Catalyst deterioration diagnosis system and catalyst deterioration diagnosis method

Patent metadata

Field	Value
Publication number	US-9891139-B2
Application number	US-201514953592-A
Country	US
Kind code	B2
Filing date	Nov 30, 2015
Priority date	Dec 3, 2014
Publication date	Feb 13, 2018
Grant date	Feb 13, 2018

Abstract

A system for diagnosing the degree of deterioration of a catalyst disposed in an exhaust path of an internal combustion engine and oxidizes or adsorbs a target gas in an exhaust gas, includes a temperature sensor measuring a temperature of the exhaust gas at the upstream from a catalyst in an exhaust path and a gas sensor detecting a target gas at the downstream of the exhaust path and outputting an output value in accordance with a concentration of the target gas, wherein a control element is configured to diagnose the degree of deterioration in the catalyst, based on at least the output value in the gas sensor, the temperature of the catalyst identified based on a measurement value in the temperature sensor, and the threshold value at the temperature of the catalyst.

First claim

What is claimed is:

1. A catalyst deterioration diagnosis system for diagnosing a degree of deterioration of a catalyst, said catalyst being disposed in an exhaust path of an internal combustion engine and oxidizing or absorbing a target gas that includes at least one of a hydrocarbon gas and a carbon monoxide gas, the target gas being contained in an exhaust gas from said internal combustion engine, said system comprising:
a temperature sensor disposed upstream from said catalyst in said exhaust path and configured to measure a temperature of said exhaust gas containing said target gas upstream from said catalyst;
a first gas sensor disposed downstream from said catalyst in said exhaust path, said first gas sensor configured to detect said target gas downstream from said catalyst and output an output value in accordance with a concentration of said target gas;
an electronic control element configured to control said catalyst deterioration diagnosis system; and
a storage part, wherein:
a threshold data describing threshold values to be used for said catalyst deterioration diagnosis according to a temperature of said catalyst is previously defined and stored in said storage part,
said electronic control element is configured to diagnose the degree of deterioration in said catalyst, based on at least said output value from said first gas sensor, the temperature of said catalyst identified based on a measurement value in said temperature sensor, and said threshold value at the temperature of the catalyst which is described in said threshold data,
when the concentration of said target gas on an upstream side of said catalyst is denoted by Nu and the concentration of said target gas on a downstream side of said catalyst is denoted by Nl, a conversion rate defined by the following calculation formula is used as an index representing a degree of oxidation or adsorption occurring in said catalyst,
Conversion rate (%)=100×( Nu−Nl )/ Nu , and

said threshold value is defined based on said calculation formula,
said internal combustion engine is capable of intentionally generating, in response to an injection instruction from said electronic control element, a diagnosis-gas atmosphere containing a target gas higher in concentration than said target gas during a steady-operation state of said internal combustion engine,
an allowable conversion rate range being a range of said conversion rate allowable in said catalyst is previously defined according to a possible temperature of said catalyst and a possible concentration range of said target gas on an upstream side of said catalyst during deterioration diagnosis,
a first value of said Nl with respect to said possible temperature of said catalyst, which is calculated by substituting, into said calculation formula, a lower limit value of said allowable conversion rate range at the temperature as said conversion rate, and an upper limit value of a range of an upstream gas concentration during a steady state being a possible concentration range of said target gas on an upstream side of said catalyst during a steady-operation state of said internal combustion as said Nu, is defined as a first said threshold value in said threshold data, and
a second value of said Nl with respect to said possible temperature of said catalyst, which is calculated by substituting, into said calculation formula, a lower limit value of said allowable conversion rate range at the temperature as said conversion rate, and an upper limit value of a range of an upstream gas concentration during diagnosis being a possible concentration range of said diagnosis-gas atmosphere on an upstream side of said catalyst as said Nu, is defined as a second threshold value, and
said electronic control element is configured to execute both a first diagnosis and a second diagnosis, and is further configured to selectively execute one of the first diagnosis and the second diagnosis,
said first deterioration diagnosis being executable at a timing when said internal combustion engine is in a state of a steady operation, which diagnoses the degree of deterioration in said catalyst, based on said output from said first gas sensor, the temperature of said catalyst at the timing identified based on a measurement value in said temperature sensor, and said first threshold value at the temperature of the catalyst which is described in said threshold data, and
said second deterioration diagnosis being executed after introducing said diagnosis-gas atmosphere into said catalyst, which diagnoses the degree of deterioration in said catalyst, based on said output value in said first gas sensor at the timing of discharging said diagnosis-gas from said catalyst, the temperature of said catalyst at the timing of introducing the said diagnosis-gas atmosphere identified based on a measurement value in said temperature sensor, and said second threshold value corresponding to the temperature of said catalyst at the timing.

2. The catalyst deterioration diagnosis system according to claim 1 ,
wherein said first gas sensor is a mixed-potential hydrocarbon gas sensor comprising a sensing electrode whose catalyst activity is disabled with said sensing electrode being formed of a Pt—Au alloy.

3. The catalyst deterioration diagnosis system according to claim 1 , further comprising a second gas sensor disposed upstream from said catalyst in said exhaust path, detecting said target gas at said upstream side and outputting an output value in accordance with a concentration of said target gas,
wherein said electronic control element is configured to diagnose the degree of deterioration in said catalyst, based on said output values in said first and second gas sensors, the temperature of said catalyst identified based on a measurement value in said temperature sensor, and said threshold value at the temperature of the catalyst which is described in said threshold data.

4. The catalyst deterioration diagnosis system according to claim 3 , the lower limit value of said allowable conversion rate range with respect to said possible temperature of said catalyst is defined as said threshold value in said threshold data, and
said electronic control element is configured to determine that deterioration exceeding an acceptable level of a catalyst occurs in said catalyst when the conversion rate calculated based on said output values in said first and the second gas sensors is smaller than said threshold value.

5. The catalyst deterioration diagnosis system according to claim 4 ,
wherein said first gas sensor is a mixed-potential hydrocarbon gas sensor comprising a sensing electrode whose catalyst activity is disabled with said sensing electrode being formed of a Pt—Au alloy.

6. The catalyst deterioration diagnosis system according to claim 3 ,
wherein said first and second gas sensors are each a mixed-potential hydrocarbon gas sensor comprising a sensing electrode whose catalyst activity is disabled with said sensing electrode being formed of Pt—Au alloy.

7. A method for diagnosing a degree of deterioration of a catalyst, said catalyst being disposed in an exhaust path of an internal combustion engine and oxidizing or absorbing a target gas that includes at least one of a hydrocarbon gas and a carbon monoxide gas, the target gas being contained in an exhaust gas from said internal combustion engine, said method performed by a catalyst deterioration diagnosis system comprising,
a temperature sensor disposed upstream from said catalyst in said exhaust path and configured to measure a temperature of said exhaust gas containing said target gas upstream from said catalyst;
a first gas sensor disposed downstream from said catalyst in said exhaust path, said first gas sensor configured to detect said target gas downstr

Assignees

• Ngk Insulators Ltd

Inventors

• Nakasone Osamu
• Hirata Noriko
• Nakayama Yuki

Classifications

• F01N3/103 Primary

  Oxidation catalysts for HC and CO only · CPC title

• F01N3/106

  Auxiliary oxidation catalysts · CPC title

• G01M15/102 Primary

  by monitoring exhaust gases · CPC title

• F02D41/1446

  the characteristics being exhaust temperatures · CPC title

• F01N2560/06

  the means being a temperature sensor · CPC title