A regenerative braking algorithm is proposed for a hybrid electric vehicle with a continuously variable transmission (CVT) to make the maximum use of the regenerative braking energy. In the regenerative braking algorithm, the regenerative torque is determined by considering the motor capacity, battery state of charge (SOC), and vehicle velocity. The regenerative braking force is calculated from the brake control unit by comparing the demanded brake torque and the motor torque available. The wheel pressure is reduced by the amount of the regenerative braking force and is supplied from the hydraulic brake module. In addition, the CVT speed ratio control algorithm is suggested during braking for optimal motor operation. The optimal operation line is proposed to operate the motor in the most efficient region while keeping the motor speed as low as possible by considering engine noise and friction. It is found from the experiments that the regenerative braking algorithm with CVT ratio control offers an improved battery SOC, which provides increased recuperation energy by 8 per cent for the federal urban driving schedule compared with that of the conventional CVT ratio control.

A regenerative braking algorithm and a hydraulic module are proposed for a parallel hybrid electric vehicle ( HEV ) equipped with a continuous variable transmission (CVT ). The regenerative algorithm is developed by considering the battery state of charge, vehicle velocity and motor capacity. The hydraulic module consists of a reducing valve and a power unit to supply the front wheel brake pressure according to the control algorithm. In addition, a stroke simulator is designed to provide a similar pedal operation feeling. In order to evaluate the performance of the regenerative braking algorithm and the hydraulic module, a hardware-in-the-loop simulation ( HILS ) is performed. In the HILS system, the brake system consists of four wheel brakes and the hydraulic module. Dynamic characteristics of the HEV are simulated using an HEV simulator. In the HEV simulator, each element of the HEV powertrain such as internal combustion engine, motor, battery and CVT is modelled using MATLAB SIMULINK. In the HILS, a driver operates the brake pedal with his or her foot while the vehicle speed is displayed on the monitor in real time. It is found from the HILS that the regenerative braking algorithm and the hydraulic module suggested in this paper provide a satisfactory braking performance in tracking the driving schedule and maintaining the battery state of charge. Keywords: hybrid electric vehicle, regenerative braking, stroke simulator, continuously variable transmission NOTATION A front wheel cylinder area B battery power F force i speed ratio I current J inertia K t torque constant M vehicle mass N nal reduction gear ratio P pressure r brake e ective radius R t tyre radius T torque V velocity W weight factor The MS was

A cooperative regenerative braking control algorithm is proposed for a six-speed automatic-transmission-based parallel hybrid electric vehicle (HEV) during a downshift that satisfies the requirements for braking force and driving comfort. First, a downshift strategy during braking is suggested by considering the re-acceleration performance. To maintain driving comfort, a cooperative regenerative braking control algorithm is developed that considers the response characteristics of the electrohydraulic brake. Using the electrohydraulic brake’s hardware and an HEV simulator, a hardware-in-the-loop simulation (HILS) is performed. From the HILS results, it is found that the proposed cooperative regenerative braking control algorithm satisfies the demanded braking force and driving comfort during the downshift with regenerative braking.

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