Dynamical Blending Control Of Regenerative Braking And Frictional Braking For Electrified Vehicles

With the rising concern in global environmental issues and energy crisis, new energy vehicles, including hybrid electric vehicles, electric vehicle, and fuel cell electric vehicles, become worldwide research topics. In urban driving situations, about one third to one half of the energy used for directly driving the wheels is consumed during deceleration processes. A regenerative brake system, which has the ability to convert kinetic energy into electrical energy and stored in battery during decelerations, can significantly improve the energy efficiency of a vehicle. However, compared to the conventional friction brake, the regenerative brake presents quite different generation,transfer and response mechanisms, because of the effects exerted by the components of the electric powertrains. Thus, the utilization of the regenerative brake system presents tremendous challenges to the existing vehicle theories and control methods.Several key scientific problems of regenerative brake of electric passenger vehicles,including regenerative brake system design, comprehensive optimization strategy of regenerative energy management, high-precision control method of hydraulic braking pressure during regenerative decelerations, and dynamical blending control algorithm of regenerative brake and frictional brake, are investigated in this paper.A new type of cooperative regenerative braking system, which integrates the functions of wheel brake pressure modulation and brake pedal feel simulation, is proposed. By utilizing the hydraulic pressure modulating actuators and brake pedal stroke simulators cooperatively, the applicaition complexity of the cooperative regenerative braking system can be significantly dcreased.Models of the vehicle, the tyre, and the main components related to the regenerative brake and the frictional blending brake of the electric passenger car are built. The coordination regenerative management strategy cooperating regeneration efficiency, brake pedal feel, and vehicle jerk, are developed. The proposed regenerative brake system with control strategy has the capability to handle the conflict between regeneration efficiency and brake comfort.The mechanical-electro-hydraulic coupling models of a solenoid valve are built. A linear relationship between limited pressure difference and coil current of an on/offvalve in its critical closed state is proposed and illustrated. Then, a novel pressure-difference-limiting modulation method of the hydraulic pressure is developed.It widens the existing hydraulic modulation approaches, and has a great capability to improve the control accuracy of the hydraulic brake pressure during regenerative decelerations.An electric powertrain model with nonlinear backlash and axle flexibility is developed. The effects of the powertrain backlash and the flexibility on the control performance of the blending brake are analyzed. Then, an observer for reconstructing the states of the electric powertrain are designed using hybrid systems approach.Targeting the non-linear backlash and the axle flexibility, a mode-switching-based active compensating algorithm is developed. The proposed algorithm can damp the torsional oscillations of the electric powertrain during regenerative braking,significantly enhancing the blended braking performance.