Sensors for Engine and Emission Control

Hannu Jääskeläinen

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• Introduction
• Physical Sensors
• Virtual Sensors
• Application Example

Introduction

The conventional definition of sensors describes them as “devices that transform physical quantities such as pressure or acceleration into output signals that serve as inputs for control systems” [3333]. Automobiles and heavy vehicles have a number of sensors installed in the powertrain, body and chassis. New, sophisticated strategies for the control of vehicle powertrain and emission systems have been driving not only the use of new types of sensors, but also new sensor concepts and functionalities. As a result, the above definition can no longer adequately capture all of the “sensors” used in modern automotive applications.

In automobile engine applications, sensors are used not only for control purposes but also for diagnostics. Modern engines must control a wide range of parameters in order to meet emission standards. These parameters include: fuel injection amount, air flow, EGR, intake air temperature, engine temperature, exhaust oxygen content, exhaust temperature and so on. To meet these control objectives, a wide range of sensors are used. A further challenge in modern automobiles is that exhaust emissions must be maintained over the useful life of the vehicle. In order to achieve this objective, the control system must have diagnostic capabilities to identify any malfunctions not only in sensors themselves but also in critical emission control devices that could cause emissions to increase. This also requires a variety of sensors. In many cases, the same sensor can be used for control and diagnostic functions. However, some sensors can be used strictly for diagnostics or strictly for control.

Another concept not adequately captured in a conventional definition of sensors is the concept of virtual sensors. Virtual sensors are not actually physical sensors but software routines that use inputs, usually from physical sensors, to estimate the value of parameters that are either difficult to measure adequately with existing sensor technology or for which no adequate sensors exist.

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