Observer-based multivariable control of gear shift for parallel hybrid electric vehicles with dual-clutch transmission

Abstract

This study deals with cooperated control of drive motor and clutches for the gear shift of a parallel hybrid electric vehicle (HEV) with dual-clutch transmission (DCT). The HEV with DCT powertrain requires sophisticated control of two clutch actuators and power sources to achieve good shift performances, i.e. smooth and fast gear shifts. In this dissertation, a new shift control approach based on the feedback of both speed and torque states is implemented to improve the shift quality of a parallel HEV with a dry DCT. Differently from previous approaches, the proposed control uses the dynamic torque observer to accurately track the desired transient torque as well as the desired clutch slip speed during the inertia phase to attain smooth and fast shift. In addition, since the drive motor is installed in the HEV’s driveline, the transient torque through the driveline can be effectively controlled by using the fast dynamic characteristics of the drive motor. A major difficulty arising from the shift control of DCT is the interactions between the speed and torque control loops. To treat the coupling effects effectively even in the presence of various model uncertainties and disturbances, a robust multivariable control scheme using H-infinity loop shaping is suggested especially for the inertia phase control. The developed control structure is divided into two stages: the upper level control that governs the procedure to determine the most suitable torque trajectories of the clutches and power sources, and the lower level control that manages the strategy for each actuator controller to track the given torque trajectories.

Because the proposed controller requires information of the driveline torque states in real time, a new torque observer for the DCT driveline is also developed. Knowledge of the driveline torque states, such as the torque transmitted through a clutch, and transmission output torque, allows a significant improvement in powertrain control performance, especially during gear shifts and vehicle launch. Furthermore, vehicles with DCT or automatic transmission whose gear shift processes involve clutch-to-clutch shifts require information about the individual clutch torques for sophisticated torque transfer control. Thus, an adaptive torque observer, which is applicable to DCT drivelines, is developed to estimate the torque transmitted through each clutch and output shaft simultaneously. In order to overcome the lack of measurements in a production car, the proposed observer uses multiple adaptation laws in accordance with driving conditions so that it treats parameter uncertainties effectively, such as those of the clutch friction coefficient, nominal engine torque as well as vehicle load torque. The estimation performance of the observer is evaluated through simulations using SimDriveline, and experiments on a real vehicle as well as a test-bench equipped with torque sensors. Then, the performance of the closed-loop observer-based controller is demonstrated through real time experiments and simulations. Various comparative studies with the conventional approaches are also conducted, and detailed discussions of the results are provided.