JPS62165544A - Air-fuel ratio control device for engine - Google Patents

Abstract

PURPOSE:To reduce an output fluctuation due to a change in air-fuel ratio by changing an air-fuel ratio control means over to the lean side in step rather than to a theoretical air-fuel ratio, and opening and closing a valve device within a bypass passage bypassing a throttle valve with a control means. CONSTITUTION:When an engine 1 is running, ECU 22 is inputted with a water temperature signal 'Tw' from a water temperature sensor and an opening signal 'TVtheta' from a throttle sensor 21. If water temperature 'Tw' is lower than predetermined temperature 'T1', or 'Tw' is higher than 'T1' and the throttle opening 'TVtheta' exceeds predetermined opening 'theta1', air-fuel ratio control is made to go on according to a theoretical air-fuel ratio. Namely, when the engine 1 is in an idling state in this case, a valve device 18 within a bypass passage 17 formed bypassing a throttle valve 5 is made to open, while said device 18 is made to close in non-idling operation. Also, when 'Tw' is higher than 'T1' and 'TVtheta' is less than 'theta1', the valve device 18 is made to open and a large quantity of intake air is fed to a combustion chamber 9, thereby enabling the engine 1 to be operated on a lean air-fuel ratio.

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.

[Prior art]

In order 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. 1983-1999. It is generally known from Publication No. 210137 and the like.

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 remaining, 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. will gradually pass through
Since the amount of nitrogen oxides produced increases, this is disadvantageous in purifying exhaust gas.

[Purpose of the invention]

The present invention has been made in consideration of the above circumstances, and is an air-fuel ratio control for an engine that can switch the air-fuel ratio without fluctuations in output and is advantageous in purifying exhaust gas. The purpose is to provide equipment.

[Structure of the Invention] In order to achieve the above object, the engine air-fuel ratio control device according to the present invention detects a predetermined operating state of the engine and gradually switches the air-fuel ratio to leaner than the stoichiometric air-fuel ratio. In an air-fuel ratio control device for an engine, the air-fuel ratio control means includes a bypass passage that bypasses a throttle valve, a valve device provided in the bypass passage, and a valve device that controls the air-fuel ratio by theoretically controlling the air-fuel ratio. comprising control means for controlling the air-fuel ratio to open when switching from lean to lean and to close when switching from lean to another air-fuel ratio;
By opening and closing the bypass passage using the valve device, the air-fuel ratio can be switched stepwise by changing the intake air amount relative to the fuel supply amount without changing the fuel supply amount relative to the intake air amount.

[Embodiment 1] An embodiment of the present invention will be described below based on FIGS. 1 to 6.

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 and a throttle valve that sequentially detect the amount of intake air from there toward the end and output an intake air amount signal corresponding to the intake air ff1qA. 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. Further, an exhaust valve 11 is disposed at the starting end of an exhaust path 10 led out from the combustion chamber 9, and an air-fuel ratio signal corresponding to the air-fuel ratio is provided by detecting gas components in the exhaust gas in the middle of the exhaust path 10. An air-fuel ratio sensor 12 and a catalytic exhaust purification device 13 are provided in this order. 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 interlocked and 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 to the size of the intake passage so that when the solenoid valve 18 is opened with the fuel injection ffiQr fixed, an amount of air can be sucked in to ensure an air-fuel ratio of 18 or more for stable idling 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, when installing the sub-throttle valve 19, variations in the amount of bypass air passing through the bypass passage 17 occur due to the opening degree and manufacturing errors of the bypass passage 17.
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, but in order to reduce the effect that this variation in the amount of bypass air has on the air-fuel ratio, the above-mentioned The upstream opening of the bypass passage 17 is as close as possible to the throttle valve 5.
is placed near.

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
has a water temperature signal input port for inputting a water temperature signal corresponding to the water temperature T of the cooling water of the engine l from a water temperature sensor (not shown), and a throttle opening signal input port for manually inputting a throttle opening signal from the throttle sensor 21, As will be described later, the operating state of the engine 1 can be determined from the water temperature Tu, the throttle opening TVθ, and the presence or absence of an idling signal.

In other words, this ECU 22 maintains the above water temperature T. is higher than a predetermined temperature T1 corresponding to the minimum temperature at which the engine can be operated stably in a lean region, for example, approximately 50°C to 60°C; When l exceeds the predetermined temperature TI, the throttle opening T
Predetermined opening degree θ1 at which Vθ is opened to obtain a predetermined output
and a throttle opening determination unit that determines whether or not the water temperature T exceeds the predetermined temperature T, or the water temperature T. exceeds the predetermined temperature T, and the throttle opening degree TVθ exceeds the predetermined opening degree θ8, the engine has an idling determination unit that determines the presence or absence of an idling signal.

The ECU 22 further controls the solenoid when the throttle opening degree determining unit determines that the throttle opening degree TVθ is equal to or less than the predetermined opening degree θ1, or when the idling determining unit 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 no idling signal is input.

Furthermore, the ECU 22 includes an intake air amount signal input boat that inputs an intake air amount signal from the air flow meter 4, and an intake air amount signal input boat that inputs an intake air amount signal from the air flow meter 4, in order to control the fuel injection amount corresponding to the intake air ffiQA and the engine speed N. When the water temperature T8 exceeds the predetermined temperature T, the throttle opening TVθ
is less than the above predetermined opening θ1, the intake air it Q
A and a lean operation map that stores in advance a lean target air-fuel ratio read out corresponding to the engine speed N, and when the water temperature T is equal to or less than the predetermined temperature T, or the water temperature T. exceeds the predetermined temperature T1,
In addition, when the throttle opening degree TVθ exceeds the above-mentioned predetermined opening degree θ1, the stoichiometric air-fuel ratio corresponding to the intake air amount QA and the engine speed N or an air-fuel ratio close to this is stored in advance as the target air-fuel ratio. The intake air ffiQA detected by the air flow meter 4 and the engine rotation detected via the distributor 15 are calculated from the operation map and the lean operation map or normal operation map corresponding to the water temperature T and throttle opening TVθ. It has a target air-fuel ratio determination section that reads out a target air-fuel ratio corresponding to the number N and determines the target air-fuel ratio, and a fuel injection amount control section that controls the fuel injection amount of the fuel injection device 7 according to this target air-fuel ratio.

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 the air-fuel ratio signal of the air-fuel ratio sensor 12. It is being

In the above configuration, the air-fuel ratio is controlled inside the ECU 22 according to the sequence shown in FIG.

That is, first, a water temperature signal corresponding to the above-mentioned water temperature Tu is input from the water temperature sensor to the water temperature determination section via the water temperature signal input port (Fl), and then a throttle opening signal is sent from the throttle sensor 21 to the human-powered boat. The information is input to the throttle opening determination unit via the throttle opening determination unit (F2). Next, the water temperature discriminator determines the water'/AT. is the above predetermined temperature T
It is determined whether or not it exceeds (F3). Here, if the water temperature T w exceeds the predetermined temperature T, the throttle opening determination unit determines whether or not the throttle opening TVθ exceeds the predetermined opening θ1. F4).

The above water temperature T is determined by the water temperature discrimination section. If it is determined that the temperature is below the above-mentioned predetermined temperature T, the engine temperature has not risen sufficiently, and if the air-fuel ratio is set to a range higher than the stoichiometric air-fuel ratio, the engine This is the case when the rotation becomes unstable. In addition, the above water temperature T. is the above predetermined temperature T.

, and when the throttle opening degree TVθ exceeds the above-mentioned predetermined opening degree θ1, it means that the throttle valve 5 is being operated to open in order to obtain an output corresponding to the engine load. Therefore, the above water temperature T. is determined to be below the predetermined temperature T, or the water temperature T8 exceeds the predetermined temperature T1, and the throttle opening T■θ exceeds the predetermined opening θ1. In this case, 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). Here, if it is determined that the idling signal is correct, the water temperature T8 is the predetermined temperature T, and if it is below, a large amount of air and fuel is supplied to increase the stability of idling operation and shorten the warm-up time. It is preferable to supply the above-mentioned temperature T. is the above predetermined temperature T
When it exceeds 1, it is preferable to give a kind of dash-boso effect to the intake air control in order to prevent an increase in the generation of nitrogen oxides due to a delay in fuel control during deceleration. Therefore, in this case, the solenoid valve 1 is
8 is opened (F6). 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 execute the air-fuel ratio control using the normal throttle valve 5, the solenoid valve 18 is closed via the drive section (
F7). In these cases, the solenoid valve 18
After executing the opening/closing control (F6 or F7), an intake air amount signal is input from the air flow meter 4 through the intake air amount signal input port, and at the same time, an intake air amount signal is input from the distributor 15 through the rotation speed signal input port. Manually input the rotation speed signal corresponding to the engine rotation speed N (F8),
From the normal operation map, the target air-fuel ratio corresponding to the intake air it QA and the engine speed N is determined by the target air-fuel ratio determination section (F9), and the fuel quantity control section injects from the fuel injection device 7 according to this target air-fuel ratio. The fuel injection amount is controlled (FIO). If it is determined that the water temperature QA exceeds the predetermined temperature T1, but the throttle opening TVθ is less than the predetermined opening θ1, the engine temperature has risen sufficiently to achieve a lean air-fuel ratio. In this case, the engine is in a state where stable lean operation is possible, and 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 valve 18 is opened (Fil) via the drive section, and a large amount of intake air is drawn into the combustion chamber 9 through the intake passage 2 and the bypass passage 17. Then, input an intake air amount signal from the air flow meter 4 via the intake air amount signal input port, and input a rotation speed signal corresponding to the engine rotation speed N from the distributor 15 via the rotation speed signal input port. ), the target air-fuel ratio corresponding to the intake air ffiQA and the engine speed N is determined by the air-fuel ratio determination section based on the lean operation map (F13), and the fuel injection amount control section controls the fuel injection according to this target air-fuel ratio. The amount of fuel injected from the device 7 is controlled (FIO).

The water temperature is now T. exceeds a predetermined temperature T, for example, as shown in FIG. For example, if the throttle opening TV is changed as shown in Fig. 4 (B),
The solenoid valve 18 is opened while θ is below the predetermined opening θ1, and when the throttle opening TVθ exceeds the predetermined opening θ1, the solenoid valve 18 is closed, and the intake air amount QA is As shown in FIG. 5C and FIG. 5, the intake air amount Q, which corresponds to a lean air-fuel ratio, rapidly decreases to the intake air amount Q2, which corresponds to the stoichiometric air-fuel ratio. When this air-fuel ratio region is switched, the change in the fuel injection amount Q is zero as shown in FIG. Fuel injection amount P2 corresponding to the stoichiometric air-fuel ratio from the injection amount Pl
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, 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 during lean operation.

When changing the throttle opening TVθ from a region above the predetermined opening θ1 to a region below the predetermined opening θ1, conversely, the intake air amount Q2 corresponding to the stoichiometric air-fuel ratio is changed to a lean air-fuel ratio. Although the corresponding intake air amount Q increases rapidly, there is no change in the fuel injection amount Q, so there is no output fluctuation, and the generation of nitrogen oxides is small.

[Embodiment 2] In the above embodiment, the inflow air amount QA is related to the determination of the target air-fuel ratio, but it is also possible to determine the target air-fuel ratio regardless of the inflow air amount QA.

That is, in this case, the throttle opening T is sent to the ECU 22.
A fuel injection pulse map in which basic fuel injection pulses with Vθ and engine speed N as parameters are stored, throttle opening TVθ detected by the throttle sensor 21 from this fuel injection pulse map, and distributor 1
A basic injection amount determining section is provided which reads out a basic fuel injection pulse corresponding to the engine rotational speed N detected through 5 and determines the basic injection amount. Further, in this embodiment, the throttle opening degree TVθ is adjusted to the above-mentioned predetermined opening degree θ as necessary.
A rotation lower limit determining section is provided that determines whether or not the engine rotation speed N exceeds a predetermined rotation speed R1 corresponding to the lower limit of the rotation speed at which the engine can rotate stably when the engine rotation speed N is 1 or less. Further, the idling discrimination section of this embodiment determines whether the water temperature T8 is equal to or less than the predetermined temperature T, or the water temperature T8 is the water temperature T8. Throttle opening degree TV exceeds the above predetermined temperature T.
When θ exceeds the predetermined opening θ, or the water temperature T8 exceeds the predetermined temperature T1, and the throttle opening TVθ exceeds the predetermined opening θ1,
Furthermore, engine rotation #! IN is the above predetermined rotation ￥i,
It is configured to determine the presence or absence of an idling signal when it exceeds Rl.

In addition, in this embodiment, in order to perform idle up, the above water temperature T. A warm-up increase coefficient calculation unit calculates a warm-up increase coefficient C based on the warm-up increase coefficient C, and a warm-up increase coefficient C, which is calculated by multiplying the basic injection amount using the throttle opening TVθ and the engine speed N as parameters by a warm-up increase coefficient 01 to obtain the warm-up target. A warm-up target air-fuel ratio determination unit is provided to determine the air-fuel ratio. Further, the drive unit determines the water temperature T in the idling determination unit. is determined to have an idling signal when it is below the above-mentioned predetermined temperature T (during warm-up), or when the above-mentioned water temperature T8 exceeds the above-mentioned predetermined temperature T1 and the throttle opening degree TVθ is below the above-mentioned temperature. The solenoid valve 18 is opened when the opening degree is less than or equal to the predetermined opening θ and the engine rotation speed N is less than or equal to the predetermined rotation speed R, and the idling determination section determines that there is no idling signal. In such a case, the solenoid valve 18 is closed. Furthermore, this ECU 22 includes a normal target air-fuel ratio determining unit that determines the basic injection amount using the throttle opening TVθ and engine rotational speed N as parameters as the target air-fuel ratio when the idling determining unit determines that there is no idling signal. and the above water temperature T1. The throttle is opened when l exceeds the predetermined temperature T, the throttle opening TVθ is less than the predetermined opening θ1, and the engine speed N is less than the predetermined rotational speed R1. a lean target air-fuel ratio determination unit that determines a lean target air-fuel ratio by multiplying the basic injection amount by a predetermined slope operation correction coefficient C2 using the degree TVθ and engine rotational speed N as parameters; , has a fuel injection amount control section that controls the fuel injection amount of the fuel injection device 7 according to one target air-fuel ratio selected from among the normal target air-fuel ratio and the lean target air-fuel ratio according to the operating state.

Note that the other configurations of this embodiment are similar to those of the above-mentioned embodiment.

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

That is, first, the water temperature T8 of engine l is determined from the water temperature sensor.
The water temperature signal corresponding to
1 to the throttle opening number 43 are input to the basic injection amount determination section through the throttle opening signal input port, and the rotation speed signal from the distributor 15 is input to the basic injection amount determination section through the rotation speed signal input port. do(
F22). Next, based on the detected throttle opening TVθ and engine rotational speed N, a fuel injection pulse value is read out from the fuel injection pulse map to the basic injection amount determination unit (F23), and the basic injection amount determination unit determines the basic injection amount. (F24). Thereafter, a predetermined operating state is detected by the water temperature determination section, the throttle opening degree determination section, and the rotation lower limit determination section. That is, the water temperature determination unit determines whether the water temperature T exceeds the predetermined temperature T1 (F25);
Here, if the water temperature T,1 exceeds the predetermined temperature T1, the throttle opening determination section determines the throttle opening TVθ.
It is determined whether or not exceeds the predetermined opening θ (F
26) Here, when it is determined that the throttle opening degree TVθ is equal to or less than the above-mentioned predetermined opening degree θ1, the rotation lower limit determination section further determines whether the engine rotation speed N exceeds the above-mentioned predetermined rotation speed R1. (F27), and if it is determined here that the engine speed N is below the predetermined speed R1, an operating state in which the engine is operated at a lean air-fuel ratio is detected. If the water temperature determination unit determines that the water temperature T1 is equal to or lower than the predetermined temperature T (F25), or the water temperature T
If it is determined that u exceeds the predetermined temperature T, and the throttle opening TVθ exceeds the predetermined opening θ1 (F25°F26), or the water? L T
. exceeds the predetermined temperature T1, the throttle opening TVθ exceeds the predetermined opening θ, and the engine speed N exceeds the predetermined rotational speed R1.
If it is determined that the air-fuel ratio exceeds (F25 to F27), this means that operation at a lean air-fuel ratio is inconvenient. In such a case, the idling determination unit determines whether or not there is an idling signal (F28). If it is determined that there is an idling signal, the warm-up increase coefficient calculation unit calculates the warm-up increase coefficient CI based on the water temperature T, 1 in order to increase the idle (F29), thereby stabilizing the idling operation of the engine 1. After the solenoid valve 18 is opened via the drive section in order to improve performance (F30), the warm-up air-fuel ratio determination section determines the warm-up increase target air-fuel ratio (F31). Then, the fuel injection amount of the fuel injection device 7 is controlled by the fuel injection amount control section in accordance with this target air-fuel ratio (F32). If the idling determination unit determines that there is no idling signal, the solenoid valve 18 is closed via the drive unit (F33) in order to obtain the required output, and the normal target air-fuel ratio determination unit determines the basic injection amount. is determined as the target air-fuel ratio (F34), and the fuel injection amount control section controls the fuel injection device 7 according to this target air-fuel ratio.
The fuel injection amount is controlled (F32). If the engine rotational speed lower limit determining section determines that the engine rotational speed N is equal to or lower than the predetermined rotational speed R1 (F27), it is permitted to operate the engine leaner than the stoichiometric air-fuel ratio. , the solenoid valve 18 is opened via the drive section (F35). Then, the lean air-fuel ratio determination section determines a lean target air-fuel ratio (F36), and the fuel injection amount control section controls the fuel injection amount of the fuel injection device 7 according to this lean target air-fuel ratio (F3.2).

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 degrees of the throttle valve 5 and sub-throttle valve 19 are small, and the amount of intake air tends to be small. 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.

Also, during deceleration, an idling signal is input to the ECU 22, and there is a deceleration determination section that uses this idling signal and rotational speed signal as parameters to determine whether deceleration is in progress, and a deceleration determination section that determines whether or not it is within a predetermined period of time after the start of deceleration. The ECU 22 is provided with a deceleration time determining section for determining whether the deceleration is occurring, and the deceleration determining section determines that the deceleration is in progress, and the solenoid valve 18 is opened within a predetermined time after the start of the deceleration to exhibit the dashpot effect. It is advantageous to configure the ECU 22 to close the solenoid valve 18 after a predetermined period of time has elapsed since the start of deceleration to prevent the braking effect from decreasing.

Furthermore, when the solenoid valve 18 is locked in the 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.

[Brief explanation of drawings]

FIG. 1 is a block diagram schematically showing an embodiment of the present invention;
Figure 2 is a longitudinal sectional view of the intake passage and bypass passage, Figure 3 is a flow diagram of the control sequence executed within the ECU, and Figure 4 (A) is a time chart showing the opening and closing operations of the throttle valve over time. The chart, FIG. 4(B) is a time chart showing over time the opening/closing operation of a solenoid valve that opens and 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. FIG. 4(D) is a time chart showing how the amount of fuel injection changes over time in response to the opening/closing operation of the throttle valve; FIG. 5 is a fuel supply amount-air amount-engine output relationship diagram showing the relationship between the air amount, fuel supply amount, and engine output when changing the air-fuel ratio range, and FIG. 6 is an ECU of another embodiment of the present invention. FIG. 3 is a flow diagram of a control sequence executed within the system. In the figure, ■ is an engine, 5 is a throttle valve, 17 is a bypass passage, 18 is a valve device (solenoid valve), 22 is a control means (electronic control unit,
ECU). Figure $6 Figure $2 Figure 3

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 valve device provided in the bypass passage;
An air-fuel ratio control device for an engine, comprising control means for controlling the valve device to open when switching the air-fuel ratio from the stoichiometric air-fuel ratio to lean, and to close when switching from lean to another air-fuel ratio.