199001838 - 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, a float valve, a two-way ventilation valve inside the fuel filler cap, a carbon filter 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 valve remains open as it is located higher than the breather pipe and it consequently always allows 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.
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
SpecificationsIt is fitted directly on the intake chamber and is operated by the injection control unit.The solenoid allows fuel vapours stored in the canister to flow through to the engine intake.If the power is off, the solenoid is closed and prevents fuel vapours from enriching the mixture excessively.OperationThe solenoid valve is operated by the control unit according to a strategy.When the electromagnet (3) is energized, it attracts valve core (1) which overcomes the loading of the spring (2) to bring the active charcoal filter into contact with the air intake manifold.
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).
