FUEL VAPOR LEAK DETECTION SYSTEM

摘要

Differential flow sensing through respective flow path portions of a system for detecting leakage from an evaporative emission control system. A series flow path comprises a first flow (26) sensor for sensing the entire output flow of an impeller pump (24) used to positively pressurize the system under test, a second sensor (28) in a portion of the series flow path that is downstream of the first flow sensor, and a calibrated orifice (30) downstream of the second flow sensor. A branch circuit to the evaporative emission space under leakage test tees into the aforementioned series circuit between the first flow sensor and the second flow sensor. A differential amplifier (32) receives signal from the respective sensors. Any difference in sensed flows, once the pressure has been brought to a predetermined pressure, is output by the differential amplifier to signify leakage in an amount correlated with the sensed difference in the flows.