- What is a car ignition coil
- The device and principle of operation of the ignition coil
- Ignition coil functions
- Coil operation in the general circuit of the ignition system
- Main characteristics of the ignition coil:
- Types of ignition coils
- Service life and malfunctions of ignition coils
- How to tell if a coil is defective?
- Can the ignition coil be repaired?
As all motorists know, gasoline and diesel powertrains operate on different principles from each other. If in a diesel engine the fuel is ignited from the temperature of the air compressed in the cylinder (only air is in the chamber during the compression stroke, and diesel fuel is supplied at the end of the stroke), then in a gasoline analogue this process is activated by a spark formed by a spark plug.
We have already talked about the internal combustion engine in detail in separate review... Now we will focus on a separate element of the ignition system, on the serviceability of which the stability of the engine depends. This is the ignition coil.
Where does the spark come from? Why is there a coil in the ignition system? What types of coils are there? How do they work and what is their device?
What is a car ignition coil
In order for the gasoline in the cylinder to ignite, a combination of such factors is important:
- A sufficient amount of fresh air (the throttle valve is responsible for this);
- Good mixing of air and gasoline (this depends on type of fuel system);
- High-quality spark (it is formed spark plugs, but it is the ignition coil that generates an impulse) or a discharge within 20 thousand volts;
- The discharge should occur when the VTS in the cylinder is already compressed, and the piston by inertia has left the top dead center (depending on the operating mode of the motor, this pulse may be generated a little earlier than this moment or a little later).
While most of these factors depend on injection operation, valve timing and other systems, it is the coil that creates the high-voltage pulse. This is where this huge voltage comes from in a 12-volt system.
In the ignition system of a gasoline car, a coil is a small device that is part of the car's electrical system. It contains a small transformer that stores energy and, if necessary, releases the entire supply. By the time the high-voltage winding is triggered, it is already about 20 thousand volts.
The ignition system itself works according to the following principle. When the compression stroke is completed in a particular cylinder, the crankshaft sensor sends a small signal to the ECU about the need for a spark. When the coil is at rest, it operates in energy storage mode.
Having received a signal about the formation of a spark, the control unit activates the coil relay, which opens one winding and closes the high-voltage one. At this moment, the necessary energy is released. The impulse passes through the distributor, which determines which spark plug needs to be energized. The current flows through high voltage wires connected to the spark plugs.
In older cars, the ignition system is equipped with a distributor that distributes the voltage to the spark plugs and activates / deactivates the coil windings. In modern machines, such a system has an electronic type of control.
As you can see, the ignition coil is needed in order to create a short-term high-voltage pulse. Energy is stored by the vehicle's electrical system (battery or generator).
The device and principle of operation of the ignition coil
The photo shows one of the types of coils.
Depending on the type, the short circuit can consist of:
- An insulator preventing current leakage from the device;
- The case in which all the elements are collected (most often it is metal, but there are also plastic analogs made of heat-resistant material);
- Insulating paper;
- Primary winding, which is made of an insulated cable wound in 100-150 turns. It has 12V outputs;
- The secondary winding, which has a structure similar to the main one, but has 15-30 thousand turns, wound inside the primary. Elements with a similar design can be equipped with an ignition module, a two-pin and a double coil. In this part of the short circuit, a voltage exceeding 20 thousand V is created, depending on the modification of the system. In order for the contact of each element of the device to be insulated as much as possible, and no breakdown is formed, a tip is used;
- Primary terminal contact. On many reels, it is denoted by the letter K;
- Contact bolt, with which the contact element is fixed;
- The central outlet, on which the central wire goes to the distributor;
- Protective cover;
- Terminal battery of the on-board network of the machine;
- Contact spring;
- Fixing brackets, with which the device is fixed in a fixed position in the engine compartment;
- External cable;
- A core that prevents eddy current formation.
Depending on the type of car and the ignition system that is used in it, the location of the short circuit is individual. To quickly find this element, you need to familiarize yourself with the technical documentation for the car, which will indicate the electrical diagram of the entire car.
The operation of the short circuit has the principle of functioning of the transformer. The primary winding is connected to the battery by default (and when the engine is running, the energy generated by the generator is used). While it is at rest, current flows through the cable. At this moment, the winding forms a magnetic field that acts on the thin wire of the secondary winding. As a result of this action, high voltage builds up in the high-voltage element.
When the breaker is triggered and the primary winding is turned off, an electromotive force is generated in both elements. The higher the self-induction EMF, the faster the magnetic field disappears. To accelerate this process, a low voltage current can also be supplied to the short-circuit core. The current increases on the secondary element, due to which the voltage in this section drops sharply and the arc voltage is formed.
This parameter is retained until the energy is completely removed. In most modern cars, this process (voltage reduction) lasts for 1.4ms. This is quite enough for the formation of a powerful spark capable of piercing the air between the electrodes of the candle. After the secondary winding is completely discharged, the rest of the energy is used to maintain the voltage and damped oscillations of electricity.
Ignition coil functions
The efficiency of the ignition coil is highly dependent on the type of distributor used in the vehicle system. Thus, a mechanical distributor loses a small amount of energy in the process of closing / opening contacts, since a small spark may form between the elements. The lack of mechanical contact elements of the breaker manifests itself at high or low motor speeds.
When the crankshaft has a small number of revolutions, the contact elements of the distributor generate a small arc discharge, as a result of which less energy is supplied to the spark plug. But at high crankshaft speeds, the breaker contacts vibrate, causing the secondary voltage to drop. To eliminate this effect, a resistor element is installed on the coils operating with a mechanical chopper.
As you can see, the purpose of the coil is the same - to convert a low voltage current to a high one. Other parameters of the SZ operation depend on other elements.
Coil operation in the general circuit of the ignition system
Details about the device and types of car ignition systems are described in a separate review... But in short, in the SZ circuit, the coil will work according to the following principle.
The low voltage contacts are connected to the low voltage wiring from the battery. To prevent the battery from discharging during the operation of the short circuit, the low-voltage section of the circuit must be doubled with the generator, so the wiring is assembled into one harness for plus and one harness for minus (along the way, during the operation of the internal combustion engine, the battery is recharged).
If the generator stops working (how to check its malfunction, it is described here), the vehicle uses the battery power. On the battery, the manufacturer can indicate how long the car can work in this mode (for details on how to select a new battery in your car, it is described in another article).
One high-voltage contact comes out of the coil. Depending on the modification of the system, its connection can be either to a breaker or directly to a candle. When the ignition is turned on, voltage is supplied from the battery to the coil. A magnetic field is formed between the windings, which is amplified by the presence of the core.
At the moment the engine is started, the starter turns the flywheel, with which the crankshaft rotates. DPKV fixes the position of this element and gives impulse to the control unit when the piston reaches top dead center on the compression stroke. In the short circuit, the circuit opens, which provokes a short-term burst of energy in the secondary circuit.
The generated current flows through the central wire to the distributor. Depending on which cylinder is triggered, such a spark plug receives the appropriate voltage. A discharge occurs between the electrodes, and this spark ignites a mixture of air and fuel compressed in the cavity. There are ignition systems in which each spark plug is equipped with an individual coil or they are doubled. The sequence of operation of the elements is determined on the low-voltage part of the system, due to which high-voltage losses are minimized.
Main characteristics of the ignition coil:
Here is a table of the main characteristics and their values for short circuit:
|Resistance||On the primary winding, this characteristic should be within 0.25-0.55 Ohm. The same parameter on the secondary circuit should be within 2-25kOhm. This parameter depends on the engine and the type of ignition system (it is separate for each model). The higher the resistance, the less power to generate a spark.|
|Spark energy||This value should be about 0.1J and consumed within 1.2ms. In candles, this value corresponds to the parameter of the arc discharge between the electrodes. This energy depends on the diameter of the electrodes, the gap between them and their material. It also depends on the temperature of the BTC and the pressure in the cylinder chamber.|
|Breakdown voltage||Breakdown is a discharge that forms between the electrodes of a candle. The operating voltage depends on the SZ gap and the same parameters as when determining the spark energy. This parameter should be higher when the motor is just starting. The engine itself and the air-fuel mixture in it are still poorly heated, so the spark must be powerful.|
|Number of sparks / min.||The number of sparks per minute is determined by the revolutions of the crankshaft and the number of cylinders of the internal combustion engine.|
|Transformation||This is a value that shows how much the primary voltage increases. When 12 volts arrive at the winding and its subsequent disconnection, the current strength drops sharply to zero. At this moment, the voltage in the winding begins to rise. This value is the transformation parameter. It is determined by the ratio of the number of turns of both windings.|
|Inductance||This parameter determines the storage properties of the coil (it is measured in G.). The amount of inductance is proportional to the amount of stored energy.|
Types of ignition coils
A little higher, we examined the design and principle of operation of the simplest modification of the short circuit. In such a system arrangement, the distribution of the generated impulses is provided by a distributor. Modern cars are equipped with electronic governors, and with them different types of coils.
A modern KZ must meet the following criteria:
- Small and lightweight;
- Must have a long service life;
- Its design should be as simple as possible so that it is easy to install and maintain (when a malfunction appears, the motorist can independently identify it and take the necessary actions);
- Be protected from moisture and heat. Thanks to this, the car will continue to work efficiently under changing weather conditions;
- When installed directly on the spark plugs, vapors from the motor and other aggressive conditions should not damage the body of the part;
- Should be as protected as possible from short circuits and current leakage;
- Its design must provide effective cooling and, at the same time, ease of installation.
There are such types of coils:
- Classic or common;
- Dual or two-pin;
Regardless of the type of short circuit, they have the same effect - they convert low voltage into high voltage current. However, each type has its own design features. Let's consider each of them in more detail.
Classic ignition coil design
Such short circuits were used in old cars with contact and then contactless ignition. They have the simplest design - they consist of a primary and a secondary winding. On a low-voltage element there can be up to 150 turns, and on a high-voltage element - up to 30 thousand. To prevent a short circuit from forming between them, the wires used to form turns are insulated.
In the classic design, the body is made of metal in the form of a glass, muffled on one side and closed with a lid on the other. Low-voltage contacts and one contact to the high-voltage line are brought to the cover. The primary winding is located on top of the secondary.
At the center of the high-voltage element is a core that increases the strength of the magnetic field.
Such an automobile transformer is now practically not used due to the peculiarities of modern ignition systems. They can still be found on old domestically produced cars.
The general short circuit has the following features:
- The maximum voltage that it can generate is in the range of 18-20 thousand volts;
- A lamellar core is installed in the center of the high-voltage element. Each element in it has a thickness of 0.35-0.55mm. and insulated with varnish or scale;
- All plates are assembled into a common tube around which a secondary winding is wound;
- For the manufacture of the flask of the device, aluminum or sheet steel is used. On the inner wall there are magnetic circuits, which are made of electrical steel material;
- The voltage in the high-voltage circuit of the device increases at a rate of 200-250 V / μs;
- The discharge energy is about 15-20 mJ.
Design differences of individual coils
As it becomes clear from the name of the element, such a short circuit is installed directly on the candle and generates an impulse only for it. This modification is used in electronic ignition. It differs from the previous type only in its location, as well as in its design. Its device also includes two windings, only the high-voltage is wound here over the low-voltage.
In addition to the central core, it also has an external analogue. A diode is installed on the secondary winding, which cuts off the high voltage current. During one motor cycle, such a coil generates one spark for its spark plug. Because of this, all short circuits must be synchronized with the position of the camshaft.
The advantage of this modification over the one mentioned above is that the high voltage current passes the minimum distance from the winding lead to the rod of the candle. Thanks to this, energy is not lost at all.
Dual lead ignition coils
Such short circuits are also used mainly in the electronic type of ignition. They are an improved form of the common coil. Unlike a classical element, this modification has two high-voltage terminals. One coil serves two candles - a spark is generated on two elements.
The advantage of this scheme is that the first candle is triggered to ignite the compressed mixture of air and fuel, and the second creates a discharge when the exhaust stroke occurs in the cylinder. An additional spark appears idle.
Another plus of these coil models is that such an ignition system does not need a distributor. They can connect to candles in two ways. In the first case, the coil stands separately, and one high-voltage wire goes to the candlesticks. In the second version, the coil is installed on one candle, and the second is connected through a separate wire coming out of the device body.
This modification is used only on engines with a paired number of cylinders. They can also be assembled into one module, from which a corresponding number of high-voltage wires emerge.
Dry and oil filled coils
The classic short circuit is filled with transformer oil inside. This liquid prevents overheating of the device windings. The body of such elements is metal. Since iron has good heat dissipation, but at the same time it heats up itself. This ratio is not always rational, since such modifications are often very hot.
To eliminate this effect, modern devices are manufactured without a case at all. An epoxy compound is used instead. This material simultaneously performs two functions: it cools the windings and protects them from moisture and other negative environmental influences.
Service life and malfunctions of ignition coils
In theory, the service of this element of the ignition system of a modern car is limited to 80 thousand kilometers of the car. However, this is not constant. The reason for this is the different operating conditions of the vehicle.
Here are just a few factors that can significantly reduce the life of this device:
- Short circuit between windings;
- The coil often overheats (this happens with common modifications installed in a poorly ventilated compartment of the engine compartment), especially if it is no longer fresh;
- Long-term operation or strong vibrations (this factor often affects the serviceability of the models that are installed on the engine);
- When the battery voltage is bad, the energy storage time is exceeded;
- Damage to the case;
- When the driver does not turn off the ignition during deactivation of the internal combustion engine (the primary winding is under constant voltage);
- Damage to the insulating layer of explosive wires;
- Wrong pinout when replacing, servicing the device or connecting additional equipment, for example, an electric tachometer;
- Some motorists, when decoking the engine or other procedures, disconnect the coils from the candles, but do not disconnect them from the system. After the cleaning work has been performed on the engine, they crank the crankshaft with a starter to remove all the dirt from the cylinders. If you do not disconnect the coils, in most cases they fail.
In order not to shorten the life of the coils, the driver should:
- Turn off the ignition when the engine is not running;
- Keep the case clean;
- Periodically re-check the contact of high-voltage wires (not only to monitor oxidation on the candlesticks, but also on the central wire);
- Make sure that no moisture gets into the body, much less inside;
- When servicing the ignition system, never handle high-voltage components with bare hands (this is hazardous to health), even if the engine is turned off. If there is a crack in the case, a person can get a serious discharge, therefore, for the sake of safety, it is better to work with rubber gloves;
- Periodically diagnose the device at a service station.
How to tell if a coil is defective?
Modern cars are equipped with on-board computers (about how it works, why it is needed and what modifications of non-standard models are, it is told in another review). Even the simplest modification of this equipment is capable of detecting faults in the electrical system, which includes the ignition system.
If the short circuit breaks down, the motor icon will shine. Of course, this is a very extensive signal (this icon on the dashboard lights up, for example, and in case of failure lambda probe), so don't rely on this alert alone. Here are some other signs that accompany coil breakage:
- Periodic or complete shutdown of one of the cylinders (about why else the motor can triple, it is told here). If some modern gasoline engines with direct injection are equipped with such a system (it cuts off the fuel supply to some injectors at the minimum load of the unit), then conventional engines demonstrate unstable operation regardless of the load;
- In cold weather and with high humidity, the car either does not start well or does not start at all (you can wipe the wires dry and try to start the car - if it helps, then you need to replace the set of explosive cables);
- A sharp press on the accelerator leads to engine failure (before changing the coils, you need to be sure that the fuel system is working properly);
- Traces of breakdown are visible on the explosive wires;
- In the dark, slight sparking is noticeable on the device;
- The engine has sharply lost its dynamics (this may also indicate breakdowns of the unit itself, for example, burnout of valves).
You can check the health of individual elements by measuring the resistance of the windings. For this, a conventional device is used - a tester. Each part has its own range of acceptable resistance. Serious deviations indicate a defective transformer and must be replaced.
When determining a coil malfunction, it should be borne in mind that many of the symptoms are identical to spark plug breakdowns. For this reason, you need to make sure that they are in good order, and then proceed to diagnosing the coils. How to determine a candle breakage is described separately.
Can the ignition coil be repaired?
Repairing conventional ignition coils is quite possible, but it takes a lot of time. So, the foreman must know exactly what to repair in the device. If you need to rewind the winding, then this procedure requires exact knowledge of what the cross-section and material of the wires should be, how to properly wind them and fix them.
Several decades ago, there were even specialized workshops that provided such services. However, today it is more a whim of those who like to tinker with their car than a need. A new ignition coil (in an old car it is one) is not so expensive as to save money on its purchase.
As for modern modifications, most of them cannot be disassembled to get to the windings. Because of this, they cannot be repaired at all. But no matter how high-quality the repair of such a device is, it cannot replace the factory assembly.
You can install a new coil yourself if the ignition system device allows a minimum of dismantling work for this. In any case, if there is uncertainty about a quality replacement, it is better to entrust the work to the master. This procedure will not be expensive, but there will be confidence that it is performed with high quality.
Here is a short video on how you can independently diagnose the malfunction of individual coils: