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" (*) | water in fuel sensor | 4050 |
| "d" | 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
Peaks of pressure are authorised in the fuel high pressure common injection rail for a limited time during the life of the vehicle
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
The minimum fuel injection pressure to allow starting of the engine varies according to the ambient temperature
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 several points when the "driver has their foot off the pedal"
- Controlling the fuel injectors one by one, progressively increasing the injection time
- Recording the flywheel acceleration generated by the fuel injection
NoteWhen the flywheel acceleration corresponds to a fuel injection flow of 1 mg/stroke, the engine ECU records in its memory the injection time necessary to obtain this flow
Adaptation of the mixture
The engine ECU can reset the engine mixture to compensate for the injector and air flow sensor drifts
The mixture adaptation operates in 2 stages
- The programming of the nominal mixture
- The correction of the drift in the mixture
Programming the nominal mixture
The engine ECU programmes the nominal mixture during the first 300 kilometres of the life of the vehicle
When the driver releases the accelerator pedal, the engine ECU compares the values from the oxygen sensor with those from the air flow sensor to calculate the actual flow of fuel injected
The fuel flow calculated makes it possible to obtain a torque value which is compared with the actual torque value, the difference between these two values being memorised in the engine ECU mapping
The operation is repeated at different (engine speed/load) operating points to produce a complete mapping that gives a nominal mixture value on a new engine
Correction of the drift in the mixture
After the first 300 kilometres, the engine ECU records the mixture measured in a mixture drift mapping
The engine ECU compares the nominal mixture mapping with the mixture drift mapping and defines a new torque value to correct the mixture drift
The corrected torque value is directly taken into account in the mappings for the exhaust gas recycling, the air flow and the turbo pressure
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 "e"
- The main fuel injections are positioned in the range "f"
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
Oil ingestion strategy
A risk of autocombustion exists when oil from the lubrication circuit in a diesel engine happens to penetrate into the combustion chamber in a sufficient quantity
Such autocombustions are outside the control of the engine ECU, and can rapidly destroy the engine
To prevent destruction of the engine, the engine ECU uses an oil ingestion strategy
Detection of engine racing (oil ingestion)
The engine ECU detects oil ingestion in the following instances
- Specific engine speed
- Injection cut off (foot off)
- Discrepancy between the turbo pressure setting and the specific turbo pressure
Engine stopping following racing
The engine ECU makes the engine cut out as soon as an oil ingestion is detected
Actions by the engine ECU to make the engine cut out
- Forcing the closure of the inlet air mixer
- Forcing the closure of the EGR valve
- Prohibiting the injection of fuel
- Reduced flow after starting
- Minimum pressure in the fuel high pressure common injection rail (opening of the high pressure pump actuator)
- The activation of the regeneration of the particle emission filter
- Request for maximum opening of the impeller
- Cruise control / speed limiter cut-off
- Deactivation of monitoring of the air mixer
- Deactivation of monitoring of the EGR valve
- Deactivation of monitoring of the ratio of oxygen in the exhaust
Once the engine cuts out, the engine management ECU authorises restarting in down-grade mode: with reduced flow only, limiting the engine speed
An operation using the diagnostic tool is necessary in order to restore normal operation
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