injection types. Fuel injection system - schemes and principle of operation

12.07.2019

System direct injection fuel in gasoline engines today is the most advanced and modern solution. Main Feature direct injection can be considered that the fuel is supplied to the cylinders directly.

For this reason, this system is also often referred to as direct fuel injection. In this article, we will look at how a direct injection engine works, as well as what advantages and disadvantages such a scheme has.

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Direct fuel injection: direct injection system device

As mentioned above, the fuel in these is supplied directly to the combustion chamber of the engine. This means that the injectors do not spray gasoline into, after which the fuel-air mixture enters through the cylinder, but directly inject fuel into the combustion chamber.

The first direct injection gasoline engines were . In the future, the scheme became widespread, as a result of which today with such a fuel supply system can be found in the lineup of many well-known automakers.

For example, concern VAG introduced a number Audi models and Volkswagen with naturally aspirated and turbocharged ones that received direct fuel injection. Direct injection engines are also produced by BMW, Ford, GM, Mercedes and many others.

Direct fuel injection has received such widespread use due to the high efficiency of the system (about 10-15% compared to distributed injection), as well as more complete combustion. working mixture in cylinders and reduce the level of toxicity of exhaust gases.

Direct injection system: design features

So let's take as an example FSI engine with its so-called "layered" injection. The system includes the following elements:

circuit high pressure;
gasoline;
pressure regulator;
fuel rail;
high pressure sensor;
injection nozzles;

Let's start with the fuel pump. The specified pump creates a high pressure under which fuel is supplied to fuel rail as well as injectors. The pump has plungers (there can be several plungers, or one in rotary pumps) and is driven by the inlet camshaft.

RTD (fuel pressure regulator) is integrated into the pump and is responsible for the metered fuel supply, which corresponds to the injector injection. A fuel rail (fuel rail) is needed in order to distribute fuel to the injectors. Also availability given element allows you to avoid pressure surges (pulsations) of the fuel in the circuit.

By the way, the circuit uses a special safety valve, which is in the rail. This valve is needed in order to avoid too high fuel pressure and thus protect individual elements systems. An increase in pressure can occur due to the fact that the fuel tends to expand when heated.

The high pressure sensor is a device that measures the pressure in fuel rail. Signals from the sensor are transmitted to, which, in turn, is able to change the pressure in the fuel rail.

Concerning injector nozzle, the element ensures the timely supply and atomization of fuel in the combustion chamber in order to create the necessary fuel-air mixture. Note that the processes described are controlled by . The system has a group of various sensors, an electronic control unit, as well as actuators.

If we talk about the direct injection system, together with the high fuel pressure sensor, the following are involved for its operation:, DPRV, air temperature sensor during intake manifold, coolant temperature sensor, etc.

Thanks to the operation of these sensors, the computer receives necessary information, after which the block sends signals to the actuators. This allows for a coherent and precise work solenoid valves, nozzles, safety valve and a number of other elements.

How Direct Fuel Injection Works

The main advantage of direct injection is the ability to achieve various types mixture formation. In other words, such a power supply system is able to flexibly change the composition of the working fuel-air mixture, taking into account the operating mode of the engine, its temperature, the load on the internal combustion engine, etc.

It is necessary to single out layer-by-layer mixing, stoichiometric, and also homogeneous. It is this mixture formation that ultimately makes it possible to use fuel as efficiently as possible. The mixture always turns out to be of high quality, regardless of the mode. ICE operation, gasoline burns fully, the engine becomes more powerful, while exhaust toxicity is reduced at the same time.

Layered mixture formation is activated when the engine loads are low or medium, and the crankshaft speed is low. Simply put, in such modes, the mixture is somewhat leaner in order to save money. Stoichiometric mixing involves preparing a mixture that is highly flammable without being overly enriched.
Homogeneous mixture formation allows you to get the so-called "power" mixture, which is needed at high engine loads. On a lean homogeneous mixture for additional savings power unit works in transitional modes.
When stratification is engaged, the throttle is wide open with the intake flaps closed. Air is supplied to the combustion chamber at a high speed, turbulence of air flows occurs. Fuel is injected near the end of the compression stroke, injection is made in the area where the spark plug is located.

In the short time before a spark appears on the spark plug, a fuel-air mixture is formed in which the excess air ratio is 1.5-3. Next, the mixture is ignited by a spark, while a sufficient amount of air is retained around the ignition zone. This air acts as a thermal "insulator".

If we consider homogeneous stoichiometric mixture formation, such a process occurs when the intake flaps are open, while the throttle is also open at one angle or another (depending on the degree of pressing the accelerator pedal).

In this case, the fuel is injected even during the intake stroke, as a result of which it is possible to obtain a homogeneous mixture. Excess air has a coefficient close to unity. Such a mixture is highly flammable and fully burns throughout the entire volume of the combustion chamber.

A lean homogeneous mixture is created when the throttle is fully open and the intake flaps are closed. In this case, air is actively moving in the cylinder, and fuel injection falls on the intake stroke. The ECM maintains excess air at 1.5.

In addition to clean air, exhaust gases can be added. This is due to work. As a result, the exhaust “burns out” again in the cylinders without damage to the engine. This reduces the emission harmful substances in atmosphere.

What is the result

As you can see, direct injection allows you to achieve not only fuel economy, but also a good return on the engine in both low and medium, and high loads. In other words, the presence of direct injection means that the optimal composition of the mixture will be maintained in all modes of operation of the internal combustion engine.

As for the disadvantages, the disadvantages of direct injection can only be attributed increased complexity during repairs and the price of spare parts, as well as the high sensitivity of the system to the quality of the fuel and the condition of the fuel and air filters.

Brief history of appearance

The fuel injection system began to be actively introduced in the 70s, as a reaction to the increased level of pollutant emissions into the atmosphere. It was borrowed from the aircraft industry and was an environmentally friendly alternative to a carbureted engine. The latter was equipped with a mechanical fuel supply system, in which fuel entered the combustion chamber due to the pressure difference.

The first injection system was almost completely mechanical and was characterized by low efficiency. The reason for this was the insufficient level of technological progress, which could not fully reveal its potential. The situation changed in the late 90s with the development of electronic engine control systems. The electronic control unit began to control the amount of fuel injected into the cylinders and percentage air-fuel mixture components.

Types of injection systems for gasoline engines

There are several main types of fuel injection systems, which differ in the way the air-fuel mixture is formed.

Single injection, or central injection

Scheme of operation of the mono-injection system

The central injection scheme provides for the presence of one nozzle, which is located in the intake manifold. Such injection systems can only be found on older cars. It consists of the following elements:

Pressure regulator - provides a constant working pressure of 0.1 MPa and prevents the occurrence of air locks in the fuel system.
Injection nozzle - performs a pulsed supply of gasoline to the engine intake manifold.
Throttle valve - regulates the amount of air supplied. May be mechanical or electric drive.
Control unit - consists of a microprocessor and a memory unit that contains the reference data of the fuel injection characteristics.
Position sensors crankshaft engine, throttle position, temperature, etc.

Gasoline injection systems with a single nozzle work according to the following scheme:

The engine is running.
Sensors read and transmit information about the state of the system to the control unit.
The received data is compared with the reference characteristic, and, based on this information, the control unit calculates the moment and duration of the nozzle opening.
A signal is sent to the electromagnetic coil to open the nozzle, which leads to the supply of fuel to the intake manifold, where it mixes with air.
A mixture of fuel and air is supplied to the cylinders.

Multiport Injection (MPI)

A multiport injection system consists of similar elements, but in this design there are separate nozzles for each cylinder, which can be opened simultaneously, in pairs or one at a time. The mixing of air and gasoline also occurs in the intake manifold, but, unlike mono-injection, fuel is supplied only during intake tracts corresponding cylinders.

Scheme of operation of the system with distributed injection

The control is carried out by electronics (KE-Jetronic, L-Jetronic). These are universal Bosch fuel injection systems that are widely used.

The principle of operation of distributed injection:

Air is supplied to the engine.
With the help of a number of sensors, the volume of air, its temperature, the speed of rotation of the crankshaft, as well as the parameters of the throttle position are determined.
Based on the received data, the electronic control unit determines the amount of fuel that is optimal for the incoming amount of air.
A signal is given and the corresponding nozzles are opened for the required period of time.

Direct fuel injection (GDI)

The system provides for the supply of gasoline by separate nozzles directly to the combustion chambers of each cylinder under high pressure, where air is simultaneously supplied. This injection system provides the most accurate concentration of the air-fuel mixture, regardless of the engine operating mode. At the same time, the mixture burns out almost completely, thereby reducing the amount of harmful emissions into the atmosphere.

Diagram of the direct injection system

Such an injection system is complex and susceptible to fuel quality, making it expensive to manufacture and operate. Since nozzles operate in more aggressive conditions, for correct operation such a system, it is necessary to provide high fuel pressure, which should be at least 5 MPa.

Structurally, the direct injection system includes:

High pressure fuel pump.
Fuel pressure control.
Fuel rail.
Safety valve(installed on the fuel rail to protect system elements from pressure increase more than acceptable level).
High pressure sensor.
Nozzles.

An electronic injection system of this type from Bosch received the name MED-Motronic. The principle of its operation depends on the type of mixture formation:

Layered - implemented at low and medium engine speeds. Air is supplied to the combustion chamber high speed. The fuel is injected towards the spark plug and, mixing with air along the way, ignites.
Stoichiometric. When you press the gas pedal, the throttle opens and fuel is injected simultaneously with the air supply, after which the mixture ignites and burns completely.
Homogeneous. In the cylinders, intensive air movement is provoked, while gasoline is injected on the intake stroke.

Direct fuel injection in a gasoline engine is the most promising direction in the evolution of injection systems. It was first implemented in 1996 on passenger cars. Mitsubishi cars Galant, and today it is installed on their cars by most of the largest automakers.

Direct injection (also known as "direct injection", or GDI) started to appear on cars not so long ago. However, the technology is gaining popularity and is increasingly found on the engines of new cars. Today we are in in general terms we will try to answer what is direct injection technology and is it worth it to be afraid of?

To begin with, it should be noted that the main distinctive feature technology is the location of the injectors, which are placed directly in the cylinder head, respectively, and injection under huge pressure occurs directly into the cylinders, in contrast to the long-established better side fuel into the intake manifold.

Direct injection was first tested in serial production Japanese automaker Mitsubishi. The operation showed that among the advantages, the main advantages were efficiency - from 10% to 20%, power - plus 5% and environmental friendliness. The main disadvantage is that injectors are extremely demanding on fuel quality.

It is also worth noting that a similar system has been successfully installed on for many decades. However, it was on gasoline engines that the application of the technology was fraught with a number of difficulties that have not yet been finally resolved.

A video from the YouTube channel "Savagegeese" explains what direct injection is and what can go wrong while driving a car with this system. In addition to the main pros and cons, the video also explains the intricacies preventive maintenance systems. In addition, the video touches on the topic of injection systems into the intake channels, which can be seen in abundance on older engines, as well as those that use both methods of fuel injection. Visually using Bosch diagrams, the facilitator explains how it all works.

To find out all the nuances, we suggest watching the video below (turning on the translation of subtitles will help you figure it out if you do not know English very well). For those who are not too interested to watch, you can read about the main pros and cons of direct gasoline injection below, after the video:

So, environmental friendliness and economy are good goals, but here's what the use is fraught with modern technology in your vehicle:

Minuses

1. Very complex design.

2. From this follows the second important problem. Since young gasoline technology involves major changes in the design of engine cylinder heads, the design of the injectors themselves, and the associated change in other engine parts, such as high pressure fuel pump (high pressure fuel pump), the cost of cars with direct fuel injection is higher.

3. The production of the parts of the power system itself must also be extremely precise. Nozzles develop pressure from 50 to 200 atmospheres.

Add to this the operation of the injector in close proximity to the combustible fuel and the pressure inside the cylinder, and you get the need to produce very high strength components.

4. Since the injector nozzles look into the combustion chamber, all gasoline combustion products are also deposited on them, gradually clogging or disabling the injector. This is perhaps the most serious disadvantage of using the GDI construct in Russian realities.

5. In addition, it is necessary to carefully monitor the condition of the engine. If oil burnout begins to occur in the cylinders, the products of its thermal decomposition will quickly disable the nozzle, clog the intake valves, forming an indelible coating of deposits on them. Do not forget that the classic injection with nozzles located in the intake manifold cleans the intake valves well, washing them with fuel under pressure.

6. Expensive repairs and the need for preventive maintenance, which is also expensive.

In addition, it also explains that direct injection vehicles can lead to valve fouling and poor performance if used improperly, especially on turbocharged engines.

D. Sosnin

We start publishing articles on modern fuel injection systems for gasoline engines internal combustion of cars.

1. Preliminary remarks

Fuel supply of gasoline engines in modern passenger cars is implemented using injection systems. These systems, according to the principle of operation, are usually divided into five main groups (Fig. 1): K, Mono, L, M, D.

2. Advantages of injection systems

The air-fuel mixture (TV-mixture) is supplied from the carburetor to the cylinders of the internal combustion engine (ICE) through long intake manifold pipes. The length of these pipes to different engine cylinders is not the same, and in the collector itself there is an uneven heating of the walls, even on a fully warmed up engine (Fig. 2).

This leads to the fact that from a homogeneous TV mixture created in the carburetor, different cylinders Internal combustion engines produce unequal air-fuel charges. As a result, the engine does not deliver its design power, torque uniformity, fuel consumption and the amount of harmful substances in the engine are lost. exhaust gases increase.

It is very difficult to deal with this phenomenon in carbureted engines. It should also be noted that a modern carburetor works on the principle of atomization, in which gasoline is atomized in a stream of air sucked into the cylinders. In this case, rather large drops of fuel are formed (Fig. 3, a),

That does not provide high-quality mixing of gasoline and air. Poor mixing and large droplets make it easier for gasoline to settle on the walls of the intake manifold and on the walls of the cylinders during the absorption of the TV mixture. But when gasoline is forced to be sprayed under pressure through a calibrated injector nozzle, fuel particles can be much smaller than when gasoline is sprayed during spraying (Fig. 3, b). Gasoline is sprayed especially effectively by a narrow beam under high pressure (Fig. 3, c).

It has been established that when gasoline is sprayed into particles with a diameter of less than 15–20 µm, its mixing with atmospheric oxygen occurs not as a particle weighing, but at the molecular level. This makes the TV mixture more resistant to temperature and pressure changes in the cylinder and long intake manifold pipes, which contributes to more complete combustion.

Thus, the idea was born to replace the spray jets of a mechanical inertial carburetor with a central inertial-free injection nozzle (CFI), which opens for a predetermined time according to an electric pulse control signal from the electronic automation unit. At the same time, in addition to high-quality atomization and efficient mixing of gasoline with air, it is easy to obtain a higher accuracy of their dosing in the TV mixture at all possible operating modes of the internal combustion engine.

Thus, due to the use of a fuel supply system with gasoline injection, the engines of modern passenger cars do not have the above disadvantages inherent in carburetor engines, i.e. they are more economical, have a higher specific power, maintain a constant torque over a wide range of speeds, and the emission of harmful substances into the atmosphere with exhaust gases is minimal.

3. Petrol injection system "Mono-Jetronic"

For the first time, the system of central single-point impulse fuel injection for gasoline engines of passenger cars was developed by BOSCH in 1975. This system was called "Mono-Jetronic" (Monojet - a single jet) and was installed on a Volkswagen car.

On fig. 4 shows the central injection unit of the "Mono-Jetronic" system. It can be seen from the figure that central nozzle injection (CFV) is installed on a standard intake manifold instead of a conventional carburetor.

But unlike a carburetor, in which automatic mixture formation is implemented by mechanical control, a mono injection system uses purely electronic control.

On fig. 5 shows a simplified functional diagram of the "Mono-Jetronic" system.

The electronic control unit (ECU) operates from input sensors 1-7, which record the current state and mode of operation of the engine. Based on the combination of signals from these sensors and using information from the three-dimensional injection characteristics, the ECU calculates the beginning and duration of the open state of the central injector 15.

On the basis of the calculated data in the ECU, an electrical impulse control signal S for the digital filter is generated. This signal acts on the winding 8 of the magnetic solenoid of the injector, the shut-off valve 11 of which opens, and through the spray nozzle 12, gasoline is forcibly sprayed at a pressure of 1.1 bar in the fuel supply line 19 into the intake manifold through the open throttle valve 14.

At given sizes of the throttle diaphragm and the calibrated section of the spray nozzle, the mass amount of air passed into the cylinders is determined by the degree of opening of the throttle valve, and the mass amount of gasoline injected into the air flow is determined by the duration of the open state of the nozzle and the boost (working) pressure in the fuel supply line 19.

In order for gasoline to burn completely and most efficiently, the masses of gasoline and air in the TV mixture must be in a strictly defined ratio, equal to 1/14.7 (for high-octane gasoline grades). This ratio is called stoichiometric, and it corresponds to the coefficient a of excess air equal to one. Coefficient a \u003d Md / M0, where M0 is the amount of air mass theoretically necessary for complete combustion given portion of gasoline, and Md is the mass of actually burnt air.

From this it is clear that in any fuel injection system there must be a meter for the mass of air admitted into the engine cylinders during suction.

In the "Mono-Jetronic" system, the air mass is calculated in the ECU according to the readings of two sensors (see Fig. 4): intake air temperature (AAT) and throttle position (TPP). The first one is located directly on the way air flow in the upper part of the central injection nozzle and is a miniature semiconductor thermistor, and the second is a resistive potentiometer, the engine of which is mounted on the rotary axis (PDA) of the throttle.

Since a specific angular position of the throttle valve corresponds to a strictly defined volumetric amount of air passed, the throttle potentiometer performs the function of an air flow meter. In the "Mono-Jetronic" system, it is also an engine load sensor.

But the mass of air taken in depends to a large extent on temperature. Cold air is denser and therefore heavier. As the temperature rises, the density of air and its mass decrease. The effect of temperature is taken into account by the DTV sensor.

The DTV intake air temperature sensor, as a semiconductor thermistor with a negative temperature coefficient of resistance, changes the resistance value from 10 to 2.5 kOhm when the temperature changes from -30 to +20°C. The DTV sensor signal is used only in this temperature range. In this case, the basic duration of petrol injection is corrected by the ECU in the range of 20...0%. If the intake air temperature is above + 20 ° C, then the DTV sensor signal is blocked in the ECU and the sensor is not used.

The signals from the throttle position sensors (DPD) and intake air temperature (DTV) in cases of their failures are duplicated in the ECU by the signals of the speed sensors (DOD) and the engine coolant temperature (DTD).

The air volume calculated in the ECU and the engine speed signal from the ignition speed sensor determine the required (basic) duration for the central injection nozzle to be open.

Since the boost pressure Pt in the fuel supply line (PBM) is constant (for "Mono-Jetronic" Pt = 1 ... 1.1 bar), and throughput nozzle is given by the total cross section of the spray nozzle openings, then the time of the open state of the nozzle uniquely determines the amount of injected gasoline. The moment of injection (in Fig. 5, the signal from the DMV sensor) is usually set simultaneously with the signal to ignite the TV mixture from the ignition system (through 180° of rotation of the engine crankshaft).

Thus, with electronic control of the mixture formation process, ensuring a high accuracy of dosing of injected gasoline into a measured amount of air mass is an easily solved problem, and, ultimately, the dosing accuracy is determined not by electronic automation, but by the manufacturing accuracy and functional reliability of the input sensors and the injection nozzle.

On fig. 6 shows the main part of the "Mono-Jetronic" system - the central injection nozzle (CFI).

The central injection nozzle is a petrol valve, which is opened by an electrical impulse coming from electronic block management. To do this, the nozzle has an electromagnetic solenoid 8 with a movable magnetic core 14. The main problem in creating valves for pulsed injection is the need to ensure a high speed of operation of the shut-off device 9 of the valve both for opening and closing. The solution to the problem is achieved by lightening the magnetic core of the solenoid, increasing the current in the pulse control signal, selecting the elasticity of the return spring 13, and also the shape of the ground surfaces for the spray nozzle 10.

The nozzle nozzle (Fig. 6, a) is made in the form of a socket of capillary tubules, the number of which is usually at least six. The angle at the top of the socket is set by the opening of the injection jet, which has the shape of a funnel. With this form, the jet of gasoline does not hit the throttle even with its small opening, but flies into two thin crescents of the opened slot.

The central nozzle of the "Mono-Jetronic" system reliably ensures the minimum duration of the open state of the spray nozzle 11 within 1 ± 0.1 ms. During such a time and at an operating pressure of 1 bar, about one milligram of gasoline is injected through a spray nozzle with an area of \u200b\u200b0.08 mm2. This corresponds to a fuel consumption of 4 l/h at minimum idling(600 rpm) warm engine. When starting and warming up a cold engine, the injector opens for a longer time (up to 5...7 ms). But on the other hand, the maximum duration of injection on a warm engine (time of the open state of the injector) is limited by the maximum speed of the engine crankshaft (6500 ... 7000 min-1) in full throttle mode and cannot be more than 4 ms. In this case, the clock frequency of operation of the locking device of the injector at idle is not less than 20 Hz, and at full load - not more than 200...230 Hz.

With special care, the DPD throttle position sensor (throttle potentiometer), shown in fig. 7. Its sensitivity to the rotation of the engine must meet the requirement of ±0.5 angular degrees of rotation of the axis 13 of the throttle. According to the strict angular position of the throttle axis, the beginnings of two engine operation modes are determined: idle mode (3 ± 0.5 °) and full load mode (72.5 ± 0.5 °).

To ensure high accuracy and reliability, the resistive tracks of the potentiometer, of which there are four, are connected according to the circuit shown in fig. 7, b, and the axis of the potentiometer slider (two-pin slider) is seated in a backlash-free Teflon plain bearing.

The potentiometer and the ECU are connected to each other by a four-wire cable through a connector. To increase the reliability of the connections, the contacts in the connector and in the potentiometer chip are gold-plated. Pins 1 and 5 are for supplying reference voltage 5 ± 0.01 V. Contacts 1 and 2 - to remove the signal voltage when the throttle valve is turned at an angle from 0 to 24 ° (0 ... 30 - idle mode; 3 ... 24 ° - low engine load mode) . Contacts 1 and 4 - to remove the signal voltage when the throttle valve is turned at an angle of 18 to 90 ° (18 ... 72.5 ° - medium load mode, 72.5 ... 90 ° - engine full load mode).

The signal voltage from the throttle potentiometer is additionally used:
to enrich the TV mixture during acceleration of the car (the rate of change of the signal from the potentiometer is recorded);
to enrich the TV mixture in full load mode (the value of the signal from the potentiometer is recorded after 72.5 ° turning the throttle upwards);
to stop fuel injection in the forced idle mode (a potentiometer signal is recorded if the throttle valve opening angle is less than 3 °. At the same time, the engine speed W is monitored: if W> 2100 min-1, then the fuel supply is stopped and restored again at W
An interesting feature of the "Mono-Jetronic" injection system is the presence in its composition of the idle speed stabilization subsystem using an electric servo drive that acts on the throttle valve axis (Fig. 8). The electric servomotor is equipped with a reverse electric motor 11 DC.

The servo drive is activated in idle mode and, together with the circuit for turning off the vacuum ignition timing regulator (idling stabilization - Fig. 2), ensures stabilization of the engine speed in this mode.

Such an idle stabilization subsystem works as follows.

When the throttle open angle is less than 3°, signal K (see Fig. 9)

It is an idle mode signal for the ECU (the limit switch VK is closed by the servo rod). On this signal, the shut-off pneumatic valve of the ZPK is activated and the vacuum channel from the throttle zone of the intake manifold to the BP vacuum regulator is blocked. Vacuum regulator from that moment on, it does not work and the ignition timing becomes equal to the value of the setting angle (6 ° to TDC). At the same time, the engine runs stably at idle. If at this time the air conditioner or other powerful consumer of engine energy (for example, headlights high beam indirectly through the generator), then its speed begins to fall. The engine may stall. To prevent this from happening, at the command of electronic circuit idle control (ESHH) in the controller, the electric servo is turned on, which slightly opens the throttle valve. RPM is increased to the nominal value for a given engine temperature. It is clear that when the load is removed from the engine, its speed is reduced to the norm by the same electric servo drive.

The ECU of the "Mono-Jetronic" system has a MCP microprocessor (see Fig. 5) with permanent and random-access memory (memory unit). The reference three-dimensional injection characteristic (THV) is "hardwired" into the permanent memory. This characteristic is somewhat similar to the three-dimensional ignition characteristic, but differs in that its output parameter is not the ignition timing, but the time (duration) of the open state of the central injection nozzle. The input coordinates of the TXV characteristic are the engine speed (the signal comes from the ignition system controller) and the intake air volume (calculated by the microprocessor in the injection computer). The reference characteristic of TXV contains reference (basic) information about the stoichiometric ratio of gasoline and air in the TV mixture under all possible modes and conditions of engine operation. This information is selected from the memory memory into the microprocessor of the computer according to the input coordinates of the characteristics of the TXV (according to the signals of the DOD, DPD, DTV sensors) and is corrected according to the signals from the coolant temperature sensor (CTD) and oxygen sensor(KD).

About the oxygen sensor must be said separately. Its presence in the injection system allows you to keep the composition of the TV-mixture constantly in the stoichiometric ratio (a=1). This is achieved by the fact that the CD sensor operates in a deep adaptive circuit. feedback from the exhaust system to the fuel supply system (to the injection system).

It reacts to the difference in the concentration of oxygen in the atmosphere and in the exhaust gases. Essentially, the KD sensor is chemical source current of the first kind (galvanic cell) with a solid electrolyte (special honeycomb cermet) and with a high (not lower than 300°C) operating temperature. The EMF of such a sensor almost according to a stepwise law depends on the difference in the oxygen concentration on its electrodes (platinum-radium film coating on different sides of the porous ceramic). The greatest steepness (difference) of the EMF step falls on the value a=1.

The KD sensor is screwed into the pipe of the exhaust channel (for example, into exhaust manifold) and its sensitive surface (positive electrode) is in the flow exhaust gases. Above the mounting thread of the sensor there are slots through which the outer negative electrode communicates with atmospheric air. On vehicles with a catalytic gas converter, the oxygen sensor is installed in front of the converter and has an electric heating coil, since the temperature of the exhaust gases in front of the converter can be below 300 ° C. In addition, the electrical heating of the oxygen sensor speeds up its preparation for operation.

The sensor is connected by signal wires to the injection computer. When the cylinders enter lean mixture(a>1), then the oxygen concentration in the exhaust gases is slightly higher than the standard one (at a=1). The CD sensor produces low voltage(about 0.1 V) and the ECU, using this signal, corrects the petrol injection duration time in the direction of its increase. The coefficient a again approaches unity. When the engine is running on rich mixture the oxygen sensor outputs a voltage of about 0.9 V and works in reverse.

It is interesting to note that the oxygen sensor is involved in the process of mixture formation only in engine operating modes, in which the enrichment of the TV mixture is limited by the value a > 0.9. These are modes such as load at low and medium speeds and idling on a warm engine. Otherwise, the KD sensor is disabled (blocked) in the ECU and the composition of the TV mixture is not corrected for the oxygen concentration in the exhaust gases. This takes place, for example, in the modes of starting and warming up a cold engine and in its forced modes (acceleration and full load). In these modes, a significant enrichment of the TV mixture is required and, therefore, the operation of the oxygen sensor ("pressing" the coefficient a to unity) is unacceptable here.

On fig. 10 shows a functional diagram of the "Mono-Jetronic" injection system with all its components.

Any injection system in its fuel supply subsystem necessarily contains a closed fuel ring, which starts from the gas tank and ends there. This includes: BB gas tank, EBN electric fuel pump, filter fine cleaning FTOT fuel, RT fuel distributor (in the "Mono-Jetronic" system - this is the central injection nozzle) and the pressure regulator RD, operating on the principle of a bleed valve when the specified operating pressure in the closed ring is exceeded (for the "Mono-Jetronic" system 1 ... 1.1 bar).

Closed fuel ring performs three functions:

With the help of a pressure regulator, it maintains the required constant operating pressure for the fuel distributor;

By means of a spring-loaded diaphragm in the pressure regulator, it maintains a certain residual pressure (0.5 bar) after the engine is switched off, which prevents the formation of steam and air locks in fuel lines when the engine cools down;

Provides cooling of the injection system due to the constant circulation of gasoline in a closed circuit. In conclusion, it should be noted that the "Mono-Jetronic" system is used only on passenger cars of the middle consumer class, such as West German cars: "Volkswagen-Passat", "Volkswagen-Polo", "Audi-80".
REPAIR&SERVICE-2"2000

To date, injection systems are actively used on gasoline and diesel internal combustion engines. It is worth noting that for each variation of the motor, such a system will be significantly different. More on this later in the article.

Injection system, purpose, what is the difference between a gasoline engine injection system and a diesel injection system

The main purpose of the injection system (another name is the injection system) is to ensure the timely supply of fuel to the working cylinders of the engine.

In gasoline engines, the injection process maintains the formation of air fuel mixture, after which it is ignited with a spark. In diesel engines, fuel is supplied under high pressure - one part of the combustible mixture is combined with compressed air and ignites almost instantly.

Gasoline injection system, arrangement of fuel injection systems for gasoline engines

Fuel injection system - component fuel system of the vehicle. The main working body of any injection system is the nozzle. Depending on the method of formation of the air-fuel mixture, there are systems of direct injection, distributed injection and central injection. Distributed and central injection systems are pre-injection systems, that is, injection in them is carried out in the intake manifold, not reaching the combustion chamber.

injection systems gasoline engines may have electronic or mechanical control. The most advanced is electronic injection control, which provides significant fuel savings and a reduction in harmful emissions into the atmosphere.

Fuel injection in the system is carried out pulsed (discretely) or continuously. From the point of view of economy, impulse fuel injection, used by all modern systems, is considered promising.

In the engine, the injection system is usually connected to the ignition system and creates a combined ignition and injection system (for example, Fenix, Motronic systems). The motor control system ensures the coordinated operation of the systems.

Injection systems for gasoline engines, types of fuel injection systems, advantages and disadvantages of each type of injection systems for gasoline engines

Gasoline engines use such fuel supply systems - direct injection, combined injection, distributed injection (multipoint), central injection (single injection).

Central injection. The fuel supply in this system is carried out by means of a fuel injector located in the intake manifold. And since there is only one nozzle, this system is also called mono-injection.

To date, central injection systems have lost their relevance, which is why they are not provided for in new car models, however, they can still be found in some old vehicles.

The advantages of single injection are reliability and ease of use. The disadvantages of this system include high flow fuel and low level environmental friendliness of the motor. Distributed injection. In system multipoint injection a separate fuel supply is provided for each cylinder, which is equipped with an individual fuel injector. FA, in this case, occurs only in the intake manifold.

To date, most gasoline engines are equipped with a distributed fuel supply system. Advantages similar system- optimal fuel consumption, high environmental friendliness, optimal requirements for the quality of consumed fuel.

Direct injection. One of the most progressive and perfect injection systems. The principle of operation of this system is based on the direct (direct) supply of fuel to the combustion chamber.

The direct fuel supply system makes it possible to obtain a high-quality fuel composition at all stages of engine operation in order to improve the combustion process of fuel assemblies, increase the engine's operating power and reduce the level of exhaust gases.

The disadvantages of this injection system are a rather complicated design and high requirements for fuel quality.

Combined injection. In a system of this type, two systems are combined - distributed and direct injection. As a rule, it is applied to reduce emissions of toxic components and waste gases, with which it is possible to achieve high performance environmental friendliness of the motor.

Diesel injection systems, types of systems, advantages and disadvantages of each type of diesel fuel injection systems

The following injection systems are used on modern diesel engines - a common rail system, a pump-injector system, a system with a distribution or in-line high-pressure fuel pump (TNVD).

The most popular and progressive are pump injectors and Common Rail. High pressure fuel pump is a central component of any diesel engine fuel system.
The fuel mixture in diesel engines can be supplied to the preliminary chamber or directly to the combustion chamber.

At present, a direct injection system is preferred, characterized by increased level noise and less smooth operation of the motor compared to feeding into the preliminary chamber, however, it provides more important indicator- economy.

Pump-injector system. This system It is used for supplying, as well as for injecting a combustible mixture under high pressure by unit injectors. Key Features of this system - two functions are combined in one device - injection and pressure generation.

The design flaw of this system is that the pump is equipped permanent drive from camshaft motor (not switched off), which can lead to rapid wear of the system. As a result, manufacturers are increasingly opting for common rail systems.

Battery injection (Common Rail). Improved fuel mixture supply design for many diesel engines. In such a system, fuel is supplied from the rail to fuel injectors, which is also called a high-pressure accumulator, as a result of which the system has another name - accumulator injection.

The Common Rail system provides for the following injection stages - preliminary, main and additional. This makes it possible to reduce vibration and engine noise, make the self-ignition of fuel more efficient, and reduce harmful emissions.

conclusions

To control injection systems on diesel engines, electronic and mechanical devices. Mechanical systems make it possible to control the operating pressure, moment and volume of fuel injection. IN electronic systems provides for more efficient management diesel engines generally.