Vibrational Characteristics And Optimization Of Commercial Vehicle Suspension System With Electric Drive Axle

In recent years,limited to environmental protection pressures and energy shortages,pure electric vehicles have become a mainstream direction in the development of the automotive industry.Vehicle with electric drive axle has a development trend of high integration and wide application for commercial electric vehicles.However,this type of vehicle integrates the powertrain assembly into the drive axle.This design creates two problems: the change of vehicle mass distribution variation and the electromagnetic unbalanced magnetic pull force excitation that affects the vibration of the vehicle suspension system NVH.In view of this,this thesis takes a commercial electric vehicle suspension system with electric drive axle as the research object.The vibration characteristics of suspension and body structure under the road excitation and motor excitation are studied.The uncertainty design optimization of suspension system based on road excitation is studied,and the reliability-based optimization method on uncertain parameters of the suspension and vehicle is proposed.Research content includes:The dynamic model of the electric vehicle suspension system is established and its vibration characteristics are studied.In the suspension dynamics modeling,the nonlinear characteristics of the suspension system are considered to more accurately simulate the real suspension model,and the modelling of road excitation is given.An improved incremental balanced harmonic method with equivalent linearization is proposed to solve the vibration problem of nonlinear suspension systems.Applying the above dynamic model and the proposed method,the vibration characteristics of the suspension and the body system before and after the modification of the electric vehicle under the corrugated road are studied,the research shows that the dynamic load of the rear wheel of the electric vehicle is worsened by the replacement of the power transmission assembly,which affects the safety performance of the vehicle.It has less impact on vehicle ride comfort.The vibrational characteristics of the electric vehicle under random road excitation are studied.Firstly,the incremental balance harmonic method combined with the intercell integration method is proposed to obtain the power spectral density of the vibration response of the suspension and the body system under random excitation,and compared with the Runge-Kutta method,the error is in the range of 10%while the computation efficiency is increased by 380%.Secondly,the five-degree-of-freedom suspension half-vehicle dynamics model considering seat stiffness and damping is established to study the vertical vibration characteristics of electric vehicles under random road excitation.Finally,the parameter sensitivity analysis of the main body mass parameters and suspension parameters is carried out.The results show that the vehicle mass parameters have a great influence on the vehicle comfort and safety.In the subsequent suspension design and optimization analysis,the load weight factor should be considered in the optimization design of the stiffness and damping of the suspension system.The vibration characteristics of the motor and electric rear axle structure under electromagnetic excitation are studied.The electromagnetic excitation characteristics of permanent magnet synchronous motor are discussed.According to the operation of the motor in the electric rear axle,the influence law of the dynamic and static eccentricity of the rotor on the electromagnetic force characteristics of the motor is revealed.Secondly,based on the Ansoft+ANSYS multiphysics simulation method,the vibration characteristics of the motor and the rear axle structure under the above electromagnetic excitation are studied.Finally,the corresponding electric drive axle bench test is carried out.The test results verify the existence of the motor eccentricity.When the motor speed is 1650 rpm,the frequency spectrum of the rear axle housing is observed to be 27.5 Hz,twice the electric frequency 220 Hz,etc.The vibrational characteristics of the electric vehicles with electric rear axle under electromagnetic excitation and road excitation is studied.First,the vibration characteristics of the motor excitation transmitted to the vehicle body structure through the suspension system are analyzed.Secondly,the influence of the uncertainty of the key parameters like the rotor eccentricity of the motor on the vibration of the vehicle body is discussed.Then,considering the frequency characteristics of motor excitation and road excitation,the vibrational characteristics of the vehicle body under the joint excitations are analyzed.The research results show that the reduction ratio of the electric drive axle reducer has a certain influence on the comfort and safety of the electric vehicle.When the reduction ratio is 5.0,the motor excitation of the Class A road deteriorates the root mean square value of the vertical acceleration at the center of gravity of the vehicle body by 10.7%.The larger reduction ratio ig(ig>8)can basically eliminate the influence of the motor excitation on the performance of the above vehicle.Finally,the road test of this kind of electric vehicle is given and compared with the previous analysis.The reliability-based design and optimization of the electric vehicle suspension system is obtained.The reliability-based design and optimization method are studied.The reliability index calculation method based on the fourth-order moment polynomial transformation combined with the generalized polynomial chaos method is proposed.Compared with other methods,the method has high calculation accuracy,wide application range and high computational efficiency,and the response surface methode is used to fit the objective function to save computational resources,and the fitting accuracy is within 1%.The above design and optimization method are applied to study the optimization of the suspension uncertain parameters of the electric vehicle under the determined load and the uncertain load.It indicates that the load has a great influence on the reliability-based optimization results of the suspension parameters.The design and optimization of the suspension parameters should be based on the statistical probability density distribution characteristics of the load.The work carried out has certain theoretical value and engineering practical values for the design and optimization of NVH performance of the commercial vehicles with electric drive axle.It can be extended to other types of electric vehicle systems,and the research conclusion can be used as a front-end condition in the body structure NVH study.