Ignition system device (Mondeo 3)

Basic design of a fully electronic ignition system

1 - Spark plugs, 2 - Dual spark ignition coil, 3 — Throttle switch, 4 — Control unit (PCM), including the final stage, 5 — Lambda sensor,	6 — Engine temperature sensor, 7 — Speed sensor and reference signal sensor, 8 - Flywheel, 9 — Battery, 10 — Ignition switch.

Older coil-type ignition systems – consisting of a coil, distributor, condenser, distributor rotor, breaker contacts and high-tension ignition cable – helped, with their relatively limited flexibility, to sometimes keep old carburettor engines "on a leash": the coil "produced" a voltage capable of breakdown and the mechanical distributor once gave the spark plugs plenty of "fire". In the upper speed range, this happened with a modest early ignition, just before the top dead center of the piston, which was directly in the compression stroke. In other words: the engine periphery, all the components for the preparation of the combustible mixture and the valve actuators were more or less dependent on the static performance of the ignition system. Coil-type ignition systems "distributed" their sparks with the flexibility of a matchbox.



This is not the case in the era of electronic engine control: behind the scenes and completely unnoticed by the untrained eye, electronic components are used to "ignite" and flex connections (see the chapter Engines).

Without special equipment there is little chance - for an amateur in a modern ignition system

For the amateur and ambitious "screwdriver", this can have consequences: ignition systems firmly integrated into the engine management system without special equipment hardly offer starting points for proper homework. Also, sparks do not jump under the hood of the Mondeo without "orders" from the transmission control unit (PCM) and various black boxes.

The inner life of these electronic components can, of course, be learned with the necessary special knowledge and highly sensitive devices. However, this will not give you the opportunity to take care of them and may even disappoint you: fully electronic ignition systems (VZ) have had their childhood illnesses for a long time and meanwhile have been keeping the car in full "juice" for a long time. However, it will still be useful to give a short overview of the type "in the world of igniting sparks controlled by electronics".

Touch control: Igniting sparks in the Mondeo. In DuraTec-HE engines, the control unit (arrow) is mounted directly on the cylinder head, close to the fourth cylinder. This module converts the 12-volt on-board voltage into an ignition voltage of 30,000 volts.

Constantly 'double-bagged' - igniting sparks in Mondeo

The design of the twin-spark ignition coils in the Mondeo is such that they deliver their high voltage to the spark plugs in a "double pack": the first spark ignites the fresh fuel mixture in the cylinder on the compression stroke, while the other is "thrown" into the "opposite" cylinder on the expulsion stroke. This is clearly visible in the Duratec-HE engine: cylinders 1 and 4, as well as cylinders 3 and 2, always receive "their sparks" at the same time.

RSM supplies basic data – SKR sensor

The basis for calculating each individual ignition spark is primarily the signal from the crankshaft position sensor (CPS). Its signal, after it has been converted into digital form by the PCM, controls the primary winding of the ignition coil. To do this, the PCM briefly interrupts the current supply to the PCM. As a result, a high voltage (ignition voltage) is generated, which is fed via the high-voltage cable to the spark plugs and discharged there.

To ensure that sparks appear in a timely manner – an engine control unit (ECM) with various spatial parametric characteristics

The PCM is responsible for the "proper" coordination of the ignition sparks in the Mondeo. Among other things, its memory stores theoretical basic data on the most varied spatial characteristics of the ignition timing. In order to closely link the vague theory with practice, the trip computer processes the relevant sensor signals from the engine periphery in a few milliseconds. For example, it supplements its "hard disk information" with current data from the crankshaft position sensor and the knock sensor. In addition, before each gas exchange, the PCM communicates with the accelerator pedal, the oxygen sensor, the speed sensor and various temperature sensors and the air flow meter located under the engine bonnet.



Depending on the load condition (idle, partial load, full load) and the quality of fresh air, the fuel mixture burns in the combustion chambers at different speeds. In order to use the fuel energy as best as possible, the black box changes the parametric characteristic of the ignition advance angle in accordance with the load condition for each individual cylinder. The best moment accordingly occurs when the fresh fuel mixture ignites at the moment of maximum compression. In four-stroke engines, this is the moment when the piston switches from moving upwards on the compression stroke to moving downwards on the power stroke.

To carry out in a timely manner – ignition and combustion

Three-dimensional characteristic: spatial parametric characteristic of the ignition advance angle. Each individual ignition spark is prepared in advance in terms of fuel consumption, torque, exhaust gas, distance from the engine knock limit, engine temperature, travel, etc. Depending on the philosophy of the engine manufacturer, one or another "point of view" receives different priorities. This procedure takes place on the spatial parametric characteristic of the ignition advance angle, a three-dimensional "surface of mountains and valleys" with almost 4,000 individually evoked ignition advance angles. This "crater landscape" is supervised by the engine control unit (PCM).

Naturally, the ignition moment does not exactly occur at the top dead center (TDC), since approximately three thousandths of a second is needed before the mixture is ignited. Therefore, the igniting sparks receive the "green light" even during the piston's upward movement.



The maximum combustion pressure, on the contrary, is established when the piston immediately passes TDC. Since the fuel-air mixture always requires the same time to ignite, the ignition point moves further from TDC as the engine speed increases.

TECHNICAL DICTIONARY

Invisible Helpers (General Information) Pressure regulator: connected to the intake manifold via a hose, it transmits information about the reduced pressure in the intake manifold to the control unit. The sensor is a pressure-sensitive crystal chip, it changes its electrical resistance depending on the corresponding reduced pressure. Based on the difference obtained, as well as information about the rotation speed, the control unit "learns" about the current operating state. Combustion knock sensor: works on the basis of piezoceramics, i.e. a material that has long replaced flint in gas heating systems. Piezoceramics convert mechanical energy, such as traction force or pressure, into electrical voltage. Minimal disharmonies, such as those that occur during "explosive combustion" of uncontrolled vibrations of the engine cylinder block, are enough to activate the sensor. It monitors the vibrations and reports them to the on-board computer. Based on this, the ignition timing of the corresponding cylinder is immediately adjusted (about -5°). The remaining cylinders operate in their mode until the sensor detects the corresponding irregularities in them and reports them. The ignition timing is shifted, based on the set ignition timing and for each working stroke, until the late ignition direction, until the combustion process returns to normal. The maximum adjustment range is -15°. With proper combustion, after a certain time the ignition timing in the cylinder is successively set again in the "early" direction. Speed sensor: an inductive sensor that switches the current supply to both ignition coils on or off with the help of the control unit. The sensor contains an electromagnet and a coil. Control is carried out by special pulse jumpers on the engine flywheel. Whenever the jumper passes the sensor, the electromagnetic field in the permanent magnets changes - after which a voltage is generated in the coil. In order to now register the position of the crankshaft as a convincing TDC signal, pulse jumpers are placed on the flywheel for the first and last cylinders - before their respective TDC - as reference marks. The control unit processes these voltage signals as a source of information on the engine speed. Works accurately in angular units: crankshaft position sensor. 1 - Sensor, 2 - Sectional fields.