Overview. Mercedes-Benz E-Class

If a gasoline engine is fed fuel mixture which is subsequently ignited by a spark of the spark plug, the diesel engine it occurs under high temperature. At the end of the compression stroke the air pressure in the cylinder is 28 bar and the temperature - about + 700 ?� C. Fuel is ignited by hot air and the pressure in the combustion chamber reaches 145 bar (D, TD) at 1350 bar or CDI. The diesel fuel is atomized instantly consumed. When and how much fuel should be injected into the chamber is determined by adjustment and setting of injection.

Section of the cylinder head with a swirl chamber

Fig. 4.60. Cut the cylinder head with a swirl chamber: 1 - nozzle; 2 - glow plug; 3 - the vortex chamber to the inlet; 4 - cylinder

In diesel engines with swirl system (Fig. 4.60), the combustion chamber is divided. The vortex chamber is connected to the overpiston space, and at the approach of the piston to the top point it creates a vortex flow which efficiently mixes the fuels with air. A mixture ignited, extends into the main combustion chamber. Engines with a vortex chamber have proven themselves, especially at high speed (5000 ^min -1).

Fig. 4.61. Incision cylinder head prechamber 1 - nozzle; 2 - glow plug; 3 - pre-chamber with the inlet; 4-cylinder

When pre-chamber system (Fig. 4.61), which is used in the diesel engines of Mercedes, the working chambers are separated, as in the vortex system. Prechamber is located in the top cylinder head. Ignition of the fuel occurs in the combustion chamber through fine nozzles, extending from the prechamber.

This system has a high efficiency, but it has its drawbacks: the high level of engine noise, especially at start-up and a sharp increase in turns.

Direct injection in the Common Rail system

Fig. 4.62. Direct injection system Common Rail: 1 - nozzle; 2 - inlet; 3 - piston with a special recess

Fig. 4.63. Scheme of Common Rail: 1 - common fuel rail; 2 - pressure sensor; 3 - pump; 4 - nozzle; 5 - Pressure control valve

System Common Rail (Fig. 4.62, 4.63, 4.68) not only ensures efficiency and minimum emission of environmentally harmful gases, but also for comfort and noise of the engine exceeds the modern diesel engines with prechamber injection. Therefore, CDI diesel engines have occupied the main place in the development Motors Mercedes-Benz.

?�Common Rail?� means "total highway." If systems with direct injection fuel pressure supplied to each injector individually, then in the Common Rail fuel injection, regardless of the sequence it is in the common rail, the so-called battery.

The electronic control regulates the pressure of fuel injection depending on the engine speed and engine load. Sensors, receiving data on operation of distributive and cranked shaft, issue commands to the optimal injection under the regime of the engine. Moreover, the supply of fuel and fuel injection are independent of each other.

Fig. 4.64. Key elements of the Common Rail: 1 - high pressure pump; 2 - pressure pump; 3 - nozzle; 4 - solenoid valve dispensing system; 5 - return line; 6 - high pressure pipe; 7 - the fuel pressure sensor; 8 - pressure accumulator; 9 - the fuel pressure control valve

A special feature of this development is a special storage device (battery) 8 (Fig. 4.64), which is always maintained the pressure up to 1350 bar. This is to ensure that the line that connects the pump with the injector, there are always under the desired fuel pressure, ready for injection.

The line is connected to the nozzles. Each nozzle should solenoid valve which controls the pressure and flow quantity of fuel. The microcomputer controls the valve based on the operating mode and the engine load. This system has significantly enhanced efficiency of the engine and contributed to a significant reduction in the emission of harmful gases.

Pump used to supply diesel fuel to the injectors under high pressure (about 120 bar). 4- and 5-cylinder engines are equipped with a distributor injection pump. At 6-cylinder in-line engine is the injection pump. All pump located on the left motor and the drive chain from the crankshaft. The frequency of the pump shaft half the speed of the crankshaft. Pump are electronically controlled.

Fig. 4.64, 4.65). Pump has built fuel pump and a temperature sensor, via which outputs the signal to stop the fuel supply. Arranged outside the solenoid valves, one for stopping the engine, the second fuel injection. The supply of the fuel injection pump carries through thin channels in the corresponding cylinder.

The shaft is connected to the channel head and the injection pistons are separated by pressurized fuel (approximately 8 bar) until the projections on the cam disc does not produce forces on the bearing ends. During rotation of the shaft discharge passage is closed and the high pressure channel.

The dispensing head of the pump has 4 (or 5 - 5-cylinder engine) of injection channels and respectively named 4 (5) channels high pressure. Once the cams on the cam ring are aligned with the support arms, the pistons begin to compress the fuel pressure rises, and when it reaches about 120 bar is injected.

Fuel injection amount determined by the length of the delivery stroke of the piston, which is regulated by the axial movement of the support arms. Axial installation shaft distribution pump is controlled by two solenoid valves and the return spring regulator fuel.

The angle of the fuel injection timing is governed by the position of the cam disc in relation to the distribution pump head. Turn the washer against the direction of rotation is set earlier time of injection, respectively, in the direction of rotation - later. Rotating the cam ring about the axis of the shaft by means of a control valve and a return spring. When set to "early" control valve is opened, the pressure will increase, and the control piston will go to the left. When closing the valve, the pressure drops and the piston under the action of the spring is to the right.

Fig. 4.66. Distributor-type injection pump, mounted on the models E 220 D and E 290 TD, in the context of

On models E 300 D is set in-line injection pump (Fig. 4.66) with electronic control - ERE (Elektronisch geregeltes Reien-Einspritzsystem). Row pump has a separate section of the pump for each cylinder, which supplies fuel to the corresponding injector for high pressure steel pipelines. The main units of ERE-systems are in-line pump and an electronic control unit injection system.

Fig. 4.68. Terraced pump (ERE) in section 1 - receiving portion for connecting the high pressure pipe to the nozzle; 2 - pressure valve; 3 - plunger; 4 - speed adjustment mechanism (ERE); 5 - Managing rail; 6 - set lever plunger; 7 - connector; 8 - roller plunger; 9 - a spring plunger; 10 - the fuel pump; 11 - electro-hydraulic control; 12 - camshaft

At the bottom of the pump shaft is a cam 12 (Fig. 4.68). With its cam actuated pumping section according to the sequence of injection. The main parts of the pump section are: the discharge valve 2, a cylinder and a plunger 3, rotary plunger sleeve and the spring 9.

When the plunger is in the lower position, through the inlet cavity above it is filled with fuel. The cam shaft of the pump plunger moves upward, plunger spring is compressed, the plunger closes the inlet pressure increases.

When pressure reaches 120 bar, the nozzle needle rises and fuel enters the mixing chamber. Injection is carried out until the plunger is not open outlet adjusting the fuel supply. At this point, the pressure drops sharply above the plunger, a delivery valve is closed, after having passed a small amount of fuel back into the cylinder. The pressure in the fuel pipe and the nozzle falls off sharply. The nozzle is closed.

The plunger has on the lateral surface grinded helical channel, and depending on the position of the plunger the outlet adjusting the fuel supply remains closed for some time. The path, which runs the plunger at the closed outlet, called swing pumping. The greater the pressure stroke, the more fuel is injected into the engine cylinder.

Spigot plunger pump sections all connected via a short lever on the control rack. When assembling the pump spigot installed in such a way that all the pumping section of the same amount of fuel injected.

Rake adjustment of the fuel delivery is an important part of the pump, via which the dosing fuel injected into each cylinder. The control rack is connected to the accelerator pedal through the electronically controlled speed controller (ERE).

Electronic speed controller is located at the rear side of the fuel pump, and controls the rack. The regulator is controlled by a rectangular pulse voltage with a frequency of about 190 Hz. Depending on the mode of action of the executive, the strength of the magnet, and it is against the force of the spring, promotes rail in the direction of ?�Start?� or, respectively, ?�Volllast?� (full load). The stroke length of the rack when it is 19.5 mm.

The previously used pump direct injection at high pressure (up to 145 bar), the noise of the engine was much higher than the pre-chamber models. System Common Rail before the main portion of the fuel is injected a little, so-called pilot, fuel dose which provides a "pre-heating" of the combustion chamber. This creates optimal conditions for the ignition of the main fuel is ignited much faster, because the pressure and the temperature raised gradually rather than abruptly. It affects not only the noise reduction, but also to reduce emissions.

For this reason Mercedes-Benz has taken additional measures to reduce engine noise. These include a special sound-absorbing casing (damper) of the cylinder head and intake manifold, increased housing and camshaft cover.