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.

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.

In a gasoline engine, the air-fuel mixture is ignited to cause combustion, and the force that is generated by the explosion causes the piston to push downward. The thermal energy can be most efficiently converted into a motive force when the maximum combustion force is generated at a crankshaft position of 1ATDC (After Top Dead Center). An engine does not produce the maximum combustion force simultaneously with ignition; instead, it generates the maximum combustion force slightly after ignition has occurred. Therefore, ignition takes place in advance so that the maximum combustion force is generated at 10ATDC. The ignition timing that enables the engine to generate the maximum combustion force at 10ATDC changes every moment, depending on the operating conditions of the engine. Therefore, the ignition system must be able to ignite the air-fuel mixture at a timing that enables the engine to generate an explosive force in the most efficient manner in accordance with the operating conditions.

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

The three essential elements of a gasoline engine aregood air-fuel mixture, good compression, and good spark. The ignition system generates a powerful spark through proper ignition timing in order to ignite the air-fuel mixture.

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.

In the TDI system, the conventional distributor is no longer used as in the ignition system. Instead, it provides an ignition coil with an independent integrated igniter for each of the cylinders. Because this system does not require the use of a distributor or high-tension cords, it can reduce energy loss in the high-voltage area and improve durability. At the same time, it minimizes electromagnetic interference because contact points are no longer used in the highvoltage area. The ignition timing control is performed through the use of the ESA.

The ignition coil generates a high voltage that is sufficient for arcing sparks between the electrodes of a spark plug. The primary and secondary coils are wound around the core. The secondary coil is wound approximately 10times more than the primary coil. One end of the primary coil is connected to the igniter, and one end of the secondary coil is connected to the spark plug. The other end of each coil is connected to the battery.

Operation of Ignition Coil

1. Current flowing to the primary coil When the engine is running, the current from the battery flows via the igniter to the primary coil, in accordance with the ignition timing signal (IGT) that is output by the engine ECU. As a result, lines of magnetic force are generated around the coil, which contains a core in the center.

2. Current stopped to the primary coil

As the engine continues to run, the igniter rapidly stops the current to the primary coil, in accordance with the IGT signals that are output by the engine ECU. As a result, the magnetic flux of the primary coil starts to decrease. Thus, an EMF (Electromotive Force) is generated in a direction that impedes the loss of the existing magnetic flux through the self-induction of the primary coil and the mutual induction of the secondary coil. The self-induction effect generates approximately 50V of EMF in the primary coil, and the accompanying mutual induction effect of the secondary coil generates a high EMF voltage of approximately 3kV. This induces the spark plug to produce a spark. The more abruptly the primary current stops and the greater the primary current, the higher the corresponding secondary voltage will be.