Operation

OPERATION

There are several modes of operation for the Common Rail Diesel Injection System.

Pre-injection

The purpose of the pre-injection function is to reduce noise and pollutants. The coolant temperature, charge air temperature and atmospheric pressure are use to correct the quantity of pilot injection. The quantity of pilot injection now determined is deducted from the quantity of main injection in order to establish whether sufficient quantity is available for the following main injection.

The rail pressure is chosen sufficiently high so that a minimum quantity is injected. If the quantity of main injection is too small the pilot injection is switched off by the ECM.

The start of actuation of pilot injection is calculated dependent on operating point, the following data being taken into account:

Shutting Off Pre-injection

The pre-injection is shut off when:

- The moment of pre-injection is exceeded
- Engine speed too high
- Pre-injected quantity too low
- Main injected quantity too low
- Insufficient fuel rail pressure
- Engine is switched off

Calculating Pre-injection Quantity

The pre-injection quantity is calculated on the basis of:

- Engine speed
- Atmospheric pressure
- Coolant temperature
- Boost air temperature
- Fuel rail pressure

Main Injection

The purpose of main injection function is to enable the injection time and injection period calculated by the ECM. The injection quantity required by the engine is divided into the per-injection and main injection quantity. If the main injection quantity computed by the ECM is too small, no pre-injection takes place.

Start of Actuation

The start of actuation of main injection is dependent on engine speed and quantity. In addition, it is corrected depending on the following values:

- Coolant temperature
- Boost air temperature
- Atmospheric pressure
- Pre-injection corrected YES/NO

Switching Off Main Injection

Main injection is switched off when:

- Engine speed is too high greater then 4700 - 4800 rpm
- Main injection quantity too low
- Low fuel pressure in fuel rail
- Engine off
- External quantity control
- Deceleration mode

Calculating Main Injection

The quantity of main injection is calculated by:

- Engine speed
- Atmospheric pressure
- Coolant temperature
- Boost air temperature
- Fuel rail pressure
- Boost pressure

Period of Actuation

For calculating the period of actuation of the main injection it is necessary to know whether a pre-injection has occurred or not.

The coolant temperature, charge air temperature and the atmospheric pressure are used for correcting the main injection quantity. If main injection quantity is less than a minimum quantity which is dependent on fuel rail pressure, no preinjection takes place. In this case, only main injection is performed. If the quantity is then still below the minimum quantity, neither main injection or pre-injection takes place (deceleration mode).

Deceleration Mode

The purpose of the deceleration mode is to interrupt the operation of the injectors. The ECM determines the accelerator pedal position from a supplied signal and it determines the engine speed by the crank sensor. In the overrun and with the engine speed above 1600, with the accelerator pedal no pressed, the injectors are no longer actuated and the fuel rail pressure is lowered by the pressure regulator valve.

Full Load Injected Quantity

The purpose of the full load injected quantity is to minimize the formation of smoke. The ECM limits the fuel rail pressure when the engine is operating at full load by way of the quantity control valve, and quantity of fuel injected by the injectors. this minimizes the formation of smoke when accelerating and driving at constant speeds. If a fault occurs at the boost pressure control, full load injected quantity is reduced.

Limiting Maximum Engine Speed

The ECM determines the engine speed based on the signal supplied by the crankshaft sensor and limits this by interrupting the operation of the fuel injectors.

Fuel Quantity Control

The fuel quantity is controlled separately for each cylinder by the ECM inline with the firing order.The ECM detects the operating state which exists at the engine by means of the sensors. In order adapt the quantity injected, either the fuel rail pressure can be adjusted by the fuel solenoid and quantity control valve or the actuation time of the solenoid valves in the injectors

Boiling Protection

In order to protect against thermal overload and along with criteria programmed in the ECM, the injection quantity is reduced as a function of the coolant temperature and vehicle speed. If the coolant temperature sensor fails the oil temperature signal from the oil sensor is used as a suitable value.

Fuel Tank Protection

The fuel rail pressure is lowered in order to protect the fuel tank from overheating. The fuel temperature sensor measures the temperature of the fuel being supplied from the tank, in the high pressure flange. If the fuel is too warm the fuel rail pressure is further reduced by the quantity control valve.