MEANS AND METHOD FOR OPERATING EVAPORATIVE EMISSION SYSTEM LEAK DETECTION PUMP.

摘要

An on-board diagnostic system for an evaporative emission control system of an internal combustion engine 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 (74) is increasingly compressed and a charge of ambient atmospheric air is created in an air pumping chamber space (62). Vacuum is then removed, and the spring (74) relaxes to force a compression stroke wherein a portion of the air charge is forced into the evaporative emission space. The pump operation is under the control of a computer that contains an algorithm for operating the pump in particular modes of operating to arrive at a decision concerning integrity of the evaporative emission space against leakage.