PRESSURE CONTROL (SCR system running)

PRESSURE CONTROL mode is the normal operating status of the SCR system and has four submodes.

PRESSURE CONTROL mode is maintained until terminal 15 is switched off. A change to PRESSURE REDUCTION mode then takes place. A change to PRESSURE REDUCTION mode also takes place if a fault occurs in the system.

The four submodes of PRESSURE CONTROL are described in the following:

• REFILL 

  The delivery module, metering line and the metering module are filled when REFILL mode is assumed. The pump is actuated and the metering valve opened by a defined value. The fill level is calculated.

  The mode changes to PRESSURE BUILDUP when the required fill level is reached or a defined pressure increase is detected.

  PRESSURE REDUCTION mode is assumed if terminal 15 is switched off or a fault occurs in the system.

• PRESSURE BUILDUP 

  In this mode, the pressure is built up to a certain value. For this purpose, the pump is actuated while the metering valve is closed.

  If the pressure is built up within a certain time, the system switches to the next mode of METERING CONTROL. If the required pressure built-up is not achieved after the defined period of time has elapsed, a status loop is initiated, and VENTILATION mode is assumed.

  If the pressure cannot be built up after a defined number of attempts, the system signals a fault and assumes PRESSURE REDUCTION mode.

  PRESSURE REDUCTION mode is also assumed when terminal 15 is switched off or another fault occurs in the system.

• VENTILATION 

  If the pressure could not be increased beyond a certain value in PRESSURE BUILDUP mode, it is assumed that there is still air in the pressure line.

  The metering valve is opened for a defined period of time to allow this air to escape. This status is exited after this time has elapsed and the system returns to PRESSURE BUILDUP mode. The loop between PRESSURE BUILDUP and VENTILATION varies corresponding to the condition of the reducing agent. The reason for this is that a different level is established after REFILL depending on the ambient conditions. Repeating the ventilation function will ensure that the pressure line is completely filled with reducing agent. PRESSURE REDUCTION mode is assumed if terminal 15 is switched off or a fault occurs in the system.

• METERING CONTROL 

  The system can enable metering in METERING CONTROL mode. This is the actual status during normal operation. The urea-water solution is injected in this mode. In this mode, the pump is actuated in such a way that a defined pressure is established. This pressure is monitored. If the pressure progression overshoots or undershoots defined parameters, a fault is detected and the system assumes PRESSURE REDUCTION mode. These faults are reset on return to METERING CONTROL mode.

  PRESSURE REDUCTION mode is also assumed if terminal 15 is switched off or another fault occurs in the system.