Technical Description: Purging: Notes

The illustration shows a system with vapor recirculation (ORVR) and tank integrity diagnosis.

The fuel that evaporates in the tank passes through a pipe to the EVAP canister. The active charcoal in the EVAP canister will eventually become saturated as it absorbs the hydrocarbon vapor. When the engine is started, the surrounding air is drawn through the EVAP canister via a purge valve and a non-return valve in the intake manifold. The petrol vapor is drawn with the air and burned in the engine. When the pressure in the intake manifold exceeds the barometric pressure, another non-return valve opens and purging will now take place to the suction side of the turbocharger.

With zero current, the purge valve is closed. It is powered from the main relay valve and controlled with a 16 Hz PWM from control module pin 27, 8 Hz during tank integrity diagnosis.

The pulse ratio regulates the flow so that it always constitutes a specific proportion of the total flow consumed by the engine.

If the air/fuel ratio in the flow deviates from 14.7: 1, the closed loop will be affected. However, it is not the task of closed loop to correct for the excess caused by the purge so the purge has a correction factor that is affected by the closed loop as soon as the purge starts. The entire closed loop deviation from 1.00 is transferred to the purge correction factor, which means that closed loop fluctuates around 1.00 (0%) even if the purge contains large amounts of hydrocarbons or consists of pure air.

When the purge is inactive, a factor of 1.00 is used and the entire fuel fault is corrected by the closed loop and the multiplicative and additive adaptations.

The limits for purge adaptation are 0.75 and 1.25 respectively.

The following conditions must be fulfilled before purging can be activated:

• Closed loop active.
• No fuel adaptation in progress; this takes place for 30 seconds every 5 minutes.
• Engine coolant temperature exceeds 50°C.
• If the engine coolant temperature is below 5°C when the engine is started, the vehicle speed must exceed 10 km/h.

  The function is active during the whole driving cycle and reduces the risk of noise being heard from the valve. The valve makes more noise when it is cold.

• Battery voltage below 16V.
• Tank integrity diagnosis not active.
• Engine speed exceeding 770 RPM.

The diagnostic tool shows 25% when the correction factor is 1.25 and -25% when the correction factor is 0.75.