Research On Dynamic Modeling Of Cylindrical Gear Split Torque Transmission System And Load Sharing Technology With Flexible Web

As one of the three key moving parts of a helicopter, transmission system determines the overall performance of the helicopter. Different from the general ground gearbox, helicopter main gearbox demands for high power to weight ratio, high reduction ratio, high reliability, high survivability, etc. Therefore split-path transmissions are widely used. A torque split transmission system is promoted in ART program, which offers the advantages of s imple structure, fewer gears and bearings, fewer transmission stages and high power to weight ratio, etc. Obviously, a torque split design can offer significant advantages over the commonly used planetary design. The core problems of the helicopter torque split transmission system are the complex dynamic characteristics and the risk of unequal torques in the two parallel paths.This paper studies the dynamics and load sharing of the helicopter torque split transmission system, especially putting forward a method to establish the dynamic model of the helicopter torque split transmission system quickly and a design of load sharing device based on flexible web. The main work and innovation includes:(1) Analyze the limitations of the mainstream dynamics modeling method of helical gear, and put forward a general dynamics modeling method for helical gear with full degrees of freedom coupled. This method avoids the judgment for symbol when project a generalized displacement to the engage line direction, and also avoid the judgment of the component force direction when broken down the dynamic meshing force into the various degrees of freedom, which reflects the simplicity and superiority for modeling using vector ideas. Based on the general dynamic model of the helical gears pair, the dynamic models of multi- mesh gear system and multi-shaft gear system are deduced. Lastly, regard the torque split transmission system as combinations of multi- mesh and multi-shaft gear systems, and assemble the dynamic equations directly according to the coupling relationship.(2) Firstly, the dynamic model of certain aviation torque split transmission system is established based on previous work and the equations are handled dimen- sionless. Then the methods for calculating the value of key parameters in the dynamic model are researched. The key parameters includes: mass and inertia, mesh stiffness and damping, support stiffness and coupling stiffness, etc. In addition, the dynamic excitations of the system are analyzed, mesh stiffness excitation caused by phase and synthetic meshing error excitation based on pitch error and profile error are especially considered. Lastly, the dynamic response of torque split transmission system is numerically solved using ode45 command of Matlab. N umerical results indicate that the dynamic response of the system shows typical nonlinear characteristics and there is a significant difference between the two paths. The causes of nonlinear and differences are investigated using a set of control experiments. The results shows that the cause of nonlinear is mesh error and phase, while the cause of difference is phase.(3) In order to quantitatively study the dynamic load sharing characteristics of torque split transmission system, the dynamic load coefficient and load sharing coefficient are used. In order to study the sensitivity of the dynamic load sharing of the meshing phase, mesh stiffness, support and coupling stiffness, errors and working conditions and other factors, several numerical experiments of sensitivity analysis are conducted. Conclusions can be drawn from the experiments results that: designing appropriate phase difference and mean mesh stiffness, improving support stiffness, reducing coupling stiffness, reducing errors of the first stage, as well as choosing the appropriate input speed help to improve the dynamic load sharing characteristics.(4) Based on the conclusions of the previous chapter, a practical way to realize load sharing is reducing the torsional stiffness. Therefore, a design of load sharing device is promoted and a structural parameter optimization is conducted based on it. Specific work includes: Firstly, a flexible web load sharing device with hyperbolic surface are designed, and the working principle and load sharing effect of the device are analyzed. After that, simplify the torsion of the flexible web to bending of beams with variable section, and resolve the torsional stiffness and the shear strength of the flexibility web using mechanics of materials methods. At last, based on the matching results of the stiffness and strength with structural parameters, with torsional stiffness minimized, total mass lightest and safety factor maximized posted as the objective functions, a multi-objective optimization model for flexible web is established. The model is solved through Matlab programming, with fast non-dominated sorting genetic algorithm adopted. A optimum design is selected from the pareto set which achieves satisfactory results in all the three objective functions.