ENGINE DIAGNOSTIC WITH EXHAUST GAS SAMPLING DELAY

摘要

A diagnostic method comprising the steps of: first sampling exhaust gas; implementing a forced change of engine operating condition; second sampling exhaust gas associated with said change at a delay after initiating said change, said second sampling being at a location corresponding to said delay; and comparing said first sampling and second sampling to detect a change in exhaust constituents.

主权项

1. A method of detecting degradation in a cam profile switching system of an internal combustion engine, comprising assigning a delay between commencement of a momentary engine diagnostic and detecting the corresponding exhaust emissions at a defined location downstream of combustion, the delay being determined by one of:
determining from a look-up table the transit time of exhaust gases from a combustion chamber to said location by reference to engine speed; determining from an algorithm the transit time of exhaust gases from a combustion chamber to said location by reference to engine speed; determining a number of engine revolutions corresponding to the transit time of exhaust gases from a combustion chamber to said location; determining the mass of fuel entering a combustion chamber whereby said delay corresponds to a pre-determined threshold of the integrated fuel mass; determining the mass of air entering a combustion chamber whereby said delay corresponds to a pre-determined threshold of the integrated air mass; determining the mass of air/fuel mixture entering a combustion chamber whereby said delay corresponds to a pre-determined threshold of the integrated air/fuel mass, and determining the volume of air entering a combustion chamber whereby said delay corresponds to a pre-determined threshold of the integrated air volume.