INTEGRITY CONFIRMATION OF EVAPORATIVE EMISSION CONTROL SYSTEM AGAINST LEAKAGE

摘要

An on-board diagnostic system for an evaporative emission control system (10) of an internal combustion engine (12) powered vehicle employs a positive displacement reciprocating pump (24) to create in evaporative emission space a pressure that differs significantly from ambient atmospheric pressure. The pump (24) is powered by using engine intake manifold vacuum to force an intake stroke during which both an internal spring is increasingly compressed and a charge of ambient atmospheric air is created in an air pumping chamber space. Vacuum is then removed, and the spring relaxes to force a compression stroke wherein a portion of the air charge is forced into the evaporative emission space. The rate at which the pump reciprocates to alternately execute intake and compression strokes indicates the pressure and flow through a leak in the evaporative emission space. Detection of this rate serves as a measurement of leakage for the purpose of distinguishing integrity of the evaporative emission space from non-integrity.