Diagnostic system for a secondary air supplier in an engine

Claim 2

A diagnostic system for a secondary air supplier in an engine, the engine including an intake passage and an exhaust passage, the secondary air supplier including an air supply unit for supplying secondary air from the intake passage to the exhaust passage, for mixing with existing exhaust gas, and for changing an air-fuel ratio of the exhaust gas; a detection unit for detecting a condition of the engine; and a control unit for controlling the air supply unit in accordance with the engine condition, the diagnostic system comprising: command means for instructing the secondary air supplier to supply air to the exhaust passage for a predetermined period of time; first detection means for detecting the air-fuel ratio (A/F) of the exhaust gas within the exhaust passage; second detection means for detecting whether said air-fuel ratio indicates a lean condition of the exhaust gas; measuring means for measuring a lean period, during which said second detection means continuously detects said lean condition, while the secondary air supplier supplies air in response to an instruction from said command means; diagnostic means for determining the condition-of the secondary air supplier, said diagnostic means determining that the air supplier is malfunctioning, when a ratio of said lean period to said predetermined period of time is smaller than a predetermined ratio.

Claim 3

The diagnostic system according to claim 1, wherein said predetermined ratio is about 80 percent.

Claim 4

The diagnostic system according to claim 1, wherein said predetermined period of time is around three seconds.

Claim 5

The diagnostic system according to claim 1, for use when the engine is in a warm condition.

Claim 6

The diagnostic system according to claim 1, whereby the diagnosis of the secondary air supplier is performed in the condition where air-fuel ratio should be a rich condition.

Claim 7

The diagnostic system according to claim 1, wherein the secondary air supplier includes: a passage for connecting the intake passage and the exhaust passage; and an air pump provided along said passage.

Claim 8

The diagnostic system according to claim 1, wherein the secondary air supplier includes: a passage for connecting the intake passage and the exhaust passage; switch means provided along said passage, for switching between a first position, where air is allowed to flow along said passage, and a second position, where air is prohibited from flowing along said passage; and valve means for controlling said switch means.

Claim 11

The method according to claim 8, wherein said predetermined ratio is about 80 percent.

Claim 12

The method according to claim 8, wherein said predetermined period of time is around three seconds.

Claim 13

The method according to claim 8, for use when the engine is in a warm condition.

Claim 14

The method according to claim 8, whereby the diagnosis of the secondary air supplier is performed in the condition where air-fuel ratio should be a rich condition.

Claim 15

A diagnostic system for a secondary air supplier in an engine, the engine including an intake passage and an exhaust passage, the secondary air supplier including an air supply unit for supplying secondary air from the intake passage to the exhaust passage, for mixing with existing exhaust gas, and for changing an air-fuel ratio of the exhaust gas; a detection unit for detecting a condition of the engine; a control unit for controlling the air supply unit in accordance with the engine condition; and the secondary air being supplied to the exhaust passage when the engine is in a predetermined condition, the diagnostic system comprising: first detection means for detecting the air-fuel ratio (A/F) of the exhaust gas within the exhaust passage; second detection means for detecting a lean condition of the air-fuel ratio, while the secondary air supplier supplies air to the exhaust passage; third detection means for detecting a temporary rich condition, in which the air-fuel ratio indicates a rich condition, regardless of the air supply by the secondary air supplier; measuring means for measuring a lean period, during which said second detection means continuously detects said lean condition; regulation means for regulating said measuring means, and for stopping the measurement of said lean period by said measuring means during said temporary rich condition, so as to keep a measured value of said lean period during said temporary rich condition, and said regulation means resuming the measurement of said lean period, after the completion of said temporary rich condition; and diagnostic means for determining the condition of the secondary air supplier, said diagnostic means determining that the secondary air supplier is functioning properly, when the total measured lean period exceeds a predetermined value.

Claim 16

A diagnostic system for a secondary air supplier in an engine, the engine including an intake passage and an exhaust passage, the secondary air supplier including an air supply unit for supplying secondary air from the intake passage to the exhaust passage, for mixing with existing exhaust gas, and for changing an air-fuel ratio of the exhaust gas; a detection unit for detecting a condition of the engine; a control unit for controlling the air supply unit in accordance with the engine condition; and the secondary air being supplied to the exhaust passage when the engine is in a predetermined condition, the diagnostic system comprising: first detection means for detecting the air-fuel ratio (A/F) of the exhaust gas within the exhaust passage; second detection means for detecting a lean condition of the air-fuel ratio, while the secondary air supplier supplies air to the exhaust passage; third detection means for detecting a temporary rich condition, in which the air-fuel ratio indicates a rich condition, regardless of the air supply by the secondary air supplier; measuring means for measuring a lean period, during which said second detection means continuously detects said lean condition; regulation means for regulating said measuring means, and for stopping the measurement of said lean period by said measuring means during said temporary rich condition, so as to keep a measured value of said lean period during said temporary rich condition, and said regulation means resuming the measurement of said lean period, after the completion of said temporary rich condition; and diagnostic means for determining the condition of the secondary air supplier, said diagnostic means determining that the secondary air supplier is functioning properly, when the total measured lean period exceeds a predetermined value.

Claim 17

The diagnostic system according to claim 13, wherein said predetermined value is around five seconds.

Claim 18

The diagnostic system according to claim 13, for use when the engine is in a cold condition.

Claim 19

The diagnostic system according to claim 13, wherein the secondary air supplier includes: a passage for connecting the intake passage and the exhaust passage; and an air pump provided along said passage.

Claim 20

The diagnostic system according to claim 13, wherein the secondary air supplier includes: a passage for connecting the intake passage and the exhaust passage; switch means provided along said passage, for switching between a first position, where air is allowed to flow along said passage, and a second position, where air is prohibited from flowing along said passage; and valve means for controlling said switch means.