Ignition Coil Pack: Description and Operation

Ignition Discharge Module

Ignition
The ignition discharge module is mounted on the camshaft cover over the spark plugs. The ignition discharge module contains 4 ignition coils, the secondary windings of which are connected directly to the spark plugs.

The ignition discharge module is supplied with current (B+ circuit) from the main relay and grounded at grounding point G7.

When the main relay operates, B+ is supplied to the ignition discharge module which converts the 12 V to 400 V DC which is stored in a capacitor. This voltage (400 V DC) is connected to one pole of the primary windings of the 4 ignition coils.

From the control module, 4 trigger leads go to the ignition discharge module as follows:
- Cyl. No. 1 is connected to control module pin 7.
- Cyl. No. 2 is connected to control module pin 54.
- Cyl. No. 3 is connected to control module pin 55.
- Cyl. No. 4 is connected to control module pin 8.

When the control module grounds pin 7, the other pole of the primary winding of the ignition coil for cylinder No. 1 is connected to the B+ input of the ignition discharge module. The 400 V current is stepped up to a maximum of 40 kV in the ignition coil for cylinder No. 1. Ignition for cylinder Nos. 2, 3 and 4 takes place in the same way.

Diagnostics
- If a break occurs in the supply of current to the ignition discharge module the voltage on all trigger leads is 0 V and trouble code P1310 will then be generated.
- If a break occurs in an individual trigger lead, no diagnostic trouble code will be generated.

System reaction to a fault
Fuel shut-Off






Combustion Signals, Synchronization

The Trionic T7 has no camshaft position sensor as normally required for sequential knock control and fuel injection.

On starting, the control module does not know which of cylinders No. 1 and No. 4 is in the compression position, so ignition takes place in both these cylinders at the same time. Ignition takes place in cylinders No. 2 and No. 3 in the same way.

The control module must determine whether ignition takes place in cylinder No. 1 or cylinder No. 4, and also in cylinder No. 2 or No. 3 when these are triggered. This is done as follows.

One pole of the secondary windings of the 4 ignition coils is normally connected to the relevant spark plug. The other pole is not grounded direct but connected to 80 V. This means that a voltage of 80 V is always present across the spark plug gap except just as the spark is produced.

When combustion takes place, the temperature in the combustion chamber is very high. The gases are ionized and begin to conduct current. This means that current passes between the spark plug electrodes without producing a spark.

As the circuit is completed between the spark plug electrodes, the current (80 V) flowing across the gap drops sharply. The voltage drop will be proportional to the pressure and temperature in the combustion chamber.







Two detectors measure the voltage drop across cylinder Nos. 1+2 and 3+4 respectively. If combustion occurs in cylinder No. 1 or No. 2, the ignition discharge module sends a B+ pulse to control module pin 53. Similarly, the ignition discharge module sends a B+ pulse to control module pin 6 if combustion occurs in cylinder No. 3 or No. 4.

If cylinders No. 1 and No. 4 are triggered and a B+ pulse is received on control module pin 53 at the same time, the control module knows that cylinder No. 1 has fired.
As soon as combustion signals are received on control module pins 53 and 6, both ignition and fuel injection are synchronized to the engine firing order.

Diagnostics
- If ignition and the camshaft position are not synchronized, diagnostic trouble code P0340 will be generated.

System reaction to a fault
If a break occurs in any of the leads to control module pins 53 and 6, no synchronization of the ignition or fuel injection will take place. Knock detection then takes place on cylinder Nos. 1+4 and 2+3 at the same time.