Method and apparatus for correcting a gas sensor response for moisture in exhaust gas

• US 6,743,352 B2
• Filed: 02/06/2002
• Issued: 06/01/2004
• Est. Priority Date: 03/21/1997
• Status: Expired due to Term

• Current Assignee: NGK Spark PLUG Company Limited
• Original Assignee: NGK Spark PLUG Company Limited
• Inventors: Ando, Masashi, Sato, Yoshikuni, Ishida, Noboru, Sugaya, Satoshi, Nadanami, Norihiko, Oshima, Takafumi, Otsuka, Takaki, Kuzuya, Yasuhisa, Okumura, Tatsuo
• Primary Examiner(s): Olsen, Kaj K.
• Application Number:
  US10/066,684
• Publication Number:
  US 20020130053A1
• Time in Patent Office: 846 Days
• Field of Search: 204/425, 204/426, 204/427, 205/781, 205/784.5, 205/785, 205/788, 73/233.1, 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 for 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 gas (NOx) in an engine exhaust gas using a gas sensor and a process of correcting the gas sensor. According to the correcting process, the amount of moisture in the exhaust gas is estimated, then a a gas concentration detection signal output by the gas sensor on the basis of an estimated amount of moisture is corrected.

Finally, the effect of the amount of moisture in the exhaust gas is removed or reduced from the detected value of gas concentration.

Claims

1. A method for detecting the concentration of a specific gas in an engine exhaust gas with a gas sensor outputting a gas concentration detection signal, comprising:

estimating the amount of moisture in the exhaust gas from engine driving conditions;

estimating an air to fuel ratio supplied to said engine to correspond to the amount of moisture in said exhaust gas; and

correcting the gas concentration detection signal output by the gas sensor based on the estimated air to fuel ratio.

2. The method as claimed in claim 1, wherein said correcting step comprises:

pre-formulating a map containing correction data for said gas concentration detection signal corresponding to said estimated ratio based on said estimated ratio, said gas concentration detection signal and true gas concentration value;

reading-out, from said map, specific correction data corresponding to said estimated ratio as determined by engine driving conditions; and

correcting said gas concentration detection signal by the read-out correction data.

3. The method as claimed in claim 1, wherein said gas sensor is a NOx sensor.

4. A method for correcting a NOx concentration detection signal output from a NOx sensor, said NOx sensor having at least two solid electrolyte oxygen ion pump cells, in which a voltage is applied across a first oxygen ion pump cell for pumping out oxygen in the measurement gas, a current corresponding to the oxygen concentration in the measurement gas is caused to flow in said first oxygen ion pump cell, a second oxygen ion pump cell decomposes NOx in the gas not pumped by the first oxygen ion pump cell to pump out dissociated oxygen, with a current corresponding to the NOx gas concentration flowing in the second oxygen ion pump cell, said method comprising:

applying voltage across the first oxygen ion pump cell for sufficiently pumping out oxygen in the measurement gas to an extent not to allow all NOx to decompose in the measurement gas;

correcting a NOx concentration detection signal corresponding to the current flowing in the second oxygen ion pump cell based on current flowing in the first oxygen ion pump cell, to thereby remove or reduce the effect of the amount of moisture in the measurement gas from the NOx gas concentration as found based on said NOx gas concentration detection signal,

said correcting step comprising;

estimating the current flowing in said first oxygen ion pump cell to correspond to the amount of the moisture in said measurement gas,

pre-formulating a map containing correction data of said NOx gas concentration detection signal corresponding to current flowing in the first oxygen ion pump cell based on the current flowing in said first oxygen ion pump cell,

reading out, from said map, pre-set correction data corresponding to current flowing in the first oxygen ion pump cell, and

correcting the NOx gas concentration detection signal by the read-out correction data.

5. The method as claimed in claim 4, which comprises applying voltage across the first oxygen ion pump cell for sufficiently pumping out oxygen in the measurement gas to an extent substantially not to allow NOx in the measurement gas to decompose.

6. An apparatus for detecting the concentration of a specific gas in an engine exhaust gas, comprising:

a gas sensor for detecting the concentration of a specific gas in an engine exhaust gas and outputting a gas concentration signal;

means for estimating the amount of moisture in the exhaust gas from driving conditions of an engine;

means for estimating an air to fuel ratio supplied to said engine to correspond to the amount of moisture in said exhaust gas;

memory means for storing a map containing correction data for said gas concentration detection signal corresponding to said estimated air to fuel ratio based on said estimated ratio, said gas concentration detection signal and true gas concentration value;

reading means for reading out, from said map, specific correction data corresponding to said estimated ratio as determined by an engine driving condition; and

correcting means for correcting said gas concentration detection signal by the read-out correction data.

7. The apparatus as claimed in claim 6, wherein said gas sensor is a NOx sensor.

8. A method for determining the NOx concentration in a measurement gas, under a varying condition of the NOx gas concentration in the measurement gas in the course that the measurement gas is allowed to travel through a flow channel facing a ceramic body having an electrically controllable conducting state of oxygen ions, comprising:

(1) introducing the measurement gas into the flow channel;

(2) forming in said flow channel a residual gas having a NOx concentration different from that before entrance into said flow channel by extracting an oxygen gas from the measurement gas of step (1) through the ceramic body to outside of the flow channel;

(3) dissociating NOx of said NOx-concentrated residual gas into nitrogen and oxygen by applying a voltage across electrodes formed on the ceramic body;

(4) measuring an electric current flowing through the ceramic body between the electrodes, said electric current being generated by the electrochemical action of the oxygen dissociated from NOx in step (3);

(5) determining a basic NOx concentration of the measurement gas, based on the electric current measured in step (4); and

(6) correcting the basic NOx concentration wherein the amount of moisture in said measurement gas is estimated from a driving condition of an engine, and said NOx concentration of step (5) is corrected depending on an estimated amount of moisture.