JPH04370312A - Exhaust gas device for internal combustion engine - Google Patents

Abstract

PURPOSE:To enable detection of the air-fuel ratio while introducing the secondary air, and realize prevention of thermal deterioration of a catalyst and improvement of conversion efficiency in a compatible manner. CONSTITUTION:Catalysts 8, 9 for exhaust gas purification are interposed at a front tube part 7 and at a merged part of a plurality of branch passage parts 4 respectively, and throttle valves 10 are interposed at respective branch passage parts 3. A secondary air introducing pipe 17 is provided in a branch passage part 4, and an oxygen sensor 19 is interposed at a branch passage part 5. In the partially loaded region of the engine cooling period, when the exhaust gas flow rate is throttled by means of the throttle valves 10, the radiating area of the passage parts where the total volume of the exhaust gas passes is decreased, the radiating quantity of the exhaust gas is decreased, the entrance temperature at the catalysts 8, 9 is kept at high temperature, and the conversion efficiency of the catalysts 8, 9 is greatly improved, enabling detection of the air-fuel ratio by means of the oxygen sensor 19 while introducing the secondary air. In the higly loaded region after warming up the engine, the exhaust gas flows through the branch passage parts 3, 4 and the branch passage parts 5, 6, and the heat radiating areas of the passage parts are increased and the heat radiating quantity of the exhaust gas is increased, preventing thermal deterioration of the catalysts 8, 9.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to an exhaust system for an internal combustion engine, and in particular, for an internal combustion engine that supplies secondary air to exhaust gas, it is possible to prevent thermal deterioration of a catalyst and improve conversion efficiency at the same time. This invention relates to technology for improving secondary air volume controllability.

0002

[Prior Art] Conventionally, as an exhaust passage structure in an exhaust system for an internal combustion engine, a catalyst for purifying exhaust gas is provided in the exhaust passage, and a secondary air introduction part is provided in the exhaust passage upstream of the catalyst. is known (Japanese Unexamined Patent Publication No. 6
1-247842, etc.).

That is, in order to promote the chemical reaction of exhaust gas within the catalyst, it is necessary to maintain the catalyst at a high temperature that activates the catalyst, and secondary air is supplied to the exhaust passage upstream of the catalyst. This accelerates the combustion of exhaust gas, and the heat of combustion raises the temperature of the catalyst. It is also known that an oxygen sensor as an air-fuel ratio detection means and a three-way catalyst are arranged in the exhaust passage in order from the upstream side (Japanese Patent Application Laid-open No. 6
(See Publication No. 2-75043, etc.).

0004

[Problem to be Solved by the Invention] However, in such a conventional exhaust system for an internal combustion engine, when attempting to detect the air-fuel ratio while introducing secondary air, the following problems occur. had. That is, in the case of the former device in which the secondary air introduction section is provided in the exhaust passage upstream of the catalyst, the oxygen sensor of the latter device is installed between the catalyst in the exhaust passage and the secondary air supply section. This oxygen sensor cannot be installed (because the air-fuel ratio becomes undetectable), and it is necessary to install this oxygen sensor upstream of the secondary air supply section.

[0005] As a result, the position of the oxygen sensor is close to the exhaust port, and thermal influence on the oxygen sensor becomes a problem, which may cause deterioration of the oxygen sensor. On the other hand, in the case of the latter device, which has an oxygen sensor in the exhaust passage upstream of the catalyst, it is not possible to arrange the secondary air supply section upstream of the oxygen sensor in the exhaust passage (the air-fuel ratio cannot be detected). (because it becomes impossible),
It is necessary to arrange this secondary air supply section downstream of the oxygen sensor.

As a result, the secondary air introduction section is located away from the exhaust port, the passage length up to the secondary air introduction section is long, and the heat dissipation area of the passage section is widened, so that high loads can be avoided after the engine warms up. However, in the low load range when the engine is cold, the exhaust gas temperature decreases significantly, the inlet temperature of the catalyst becomes low, and the conversion efficiency of the catalyst decreases. There is also the problem that the oxygen sensor cannot be sufficiently improved and the warm-up performance of the oxygen sensor is also poor.

Therefore, in view of the above-mentioned conventional problems, the present invention aims to improve the structure of the exhaust passage, and takes into account the arrangement positions of the air-fuel ratio detection means, the secondary air introduction part, and the catalyst in the exhaust passage. The purpose of this is to enable detection of the air-fuel ratio while introducing secondary air, and to simultaneously prevent thermal deterioration of the catalyst and improve conversion efficiency.

[0008]

[Means for Solving the Problems] Therefore, the exhaust system for an internal combustion engine according to the first invention provides an exhaust system for each cylinder in an internal combustion engine having two exhaust ports each having an exhaust valve for each cylinder. It has an exhaust passage structure in which a plurality of branch passages each communicating with the exhaust port are divided and collected from a single passage part into two branch passage parts, and the one branch passage part and the single While installing a catalyst for exhaust purification in the passage section of the
a flow rate control means for controlling the flow rate of exhaust gas passing through a branch passage communicating with the other branch passage or the other branch passage; The configuration includes a secondary air introducing means for introducing secondary air, and an air-fuel ratio detecting means interposed in the other branch passage section.

[0009] The exhaust system for an internal combustion engine according to the second aspect of the present invention is an internal combustion engine having two exhaust ports each having an exhaust valve for each cylinder. It has an exhaust passage structure in which the passage is divided into a plurality of branch passage parts branched from a single passage part and gathered together, and an exhaust purification catalyst is interposed in at least the single passage part of the exhaust passage. an opening/closing means for opening and closing a branch passage or a branch passage communicating with one exhaust port in each cylinder; and a branch passage that is upstream of the catalyst and through which exhaust gas flows when the opening/closing means is open. The configuration includes a secondary air introducing means for introducing secondary air into the exhaust port, and an air-fuel ratio detecting means interposed in the branch passage communicating with the other exhaust port.

0010

[Operation] In the first invention, for example, in a partial load region when the engine is cold, the flow rate control means narrows the passage and introduces secondary air. As a result, exhaust gas discharged from each cylinder passes through one branch passage from one exhaust port, passes through the catalyst, reaches the branch passage, and then passes through a single passage and is exhausted via the catalyst. . Further, the exhaust gas reaches the other branch passage from the other exhaust port, the flow rate is throttled by the flow rate control means of the branch passage, and reaches the branch passage, and passes through the air-fuel ratio detection means in the branch passage. Furthermore,
It passes through a single passage and is discharged via a catalyst.

Further, in a high load region after warming up the engine, the flow rate control means allows the entire flow rate of exhaust gas to flow through the passage, and also introduces secondary air. As a result, exhaust gas discharged from each cylinder passes from both exhaust ports to both branch passages, from one branch passage to the branch passage through the catalyst, and from the other branch passage to the branch passage. Then, both branch passages lead to a single passage and are discharged via the catalyst.

As described above, in the partial load region when the engine is cold, the flow rate control means restricts the flow rate of exhaust gas passing through one of the branch passages, so that the entire amount of exhaust gas for each cylinder does not pass through. The heat dissipation area of the passage section is reduced compared to the conventional case. As a result, the amount of heat dissipated from the exhaust gas is reduced, and even if secondary air is introduced, the catalyst inlet temperature is maintained at a higher temperature than before, significantly improving the conversion efficiency of the catalyst.

Furthermore, since a small amount of exhaust gas also flows through one branch passage and comes into contact with the air-fuel ratio detection means, the air-fuel ratio can be detected by the air-fuel ratio detection means while introducing secondary air. It is also possible to accurately feedback control the amount of secondary air introduced according to the air-fuel ratio. In addition, in the high load region after the engine warms up, exhaust gas flows through both branch passages that are completely opened, and both branch passages, so the entire amount of exhaust gas for each cylinder passes through. The heat dissipation area of the passage portion is increased compared to the conventional one. As a result, the amount of heat dissipated from the exhaust gas increases, making it possible to prevent thermal deterioration of the catalyst.

In this case as well, the air-fuel ratio can be detected by the air-fuel ratio detection means while introducing secondary air, and the secondary air is introduced in accordance with the air-fuel ratio detected by the air-fuel ratio detection means as in the case of cold conditions. Feedback control with good quantity accuracy is also possible. In the second invention, for example, in a partial load region when the engine is cold, the opening/closing means is closed and secondary air introduction is stopped. As a result, exhaust gas discharged from each cylinder passes through only one exhaust port through one branch passage, contacts the air-fuel ratio detection means, passes through the catalyst, reaches the branch passage, and then passes through the single passage. It passes through the catalyst and is discharged.

Further, when the engine is cold or in a high load region after warming up, the opening/closing means is opened and secondary air is introduced. As a result, exhaust gas discharged from each cylinder passes through both exhaust ports and both branch passages. As described above, in the partial load region when the engine is cold, the heat radiation area of the passage through which the entire amount of exhaust gas for each cylinder passes is reduced compared to the conventional one, and the branch passage that communicates with the other exhaust port is reduced. Since the air-fuel ratio detection means is interposed in the air-fuel ratio detection means, the warm-up performance of the air-fuel ratio detection means is improved.

Furthermore, in a high load region when the engine is cold, the air-fuel ratio can be detected by the air-fuel ratio detection means while introducing secondary air, and the secondary air-fuel ratio is detected by the air-fuel ratio detection means. Accurate feedback control of the amount of air introduced is also possible. Furthermore, in a high load region after warming up the engine, the heat dissipation area of the passage through which the entire amount of exhaust gas for each cylinder passes is increased compared to the prior art. As a result, the amount of heat dissipated from the exhaust gas increases, making it possible to prevent thermal deterioration of the air-fuel ratio detection means and the catalyst.

In this case as well, the air-fuel ratio can naturally be detected by the air-fuel ratio detection means while introducing secondary air, and the secondary air is introduced in accordance with the air-fuel ratio detected by the air-fuel ratio detection means as in the case of cold conditions. Feedback control with good quantity accuracy is also possible.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the accompanying drawings. FIG. 1 shows an embodiment corresponding to claim 1. In this figure, two exhaust ports 1 and 2 each equipped with an exhaust valve are provided for each cylinder #1 to #4 of an internal combustion engine E, and the exhaust passage structure thereof is as follows.

That is, branch passage portions 3 and 4 are connected to the exhaust ports 1 and 2 of each of the cylinders #1 to #4, respectively. In each cylinder #1 to #4, a plurality of branch passages 3 which are connected to one exhaust port 1 respectively merge and are connected to a single branch passage 5, which is connected to the other exhaust port 2. The plurality of branch passage sections 4 are respectively merged and connected to a single branch passage section 6. Both branch passage sections 5 and 6 are further merged into a single passage section (hereinafter referred to as the front tube section).
Connected to 7.

Here, in the exhaust passage having the above-described structure, a catalyst for exhaust purification is provided at the front tube part 7 and the joint part of the plurality of branch passage parts 4 connected to one exhaust port 2, respectively. 8 and 9 are interposed. And each cylinder #
Immediately downstream of the exhaust port 1 of the branch passage section 3 communicating with one of the exhaust ports 1 in #1 to #4, a throttle valve 10 as a flow rate control means is interposed, respectively. These throttle valves 10 are
It has a configuration in which an arc-shaped notch 10a is provided on the outer periphery of the valve body 10A, so that when it is opened, the branch passage 3 is completely opened, and when it is closed, a small amount of exhaust gas flows through only the notch 10a. This narrows the branch passage section 3. These throttle valves 10 are linked together by a common rotary drive shaft 11,
An actuator 12 that rotationally drives the shaft 11 is connected to one end of the rotational drive shaft 11 . This actuator 12 is driven based on a control signal output from a control unit 13, and controls opening and closing of the throttle valve 10.

In this case, the control unit 13 includes engine operating state detection means such as a water temperature sensor 14 that detects the engine cooling water temperature representative of the engine temperature, an intake air negative pressure sensor 15 in the intake passage, and an engine rotation speed sensor 16. The output detection signal is input, and the actuator 12 is controlled based on engine operating conditions such as water temperature, intake negative pressure, and engine speed.

On the other hand, secondary air is supplied to the branch passages 4 that converge on one branch passage 6 in which the catalyst 9 is interposed, that is, the branch passages 4 that communicate with the exhaust ports 1 of each cylinder #1 to #4. Means for introducing secondary air is provided. This secondary air introduction means has a configuration in which, for example, a secondary air introduction pipe 17 connected to the intake system of the engine E is communicated with one branch passage section 4. A control valve 18 is interposed. An actuator 21 that drives this secondary air control valve 18 is provided, and this actuator 21
is driven based on a control signal output from the control unit 13, and controls the opening degree of the secondary air control valve 18. In this case, the control unit 13 controls the actuator 21 based on the water temperature, intake negative pressure, engine speed, etc.

[0023] An oxygen sensor 19 is interposed in the branch passage portion 5 as an air-fuel ratio detecting means. This oxygen sensor 19
A signal corresponding to the oxygen concentration in the exhaust gas is outputted to the control unit 13, and the control unit 13 executes fuel supply amount control to control the air-fuel ratio of the engine based on this signal. In this configuration, for example, in a partial load region when the engine is cold, each actuator 13, 21 is controlled based on a control signal output from the control unit 13, the throttle valve 10 is closed, and the control valve 18 is closed. The amount of secondary air introduced is controlled by As a result, the exhaust gas discharged from each cylinder #1 to #4 passes from one exhaust port 2 through one branch passage section 4, passes through the catalyst 9, reaches the branch passage section 6, and further,
It passes through the front tube section 7 and is discharged via the catalyst 8. Further, the exhaust gas reaches the other branch passage section 3 from the other exhaust port 1, and the notch 10a of the throttle valve 10 of the branch passage section 3.
The flow rate is narrowed and reaches the branch passage section 5, passes through the oxygen sensor 19 in the branch passage section 5, further passes through the front tube section 7, and is discharged via the catalyst 8.

At this time, secondary air controlled according to the engine operating state at that time is introduced from the secondary air introduction pipe 17 into one of the branch passages 4, and the secondary air is supplied into the exhaust gas. . Further, the throttle valve 10 is opened in a high load region after the engine is warmed up. As a result, exhaust gas discharged from each cylinder #1 to #4 passes from both exhaust ports 1 and 2 through both branch passages 3 and 4, and from one branch passage 4 through the catalyst 9 to the branch passage. 6, and from the other branch passage section 3 to the branch passage section 5
The fuel then reaches the front tube part 7 from both branch passages 5 and 6, and is discharged via the catalyst 8. Then, secondary air controlled according to the engine operating state at that time is introduced from the secondary air introduction pipe 17 into one branch passage section 4, and the secondary air is supplied into the exhaust gas.

As described above, in the partial load region when the engine is cold, the flow rate of exhaust gas passing through one branch passage section 3 is throttled by the throttle valve 10.
The heat dissipation area of the passage through which the entire amount of exhaust gas passes through is reduced by about 30% compared to the conventional case. As a result, the amount of heat dissipated from the exhaust gas is reduced, and even if secondary air is introduced, the inlet temperature of the catalysts 8, 9 is maintained higher than before, and the catalysts 8, 9 are kept at a higher temperature than before.
The conversion efficiency is significantly improved.

Furthermore, a small amount of exhaust gas also flows through one branch passage section 3 and contacts the oxygen sensor 19 in the branch passage section 5, so that the air-fuel ratio can be detected by the oxygen sensor 19 while introducing secondary air. This also enables highly accurate feedback control of the amount of secondary air introduced in accordance with the air-fuel ratio detected by the oxygen sensor 19. On the other hand, in the high load region after the engine warms up, exhaust gas flows through both branch passages 3 and 4 that are completely open and both branch passages 5 and 6, so exhaust gas flows through cylinders #1 to ##. The heat dissipation area of the passage through which the entire amount of exhaust gas passes through is increased by about 40% compared to the conventional case. As a result, the amount of heat dissipated from the exhaust gas increases, and the catalyst 8,
The thermal deterioration of No. 9 can be prevented.

In this case as well, it is naturally possible to detect the air-fuel ratio by the oxygen sensor 19 while introducing secondary air, and the amount of secondary air introduced can be adjusted according to the air-fuel ratio detected by the oxygen sensor 19, as in the case of cold conditions. Feedback control with good accuracy is also possible. 2 and 3 show another embodiment corresponding to claim 1. The embodiment of FIG. 2 has a throttle valve 1 in the branch passage section 5.
0 is provided, and each cylinder #1 to #1 is controlled by this throttle valve 10.
Branch passage portion 3 communicating with one exhaust port 1 in #4
An oxygen sensor is interposed on the upstream side of the throttle valve 10 in the branch passage section 5 to control the flow rate of exhaust gas flowing from the branch passage section 5.

In the embodiment shown in FIG. 3, a throttle valve 10 is provided at the same position as in the embodiment shown in FIG. 2, and in addition, in the embodiment shown in FIGS. The branch passage portions 3 and 4, which were connected to each other independently, are integrated at the communication portions with the exhaust ports 1 and 2 so that they communicate with each other. According to this embodiment, since only a single throttle valve 10 needs to be provided in each case, the structure can be simplified and it is advantageous in terms of cost. In particular, in the embodiment shown in FIG. 3, the configuration of the branch passage section can be simplified.

In the embodiments shown in FIGS. 1 and 2, the air-fuel ratio detection accuracy is high because the mixture of secondary air and exhaust gas does not flow to the oxygen sensor 19 side. 4 and 5 show an embodiment corresponding to claim 2. That is, FIG.
In the branch passage section 3, an on-off valve 20 as an on-off means is provided immediately downstream of the exhaust port 1, respectively. A rotary drive shaft 11 that links these on-off valves 20 with each other and an actuator 12 that rotationally drives the shaft 11 are provided. The actuator 12 is driven based on a control signal output from the control unit 13 to control opening and closing of the on-off valve 20 .

On the other hand, in the passage section which is upstream of the catalyst 8 and through which exhaust gas flows when the on-off valve 20 is opened, that is,
A secondary air introducing means is provided for introducing secondary air into the branch passage portion 3 communicating with the exhaust port 1 in each cylinder #1 to #4. This secondary air introduction means includes a secondary air introduction pipe 1
7, a secondary air control valve 18, and an actuator 21, and the actuator 21 is connected to the control unit 13.
The secondary air control valve 18 is driven based on a control signal output from the secondary air control valve 18 and controls the opening degree of the secondary air control valve 18.

An oxygen sensor 19 is interposed at the junction of the branch passages 4 and immediately upstream of the catalyst 9. In such a configuration, for example, in a partial load region when the engine is cold, each actuator 13, 21 is controlled based on a control signal output from the control unit 13.
The on-off valve 20 is closed, and the control valve 18 closes the secondary air introduction pipe. As a result, each cylinder #1~
Exhaust gas discharged from #4 passes only through one exhaust port 2, through one branch passage 4, contacts the oxygen sensor 19, passes through the catalyst 9, reaches the branch passage 6, and further passes through the front tube section 7. It passes through the catalyst 8 and is discharged.

Furthermore, when the engine is cold or in a high load region after warming up, each actuator 13, 21 is controlled based on a control signal output from the control unit 13, and the on-off valve 20 is opened. The control valve 18 opens the secondary air introduction pipe and controls the amount of air introduced. As a result, exhaust gas discharged from each cylinder #1 to #4 passes through both branch passages 4 from both exhaust ports 2. Then, secondary air controlled according to the engine operating state at that time is introduced from the secondary air introduction pipe 17 into one branch passage section 4, and the secondary air is supplied into the exhaust gas.

As described above, in the partial load region when the engine is cold, the heat dissipation area of the passage through which the entire amount of exhaust gas for each cylinder #1 to #4 passes is reduced by approximately 30% compared to the conventional system. Furthermore, since the oxygen sensor 19 is interposed in the gathering part of the branch passage section 4, the warm-up performance of the oxygen sensor 19 is improved. In addition, in a high load region when the engine is cold, the air-fuel ratio can be detected by the oxygen sensor 19 while introducing secondary air, and the amount of secondary air introduced can be accurately determined according to the air-fuel ratio detected by the oxygen sensor 19. Feedback control is also possible.

Furthermore, in a high load region after warming up the engine, the heat dissipation area of the passage through which the entire amount of exhaust gas from each cylinder #1 to #4 passes is increased by about 40% compared to the conventional one. As a result, the amount of heat dissipated from the exhaust gas increases, and thermal deterioration of the oxygen sensor 19 and the catalysts 8 and 9 can be prevented. In this case as well, the air-fuel ratio can be detected by the oxygen sensor 19 while naturally introducing secondary air.
It is also possible to accurately feedback control the amount of secondary air introduced in accordance with the air-fuel ratio detected by.

The embodiment shown in FIG. 5 has an on-off valve 2 in the branch passage section 5.
0, and the branch passages 3 and 4 are connected to the exhaust ports 1 and 2.
It is designed to be integrated at the communicating part with the two so that they can communicate with each other. According to this embodiment, since it is only necessary to provide a single on-off valve 20, the structure can be simplified;
This is advantageous in terms of cost because the structure of the branch passage section can be simplified.

Although the present invention has been described above with reference to specific examples, the present invention is not limited thereto. Without departing from the scope of the appended claims,
It should be noted that various changes and modifications are possible. For example, although a throttle valve is used in the above embodiment as the flow rate control means of the present invention, a bypass passage may be provided that communicates between the upper and downstream of the on-off valve of the passage opened and closed by the on-off valve.

[0037]

Effects of the Invention As described above, the present invention has a plurality of branch passages that communicate with the exhaust ports of each cylinder, which are divided into two branch passages that are separated from a single passage and assembled. By creating an exhaust passage structure with a high temperature and taking into account the placement positions of the air-fuel ratio detection means, secondary air introduction part, and catalyst in the exhaust passage, it becomes possible to detect the air-fuel ratio while introducing secondary air, and also to detect the air-fuel ratio of the catalyst. It is highly useful because it has the advantage of being able to both prevent thermal deterioration and improve conversion efficiency, and also to improve warm-up of the air-fuel ratio detection means and prevent thermal deterioration.

[Brief explanation of drawings]

[Fig. 1] A cross-sectional plan view showing an embodiment of an exhaust system for an internal combustion engine according to the present invention.

[Figure 2] Plane sectional view of another embodiment

[Figure 3] Plane sectional view of yet another embodiment

[Figure 4]
Plane sectional view of still another embodiment

[Figure 5] Plane sectional view of yet another embodiment

[Explanation of symbols]

1 Exhaust port 2 Exhaust port 3 Branch passage section 4 Branch passage section 5 Branch passage section 6 Branch passage section 7 Front tube section 8. Catalyst 9 Catalyst 10 Throttle valve 17 Secondary air introduction pipe 19 Oxygen sensor 20 Open/close valve E Internal combustion engine

Claims (2)

[Claims] Claim 1: In an internal combustion engine having two exhaust ports each having an exhaust valve for each cylinder, a plurality of branch passages each communicating with the exhaust port of each cylinder are connected from a single passage. It has an exhaust passage structure in which a plurality of branch passages are divided into two and gathered together, and a catalyst for exhaust purification is interposed in one of the branch passage parts and the single passage part, while a catalyst for exhaust purification is interposed in the one branch passage part and the single passage part. a flow rate control means for controlling the flow rate of exhaust gas passing through one branch passage communicating with the branch passage or the other branch passage; and a flow rate control means for controlling the flow rate of exhaust gas passing through one of the branch passages communicating with the branch passage; What is claimed is: 1. An exhaust system for an internal combustion engine, comprising: a means for introducing secondary air; and an air-fuel ratio detecting means interposed in the other branch passage. Claim 2: In an internal combustion engine having two exhaust ports each equipped with an exhaust valve for each cylinder, a plurality of branch passages each communicating with the exhaust port of each cylinder are connected from a single passage. It has an exhaust passage structure in which a plurality of branch passages are divided into two and gathered together, and at least one of the single passage parts of the exhaust passage is interposed with an exhaust purifying catalyst, and one of the exhaust passages in each cylinder is An opening/closing means for opening and closing a branch passage or a branch passage communicating with the exhaust port, and a secondary passage that is upstream of the catalyst and introduces secondary air into the branch passage through which exhaust gas flows when the opening/closing means is opened. 1. An exhaust system for an internal combustion engine, comprising: an air introducing means; and an air-fuel ratio detecting means interposed in a branch passage communicating with the other exhaust port.