Controller structure for high response engine exhaust throttles

Exhaust throttles are widely used as cost-effective endurance brakes on commercial vehicle diesel engines. To fulfil the requirements as endurance brakes exhaust flaps have only two states: fully opened and fully closed. However, there are several possible new applications, suggested by the authors, in which exhaust throttles could be utilised. To provide these functionalities a backpressure controller that can adjust the exhaust manifold pressure arbitrarily is needed. In this paper, the design and performance evaluation of an exhaust pressure controller is described. A first engineering principle-based, mean-value, nonlinear model of the engine and the actuator is described and validated with test bench measurements. Based on the nonlinear model a feedforward term was obtained. As feedback, an LQ servo controller was designed. The controller performance and the compliance of requirements was evaluated in three different test cycles on a medium-duty diesel engine, simulating brake blending, thermomanagement, and EGR support operations.