Research On Coupling Fault Mechanism Of Electric Vehicle Range Extender Based On Numerical Analysis

Facing the plight of energy shortage and environmental pollution restricting the development of automotive industry,many countries actively develop electric vehicles.As a transitional vehicle,the Range Extended Electric Vehicle(REEV)has received widespread social attention.And the range extender is an auxiliary power source for REEV,which performance directly affects the stability and safety of whole vehicle.Due to the complex structure and wide excitations of range extender,the coupling faults are easy to occur.Besides the types of range extender coupling faults are various,its faults diagnosis are difficult.Therefore,it is necessary to study the coupling fault mechanism of range extender,analyze the cause of the fault and the evolution law of fault,and diagnose the coupling fault through coupling fault characteristics ultimately.In this paper,a range extender is taken as research object.By establishing a nonlinear dynamic model and using Runge-Kutta method with variable step size,the dynamic response characteristics of system under different working conditions are analyzed to study the single fault and coupling fault mechanism.The main contents are as follows:(1)Dynamic analysis and mechanism research of misfire fault.According to dynamics of internal combustion engine,the bending-torsional coupled dynamics model of crankshaft is established.And the torsional vibration characteristics of single-cylinder misfire at 0%,50% and 100% are studied by frequency domain analysis.Furthermore the characteristics of misfire fault are extracted and verified by experiment.(2)Dynamic analysis and mechanism research of stator short-circuit fault.Using energy method,the unbalanced electromagnetic force and electromagnetic torque are calculated by analyzing the air gap permeability and air gap magnetic potential of the stator during stator short-circuit fault.And the bending and torsion electromagnetic stiffness is further derived,so as to build the motion differential equations of generator considering electromagnetic stiffness.What’s more,the bending and torsional vibration characteristics of generator with short circuit 1%,5% and 10% are analyzed by time domain diagram,axial trajectory diagram and frequency domain diagram.Finally the stator short-circuit fault characteristics are extracted.(3)Dynamics analysis and mechanism research of misalignment fault.In order to establish the coupled bending-torsion vibration model of generator rotor with misalignment,the fault excitation is deduced according to the motion law analysis of the left and right half coupling.Besides,the variation laws of the system vibration response in parallel misalignment,misalignment and comprehensive misalignment faults are also analyzed by using time domain diagram,axis trajectory diagram and frequency domain diagram.So the characteristics of misalignment faults are extracted.(4)Dynamics analysis and mechanism research of coupling fault.Based on the shafting structure analysis of range extender,the dynamic model is established.And the misfire-stator short-circuit coupling fault characteristics are studied by setting the fault parameters.Meanwhile,the generator dynamic model is also established considering the misalignment and stator short-circuit faults excitation.Using the time-domain diagram,the axial trajectory map and the frequency waterfall diagram,the fault characteristics of misalignment-stator short-circuit coupling fault are studied.