JPS638307B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an air-fuel ratio control device for an engine, and more particularly to an air-fuel ratio control device for an engine to which an air-fuel mixture is supplied by a carburetor.

In carburetor type engines, in order to effectively operate the three-way catalytic converter and improve fuel efficiency, the air-fuel ratio of the mixture supplied to the engine is kept within a fairly narrow range around the stoichiometric air-fuel ratio. Air-fuel ratio control devices have been proposed in the past.

As one type of air-fuel ratio control device, the air _- fuel ratio is controlled by feedback controlling the amount of air bleed from the carburetor while detecting the concentration of exhaust components in the exhaust gas emitted from the engine using an exhaust sensor such as an O 2 sensor. What controls is known.

By the way, when the engine is operated at low load, the NO _x concentration in the exhaust gas is originally low, so the air-fuel ratio of the air-fuel mixture supplied to the engine is corrected to an air-fuel ratio that is biased from the stoichiometric air-fuel ratio, for example, to a lean air-fuel ratio. This makes it possible to maintain the NO _x concentration in the exhaust gas released into the atmosphere at a sufficiently low value even without the catalytic converter operating.

In view of this, when the engine is operating at low load, feedback control is stopped and a lean air-fuel mixture with an air-fuel ratio greater than the stoichiometric air-fuel ratio is supplied to the engine, thereby improving fuel efficiency and purifying exhaust gas. An air-fuel ratio control device that achieves this has already been proposed, and is disclosed in, for example, Japanese Patent Laid-Open No. 122013/1983.

The lean air-fuel ratio that should be set during low-load operation is:
In order to both improve fuel efficiency and reduce NO _x in exhaust gas, the value should be set as large as possible within the flammable limit air-fuel ratio. However, if the actual base air-fuel ratio of the carburetor fluctuates due to changes in atmospheric pressure, temperature, etc., or changes in the characteristics of the carburetor itself over time, If the lean air-fuel ratio when increasing the air bleed amount fluctuates, especially if the base air-fuel ratio of the carburetor shifts to the lean side due to a decrease in the fuel discharge amount, the lean air-fuel ratio when increasing the air bleed amount will become excessive than the control target value. , there is a risk that this will exceed the flammable limit air-fuel ratio.

For this reason, when lean air-fuel ratio control as described above is performed by increasing the air bleed amount by a predetermined constant flow rate, the control target air-fuel ratio when increasing the air bleed amount is adjusted in anticipation of fluctuations in the base air-fuel ratio of the carburetor. Since the air-fuel ratio must be set on the safe side, that is, on the stoichiometric air-fuel ratio side, the maximum effect cannot be obtained in lean air-fuel ratio control.

An object of the present invention is to provide an improved air-fuel ratio control device capable of performing not only stoichiometric air-fuel ratio control but also lean air-fuel ratio control while always maintaining an appropriate control target air-fuel ratio even if the base air-fuel ratio of a carburetor varies. It is an object.

According to the present invention, this purpose includes an exhaust sensor that detects the concentration of exhaust components of exhaust gas discharged from the engine, and a signal that indicates the air-fuel ratio of the air-fuel mixture supplied to the engine based on a signal generated by the exhaust sensor. an arithmetic device that generates a signal; an air bleed control device that is driven based on the signal generated by the arithmetic device and performs feedback control of the air bleed amount of the carburetor so that the air-fuel ratio becomes an air-fuel ratio near the stoichiometric air-fuel ratio; A time-based average air-fuel ratio calculation device that calculates and stores a time-based average value of the air-fuel ratio based on a signal generated by the exhaust sensor when the air-fuel ratio is feedback-controlled by the bleed control device, and a low-load operation other than during idling operation. During operation, the feedback control based on the signal from the arithmetic unit is stopped, and the air bleed amount by the air bleed control device is increased based on the temporal average air-fuel ratio calculated by the temporal average air-fuel ratio calculation device, and the air-fuel ratio is theoretically calculated. This is achieved by an engine air-fuel ratio control device characterized by having an air bleed correction device that corrects the air-fuel ratio to a predetermined air-fuel ratio substantially larger than the air-fuel ratio during low-load operation.

According to the configuration described above, the air-fuel ratio is feedback-controlled to the stoichiometric air-fuel ratio by air bleed amount control based on the signal from the exhaust sensor at times other than during low-load operation, and during this feedback control, the signal from the exhaust sensor is The average value of the air-fuel ratio over time is calculated from . This average value of the air-fuel ratio over time represents the base air-fuel ratio of the carburetor. During low load operation, the feedback control is stopped and the air bleed amount is increased at a flow rate determined based on the time-dependent average value of the air-fuel ratio at this time, that is, the base air-fuel ratio of the carburetor at this time. The fuel ratio is set to a predetermined lean air-fuel ratio, so that even if the actual base air-fuel ratio of the carburetor changes due to changes in atmospheric pressure, temperature, etc. or changes in the characteristics of the carburetor itself over time, the lean air-fuel ratio will be maintained in advance. It is maintained at a predetermined control target value. This makes it possible to set the lean air-fuel ratio control target value to a larger value that is closer to the flammable limit air-fuel ratio of the air-fuel mixture, and to obtain the maximum effect in lean air-fuel ratio control. become.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the accompanying drawings. The attached FIG. 1 is a schematic configuration diagram showing one embodiment of an air-fuel ratio control device according to the present invention. In the figure, 1 indicates the engine,
The engine 1 takes in a mixture of fuel and air through the carburetor 2 through the intake manifold 3, and discharges exhaust gas to the exhaust manifold 4.

The carburetor 2 has a large bench lily 6 in its intake bore 5 . A throttle valve 7 is provided in the intake bore 5 on the downstream side of the large bench lily 6, and a choke valve 8 is provided in the intake bore 5 on the upstream side of the large bench lily 6. A small bench lily 9 is provided at the throat of the large bench lily 6, and a main fuel nozzle 10 opens at the throat of this small bench lily. The main fuel nozzle 10 has a float chamber 1
A liquid fuel such as gasoline stored in the fuel tank 1 is supplied through a main fuel passage 13 while its flow rate is adjusted by a main fuel jet 12. A well 14 is formed in the middle of the main fuel passage 13, and within this well 14 is provided an air bleed tube 15 having a plurality of small holes. Air bleed tube 15 is connected to a fixed air bleed jet 38. An air bleed conduit 16 is connected to the base of the main fuel nozzle 10, and a proportional actuator 17 is connected to this conduit for controlling the flow rate of air flowing through the conduit. The proportional actuator 17 is a flow rate control valve, and this device includes a cylindrical guide tube 19 having a valve port 18 and a cylindrical guide tube 19 that moves in the axial direction of the guide tube 19 and controls the effective opening of the valve boat 18. A slide sleeve 20 for controlling the area is included. An electromagnetic coil 21 is attached to the slide sleeve 20, and as the current supplied to the electromagnetic coil increases, the slide sleeve 20 cooperates with a permanent magnet 22 to resist the action of a compression coil spring 23. Move to the right in the diagram and select valve port 18.
The effective aperture area of the Power supply control to the electromagnetic coil 21 is performed by a computer 24, which will be described later.

The carburetor 2 is also provided with a slow port 25, into which a part of the fuel flowing through the main fuel passage 13 is branched off from the middle of the passage. 26 and a slow jet 27a provided on the way
The gas is supplied while its flow rate is adjusted by the economizer jet 27b. Further, an idle adjustment screw 28 is provided in the slow port 25 portion. Further, a fixed air bleed jet 29 is provided in the middle of the slow fuel passage 26.

An air bleed conduit 30 is connected to the slow port 25, and a proportional actuator 31 is connected to this conduit. The proportional actuator 31, like the proportional actuator 17, has a guide tube 33 with a valve port 32.
, a slide sleeve 34 to which an electromagnetic coil 35 is attached, a permanent magnet 36, and a compression coil spring 3.
7, which operates in the same manner as the proportional actuator, and whose operation is controlled by the computer 24. Proportional actuator 3
1 is designed so that when the valve port 32 of this valve is fully opened, air bleed is performed with a relatively large amount of air to the extent that it substantially prevents fuel from being discharged from the slow port 25 to the intake bore 5. The size of the valve port is set.

An O ₂ sensor 40 is attached to the exhaust manifold 4. The O ₂ sensor 40 detects excess oxygen in the exhaust gas flowing inside the exhaust manifold 4,
It is designed to generate an electrical signal in response to that. This O ₂ sensor 40 outputs a voltage signal of about 1.0V when the air-fuel ratio is smaller than the stoichiometric air-fuel ratio, whereas it outputs a voltage signal of about 0.1V when the air-fuel ratio is larger than the stoichiometric air-fuel ratio, that is, when lean. death,
These voltage signals are input to the computer 24.

FIG. 2 is an electrical circuit diagram illustrating one embodiment of computer 24. The voltage signal generated by the O ₂ sensor 40 is sent to a comparator 44 via a voltage follower 41, a variable gain amplifier AGC 42, and a resistive element 43.
is input to the non-inverting terminal of The comparator 44 compares the output voltage V _x of the variable gain amplifier 42 with the set voltage V _r of the constant voltage generation circuit 45 inputted to its inverting terminal, and when V _x ≧ V _r , in other words, the air-fuel ratio is determined. When V x is smaller than a predetermined air-fuel ratio (theoretical air-fuel ratio), a high-level voltage signal “1” is output, and when V _x <V _r , a low-level voltage signal “0” is output. That is,
The comparator 44 outputs a pulse signal according to fluctuations in the air-fuel ratio. This pulse signal is input to the inverting terminals of an integrator 46 and an inverting amplifier 47, which are connected in parallel. The integrator 46 is an operational amplifier 46a
It consists of a resistor element 46b and a capacitor 46c, and integrates the input voltage according to an integration constant determined by the resistor element 46b and capacitor 46c, and outputs a voltage signal proportional to the integrated value. A non-inverting terminal of the integrator 46 is connected to a constant voltage generating circuit 46d. The inverting amplifier 47 is the operational amplifier 4
7a and resistance elements 47b and 47c,
Invert and amplify the input signal. A non-inverting terminal of the inverting amplifier 47 is connected to a constant voltage generating circuit 47d. The output signals of the integrator 46 and the inverting amplifier 47 are each input to the inverting terminal of the adder 48. The adder 48 includes an operational amplifier 48a and resistance elements 48b, 48.
c and 48d, and performs non-in-phase addition of both signals and outputs an integral signal with a skip. A non-inverting terminal of the adder 48 is connected to a constant voltage generating circuit 48e. This output signal is selectively inputted to a non-inverting terminal of a comparator 51 via an analog switch 49 and a resistive element 50. The comparator 51 receives the triangular wave generated by the triangular wave generating circuit 52 via the resistor 53 to its inverting terminal, compares this triangular wave with the signal from the adder 48, and generates a pulse signal with a duty ratio based on the comparison result. occurs. The triangular wave generated by the triangular wave generation circuit 52 is 200
It may have a frequency of about Hz.

When the comparator 51 receives a signal from the adder 48, it generates a pulse signal with a larger duty ratio when the air-fuel ratio is smaller, that is, when the air-fuel mixture is richer.

The pulse signal generated by the comparator 51 is transmitted to the resistive element 5.
4 and 55, and are input to the base terminals of transistors 56 and 57, respectively. The transistor 56 has its collector terminal connected to the electromagnetic coil 21 of the proportional actuator 17, and its emitter terminal grounded. The transistor 57 has its collector terminal connected to the electromagnetic coil 35 of the proportional actuator 31, and its emitter terminal grounded. Further, the base terminal and collector terminal of each of the transistors 56 and 57 are connected to a capacitor 58,
59.

The pulse signal generated by the comparator 51 is input to the electromagnetic coil of the proportional actuator via a transistor. The pulse signal given to the electromagnetic coil is
Since it is a pulse signal with a frequency of about 200Hz, this pulse signal acts on the electromagnetic coil as an averaged DC current signal, and the larger the duty ratio, the more the slide sleeve is driven to the right as seen in Figure 1, and the valve is activated. This increases the effective opening area of the port.

The output signal of the comparator 44 is input to the temporal average air-fuel ratio calculation device 60 via the NOT gate 82.
The temporal average air-fuel ratio calculation device 60 includes an up-down counter and a ladder network circuit, and the up-down counter is input to the count terminal a only when a "1" signal is given to the enable terminal b. It is designed to count signals. The up-down counter counts up when the signal input to the count terminal a is "1", that is, when the output signal of the comparator 44 is "0", and the signal input to the count terminal a is "0". , that is, the output signal of the comparator 44 is "1"
When , it becomes a down count. The ladder network circuit converts the digital signal of the up-down counter into an analog signal, that is, a voltage, and generates a voltage signal representing the average value of the air-fuel ratio over time at the output terminal c. It is designed to output to the non-inverting terminal.

The non-inverting amplifier 61 includes an operational amplifier 61a and resistance elements 61b and 61c, and generates an output signal having a value that is a predetermined multiple of the input voltage. The output signal of the non-inverting amplifier 61 is selectively input to the non-inverting terminal of the comparator 51 via an analog switch 73.

When the output signal generated by non-inverting amplifier 61 is input to comparator 51 via analog switch 73, comparator 51 generates a pulse signal with a relatively large duty ratio based on the average air-fuel ratio over time. When this pulse signal is given to the electromagnetic coils 21 and 35, the proportional actuators 17 and 31 operate so that the air-fuel ratio of the mixture supplied to the engine 1 becomes a predetermined lean air-fuel ratio larger than the stoichiometric air-fuel ratio. In this case, the effective opening area of the valve ports 18 and 32 is adjusted to be about 18, for example.

FIG. 3 is an electrical circuit diagram showing one embodiment of the temporal average air-fuel ratio calculating device. The temporal average air-fuel ratio calculating device 60 includes an up-down counter 62, a ladder network circuit 63, an astable multivibrator 64, and a plurality of logic gates. The up-down counter 62 is a binary up-down counter, and the clock input terminal CL
is connected to the output terminal of the AND gate 65, and the output terminals _Q1 to _Q5 are connected to the R-2R ladder network circuit 6.
3 are connected in order from the lower digits.

Each input terminal of the 5-input AND gate 66 is connected to each output terminal of the up-down counter 62, respectively. Each input terminal of the 5-input OR gate 67 is connected to each output terminal of the up-down counter 62, respectively. One input terminal of the NAND gate 68 is connected to the count terminal a, and the other input terminal is connected to the output terminal of the AND gate 66.
The output terminal of the NAND gate 68 is the AND gate 69
is connected to one input end of the OR gate 6
One input terminal of 7 is connected to the count terminal a, and the other input terminal is connected to the output terminal of the OR gate 67. The output end of each of AND gate 69 and OR gate 70 is connected to the input end of AND gate 65. Further, one input terminal of the AND gate 65 is connected to the enable terminal b. The other input terminal of AND gate 69 is connected to astable multivibrator 64 . The oscillation frequency of the astable multivibrator 64 is determined by the time constant of a capacitor 71 and a resistive element 72.

The up-down counter 62 counts up when a "1" signal is input to the count terminal a, and counts down when a "0" signal is input to the count terminal a. 5 input AND
The gate 66 is for preventing the up-down counter 62 from overflowing, and when all the outputs of the up-down counter 62 are "1", the AND
The output of gate 66 becomes "1". When the U/D input is "1", the output of the NAND gate 68 becomes "0", so the output of the AND gate 65 becomes "0", and the clock signal generated by the astable multivibrator 64 becomes the up-down counter. Input to the CL terminal of 62 is prohibited. The 5-input OR gate 67 is provided to prevent further down-counting after the outputs of the up-down counter 62 have all become "0".
When all the outputs of the up-down counter 62 become "0", the output of the 5-input OR gate 67 becomes "0". When the U/D input is "0", the output of the OR gate 70 is "0", so the AND gate is passed from the astable multivibrator 64 to the AND gate 69.
The clock signal input to gate 65 is
CL of up-down counter 62 at AND gate
Transmission to the terminal is blocked. That is, when the U/D input is "1" and all the outputs of the up-down counter 62 are "1", and when the U/D input is "0" and all the outputs of the up-down counter 62 are "1". When it is "0", no clock signal is input to the clock input terminal CL. Further, even when a "0" signal is input to enable terminal b, no clock signal is input to clock input terminal CL.

When the air-fuel ratio is smaller than the stoichiometric air-fuel ratio and the output of the comparator 44 is "0", the up-down counter 62
Since "1" is input to the U/D terminal, it counts up by one for each clock from the astable multivibrator 64, and when the air-fuel ratio becomes larger than the stoichiometric air-fuel ratio, the output of the comparator 44 becomes "1". '', the up-down counter 62 receives ``0'' at the U/D terminal, so it counts down by one for each clock signal generated by the astable multivibrator 64. The ladder network circuit 63 is an up-down counter 62
This is a well-known D/A converter that converts a binary output value into an analog voltage.

Analog switches 49 and 73 shown in FIG. 2 are each in a conductive state when a "1" signal is applied to its gate terminal, and are non-conductive when a "0" signal is applied to its gate terminal. become a state.

The negative pressure switch 74 is sensitive to the intake pipe negative pressure of the engine 1, and when it is larger than a predetermined value, for example -
When it is greater than 300mmHg, a “1” signal is generated, and the signal is sent to the NOR gate 76 via the NOT gate 75.
Output to. Further, the output signal of the NOT gate 75 is input to the enable terminal b of the temporal average air-fuel ratio calculation device 60. The idling switch 77 is
For example, in response to the opening degree of the throttle valve 7, a "1" signal is generated when the throttle valve is at or near the idling position, and this signal is sent to the NOR gate 76 and another gate.
Output to NOR gate 78. The NOR gate 76 generates a "1" signal only during low load operation, excluding idling operation.

Another negative pressure switch 79 is sensitive to the engine intake pipe negative pressure, and when it is less than a predetermined value, -
When it is less than 100 mmHg, a "1" signal is generated, which is output to the NAND gate 78 via the delay circuit 80.

The output signal of the NOR gate 76 is inputted to the gate terminal of the analog switch 73 via a delay circuit 81, and is also inputted to the NOR gate 78. The output signal of NOR gate 78 is input to the gate terminal of analog switch 49.

The air-fuel ratio control device constructed as described above operates as follows.

When the engine 1 is operated under medium load, each of the negative pressure switch 74, idling switch 77, and negative pressure switch 79 outputs a "0" signal, so the gate terminal of the analog switch 73 receives a "0" signal. However, a “1” signal is input to the gate terminal of the analog switch 49. At this time, the analog switch 49 becomes conductive, and the voltage signal generated by the adder 48 is inputted to the comparator 51 via the analog switch 49. Therefore, at this time
The electromagnetic coils 21 and 35 are driven by a pulse signal with a duty ratio determined based on the signal generated by the O ₂ sensor 40, thereby adjusting the effective opening areas of the valve ports 18 and 32, thereby reducing the amount of air bleed. controlled. This air bleed control allows the engine 1 to be supplied with an air-fuel mixture having an air-fuel ratio near the stoichiometric air-fuel ratio. During this operation, the three-way catalytic converter provided in the exhaust system acts as a three-way catalytic converter that simultaneously purifies the three components of HC, CO, and NOx.

Also at this time, the temporal average air-fuel ratio calculation device 60
Since a "1" signal is input to the enable terminal b of the device, the device accepts the output signal of the comparator 44 and calculates the average air-fuel ratio over time.

When the engine 1 is operated at a low load, the negative pressure switch 74 generates a "1" signal, and the idling switch 77 and the negative pressure switch 79 each output a "0" signal.
Since the analog switch 49 generates a signal, the gate terminal of the analog switch 49 receives a “0” signal, and the analog switch 7
A "1" signal is input to each gate terminal of No. 3. Therefore, at this time, the non-inverting amplifier 61
The voltage generated is input to the comparator 51, and the comparator 51 generates a pulse signal with a relatively large duty ratio based on the voltage. As a result, the electromagnetic coils 21 and 3 of the proportional actuators 17 and 31
5 substantially increases, and the effective opening area of valve ports 18 and 32 increases accordingly.

The non-inverting amplifier 61 generates an output signal that is a predetermined multiplication of the input voltage, that is, a voltage signal representing the average air-fuel ratio over time, and inputs it to the non-inverting terminal of the comparator 51, so that the amount of air bleed at this time is The correction is made based on the average value of the air-fuel ratio under feedback control, in other words, the average base air-fuel ratio of the carburetor 2. Therefore, even if the base air-fuel ratio of the carburetor 2 fluctuates due to changes in atmospheric pressure, temperature, etc. or changes in characteristics over time, the engine 1 is supplied with a lean air-fuel mixture having a predetermined lean air-fuel ratio that is greater than the stoichiometric air-fuel ratio. It becomes like this. In this way, by constantly supplying a lean air-fuel mixture with a constant lean air-fuel ratio during low-load operation,
It becomes possible to bring the control target air-fuel ratio even closer to the flammable limit air-fuel ratio, and it is possible to significantly improve fuel efficiency. Furthermore, during this operation,
The three-way catalytic converter installed in the exhaust system
It acts as an oxidation catalytic converter that purifies unburned components such as HC and CO.

The delay circuit 81 delays the transmission of the output signal of the NOR gate 76 to the gate terminal of the analog switch 73, and the analog switch 73 is activated only when the engine 1 is continuously operated at a low load for a predetermined period of time or more.
acts so that it becomes conductive.

When the engine 1 is idling, the idling switch 77 generates a "1" signal even if the negative pressure switch 74 generates a "1" signal, so both NOR gates 76 and 78 are "0".
It will start outputting a signal. At this time, no current is applied to the electromagnetic coils 21 and 35, so the valve ports 18 and 32 are fully closed, and the carburetor 2 supplies the engine 1 with a relatively rich air-fuel mixture necessary for idling operation. .

Further, when the engine 1 is operated under high load, the negative pressure switch 74 and the idling switch 77 each generate a "0" signal, and the negative pressure switch 79 generates a "1" signal.
Since a signal is generated, the NOR gate 76 is also activated at this time.
and 78 both generate a "0" signal. Therefore, since no current is applied to the electromagnetic coils 21 and 35 at this time, the valve ports 18 and 32 are fully closed.
The carburetor 2 supplies the engine 1 with a relatively rich air-fuel mixture necessary for high-load operation. Note that due to the action of the delay circuit 80, the relatively rich air-fuel mixture as described above is supplied during high-load operation only after a predetermined period of time has elapsed since the transition from medium-load operation to high-load operation.

Although the present invention has been described in detail with respect to specific embodiments above, it will be understood by those skilled in the art that the present invention is not limited thereto and that various embodiments can be made within the scope of the present invention. It should be obvious.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram showing one embodiment of the air-fuel ratio control device for an engine according to the present invention, Fig. 2 is an electric circuit diagram of the air-fuel ratio control device according to the present invention, and Fig. 3 is a temporal average air-fuel ratio calculation. FIG. 1 is an electrical circuit diagram showing one embodiment of the device. 1... Engine, 2... Carburetor, 3... Intake manifold, 4... Exhaust manifold, 5... Intake bore, 6
...Large bench lily, 7...Throttle valve, 8
...Chiyoke valve, 9...Small bench lily, 1
0... Main fuel nozzle, 11... Float chamber, 12
...Main fuel jet, 13...Main fuel passage,
14...well, 15...air bleed tube, 1
6... Air bleed conduit, 17... Proportional actuator, 18... Valve port, 19... Guide tube, 2
0... Slide sleeve, 21... Electromagnetic coil, 22
...Permanent magnet, 23...Compression coil spring, 24...Computer, 25...Slow port, 26...Slow fuel passage, 27a...Slow jet, 27b...Economizer jet, 28...Idle adjuster screw, 29...Air bleed jet, 30...Air bleed conduit, 31...Proportional actuator, 3
2... Valve port, 33... Guide tube, 34... Slide sleeve, 35... Electromagnetic coil, 36... Permanent magnet, 37... Compression coil spring, 38... Air bleed jet, 40... O ₂ sensor, 41... Voltage follower, 42... Variable gain amplifier, 43... Resistance element, 44... Comparator, 45... Constant voltage generation circuit, 4
6... Integrator, 47... Inverting amplifier, 48... Adder,
49... Analog switch, 50... Resistance element, 51
... Comparator, 52 ... Triangular wave generation circuit, 53 ... Resistance element, 54, 55 ... Resistance element, 56, 57 ... Transistor, 58, 59 ... Capacitor, 60 ... Temporal average air-fuel ratio calculation device, 61 ... Non-inverting amplifier, 62
...Up-down counter, 63...Ladder network circuit, 64...Astable multivibrator, 6
5...AND gate, 66...5 input AND gate, 6
7...5 input OR gate, 68...NAND gate, 6
9...AND gate, 70...OR gate, 71...capacitor, 72...resistance element, 73...analog switch, 74...negative pressure switch, 75...NOT gate,
76...NOR gate, 77...idling switch, 78...NOR gate, 79...negative pressure switch,
80, 81...Delay circuit.

Claims (1)

[Claims] 1: an exhaust sensor that detects the concentration of exhaust components in exhaust gas discharged from the engine; an arithmetic device that generates a signal representing the air-fuel ratio of the air-fuel mixture supplied to the engine based on a signal generated by the exhaust sensor; an air bleed control device that is driven based on a signal generated by a calculation device and performs feedback control of the air bleed amount of the carburetor so that the air fuel ratio becomes an air fuel ratio near the stoichiometric air fuel ratio; and the air bleed control device performs feedback control of the air fuel ratio. a time-based average air-fuel ratio calculation device that calculates and stores a time-based average value of the air-fuel ratio based on a signal generated by the exhaust sensor when The air bleed amount by the air bleed control device is increased based on the temporal average air-fuel ratio calculated by the temporal average air-fuel ratio calculation device, and the air-fuel ratio is adjusted to a predetermined value substantially larger than the stoichiometric air-fuel ratio. 1. An air-fuel ratio control device for an engine, comprising: an air bleed correction device during low-load operation that corrects the air-fuel ratio.