1. Warm-up correction
An advanced angle is used for the ignition timing when the coolant temperature is low to improve drivability. Some engine models conduct correction advancing in response to the intake mass. The ignition timing angle is advanced approx. 15 °by this correction function during extremely cold conditions.
HINT:
For some engine models, the IDL signal or NE signal is used as a related signal for this correction.
2. Over-temperature correction
When the coolant temperature is extremely high, the ignition timing is retarded to prevent knocking and overheating. The ignition timing angle is retarded a maximum of 5 by this correction.
HINT:
Some engine models also use the following signals for correction.
Intake air mass signal (VG or PIM)
Engine speed signal (NE)
Throttle position signal (IDL) etc.
3. Stable idle correction
If the engine speed changes from the target idling speed while idling, the engine ECU regulates the ignition timing to stabilize the engine speed. The engine ECU continuously calculates the average engine speed, so if the engine speed falls below the target engine speed, the engine ECU advances the ignition timing by the predetermined angle. If the engine speed exceeds the target idling speed, the engine ECU retards the ignition timing by the predetermined angle. The ignition timing angle can be varied a maximum of ±5 °by this correction.
REFERENCE:
Some engine models conduct angle advancement according to whether the air conditioner is turned ON or OFF. In addition, some models only make this correction when the engine speed is below the target engine speed.
4. Knocking correction
If knocking occurs in the engine, the knocking sensor converts the vibration generated by the knocking into a voltage signal (KNK signal) and sends it to the engine ECU. The engine ECU determines whether the knocking is strong, medium, or weak from the strength of the KNK signal. Then it corrects the ignition timing by retarding it in accordance with the strength of the KNK signal. In other words, when the knocking is strong, the ignition timing is retarded a great deal, and when the knocking is weak, the ignition timing is only retarded slightly. When the engine knocking ceases, the engine ECU stops retarding the ignition timing and advances it a little at a time by the predetermined timing. This advancing is conducted until knocking occurs again, and then when the knocking occurs the control is repeated by retarding the ignition timing. The ignition timing angle is retarded a maximum of 10° by this correction. Some models conduct this correction over nearly the entire range of the engine load, and other models only conduct this correction during high loads.
5. Other correction
There are some engine models that add the following corrections to the ESA system to more correctly and accurately control the ignition timing.
(1) Air-fuel ratio feedback correction
During air-fuel ratio feedback correction, the engine speed varies in accordance with increase/decrease of the fuel injection volume. To maintain stable idling, the ignition timing is advanced during the air-fuel feedback correction to match the injection amount. This correction is not performed while the vehicle is driving.
(2) EGR (Exhaust Gas Recirculation) correction
When the EGR is operating and the IDL contact is turned OFF, the ignition timing is advanced in accordance with the intake air mass and engine speed to improve drivability.
(3) Torque control correction
For vehicles equipped with an ECT (Electronically-Controlled Transmission), the transmission or transaxle planetary gear unit clutch and brake generate a certain amount of shock during shifting. Some models retard the ignition timing to lower the engine torque when shifting up or down to minimize this shock.
(4) Transition correction
When changing from deceleration to acceleration, the ignition timing is advanced or retarded in accordance with the acceleration.
(5) Cruise control correction
When driving downhill while the cruise control is in operation, a signal is sent from the cruise control ECU to the engine ECU to retard the ignition timing minimize the change in engine torque generated by the fuel cut-off during engine braking to execute smooth cruise control.
(6) Traction control correction
The ignition timing is retarded when traction control is operating to lower the engine torque.

The ignition timing control consists of two basic controls.
1. Starting ignition control
The starting ignition control is performed by conducting ignition at the predetermined crankshaft angle regardless of the engine operation conditions. This crankshaft angle is called the “initial ignition timing angle”.
2. After-start ignition control
The after-start ignition timing control is performed with the initial ignition timing angle, the basic ignition advance angle, which is calculated by the engine load and engine speed, and various corrections.
Initial Ignition Timing Angle Judgement
The initial ignition timing angle is determined as follows. When the engine ECU receives the NE signal (point B in figure at left) after receiving the G signal (point A in the figure at left), it determines that it is the initial ignition timing angle when the crankshaft reaches 5 °, 7 °, or 10 ° (this differs between engine models) BTDC (Before Top Dead Center).
Starting Ignition Control and After-start Ignition Control
1. Starting ignition control
When starting the engine, the engine speed is low and the intake air mass is unstable, so the VG or PIM signal cannot be used as control signals. Therefore, the ignition timing is set to the initial ignition timing angle. This initial ignition timing angle is controlled in the engine ECU backup IC. In addition, the NE signal is used to determine when the engine is being started, and an engine speed of 500 rpm or less indicates start-up is occurring.
HINT:
Depending on the engine model, there are some types that determine the engine is being started when the engine ECU receives a starter signal (STA).
2.After-start ignition control
After-start ignition control is the control that is activated while the engine is running after starting. This control is performed by making various corrections to the initial ignition timing angle and basic ignition advance angle. Ignition timing = initial ignition timing angle + basic ignition advance angle + corrective ignition advance angle When after-start ignition control is activated, the IGT signal is calculated by the microprocessor and output via the backup IC.

The basic ignition advance angle is determined using the NE signal and the VG signal or PIM signal. The NE and VG signal data used to determine the basic ignition advance angle is stored in the engine ECU memory.
1. Control when the IDL signal is ON
When the IDL signal is ON, the ignition timing is advanced in accordance with the engine speed.
HINT:
In some engine models the basic ignition advance angle is changed depending on whether or not the air conditioner is ON or OFF. In addition, of these models, some have an advance angle of 0 during standard idling speed.
2. Control when the IDL signal is OFF
The ignition timing is determined in accordance with the NE signal and VG or PIM signal based on the data stored in the engine ECU. Depending on the model, two basic ignition advance angles are stored in the engine ECU. The data for one of these is used to determine the advance angle based on the fuel octane value, so the data that matches the fuel used by the driver can be selected. In addition, some models of vehicles with fuel octane judgment capability use the KNK signal to automatically change the data used to determine the ignition timing.

The engine ECU determines the ignition timing based on the G signal, NE signal and the signals from other various sensors. When the ignition timing has been determined, the engine ECU sends the IGT signal to the igniter. While the IGT signal sent to the igniter is ON, the primary current flows to the ignition coil. While the IGT signal turns OFF, the primary current to the ignition coil is shut off. At the same time, the IGF signal is sent to the engine ECU. Currently, the main ignition circuitry used is the DIS (Direct Ignition System). The engine ECU distributes the highvoltage current to the cylinders by sending each IGT signal to the igniters in the order of ignition. This makes it possible to provide highly accurate ignition timing control.
Distributor Type Ignition Circuitry
The distributor type ignition circuitry is a system that uses a distributor to send high-voltage current to the spark plugs. The distributor type ignition circuitry conducts basically the same control as the DIS. However, because there is only a single igniter and ignition coil, only one IGT and IGF are output. The high voltage generated by the ignition coil is distributed to each cylinder by the distributor.
IGT and IGF Signal
1. IGT signal
The engine ECU calculates the optimum ignition timing according to the signals from various sensors and sends the IGT signal to the igniter. The IGT signal is turned ON immediately before the ignition timing calculated by the microprocessor in the engine ECU, and then is turned OFF. When the IGT signal is turned OFF, the spark plug sparks.
2. IGF signal
The igniter sends an IGF signal to the engine ECU by using the counter-electromotive force that is generated when the primary current to the ignition coil is shut off or by using the primary current volume. When the engine ECU receives the IGF signal, it determines that ignition occurred. (This does not mean, however, that there was actually a spark.) If the engine ECU does not receive an IGF signal, the diagnosis function operates and a DTC is stored in the engine ECU and the fail-safe function operates and stops injecting fuel.

This ignition device consists of an igniter and an ignition coil that is integrated into a single unit. In the past, high-voltage current was sent to the cylinders via high-tension cords. Now, an ignition coil can be connected directly to the spark plug of each cylinder through the use of the ignition coil united with igniter. The distance that the high voltage flows will be short by directly connecting the ignition coil and spark plug, causing the voltage-loss and electromagnetic interference to be decreased. Thus, the reliability of the ignition system is improved.

Operation

Here is an operation example based on the DIS of the 1NZ-FE engine, which uses the ignition coil united with igniter.

1. The engine ECU receives signals from various sensors and calculates the optimal ignition timing. (The engine ECU also effects timing advance control).

2. The engine ECU sends the IGT signals to the ignition coil united with igniters. The IGT signals are sent to each igniter according to the ignition order (1-3-4-2).

3. The ignition coil, to which the primary current has been shut off rapidly, generates a high-voltage current.

4. The IGF signal is sent to the engine ECU when the primary current exceeds a prescribed value. 5. High-voltage current, which is the generated in the secondary coil, flows to the spark plugs, causing ignition.

Operation Principle of the Transistorized Type

1. The signal generator generates an ignition signal.

2. The igniter receives the ignition signal and causes the primary current to flow intermittently.

3. The ignition coil, to which the primary current has been shut off abruptly, generates a high-voltage current.

4. The distributor distributes the highvoltage current generated by the secondary coil to the spark plugs.

5. The spark plugs receive the highvoltage current and ignite the air-fuel mixture. The timing advance is controlled through the use of the governor advancer or vacuum advancer.

The engine ECU, which receives signals from various sensors, calculates the ignition timing and transmits ignition signals to the igniter. The ignition timing is calculated continuously in accordance with the conditions of the engine, based on the optimal ignition timing values that are stored in the computer in the form of an ESA map. Compared to the mechanical ignition timing control of the conventional system, the control method with the ESA provides higher precision, and the freedom to set the ignition timing. As a result, this system offers improved fuel economy and power output.

REFERENCE:

The TDI is also known as DIS (Direct Ignition System) or DLI (Distributor- Less Ignition).

Components

The direct ignition system consists of the following components:

1. Crankshaft position sensor (NE)

Detects the crankshaft angle (Engine speed).

2. Camshaft position sensor (G)

Identifies the cylinder and the stroke and detects the camshaft timing.

3. Knock sensor (KNK)

Detects the knocking of the engine.

4. Throttle position sensor (VTA)

Detects the opening angle of the throttle valve.

5. Air flow meter (VG/PIM)

Detects the amount of the intake air. (On some models, this detection is performed by a manifold pressure sensor)

6. Water temperature sensor (THW)

Detects the engine coolant temperature.

7. Ignition coil with igniter

Turns the primary coil current on and off at the optimal timing. Sends the IGF signal to the engine ECU.

8. Engine ECU

Generates an IGT signal based on

the signals from various sensors and

sends the signal to the ignition coil

with igniter.

9. Spark plug

Generates electric sparks to ignite

the air-fuel mixture.

The high voltage generated in the secondary winding of the ignition coil produces a spark between the center and ground electrodes of the spark plug in order to ignite the air-fuel mixture that is compressed in the cylinder.

Ignition Mechanism

The explosion of the air-fuel mixture by a spark from the spark plug is generally called combustion. Combustion, however, does not occur in an instant, but proceeds as described below. The spark travels through the air-fuel mixture from the center electrode to the ground electrode. As a result, the air-fuel mixture is activated along the path of the spark, reacts chemically (through oxidation), and generates heat to form a so-called flame nucleus. The flame nucleus activates the surrounding air-fuel mixture, which further activates the surrounding air-fuel mixture. Thus, the heat of the flame nucleus expands outward in a process known as flame propagation, to burn the air-fuel mixture. If the temperature of the electrodes is too low or the spark plug gap is too small, the electrodes will absorb the heat that was generated by the spark. As a result, the flame nucleus is extinguished, causing a misfire. This phenomenon is called electrode quenching. If the quenching effect of the electrodes is great due to the heat generated by the flame nucleus, the flame nucleus will be extinguished. The smaller the electrode is, the lesser the quenching function will be. And the squarer the electrode is, the easier the discharge will be. Some spark plugs have a U-shaped groove in the ground electrode or a V-shaped groove in the center electrode in order to improve ignitability. Those spark plugs provide a smaller quenching effect than the spark plugs without grooved electrodes, which allows the flame to form a large nucleus. Also, there are some spark plugs that reduce the quenching effect by providing thinner electrodes.

On the platinum-tipped and iridiumtipped spark plugs, the center electrode and the opposing ground electrode are covered with a thin platinum or iridium tip. Therefore, these spark plugs provide a longer service life than conventional spark plugs. Because platinum and iridium resist wear, the center electrode of these spark plugs can remain small and offer excellent sparking performance.

1. Platinum-tipped spark plug

On the platinum-tipped spark plug, platinum is welded onto the tip of the center electrode and the ground electrode. The diameter of the center electrode is smaller than in the conventional spark plug.

2. Iridium-tipped spark plug

On the iridium-tipped spark plug, iridium (which provides a higher wear resistance than platinum) is welded onto the tip of the center electrode, and platinum is welded onto the ground electrode. The diameter of the center electrode is smaller than in the platinum-tipped spark plug.

HINT:

Some of these plugs do not have platinum welded onto their ground electrodes.

The platinum-tipped and iridium-tipped spark plugs must be replaced at the specified intervals. They do not require the plug gap adjustment or cleaning between replacements if the engine is running properly.

HINT:

Platinum- and iridium-tipped spark plug replacement intervalsEvery 100,00to 240,000km The replacement intervals may vary by vehicle model, engine specifications, and area of use.

NOTICE:

To prevent the electrodes from being damaged, do not clean platinum- or iridium-tipped spark plugs. Cleaning will damage the electrodes and will inhibit the full ability of the spark plugs. However, if the electrodes are sooty or excessively dirty, they may be cleaned for a short period of time (2seconds maximum) in a spark plug cleaner. The gap of these spark plugs does not require adjustment except when installing as new. The illustration on the left shows the type of caution label that is affixed in the engine compartment of a vehicle using platinum- or iridium-tipped spark plugs.

The following factors affect the ignition performance of a spark plug:

1. Electrode shape and discharge performance

Rounded electrodes make discharging difficult, while squared-off or pointed electrodes facilitate discharging. As electrodes are rounded off through long use, it becomes difficult for the spark plug to discharge sparks. Therefore, the spark plugs must be replaced regularly. It is easier for a spark plug with thin and pointed electrodes to discharge sparks. However, those electrodes wear faster and shorten the service life of the spark plug. For this reason, some spark plugs have platinum or iridium, which resist wear, welded to their electrodes. They are usually called platinum-tipped or iridium-tipped spark plugs.

HINT

Spark plug replacement intervals Conventional typeEvery 10,00to 60,00km Platinum- or iridium-tipped typeEvery 100,00to 240,00km The replacement intervals may vary by vehicle model, engine specifications, and country of use.

2. Spark plug gap and required voltage

As the spark plug becomes worn and the gap between its electrodes widens, the engine can misfire. When the distance between the center electrode and the ground electrode increases, it is more difficult for the spark to jump across the electrodes. Thus, a greater voltage will be required to generate a spark. For this reason, the gap must be adjusted or the spark plug must be replaced at regular intervals.

HINT:

If the required voltage can be provided despite a wide gap, the spark plug will be able to produce a strong spark and facilitate ignition. For this reason, there are many spark plugs on the market with a gap as wide as 1.1 mm. The platinum- and iridium-tipped spark plugs do not require gap adjustments because they are not susceptible to wear (they only need to be replaced).

Heat Range of Spark Plug

The amount of heat radiated by a spark plug varies by the shape and the material of the spark plug. The amount of radiated heat is called a heat range. A spark plug that radiates more heat is called a cold type, because the plug itself stays cooler. One that radiates less heat is called a hot type, because its heat is retained. Spark plugs are printed (inscribed) with an alphanumeric code, which describes their structure and characteristics. Codes differ somewhat depending on the manufacturer. Usually, the larger the number of the heat range, the cold plug, because it radiates heat well. The smaller the number, the hot plug, because it does not radiate heat easily. Spark plugs perform best when the minimum center electrode temperature is between the self-cleaning temperature of 450C (842 F) and the pre-ignition temperature of 95C (1,742 F).

SERVICE HINT:

The most appropriate spark plug heat range for a particular vehicle is determined by the model. Installing a spark plug of a different heat range will upset the selfcleaning and pre-ignition temperatures. To prevent these problems, always use the specified type of spark plugs for replacement. Using a cold spark plug when the engine is operating under low-speed and low-load conditions will reduce the electrode temperature and cause the engine to run poorly. Using a hot spark plug when the engine is operating under high-speed and heavy-load conditions will excessively increase the electrode temperature, causing the electrode to melt.

1. Self-cleaning temperature

When a spark plug reaches a certain temperature, it burns off the carbon that has accumulated in the ignition area during ignition, in order to maintain the cleanliness of the ignition area of the plug. This temperature is called the self-cleaning temperature. The self-cleaning effect of the spark plug takes place when the temperature of the electrodes exceeds 45C (842 F). If the self-cleaning temperature has not been reached, meaning the temperature of the electrodes is below 45C (842 F), carbon accumulates in the ignition area of the spark plug. This can cause the spark plug to misfire.

2. Pre-ignition temperature

If the spark plug itself becomes a heat source and ignites the air-fuel mixture without sparking, this is called the pre-ignition temperature. Pre-ignition takes place when the temperature of the electrodes is above 95C (1,742 F). If it occurs, the engine output will drop due to incorrect ignition timing, and the electrodes or pistons may partially melt.

Outline

The igniter carries out the precise interruption of the primary current that flows to the ignition coil in accordance with the ignition signal (IGT) that is output by the engine ECU.

IGT signal

When the IGT signal turns from off to on, the igniter starts the flow of the primary current.

Constant current control

When the primary current reaches a specified value, the igniter limits the maximum amperage by regulating the current.

Dwell angle control

To ensure the proper duration of the primary current, which decreases as the engine speed rises, this control regulates the length of time (dwell angle) during which current flows. (On some of the recent models, this control is effected through the IGT signal.) When the IGT signal turns from on to off, the igniter shuts off the primary current. At the instant the primary current is shut off, hundreds of volts are generated in the primary coil and tens of thousands of volts are generated in the secondary coil, which cause the spark plug to spark.

IGF signal

The igniter carries out the precise interruption of the primary current in the ignition coil in accordance with the IGT signal of the engine ECU. Then, the igniter transmits an ignition confirmation signal (IGF) to the engine ECU in accordance with the amperage of the primary current. The IGF is output when the primary current that flows from the igniter reaches the prescribed value IF1. When the primary current exceeds the prescribed value IF2, the system determines that the required amount of current has flowed, and allows the IGF signal to return to its original voltage. (The waveforms of the IGF signal vary from model to model.) If the engine ECU does not receive an IGF signal, it determines that a failure has occurred in the ignition system. To prevent the catalyst from overheating, the engine ECU stops the fuel injection and stores the failure in the diagnosis function. However, the engine ECU will be unable to detect a failure in the secondary current circuit because the engine ECU monitors only the primary current circuit for an IGF signal.

HINT:

On some models, an IGF signal is determined through the primary voltage.