Traditional flying vehicles refer to land and air amphibious vehicles that can drive on the ground and fly in the air. In recent years, with the rise of the concept of air traffic, the vertical takeoff and landing aircraft with only air flight function is also called flying vehicle.
Effectively improving the efficiency of VTOL propulsion and reducing the size of the system is one of the important goals pursued by the design of flying vehicles, which also puts forward higher requirements for the service life and reliability of the transmission system in flying vehicles. As the power transmission device in the flying vehicle, the performance of its transmission system determines the reliability and safety of the flying vehicle. A foreign organization has carried out technical research on large civil tilt rotor aircraft (i.e. flying vehicle), and analyzed its transmission system configuration and performance. Uber, Airbus, bell, Boeing, AVIC and other companies have laid out the research and development of flying vehicles, and put forward flying vehicles with different vertical takeoff and landing modes and power forms.
However, at present, there is a lack of research methods on the reliability of the gear transmission system of flying vehicles. As an important basic part of the transmission system of flying vehicles, the reliability of gears is related to the safety of the whole transmission system. Therefore, it is of great significance to study the reliability of gear transmission system of flying vehicle.
Scholars at home and abroad have done a lot of research on the reliability prediction method of gear transmission system. In 1947, Freudenthal a m put forward the stress strength interference theory, which laid the theoretical foundation of mechanical reliability analysis. Wang Zheng et al. [6] established a system reliability model considering failure correlation by using the stress strength interference theory, and studied the variation law of system reliability and failure rate under random load. Qin Datong and others considered the randomness of the dynamic meshing force of gear pair and the dynamic contact force of rolling bearing, and established the dynamic reliability model of gear by using the stress strength interference theory. An Zongwen et al. Used Markov state process to characterize the law of gear strength degradation, and further analyzed the reliability of gear transmission system. Li Yao et al. Extracted the probabilistic statistical characteristics of gear and bearing stress in wind turbine, and studied the dynamic reliability of wind turbine drive chain considering strength degradation and fatigue damage accumulation. Wang Mingqing and others established a time-varying model of gear strength based on gear S-N curve, and then established a reliability analysis model considering both tooth surface contact fatigue failure and tooth root bending fatigue failure. Zhao Yong et al. Established a reliability model considering failure units such as gears and bearings for multistage planetary transmission system; Then, considering the main failure modes in the system and the correlation between each failure mode on load and service coefficient, the reliability model of transmission system is established. Qu Yanjing et al. Established a gear reliability calculation model based on strength degradation by using the dynamic stress strength interference model, and studied the influence of strength degradation on gear reliability. Zhou Zhigang et al. Obtained the dynamic meshing force of each gear pair and the dynamic contact force of rolling bearing by establishing the dynamic model of gear bearing coupling of wind turbine transmission system; Based on the stress strength interference theory, a dynamic reliability model of wind turbine gear transmission system considering failure correlation is established.
However, most of the above studies are aimed at single failure mode or independent reliability analysis of each failure mode, or fail to consider the impact of strength degradation on reliability, and can not accurately characterize the overall reliability change trend of the system. On the basis of considering the correlation between strength degradation and failure, based on the stress strength interference theory, the dynamic reliability analysis model of flight vehicle transmission system is established, and the variation law of the reliability of the transmission system with time is obtained, which provides a new method for the reliability analysis of flight vehicle.