Research On Dynamic Characteristics And Vibration Limit Value Of Helicopter Main Gearbox

Helicopters are widely used in military strikes,public security,firefighting,medical rescue and communications,which play a significant role in those important fields.As the main body of the transmission system,the helicopter main gearbox is the key core device and complex multi-body coupling system of the helicopter,including multistage and multitype gears,shafting,bearings,and special-shaped casings.The helicopter main gearbox is developing towards high speed,heavy load and light weight.In order to reduce the mass and increase the power-to-weight ratio,the structure is often more flexible,which will prone to problems such as excessive vibration.However,excessive vibration will lead to structural fatigue and damage in a very short time,cause major accidents such as plane crashes and deaths,and bring immeasurable losses.Therefore,engineers must pay attention to the degree of fatigue damage at the beginning of the main gearbox design,limit the vibration to an acceptable range,and ensure the main gearbox works properly.Take a certain type of helicopter main gearbox transmission system as the research object,establish a flexible multi-body system dynamic model,analyze dynamic response characteristics,calculate the vibration limit value of key components based on the stress-life method,and establish the relationship between vibration response and fatigue life,achieving the accurate estimation of the vibration limit value.The main research contents are as follows:(1)Establish the super element model of the casing substructure and the shafting substructure based on the model condensation theory;propose the accuracy evaluation standard of the special-shaped casing model,verify the accuracy of the model through the mutual comparison of the experimental mode-finite element mode-super element mode;based on the actual parameters of a certain helicopter main gearbox,the coupling topology relationship of the system is analyzed.Coupling the super element model of each substructure through force elements and constraints,the helicopter main gearbox flexible multi-body system dynamics model is established on the SIMPACK simulation platform.(2)In order to compare and verify the validity of the dynamic simulation model,a test platform for the vibration characteristics of the helicopter main gearbox is established.By selecting the input shaft bearing node,planet carrier shaft bearing node and tail output shaft bearing node as the vibration test point,the system dynamic characteristics based on the time/frequency analysis method is studied.The vibration response of the gear rotor system model without coupling casing and the overall system model with coupling casing is compared and analyzed;based on the harmonic response analysis method,the influence of structural flexibility on the natural frequency,vibration displacement,gear contact stress and vibration acceleration of the system is also studied.(3)The S-N curve of the component material is fitted by the material parameters in fe-safe;based on the modal stress recovery method,calculate the dynamic stress of the three key components in the main power flow area,including high-speed input bevel gear shaft,intermediate stage double coupling bevel gear shaft,and low-speed planet carrier output shaft.Based on Miner’s law,the dynamic stress-fatigue life-vibration response relationship of each component is established under variable load conditions,and the vibration limit value is accurately estimated from the perspective of fatigue life.This research can provide a theoretical basis and engineering guidance for the highly reliable dynamic design of the helicopter transmission system.