JP2007051597A - Exhaust control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust control device capable of maintaining good emission by sufficiently supplying secondary air in an exhaust gas passage. <P>SOLUTION: This exhaust control device 10 for an internal combustion engine is provided with purification catalysts 31, 32 arrange in an exhaust gas passage 7 of the internal combustion engine 1, a secondary air supply means 20 supplying secondary air to the exhaust gas passage, gas pressure adjusting means 33, 34, 35 changing exhaust gas pressure in a downstream side of the purification catalyst, and a control means 40 controlling the gas pressure adjusting means to reduce exhaust gas pressure when the secondary air supply means supplies secondary air. Secondary air can be smoothly introduced to the exhaust gas passage. Consequently, reaction is accelerated and good emission can be maintained since exhaust gas and sufficient secondary air are mixed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust control device for an internal combustion engine, and more particularly to an exhaust control device provided with a structure for supplying secondary air to an exhaust passage so as to promote purification of exhaust gas.

An exhaust purification catalyst is provided in the exhaust system of the internal combustion engine to purify the exhaust gas, and air pollutants such as HC and CO in the exhaust gas are converted into harmless H ₂ O, CO _{2 and the} like. In order for the exhaust purification catalyst to fully perform its function, the exhaust purification catalyst is required to be placed in an environment with a certain activation temperature (for example, 350 ° C. or higher). However, when the internal combustion engine is cold started, the exhaust purification catalyst may not fully perform its function.

  Thus, in order to improve the purification function at the time of cold start, an internal combustion engine provided with a mechanism for supplying secondary air to the exhaust system (hereinafter simply referred to as a secondary air supply mechanism) has been proposed. In this secondary air supply mechanism, a secondary air supply passage is provided upstream of an exhaust purification catalyst installed in an exhaust pipe, and secondary air is supplied by an air pump. By supplying secondary air into the exhaust system, the oxygen concentration in the exhaust pipe is increased, and the oxidation of unburned gas such as HC and CO contained in the exhaust gas is promoted to purify the exhaust gas. it can. In addition, the temperature of the exhaust gas can be increased by an oxidation reaction of HC, CO, etc., thereby shortening the time until the ambient temperature of the exhaust purification catalyst becomes the activation temperature.

  However, it is difficult to promote the oxidation of HC, CO, etc. simply by supplying secondary air into the exhaust gas. Therefore, for example, Patent Document 1 proposes an exhaust gas temperature raising device that provides a throttle valve in the exhaust passage downstream of the purification catalyst and raises the exhaust gas temperature by fully closing the throttle valve when supplying secondary air. This device forms a state where hot exhaust gas stays in the exhaust passage by fully closing the throttle valve and reducing the flow rate of the exhaust gas. By supplying secondary air to the exhaust passage, the reaction between unburned gas and oxygen is promoted to improve emissions.

JP 2001-132436 A

  However, since an internal combustion engine to which a secondary air supply mechanism is added drives the air pump to supply secondary air, the load increases accordingly. In Patent Document 1, since the temperature in the exhaust passage is increased by fully closing the throttle valve, the exhaust gas pressure inevitably increases. When the gas pressure in the exhaust passage becomes high, it becomes difficult for secondary air to enter the passage. As a result, the supply amount of secondary air decreases, and it becomes impossible to maintain emissions well. It is possible to cope with this by increasing the capacity of the air pump, but in this case, the size of the apparatus and the cost increase are caused.

  Accordingly, an object of the present invention is to provide an exhaust control device capable of sufficiently supplying secondary air into the exhaust passage and maintaining good emission.

  The object is to provide a purification catalyst arranged in an exhaust passage of an internal combustion engine, a secondary air supply means for supplying secondary air to the exhaust passage, and a gas pressure adjusting means for changing an exhaust gas pressure downstream of the purification catalyst. And an exhaust control device for an internal combustion engine comprising: control means for controlling the gas pressure adjusting means so as to reduce the exhaust gas pressure when the secondary air supply means supplies secondary air.

  According to the present invention, when the secondary air supply means supplies the secondary air, the control means controls the gas pressure adjusting means so that the exhaust gas pressure is reduced. Therefore, the exhaust gas downstream of the purification catalyst. The pressure can be lowered relatively. Therefore, secondary air can be smoothly introduced into the exhaust passage. As a result, since the exhaust gas and sufficient secondary air are mixed, the reaction is promoted and the emission can be maintained well.

  A plurality of the purification catalysts are arranged in the exhaust passage, and the gas pressure adjusting means includes a bypass passage that bypasses the purification catalyst located on the downstream side, a switching valve that switches between the exhaust passage and the bypass passage, The control means may control the switching valve according to the state of the internal combustion engine. In this case, a passage that bypasses the purification catalyst on the downstream side is provided, and the switching valve is controlled, so that the exhaust gas pressure on the downstream side can be relatively lowered with respect to the purification catalyst located on the upstream side. it can.

  Further, if the control means opens the switching valve when the internal combustion engine is cold-started and allows the exhaust gas to flow into the bypass passage, the emission during the cold start can be maintained well.

  The control means further includes an atmospheric pressure detection means for detecting an atmospheric pressure, the control means confirms the atmospheric pressure based on the output of the atmospheric pressure detection means, and expands the opening of the switching valve as the pressure is lower. It may be. In this case, the emission can be satisfactorily maintained even in a place with a low atmospheric pressure such as an altitude.

  The control means preferably closes the switching valve when the intake air amount to the internal combustion engine exceeds a predetermined value. With this configuration, when a large amount of exhaust gas is generated, it is possible to close the bypass passage and reliably perform purification with a plurality of purification catalysts.

  Further, the gas pressure adjusting means further includes a variable muffler device that is disposed downstream of the purification catalyst and can change an internal exhaust gas pressure, and the control means is configured to change the variable muffler device according to the state of the internal combustion engine. The pressure regulating valve may be controlled. In this case, the exhaust gas pressure on the downstream side of the purification catalyst can be relatively lowered with a simple structure of controlling the pressure regulating valve of the variable muffler device arranged downstream of the purification catalyst.

  Further, if the control means controls the pressure regulating valve to reduce the exhaust gas pressure when the internal combustion engine is cold started, the emission during the cold start can be maintained satisfactorily.

  Further, it further includes an atmospheric pressure detecting means for detecting atmospheric pressure, the control means confirms the atmospheric pressure based on the output of the atmospheric pressure detecting means, and controls the pressure regulating valve as the pressure is lower to control the exhaust gas. The pressure may be reduced.

  Further, it is preferable that the control means controls the pressure regulating valve to increase the exhaust gas pressure when the intake air amount to the internal combustion engine exceeds a predetermined value. With this configuration, when a large amount of exhaust gas is generated, the gas pressure in the variable muffler can be increased and the purification catalyst can reliably perform purification.

  According to the present invention, it is possible to provide an exhaust control device capable of sufficiently supplying secondary air into an exhaust passage and maintaining good emission.

  Hereinafter, an exhaust control device for an internal combustion engine according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram illustrating a state in which an exhaust control device according to a first embodiment is applied to an exhaust passage of a gasoline engine 1 (hereinafter simply referred to as an engine 1) that is one of internal combustion engines. An intake manifold 2 is connected to the intake side of the engine 1, and an intake pipe 3 is connected to the intake manifold 2. An air cleaner 4 and a throttle valve 5 are disposed in the intake pipe 3 in order from the upstream side. An exhaust manifold 6 is connected to the exhaust side of the engine 1, and an exhaust pipe 7 serving as an exhaust passage is connected to the exhaust manifold 6. An exhaust control device 10 according to an embodiment that purifies the exhaust gas EG discharged from the engine 1 is disposed around the exhaust pipe 7.

  The exhaust control device 10 includes a secondary air supply mechanism 20, an exhaust purification catalyst device 30, and an ECU (Electronic Control Unit) 40 that controls them.

  The secondary air supply mechanism 20 supplies the secondary air SA to the exhaust manifold 6. The secondary air supply mechanism 20 includes a secondary air supply pipe 21 that connects the intake pipe 3 downstream of the air cleaner 4 and the exhaust manifold 6, and an air pump 22 disposed in the secondary air supply pipe 21. . In addition, the secondary air supply mechanism 20 shown here is a structure as an example of a secondary air supply means. For example, the downstream side of the secondary air supply pipe 21 may be connected to the exhaust pipe 7 downstream of the exhaust manifold 6. Furthermore, although the structural example which arrange | positions the secondary air supply pipe | tube 21 as one aspect | mode which utilizes the intake air AG which flows through the inside of the intake pipe 3 also as secondary air is shown, it does not restrict to this. The secondary air supply mechanism 20 may be provided with a unique supply pipe for taking in secondary air. In short, a structure in which the secondary air SA is supplied to the exhaust system downstream from the exhaust manifold 6 and upstream from the exhaust purification catalyst device 30 may be appropriately employed.

  The exhaust purification catalyst device 30 includes a purification catalyst (hereinafter referred to as upstream purification catalyst 31) disposed on the upstream side (engine 1 side) and a purification catalyst (hereinafter referred to as downstream purification catalyst 32) disposed downstream thereof. ). A bypass pipe (passage) 33 that connects the exhaust pipe 7 upstream from the downstream purification catalyst 32 and the exhaust pipe 7 downstream from the downstream purification catalyst 32 is provided. A switching valve 34 that switches when exhaust gas EG flows into the bypass passage 33 is disposed at a branch portion between the exhaust pipe 7 and the bypass pipe 33. The switching valve 34 is, for example, a butterfly type gas flow control valve, and the opening degree is changed by driving a motor 35. For example, a three-way catalyst is held inside the upstream side purification catalyst 31 and the downstream side purification catalyst 32, and HC, CO, etc. are oxidized to purify the exhaust gas EG.

  The ECU 40 controls driving of the air pump 22 of the secondary air supply mechanism 20 and the motor 35 of the exhaust purification catalyst device 30 according to the state of the engine 1. The ECU 40 is configured as a computer that combines a CPU (Central Processing Unit) and peripheral devices such as RAM and ROM. The ECU 40 is supplied with detection signals from various sensors for detecting the state of the engine 1. For example, a detection signal from a water temperature sensor 8 that detects the cooling water temperature of the engine 1 is supplied to the ECU 40 so that it can be confirmed that the engine 1 has been cold started. The ECU 40 executes a predetermined program for purifying the exhaust gas EG based on the detection signal.

  For example, when the engine 1 is cold-started and the secondary air is supplied to the exhaust manifold 6, the ECU 40 drives the motor 35 to open the switching valve 34 and flow the exhaust gas EG through the bypass passage 33. When such control is executed, the exhaust gas pressure downstream of the upstream side purification catalyst 31 is reduced, so that the secondary air SA can be smoothly introduced into the exhaust pipe 7. As a result, the secondary air SA can be sufficiently supplied to the upstream side purification catalyst 31, so that the secondary air and the exhaust gas can be sufficiently mixed to promote the combustion reaction between the unburned fuel (unburned gas) and oxygen. . Heat generation of the purification catalyst can be promoted by heat generated by the combustion. Therefore, exhaust emission can be improved at an early stage. Further, since the exhaust control device 10 has a simple structure in which a bypass pipe 33 that bypasses the downstream side purification catalyst 32 is provided and the flow of the exhaust gas EG is switched by the switching valve 34, it can be implemented at low cost.

  Hereinafter, further details of the control executed by the ECU 40 when the secondary air is supplied to the exhaust system of the engine 1 will be described in detail with reference to the drawings. FIG. 2 is a flowchart showing an example of a routine executed when the ECU 40 supplies secondary air to the exhaust manifold 6 of the engine 1.

  The ECU 40 activates this routine when, for example, an ignition switch of a vehicle on which the engine 1 is mounted is turned on, and checks whether or not the engine 1 has been started when it is cold (S11). At this time, the ECU 40 detects the cooling water temperature of the engine 1 from the water temperature sensor 8, for example, and confirms whether or not it is a cold start time. Therefore, when the ignition switch is turned on immediately after the vehicle has traveled and the engine 1 is sufficiently warmed up, the ECU 40 determines in step 11 that it is not during cold start. become. In such a case, it is preferable to purify the exhaust gas EG with both the upper and lower purification catalysts 31 and 32. Therefore, the ECU 40 sets the opening target of the switching valve 34 to be fully closed (that is, the opening target value is zero) (S16). The ECU 40 controls the opening degree of the switching valve 34 to this opening degree target (S15), and ends the processing by this routine. As described above, when the engine 1 is sufficiently warmed up at the time of start-up and it can be predicted that the temperature in the exhaust pipe 7 has sufficiently increased, the ECU 40 closes the switching valve 34 and performs two purifications. The catalysts 31 and 32 are caused to function. As a result, the exhaust gas is reliably purified by the purification catalysts 31 and 32, so that the emission can be maintained well.

  On the other hand, when the ECU 40 determines in step 11 that the engine 1 has been started when it is cold, the ECU 40 enters preparations for supplying secondary air to the exhaust manifold 6 (AI control), and the conditions for executing the AI control are satisfied. (S12). The AI control execution condition here is a predetermined condition that is assumed that the exhaust gas EG cannot be sufficiently purified unless secondary air is supplied to the exhaust system of the engine 1. The AI control execution condition can be determined as appropriate. For example, the cooling water temperature of the engine 1 is not more than a certain value, the internal temperature of the downstream side purification catalyst 32 is not more than a certain value, and the intake air amount is a certain value. And so on. These can be used alone or in combination as the AI control execution condition. If the execution condition is not satisfied in step 12, for example, if it is determined that the downstream side purification catalyst 32 has sufficiently raised the temperature, the ECU 40 sets all the switching valves 34 in the same manner as described in step 16 above. The control to close is executed.

  On the other hand, when the ECU 40 determines that the execution condition of the AI control is satisfied in step 12, the secondary air is supplied to the exhaust manifold 6 and the intake air amount is not more than a predetermined value (threshold value) set in advance. It is confirmed whether or not there is (S13). In general, when the engine 1 is cold-started and in an idle state and a light load state, the intake air amount here is equal to or less than a threshold value. Therefore, it is judged as Yes in this step 13, and the processing in the next step 14 is executed. On the contrary, if the engine 1 is driven at a medium load or higher within a short time after the cold start, the exhaust gas increases at a stretch. In such a case, if the exhaust gas EG is flowed to the bypass pipe 33 side, the emission is worsened. Therefore, the ECU 40 performs control so that the switching valve 34 is fully closed and the exhaust gas EG is purified by the two purification catalysts 31 and 32 when the intake air amount exceeds a predetermined value (S13, S16).

  In step 14, the ECU 40 reads an opening target corresponding to the state of the engine 1 from the ROM, and sets it as a target value for the opening (valve opening) of the switching valve 34 (S14). FIG. 3 is a diagram showing the relationship between the opening degree of the switching valve 34 and the flow rate of the exhaust gas flowing to the bypass pipe 33 side. As shown in FIG. 3, the exhaust gas flow that flows toward the bypass pipe 33 immediately after opening the switching valve 34 increases rapidly, and then tends to increase gradually. On the premise that there is such a tendency, a target opening value of the switching valve 34 corresponding to the cold state of the engine 1 is preset and stored in the ROM. The ECU 40 controls the opening degree of the switching valve 34 so as to be the target value (S15), and ends the processing by this routine.

  Note that the target value of the opening degree of the switching valve read by the ECU 40 in step 14 may be calculated by storing the data of FIG. 3 in the ROM. Further, a plurality of target values may be prepared in the ROM, and for example, a specific target value may be automatically selected according to the detected engine water temperature.

  As described above, when the engine 1 is started when the engine 1 is cold and the secondary air is supplied, the ECU 40 executes the control to bypass the downstream side purification catalyst 32 and flow the exhaust gas EG. When such control is executed, the exhaust gas pressure (back pressure) on the downstream side of the upstream side purification catalyst 31 is reduced, so that the secondary air easily flows into the exhaust manifold 6. Therefore, at the time of cold start, sufficient secondary air can be supplied to the upstream side purification catalyst 31, and the unburned fuel and oxygen contained in the exhaust gas can be mixed to promote the combustion reaction. Therefore, it is possible to prevent the deterioration of the emission during the cold start of the engine 1 and maintain the emission well. Further, warming up can be promoted by increasing the exhaust gas temperature by promoting the oxidation reaction in the upstream purification catalyst 31.

  Furthermore, Example 2 will be described with reference to FIG. The second embodiment is an exhaust control apparatus improved so that the emission can be maintained even when the engine 1 is cold-started at a high altitude where the atmospheric pressure is low. In addition, the structure of the main parts of the exhaust control device and the engine 1 of the second embodiment is the same as that of the first embodiment shown in FIG. In the case of the second embodiment, an atmospheric pressure sensor 41 is further provided as an atmospheric pressure detection unit. The difference is that a detection signal from the atmospheric pressure sensor 41 is supplied to the ECU 40. Therefore, the duplicated explanation is omitted by illustrating the atmospheric pressure sensor 41 with a dotted line in FIG. Below, with reference to FIG. 4, the control content which ECU40 performs when supplying secondary air to the exhaust pipe 7 of the engine 1 is demonstrated concretely.

  FIG. 4 is a flowchart illustrating an example of a routine executed by the ECU 40 of the exhaust control device according to the second embodiment. Processing until confirmation of cold start (S21), confirmation of AI control execution condition (S22) and confirmation of intake air amount (S23), and when the switching valve 34 is judged No (No) in these steps The process of setting the opening target to be fully closed (S28) is the same as in the first embodiment.

  In FIG. 4, the steps after step 24 are different from those in FIG. 2 (Example 1). That is, in step 24, the ECU 40 captures the output of the atmospheric pressure sensor 41. Based on this, the ECU 40 calculates the target opening value of the switching valve 34 (S25). The ECU 40 calculates a target value of the valve opening from, for example, a target opening map (map) of the atmospheric pressure-switching valve shown in FIG. 5A (S25). A target opening degree map of the atmospheric pressure-switching valve shown in FIG. 5A is stored in advance in a ROM in the ECU 40. As shown in FIG. 5A, the target opening degree map is set so that the opening degree of the switching valve 34 increases as the atmospheric pressure decreases. That is, the exhaust gas pressure (back pressure) downstream from the upstream side purification catalyst 31 is set to be reduced as the atmospheric pressure is lower. When the switching valve 34 is opened on the basis of the target opening degree map of FIG. 5A, as compared with the case where exhaust gas flows through the exhaust pipe 7 as shown in FIG. Pressure can be reduced.

  The ECU 40 of the second embodiment sets an opening target of the switching valve 34 based on the output of the atmospheric pressure sensor 41 (S26). The ECU 40 controls the motor 35 so that the opening degree of the switching valve 34 becomes the target opening degree (S27), and ends the processing by this routine. As a result, the lower the atmospheric pressure when the engine 1 is cold started, the larger the opening of the switching valve 34 and the greater the amount of exhaust gas flowing to the bypass pipe 33 side.

  If the atmospheric pressure is low when the engine 1 is cold started, the ECU 40 of the second embodiment increases the amount of exhaust gas to be bypassed according to the atmospheric pressure. Thus, if the bypass flow rate of the exhaust gas is increased as the atmospheric pressure becomes lower, the gas pressure in the exhaust pipe 7 is further reduced. Therefore, even if it is a place where atmospheric pressure is low, back pressure can be reduced and introduction of secondary air can be promoted. Thereby, the secondary air can be sufficiently supplied to the upstream side purification catalyst 31, and the exhaust gas EG and oxygen can be sufficiently mixed to promote the oxidation reaction. Therefore, even when the engine 1 is cold started in a highland such as a mountainous area, the emission can be maintained well.

  Furthermore, the exhaust control device 11 according to the third embodiment will be described with reference to FIGS. 6 and 7. FIG. 6 is a diagram illustrating a state in which the exhaust control device 11 according to the third embodiment is applied to the exhaust pipe 7 of the engine 1. The exhaust control device 11 is the same as the exhaust control device 10 of the first embodiment in that it includes two purification catalysts 31, 32, but does not include a bypass pipe 33 that bypasses the downstream purification catalyst 32. . Instead, the variable muffler device 50 is disposed on the downstream side of the downstream side purification catalyst 32. Note that the same parts as those shown in FIG.

  The variable muffler device 50 is provided with a pressure adjusting unit 52 on the downstream side of the muffler main body 51. The pressure adjusting unit 52 includes a piston 54 that slides inside a cylindrical muffler cover 53. The piston 54 has a through passage 55 through which exhaust gas EG passes. The positions of the through passage 55 and the outlet 56 of the variable muffler device 50 are offset. When the piston 54 is moved to the upstream side, the flowability of the exhaust gas EG is improved, so that the internal gas pressure is reduced. On the contrary, when the piston 54 is moved downstream and the through passage 55 is brought close to the outlet 56, the flowability of the exhaust gas EG is lowered, so that the internal gas pressure is increased. When the piston 54 moves to the most downstream side, the flow of the exhaust gas EG is almost stopped (fully closed state). At this time, since the gas pressure in the variable muffler device 50 becomes maximum, it becomes difficult for the exhaust gas EG to flow downstream. Thus, the piston 54 functions as a pressure regulating valve that adjusts the exhaust gas pressure in the variable muffler device 50. The piston 54 is driven by an actuator 57, and the actuator 57 is controlled by the ECU 40.

  In this manner, the exhaust control device 11 can reduce the exhaust gas pressure downstream of the purification catalysts 31 and 32 by moving the position of the piston 54 of the variable muffler device 50 to the upstream side. Similarly to the case of the second embodiment, the exhaust control device 11 moves the position of the piston 54 to the upstream side and reduces the exhaust gas pressure on the downstream side as the atmospheric pressure detected by the atmospheric pressure sensor 41 is lower. It is configured. Below, with reference to FIG. 7, the control content which ECU40 performs when supplying secondary air to the exhaust system of the engine 1 is demonstrated concretely.

  FIG. 7 is a flowchart illustrating an example of a routine executed by the ECU 40 of the exhaust control device according to the third embodiment. Even in this flowchart, the processes until the cold start confirmation (S31), the AI control execution condition confirmation (S32), the intake air amount confirmation (S33) and the intake of atmospheric pressure (S34), and these steps 31 to 33 are performed. The process (S38) for setting the target position of the piston 54 to the highest pressure side (the most downstream side forming the fully closed state) when it is determined No (No) is the same as in the second embodiment.

  In FIG. 7, the steps after step 35 are different from those shown in FIG. The ECU 40 calculates the target position of the piston 54 from, for example, an atmospheric pressure-piston target position map (map) shown in FIG. 8 (S35). This atmospheric pressure-piston target position map is stored in advance in a ROM in the ECU 40. As shown in FIG. 8, the target position map is such that the lower the atmospheric pressure, the higher the target position to which the piston 54 should move, and the higher the gas flowability in the variable muffler device 50. Is set. FIG. 8 corresponds to the target opening degree map of the atmospheric pressure-switching valve of FIG. Therefore, the lower the atmospheric pressure, the lower the exhaust gas pressure (back pressure) on the downstream side of the purification catalysts 31 and 32 is set.

  The ECU 40 of the third embodiment sets the movement position of the piston 54 as a target position based on the output of the atmospheric pressure sensor 41 (S36). The ECU 40 controls the actuator 57 so that the piston 54 moves to the target position (S37), and ends the processing by this routine.

  When the atmospheric pressure is low when the engine 1 is cold-started, the ECU 40 of the third embodiment performs control so that the amount of exhaust gas flowing through the variable muffler device 50 increases according to the atmospheric pressure. Therefore, similarly to the exhaust control device of the second embodiment, even when the engine 1 is cold started at a high altitude such as a mountainous area, the emission can be maintained satisfactorily.

  Note that. In the third embodiment, the exhaust gas pressure is lowered by moving the position of the piston 54 to the upstream side as the external atmosphere has a lower pressure corresponding to the second embodiment. However, an example of using the variable muffler device 50 is not limited to the form of the third embodiment. The ECU 40 may control the position of the piston 54 according to the state of the engine 1 without referring to the atmospheric pressure. That is, even when the variable muffler device 50 is used, the same control as in the first embodiment can be performed.

  Moreover, although the variable muffler apparatus 50 of Example 3 uses the piston 54 as a pressure regulating valve, it is not limited to this. The pressure regulating valve may be any valve that can adjust the exhaust gas pressure in the variable muffler device 50, and may be, for example, the butterfly flow control valve shown in the first embodiment.

  In the third embodiment, since the two disposed purification catalysts 31 and 32 are always used, it is possible to reliably improve the emission. In the first and second embodiments, since the downstream purification catalyst is bypassed, at least two purification catalysts are required. However, in the case of the third embodiment, it is possible to use one purification catalyst. However, on the contrary, in all the embodiments, it is possible to adopt a structure in which three or more purification catalysts are arranged.

  Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the specific embodiments, and various modifications and changes can be made within the scope of the gist of the present invention described in the claims. It can be changed.

It is the figure which showed a mode that the exhaust_gas | exhaustion control apparatus which concerns on Example 1 was applied to the exhaust passage of the engine. 3 is a flowchart illustrating an example of a routine that is executed when the ECU of the exhaust control device according to the first embodiment supplies secondary air to an exhaust system of an engine. It is the figure shown about the relationship between the opening degree of a switching valve, and the exhaust gas flow volume which flows into the bypass pipe side. 7 is a flowchart illustrating an example of a routine that is executed by the ECU of the exhaust control device according to the second embodiment. (A) is a view showing a target opening degree map of the atmospheric pressure-switching valve, and (B) is a comparison of the back pressure when exhaust gas flows through the exhaust pipe and when exhaust gas flows through the bypass pipe. FIG. It is the figure which showed a mode that the exhaust control apparatus which concerns on Example 3 was applied to the exhaust pipe of the engine. 12 is a flowchart illustrating an example of a routine that is executed by the ECU of the exhaust control device according to the third embodiment. It is the figure which showed the atmospheric pressure-piston target position map.

Explanation of symbols

1 Gasoline engine (internal combustion engine)
2 Intake pipe 7 Exhaust pipe (exhaust passage)
10, 11 Exhaust control device 20 Secondary air supply mechanism (secondary air supply means)
21 Bypass pipe (gas pressure adjusting means)
22 Air pump (gas pressure adjusting means)
DESCRIPTION OF SYMBOLS 30 Exhaust purification catalyst apparatus 31 Upstream purification catalyst 32 Downstream purification catalyst 33 Bypass pipe 34 Switching valve 40 ECU (control means)
41 Barometric pressure sensor (atmospheric pressure detection means)
50 Variable muffler EG Exhaust gas SA Secondary air

Claims (9)

A purification catalyst disposed in the exhaust passage of the internal combustion engine;
Secondary air supply means for supplying secondary air to the exhaust passage;
Gas pressure adjusting means for changing the exhaust gas pressure downstream of the purification catalyst;
An exhaust control device for an internal combustion engine, comprising: control means for controlling the gas pressure adjusting means so that the exhaust gas pressure is reduced when the secondary air supply means supplies secondary air. . A plurality of the purification catalyst is disposed in the exhaust passage;
The gas pressure adjusting means includes a bypass passage that bypasses the purification catalyst located on the downstream side, and a switching valve that switches between the exhaust passage and the bypass passage,
The exhaust control device for an internal combustion engine according to claim 1, wherein the control means controls the switching valve in accordance with a state of the internal combustion engine. The exhaust control device for an internal combustion engine according to claim 2, wherein the control means opens the switching valve to flow the exhaust gas to the bypass passage when the internal combustion engine is cold-started. It further comprises an atmospheric pressure detection means for detecting atmospheric pressure,
4. The internal combustion engine according to claim 2, wherein the control unit confirms an atmospheric pressure based on an output of the atmospheric pressure detection unit, and increases the opening of the switching valve as the pressure is lower. Exhaust control device. The exhaust control device for an internal combustion engine according to any one of claims 2 to 4, wherein the control means closes the switching valve when an intake air amount to the internal combustion engine exceeds a predetermined value. The gas pressure adjusting means includes a variable muffler device that is arranged downstream of the purification catalyst and can change an exhaust gas pressure inside,
The exhaust control device for an internal combustion engine according to claim 1, wherein the control means controls a pressure regulating valve of the variable muffler device in accordance with a state of the internal combustion engine. The exhaust control device for an internal combustion engine according to claim 6, wherein the control means controls the pressure regulating valve to reduce the exhaust gas pressure when the internal combustion engine is cold-started. It further comprises an atmospheric pressure detection means for detecting atmospheric pressure,
The said control means confirms atmospheric pressure based on the output of the said atmospheric pressure detection means, and controls the said pressure regulation valve, and the said exhaust gas pressure is reduced, so that it is low pressure. An exhaust control device for an internal combustion engine according to claim 1. 9. The control device according to claim 6, wherein, when the amount of intake air to the internal combustion engine exceeds a predetermined value, the control unit controls the pressure regulating valve to increase the exhaust gas pressure. Exhaust control device for internal combustion engine.

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