Intake System/Turbocharging
Intake System/Turbocharging
Air filter, air guide
The unfiltered raw air is drawn in under the right headlight, via the air filter housing, the air filter element to the throttle valve control unit (electronic throttle).
NOTE: The service interval of the air-cleaner element is specified in the maintenance schedule.
Pressure sensors with temperature sensor
These are sensors for detecting the air mass and the boost pressure.
The main control variables for controlling the boost are
- mass air flow and
- boost pressure.
A total of three sensors with identical functionality are used in this case.
1 Sensor for pressure downstream of throttle valve and intake air temperature
The first sensor is located downstream of the throttle valve control unit and measures the pressure downstream of the throttle valve as well as the intake air temperature. The intake air temperature sensor is a temperature sensor with negative temperature coefficient (NTC).
Signal utilisation
The signal is used to calculate the required position of the bypass valve in advance. This is necessary for regulating the desired intake manifold pressure (boost pressure). The required position of the bypass valve depends greatly on the pressure level upstream of the air-charging module.
2 Boost pressure and intake manifold temperature sensor
Two additional sensors are located in the air-charging module and measure the pressure (or boost pressure) and the air temperature downstream of the charge-air cooler of each cylinder bank.
Signal utilization
The two boost pressure sensors are used to regulate the boost pressure at the required value. The total mass air flow is also calculated in the DME control unit from these input signals. The mass air flow is an important input value of torque-based engine control, which determines the injection quantity, injection timing and ignition timing angle.
The intake air temperature sensor signal is also required:
- For activation of the pump for coolant run-on. If the temperature difference for the charge air upstream and downstream of the charge-air cooler is less than 46° F. (8° C.), the coolant pump is activated.
- For plausibility checking of the coolant pump. If the temperature difference for the charge air upstream and downstream of the charge-air cooler is less than 36° F. (2° C.), a fault in the pump is assumed. The Check Engine light (MIL) is switched on.
Effects in the event of signal failure
Failure of the intake manifold pressure sensor means that regulation of the boost pressure is not optimal, which can be experienced by the driver in the form of uneven acceleration. Boost pressure sensor failures lead to the mixture composition not being adapted across the entire load/engine speed range, which in turn has a negative impact on emissions. The Check Engine light (MIL) is therefore switched on in the event of a failure. At the same time, a fault entry is made and there is a switch to alternative data.
Load-dependent boost pressure control
Control of the air flow and boost pressure
The supercharger is driven full-time via the second groove of the belt pulley. If there were no boost pressure control available, the supercharger would always generate the maximum air flow and therefore also the maximum achievable boost pressure for the respective speed. However, as charge air is not required under all operating conditions, this would result in excessive air build-up on the pressure side of the blower. This in turn would lead to unnecessary engine load. It must therefore be possible to control the boost pressure.
The bypass valve control unit is used for boost pressure control. It is screwed into the air-charging module and connects the pressure side of the compressor with the intake side. When the bypass valve is opened, some of the delivered air volume is returned to the intake side of the supercharger via the open bypass. The function of the bypass valve is similar to a wastegate valve on a spark-ignition engine with turbocharger.
The bypass valve control unit works in combination with the throttle valve control unit (electronic throttle). With this control, particular importance was attached to achieving throttle-free operation as much as possible along with superior power development. The division of work between the two valves is shown in the illustration.
In the partial-load/intake area, the bypass valve is open (no boost pressure) and the throttle valve control unit (electronic throttle) assumes load control.
In the boost pressure area, the bypass valve assumes load control, as the electronic throttle is fully open.
Load conditions
Idle speed, partial load, overrun
At idle speed, in the partial load range and in deceleration, some of the delivered air volume is returned to the intake side through the open bypass valve. This is controlled by the electronic throttle position.
Full throttle
At full throttle, the air flows directly to the engine via the supercharger and charge-air cooler with the electronic throttle open. The desired boost pressure is now regulated by the bypass valve.
NOTE: Further information is provided in the brochure "Cayenne S Hybrid Training Information", section 1 "Combustion engine".
Bypass valve control unit
Tasks
- Regulation to the boost pressure specified by the DME control unit
- Limitation of the maximum boost pressure to 28 psi (1.9 bar) absolute pressure
Potentiometer for bypass valve
This component detects the current bypass valve position. It is installed inside the cover of the adjuster housing. Its output voltage range is between 0.5 and 4.5 V. The potentiometer is designed to be resistant to electromagnetic radiation (EMC).
Signal utilization
The feedback signal from the bypass valve position is used to define the regulator input values. It is also used to determine the adaptation values.
Effects in the event of signal failure
The valve is de-energized and moves spring-loaded to the open stop. The fault is irreversible for one driving cycle. No boost pressure is built up in this case. Neither the full power nor the full torque are available.
The component is subject to OBD, which means that the Check Engine light (MIL) is switched on in the event of a failure.
Intake manifold flaps
To improve internal mixture formation, the 3.0 l V6 DFI engine uses intake manifold flaps (S). They are located in an intermediate flange between the air-charging module and cylinder head.
The intake manifold flaps have the task of setting the air in the combustion chamber in a charge motion, thus achieving optimum mixture formation.
Valve for intake manifold flap
The intake manifold flaps, which are secured on a common shaft, are actuated by a vacuum unit (U). The required vacuum is applied by the valve (V) for the intake manifold flap. The engine control unit actuates the valve for the intake manifold flap according to the map.
Effects in the event of failure
No vacuum is applied if a valve is not actuated or is faulty. In this state, the intake manifold flaps close the duct in the cylinder head via the spring force of the vacuum unit The engine power is thus reduced.
Potentiometer for intake manifold flaps
The position of the intake manifold flaps is monitored by one sensor (P) per cylinder bank. The sensors are integrated directly in the flange of the vacuum unit. They are contactless torque angle sensors, which operate according to the Hall sender principle. They generate a voltage signal, which is evaluated by the engine control unit. The magnitude of the signal voltage depends on the opening angle of the intake manifold flap.
Signal utilisation
The signal monitors the position and is used for diagnostic purposes.
Effects in the event of signal failure
The component is subject to OBD. Incorrect positioning will be detected via diagnosis. The Check Engine light (MIL) is switched on in the event of a failure.
The engine power is reduced.