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.

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.

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.

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.

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.

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.

1. Ignition delay period

Combustion of the air-fuel mixture does not occur instantly after ignition. Instead, a small area (flame nucleus) in the immediate vicinity of the spark starts to burn, and this process eventually expands to the surrounding area. The period from the time when the air-fuel mixture is ignited until it is burned is called the ignition delay period (between A and B in the diagram). The ignition delay period is practically constant, and is not affected by the changes in the conditions of the engine.

2. Flame propagation period

After the flame nucleus is formed, the flame gradually expands outward. The speed at which the flame expands is called the flame propagation speed, and its period is called the flame propagation period (B~C~D in the diagram). When there is a large amount of the intake air, the airfuel mixture becomes denser. For this reason, the distance between the particles in the air-fuel mixture decreases, thus accelerating the flame propagation. Also, the stronger the swirl of the air-fuel mixture, the faster the flame propagation speed will be. When the flame propagation speed is fast, it is necessary to advance the ignition timing. Therefore, it is necessary to control the ignition timing according to the engine condition.

Ignition timing control

The ignition system controls the ignition timing in accordance with the engine speed and load so that the maximum combustion force occurs at 10ATDC.

HINT:

In the past, ignition systems used a governor advancer and vacuum advancer to control timing advancing and retarding. However, most ignition systems today use the ESA system.

1. Engine speed control

(1) It is considered an engine to output power most efficiently when the maximum combustion force occurs at 10 ATDC, on which the optimal ignition timing is set to 10BTDC (Before Top Dead Center) at a speed of 1,00rpm.

(2) It is supposed that the engine speed is increased to 2,00rpm. The duration for the ignition delay is practically constant regardless of the engine speed. Therefore, the crankshaft rotational angle increases, as compared to when the engine is running at 1,00rpm. If the same ignition timing described in (1) is used at 2,00rpm, the timing at which the engine produces the maximum combustion force will be retarded more than 10 ATDC.

(3) Therefore, to produce the maximum combustion force at 10ATDC while the engine is running at 2,00rpm, the ignition timing must be advanced in order to compensate for the crankshaft rotational angle that was retarded in (2). This process for advancing the ignition timing is called timing advance, and for retarding the ignition timing is called timing retard.

T – Duration for ignition delay

1 – Ignition timing

2 – Timing that produces the maximum combustion force

3 – Boundary between the ignition delay period and flame propagation speed

A – Ignition delay period

B – Flame propagation period

C – Timing retard

D – Crankshaft rotational angle

2. Engine load control

(1) It is considered when the maximum combustion force occurs at 10 ATDC, on which the optimal ignition timing is set to 20BTDC when the engine load is low.

(2) As the engine load increases, the air density increases and the flame propagation period decreases. Therefore, if the same ignition timing described in (1) is used when the engine load is high, the timing at which the engine produces the maximum combustion force will be more advanced than 10ATDC.

(3) To produce the maximum combustion force at 10ATDC when the engine load is high, the ignition timing must be retarded in order to compensate for the crankshaft rotational angle that was advanced in (2). Conversely, when the engine load is low, the timing must be advanced. (When the engine is idling, however, the amount of timing advance must be kept small or zero, to prevent unstable combustion.)

Knocking control

Knocking in the engine is caused by spontaneous combustion that occurs when the air-fuel mixture selfignites in the combustion chamber. An engine becomes more susceptible to knocking as its ignition timing is advanced. Excessive knocking negatively affects the performance of the engine, such as by causing poor fuel economy or reduced power output. On the other hand, slight knocking has the opposite effect of improving both fuel economy and power output. Recent ignition systems effect ignition timing control to retard the timing when a knock sensor detects knocking, and advance the timing when the knocking is no longer detected. By preventing the engine from knocking in this manner, these systems improve the power output and fuel economy.

1- Ignition timing

2 – Timing that produces the maximum combustion force

3 – Boundary between the ignition delay period and flame propagation

speed

A – Ignition delay period

B – Flame propagation period

C – Timing retard

D – Crankshaft rotational angle

1. Powerful sparks

In the ignition system, sparks are generated between the electrodes of the spark plugs to burn the air-fuel mixture. Because even air has electrical resistance, when it is compressed highly, tens of thousands of volts must be generated to ensure the generation of powerful sparks that can ignite the air-fuel mixture.

2. Proper ignition timing

The ignition system must provide proper ignition timing at all times to accommodate the changes in engine speed and load.

3. Sufficient durability

The ignition system must be able to provide sufficient reliability to withstand the vibrations and heat that are generated by the engine.

The ignition system uses the high voltage that is generated by the ignition coil to produce sparks, which ignite the airfuel mixture that has been compressed. The air-fuel mixture is compressed and burns in the cylinder. This combustion generates the motive force of the engine. Through self-induction and mutual induction, the coil generates the high voltage that is necessary for ignition. The primary coil generates several hundred volts and the secondary coil generates tens of thousands of volts.

Changes in Ignition Systems

The types of ignition systems are as follows:

1. Breaker points type

This type of ignition system has the most basic construction. With this type, the primary current and ignition timing are mechanically controlled. The primary current of the ignition coil is controlled to flow intermittently through the breaker points. The governor advancer and the vacuum advancer control the ignition timing. The distributor distributes the high voltage that is generated by the secondary coil to the spark plugs.

HINT

In this type, the breaker points must be regularly adjusted or replaced. An external resistor is used for reducing the number of windings of the primary coil, improving the rise of the primary current, and minimizing the reduction in the secondary voltage at high speeds. Reducing the number of windings of the primary coil reduces resistance, increases the primary current, and increases the generation of heat. For this reason, an external resistor is provided to prevent the primary current from increasing excessively.

2. Transistorized type

In this type, the transistor controls the primary current so that it flows intermittently in accordance with the electric signals that are generated by the signal generator. Timing advance is controlled mechanically in the same way as in the breaker points type system.

3. Transistorized type with ESA

(Electronic Spark Advance)

The use of the mechanical vacuum advancer and the governor advancer has been discontinued in this type. Instead, the ESA function of the engine ECU controls the ignition timing.

4. DIS (Direct Ignition System)

Instead of a distributor, this type employs multiple ignition coils to supply high voltage directly to the spark plugs. The ignition timing is controlled by the ESA function of the engine ECU. This system is predominant in recent gasoline engines.

HINT

Type 2 ignites two cylinders simultaneously. One spark occurs in the compression stroke and the other in the exhaust stroke.

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.

How to check if Ignition System works?

1. Check initial timing

(1) Allow the engine to warm up and short the terminals TE1 and E1 on DLC1, or TC and CG on DLC3.

(2) Connect the pick-up of the timing light to the power source line of the ignition coil.

(3) Inspect the ignition timing with throttle valve fully closed.

HINT:

The initial timing is set by shortening TE1 and E1 on DLC1, or TC and CG on DLC3. There are two types of pick-up for the timing light:

Detection of the primary current ON/OFF or detection of the secondary voltage. Since the ignition timing is advanced when the throttle valve is opened, the throttle valve should be inspected while fully closed. Incorrect initial timing may cause decreases in output, worsened fuel consumption or knocking.

2. Check spark plug

A spark will not be generated when there are cracks, a dirty electrode, wear or too large of a gap. When the plug gap is too small, quenching is possible. In this case, the fuel does not ignite even if a spark is generated.

HINT:

If a spark plug of an improper heat range is used, it may cause the spark plug to accumulate carbon on the electrode or to melt.

3. Spark test

(1) Disconnect all injector connecters so that fuel cannot be injected.

(2) Remove the ignition coil (with igniter) and spark plug.

(3) Re-install the spark plug in the ignition coil.

(4) Connect the connectors with it, and ground the spark plug. Check that the spark plug generates a spark when cranking at this condition. This test determines which cylinder does not have a spark.

NOTICE:

Do not crank for the spark test over 5 – 1seconds.