Patent ID: 6347512
Filing Date: 2002-02-19
Classification: F01N,F02D

Abstract:
A method of terminating the purge of a trap located in the exhaust path of an engine with an exhaust gas oxygen sensor located downstream of the trap, comprising a sequence of the following steps:periodically updating an estimation of the amount of NOx accumulated in the trap based on a NOx model; said NOx model comprising a plurality of adaptable parameters; initiating a purge of the trap to remove NOx when the amount of estimated NOx accumulated in the trap exceeds a predetermined amount; during purging of the trap periodically updating the estimation of the amount of NOx remaining in the trap based on the NOx model; terminating the purge and determining an estimation error based on the relationship between the estimated amount of NOx remaining in the trap and a NOx window having predetermined upper and lower threshold values; using the estimation error to update said adaptable parameters of the NOx model; and resetting the estimated amount of NOx in the trap to zero wherein the NOx model is represented by the following equations: Wnox=(a(N,P,rc,Fc)+b(N,P,rc,Fc)(&dgr;âˆ’&dgr;MBT))Wfâ€ƒâ€ƒ(1) m.nox=fc&it;Wnox&af;(1-mnoxclnt)&it;â€ƒ&it;in&it;â€ƒ&it;normal&it;â€ƒ&it;operation(2)â€ƒ{dot over (m)}nox=âˆ’Wco(N,P) in purge operationâ€ƒâ€ƒ(3)whereWf fueling rate Wnox estimate of feedgas NOx flow rate Wco estimate of feedgas CO flow rate mnox total NOx stored in LNT N engine speed P intake manifold pressure rc in-cylinder air/fuel ratio Fc in-cylinder burned gas fraction &dgr; spark timing &dgr;MBT spark timing corresponds to maximum brake torque clnt the LNT storage capacity, dependent on trap temperature fc a compounded factor of TWC conversion and LNT absorbing efficiencies and wherein the amount of NOx stored in the trap at the end of a NOx purge cycle of time interval &Dgr;p following a NOx accumulation cycle of time interval &Dgr;n is given by: mnoxe=Î¸2(1-&ee;-Î¸1&it;fc0&it;Wnox0&it;Î”nclnt0)&it;clnt0-Î¸3&it;Wco0&it;Î”pand wherein the estimation error used to adapt &thgr;1, &thgr;2, &thgr;3, is defined as: e=mnoxe-mnoxd=Î¸2(1-&ee;-Î¸1&it;fc0&it;Wnox0&it;Î”nclnt0)&it;clnt0-Î¸3&it;Wco0&it;Î”p-mnoxdwhere mnox is the NOx stored in the LNT when the sensor switches state, and where WNOx0,WCO0,fc0,clnt0 are nominal models for feedgas NOx flow rate, feedgas CO flow rate, compounded factor of TWC conversion and LNT absorbing efficiencies and the LNT storage capacity.