Vehicle emission control typically involves an evaporative emission control system that traps fuel vapors emitted from the fuel tank in a carbon-filled (e.g., charcoal) canister. The evaporative emission control system is periodically purged by drawing fuel vapors from the canister into the engine intake system. In this manner, fuel vapors from the fuel tank are delivered to the engine for subsequent combustion. Thus, the charcoal canister absorbs gasoline vapors emitted by the fuel tank including the vapors generated during re-fueling. A purge valve allows continuous purging of the charcoal canister when the engine is running by controlling a flow of fresh ambient air through the canister and into the intake manifold.
Conventional purge valves regulate the flow rate of fuel vapors introduced into the intake system in response to the pressure difference between the intake manifold and atmosphere. Typical purge valves utilize a pulse width modulated (PWM) solenoid valve that responds to a duty cycle control signal from an engine controller unit (ECU) for selectively establishing and terminating communication between the canister and the intake system. However, the cost of a solenoid purge valve is significant in the overall cost of providing a vapor containment system.
Thus, there is a need to provide a low-cost vapor purge valve for a vapor containment system.