DESCRIPTION
On-Board Refuelling Vapor Recovery (ORVR) system is properly designed to prevent fuel tank vapor (HC) emission during refueling at the gas station.
This system consists of fill vent valve (ORVR), fuel shut-off valve, fuel cut valve (roll over), fuel liquid/vapor separator (which is installed on the fuel tank), charcoal canister (which is mounted under the rear floor LH side member with protector), tubes and miscellaneous connections.
During refueling, the flow and column of the refueling fuel draws the ambient air into filler pipe so as not to emit fuel vapor in the air. The fuel valve and the fuel liquid/vapor separator which isolates liquid fuel ingredient and transfers the pure vapor to the carbon canister.
While the engine is operating the trapped vapor emission in the canister is drawn and fed by the intake manifold vacuum into the engine combustion chamber. According to this purge process, the carbon canister is purged and recovers its absorbing capability.
Scheme 12
Scheme 13
OPERATION
The diagnosis module comprises an electromechanically driven (1)-overpressure pump together with a (2)-change-over valve with integrated (3)-reference restriction. In the change-over valve's setting "A" as shown, the pump delivers through the reference restriction. In the other setting the pump delivers through the (4)-canister into the fuel-tank system. The engine-management system measures the pump's electrical current consumption in each setting. A comparison of the current is measured. If the electrical current consumption is identical in both settings, there is a tank-system leak which is equal to the reference restriction. In order to make the procedure independent of environmental influences and tolerances in the overpressure pump, the system performs a comparison with a reference restriction. Outside of the leakage-diagnosis mode, the change-over valve remains in the "A" setting. The canister can be regenerated via a large flow cross-section, and only an insignificant pressure loss occurs. This is advantageous above all on vehicles with high canister-regeneration rates.
Scheme 14
The fuel filler cap is equipped with a vacuum relief valve to prevent the escape of fuel vapor into the atmosphere.
Scheme 15
Exhaust emissions (CO, HC, NOx) are controlled by a combination of engine modifications and the addition of special control components.
Modifications to the combustion chamber, intake manifold, camshaft and ignition system form the basic control system.
These items have been integrated into a highly effective system which controls exhaust emissions while maintaining good driveability and fuel economy.