Engine management system - EDC (Operation): Description and operation

Operation

General

The ECM controls the operation of the engine using information stored within memory in the form of maps. The maps contain data which is used to determine the most efficient fuelling for any given driving condition. The ECM also has maps for the operation of sub systems such as EGR. The ECM is an adaptive unit which 'learns' the characteristics of the vehicle components. This feature allows the ECM to compensate for any variations in components fitted to the vehicle in production, and to adapt to changes which may occur in service. The ability to compensate for 'wear and tear' and environmental changes during the life of the vehicle ensures that the ECM can comply with the emission control legislation over extended periods. The ECM is programmed with a 'strategy', this controls the decisions about 'when' to turn specific functions on and off. The inputs to this decision making process are supplied by sensors, mounted at various locations on the vehicle, which supply information to the ECM. If a sensor fails to supply information, the ECM will use the remaining sensors, and insert a default value for the missing information. This is not always possible, in which case the vehicle will be disabled. Where a default is used, this may result in reduced driveability, or an increase in fuel consumption and exhaust emissions. The ECM is programmed with vehicle specific information known as a 'calibration', this is the data required to calculate the 'outputs'. This information along with sensor inputs and interfaced data determines actuator output signals.

The ECM facilitates strategies such as: l Smoke limitation. l Active surge damping. l Automatic gear change. l Fuel reduction. l Engine cooling. l Combustion noise limitation.

During idle and wide open 'throttle' conditions the ECM uses mapped information to respond to the input from the Throttle Position sensor. To implement the optimum fuelling strategy for idle and wide open 'throttle' the ECM requires input information from the following: l CKP sensor. l Throttle Position sensor. l ECT sensor. l MAF/ IAT sensor. l High pressure fuel sensor.

This information is then compared to mapped information within the ECM to facilitate acceleration using the following actuators and controllers: l EGR modulator - closed for cleaner combustion. l Fuel pressure regulator - increase fuel pressure to injector rail. l Electronic fuel injectors - injection duration longer. l A/C compressor clutch relay - de-energised during wide-open 'throttle' to reduce engine load. l EAT ECU - kickdown (automatic gearbox models).

During cold start conditions the ECM uses ECT information to determine if cold start strategy is required. During cold start conditions the ECM will inject more fuel into the cylinders and will initiate glow plug timing strategy for effective cold starting. Normal fuel strategy is used during hot starts.

Injection Control

The purpose of the injection control is to deliver a precise quantity of finely atomised fuel into the combustion chambers at the correct times in the engine cycle.

To precisely control fuel injection quantity and timing, the following information must be available to the ECM: l Crankshaft speed and position: This information enables the ECM to determine the volume of air induced into the cylinders and the position of the crankshaft for timing purposes. l Camshaft position: This information enables the ECM to determine the relative positions of the crankshaft and camshaft for timing purposes. l Injection timing map information: This information provides the basic data which is used by the ECM when calculating the injection timing and quantity.