JPH06200834A - Air-fuel ratio control device of internal combustion engine - Google Patents

Abstract

PURPOSE:To prevent the increase of NOx and to suppress the torque variation by composing the system to convert the air-fuel ratio instantly by a control means, when the air-fuel ratio of a mixture is converted from a lean air-fuel ratio scope to a logical air-fuel ratio scope, or reversely, and at the same time, to control a bypass air flow control valve and an EGR control valve. CONSTITUTION:A bypass passage 38 is provided to a suction passage 18, and the bypass air flow is controlled by a flow control valve 40. And an EGR passage 54 to recirculate a part of the exhaust gas of an internal combustion engine 2, and an EGR control valve 60 to control the recirculating exhaust gas are provided to the suction passage 18. When the air-fuel ratio is converted from a lean air-fuel ratio scope to a logical air-fuel ratio scope, the mixing ratio is converted temporarily by a controller 28, and at the same time, a flow control valve 44 is controlled to fully close, and the EGR control valve is controlled to open and close according to the operating condition. And when the air-fuel ratio is converted reversely to the above condition, the flow control valve 44 is opened or closed according to the operating condition, while the EGR control valve 60 is controlled to fully close. By such a control, the air-fuel ratio scope to generate plenty of NOx is never used.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control system for an internal combustion engine, and more particularly, when changing the air-fuel ratio of an air-fuel mixture from a lean air-fuel ratio range to a stoichiometric air-fuel ratio range or from a stoichiometric air-fuel ratio range to a lean air-fuel ratio range. It is possible to suppress the sudden torque fluctuation when changing to N
The present invention relates to an air-fuel ratio control device for an internal combustion engine that can prevent an increase in Ox.

[0002]

2. Description of the Related Art Recently, internal combustion engines mounted on vehicles are
There is an air-fuel ratio control device for controlling the air-fuel ratio of the air-fuel mixture into a stoichiometric air-fuel ratio range (lean range) and a lean air-fuel ratio range (stoichiometric range). An air-fuel ratio control device for such an internal combustion engine is shown in FIG. In the figure, 402
Is an internal combustion engine, 404 is an intake passage, 406 is an exhaust passage, 4
Reference numeral 08 is a throttle valve, and 410 is a fuel injection valve. The fuel injection valve 410 is connected to the control unit 414 that is a control unit of the air-fuel ratio control device 412.

The control unit 414 includes an opening sensor 416 for detecting the throttle valve opening, a pressure sensor 418 for detecting the intake pressure, and a rotation speed sensor 42 for detecting the engine speed.
0, and an air-fuel ratio sensor 422 that detects the air-fuel ratio of exhaust gas,
Are connected. The control unit 414 controls the sensors 416-4.
Drive control of the fuel injection valve 410 by the detection signal of 22,
Based on the detection signal of the air-fuel ratio sensor 422, the air-fuel ratio of the air-fuel mixture is controlled to be the target value in the stoichiometric air-fuel ratio range and the lean side air-fuel ratio range.

The internal combustion engine 402 has an intake passage 404.
A bypass passage 424 for supplying bypass air to the
A flow rate control valve 426 is provided to control the flow rate of bypass air in the bypass passage 424. The flow control valve 426 communicates with the other end of a bypass pressure guiding passage 428 having one end communicating with the intake passage 402. A bypass switching valve 430 is provided in the bypass pressure guiding passage 428.
The bypass switching valve 430 is connected to the control unit 414.

Further, the internal combustion engine 402 is provided with an EGR passage 432 for recirculating a part of exhaust gas in the intake passage 404, and an EGR control valve 434 for controlling a flow rate of recirculated exhaust gas in the EGR passage 432. There is. One end of the EGR control valve 434 is connected to the other end of an EGR pressure guiding passage 436 that communicates with a bypass pressure guiding passage 428 on the intake passage 402 side of the bypass switching valve 430. EG
An EGR switching valve 438 is provided in the R pressure guiding passage 436. The EGR switching valve 438 is connected to the control unit 414.

The control unit 414 drives and controls the bypass / EGR switching valves 430 and 438 to supply / exhaust the intake negative pressure and the atmospheric pressure to / from the flow rate control valve 426 and the EGR control valve 434, respectively.
It controls the flow rate of bypass air and the flow rate of recirculated exhaust gas.

As such an air-fuel ratio control device, there are those disclosed in JP-A-63-186945 and JP-A-4-36052. JP-A-63-18694
The air-fuel ratio control device disclosed in Japanese Patent Publication No. 5 has a change amount of the target output value equal to or more than a predetermined value and a change in the target value when the difference between the target output value and the output value of the air-fuel ratio sensor is within a predetermined range. When the difference between the amount and the change amount of the output value of the air-fuel ratio sensor is less than or equal to a predetermined value, it is determined that the air-fuel ratio sensor is in the active state.

Further, the air-fuel ratio control device disclosed in Japanese Patent Application Laid-Open No. 4-36052 is provided with a bypass passage for supplying bypass air to the intake passage and a flow control valve for controlling the flow rate of the bypass air. When switching from the stoichiometric air-fuel ratio feedback control to the lean air-fuel ratio feedback control, the cooling water temperature is higher than the feedback start water temperature, the mode other than the stoichiometric air-fuel ratio feedback control, the air-fuel ratio sensor is activated and normal. When a certain condition is satisfied, the flow control valve is controlled to be opened, and when the condition is not satisfied, the flow control valve is controlled to be closed, so that the feedback control from the stoichiometric air-fuel ratio range to the feedback of the lean air-fuel ratio range is performed. This is to prevent a decrease in torque when switching to control.

[0009]

By the way, as shown in FIG. 12, the torque of the internal combustion engine is as follows:
There is a 30% difference between the lean air-fuel ratio range (eg A / F = 23) and the theoretical air-fuel ratio range (eg A / F = 14.7). Therefore, when the air-fuel ratio is changed from the stoichiometric air-fuel ratio range to the lean air-fuel ratio range or when changing from the lean air-fuel ratio range to the stoichiometric air-fuel ratio range, there is a disadvantage that torque fluctuation occurs.

Therefore, in order to deal with such a problem, like the air-fuel ratio control device disclosed in Japanese Patent Laid-Open No. 4-36052, the flow control valve in the bypass passage is controlled to reduce the fluctuation of torque. There is something.

However, the air-fuel ratio control device disclosed in this publication suppresses only the torque fluctuation when the air-fuel ratio is changed from the stoichiometric air-fuel ratio range to the lean air-fuel ratio range. For this reason, when the lean air-fuel ratio range is changed to the stoichiometric air-fuel ratio range, it is not possible to suppress the increase fluctuation of the torque, and there is a disadvantage that a shock is generated and the riding comfort is deteriorated. Further, the air-fuel ratio control device disclosed in this publication suppresses the decrease fluctuation of the torque when the air-fuel ratio is changed from the stoichiometric air-fuel ratio range to the lean air-fuel ratio range only by controlling the flow rate of the bypass air. Therefore, there is an inconvenience that an increase in NOx cannot be prevented. Further, when changing from the lean air-fuel ratio range to the stoichiometric air-fuel ratio range, if the air-fuel ratio is gradually changed, as shown in FIG. 13, NOx is increased by passing through the air-fuel ratio range in which a large amount of NOx is generated. There are inconveniences that cannot be prevented.

[0012]

Therefore, in order to eliminate the above-mentioned inconvenience, the present invention provides an air-fuel ratio sensor for detecting the air-fuel ratio of exhaust gas in the exhaust passage of an internal combustion engine, and based on the detection signal of this air-fuel ratio sensor. In an air-fuel ratio control device for an internal combustion engine, which controls an air-fuel ratio of an air-fuel mixture to be a target value in a stoichiometric air-fuel ratio region and a lean air-fuel ratio region, a bypass passage for supplying bypass air to an intake passage of the internal combustion engine is provided. A flow control valve for controlling the flow rate of the bypass air is provided, and a part of the exhaust gas is recirculated to the intake passage of the internal combustion engine E
A GR passage is provided, and an EGR control valve is provided to control the flow rate of the recirculated exhaust gas. When the air-fuel ratio of the air-fuel mixture is changed from the lean air-fuel ratio range to the stoichiometric air-fuel ratio range, the air-fuel ratio is changed instantaneously. At the same time, the flow control valve is fully closed and the EGR control valve is controlled to open and close according to the operating state of the internal combustion engine, and the air-fuel ratio of the air-fuel mixture is changed from the stoichiometric air-fuel ratio range to the lean air-fuel ratio range. Is provided with control means for instantaneously changing the air-fuel ratio and, at the same time, opening and closing the flow control valve according to the operating state of the internal combustion engine and controlling the EGR control valve to be fully closed.

[0013]

According to the structure of the present invention, the control means causes
When the air-fuel ratio of the air-fuel mixture is changed from the lean air-fuel ratio range to the stoichiometric air-fuel ratio range or when changing from the stoichiometric air-fuel ratio range to the lean air-fuel ratio range, the air-fuel ratio is changed instantaneously to obtain NOx.
The air-fuel ratio region that generates a large amount of NOx is not used, and the flow rate of the bypass air supplied to the intake passage and the flow rate of the exhaust gas recirculated to the intake passage are controlled at the same time when the air-fuel ratio changes. The torque fluctuation can be suppressed while preventing the increase.

[0014]

Embodiments of the present invention will be described in detail below with reference to the drawings.

1 to 5 show an embodiment of an air-fuel ratio control device according to the present invention. In FIG. 1, 2 is an internal combustion engine, 4 is a piston, 6 is a combustion chamber, 8 is an intake port,
10 is an exhaust port, 12 is an intake valve, 14 is an exhaust valve, 16
Is a spark plug, 18 is an intake passage, 20 is an exhaust passage, 22
Is a throttle valve. The internal combustion engine 2 is provided with a fuel injection valve 24 in the intake passage 18 facing the combustion chamber 4. The fuel injection valve 24 is connected to a control unit 28 which is a control means of the air-fuel ratio control device 26.

The control unit 28 has an opening sensor 30 for detecting the throttle opening θ, a pressure sensor 32 for detecting the intake pressure P, and a rotation speed sensor 34 for detecting the engine speed N.
And an air-fuel ratio sensor 36 that detects the air-fuel ratio of the exhaust gas. The control unit 28 drives and controls the fuel injection valve 24 based on the detection signals of the sensors 30 to 36, and based on the detection signal of the air-fuel ratio sensor 36, changes the air-fuel ratio of the air-fuel mixture to the stoichiometric air-fuel ratio range (stoichiometric range) and the lean air-fuel ratio. It is controlled to reach the target value in the range (lean range).

The internal combustion engine 2 is provided with a bypass passage 38 for supplying bypass air to the intake passage 18. The bypass passage 38 has one end communicating with a bypass inlet 40 of the intake passage 18 upstream of the throttle valve 22 and the other end of the bypass outlet 4 of the intake passage 18 downstream of the throttle valve 22.
It communicates with 2.

The bypass passage 38 is provided with a flow rate control valve 44 for controlling the flow rate of bypass air. The flow control valve 44 is composed of, for example, a duty-controlled solenoid valve or the like. The flow rate control valve 44 is provided with a valve hole 48 in the bypass passage 38 in the main body 46, and a solenoid 52 for duty-driving a valve body 50 that opens and closes the valve hole 48. The flow control valve 44 is connected to the control unit 28. The control unit 28 drives and controls the flow control valve 44,
Controls the flow rate of bypass air.

The internal combustion engine 2 also includes an intake passage 20.
Is provided with an EGR passage 54 that recirculates a part of the exhaust gas.
The EGR passage 54 has one end communicating with the EGR inlet 56 of the exhaust passage 20 and the other end EG in the middle of the bypass passage 38.
It communicates with the R outlet 58. In this EGR passage 54,
An EGR control valve 60 that controls the flow rate of the recirculated exhaust gas is provided. The EGR control valve 60 is provided with a valve hole 64 in the EGR passage 54 in the main body 62 and opens and closes the valve hole 64.
Is supported by a diaphragm 68, and the diaphragm 6
A pressure chamber 70 is defined by 8 and a spring 72 for urging the diaphragm 68 to push the valve body 66 in the direction of closing the valve hole 64 is provided.

In the pressure chamber 70 of the EGR control valve 60,
One end side communicates with the other end side of the pressure guide passage 74 that communicates with the intake passage 18 downstream of the throttle valve 22. Pressure passage 7
4 is provided with an EGR switching valve 76 for switching and introducing intake negative pressure and atmospheric pressure into the pressure chamber 70. EGR switching valve 7
6 is connected to the control unit 28. Control unit 28
Drives the EGR switching valve 76 to control the EGR control valve 6
The intake negative pressure and the atmospheric pressure are supplied to and discharged from the zero pressure chamber 70, and the flow rate of the recirculated exhaust gas is controlled.

The air-fuel ratio control device 26 of the internal combustion engine 2 is
When the air-fuel ratio of the air-fuel mixture is changed from the lean air-fuel ratio range to the stoichiometric air-fuel ratio range by the control unit 28, the air-fuel ratio is instantaneously changed and the flow control valve 44 is fully closed and EG
The R control valve 60 is controlled to open and close according to the operating state of the internal combustion engine 2. Further, when the air-fuel ratio control device 26 changes the air-fuel ratio of the air-fuel mixture from the stoichiometric air-fuel ratio region to the lean air-fuel ratio region by the control unit 28, it instantaneously changes the air-fuel ratio and, at the same time, the flow control valve 44. Is opened and closed according to the operating state of the internal combustion engine 2 and the EGR control valve 60 is fully closed.

That is, when changing the air-fuel ratio of the air-fuel mixture from the lean air-fuel ratio range to the stoichiometric air-fuel ratio range, the air-fuel ratio control unit 26 instantaneously changes the air-fuel ratio and shuts off the bypass air. By recirculating exhaust gas in an amount corresponding to the operating state of the internal combustion engine 2 to the intake passage 18, torque fluctuation is suppressed and NOx increase is prevented, while the air-fuel ratio of the air-fuel mixture is diluted from the stoichiometric air-fuel ratio range. When changing to the air-fuel ratio region, the air-fuel ratio is instantaneously changed, and at the same time, the exhaust gas recirculation to the intake passage 18 is stopped to supply the intake passage with an amount of bypass air according to the operating state of the internal combustion engine 2. By doing so, the amount of air is increased to suppress the torque fluctuation due to the dilution.

Next, the control by the air-fuel ratio control device 26 will be described with reference to FIGS.

In FIG. 2, when the control starts (step 100), the engine speed N is detected (step 10).
1) Then, the intake pressure P is detected (step 102), the throttle opening θ is detected (step 103), the duty ratio of the flow control valve 44 is calculated (step 104), and the flow control is performed by the calculated duty ratio. The valve 44 is drive-controlled to supply bypass air to the intake passage 18 downstream of the throttle valve 22.

Next, the control mode is judged (step 10
5) Do. In this determination (step 105), if the air-fuel ratio of the air-fuel mixture changes from the lean air-fuel ratio range to the stoichiometric air-fuel ratio range, the flow control valve 44 should be closed to close the bypass passage 38.
Is controlled to be fully closed (step 106), and the EGR switching valve 76 is operated to recirculate exhaust gas in an amount corresponding to the operating state to the intake passage 18 by causing an intake negative pressure to act on the pressure chamber 70 of the EGR control valve 60. The drive control is turned on (step 107), and the drive control of the fuel injection valve 24 based on the theoretical air-fuel ratio map is started (step 108) and finished (step 109) so that the air-fuel ratio becomes the target value in the theoretical air-fuel ratio range. To do.

On the other hand, in the judgment (step 105), when the operating state of the internal combustion engine 2 changes from the stoichiometric air-fuel ratio region to the lean air-fuel ratio region, the bypass passage 38 is opened and the amount corresponding to the operating state is opened. In order to supply the bypass air to the intake passage 18, the flow control valve 44 is opened (step 110), and the atmospheric pressure is applied to the pressure chamber 70 of the EGR control valve 60 to stop the exhaust gas recirculation. The switching valve 76 is controlled to be turned off (step 111), and the drive control of the fuel injection valve 24 based on the lean air-fuel ratio map is started so that the air-fuel ratio becomes the target value in the lean air-fuel ratio range (step 1).
12) and ends (step 109).

More specifically, when the internal combustion engine 2 is operated in the lean air-fuel ratio range, the amount of air flowing through the intake passage 18 is calculated from the engine speed N and the intake pressure P, and the calculated air amount is calculated. Of the flow control valve 44 so that about 10% to 30% of the air flows as bypass air through the bypass passage 38.
Drive control.

At this time, the EGR switching valve 76 is
OF is applied to apply atmospheric pressure to the pressure chamber 70 of the control valve 60.
The EGR control valve 60 is fully closed by being driven and controlled by F. Therefore, the combustion chamber 6 of the internal combustion engine 2 is supplied with the air that has passed through the throttle valve 22 of the intake passage 18 and the bypass air that is measured by the flow rate control valve 44 and flows through the bypass passage 38. The fuel injection valve 24 is driven and controlled by the lean air-fuel ratio region map so that the air-fuel ratio becomes a target value in the lean air-fuel ratio region, and injects fuel.

From such an operating state, the throttle valve 22
Is opened and the throttle opening θ increases, and the internal combustion engine 2
As shown in FIG. 3, in order to set the output air-fuel ratio range required by the internal combustion engine 2 when the operating state of is shifted to the acceleration state,
The air-fuel ratio is changed from the lean air-fuel ratio range to the stoichiometric air-fuel ratio range. Alternatively, when the load on the internal combustion engine 2 gradually increases, the air-fuel ratio is changed from the lean air-fuel ratio range to the stoichiometric air-fuel ratio range.

As described above, when the air-fuel ratio is changed from the lean air-fuel ratio range to the stoichiometric air-fuel ratio range to shift to the stoichiometric air-fuel ratio range control, the flow control valve 44 is fully closed as shown in FIG. The bypass passage 38 is closed, and the EGR control valve 60 is opened / closed according to the operating state to recirculate a part of the exhaust gas to the intake passage 18,
At the same time, immediately the fuel injection valve 2 based on the theoretical air-fuel ratio map
The drive control of No. 4 is started, and the fuel is injected to reach the target value in the stoichiometric air-fuel ratio range.

When the opening degree θ of the throttle valve 22 further increases, the intake negative pressure in the intake passage 18 weakens, so the EGR switching valve 76 is turned off and the EGR control valve 6 is turned off.
The atmospheric pressure is applied to the zero pressure chamber 70 to stop the exhaust gas recirculation.

As described above, when the air-fuel ratio of the air-fuel mixture is changed from the lean air-fuel ratio range to the stoichiometric air-fuel ratio range, the air-fuel ratio is instantaneously changed to use the air-fuel ratio range in which a large amount of NOx is generated. In addition, the flow rate of the bypass air supplied to the intake passage 18 is controlled to "0" at the same time as the change of the air-fuel ratio, and the flow rate of the exhaust gas recirculated to the intake passage 18 is controlled according to the operating state. As a result, torque fluctuation can be suppressed while preventing an increase in NOx.

Therefore, as shown in FIG. 5, when the air-fuel ratio of the air-fuel mixture is changed from the lean air-fuel ratio range to the stoichiometric air-fuel ratio range,
It is possible to suppress a sudden torque fluctuation, prevent a shock from occurring, improve a riding feeling, and prevent an increase in NOx.

On the other hand, the controller 28 changes the air-fuel ratio from the stoichiometric air-fuel ratio range to the lean air-fuel ratio range when the load gradually decreases from the state where the internal combustion engine 2 is operating in the stoichiometric air-fuel ratio range. I will let you.

When the air-fuel ratio is changed from the stoichiometric air-fuel ratio range to the lean air-fuel ratio range to shift to the lean air-fuel ratio range control, the flow control valve 44 is opened and closed according to the operating condition to bypass the bypass air 38. And exhaust gas recirculation is stopped by fully closing the EGR control valve 60, and at the same time, the drive control of the fuel injection valve 24 based on the lean air-fuel ratio region map is immediately started to reach the target value in the lean air-fuel ratio region. Inject fuel into.

As described above, when the stoichiometric air-fuel ratio range is changed to the lean air-fuel ratio range, the air-fuel ratio is changed instantaneously so that the air-fuel ratio range where a large amount of NOx is generated is not used, and At the same time as the change of the air-fuel ratio, the flow rate of the bypass air supplied to the intake passage 18 is controlled according to the operating state, and the flow rate of the exhaust gas recirculated to the intake passage 18 is controlled to "0" to increase the NOx. It is possible to suppress the torque fluctuation due to the leaning by increasing the air amount while preventing it.

Therefore, as shown in FIG. 5, when the air-fuel ratio of the air-fuel mixture is changed from the stoichiometric air-fuel ratio range to the lean air-fuel ratio range,
It is possible to suppress a sudden torque fluctuation, prevent a shock from occurring, improve a riding feeling, and prevent an increase in NOx. Moreover, by controlling the duty of the flow rate control valve 44, it is possible to appropriately deal with the fluctuation of the load and to secure the optimum flow rate of the bypass air.

6 to 10 show another embodiment of the present invention. In FIG. 6, 202 is an internal combustion engine, 2
Reference numeral 04 is a piston, 206 is a combustion chamber, 208 is an intake port, 210 is an exhaust port, 212 is an intake valve, 214 is an exhaust valve, 214 is a spark plug, 218 is an intake passage, 220
Is an exhaust passage and 222 is a throttle valve. Internal combustion engine 2
02 has a fuel injection valve 224 in the intake passage 218 directed toward the combustion chamber 204. The fuel injection valve 224 is connected to a control unit 228 that is a control unit of the air-fuel ratio control device 226.

The control unit 228 includes an opening sensor 230 for detecting the throttle opening θ, a pressure sensor 232 for detecting the intake pressure P, a rotation speed sensor 234 for detecting the engine speed N, and an exhaust air-fuel ratio. Air-fuel ratio sensor 236 for detecting
And are connected. The control unit 228 controls each sensor 230.
To 236 drive control the fuel injection valve 224, and based on the detection signal of the air-fuel ratio sensor 236, set the air-fuel ratio of the air-fuel mixture to the target value in the stoichiometric air-fuel ratio range (stoichiometric range) and the lean air-fuel ratio range (lean range). Control to become.

The internal combustion engine 202 has an intake passage 218.
A bypass passage 238 for supplying bypass air is provided. The bypass passage 238 has one end communicating with the bypass inlet 240 of the intake passage 218 near the valve end 222e of the closed throttle valve 222, and the other end of the bypass passage 238.
22 is connected to the bypass outlet 242 of the intake passage 218 on the downstream side.

As shown in FIGS. 7 to 9, the bypass inlet 240 gradually tapers toward the downstream side in the opening direction of the closed throttle valve 222 of the throttle valve 222 pivotally supported by the throttle body 244 by the valve shaft 246. It is formed in a shape that expands. That is, the bypass inlet 240
Is formed in a substantially isosceles triangular shape having a vertex near the valve end 222e that opens downstream of the closed throttle valve 222 and gradually expanding toward the downstream side in the opening direction of the valve end 222e. .

A flow rate control valve 248 for controlling the flow rate of bypass air is provided in the bypass passage 238. The flow control valve 248 is used in the bypass passage 2 in the main body 250.
38 is provided with a valve hole 252 and opens and closes the valve hole 252.
54 is supported by the diaphragm 256, and the pressure chamber 258 is defined by the diaphragm 256.
A spring 260 for urging the diaphragm 256 to push the valve body 254 in the direction of closing the valve 52 is provided.

The pressure chamber 258 of the flow rate control valve 248 communicates with the other end of a bypass pressure guiding passage 262 which communicates with the intake passage 218 downstream of the throttle valve 222. The pressure chamber 25 is provided in the bypass pressure passage 262.
8 is provided with a bypass switching valve 264 for switching and introducing intake negative pressure and atmospheric pressure. The bypass switching valve 264 is connected to the control unit 228. The controller 228 drives and controls the bypass switching valve 264 to control the flow rate control valve 248.
The intake negative pressure and the atmospheric pressure are supplied to and discharged from the pressure chamber 258 of (1) to control the flow rate of the bypass air.

The internal combustion engine 2 also includes an intake passage 22.
An EGR passage 266 for recirculating a part of exhaust gas is provided at 0. The EGR passage 266 has one end side of the E
It communicates with the GR inlet 268 and the other end side is a bypass passage 238.
Communicating with the EGR outlet 270 on the way. This EGR
The passage 266 has an EG for controlling the flow rate of the recirculated exhaust gas.
An R control valve 272 is provided.

The EGR control valve 272 is connected to the E in the main body 274.
A valve hole 276 is provided in the GR passage 266, a valve body 278 for opening and closing the valve hole 276 is supported by a diaphragm 280, the pressure chamber 282 is defined by the diaphragm 280, and the valve body 278 is closed in the direction to close the valve hole 276. A spring 284 is provided which biases the diaphragm 280 to push forward.

In the pressure chamber 282 of the EGR control valve 272, the other end side of the EGR pressure guiding passage 286 which communicates one end side with the bypass pressure guiding passage 262 closer to the intake passage 218 than the bypass switching valve 264 is provided. It is in communication. The EGR pressure guiding passage 286 is provided with an EGR switching valve 288 for switching and introducing intake negative pressure and atmospheric pressure into the pressure chamber 282. EG
The R switching valve 288 is connected to the control unit 228. The control unit 228 drives and controls the EGR switching valve 288 to supply / exhaust the intake negative pressure and the atmospheric pressure to / from the pressure chamber 282 of the EGR control valve 272 to control the flow rate of the recirculated exhaust gas.

Air-fuel ratio control device 22 of this internal combustion engine 202
When changing the air-fuel ratio of the air-fuel mixture from the lean air-fuel ratio range to the stoichiometric air-fuel ratio range by the control unit 228, the air-fuel ratio is instantaneously changed and the flow control valve 248 is fully closed and EGR is performed. The control valve 272 is controlled to open and close according to the operating state of the internal combustion engine 202. In addition, the air-fuel ratio control device 2
When changing the air-fuel ratio of the air-fuel mixture from the stoichiometric air-fuel ratio range to the lean air-fuel ratio range by the control unit 228, the control unit 228 instantaneously changes the air-fuel ratio and simultaneously causes the flow control valve 248 to operate the internal combustion engine 202. According to the EGR control valve 2
Control 72 to fully close.

That is, when changing the air-fuel ratio of the air-fuel mixture from the lean air-fuel ratio range to the stoichiometric air-fuel ratio range, the air-fuel ratio control device 226 instantaneously changes the air-fuel ratio and shuts off the bypass air. By recirculating exhaust gas in an amount corresponding to the operating state of the internal combustion engine 202 to the intake passage 218, torque fluctuation is suppressed and NOx increase is prevented, while the air-fuel ratio of the air-fuel mixture is diluted from the stoichiometric air-fuel ratio range. When changing to the air-fuel ratio range, the air-fuel ratio is changed instantaneously and at the same time, the intake passage 2
The exhaust gas recirculation to 18 is stopped and the amount of bypass air corresponding to the operating state of the internal combustion engine 202 is supplied to the intake passage to increase the air amount and suppress the torque fluctuation due to the leaning. .

The bypass air is supplied to the bypass passage 23.
The flow rate is controlled by the shape of the bypass inlet 240 and the flow rate control valve 248.

Next, the control by the air-fuel ratio control device 226 will be described with reference to FIG.

In FIG. 10, when the control starts (step 300), the engine speed N is detected (step 30).
1) Then, the intake pressure P is detected (step 302), the throttle opening θ is detected (step 303), and the bypass switching valve 264 is drive-controlled by the value calculated from these values to control the pressure of the flow control valve 248. The intake negative pressure and the atmospheric pressure are supplied to and discharged from the chamber 258, and the intake passage 2 on the downstream side of the throttle valve 222 is provided.
Bypass air is supplied to 18.

Next, the control mode is judged (step 30
4) Do. In this determination (step 304), when the air-fuel ratio of the air-fuel mixture changes from the lean air-fuel ratio range to the stoichiometric air-fuel ratio range, the intake negative pressure acting on the pressure chamber 258 of the flow control valve 248 is weakened to bypass the bypass passage. The bypass switching valve 264 is controlled to be turned off (step 305) so as to close the valve 238, and the negative pressure of the intake air is applied to the pressure chamber 282 of the EGR control valve 272 so that the amount of exhaust gas corresponding to the operating state is taken into the intake passage 218.
The EGR switching valve 288 is turned on (step 3
The driving control of the fuel injection valve 224 based on the theoretical air-fuel ratio map is started (step 307) and finished (step 308) so that the air-fuel ratio becomes the target value in the theoretical air-fuel ratio range.

On the other hand, in the determination (step 304), when the operating state of the internal combustion engine 2 changes from the stoichiometric air-fuel ratio range to the lean air-fuel ratio range, the pressure chamber 2 of the flow control valve 248 is changed.
The bypass switching valve 264 is turned on to increase the intake negative pressure acting on 58 and open the bypass passage (step 309).
Drive control is performed to control the EGR switching valve 288 to OFF (step 310) so that the atmospheric pressure is applied to the pressure chamber 282 of the EGR control valve 272 to stop the exhaust gas recirculation, and the air-fuel ratio is in the lean air-fuel ratio range. The drive control of the fuel injection valve 224 based on the lean air-fuel ratio region map is started (step 311) so as to reach the target value in (3), and is ended (step 308).

More specifically, when the internal combustion engine 202 is operating in the lean air-fuel ratio range, the amount of air flowing through the intake passage 218 is calculated from the engine speed N and the intake pressure P, and the calculated air amount is calculated. The flow rate control valve 248 is controlled so that approximately 10% to 30% of the air flows as bypass air through the bypass passage 238.

At this time, the EGR switching valve 288 is set to the EG
The EGR control valve 272 is fully closed by being controlled to be turned off so that the atmospheric pressure acts on the pressure chamber 282 of the R control valve 272. Therefore, the combustion chamber 206 of the internal combustion engine 202
Is supplied with the air that has passed through the throttle valve 222 of the intake passage 218, as well as the bypass air that is measured by the bypass inlet 240 and the flow rate control valve 248 and flows through the bypass passage 238. The fuel injection valve 224 is drive-controlled by the lean air-fuel ratio region map so that the air-fuel ratio becomes a target value in the lean air-fuel ratio region, and injects fuel.

From such an operating state, the throttle valve 22
2 is opened, the throttle opening θ is increased, the load of the internal combustion engine 2 is increased, and the engine enters the acceleration state, so that the output air-fuel ratio range required by the internal combustion engine 202 is set.
As shown in, the air-fuel ratio is changed from the lean air-fuel ratio range to the stoichiometric air-fuel ratio range. Alternatively, when the load on the internal combustion engine 202 gradually increases, the air-fuel ratio is changed from the lean air-fuel ratio range to the stoichiometric air-fuel ratio range.

As described above, when the air-fuel ratio is changed from the lean air-fuel ratio range to the stoichiometric air-fuel ratio range to shift to the stoichiometric air-fuel ratio range control, the flow control valve 248 is fully closed as shown in FIG. The bypass passage 238 is closed, the EGR control valve 272 is opened / closed according to the operating state to recirculate a part of the exhaust gas to the intake passage 218, and at the same time, the drive control of the fuel injection valve 224 based on the theoretical air-fuel ratio region map is immediately started. Then, the fuel is injected to reach the target value in the stoichiometric air-fuel ratio range.

When the opening degree θ of the throttle valve 222 further increases, the intake negative pressure in the intake passage 218 weakens, and the EGR switching valve 288 is turned off to apply atmospheric pressure to the pressure chamber 282 of the EGR control valve 272. Then, the exhaust gas recirculation is stopped.

As described above, when the air-fuel ratio of the air-fuel mixture is changed from the lean air-fuel ratio range to the stoichiometric air-fuel ratio range, the air-fuel ratio is instantaneously changed to use the air-fuel ratio range where much NOx is generated. In addition, the flow rate of the bypass air supplied to the intake passage 218 at the same time as the change of the air-fuel ratio is controlled to "0", and the flow rate of the exhaust gas recirculated to the intake passage 128 is controlled according to the operating state. As a result, torque fluctuation can be suppressed while preventing an increase in NOx.

Therefore, as shown in FIG. 5, when the air-fuel ratio of the air-fuel mixture is changed from the lean air-fuel ratio range to the stoichiometric air-fuel ratio range,
It is possible to suppress a sudden torque fluctuation, prevent a shock from occurring, improve a riding feeling, and prevent an increase in NOx.

On the other hand, when the load gradually decreases from the state where the internal combustion engine 202 is operating in the stoichiometric air-fuel ratio range, the control section 228 changes the air-fuel ratio from the stoichiometric air-fuel ratio range to the lean air-fuel ratio range. I will let you.

When changing the air-fuel ratio from the stoichiometric air-fuel ratio range to the lean air-fuel ratio range and shifting to the lean air-fuel ratio range control, the flow rate control valve 248 is opened and closed according to the operating condition to bypass the bypass air 238. To the EGR control valve 272.
Is completely closed to stop the exhaust gas recirculation, and at the same time, the drive control of the fuel injection valve 224 based on the lean air-fuel ratio region map is immediately started to inject the fuel to the target value in the lean air-fuel ratio region.

As described above, when the stoichiometric air-fuel ratio range is changed to the lean air-fuel ratio range, the air-fuel ratio is changed instantaneously so that the air-fuel ratio range where a large amount of NOx is generated is not used, and At the same time when the air-fuel ratio changes, the intake passage 218
The flow rate of the bypass air supplied to the intake passage 218 is controlled according to the operating state, and the flow rate of the exhaust gas recirculated to the intake passage 218 is set to "0".
By controlling to 1., it is possible to prevent the NOx increase and suppress the torque fluctuation due to the dilution by increasing the air amount.

Therefore, as shown in FIG. 5, when the air-fuel ratio of the air-fuel mixture is changed from the stoichiometric air-fuel ratio range to the lean air-fuel ratio range,
It is possible to suppress a sudden torque fluctuation, prevent a shock from occurring, improve a riding feeling, and prevent an increase in NOx.

In this alternative embodiment, the flow rate of the bypass air is controlled by the shape of the bypass inlet 240 of the bypass passage 238 and the flow rate control valve 248.
The bypass inlet 240 has a closed throttle valve 222.
Is formed in the shape of a substantially isosceles triangle having a vertex in the vicinity of the valve end 222e that opens to the downstream side and gradually expanding toward the downstream side in the opening direction of the valve end 222e.

As a result, the amount of bypass air can be set according to the operating state by expanding or contracting the area of the bypass inlet 22 according to the opening degree of the throttle valve 22. Therefore, the bypass air can appropriately set the flow rate in cooperation with the control by the flow rate control valve 248. As a result, torque fluctuations can be suppressed while preventing an increase in NOx.

[0067]

As described above, according to the present invention, when the air-fuel ratio of the air-fuel mixture is changed from the lean air-fuel ratio range to the stoichiometric air-fuel ratio range or when changing from the stoichiometric air-fuel ratio range to the lean air-fuel ratio range. By changing the air-fuel ratio instantaneously, the air-fuel ratio region that generates a large amount of NOx is not used, and at the same time when the air-fuel ratio changes, the flow rate of the bypass air supplied to the intake passage and the flow back to the intake passage are increased. By controlling the flow rate of the exhaust gas, the torque fluctuation can be suppressed while preventing the increase of NOx.

Therefore, when changing the air-fuel ratio of the air-fuel mixture from the lean air-fuel ratio range to the stoichiometric air-fuel ratio range or when changing the stoichiometric air-fuel ratio range to the lean air-fuel ratio range, it is possible to suppress a rapid torque fluctuation. Therefore, it is possible to prevent the occurrence of shock, improve the riding feeling, and prevent the increase of NOx.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an air-fuel ratio control device for an internal combustion engine showing an embodiment of the present invention.

FIG. 2 is a flowchart of control of an air-fuel ratio control device.

FIG. 3 is a diagram showing a relationship between a throttle opening and an air-fuel ratio.

FIG. 4 is a diagram showing a relationship between a throttle opening, a flow rate of bypass air, and a flow rate of recirculated exhaust gas.

FIG. 5 is a diagram showing a relationship between throttle opening and torque.

FIG. 6 is a schematic configuration diagram of an air-fuel ratio control device for an internal combustion engine showing another embodiment of the present invention.

FIG. 7 is an enlarged vertical sectional view of a throttle body.

FIG. 8 is an enlarged transverse sectional view of a throttle body.

9 is a side view taken along the arrow 〓 of FIG.

FIG. 10 is a flowchart of control of the air-fuel ratio control device according to another embodiment.

FIG. 11 is a schematic configuration diagram of an air-fuel ratio control device for an internal combustion engine showing a conventional example.

FIG. 12 is a diagram showing a relationship between an air-fuel ratio and torque.

FIG. 13 is a diagram showing a relationship between an air-fuel ratio and NOx.

[Explanation of symbols]

 2 Internal Combustion Engine 18 Intake Passage 20 Exhaust Passage 22 Throttle Valve 24 Fuel Injection Valve 26 Air-Fuel Ratio Control Device 28 Control Unit 30 Opening Sensor 32 Pressure Sensor 34 Rotation Speed Sensor 36 Air-Fuel Ratio Sensor 38 Bypass Passage 44 Flow Control Valve 54 EGR Passage 60 EGR control valve 74 Pressure passage 76 EGR switching valve

Continuation of the front page (51) Int.Cl. ⁵ Identification code Reference number within the agency FI Technical display location F02D 43/00 N 7536-3G 45/00 301 G 7536-3G F 7536-3G F02M 23/04 301 C

Claims (2)

[Claims] 1. An air-fuel ratio sensor for detecting an air-fuel ratio of exhaust gas is provided in an exhaust passage of an internal combustion engine, and an air-fuel ratio of an air-fuel mixture is set as a target in a stoichiometric air-fuel ratio range and a lean air-fuel ratio range based on a detection signal of the air-fuel ratio sensor. In an air-fuel ratio control device for an internal combustion engine that controls the intake air of the internal combustion engine, a bypass passage that supplies bypass air to the intake passage of the internal combustion engine is provided, and a flow rate control valve that controls the flow rate of the bypass air is provided. An EGR passage is provided in the intake passage for recirculating a part of the exhaust gas, and the EGR is for controlling the flow rate of the recirculated exhaust gas.
A control valve is provided, and when changing the air-fuel ratio of the air-fuel mixture from the lean air-fuel ratio range to the stoichiometric air-fuel ratio range, the air-fuel ratio is instantaneously changed, the flow control valve is fully closed, and the EGR control valve is opened. When controlling the air-fuel ratio of the air-fuel mixture to change from the stoichiometric air-fuel ratio range to the lean air-fuel ratio range while controlling to open / close according to the operating state of the internal combustion engine, the air-fuel ratio is instantaneously changed and at the same time, the flow control valve. An air-fuel ratio control apparatus for an internal combustion engine, comprising: a control means for opening and closing the engine according to an operating state of the internal combustion engine and fully closing the EGR control valve. 2. A bypass passage for supplying bypass air to the intake passage of the internal combustion engine is provided with a bypass inlet communicating with an intake passage near a valve end of the closed throttle valve, and the bypass inlet is provided in the closed throttle valve. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the air-fuel ratio control device is formed to have a shape that gradually expands toward the downstream side in the opening movement direction.