Method of reducing the Nox content in the exhaust gas of a diesel internal combustion engine

• US 6,209,313 B1
• Filed: 11/09/1998
• Issued: 04/03/2001
• Est. Priority Date: 11/07/1997
• Status: Expired due to Fees

• Current Assignee: Siemens AG
• Original Assignee: Siemens AG
• Inventors: Weigl, Manfred, Hofmann, Lothar, Wissler, Gerhard, Pajonk, Gunther
• Primary Examiner(s): Denion, Thomas
• Assistant Examiner(s): TRAN, BINH Q
• Application Number:
  US09/188,723
• Time in Patent Office: 876 Days
• Field of Search: 60/274, 60/286, 60/303, 60/301, 60/285, 60/278, 123/698, 123/568.11
• US Class Current: 60/274
• CPC Class Codes: F01N 2430/00 Influencing exhaust purification, e.g. starting of catalytic reaction, filter regeneration, or the like, by controlling engine operating characteristics
• CPC Class Codes: F01N 2610/02 the substance being ammonia or urea
• CPC Class Codes: F01N 3/2066 Selective catalytic reduction [SCR]
• CPC Class Codes: F02D 21/08 the other gas being the exhaust gas of engine
• CPC Class Codes: F02D 2250/36 Control for minimising NOx emissions
• CPC Class Codes: F02D 31/008 for idle speed control
• CPC Class Codes: F02D 41/0235 in relation with the state of the exhaust gas treating apparatus control of exhaust gas treating apparatus per se F01N
• CPC Class Codes: F02D 41/40 with means for controlling injection timing or duration
• CPC Class Codes: Y02T 10/12 Improving ICE efficiencies
• CPC Class Codes: Y02T 10/40 Engine management systems

Abstract

Excessive NO_x emission in a diesel internal combustion engine with SCR exhaust gas treatment is detected by a control unit. The excessive NO_x emission value is determined from the catalytic-converter efficiency calculated for the metering of the reducing agent. In response, measures are taken, such as delayed start of the fuel injection, deactivation of a coasting cutoff, reducing an exhaust gas recirculation rate and/or increasing the idling speed. As a result, the NO_x content in the untreated exhaust gas drops, the catalytic-converter temperature increases more quickly after a cold start, and the NO_x emission is reduced.

Claims

1. A method of reducing a NO_x content in the exhaust gas of a diesel internal combustion engine, which comprises:

treating exhaust gas of a diesel internal combustion engine in an SCR catalytic converter, the exhaust gas having an exhaust gas mass flow;

feeding reducing agent into the exhaust gas upstream of the catalytic converter in a flow direction of the exhaust gas;

determining, with a control unit, control parameters of the diesel internal combustion engine and a respective catalytic-converter efficiency, the respective catalytic converter efficiency determined from control parameters of the diesel internal combustion engine including the exhaust gas mass flow and a measured exhaust gas temperature;

calculating a setpoint value for a reducing agent feed in dependence on the catalytic-converter efficiency; and

if the catalytic-converter efficiency drops below a predetermined value, changing the control parameters of the diesel internal combustion engine with the control unit as a function of the catalytic-converter efficiency such that NO_x in the exhaust gas upstream of the catalytic converter is reduced and the exhaust gas temperature is increased.

2. The method according to claim 1, wherein the control parameters include a start of fuel injection into the diesel internal combustion engine and an idling speed of the diesel internal combustion engine.

3. The method according to claim 1, which comprises, if the catalytic-converter efficiency drops below the predetermined value, delaying an injection instant of the fuel.

4. The method according to claim 1, which comprises, if the catalytic-converter efficiency drops below the predetermined value, increasing an idling speed of the diesel internal combustion engine.

5. The method according to claim 1, wherein the diesel internal combustion engine is operated with cutoff of the fuel feed during a coasting operation, and wherein the method further comprises deactivating the coasting cutoff if the catalytic-converter efficiency drops below the predetermined value.

6. The method according to claim 1, wherein the diesel internal combustion engine is equipped with exhaust gas recirculation, and wherein the method further comprises increasing an exhaust gas recirculation rate if the catalytic-converter efficiency drops below the predetermined value.

7. The method according to claim 1, which comprises determining the exhaust gas mass flow by a model computation incorporating an engine speed and one of an intake pressure and a boost pressure.