Turbocharger System

Operation:

Idle: The engine draws-in fresh air through air filter (1). The air flows across the sensor plate of mixture control unit (2) into intake duct (3) and to compressor (4) of the turbocharger. From here, the intake air is fed to the engine by way of a pressure duct (6) through the throttle valve housing (7). The exhaust gases are routed through exhaust manifold (10) to turbine (11) of the turbocharger and from there through the catalytic converter and muffler. At idle there is no pressurization of the intake air, the engine operates as a normally aspirated engine.

The pop-off valve (5) is opened by the intake vacuum, the waste gate (15) is closed.

Partial load: When the throttle valve is open, more fuel-air mixture is drawn-in. Speed and volume of exhaust gases increases. The increasing exhaust gas volume also increases the turbocharger speed and thereby the boost pressure. Since opening of throttle valve will reduce the manifold vacuum, the pop-off valve (5) closes.

Vacuum 924 Turbo

Full load: At full load, a very large volume of exhaust gases are fed to the turbine of the turbocharger. The turbocharger speed and thereby the boost pressure will attain a maximum value. When the boost pressure increases to 0.52 bar, the waste gate (15) is opened via control line (16). A part of the exhaust gases are now routed directly into the main exhaust pipe via the waste gate line — bypassing the turbocharger turbine. The turbocharger speed and the boost pressure remain almost constant a 0.52 bar.

An electric boost pressure safety switch (24) located at pressure duct (6) switches the electric fuel pumps off when a boost pressure between 1.1 — 1.4 bar is attained. This will prevent engine damage resulting from excessive boost pressure if the waste gate should fail.

Deceleration (coasting): The throttle valve is closed during deceleration. The turbocharger would now operate against a closed throttle valve, which might result in damage to the turbocharger. To prevent such damage, a pop-off valve (5) is located between pressure and intake ducts (3/6). The vacuum established in the intake manifold when the throttle valve is closed is also present in the control line (18) and at pop-off valve (5). The pop-off valve opens and thereby establishes a bypass circuit between pressure (6) and intake duct (3).

Since the waste gate is closed, all the exhaust gases will be routed to the turbocharger turbine upon subsequent acceleration.

Air Auxiliary Porsche 924Systeme Injection Porsche 924

1

Air filter

2

Mixture control unit

3

Intake duct

4

Turbocharger (compressor)

17

Vent line

5

Pop-off valve

18

Control pressure line

6

Pressure duct

(pop-off valve)

7

Throttle valve

19

Auxiliary air regulator

8

Intake manifold

20

Deceleration valve

9

Fuel injection line

21

Line to auxiliary air

10

Exhaust manifold

regulator and

11

Turbocharger (turbine)

deceleration valve

12

Exhaust pipe

22

Connecting line

13

Catalytic converter

23

Control line

14

Muffler

24

Boost pressure control

15

Waste gate

switch

16

Control pressure line

25

Oxygen sensor

(waste gate)

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