Principle of operation of car ignition system

The internal combustion engine has a history of over 100 years of development. Since its inception, designers are always looking for ways to improve, increase productivity, reduce fuel consumption and reduce the level of toxicity in engine exhaust.

The internal combustion engine is a ' machine ' that has many auxiliary systems such as fuel system, cooling system, gas distribution system, booster system . Particularly for gasoline engines, the system hits Fire is one of the most important components. It works to convert low-voltage current (6-12V, 24V) into high-voltage electrical impulses (12,000-40,000) enough to create sparks at spark plugs to ignite the air at the right time. in a certain order.

Figure 1: Principle diagram simulating the operating principle of the ignition system.

Note : A, D: High voltage wire; B: Power split cover; C: Spindle; E: Power split covers; F: Cam divides electricity; G: Ignition sensor; H: Ignition IC; I: Bobbin; J: Spark plugs on fire.

In this article refers to the ignition system of the engine. Starting with the ignition time, then let's see all the components to create sparks like electric candles (spark plugs), turbochargers (bobbin) and power dividers. Finally, we will go through an existing programmable ignition system.

Why fire early?

The ignition system on your car needs to work in accordance with other engine systems. It needs to release the spark exactly at a certain time to ignite the mixture of expansion gas in the cylinder to maximize its capacity. If the ignition is wrong, the engine capacity will be reduced, fuel consumption and the amount of toxic substances in the exhaust gas increase.

Figure 2: Spark plugs ignite before the piston reaches the Dead Point

Note : 1: Period of loading; 2: Compression period; 3: Explosive period; 4: Discharge period; 5: Spark plugs; 6: Dead point on

When the air and fuel mix in the cylinder is burned, the temperature rises and the fuel burns into exhaust gas. This results in a sudden increase in cylinder pressure and a piston push down.

In order to increase engine power and torque, it is necessary to increase the pressure in the cylinder during combustion. The maximum pressure will result in high engine efficiency and this is entirely dependent on the time of spontaneous ignition to ignite the gas mixture.

There will be a delay from when the bu-spark sparks until the gas mixture is completely burned and the cylinder pressure is highest. If the spark occurs when the piston reaches the upper dead end of the compression period, the piston is ready to move down before the pressure in the cylinder reaches the highest value. This is not the optimal time.

To fully utilize the energy of the fuel, sparks need to appear before the piston reaches the dead end of the compression period until the piston comes down in time when the pressure in the cylinder reaches the highest value.

We know that: Gong = force * distance; And in cylinder: Force = pressure * piston peak area; Distance = piston journey. So: Public = pressure * peak piston area * piston stroke.

For a specific engine, the piston diameter and stroke are constant, so there is only way to increase the pressure to increase the engine power. The ignition time is very important, and the timing of ignition is soon to be good. late depends on other conditions. The time of the combustion mixture is almost constant, but the speed of the piston will increase as the engine speed increases. That is, the higher the engine speed, the earlier the ignition time will be.

In addition to increasing capacity, consider other goals, such as minimizing toxic substances in exhaust gas. The time of late ignition (ie the time of ignition is near the time of piston to the upper dead point), the maximum pressure in the cylinder and the temperature can be reduced. Reduced temperature will reduce nitrogen NoX (a toxic substance in exhaust gas). Late ignition also reduces the knock on the phone (some cars now have engine knock sensors to detect engine knocking automatically).

The main components of the ignition system

Spark : in theory, it is quite simple, it is a tool for power to emit arc through a gap (like lightning). This power supply must have a very high voltage so that the spark can be discharged through gaps and strong sparks. Normally, the voltage between two poles of electric candles ranges from 40,000 to 100,000 volts.

Figure 3: Spark plugs placed in the middle of 4 valves of the air distribution mechanism

The spark plug must be isolated from the high voltage so that the spark appears in accordance with the predetermined position of the electrode of the candle, on the other hand it must withstand the harsh conditions in the cylinder such as very high pressure and temperature, more moreover, it must be designed so that coal dust does not cling to electrode surfaces during work.

Spark plugs use insulating porcelain to insulate high-voltage sources between electrodes, it must ensure that sparks emit at the ends of the electrode, not at any of the two poles. In addition, this porcelain also works to prevent coal dust from sticking during use. Porcelain is a very poor thermal conductive material, so the material is very hot during work. Heat has helped to remove coal dust from the electrode.

Figure 4: Structure of spark plugs

Some vehicles require the use of hot spark plugs. This type of spark plug is designed to have less enveloping porcelain in contact with the metal so the heat exchange is worse and the candles are hotter and the dirt is better cleaned. Cold spark plugs, on the other hand, are designed with larger heat exchangers so they will be cooler when operating.

The designer has chosen the suitable working temperature of electric candle for each type of vehicle. Some high-performance cars will produce more heat so have to use cooler candles. If the electric candle is too hot, it will cause the mixture to burn before sparks are emitted, so it is necessary to choose the correct type of electric candle for each type of vehicle.

Figure 5: Hot spark plugs (left), cool spark plugs (right)

Bobbin (Figure 6): is a high-pressure component to create sparks. Very simply, the high voltage is generated by the induction between two coils. A little coil is called the primary roll (yellow), rolled around the primary coil (black) but more round than the secondary roll. The secondary coil has a number of rings that are hundreds of times larger than the primary one.

The current from the power source passes through the coil of the coil, suddenly, the current is disconnected at the time of ignition by the screw cheek (closing the circuit then suddenly opens). When the current in the primary coil is disconnected, the electric field due to the primary coil is suddenly reduced. Under the principle of electromagnetic induction, the secondary coil generates an electric current to counteract the change from that field. Since the number of turns of the secondary coil is many times higher than the number of primary windings, the current in the secondary coil has a very high voltage (up to 100,000 volts). This high-voltage current is sent to a candle by the power divider via a high-voltage wire.

Figure 6: Turbocharger

Power divider (Figure 7): There are some functions as follows: first, it divides high voltage power from power boost to cylinders. This is done by the power divider shaft and the gyroscope mounted at the top. The secondary coil of the power boost is connected to the gyroscope, the power divider cap has connectors for high-voltage wires to the cylinders. When the gyroscope rotates the circle it will divide the high voltage power to the cylinders in a certain sequence.

Figure 7: Power divider

Note : A: High-pressure currents come from the bunker ignited; B: Spinners; C: Power split cover; D: High-voltage current to the cylinders.

The older power divider (using a screwdriver) (Figure 8) has two parts, the upper part is the high voltage divider as mentioned, while the bottom is the part to disconnect the primary current of the coil. The grounding of the power boost is connected to the power divider screw.

A camshaft in the center of the power divider will cause the screw's part to separate from the static part at the time of ignition. This explains why the current of the primary coil is suddenly lost and produces a high-voltage pulse.

Figure 8: The old power divider uses cam, screw cheek and capacitor

Note : A: The wire connects to the igniter; B: Cheek screw; C: Screw the timing of the ignition early; D: Orange guide; E: Cam spinning; F: Capacitor.

In the last few years, you've probably heard about new cars that only need to be adjusted and maintained after 100,000 miles. One of the long-term maintenance technologies is the ignition system without a power divider, often called the ESA programmable ignition system. This system not only has a turbocharger, but every cylinder has its own power boost. The central ECU block will determine the exact timing of ignition for the cylinders. The main advantage of ESA ignition system is: first, there is no power divider; second, do not need high-voltage wires; and finally the ignition time is automatically adjusted according to the preset program. This increases engine efficiency, reduces fuel consumption and toxic substances in exhaust gas while increasing the overall engine capacity.

To control the timing of ignition (the time of opening the screw), people use a vacuum early system or centrifugal premature system. These mechanical systems control early fire according to load and engine speed.

The timing of ignition plays a very important role for the engine's performance, so vehicles now use ignition sensors instead of screw chucks. These sensors will tell the ECU block the exact position of the piston, the car computer will decide when to open or close the current in the primary coil.

Figure 9: Ignition system does not use a power divider, each spark plug has its own turbocharger

The ignition system of modern vehicles has many interesting and interesting things. If you're a car lover, keep up to date with new car systems.

Đức Hùng (Compile)