Fuel injection systems in the engine. Fuel injection systems: difference and principles of operation Fuel injection methods

In modern cars in gasoline power plants The principle of operation of the power supply system is similar to that used on diesel engines. In these engines, it is divided into two - intake and injection. The first provides air supply, and the second - fuel. But due to constructive and operational features the operation of the injection is significantly different from that used on diesel engines.

Note that the difference in the injection systems of diesel and gasoline engines is increasingly being erased. For getting best qualities designers borrow design solutions and apply them to different types power systems.

The device and principle of operation of the injection injection system

The second name for injection systems for gasoline engines is injection. Its main feature is the exact dosage of fuel. This is achieved by using nozzles in the design. Device injector injection The engine includes two components - executive and control.

The task of the executive part is the supply of gasoline and its spraying. It includes not so many components:

1. Pump (electric).
2. filter element ( fine cleaning).
3. Fuel lines.
4. Ramp.
5. Nozzles.

But these are just the main components. The executive component may include a number of additional components and parts - a pressure regulator, a system for draining excess gasoline, an adsorber.

The task of these elements is to prepare the fuel and ensure its supply to the nozzles, which are used to inject them.

The principle of operation of the executive component is simple. When turning the ignition key (on some models - when opening driver's door) turns on electric pump, which pumps gasoline and fills the rest of the elements with it. The fuel undergoes cleaning and enters the rail through the fuel lines, which connects the nozzles. Due to the pump, the fuel in the entire system is under pressure. But its value is lower than on diesels.

The opening of the nozzles is carried out due to electrical impulses supplied from the control part. This component of the fuel injection system consists of a control unit and a whole set of tracking devices - sensors.

These sensors monitor performance and operating parameters - crankshaft rotation speed, amount of air supplied, coolant temperature, throttle position. The readings are sent to the control unit (ECU). He compares this information with the data entered in the memory, on the basis of which the length of the electrical pulses supplied to the nozzles is determined.

The electronics used in the control part of the fuel injection system is needed to calculate the time for which the nozzle should open in a particular mode of operation of the power unit.

Types of injectors

But note that this general design gasoline engine supply systems. But several injectors have been developed, and each of them has its own design and operating features.

On cars, engine injection systems are used:

• central;
• distributed;
• direct.

The central injection is considered the first injector. Its peculiarity lies in the use of only one nozzle, which injected gasoline into the intake manifold simultaneously for all cylinders. Initially, it was mechanical and no electronics were used in the design. If we consider the device of a mechanical injector, then it is similar to a carburetor system, with the only difference being that a nozzle with mechanical drive. Over time, the central feed was made electronic.

Now this type is not used due to a number of shortcomings, the main of which is the uneven distribution of fuel over the cylinders.

Distributed injection on this moment is the most common system. The design of this type of injector is described above. Its peculiarity lies in the fact that the fuel for each cylinder is supplied by its own nozzle.

In the design of this type, the nozzles are installed in the intake manifold and are located next to the cylinder head. The distribution of fuel over the cylinders makes it possible to ensure an accurate dosage of gasoline.

Direct injection is now the most advanced type of gasoline delivery. In the previous two types, gasoline was fed into the passing air stream, and mixture formation began to take place even in the intake manifold. The same injector by design copies the diesel injection system.

In a direct feed injector, the nozzle nozzles are located in the combustion chamber. As a result, the components of the air-fuel mixture are launched into the cylinders separately here, and they are already mixed in the chamber itself.

The peculiarity of this injector is that high fuel pressure is required for gasoline injection. And its creation provides another node added to the device of the executive part - a high pressure pump.

Diesel engine power systems

And diesel systems are being upgraded. If earlier it was mechanical, now diesel engines are also equipped with electronic control. It uses the same sensors and control unit as in the gasoline engine.

Now cars use three types of diesel injection:

1. With distribution injection pump.
2. common rail.
3. Injector pump.

As in gasoline engines, the design diesel injection consists of executive and management parts.

Many elements of the executive part are the same as those of the injectors - a tank, fuel lines, filter elements. But there are also components that are not found on gasoline engines - a fuel priming pump, high-pressure fuel pump, lines for transporting high-pressure fuel.

In the mechanical systems of diesel engines, in-line injection pumps were used, in which the fuel pressure for each nozzle was created by its own separate plunger pair. These pumps are different high reliability but were bulky. The moment of injection and the amount of injected diesel fuel were regulated by a pump.

In engines equipped with a distribution injection pump, only one plunger pair is used in the pump design, which pumps fuel for the injectors. This node is compact in size, but its resource is lower than in-line ones. This system is used only on passenger vehicles.

Common Rail is considered one of the most efficient diesel engine injection systems. Its general concept is largely borrowed from the injector with separate supply.

In such a diesel engine, the moment the supply starts and the amount of fuel is “managed” by the electronic component. The task of the high pressure pump is only to pump diesel fuel and create high pressure. Moreover, diesel fuel is not supplied immediately to the nozzles, but to the ramp connecting the nozzles.

Pump injectors are another type of diesel injection. In this design, there is no injection pump, and plunger pairs, which create diesel fuel pressure, are included in the injector device. Such constructive solution allows you to create the most high values fuel pressure among the existing types of injection on diesel units.

Finally, we note that here information is provided on the types of engine injection in general. To deal with the design and features of these types, they are considered separately.

Video: Fuel injection system control

The fuel injection system is used for metered fuel supply to the engine internal combustion at a strictly defined point in time. The power, efficiency and environmental class of the car engine 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 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 insufficient level 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 control unit began to control the amount of fuel injected into the cylinders and the percentage of the components of the air-fuel mixture.

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 passenger 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 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 are compared with 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.

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 components 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 fed into the combustion chamber at 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 Mitsubishi Galant passenger cars, and today most of the largest automakers install it on their cars.

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. For the first time, a mechanical fuel injection system was developed by Daimler Benz, and the first stock car with gasoline injection was released back in 1954. The main advantages of the injection system compared to carburetor systems are the following:

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 they were a carburetor, from which all "passive" fuel systems were removed and one or two nozzles were installed. 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 characterized by the fact that during intake tract Each cylinder is equipped with a separate injector, 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 fuel systems have better fuel efficiency and lower content of harmful substances in exhaust gases compared to carbureted 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 and in the event of a malfunction warns the driver with the help of control 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 of the fuel pump with 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. Used to limit pressure safety valve.

The fuel coming from the gasoline pump, under a pressure of at least 280 kPa, passes through the fine fuel filter 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 of which there is an electromagnetic valve, consisting of an electric winding, a steel core, a spring and a locking needle. At the top of the nozzle there is a small mesh filter that protects the nozzle nozzle (which has 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 does not have a 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 the throttle valve is 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 computers engine control, dispense with idle speed controllers. 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.

Between air filter and the inlet pipe fitting is installed 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 different size 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 impulses electric current when rotating the flywheel with marks on it.

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 position sensor camshaft. 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 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 that open and close at the command of the computer.

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 the engine is fed with a stoichiometric mixture, i.e. 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 - outer protective screen with hole 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 exhaust gases) is significantly different, 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. This is why the electronic systems of modern engines must detect and prevent misfiring and warn the driver of the severity of the problem. Sometimes, to accelerate the warm-up of the catalytic converter after starting a cold engine, electric heaters. 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) to ensure that the converter quickly warms up to operating temperature. Oxygen sensors are 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 ensure more complete combustion and low level CO. 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 common way to neutralize 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 car engines were discontinued in the 40s of the 19th century, because such engines turned out to be expensive, uneconomical and smoked heavily at high power modes. Injecting gasoline directly into the cylinders is associated with certain difficulties. Injectors for direct injection of gasoline operate in more than 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.

All these difficulties were overcome by specialists Mitsubishi, which pioneered the use of gasoline direct injection on 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 Volkswagen engine FSI 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 engine GDI fuel the 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 GDI engine - the first mass-produced engine with a gasoline direct injection system

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

Rice. 2.82. The GDI engine injector can operate in two modes, providing a powerful (a) or compact (b) atomized gasoline jet

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 poor 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 driving with high speed and at sharp accelerations, when you need to get high power. 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 necessary to obtain a large torque when the gas pedal is pressed sharply 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 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 to a conventional gasoline port injection engine, 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 a powerful torch is injected into the cylinder fuel-air mixture in the form of an aerosol (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.

One of the most important working systems of almost any car is the fuel injection system, because it is thanks to it that the volume of fuel is determined. required by the engine at a specific point in time. Today we will consider the principle of operation of this system using the example of some of its types, and also get acquainted with the existing sensors and actuators.

1. Features of the fuel injection system

On engines manufactured today, it has not been used for a long time carburetor system, which was completely superseded by a newer and more advanced fuel injection system. Fuel injection is called the system of metered supply of fuel liquid to the engine cylinders. vehicle. It can be installed on both petrol and diesel engines, however, it is clear that the design and principle of operation will be different. When used on gasoline engines, when injected, a homogeneous air-fuel mixture which is forced to ignite by the spark of a spark plug.

Concerning diesel type engine, then here the fuel is injected under very high pressure, and the necessary portion of the fuel is mixed with hot air and ignites almost immediately. The amount of injected fuel portion, and at the same time general power engine is determined by the injection pressure. Therefore, the greater the pressure, the higher the power of the power unit becomes.

Today, there is a fairly significant amount of species diversity of this system, and the main types include: a system with direct injection, with mono injection, mechanical and distributed systems.

The principle of operation of the direct (direct) fuel injection system is that the fuel liquid, using nozzles, is supplied directly to the engine cylinders (for example, like a diesel engine). For the first time such a scheme was used in military aviation during the Second World War and on some cars of the post-war period (the first was the Goliath GP700). However, the direct injection system of that time failed to gain due popularity, the reason for which was the expensive high-pressure fuel pumps required for operation and the original cylinder head.

As a result, the engineers did not manage to achieve working accuracy and reliability from the system. Only at the beginning of the 90s of the twentieth century, due to the tightening environmental standards, interest in direct injection began to increase again. Among the first companies to launch the production of such engines were Mitsubishi, Mercedes-Benz, Peugeot-Citroen, Volkswagen, BMW.

In general, direct injection could be called the peak of the evolution of power systems, if not for one thing ... Such engines are very demanding in terms of fuel quality, and when using lean mixtures, they also strongly emit nitrogen oxide, which has to be dealt with by complicating the design of the motor .

Single-point injection (also called "mono-injection" or "central injection") - is a system that began to be used in the 80s of the twentieth century as an alternative to a carburetor, especially since the principles of their operation are very similar: air flows are mixed with the fuel liquid during intake manifold, but the nozzle came to replace the complex and sensitive to the settings of the carburetor. Of course, at the initial stage of the development of the system, there was no electronics at all, and the supply of gasoline was controlled mechanical devices. However, despite some shortcomings, the use of injection still provided the engine with much higher power ratings and significantly greater fuel efficiency.

And all thanks to the same nozzle, which made it possible to dose the fuel liquid much more accurately, spraying it into small particles. As a result of the mixture with air, it turned out homogeneous mixture, and when the conditions for the movement of the car and the mode of operation of the motor change, its composition almost instantly changed. Admittedly, it wasn't without its downsides. For example, since, in most cases, the nozzle was installed in the body of the former carburetor, and bulky sensors made it difficult for the “motor to breathe”, the air flow entering the cylinder met with serious resistance. On the theoretical side, such a disadvantage could be easily eliminated, but with the existing poor distribution fuel mixture, no one could do anything then. Perhaps that is why, in our time, single point injection so rare.

The mechanical injection system appeared in the late 1930s, when it began to be used in aircraft fuel supply systems. It was presented in the form of a gasoline injection system of diesel origin, using high-pressure fuel pumps and closed nozzles for each individual cylinder. When they tried to install them on a car, it turned out that they could not withstand the competition of carburetor mechanisms, and this was due to the significant complexity and high cost of the structure.

For the first time, a low pressure injection system was installed on a MERSEDES car in 1949 and performance characteristics immediately surpassed the carburetor-type fuel system. This fact gave impetus to further development of the idea of ​​gasoline injection for cars equipped with an internal combustion engine. From the point of view of pricing policy and reliability in operation, the most successful in this regard was mechanical system Bosch K-Jetronic. Her batch production was established back in 1951 and, almost immediately, it became widespread on almost all brands of European automobile manufacturers.

The multi-point (distributed) version of the fuel injection system differs from the previous ones in the presence of an individual nozzle, which was installed in the inlet pipe of each individual cylinder. Its task is to supply fuel directly to the intake valve, which means preparing the fuel mixture right before it enters the combustion chamber. Naturally, under such conditions, it will have a homogeneous composition and approximately same quality in each of the cylinders. As a result, the engine power, its fuel efficiency is significantly increased, and the level of exhaust toxicity is also reduced.

On the way to the development of a system of distributed fuel injection, certain difficulties were sometimes encountered, however, it still continued to improve. At the initial stage, it was also controlled mechanically, like the previous version, however, the rapid development of electronics not only made it more efficient, but also gave it a chance to coordinate with the rest of the motor design components. So it turned out that a modern engine is able to signal a malfunction to the driver, if necessary, independently switch to emergency operating mode or, with the support of security systems, correct individual errors in control. But all this, the system performs with the help of certain sensors, which are designed to record the slightest changes in the activity of one or another of its parts. Let's consider the main ones.

2. Sensors of the fuel injection system

The sensors of the fuel injection system are designed to capture and transmit information from the actuators to the engine control unit and vice versa. These include the following devices:

Its sensitive element is placed in the exhaust (exhaust) gas flow, and when the operating temperature reaches 360 degrees Celsius, the sensor begins to generate its own EMF, which is directly proportional to the amount of oxygen in the exhaust gases. From a practical standpoint, when the feedback loop is closed, the oxygen sensor signal is a rapidly changing voltage between 50 and 900 millivolts. The possibility of changing the voltage is caused by a constant change in the composition of the mixture near the stoichiometry point, and the sensor itself is not suitable for generating an alternating voltage.

Depending on the power supply, two types of sensors are distinguished: with pulsed and constant power heating element. In the pulse version, the oxygen sensor is heated by an electronic control unit. If it is not warmed up, then it will have a high internal resistance, which will not allow it to generate its own EMF, which means that the control unit will “see” only the specified stable reference voltage. During the warm-up of the sensor, its internal resistance decreases and the process of generating its own voltage begins, which immediately becomes known to the ECU. For the control unit, this is a signal of readiness for use in order to adjust the composition of the mixture.

Used to get an estimate of the amount of air that enters the engine of a car. He is a part electronic system engine control. This device can be used together with some other sensors, such as an air temperature sensor and an atmospheric pressure sensor, which correct its readings.

The air flow sensor consists of two platinum filaments heated by electric current. One thread passes air through itself (cooling in this way), and the second is a control element. With the help of the first platinum thread, the amount of air that has entered the engine is calculated.

Based on the information received from the air flow sensor, the ECU calculates the required amount of fuel required to maintain the stoichiometric ratio of air and fuel in the given engine operating modes. In addition, the electronic unit uses the received information to determine the regime point of the motor. To date, there are several different types of sensors responsible for mass flow air: for example, ultrasonic, vane (mechanical), hot-wire, etc.

Coolant temperature sensor (DTOZH). It has the form of a thermistor, that is, a resistor, in which the electrical resistance can vary depending on temperature indicators. The thermistor is located inside the sensor and expresses a negative coefficient of resistance of temperature indicators (with heating, the resistance force decreases).

Accordingly, at high temperature coolant - there is a low resistance of the sensor (approximately 70 ohms at 130 degrees Celsius), and at low resistance - high (approximately 100800 ohms at -40 degrees Celsius). Like most other sensors, this device does not guarantee accurate results, which means that it is only possible to speak about the dependence of the resistance of the coolant temperature sensor on temperature indicators. In general, although the described device practically does not break, it is sometimes seriously “mistaken”.

. It is mounted on the throttle pipe and connected to the axis of the damper itself. It is presented in the form of a potentiometer with three ends: one is supplied with positive power (5V), and the other is connected to ground. The third pin (from the slider) sends the output signal to the controller. When the throttle is turned when the pedal is depressed, the output voltage of the sensor changes. If the throttle is in the closed state, then, accordingly, it is lower than 0.7 V, and when the damper starts to open, the voltage rises and in the fully open position should be more than 4 V. Following the output voltage of the sensor, the controller, depending on the angle throttle opening, performs fuel correction.

Given that the controller itself determines the minimum voltage of the device and takes it as zero, this mechanism does not need adjustment. According to some motorists, the throttle position sensor (if it domestic production) is the most unreliable element of the system, requiring periodic replacement (often after 20 kilometers). Everything would be fine, but it’s not so easy to make a replacement, especially without having a high-quality tool with you. It's all about fastening: the bottom screw is unlikely to be unscrewed with a conventional screwdriver, and if it does, it is rather difficult to do so.

In addition, when tightening at the factory, the screws are “planted” on a sealant, which “seals” so much that the cap often breaks off when unscrewed. In this case, it is recommended to completely remove the entire throttle assembly, and in the worst case, you will have to pick it out by force, but only if you are completely sure that it is not in working condition.

. Serves to transmit a signal to the controller about the speed and position of the crankshaft. Such a signal is a series of repeated electrical voltage pulses that are generated by the sensor during the rotation of the crankshaft. Based on the received data, the controller can control the injectors and the ignition system. The crankshaft position sensor is mounted on the cover oil pump, at a distance of one millimeter (+0.4mm) from the crankshaft pulley (has 58 teeth arranged in a circle).

To enable the generation of a “synchronization pulse”, two pulley teeth are missing, that is, in fact, there are 56 of them. When it rotates, the teeth of the disk change the magnetic field of the sensor, thereby creating an impulse voltage. Based on the nature of the pulse signal coming from the sensor, the controller can determine the position and speed of the crankshaft, which allows you to calculate the moment of operation of the ignition module and injectors.

The crankshaft position sensor is the most important of all those listed here, and in the event of a malfunction of the mechanism, the car's engine will not work. Speed ​​sensor. The principle of operation of this device is based on the Hall effect. The essence of his work is to transfer voltage pulses to the controller, with a frequency directly proportional to the speed of rotation of the driving wheels of the vehicle. Based on the connectors of the harness block, all speed sensors may have some differences. So, for example, a square-shaped connector is used in Bosch systems, and a round connector corresponds to January 4 and GM systems.

Based on the outgoing signals of the speed sensor, the control system can determine the thresholds for shutting off the fuel supply, as well as set electronic speed limits car (available in new systems).

Camshaft position sensor(or as I also call it a "phase sensor") is a device designed to determine the angle of the camshaft and transmit the relevant information to the vehicle's electronic control unit. After that, based on the data received, the controller can control the ignition system and the fuel supply to each individual cylinder, which, in fact, he does.

Knock sensor used to search for detonation shocks in an internal combustion engine. From a constructive point of view, it is a piezoceramic plate enclosed in a housing, located on the cylinder block. Nowadays, there are two types of knock sensor - resonant and more modern broadband. In resonant models, the primary filtering of the signal spectrum is carried out inside the device itself and directly depends on its design. Therefore, on different types engine used different models knock sensors that differ from each other resonant frequency. The broadband view of the sensors has a flat characteristic in the range of detonation noise, and the signal is filtered by the electronic control unit. To date, resonant knock sensors are no longer installed on production models cars.

Sensor absolute pressure. Provides tracking of changes in barometric pressure that occur as a result of changes in barometric pressure and/or changes in altitude. The barometric pressure can be measured during ignition on, before the engine starts to crank. With the help of the electronic control unit, it is possible to "update" the barometric pressure data with the engine running, when, at a low engine speed, the throttle is almost fully open.

Also, using an absolute pressure sensor, it is possible to measure the change in pressure in the intake pipe. Changes in pressure are caused by changes in engine loads and crankshaft speed. The absolute pressure sensor transforms them into an output signal having a certain voltage. When the throttle is in the closed position, it turns out that the absolute pressure output signal gives a relatively low voltage, while wide open throttle - corresponds to a high voltage signal. The appearance of a high output voltage is explained by the correspondence between atmospheric pressure and the pressure inside the intake pipe at full throttle. Pipe internal pressure indicators are calculated electronic unit control based on the sensor signal. If it turned out that it is high, then an increased supply of fuel fluid is required, and if the pressure is low, then vice versa - reduced.

(ECU). Although this is not a sensor, but given that it is directly related to the operation of the described devices, we considered it necessary to include it in this list. The ECU is the "brain center" of the fuel injection system, which constantly processes information data received from various sensors and, on the basis of this, controls the output circuits (systems electronic ignition, injectors, idle speed controller, various relays). The control unit is equipped with a built-in diagnostic system capable of recognizing malfunctions in the system and, using the “CHECK ENGINE” warning lamp, warn the driver about them. Moreover, in his memory are stored diagnostic codes, which indicate specific areas of failure, which greatly facilitates the repair work.

The ECU contains three types of memory: programmable read-only memory (RAM and PROM), random access memory (RAM or RAM), and electrically programmable memory (EPROM or EEPROM). RAM is used by the unit's microprocessor for temporary storage of measurement results, calculations and intermediate data. This type of memory depends on energy supply, which means that it requires a constant and stable power supply to store information. In the event of a power failure, all diagnostic trouble codes and calculation information stored in RAM are immediately erased.

EPROM stores the total work program, which contains a sequence of necessary commands and various calibration information. Unlike the previous version, this type of memory is not volatile. The EPROM is used to temporarily store immobilizer password codes (anti-theft automotive system). After the controller has received these codes from the immobilizer control unit (if any), they are compared with those already stored in the EEPROM, and then a decision is made to allow or prohibit the engine from starting.

3. Actuators of the injection system

The actuators of the fuel injection system are presented in the form of a nozzle, a gasoline pump, an ignition module, an idle speed controller, a cooling fan, a fuel consumption signal and an adsorber. Let's consider each of them in more detail. Nozzle. fulfills the role solenoid valve with standard performance. It is used to inject a certain amount of fuel calculated for a specific operating mode.

Gasoline pump. Used to move fuel fuel rail, the pressure in which is maintained by means of a vacuum-mechanical pressure regulator. In some system variants, it can be combined with a gasoline pump.

ignition module is electronic device designed to control the process of sparking. It consists of two independent channels for setting fire to the mixture in the engine cylinders. In the latest, modified versions of the device, its low-voltage elements are defined in the ECU, and in order to get high voltage either a two-channel remote ignition coil is used, or those coils that are located directly on the candle itself.

Idling regulator. Its task is to maintain the set speed in idle mode. The regulator is presented in the form of a stepper motor that controls the air bypass channel in the throttle body. This provides the motor with the necessary air flow especially when the throttle is closed. The fan of the cooling system, as the name implies, does not allow overheating of parts. Controlled by the ECU, which responds to the signals of the coolant temperature sensor. As a rule, the difference between the on and off positions is 4-5°C.

Fuel consumption signal- goes to trip computer in the ratio of 16,000 pulses per 1 calculated liter of fuel used. Of course, these are only approximate data, because they are calculated based on the total time spent opening the nozzles. In addition, a certain empirical coefficient is taken into account, which is needed to compensate for the assumption in the measurement of the error. Inaccuracies in the calculations are caused by the operation of the injectors in the non-linear section of the range, non-synchronous fuel output and some other factors.

Adsorber. It exists as an element of a closed circuit during the recirculation of gasoline vapors. Euro-2 standards exclude the possibility of contact between the ventilation of the gas tank and the atmosphere, and gasoline vapors must be adsorbed and sent for afterburning during the purge.