Injection Control

OPERATION
Injection Timing Control
On the basis of the engine speed and load signals, the Digital Motor Electronic (DME) control unit determines the ignition angle (ignition timing) which is output via the ignition output stage. This function also takes into consideration other input signals such as the engine temperature, intake air temperature, throttle position and signals from the Electronic Throttle Control (EML), Automatic Stability Control (ASC), Engine Drag Torque control (MSR) and from the Electronic Transmission Control (EGS).

Injection Control
The DME control unit calculates the correct injection timing on the basis of the engine speed, air flow or air mass, throttle position, oxygen sensor voltage, engine temperature and intake air temperature. The mixture is varied by the opening time of the injector valves. The battery or system voltage is also taken into consideration in calculating the injection timing since the pullup and dropout times of the injector valves are extended as the voltage decreases.

Types of Injection
Each injector valve group is driven by one output stage (power amplifier). This arrangement makes it possible to divide the injection cycle into cylinder groups (semisequential injection).

Arrangement of injector valve groups:
12-cylinder: Cylinders 1+3+5 and 2+4+6,
Cylinders 7+9+11 and 8+10+12

Semisequentlal Injection
At an engine speed of 600 rpm, fuel is injected only once per 7200 crank angle into one cylinder group. This facilitates precise metering of the quantity of fuel since the injector valves need not be activated so often. It also enables restricted engine operation in the event of failure of one group.
Semisequential injection is only active when the DME control unit has received a signal from the cylinder reference point pulse generator. If this signal is not received during engine operation, the control system remains set to semisequential injection.

Two cylinder reference point sensor (pulse generator) are used:
The cylinder reference point sensor is mounted on the ignition lead of cylinder No. 6 at the distributor of the respective row of cylinders.

Parallel Injection
Parallel injection refers to simultaneous activation of all injector valves and takes place only when the cylinder reference point sensor has supplied no signal since starting the engine. As soon as a signal is applied, the system switches over to semisequential injection after the next deceleration phase.