Drivability enhancement and transient emission reduction for a mild hybrid diesel-electric truck

This paper deals with modelling and control methodologies applied to a heavy truck equipped with a parallel hybrid electric drivetrain. The actuator redundancy, typical of the mild-hybrid vehicle configuration, allows the powertrain control system to enhance the vehicle drivability, in terms of smooth driving and promptness, while reducing transient diesel engine emissions, in comparison with conventional pure thermal engine vehicles. The electric motor, characterised by a high-bandwidth torque control, is here utilised not only to dampen the driveline oscillations that arise during rapid torque transients, e.g., when the driver accelerates the vehicle at full load in low gears, but also to keep the engine working with slow torque gradients, as required by transient emission reduction strategies. The driveline is modelled by lumped parameters, considering also the damping effects of the tyres. A detailed non-linear model is used as reference for the performance comparison of different simplified linear models. The best linear model is selected and used for the design of a LQR-based closed-loop controller aiming at reducing the driveline torsional vibrations. The regulation task (active vibration damping) is separated from the distribution task (torque splitting between the two motors).