198003696 - INTRODUCTION - EVAPORATION CONTROL SYSTEM

SPECIFICATIONS

The evaporation control system is designed to prevent the fuel vapours, made up of the lightest parts of hydrocarbons that basically form in the tank, from being released into the atmosphere.

COMPOSITION

The system comprises a tank, two float valves, a two-way ventilation valve inside the fuel filler cap, an active charcoal filter, one-way safety valves and a carbon filter scavenging solenoid valve operated by the control unit.

OPERATION

The system works at high outside temperatures when the temperature of the fuel increases and as a result the tendency to evaporation also increases: in this situation the pressure inside the tank increases.In particular, even with the tank full, the float valves remain open as they are located higher than the breather pipe and consequently they always allow the fuel vapours to reach the active charcoal filter thereby preventing fuel from escaping.The fuel vapours reach the active charcoal filter when the pressure inside the tank causes the opening of the ventilation valve. This valve also allows an intake of air into the tank via the active charcoal filter if it is necessary following a decrease in the fuel level.When the engine is running, the control unit controls the active charcoal filter scavenging solenoid valve which allows the intake of vapours by the engine and the consequent scavenging of the active charcoal filter.If, as a result of a malfunction in one of the components, the pressure inside the tank increases to dangerous levels, the safety valve located in the fuel filler cap allows the pressure to be discharged outwards. If necessary, this valve can open in the opposite direction to ventilate the tank and prevent the vacuum reaching level that are too high.1. Fuel tank2. Float valves3. Activated charcoal filter4. Active charcoal filter scrubbing solenoid5. One-way valves6. Fuel vapour supply pipe to turbocharger intake7. Fuel vapour supply pipe downstream of the throttle

EVAPORATION CONTROL SYSTEM COMPONENTS

Valve assembly

The fuel vapour solenoid valve (1) is located in the lower part of the air chamber and is connected to a pipe (2) which branches into two to reach a connector (3) downstream of the throttle on one side and a connector (4) upstream of the turbocharger on the other side.This arrangement makes it possible to draw in the fuel vapours both when idling and during supercharging.The recirculation pipes are fitted with one-way safety valves (5).

Float valve

This valve is used to perform the following functions:- prevent the outflow of liquid fuel in the case of accidents where the vehicle overturns;- allow the breathing of fuel vapours from the tank to the separator and to the active charcoal filter;- allow tank ventilation if a vacuum builds up inside.This valve consists of a casing (1) and float/needle valve (2).Valve operation may be illustrated by the following scenarios that occur with different levels of fuel in the tank.Full tankIf the tank is full, the float (2) blocks the opening (3) to prevent liquid fuel from reaching the active charcoal filter.Medium fuel levelIf the level of the fuel in the tank decreases, the float (2) descends and rests by means of the side tabs (4) on the slots in the valve casing (1) opening the port (3) that can be reached by the gases via the ring section between the float (2) and the valve body inner seat (1). This allows the fuel vapours to leave the tank and reach the active charcoal filter or, through the same circuit, to ventilate the tank when the internal pressure is lower than the outside pressure.Seal in the case of roll overIf the vehicle rolls over, with the tank filled to any level, float (2) acts under its own weight and the weight of the fuel on hole (3) to prevent a dangerous outflow of fuel to the active carbon filters and the consequent risk of the vehicle catching fire.

Active charcoal filter (canister)

This is fitted to the right rear wheel arch and consists of an activated charcoal filter element that absorbs fuel vapours coming from the tank.A one-way valve (2) allows outside air (flushing air) to come in and flow over the charcoal granules to carry away the fuel vapours and convey them through the outlet (1) to the intake manifold when fuel vapour solenoid is open.

Fuel vapour solenoid valve

The solenoid valve is the normally open type of the recirculation of the fuel vapours.It is used by the control unit for flushing the canister and is fitted in the lower part of the air chamber.The solenoid valve comprises an outer plastic casing that encloses a shutter and an electromagnet.There are two connectors at the ends for connection to the evaporation control system pipes.The solenoid valve is controlled in PWM by the injection control unit depending on the mapped strategy.When the electromagnet (1) is energized it attracts the shutter (2) that overcomes the load of spring pack (3) to close the port (4) and prevent fuel vapours from passing through.If there is no power supply the solenoid valve is closed.Electrical propertiesSupply voltage: 13.5VResistance at 20°C: 26 OhmOperating frequency: up to 30 HzCurrent absorbed at 13.5V: 0.5 AElectrical connectionsPin 1, Power supply + 12VPin 2, Control to earth from injection control unit

Safety and ventilation valve

OperationThis valve is built into the fuel filler cap and performs as follows, depending on fuel pressure in the tank:- discharging the excessive pressure that is created inside the tank outwards (safety function);- it allows the flow of outside air into the tank when, as a result of the fuel consumption, an excessive vacuum is created in the tank (ventilation function).