Mode transitions are significant events in the operation of series-parallel hybrid electric vehicles (SPHEVs) with a clutch serving as the key enabling actuator element. Due to the friction-induced discontinuity of the clutch torque, seamless transition is difficult to achieve. In this paper, a model reference control (MRC) law is proposed to coordinate the motor torque, engine torque, and clutch torque to manage transitions. The control system is overactuated in the sense that three inputs (i.e., three torques) can be manipulated to control the two outputs (angular speeds of the two sides of the clutch). The effects of using different input combinations are analyzed to exploit the overactuation feature of the system, and performance sensitivities to various design factors are studied. The simulation and experimental results from an SPHEV bus demonstrate that the MRC achieves reduced torque interruption, less vehicle jerk, and smaller frictional losses, compared to the conventional operation method.

A non-linear multi-rigid-body system dynamic modelling is developed for the automated clutch system in power transmission during clutch engagements, especially at sharp vehicle start-up, sudden engine flame-out, low driving speed and clutch plate overwearing. In order to guarantee an ideal dynamic performance of the clutch engagement, an adaptive optimal controller is designed by considering throttle angle, engine speed, gear ratio, vehicle acceleration and road condition. A non-linear model reference adaptive controller is utilized to prevent the engine from flame-out or fly-off effectively and the minimum value principle is also introduced to achieve an optimal dynamic performance of the non-linear system compromised in friction plate wear and vehicle drive quality. The optimal trajectory of the clutch engagement can be described in the form of explicit and analytical expressions and characterized by a deterministic and accurate control strategy instead of indeterministic and soft control techniques which need thousands of experiments. For validation of the controller, test work is carried out for the automated clutch engagements in a commercial car with a traditional mechanical transmission, a hydraulic actuator, a group of sensors and a portable computer system. It is shown through experiments that dynamic behaviours of the clutch engagement operated by the adaptive optimal control are more effective and efficient than those by a fuzzy PID control.

Clutches are widely used in various vehicle powertrains. The engagement process of a friction clutch has three phases, i.e., open, slipping, and sticking. Transitions between different phases introduce a discontinuity to the powertrain dynamics, which has been neglected in previous research. A model referenced adaptive controller (MRAC), based on Popov hyper-stability criterion, is designed to compensate the discontinuity. MRAC adjusts the frictional torque along with the errors of the state variables compared with those of a referenced model. The designed MRAC is applied to a clutch in a bus. Simulation and experimental results under fast and slow startup cases show that MRAC can simultaneously reduce vehicle jerk and frictional dissipation when compared with the conventional controller.

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