# US 9,518,523 B2 · Air-fuel ratio imbalance detection device for internal combustion engine > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,518,523 B2 - Document ID: US9518523B2 - Status: Granted - Kind: B2 - Application number: 14/117,489 - Filed: 2011-05-16 - Published: 2014-10-02 - Granted: 2016-12-13 - Earliest claimed: 2011-05-16 - Assignees: Toyota Jidosha Kabushiki Kaisha - Applicants: Shinji Ikeda; Takeshi Sano; Kazumasa Shimode - Inventors: Shinji Ikeda; Takeshi Sano; Kazumasa Shimode - Web page: https://patentgrep.com/patent/US9518523B2 ## CPC - F02D 41/30: Controlling fuel injection {(F02D41/182, F02D41/24 take precedence)} - F02D 35/023: {by determining the cylinder pressure} - F02D 41/0085: {Balancing of cylinder outputs, e.g. speed, torque or air-fuel ratio} - F02D 41/1454: {the characteristics being an oxygen content or concentration or the air-fuel ratio} - F02D 41/1475: {Regulating the air fuel ratio at a value other than stoichiometry} - 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) ## Abstract A plurality of cylinders are provided. An in-cylinder pressure sensor is mounted on each of the plurality of cylinders. A combustion parameter (e.g., the amount of generated heat) is calculated from the output of the in-cylinder pressure sensor. The air-fuel ratio for a cylinder is enleaned by reducing a fuel injection amount until the combustion parameter coincides with a predetermined value. Each cylinder is subjected to fuel injection amount reduction control so that the combustion parameter coincides with the predetermined value. The air-fuel ratio for each cylinder is then calculated in accordance with the reduction amount of fuel injection amount. The calculated air-fuel ratios are compared to detect an air-fuel ratio imbalance between the cylinders. ## Claims ### Claim 1 An air-fuel ratio imbalance detection device for an internal combustion engine, comprising a controller configured to perform a method including: acquiring an output from an in-cylinder pressure sensor mounted on each of a plurality of cylinders of the internal combustion engine; calculating a combustion parameter including an amount of generated heat within the plurality of cylinders based on an output of the in-cylinder pressure sensor; providing control to enlean an air-fuel ratio for each of the plurality of cylinders by reducing a fuel injection amount so that the amount of generated heat coincides with a predetermined amount of generated heat; responsive to determining that the amount of generated heat coincides with the predetermined amount of generated heat, detecting an air-fuel ratio imbalance between the plurality of cylinders based on a reduction amount of fuel injection amount, the reduction amount being provided by control that is exercised for each of the plurality of cylinders; receiving output of an air-fuel ratio sensor disposed in an exhaust path into which exhaust gas from the plurality of cylinders is introduced; and calculating the predetermined amount of generated heat with which the amount of generated heat should coincide under the control based on a ratio and an average value, the ratio being between an air-fuel ratio value that is obtained based on the output of the air-fuel ratio sensor and a predetermined lean air-fuel ratio value, the average value being an average of the amount of generated heat for the plurality of cylinders. ### Claim 2 (depends on 1) The air-fuel ratio imbalance detection device for an internal combustion engine, according to claim 1, wherein the method further includes: reducing the fuel injection amount for each of the plurality of cylinders; comparing the amount of generated heat against the predetermined amount of generated heat after a start of reduction by the reducer; and terminating the reduction by the reducer based on a result of the comparison. ### Claim 3 (depends on 2) The air-fuel ratio imbalance detection device for an internal combustion engine according to claim 2, wherein the method further includes: calculating an air-fuel ratio for a cylinder subjected to fuel injection amount reduction, based on the reduction amount of fuel injection amount from a start of the fuel injection amount reduction to an end of the fuel injection amount reduction. ### Claim 4 (depends on 2) The air-fuel ratio imbalance detection device for an internal combustion engine according to claim 2, wherein the method further includes: reducing the fuel injection amount by a predetermined amount at a beginning of fuel injection amount reduction; and increasing an amount of the reduction when the result of comparison made indicates that the amount of generated heat is greater than the predetermined amount of generated heat. ### Claim 5 (depends on 1) The air-fuel ratio imbalance detection device for an internal combustion engine, according to claim 1, wherein the method further includes: reducing the fuel injection amounts for the plurality of cylinders so that the amount of generated heat for a target cylinder coincides with a predetermined amount of generated heat, the target cylinder being selected from the plurality of cylinders; and selecting a target cylinder from the plurality of cylinders such that each of the plurality of cylinders is selected as the target cylinder at least once during a period of operation; calculating the reduction amount of fuel injection amount for the target cylinder applied to the control; acquiring a calculated value of an air-fuel ratio for the target cylinder based on the reduction amount of fuel injection amount, the calculated value of the air fuel ratio being an air fuel ratio of the target cylinder before the target cylinder is controlled; and detecting an air-fuel ratio imbalance between the plurality of cylinders based on a comparison of the calculated values of the air-fuel ratios between the plurality of cylinders. ### Claim 6 (depends on 1) The air-fuel ratio imbalance detection device for an internal combustion engine according to claim 1, wherein the combustion parameter further includes at least one of quantities selected from a group of an in-cylinder pressure, internal energy, indicated torque, indicated work, and a burning velocity, or a physical quantity correlated with at least one of the quantities selected from the group. ### Claim 7 A non-transitory computer-readable medium storing instructions that, when executed by a controller, cause the controller to perform a method comprising: acquiring an output from an in-cylinder pressure sensor mounted on each of a plurality of cylinders of an internal combustion engine; calculating a combustion parameter including an amount of generated heat within the plurality of cylinders based on an output of the in-cylinder pressure sensor; providing control to enlean an air-fuel ratio for each of the plurality of cylinders by reducing a fuel injection amount so that the amount of generated heat calculated coincides with a predetermined amount of generated heat; and responsive to determining that the amount of generated heat coincides with the predetermined amount of generated heat, detecting an air-fuel ratio imbalance between the plurality of cylinders based on a reduction amount of fuel injection amount, the reduction amount being provided by control that is exercised for each of the plurality of cylinders by the injection amount controller; receiving output of an air-fuel ratio sensor disposed in an exhaust path into which exhaust gas from the plurality of cylinders is introduced; and calculating the predetermined amount of generated heat with which the amount of generated heat should coincide under the control based on a ratio and an average value, the ratio being between an air-fuel ratio value that is obtained based on the output of the air-fuel ratio sensor and a predetermined lean air-fuel ratio value, the average value being an average of the amount of generated heat for the plurality of cylinders.