Ignition Coil: Description and Operation
Ignition Coil:
The ignition coils (T1) have two high-voltage connections (4a, 4b). Each connection supplies one spark plug with high-voltage.
The engine control module limits the primary current to approximately 7 A. The maximum ignition voltage is approximately 32 kV.
WARNING: The primary connections deliver voltage up to 400 v. Guide sleeve (w) must always be connected to vehicle ground.
Design and Function
Ignition Coil, Cross Section View:
The ignition coil is constructed much like a transformer, where the primary and secondary windings are physically separated from one another. Both ends of the secondary winding are equipped with a high-voltage connection which form, together with two spark plugs, a closed circuit. The secondary winding produces high-voltage during ignition.
The ignition spark occurs at both spark plugs at the same time, whereby one spark jumps from the center to the ground electrode and the other from the ground to the center electrode. As a result, constant positive and negative high-voltage to ground is present at the secondary connections. The ignition spark on the exhaust stroke requires very little energy, so that nearly all the energy stored in the coil is available for the power stroke.
Ignition Coil, Circuit Diagram:
Since the secondary winding is switched in series with both spark plugs, it has the effect of an open circuit (e.g.: on the spark plug connector) on both ignition sparks.
The resistance of the secondary winding must be checked between both high-voltage connections:
Nominal value: 5.2 - 8.5 kohms
Resistance of primary winding between connection 1 and 15:
Nominal value: 0.3 - 0.4 Ohms
Advantages of static high-voltage distribution:
- Reduced electromagnetic noise level (no open sparks),
- No rotating parts,
- Noise reduction,
- Fewer high-voltage connections.
Location of Ignition Coils and Distribution of High-voltage
Ignition Coils (T1/1, T1/2, T1/3):
The ignition coils are located on the valve cover. Each ignition coil provides high-voltage simultaneously to two spark plugs.
Ignition coil Cylinders
T1/1 2 and 5
T1/2 3 and 4
T1/3 1 and 6
Ignition Firing Chart:
The engine control module (N3/4) controls three individual ignition coils. Each coil is connected to battery voltage and the engine control module switches each coil to ground. The high-voltage output of each coil is sent simultaneously to two spark plugs, each assigned to a different cylinder. When fired, one cylinder is in its power stroke and the other is in its exhaust stroke, i.e. 360 crank angle (CKA) apart. The cylinder which is in its exhaust stroke has no combustible mixture, therefore the spark has no effect. One crankshaft rotation later, the cylinders reverse their roles.
The other two ignition coils operate in the same manner, however ignition firing is offset by 120 crank angle (CKA).
Ignition Coil:
The ignition coils (T1/1, T1/2, T1/3) are connected, via the secondary output (4a), directly to a spark plug with a spark plug connector. The secondary output (4b) travels over a ignition wire to the other cylinder assigned to that coil. The guide sleeve (W) also serves as the ground connection for the ignition coil.