Methods and apparatus for measuring NOx gas concentration, for detecting exhaust gas concentration and for calibrating and controlling gas sensor

• US 6,923,902 B2
• Filed: 02/06/2002
• Issued: 08/02/2005
• Est. Priority Date: 03/21/1997
• Status: Expired due to Fees

• Current Assignee: NGK Spark PLUG Company Limited
• Original Assignee: NGK Spark PLUG Company Limited
• Inventors: Ando, Masashi, Ishida, Noboru, Sugaya, Satoshi, Nadanami, Norihiko, Oshima, Takafumi, Otsuka, Takaki, Kuzuya, Yasuhisa, Okumura, Tatsuo, Sato, Yoshikuni
• Primary Examiner(s): Olsen, Kaj K.
• Application Number:
  US10/066,638
• Publication Number:
  US 20030042151A1
• Time in Patent Office: 1,273 Days
• Field of Search: 204/424, 204/425, 204/426, 204/427, 205/781, 205/784.5, 205/785, 73/233.1, 73/233.2, 123/693, 123/694
• US Class Current: 205/781
• CPC Class Codes: F01N 11/00 Monitoring or diagnostic devices for exhaust-gas treatment apparatus , e.g. for catalytic activity safety, indicating or supervising devices for internal combustion engines F02B77/08; testing of machines G01M13/00
• CPC Class Codes: F01N 2550/02 Catalytic activity of catalytic converters
• CPC Class Codes: F01N 2550/03 of sorbing activity of adsorbents or absorbents
• CPC Class Codes: F01N 2560/026 for measuring or detecting NOx
• CPC Class Codes: F01N 2570/14 Nitrogen oxides
• CPC Class Codes: F01N 2610/03 the substance being hydrocarbons, e.g. engine fuel
• CPC Class Codes: F01N 3/0842 Nitrogen oxides
• CPC Class Codes: F01N 3/0871 Regulation of absorbents or adsorbents, e.g. purging by electrically controlling the supply of combustible mixture or its constituents only F02D41/0235
• CPC Class Codes: F01N 3/2066 Selective catalytic reduction [SCR]
• CPC Class Codes: F02D 41/146 the characteristics being an NOx content or concentration
• CPC Class Codes: F02D 41/2474 Characteristics of sensors
• CPC Class Codes: F02D 41/28 Interface circuits
• CPC Class Codes: G01N 27/4175 Calibrating or checking the analyser
• CPC Class Codes: G01N 27/419 Measuring voltages or currents with a combination of oxygen pumping cells and oxygen concentration cells
• CPC Class Codes: G01N 33/0037 NOx
• CPC Class Codes: Y02A 50/20 Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
• CPC Class Codes: Y02T 10/12 Improving ICE efficiencies
• CPC Class Codes: Y02T 10/40 Engine management systems

Abstract

A method for detecting the concentration of a specific component in gas discharged from an internal combustion engine, which includes detecting the concentration of the specific component under certain driving conditions to determine a zero point, which indicates a zero concentration of the specific component, of the detection output; calibrating the detection output of the gas sensor based on the determined zero point; and detecting the concentration of the specific component in exhaust gas based on the calibrated detection output.

Claims

1. A method for detecting the concentration of exhaust gas using a NOx sensor having first and second measurement chambers including associated first and second oxygen ion pump cells, respectively, which detects the concentration of NOx in a gas discharged from an internal combustion engine, the method comprising:

detecting oxygen concentration in a gas introduced into the first measurement chamber of the NOx sensor based on an electric current flowing through the first oxygen ion pump cell of the NOx sensor;

calibrating a detection output of the gas sensor by determining a zero point, which indicates a zero concentration of NOx, based on a detection output of the NOx sensor when the detected oxygen concentration assumes a value substantially the same as that in atmosphere, and determining the NOx concentration after the detection output has been calibrated.

2. The method as defined in claim 1,

wherein said NOx sensor has first diffusion resistance unit and a second diffusion resistance unit;

wherein said exhaust gas is diffused via said first diffusion resistance unit into said first measurement chamber, said first oxygen ion pump cell pumping out oxygen from said first measurement chamber; and

wherein the gas having the specified oxygen concentration is diffused from said first measurement chamber via said second diffusion resistance unit into said second measurement chamber;

NOx is decomposed in said second measurement chamber;

said second oxygen ion pump cell pumping out dissociated oxygen ions; and

the NOx concentration is detected from a current flowing in said second oxygen ion pump cell.

3. The method as defined in claim 1, wherein said atmosphere is atmospheric air.

4. A method for detecting the concentration of exhaust gases using a gas sensor having first and second measurement chambers including associated first and second oxygen ion pump cells, respectively, which detects the NOx concentration in a gas discharged from an internal combustion engine, comprising;

operating the internal combustion engine under a driving condition in which the NOx concentration can be estimated or in which the NOx concentration is known;

detecting oxygen concentration in a gas introduced into the first measurement chamber of the NOx sensor based on an electric current flowing through the first oxygen ion pump cell of the NOx sensor;

calibrating a detection output of said NOx sensor based on a detection output of said NOx sensor when the detected oxygen concentration assumes a value substantially the same level as that in the atmosphere; and

determining the NOx concentration after the detection output has been calibrated.

5. The method as defined in claim 4, wherein said atmosphere is atmospheric air.

6. An apparatus for detecting the NOx concentration of exhaust gases comprising:

a NOx sensor having first and second measurement chambers including associated first and second oxygen ion pump cells, respectively, for detecting the NOx concentration in a gas discharged from an internal combustion engine;

driving condition setting means for setting driving conditions for the engine which enable the NOx concentration to be estimated or which render said concentration known; and

calibration means for calibrating a detection output of said NOx sensor based on a detection output of said NOx sensor under said driving conditions as set by said driving condition setting means, said detection output being calibrated when an oxygen concentration of a gas introduced into the first measurement chamber of the NOx sensor is substantially the same as that in the atmosphere, said oxygen concentration being detected by a current flowing through the first oxygen ion pump cell of the NOx sensor.

7. The method as defined in claim 6, wherein said atmosphere is atmospheric air.

8. A method for detecting the concentration of exhaust gas using a NOx sensor which detects the concentration of a specific component in a gas discharged from an internal combustion engine, the method comprising:

calibrating detection output of the gas sensor by determining a zero point, which indicates a zero concentration of said specific component, based on a detection output of the gas sensor in atmosphere, and

detecting the concentration of said specific component after the detection output has been calibrated,

wherein said NOx sensor is mounted downstream of a NOx occlusion catalyst and wherein said zero point is calibrated based on a detection output of said NOx sensor when an air-to-fuel ratio is temporarily set to a rich side for cleaning NOx occluded in said NOx occlusion catalyst.

9. A method for detecting the concentration of exhaust gas using a NOx sensor having a detection output which detects the concentration of a specific component in a gas discharged from an internal combustion engine, the method comprising:

detecting the concentration of the specific component in atmospheric air to obtain a zero point, which indicates a zero concentration of the specific component,

calibrating the detection output of the gas sensor based on said zero point, and

detecting the concentration of said specific component in exhaust gas based on said calibrated detection output,

wherein said NOx sensor is mounted downstream of a NOx occlusion catalyst and wherein said detection output is calibrated while an air-to-fuel ratio is temporarily set to a rich side for cleaning NOx occluded in said NOx occlusion catalyst.

10. A method for detecting the concentration of exhaust gas using a NOx sensor having a detection output which detects the concentration of a NOx component in a gas discharged from an internal combustion engine, the method comprising:

detecting the concentration of the NOx component in atmospheric air to obtain a zero point, which indicates a zero concentration of the NOx component,

calibrating the detection output of the NOx sensor based on said zero point, and

detecting the concentration of said NOx component in exhaust gas based on said calibrated detection output,

wherein said NOx sensor is mounted downstream of a NOx occlusion catalyst and wherein said detection output is calibrated while an air-to-fuel ratio is temporarily set to a rich side for cleaning NOx occluded in said NOx occlusion catalyst.

11. A method for detecting the NOx concentration of exhaust gas discharged from an internal combustion engine using a NOx sensor, the method comprising:

calibrating a detection output of the NOx sensor by determining a zero point, which indicates a zero concentration of NOx, based on a detection output of the NOx sensor in atmosphere, and

detecting the NOx concentration after the detection output has been calibrated,

wherein said NOx sensor has a first measurement chamber and a second measurement chamber, a first diffusion resistance unit and a second diffusion resistance unit, and a first oxygen ion pump cell and a second oxygen ion pump cell;

wherein said exhaust gas is diffused via said first diffusion resistance unit into said first measurement chamber, said first oxygen ion pump cell pumping out oxygen from said first measurement chamber so that oxygen in the gas diffused via said first diffusion resistance unit into said first measurement chamber will be of a specified oxygen concentration; and

wherein the gas having the specified oxygen concentration is diffused from said first measurement chamber via said second diffusion resistance unit into said second measurement chamber;

NOx is decomposed in said second measurement chamber;

said second oxygen ion pump cell pumping out dissociated oxygen ions; and

the NOx concentration is detected from a current flowing in said second oxygen ion pump cell, and

wherein said NOx sensor is mounted downstream of a NOx occlusion catalyst and wherein said detection output is calibrated while an air-to-fuel ratio is temporarily set to a rich side for cleaning NOx occluded in said NOx occlusion catalyst.

12. A method for detecting the concentration of exhaust gas using a NOx sensor having first and second measurement chambers including associated first and second oxygen ion pump cells, respectively, which detects the concentration of NOx in a gas discharged from an internal combustion engine, the method comprising:

detecting oxygen concentration in a gas introduced into the first measurement chamber of the NOx sensor based on an electric current flowing through the first oxygen ion pump cell of the NOx sensor;

calibrating a detection output of the gas sensor by determining a zero point, which indicates a zero concentration of NOx, based on a detection output of the NOx sensor when the detected oxygen concentration assumes a value substantially the same as that in atmosphere, and

determining the NOx concentration after the detection output has been calibrated,

wherein said NOx sensor is mounted downstream of a NOx occlusion catalyst and wherein said zero point is calibrated based on a detection output of said NOx sensor when an air-to-fuel ratio is temporarily set to a rich side for cleaning NOx occluded in said NOx occlusion catalyst.