Method for determining a NOx concentration

• US 6,699,383 B2
• Filed: 05/28/2002
• Issued: 03/02/2004
• Est. Priority Date: 11/25/1999
• Status: Expired due to Term

• Current Assignee: Vitesco Technologies GmbH (Continental AG)
• Original Assignee: Siemens AG
• Inventors: Walde, Tim, Lemire, Bertrand
• Primary Examiner(s): Olsen, Kaj K.
• Application Number:
  US10/156,483
• Publication Number:
  US 20020179458A1
• Time in Patent Office: 644 Days
• Field of Search: 205/781, 205/783.5, 205/784, 205/784.5, 204/425, 204/426, 73/233.1, 73/233.2
• US Class Current: 205/781
• CPC Class Codes: G01N 27/4074 for detection of gases other than oxygen

Abstract

A thick-film measurement sensor includes two measurement cells and is used to measure the NOx concentration in the exhaust gas from an internal combustion engine. The 1/λ value of the exhaust gas is determined from an oxygen ion pump current flowing in the first measurement cell, for example, by a characteristic diagram, and, a measurement error, which can be used to correct the measured NOx concentration, is determined from this 1/λ value, for example, by a characteristic curve that has previously been determined in a calibration measurement. The invention is based on the discovery that the measurement error is dependent on the air ratio in the exhaust gas. If this is expressed by the 1/λ value, there is no need for a complex division calculation during the correction.

Claims

1. A method for determining the NOx concentration in an exhaust gas from an internal combustion engine, which comprises:

introducing some of the exhaust gas into a first measurement cell of a measurement sensor and establishing a first oxygen concentration in the first measurement cell through a first oxygen ion pump current;

establishing a second reduced oxygen concentration in a second measurement cell through a second oxygen pump current, the second measurement cell being connected to the first measurement cell;

measuring the NOx concentration by a third oxygen pump current from the second measurement cell;

determining from the first oxygen ion pump current an air ratio signal representing a function of a λ

value of the exhaust gas;

determining from the air ratio signal a measurement error representing a deviation of the measured NOx concentration from a true NOx concentration; and

correcting the measured NOx concentration with the measurement error.

2. The method according to claim 1, which further comprises:

determining a substantially linear relationship between 1/λ and

the measurement error in a calibration measurement by;

exposing the measurement sensor to various gas mixtures;

recording the measurement error and describing the measurement error as one of;

a characteristic diagram;

a characteristic curve; and

a functional relationship; and

varying at least the λ

value and the NOx concentration in the gas mixtures.

3. The method according to claim 1, which further comprises carrying out the correction step by correcting with at least one of multiplication/addition calculation operations and subtraction calculation operations.

4. The method according to claim 1, which further comprises using a 1/λ

value as the air ratio signal and carrying out the measurement error determining step by applying a substantially linear relationship between the 1/λ

value and the measurement error.

5. The method according to claim 1, which further comprises using one of a characteristic curve and a characteristic diagram to determine the air ratio signal from the oxygen ion pump current.