JPS638308B2 - - 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 concentration of NOx in the exhaust gas is low, and the amount of NOx in the exhaust gas is reduced by correcting the air-fuel ratio of the air-fuel mixture supplied to the engine to be deviated from the stoichiometric air-fuel ratio.
NOx concentration can be maintained at a sufficiently low value.

The present invention focuses on the above-mentioned fact, and when the engine is operated at low load, feedback control is stopped and a lean air-fuel mixture with an air-fuel ratio higher than the stoichiometric air-fuel ratio is supplied to the engine, thereby improving fuel efficiency. It is an object of the present invention to provide an improved feedback control type air-fuel ratio control device that achieves both purification of exhaust gas.

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 port 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.

Further, the carburetor 2 is provided with a slow port 25, and a part of the fuel flowing through the main fuel passage 13 is transferred to the slow port 25 into a slow fuel passage 26 which is branched from the middle of the passage. A slow jet 27a provided along 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 inverted terminal of The comparator 44 compares the output voltage Vx of the variable gain amplifier 42 with the set voltage Vr of the constant voltage generation circuit 45 inputted to its non-inverting terminal, and when Vx≦Vr, in other words, the air-fuel ratio is at a predetermined level. When the fuel ratio is larger than the stoichiometric air-fuel ratio, a high-level voltage signal "1" is output, and when Vx>Vr, 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 non-inverting terminal of the adder 48. The adder 48 includes an operational amplifier 48a and resistance elements 48b, 4.
8c and 48d, the two signals are synchronously added and an integral signal having a skip is output. The inverting terminal of the adder 48 is connected to a constant voltage generating circuit 48e. This output signal is analog switch 4
9, is selectively input to the non-inverting terminal of the comparator 51 via the resistor element 50. The comparator 51 receives a triangular wave generated by the triangular wave generating circuit 52 at its inverting terminal via a resistive element 53, and combines this triangular wave with the adder 4.
8 and generates a pulse signal with a duty ratio based on the comparison result. 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.

Further, a constant voltage generated by a constant voltage generating circuit 60 is selectively inputted to the non-inverting terminal of the comparator 51 via an analog switch 61. When the constant voltage generated by the constant voltage generating circuit 60 is input to the comparator 51 via the analog switch 61, the comparator 51 generates a pulse signal with a relatively large predetermined duty ratio. When this pulse signal is given to the electromagnetic coils 21 and 35, the proportional actuators 17 and 31 operate the valve port 18 so that the air-fuel ratio of the mixture supplied to the engine 1 is greater than the stoichiometric air-fuel ratio, for example, about 18. , 32 are adjusted.

Analog switches 49 and 61 are each in a conductive state when a "1" signal is applied to their gate terminal, and are non-conductive when a "0" signal is applied to their gate terminal.

The negative pressure switch 62 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 passed through NOT gate 63 and OR gate 87.
Output to NOR gate 64. The idling switch 65 is sensitive to the opening degree of the throttle valve 7, for example, and generates a "1" signal when the throttle valve is at or near the idling position, and transmits the signal to the NOR gate 64.
and output to 68. Therefore, NOR gate 64
generates a “1” signal only during low load operation, excluding idling operation.

Another negative pressure switch 66 is sensitive to the intake pipe negative pressure of the engine 1, and when it is smaller than a predetermined value,
For example, when it is less than -100mmHg, it generates a “1” signal and sends it through the delay circuit 67 to another signal.
Output to NOR gate 68.

The output signal of the NOR gate 64 is input to the gate terminal of the analog switch 61 via a delay circuit 69, and is also input to the NOR gate 68. The output signal of the NOR gate 68 is input to the gate terminal of the analog switch 49.

Further, a constant voltage generated by a constant voltage generating circuit 60 is selectively inputted to the inverting terminal of the inverting amplifier 47 via a resistor 70, an analog switch 71, and a resistor element 72. The resistor 70 functions to reduce the constant voltage generated by the constant voltage generating circuit 60 by a predetermined amount. This reduced voltage signal is input to the inverting terminal of the inverting amplifier 47, and based on this signal, the inverting amplifier 47 outputs a predetermined voltage signal, which is transmitted to the adder 48 and the analog switch 49.
When the air-fuel ratio of the air-fuel mixture supplied to the engine 1 is input to the comparator 52 via the A pulse signal with a predetermined duty ratio is generated to drive the electromagnetic coils 21 and 35 so that the air-fuel ratio is maintained. When the fuel is common gasoline, the lean air-fuel ratio may be about 18.

Further, the signal generated by the negative pressure switch 62 is S
-Set terminal S of R-type flip-flop circuit 73
is input. The output signal of the comparator 44 is input to the reset terminal R of this flip-flop circuit 73, and the signal generated at the output terminal Q is input to the gate terminal of the analog switch 71.

Further, the signal generated by the negative pressure switch 62 is
The signal is inputted to the set terminal S of another SR type flip-flop circuit 88 via the NOT gate 63. Output terminal Q of this flip-flop circuit 88
is connected to the base terminal of transistor 90 via OR gate 87 and resistor element 89. Transistor 90 connects comparator 44 at its collector terminal.
It is connected to the output terminal of the terminal, and is also grounded at the emitter terminal. A reset terminal R of flip-flop circuit 88 is connected to the output terminal of comparator 91. The comparator 91 compares the output voltage Vy of the adder 48 input to its inverting terminal with the set voltage Vs of the constant voltage generation circuit 92 input to its non-inverting terminal, and when Vy≦Vs, a high level is detected. A voltage signal “1” signal is output, and when Vy>Vs, a low level voltage signal “0” signal is output.

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 62, idling switch 65, and negative pressure switch 66 outputs a "0" signal, so the gate terminal of the analog switch 61 receives a "0" signal. But analog switch 4
A "1" signal is input to the gate terminal of 9.
Also, at this time, the flip-flop circuit 73 is in a reset state, and a "0" signal is input to the analog switch 71. Flip-flop circuit 88 is also in a reset state, and transistor 9
A “0” signal is given to the base terminal of “0”. At this time, only the analog switch 49 becomes conductive, and the voltage signal generated by the adder 48 is input 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 controlling the effective opening areas of the valve ports 18 and 32. The amount of air bleed is 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.

When the engine 1 is operated at a low load, the negative pressure switch 62 generates a "1" signal, and the idling switch 65 and negative pressure switch 66 each output a "0" signal.
Since a signal is generated, a “0” signal is sent to the gate terminal of analog switch 49, and
A “1” signal is now input to the gate terminal of “1”. Therefore, at this time, the voltage generated by the constant voltage generating circuit 60 is input to the comparator 51, and the comparator 51 generates a pulse signal with a relatively large predetermined duty ratio based on the voltage. As a result, the electromagnetic coils 21 of the proportional actuators 17 and 31
and 35 is substantially increased, and the effective open area of valve ports 18 and 32 is increased accordingly. As a result, the amount of air bleed increases, and the engine 1 is supplied with a lean air-fuel mixture having the lean air-fuel ratio, for example, about 18, which is higher than the stoichiometric air-fuel ratio. Furthermore, during this operation, the three-way catalytic converter installed in the exhaust system is
It acts as an oxidation catalytic converter that purifies unburned components such as HC and CO.

The delay circuit 69 delays the transmission of the output signal of the NOR gate 64 to the gate terminal of the analog switch 61, and only when the engine 1 is continuously operated at a low load for a predetermined period of time or more, the analog switch 61 is activated.
acts so that it becomes conductive.

When the engine 1 is being operated at a low load, the negative pressure switch 62 continues to output a "1" signal, so the flip-flop circuit 73 continues to output a "0" signal without being set, and the analog switch 71 becomes non-conductive. maintain the condition.

When the engine 1 shifts from low load operation to medium load operation, the output signal of the negative pressure switch 62 changes from a "1" signal to a "0" signal as shown in the time-series signal waveform diagram shown in FIG. . Therefore, the analog switch 61 becomes non-conductive, and the analog switch 49 becomes conductive.At the same time, the flip-flop circuit 73 enters the set state and outputs a "1" signal to the analog switch 71. For this reason, the constant voltage generated by the constant voltage generating circuit 60 is adjusted to be reduced in voltage by the resistor 70, and is inputted to the inverting terminal of the inverting amplifier 47 via the analog switch 71. As a result, the comparator 51 generates a pulse signal with a predetermined duty ratio that drives the electromagnetic coils 21 and 35 so that the air-fuel ratio of the air-fuel mixture supplied to the engine 1 becomes the intermediate air-fuel ratio, and the electromagnetic coil 21 and 35 are driven by this pulse signal, the engine 1
The air-fuel ratio of the air-fuel mixture supplied to the air-fuel mixture reaches the intermediate constant fuel ratio relatively quickly. At this time, the air-fuel ratio is still higher than the stoichiometric air-fuel ratio, so the comparator 44 is "1".
By outputting a signal and inputting it to the integrator 46, the voltage signal given to the comparator 51 gradually decreases, and based on this, the duty ratio of the pulse signal generated by the comparator 51 gradually decreases.
By applying this to the electromagnetic coils 21 and 35, the air-fuel ratio of the air-fuel mixture supplied to the engine 1 gradually approaches the stoichiometric air-fuel ratio in accordance with the integral constant of the integrator 46. In this way, the air-fuel ratio is gradually corrected from the lean air-fuel ratio to the stoichiometric air-fuel ratio, thereby maintaining good drivability during transient operation. Then, when the air-fuel ratio of the air-fuel mixture supplied to the engine 1 becomes smaller than the stoichiometric air-fuel ratio, the O ₂ sensor 40 is set to "1" at the reset terminal R of the flip-flop circuit 73.
As a result, a "0" signal is applied, the flip-flop circuit 73 is reset again, and the analog switch 71 is rendered non-conductive. From this point on, the air-fuel ratio is feedback-controlled based on the signal generated by the O ₂ sensor as described above, and the air-fuel ratio of the air-fuel mixture supplied to the engine 1 is maintained at approximately the stoichiometric air-fuel ratio.

Further, when the engine 1 shifts from medium load operation to low load operation, the output signal of the negative pressure switch 62 changes as shown in the time series signal waveform diagram shown in FIG.
The signal changes from a “0” signal to a “1” signal. Also, at this time, the set terminal S of the flip-flop circuit 88
Since the signal input to the flip-flop circuit 88 changes from a "1" signal to a "0" signal, the flip-flop circuit 88 becomes "1".
Output a signal. This output signal is OR gate 87
Since the signal is output to the NOR gate 64 via the analog switch 61, the analog switch 61 remains non-conductive, and the analog switch 49 maintains the conductive state. Further, the output signal of the flip-flop circuit 88 is transmitted to the transistor 90.
Therefore, the collector terminal and emitter terminal of the transistor 90 are brought into conduction, and the output terminal of the comparator 44 is grounded. Therefore, the output signal of comparator 44 becomes a "0" signal, and integrator 46 generates a voltage signal that gradually increases according to its own time constant.
As a result, the duty ratio of the pulse signal generated by the comparator 51 gradually increases, and the effective opening areas of the valve ports 18 and 32 of the proportional actuators 17 and 31 gradually increase, and the engine 1 The air-fuel ratio of the air-fuel mixture supplied to the air-fuel mixture gradually increases. When the air-fuel ratio reaches the intermediate air-fuel ratio indicating an intermediate value between the lean air-fuel ratio and the stoichiometric air-fuel ratio, the voltage Vy of the signal generated by the adder 48 becomes larger than the set voltage Vs of the constant voltage generation circuit 92, Therefore, the output signal of the comparator 91 changes from a "1" signal to a "0" signal. Therefore, flip-flop circuit 88 is reset and transistor 9
A "0" signal is now given to the base terminal of "0". Also, at this time, the output signal of the NOR gate 64 becomes a "1" signal, and the analog switch 61
becomes conductive, and analog switch 49 becomes non-conductive. As a result, the voltage signal generated by the constant voltage generation circuit 60 is applied to the comparator 51, and the comparator 51 generates a pulse signal with a predetermined duty ratio according to the voltage signal, thereby controlling the proportional actuators 17 and 31. Valve port 18,3
The effective opening area of 2 increases relatively rapidly, and the engine 1 is supplied with a lean air-fuel mixture having the lean air-fuel ratio of, for example, about 18.

In this way, when transitioning from medium-load operation to low-load operation, the air-fuel ratio gradually increases by a portion corresponding to approximately half of the range of fluctuation in the air-fuel ratio at that time, so drivability is not deteriorated due to sudden changes in the air-fuel ratio. Avoided.

When the engine 1 is idling, the negative pressure switch 62 generates a “1” signal;
Since the idling switch 65 also generates a "1" signal, the NOR gates 64 and 68 both output "0" signals. 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 62 and the idling switch 65 generate a "0" signal, and the negative pressure switch 66 generates a "1" signal.
Since a signal is generated, the NOR gate 64 is also used at this time.
and 68 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 required during high-load operation. Note that due to the action of the delay circuit 67, a relatively rich air-fuel mixture is supplied during high-load operation as described above only after a predetermined time has elapsed since the transition from low-load operation to high-load operation.

FIG. 4 shows another embodiment of the air-fuel ratio control device according to the present invention. In addition, in Figure 4, the second
Portions corresponding to the figures are designated by the same reference numerals as those in FIG. 2. In such an embodiment, the signal generated by the temporal average air-fuel ratio calculating device 74 at the non-inverting terminal of the comparator 51 is connected to the non-inverting amplifier 75.
and is selectively input via an analog switch 61. Further, the output signal of the non-inverting amplifier 75 is transmitted through a resistor 70, an analog switch 71,
The signal is selectively input to the inverting terminal of the inverting amplifier 47 via the resistive element 72 . The output signal of the non-inverting amplifier 75 is connected to the non-inverting terminal of the comparator 91 through the resistor 93.
It is now entered through the .

The temporal average air-fuel ratio calculating device 74 includes an up-down counter and a ladder network circuit, and the up-down counter has a NOT gate 94 at the count terminal a only when a "1" signal is given to the enable terminal b. The output signal of the comparator 44, which is input via the comparator 44, is counted. When the signal input to the count terminal a is "1", the up-down counter
When the output signal of the comparator 44 is "0", an up count is performed, and when the signal input to the count terminal a is "0", that is, when the output signal of the comparator 44 is "1", a down count is performed. 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 75 includes an operational amplifier 75a and resistance elements 75b and 75c, 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 75 is selectively input to the non-inverting terminal of the comparator 51 via the analog switch 61.

When the output signal generated by non-inverting amplifier 75 is input to comparator 51 via analog switch 61, 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, for example, about 18. Valve port 1 so that
Adjust the effective opening area of 8 and 32.

FIG. 5 is an electrical circuit diagram showing one embodiment of the time-course average air-fuel ratio calculating device. The temporal average air-fuel ratio calculating device 74 includes an up-down counter 76, a ladder network circuit 77, an astable multivibrator 78, and a plurality of logic gates. The up-down counter 76 is a binary up-down counter, and the clock input terminal CL
is connected to the output terminal of the AND gate 79, and the output terminals _Q1 to _Q5 are connected to the R-2R ladder network circuit 7.
7 in order from the lower digits.

Each input terminal of the 5-input AND gate 80 is connected to each output terminal of the up-down counter 76, respectively. Each input terminal of the 5-input OR gate 81 is connected to each output terminal of the up-down counter 76, respectively. One input terminal of the NAND gate 82 is connected to the count terminal a, and the other input terminal is connected to the output terminal of the AND gate 80. NAND
The output terminal of gate 82 is connected to one input terminal of AND gate 83. One input terminal of the OR gate 81 is connected to the count terminal a, and the other input terminal is connected to the count terminal a.
The output terminals of the OR gate 81 are connected to each other.
The output end of each of AND gate 83 and OR gate 84 is connected to the input end of AND gate 79.
Further, one input terminal of the AND gate 79 is connected to the enable terminal b. The other input terminal of AND gate 83 is connected to astable multivibrator 78 . Astable multivibrator 78
The oscillation frequency is determined by the time constant of the capacitor 85 and the resistive element 86.

The up-down counter 76 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 80 is for preventing the up-down counter 76 from overflowing, and when all the outputs of the up-down counter 76 are "1", the AND
The output of gate 80 becomes "1". When the U/D input is "1", the output of the NAND gate 82 becomes "0", so the output of the AND gate 79 becomes "0", and the clock signal generated by the astable multivibrator 78 becomes the up-down counter. Input to the CL terminal of 76 is prohibited. The 5-input OR gate 81 is provided to prevent further down-counting after the outputs of the up-down counter 76 have all become "0".
When all the outputs of the up-down counter 76 become "0", the output of the 5-input OR gate 81 becomes "0". When the U/D input is “0”, the output of the OR gate 84 is “0”, so the AND gate is passed from the astable multivibrator 78 to the AND gate 83.
The clock signal input to gate 79 is
CL of up-down counter 76 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 76 are "1", and when the U/D input is "0" and all the outputs of the up-down counter 76 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 76
Since "1" is input to the U/D terminal, it counts up by one for each clock from the astable multivibrator 78, 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 76 receives ``0'' at the U/D terminal, so it counts down by one for each clock signal generated by the astable multivibrator 78. The ladder network circuit 77 has an up/down counter 76
This is a well-known D/A converter that converts a binary output value into an analog voltage.

When the engine 1 is being operated at a medium load, a "1" signal is input to the enable terminal b of the temporal average air-fuel ratio calculating device 74, so that the device is connected to the comparator 4.
4 and calculates the average air-fuel ratio over time.

When the engine 1 is operated at a low load, the voltage generated by the non-inverting amplifier 75 is input to the comparator 51, and the comparator generates a pulse signal with a relatively large duty ratio based on the voltage. This substantially increases the current supplied to the electromagnetic coils 21 and 35 of the proportional actuators 17 and 31, and the effective opening area of the valve ports 18 and 32 increases accordingly.

The non-inverting amplifier 75 generates an output signal that is a predetermined multiplication of the input voltage, that is, the voltage signal representing the average air-fuel ratio over time, and inputs it to the non-inverting terminal of the comparator 51. The correction is made based on the average value of the air-fuel ratio in 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 mixture having a predetermined air-fuel ratio greater than the stoichiometric air-fuel ratio. It becomes like this. By constantly supplying a lean air-fuel mixture with a constant air-fuel ratio during low-load operation, it is possible to bring the air-fuel ratio closer to the flammable limit air-fuel ratio, significantly improving fuel efficiency. .

When the engine 1 shifts from low load operation to medium load operation, the analog switch 61 becomes non-conductive and the analog switch 4
9 and 71 become conductive. Therefore, the voltage signal generated by the non-inverting amplifier 75 is reduced in pressure by the resistor 70 and inputted to the inverting terminal of the inverting amplifier 74 via the analog switch 71. As a result,
The comparator 51 has a predetermined duty ratio that drives the electromagnetic coils 21 and 35 so that the air-fuel ratio of the air-fuel mixture supplied to the engine 1 becomes an intermediate air-fuel ratio between the average air-fuel ratio over time and an air-fuel ratio of about 18. As the electromagnetic coils 21 and 35 are driven by this pulse signal, the air-fuel ratio of the air-fuel mixture supplied to the engine 1 relatively quickly changes to the average air-fuel ratio over time, for example. The air-fuel ratio is corrected to be intermediate between the lean air-fuel ratio of about 18.
At this time, the air-fuel ratio is still higher than the stoichiometric air-fuel ratio, so the comparator 44 outputs a "1" signal, which is input to the integrator 46, which causes the comparator 51 to output a "1" signal.
The voltage signal applied to the electromagnetic coil 2 gradually decreases, and the duty ratio of the pulse signal generated by the comparator 51 gradually decreases.
1 and 35, the air-fuel ratio of the air-fuel mixture supplied to the engine 1 gradually approaches the average air-fuel ratio over time in accordance with the integral constant of the integrator 46.

Further, when the engine 1 shifts from medium load operation to low load operation, the flip-flop circuit 88 generates a "1" signal, causing the analog switch 61 to become non-conductive, and the analog switch 49 to become non-conductive, as in the embodiment described above. Maintained in conductive state.
Further, by inputting the output signal of the flip-flop circuit 88 to the base terminal of the transistor, conduction is established between the collector terminal and the limiter terminal of the transistor, and the output terminal of the comparator 44 is grounded. Therefore, the comparator 44
The output signal of will be a "0" signal and the integrator 46 will generate a gradually increasing voltage according to its own time constant. As a result, the effective opening areas of the valve ports 18 and 32 of the proportional actuators 17 and 31 gradually increase, and accordingly, the air-fuel ratio of the air-fuel mixture supplied to the engine 1 gradually increases. When the air-fuel ratio reaches a value intermediate between the lean air-fuel ratio, for example about 18, and the average air-fuel ratio over time, the voltage of the signal generated by the adder 48 becomes greater than the voltage input to its non-inverting terminal. Therefore, the output signal of the comparator 91 changes from a "1" signal to a "0" signal. In this case, a voltage signal obtained by dividing the voltage signal generated by the non-inverting amplifier 75 by a predetermined amount by the resistor 93 is input to the non-inverting terminal of the comparator 91, so that the air-fuel ratio is adjusted to the lean air ratio as described above. When the fuel ratio reaches an intermediate value between the fuel ratio and the temporal average air-fuel ratio, the output signal of the comparator 91 changes from a "1" signal to a "0" signal. Therefore, the flip-flop circuit 88 is reset, and a "0" signal is applied to the base terminal of the transistor 90 as in the above embodiment, so that the analog switch 61 becomes conductive and the analog switch 49 becomes non-conductive. become. As a result, the voltage signal generated by the non-inverting amplifier 75 is applied to the comparator 51, and the comparator 51 generates a pulse signal with a predetermined duty ratio according to the voltage signal, thereby controlling the valves of the proportional actuators 17 and 31. The effective opening area of the ports 18 and 32 increases relatively rapidly, and the engine 1 is supplied with an air-fuel mixture having the lean air-fuel ratio of about 18, for example.

Although the present invention has been described in detail with respect to specific embodiments above, it will be appreciated by those skilled in the art that the present invention is not limited to these embodiments 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 vertical sectional view showing one embodiment of the air-fuel ratio control device according to the present invention, FIG. 2 is an electric circuit diagram showing one embodiment of the electric circuit of the air-fuel ratio control device according to the present invention, and FIG. The figure is a time-series waveform diagram, FIG. 4 is an electric circuit diagram showing another embodiment of the electric circuit of the air-fuel ratio control device according to the present invention, and FIG. 5 is an implementation of the temporal average air-fuel ratio calculation device. FIG. 3 is an electrical circuit diagram illustrating an example. 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 ... Constant voltage generation circuit, 61 ... Analog switch, 62 ... Negative pressure switch, 63...NOT gate, 64...NOR gate, 65...idling switch, 66...negative pressure switch, 67...delay circuit, 68...NOR gate,
69... Delay circuit, 70... Resistor, 71... Analog switch, 72... Resistance element, 73... Flip-flop circuit, 74... Temporal average air-fuel ratio calculation device, 7
5... Non-inverting amplifier, 76... Up-down counter, 77... Ladder network circuit, 78... Astable multivibrator, 79... AND gate, 8
0...5 input AND gate, 81...5 input OR gate, 82...NAND gate, 83...AND gate,
84...OR gate, 85...capacitor, 86...resistance element, 87...OR gate, 88...flip-flop circuit, 89...resistance element, 90...transistor, 91...comparator, 92...constant voltage generation circuit, 93
…Resistor.

Claims (1)

[Scope of Claims] 1. An exhaust sensor that detects the concentration of exhaust components in exhaust gas discharged from the engine, and generates a signal representing the air-fuel ratio of the air-fuel mixture supplied to the engine based on the signal generated by the exhaust sensor. an air bleed control device that is driven based on a signal generated by the computing 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, except during idling operation. During low load 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 so that the air fuel ratio becomes substantially larger than the stoichiometric air fuel ratio. The air-fuel ratio is controlled by the air-fuel ratio during low-load operation when the operating range is shifted from the operating range where the air-fuel ratio is feedback-controlled based on the signal from the bleed correction device and the arithmetic unit to the operating range where the air-fuel ratio is controlled by the air-fuel ratio during low-load operation. the air bleed control device so as to gradually increase the air fuel ratio by an amount corresponding to substantially half of the fuel ratio fluctuation width and then rapidly increase the air fuel ratio to the air fuel ratio determined by the air bleed correction device during low load operation; 1. An air-fuel ratio control device for an engine, comprising: an air bleed correction device during excessive operation that increases the amount of air bleed due to the engine position. 2. 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 air-fuel ratio calculated by the temporal average air-fuel ratio calculation device by stopping the basic feedback control, and the air-fuel ratio is adjusted to a predetermined air-fuel ratio practically larger than the stoichiometric air-fuel ratio. An air bleed correction device during low load operation that corrects the fuel ratio, and an operation in which the air fuel ratio is controlled by the air bleed correction device during low load operation from an operating range where the air fuel ratio is feedback controlled based on a signal from the arithmetic unit. The air-fuel ratio is gradually increased by an amount equivalent to substantially half of the air-fuel ratio fluctuation width at this time, and then the air-fuel ratio is rapidly increased to the air-fuel ratio determined by the air bleed correction device during low load operation. An air-fuel ratio control device for an engine, comprising: an air bleed correction device during excessive operation, which increases the amount of air bleed by the air bleed control device so as to increase the amount of air bleed by the air bleed control device.