Research On Dynamics And Load Sharing Characteristics Of Helicopter Main Rotor Of Gear Split Torque Transmission

The main rotor is one of the three key dynamic components of helicopter which has effect on the helicopter overall performance directly.Gear split torque transmission is a new type of structure in helicopter main rotor for replacing the planetary transmission which can realize larger transmission ratio and lower weight under the same condition.The two branch gear split torque configuration of this paper,which has the adcantages of less transmission stages,lower power loss,lower noisy,higher reliability,has been applied to the foreign advanced helicopter main rotor.The core problems of this main rotor system of gear split torque transmission are the complex dynamics characteristics and uneven load distribution.In this paper,a dynamic model is established which can reflect the characteristics of the transmission system.The dynamics and load sharing characteristics of helicopter main rotor of gear split torque are calculated and analyzed.The design and analysis method of main rotor is formed.This provides theoretical guidance and technical support for the design and development of main rotor.The research work and achievements of this paper have important theoretical significance and engineering application prospect for improving the design and R&D level of helicopter main rotor.The dynamic modeling process of cylindrical gear pair is analyzed from three aspects: the deviation of gear,the movement of rigid body and the deformation of the gear.The influence of machining error is divided into flank deviation and position deviation.The profile of the real tooth profile is simulated by defining the flank deviation of the contact point.It is concluded that the variation of center distance is caused by the position deviation,which changes the engagement angle,the position angle and the coincidence degree.The position deviation affects the gear pair meshing state.Calculation formula of angular velocity and angular acceleration of driven wheel of rigid motion is derived under profile deviation.The theory Contact line in the meshing plane is discretized.Calculation formula of elastic deformation and meshing force at arbitrary contact point is derived.At the same time,the judgment and calculation method of the meshing stiffness and transmission error of the cylindrical gear pair is presented.According to Lagrange’s law,the dynamic equations of torsion and bending-torsion-shaft coupling of cylindrical gear pair are derived.Numerical solution method is given,and the model is verified.The dynamic modeling process of spiral bevel gear pair is analyzed from two aspects: the rigid body motion and the contact deformation.It is necessary and feasible to establish the dynamic equation at the middle point on width.The rigid body motion of spiral bevel gear pair is analyzed.The calculation method is presented which converts angle deviation of arbitrary contact point into meshing error of nominal meshing point.The formula of angular velocity and angular acceleration of the driven wheel with angle deviation is derived.The contact deformation of spiral bevel gear pair is analyzed.The calculation formula of meshing deformation and meshing force at nominal meshing point is deduced.According to Lagrange’s law,the dynamic equations of torsion and bending-torsion-shaft coupling of spiral bevel gear pair are derived.Numerical solution method is given,and the model is verified.Analysis of the characteristics of the helicopter main rotor of gear split torque transmission,divides the dynamics properties of each component,and builds the lumped mass dynamics model of system.The torsional dynamics equation and bending-torsion-axial coupled dynamics equation sets of helicopter main rotor of gear split torque transmission are built.A numerical calculation method for the mesh phase relationship of the gear pairs with different mesh cycles is derived by defining reference gear pair,associated gear pair and reference point.The calculation method of meshing phase of the same stage of different branch and two stage of same branch of the helicopter main rotor of gear split torque transmission is analyzed in detail.According to the structural characteristics of helicopter main rotor of gear split torque transmission,the calculation method of other related parameters in the lumped mass model is derived.The free vibration characteristics of the helicopter main rotor of gear split torque transmission are analyzed.A method for solving the inherent characteristics of the system is given.The vibration modes of the system classified into three groups: herringbone-spur compound gear mode,input gear mode and all gear mode.Formulas for solving the reduced-order mode and component energy are pulled down.Through the sensitivity analysis of the parameters of natural frequency,it is concluded that how to adjust the natural frequency to vibration and avoid vibration.The method of matrix dimensionless of dynamic equation is given.The initial contact position of the gear pairs in the locked loop of gearing is calculated based on the analysis of the mesh phase.The dynamic response characteristics of the helicopter main rotor of gear split torque transmission are analyzed.The applicability of the torsional and bending-torsion-axialcoupled dynamic model is analyzed,and concluded that bending-torsion-axial coupled model accords with the characteristics of the transmission system.According to the different types of gear deviation caused by the manufacture error,the working conditions of the single pair of gear are analyzed.The main conclusions are as follows: The angle deviation of the bevel gear has an effect on the the dynamic transmission error of the gear pair.Based on the direction of the mean deviation,the change of root mean square of dynamic transmission error can be estimated to make a general judgment.The dynamic transmission error of cylinder gear pair is shown to nonlinear characteristics because of flank deviation.Position deviation makes the gear pair to produce a new engagement state,but still in a long period linear motion state.And the working condition of the transmission system is analyzed.The influence of mean deviation caused by angle deviation with different directions and sizes,flank deviation with different processing precision and position deviation of the center direction and tangential direction of different sizes on the dynamic transmission error of the system are summarized.A method to quantify the load sharing performance is proposed.The load sharing performance of helicopter main rotor of gear split torque transmission is analyzed.The gear test models of two different configurations are adopted to carry out comparative analysis of load sharing characteristic.The result is that: The phenomenon of uneven load is appeared when the multi branch gear transmission system forms a locked loop.And the phenomenon of uneven load is an inherent feature of the locked loop of gearing,which is independent on the manufacture error and mesh phase.The load sharing performance of the locked loop of gearing is changed by the manufacture error and mesh phase.The load distribution and the deformation of gear engagement of the helicopter main rotor system of split torque transmission are calculated.Finds out that: Because the deformation of same gear engagement of the two branches is different,the locked loop of gearing has uneven load.Each of the gears produces the elastic displacement lead to different additive effects.The sensitivity analysis of load sharing coefficient and system inherent parameters reveals the laws of the variation of the load sharing performance with the inherent parameters.Three kinds of load sharing methods are proposed based on the analysis results of the load sharing performance.It is point out that load sharing can be achieved when each gear has its own elastic displacement form the same effect.A load sharing method for designing the initial meshing clearance of locked loop of gearing is proposed.The sensitivity analysis of the load sharing factor shows that the load sharing factor becomes smaller when adjusting some inherent parameters.A load sharing method for adjust system parameters is proposed.Theload sharing performance changed because of mesh phase,but the meshing phase is determined by the system parameters.Meanwhile design requirements of lightweight and high safety are considered.Optimization design method is used.A load sharing method for design the mesh phase of gear sets is proposed with the promoting of load sharing property,lightweight,and safety considered as the objectives.Based on the split torque,the experiment bench and split torque transmission gear box are constructed.The theory and method in this paper are validated by the dynamics characteristic and load sharing experiments.