Simulation and transient control of diesel engine compression brake

Licentiate thesis, 2004

The recent development of sophisticated integrated powertrain control systems for heavy duty trucks, including handling of driveline oscillations and automated gear shifting systems, requires detailed simulation models during the development process. These models need to balance the demands for accuracy, ease of parameterization and simulation efficiency. The application in focus in this work is the transient engine speed control during an automated gear shift sequence of a heavy duty truck. In the case of an upshift, the engine must rapidly be decelerated to the new synchronous speed. Since the normal engine friction is small, the engine compression brake is activated. A dedicated engine simulation model is needed in order to be able to develop a controller for this sequence. This report presents a crank angle based diesel engine model, especially well suited for simulation and development of control strategies for the transients during automated gear shifts in a heavy duty truck. It includes compression brake capabilities. The model can be characterized as a “filling and emptying”-model, using the ideal gas law and standard equations for flow restrictions connecting lumped control volumes. An empirical combustion model is used, assuming adiabatic conditions in the cylinder. During no-load or when the compression brake is active, cylinder wall heat exchange is taken into account. A tuning procedure is outlined and pursued for a 12 litre turbocharged Volvo diesel engine. The simulations agree well with measurements. An example to show the usefulness of the model is given where the rapid engine speed deceleration during an upshift is studied.