Air-fuel ratio detecting device and method

• US 5,925,088 A
• Filed: 01/25/1996
• Issued: 07/20/1999
• Est. Priority Date: 01/30/1995
• Status: Expired due to Term

• Current Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Original Assignee: Toyota Jidosha Kabushiki Kaisha (Toyota Motor Corporation)
• Inventors: Nasu, Masahiro
• Primary Examiner(s): LOUIS JACQUES, JACQUES H
• Application Number:
  US08/591,787
• Time in Patent Office: 1,272 Days
• Field of Search: 364/431.01, 364/431.03, 364/431.04, 364/431.051, 364/431.052, 364/431.053, 364/431.061, 364/431.062, 60/276, 60/277, 60/274, 60/285, 60/684, 60/6, 123/424, 123/428, 123/493, 123/686, 123/674, 123/685, 123/694, 123/681, 123/684, 123/693, 123/697, 123/689, 123/695, 123/688, 701/101, 701/102, 701/103, 701/104, 701/105, 73/233.2, 73/25.03, 73/117.3, 73/118.2, 204/406, 204/425, 204/401, 204/410, 204/412, 204/426, 204/421
• US Class Current: 701/103
• CPC Class Codes: F02D 41/1456 with sensor output signal being linear or quasi-linear with the concentration of oxygen
• CPC Class Codes: F02D 41/1495 Detection of abnormalities in the air/fuel ratio feedback system
• CPC Class Codes: G01N 27/4065 Circuit arrangements specially adapted therefor

Abstract

An air-fuel ratio detecting device and a method capable of correctly and very precisely detecting the air-fuel ratio of an internal combustion engine. The air-fuel ratio detecting device comprises an air-fuel ratio sensor disposed in the exhaust system of an internal combustion engine, an air-fuel ratio sensor circuit which applies a voltage to the air-fuel ratio sensor, detects the current through the air-fuel ratio sensor and produces an output that varies in proportion to the magnitude of the current that is detected, and a storage means for storing the data of a conversion map which is used for calculating the air-fuel ratio of the internal combustion engine in response to the output of the air-fuel ratio sensor circuit. The air-fuel ratio detecting device further comprises a circuit error detection means for detecting an error in the output caused by the air-fuel ratio sensor circuit, and a map calibration means for calibrating the data of the conversion map stored in the storage means based upon the error in the output detected by the circuit error detection means.

Claims

1. An air-fuel ratio detecting device comprising:

an air-fuel ratio sensor composed of a solid electrolyte which is disposed in an exhaust system of an internal combustion engine and passes an electric current when a voltage is applied thereto;

an air-fuel ratio sensor circuit which applies a voltage to the air-fuel ratio sensor, detects the current and generates an output that varies in proportion to the magnitude of the current; and

storage means for storing data in a conversion map which is used to calculate an air-fuel ratio of the internal combustion engine in response to the output of the air-fuel ratio sensor circuit;

inactivity determining means for determining whether the air fuel ratio sensor is in an inactive state;

circuit error detection means for detecting an error in the output as a difference between a reference output value and an output of the air-fuel ratio sensor circuit when the air-fuel ratio sensor is determined to be in the inactive state; and

map calibration means for calibrating said conversion map so that an air-fuel ratio indicated by said conversion map is calculated based on the output value of the air-fuel ratio circuit and the error detected by said circuit error detection means.

2. An air-fuel ratio detecting device according to claim 1, wherein said inactivity determining means comprises:

a low temperature start discrimination means for determining whether the internal combustion engine is started in a low-temperature condition;

an output change rate calculation means for calculating the rate of change in the output of the air-fuel ratio sensor circuit when the internal combustion engine is started in the low-temperature condition;

an output stability determining means for determining that the output of said air-fuel ratio sensor circuit is stabilized when the rate of change becomes smaller than a predetermined value;

wherein said inactivity determining means determining that the air-fuel ratio sensor is in an inactive state when said output stability determining means determined that the output of said air-fuel ratio sensor circuit is stabilized.

3. A method for detecting an air-fuel ratio of a combustion engine using:

an air-fuel ratio sensor composed of a solid electrolyte which is disposed in the exhaust system of an internal combustion engine and passes an electric current when a voltage is applied thereto;

an air-fuel ratio sensor circuit which applies a voltage to the air-fuel sensor, detects the current and generates an output that varies in proportion to the magnitude of the current; and

a storage means for storing the data of a conversion map which is used for calculating the air-fuel ratio of the internal combustion engine in response to the output of the air-fuel ratio sensor circuit, said air-fuel ratio detecting method comprising the steps of;

determining whether the air-fuel ratio sensor is in an inactive state;

a circuit error detecting step in which an error in the output caused by the air-fuel ratio sensor circuit is detected as a difference between a reference output value and an output value of the air-fuel ratio sensor circuit when the air-fuel ratio sensor is in the inactive state, and

a map calibration step in which the data of said conversion map is calibrated so that an air-fuel ratio indicated by said conversion map is calculated based on the output value of the air-fuel ratio circuit and the error detected by said circuit error detection means.

4. A method for detecting an air-fuel ratio of a combustion engine according to claim 3, wherein said inactivity determining step comprises:

a low temperature start discrimination step in which a determination is made as to whether the internal combustion engine is started in a low-temperature condition;

an output change rate calculation step in which a determination is made of the rate of change in the output of the air-fuel ratio sensor circuit when the internal combustion engine is started in the low-temperature condition;

an output stability determining step in which it is determined that the output of said air-fuel ratio sensor circuit is stabilized when the rate of change becomes smaller than a predetermined value;

wherein it is determined in said inactivity determining step that the air-fuel ratio sensor is in an inactive state when it is determined in said output stability determining step that the output of said air-fuel ratio sensor circuit is stabilized.