# US 5,341,642 A · System for diagnosing engine exhaust gas purifying device and system for diagnosing sensor > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 5,341,642 A - Document ID: US5341642A - Status: Granted - Kind: A - Application number: 07/994,344 - Filed: 1992-12-21 - Granted: 1994-08-30 - Earliest claimed: 1991-12-20 - Assignees: Hitachi, Ltd. - Inventors: Nobuo Kurihara; Toshio Ishii; Takashi Mukaihira; Kazuya Kawano; Yutaka Takaku - Web page: https://patentgrep.com/patent/US5341642A ## CPC - G01M 15/104: {using oxygen or lambda-sensors (testing catalytic converters F01N3/18, F01N11/007)} - F01N 11/007: {the diagnostic devices measuring oxygen or air concentration downstream of the exhaust apparatus} - F01N 2550/02: Catalytic activity of catalytic converters - Y02T 10/40: Engine management systems - G01M: TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR - 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) - Y02T: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION ## Abstract A system which is capable of diagnosing the deterioration condition of an engine exhaust gas purifying device has front and rear air/fuel ratio sensors for detecting the air/fuel ratio of the exhaust gas upstream and downstream of the catalyst, an autocorrelation function calculation for calculating the autocorrelation function .phi.xx of an output signal from the front air/fuel ratio sensor to output the maximum values (.phi.xx)max of the autocorrelation function .phi.xx at predetermined intervals, each maximum value (.phi.xx)max being in each of the predetermined intervals. A cross-correlation function calculator calculates the cross-correlation function .phi.xy between the output signals from the front and rear air/fuel ratio sensors to output the maximum values (.phi.xy)max of the mutual correlation function .phi.xy at predetermined intervals, each maximum value (.phi.xy)max being in each of the predetermined intervals therefore. The ratios between the maximum values (.phi.xy)max and (.phi.xx)max (successive deterioration index .PHI..sub.i) are calculated to determine the deterioration condition of the catalyst by comparing the ratio with a predetermined reference value. ## Claims ### Claim 1 A system for diagnosing an engine exhaust gas purifying device for purifying with a catalyst an exhaust gas from an engine having an air/fuel ratio control unit for adjusting the fuel injection quantity by detecting the concentration of the oxygen or the air/fuel ratio in the exhaust gas so that a constant air/fuel ratio in the exhaust gas is maintained, comprising: a front air/fuel ratio sensor for detecting the oxygen concentration or the air/fuel ratio in the exhaust gas prior to the purification thereof with said catalyst; a rear air/fuel ratio sensor for detecting the oxygen concentration or the air/fuel ratio in the exhaust gas after the purification thereof with said catalyst; feature wave form extracting means for attenuating signals in a frequency band lower than the air/fuel ratio control frequency band of said air/fuel ratio control unit in signal outputs from said front and rear air/fuel ratio sensors; correlation function calculating means for calculating the correlation function of said signal which has passed through said feature wave form extracting means; and catalyst condition determining means for determining the deterioration condition of said catalyst based upon the value of said correlation function, whereby the engine exhaust gas purifying device is diagnosed from the deterioration condition of the catalyst which was determined by said catalyst condition determining means. ### Claim 2 (depends on 1) A system for diagnosing an engine exhaust gas purifying device as defined in claim 1 in which said correlation function calculating means includes: autocorrelation function calculating means for calculating and outputting the autocorrelation function .phi.xx of a signal derived from said front air/fuel ratio sensor among signals output from said feature wave form extracting means; cross-correlation function calculating means for calculating and outputting the cross-correlation function .phi.xy representing the cross-correlation between the signals derived from said front air/fuel ratio sensor output from said feature wave form extracting means and the signals derived from said rear air/fuel ratio sensor output from said feature wave form extracting means; and deterioration index calculating means for outputting the ratio between a value of said cross-correlation function .phi.xy and a value of said autocorrelation function .phi.xx as a successive deterioration index .PHI..sub.i ; said catalyst condition determining means having a preset reference value and being capable of determining the deterioration condition of said catalyst by comparing said reference value with said successive deterioration index .PHI..sub.i. ### Claim 3 (depends on 2) A system for diagnosing an engine exhaust gas purifying device as defined in claim 2 in which said deterioration index calculating means outputs as the successive deterioration index .PHI..sub.i at predetermined intervals the ratio between the maximum value (.phi.xy)max of said cross-correlation function .phi.xy in said predetermined interval and the maximum value (.phi.xx)max of the autocorrelation function .phi.xx in said interval. ### Claim 4 (depends on 2) A system for diagnosing an engine exhaust gas purifying device as defined in claim 2 in which said deterioration index calculating means has the capability of calculating the average value of a given number of said successive deterioration indices .PHI..sub.i which have been calculated at said intervals and outputting the average value as a final deterioration index; said catalyst condition determining means being adapted to determine the deterioration condition of the catalyst by comparing said reference value with-said final deterioration index with which said successive deterioration index .PHI..sub.i is replaced. ### Claim 5 (depends on 4) A system for diagnosing an engine exhaust gas purifying device as defined in claim 4 and further including engine operating condition detecting means for detecting the engine speed and/or the temperature of said catalyst, said deterioration index calculating means being adapted to calculate said final deterioration index by using the detection result from said operating condition detecting means as coefficients. ### Claim 6 (depends on 1) A system for diagnosing an engine exhaust gas purifying device as defined in claim 1 in which said feature wave form extracting means includes a high pass filter. ### Claim 7 A system for diagnosing an engine exhaust gas purifying device as defined in claim I in which said feature wave form extracting means includes a band pass filter. ### Claim 8 (depends on 1) A system for diagnosing an engine exhaust gas purifying device as defined in claim 1 and further including crank angle detecting means for detecting that an engine crank is at a predetermined angle, said correlation function calculating means being adapted to calculate said correlation function by using data which are output from said front and rear air/fuel ratio sensors at the time when said crank angle detecting means detects that the crank is at said predetermined crank angle. ### Claim 9 (depends on 2) A system for diagnosing an engine exhaust gas purifying device as defined-in claim 2 and-further including sensor condition determining means having a preset second reference value for determining the deterioration condition of said front air/fuel ratio sensor by comparing the value of said autocorrelation function .phi.xx with the second reference value. ### Claim 10 A system for diagnosing a sensor in an apparatus having a response characteristic of the output signal which changes with the change in the condition of the sensor per se, comprising; feature wave form extracting means for attenuating signals in a frequency band lower than a control frequency band among the output signals from said sensor; autocorrelation function calculating means for calculating and outputting the autocorrelation function .phi.xx of the output signal from said sensor, said autocorrelation function calculating means being adapted to calculate the autocorrelation function .phi.xx from the signal which has passed said feature wave form extracting means, by using data obtained at predetermined intervals among the data obtained by said sensor; sensor condition determining means having a preset reference value for determining the condition of said sensor by comparing the value of said autocorrelation function .phi.xx with said preset reference value; and means for feedback controlling the apparatus having a condition detected by said sensor in accordance with the detection result of said sensor. ### Claim 11 (depends on 10) A system for diagnosing as defined in claim 10 and further including sensor condition index calculating means which calculates at predetermined intervals the maximum value (.phi.xx)max of said autocorrelation function .phi.xx in said predetermined interval for calculating the average value of a given number of previous maximum values (.phi.xx)max and for outputting the average value as a sensor condition index; said sensor condition determining means being adapted to determine the condition of said sensor by comparing said sensor condition index with said reference value. ### Claim 12 (depends on 10) A system for diagnosing an engine exhaust gas purifying device as defined in claim 10 in which said feature wave form extracting means includes a high pass filter. ### Claim 13 (depends on 10) A system for diagnosing an engine exhaust gas purifying device as defined in claim 10 in which said feature wave form extracting means includes a band pass filter. ### Claim 14 A system for diagnosing an engine exhaust gas purifying device for purifying with a catalyst an exhaust gas from an engine having an air/fuel ratio control unit for adjusting the fuel injection quantity by detecting the concentration of the oxygen or the air/fuel ratio in the exhaust gas so that a constant air/fuel ratio in the exhaust gas is maintained, comprising: a first sensor having a response characteristic of an output signal which changes with a change in the condition of the first sensor per se, said first sensor detecting oxygen concentration or air/fuel ratio in the exhaust gas at least one of prior to and after the purification of the exhaust gas with the catalyst; a second sensor that detects oxygen concentration or air/fuel ratio in the exhaust gas at least one of prior to and after the purification of the exhaust gas with the catalyst; a processor that receives output signals from the first and second sensors, determines the deterioration condition of the catalyst from the output signals from the first and second sensors, generates signals during determination of the deterioration condition of the catalyst, and determines the condition of the first sensor based upon said generated signals. ### Claim 15 A system for diagnosing an engine exhaust gas purifying device for purifying with a catalyst an exhaust gas from an engine having an air/fuel ratio control unit for adjusting the fuel injection quantity by detecting the concentration of the oxygen or the air/fuel ratio in the exhaust gas so that a constant air/fuel ratio in the exhaust gas is maintained, comprising: a front air/fuel ratio sensor for detecting the oxygen concentration or the air/fuel ratio in the exhaust gas prior to the purification thereof with said catalyst; a rear air/fuel ratio sensor for detecting the oxygen concentration or the air/fuel ratio in the exhaust gas after the purification thereof with said catalyst; a processor coupled to receive output signals from the front and rear air/fuel ratio sensors, said processor determining the deterioration condition of the catalyst and diagnosing the engine exhaust gas purifying device based upon said deterioration condition of the catalyst, the processor including: at least one feature wave form extraction that attenuates signals in a frequency band lower than the air/fuel ratio control frequency band of the air/fuel ratio control unit in signal outputs from the front and rear air/fuel ratio sensors; and a correlation function calculator that calculates a correlation function of the signal which has passed through the feature wave form extractor. ### Claim 16 (depends on 15) The system of claim 15, wherein the feature wave form extractor includes a high pass filter. ### Claim 17 (depends on 15) The system of claim 15, wherein the feature wave form extractor includes a band pass filter. ### Claim 18 (depends on 15) The system of claim 15, further comprising an analog to digital converter coupled to the front and rear air/fuel ratio sensors and that converts analog output signals from the front and rear air/fuel ratio sensors into digital signals for processing by the processor.