Evaporative Emissions System: Description and Operation

Fig. 130 Evaporative System:

The evaporative emission control system stores fuel vapor generated in the fuel tank in the cannister when the engine is not running. The fuel vapor is stored in the cannister until it is drawn into the combustion chamber and burned when the engine is started.
The evaporative emission control system is duty controlled. It consists of the solenoid valve, (purge control), the charcoal cannister, the two-way check valve, the check-and cut valve, the separator, the ECU, and the input devices. The amount of evaporative gases drawn into the engine and burned is regulated by the solenoid valve.
The engine control unit detects the engines operating condition by the various input devices. It also contains preset values for the purge amount to correspond to the operating conditions, and controls the solenoid valve operation by electrical signals (duty signals) according to these values. The solenoid valve operates when the following conditions are met.

1. After the engine has warmed up.
2. Driving in gear.
3. Accelerator depressed (idle switch off).
4. Oxygen sensor functioning normally.


CHARCOAL CANNISTER

The charcoal cannister stores gasoline vapors when the engine is not running.

FUEL VAPOR SEPARATOR

The fuel vapor separator prevents fuel from flowing into the charcoal cannister.

CHECK AND CUT VALVE

The check and cut valve controls the pressure in the fuel tank.

SOLENOID VALVE (PURGE CONTROL)

The purge control solenoid valve controls the vacuum to the charcoal cannister.

ENGINE CONTROL UNIT

The engine control unit detects signals from input sensors and switches and controls the purge control solenoid valves.