Closed loop controlled auxiliary air delivery system for internal combustion engine

Abstract

An auxiliary air delivery system for an internal combustion engine includes an intake vacuum sensor for generating an intake vacuum signal, a deceleration sensor and a microcomputer in which is stored a set of data representing different values of reference intake vacuum and programmed to retrieve a datum as a function of the length of time from the occurrence of engine deceleration. The retrieved information is used a reference signal with which the intake vacuum signal is compared to provide a control signal. A servo mechanism is provided to allow auxiliary air to be admitted into the manifold at a point downstream of the nearly closed throttle in response to the control signal to reduce the difference between the actual intake vacuum and the reference intake vacuum.

What is claimed is: .[.1. A method for controlling an internal combustion engine having a main air intake passage for introducing air into said engine, a throttle control valve in said main air intake passage, an auxiliary air intake passage for partially passing air from an upstream side to a downstream side of said throttle control valve, a second control valve in said auxiliary passage, and a vacuum pressure sensor provided downstream of said throttle control valve, the method comprising the steps of: 
     
        speed and said detected engine speed substantially to zero..]. .[.4.  A control system for use in an internal combustion engine having a main air intake passage for introducing air to said engine, a throttle control valve in said main intake passage and an auxiliary air intake passage connected to said main intake passage for partially passing air from an upstream side to a downstream sine of the throttle control valve, comprising: an engine deceleration detector for detecting when deceleration of said engine is started;   means for detecting intake vacuum pressure in said main intake passage downstream of said throttle control valve;   a programmed microcomputer, responsive to said deceleration detector and said vacuum pressure detecting means and operative for detecting a difference between said detected vacuum pressure and a reference vacuum pressure from a function defining a desired relationship between the length of time from the occurrence of said engine deceleration and the intake vacuum pressure in said main intake passage at the downstream side of said throttle control valve; and     generating a control signal representing said difference; and means provided in said auxiliary air intake passage for controlling the air passing therethrough in response to said control signal to reduce said difference substantially to zero..]. .[.5. A control system as claimed in claim 4, further comprising:     means for detecting the temperature of said engine, and   means for detecting the speed of revolution of said engine when said engine is idled;   said programmed microcomputer being further responsive to said temperature detecting means and said engine speed detecting means and operative for detecting a second difference between said detected engine speed and a reference idle engine speed from a second function defining a desired relationship between the detected engine temperature and the detected engine revolution speed; and   generating a second control signal representing said second difference;     wherein said air controlling means is further responsive to said second control signal for controlling air passing through said auxiliary intake passage to reduce said second difference substantially to zero..]. .[.6. A control system as claimed in claim 5, further comprising:   means for detecting when said engine is idled;   said programmed microcomputer being further responsive to said engine idle detecting means and operative for detecting a third difference between said detected engine speed and a second reference idle engine speed which is desired when said engine delivers power to a work load during engine idle condition from a third function defining a desired relationship beween the detected engine speed and the detected engine temperature; and   generating a third control signal representing said third difference;     wherein said air controlling means is further responsive to said third control signal for controlling air passing through said auxiliary intake   
     
     
        passage to reduce said third difference substantially to zero..]. .[.7.  A control system as claimed in claim 4, wherein said air controlling means comprises: a first control valve having a housing, a diaphragm dividing the housing into first and second chambers, the first chamber forming part of said auxiliary air intake passage, and a valve member within said first chamber and connected to said diaphragm for movement therewith to vary the cross-section of said auxiliary passage;   means for providing fluid communication of air in said main air intake passage from the upstream to the downstream side of said throttle control valve through said second chamber of said first control valve; and   a second control valve disposed in said fluid communication means for regulating the amount of air introduced into said second chamber of said first control valve in response to said control signals..]. .[.8. A control system as claimed in claim 7, wherein said controlling means further comprises a pressure regulator disposed in said fluid communication means between a point in said main air intake passage downstream of said throttle valve and said second chamber of said first control valve..]. .[.9. A control system as claimed in claims 7 or 8, wherein said second control valve is of a pulse responsive type, said control signals comprising pulses for controlling said second control valve..]. .[.10. A control system as claimed in claim 7 or 8, wherein said air controlling means further comprises an orifice in which said valve member of said first control valve is disposed, said valve member comprising larger and smaller diameter portions and a gradually varying diameter portion intermediate said larger and smaller diameter portions, the cross-sectional area of said smaller diameter portion defining a first air gap with said orifice in said auxiliary air intake passage croresponding to engine cold start condition and the cross-sectional area of said larger diameter portion defining a second air gap with said orifice corresponding to an engine idle condition which occurs at the end   
     
     
        of engine warm-up operation..]. .Iadd.11.  A method for controlling an air control valve disposed in an auxiliary passage which is connected to a main intake passage of an internal combustion engine, the auxiliary passage extending between a portion upstream of a throttle valve disposed in the main intake passage and a portion downstream of the throttle valve, the internal combustion engine having means for supplying fuel thereto in response at least to the flow of air passing through the main intake passage, said method comprising the steps of: detecting a vacuum within the main intake passage downstream of the throttle valve and generating a vacuum indicative signal;   determining that the engine is under deceleration and generating an elapsed time indicative signal indicative of time elapsed from the start of deceleration;   determining a maximum vacuum value for said elapsed time indicative signal and generating a maximum vacuum indicative signal, said maximum vacuum value being variable with variation of time elapsed from the start of deceleration;   comparing said vacuum indicative signal with said maximum vacuum indicative signal and generating a first difference indicative signal indicative of the difference between said vacuum indicative signal and said maximum vacuum indicative signal;   controlling the air control valve in response to said first difference indicative signal, to control the flow of air passing through the auxiliary passage to control the vacuum within the main intake passage downstream of said throttle valve so that the vacuum within the main intake passage downstream of the throttle valve becomes equal to said   
     
     
        maximum vacuum value. .Iaddend. .Iadd.12.  A method for controlling an air control valve disposed in an auxiliary passage which is connected to a main intake passage of an internal combustion engine, the auxiliary passage extending between a portion upstream of a throttle valve disposed in the main intake passage and a portion downstream of the throttle valve, the internal combustion engine having means for supplying fuel thereto in response at least to the flow of air passing through the main intake passage, said method comprising the steps of: detecting a vacuum within the main intake passage downstream of the throttle valve and generating a vacuum indicative signal;   determining that the engine is under deceleration and generating an elapsed time indicative signal indicative of time elapsed from the start of deceleration;   determining a maximum vacuum value for said elapsed time indicative signal and generating a maximum vacuum indicative signal, said maximum vacuum value being variable with variation of time elapsed from the start of deceleration;   comparing said vacuum indicative signal with said maximum vacuum indicative signal and generating a first difference indicative signal indicative of the difference between said vacuum indicative signal and said maximum vacuum indicative signal;   detecting an engine temperature of the engine and generating a temperature indicative signal;   determining that the engine is idling and generating an idling indicative signal;   detecting in response to said idling indicative signal an idling revolution speed of the engine and generating an idling revolution speed indicative signal;   determining in response to said idling indicative signal a first optimum idling revolution speed value for said temperature indicative signal and generating a first optimum idling revolution speed value indicative signal, said first optimum idling revolution speed value being variable with a variation of the engine temperature of the engine;   comparing said idling revolution speed indicative signal with said first optimum revolution speed indicative signal and generating a second difference indicative signal indicative of the difference between said idling revolution speed indicative signal and said first optimum idling revolution speed value indicative signal;   controlling, in response to the presence of said elapsed time indicative signal, the air control valve in response to said first difference indicative signal, to control the flow of air passing through the auxiliary passage to control the vacuum within the main intake passage downstream of said throttle valve so that the vacuum within the main intake passage downstream of the throttle valve becomes substantially equal to said maximum vacuum value; and   controlling, in response to the presence of said idling indicative signal, the air control valve in response to said second difference indicative signal to control the flow of air passing through the auxiliary passage so that the idling revolution speed of the engine becomes substantially equal   
     
     
        to said first optimum idling revolution speed value. .Iaddend. .Iadd.13. A method for controlling an air control valve disposed in an auxiliary passage which is connected to a main intake passage of an internal combustion engine, the auxiliary passage extending between a portion upstream of a throttle valve disposed in the main intake passage and a portion downstream of the throttle valve, the internal combustion engine having means for supplying fuel thereto in response at least to the flow of air passing through the main intake passage, the engine being equipped with an air conditioner which, when in operation, becomes a load of the engine, said method comprising the steps of: detecting a vacuum within the main intake passage downstream of the throttle valve and generating a vacuum indicative signal;   determining that the engine is under deceleration and generating an elapsed time indicative signal indicative of time elapsed from the start of deceleration;   determining a maximum vacuum value for said elapsed time indicative signal and generating a maximum vacuum indicative signal, said maximum vacuum value being variable with variation of time elapsed from the start of deceleration;   comparing said vacuum indicative signal with said maximum vacuum indicative signal and generating a first difference indicative signal indicative of the differene between said vacuum indicative signal and said maximum vacuum indicative signal;   detecting an engine temperature of the engine and generating a temperature indicative signal;   determining that the engine is idling and generating an idling indicative signal;   detecting in response to said idling indicative signal an idling revolution speed of the engine and generating an idling revolution speed indicative signal;   determining in response to said idling indicative signal a first optimum idling revolution speed value for said temperature indicative signal and generating a first optimum idling revolution speed value indicative signal, said first optimum idling revolution speed value being variable with a variation of the engine temperature of the engine;   comparing said idling revolution speed indicative signal with said first optimum revolution speed indicative signal and generating a second difference indicative signal indicative of the difference between said idling revolution speed indicative signal and said first optimum idling revolution speed value indicative signal;   detecting whether the air conditioner is being operated and generating an air conditioner operation indicative signal when the air conditioner is being operated;   determining in response to said air conditioner operation indicative signal a second optimum idling revolution speed value for said temperature indicative signal and generating a second optimum idling revolution speed value indicative signal, said second optimum idling revolution speed value being at least higher than said optimum idling revolution speed value;   comparing said idling revolution speed indicative signal with said second optimum idling revolution speed value indicative signal and generating a third difference indicative signal indicative of the difference between said idling revolution speed indicative signal and said second idling revolution speed value indicative signal;   controlling, in response to the presence of said elapsed time indicative signal, the air control valve in response to said first difference indicative signal to control the vacuum within the main intake passage downstream of said throttle valve so that the vacuum within the main intake passage downstream of the throttle valve becomes substantially equal to said maximum vacuum value;   controlling, in response to the presence of said idling indicative signal and the absence of said air conditioner operation indicative signal, the air control valve in response to said second difference indicative signal to control the flow of air passing through the auxiliary passage so that the idling revolution of the engine become substantially equal to said first optimum idling revolution speed value; and   controlling, in response to the presence of said idling indicative signal and the presence of said air conditioner operation indicative signal, the air control valve in response to said third difference indicative signal to control the flow of air passing through the auxiliary passage so that the idling revolution speed of the engine becomes substantially equal to   
     
     
        said second optimum idling revolution speed value. .Iaddend. .Iadd.14.  A control system for controlling an air control valve disposed in an auxiliary passage which is connected to a main intake passage of an internal combustion engine, said auxiliary passage extending between a portion upstream of a throttle valve disposed in the main intake passage and a portion downstream of the throttle valve, the internal combustion engine having means for supplying fuel thereto in response at least to the flow of air passing through the main intake passage, said control system comprising: means for detecting a vacuum within the main intake passage downstream of the throttle valve and generating a vacuum indicative signal;   a microcomputer including a memory which stores maximum vacuum values for time elapsed from the start of deceleration, and a central processor unit,   said central processor unit determining that the engine is under deceleration and generating an elapsed time indicative signal indicative of time elapsed from the start of deceleration, determining one maximum vacuum value from said stored maximum vacuum values for said elapsed time indicative signal and generating a maximum vacuum value indicative signal, and comparing said vacuum indicative signal with said maximum vacuum value indicative signal and generating a first difference indicative signal indicative of the difference between said vacuum indicative signal and said maximum vacuum value indicative signal; and   means for controlling the air control valve in response to said first difference indicative value to control the flow of air passing through the auxiliary passage to control the vacuum within the main intake passage downstream of said throttle valve so that the vacuum within the main intake passage downstream of the throttle valve becomes equal to said   
     
     
        maximum vacuum value. .Iaddend. .Iadd.15.  A control system for controlling an air control valve disposed in an auxiliary passage which is connected to a main intake passage of an internal combustion engine, said auxiliary passage extending between a portion upstream of a throttle valve disposed in the main intake passage and a portion downstream of the throttle valve, the internal combustion engine having means for supplying fuel thereto in response at least to the flow of air passing through the main intake passage, said control system comprising: means for detecting a vacuum within the main intake passage downstream of the throttle valve and generating a vacuum indicative signal;   a microcomputer including a memory which stores maximum vacuum values for time elapsed from the start of deceleration, and a central processor unit,   said central processor unit determining that the engine is under deceleration and generating an elapsed time indicative signal indicative of time elapsed from the start of deceleration, determining one maximum vacuum value from said stored maximum vacuum values for said elapsed time indicative signal and generating a maximum vacuum value indicative signal, and comparing said vacuum indicative signal with said maximum vacuum value indicative signal and generating a first difference indicative signal indicative of the difference between said vacuum indicative signal and said maximum vacuum value indicative signal;   means for detecting an engine temperature of the engine and generating a temperature indicative signal;   means for detecting the revolution speed of the engine and generating an engine revolution speed indicative signal;   said memory storing optimum idling revolution speed values, each for an engine temperature value indicated by said temperature indicative signal;   said central processor unit determining that the engine is idling to generate an idling indicative signal, determining one optimum idling revolution speed from said optimum idling revolution speed values for said temperature indicative signal to generate an optimum idling revolution speed value indicative signal, and comparing said engine revolution speed indicative signal with said optimum revolution speed value indicative signal to generate a second difference indicative signal indicative of the difference between said engine revolution speed indicative signal and said optimum idling revolution speed value indicative signal;   means for controlling, in response to the presence of said elapsed time indicative signal, the air control valve in response to said first difference indicative signal to control the flow of air passing through the auxiliary passage to control the vacuum within the main intake passage downstream of said throttle valve so that the vacuum within the main intake passage downstream of the throttle valve becomes substantially equal to said maximum vacuum value;   said controlling means controlling, in response to the presence of said idling indicative signal, the air control valve in response to said second difference indicative signal to control the flow of air passing through the auxiliary passage so that the idling revolution speed of the engine becomes substantially equal to said first optimum idling revolution speed   
     
     
        value. .Iaddend. .Iadd.16.  A control system for controlling an air control valve disposed in an auxiliary passage which is connected to a main intake passage of an internal combustion engine, said auxiliary passage extending between a portion upstream of a throttle valve disposed in the main intake passage and a portion downstream of the throttle valve, the internal combustion engine having means for supplying fuel thereto in response at least to the flow of air passing through the main intake passage, the engine being equipped with an air conditioner which, when in operation, becomes a load of the engine, said control system comprising: means for detecting a vacuum within the main intake passage downstream of the throttle valve and generating a vacuum indicative signal;   a microcomputer including a memory which stores maximum vacuum values for time elapsed from the start of deceleration, and a central processor unit,   said central processor unit determining that the engine is under deceleration and generating an elapsed time indicative signal indicative of time elapsed from the start of deceleration, determining one maximum vacuum value from said stored maximum vacuum values for said elapsed time indicative signal and generating a maximum vacuum value indicative signal, and comparing said vacuum indicative signal with said maximum vacuum value indicative signal and generating a first difference indicative signal indicative of the difference between said vacuum indicative signal and said maximum vacuum value indicative signal;   means for detecting an engine temperature of the engine and generating a temperature indicative signal;   means for detecting a revolution speed of the engine and generating an engine revolution speed indicative signal;   said memory storing first optimum idling revolution speed values, each for an engine temperature value indicated by said temperature indicative signal;   said central processor unit determining that the engine is idling to generate an idling indicative signal, determining one first optimum idling revolution speed from said first optimum idling revolution speed values for said temperature indicative signal to generate a first optimum idling revolution speed value indicative signal, and comparing said engine revolution speed indicative signal with said first optimum revolution speed value indicative signal to generate a second difference indicative signal indicative of the difference between said engine revolution speed indicative signal and said first optimum idling revolution speed value indicative signal;   said memory storing second optimum idling revolution values, each for an engine temperature value indicated by said temperature indicative signal;   said central processor unit determining that the air conditioner is operated to generate an air conditioner operation indicative signal, determining one second optimum idling revolution speed value from said stored second optimum idling revolution speed values for said temperature indicative signal to generate a second optimum idling revolution speed value indicative signal, comparing said engine revolution speed indicative signal with said second optimum idling revolution speed value indicative signal to generate a third difference indicative signal indicative of the difference between said engine revolution speed indicative signal and said second optimum idling revolution speed value indicative signal,   means for controlling, in response to the presence of said elapsed time indicative signal, the air control valve in response to said first difference indicative signal to control the flow of air passing through the auxiliary passage to control the vacuum within the main intake passage downstream of said throttle valve so that the vacuum within the main intake passage downstream of the throttle valve becomes substantially equal to said maximum vacuum value;   said controlling means controlling, in response to the presence of said idling indicative signal and the absence of said air conditioner operation indicative signal, the air control valve in response to said second difference indicative signal to control the flow of air passing through the auxiliary passage so that the idling revolution speed of the engine becomes substantially equal to said first optimum idling revolution speed value;   said controlling means controlling, in response to the presence of said idling indicative signal and the presence of said air conditioner operation indicative signal, the air control valve in response to said third difference indicative signal to control the flow of air passing through the auxiliary passage so that the engine revolution speed of the engine becomes substantially equal to said second optimum idling revolution speed value. .Iaddend. .Iadd.17. A method for controlling an air control valve disposed in an auxiliary passage which is connected to a main intake passage of an internal combustion engine, said auxiliary passage extending between a portion upstream of a throttle valve disposed in the main intake passage and a portion downstream of the throttle valve, the internal combustion engine having means for supplying fuel thereto in response at least to the flow of air passing through the main intake passage, the engine being equipped with a device which, when in operation, becomes a load of the engine, said method comprising the steps of:   detecting a temperature of the engine and generating a temperature indicative signal;   detecting an idling revolution speed of the engine and generating an idling revolution speed indicative signal;   detecting whether the device is being operated and generating device operation indicative signal when the device is being operated;   determining in response to the absence of said device operation indicative signal a first optimum idling revolution speed indicative signal for said temperature indicative signal and generating a first optimum idling revolution speed value being variable with a variation of the temperature of the engine. .Iaddend.   determining in response to the presence of said device operation indicative signal a second optimum idling revolution speed value for said temperature indicative signal and generating a second optimum idling revolution speed value indicative signal, said second optimum idling revolution speed value being at least higher than said optimum idling revolution speed value and variable with a variation of the temperature of the engine;   comparing, in response to the absence of said device operation indicative signal, said idling revolution speed indicative signal with said first optimum revolution speed value indicative signal and generating a first difference indicative signal indicative of the difference between said idling revolution speed indicative signal and said first optimum idling revolution speed value indicative signal;   comparing, in response to the presence of said device operation indicative signal, said idling revolution speed indicative signal with said second optimum idling revolution speed value indicative signal and generating a second difference indicative signal indicative of the difference between said idling revolution speed indicative signal and said second optimum idling revolution speed value indicative signal;   controlling, in response to the absence of said device operation indicative signal, the air control valve in response to said first difference indicative signal so that the idling revolution speed of the engine becomes equal to said first optimum idling revolution speed value; and   controlling, in response to the presence of said device operation indicative signal, the air control valve in response to said second difference indicative signal, to control the flow of air passing through the auxiliary passage so that the idling revolution speed of the engine becomes equal to said second optimum idling revolution speed value.   
     
     
        .Iadd.8.  A method for controlling an air control valve disposed in an auxiliary passage which is connected to a main intake passage of an internal combustion engine, said auxiliary passage extending between a portion upstream of a throttle valve disposed in the main intake passage and a portion downstream of the throttle valve, the internal combustion engine having means for supplying fuel thereto in response at least to the flow of air passing through the main intake passage, the engine being equipped with a device which, when in operation, becomes a load of the engine, said method comprising the steps of: detecting a temperature of the engine and generating a temperature indicative signal;   detecting an idling revolution speed of the engine and generating an idling revolution speed indicative signal;   detecting whether the device is being operated and generating a device operation indicative signal when the device is being operated;   determining in response to the absence of said device operation indicative signal a first optimum idling revolution speed indicative signal and generating a first optimum idling revolution speed value indicative signal, said first optimum idling revolution speed value being variable with a variation of the temperature of the engine;   determining in response to the presence of said device operation indicative signal a second optimum idling revolution speed value for said temperature indicative signal and generating a second optimum idling revolution speed value indicative signal, said second optimum idling revolution speed value being at least higher than said optimum idling revolution speed value and being variable with a variation of the temperature of the engine;   comparing, in response to the absence of said device operation indicative signal, said idling revolution speed indicative signal with said first optimum revolution speed value indicative signal and generating a first difference indicative signal indicative of the difference between said idling revolution speed indicative signal and said first optimum idling revolution speed value indicative signal;   comparing, in response to the presence of said device operation indicative signal, said idling revolution speed indicative signal with said second optimum idling revolution speed value indicative signal and generating a second difference indicative signal indicative of the difference between said idling revolution speed indicative signal and said second optimum idling revolution speed value indicative signal;   controlling, in response to the absence of said device operation indicative signal, the air control valve in response to said first difference indicative signal to control the flow of air passing through the auxiliary passage only when the difference indicated by said first difference indicative signal continues to be greater than a predetermined value for a predetermined duration of time so that the idling revolution speed of the engine becomes equal to said first optimum idling revolution speed value; and   controlling, in response to the presence of said device operation indicative signal, the air control valve in response to said second difference indicative signal, to control the flow of air passing through the auxiliary passage only when the difference indicated by said second difference indicative signal continues to be greater than said predetermined value for said predetermined duration of time so that the idling revolution speed of the engine becomes equal to said second optimum   
     
     
        idling revolution speed value. .Iaddend. .Iadd.19.  A method for controlling an air control valve disposed in an auxiliary passage which is connected to a main intake passage of an internal combustion engine, said auxiliary passage extending between a portion upstream of a throttle valve disposed in the main intake passage and a portion downstream of the throttle valve, the internal combustion engine having means for supplying fuel thereto in response at least to the flow of air passing through the main intake passage, the engine being equipped with an air conditioner which, when in operation, becomes a load of the engine, said method comprising the steps of: detecting a temperature of the engine and generating a temperature indicative signal;   detecting in response to said idling indicative signal an idling revolution speed of the engine and generating an idling revolution speed indicative signal;   detecting whether the air conditioner is being operated and generating an air conditioner operation indicative signal when the air conditioner is being operated;   determining in response to the absence of said air conditioner operation indicative signal a first optimum idling revolution speed indicative signal for said temperature indicative signal and generating a first optimum idling revolution speed value indicative signal, said first optimum idling revolution speed value being variable with a variation of the temperature of the engine;   determining in response to the presence of said air conditioner operation indicative signal and a second optimum idling revolution speed value for said temperature indicative signal and generating a second optimum idling revolution speed value indicative signal, said second optimum idling revolution speed value being at least higher than said optimum idling revolution speed value;   comparing, in response to the absence of said air conditioner operation indicative signal, said idling revolution speed indicative signal with said first optimum revolution speed value indicative signal and generating a first difference indicative signal indicative of the difference between said idling revolution speed indicative signal and said first optimum idling revolution speed value indicative signal;   comparing, in response to the presence of said air conditioner operation indicative signal, said idling revolution speed indicative signal with said second optimum idling revolution speed value indicative signal and generating a second difference indicative signal indicative of the difference between said idling revolution speed indicative signal and said second optimum idling revolution speed value indicative signal;   controlling, in response to the absence of said air conditioner operation indicative signal, the air control valve in response to said first difference indicative signal to control the flow of air passing through the auxiliary passage only so that the idling revolution speed of the engine becomes equal to said first optimum idling revolution speed value; and   controlling, in response to the presence of said air conditioner operation indicative signal, the air control valve in response to said second difference indicative signal, to control the flow of air passing through the auxiliary passage so that the idling revolution speed of the engine becomes equal to said second optimum idling revolution speed value.   
     
     
        .Iaddend. .Iadd.20.  A method for controlling an air control valve disposed in an auxiliary passage which is connected to a main intake passage of an internal combustion engine, said auxiliary passage extending between a portion upstream of a throttle valve disposed in the main intake passage and a portion downstream of the throttle valve, the internal combustion engine having means for supplying fuel thereto in response at least to the flow of air passing through the main intake passage, the engine being equipped with an air conditioner which, when in operation, becomes a load of the engine, said method comprising the steps of: detecting a temperature of the engine and generating a temperature indicative signal;   determining that the engine is idling and generating an idling indicative signal;   detecting in response to said idling indicative signal an idling revolution speed of the engine and generating an idling revolution speed indicative signal;   detecting that the air conditioner is operated and generating a air conditioner operation indicative signal;   determining in response to the absence of said air conditioner operation indicative signal a first optimum idling revolution speed indicative signal for said temperature indicative signal and generating a first optimum idling revolution speed value indicative signal, said first optimum idling revolution speed value being variable with a variation of the temperature of the engine;   determining in response to the presence of said air conditioner operation indicative signal a second optimum idling revolution speed value for said temperature indicative signal and generating a second optimum idling revolution speed value indicative signal, said second optimum idling revolution speed value being at least higher than said optimum idling revolution speed value;   comparing, in response to the absence of said air conditioner operation indicative signal, said idling revolution speed indicative signal with said first optimum revolution speed value indicative signal and generating a first difference indicative signal indicative of the difference between said idling revolution speed indicative signal and said first optimum idling revolution speed value indicative signal;   comparing, in response to the presence of said air conditioner operation indicative signal, said idling revolution speed indicative signal with said second optimum idling revolution speed value indicative signal and generating a second difference indicative signal indicative of the difference between said idling revolution speed indicative signal and said second optimum idling revolution speed value indicative signal;   controlling, in response to the absence of said air conditioner operation indicative signal, the air control valve in response to said first difference indicative signal only when the difference indicated by said first difference indicative signal continues to be greater than a predetermined value for a predetermined duration of time to control the flow of air passing through the auxiliary passage so that the idling revolution speed of the engine becomes equal to said first optimum idling revolution speed value; and   controlling, in response to the presence of said air conditioner operation indicative signal, the air control valve in response to said second control signal only when the difference indicated by said second difference indicative signal continues to be greater than said predetermined value for said predetermined duration of time to control the flow of air passing through the auxiliary passage so that the idling revolution speed of the engine becomes equal to said second optimum idling revolution speed value. .Iaddend. .Iadd.21. A method for controlling an air control valve disposed in an auxiliary passage which is connected to a main intake passage of an internal combustion engine, said auxiliary passage extending between a portion upstream of a throttle valve disposed in the main intake passage and a portion downstream of the throttle valve, the internal combustion engine having means for supplying fuel thereto in response at least to the flow of air passing through the main intake passage, the internal combustion engine being drivingly connected to a transmission, the engine being equipped with an air conditioner which, when in operation, becomes a load of the engine, said method comprising the steps of:   detecting a temperature of the engine and generating a temperature indicative signal;   detecting a revolution speed of the engine and generating an engine revolution speed indicative signal;   detecting a throttle position of a throttle valve and generating a throttle position indicative signal when the throttle valve is closed;   detecting a vehicle speed of the vehicle and generating a vehicle speed indicative signal when the vehicle speed is lower than a predetermined value;   detecting the state of the transmission and generating a neutral state indicative signal when the transmission is in the neutral state;   determining that the engine is idling when said throttle position indicative signal is present and said vehicle speed indicative signal is absent or when said throttle position indicative signal is present and said vehicle speed indicative signal is absent and said neutral state indicative signal is absent and generating an idling indicative signal;   detecting that the air conditioner is operated and generating an air conditioner operation indicative signal;   determining in response to the presence of said idling indicative signal and the absence of said air conditioner operation indicative signal a first optimum idling revolution speed value for said temperature indicative signal and generating a first optimum idling revolution speed value indicative signal, said first optimum idling revolution speed value being variable with a variation of the temperature of the engine.   determining in response to the presence of said idling indicative signal and the presence of said air conditioner operation indicative signal a second optimum idling revolution speed value for said temperature indicative signal and generating a second optimum idling revolution speed value indicative signal, said second optimum idling revolution speed value being at least higher than said first optimum idling revolution speed value and being variable with variation of the temperature of the engine;   comparing, in response to the presence of said idling signal, and the absence of said air conditioner operation indicative signal, said engine revolution speed indicative signal with said first optimum revolution speed value indicative signal and generating a first difference indicative signal indicative of the difference between said engine revolution speed indicative signal and said first optimum idling revolution speed value indicative signal;   comparing, in response to the presence of said idling indicative signal and the presence of said air conditioner operation indicative signal, said engine revolution speed indicative signal with said second optimum idling revolution speed value indicative signal and generating a second difference indicative signal indicative of the difference between said engine revolution speed indicative signal and said second optimum idling revolution speed value indicative signal;   controlling, in response to the absence of said idling indicative signal and the absence of said air conditioner operation indicative signal, the air control valve in response to said first difference indicative signal to control the flow of air passing through the auxiliary passage to control air fuel mixture in the main intake passage downstream of the throttle valve so that the idling revolution speed of the engine becomes equal to said first optimum idling revolution speed value; and   controlling, in response to the presence of said idling indicative signal and the presence of said air conditioner operation indicative signal, the air control valve in response to said second difference indicative signal, to control the flow of air passing through the auxiliary passage to control air fuel mixture in the main intake passage downstream of the main intake passage so that the idling revolution speed of the engine becomes equal to said second optimum idling revolution speed value. .Iaddend. .Iadd.22. A control system for controlling an air control valve disposed in an auxiliary passage which is connected to a main intake passage of an internal combustion engine, said auxiliary passage extending between a portion upstream of a throttle valve disposed in the main intake passage and a portion downstream of the throttle valve, the internal combustion engine having means for supplying fuel thereto in response at least to the flow of air passing through the main intake passage, the engine being equipped with an air conditioner which, when in operation, becomes a load of the engine, the engine being drivingly connected to a transmission, said control system comprising:   means for detecting a temperature of the engine and generating a temperature indicative signal;   means for detecting a revolution speed of the engine and generating an engine revolution speed indicative signal;   means for detecting a throttle position of a throttle valve and generating a throttle position indicative signal when the throttle valve is closed;   means for detecting a vehicle speed of the vehicle and generating a vehicle speed indicative signal when the vehicle speed is lower than a predetermined value;   means for detecting a neutral state of the transmission and generating a neutral state indicative signal when the transmission is in the neutral state;   means for detecting that the air conditioner is operated and generating an air conditioner operation indicative signal;   a microcomputer including a memory storing a plurality pairs of optimum idling revolution speed values, each paid being for a temperature value indicated by said temperature indicative signal and comprising a first optimum idling revolution speed value and a second optimum idling revolution speed value, said second optimum idling revolution speed value being lower than said first optimum idling revolution speed value;   said central process unit determining that the engine is idling when said throttle position indicative signal is present and said vehicle speed indicative signal is present or when the said throttle position indicative signal is present and said neutral state indicative signal is present to generate an idling indicative signal, in response to the presence of said idling indicative signal and the absence of said air conditioner operation indicative signal determining one of said first optimum idling revolution speed values for said temperature indicative signal to generate a first optimum idling revolution speed value indicative signal, in response to the presence of said idling indicative signal and the presence of said air conditioner indicative signal determining one of said second optimum idling revolution speed values for said temperature indicative signal to generate a second optimum idling revolution speed value indicative signal, said second optimum idling revolution speed value being at least higher than said first optimum idling revolution speed value, comparing, in response to the presence of said air conditioner operation indicative signal with said first optimum revolution speed value indicative signal and generating a first difference indicative signal indicative of the difference between said engine revolution speed indicative signal and said first optimum idling revolution speed value indicative signal, comparing, in response to the presence of said idling indicative signal and the presence of said air conditioner operation indicative signal, said engine revolution speed indicative signal with said second optimum idling revolution speed value indicative signal and generating a second difference indicative signal indicative of the difference between said engine revolution speed indicative signal and said second optimum idling revolution speed value indicative signal; and   means for controlling, in response to the presence of said idling indicative signal and the absence of said air conditioner operation indicative signal, the air control valve in response to said first difference indicative signal to control the flow of air passing through the auxiliary passage to control air fuel mixture in the main intake passage downtream of the throttle valve so that the idling revolution speed of the engine becomes equal to said first optimum idling revolution speed value, said controlling means controlling, in response to the presence of said idling indicative signal and the presence of said air conditioner operation indicative signal, the air control valve, in response to said second difference indicative signal, to control the flow of air passing through the auxiliary passage so that the idling revolution speed of the engine becomes equal to said second optimum idling revolution   
     
     
        speed value. .Iaddend. .Iadd.23.  A method for controlling an air control valve disposed in an auxiliary passage which is connected to a main intake passage of an internal combustion engine, said auxiliary passage extending between a portion upstream of a throttle valve disposed in the main intake passage and a portion downstream of the throttle valve, the internal combustion engine having means for supplying fuel thereto in response at least to the flow of air passing through the main intake passage, said method comprising the steps of: detecting a temperature of the engine and generating a temperature indicative signal;   detecting an idling revolution speed of the engine and generating an idling revolution speed indicative signal;   determining an optimum idling revolution speed value for said temperature indicative signal which is variable with a variation of the temperature of the engine and generating an optimum idling revolution speed value indicative signal;   comparing said idling revolution speed indicative signal with said optimum idling revolution speed value indicative signal and generating a first comparison result indicative signal when said idling revolution speed indicative signal is greater than said optimum idling revolution speed value indicative signal by a predetermined value, a second comparison result indicative signal when said idling revolution speed indicative signal is less than said optimum idling revolution speed value indicative signal by said predetermined value, and a third comparison result indicative signal when said idling revolution speed indicative signal is not greater than said optimum idling revolution speed value indicative signal by said predetermined value and not less than said optimum idling revolution speed value indicative signal by said predetermined value;   controlling the air control valve to decrease the flow of air passing through the main intake passage in response to said first comparison result indicative signal thereby to decrease the idling revolution speed of the engine;   controlling the air control valve to increase the flow of air passing through the main intake passage in response to said second comparison result indicative signal thereby to increase the idling revolution speed of the engine; and   maintaining opening degree of the air control valve as it is in response to said third comparison result indicative signal. .Iaddend. .Iadd.24. A method for controlling an air control valve disposed in an auxiliary passage which is connected to a main intake passage of an internal combustion engine, said auxiliary passage extending between a portion upstream of a throttle valve disposed in the main intake passage and a portion downstream of the throttle valve, the internal combustion engine having means for supplying fuel thereto in response at least to the flow of air passing through the main intake passage, said method comprising the steps of:   detecting a temperature of the engine and generating a temperature indicative signal;   detecting an idling revolution speed of the engine and generating an idling revolution speed indicative signal;   determining an optimum idling revolution speed for said temperature which is variable with a variation of the engine temperature of the engine and generating an optimum idling revolution speed value indicative signal;   computing a difference between said idling revolution speed indicative signal and said optimum idling revolution speed value indicative signal and generating a difference indicative signal;   comparing said difference indicative signal with a predetermined value and generating a first comparison result indicative signal when said difference indicative signal is greater than said predetermined value and a second comparison result signal when said difference indicative signal is not greater than said predetermined value;   controlling the air control valve in response to said difference indicative signal when said first comparison result indicative signal is present; and   maintaining opening degree of the air control valve as it is when said second comparison result indicative signal is present. .Iaddend.