Study On Vibro-Acoustic Identification And Spectral Characteristics For A Deep Hybrid Transmission

Deep hybrid transmission is an innovative and high technology of power split and recombination for gas-electric vehicles,with significance of energy conservation and emission reduction.With advantage of high energy efficiency,hybrid cars equipped with this transmission not only retain the characteristics of long range and high energy density,but has the advantage of low emission and high efficiency.In recent years,because of the technical limits of pure electric vehicles and fuel cell vehicles,the research and development of hybrid systems have become an inevitable trend of vehicle industry and academic community.Compared with current series or parallel hybrid system,the deep hybrid transmission of this topic research employs an advanced power-split device,which makes the fuel economy of relative cars could improve up to 40%.The kernel unit of the power-split device is a Four Shaft Planetary Gear set(FSPG),which combines powers from the internal combustion engine(ICE)and two integrated motors and synthesizes the power to drive the vehicle.On account of the complicated structure and various working conditions,the FSPG bears input excitations from the two motors in pure electric drive mode,while bearing coupling excitations from ICE and motors in hybrid drive mode.Therefore,it will produce noise problem different from classical driveline during runtime.For this key problem,vibration and noise tests are necessarily required for identification of the noise source in developing step.On the basis of sound pressure sensor,vibration acceleration sensor and speed sensor,the experimental tests of the system under different conditions in pure electric drive mode and hybrid drive mode are carried out respectively.From spectrum analysis and order tracking,the main noise source is identified.Aiming at the severity of structure resonance noise,it is quite important to study the inherent characteristics of the system.According to the structure arrangement of the present depth hybrid transmission,the modal analysis for the key unit of coupoumd planetary gear set is carried out.Based on varying levels of gear sub-model,shaft sub-model and bearings stiffness model,the plane vibration model and space vibration model of the compound planetary set are established separately through assembling the corresponding substructures.Then the mode characteristics at each natural frequency are studied and the reason of resonant vibration is found out.It is shown from test results that gear meshing is still the main source for this deep hybrid tranmission.The time-varying mesh stiffness(TVMS)calculation of gear pairs is all-important in gear dynamics.For the purpose of obtaining more accurate TVMS of gear pairs for spur and helical gears,an improved algorithm in double teeth-meshing region for spur gear pairs is proposed.Meanwhile,two models,respectively named single coupling model and double coupling model,are put forward for stiffness calculation of helical gear pairs.Compared with the results from existing algorithms,it is demonstrated that the proposed algorithms are more accurate and fit to the actual situation.Furthermore,based on the double coupling model for helical gears,the TVMS of various planetary gear layouts for this deep hybrid transmission are calculated.The spectral characteristics of stiffness is ananlyzed through Fourier Series.Finally,the best layout for the compound planetary gear set is obtained.Since there are many factors on the noise of gear meshing,it makes little sense of production mechanism merely considering one pair of meshing gears.Besides the meshing force of gear pairs,on the system level,the bearing stiffnesses and deformation of shafts and housing are also considered in this study.Based on the Component Mode Synthesis(CMS)technique,a detailed mult-flexible body dynamic model is established for the whole transmission system.Through comparsion of the vibration acceleration of sensors on the housing surface from test and simulation correspondingly,accuracy and practicability of the model is verified.On the basis of spectral charateristics validation,critical parameters of tranmission are optimized,including the axial and radial clearance between the ratchet and ring gear,the carrier position,the thickness of the input shaft,the radius of the carrier pawl,and the preloads of differential bearings etc.The optimized results provide valuable information for structure improvements.