Schematic diagram
Key
- "A" electrical links
- "B" low pressure fuel circuit
- "C" high pressure fuel circuit
- "D" heated low pressure fuel circuit
| reference | designation | electrical diagram correspondence |
|---|---|---|
| (1) | fuel high pressure common injection rail | - |
| (2) | engine ECU | 1320 |
| (3) | fuel cooler | - |
| (4) | fuel tank | - |
| (5) | fuel filter | - |
| (6) | diesel injector (1), (2), (3), (4) | (1331, 1332, 1333, 1334) |
| (7) | high pressure fuel pump | 1208 |
| (8) | fuel flow regulator | 1208 |
| "a" | fuel high pressure sensor | 1321 |
| "b" | integral diesel fuel heater | 1276 |
| "c" | manual fuel primer pump | - |
Control of the injection
The engine ECU receives and converts the demands from the driver, or from the vehicle (ABS, ESP, automatic gearbox), into information on the necessary torque that is required of the engine
The engine ECU determines the quantity of fuel that is necessary to provide the engine torque that is required
Depending on the quantity of fuel calculated, the engine ECU determines the following parameters
- Fuel pressure in the fuel high pressure common injection rail
- Fuel injection time
To comply with the pollution norms, to limit the noise of combustion, and to improve the driving quality, the engine ECU determines the following parameters
- Fuel injection advance necessary (start of injection)
- Number of fuel injections per engine cycle
- Time of each injection of fuel during an engine cycle
Fuel pressure in the fuel high pressure common injection rail
General
When the engine speed and engine load are low, the engine does not require the maximum fuel injection pressure
To reduce the injection pressure, the engine ECU commands the flow regulator to limit the supply of fuel at the high pressure pump
The high pressure fuel sensor measures the pressure in the fuel high pressure common injection rail
The engine ECU calculates a control current for the flow regulator, as a function of the pressure measured by the fuel high pressure sensor
Specificities
The high pressure pump provides a maximum injection pressure of 1600 bars, in the fuel high pressure common injection rail (the pressure is regulated by a mechanical valve internal to the pump)
The injection pressure required is calculated as a function of the following parameters
- Intake air temperature
- Engine speed
- Engine load
- Coolant temperature
- Diesel fuel temperature
NoteThe minimum fuel injection pressure to enable engine starting is 150 bars
The engine ECU may request a temporary increase in the engine power
In this case the maximum injection pressure changes to 1650 bars in stages of 40 seconds, with pauses of 40 seconds between 2 activations for a total of 20 hours cumulative
The engine ECU orders a temporary increase in power under a heavy acceleration of the engine speed, as a function of the following parameters
- Engine coolant temperature
- Air temperature entering the engine
- Atmospheric pressure
- Engine speed
Injection time
General
Fuel injection pressure being equal, a longer (or shorter) injection time allows more (or less) fuel to be injected
When there is a large engine load need, fuel injection pressure being equal, the fuel injection time is extended to obtain the maximum engine torque
The fuel injection time corresponds to the time during which the engine ECU commands the fuel injectors to be open
Specificities
The fuel injection time is calculated as a function of the following parameters
- Intake air temperature
- Engine speed
- Engine load
- Coolant temperature
- Fuel pressure in the fuel high pressure common injection rail
Compensation for fuel injector drift
The repeated injection cycles cause a wearing of the fuel injectors which creates a drift in the flow of fuel injected
The drift in the flow of fuel injected causes combustion noise and an increase in pollution
The engine ECU compensates for the drift in the flow of fuel injected by applying a correction of the injection time, making this either longer or shorter
Actions by the engine ECU to determine the correction to be applied to the injection time
- Stabilising the injection pressure at different points (400, 800 and 1200 bars) during a "driver pedal release"
- Controlling the fuel injectors one by one, progressively increasing the injection time
- Recording the flywheel acceleration generated by the fuel injection
NoteWhen the acceleration of the engine flywheel corresponds to a fuel injection flow of 1 to 2 mg/stroke, the engine management ECU records in its memory the injection time necessary to obtain this flow
The engine ECU detects the fuel injector drift when the following conditions are met
- No pressing of the accelerator pedal
- No pressing of the clutch or brake pedal
- Vehicle speed
- Engine speed
- Engine coolant temperature
- Air temperature
- Fuel temperature
- Gearbox ratio engaged
- Fuel level above minimum
Fuel injection flow
General
"E" top dead centre
"F" crankshaft angle
The fuel injected into the combustion chamber requires time to ignite
The engine ECU injects the fuel before top dead centre to compensate for the delay in the fuel igniting
The moment of injection provides for an optimum combustion with maximum pressure in the cylinder, to push on the piston as it descends
The moment of injection is determined by the crankshaft angle relative to top dead centre
There is one moment of injection for each injection of fuel in an engine cycle
- The fuel pre-injections are positioned in the range "d"
- The main fuel injections are positioned in the range "e"
Specificities
The engine ECU determines the moment of injection as a function of the following parameters
- Information from the cylinder intake and exhaust reference sensors
- Information from the engine speed sensor
- Engine load
- Air temperature
- Engine coolant temperature
- Vehicle speed
- Atmospheric pressure
In the engine starting phase: the engine ECU increases the injection advance so as to facilitate engine starting and reduce pollutant emissions
Number of fuel injections per engine cycle
General
"E" top dead centre
"F" crankshaft angle
"g" first pre-injection
"h" second pre-injection
"j" first main injection
Pre-injections inject a small quantity of fuel prior to the main injection, in order to increase the temperature in the combustion chamber
The rise in temperature in the combustion chamber enables the diesel fuel to ignite sooner and more rapidly than in a main injection (reduction in the fuel combustion noise)
The majority of the fuel quantity is injected in the main injection; the combustion produced by the diesel fuel igniting generates the movement of the piston (creation of torque)
NoteThe quantity of fuel needed for one engine cycle is spread over the 2 types of injection
Specificities
Example of the changes in the number of injections per cycle
"L" Engine torque
"M" engine speed
"G" zone with 2 pre-injections and 1 main injection
"H" zones with 2 pre-injections and 2 main injections ("split" injection)
"J" zone with 1 pre-injection and 1 main injection
"K" zone with 1 main injection only
As the engine speed increases, so the duration of each engine cycle diminishes
- The engine ECU no longer has the time to order multiple injections
- The number of injections per cycle diminishes
Reduced flow
The engine ECU can apply 4 injection flow limitation strategies in the event of a fault in a component of the injection system or in the accelerator pedal sensor
The flow limitation strategies authorise operation of the engine but with limited engine speed and engine torque, the severity of the limitation depending on the fault
When an accelerator pedal sensor fault is detected, the idle speed changes to 1300 rpm