P09.40-A011-79
1 | Turbocharger | 4 | Boost pressure positioner | |
2 | Exhaust flap switchover valve | 5 | Exhaust gas turbocharger with variable turbine geometry | |
3 | Exhaust gas recirculation cooler bypass switchover valve |
Overview
This document contains information on:
Structure
Function
Structure
The exhaust gas turbocharger with variable turbine geometry (5) consists of a compressor wheel housing and a turbine wheel housing. Compressor wheel housing and turbine wheel housing are made of cast steel.
The exhaust gas turbocharger with variable turbine geometry (5) is cooled by the coolant and integrated into the engine cooling circuit. By incorporating the exhaust gas turbocharger into the oil circuit, lubrication is ensured.
The boost pressure is controlled via the boost pressure regulator (4).
The exhaust gas turbocharger with variable turbine geometry (5) is located at the rear on the combustion engine on the exhaust manifold outlet.
1. | Guide vanes "closed" |
2. | Guide vanes "opened" |
A | Compressor inlet (fresh air) |
B | Compressor outlet (pre-compressed air) |
C | Exhaust gases to turbine wheel |
D | Exhaust outlet |
a | Turbine wheel housing |
b | Turbine wheel |
c | Compressor impeller housing |
e | Control rod guide pin |
f | Adjustment ring |
g | Guide vane guide pin |
h | Guide vane |
i1 | Flow cross section with guide vanes "closed" |
i2 | Flow cross section with guide vanes "open" |
P09.40-2185-05
Function
Exhaust gas turbocharger with variable turbine geometry
The engine exhaust gases are routed via the exhaust manifold into the turbine wheel housing (a) and to the turbine wheel (b). The flow energy of the exhaust gases sets the turbine wheel (b) in rotation. The compressor wheel that is connected via the turbine shaft with the turbine wheel (b) is also driven at the same speed. The fresh air intaken by the compressor wheel is compressed and supplied to the engine. The boost pressure is regulated by adjusting the guide vanes (h), i. e. by changing the turbine geometry. The guide pin of the control rod of the boost pressure regulator turns the adjustment ring in the turbine wheel housing. Because the guide pins of the guide vanes also engage in the adjustment ring (f), all guide vanes (h) are thus simultaneously adjusted.
At low engine speed, closing the guide vanes (1) makes the flow cross-section (i1) smaller. As a result, the air flow velocity of the exhaust gas onto the turbine wheel (b) is increased, which in turn increases the rotational speed of the exhaust gas turbocharger and thus the boost pressure.
At high engine speeds, the guide vanes continue to open further (2) thereby enlarging the flow cross-section (i2). As a result, the air flow velocity of the exhaust gas onto the turbine wheel (b) is reduced. The rotational speed of the exhaust gas turbocharger can thus be adjusted and the boost pressure maintained at a constant specified value.
The adjustment of the turbine geometry is realized via an electrical actuator.
Two-stage charging
In the case of two-stage charging, two exhaust gas turbochargers of different sizes are used. The exhaust gas turbocharger with variable turbine geometry (5) supplies the engine in the low rpm range with fresh air. For the higher rpm range, the exhaust gas flap switchover valve (2) opens the supply to the exhaust gas turbocharger (1) depending on the load requirement. The exhaust gas recirculation cooler bypass switchover valve (3) controls the bypass. The boost pressure regulator (4) controls the guide vanes, and thus the flow cross-section of the exhaust gas turbocharger with variable turbine geometry (5).
The exhaust gas flap switchover valve (2) and exhaust gas recirculation cooler bypass switchover valve (3) are opened and closed by pneumatic vacuum cells.
The pneumatic vacuum cells are actuated by the combustion engine control unit via the pressure transducer.