# US 2014/0360166 A1 · Systems and methods for nox sensor diagnostics > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2014/0360166 A1 - Document ID: US20140360166A1 - Status: Published application - Kind: A1 - Application number: 13/914,057 - Filed: 2013-06-10 - Published: 2014-12-11 - Earliest claimed: 2013-06-10 - Assignees: Cummins Emission Solutions Inc. - Applicants: Cummins Emission Solutions, Inc. - Inventors: Archana Chandrasekaran; Xiao Lin - Web page: https://patentgrep.com/patent/US20140360166A1 ## CPC - F01N 11/00: Monitoring or diagnostic devices for exhaust-gas treatment apparatus - F01N 3/208: {Control of selective catalytic reduction [SCR], e.g. by adjusting the dosing of reducing agent} - F02D 41/146: {the characteristics being an NOx content or concentration} - F02D 41/1463: {of the exhaust gases downstream of exhaust gas treatment apparatus} - F02D 41/1465: {with determination means using an estimation} - F02D 41/222: {relating to the failure of sensors or parameter detection devices} - F01N 2560/026: for measuring or detecting NOx - F01N 2900/0416: using the state of a sensor, e.g. of an exhaust gas sensor - Y02T 10/12: Improving ICE efficiencies - Y02T 10/40: Engine management systems - F01N: GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL-COMBUSTION ENGINES (arrangements in connection with gas exhaust of propulsion units in vehicles B60K13/00; combustion-air intake silencers specially adapted for, or arranged on, internal-combustion engines F02M35/00; protecting against, or damping, noise in general G10K11/16) - F02D: CONTROLLING COMBUSTION ENGINES (vehicle fittings, acting on a single sub-unit only, for automatically controlling vehicle speed B60K31/00; conjoint control of vehicle sub-units of different type or different function, road vehicle drive control systems for purposes other than the control of a single sub-unit B60W) - Y02T: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION ## Abstract Systems and methods are disclosed for diagnosing gain rationality of an NOx sensor that is downstream of a selective catalytic reduction (SCR) catalyst. Sensor diagnostics are performed while maintaining reductant dosing to the SCR catalyst. ## Claims ### Claim 1 A method, comprising: setting a diagnostic dosing command for injection of reductant at an ammonia to oxides of nitrogen (NOx) ratio (ANR) rate that is substantially less than a stoichiometric ANR rate; depleting reductant deposits and reductant storage of a selective catalytic reduction (SCR) catalyst with exhaust gas from an internal combustion engine while injecting reductant into the exhaust gas upstream of the SCR catalyst according to the diagnostic dosing command; while providing reductant to the SCR catalyst at the reductant dosing command and after depleting reductant storage with the exhaust gas: determining an engine-out NOx amount; determining an estimated system-out NOx amount from the engine-out NOx amount and the ANR rate; comparing a measured system-out NOx amount from a system-out NOx sensor downstream of the SCR catalyst with the estimated system-out NOx amount; and determining a fault condition of the system-out NOx sensor in response to the comparing. ### Claim 2 (depends on 1) The method of claim 1, wherein before setting the diagnostic doser command, further comprising determining a temperature of the exhaust gas meets an exhaust gas temperature target. ### Claim 3 (depends on 2) The method of claim 2, wherein before setting the diagnostic doser command, further comprising determining a flow of the exhaust gas meets an exhaust gas flow target. ### Claim 4 (depends on 3) The method of claim 3, wherein the exhaust gas temperature target and the exhaust gas flow target each include a minimum threshold. ### Claim 5 (depends on 1) The method of claim 1, wherein before determining the estimated system-out NOx amount, further comprising determining whether the internal combustion engine is producing greater than a threshold amount of accumulated NOx, and in response to the engine producing greater than the threshold amount of accumulated NOx aborting determining the fault condition. ### Claim 6 (depends on 1) The method of claim 1, wherein the ANR rate is between 0.1 and 0.3. ### Claim 7 (depends on 1) The method of claim 1, wherein the ANR rate is about 0.2. ### Claim 8 (depends on 1) The method of claim 1, wherein comparing the measured system-out NOx amount with the estimated system-out NOx amount includes determining a gain error from a ratio of the measured system-out NOx amount to the estimated system-out NOx amount. ### Claim 9 (depends on 8) The method of claim 8, wherein determining the fault condition of the system-out NOx sensor includes setting a fault if the gain error is less than 0.7. ### Claim 10 A method, comprising: meeting phase one conditions of a system-out NOx sensor diagnostic procedure by determining an exhaust gas temperature of an exhaust gas produced by an internal combustion engine satisfies an exhaust gas temperature target while injecting a reductant into the exhaust gas so that a selective catalytic reduction (SCR) catalyst receiving the exhaust gas operates to meet oxides of nitrogen (NOx) emissions criteria; after meeting phase one conditions, meeting phase two conditions of the diagnostic procedure by determining the exhaust gas temperature satisfies the exhaust gas temperature target and an exhaust gas flow of the exhaust gas satisfies an exhaust gas flow target; after meeting phase two conditions, determining a diagnostic dosing command in response to an ammonia to NOx ratio (ANR) rate that is less than a stoichiometric ANR rate; depleting reductant storage of the SCR catalyst with the exhaust gas from the internal combustion engine while injecting reductant into the exhaust gas according to the diagnostic dosing command; after depleting reductant storage of the SCR catalyst, meeting phase three conditions of the diagnostic procedure by determining the exhaust gas flow satisfies the exhaust gas flow target; after meeting phase three conditions, determining a gain error of a system-out NOx sensor located downstream of the SCR catalyst while injecting reductant into the exhaust gas according to the diagnostic dosing command; and determining a fault condition of the system-out NOx sensor in response to the comparing. ### Claim 11 (depends on 10) The method of claim 10, wherein determining the gain error includes comparing a measured system-out NOx amount from the system-out NOx sensor with an estimated system-out NOx amount. ### Claim 12 (depends on 11) The method of claim 11, wherein the estimated system-out NOx amount is determined from an engine-out NOx amount and the ANR rate. ### Claim 13 (depends on 10) The method of claim 10, wherein determining the gain error includes determining an average ratio of a measured system-out NOx amount from the system-out NOx sensor to an estimated system-out NOx amount over a time period. ### Claim 14 (depends on 10) The method of claim 10, wherein determining the diagnostic dosing command includes setting the diagnostic dosing command to an ANR rate that is less than 0.5. ### Claim 15 (depends on 10) The method of claim 10, wherein determining the diagnostic dosing command includes setting the diagnostic dosing command at an ANR rate that is about 0.2. ### Claim 16 (depends on 10) The method of claim 10, wherein determining the fault condition of the system-out NOx sensor includes setting a fault if the gain error is less than 0.7. ### Claim 17 (depends on 10) The method of claim 10, further comprising determining whether the internal combustion engine has produced greater than a threshold amount of accumulated NOx, during phase two and phase three and in response to the engine producing greater than the threshold amount of accumulated NOx aborting determining the fault condition. ### Claim 18 (depends on 10) The method of claim 10, wherein depleting reductant storage includes depleting reductant deposits. ### Claim 19 A system, comprising: an internal combustion engine operable to produce an exhaust gas; an exhaust path connected to the internal combustion engine, the exhaust path including a selective catalytic reduction (SCR) catalyst and a system-out oxide of nitrogen (NOx) sensor downstream of the SCR catalyst; a reductant system including a reductant storage tank and a reductant injector connected to the reductant storage tank that is configured to receive reductant from the reductant storage tank and supply reductant to the exhaust path upstream of the SCR catalyst; a controller, including: a diagnostic staging module configured to determine a temperature of the exhaust gas satisfies an exhaust gas temperature target and to determine a flow of the exhaust gas satisfies an exhaust gas flow target; a diagnostic dosing rate module configured to provide a diagnostic dosing command to the reductant injector according to an ammonia to NOx ratio (ANR) rate that is substantially less than a stoichiometric ANR rate when the exhaust gas temperature and exhaust gas flow targets are satisfied, wherein the diagnostic dosing rate module is further configured to provide the diagnostic dosing command to inject reductant during depletion of reductant in the exhaust path with the exhaust gas; a system-out NOx sensor diagnostic module configured to, after depletion of the reductant, compare a measured system-out NOx amount from the system-out NOx sensor with an estimated system-out NOx and to provide a fault setting for the system-out NOx sensor in response to the comparison. ### Claim 20 (depends on 19) The system of claim 19, wherein the system-out NOx sensor diagnostic module is configured to determine a gain error of the system-out NOx sensor from a ratio of the measured system-out NOx amount to the estimated system-out NOx amount. ### Claim 21 (depends on 20) The system of claim 20, wherein the system-out NOx sensor diagnostic module is configured to determine the estimated system-out NOx amount from a measurement of an engine-out NOx amount by a sensor upstream of the SCR catalyst and the ANR rate. ### Claim 22 (depends on 19) The system of claim 19, wherein the reductant system includes a doser tip in the exhaust path that is connected to the reductant injector. ### Claim 23 (depends on 19) The system of claim 19, wherein the system-out NOx sensor diagnostic module is further configured to provide the fault setting to a diagnostic output device. ### Claim 24 (depends on 23) The system of claim 23, wherein the diagnostic output device comprises a device selected from the devices consisting of a malfunction indicator lamp, an engine controller, an aftertreatment controller, and a datalink. ### Claim 25 A method, comprising: operating an internal combustion engine in a first mode that produces exhaust gas with oxides of nitrogen (NOx) into an exhaust system including a selective catalytic reduction (SCR) catalyst; setting a diagnostic dosing command for injection of a reductant into the exhaust system at an ammonia to NOx ratio (ANR) rate that is substantially less than a stoichiometric ANR rate; operating the internal combustion engine in a second mode in which NOx production is substantially reduced from the first mode while injecting reductant into the exhaust gas upstream of the SCR catalyst according to the diagnostic dosing command; and determining a fault condition of a system-out NOx sensor downstream of the SCR catalyst while operating the internal combustion engine in the second mode and injecting reductant according to the diagnostic dosing command. ### Claim 26 (depends on 25) The method of claim 25, further comprising depleting reductant deposits and reductant storage of the SCR catalyst with exhaust gas from the internal combustion engine before determining the fault condition of the system-out NOx sensor. ### Claim 27 (depends on 26) The method of claim 26, wherein while providing reductant to the SCR catalyst at the reductant dosing command and after depleting reductant storage with the exhaust gas: determining an engine-out NOx amount; determining an estimated system-out NOx amount from the engine-out NOx amount and the ANR rate; and comparing a measured system-out NOx amount from the system-out NOx sensor downstream of the SCR catalyst with the estimated system-out NOx amount to determining the fault condition of the system-out NOx sensor.