Malfunction monitoring apparatus and method for secondary air supply system of internal combustion engine

A malfunction monitoring apparatus for a secondary air supply system in an internal combustion engine, comprising:

• an air flow rate detecting device (2) for measuring the flow rate of an air flowing into an intake air path of the engine;
• a first secondary-air introducing path (32) disposed in said intake air path on the downstream side of a measuring position of the air flow rate for taking in a part of the air through said intake air path as a secondary air;
• a secondary air supply device (8) for supplying the secondary air to an exhaust gas path of the engine;
• a pressure detecting device (14) for detecting the internal pressure of an intake manifold of the engine;
• control means (3) including means for determining an intake air flow rate (Qpm) of the engine on the basis of the detected value of the internal pressure of said intake manifold and means for determining a secondary air flow rate (Qs) from a difference between the determined intake air flow rate and an air flow rate (Qhw) measured by said air flow rate detecting device when the secondary air is being supplied from said first secondary-air introducing path into said exhaust gas path;
• and
• diagnosis means (13) for judging said secondary air supply device as being abnormal in the case where the determined secondary air flow rate is out of a predetermined allowable range.

A malfunction monitoring method for a secondary air supply device which supplies a secondary air to an exhaust gas path of an internal combustion engine provided with an air flow rate measuring device, comprising:

• a step (204) of measuring by said air flow rate measuring device a first air flow rate (Qa) passing through an intake air path of the engine when the secondary air is not being supplied;
• a step (208) of taking in, as the secondary air, a part of the air passing through said intake air path from a secondary air introducing path disposed in said intake air path on the downstream side of a measuring position of the air flow rate;
• a step of measuring by said air flow rate measuring device a second air flow rate (Qb) when the secondary air is taken in from said secondary air introducing path;
• a step of determining a secondary air flow rate (Qs) from a difference between said first and second air flow rates;
• and
• a step (215) of judging said secondary air supply device as being abnormal in the case where the determined secondary air flow rate is out of a predetermined allowable range.

A malfunction monitoring method for a secondary air supply device which supplies a secondary air to an exhaust gas path of an internal combustion engine provided with an air flow rate measuring device, comprising:

• a step (404) of detecting the internal pressure of an intake manifold of the engine;
• a step (404) of determining an intake air flow rate (Qpm) of the engine on the basis of the detected value of the internal pressure of said manifold;
• a step (405) of taking in, a part of the air through an intake air path of the engine, as the secondary air by said secondary air supply device from a secondary air introducing path disposed in said intake air path;
• a step (407) of measuring by said air flow rate measuring device an air flow rate (Qhw) passing through the upstream side of said secondary air introducing path when the secondary air is taken in from said secondary air introducing path;
• a step (407) of determining a secondary air flow rate (Qs) from a difference between the measured air flow rate (Qhw) and the determined intake air flow rate (Qpm);
• and
• a step (408) of judging said secondary air supply device as being abnormal in the case where the determined secondary air flow rate is out of a predetermined allowable range.