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Priority shift/switch valve N185

Posted: Tue Jun 23, 2009 8:21 pm
by Deylan
The priority shift valve connects the brake and clutch vacuum circuits.

When the engine is running, providing the brake servo is sufficient, the valve opens and the two vacuum circuits are shared, the electric pump is no longer required as the engine-driven vacuum pump exhaustes (provides vacuum to) both circuits. If the clutch circuit pressure drops below 0.5bar, the electric vacuum switches on, and the priority switching valve is CLOSED, thus, the electric vacuum pump provides vacuum to the clutch circuit only. If the brake circuit vacuum drops below 0.7bar whilst the engine is off in ecomatic operation, the engine is restarted immediately and the priority shift valve is closed.

When the engine is off (both by ignition and in coasting mode), the valve closes and the circuits are not connected.

Part number: 1H0 906 283 B

Re: Priority shift/switch valve N185

Posted: Wed Jun 13, 2012 10:40 pm
by Deylan
This is a logic diagram of how the ECU controls the priority shift valve according to the brake system status. It does not show how the clutch system status influences this.

Disclaimer and warning: This is NOT totally accurate both technically and operationally, and there are various other influences that are not accounted for. The actual system is far more complicated than this. This diagram also makes some assumptions.

It is for reference only.

*silent enable = Ecomatic Automatic Override without illumination of warning lamp [k111]