Contact ignition systems, device, principle of operation
Content
Any car equipped with an internal combustion engine, in electronics, will necessarily have an ignition system. For the mixture of atomized fuel and air in the cylinders to ignite, a decent discharge is needed. Depending on the modification of the car's on-board network, this figure reaches 30 thousand volts.
Where does this energy come from if the battery in the car only produces 12 volts? The main element that generates this voltage is the ignition coil. Details on how it works and what modifications are available is described in a separate review.
Now we will focus on the principle of operation of one of the types of ignition systems - contact (about different types of SZ described here).
What is a contact car ignition system
Modern cars have received a battery-type electrical system. Its scheme is as follows. The positive pole of the battery is connected with wires to all electrical equipment of the car. The minus is connected to the body. From each electrical device, the negative wire is also connected to a metal part connected to the body. As a result, there are fewer wires in the car and the electrical circuit is closed through the body.
The car ignition system can be contact, contactless or electronic. Initially, the machines used the contact type of systems. All modern models receive an electronic system that is fundamentally different from previous types. The ignition in them is controlled by a microprocessor. A contactless system exists as a transitional modification between these varieties.
Just as in other options, the purpose of this SZ is to generate an electrical impulse of the required strength and direct it to a specific spark plug. The contact type of the system in its circuit has an interrupter-distributor or distributor. This element controls the accumulation of electrical energy in the ignition coil and distributes the impulse to the cylinders. Its device includes a cam element that rotates on a shaft and alternately closes the electrical circuits of a particular candle. More details about its structure and operation are described in another article.
Unlike the contact system, the non-contact analog has a transistor type of control over the accumulation and distribution of the pulse.
Contact ignition system diagram
The contact SZ circuit consists of:
- Ignition lock. This is a contact group with which the on-board system of the car is activated and the engine is started using the starter. This element breaks the general electrical circuit of any car.
- Rechargeable power supply. While the engine is not running, the electric current comes from the battery. The car battery also acts as a backup if the alternator does not supply enough energy to operate the electrical equipment. For details on how the battery works, read here.
- Distributor (distributor). As the name suggests, the purpose of this device is to distribute high voltage current from the ignition coil to all spark plugs in turn. In order to comply with the sequence of operation of the cylinders, high-voltage wires of different lengths go from the distributor (when connected, it is easier to correctly connect the cylinders to the distributor).
- Condenser. The capacitor is attached to the valve body. Its action eliminates sparking between the closing / opening cams of the distributor. A spark between these elements causes the cams to burn, which may lead to loss of contact between some of them. This leads to the fact that a particular plug will not fire, and the air / fuel mixture will simply be thrown unburned into the exhaust pipe. Depending on the modification of the ignition system, the capacitance of the capacitor may be different.
- Spark plug. Details about the device and their operating principle are described separately... In short, an electrical impulse from the distributor goes to the central electrode. Since there is a small distance between it and the side element, a breakdown occurs with the formation of a powerful spark, which ignites the mixture of air and fuel in the cylinder.
- Drive. The distributor is not equipped with an individual drive. It is seated on a shaft that is synchronized with the camshaft. The rotor of the mechanism rotates twice as slow as the crankshaft, just like the timing camshaft.
- Ignition coils. The job of this element is to convert the low voltage current into a high voltage pulse. Regardless of the modification, the short circuit will consist of two windings. Electricity passes through the primary from the battery (when the car is not started) or from the generator (when the internal combustion engine is running). Due to the sharp change in the magnetic field and the electrical process, the secondary element begins to accumulate high voltage current.
There are several modifications among contact systems. Here are their main differences:
- The most common scheme is KSZ. It has a classic design: one coil, breaker and distributor.
- Its modification, the device of which includes a contact sensor and an element of preliminary energy storage.
- The third type of contact system is KTSZ. In addition to contacts, its device will contain a transistor and an induction-type storage device. Compared to the classical version, the contact-transistor system has several advantages. The first plus is that high voltage does not pass through the contacts. The valve will only work with control pulses, so there is no spark between the cams. Such a device makes it possible not to use the capacitor in the distributor. In the contact-transistor modification, spark formation on the spark plugs can be improved (the voltage on the secondary winding is higher, due to which the spark plug gap can be increased so that the spark is longer).
To understand which SZ is used in a particular car, you need to look at the drawing of the electrical system. Here's what the diagrams of such systems look like:
The principle of operation of the contact ignition system
Like a contactless and electronic system, the contact analog works on the principle of converting and storing energy, which is supplied from the battery to the primary winding of the ignition coil. This element has a transformer design that converts 12V into a voltage of up to 30 thousand volts.
This energy is distributed by the distributor to each spark plug, due to which a spark is formed in the cylinders alternately, in accordance with the valve timing and engine strokes, sufficient to ignite the BTC.
All work of the contact ignition system can be conditionally divided into the following stages:
- Onboard network activation. The driver turns the key, the contact group closes. Electricity from the battery goes to the primary short circuit.
- High voltage current generation. This process occurs due to the formation of a magnetic field between the turns of the primary and secondary circuits.
- Starting the motor. Turning the key in the lock all the way provokes connecting the starter to the car's electrical network (everything you need to know about the operation of this mechanism is described here). Turning the crankshaft activates the operation of the gas distribution mechanism (for this, a belt or chain drive is used, which is described in another article). Since the distributor often begins to work together with the camshaft, its contacts are alternately closed.
- High voltage current generation. When the breaker is triggered (electricity abruptly disappears on the primary winding), the magnetic field abruptly disappears. At this moment, due to the induction effect, a current appears in the secondary winding with the voltage necessary for the formation of a spark in the candle. This parameter depends on the system modification.
- Distribution of impulses. As soon as the primary winding opens, the high-voltage line (center wire from the coil to the distributor) is energized. In the process of rotation of the distributor shaft, its slider also rotates. It closes the loop for a specific candle. Through the high-voltage wire, the impulse immediately enters the corresponding candlestick.
- Spark formation. When a high voltage current is applied to the center core of the plug, the small distance between it and the side electrode provokes an arc flash. The fuel / air mixture ignites.
- Accumulation of energy. In a split second, the distributor contacts open. At this moment, the primary winding circuit is closed. A magnetic field is again formed between it and the secondary circuit. Further KSZ works according to the principle described above.
Contact ignition system malfunctions
So, the efficiency of the engine depends not only on the proportion in which the fuel will be mixed with air and on the opening time of the valves, but also on the moment when an impulse is applied to the spark plugs. Most motorists know the term ignition timing.
Without going into details, this is the moment when the spark is applied during the execution of the compression stroke. For example, at high engine speeds, due to inertia, the piston can already begin to perform the stroke, and the VTS has not yet had time to ignite. Due to this effect, the acceleration of the car will be sluggish, and detonation may form in the engine, or when the exhaust valve is opened, the after-burning mixture will be thrown into the exhaust manifold.
This will definitely lead to all sorts of breakdowns. To avoid this, the contact ignition system is equipped with a vacuum regulator that responds to pressing the accelerator pedal and changes the SPL.
If the SZ is unstable, the motor will either lose power or not be able to work at all. Here are the main faults that can be in contact modifications of systems.
No spark on candles
The spark disappears in such cases:
- A break in the low-voltage wire has formed (goes from the battery to the coil) or the contact has disappeared due to oxidation;
- Loss of contact between the slider and the distributor contacts. Most often this is due to the formation of carbon deposits on them;
- Short circuit breakdown (breakage of winding turns), failure of the capacitor, the appearance of cracks on the distributor cover;
- The insulation of high-voltage wires is broken;
- Breakage of the candle itself.
To eliminate malfunctions, it is necessary to check the integrity of the high and low voltage circuits (whether there is contact between the wires and the terminals, if it is missing, then clean the connection), and also conduct a visual inspection of the mechanisms. In the process of diagnostics, the gaps between the breaker contacts are adjusted. Defective items are replaced with new ones.
Since the impulses of the system are controlled by mechanical devices, malfunctions in the form of carbon deposits or an open circuit are quite natural, since they are provoked by the natural wear of some parts.
Engine runs intermittently
If, in the first case, the absence of a spark on the candles will not allow the motor to start, then the unstable operation of the internal combustion engine can be triggered by malfunctions in a separate electrical circuit (for example, a breakdown of one of the explosive wires).
Here are some problems in the SZ that can cause unstable operation of the unit:
- Breakage of a candle;
- Too large or small gap between the spark plug electrodes;
- Wrong gap between breaker contacts;
- The distributor cover or rotor burst;
- Errors in setting UOZ.
Depending on the type of breakdown, they are eliminated by setting the correct UOZ, gaps and replacing the broken parts with new ones.
Diagnostics of any malfunctions of this type of ignition systems consists in a visual inspection of all nodes of the electrical circuit. If the coil breaks down, this part is simply replaced with a new one. Its malfunctions can be detected by checking for breaking the turns using a multimeter in the dial mode.
Additionally, we suggest watching a short video review on how the ignition system with a mechanical distributor works:
Questions and answers:
Why is the contactless ignition system better? Since there are no movable distributor and breaker in it, the contacts in the BC system do not require frequent maintenance (adjustment or cleaning from carbon deposits). In such a system, a more stable start of the internal combustion engine.
What ignition systems are there? In total, there are two types of ignition systems: contact and non-contact. In the first case, there is a contact breaker-distributor. In the second case, the switch plays the role of a breaker (and a distributor).
How does the electronic ignition system work? In such systems, the sparking impulse and the high voltage current distribution are electronically controlled. They have no mechanical elements that affect the distribution or interruption of the pulses.
