Exhaust emission control device for internal combustion engine

• US 6,263,666 B1
• Filed: 03/16/2000
• Issued: 07/24/2001
• Est. Priority Date: 03/18/1999
• Status: Expired due to Fees

• Current Assignee: Nissan Motor Co., Ltd.
• Original Assignee: Nissan Motor Co., Ltd.
• Inventors: Nishizawa, Kimiyoshi, Kubo, Kengo, Ishizuka, Yasuji
• Primary Examiner(s): Denion, Thomas
• Assistant Examiner(s): TRAN, DIEM T
• Application Number:
  US09/527,511
• Time in Patent Office: 495 Days
• Field of Search: 602/77, 602/95, 603/00, 603/01
• US Class Current: 60/277
• CPC Class Codes: F01N 13/009 having two or more separate purifying devices arranged in series
• CPC Class Codes: F01N 2250/12 absorption or adsorption, and catalytic conversion
• CPC Class Codes: F01N 2550/03 of sorbing activity of adsorbents or absorbents
• CPC Class Codes: F01N 2570/04 Sulfur or sulfur oxides
• CPC Class Codes: F01N 3/0842 Nitrogen oxides
• CPC Class Codes: F02D 2200/0808 NOx storage capacity, i.e. maximum amount of NOx that can be stored on NOx trap
• CPC Class Codes: F02D 2200/0818 SOx storage amount, e.g. for SOx trap or NOx trap
• CPC Class Codes: F02D 41/024 to increase temperature of the exhaust gas treating apparatus
• CPC Class Codes: F02D 41/028 Desulfurisation of NOx traps or adsorbent
• CPC Class Codes: F02D 41/1463 of the exhaust gases downstream of exhaust gas treatment apparatus
• CPC Class Codes: F02P 5/1506 with particular means during starting
• CPC Class Codes: Y02T 10/12 Improving ICE efficiencies
• CPC Class Codes: Y02T 10/40 Engine management systems

Abstract

An exhaust emission control device of an engine 1 comprises an NOx storage catalyst 9 which traps and stores NOx in exhaust gas and reduces the stored NOx according to an air fuel ratio of inflowing exhaust gas. A controller 6 determines conditions for discharging the SOx stored in the catalyst 9. When SOx discharge conditions are satisfied and the engine running conditions are in a predetermined SOx discharge running region, the controller 6 performs SOx discharge control of the catalyst 9. As lean air fuel ratio control is prohibited from when SOx discharge conditions are satisfied to when SOx discharge is complete, lean air fuel ratio control is prevented from taking place when the NOx trapping capacity of the catalyst 9 is insufficient, and increase of exhaust emission is thereby prevented.

Claims

1. An exhaust emission control device for an engine comprising:

an exhaust pipe,

a catalyst provided in said exhaust pipe which traps and stores NOx in exhaust gas and reduces the stored NOx according to an air-fuel ratio of the exhaust gas flowing into said catalyst,

a microprocessor programmed to;

determine whether or not conditions for discharging SOx stored in said catalyst are satisfied,

raise the temperature of said catalyst to discharge SOx when SOx discharge conditions are satisfied and the running conditions of said engine are in a predetermined SOx discharge running region, and

prohibit lean air fuel ratio running of said engine from when SOx discharge conditions are satisfied to when SOx discharge is complete, and

a sensor which detects an NOx concentration downstream of said catalyst, and wherein said microprocessor is further programmed to;

detect an NOx storage capacity of said catalyst based on said detected NOx concentration, and

prohibit lean air-fuel ratio running of said engine when an NOx storage capacity detected after SOx discharge is complete, is less than a predetermined capacity.

2. An exhaust emission control device as defined in claim 1, wherein said microprocessor is further programmed to prohibit SOx discharge control when said NOx storage capacity detected immediately after SOx discharge is complete is less than a predetermined amount.