| Braking energy recovery system, which operates according to the driver’s operating intention and the working surrounding, can make the electric vehicle brake safely by distributing mechanical braking force and controlling the electric motor generation which also produce braking force. Then braking energy is recycled as much as possible, so it is an effective way to increase the cruising mileage of the electric vehicle. The premise of the braking energy recycling is to accurately judge the braking intention. Previous studies mainly concentrated on judging brake intentions through the movement of brake pedal, while less studies do that through the movement of accelerator pedal. It can better predict the real driving intention of the driver through the analysis of the accelerator pedal and driving environment.As the previous braking energy recovery technology mostly focused on passive recovery and did not include enough parameters of braking intention, this paper puts forward an active energy recovery control system based on the movement of accelerator pedal and the time headway, and then studies the fuzzy recognition of the braking intention and barking energy recovery control strategy.(1) Fuzzy recognition of braking intention based on the movement of accelerator pedal and the time headway.Braking intentions based on the accelerator pedal were classified. The three driving intentions, include free coasting, running with braking and pressing accelerator pedal mistakenly, were judged as decelerating intentions through the accelerator pedal. A fuzzy identifier which selects the time headway, the accelerator pedal displacement, and its changing rate as the input parameters was studied. Based on the analysis of statistical data, universes of the changing rate of the accelerator pedal displacement and the time headway were discussed. And then a hierarchical fuzzy identifier with three input and single output was designed, which is strongly timeliness, and with less rules.(2) Control strategy of braking force distribution.Factors which would influence the maximum braking force of the electric motor, such as its torque characteristics, power generation efficiency of the electric motor and the battery SOC(State of Charge), were studied. Then the maximum braking force equation of the motor was deduced. To reach goals of safety braking and braking energy recovery, the power distribution curve of the front and back axles was established based on I curve and ECE regulation curve. Based on that, braking torque distribution control strategy between electrical and mechanical brake of the front and back axles was studied.(3) Simulation experiment and analysis.The model of a four-wheel independent drive electric vehicle was established by AVL – CRUISE. Mechanical braking force distribution strategies of the front and back axles were established by MATLAB/SIMULINK. And then a joint simulation analysis of the braking intention recognition and operating characteristics of active energy recovery control system was done.Simulation results showed that:(1) The settled fuzzy recognition strategy can identify the required braking intensity by recognizing the intention of the driver’s operation on the accelerator pedal when time headway is small. The vehicle’s active safety was improved by high strength braking when the driver operated wrongly such as slammed pressing the accelerator pedal when the time headway is small.(2) The control system of braking energy recovery can meet the braking intensity demands which are outputted by fuzzy recognizer and the need of braking efficiency. The braking force distribution of the electric motors of the front and back axles are accorded with the requirements of motor torque characteristics, braking efficiency, I curve and ECE curve. The settled distribution curve between the braking force of the front and back axles and the motors’ mechanical braking force can meet the needs of the brake directional stability.(3) In the simulation experiment, when the charging current was limited to be 30 A, the sliding speed was 20 km/h, 25 km/h, and 20 km/h at the beginning, and the braking intensity accordingly was 0.05, 0.25, and 0.05, the energy recovery rate could reach up to 46.8%, 35.3%, and 46.8% respectively. And when braking with low intensity, the energy recovery rate was higher, while it was on the opposite when the brake intensity increased. And if limited power of charging was increased under the same braking intensity, the energy recovery rate would increase. |
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