NOx concentration detection apparatus and NOx concentration detection method

Patent metadata

Field	Value
Publication number	US-9823220-B2
Application number	US-201213398095-A
Country	US
Kind code	B2
Filing date	Feb 16, 2012
Priority date	Feb 17, 2011
Publication date	Nov 21, 2017
Grant date	Nov 21, 2017

Abstract

An apparatus and method for individually detecting NO and NO 2 concentrations as NO X components of an object gas. An NO concentration corresponding value is obtained from a first detection element not having a reduction section. An NO concentration corresponding value is obtained from a second detection element having a reduction section, and having an NO 2 /NO sensitivity ratio greater than that of the first detection element. The difference ΔC between the NO concentration corresponding values of the two detection elements is obtained, and divided by the difference ΔS between the NO 2 /NO sensitivity ratios of the two detection elements, whereby an NO 2 concentration corresponding value is obtained. A value obtained by multiplying the NO 2 concentration corresponding value by the NO 2 /NO sensitivity ratio of the second detection element is subtracted from the NO concentration corresponding value of the second detection element, whereby an NO concentration corresponding value is obtained.

First claim

What is claimed is:

1. An NO X concentration detection apparatus comprising:
a first element section through which current corresponding to a concentration of NO X in an object gas flows and which has a first sensitivity ratio between sensitivity to NO concentration and sensitivity to NO 2 concentration;
a second element section comprising:
a second diffusion resistor section which is a porous body and restricts an amount of flow of the object gas, a reduction section which is a porous body and disposed on an upstream side of the second diffusion resistor section, said reduction section reducing NO 2 contained in the object gas to NO, and a heater for heating the reduction section, wherein the second element section is a second element section through which current corresponding to a concentration of NO X contained in the object gas flows and which has a second sensitivity ratio between sensitivity to NO concentration and sensitivity to NO 2 concentration, the second sensitivity ratio being greater than the first sensitivity ratio;
first obtaining means for obtaining a first concentration corresponding value which corresponds to a concentration of NO on a basis of a magnitude of the current flowing through the first element section;
second obtaining means for obtaining a second concentration corresponding value which corresponds to the concentration of NO on a basis of a magnitude of the current flowing through the second element section;
first calculation means for calculating a concentration difference, which is a difference between the first concentration corresponding value and the second concentration corresponding value;
second calculation means for calculating a sensitivity difference, which is a difference between the first sensitivity ratio and the second sensitivity ratio, and for calculating an NO 2 concentration corresponding value corresponding to the concentration of NO 2 in the object gas on a basis of the concentration difference and the sensitivity difference; and
third calculation means for calculating an NO concentration corresponding value corresponding to the concentration of NO in the object gas on a basis of the first concentration corresponding value or the second concentration corresponding value, and the NO 2 concentration corresponding value,
wherein a porosity of the reduction section is higher than that of the second diffusion resistor section.

2. The NO X concentration detection apparatus according to claim 1 , wherein
the first element section is a first detection element comprising a first measurement chamber into which the object gas is introduced via a first diffusion resistor section which restricts flow of the object gas therethrough, a first oxygen pump cell having a first solid electrolyte layer and a pair of first electrodes provided on inner and outer sides of the first measurement chamber, a second measurement chamber which is located downstream of the first measurement chamber and into which the object gas is introduced from the first measurement chamber, and a second oxygen pump cell having a second solid electrolyte layer and a pair of second electrodes provided on inner and outer sides of the second measurement chamber;
the second element section is a second detection element comprising a third measurement chamber into which the object gas is introduced via the second diffusion resistor section which restricts flow of the object gas therethrough, a third oxygen pump cell having a third solid electrolyte layer and a pair of third electrodes provided on inner and outer sides of the third measurement chamber, a fourth measurement chamber which is located downstream of the third measurement chamber and into which the object gas is introduced from the third measurement chamber, a fourth oxygen pump cell having a fourth solid electrolyte layer and a pair of fourth electrodes provided on inner and outer sides of the fourth measurement chamber, the reduction section provided upstream of the second diffusion resistor section, said reduction section reducing NO 2 contained in the object gas introduced into the third measurement chamber to NO, and the heater for heating the reduction section; and
the NO X concentration detection apparatus comprises
a first element control section which controls the first detection element, the first element control section controlling a supply of electric current to the first oxygen pump cell so as to pump out oxygen contained in the object gas introduced into the first measurement chamber or pump oxygen thereinto, to thereby control the oxygen concentration within the first measurement chamber to a constant level, and the first element control section applying a voltage to the second oxygen pump cell to thereby control decomposition of NO X contained in the object gas and pumping out of dissociated oxygen from the second measurement chamber,
a second element control section which controls the second detection element, the second element control section controlling a supply of electric current to the third oxygen pump cell so as to pump out oxygen contained in the object gas introduced into the third measurement chamber or pump oxygen thereinto, to thereby control the oxygen concentration within the third measurement chamber to a constant level, and the second element control section applying a voltage to the fourth oxygen pump cell to thereby control decomposition of NO X contained in the object gas and pumping out of dissociated oxygen from the fourth measurement chamber, and
a heater control section which supplies a drive current to the heater so as to heat the object gas flowing through the reduction section at least to a reduction temperature required for reducing NO 2 to NO.

3. A method for detecting NO X concentration including obtaining concentrations of NO and NO 2 contained in an object gas, which method is executed by a microcomputer provided in a detection apparatus which includes two element sections having different sensitivity ratios, each being a ratio between sensitivity to concentrations of NO and NO 2 contained in the object gas,
said method comprising:
obtaining a first concentration corresponding value corresponding to the concentration of NO on a basis of a magnitude of current flowing through a first element section having a first sensitivity ratio;
obtaining a second concentration corresponding value corresponding to the concentration of NO on a basis of a magnitude of current flowing through a second element section having a second sensitivity ratio greater than the first sensitivity ratio;
calculating a concentration difference, which is a difference between the first concentration corresponding value and the second concentration corresponding value;
calculating a sensitivity difference, which is a difference between the first sensitivity ratio and the second sensitivity ratio, and calculating an NO 2 concentration corresponding value corresponding to the concentration of NO 2 contained in the object gas on a basis of the concentration difference and the sensitivity difference; and
calculating an NO concentration corresponding value corresponding to the concentration of NO contained in the object gas on a basis of the first concentration corresponding value or the second concentration corresponding value, and the NO 2 concentration corresponding value,
wherein the second element section comprises:
a second diffusion resistor section which is a porous body and restricts an amount of flow of the object gas,
a reduction section which is a porous body and disposed on an upstream side of the second diffusion resistor section, said reduction section reducing NO 2 contained in the object gas to NO, and
a heater for heating the reduction section; and
wherein a porosity of the reduction section is higher than that of the second diffusion

Assignees

• Kato Kenji
• Shiotani Kouji
• Kawai Takeshi
• Teramoto Satoshi
• Ngk Spark Plug Co

Inventors

• Kato Kenji
• Shiotani Kouji
• Kawai Takeshi
• Teramoto Satoshi

Classifications

• G01N27/419 Primary

  Measuring voltages or currents with a combination of oxygen pumping cells and oxygen concentration cells · CPC title