Fuel system Common Rail

System of injection of fuel Common Rail

Fuel system Common Rail includes a step of giving of fuel under low pressure and a step of giving of fuel under a high pressure and ECU (11).

Fuel giving under low pressure

Fuel giving under low pressure of system Common Rail includes:

– A fuel tank with the preliminary fuel filter;
– The pumping up fuel pump;
– The fuel filter;
– топливопроводы low pressure.

The pumping up fuel pump

The electric pumping up fuel pump with the preliminary fuel filter continuously submits certain quantity of fuel from a fuel tank to the fuel pump of a high pressure. The pump not only submits fuel, but within work of system of safety should stop giving of fuel in case of failure, i.e. at the included ignition and the stopped engine.

The fuel pump consists of three basic elements:

– The pump;
– The electric motor;
– Covers.

The fuel filter

Insufficient clearing of fuel can lead to damage of knots of the fuel pump of a high pressure, delivery valves and sprays of atomizers. The fuel filter clears fuel before its receipt in the fuel pump of a high pressure and thus prevents premature deterioration in sensitive knots of the pump.

Diesel fuel can contain water or in the connected form (эмульсия), or in the free form (for example, condensation of steams of water at temperature change). If water gets to injection system, it can lead to corrosion of elements of system of injection, the precautionary alarm system which includes a control lamp in combinations of devices if it is necessary to merge water from the fuel filter therefore is established.

Fuel giving under a high pressure

Fuel giving under system Common Rail high pressure includes:

– The fuel pump of a high pressure with the valve of adjustment of pressure;
– топливопроводы a high pressure;
– The high pressure accumulator (rail) with the pressure gauge, the pressure terminator, the stream terminator, atomizers;
– Returnable топливопровод.

The fuel pump of a high pressure

The fuel pump of a high pressure (the schematic image of longitudinal section)

The fuel pump of a high pressure (the schematic image of cross-section section)

The fuel pump of a high pressure through топливопроводы a high pressure submits fuel under the pressure of 1350 bar to the high pressure accumulator.

The fuel pump of a high pressure is located on border of steps low and a fuel high pressure. At all operational modes service life of the fuel pump corresponds to car service life.
The fuel pump is greased with diesel fuel. Fuel is compressed by three pistons established radially at an angle 120 to each other. The pump submits three portions of fuel for one turn of a cranked shaft. For the diesel engine with working volume 2,0 l, rotation of a cranked shaft working with nominal frequency and created pressure 1350 bar, capacity is necessary for a pump drive of 3,8 kw taking into account mechanical к.п.д. Approximately 90 %.

Pump functioning

The pumping up fuel pump submits fuel through the filter with a water separator to an input and a safety valve of the fuel pump of a high pressure. Fuel through a throttle aperture of a safety valve greases mobile elements of the pump, and also cools it. The power shaft with эксцентриковыми cams moves three плунжера the pump upwards and downwards according to the cam form. As soon as pressure of giving exceeds pressure of opening of a safety valve (0,5... 1,5 bar), forces fuel to pass pumping up pump through the inlet valve of the fuel pump of a high pressure in a compartment of the pump element which piston moves downwards (an admission step). The inlet valve is closed, when the pump piston passes through НМТ and as fuel cannot flow out from a compartment of a pump element, it is compressed irrespective of pressure of giving.

Increasing pressure opens the final valve and as soon as the pressure equal to pressure in the accumulator is reached, the compressed fuel is included into a high pressure contour. The pump piston continues to deliver fuel, yet does not reach ВМТ (the delivery course) then pressure decreases also the final valve is closed. The fuel remaining in a compartment of a pump element, extends also the pump piston moves downwards. As soon as pressure in a compartment of a pump element decreases below the pressure created by the pumping up pump, the inlet valve opens also process repeats.

As productivity of the pump exceeds consumption of fuel by the engine, superfluous fuel under a high pressure through the valve of adjustment of pressure comes back in a fuel tank. It leads to unnecessary heating of fuel and decrease in the general EFFICIENCY.

The high pressure accumulator (rail)

The pressure created by the fuel pump of a high pressure, extends through the accumulator and топливопроводы to an atomizer. Simultaneously, at the expense of fuel volume in the accumulator fluctuations of pressure of the fuel, created by the fuel pump of a high pressure and opening atomizers decrease. Compressibility of fuel as consequence of a high pressure is used for achievement of effect of the accumulator. Pressure of fuel is measured by the gauge and supported at demanded level by the valve of regulation of pressure.

Топливопроводы a high pressure

Топливопроводы a high pressure are intended for transfer of fuel from the high pressure accumulator to atomizers and should resist to the high-frequency fluctuations of pressure arising at work of the engine. Топливопроводы are made of a steel and have external diameter of 6 mm and internal diameter of 2,4 mm. All топливопроводы a high pressure should have identical length. The distance difference between the accumulator and each fuel atomizer is compensated for the bending account топливопроводов.

The pressure gauge

The pressure gauge transmits signal ECU which corresponds to real pressure in the pressure accumulator.

The pressure gauge consists of following elements:

– An incorporated element of the gauge welded on the case;
– The printed-circuit board with an electric contour;
– Cases of the gauge with an electric socket.

Fuel under pressure through an aperture influences a gauge diaphragm on which the gauge element (the semi-conductor device) reformative pressure in an electric signal is established. Through contacts of a socket both an electric chain the generated and strengthened signal is transferred ECU. The gauge works as follows: at change of the form of a diaphragm electric resistance of the layers pasted to a diaphragm changes. Change of pressure upon 1500 bar leads to change of the form of a diaphragm on 1 mm.

Depending on put pressure target pressure of the gauge changes from 0 to 70 мВ and after strengthening makes 0,5–4,5 V.Tochnoe pressure measurement in the accumulator it is necessary for correct functioning of system of injection of fuel. In a working range measuring accuracy should be in limits 2 %. At an exit of the gauge of pressure out of operation the valve of adjustment of pressure is passed in a mode by""diaphragm"and injection system, using spare (soft) function, accepts in advance set size of pressure.

The valve of restriction of pressure

The valve of restriction of pressure carries out the same function, as the valve of superfluous pressure. In case of superfluous pressure the valve opening limits pressure in the accumulator. Pressure of opening of the valve of restriction of pressure – 1500 bar.

The valve of restriction of pressure – the mechanical device including following elements:

– The case with an external carving for вворачивания in the pressure accumulator;
– Connection of a tube of return of fuel in a fuel tank;
– Mobile плунжер;
– A spring.

Atomizers

Atomizer: A – the atomizer is closed (a motionless condition); In – the atomizer is opened (fuel injection)

The atomizer provides giving of the necessary quantity of fuel in the combustion chamber. During precisely established moment ЕCU transmits an excitation signal to the atomizer solenoid that means the beginning of giving of fuel. The quantity of injected fuel is defined by the period of opening of a spray and pressure in system. The fuel which is coming back from the valve of regulation of pressure and a step of low pressure, moves in a collector together with fuel which carried out greasing of the fuel pump of a high pressure.

The atomizer consists of following knots:

– A spray;
– Hydraulic system;
– The solenoidal valve.

Fuel from carving connection of a high pressure through the channel moves to a spray and through a giving aperture in a compartment of management of the valve. The compartment of management is connected by the valve with returnable топливопроводом through the aperture of leak connected to the solenoidal valve. At closing of an aperture of leak the hydraulic effort put to плунжеру of management by the valve, exceeds effort from pressure on конусный an end face of a needle of a spray. As a result the spray needle falls downwards and tightly blocks fuel giving under a high pressure in the combustion chamber.

At opening of the solenoidal valve of an atomizer the leak aperture that leads to pressure decrease in a compartment of management of the valve therefore hydraulic pressure on плунжер also decreases opens. As soon as the hydraulic effort becomes below effort from pressure on конусный an end face of a needle of a spray, the spray needle opens also fuel is injected into the combustion chamber. This indirect management of a needle of a spray with use of hydraulic system of increase in effort is applied because forces which are required for fast opening of a needle, cannot be generated directly solenoidal valve. The so-called quantity of fuel for the management, necessary for opening of a needle of a spray, moves in addition to quantity of fuel which is necessary for entering actually into the cylinder, and it through the aperture of leak connected to the solenoidal valve, moves in returnable топливопровод.

In addition to quantity of fuel for management also there is a fuel loss in a directing pusher of the valve and a spray needle.

Atomizer action at work of the engine and pressure creation by the fuel pump of a high pressure is subdivided into following four stages:

– The atomizer is closed (with the high pressure appendix);
– The atomizer opens (the beginning of injection of fuel);
– The atomizer is opened completely;
– Atomizer closing (the termination of injection of fuel).

At the switched off engine and absence of pressure in the accumulator of pressure the spray spring closes an atomizer.

The atomizer is closed

The solenoidal valve of an atomizer is not raised in a motionless condition and consequently is closed. The leak aperture is closed also a valve spring presses a ball to a nest of an aperture of leak. The high pressure from the pressure accumulator increases in a compartment of management of the valve and simultaneously is present at volume of a compartment of a needle of a spray. Pressure from the pressure accumulator, put in a face surface плунжера managements, together with force of a spring of a needle of a spray keeps a needle in the closed position, counteracting against the forces of opening enclosed in a stage of pressure.

The atomizer opens

The atomizer is in motionless position. The solenoidal valve is raised by a current which provides fast opening of the valve. Immediately big current submitted to the solenoid, decreases to a current, sufficient for deduction of the solenoidal valve in open position. When the leak aperture opens, fuel follows from a compartment of management of the valve in a cavity located over the valve, and therefrom through the returnable pipeline in a fuel tank.

The effort created by the solenoid, exceeds effort of a spring and the leak aperture that leads to pressure decrease in a compartment of management of the valve therefore hydraulic pressure on плунжер also decreases opens. As soon as the hydraulic effort becomes below effort from pressure on конусный an end face of a needle of a spray, the spray needle opens also fuel is injected into the combustion chamber.

Speed of opening of a needle of a spray is defined by a difference in speed of a stream through an aperture of leak and a giving aperture. Плунжер managements reaches the top position where there is the pillow of fuel formed by a stream of fuel between apertures of leak and giving of fuel. In this position the atomizer spray is completely open also fuel is injected into the combustion chamber under the pressure equal to pressure in the accumulator of pressure.

Atomizer closing

After a pressure stopping delivery to the solenoidal valve клапанная the spring moves an anchor downwards and the ball closes a leak aperture. The anchor consists of two parts. However, in spite of the fact that the anchor plate copes плечиком at moving downwards, it can отпружинить with a returnable spring so that there will be no the forces operating downwards on an anchor and a ball.

At closing of an aperture of leak the hydraulic effort put to плунжеру of management by the valve, exceeds effort from pressure on конусный an end face of a needle of a spray. As a result the spray needle falls downwards and tightly blocks fuel giving under a high pressure in the combustion chamber. Speed of movement of a needle of a spray is defined by a stream through a giving aperture.