Control of Engine Systems

Abstract

As discussed in the preceding chapters, engine systems contain a large number of control loops. For the design of these feedforward and feedback control systems, the main objectives are:

• The driver’s demands for immediate torque response, good drivability, and low fuel consumption must be met.

• The engine must be kept in a safe operating region where damage to or fatigue of the material is avoided. Knocking must be prevented, the catalytic converter must not overheat, etc.

• The emission limits must be met.

• In the case of SI engines, this requires a rapid light-off of the catalytic converter, precise stationary air/fuel ratio control, and good compensations of the transient phenomena.

Since these requirements are partially contradictory, they must be fulfilled ac- cording to the priorities set by legislation and customer demands. In this optimization, control systems play a major role as enabling technology.

The complete treatment of all control problems arising in engine systems is beyond the scope of this text. The following five important case studies are presented with the intention to show how model-based methods can be used to streamline the design process:

• Physics-based modeling and control of engine knock as an example for model-based signal processing, Sec. 4.2

• The air/fuel-ratio control as a typical combined feedforward and feedback control problem. The conventional approach is discussed in Sec. 4.3.2, whereas model-based design methods are presented in Sec. 4.3.3 and 4.3.4.

• The combined engine-speed and air/fuel-ratio control system as an example of a MIMO control problem, Sec. 4.3.5

• The SCR control system in Sec. 4.4 shows how sensor models can help to improve the system performance.

• The engine-temperature control-system or “thermomanagement” as an example of a control system that must cope with a changing system structure, Sec. 4.5