JPS62165553A - Air-fuel ratio control device for engine - Google Patents

Abstract

PURPOSE:To prevent a shock to an engine at the time of restoring fuel supply by constituting an air-fuel ratio control means with two valves in a bypass passage bypassing a throttle valve, and opening a valve device for changing over an air-fuel ratio control range prior to releasing a fuel cut. CONSTITUTION:When an engine 1 is running, ECU 22 is inputted with a water temperature signal 'Tw' and a throttle opening signal 'TVtheta'. If 'Tw' is over predetermined temperature 'T1' and 'TVtheta' is less than predetermined opening 'theta1', a secondary valve device 18 is opened and the engine 1 is operated with a lean air-fuel ratio. And when the secondary valve device 18 is opened, a primary valve device 19 provided in series therewith is controlled for the opening and closing thereof interlocked with a throttle valve 5 for keeping constant the ratio of air passing through a bypass passage 17 and said valve 5. Also, at the time of a fuel cut for engine speed reduction, the secondary valve device 18 is opened and in a process of return to fuel supply, controlled for the opening and closing thereof prior to the resumption of fuel supply.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention detects a predetermined operating state of an engine and gradually switches the air-fuel ratio to leaner than the stoichiometric air-fuel ratio without sudden changes in output. The present invention relates to an air-fuel ratio control device for an engine, which is capable of reducing fuel consumption during deceleration, and alleviating recovery shock from fuel cut during deceleration.

[Prior art]

Mainly to save fuel consumption, an engine air-fuel ratio control device that detects a predetermined operating state of the engine and gradually switches the air-fuel ratio to leaner than the stoichiometric air-fuel ratio has already been disclosed in Japanese Patent Application Laid-Open No. 57-210137. It is generally known from publications such as No.

Normally, conventional engine air-fuel ratio control devices detect operating conditions that do not require much engine output, such as during low rotation and low load, fix the amount of intake air, and supply fuel to this amount of intake air. By reducing the amount of fuel, the air-fuel ratio is switched to be leaner than the stoichiometric air-fuel ratio.

However, since the output of an engine is proportional to the amount of fuel supplied, rapidly increasing or decreasing the amount of fuel to switch the air-fuel ratio between lean and other regions causes sudden fluctuations in output, resulting in so-called torque shock and vibration. There is a problem that occurs. Therefore, when an engine employing such a conventional air-fuel ratio control device is installed in a vehicle such as an automobile, a problem arises in that the ride comfort of the vehicle is deteriorated.

In order to change the air-fuel ratio to lean without such sudden output fluctuations, it is possible to gradually change the fuel supply amount to gradually change the air-fuel ratio to lean, but in this case, the exhaust gas This will be disadvantageous when trying to purify the environment. That is, for example, when the air-fuel ratio is gradually changed from the stoichiometric air-fuel ratio (air-fuel ratio 14.7) to a leaner air-fuel ratio of 22, the air-fuel ratio is in the region of about 16 where the amount of nitrogen oxides produced is almost the maximum. As the nitrogen oxides gradually pass through the exhaust gas, the amount of nitrogen oxides produced increases, which is disadvantageous in purifying the exhaust gas.

Furthermore, it is already generally known to cut off the supply of fuel to the engine during deceleration operation of the engine in order to accelerate the deceleration of the engine and prevent the generation of hydrocarbons and the like. When cutting off the fuel supply to the engine in this way, if the engine speed drops below a certain level, the engine rotation becomes unstable and engine stall occurs. When the fuel supply cutoff ends, the fuel supply is suddenly restarted, which causes problems such as a sudden increase in engine output and the occurrence of so-called recovery shock and vibration. be.

[Purpose of the invention]

The present invention has been made in consideration of the above circumstances, and is capable of switching the air-fuel ratio without fluctuations in output, and also alleviates vehicle recovery shock from fuel cut during deceleration. It is an object of the present invention to provide an air-fuel ratio control device for an engine that is advantageous in purifying exhaust gas.

[Structure of the invention]

In order to achieve the above object, the air-fuel ratio control device for an engine according to the present invention includes an air-fuel ratio control means that detects a predetermined operating state of the engine and changes the air-fuel ratio stepwise to leaner than the stoichiometric air-fuel ratio. In the air-fuel ratio control device for an engine, the air-fuel ratio control means includes a bypass passage that bypasses a throttle valve, and a first pulp device that is provided in the bypass passage and is opened and closed in conjunction with the throttle valve; A second valve device is provided in the bypass passage in series with the first valve device and opens and closes the bypass passage, and the second valve device is opened when the air-fuel ratio is controlled to be leaner than the stoichiometric air-fuel ratio. , a second valve control means for controlling the valve to be closed in other operating states, and by opening and closing the bypass passage by the second valve device, the amount of fuel supplied relative to the amount of intake air can be adjusted without changing the amount of fuel supplied relative to the amount of intake air. A fuel supply control means that changes the air-fuel ratio in stages by changing the amount of intake air, and cuts off the supply of fuel to the engine when a deceleration operating state of the engine is detected; and this fuel supply control means control means for controlling the second valve device to close the second valve device when the fuel supply is cut off, and to open the second valve device when the fuel supply cutoff ends and before restarting the fuel supply; and the bypass passage is opened just before the cutoff of the fuel supply ends as the engine speed decreases, weakening the braking effect of the engine, and then the cutoff of the fuel supply ends. It is.

[Embodiment 1] An embodiment of the present invention will be described below based on FIGS. 1 to 5.

An air cleaner 3 is provided at the starting end of the intake passage 2 of the engine 1, and an air flow meter 4 that sequentially detects the amount of intake air from there toward the end and outputs a Z intake air amount signal in response to the intake air ffi QA. , throttle valve 5
, a swirl control valve 6 , and a fuel injection device 7 are provided, and the terminal end of the intake passage 2 is connected to a combustion chamber 9 via an intake valve 8 . In addition, an exhaust path 10 led out from the combustion chamber 9
An exhaust pulp 11 is disposed at the starting end of the exhaust path 10, and an air-fuel ratio sensor 12 that detects gas components in the exhaust gas and outputs an air-fuel ratio signal corresponding to the air-fuel ratio and a catalytic exhaust purification device are disposed in the middle of the exhaust path 10. A device 13 is provided in turn. A spark plug 14 provided in the combustion chamber 9 is connected to an ignition coil 16 via a distributor 15.

The intake passage 2 is further provided with a bypass passage 17 that bypasses the throttle valve 5. This bypass passage 1
7 is provided with a solenoid valve 18 for opening and closing the bypass passage 17, and a sub-throttle valve 19 arranged in series with the solenoid valve 18. As shown in FIG. 2, this sub-throttle valve 19 is designed so that the ratio of the amount of air passing through the bypass passage 17 and the amount of air passing through the throttle valve 5 is constant when the solenoid valve 18 is open. , is operatively connected to the throttle valve 5 via a common valve shaft 20, and is operated by an accelerator operating device (not shown).
The opening and closing are adjusted in conjunction with the The throttle valve 5 is provided with a throttle sensor 21 that detects the throttle opening TVθ and outputs a throttle opening signal corresponding to the throttle opening. This throttle sensor 2
Reference numeral 1 also serves as an idling switch that outputs an idling signal when the throttle valve 5 is fully closed. In addition, the diameter of the bypass passage 17 is set in the intake passage so that when the solenoid valve 18 is opened with the fuel injection quantity Q fixed, an amount of air can be sucked in to ensure an air-fuel ratio of 18 or more for stable idling operation of the engine. The diameter is set to 20% or more of the diameter of the portion where the second throttle valve 5 is arranged. Furthermore, the installation of the sub-throttle valve 19 depends on the opening degree,
Bypass passage 17 due to production error of bypass passage 17
Variations occur in the amount of bypass air passing through the engine, and this variation can have a large effect on the air-fuel ratio when the amount of intake air is very small, such as during idling.
In order to reduce the influence of this variation in the amount of bypass air on the air-fuel ratio, the upstream opening of the bypass passage 17 is arranged as close to the throttle valve 5 as possible.

This engine air-fuel ratio control device is further provided with an electronic control unit (hereinafter referred to as ECU) 22, which is made up of, for example, a computer and controls the operations of the fuel injection device 7 and the solenoid valve 18. This ECU22
is the coolant temperature T of the engine 1 from a water temperature sensor (not shown). A water temperature signal input port inputs a water temperature signal corresponding to the water temperature signal, a throttle opening signal input port inputs a throttle opening signal from the throttle sensor 21, and an engine rotation speed signal corresponding to the engine rotation speed Ne from the distributor 15. It has a rotation speed signal input port to input the water temperature T8 and the throttle opening T8 as described below.
It is configured such that the operating state of the engine 1 can be determined from the magnitude of Vθ, the engine speed Ne, and the presence or absence of an idling signal.

That is, this ECU 22 has a water temperature determination unit that determines whether or not the water temperature T exceeds a predetermined temperature TI, which corresponds to the lowest temperature at which the engine can operate stably in the lean region, for example, approximately 50°C to 60°C. , the above water temperature T. a throttle opening degree determination unit that determines whether the throttle opening degree TVθ exceeds a predetermined opening degree θ that is opened to obtain a predetermined output when the throttle opening degree TVθ exceeds the predetermined temperature T+; and the water temperature T.

is below the predetermined temperature T1, or the water temperature T,4 exceeds the predetermined temperature T, and the throttle opening TVθ is the predetermined opening θ.

It has an idling determination section that determines whether or not there is an idling signal when the value exceeds the idling signal.

The ECU 22 also controls the solenoid when the throttle opening degree determining section determines that the throttle opening degree TVθ is equal to or less than the predetermined pA degree θ1, or when the idling determining section determines that an idling signal is present. It has a drive section that opens the valve 18 and closes the solenoid valve 18 when the idling discrimination section determines that there is no input of an idling signal.

Further, the ECU 22 has an intake air amount signal input port for inputting an intake air amount signal from the air flow meter 4, and an intake air amount signal input port for inputting an intake air amount signal from the air flow meter 4, in order to control the fuel injection amount corresponding to the intake air amount QA and the engine speed N.
5, a rotation speed signal input boat inputting a rotation speed signal corresponding to the engine rotation speed N, and the water temperature T mentioned above. is above the predetermined temperature T1, the throttle opening TVθ is equal to or less than the predetermined opening θ, and a lean target air-fuel ratio is stored in advance in accordance with the intake air amount Q^ and the engine rotation speed N. The lean operation map and the above water temperature T, 4
is below the predetermined temperature T+, or when the water temperature T1 exceeds the predetermined temperature T1 and the throttle opening TVθ exceeds the predetermined opening θ1, the intake air amount QA and engine speed change. A normal operation map in which a stoichiometric air-fuel ratio corresponding to the number N or an air-fuel ratio close to this is stored in advance as a target air-fuel ratio, and the above-mentioned water temperature T, 1 and slot 7.
The intake air amount Q detected by the air flow meter 4 and the distributor 15 are calculated from the lean operation map or the normal operation map according to the state of the torque opening TVθ.
a target air-fuel ratio determination unit that reads out a target air-fuel ratio corresponding to the engine rotational speed N detected via the target air-fuel ratio and determines the target air-fuel ratio; and a fuel that controls the fuel injection amount of the fuel injection device 7 in accordance with the target air-fuel ratio. and an injection amount control section.

Furthermore, the ECU 22 is configured to cut off the supply of fuel in a predetermined rotational speed range, especially when the engine 1 is decelerating.

That is, the ECU 22 includes a throttle valve closing determination unit that determines whether the throttle opening degree TVθ is the minimum based on the presence or absence of an idling signal, and a throttle valve closing determination unit that determines whether or not the throttle opening degree TVθ is the minimum, based on the presence or absence of an idling signal, and a throttle valve closing determination unit that determines whether the engine rotation speed N is the minimum rotation speed at which fuel can be cut, that is, the fuel A fuel cut determination unit that determines whether or not the cut return rotation speed N is exceeded, and a fuel cut that stops fuel cut when the throttle opening TVθ is the minimum and the engine rotation speed N8 is less than or equal to the fuel cut return rotation speed N1. Fuel cut control that outputs a return command to the fuel injection device 7, and outputs a fuel cut execution command to the fuel injection device 7 when the throttle opening degree TVθ is the minimum and the engine speed N exceeds the fuel cut return speed N1. and dashbot operation determination at the time of return to determine whether or not the engine rotational speed N for this fuel supply exceeds the dashbot start rotational speed Ng, which is slightly higher than the fuel cut return rotational speed N, at the time of fuel cut. and the second valve control section controls the engine rotation speed N, especially during fuel cut.
The solenoid valve 18 is closed to enhance the braking effect while the engine speed N is higher than the dashpot starting speed Ng, and the braking effect is reduced when the engine speed N becomes lower than the dashbot starting speed N2 just before returning from the fuel cut. Open the solenoid valve 18 to lower the
The drive section is configured to control the solenoid valve 18 to close the solenoid valve 18 again when the engine rotation speed N0 falls below the fuel consumption rotation speed N1.

The ECU 22 is also provided with a vehicle speed signal input boat for inputting a vehicle speed signal corresponding to the vehicle speed of an automobile (not shown) driven by the engine 1, and an air-fuel ratio signal input boat for inputting the air-fuel ratio signal of the air-fuel ratio sensor 12. It is being

In the above configuration, the inside of the ECU 22 is as shown in FIG.
) and the air-fuel ratio control is executed according to the sequence shown in FIG. 3(B).

That is, as shown in FIG. 3 CB, excluding the deceleration operation state described later (the sequence executed in the ECU 22 in the operation state is shown in FIG. 3 CB), first, the water temperature sensor starts the water '/14T.
A water temperature signal corresponding to the water temperature signal is inputted to the water temperature discrimination section via the water temperature signal input boat (Fll, and then a throttle opening signal from the throttle sensor 21 is inputted to the throttle opening discrimination section via the throttle opening signal input boat. (F
2). Next, the water temperature determining unit determines whether the water temperature T exceeds the predetermined temperature T+ (F3). Here, if the water temperature T,1 exceeds the predetermined temperature T1, the throttle opening determination unit determines whether the throttle opening TVθ exceeds the predetermined opening θ1 (F4
). The water temperature determination section determines that the water temperature T8 is the predetermined temperature T,
If it is determined that the engine temperature is below, the engine temperature has not risen sufficiently, and if the air-fuel ratio is set to a lean range greater than the stoichiometric air-fuel ratio, the engine rotation will become unstable during engine operation. Further, when the water temperature T8 exceeds the predetermined temperature T, and the throttle opening TVθ exceeds the predetermined opening θ, the throttle valve 5 is opened in order to obtain an output corresponding to the engine load. This is the case when the valve is opened. Therefore, if it is determined that the water temperature T8 is equal to or lower than the predetermined temperature T, or if the water temperature Tw exceeds the predetermined temperature T1 and the throttle opening TVθ is equal to or lower than the predetermined opening θ. , the air-fuel ratio control is performed according to the stoichiometric air-fuel ratio or an air-fuel ratio close to it. In these cases, first, the presence or absence of an idling signal is determined in the idling determining section (F5). If it is determined that there is an idling signal, the above water temperature T.

When the water temperature T is below the predetermined temperature T1, the water temperature T is set to increase the stability of idling operation and shorten the warm-up time. When the temperature exceeds the above-mentioned predetermined temperature TI, it is preferable to supply a large amount of air and fuel in order to obtain a kind of dashpot effect that prevents generation of hydrocarbons at the beginning of deceleration. Therefore, in this case, the solenoid pulp 18 is opened via the drive section (F6).
.

However, when the water ATW exceeds the predetermined temperature TI, the solenoid pulp 18 is closed after a predetermined period of time, as will be described later, in order to enhance the braking effect. If the idling determination section determines that there is no idling signal, it means that the throttle valve 5 is opened to obtain an output corresponding to the load of the engine 1, and the stoichiometric air-fuel ratio is Alternatively, it is necessary to execute air-fuel ratio control at an air-fuel ratio close to this.

Therefore, in this case, in order to perform normal air-fuel ratio control using the throttle valve 5, the solenoid valve 18 is closed via the drive section (F7). In these cases, the opening/closing control of the solenoid pulp 18 (F6
, or F7), input the intake air amount signal from the air flow meter 4 through the intake air amount signal input port, and input the engine rotation speed N from the distributor 15 through the rotation speed signal input port. Input the corresponding rotational speed signal (F8), and the target air-fuel ratio determination unit determines the target air-fuel ratio corresponding to the intake air amount QA and engine rotational speed N from the normal operation map (F9), and according to this target air-fuel ratio, the fuel The amount of fuel injected from the fuel injection device 7 is controlled by the amount control section (FIO).

If the water temperature QA exceeds the predetermined temperature T1, but the throttle opening TVθ is determined to be less than the predetermined opening θ1, the engine temperature has risen sufficiently to maintain a lean air-fuel ratio. This is a case where stable lean operation is possible, the load on the engine is small, and operation at an air-fuel ratio leaner than the stoichiometric air-fuel ratio is permitted in order to save fuel consumption. Therefore, in this case, the solenoid pulp 18 is opened via the drive section (F
il), a large amount of intake air is drawn into the combustion chamber 9 through the intake passage 2 and the bypass passage 17. Then, an intake air amount signal is inputted from the air flow meter 4 through the intake air amount signal input port, and at the same time, a rotation speed signal corresponding to the engine rotation speed N is inputted from the distributor 15 through the rotation speed signal input port. 12
), a target air-fuel ratio corresponding to the intake air amount QA and the engine speed N is determined by the air-fuel ratio determination section based on the lean operation map (F1a), and the fuel injection amount control section controls the fuel injection device according to this target air-fuel ratio. The amount of fuel injected from step 7 is controlled (F10).

Now, assuming that the water temperature Tw exceeds a predetermined temperature T1, the throttle opening TVθ is changed from a region below the above-mentioned predetermined opening θ1 to a range above the above-mentioned predetermined opening θ1, as shown in FIG. 4(A), for example. For example, if the throttle opening is changed uniformly up to the range, as shown in FIG.
The solenoid valve 18 is opened while θ is below the predetermined opening 01, and when the throttle opening TVθ exceeds the predetermined opening θ, the solenoid valve 18 is closed, and the intake air amount QA is As shown in FIG. 4(C) and FIG. 5, the intake air amount Q corresponding to the lean air-fuel ratio rapidly decreases to the intake air amount Q2 corresponding to the stoichiometric air-fuel ratio. The change in the fuel injection amount Qr when this air-fuel ratio region is switched is zero as shown in FIG. P, the fuel injection amount P2 corresponding to the stoichiometric air-fuel ratio
Unlike the conventional engine, in which the amount of fuel is increased, there is no change in the output of the engine 1. Further, since the air-fuel ratio is changed so as to instantaneously pass through an air-fuel ratio region in which a relatively large amount of nitrogen oxides are generated, less nitrogen oxides are generated, which is advantageous in purifying the exhaust gas. Further, the throttle valve 5 and the sub-throttle valve 19 are interlocked and connected so that the ratio of the amount of air passing through the bypass passage 17 and the amount of air passing through the throttle valve 5 is constant when the solenoid valve 18 is open. Therefore, during lean operation, the air-fuel ratio can be controlled easily and accurately in the same way as controlling the air-fuel ratio using a single throttle valve 5.

The throttle opening degree TVθ is set to the above-mentioned predetermined opening degree θ.

Conversely, when changing from a region exceeding the opening degree θ1 to a region below the predetermined opening θ1, the intake air i
i Qz to intake air corresponding to lean air-fuel ratio t c
Although the fuel injection amount Qf increases rapidly at t + , there is no change in the fuel injection amount Qf, so there is no output fluctuation, and the generation of nitrogen oxides is small.

Independently of the sequence as described above, the ECU 22
During deceleration, fuel cut control as shown in FIG. 3(A) is executed.

That is, after sequentially reading the output of the throttle sensor 21 and the engine speed N (F21°F22), first, the throttle valve close determination unit determines whether or not the throttle opening TVθ is at the minimum based on the presence or absence of an idling signal. (F23).

If there is no idling signal, the throttle valve 5 is being operated to open, and it is not suitable for executing a fuel cut, so the previous sequence (F21-F23
) is repeated. If there is an idling signal, it means that the throttle valve 5 is closed for deceleration, and in this case, it is determined whether the engine speed N exceeds the fuel cut return speed N. It is determined by the cut determination unit (F24>. When the throttle opening degree TVθ is the minimum and the engine speed N8 exceeds the fuel cut return speed N1, a fuel cut execution command to execute the fuel cut is output to the fuel injection device 7. (F25), fuel injection device 7
stops fuel injection based on this fuel cut execution command. After the fuel cut execution command is output, the return dashbot operation determination unit determines whether the engine rotation speed N8 exceeds the dashpot start rotation speed N2 (F
26). When the engine speed N8 exceeds the dashpot starting speed N2, the solenoid valve 18 is closed via the drive section to enhance the braking effect of the engine 1 (F27). When the engine speed N8 gradually decreases to below the dashpot starting speed N2, the solenoid valve 18 is opened (F28) and the braking effect of the engine 1 is weakened.

Then, when the engine rotation speed N further decreases and it is determined that the fuel cut return rotation speed N is below (F24), the solenoid valve 18 is closed again (F29), and the fuel cut control section controls the fuel injection device 7. A fuel cut return command is output (F30), and the fuel injection device 7 resumes fuel supply based on this fuel cut return command.

In this way, the solenoid valve 18 is opened (F28) just before the return of the fuel cut, and the braking effect of the engine 1 is weakened before the fuel cut is stopped, so the output fluctuation when the fuel cut is returned is alleviated. be.

In each of the embodiments described above, during warm-up of the engine 1, the solenoid valve 18 is opened to increase the amount of intake air and correspondingly increase the amount of fuel supplied.
Although it is configured to increase the idling speed and shorten the warm-up time, during warm-up operation, the opening degree of the throttle valve 5 and sub-throttle valve 19 is small, and the amount of intake air is small (as it tends to be). It is preferable to form a notch in the sub-throttle valve 19 to further increase the amount of intake air and, correspondingly, further increase the amount of fuel supplied, further increasing the idling speed and shortening the warm-up time.

Further, when the solenoid valve 18 is locked in a closed state for some reason, this locked state is detected,
It is advantageous to configure the ECU 22 to change the fuel supply amount to switch the air-fuel ratio range between the lean range and other ranges.

It is also advantageous to configure the ECU 22 to forcibly stop the fuel supply in order to prevent the engine from running out of control when the solenoid valve 18 is locked in the open state for some reason.

The present invention is applicable not only to fuel injection engines but also to engines having a carburetor, and in fuel injection engines, an existing air valve is used to increase the amount of bypass air,
It is also possible to change the air-fuel ratio to lean. Furthermore, it is also possible to perform idle rotation speed control by duty-controlling the solenoid valve 18.

〔Effect of the invention〕

As described above, the engine air-fuel ratio control device of the present invention provides a bypass passage that bypasses the throttle valve, and by opening and closing this bypass passage with a valve device, the air-fuel ratio control device for an engine does not change the fuel supply amount relative to the intake air amount. Since the air-fuel ratio is changed by changing the intake air amount relative to the fuel supply amount, it is possible to eliminate output fluctuations caused by changes in the air-fuel ratio, and to prevent so-called torque shock and vibration. Further, when switching the air-fuel ratio, the air-fuel ratio region where a large amount of nitrogen oxides are generated is instantaneously passed through, so the amount of nitrogen oxides generated is small, which is advantageous in purifying exhaust gas. Furthermore, when the fuel cut during deceleration is canceled as the engine speed decreases, the bypass passage is opened immediately before the fuel cut is canceled to weaken the braking effect of the engine, and then the fuel cut is canceled. The recovery shock at the end of fuel cut is alleviated.

[Brief explanation of drawings]

FIG. 1 is a block diagram schematically showing an embodiment of the present invention;
Figure 2 is a longitudinal cross-sectional view of the intake passage and bypass passage, Figure 3 (A) is a flow diagram of the fuel cut control sequence executed within the ECU, and Figure 3 (B) is a flow diagram of the fuel cut control sequence executed within the ECU. A flow diagram of the air-fuel ratio control sequence, Figure 4 (
A) is a time chart showing the opening/closing operation of the throttle valve over time; FIG. Figure (C) is a time chart showing how the amount of intake air changes over time in response to the opening and closing operations of the throttle valve.
D) is a time chart showing how the fuel injection amount changes over time in response to the opening/closing operation of the throttle valve, and Figure 5 shows the relationship between the air amount, fuel supply amount, and engine output when changing the air-fuel ratio range. It is a relationship diagram of fuel supply amount-air amount-engine output which shows the relationship. In the figure, 1 is an engine, 5 is a throttle valve, 17 is a bypass passage, 18 is an N' lube device (solenoid valve), and 22 is a control unit (electronic control unit, ECU). Figure 3 (A) Figure 3 (B) 5

Claims (1)

[Claims] 1. An engine air-fuel ratio control device comprising air-fuel ratio control means for detecting a predetermined operating state of the engine and switching the air-fuel ratio stepwise to a leaner air-fuel ratio than the stoichiometric air-fuel ratio, wherein the air-fuel ratio control means includes a throttle control means. a bypass passage that bypasses the valve; a first valve device that is provided in the bypass passage and is opened and closed in conjunction with the throttle valve; and a first valve device that is provided in the bypass passage in series with the first valve device that controls the bypass passage. a second valve device that switches between opening and closing, and a second valve control means that controls the second valve device to open when the air-fuel ratio is controlled to be leaner than the stoichiometric air-fuel ratio and close when the air-fuel ratio is controlled to be leaner than the stoichiometric air-fuel ratio. and a fuel supply control means for cutting off the supply of fuel to the engine when a deceleration operating state of the engine is detected;
An air-fuel ratio control device for an engine, comprising a control means for controlling the second valve device to close the valve device and open the second valve device before restarting the fuel supply when the cutoff of the fuel supply ends. .