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 high pressure pump | 1208 |
| (4) | fuel cooler | - |
| (5) | fuel tank | - |
| (6) | manual fuel primer pump | - |
| (7) | hybrid control ECU | 1919 |
| (8) | diesel injector (1), (2), (3), (4) | (1331, 1332, 1333, 1334) |
| (9) | Fuel filter | - |
| "a" | fuel high pressure sensor | 1321 |
Control of the injection
The hybrid control ECU receives the driver requests (ABS, ESP, automatic gearbox), and converts them into the data for the torque that is required of the engine
The hybrid control ECU transmits the engine torque requirement to the engine ECU
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
The engine ECU uses different combustion modes
- "Cold" mode
- Nominal mode
- Hot mode
- Mode: particle emission filter regeneration
The different modes of combustion are activated depending on the following elements
- The engine coolant temperature
- Activation state of the particle filter regeneration
Each mode of combustion influences the number as well as the moment of injections
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 1800 bars, with possible peaks of 2000 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
The minimum fuel injection pressure to enable engine starting is 100 bars
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 more than one point (250, 450, 800 and 1300 bars with engine speed between 1400 and 2300 rpm) on the overrun
- 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
The engine ECU detects the fuel injector drift when the following conditions are met
- Atmospheric pressure higher than 799 mbar
- No pressure on the accelerator and brake pedals
- Gear engaged 3rd, 4th or 5th
- Vehicle speed higher than 40 km/h
- Engine speed between 1400 and 2300 rpm
- Particulate filter regeneration: inactive
- Coolant temperature between 70°C and 95°C
- Air temperature higher than 5°C
- Fuel temperature between 20°C and 80°C
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
Conditions for activation of the measuring for mixture adaptation
The strategy for adaptation of the mixture is activated depending on the following conditions
- "nominal" or "hot" combustion mode
- Activation phase: egr
- Coolant temperature between 47°C and 100°C
- Air temperature between - 20°C and 40°C
- Fuel temperature between - 20°c and 100°c
- Atmospheric pressure between 900 mbar and 1100 mbar
- The measured lambda is between 1 and 4,5
Start of injection
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 "b"
- The main fuel injection is positioned in the range "c"
- The fuel post-injections are positioned in the range "d"
Specificities
The engine ECU determines the moment of injection as a function of the following parameters
- Information from the camshaft sensor
- 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
During the particle emission filter regeneration phase
- The engine ECU retards the injection
- The combustion terminates in the catalytic converter, which increases the temperature of the exhaust gases
Number of fuel injections
General
"E" top dead centre
"F" crankshaft angle
"e" first pre-injection
"f" second pre-injection
"g" main injection
"h" "split" injection
"j" first post-injection
"k" second post-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)
The post-injection, used on vehicles that have a particle filter, consists of injecting a quantity of fuel during the exhaust phase in order to increase the temperature of the exhaust gases
The increase in the temperature of the exhaust gases enables the destruction of the particulates that are retained in the particle filter
The two post-injections are used from the pre-defined idle speed up to an engine speed of 1250 rpm under light load
NoteThe quantity of fuel needed for one engine cycle is spread over the 3 types of injection
Specificities
The engine ECU can order up to 6 injections per engine cycle
- 4 injections; engine idling (2 pre-injections; 1 main injection; 1 post-injection)
- 4, 5 or 6 injections; engine under load (1 or 2 pre-injections; 1 or 2 main injections; 1 or 2 post-injections)
- 3, 4, 5 or 6 injections in particle filter regeneration (1 or 2 pre-injections; 1 or 2 main injections; 1 or 2 post-injections)
Example of the changes in the number of injections per cycle
"T" Torque indicated
"N" engine speed
"G" double pilot injection zone
"H" single pilot injection zone
"J" zone without pilot injection
NoteThe indicated torque corresponds to the torque provided by the combustion of fuel, the actual torque corresponds to the indicated torque minus the various losses (piston friction losses, heat losses, etc.)
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
- Engine speed higher than 6000 rpm for at least 2 seconds
- Injection cut off (foot off)
- Difference between the reference turbocharging pressure and the measured turbocharging pressure more than 1500 mbars
- Lambda value less than 1.1
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
- Forced closure of the air mixer
- Cutting of the fuel injection
Once the engine has cut out, the engine ECU authorises restarting in "Limp Home" downgrade mode only (maximum engine speed at 1300 rpm)