Nonlinear model-based control of automotive powertrains

In recent years the focus of powertrain control has shifted perspective from control of the individual powertrain components to control of the complete powertrain, so-called integrated powertrain control. The idea presented in this thesis is to view the powertrain as one single control object and to used the engine as a torque actuator to the rest of the driveline. The investigated powertrain consists of a diesel engine with a variable geometry turbocharger, an automated manual transmission, flexible driveshafts and wheels and chassis to make the vehicle complete. The vehicle in focus is a heavy duty truck. The power a diesel engine can generate is limited by the amount of fuel that can be burnt efficiently. The combustion efficiency is determined mainly by the amount of air that is available for combustion. An insufficient amount of air results in increased particulate emissions and visible smoke, while a surplus of air results in NOx emissions. This means that active engine control not only deals with manipulation of the engine speed or the engine torque but also includes efficient control of the engine itself. The idea of integrated powertrain control is to use the engine as an active part of the control system. A turbocharged diesel engine is a complex and different actuator compared to other actuators used in control systems. The working region is limited, the outcome from the actuator (torque) is uncertain, the capacity varies with operating point and the performance is directional dependent. Several different solutions to the problem of controlling the air-to-fuel ratio for a turbocharged diesel engine are proposed. The solutions are nonlinear model-based control laws, designed using stability analysis by means of Lyapunov functions. Two applications are also studied; driveline oscillations and gearshifting in an automated manual transmission. In both cases engine control becomes an essential part of the solution. The engine is used actively in order to remove oscillations in the driveline and to perform fast and smooth gearshifts. The resulting solutions are obtained by combining engine speed/torque and air-to-fuel ratio control.