Flow chart
| element | designation |
|---|---|
| BSI1 | built-in systems interface |
| 8235 | engine starting switch |
| 0004 | instrument panel |
| 1158 | pre-postheating control unit |
| 1160 | pre-heater plugs |
| 1220 | engine coolant temperature sensor |
| 1310 | air flow meter |
| 1320 | engine ECU |
| 7500 (*) | semi-automatic parking assistance ECU |
| 7800 | ESP ECU |
| connection number | signal | transmitter/receiver | nature of signal |
|---|---|---|---|
| 1 | inlet air temperature information | 1310 / 1320 | filament |
| 2 | engine coolant temperature information | 1220 / 1320 | filament |
| 3 | request for display of the preheating warning lamp | BSI1 / 0004 | CAN INFO DIV |
| 4 | engine starting switch information | 8235 / BSI1 | filament |
| 5 (*) | request for display of the preheating warning lamp | 7500 / BSI1 | CAN Is |
| 6 (*) | request for display of the preheating warning lamp | 7800 / 7500 | CAN Is |
| 7 | request for display of the preheating warning lamp | 1320 / 7800 | CAN Is |
| 8 | control of the pre-postheating unit | 1320 / 1158 | filament |
| 9 | information on a fault in the control of the pre-postheating unit | 1158 / 1320 | filament |
| 10 | activation of the pre-postheating plugs | 1158 / 1160 | filament |
Pre-heating
Role
The preheater plugs enable the temperature to rise rapidly in the combustion chambers prior to the engine being started, when starting from cold or when the outside temperature is low
Role of preheating
- To facilitate starting from cold (the air is heated up to enable the injected diesel fuel to combust more easily)
- To reduce smoke emissions (the heated air reduces the incidence of unburnt gases)
NoteThe change from preheating to postheating occurs without interruption during the starting phase
Function
The engine ECU controls the pre-postheating control unit by means of an open cycle ratio
The electrical supply of the preheater plugs is via the pre-postheating control unit, as a function of the commands from the engine ECU
Phases of electrical supply of the preheater plugs
- Rapid heating
- Stabilised heating
The maximum activation time for rapid heating is no more than 2 seconds
The rapid heating phase enables the temperature of the preheater plugs to rise as rapidly as possible, to aid combustion
During the rapid heating phase, the pre-postheating control unit is controlled by an open cycle ratio of 99%
The stabilised heating phase comes in after the rapid heating phase, to maintain the temperature of the preheater plugs, while waiting for the engine to start
During the stabilised phase, the pre-postheating control unit is controlled by an open cycle ratio of around 60%
If a pre-post heating control unit failure occurs, the engine management ECU memorises a fault
The preheating times are determined by the engine ECU as a function of the following parameters
- Coolant temperature (measurement done by the engine coolant temperature sensor)
- Atmospheric pressure (measurement done by the atmospheric pressure sensor internal to the engine ECU)
Activation conditions
The preheating is activated for 1,9 s if the following conditions are met
- Engine coolant temperature lower than 15°C (lower than 25°C at an altitude of more than 2000 m)
- Battery voltage more than 6,5 V
NoteLighting of the preheating warning lamp is requested when the engine coolant temperature is lower than or equal to 10°C
Post heating
Role
Within the first few seconds of the engine starting, the temperature in the combustion chambers does not permit a combustion of sufficient quality, this causing the engine to be unstable at idle and to emit excessive pollution
Role of postheating
- To prolong the operation of the preheater plugs after the cold starting phase
- To achieve good combustion on starting
- Reducing the emissions of pollutants in the first few minutes after starting
- To stabilise the engine at idle
- To reduce blue smoke emissions
Function
The engine ECU controls the pre-postheating control unit by means of an open cycle ratio
The unit supplies the pre-heater plugs with power in accordance with the orders of the engine management ECU
If a pre-post heating control unit failure occurs, the engine management ECU memorises a fault
The postheating times are determined by the engine ECU as a function of the following elements
- The temperature of the coolant fluid (measured by the engine coolant temperature sensor)
- The atmospheric pressure sensor (measured by the atmospheric pressure sensor internal to the engine ECU)
NoteThe postheating timing can vary as a function of the inlet air temperature
Activation conditions
The preheating is actived immediately the engine starts with coolant temperature lower than 50°C
The duration of the postheating varies according to the engine speed and engine load but cannot exceed 900 seconds
NoteThe glow plugs are only activated when the engine is operating in medium load conditions, in order to prevent the engine overheating
Activation of the postheating for reduction of blue smoke at altitude
In order to limit the emission of blue smoke, especially at altitude (atmospheric pressure less than 900 mbar), the timing of the activation of the preheater plugs is defined in the base mapping, taking account of the following parameters
- Inlet air temperature
- Engine coolant temperature
- Engine torque
- Atmospheric pressure