Function: air supply Citroen Nemo I

Schematic diagram

Key

• "A" fresh air
• "B" hot compressed air
• "C" cooled compressed air
• "D" control vacuum
• "E" electrical links

Management of the air supply

The engine ECU adapts the mass of air entering the engine to the needs relating to the different life phases

In order to adapt the mass of air entering the engine, the engine ECU acts on the following components

• Pneumatic control of the turbocharger discharge valve to vary the pressure of the turbocharging air (via a solenoid valve)
• EGR (exhaust gas recycling) electrovalve
• Air metering unit

The flowmeter for the air mass measures the flow and the temperature of the air entering the turbocharger and transmits the information to the engine ECU

The inlet air pressure and the temperature on exit from the air metering unit are measured and transmitted to the engine ECU by the inlet air pressure and temperature sensor

The atmospheric pressure sensor is incorporated in the engine ECU

Turbo air pressure

General

At an equal temperature, the mass of air entering the cylinder increases with the turbo air pressure

The turbo air pressure delivered by the turbocharger increases with the engine speed

The engine ECU has to adapt the turbo air pressure to the user's requirements

Specificities

The engine ECU commands the control electrovalve of the turbocharger discharge valve as a function of a calculated turbo air pressure setting

The turbocharger discharge valve has no position copy sensor

The engine ECU operates the control electrovalve of the turbocharger discharge valve in order to regulate the turbo pressure in closed loop (regulated mode)

The turbo air pressure reference is calculated from the following parameters

• Engine speed
• Engine load
• Engine coolant temperature
• Inlet air temperature
• Atmospheric pressure

The following strategies are used in the event of a turbocharging pressure sensor fault

• Reduction of the turbo pressure via the control electrovalve of the turbocharger discharge valve
• Reduced fuel flow
• Cutting off of the exhaust gas recirculation (EGR) function
• Deactivation of the vehicle cruise control and speed limiter (according to model)
• The activation of the regeneration of the particle emission filter

Reference values

The maximum turbo pressure is 2,2 bars absolute pressure

Drift of the air flow sensor

The flowmeter drift causes a modification of the richness of the air/fuel mixture

The flowmeter drift is compensated by the engine ECU as a function of the richness value measured by the proportional lambda sensor

An excessive flowmeter drift causes the emission limits for the particles or pollutants, notably nitrous oxides (NOx), to be exceeded

The engine ECU calculates the flowmeter drift after each start-up

If the flowmeter drift is greater than 35%, a fault is reported

The following conditions allow the flowmeter drift to be calculated

• Exhaust gas recycling valve closed
• Fuel supply cut off (for example when the driver takes his foot off the accelerator)
• Engine speed between 1400 and 2400 revs per minute
• Engine coolant temperature higher than 80°C

The engine ECU calculates the temperature of the air inside the cylinders as well as the total mass of air taken into the cylinders as a function of the following parameters

• Turbocharger pressure
• Atmospheric pressure
• Engine speed
• Air temperature at flowmeter
• Engine coolant temperature

The engine ECU compares the total mass of inlet air calculated with the total mass of inlet air measured by the flowmeter

When the difference between these 2 values is greater than 35%, a fault is reported

The following strategies are used in the event of a fault with the flowmeter

• Reduction of the turbo pressure via the control electrovalve of the turbocharger discharge valve
• Reduced fuel flow
• Cutting off of the exhaust gas recirculation (EGR) function
• Deactivation of the vehicle cruise control and speed limiter (according to model)
• The activation of the regeneration of the particle emission filter