Research On Yaw Stability Control Of Distributed Drive Electric Vehicles

Energy conservation, safety, environmental protection concept is the main part of thevehicle sustainable development, and electric vehicle is generally accepted that the mostpromising new energy vehicles. With the development of automotive, social issues increasesapparently and the security is the most concerned about the topic. For conventional cars,active safety control technology has developed to be a research focus in this direction inrecent years, and the electronic stability program(ESP) is an effective way to improve theactive safety. For electric vehicles, conventional engine and the powertrain system weresubstituted by motor battery system，but motor braking energy could feedback and torqueoutput capacity is limited,so the stability implemented in either of two ways of thehydraulic system and the motor become an important object of research and concern.Thispaper aims to study on yaw stability control based on the characteristics of the distributeddrive electric vehicle.Firstly, this paper selected four in-wheel motor to drive each wheel, and for thedynamics simulation of the distributed driving electric vehicle, we build10degrees offreedom vehicle model including vehicle body model, tires model, motor model, drivermodel, braking model.So we made the vehicle dynamics model validated in thecorresponding simulation conditions. And this lay a solid foundation for yaw stabilitycontrol in next step work.Real time and online to know the state of the vehicle parameters of vehicle stabilitycontrol is very important, and the sideslip angle is one of the important parameters formeasuring the stability of the vehicle, but it is difficult to be obtained by the directmeasurement method. This paper uses the Kalman filter method to estimate the vehiclesideslip angle. On this basis, we make the output value of linear two degree of freedommodel of the vehicle as the control target, and the control variable is the error between actual yaw angular velocity,the sideslip angle and the ideal value with the linear quadraticoptimal control theory, that to decide and maintain additional yaw moment of vehicle yawstability.Secondly, the paper studied on yaw moment stability control based on the hydraulicbrake characteristics and motor diving/braking characteristics.Through real-timedecision-making needs to exert control wheel, use hydraulic differential braking to allocateadditional yaw moment between the wheels. This stability control is the same as theconventional cars. And then study the yaw moment distribution based on the motorcharacteristics, sowe use torque average distribution that is the one side of the wheel drivingtorque decreases, and the other side of the wheel driving torque increases, in order toachieve the yaw moment of demand. Finally, we make optimal allocation of each wheeldrive torque optimization goals based on the minimum load on the tire-road. Drawn fromthe simulation that the optimizing allocation method can improve vehicle yaw stability isbetter than average allocation method.Then, the paper studies the method of combining hydraulic brake and motordrive/braking execution to ensure the realization of yaw stability. When the vehicle needsyaw moment control，it precedently use motor control, but if motor braking still can’t meetthe demand until it has reached the limit, and it use hydraulic braking as compensationcontrol. Then we studied the yaw stability of coordination control under different failuremodes of failure motor. For motor failure of vehicles in the stable travel, vehicle priorityshould be given to achieve the yaw stability with ensuring vehicle’s power method, for thatthe yaw moment reallocation in the remaining wheels. For the failure of motor when thevehicle is in limit condition, the best selection of hydraulic differential braking to meet thedemand of the stability when it comes to the diagonal wheel motor failure and multi-motorfailure, and as for the other motor failure mode, control method is consistent with themotor failure control for the vehicle in stable state of motion.Finally,the paper makes comprehensive summary of yaw stability control for thedistributed drive electric vehicle, and makes the looking of yaw stability control to continue to explore in the future.