Abstract
Diesel engines provide superior fuel economy but have some drawbacks regarding the reduction of exhaust emissions. Developing aftertreatment technologies has become a hot issue recently, and it is essential to use an aftertreatment system effectively in addition to reducing engine-out emissions. Toward that end, there is a need to control the excess air ratio (lambda) and the EGR ratio accurately, which are important control parameters.
On the other hand, the engine output torque must be controlled to ensure comfortable driving. Accordingly, it is necessary to deal with torque fluctuations caused by changes in fuel consumption characteristics as a result of controlling lambda accurately.
This study examined a control algorithm for dealing with these issues from the following two approaches. One concerns a method of calculating the fuel injection quantity based on acceleration pedal travel and engine speed and then setting the other control parameters according to the calculated result. This approach is applied to most conventional diesel engines. One of the characteristics of this method is that torque response is good because the fuel injection quantity is calculated from acceleration pedal travel, which is operated directly by the driver. However, it is difficult to control lambda precisely. The other approach concerns a method of calculating the fuel injection quantity based on the intake air mass flow. This method is generally used with gasoline engines and it was applied to a diesel engine in this study. One of the characteristics of this method is that lambda controllability is good, but torque response tends to show some delay. After confirming the respective advantages of these control algorithms, an algorithm was constructed that provides the benefits of both.
This paper presents the results of this study conducted with a simulator that used a control system CAD program to calculate physical models of a diesel engine, transmission and vehicle. It also describes the experimental results.