The fuel injection system is used for metered fuel supply to the engine internal combustion at a strictly defined point in time. Power, efficiency and depend on the characteristics of this system. Injection systems can have different designs and versions, which characterizes their efficiency and scope.

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 in the aircraft industry and was environmentally more safe alternative carbureted engine. The latter was equipped mechanical system fuel supply, 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 lack of technical progress who could not reach her full potential. The situation changed in the late 90s with the development of electronic engine control systems. The electronic unit management 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, 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 appearance of air pockets in.
• Injection nozzle - performs a pulsed supply of gasoline during intake manifold engine.
• — regulates the volume of supplied air. May be mechanical or electrically driven.
• Control unit - consists of a microprocessor and a memory unit that contains the reference data of the fuel injection characteristics.
• Sensors for engine crankshaft position, 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 to the intake tracts of the 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.

System operation scheme direct injection

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

Structurally, the direct injection system includes:

• High pressure fuel pump.
• Fuel pressure control.
• Fuel rail.
• Safety valve (mounted on fuel rail to protect the elements of the system from an increase in pressure above the permissible 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 fed into the combustion chamber at high speed. Fuel is injected towards 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.

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

Dear readers and subscribers, it's nice that you continue to study the structure of cars! And now to your attention is an electronic fuel injection system, the principle of which I will try to tell in this article.

Yes, it is about those devices that have replaced the time-tested power supplies from under the hoods of cars, and we will also find out if modern gasoline and diesel engines have much in common.

Perhaps we would not have discussed this technology with you if a couple of decades ago humanity had not seriously taken care of the environment, and toxic exhaust gases from cars turned out to be one of the most serious problems.

The main drawback of cars with engines equipped with carburetors was the incomplete combustion of fuel, and to solve this problem, systems were needed that could regulate the amount of fuel supplied to the cylinders depending on the mode of operation of the engine.

Thus, injection systems or, as they are also called, injection systems, appeared on the automotive arena. In addition to improving environmental friendliness, these technologies have improved the efficiency of engines and their power characteristics, becoming a real boon for engineers.

Today, fuel injection (injection) is used not only on diesel, but also on gasoline units, which undoubtedly unites them.

They are also united by the fact that the main working element of these systems, whatever type they are, is the nozzle. But due to differences in the method of burning fuel, the designs of the injection units for these two types of engines, of course, differ. Therefore, we will consider them in turn.

Injection systems and gasoline

Electronic fuel injection system. Let's start with gasoline engines. In their case, injection solves the problem of creating an air- fuel mixture, which is then ignited in the cylinder by a spark from a spark plug.

Depending on how this mixture and fuel is supplied to the cylinders, injection systems can have several varieties. The injection happens:

central injection

The main feature of the technology located first in the list is one single nozzle for the entire engine, which is located in the intake manifold. It should be noted that this type of injection system does not differ much from the carburetor system in its characteristics, therefore, today it is considered obsolete.

Distributed injection

More progressive is distributed injection. In this system, the fuel mixture is also formed in the intake manifold, but, unlike the previous one, each cylinder here boasts its own injector.

This variety allows you to experience all the advantages of injection technology, therefore it is most loved by automakers, and is actively used in modern engines.

But, as we know, there are no limits to perfection, and in pursuit of even higher efficiency, engineers have developed an electronic fuel injection system, namely the direct injection system.

Her main feature is the location of the nozzles, which, in this case, with their nozzles go into the combustion chambers of the cylinders.

The formation of an air-fuel mixture, as you might already guess, occurs directly in the cylinders, which has a beneficial effect on the operating parameters of the engines, although this option is not as environmentally friendly as that of distributed injection. Another tangible drawback of this technology is the high requirements for the quality of gasoline.

Combined injection

The most advanced in terms of emissions of harmful substances is a combined system. This is, in fact, a symbiosis of direct and distributed fuel injection.

How about diesels?

Let's move on to diesel units. Their fuel system is faced with the task of supplying fuel at very high pressure, which, mixing in a cylinder with compressed air, ignites itself.

A lot of options for solving this problem have been created - both direct injection into cylinders and with an intermediate link in the form of a preliminary chamber are used, in addition, there are various layouts of high pressure pumps (high pressure pumps), which also adds variety.

However, modern motorists prefer two types of systems that supply diesel fuel directly to the cylinders:

• with pump nozzles;
• injection common rail.

Pump nozzle

The pump-injector speaks for itself - it has an injector that injects fuel into the cylinder, and a high-pressure fuel pump are structurally combined into one unit. The main problem of such devices is increased wear, since the unit injectors are connected by a permanent drive to the camshaft and are never disconnected from it.

common rail system

The Common Rail system takes a slightly different approach, making it the preferred choice. There is one common injection pump, which supplies diesel to the fuel rail, which distributes fuel to the cylinder nozzles.

This was only a brief overview of injection systems, so, friends, follow the links in the articles, and using the Engine section, you will find all the injection systems of modern cars to study. And subscribe to the newsletter so as not to miss new publications, in which you will find a lot of detailed information on the systems and mechanisms of the car.

Now one of the main tasks for the design bureaus of automakers is to create power plants that consume as little fuel as possible and emit a reduced amount of harmful substances into the atmosphere. In this case, all this must be achieved with the condition that the impact on the operating parameters (power, torque) will be minimal. That is, it is necessary to make the motor economical, and at the same time powerful and high-torque.

To achieve the result, almost all components and systems of the power unit are subjected to alterations and improvements. This is especially true of the power system, because it is she who is responsible for the flow of fuel into the cylinders. The latest development in this direction is the direct injection of fuel into the combustion chambers of a power plant operating on gasoline.

The essence of this system is reduced to the separate supply of the components of the combustible mixture - gasoline and air into the cylinders. That is, the principle of its operation is very similar to the operation of diesel plants, where mixture formation is carried out in combustion chambers. But the gasoline unit, on which the direct injection system is installed, has a number of features in the process of pumping the components of the fuel mixture, its mixing and combustion.

A bit of history

Direct injection is not a new idea, there are a number of examples in history where such a system was used. The first mass use of this type of motor power was in aviation in the middle of the last century. They also tried to use it on vehicles, but it was not widely used. The system of those years can be considered as a kind of prototype, since it was completely mechanical.

The direct injection system received a “second life” in the mid-90s of the 20th century. The Japanese were the first to equip their cars with direct injection installations. The unit developed by Mitsubishi received the designation GDI, which is an abbreviation for Gasoline Direct Injection, which stands for direct fuel injection. A little later, Toyota created its own engine - D4.

Direct fuel injection

Over time, engines that use direct injection appeared from other manufacturers:

• Concern VAG - TSI, FSI, TFSI;
• Mercedes-Benz - CGI;
• Ford-EcoBoost;
• GM - EcoTech;

Direct injection is not a separate, completely new type, and it belongs to fuel injection systems. But unlike its predecessors, its fuel is injected under pressure directly into the cylinders, and not, as before, into the intake manifold, where gasoline was mixed with air before being fed into the combustion chambers.

Design features and principle of operation

Direct injection of gasoline is very similar in principle to diesel. The design of such a power supply system has additional pump, after which gasoline is already under pressure supplied to the nozzles installed in the cylinder head with sprayers located in the combustion chamber. At the required moment, the nozzle supplies fuel to the cylinder, where air has already been pumped through the intake manifold.

The design of this power system includes:

• a tank with a fuel priming pump installed in it;
• low pressure lines;
• filter elements for fuel purification;
• a pump that creates increased pressure with an installed regulator (high pressure fuel pump);
• high pressure lines;
• ramp with nozzles;
• relief and safety valves.

Scheme of the fuel system with direct injection

The purpose of parts of the elements, such as a tank with a pump and a filter, are described in other articles. Therefore, consider the appointment of a number of nodes that are used only in the direct injection system.

One of the main elements in this system is the high pressure pump. It provides fuel under significant pressure to the fuel rail. Its design is different for different manufacturers - single or multi-plunger. The drive is carried out from camshafts.

The system also includes valves that prevent the fuel pressure in the system from exceeding critical values. In general, pressure adjustment is carried out in several places - at the outlet of the high-pressure pump by a regulator, which is included in the design of the high-pressure fuel pump. There is a bypass valve that controls the pressure at the inlet to the pump. The safety valve monitors the pressure in the rail.

Everything works like this: the fuel priming pump from the tank delivers gasoline to the high-pressure fuel pump through the low-pressure line, while gasoline passes through a fine fuel filter, where large impurities are removed.

Plunger pairs of the pump create fuel pressure, which varies from 3 to 11 MPa under different engine operating modes. Already under pressure, the fuel enters the rail through high-pressure lines, which is distributed over its nozzles.

The operation of the injectors is controlled by an electronic control unit. At the same time, it is based on the readings of many engine sensors, after analyzing the data, it controls the injectors - the moment of injection, the amount of fuel and the method of spraying.

If the injection pump is supplied with more fuel than necessary, then the bypass valve is activated, which returns part of the fuel to the tank. Also, part of the fuel is dumped into the tank in case of excess pressure in the rail, but this is already done by a safety valve.

direct injection

Mixing types

Using direct fuel injection, engineers managed to reduce gasoline consumption. And everything is achieved by the possibility of using several types of mixture formation. That is, under certain operating conditions of the power plant, its own type of mixture is supplied. Moreover, the system controls and manages not only the fuel supply, to ensure one or another type of mixture formation, a certain mode of air supply to the cylinders is also set.

In total, direct injection is able to provide two main types of mixture in the cylinders:

• Layered;
• Stoichiometric homogeneous;

This allows you to choose a mixture that, with a certain operation of the motor, will provide the greatest efficiency.

Layered mixture formation allows the engine to operate at very lean mixture, in which the mass fraction of air is more than 40 times greater than the fuel fraction. That is, a very large amount of air is supplied to the cylinders, and then a little fuel is added to it.

Under normal conditions, such a mixture does not ignite from a spark. In order for ignition to occur, the designers gave the piston head a special shape that provides turbulence.

With this mixture formation, the air directed by the damper enters the combustion chamber at high speed. At the end of the compression stroke, the injector injects fuel, which, reaching the bottom of the piston, is swirled up to the spark plug. As a result, in the area of ​​the electrodes, the mixture is enriched and flammable, while around this mixture there is air practically free of fuel particles. Therefore, such mixture formation is called layered - inside there is a layer with an enriched mixture, on top of which there is another layer, practically without fuel.

This mixture formation ensures minimal consumption of gasoline, but the system also prepares such a mixture only with uniform movement, without sharp accelerations.

Stoichiometric mixture formation is the production of a fuel mixture in optimal proportions (14.7 parts of air to 1 part of gasoline), which ensures maximum power output. Such a mixture already ignites easily, so there is no need to create an enriched layer near the candle, on the contrary, for efficient combustion it is necessary that gasoline is evenly distributed in the air.

Therefore, the fuel is injected by the injectors at the same compression, and before ignition it has time to move well with the air.

This mixture formation is provided in the cylinders during accelerations when maximum power output is needed, not economy.

The designers also had to deal with the issue of switching the engine from lean to rich during hard accelerations. To prevent detonation combustion, dual injection is used during the transition.

The first injection of fuel is carried out on the intake stroke, while the fuel acts as a cooler of the walls of the combustion chamber, which eliminates detonation. The second portion of gasoline is supplied already at the end of the compression stroke.

The direct fuel injection system, due to the use of several types of mixture formation at once, allows you to save fuel well without much effect on power performance.

During acceleration, the engine runs on a normal mixture, and after picking up speed, when the driving mode is measured and without sudden changes, power point switches to a very lean mixture, thereby saving fuel.

This is the main advantage of such a power supply system. But it also has an important drawback. The high pressure fuel pump as well as the injectors use highly processed precision pairs. It is they who are the weak point, since these vapors are very sensitive to the quality of gasoline. The presence of third-party impurities, sulfur and water can disable high-pressure fuel pumps and nozzles. Additionally, gasoline has very poor lubricating properties. Therefore, the wear of precision pairs is higher than that of the same diesel engine.

In addition, the direct fuel supply system itself is structurally more complex and expensive than the same separate injection system.

New developments

The designers don't stop there. A peculiar refinement of direct injection was made in concern VAG in the TFSI powertrain. His power system was combined with a turbocharger.

An interesting solution was proposed by Orbital. They have developed a special injector that, in addition to fuel, also injects fuel into the cylinders. compressed air supplied by an additional compressor. This air-fuel mixture has excellent flammability and burns well. But this is still only a development and whether it will find application on a car is still unknown.

In general, direct injection is now the most the best system nutrition in terms of economy and environmental friendliness, although it has its drawbacks.

Autoleek

In the case of fuel injection, your engine is still ​sucking, but instead of relying solely on the amount of fuel being sucked in, the fuel injection system fires exactly the right amount of fuel into the combustion chamber. Fuel injection systems have already gone through several stages of evolution, electronics have been added to them - this was perhaps the biggest step in the development of this system. But the idea of ​​such systems remains the same: an electrically activated valve (injector) sprays a measured amount of fuel into the engine. In fact, the main difference between a carburetor and an injector is precisely in electronic management ECU - exactly on-board computer delivers exactly the right amount of fuel to the combustion chamber of the engine.

Let's see how the fuel injection system and the injector in particular work.

What does the fuel injection system look like?

If the heart of a car is its engine, then its brain is the engine control unit (ECU). It optimizes the performance of the motor by using sensors to decide how to control some of the actuators in the motor. First of all, the computer is responsible for 4 main tasks:

1. manages the fuel mixture,
2. controls idle speed
3. is responsible for the ignition timing,
4. controls the valve timing.

Before we talk about how the ECU performs its tasks, let's talk about the most important thing - let's trace the path of gasoline from the gas tank to the engine - this is the work of the fuel injection system. Initially, after a drop of gasoline leaves the walls of the gas tank, it is sucked up by an electric fuel pump into the engine. Electric fuel pump, as a rule, consists of the pump itself, as well as a filter and a transmission device.

A fuel pressure regulator at the end of the vacuum-fed fuel rail ensures that fuel pressure is constant with respect to suction pressure. For a gasoline engine, fuel pressure is typically on the order of 2-3.5 atmospheres (200-350 kPa, 35-50 PSI (psi)). The fuel injectors are connected to the engine, but their valves remain closed until the ECU allows fuel to be sent to the cylinders.

But what happens when the engine needs fuel? This is where the injector comes into play. Usually injectors have two pins: one pin is connected to the battery through the ignition relay, and the other pin goes to the ECU. The ECU sends pulse signals to the injector. Due to the magnet, to which such pulsating signals are applied, the injector valve opens, and a certain amount of fuel is supplied to its nozzle. Since there is a very high pressure in the injector (the value is given above), the opened valve directs fuel with high speed into the injector nozzle. The duration with which the injector valve is open affects how much fuel is supplied to the cylinder, and this duration, respectively, depends on the pulse width (i.e., how long the ECU sends a signal to the injector).

When the valve opens, the fuel injector sends fuel through the spray tip, which atomizes the liquid fuel into mist, directly into the cylinder. Such a system is called direct injection system. But the atomized fuel may not be supplied immediately to the cylinders, but first to the intake manifolds.

How the injector works

But how does the ECU determine how much fuel needs to be supplied to the engine at the moment? When the driver presses the accelerator pedal, he actually opens the throttle by the amount of pedal pressure, through which air is supplied to the engine. Thus, we can confidently call the gas pedal the "air regulator" to the engine. So, the car's computer is guided, among other things, by the throttle opening value, but is not limited to this indicator - it reads information from many sensors, and let's find out about them all!

Sensor mass flow air

First things first, the Mass Air Flow (MAF) sensor detects how much air is entering the throttle body and sends that information to the ECU. The ECU uses this information to decide how much fuel to inject into the cylinders to keep the mixture in ideal proportions.

Throttle position sensor

The computer constantly uses this sensor to check the throttle position and thus learn how much air is passing through the air intake in order to regulate the pulse sent to the injectors, ensuring that the correct amount of fuel enters the system.

Oxygen sensor

In addition, the ECU uses the O2 sensor to find out how much oxygen is in the car's exhaust. The oxygen content of the exhaust gases provides an indication of how well the fuel is burning. Using linked data from two sensors: oxygen and mass air flow, the ECU also controls the saturation of the fuel-air mixture supplied to the combustion chamber of the engine cylinders.

crankshaft position sensor

This is perhaps the main sensor of the fuel injection system - it is from him that the ECU learns about the number of engine revolutions at a given time and corrects the amount of fuel supplied depending on the number of revolutions and, of course, the position of the gas pedal.

These are the three main sensors that directly and dynamically affect the amount of fuel supplied to the injector and subsequently to the engine. But there are a number of other sensors:

• The voltage sensor in the electrical network of the car is needed so that the ECU understands how low the battery is and whether it is necessary to increase the speed in order to charge it.
• Coolant temperature sensor - ECU increases the number of revolutions if the engine is cold and vice versa if the engine is warm.

The first injection systems were mechanical (Figure 2.61) rather than electronic, and some of them (such as the high-performance BOSCH system) were extremely ingenious and worked well. The first mechanical fuel injection system was developed by Daimler Benz, and the first mass-produced car with gasoline injection was produced back in 1954. The main advantages of the injection system compared to carburetor systems are as follows:

The absence of additional resistance to the air flow at the inlet, which takes place in the carburetor, which ensures an increase in the filling of the cylinders and the liter engine power;

More accurate distribution of fuel to individual cylinders;

A significantly higher degree of optimization of the composition of the combustible mixture in all modes of engine operation, taking into account its condition, which leads to improved fuel economy and a decrease in exhaust gas toxicity.

Although in the end it turned out that it was better to use electronics for this purpose, which makes it possible to make the system more compact, more reliable and more adaptable to the requirements various engines. Some of the first systems electronic injection were a carburetor, from which all "passive" fuel systems and installed one or two nozzles. Such systems are called "central (single-point) injection" (Fig. 2.62 and 2.64).

Rice. 2.62. Central (single point) injection unit

Rice. 2.64. Scheme of the central fuel injection system: 1 - fuel supply;

Rice. 2.63. Electronic control unit 2 - air intake; 3 - throttle valve for a four-cylinder engine; 4 - inlet pipeline; Valvetronic BMW 5 - nozzle; 6 - engine

At present, distributed (multi-point) electronic injection systems are most widely used. It is necessary to dwell on the study of these nutritional systems in more detail.

POWER SYSTEM WITH ELECTRONIC DISTRIBUTED GASOLINE INJECTION (MOTRONIC TYPE)

In the central injection system, the mixture is supplied and distributed among the cylinders inside the intake manifold (Fig. 2.64).

The most modern system of distributed fuel injection is distinguished by the fact that a separate nozzle is installed in the intake tract of each cylinder, which at a certain moment injects a metered portion of gasoline onto the intake valve of the corresponding cylinder. Gasoline received

into the cylinder, evaporates and mixes with air, forming a combustible mixture. Engines with such power supply systems have better fuel efficiency and a lower content of harmful substances in exhaust gases compared to carburetor engines.

The operation of the injectors is controlled by an electronic control unit (ECU) (Fig. 2.63), which is a special computer that receives and processes electrical signals from a system of sensors, compares their readings with the values

stored in the computer memory, and generates electrical control signals to the injector solenoid valves and other actuators. In addition, the ECU constantly carries out diagnostics

Rice. 2.65. Scheme of the Motronic distributed fuel injection system: 1 - fuel supply; 2 - air supply; 3 - throttle valve; 4 - inlet pipeline; 5 - nozzles; 6 - engine

The fuel injection system also warns the driver in the event of a malfunction with the help of a warning lamp installed in the instrument panel. Serious faults are recorded in the memory of the control unit and can be read out during diagnostics.

The power supply system with distributed injection has the following components:

Fuel supply and purification system;

Air supply and purification system;

Gasoline vapor capture and combustion system;

Electronic part with a set of sensors;

Exhaust gas exhaust and afterburning system.

Fuel supply system consists of a fuel tank, an electric fuel pump, a fuel filter, pipelines and a fuel rail, on which nozzles and a fuel pressure regulator are installed.

Rice. 2.66. Submersible electric fuel pump; a - fuel intake with pump; b - the appearance of the pump and the pump section of the rotary type fuel pump with an electric drive; in - gear; g - roller; d - lamellar; e - scheme of operation of the pump section of the rotary type: 1 - housing; 2 - suction zone; 3 - rotor; 4 - injection zone; 5 - direction of rotation

Rice. 2.67. Fuel rail of a five-cylinder engine with nozzles installed on it, a pressure regulator and a fitting for pressure control

Electric fuel pump(usually roller) can be installed both inside the gas tank (Fig. 2.66) and outside. The fuel pump is switched on by an electromagnetic relay. Gasoline is sucked by the pump from the tank and at the same time washes and cools the pump motor. At the outlet of the pump there is a check valve that does not allow fuel to flow out of the pressure line when the fuel pump is turned off. A safety valve is used to limit the pressure.

The fuel coming from the gasoline pump, under a pressure of at least 280 kPa, passes through fuel filter fine cleaning and enters the fuel rail. The filter has a metal housing filled with a paper filter element.

Ramp(Fig. 2.67) is a hollow structure to which nozzles and a pressure regulator are attached. The ramp is bolted to the engine intake manifold. A fitting is also installed on the ramp, which serves to control fuel pressure. The fitting is closed with a screw plug to protect it from contamination.

Nozzle(Fig. 2.68) has a metal case, inside which is located solenoid valve, consisting of an electrical winding, a steel core, a spring and a locking needle. At the top of the nozzle is a small strainer, which protects the nozzle atomizer (having very small holes) from contamination. Rubber rings provide the necessary seal between the rail, nozzle and seat in the inlet pipeline. Nozzle fixation

on the ramp is carried out using a special clamp. On the body of the nozzle there are electrical contacts for

Rice. 2.68. Gasoline engine solenoid injectors: left - GM, right - Bosch

Rice. 2.69. Fuel pressure control: 1 - body; 2 - cover; 3 - a branch pipe for a vacuum hose; 4 - membrane; 5 - valve; A - fuel cavity; B - vacuum cavity

Rice. 2.70. Plastic intake pipe with reservoir and throttle connection

electrical connector switch. The regulation of the amount of fuel injected by the injector is carried out by changing the length of the electrical pulse applied to the injector contacts.

pressure regulator fuel (Fig. 2.69) serves to change the pressure in the rail, depending on the vacuum in the intake pipeline. The steel body of the regulator contains a spring-loaded needle valve connected to the diaphragm. The diaphragm, on the one hand, is affected by the fuel pressure in the rail, and on the other hand, by the vacuum in the intake manifold. With an increase in vacuum, while closing the throttle, the valve opens, excess fuel is drained through the drain pipe back into the tank, and the pressure in the rail decreases.

Recently, injection systems have appeared in which there is no fuel pressure regulator. For example, on a V8 engine ramp car New range rover there is no pressure regulator, and the composition of the combustible mixture is provided only by the operation of the nozzles that receive signals from the electronic unit.

Air supply and purification system consists of an air filter with a replaceable filter element, a throttle pipe with a damper and an idle speed controller, a receiver and an exhaust pipe (Fig. 2.70).

Receiver must have a sufficiently large volume in order to smooth out the pulsations of the air entering the engine cylinders.

Throttle pipe fixed on the receiver and serves to change the amount of air entering the engine cylinders. The change in the amount of air is carried out with the help of a throttle valve, rotated in the housing with the help of a cable drive from the “gas” pedal. Throttle position sensor and idle speed control are installed on the throttle pipe. The throttle pipe has openings for vacuum intake, which is used by the gasoline vapor recovery system.

Recently, designers of injection systems have begun to use an electric control drive when there is no mechanical connection between the “gas” pedal and the throttle valve (Fig. 2.71). In such designs, sensors of its position are installed on the "gas" pedal, and throttle valve rotated by a stepper motor with a gearbox. The electric motor turns the damper according to the signals of the computer that controls the operation of the motor. In such designs, not only the precise execution of the driver's commands is ensured, but it is also possible to influence the operation of the engine, correcting driver errors, by the operation of electronic systems for maintaining vehicle stability and other modern electronic security systems.

Rice. 2.71. Throttle valve with electric Rice. 2.72. Inductive sensors with a posi- tive drive provides crankshaft and distribu- tion control of the engine through dips

Waters

Throttle position sensor is a potentiometer whose slider is connected to the throttle axis. When the throttle is turned, the electrical resistance of the sensor and its supply voltage change, which is the output signal for the ECU. Motorized throttle control systems use at least two sensors to allow the computer to determine the direction in which the throttle is moving.

idle speed controller serves to adjust the engine idle speed by changing the amount of air passing around the closed throttle valve. The regulator consists of a stepper motor controlled by an ECU and a cone valve. In modern systems with more powerful engine control computers, idle controllers are dispensed with. The computer, analyzing the signals from numerous sensors, controls the duration of the electric current pulses supplied to the injectors and the operation of the engine in all modes, including idling.

Installed between the air filter and the intake pipe fuel mass flow sensor. The sensor changes the frequency of the electrical signal to the computer, depending on the amount of air passing through the pipe. From this sensor comes to the ECU and an electrical signal corresponding to the temperature of the incoming air. The first electronic injection systems used sensors that estimated the volume of incoming air. A damper was installed in the inlet pipe, which deviated by a different amount depending on the pressure of the incoming air. A potentiometer was connected to the damper, which changed the resistance depending on the amount of damper rotation. Modern mass air flow sensors operate using the principle of changing the electrical resistance of a heated wire or conductive film when it is cooled by an incoming air stream. The control computer, which also receives signals from the intake air temperature sensor, can determine the amount of air entering the engine.

For the correct control of the operation of the distributed injection system, the electronic unit requires signals from other sensors. The latter include: coolant temperature sensor, crankshaft position and speed sensor, vehicle speed sensor, knock sensor, oxygen concentration sensor (installed in the exhaust pipe of the exhaust system in the version of the feedback injection system).

At present, semiconductors are mainly used as temperature sensors, which change the electrical resistance with a change in temperature. The position and speed sensors of the crankshaft are usually of the inductive type (Fig. 2.72). They give out pulses of electric current when the flywheel with marks on it rotates.

Rice. 2.73. Scheme of the adsorber: 1 - intake air; 2 - throttle valve; 3 - intake manifold of the engine; 4 - purge valve of the vessel with activated carbon; 5 - signal from ECU; 6 - a vessel with activated carbon; 7 - ambient air; 8 - fuel vapor in the fuel tank

The power supply system with distributed injection can be sequential or parallel. In a parallel injection system, depending on the number of engine cylinders, several injectors fire simultaneously. In a sequential injection system, only one specific injector fires at the right time. In the second case, the ECU must receive information about the moment each piston is near TDC in the intake stroke. This requires not only a crankshaft position sensor, but also camshaft position sensor. On modern cars, as a rule, engines with sequential injection are installed.

For catching gasoline vapors, which evaporates from the fuel tank, special adsorbers with activated carbon are used in all injection systems (Fig. 2.73). Activated carbon, located in a special container connected by a pipeline to the fuel tank, absorbs gasoline vapors well. To remove gasoline from the adsorber, the latter is purged with air and connected to the engine intake pipe, in order to

so that the operation of the engine is not disturbed, purge is carried out only at certain engine operating modes, with the help of special valves, which open and close at the command of the ECU.

Feedback injection systems use oxygen concentration sensors yes in exhaust gases that are installed in the exhaust system with an exhaust gas catalytic converter.

catalytic converter(Fig. 2.74;

Rice. 2.74. Two-layer three-way catalytic converter for exhaust gases: 1 - oxygen concentration sensor for a closed control loop; 2 - monolithic carrier block; 3 - mounting element in the form of a wire mesh; 4 - double-shell thermal insulation of the neutralizer

2.75) is installed in the exhaust system to reduce the content of harmful substances in the exhaust gases. The neutralizer contains one reducing (rhodium) and two oxidizing (platinum and palladium) catalysts. Oxidation catalysts promote the oxidation of unburned hydrocarbons (CH) into water vapour,

Rice. 2.75. Appearance neutralizer

and carbon monoxide (CO) into carbon dioxide. The reduction catalyst reduces harmful nitrogen oxides NOx into harmless nitrogen. Since these converters reduce the content of three harmful substances in the exhaust gases, they are called three-component.

The operation of a car engine on leaded gasoline leads to the failure of an expensive catalytic converter. Therefore, the use of leaded gasoline is prohibited in most countries.

A three-way catalytic converter works most efficiently when a stoichiometric mixture is supplied to the engine, i.e. with an air-fuel ratio of 14.7:1 or an excess air ratio of one. If there is too little air in the mixture (i.e. not enough oxygen), then CH and CO will not completely oxidize (burn) to a safe by-product. If there is too much air, then the decomposition of NOX into oxygen and nitrogen cannot be ensured. Therefore, a new generation of engines appeared, in which the composition of the mixture was constantly adjusted to obtain an exact correspondence to the excess air ratio cc = 1 using an oxygen concentration sensor (lambda probe yes) (Fig. 2.77), built into the exhaust system.

Rice. 2.76. Dependence of the efficiency of the neutralizer on the coefficient of excess air

Rice. 2.77. Oxygen concentration sensor device: 1 - sealing ring; 2 - metal case with thread and turnkey hexagon; 3 - ceramic insulator; 4 - wires; 5 - sealing cuff of wires; 6 - current-carrying contact of the heater power wire; 7 - external protective screen with an opening for atmospheric air; 8 - current pickup of electrical signal; 9 - electric heater; 10 - ceramic tip; 11 - protective screen with a hole for exhaust gases

This sensor detects the amount of oxygen in the exhaust gases, and its electrical signal is used by the ECU, which changes the amount of fuel injected accordingly. The principle of operation of the sensor is the ability to pass oxygen ions through itself. If the oxygen content on the active surfaces of the sensor (one of which is in contact with the atmosphere, and the other with the exhaust gases) differs significantly, there is a sharp change in the voltage at the sensor outputs. Sometimes two oxygen concentration sensors are installed: one before the converter, and the other after.

In order for the catalyst and the oxygen concentration sensor to work effectively, they must be heated to a certain temperature. The minimum temperature at which 90% of harmful substances are retained is about 300 °C. It is also necessary to avoid overheating of the converter, as this can lead to damage to the filler and partially block the passage for gases. If the engine starts to work intermittently, then the unburned fuel burns out in the catalyst, sharply increasing its temperature. Sometimes a few minutes of intermittent operation of the engine can be enough to completely damage the catalytic converter. That's why electronic systems Modern engines must detect and prevent misfiring and warn the driver of the severity of the problem. Sometimes electric heaters are used to speed up the warming up of the catalytic converter after starting a cold engine. Oxygen concentration sensors currently in use almost all have heating elements. In modern engines, in order to limit emissions of harmful substances in the atmosphere

ru during engine warm-up, pre-catalytic converters are installed as close as possible to the exhaust manifold (Fig. 2.78) in order to ensure quick heating of the converter to operating temperature. oxygen sensors installed before and after the converter.

To improve the environmental performance of the engine, it is necessary not only to improve the exhaust gas converters, but also to improve the processes occurring in the engine. The content of hydrocarbons became possible to reduce by reducing

"gap volumes", such as the gap between the piston and the cylinder wall above the top compression ring, and cavities around the valve seats.

A thorough study of the flow of the combustible mixture inside the cylinder using computer technology made it possible to provide more complete combustion and low CO levels. The NOx level has been reduced by the EGR system by taking some of the gas from the exhaust system and feeding it into the intake air stream. These measures and fast, precise control of engine transients can keep emissions to a minimum even before the catalyst. To accelerate the heating of the catalytic converter and its entry into the operating mode, the method of secondary air supply to the exhaust manifold using a special electric pump is also used.

Another effective and widespread method of neutralizing harmful products in exhaust gases is flame afterburning, which is based on the ability of combustible components of exhaust gases (CO, CH, aldehydes) to oxidize at high temperatures. The exhaust gases enter the afterburner chamber, which has an ejector through which heated air enters from the heat exchanger. The combustion takes place in the chamber,

Rice. 2.78. Engine exhaust manifold and for ignition is the ignition

with pre-neutralizer candle.

DIRECT GASOLINE INJECTION

The first gasoline injection systems directly into the engine cylinders appeared in the first half of the 20th century. and used on aircraft engines. Attempts to use direct injection in gasoline engines cars were discontinued in the 40s of the 19th century, because such engines turned out to be expensive, uneconomical and smoked heavily in modes high power. Injecting gasoline directly into the cylinders is associated with certain difficulties. Gasoline direct injection injectors operate under more difficult conditions than those installed in the intake manifold. The head of the block, in which such nozzles must be installed, turns out to be more complex and expensive. The time allotted for the carburetion process with direct injection is significantly reduced, which means that for good carburetion it is necessary to supply gasoline under high pressure.

Mitsubishi specialists managed to cope with all these difficulties, which for the first time applied the gasoline direct injection system to automotive engines. First serial Mitsubishi car Galant with a 1.8 GDI engine (Gasoline Direct Injection - gasoline direct injection) appeared in 1996 (Fig. 2.81). Now engines with direct gasoline injection are produced by Peugeot-Citroen, Renault, Toyota, DaimlerChrysler and other manufacturers (Fig. 2.79; 2.80; 2.84).

The benefits of the direct injection system are mainly in improved fuel economy, but also some increase in power. The first is due to the ability of a direct injection engine to operate

Rice. 2.79. Scheme of the Volkswagen FSI engine with gasoline direct injection

Rice. 2.80. In 2000, PSA Peugeot-Citroen introduced its 2.0-litre, four-cylinder HPI direct injection engine that could run on lean mixtures.

on very lean mixtures. The increase in power is mainly due to the fact that the organization of the process of supplying fuel to the engine cylinders allows you to increase the compression ratio to 12.5 (in conventional gasoline engines, it is rarely possible to set the compression ratio above 10 due to detonation).

In the GDI engine, the fuel pump provides a pressure of 5 MPa. An electro-magnetic injector installed in the cylinder head injects gasoline directly into the engine cylinder and can operate in two modes. Depending on the supplied electrical signal, it can inject fuel either with a powerful conical torch or with a compact jet (Fig. 2.82). The bottom of the piston has a special shape in the form of a spherical recess (Fig. 2.83). This shape allows the incoming air to be swirled, directing the injected fuel to a spark plug mounted in the center of the combustion chamber. The inlet pipe is not located on the side, but vertical

Rice. 2.81. Mitsubishi engine GDI - the first production engine with direct petrol injection

but on top. It does not have sharp bends, and therefore the air enters at a high speed.

Rice. 2.82. Nozzle GDI engine can operate in two modes, providing a powerful (a) or compact (b) flame of atomized gasoline

In the operation of an engine with a direct injection system, three different modes can be distinguished:

1) mode of operation on super-poor mixtures;

2) operating mode on a stoichiometric mixture;

3) the mode of sharp accelerations from low speeds;

First mode is used when the car is moving without sudden accelerations at a speed of about 100-120 km/h. This mode uses a very lean combustible mixture with an excess air ratio of more than 2.7. Under normal conditions, such a mixture cannot be ignited by a spark, so the injector injects fuel in a compact flame at the end of the compression stroke (as in a diesel engine). The spherical recess in the piston directs the jet of fuel to the spark plug electrodes, where the high concentration of gasoline vapor allows the mixture to ignite.

Second mode used when the car is moving at high speed and during hard accelerations when high power is needed. Such a mode of motion requires a stoichiometric composition of the mixture. A mixture of this composition is highly flammable, but the GDI engine has an increased degree of

compression, and in order to prevent detonation, the nozzle injects fuel with a powerful torch. The finely atomized fuel fills the cylinder and, as it evaporates, cools the cylinder surfaces, reducing the likelihood of detonation.

Third mode required for high torque hard pressing pedal "gas" when the engine is running

runs at low speeds. This mode of engine operation differs in that the injector fires twice during one cycle. During the intake stroke to the cylinder for

Rice. 2.83. The piston of an engine with gasoline direct injection has a special shape (combustion process above the piston)

4. Order No. 1031. 97

Rice. 2.84. Design features of the Audi 2.0 FSI direct injection engine

cooling it with a powerful torch, an extra-poor mixture (a = 4.1) is injected. At the end of the compression stroke, the injector injects fuel again, but with a compact flame. In this case, the mixture in the cylinder is enriched and detonation does not occur.

Compared with conventional engine with a gasoline port injection system, a GDI engine is about 10% more economical and emits 20% less carbon dioxide into the atmosphere. The increase in engine power is up to 10%. However, as the operation of vehicles with engines of this type has shown, they are very sensitive to the sulfur content in gasoline.

The original gasoline direct injection process was developed by Orbital. In this process, gasoline is injected into the engine cylinders, pre-mixed with air using a special nozzle. The Orbital nozzle consists of two jets, fuel and air.

Rice. 2.85. Orbital nozzle operation

Air is supplied to the air jets in compressed form from a special compressor at a pressure of 0.65 MPa. The fuel pressure is 0.8 MPa. First, the fuel jet fires, and then the air jet at the right time, so the fuel-air mixture in the form of an aerosol is injected into the cylinder with a powerful torch (Fig. 2.85).

An injector, located in the cylinder head next to the spark plug, injects a fuel-air jet directly onto the spark plug electrodes, which ensures good spark plug ignition.