Ignition Coil
Ignition Coil
Ignition coil
The engine has an inductive ignition system with static ignition voltage distribution. Each cylinder has a separate ignition coil, which is plugged directly into the cylinder head cover.
The ignition circuit of this coil ignition consists of:
- Ignition coil with primary and secondary coil
- Ignition output stage in the engine control unit
- Spark plug, connected to the secondary coil
Each spark plug receives its high-tension voltage from its own ignition coil (pencil coil) and a separate individual ignition output stage within the engine control unit.
Functional description
The ignition output stage switches on a current from the on-board electrical system through the primary coil before the required ignition time. While the primary circuit is closed (closing time), a magnetic field is built up in the primary coil. When the ignition time is reached, the current is interrupted again by the primary coil. The energy of the magnetic field discharges via the magnetically coupled secondary coil (induction). This creates a high voltage in the secondary coil, which generates the ignition spark at the spark plug.
The ignition voltage that is needed at the spark plug (required ignition voltage) must always be greater than the maximum possible ignition voltage of the ignition system (available ignition voltage). Once the ignition spark has broken through, the remaining energy is converted at the spark plug during the spark duration.
The ignition time when the ignition spark ignites the fuel-air mixture in the combustion chamber must be set with extreme accuracy. This provides an optimum torque and low consumption, together with minimal emissions.
The main influential parameters are:
- Engine speed
- Engine torque
- Charging pressure
- Current lambda value
- Coolant temperature and intake air temperature
- Fuel grade (octane number)
- Engine operation (engine start, idling, partial throttle, full throttle)
Structure and inner electrical connection
The ignition coil operates according to the principle of a transformer. 2 coils are placed onto a shared ferric core. The primary coil consists of a thick wire with just a few windings. One end of the coil is attached to the positive terminal (terminal 15) of the vehicle voltage via the load-shedding relay terminal 15. The other end (terminal 1) is connected to the ignition output stage, which can use it to switch the primary current. The secondary coil consists of thin wire with many windings.
Signal shape and setpoint values
The ignition signal calculation also ensures that the ignition spark is produced in the correct cylinder, with optimum ignition timing and with the necessary energy. To do this, the speed signal from the crankshaft is recorded. From this the engine control unit calculates the crank angle and the current engine speed.
The ignition output stages are then switched on and off for any required crank angle (sensible range for petrol engine: -70 crankshaft degrees before top dead centre up to +30 crankshaft degrees after top dead centre. In a 4- stroke engine, ignition is only required after every second revolution which means the camshaft sensor is necessary in order to clearly allocate a cylinder.
The basis for multiple spark ignition is repeated switching on and off of the ignition coil. As a result, the actual ignition spark is extended to produce a band of sparks. The individual sparks are cancelled by recharging early with the result that no further energy at the spark plug is transmitted to the fuel-air mixture. Residual energy is left In the ignition coil which also minimizes the recharging time. Multiple spark ignition is only intended to be used in the low engine speed range and also during the warm-up phase (spark plug cleaning).
Observe the following setpoint values for the ignition coil:
Size Value
Voltage range 6 to 16 V
Voltage, secondary coil, in normal up to 29 kV
operating mode
Maximum current consumption in 8 to 10.5 A
normal operating mode
Primary resistance less than 600 mOhms
Ratio, primary coil to secondary 1:80
coil
Temperature range -40 to 140 deg C
Diagnosis instructions
Failure of the component
If an ignition coil fails, the following behavior is to be expected:
- Fault entry in the engine control unit
- Misfire
General notes
NOTICE: Observe exact position of the spark plug.
In contrast to naturally aspirated engines, a pronounced charge movement is generated in spray-guided direct injection engines. The spark plug must be geometrically situated directly in the respective injected fuel spray. In the N63 and N74 the exact seating is ensured by a straight-cut thread on the spark plug and in the cylinder head. A precise tightening torque of 23 Nm ± 3 Nm must be observed in the process. As the spark plug electrodes are positioned particularly deep inside the combustion chamber,. lean mixture compositions can also be ignited. This is important in the cold-start phase and in the catalytic converter warm-up phase. Multiple sparks are also discharged during this phase when, in contrast to previous engine management systems, all ignition-related diagnostic functions remain active.
We can assume no liability for printing errors or inaccuracies in this document and reserve the right to introduce technical modifications at any time.