Failure diagnostic apparatus and method for an air-fuel ratio sensor

• US 20050131601A1
• Filed: 07/22/2004
• Published: 06/16/2005
• Est. Priority Date: 12/11/2003
• Status: Active Grant

• Current Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Original Assignee: Mitsubishi Denki Kabushiki Kaisha (Mitsubishi Electric Corporation)
• Inventors: Nishimoto, Koji, Kunihiro, Mitsuyasu
• Granted Patent: US 7,536,244 B2
• Time in Patent Office: Days
• US Class Current: 701/34
• CPC Class Codes: F02D 41/1495 Detection of abnormalities in the air/fuel ratio feedback system

Abstract

A failure diagnostic apparatus is provided with an offset power source for offsetting a ground-side voltage of an air-fuel ratio sensor, an activation state judging unit for judging whether the air-fuel ratio sensor is active, a failure diagnosing unit for judging for a failure from an offset-added output signal of the air-fuel ratio sensor in a period when the activation state judging unit judges that the air-fuel ratio sensor is active, an input resistance switching unit for switching the level of an input signal from the air-fuel ratio sensor when the failure diagnosing unit has detected a failure in the air-fuel ratio sensor, and a failure state judging unit for determining a type of failure of the air-fuel ratio sensor on the basis of a voltage level obtained when the input resistance switching unit has switched the input signal level.

Claims

1. A failure diagnostic apparatus for an air-fuel ratio sensor, comprising:

an air-fuel ratio sensor attached to an exhaust pipe of an internal combustion engine, for detecting an air-fuel ratio from an oxygen concentration of exhaust gas;

an offset power source for offsetting a ground-side voltage of the air-fuel ratio sensor;

activation state judging means for judging whether the air-fuel ratio sensor is active;

failure diagnosing means for judging for a failure from an offset-added output signal of the air-fuel ratio sensor in a period when the activation state judging means judges that the air-fuel ratio sensor is active;

input resistance switching means for switching a level of an input signal from the air-fuel ratio sensor when the failure diagnosing means has detected a failure in the air-fuel ratio sensor; and

failure state judging means for determining a type of failure of the air-fuel ratio sensor on the basis of a voltage level obtained when the input resistance switching means has switched the input signal level.

2. The failure diagnostic apparatus for an air-fuel ratio sensor according to claim 1, wherein the failure diagnosing means always monitors the output signal of the air-fuel ratio sensor in the period when the activation state judging means judges that the air-fuel ratio sensor is active.

3. The failure diagnostic apparatus for an air-fuel ratio sensor according to claim 1, further comprising A/D converting means for inputting an output voltage of the air-fuel ratio sensor to the failure diagnosing means, wherein an offset voltage of the offset power source is set higher than a maximum output voltage of the air-fuel ratio sensor and a maximum offset-added output voltage of the air-fuel ratio sensor is set lower than a maximum allowable input voltage of the A/D converting means.

4. The failure diagnostic apparatus for an air-fuel ratio sensor according to claim 1, further comprising an alarm device for announcing occurrence of an abnormality or an abnormality condition when the failure diagnosing means or the failure state judging means has detected a failure in the air-fuel ratio sensor.

5. The failure diagnostic apparatus for an air-fuel ratio sensor according to claim 1, wherein a fuel supply amount of the internal combustion engine is feedback-controlled by using the offset-added output signal of the air-fuel ratio sensor.

6. A failure diagnostic method for an air-fuel ratio sensor, comprising the steps of:

an offset power source'"'"'s offsetting a ground-side voltage of the air-fuel ratio sensor that is attached to an exhaust pipe of an internal combustion engine and detects an air-fuel ratio from an oxygen concentration of exhaust gas, an offset voltage being set higher than a maximum output voltage of the air-fuel ratio sensor by a prescribed voltage;

failure diagnosing means'"'"'s judging for a failure by reading an offset-added output signal of the air-fuel ratio sensor in a period when the air-fuel ratio sensor is active;

switching a level of an input signal from the air-fuel ratio sensor by switching an input resistance when the failure diagnosing means has detected a failure in the air-fuel ratio sensor; and

failure state judging means for determining whether the air-fuel ratio sensor is in a disconnection state or a ground fault state on the basis of a voltage level of the switched input signal.

7. The failure diagnostic method for an air-fuel ratio sensor according to claim 6, wherein the offset voltage is set so that a minimum value of an offset-added output voltage of the air-fuel sensor in higher, by a prescribed voltage, than a voltage that enables detection of a ground fault in the air-fuel sensor.