Preheat, Function - GF15.20-D-3005TSA
Engine 651 in model 907
Block diagram
Function requirements of CDI preheating, general points
- Circuit 15 ON
- Preglow system functional
Preheat (CDI), general points
The preglowing system warms up the engine combustion chambers to the ignition temperature required for ignition of the fuel/air mixture.
At colder temperatures, the vent line heater element is actuated by the CDI control unit. This prevents freezing of the crankcase ventilation system and any associated engine damage.
Function sequence for preheat (CDI) ,
The function sequence is subdivided into the following steps:
- Function sequence for preglowing
- Function sequence for start-ready glowing
- Function sequence for start-up glowing
- Function sequence for afterglowing
- Function sequence for diagnostic glowing
- Function sequence for diesel particulate filter (DPF) preheating
- Function sequence for emergency glowing
Function sequence for preglowing
The CDI control unit receives the message "circuit 15 ON" from the electronic ignition lock (EZS) control unit via the suspension FlexRay, powertrain control unit and via the drive CAN. The CDI control unit reads in the engine oil temperature via the engine oil temperature sensor and, via the drive LIN and thus depending on coolant temperature, actuates the glow output stage. Via the drive CAN, it actuates the powertrain control unit. Via suspension FlexRay, it actuates the electronic ignition lock (EZS) control unit. Via the user interface CAN, it actuates the preglow indicator lamp symbol (A1e16). The glow output stage then actuates the glow plugs on the plus side.
If an error occurs in the preglow system, at the glow plugs, or on the lines, this is indicated by the preglow indicator lamp (A1e16) and additionally stored in the CDI control unit.
Function sequence for start-ready glowing
Start-ready glowing ensures an adequately high temperature until the engine finally begins to run. If the CDI control unit receives the "circuit 50 ON" information via the drive CAN, from and via the powertrain control unit, suspension FlexRay, from the electronic ignition lock (EZS) control unit, it then continues to actuate the glow output stage for a specific period of time irrespective of the engine oil temperature, which, in turn, actuates the glow plugs.
After reaching the start-ready temperature of 1,250 °C, the preglow indicator lamp (A1e16) goes out.
Function sequence for start-up glowing
Start-up glowing is used to stabilize the cold start speed of the engine. If the CDI control unit receives the "circuit 61 ON" information from the alternator via the drive LIN, the glow output stage is actuated over the drive LIN. The glow output stage then actuates the glow plugs. In this way the first working cycles and the eventual running of the engine are supported.
Function sequence for afterglowing
Afterglowing improves engine running after a cold start and the engine warm-up characteristics.
After a successful engine start, the CDI control unit reads in the engine oil temperature via the engine oil temperature sensor and actuates the glow plugs via the glow output stage dependent on the engine oil temperature.
Function sequence for diagnostic glowing
This function is used to energize the glow plugs to a low temperature level and a system diagnosis is performed. This function is activated during troubleshooting and when the preglow system has been inactive for a long period (no preheating required owing to high ambient temperature).
Function sequence for diesel particulate filter (DPF) preheating
The DPF glowing function is used to raise the load and to stabilize combustion and thus to assist regeneration of the DPF.
To do this, the CDI control unit receives the "circuit 50 ON" message from the powertrain control unit via the drive CAN and from the electronic ignition lock (EZS) control unit via the suspension FlexRay. The CDI control unit then actuates the glow output stage through the drive-LIN.
Function sequence for emergency glowing
If a problem in communication occurs between the CDI control unit and the glow output stage, so that the glow output stage does not recognize any activity 2 seconds after activation through circuit 87, the emergency glowing function is actuated for 180 s. If communication malfunctions during the glowing process for more than 250 ms, the glowing process is continued for 180 s.
If a new glow request is not received from the CDI control unit, the emergency glowing is ended after 180 s.
For alternators with an alternator interface the "circuit -61" line is not needed. Using the information received by the CDI control unit through the alternator interface, the "circuit 61 signal" is simulated in the CDI control unit and sent through an output stage connected to ground connection (e.g. for the instrument cluster).
| Overview of system components for common rail diesel injection (CDI) | GF07.16-D-9997TSA |