The principle of operation of the Common Rail System 2
Battery-type fuel system - Commonrailsistem 2 (СЭЗ2) with electronic fuel supply control manufactured by Robert Bosch (Germany).
CRS2 BOSCH with electronic control unit provides:
- - exact dosage of cyclic fuel supply for each operating mode;
- - adjustment of fuel injection advance angles depending on speed, load, temperature;
- - easy engine start with minimal emissions of harmful substances into the atmosphere under any temperature conditions;
- - adjustment of the fuel supply process depending on environmental conditions in order to reduce emissions of harmful substances;
- - compatibility with the car's electronic control unit (ABS, ASR, cruise control, etc.).
The fuel system works like this:
Fuel from the fuel tank is sucked in by the fuel priming pump through the coarse filter and the cooler of the electronic control unit and at a pressure of 700-800 kPa (7-8 kgf / cm2) is fed into the fine filter with very high degree of cleaning, since the CommonRail system is more sensitive to contamination than systems with a conventional plunger fuel pump.
Next, the fuel enters the high-pressure fuel pump, which has two sections, each of which is fed through a metering device with an electrovalve.
From the fuel pump, fuel under pressure enters the common fuel storage line (ramp) and is then supplied to each injector through individual fuel lines.
Injectors supply fuel under pressure to the combustion chamber, the duration of injection is determined by the duration of the electrical impulse from the electronic engine control unit.
The peak electrical impulse to the injector is characterized by a voltage of up to 80 V and 20 A.
Fuel injection is carried out in steps:
- - pilot injection (1-3%) at early injection advance angles - to reduce engine noise;
- - main injection (94-96%);
- - additional injection after the main one - to reduce exhaust smoke (1-5%).
The fuel injection balance for the specified injections is determined by the engine operating mode.
Solenoid valves allow you to regulate the pressure of the fuel entering the over-plunger space of the fuel pump.
In the rail fittings at the inlet to the high-pressure pipelines, there are hydraulic fuel flow limiters (one for each cylinder), which shut off the fuel supply to the injectors when the specified injection duration is exceeded (for example, when the injector is clogged).
After the injector failure is corrected, the limiter will automatically return to normal operation.
Sensors located on the engine transmit information to the electronic control unit about the operation of the systems.
The electronic control unit uses this information to control injection and signal the operation of other systems to the instrument panel, and control the actuators that ensure the operation of the engine.
This information comes from the following sensors (see Figure 2):
- - rail pressure sensor (1);
- - phase sensor (2);
- - air temperature and pressure sensor in the intake manifold (3);
- - engine speed sensor (4) (on the flywheel housing);
- - oil pressure sensor (5);
- - coolant temperature sensor (6) (see Fig. 3);
- - fuel temperature and pressure sensor (7);
- - fan operation mode sensor (built into the fan clutch).
Electronic control unit (ECU)
The electronic control unit (see Fig. 4a) receives information from the sensors and the computing unit that controls the vehicle.
Depending on the input parameters, this block controls fuel injection and a number of auxiliary functions (engine fan).
This unit informs the driver about the state of the fuel injection system by means of signaling devices (lamps, light signals) located on the instrument panel (see Fig. 46), and in case of any malfunction, it operates in emergency mode.
Coarse fuel filter. (See Fig. 5) Full flow sump filter with water separator, manual primer pump and replaceable filter element (vehicle mounted). (1) - MAZ car filter, (2) - Ural car filter.
Fine filter for fuel. (See Fig. 6) Full flow filter with two replaceable filter elements and a device for automatic fuel heating in the cold season.
High pressure fuel pump. (See Fig. 7)
With gear-driven fuel priming pump and two high-pressure plunger sections, gear-driven; drive ratio 0.5:1.
High pressure rail (see Fig. 8)
It provides communication between the fuel injector pump.
The ramp is equipped with:
- - pressure sensor,
- - bypass valve.
The bypass valve prevents overpressure in the high pressure circuit by diverting fuel to the tank return system. Bypass valve calibration: 1650± 50 bar.
A rail pressure sensor with a 5-volt supply voltage produces an output voltage in the range of 0.5 - 4.5 volts, depending on the value of the measured pressure.
Information about this value is transmitted by the engine ECU.
Electrically controlled nozzle (see Fig. 9)
This nozzle includes an electrovalve that controls the opening and closing of the atomizer.
The electrically controlled nozzle is not repairable. The seals must always be replaced after each disassembly. The clips are not polarized.
Fuel supply fitting to the injector. (650.1112154)
Equipped with a device that prevents it from rotating with two balls. This fitting, as well as its seal, must be changed every time it is dismantled.
Phase sensor. (See Fig.10) This inductive type sensor outputs a sinusoidal voltage caused by passing through the cavity of the flywheel and pump gear. The frequency of this signal is proportional to the engine speed. The flywheel has 58 cavities.
Coolant temperature sensor. (See Fig. 11)
Air pressure and temperature sensor in the intake manifold. (See Fig. 12) 2 measuring elements are integrated in one sensor.
With a 5-volt supply voltage, this sensor produces an output voltage in the range of 0.5 V and 4.5 V.
Technical data (between clips 1 and 2).
Oil pressure sensor. (See Fig. 13)
At a 5 volt supply voltage, this sensor outputs a certain voltage, depending on the pressure in the oil circuit (from 0 to 7 bar).
Fuel filter clogging sensor. (see Fig. 14) Switches when the difference in pressure between P1 (1) and P2 (2) reaches approximately 3 bar.
Information about clogged filters is displayed only when the engine is hot (to avoid detection of malfunctions that occur during a pressure peak situation or due to an increase in fuel viscosity in the cold season).
Fan clutch. (See Fig. 15)
The fan clutch consists of a speed sensor, a viscous coupling control electrovalve.
An electronic computer unit controls the viscous coupling by means of an electrovalve according to the parameter demanded by the engine (temperature, reduced efficiency mode, turning on the heater or air conditioner).
This system operates at very high injection pressures (up to 1400 bar.) with medium voltage current.
Before starting disassembly, thoroughly clean the system and then take all necessary precautions to prevent any contamination from entering it.
Use clean solvent and blow with compressed air. In normal operation, after stopping the vehicle, the pressure in the high pressure circuit drops quickly (1 - 3 minutes).
It is necessary to make sure that there is no pressure in the circuit by creating a fuel leak by loosening the injector fitting.
All work on the injection system must be carried out with the engine stopped.
Repairs should be carried out in a clean, dust-free environment using suitable products and tools. The use of fibrous gloves is prohibited.
Clean the parts thoroughly with solvent and check them carefully. Use the best grade brushes, checking for cleanliness and condition. The use of fibrous and dirty rags is prohibited.
Close up all openings with special plugs and plugs as soon as the pipelines are dismantled.
Avoid using compressed air. The injector brackets are not repairable.
If they fail, they need to be replaced.
When testing injector performance, proceed with great care so as not to suffer from a jet of atomized fuel or high pressure leakage.
Follow the chronological order of disassembly and reassembly described in the repair manual.
When reassembling, do not make any modifications or apply excessive force. Replace part if necessary. Always tighten to the recommended torque.
Bleed the circuit without using the starter.
If the above recommendations are followed, the quality and reliability of the “CommonRail” system are ensured.
The inner surfaces of new tubes are coated with a protective anti-corrosion agent. The tubes should be rinsed and wiped with industrial alcohol and then put back in place immediately to prevent corrosion.