Powertrain Control for Improved Driver Comfort During Automated Gear Shifts
Abstract: Driveability is an important issue in the development of modern trucks. Comfort and sense of control are key for the driver. During a gear shift, the flywheel torque is lowered to zero before disengaging the clutch and then increased again after engaging the clutch. Lowering and increasing the flywheel torque creates movements in the cab. The previous developments of the gear shift functionality has had the purpose to maintain a good behaviour in the powertrain. This Master’s thesis has instead investigated whether it was possible to improve the cab comfort during autonomous gear shifts by altering the way it is performed. A measure of cab comfort has been developed through experiments and cooperation a test driver. The main differences between good and bad gear shifts were identified as the amplitudes of cab accelerations and jerk. Therefore, the goal was to minimize acceleration and jerk in order to improve the cab comfort. A model of how the powertrain affects the cab movements has been developed. Sub models of the powertrain, chassis and cab were developed individually and combined into one large model. The models performed well individually and the combined model was judged to be good enough for developing a controller. At the time of writing the existing controller had the purpose of preventing oscillations and jerk in the driveline. To avoid having to consider behaviour in the powertrain the developed controller were to control the existing controller. Two approaches have been investigated, open loop control and feedback control. The functionality of the open loop controller was to low pass filter inputs to the existing controller. The other approach was a feedback controller using the z-acceleration (upwards) as feedback. The purpose was to keep the acceleration low using a reference developed with experience from the comfort experiments. Simulations of the open loop controller showed that it was possible to alter the cab comfort by altering the engine torque. The comfort was improved in most parts of the gear shift and worsend in some parts. The feedback controller showed promising results in simulations. It was problematic to combine the existing controller with the developed controller since they have different purposes. By a fusion of the controllers there would be good opportunities to improve the gearshift with respect to both powertrain behaviour and cab comfort.
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