JP4962418B2 - Exhaust control device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust control device for an internal combustion engine that performs exhaust purification using a catalytic converter, and in particular, immediately after a cold start when the main catalytic converter is not activated, guides exhaust to the bypass flow path side provided with another catalytic converter. The present invention relates to an improvement of an exhaust control device of the type described above.

  As conventionally known, in a configuration in which the main catalytic converter is disposed relatively downstream of the exhaust system such as under the floor of a vehicle, the temperature of the catalytic converter rises and is activated after a cold start of the internal combustion engine. In the meantime, a sufficient exhaust purification action cannot be expected. On the other hand, the closer the catalytic converter is to the upstream side of the exhaust system, that is, the internal combustion engine side, the lower the durability due to thermal degradation of the catalyst.

  Therefore, as disclosed in Patent Document 1, a bypass flow path is provided in parallel with the upstream portion of the main flow path including the main catalytic converter, and another bypass catalytic converter is interposed in the bypass flow path. However, an exhaust control device has been conventionally proposed in which the exhaust gas is guided to the bypass flow channel side immediately after the cold start by the flow channel switching valve for switching between the two. In this configuration, the bypass catalytic converter is positioned relatively upstream of the main catalytic converter in the exhaust system and is activated relatively early, so that exhaust gas purification can be started from an earlier stage.

The operation of the flow path switching valve detects, for example, the exhaust temperature downstream of the main catalytic converter using an exhaust temperature sensor, and determines the active state of the exhaust purification catalyst according to the exhaust temperature. That is, when the exhaust temperature is equal to or lower than the predetermined catalyst activity determination temperature, it is determined that the main catalytic converter is inactive, the flow path switching valve is closed to guide the exhaust to the bypass flow path side, and the exhaust temperature is the catalyst temperature. When the activation determination temperature is exceeded, it is determined that the main catalytic converter has been activated, and the flow path switching valve is opened.
Japanese Patent Laid-Open No. 2005-351088

  Thus, the flow path switching valve (hereinafter also simply referred to as “switching valve”) is closed immediately after the engine cold start in which the main catalytic converter (hereinafter also referred to as “underfloor catalyst”) has not been activated after engine startup. However, in situations where idle operation continues for a relatively long time, such as when there is a traffic jam or when visiting a convenience store, the exhaust gas volume is low, so the temperature of the underfloor catalyst decreases, and again May become inactive. Therefore, for example, it is preferable to determine whether or not the exhaust gas temperature downstream of the catalyst is inactive again (that is, whether the temperature is lower than the predetermined catalyst activation temperature), and in that case, it is preferable to close the flow path switching valve again.

  However, for example, immediately after engine cold start, the flow path switching valve after the warming-up of the first time when the flow path switching valve including the underfloor catalyst is sufficiently low and the underfloor catalyst is already activated as described above. In the case where the valve is closed again, that is, in the second and subsequent closed states where the flow path switching valve has already been opened during one trip from engine start to engine stop, the temperature rise characteristics of the underfloor catalyst are greatly different. It will be a thing.

  FIG. 5 shows the rise of the inlet gas temperature of the underfloor catalyst in the first closed state (A) and the second and subsequent closed states (B), and the catalyst temperature (BED temperature) at the head, middle stage, and rear end of the underfloor catalyst. Temperature characteristics are shown. As shown in the figure, in the initial closed state, the exhaust system including the catalyst is cold, so the underfloor catalyst is gradually warmed from the beginning, and the catalyst temperature rises in order from the beginning to the rear end. On the other hand, in the second and subsequent closed states, the catalyst has already been warmed up to the vicinity of the catalyst activity determination temperature, and therefore the temperature tends to rise evenly. Therefore, when determining the active state of the catalyst based on the exhaust gas temperature downstream of the catalyst, in the initial closed state, the time for the catalytic reaction heat to flow to the downstream side of the catalyst is slow, so the downstream side of the catalyst with respect to the actual catalyst temperature. The exhaust temperature of the engine tends to be lower, whereas in the second and subsequent closed states, the heat of the catalytic reaction flows down the catalyst at an early stage because it warms relatively evenly. As a result, the exhaust gas temperature on the downstream side of the catalyst tends to be relatively high.

  Due to such a difference, if the activation state is determined by comparing the exhaust gas temperature downstream of the catalyst with the fixed catalyst activity determination temperature, an erroneous determination may occur. For example, if the catalyst activation determination temperature is set according to the first closed state, the flow switching valve may be opened before the activation of the main catalytic converter in the second and subsequent closed states, and exhaust emission may be deteriorated. When the catalyst activation determination temperature is set according to the second and subsequent closed states, the flow path switching valve remains closed for a while in the first closed state even though the main catalytic converter is already activated, and the bypass catalytic converter The chances of exposure to the exhaust gas increase, and the thermal degradation of the bypass catalytic converter may progress.

  Accordingly, an object of the present invention is to optimize the switching timing of the flow path switching valve from closing to opening to reduce or eliminate deterioration of exhaust emission, thermal deterioration of the bypass catalytic converter, and deterioration of durability.

  A flow switching valve is interposed in the main flow path of the exhaust upstream of the main catalytic converter, and a bypass catalytic converter is interposed in the bypass flow path arranged in parallel with the upstream portion of the main flow path, In an exhaust control device for an internal combustion engine configured so that exhaust flows into the bypass flow path when the flow path switching valve is closed, exhaust temperature detection means for detecting an exhaust temperature downstream of the main catalytic converter, and the exhaust temperature is And a controller that opens the flow path switching valve when a predetermined catalyst activity determination temperature is exceeded. Then, the control unit includes a closed state determining means for determining whether the flow path switching valve is in a first closed state after engine start or a second or later closed state, and the second time. In the subsequent closed state, compared with the first closed state, the catalyst activity determination temperature correcting means for correcting the catalyst activity determination temperature to the increasing side is provided.

  According to the present invention, the switching timing from closing to opening of the flow path switching valve is appropriate, deterioration of exhaust emission due to delay in switching to opening of the flow path switching valve, and opening of the flow path switching valve. It is possible to reduce / eliminate the thermal deterioration and the deterioration of durability of the bypass catalytic converter due to the switching being too early.

  Hereinafter, an embodiment in which the present invention is applied as an exhaust control device for an in-line four-cylinder internal combustion engine will be described in detail with reference to the drawings. FIG. 1 is an explanatory view schematically showing the piping layout of the exhaust control device. First, the configuration of the entire exhaust control device will be described based on FIG. An upstream main passage 2 is connected to each cylinder 1 including # 1 cylinder to # 4 cylinder arranged in series. Among the four cylinders, the upstream main passage 2 of the # 1 cylinder and the upstream main passage 2 of the # 4 cylinder where the exhaust stroke is not continuous merge as one intermediate main passage 3, and the exhaust stroke is similarly performed. The upstream main passage 2 of the # 2 cylinder and the upstream main passage 2 of the # 3 cylinder are joined together as one intermediate main passage 3. Here, the flow path switching valve 4 is provided in the junction where the two upstream main passages 2 join each other. The flow path switching valve 4 is closed when it is cold. When closed, the flow path switching valve 4 blocks the upper and lower communication between the upstream main passage 2 and the intermediate main passage 3, and the two upstream main passages. It is the structure which makes between 2 and a non-communication state. A pair of flow path switching valve 4 is comprised as one valve unit 5 so that it may mention later. The two intermediate main passages 3 positioned downstream of the valve unit 5 merge with each other at a junction 6 to form one downstream main passage 7. A main catalytic converter 8 is interposed in the middle of the downstream main passage 7. The catalyst in the main catalytic converter 8 includes a three-way catalyst and an HC trap catalyst. The main catalytic converter 8 has a large capacity arranged under the floor of the vehicle. The upstream main passage 2, the intermediate main passage 3, the downstream main passage 7, and the main catalytic converter 8 constitute a main passage through which exhaust flows during normal operation. This main flow path has a piping layout that is gathered in the well-known “4-2-1” form in an in-line four-cylinder internal combustion engine, and therefore, an improvement in charging efficiency utilizing the exhaust dynamic effect is realized.

  On the other hand, an upstream bypass passage 11 is branched from each of the upstream main passages 2 as bypass passages. The upstream bypass passage 11 has a sufficiently smaller passage cross-sectional area than the upstream main passage 2, and the branch point 12 serving as the upstream end of the upstream bypass passage 11 is set at a position as upstream as possible in the upstream main passage 2. Has been. The upstream bypass passage 11 of the # 1 cylinder and the upstream bypass passage 11 of the # 2 cylinder, which are adjacent to each other, merge with each other as a single intermediate bypass passage 14 at the merge point 13. The upstream bypass passage 11 of the # 3 cylinder and the upstream bypass passage 11 of the # 4 cylinder which are adjacent to each other join each other as a single intermediate bypass passage 14 at the junction 13. In FIG. 1 schematically showing each passage, each upstream bypass passage 11 is drawn relatively long, but in practice it is as short as possible. In other words, it merges as the intermediate bypass passage 14 with the shortest distance. The two intermediate bypass passages 14 join each other as one downstream bypass passage 16 at the junction 15. The downstream end of the downstream bypass passage 16 joins the downstream main passage 7 at a junction 17 upstream of the main catalytic converter 8 in the downstream main passage 7. In the middle of the downstream bypass passage 16, a bypass catalytic converter 18 using a three-way catalyst is interposed. The bypass catalytic converter 18 is disposed as upstream as possible in the bypass flow path. That is, the intermediate bypass passage 14 is as short as possible.

  In the present embodiment, a configuration in which the four upstream bypass passages 11 are aggregated as one downstream bypass passage 16 immediately before the bypass catalytic converter 18 without being assembled as the intermediate bypass passage 14 is also possible. However, when the position of the branch point 12 and the position of the bypass catalytic converter 18 are compared with each other, the intermediate position between the upstream side and the downstream side of the four upstream bypass passages 11 is longer than that of the four upstream bypass passages 11. In the case where the bypass passages 14 are combined, the overall passage length (the sum of the bypass passages of each cylinder) is shortened, and the heat capacity of the piping itself and the heat radiation area for the outside air are reduced.

  The bypass catalytic converter 18 includes two monolith catalyst carriers, that is, a first catalyst 18a and a second catalyst 18b, which are divided in the front and rear directions. One end of the exhaust gas recirculation passage 20 is connected to the gap 19 between the first catalyst 18a and the second catalyst 18b. The other end of the exhaust gas recirculation passage 20 extends to the engine intake system via an exhaust gas recirculation control valve (not shown). That is, the gap 19 serves as a recirculation exhaust outlet. The bypass catalytic converter 18 has a small capacity as compared with the main catalytic converter 8, and a catalyst excellent in low temperature activity is desirably used.

  In the exhaust control device configured as described above, at the stage where the engine temperature or the exhaust temperature after the cold start is low, the flow path switching valve 4 is closed via an appropriate actuator, and the main flow path is shut off. . Therefore, the entire amount of exhaust discharged from each cylinder 1 flows from the branch point 12 to the bypass catalytic converter 18 through the upstream bypass passage 11 and the intermediate bypass passage 14. Since the bypass catalytic converter 18 is located upstream of the exhaust system, that is, close to the cylinder 1 and is small in size, the bypass catalytic converter 18 is activated quickly and exhaust purification is started at an early stage. At this time, the flow path switching valve 4 is closed, so that the upstream main passages 2 of the cylinders 1 are not in communication with each other. Therefore, a phenomenon in which the exhaust discharged from a certain cylinder wraps around the upstream main passage 2 of the other cylinder is prevented, and a decrease in the exhaust gas temperature due to this wraparound is surely avoided. Further, when exhaust gas recirculation is performed with the flow path switching valve 4 closed, the recirculated exhaust gas taken out from the exhaust gas recirculation passage 20 to the intake system is clean exhaust gas after passing through the first catalyst 18a, that is, foreign matter and Since the fuel component and the like are removed, deposit adhesion and fouling in the exhaust gas recirculation control valve and the intake system are prevented.

  On the other hand, when the engine warm-up proceeds and the engine temperature or the exhaust temperature becomes sufficiently high, the flow path switching valve 4 is opened. As a result, the exhaust discharged from each cylinder 1 mainly passes from the upstream main passage 2 through the intermediate main passage 3 and the downstream main passage 7 and through the main catalytic converter 8. At this time, the bypass flow path side is not particularly shut off, but the bypass flow path side has a smaller passage cross-sectional area than the main flow path side, and the bypass catalytic converter 18 is interposed. Most of the exhaust flow passes through the main flow path side and hardly flows into the bypass flow path side. Therefore, the thermal deterioration of the bypass catalytic converter 18 is sufficiently suppressed. In addition, since the bypass flow path side is not completely cut off, a part of the exhaust flow flows through the bypass flow path side at a high speed and high load where the exhaust flow rate becomes large, so that a reduction in charging efficiency due to back pressure can be avoided.

  Further, as described above, the main flow path side has a “4-2-1” piping layout in consideration of avoidance of exhaust interference, so that it is possible to obtain an effect of improving the filling efficiency by the exhaust dynamic effect. Here, the bypass channel side communicates and aggregates in a manner that does not particularly consider exhaust interference avoidance, but by making the cross-sectional area of the upstream bypass passage 11 sufficiently small, exhaust by communication of each cylinder is achieved. Interference can be reduced to a level that is substantially negligible. If the passage cross-sectional area of the upstream bypass passage 11 is larger than a certain upper limit dimension, the charging efficiency is reduced due to the exhaust interference, and conversely if smaller than a certain lower limit dimension, the flow path switching valve 4 is closed. The exhaust flow rate during a certain period is limited to an excessively small value, and the operable range is excessively narrowed. Therefore, the optimum value of the passage cross-sectional area of the upstream bypass passage 11 is within a range between a predetermined upper limit dimension and a lower limit dimension corresponding to the engine displacement. As an example, in an internal combustion engine having a total displacement of about 2000 cc, good results were obtained when the equivalent diameter was in the range of 5 mm to 15 mm.

  Further, when exhaust gas recirculation is performed with the flow path switching valve 4 closed, the recirculated exhaust gas is also taken out from the bypass catalytic converter 18. At this time, even if part of the exhaust gas flows from the downstream main passage 7 to the exhaust gas recirculation passage 20 so as to flow backward through the downstream bypass passage 16, it is taken out from the exhaust gas recirculation passage 20 to the intake system. Since the recirculated exhaust gas becomes clean exhaust gas after passing through the second catalyst 18b, deposits and fouling in the exhaust recirculation control valve and the intake system are also prevented. In addition, since the flow speed when the second catalyst 18b flows back in this way is relatively slow and the residence time (passing time) in the second catalyst 18b becomes longer, as shown in the figure, the second catalyst 18b The axial length can be set shorter than the axial length of the first catalyst 18a.

  FIG. 2 shows the above-described exhaust control device as a more specific form, in which an internal combustion engine 31 having a cylinder block 32 and a cylinder head 33 is mounted in a so-called horizontal configuration in an engine room of a vehicle. An exhaust manifold 34 that mainly constitutes the upstream main passage 2 is attached to a side surface of the cylinder head 33 that is located behind the vehicle. A valve unit 5 having a pair of flow path switching valves 4 is attached to an outlet portion of the exhaust manifold 34, and a front tube 35 serving as a downstream main passage 7 is connected downstream thereof. A part of the upstream side of the front tube 35 is internally partitioned into two passages, that is, the intermediate main passage 3 described above. The main catalytic converter 8 is provided in the middle of the front tube 35.

  The bypass catalytic converter 18 and the like serving as a bypass flow path are disposed in a space below the main flow path extending from the cylinder head 33 toward the rear of the vehicle. Since the bypass catalytic converter 18 is located in the engine room and in front of the front tube 35 with respect to the vehicle traveling direction, the bypass catalytic converter 18 is effectively cooled by the traveling wind during traveling, and the bypass catalytic converter 18 is excessively cooled. Temperature rise is prevented.

  Further, the upstream bypass passage 11 is branched so as to form an acute angle with respect to the upstream main passage 2, so that when the flow path switching valve 4 is closed, the exhaust gas smoothly flows to the bypass flow path side.

  An upstream oxygen sensor (upstream oxygen concentration detection means) 41 and a downstream oxygen sensor (downstream oxygen concentration detection means) for detecting an oxygen concentration corresponding to the air-fuel ratio of the exhaust are disposed upstream and downstream of the main catalytic converter 8. ) 42 and an exhaust temperature sensor (exhaust temperature detecting means) 43 for detecting the exhaust temperature downstream of the catalyst is provided on the downstream side of the main catalytic converter 8. In this embodiment, an oxygen sensor whose output is simply reversed in the vicinity of the theoretical air-fuel ratio is used in this embodiment, but this is not limited to this, and a wide-area sensor that can widely detect oxygen concentration and air-fuel ratio is used. It may be used. The control unit 40 (see FIG. 1) is a digital computer system having a function of storing and executing various control processes, and controls the flow path switching valve 4 as will be described later in accordance with detection signals of these sensors. Do.

  FIG. 3 is a flowchart showing the flow of switching control from closing to opening of the flow path switching valve 4 according to this embodiment. In step S11, it is determined whether the flow path switching valve 4 is in a closed state, in other words, whether the main catalytic converter 8 is in an inactive state. Here, in the present embodiment, the main catalytic converter 8 is operated on the basis of the exhaust gas temperature downstream of the catalyst by the exhaust temperature sensor 43 even in a state after warm-up other than the cold start by other routines (not shown). Is determined to be inactive, and when it is determined to be inactive, the flow path switching valve 4 is closed again.

  In step S12, it is determined whether or not the passage of the flow path switching valve 4 has already been experienced during one trip from the engine start to the engine stop, that is, the second and subsequent close states. In the second and subsequent closed states, the process proceeds to step S13, and the catalyst activity determination temperature T0 for switching the flow path switching valve 4 from closed to open is corrected to the increasing side. Specifically, as shown in FIG. 4, a predetermined temperature correction value α is added to the catalyst activity determination temperature T0. On the other hand, when the engine is in the first closed state after the engine start, such as during a cold start, the process proceeds from step S12 to step S14 without executing step S13. In step S14, it is determined whether the exhaust temperature downstream of the catalyst detected by the exhaust temperature sensor 43 has reached the catalyst activity determination temperature T0. If the catalyst activity determination temperature T0 has been reached, the process proceeds to step S15, and the flow path switching valve 4 is switched from closed to open.

  In step S16, the outputs of the upstream oxygen sensor 41 and the downstream oxygen sensor 42, that is, the oxygen concentrations on the upstream and downstream sides of the catalyst are read. In step S17, it is determined whether the main catalytic converter 8 is activated based on the outputs of the upstream oxygen sensor 41 and the downstream oxygen sensor. Specifically, as shown in FIG. 4, the output of the upstream oxygen sensor 41 has a waveform that is periodically inverted between the rich side and the lean side by air-fuel ratio feedback control, while the output of the downstream oxygen sensor 42 is inverted. It is determined whether or not it has converged to a substantially constant value corresponding to the theoretical air-fuel ratio without doing so. If it is determined that the air flow has converged, the process proceeds to step S18, where a delay period ΔD (see FIG. 4) from the start timing of switching the flow path switching valve 4 from closing to opening to the convergence time is obtained, and the exhaust temperature during this delay period ΔD. In accordance with the change, a learning value α2 for the catalyst activity determination temperature T0 used for the activity determination in step S14 is obtained. In step S19, the catalyst activity determination temperature T0 is corrected and learned. Specifically, as shown in FIG. 4, based on the detection signal of the exhaust temperature sensor 43, the difference, that is, the increase in the exhaust temperature in the delay period ΔD is calculated as a learning value α2, and this α2 is calculated as the catalyst activity determination temperature T0. Add to. This learning content is reflected in the activity determination process using the catalyst activity determination temperature T0 in the next step S14.

  Referring to FIG. 4, when it is determined in step S14 that the main catalytic converter 8 has been activated and the flow path switching valve 4 is switched from closed to open, air-fuel ratio feedback control is performed, and the upstream oxygen sensor The output of 41 has a waveform that periodically inverts between the rich side and the lean side. Here, if the main catalytic converter 8 is activated, the output of the downstream oxygen sensor 42 periodically reverses like the output of the upstream oxygen sensor 41, as indicated by reference numeral P2 in FIG. However, if the main catalytic converter 8 is not activated, as shown by the symbol P1, it will have a wave shape similar to the output of the upstream oxygen sensor 41. Therefore, in the present embodiment, as described above, the timing at which the output of the downstream oxygen sensor 42 converges to a substantially constant value from the switching start timing of the flow path switching valve 4 from closing to opening, that is, the oxygen sensors 41 and 42. A delay period ΔD until a time when it is determined to be activated by the output is obtained, and learning of the catalyst activation determination temperature T0 is performed according to the delay period ΔD. In this way, the existing oxygen sensors 41 and 42 used for feedback control and the like are used, and the catalyst activity determination temperature T0 is well corrected with a simple structure that does not require a dedicated new sensor component.・ You can learn.

  Next, the characteristic configuration and operational effects of this embodiment will be listed.

  A flow path switching valve 4 is interposed in the main flow path (2, 3, 7) of the exhaust upstream of the main catalytic converter 8, and a bypass flow path (in parallel with the upstream portion of the main flow path ( 11, 14, 16) is provided with a bypass catalytic converter 18 so that the exhaust gas flows into the bypass channel when the channel switching valve 4 is closed. An exhaust temperature sensor 43 (exhaust temperature detecting means) that detects the exhaust temperature downstream of the main catalytic converter 8 and a control unit 40 that opens the flow path switching valve 4 when the exhaust temperature exceeds a predetermined catalyst activity determination temperature T0. And having.

  As a first feature, when the flow path switching valve 4 is closed, it is determined whether it is in the first closed state after engine startup or the second and subsequent closed states (step S12, closed state determining means). In the second and subsequent closed states, the catalyst activity determination temperature T0 is corrected to the increasing side as compared to the first closed state (step S13, catalyst activity determination temperature correction means). Thus, in both the first closed state of the switching valve 4 and the second and subsequent closed states, the switching timing of the flow path switching valve 4 from closing to opening based on the exhaust temperature downstream of the main catalytic converter 8. Bypass catalytic converter due to deterioration of exhaust emission due to delay in switching to opening of the flow path switching valve 4 and switching of the flow path switching valve 4 to opening too early 18 can be reduced or eliminated.

  As a second feature, an upstream oxygen sensor 41 (upstream oxygen concentration detecting means) for detecting the oxygen concentration of the exhaust upstream of the main catalytic converter 8 and the oxygen concentration of the exhaust downstream of the main catalytic converter 8 are detected. And downstream oxygen sensor 42 (downstream oxygen concentration detection means), and after the opening switching in which the flow path switching valve 4 is switched from closed to open, the upstream exhaust oxygen concentration and the downstream exhaust oxygen Based on the concentration, it is determined whether or not the main catalytic converter 8 has been activated (step S17, activity determination means after closing), and according to the change in the exhaust temperature from when the switching valve 4 is switched to when it is determined to be active. The learning value α2 of the catalyst activity determination temperature T0 is calculated (step S18, catalyst activity determination temperature learning means). By reflecting the learned value α2 on the catalyst activity determination temperature T0 (step S19), the existing oxygen sensors 41 and 42 used for feedback control and the like are used, and a dedicated new sensor component is required. With a simple structure without this, the switching timing of the flow path switching valve 4 from closing to opening can be made more appropriate.

  As described above, the present invention has been described based on the specific embodiments. However, the present invention is not limited to the above-described embodiments, and includes various modifications and changes without departing from the spirit of the present invention. . For example, although one embodiment applied to an in-line four-cylinder internal combustion engine has been described here, the present invention is applicable to various types of internal-combustion engines such as an in-line multi-cylinder internal combustion engine other than the in-line four-cylinder engine or a V-type multi-cylinder internal combustion engine. It can be applied as an exhaust control device.

BRIEF DESCRIPTION OF THE DRAWINGS The structure explanatory drawing which shows one Example of the exhaust control apparatus which concerns on this invention. The side view of the exhaust system of the said Example. The flowchart which shows the flow of switching control from closing to opening of the flow-path switching valve of the said Example. 4 is a timing chart showing changes in sensor output and the like before and after switching from closing to opening of the flow path switching valve. Explanatory drawing which shows the difference in the temperature rising characteristic of a catalyst in the closed state for the first time and the closed state after the 2nd time.

Explanation of symbols

2… Upstream main passage (main passage)
3 ... Intermediate main passage (main passage)
4 ... Flow path switching valve 8 ... Main catalytic converter 11 ... Upstream side bypass passage (bypass passage)
14 ... Intermediate bypass passage (bypass passage)
16: Downstream bypass passage (bypass passage)
DESCRIPTION OF SYMBOLS 18 ... Bypass catalytic converter 40 ... Control part 41 ... Upstream oxygen sensor (upstream oxygen concentration detection means)
42. Downstream oxygen sensor (downstream oxygen concentration detection means)
43. Exhaust temperature sensor (exhaust temperature detection means)

Claims (5)

A flow switching valve is interposed in the main flow path of the exhaust upstream of the main catalytic converter, and a bypass catalytic converter is interposed in the bypass flow path arranged in parallel with the upstream portion of the main flow path, In an exhaust control device for an internal combustion engine configured to allow exhaust to flow to a bypass flow path when the flow path switching valve is closed,
Exhaust temperature detecting means for detecting the exhaust temperature downstream of the main catalytic converter;
A controller that opens the flow path switching valve when the exhaust temperature exceeds a predetermined catalyst activity determination temperature,
This control unit
Closed state determining means for determining whether the flow path switching valve is closed for the first time after engine startup or the second and subsequent closed states;
In the second and subsequent closed states, compared to the first closed state, the catalyst activity determination temperature correction means for correcting the catalyst activity determination temperature to the increase side;
An exhaust control device for an internal combustion engine, comprising: Upstream oxygen concentration detection means for detecting the oxygen concentration of the exhaust gas upstream of the main catalytic converter;
Downstream oxygen concentration detection means for detecting the oxygen concentration of the exhaust gas downstream of the main catalytic converter,
The control unit
After opening the flow path switching valve is switched from closed to open, it is determined whether or not the main catalytic converter is activated based on the oxygen concentration in the upstream exhaust and the oxygen concentration in the downstream exhaust. A determination means;
A catalyst activity determination temperature learning means for calculating a learning value of the catalyst activity determination temperature in accordance with a change in exhaust temperature from the opening switching of the switching valve until the activation state is determined by the post-closed activity determination means;
The exhaust control device for an internal combustion engine according to claim 1, comprising: A flow switching valve is interposed in the main flow path of the exhaust upstream of the main catalytic converter, and a bypass catalytic converter is interposed in the bypass flow path arranged in parallel with the upstream portion of the main flow path, In an exhaust control device for an internal combustion engine configured to allow exhaust to flow to a bypass flow path when the flow path switching valve is closed,
Upstream oxygen concentration detection means for detecting the oxygen concentration of the exhaust gas upstream of the main catalytic converter;
Downstream oxygen concentration detection means for detecting the oxygen concentration of the exhaust gas downstream of the main catalytic converter;
Exhaust temperature detecting means for detecting the exhaust temperature downstream of the main catalytic converter;
A controller that opens the flow path switching valve when the exhaust temperature exceeds a predetermined catalyst activity determination temperature,
The control unit
After opening the flow path switching valve is switched from closed to open, it is determined whether or not the main catalytic converter is activated based on the oxygen concentration in the upstream exhaust and the oxygen concentration in the downstream exhaust. A determination means;
A catalyst activity determination temperature learning means for calculating a learning value of the catalyst activity determination temperature in accordance with a change in exhaust temperature from the opening switching of the switching valve until the activation state is determined by the post-closed activity determination means;
An exhaust control device for an internal combustion engine, comprising:   In the post-closing activity determination means, the main catalytic converter is activated when the output of the upstream oxygen concentration detection means fluctuates periodically while the output of the downstream oxygen concentration detection means converges to a substantially constant value. The exhaust gas purification apparatus for an internal combustion engine according to claim 2 or 3, wherein the determination is made. The main flow path is formed by joining the upstream main passage for each cylinder connected to each cylinder and the plurality of upstream main passages into one flow path, and the main catalytic converter is interposed. A downstream main passage,
The bypass passage branches from an upstream portion of the upstream main passage, and has an upstream bypass passage for each cylinder having a smaller passage cross-sectional area than the upstream main passage, and the plurality of upstream bypass passages are 1 A downstream bypass passage having a downstream end connected to the downstream main passage at a position upstream of the main catalytic converter and having the bypass catalytic converter interposed therebetween. ,
The flow path switching valve is provided at a merging portion of a plurality of upstream main passages, and when the flow path switching valve is closed, the upstream main passages are not in communication with each other. An exhaust control device for an internal combustion engine according to any one of claims 1 to 4.

Images