Development and Implementation of Drive Away Release Function for a Vehicle

University essay from Linköpings universitet/Fordonssystem; Linköpings universitet/Fordonssystem

Abstract: As autonomy increases in today’s vehicles, the demands increase on both safety and comfort functions. Vehicle Hold, which holds the vehicle stationary without requiring the driver to press the brake pedal, is an example of such as function. This thesis aims to develop a concept for a Drive Away Release from this hold state, following several requirements regarding such as rollback, comfort, manual and autonomous drive mode, driving direction, road inclinations, with or without a trailer, and following the safety standard ISO 26262. In order to develop the concept function, a study of the state-of-the-art was made, followed by modeling the dynamics and control. The control algorithm was validated and tested first by running co-simulations between Matlab/Simulink and CarMaker. It was then implemented in a test vehicle. The test vehicle did not have all systems which are usually provided, demanding estimations to be made, such as the road inclination and vehicle mass. For manual drive mode, the driver controls the propulsion torque, and the control algorithm is based on releasing the brakes depending on estimations of the gravitational and propulsion torques. For autonomous drive mode, the vehicle is supposed to follow an acceleration reference. The control algorithm for autonomous drive mode is then extended with two feedforward compensators, one from reference and one from the gravitational torque, which is regarded as a disturbance, and with a feedback PI controller. To ensure that rollback do not occur at drive away release, a rollback prevention safety feature was also developed. The results of both the simulations and the test drives show that the concept function provides comfortable drive-off for most inclinations, drive modes and directions, without causing an undesired rollback

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