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Common Rail fuel system
System Common Rail fuel injection
Fuel System Common Rail fuel supply stage includes a low pressure feed stage and the high pressure fuel and the ECU (11). The fuel supply at low pressure Fuel supply low-pressure Common Rail system includes: - The fuel tank with the preliminary fuel filter;
- Booster fuel pump;
- fuel filter;
- A low-pressure fuel.
The booster fuel pump Electric booster fuel pump with pre-fuel filter continuously supplies a certain amount of fuel from the fuel tank to the fuel injection pump. The pump delivers not only fuel but within the security system must stop the fuel supply in case of failure, i.e. with the ignition on and the engine stopped. The fuel pump is comprised of three basic elements: - Pump;
- Electric motor;
- Cover.
Fuel filter Insufficient cleaning of the fuel can damage the units high pressure fuel pump, injection valves and injection nozzles. Fuel filter cleans the fuel before it enters the high pressure fuel pump, and thus prevents premature wear at sensitive nodes of the pump. Diesel fuel may contain water or in a bound form (emulsion), or in free form (for example, the condensation of water vapor at the temperature). If water gets into the injection system, it may lead to corrosion of injection system, so set the warning system, which includes a warning lamp in the instrument cluster if necessary to drain the water from the fuel filter. Fuel supply high pressure Fuel supply high-pressure Common Rail system includes: - High pressure fuel pump with pressure control valve;
- High-pressure fuel;
- High-pressure accumulator (rail) pressure transducer, pressure limiter, a flow limiter, nozzles;
- The fuel return line.
High pressure fuel pump High pressure fuel pump (schematic longitudinal section) High pressure fuel pump (schematic cross sectional view) High pressure fuel pump via a high pressure fuel supplies fuel under pressure to 1350 bar in a high pressure accumulator. High pressure fuel pump is located on the border of low-stage and high-pressure fuel. In all operating conditions, the service life of the fuel pump corresponds to the period of the car.
The fuel pump is lubricated by diesel fuel. Fuel is compressed three pistons mounted radially at an angle of 120 ?� to each other. The pump delivers fuel three servings per crankshaft revolution. For the diesel engine with a displacement of 2.0 liters, operating with a rated engine speed and generate a pressure 1350 bar, the pump is needed to drive power of 3.8 kW, taking into account the mechanical efficiency approximately 90%. The operation of the pump The booster fuel pump supplies fuel through a filter with water separator to the entrance of the safety valve and high pressure fuel pump. Fuel through the relief valve orifice lubricate movable members of the pump, as well as cools it. Drive shaft with eccentric cams three pump plunger moves up and down according to the shape of the cam. Once the delivery pressure exceeds the opening pressure of the safety valve (0.5 ... 1.5 bar), feed pump causes fuel to pass through the intake valve of a fuel pump of a high pressure pumping element chamber, the piston is moved downward (intake stroke). The intake valve closes when the piston pump passes through the BDC and as fuel can not flow out of the chamber pump element, it shrinks regardless of the feed pressure. Increasing pressure opens the exhaust valve and once reached a pressure equal to the pressure in the accumulator, a pressurized fuel enters the high pressure. Piston pump continues to deliver fuel, until it reaches the top dead center (discharge stroke), whereupon the pressure decreases and the vent valve closes. Fuel remaining in the pump compartment element expands and pump piston moves downwards. Once the pressure in the compartment of the pump element is reduced below the pressure generated by priming pump, the inlet valve opens and the process is repeated. Since the pump output exceeds the fuel consumption of the engine, excessive fuel under high pressure through a pressure control valve is returned to the fuel tank. This leads to unnecessary heating of the fuel and reduce overall efficiency. Battery of high pressure (rail) The pressure created by the fuel pump of high pressure extends through the battery and the fuel to the injector. At the same time, due to the volume of fuel in the accumulator Reduces the fuel pressure caused by the high pressure fuel pump and injector opening. The compressibility of the fuel as a result of high pressure is used to achieve the effect of the battery. The fuel pressure sensor is measured and maintained at the desired level, pressure regulating valve. High pressure pipe High pressure pipe designed to transfer fuel from the high-pressure accumulator, and the injectors must resist the pressure of high-frequency oscillations arising during operation of the engine. Fuel pipes are made of steel and have an outer diameter of 6 mm and an inner diameter of 2.4 mm. All high pressure pipes need to have the same length. The difference in distance between the battery and each fuel injector is compensated by bending the fuel. Pressure sensor The pressure sensor sends a signal to ECU, which corresponds to the actual pressure in the pressure accumulator. The pressure sensor includes the following elements: - The combined sensor element welded to the shell;
- PCB electric circuit;
- Sensor housing with an electrical connector.
Fuel under pressure through the orifice acts on the diaphragm of the sensor on which the sensor element (semiconductor device) which converts the pressure into an electrical signal. Through the contacts of the connector and an electrical circuit generated and amplified signal is transferred to ECU. The sensor works as follows: when changing the shape of the diaphragm changes the electrical resistance of the layers glued to the diaphragm. Change in pressure of 1500 bar changes the shape of the aperture is 1 mm. Depending on the applied pressure sensor output voltage varies from 0 to 70 mV and after the gain of 0.5-4.5 V. The exact measurement of the pressure in the accumulator is necessary for the proper functioning of the fuel injection system. The working range of the measuring accuracy must be within ?� 2%. When the output pressure sensor failure pressure control valve switches to "iris" and the injection using a spare (soft) function accepts a predetermined amount of pressure. Pressure relief valve Pressure relief valve performs the same function as the overpressure valve. In case the overpressure valve opening limits the pressure in the accumulator. The opening pressure relief valve - 1500 bar. Pressure relief valve - a mechanical device, which includes the following elements: - Housing with an external thread for screwing in a pressure accumulator;
- Connect the fuel return pipe to the fuel tank;
- Movable plunger;
- Spring.
Sprayers Nozzle: A - Nozzle closed (standstill); In - the injector is opened (fuel injection) The nozzle supplies the desired quantity of fuel into the combustion chamber. The exact time of the specified ECU transmits a drive signal to the solenoid injectors, which means the beginning of the fuel supply. The amount of fuel injected is determined by the period of the opening of the spray gun and system pressure. The fuel returning from the pressure control valve and low pressure stages, is fed into the manifold with the fuel, which carried lubricant high pressure fuel pump. The nozzle consists of the following components: - Sprayer;
- The hydraulic system;
- Solenoid valve.
Fuel from a high pressure of a threaded joint through the channel and is fed to the spray gun through a supply opening in the control valve chamber. Valve control module is connected to the fuel return line through the hole leak, coupled with the solenoidal valve. When closing the drain hole hydraulic force applied to the plunger control valve exceeds the force of pressure on the tapered needle end sprayer. As a result, nozzle needle is lowered and sealingly shuts off the high pressure fuel in the combustion chamber. When opening the solenoid valve opens the nozzle hole leaks, which leads to a decrease in pressure in the valve control section, thereby also decreasing the hydraulic pressure on the plunger. Once the hydraulic force becomes lower than the pressure force on the tapered end of the nozzle needle, nozzle needle opens and the fuel is injected into the combustion chamber. This indirect control needle sprayer using hydraulic system increasing the force applied because the forces required for fast opening of the needle can not be generated directly solenoidal valve. The so-called to control the amount of fuel required to open the nozzle needle, is applied in addition to the amount of fuel to be actually introduced into the cylinder, and it leaks through the hole, connected to a solenoidal valve is supplied to the fuel return line. In addition to the amount of fuel to control the loss also occurs in the fuel rail and injector plunger needle dispenser. The action of the nozzle when the engine and pressurizing the high pressure pump is divided into the following four steps: - Injector is closed (with the application of high pressure);
- Injector opens (start of injection);
- Nozzle completely open;
- The closure of the nozzle (end of injection).
When the engine is off and there is no pressure in the accumulator pressure spring closes the nozzle sprayer. The nozzle is closed The stationary nozzle solenoid valve is not excited, and therefore closed. Drain holes closed and the valve spring pushes the ball to the jack hole leaks. High pressure from the accumulator pressure increases in the compartment and the control valve is simultaneously present in the volume chamber nozzle needle. The pressure from the accumulator pressure applied to the end surface of the plunger control, together with the spring force holds needle nozzle needle in the closed position against the opposing forces of the opening attached to the pressure stage. The nozzle opens The nozzle is stationary. Solenoid valve is excited by a current which provides a rapid opening of the valve. Immediately a large current supplied to the solenoid is reduced to a current sufficient to hold the solenoid valve open. When the leak hole is opened, fuel flows from the valve control chamber into the cavity above the valve, and thence through the return line to the fuel tank. The force created by the solenoid exceeds the spring force and opens the leak hole, which leads to a decrease in pressure in the valve control section, thereby also decreasing the hydraulic pressure on the plunger. Once the hydraulic force becomes lower than the pressure force on the tapered end of the nozzle needle, nozzle needle opens and the fuel is injected into the combustion chamber. Opening the nozzle needle speed determined by the difference in the rate of flow through the leak hole and a supply opening. The piston reaches the top management position, where there is a theft of fuel, formed by the flow of fuel between the drain hole and the fuel supply. In this position the spray nozzle is fully open and the fuel is injected into the combustion chamber at a pressure equal to the pressure in the pressure accumulator. Closing the nozzle After the termination of the supply voltage to the SOLENOID VALVE valve spring moves the anchor down and the ball closes the opening of the leak. The anchor consists of two parts. However, despite the fact that the armature plate is controlled by a shoulder in the downward movement it can "otpruzhinit" spring return so that there will be no forces acting downward on the ball and the anchor. When closing the drain hole hydraulic force applied to the plunger control valve exceeds the force of pressure on the tapered needle end sprayer. As a result, nozzle needle is lowered and sealingly shuts off the high pressure fuel in the combustion chamber. The velocity of the nozzle needle is determined by the flow through the feed opening.
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