Torque Coordination Control Strategy For Brake Mode-Switch Of Plug-in Four-wheel Drive Hybrid

With the rising threaten of environmental pollution and energy crisis,the green-car become the research hotspot of global vehicle manufacturers.Plug-in hybrid electric vehicles have become one of the ideal transitional cars because they can effectively reduce fuel consumption and emissions,and also have better performance of power and drive range.Regenerative braking is a key technology for improving fuel efficiency of the hybrid vehicle.It can convert kinetic or potential energy into electric energy and store in battery during braking,thus achieving energy recovery;hydraulic braking system as a mature technology,it can provide a stable and efficient braking force for a vehicle.The dynamic characteristics of the electro-hydraulic compound braking system have a direct impact on the fuel economy,emissions,braking safety,and ride comfort of a vehicle.In order to ensure both the energy recovery and braking safety of vehicle,the demanded braking force cannot be guaranteed through regenerative braking alone,therefore,there are several braking modes during braking.The different dynamic characteristics of hydraulic and motor braking systems cause torque fluctuations during braking mode switch,which deteriorates the riding comfort and the vehicle safety.A new type of plug-in hybrid vehicle is taken as the research object,this paper designed the structure of powertrain,matched the parameters of vehicle and simulated on MATLAB/Simulink,finally,put forward the control strategies of braking force distribution and braking mode switches.As shown in follows:(1)The scheme on powertrain of plug-in electric hybrid electric is designed,then,according to the target performance requirements,the type of power,battery and transmission systems were selected,and their parameters are designed.Finally,the simulation model is established on the platform of Cruise,and the performance of power and fuel economy is simulated.(2)The combined maximum braking strength characteristics of front and rear motors of hybrid vehicles is studied,and the figure of braking strength with the change of speed and CVT ratio is plotted.Finally,this paper put forward the braking force distribution strategy based on the energy recovery and brake safety.(3)Based on the MATLAB/Simulink,the simulation model of engine,battery and driver etc.were established,then,the mathematical model of the permanent magnet synchronous motor and vector control principle were analyzed.Above all,the forward simulation model of hybrid electric vehicle was built.(4)The evaluation index for braking mode switches was proposed,and the kinetics of braking modes were analyzed.The dynamic response characteristics of the motor and hydraulic braking torque are introduced,based on model of the motor and hydraulic braking systems built in this paper,then,the coordination control strategy of braking mode switching is proposed,and a fuzzy controller is designed for the control strategy.(5)The effectiveness of the coordinated control strategy was shown by comparing the results with and without a control strategy,the simulation results about torque fluctuation and vehicle jerk during braking mode switches were analyzed.