US 6,167,696 AGranted

Exhaust gas purification system for low emission vehicle

AssigneeFord Motor Company

InventorsFrode Maaseidvaag, Jeffrey Scott Hepburn

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Abstract

An exhaust gas purification system for a lean burn internal combustion engine including a three-way catalyst, a hydrocarbon trap downstream of the three-way catalyst, a NOx trap downstream of the hydrocarbon trap, and an electrically heated catalyst located between the hydrocarbon trap and NOx trap. In one embodiment, the NOx trap includes an integral particulate filter having alternating blocked channels extending longitudinally. The inlet channels filter particulate matter and the outlet channels have a NOx absorbent wash coat for absorbing exhaust gas NOx. A method of controlling the exhaust system during cold start engine operation is provided to reduce cold start emissions. The method further includes a control procedure for activating the electrically heated catalyst for desulfation and particulate matter burn-off.

Claims6

Dependent claims

An exhaust gas purification system for an internal combustion engine comprising:

a hydrocarbon trap;
an electrically heated catalyst located downstream of said hydrocarbon trap;
an integrated NOx trap-particulate filter downstream of said electrically heated catalyst;
first and second temperature sensors providing first and second temperature signals upstream and downstream of said electrically heated catalyst, respectively;
and
an engine control module including a central processing unit and associated memory, said central processing unit programmed to perform the following steps:
monitor the level of accumulated particulate matter in said NOx trap-particulate filter;
monitor the level of absorbed sulfur in said NOx trap-particulate filter;
and
if the total amount of particulate matter accumulated in said NOx trap-particulate filter exceeds a predetermined level, then operate the engine at a lean air-fuel setpoint, and activate said electrically heated catalyst for a first predetermined period of time, otherwise;
if the total amount of sulfur absorbed in said NOx trap exceeds a predetermined level, then operate the engine at a rich air-fuel setpoint, and activate said electrically heated catalyst for a second predetermined period of time.

8 more elements

In an internal combustion engine having an exhaust gas purification system comprising a hydrocarbon trap, an electrically heated catalyst located downstream of said hydrocarbon trap, an integrated NOx trap-particulate filter downstream of said electrically heated catalyst, first and second temperature sensors providing first and second temperature signals upstream and downstream of said electrically heated catalyst, respectively, and an engine control module including a central processing unit and associated memory, a method of purifying exhaust gas comprising the steps of:

monitoring the level of accumulated particulate matter in said NOx trap-particulate filter;
monitoring the level of absorbed sulfur in said NOx trap-particulate filter;
and
if the total amount of particulate matter accumulated in said NOx trap-particulate filter exceeds a predetermined level, then operating the engine at a lean air-fuel setpoint, and activating said electrically heated catalyst for a first predetermined period of time, otherwise;
if the total amount of sulfur absorbed in said NOx trap exceeds a predetermined level, then operating the engine at a rich air-fuel setpoint, and activating said electrically heated catalyst for a second predetermined period of time.

2 more elements

Dependencies are inferred from the claim text.