Advantages of gear transmission in civil aircraft engines

In order to reduce the unstable factors, the designer thought of the gear transmission technology, which is different from the original control of the engine speed through the change of air flow. The gear transmission changes the speed by adjusting the meshing of different specifications of gears. This design has the following advantages: first of all, the gear transmission structure has good stability, thus reducing the vibration of the engine; in addition, the speed ratio of the meshing gears is the reciprocal of their radius ratio, so only controlling the speed of one gear can accurately control the speed of all the gears directly or indirectly meshed with it, compared with the traditional engine, it not only saves the right The results are more accurate.

With gear drive technology, fans can be made larger. At the same time, this design will allow other components, such as the compressor and turbine, to run stably at the optimal speed without the influence of air flow changes. What’s more, to realize all these functions is to install a completely reliable reduction gearbox on the basis of keeping the original engine structure unchanged.

Although the gear driven engine has obvious advantages over the traditional engine, its stability is obtained by increasing the risk of overheating of the gear structure, or it transforms the instability of the engine structure into the instability of heat. At present, aircraft engines have to run at tens of thousands of revolutions per minute. At such a high speed, the gear structure must rub and generate heat. This not only puts forward higher requirements for the performance of gear material and heat dissipation system, but also increases the uniform cooling time of the engine after the aircraft landing, which will affect the operation of the airliner.

As early as 2007, Pratt & Whitney discovered the problem of traditional aircraft engines and put forward the concept of gear driven engines. Finally, pw1100g-jm gear driven turbofan engine, as the landmark brand of Pratt & Whitney’s “Jingjie power”, was launched, and equipped with Airbus a320neo in 2013, successfully completed the first test flight, and is scheduled to be delivered in 2015. The previous successful ground test project provided preparation for the first flight. It is reported that the ground test project has carried out ground performance test and operability test for more than 365 hours. The pw1100g-jm engine has a thrust of 33000 pounds, which is also the maximum thrust of the “static clean power” series engine.

Since then, all the work has been carried out smoothly, and the gear drive engine seems to set off a revolution of civil aviation engine. But on the last day of 2015, Airbus and Pratt & Whitney said that the first Airbus a320neo with a Pratt & Whitney engine announced a delay in delivery, possibly due to uneven cooling of the aeroengine caused by the reduction gearbox. Although Pratt & Whitney has encountered some problems in the project of gear drive engine, the concept has been widely recognized. In addition to Pratt & Whitney, Russia and China are also independently developing aircraft engines on gear drive technology.

The UK’s Luoluo company is a global leader in gear transmission technology. At present, the lift fan of the fifth generation F-35, which has been put into use, uses the company’s gear drive technology, with a thrust of 29000 pounds and high efficiency. In order to meet the challenge of R & D of higher power gearbox, Luoluo company has invested US $87 million to build the ultrafan engine gearbox test platform in Germany. At present, the company’s most advanced engine adopts a three-axis system, which is composed of three independent rotating shafts, so that the compressor and turbine can work under more optimal conditions, so as to improve engine efficiency and reduce the number of compressor and turbine stages. The rotation speed of each shaft can also be adjusted relatively independently according to the needs, expanding the stable working range. According to the plan, gear transmission technology may be integrated into the three-axis engine system, making it a two-axis and half engine, so that its transmission mode will be more diversified, and the engine power will be improved.