Blow-Off Valve

Blow-Off Valve

Blow-off valve
The blow-off valve is attached directly to the exhaust turbocharger.
In order to avoid the occurrence of strong vibrations at the impeller in the case of suddenly closing of the throttle valve (e.g. during gear shift), the blow-off valve opens. This creates a circuit around the compressor. The charging pressure is diverted to the intake side of the compressor.

Functional description
The blow-off valve prevents "pumping" against the closed throttle valve, thus improving engine acoustics. In addition, the blow-off valve protects the exhaust turbocharger against damage. Another effect: the exhaust turbocharger reacts quickly when the throttle valve is opened again. Without the blow-off valve, the exhaust turbocharger would work against the ram pressure of the closed throttle valve and become slower. On opening the throttle valve, the exhaust turbocharger would react with a delay.
The engine control activates the blow-off valve.The blow-off valve has the positions: open and closed (no intermediate positions).







Structure and inner electrical connection
The blow-off valve is connected via a two-pin plug connection.
The blow-off valve is a solenoid valve. The blow-off valve is supplied with voltage via terminal 15N. Activation by the engine control occurs on the earth side.







Schematic overview and setpoint values
The blow-off valve dissipates unwanted charging pressure peaks that can occur when the throttle valve is closed.







Observe the following setpoint values for the blow-off valve:

Size Value
Voltage range 8 to 16 V

Response time at 20 C ≤40 ms
and 13 V

Power consumption at approx. 1 A
25 C and 13 V

Temperature range -40 °C to 140 °C

Diagnosis instructions

Failure of the component
If the blow-off valve fails, the following behaviour is to be expected:
- Fault entry in the engine control unit
- Emergency operation with substitute value

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