Air Supply

Air Supply

Air supply
The 4-cylinder petrol engine is charged by an exhaust turbocharger by combining the ducts of 2 cylinders at a time separate to one another in the exhaust manifold and exhaust turbocharger. This is referred to as "twin-scroll" technology. As the gas dynamics in the exhaust manifold increase at low engine speeds, this utilizes the energy in the pulsating columns of gases more effectively. This means the maximum torque is reached at engine speeds as low as 1600 rpm. The effect is clearly evident. This makes it possible to avoid "turbo lag", a much criticized drawback, almost entirely.







Brief component description
Descriptions of the following components of the air supply are provided:

Intake air temperature pressure sensor
This combined sensor delivers the following information to the engine control system: Temperature and pressure of the charge air upstream of the throttle valve (absolute). The purpose of the intake air temperature pressure sensor is to control the charging pressure. The engine control also uses the signal from the intake-manifold pressure sensor to adjust the position of the throttle valve.

A voltage of 5 volts is supplied to the sensor by the engine control, which also provides the ground. The charging pressure information is sent to the engine control across a signal line. The signal for evaluation of the differential pressure fluctuates depending on the pressure. The measuring range of between approx. 0.5 and 4.5 volts corresponds to a charging pressure of between 0.2 bar (20 kPa) and 2.5 bar (250 kPa).
The engine control supplies the ground for the intake air temperature sensor. An additional connection is connected to a voltage divider circuit in the engine control. The resistance changes from 167 kOhms to 150 Ohms depending on temperature, which corresponds to a temperature of -40 °C to 130 °C.







The intake air temperature pressure sensor can be found in the air duct downstream of the charge air cooler.

Intake pipe pressure sensor
The intake-manifold pressure sensor measures the pressure in the differentiated air intake system (absolute). The engine control uses the signal from the intake-manifold pressure sensor to calculate the air mass drawn in. The pressure also serves as a substitute value for the load signal.
A voltage of 5 volts is supplied to the sensor by the engine control, which also provides the ground. The information is transmitted to the engine control via a signal line. The signal for evaluation fluctuates depending on the pressure. The measuring range of between approx. 0.5 and 4.5 volts corresponds to a charging pressure of between 0.2 bar (20 kPa) and 2.5 bar (250 kPa).







The intake-manifold pressure sensor can be found on the intake plenum.

Hot-film air mass meter
The hot film air mass meter is a combined sensor. The hot film air mass meter detects the actual amount of air independently from the air pressure. In conjunction with other sensors, the engine control unit calculates the amount of fuel to be injected. An intake air temperature sensor is integrated into the hot film air mass meter.
The hot film air mass meter increases the load sensing accuracy. This measure was necessary due to exhaust emissions legislation. The signal from the intake air temperature sensor is not used. Evaluation electronics evaluate the measured data in the hot film air mass meter. This enables exact detection of the air mass flowing through, including the direction of flow.
When the automatic engine start-stop function shuts the engine down, the heating for the sensor electronics is switched off to minimize oil coking.
Voltage (14 volts) is supplied to the hot film air mass meter via the engine control, which also provides the ground.







The hot film air mass meter is behind the intake silencer.

Electromotive throttle actuator
The engine control calculates the position of the throttle valve: from the position of the accelerator pedal and the torque request by other control units. The position of the throttle valve is monitored contactlessly in the electromotive throttle actuator by 2 hall effect sensors. The electromotive throttle actuator is opened or closed electrically by the engine control. The charging pressure also influences the position of the throttle valve.
A position sensor is integrated into the electromotive throttle actuator. A voltage of 5 volts is supplied to the position sensor by the engine control, which also provides the ground. 2 data lines ensure a redundant throttle valve position feedback signal to the engine control.
The servomotor that activates the throttle flap is a direct current motor. This is done using an H bridge which means the motor can also be activated in the opposing direction. The H bridge in the engine control is monitored by the diagnostic system.







The electromotive throttle actuator is secured to the intake plenum.

Blow-off valve
In order to avoid the occurrence of strong vibrations at the impeller in the case of suddenly closing of the throttle valve (e.g. during gear shift), the blow-off valve opens. This creates a circuit around the compressor. The blow-off valve prevents "pumping" against the closed throttle valve: improved engine acoustics. Additional effect: the exhaust turbocharger reacts quickly when the throttle valve is opened again. Without the blow-off valve, the exhaust turbocharger would work against the ram pressure of the closed throttle valve and become slower. On opening the throttle valve, the exhaust turbocharger would react with a delay.
Vehicle voltage is supplied to the blow-off valve via the DME main relay. The engine control activates the blow-off valve on the ground side.







The blow-off valve is attached with the wastegate valve to the exhaust turbocharger.

Exhaust turbocharger with wastegate valve
The engine features what is referred to as a "twin-scroll" exhaust turbocharger. by combining the ducts of 2 cylinders at a time separate to one another in the exhaust manifold and exhaust turbocharger: Cylinders 1 and 4, cylinders 2 and 3. As the gas dynamics in the exhaust manifold increase at low engine speeds, this utilizes the energy in the pulsating columns of gases more effectively. This means the maximum torque is reached at engine speeds as low as 1600 rpm. This makes it possible to avoid "turbo lag", a much criticized drawback, almost entirely.
The charging pressure is regulated by the engine control via a wastegate valve. The wastegate valve is adjusted pneumatically by a diaphragm box. An pressure converter applies a partial vacuum to the diaphragm box.







The exhaust turbocharger has 2 connections for cooling and 2 connections for lubricating the exhaust turbocharger. 2 connections for the engine cooling circuit and 2 connections for the oil circuit. The exhaust turbocharger is cooled by a separate pump. The engine control switches the turbocharger coolant pump on once the engine is stopped.

System functions
A description of the following system function is provided for the air supply:

Calculation of air mass
The air mass drawn in is no longer measured directly by the air mass meter, and is calculated by the engine control instead. A filling calculation (filling model) has been programmed in the engine control in order to do this. The following signals are input into this calculation:
- VANOS setting (load sensing)
- Intake air temperature (correction of air density)
- Engine speed (cylinder filling levels)
- Intake pipe vacuum (correction during throttling)
- Ambient pressure (air density divided by altitude correction)

The air mass calculated in this way is synchronized with:
- Signal from oxygen sensor (air/fuel ratio)
- Fuel injection period (fuel quantity)

If necessary, the calculated air mass is corrected. In the event of the oxygen sensor failing, a fault will be entered in the DME fault memory (air mass plausibility check). In such cases, the calculated air mass is no longer compared.

Charging pressure control
The charging pressure is adjusted with reference to a maximum pressure of 0.8 bar by the engine control via a wastegate valve.
A portion of the exhaust gases is fed via the wastegate valve to the turbine. The wastegate valve is adjusted pneumatically by a diaphragm box. The wastegate valve can be set variably. An pressure converter applies a partial vacuum to the diaphragm box.
The engine control controls the pressure converter.
An additional charging pressure control function is available. This increases the charging pressure briefly (roughly 12 seconds) by around 150 mbar. This increase in charging pressure (overboost) is available between engine speeds of roughly 1700 rpm and roughly 4500 rpm. and allows the torque and performance to be increased without changing the engine speed.







The increase in charging pressure is activated by the engine control if the accelerator pedal is depressed extremely quickly.

Idle speed control
The DSC control unit sends the driving speed signal via the engine control PT-CAN. This signal is required for several functions e.g. the idle speed control. The engine control activates the electromotive throttle actuator in order to control the idle speed. If the vehicle is not at a standstill, the idle speed is controlled with reference to a fixed value (which is slightly higher than the vehicle standstill engine speed). If the driving speed is 0 km/h, the idle speed is regulated (depending on air conditioning compressor ON, engaged drive position with automatic transmission, light on).
We can assume no liability for printing errors or inaccuracies in this document and reserve the right to introduce technical modifications at any time.