Design And Function: Turbocharger
Component location, turbo control system
- Vacuum pump
- Vacuum line
- Vacuum regulator
- Fresh air hose (from supercharger if the engine has it)
- Vacuum actuator wastegate (boost pressure control)
- Throttle shaft Wastegate
- Solenoid valve recirculation
- Connection - coolant inlet pipe
- Connection - coolant outlet pipe
In combination with the belt-driven compressor, a turbocharger with single scroll technology is used. Turbine housing and manifold are combined in one unit of welded steel. The structure is similar to the manifold on engine B4204T6 (09W46) but is built with more cast parts.
Less powerful engine variants (B4204T11/T12/T15), have a boost system consisting of only exhaust turbo. The turbochargers used on these variants, have a smaller bearing, and slightly smaller compressor and turbine sections compared to turbochargers for engines B4204T9 & T10.
Turbo control system
The petrol engine is fitted with a wastegate turbo with an electric compressor bypass. The turbocharger is cooled with coolant from the engine's coolant circuit and from the engine oil. The turbocharger wastegate is controlled by a vacuum system with vacuum from the mechanical vacuum pump and control via the vacuum regulator. Such a system provides, as opposed to a pressure controlled system, the ability to control the wastegate valve regardless of the available boost pressure. This gives better accuracy, faster control and the ability to open the wastegate valve at the appropriate time, which previously could not be controlled. For example, the catalytic converter can achieve faster heating by opening the wastegate valve at idle. The exhaust gases can then pass via the turbine housing without being slowed down by the turbine. The exhaust gases then lose less in temperature and the power losses are reduced. Unregulated is when the wastegate valve closed. In the event of a fault in the vacuum system, ETA is used with assistance from the throttle to prevent the air flow and thereby avoid a dangerous engine speed.
Relief valve
To recirculate the air at closed throttle, there is a recirculating relief valve. The valve, which is electrically controlled is similar to the bypass valve used on engine B6304T. In the event of boost in the intake manifold (boost pressure) and when the accelerator pedal is released quickly, an increasing pressure builds up that can result in noise (pulsations). The task of the relief valve is to route this pressure back to the turbocharger's inlet side.
This means that the turbo's speed is maintained and that the boost pressure is available immediately, at the same time as the noise is reduced. The air is routed back again between the mass air flow sensor and turbo compressor so as not to affect the measured mass air value. The ECM controls the valve's position on/off with 12V.