Hanho Son

Development of Brake System and Regenerative Braking Cooperative Control Algorithm for Automatic-Transmission-Based Hybrid Electric Vehicles

In this paper, a brake system for an automatic transmission(AT)-based hybrid electric vehicle (HEV) is developed, and a regenerative braking cooperative control algorithm is proposed, with consideration of the characteristics of the brake system. The brake system does not require a pedal simulator or a fail-safe device, because a hydraulic brake is equipped on the rear wheels, and an electronic wedge brake (EWB) is equipped on the front wheels of the vehicle. Dynamic models of the HEV equipped with the brake system developed in this study are obtained, and a performance simulator is developed. Furthermore, a regenerative braking cooperative control algorithm, which can increase the regenerative braking energy recovery, is suggested by considering the characteristics of the proposed hydraulic brake system. A simulation and a vehicle test show that the brake system and the regenerative braking cooperative control algorithm satisfy the demanded braking force by performing cooperative control between regenerative braking and friction braking. The regenerative braking cooperative control algorithm can increase energy recovery of the regenerative braking by increasing the gradient of the demanded braking force against the pedal stroke. The gradient of the demanded braking force needs to be determined with consideration of the drivers braking characteristics, regenerative braking energy, and the driving comfort.

Shift control of a dry-type two-speed dual-clutch transmission for an electric vehicle:

In this paper, a shift control algorithm to improve the shift quality was proposed for an electric vehicle with a dry-type two-speed dual-clutch transmission. To analyse the shift characteristics of the target electric vehicle, dynamic models for the two-speed dual-clutch transmission and the drivetrain were developed. Based on the dynamic models, dynamic equations for the transient shift states were derived, and a shift performance simulator was constructed. From analysis of the transient shift state, it was found that the fluctuations in the driveshaft torque, which cause the shift quality to deteriorate, occurred as a result of the inertia torque. Based on the analytical results, a control algorithm was proposed using traction motor torque control as well as shift actuator stroke control. For traction motor control, a compensation torque was applied during the inertia phase. In that phase, actuator stroke control was performed by considering the torque margin and the kissing point during the torque phase instead of the existing map-based control. To evaluate the performance of the proposed control algorithm, a test bench for the target electric vehicle was developed. From the experimental results, it was found that the variations in the driveshaft torque and in the jerk were reduced by the proposed control algorithm, which thereby provides an improved shift quality.

Development of a gear fork control algorithm to improve the shift quality of a dual-clutch transmission

In this study, a gear fork control algorithm for a dual-clutch transmission is proposed to improve the shift quality for the downshift from second gear to first gear during coast-down. First, to investigate the shift characteristics, a dual-clutch transmission shift performance simulator was developed including the gear fork system. Using the dual-clutch transmission simulator, the shift characteristics for the downshift from second gear to first gear were investigated during coast-down. From the simulations and the test results, it was found that vibrations occur in the speed of the output shaft owing the large change in the speed gradient of the input shaft at the moment of synchronization, resulting in a change in the longitudinal acceleration of the vehicle, which causes the shift quality to deteriorate. Based on the dynamic models of the gear fork system and the test results, a gear fork control algorithm is proposed which generates a constant cone torque to reduce the speed gradient of the input shaft. It was found from the simulations and the vehicle test results that the amplitudes of the vibrations in the speed of the output shaft and the peak-to-peak acceleration of the vehicle were reduced by the gear fork control algorithm proposed in this study, which improved the shift quality by as much as 50%.

Optimal Control of Plug-in Hybrid Electric Vehicle based on Pontryagin's Minimum Principle Considering Driver's Characteristic.

In this study, an optimal control was investigated for a power split type plug-in hybrid electric vehicle (PHEV) considering the driver’s characteristic. Using the dynamic model of the PHEV powertrain, Hamiltonian was defined and the optimal co-state was obtained for Pontryagin’s minimum principle (PMP) control. The PMP control was performed for a normal driver who was selected based on extended driving style questionnaire (EDSQ), and the battery SOC behaviour and equivalent fuel economy were evaluated. It was found that the equivalent fuel economy by the PMP control is improved compared with the existing charge depleting/charge sustaining (CD/CS) control and the battery SOC decreased faster as the sportiness of the driver increased.

Development of a new sub-shift schedule and control algorithm for a hydro-mechanical transmission

In this study, a new sub-shift schedule was proposed for a hydro-mechanical transmission. To develop the sub-shift schedule, a network analysis was performed by considering the hydrostatic unit loss and mechanical component losses. In the new sub-shift schedule, the sub-shift gear can be selected with respect to the demanded wheel torque and vehicle speed, which provides improved system efficiency for the given vehicle operating condition. Since the sub-shift can only be carried out at a speed ratio where the off-going and on-coming clutch speeds are synchronized in the existing sub-shift control, a sub-shift control algorithm without the clutch speed synchronization was proposed to apply the new sub-shift schedule using the forward clutch pressure and hydrostatic unit stroke control. The performance of the sub-shift control algorithm without the clutch speed synchronization was evaluated by the simulation and experiment. It was found from the simulation and experimental results that the sub-shift can be achieved, showing an acceptable peak-to-peak torque variation in the driveshaft.

Motor-generator control to improve shift quality for a dual mode power split transmission

In this paper, a motor-generator (MG) control algorithm was proposed to improve the shift quality for a dual mode power split transmission (PST) hybrid electric vehicle (HEV). In order to analyze the shift characteristics during the mode shift, Bondgraph models for transient-state were constructed and state equations were derived. From the state equations, it was found that inertia torque of MG2 causes a transient torque during the mode shift. Based on the transient torque, a MG torque control algorithm which compensates the transient torque was developed to reduce the driveshaft torque variation. To evaluate the performance of the MG2 control algorithm, dynamic models of the dual mode PST HEV were obtained and an AMESim-MATLAB/Simulink based mode shift performance simulator was developed. It was found from the simulation results that the driveshaft torque variation was reduced by the proposed control algorithm which provides improved shift quality.