Optimal And Integrated Design Of In-wheel Drive Electric Vehicle Chassis System Mechanism Synthesis

In-wheel drive electric vehicles(IWD-EV)have the powertrain mounted directly in or near the wheel space.It has significant advantages in terms of vehicle dynamics and economy,safety,multi-mode driving functions,modular production and mainte-nance,and individual sales.In the trend of development of intelligent city and trans-portation,combined with intelligent control system,this kind of vehicle can be the ideal carrier of future intelligent city vehicle with high energy efficiency,flexible mobility,stability and safety.However,facing the various demands of multiple functions and basic performance,there are many contradictions in the design elements of IWD-EV chassis system,thus the configuration of chassis system needs to be optimized and up-dated.This thesis focuses on the problems of IWD-EV chassis mechanical system config-uration synthesis,and carries out the research of chassis system configuration optimal and integrated design for vehicle mobility,handling stability and ride comfort.1.The high mobility requirements of IWD-EV require multiple steering modes such as lateral driving and pivot steering which mean that each wheel should have a steer angle at least 90°.Meanwhile,the handling stability requirements require the suspension steering system to have good kinematic characteristics and force transmis-sion characteristics.Therefore,it is difficult to satisfy the high mobility and handling stability of the vehicle with the conventional suspension system configuration.In this thesis,after analyzing the design elements of IWD-EV suspension-steering system,a novel multi-bar suspension system mechanism and a novel dual-kingpin independent differential steering system mechanism are proposed and integrated into the design.By checking the motion interference,the new suspension-steering system prototype dia-gram is verified to be able to meet the high mobility requirements;by building a full vehicle model equipped with the new suspension steering system,the system can be validated to meet the vehicle handling stability requirements by simulation testing.2.The excessive unsprung mass of the IWD-EV worsens its ride comfort.The Dy-namic vibration absorber embedded in-wheel powertrain(IWP-DVA)can compensate for the theoretical limitations of semi-active suspension in suppressing second-order resonance at a small cost in lightweighting,to improve vehicle ride performance.The basic idea of this configuration scheme is to suspend the in-wheel drive motor and some other components to act as a mass block of the dynamic vibration absorber system at-tached to the unsprung mass(steering knuckle).In this thesis,the motion coupling char-acteristics of the external gear-slider-rocker(E-GSR)mechanism are analyzed first,and the principle of two-degree-of-freedom decoupling reduction mechanism is proposed which is based on the Symmetrical E-GSR mechanism and differential gear mechanism.This novel mechanism is applied to design a new IWP-DVA system configuration.To solve the dynamics modeling problem of the quarter-vehicle system equipped with the new IWP-DVA,an improved dynamics modeling method is proposed for the multi-branch parallel mechanism based on the screw theory and the Lagrange method.Using this method,the vehicle vertical dynamics model is built,the spring/damper parameters of the DVA system are designed,and the improvement of the vehicle ride performance by the novel IWP-DVA system is investigated.3.The battery pack,which is the energy storage device for the electric vehicle propulsion system,generally has a large size and mass,to extend the power volume and discharge capacity to meet the range and power requirements.Further,the change of IWD-EV powertrain configuration has increased the proportion of fixed equipment mounted on the vehicle body.The battery pack and other fixed devices occupy a certain amount of yaw rotational inertia of the full vehicle,and the excessive rotational inertia worsens the vehicle's yaw response.In this thesis,a Yaw-direction oscillatable battery-pack(YOB)chassis system configuration is proposed to improve the vehicle transient yaw response by equivalently reducing the vehicle inertia while meeting the mileage and vehicle layout requirements.To analyze the effectiveness of this novel chassis config-uration,a linear 3-degree-of-freedom dynamics model and an ADAMS/Car multi-body dynamics model are built.Using these models,system parameters are designed and the lateral dynamic response of the vehicle is evaluated by simulation tests;compared with conventional chassis configurations,the novel chassis is validated to have certain advantages in handling and stability performance.4.The novel suspension steering integrated system and the novel IWP-DVA sys-tem can be formed into a novel In-wheel Integrated chassis system,and can further be integrated with the YOB chassis system to develop a novel IWD-EV chassis system configuration.In this thesis,for this novel IWD-EV chassis system configuration,an ADAMS/Car full-vehicle dynamics model is built,then a series of handling stability and ride comfort simulation tests are performed to investigate the validity of the principles and design parameters of the novel chassis subsystem configuration.