Air Intake And Exhaust System
Boost system
The petrol engines from the VEA family, depending on the engine variant, have a boost system that consists of only a turbo (B4204T9/T10/T11/T12/T15) or combined turbo and compressor (B4204T9, T10). Engine B4204T9 and T10 have a maximum output of 306 hp and 400 Nm of torque at 2100 r/min. In order to get the relatively small engine to deliver such a high level of torque from really low revs, a belt driven compressor driven by crankshaft is used. The compressor is used at low revs whilst the turbocharger is used at high revs. The system produces a high level of torque directly from low revs.
Air filter housing
The air filter housing has a conventional air filter with replacement interval of 60 000 km (may vary depending on market). The mass air flow (MAF) sensor is a detachable type with integrated seat in the air filter housing. The compressor engines B4204T9 and T10 have a resonator built into the upper part of the air filter housing.
- Mass airflow meter
- Resonator
- Air cleaner (ACL)
Intake manifold
The intake manifold is made of glass fibre reinforced polyamide and is screwed directly to the cylinder head with six screws. When the engine works with boosting, the primary pipe is relatively short and the collective volume rather small. The intake manifold consists of:
- Manifold pressure sensor MAP
- EVAP connection
- ETA (Electronic Throttle Actuator)
- Two of four attachments to upper engine cover
The intake manifold is sealed to the cylinder head by means of a vertical rubber gasket.
Throttle housing, ETA
Is located on the intake manifold, facing down. The charge air pipe is located with a quick coupler. The ETA regulates the amount of air for engine combustion based on the current torque demand. The throttle position is controlled by a DC motor, which is controlled by the engine control module (ECM) via a 12 V PWM signal. The direction of rotation switches via an H-bridge located in the engine control module (ECM). A potentiometer registers the position of the throttle, which is sent as an analogue 5 V signal to the engine control module (ECM).
Pressure sensor
- MAP (Manifold Absolute Pressure)
- TMAP (Temperature Manifold Absolute Pressure)
- CMAP (Compressor Manifold Air Pressure)
MAP (Manifold Absolute Pressure), intake manifold
The sensor contains a Piezo sensor (pressure) which, amongst other things, is used for the following:
- to calculate the flow in the engine, via the volumetric efficiency.
- to calculate the adaptation of the volumetric efficiency to request correct boost pressure levels.
- to estimate the stored mass in the intake manifold's volume, via the pressure, to thereby calculate the flow in the intake system.
TMAP (Temperature Manifold Absolute Pressure), ahead of the throttle ETM
The sensor contains a Piezo sensor (pressure) and NTC sensor (temperature) used for:
- adjustment of boost pressure.
- calculating the flow through the throttle ETA via pressure and temperature.
- calculating estimated stored mass in the charge air cooler's volume, which means that the flow in the intake system can be calculated.
- calculating the pressure in the manifold.
- using the actual temperature, calculate the engine's efficiency.
CMAP (Compressor Manifold Air Pressure), after compressor, engines B4204T9/T10
Is a Piezo sensor (pressure), which is used for:
- adjustment of the compressor's boost pressure.
- calculating the stored mass in the pressurized compressor volume.
Resonators
Depending on engine variant, there are up to six integrated or separate resonators in a number of places in the air distribution system.
The resonators are designed to reduce intake noise and tuned to operate within a high frequency range of 500-5000 Hz. This means that they very effectively reduce the noise from the pressure pulses produced by the compressor. This is in contrast to previously used resonators on, for example, engine D5244T10 and B6324S, both of which had resonators tuned to 100-500Hz.
Compressor
To produce an engine with high torque from very low revs, we have chosen to use a compressor belt-driven by the crankshaft. The working range of the compressor is from 0-3500 r/min of the engine. The ratio means that 3500 r/min at the crankshaft provides 23000 r/min at the compressor. At engine speeds above 3500 r/min, the compressor is always disengaged mechanically via the electrical clutch.
Compressor
- Inlet
- Exhaust
- Pinion gear
- Clutch
- Contact
- Pulley
The compressor is made by Eaton and works according to the Roots principle. A Roots compressor is basically a piston pump that moves a volume of air in pockets between the rotors from inlet to outlet with no internal compression. Instead the compressor creates boost by pushing more air into the intake manifold than the engine currently can use. This in turn creates a pressure higher than the current atmospheric pressure in the intake manifold.
The compressor is normally engaged directly from idle to ensure good response (does not apply at activated ECO+). Otherwise, engagement/disengagement is controlled strictly according to the torque request. Engagement occurs if the torque request to the engine control module (ECM) is above 130 Nm and the engine speed is less than 2400 r/min at the same time. Disengagement occurs if the torque request has decreased to less than 90 Nm.
At speeds above 2400 r/min the compressor only engages if the demand exceeds what the turbo can deliver alone. At high torque requests at speeds above 2600 r/min the compressor does not activate. The compressor can however be switched on if activation occurred earlier at an acceleration from low speed. At engine speeds above 3500 r/min, the compressor is always disengaged mechanically via the electrical clutch.
Sound insulation
To reduce noise from air currents and propulsion, all pipes are flow optimized and equipped with resonators and other sound inhibitors. There is more sound insulation on and around the compressor.
Magnetic clutch
- Gear wheel to gear unit
- Return springs (x3)
- Flange
- Friction plate
- Contact
- Coil
Clutch
In order to disengage the compressor from the crankshaft, there is a magnetic clutch. The clutch is very similar in its design to an A/C compressor clutch. In no power state, the clutch is disengaged by the return springs. During the mechanical connection of the compressor, as smooth an engagement as possible is ensured by retarding the ignition while the clutch engagement is controlled to a controlled slippage for approx. half a second. The control signal, a custom PWM signal, initially gives a strong signal to quickly move the magnetic clutch to the engaged position. Thereafter, the signal strength is reduced to allow the clutch to slip easily during the action. Exactly how the PWM signal looks depends on relevant parameters such as speed, temperature and ageing.
Check
To check for any wear on the clutch, there is an inspection hole in the bottom of the compressor housing. It is possible to check the clearance between the friction linings and clutch surface using a feeler gauge through the hole. If the check shows that there is no or not enough play, this means that the compressor is likely to engage continually, which can damage the compressor. In the event of a defective clutch, the compressor is replaced as a complete replacement part.
Bypass
When the compressor has reached its maximum speed (at 3500 engine revs), it shall be disengaged at the same time as the turbocharger takes over the task of boosting the engine. At the handover, the compressor's maximum boost pressure is approx. 0.5 bar (relative pressure). While the compressor is working, the turbo comes up to speed and, when engagement is transferred, provides approximately the same boost that came from the compressor. While the magnetic clutch mechanically disconnects from the compressor, the bypass damper is operated to open. Fresh air is then controlled directly to the turbocharger past the compressor.
Control
The ECM controls the by-pass valve's (throttle's) position via a brushless electric motor with integrated position sensor (Hall sensor). The throttle position is controlled via a 12V PWM signal. Depending on whether the throttle is to open or close, the ECM switches the polarity using an H-bridge.
In no power state, a spring keeps the throttle open. The ECM controls the throttle position continuously based on the calculation models where the air pressure upstream of the turbo must have a desired setpoint value.
When the throttle is completely closed, the air is only controlled to the compressor and when the throttle is fully open the air is controlled to the turbo without passing the compressor. When the throttle is partially open, the air is distributed to both compressor and turbo, so that the desired pressure upstream of the turbo is achieved. Note that in certain driving conditions, the air goes the back way back to the compressor.