JPH0788787B2 - Air-fuel ratio controller for engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention detects a predetermined operating state of an engine, and switches the air-fuel ratio to a leaner than stoichiometric air-fuel ratio stepwise without abrupt output fluctuation. The present invention relates to an engine air-fuel ratio control device.

[Prior art]

An air-fuel ratio control device for an engine which detects a predetermined operating state of the engine and switches the air-fuel ratio to leaner than the stoichiometric air-fuel ratio mainly in order to save fuel consumption has already been disclosed in JP-A-57-210137. Commonly known by.

Usually, a conventional engine air-fuel ratio control device detects an operating state that does not require much engine output, such as at low rotation and low load, fixes the intake air amount, and supplies fuel to this intake air amount. By reducing the amount, the air-fuel ratio is switched to leaner than the stoichiometric air-fuel ratio.

However, since the output of the engine is proportional to the fuel supply amount, if the fuel is suddenly increased or decreased in order to switch the air-fuel ratio between the stoichiometric air-fuel ratio and lean, a sudden output change is accompanied, and so-called torque shock and vibration. There is a problem that occurs. Therefore, when an engine that employs such a conventional air-fuel ratio control device is mounted on a vehicle such as an automobile, the problem that the riding comfort of the vehicle is deteriorated arises.

In order to change the air-fuel ratio to lean without such a sudden output change, it is possible to gradually change the fuel supply amount and gradually change the air-fuel ratio to lean. Will be disadvantageous in purifying That is, for example, when gradually changing the air-fuel ratio from the logical air-fuel ratio (air-fuel ratio 14.7) to the leaner air-fuel ratio 22, the region where the production amount of nitrogen oxides is approximately maximum is gradually increased to about 16 regions. As a result, the amount of nitrogen oxides produced increases, which is disadvantageous in purifying the exhaust gas.

[Object of the Invention]

The present invention has been made in consideration of the above circumstances, and it is possible to switch the air-fuel ratio without fluctuation of the output, and moreover, the air-fuel ratio control of the engine which is advantageous in purifying exhaust gas. The purpose is to provide a device.

[Structure of Invention]

In order to achieve the above-mentioned object, the air-fuel ratio control device for an engine according to the present invention detects the predetermined operating state of the engine, and includes an air-fuel ratio control means for stepwise switching the air-fuel ratio to leaner than the stoichiometric air-fuel ratio. In an engine air-fuel ratio control device provided with the air-fuel ratio control means, a bypass passage bypassing the throttle valve, and provided in the bypass passage,
A first valve device that is opened and closed in conjunction with the opening and closing operation of the throttle valve, and a second valve device that is provided in the bypass passage in series with the first valve device and that is opened and closed.
The second valve device includes a valve device and second valve control means for controlling the second valve device to open when the air-fuel ratio is switched from the stoichiometric air-fuel ratio to lean and to close when the air-fuel ratio is switched from lean to another air-fuel ratio. By opening and closing the bypass passage, the air-fuel ratio region is switched stepwise by changing the intake air amount with respect to the fuel supply amount without changing the fuel supply amount with respect to the intake air amount.
In addition, the engine air-fuel ratio control device according to the present invention controls the opening / closing of the throttle valve and the first valve device in conjunction with each other, so that the air-fuel ratio during lean operation is the same as the air-fuel ratio control using a single throttle valve. It is characterized by easy and accurate control.

[Embodiment 1] The following will describe one embodiment of the present invention with reference to FIGS. 1 to 5.

An air cleaner 3 is provided at the start end of the intake passage 2 of the engine 1, and the intake air amount is sequentially detected from there to the end, and an air flow meter 4 that outputs an intake air amount signal corresponding to the intake air amount Q _A , A throttle valve 5, a swirl control valve 6 and a fuel injection device 7 are provided,
The end of the intake passage 2 is connected to the combustion chamber 9 via the intake valve 8. Further, an exhaust valve 11 is arranged at the beginning of the exhaust passage 10 led out of the combustion chamber 9, and an air-fuel ratio signal corresponding to the air-fuel ratio is detected in the middle of the exhaust passage 10 by detecting a gas component in the exhaust gas. An air-fuel ratio sensor 12 and a catalytic exhaust purification device 13 for outputting The ignition 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. The bypass passage 17 is provided with a solenoid valve 18 as a second valve device for opening and closing the bypass passage 17, and a sub-throttle valve 19 as a first valve device arranged in series with the solenoid valve 18. This sub-throttle valve 19 is, as shown in FIG.
Is linked with the throttle valve 5 via a common valve shaft 20 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 becomes constant when the valve is open. Opening / closing control is performed in conjunction with the throttle valve 5 by an accelerator operating device (not shown).
The throttle valve 5 has a throttle opening TVθ.
Is attached, and a throttle sensor 21 that outputs a throttle opening signal corresponding to the throttle opening is attached. The throttle sensor 21 is also used as an idling switch that outputs an idling signal when the throttle valve 5 is fully closed. Also, by opening the solenoid valve 18 while fixing the fuel injection amount Q _f , the diameter of the bypass passage 17 is set so that the air amount that can secure an air-fuel ratio of 18 or more for stable engine idling can be taken. It is set to 20% or more of the diameter of the road 2. Further, variations in the amount of bypass air passing through the bypass passage 17 caused by the mounting opening of the sub-throttle valve 19 and the production error of the bypass passage 17 occur, and this variation occurs when the intake air amount during idling is extremely small. Although the air-fuel ratio may be greatly affected, the upstream opening of the bypass passage 17 is arranged as close to the throttle valve 5 as possible in order to reduce the influence of the variation in the bypass air amount on the air-fuel ratio. Curious.

The air-fuel ratio control device for the engine further controls the operations of the fuel injection device 7 and the solenoid valve 18. For example, an electronic control unit (hereinafter referred to as ECU) 22 including a computer is provided. A water temperature signal input port for inputting a temperature signal corresponding to the water temperature sensor the ECU22 is not shown in the water temperature T _W of the engine 1, a throttle sensor
It has a throttle opening signal input port for inputting a throttle opening signal from 21, and as described later, the water temperature T _W is high or low,
The operation state of the engine 1 can be determined by the magnitude of the throttle opening TVθ.

That is, the ECU 22 is a water temperature determination unit that determines whether the water temperature T _W exceeds a predetermined temperature T ₁ corresponding to the minimum temperature at which the engine can be operated stably in the lean region, for example, about 50 ° C. to 60 ° C. And a throttle opening discriminating unit for discriminating whether or not the throttle opening TVθ exceeds a predetermined opening θ ₁ opened to obtain a required output when the water temperature T _W exceeds the predetermined temperature T _1. Have.

Also, the ECU 22 checks the open / closed state of the solenoid valve 18, and in a predetermined operating state, the solenoid valve 18
The valve 18 is opened, and the solenoid valve 18 is closed in other operating states.

That is, the ECU 22 is configured such that when the water temperature T _W is equal to or lower than the predetermined temperature T ₁ , or the water temperature T _W is higher than the predetermined temperature T ₁ , and the throttle opening TVθ is the predetermined temperature. a closing determination unit for determining whether the solenoid valve 18 is opened when exceeding the opening theta _1, and predetermined opening theta ₁ below throttle opening TVθ is above the throttle opening degree determination unit When the determination is made, the solenoid valve 18 has a valve opening determination unit that determines whether or not the valve is opened.
When the ECU 22 determines that the solenoid valve 18 is not closed, the ECU 22 determines that the solenoid valve 18
And a solenoid valve drive unit that opens the solenoid valve 18 when the solenoid valve 18 is determined not to be opened by the valve opening determination unit.

Further, the ECU 22 is configured to determine a target air-fuel ratio based on the operating state, the intake air amount Q _A and the engine speed N, and control the fuel injection amount of the fuel injection device 7 according to the target air-fuel ratio. It

That is, 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 a rotation speed signal input port for inputting a rotation speed signal corresponding to the engine rotation speed N from the distributor 15. At the same time, when the solenoid valve 18 is closed, the theoretical air-fuel ratio read in correspondence with the intake air amount Q _A and the engine speed or an air-fuel ratio close thereto is stored in advance as a target air-fuel ratio for normal operation. And a lean operation map in which a lean air-fuel ratio read in advance corresponding to the intake air amount Q _A and the engine speed when the solenoid valve 18 is opened is stored as a target air-fuel ratio. state, the target air-fuel ratio corresponding to the intake air quantity Q _a and the engine speed N or lean operation map or the normal operation map It has an air-fuel ratio determination unit that reads out and determines the target air-fuel ratio, and a fuel injection amount control unit that determines the fuel injection pulse width τ according to the target air-fuel ratio and controls the fuel injection amount of the fuel injection device 7. There is.

In addition, in the ECU 22, immediately after the normal operation in which the target air-fuel ratio is at or near the stoichiometric air-fuel ratio is changed to the lean operation in which the lean air-fuel ratio is set as the target air-fuel ratio, the inertia of the air flow meter 4 is increased. In order to prevent enrichment that occurs due to overshooting, the intake air amount Q _A for reading the target air-fuel ratio from the lean operation map for a predetermined period from the time when the normal operation is switched to the lean operation is set to a predetermined value. It is configured to limit to:

That is, the ECU 22 is a timer that is initialized when it is determined that the solenoid valve 18 is not opened by the valve open determination unit, and the solenoid valve 18 is opened by the solenoid valve drive unit, overshoot determination unit intake air quantity Q _a is determined whether or not above a predetermined maximum intake air quantity Q _max, the intake air quantity Q _a at this overshoot determination section a predetermined maximum intake air quantity Q _max When it is determined that it exceeds, the guard time determination unit that determines whether or not this determination is within the preset time T of the timer, and the intake air amount Q _A within the preset time of the timer It has an intake air amount conversion unit that makes the maximum intake air amount Q _{max the} intake air amount Q _A used for reading the target air-fuel ratio from the lean operation map when the amount Q _max is exceeded.

The ECU 22 is also provided with a vehicle speed signal input port 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 port for inputting an air-fuel ratio signal of the air-fuel ratio sensor 12. Has been. The data used in the ECU 22 includes a flag 1 for determining whether the solenoid valve 18 is closed and a flag 2 for determining whether the solenoid valve 18 is closed.
And three flag bits of flag 3 for determining whether it is within the set time of the timer.

In the above configuration, the air-fuel ratio control is executed inside the ECU 22 in accordance with the sequence shown in FIG.

That is, first, a water temperature signal corresponding from the water temperature sensor in the water temperature T _W of the engine 1 is inputted to the water temperature determination section via the coolant temperature signal input port (F1), then via a throttle opening signal input port from the throttle sensor 21 A throttle opening signal is input to the throttle opening determination unit (F2). Next, the water temperature determination unit determines whether or not the water temperature T _W is higher than the predetermined temperature T ₁ (F3), and when the water temperature T _W is higher than the predetermined temperature T ₁ here, The throttle opening determination unit determines whether or not the throttle opening TVθ exceeds the predetermined opening θ ₁ (F4). If the water temperature determination unit determines that the water temperature T _W is lower than or equal to the predetermined temperature T ₁ , the engine temperature has not risen sufficiently and the air-fuel ratio is set to a lean region that is higher than the theoretical air-fuel ratio. Then, the rotation of the engine becomes unstable when the engine is operating. Further, when the water temperature T _W is higher than the predetermined temperature T ₁ and the throttle opening TVθ is larger than the predetermined opening θ ₁ , the throttle valve is used to obtain an output corresponding to the load of the engine 1. This is when the valve 5 is being opened. Therefore, in these cases, the solenoid valve 18 is closed and the air-fuel ratio control in the logical air-fuel ratio and the air-fuel ratio region in the vicinity thereof is executed. Further, when the water temperature T _W is higher than the predetermined temperature and the throttle opening TVθ is equal to or smaller than the predetermined opening θ ₁ , the engine can be stably operated in the lean region and the output is unnecessary. In this case, the air-fuel ratio control in the lean range is executed to save fuel consumption.

That is, in the water temperature determination unit, the water temperature T _W is the predetermined temperature.
When it is determined that the temperature is equal to or lower than T ₁ , or the water temperature T _W is higher than the predetermined temperature T ₁ and the throttle opening TV
When θ exceeds the predetermined opening θ ₁ , the solenoid valve 18 is first checked depending on whether the flag 1 indicating the closing of the solenoid valve 18 is set (whether it is “1”). It is determined whether the valve is closed (F5). In the initial state, the flag 1 is "0", and it is determined that the solenoid valve 18 is not closed. Therefore, after setting the flag 1 (F6), the solenoid valve drive unit closes the solenoid valve 18 (F7). ). Then, by inputting the intake air amount signal and the rotation speed signal (F8), the target air-fuel ratio TAF is set by the air-fuel ratio determination unit based on the normal operation map that sets the theoretical air-fuel ratio and the air-fuel ratio in the air-fuel ratio region in the vicinity thereof. (F
9), the fuel injection amount control unit determines the injection pulse width τ for controlling the fuel injection amount of the fuel injection device 7 from the intake air amount Q _A , the rotation speed N and the target air-fuel ratio TAF (F10), and the injection pulse Fuel is injected from the fuel injection device 7 over the width τ (F11). After this, the sequence returns to the first stage (F1) and the sequence after this first stage (F1) is repeated. Then, if it is determined again that the water temperature T _W is lower than or equal to the predetermined temperature T ₁ (F2), or if the water temperature T _W exceeds the predetermined temperature T ₁ but the throttle opening TVθ is equal to or higher than the predetermined temperature T _1. If the opening angle θ ₁ of the solenoid valve 18 exceeds (F2, F3), the step of determining whether or not the solenoid valve 18 is closed (F
It is confirmed that flag 1 is set in 5), and after this flag 1 is lowered (F12), the intake air amount signal and the rotation speed signal are input (F8), and the air-fuel ratio is determined based on the normal operation map. Part determines the target air-fuel ratio TAF (F9), and the fuel injection amount control part determines the injection pulse width τ that controls the fuel injection amount of the fuel injection device 7 from the intake air amount Q _A , the rotation speed N and the target air-fuel ratio TAF. After determining (F10), fuel is injected from the fuel injection device 7 over the injection pulse width τ (F11). It said water temperature T _W is or is above the predetermined temperature T ₁ of less, or the water temperature T _W is or exceeds a predetermined temperature T ₁ of the above but the throttle opening TVθ above a predetermined opening theta ₁ above, any As long as the above condition is satisfied, the sequence up to this point is repeated while flag 1 is set and lowered. When the water temperature T _W is higher than the predetermined temperature T ₁ and the throttle opening TVθ is equal to or smaller than the predetermined opening θ ₁ after these conditions are sequentially confirmed (F2, F3), It is determined whether or not the solenoid valve 18 is opened by determining whether or not the flag 2 indicating that the solenoid valve 18 is opened (is "1"). F13). Flag 2 is set to "0" in the initial state, so at this stage (F1
At the first time in 3), it is determined that the solenoid valve 18 has not been opened, and after flag 2 is set (F14), the solenoid valve drive unit opens the solenoid valve 18 and the timer is started. At the same time when this timer is started (initialized), a flag 3 indicating that the prevention of enrichment that occurs during the transition period from normal operation to lean operation is being executed is established (F15). Then, after inputting the intake air amount signal and the rotation speed signal (F16), it is confirmed that the flag 3 is established (F17), and the intake air amount Q _A is set to the predetermined maximum value by the overshoot determination unit. It is determined whether or not the intake air amount Q _max is exceeded (F18). Air flow meter 4 here
The intake air amount Q _A detected by
When it is determined that the value exceeds Q _max (F18), when it is confirmed that it is within the set time T of the above timer (F1
9) Replace the value of the intake air amount Q _A used for reading the target air-fuel ratio in the intake air amount conversion unit with the maximum intake air amount Q _max (F20), and use this replaced intake air amount Q _A. Corresponding to the engine speed N, the target air-fuel ratio TAF is determined by the air-fuel ratio determination unit based on the lean operation map (F21), and the intake air amount Q _A , the rotation speed N and the target air-fuel ratio are controlled by the fuel injection amount control unit. The injection pulse width τ that controls the fuel injection amount of the fuel injection device 7 is determined from the TAF (F10), and the fuel injection device 7 injects fuel over the injection pulse width τ (F11). When the sequence is repeated and it is confirmed that the water temperature T _W again exceeds the above-mentioned predetermined temperature T ₁ and the throttle opening TVθ is equal to or less than the above-mentioned predetermined opening θ ₁ (F2, F3) After confirming that flag 2 is set (F22), lower this flag 2 (F23), input the intake air amount signal and the rotation speed signal (F16), and check if flag 3 is established. Is determined (F17). Flag 3 is an overshoot determination unit, where the intake air amount Q _A is a predetermined maximum intake air amount Q
_When it is determined that it is less than or equal to _max (F18), or when it is confirmed that the set time T of the timer has elapsed (F19), it is lowered (F24). Therefore, in the stage (F17) in which it is judged whether or not the flag 3 has been established for the second time and thereafter, there are cases where the flag 3 is set and cases where it is set down. When the flag 3 is set, the air-fuel ratio control is executed in the same manner as described above. When the flag 3 is set down, the intake air amount Q _A detected by the air flow meter 4 and the distributor 15 are detected. The target air-fuel ratio corresponding to the determined engine speed N is read from the lean operation map to determine the target air-fuel ratio TAF (F21), and the fuel injection amount control unit intake air amount Q _A , the engine speed N and the target air-fuel ratio TAF. The injection pulse width τ for controlling the fuel injection amount of the fuel injection device 7 is determined (F10), and the injection pulse width τ is determined.
To inject fuel from the fuel injector 7 (F1
1).

Now, assuming that the water temperature T _W exceeds the predetermined temperature T ₁ , for example, as shown in FIG. 4 (A), the throttle opening TVθ is set to the above-mentioned predetermined opening from a region exceeding the above-mentioned predetermined opening θ _1. θ ₁
Taking the case of uniformly changing to the following region as an example, as shown in FIG. 4 (B), the solenoid valve 18 is closed while the throttle opening TVθ is above the predetermined opening θ _1. When the throttle opening TVθ is equal to or smaller than the predetermined opening θ _{1, the} solenoid valve 18 is opened. The intake air amount Q _A rapidly increases from the intake air amount Q ₂ corresponding to the air-fuel ratio in the lean region to the intake air amount Q ₁ corresponding to the stoichiometric air-fuel ratio as shown in FIGS. 4 (C) and 5. When the air-fuel ratio region is switched, the air flow meter 4 changes due to inertia more greatly than the actual flow rate variation ratio, and corresponds to the apparently large intake air amount [hatched portion in FIG. 4 (C)]. The problem of excessive fuel supply is
Replace the value of intake air amount Q _A used for reading the target air-fuel ratio in the intake air amount conversion unit with the maximum intake air amount Q _max (= Q ₁ ) within the guard time set by the above timer (F20) , in response to this replacement intake air quantity Q _a and the engine speed N, it is solved by determining the target air-fuel ratio TAF by the air-fuel ratio determining unit based on the lean operation map (F21). Moreover, the switching of the air-fuel ratio region is executed without delay in opening the solenoid valve 18. Further, the change amount of the fuel injection amount Q _f when the air-fuel ratio region is switched is zero as shown in FIG. 4 (D), and the fuel injection amount Q _f is the fuel injection amount P corresponding to the theoretical air-fuel ratio. Unlike the conventional one from the ₂ is reduced to the fuel injection amount P ₁ corresponding to the lean region, the change in the output of the engine 1 does not occur. Further, the air-fuel ratio can be changed by instantaneously passing through the air-fuel ratio region where a relatively large amount of nitrogen oxides is generated, so that the generation of nitrogen oxides is small and it is advantageous in purifying the exhaust gas.

The throttle opening TVθ from the intake air quantity Q ₁ corresponding to the air-fuel ratio in the lean region to the opposite case of changing the area below the above predetermined opening theta ₁ from a predetermined opening theta ₁ following areas of the The intake air amount Q ₂ corresponding to the stoichiometric air-fuel ratio suddenly increases, but similarly, there is no output fluctuation and the generation of nitrogen oxides is small.

Before and after switching the air-fuel ratio range, the throttle valve 5
And the sub-throttle valve 19 are interlocked with each other to adjust the opening and closing. Therefore, when the solenoid valve 18 is open, 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 made constant. The intake air amount can be adjusted as it is, and the air-fuel ratio control can be easily executed as in the case of using one valve.

Although the solenoid valve 18 is closed during the warm-up operation of the engine 1 in the above-described embodiment, the sub-throttle valve 19 is provided with a notch to increase the intake air amount. Correspondingly, it is preferable to increase the fuel supply amount and increase the idling speed to shorten the warm-up time.

Further, the throttle opening TVθ is set to be equal to or smaller than the predetermined opening during deceleration, and the solenoid valve 18 is opened. However, whether the throttle air is decelerated from the intake air amount Q _A and the engine speed N in the ECU 22. The ECU 22 is provided with a deceleration determination unit that determines whether or not the deceleration is started and a deceleration time determination unit that determines whether or not it is within a predetermined time after the deceleration is started. The solenoid valve 18 is opened within a predetermined relaxation after the start so as to exert a dashpot effect, and after a predetermined time has elapsed from the start of deceleration, the solenoid valve 18 is closed to prevent the brake effect from being lowered. It is advantageous to configure the ECU. Furthermore,
When the solenoid valve 18 is locked in the closed state for some reason, the locked state is detected, and the fuel supply amount is changed to switch the air-fuel ratio region to the lean region and other regions. It is advantageous to configure the ECU 22. It is also advantageous to configure the ECU 22 to forcibly stop the fuel supply to prevent runaway of the engine when the solenoid valve 18 is locked in the open state for some reason.

The present invention is not limited to a fuel injection engine, but can be applied to an engine having a carburetor, and in a fuel injection engine, an existing air valve is used to increase the bypass air amount,
It is also possible to change the air-fuel ratio region to the lean region. Further, it is also possible to control the idle rotation by controlling the duty of the solenoid valve 18.

〔The invention's effect〕

As described above, the engine air-fuel ratio control device of the present invention is provided with the second valve device for opening and closing the bypass passage in the bypass passage bypassing the throttle valve, and the valve device is adapted to the operating state of the engine. A second valve control means is provided to open when the air-fuel ratio is switched to a lean region that is leaner than the stoichiometric air-fuel ratio, and to close when switching from the lean region to another region, and the intake air amount without changing the fuel amount. Is configured to switch the air-fuel ratio, the output fluctuation due to the change of the air-fuel ratio region can be eliminated, and so-called torque shock and vibration can be prevented. In addition, when switching the air-fuel ratio region, the amount of nitrogen oxides generated is small, because it instantaneously passes through the air-fuel ratio region where the amount of nitrogen oxides generated is large.
This is advantageous in purifying exhaust gas. Further, the air-fuel ratio control system for an engine of the present invention is provided with a first valve device in the bypass passage, which is in series with the second valve device for adjusting the opening / closing of the bypass passage, and the first valve device is linked with the throttle valve. Thus, the intake air amount can be adjusted by keeping the ratio of the air amount passing through the throttle valve and the air amount passing through the bypass passage constant, so that the air-fuel ratio control in the lean region is easy.

[Brief description of drawings]

FIG. 1 is a block diagram schematically showing an embodiment of the present invention,
FIG. 2 is a longitudinal sectional view of the intake passage and the bypass passage, FIG. 3 is a flow chart of a control sequence executed in the ECU, and FIG. 4 (A) is a time chart showing opening / closing operation of the throttle valve. FIG. 4 (B) is a time chart showing the opening / closing operation of the solenoid valve which opens / closes in response to the opening / closing operation of the throttle valve, and FIG. 4 (C) corresponds to the opening / closing operation of the throttle valve. 4 is a time chart showing a change state of the intake air amount that changes over time, and FIG. 4D is a time chart showing a change state of the fuel injection amount that changes corresponding to the opening / closing operation of the throttle valve. FIG. 5 is a relationship diagram of fuel supply amount-air amount-engine output showing the relationship between the air amount, the fuel supply amount, and the engine output when the air-fuel ratio region is changed. In the figure, 1 is an engine, 5 is a throttle valve (throttle valve), 17 is a bypass passage, 18 is a second valve device, 19 is a first valve device, and 22 is a second valve control means (electronic control unit, ECU). is there.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hideki Tanaka 3-3 Shinchi, Fuchu-cho, Aki-gun, Hiroshima Prefecture Mazda Co., Ltd. (56) References JP-A-58-13131 (JP, A) JP-A-58- 211543 (JP, A) JP 59-70853 (JP, A) Actual development 60-28259 (JP, U)

Claims (1)

[Claims] Claim: What is claimed is: 1. An air-fuel ratio control device for an engine, comprising: an air-fuel ratio control means for detecting a predetermined operating state of the engine and stepwise switching the air-fuel ratio to a leaner than the stoichiometric air-fuel ratio. Is a bypass passage that bypasses the throttle valve, a first valve device that is provided in the bypass passage and that is opened and closed in conjunction with the opening and closing operation of the throttle valve, and the bypass passage that is in series with the first valve device. And a second valve device which is opened and closed when the air-fuel ratio is switched from the stoichiometric air-fuel ratio to lean and is closed when the air-fuel ratio is switched from lean to another air-fuel ratio. An engine air-fuel ratio control device comprising valve control means.