Air/fuel ratio control system for internal combustion engines, having secondary air supply control

Claim 2

In an air/fuel ratio control system for performing feedback control of the air/fuel ratio of an air/fuel mixture being supplied to an internal combustion engine having an intake system and an exhaust system, which includes a three-way catalyst provided in said exhaust system of said engine, an O 2 sensor arranged in said exhaust system at a location upstream of said three-way catalyst for detecting the concentration of oxygen in exhaust gases emitted from said engine, and an electrical circuit operatively connecting said O 2 sensor in a manner effecting feedback control operation to control the air/fuel ratio in response to said O 2 sensor, the combination comprising: means for supplying atmospheric air as secondary air into said exhaust system at a zone between said engine and said O 2 sensor; an engine speed sensor for detecting the rotational speed of said engine; a pressure sensor for detecting absolute pressure in said intake system; means for determining activation of said O 2 sensor; electrical means connected to said engine speed sensor, said pressure sensor and said O 2 sensor activation determining means for producing a feedback control interrupting signal when there occurs at least one of the conditions of engine idle, engine deceleration and deactivation of said O 2 sensor, and electrical means responsive to said feedback control interrupting signal to actuate, after the generation of said interrupting signal, said secondary air supply means.

Claim 3

In an air/fuel ratio control system for performing feedback control of the air/fuel ratio of an air/fuel mixture being supplied to an internal combustion engine having an intake system and an exhaust system, which includes a three-way catalyst provided in said exhaust system of said engine, an O 2 sensor arranged in said exhaust system at a location upstream of said three-way catalyst for detecting the concentration of oxygen in exhaust gases emitted from said engine, fuel quantity adjusting means for producing said mixture being supplied to said engine, and an electrical circuit operatively connecting said O 2 sensor with said fuel quantity adjusting means in a manner effecting feedback control operation to control the air/fuel ratio of said mixture to a predetermined value in response to an output signal produced by said O 2 sensor, the combination comprising: means for supplying atmospheric air as secondary air into said exhaust system at a zone between said engine and said O 2 sensor, an engine speed sensor for detecting the rotational speed of said engine; and a pressure sensor for detecting absolute pressure in said intake system; said electrical circuit including a first circuit for determining activation of said O 2 sensor, a second circuit responsive to output signals from said engine speed sensor, said pressure sensor and said first circuit thereby to produce a feedback control interrupting signal when there occurs at least one of the conditions of engine idle, engine deceleration and deactivation of said O 2 sensor, and a third circuit responsive to said feedback control interrupting signal for actuating said secondary air supply means.

Claim 4

In an air/fuel ratio control system for performing feedback control of the air/fuel ratio of an air/fuel mixture being supplied to an internal combustion engine having an intake system and an exhaust system, which includes a three-way catalyst provided in said exhaust system of said engine, an O 2 sensor arranged in said exhaust system at a location upstream of said three-way catalyst for detecting the concentration of oxygen in exhaust gases emitted from said engine, fuel quantity adjusting means for producing said mixture being supplied to said engine, and an electrical circuit operatively connecting said O 2 sensor with said fuel quantity adjusting means in a manner effecting feedback control operation to control the air/fuel ratio of said mixture to a predetermined value in response to an output signal produced by said O 2 sensor, the combination comprising: means for supplying atmospheric air as secondary air into said exhaust system at a zone between said engine and said O 2 sensor, an engine speed sensor for detecting the rotational speed of said engine; and a pressure sensor for detecting absolute pressure in said intake system; said electrical circuit including a first circuit for determining activation of said O 2 sensor, a second circuit responsive to output signals from said engine speed sensor, said pressure sensor and said first circuit thereby to produce a feedback control interrupting signal when there occurs at least one of the conditions of engine idle, engine deceleration and deactivation of said O 2 sensor, and a third circuit responsive to said feedback control interrupting signal for actuating said secondary air supply means.

Claim 5

The air/fuel ratio control system as claimed in claim 1 or 2, wherein said secondary air supply means comprises: an air passage communicating at one end thereof with said exhaust system of said engine and at another end thereof with atmospheric air, respectively; a reed valve arranged in said air passage for allowing flow of said atmospheric air solely toward said exhaust system; a valve arranged to close said air passage; means actuatable by negative pressure for actuating said valve; and a negative pressure passage communicating said negative pressure-actuated means with said intake system of said engine; said means for actuating said secondary air supply means comprising a three way valve connected to said negative pressure passage; wherein said three way valve is arranged to open said negative pressure passage at one position thereof, and close same and simultaneously allow introduction of atmospheric air into said negative pressure-actuated means at another position thereof, said three way valve being responsive to said feedback control interrupting signal to take said another position.

Claim 6

The air/fuel ratio control system as claimed in either claim 1 or 2 wherein said engine is in said condition of engine idle when said engine speed sensor produces an output signal indicative of an actual value of the rotational speed of said engine lower than a predetermined value.

Claim 7

The air/fuel ratio control system as claimed in either claim 1 or 2 wherein said engine is in said condition of deceleration when said pressure sensor produces an output signal indicative of an actual value of absolute pressure in said intake system lower than a predetermined value.

Claim 8

The air/fuel ratio control system as claimed in either claim 1 or 2 wherein said O 2 sensor is in said condition of deactivation when a predetermined period of time has elapsed after said O 2 sensor produces an output signal indicative of a voltage value lower than a predetermined value for the first time.

Claim 9

The air/fuel ratio control system as claimed in either claim 1 or 2 further including a temperature sensor for detecting the temperature of said engine, and wherein said O 2 sensor is in said condition of deactivation when a predetermined period of time has elapsed after said O 2 sensor produces an output signal indicative of a voltage value lower than a predetermined value for the first time, while simultaneously said temperature sensor produces an output signal indicative of an actual value of the temperature of said engine lower than a predetermined value.