gear transmission, it is necessary to establish an accurate theoretical model at the beginning of bevel gear design, accurately simulate its working process under actual working conditions, deeply study and analyze its dynamic performance, and ensure sufficient accuracy and correct operation in strict accordance with process specifications in the process of manufacturing and installation, Regular maintenance and repair can ensure the safety and reliability of bevel gear transmission system and provide reliable power for aircraft.

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