JP5233487B2 - Engine exhaust system - Google Patents

Description

  The present invention is directed to an exhaust device of an engine (internal combustion engine) that performs exhaust gas purification with a catalyst, in particular, to guide the exhaust gas to the bypass flow path side provided with another catalyst immediately after a cold start in which the main catalyst is not activated. It relates to the improvement of the exhaust system of the type.

A main flow path that is connected to a cylinder of the engine and flows exhaust gas from the cylinder, a main catalyst that is interposed in the main flow path, and a bypass flow path that branches from the main flow path and joins upstream of the main catalyst And a bypass catalyst interposed in the bypass flow path, and a flow path switching valve for flowing the exhaust gas only to the bypass flow path when there is a close request and flowing the exhaust gas to the main flow path when there is a open request. The closing request is issued before the main catalyst is activated, the opening request is issued when the main catalyst is activated, and the third air-fuel ratio sensor and the fourth air-fuel ratio sensor are provided upstream and downstream of the bypass catalyst. When the first air-fuel ratio sensor and the second air-fuel ratio sensor are provided upstream and downstream of the main catalyst, and the exhaust gas is allowed to flow through the bypass flow path, it is based on the two outputs of the third air-fuel ratio sensor and the fourth air-fuel ratio sensor. Bypass catalyst When air-fuel ratio feedback control is performed so that the oxygen storage amount of the three-way catalyst) matches the target oxygen storage amount, and when exhaust gas is allowed to flow only through the main flow path, the first air-fuel ratio sensor and the second Some air-fuel ratio feedback control is performed based on two outputs of the air-fuel ratio sensor so that the oxygen storage amount of the main catalyst (three-way catalyst) matches the target oxygen storage amount (see Patent Document 1).
JP 2008-57481A

  By the way, in the technique of the above-mentioned Patent Document 1, there are three types of states of the bypass catalyst and the main catalyst depending on the operating conditions. For this reason, if the main catalyst is not in the stoichiometric state at the beginning of switching the flow path switching valve and flowing the exhaust gas only to the main exhaust passage, the conversion rate of the main catalyst is lowered and the exhaust emission is deteriorated.

  Therefore, the present invention switches the flow path switching valve and maintains the conversion rate of the main catalyst at a high level even when the main catalyst is not in the stoichiometric state at the beginning of flowing the exhaust gas only to the main exhaust passage. The purpose is to reduce the deterioration of exhaust emissions.

  The present invention solves the above problems by the following means. In addition, in order to make an understanding easy, although the code | symbol corresponding to embodiment of this invention is attached | subjected, it is not limited to this.

The present invention includes a main flow path (2, 3) that is connected to a cylinder of an engine and flows exhaust gas from the cylinder, a main catalyst (8) interposed in the main flow path (2, 3), and the main flow path A bypass channel (11, 13) branched from the channel (2, 3) and joined upstream of the main catalyst (8), and a bypass catalyst (18) interposed in the bypass channel (11, 13) And a flow path switching valve (4) for flowing the exhaust gas only to the bypass flow channels (11, 13) when there is a closing request, and flowing the exhaust gas to the main flow channels (2, 3) when there is a request for opening, A first air-fuel ratio sensor (46) interposed upstream of the main catalyst (8), a second air-fuel ratio sensor (47) interposed downstream of the main catalyst (8), and the main catalyst ( The request for closing is made before 8) is activated, and the request for closing is made when the main catalyst (8) is activated. A request output means for issuing an open request, when the exhaust at the open request from the request output means is flowing the main flow path (2, 3), the first air-fuel ratio sensor (46) Based on the outputs of the second air-fuel ratio sensor (47), air-fuel ratio feedback control is performed so that the oxygen storage amount of the main catalyst (8) matches the target oxygen storage amount, and the closing request from the request output means. When the exhaust is flowing only through the bypass flow path (11, 13), when the output of the second air-fuel ratio sensor (47) is not stoichiometric and the opening request is issued from the request output means, Until the output of the second air-fuel ratio sensor (47) is switched to stoichiometric, the opening request is delayed from being applied to the flow path switching valve (4).

According to the present invention, a main flow path that is connected to a cylinder of an engine and flows exhaust gas from the cylinder, a main catalyst that is interposed in the main flow path, and an upstream side of the main catalyst that is branched from the main flow path. And a bypass catalyst interposed in the bypass channel, and a flow for flowing the exhaust gas only to the bypass channel when there is a request for closing, and to the main channel when there is a request for opening. A path switching valve, a first air-fuel ratio sensor interposed upstream of the main catalyst, a second air-fuel ratio sensor interposed downstream of the main catalyst, and before the main catalyst is activated, A request output means for issuing an opening request when the main catalyst is activated, and the exhaust request is sent from the request output means to the main flow path . 1 air-fuel ratio sensor and the first Performs air-fuel ratio feedback control so that the oxygen storage amount of the main catalyst coincides with the target oxygen storage amount based on the output of the air-fuel ratio sensor, the bypass flow passage said exhaust in said closed request from the request output means only If the output of the second air-fuel ratio sensor is not stoichiometric and the request for opening is issued from the request output means, the opening request is made until the second air-fuel ratio sensor output is switched to stoichiometric. Delaying the application to the flow path switching valve. That is, since the main catalyst is brought into the stoichiometric state, the flow path switching valve is switched and the exhaust gas is allowed to flow only through the main flow path, so that the conversion rate of the main catalyst can be kept high and exhaust emission can be reduced.

  A first embodiment in which the present invention is applied as an exhaust system for an in-line four-cylinder engine will be described below with reference to the drawings.

  FIG. 1 is a schematic diagram of a piping layout of an exhaust device. First, the configuration of the entire exhaust device will be described based on FIG. For each cylinder 1 consisting of a first cylinder (# 1 cylinder), a second cylinder (# 2 cylinder), a third cylinder (# 3 cylinder), and a fourth cylinder (# 4 cylinder) arranged in series, Is connected to the upstream main passage 2. The four upstream main passages 2 individually connected to the four cylinders merge as one downstream main passage 3 at the downstream side, and in other words, the upstream main passage 2 A flow path switching valve 4 that opens and closes the four upstream main passages 2 at the same time is provided at a portion that becomes a boundary with the downstream main passage 3. The switching valve 4 is closed when it is cold, and when closed, the upper and lower communication between the upstream main passage 2 and the downstream main passage 3 is blocked and the four upstream main passages 2 are closed. It is the structure which is made into a mutually non-communication state between.

  A main catalyst 8 is interposed in the middle of the downstream main passage 3 extending downstream from the flow path switching valve 4. The main catalyst 8 has a large capacity arranged under the floor of the vehicle, and includes a three-way catalyst and an HC trap catalyst as the catalyst. The upstream main passage 2, the downstream main passage 3, and the main catalyst 8 constitute a main flow path through which exhaust flows during normal operation.

  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 four upstream bypass passages 11 merge as one downstream bypass passage 14 at the downstream 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, the downstream bypass passage 14 joins with the shortest distance.

  The downstream end of the downstream bypass passage 14 joins the downstream main passage 3 at a junction 17 upstream of the main catalyst 8 in the downstream main passage 3. A bypass catalyst 18 using a three-way catalyst is interposed in the downstream bypass passage 14. The bypass catalyst 18 is disposed as upstream as possible in the bypass flow path. The bypass catalyst 18 is a small one having a smaller capacity than the main catalyst 8, and a catalyst excellent in low temperature activity is preferably used.

  One end of the exhaust gas recirculation passage 15 is connected to the downstream main passage 3 upstream of the junction 17 to the downstream main passage 3 of the downstream bypass passage 14. The other end of the exhaust gas recirculation passage 15 extends to the intake system of the engine via an exhaust gas recirculation control valve (not shown).

  FIG. 2 shows input / output to the engine control unit 31. In the engine exhaust system configured as described above, the flow path switching valve 4 is closed by an engine control unit 31 via an appropriate motor (actuator) when the engine temperature after the cold start or the exhaust temperature is low. And the main flow path is blocked. Therefore, the entire amount of exhaust discharged from each cylinder 1 flows from the branch point 12 to the bypass catalyst 18 through the upstream bypass passage 11 and the downstream bypass passage 14. Since the bypass catalyst 18 is located upstream of the exhaust system, that is, close to the cylinder 1 and is small in size, the bypass catalyst 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.

  On the other hand, when the warm-up of the main catalyst 8 proceeds and becomes activated, the engine control unit 31 opens the flow path switching valve 4. As a result, the exhaust discharged from each cylinder 1 passes through the main catalyst 8 mainly through the upstream main passage 2 and the downstream main passage 3. 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 catalyst 18 is interposed. Most of the flow passes through the main flow path side and hardly flows into the bypass flow path side. Therefore, the thermal deterioration of the bypass catalyst 18 is sufficiently suppressed. In addition, since the bypass flow path side is not completely shut off, at high rotation speed and high load where the exhaust flow rate becomes large, a part of the exhaust flow flows through the bypass flow path side, thereby avoiding a reduction in charging efficiency due to back pressure. it can.

A third air-fuel ratio sensor 44 and a fourth air-fuel ratio sensor 45 are disposed upstream and downstream of the bypass catalyst 18, and a first air-fuel ratio sensor 46 and a second air-fuel ratio sensor 47 are disposed upstream and downstream of the main catalyst 8. I have. Here, the air-fuel ratio sensor is preferably a sensor that can linearly detect the air-fuel ratio from the lean side to the rich side. However, in the present embodiment, the air-fuel ratio sensor downstream of the catalyst is A so-called O ₂ sensor that switches between binary and rich around the theoretical air-fuel ratio is used.

  The engine control unit 31 performs air-fuel ratio feedback control based on these sensor outputs so that the oxygen storage amount of the three-way catalyst (bypass catalyst, main catalyst) matches the target oxygen storage amount. That is, when the flow path switching valve 4 is closed, air-fuel ratio feedback control is performed based on the two outputs of the third air-fuel ratio sensor 44 and the fourth air-fuel ratio sensor 45, and when the flow path switching valve 4 is opened, this time, Air-fuel ratio feedback control is performed based on the two outputs of the first air-fuel ratio sensor 46 and the second air-fuel ratio sensor 47.

  Each cylinder of the engine is provided with a fuel injection valve 21 and a spark plug 22. In the engine control unit 31, the intake air flow rate Qa detected by the air flow meter 41 and the engine detected by the crank angle sensor 42. A basic injection pulse width Tp is calculated based on the rotational speed Ne, and this basic injection pulse width Tp is calculated based on the outputs of the two sensors 44 and 45 when the flow path switching valve 4 is closed. At the time of opening, the fuel injection pulse width Ti is calculated by correcting with the air-fuel ratio feedback correction coefficient α calculated based on the outputs of the two sensors 46 and 47, and a predetermined injection timing is calculated only during the period of the fuel injection pulse width Ti. Then, the fuel injection valve 21 of each cylinder is opened to perform fuel injection.

  When the flow path switching valve 4 is switched from the closed position (valve closed state) to the open position (valve open state), the main flow of exhaust gas is switched from the bypass passage to the main passage. In accordance with the switching, the sensors used for the air-fuel ratio feedback control are switched from the third air-fuel ratio sensor 44 and the fourth air-fuel ratio sensor 45 to the first air-fuel ratio sensor 46 and the second air-fuel ratio sensor 47.

  In this case, as shown in FIG. 3, there are three types of states of the bypass catalyst 18 and the main catalyst 8 depending on the operating conditions, so that a total of nine combinations of the catalyst states can be considered. For this reason, if the main catalyst 8 is not in the stoichiometric state when the flow path switching valve 4 is opened, the conversion rate of the main catalyst is lowered, and the exhaust emission is deteriorated. For example, FIG. 4 shows what happens to the exhaust emission when the bypass catalyst 18 is lean and the main catalyst is rich. Air-fuel ratio feedback control (abbreviated as “OSC control” in the figure) is performed from the bypass side to the main side. Since the main catalyst becomes rich immediately after switching, the HC and CO deteriorate.

  Therefore, in the present invention, the conversion rate of the main catalyst 8 is kept high by switching the flow path switching valve 4 to the open state after the main catalyst 8 is stoichiometrically controlled according to the operating conditions. Reduces exhaust emissions when switching to the open state.

  This will be further described with reference to FIGS. Whether the bypass catalyst 18 or the main catalyst 8 is in a rich, stoichiometric or lean state can be known from the air-fuel ratio sensor output downstream of the catalyst. That is, whether the bypass catalyst 18 is in the rich, stoichiometric, or lean state depends on whether the main catalyst 8 is in the rich, stoichiometric, or lean state based on the output of the fourth air-fuel ratio sensor 45. This can be known from the output of the fuel ratio sensor 47. When the main catalyst 8 is in the lean state, the air-fuel ratio is controlled to the rich side in order to place the main catalyst 8 in the stoichiometric state. On the contrary, when the main catalyst 8 is in the rich state, the main catalyst 8 is in the stoichiometric state. In order to achieve this, the air-fuel ratio should be controlled to the lean side.

Note that a rich slice level and a lean slice level are provided centering on the O ₂ sensor output at the stoichiometric air-fuel ratio, and when it is within these two slice levels, it is “stoichiometric” or “stoichiometric state”. The width of these two slice levels is a so-called window. When the air-fuel ratio is swung within the width of the window by air-fuel ratio feedback control, the three-way catalyst (main catalyst, bypass catalyst) is NOx, HC, CO. Can be reduced at the same time.

  Accordingly, when the main catalyst 8 is in the lean state before switching the flow path switching valve 4 to the open state, after the rich spike process (air-fuel ratio enrichment process) is performed and the state of the main catalyst 8 is stoichiometric. The flow path switching valve 4 is switched to the open state (see FIG. 5). In this case, the rich spike amount A varies depending on the state of the bypass catalyst 18 when the flow path switching valve 4 is closed. That is, the rich spike amount when the bypass catalyst 18 is in the rich state is A1, the rich spike amount when the bypass catalyst is in the stoichiometric state, A2, and the rich spike amount when the bypass catalyst is in the lean state is A3. A1 <A2 <A3.

  Specifically, in FIG. 5, when the main catalyst 8 is in a lean state before the main catalyst 8 is activated, and the main catalyst 8 is activated and an opening request is issued to the flow path switching valve 4 at t1, During the predetermined time Δt1 from the timing of t1, it is determined whether the fourth air-fuel ratio sensor output is rich, stoichiometric, or lean, and the rich spike amount A is determined to be A1, A2, or A3. The rich spike processing is performed for a predetermined time Δt2 using the determined rich spike amount at the timing t2 when the predetermined time Δt1 has elapsed, and after the rich spike processing is completed, the second air-fuel ratio sensor output is switched from lean to stoichiometric. At time t3, the flow path switching valve 4 is switched to the open state. In other words, when an opening request is issued, rich spike processing is performed, and the application of this opening request to the flow path switching valve 4 is delayed until the second air-fuel ratio sensor output is switched from lean to stoichiometric by this rich spike processing. .

  On the contrary, when the main catalyst 8 is in the rich state before switching the flow path switching valve 4 to the open state, the lean spike process (air-fuel ratio lean process) is performed to make the state of the main catalyst 8 stoichiometric. After that, the flow path switching valve 4 is switched to the open state (see FIG. 6). In this case, the lean spike amount B varies depending on the state of the bypass catalyst 18 when the flow path switching valve 4 is closed. That is, the lean spike amount when the bypass catalyst 18 is in a rich state is B1, the lean spike amount when the bypass catalyst is in a stoichiometric state is B2, and the lean spike amount when the bypass catalyst is in a lean state is B3. B1> B2> B3.

  Specifically, in FIG. 6, when the main catalyst 8 is in a rich state before the activation of the main catalyst 18, and the main catalyst 8 is activated and an opening request is issued to the flow path switching valve 4 at t11, During the predetermined time Δt11 from the timing of t11, it is determined whether the fourth air-fuel ratio sensor output is rich, stoichiometric, or lean, and it is determined whether the lean spike amount B is B1, B2, or B3. The lean spike processing is performed for a certain time Δt12 using the determined lean spike amount at the timing t12 when the predetermined time Δt11 has elapsed, and the second air-fuel ratio sensor output is switched from rich to stoichiometric after the lean spike processing is completed. At time t13, the flow path switching valve 4 is switched to the open state. In other words, when an opening request is issued, a lean spike process is performed, and the application of the opening request to the flow path switching valve 4 is delayed until the second air-fuel ratio sensor output is switched from rich to stoichiometric by the lean spike process. .

  This control executed by the engine control unit 31 will be described in detail based on the following flowchart.

  However, as described in FIGS. 5 and 6, the main catalyst 8 is in the lean state when the flow path switching valve 4 is closed, and the main catalyst 8 is in the rich state when the flow path switching valve 4 is closed. In this case, the flow of FIGS. 7 to 10 is created corresponding to the case where the main catalyst is in the lean state when the flow path switching valve 4 is closed. That is, the following description is based on the assumption that the main catalyst 8 is in a lean state with the flow path switching valve 4 closed.

  FIG. 7 is for setting a flag, and is executed at regular intervals (for example, every 10 ms).

  In step 1, it is determined whether or not there is a request to open the flow path switching valve 4. This is because if the catalyst temperature Tcat of the main catalyst 8 detected by the temperature sensor 48 is equal to or higher than a predetermined value, it is determined that the main catalyst 8 has been activated and a request to open the flow path switching valve 4 is issued. It has become. Therefore, if the request for opening the flow path switching valve 4 is not issued, the current process is terminated.

  When there is a request to open the flow path switching valve 4, the process proceeds to step 2 to check whether or not a predetermined time Δt1 has elapsed since the request to open the flow path switching valve 4 was issued. The predetermined time Δt1 determines the time required to calculate the rich spike amount A. This predetermined time Δt1 is determined in advance by adaptation.

  When the predetermined time Δt1 has not elapsed since the opening request of the flow path switching valve 4 has been issued, the routine proceeds to step 3 where a spike amount setting flag (initially set to zero when the engine is started) is viewed. Here, assuming that the spike amount setting flag = 0, the routine proceeds to step 4 where the rich spike amount A is set. The setting of the rich spike amount A will be described with reference to the flow of FIG.

  In FIG. 8 (subroutine of step 4 in FIG. 7), in step 11, the fourth air-fuel ratio sensor output is read, and in step 12, whether the fourth air-fuel ratio sensor output is rich, stoichiometric, or lean is checked. Here, when the fourth air-fuel ratio sensor output falls between the rich-side slice bell and the lean-side slice bell, stoichiometric, when the fourth air-fuel ratio sensor output exceeds the rich-side slice bell, rich, the fourth air-fuel ratio Lean when the sensor output is less than the lean slice bell.

  When the fourth air-fuel ratio sensor output is rich, the routine proceeds to step 13 where the predetermined value A1 is reached. When the fourth air-fuel ratio sensor output is stoichiometric, the routine proceeds to step 14 where the predetermined value A2 is reached and the fourth air-fuel ratio sensor output is lean. When it is, the routine proceeds to step 15 where the predetermined value A3 is set as the rich spike amount A. Here, a relationship of A1 <A2 <A3 is generated between the predetermined values A1, A2, and A3. For example, A1 = 0.1, A2 = 0.2, and A3 = 0.3.

  When the rich spike amount A is calculated in this way, the processing returns to FIG. 7, and the spike amount setting flag = 1 is set in step 5 to indicate that the rich spike amount A has been calculated.

  By this spike amount setting flag = 1, step 4 is skipped from step 3 and the process proceeds to step 5 next time, and the operation of step 5 is executed.

  Eventually, when a predetermined time Δt1 has elapsed since the request to open the flow path switching valve 4 was issued in step 2, the process proceeds to step 6 to perform rich spike processing (rich spike flag (initially set to zero when the engine is started)) = 1. And

  FIG. 9 is for calculating the fuel injection pulse width Ti, and is executed at regular time intervals (for example, every 10 ms) following FIG.

  In step 21, the intake air flow rate Qa detected by the air flow meter, the engine rotational speed Ne detected by the crank angle sensor 42, and the rich spike amount A (calculated in step 4 in FIG. 7) are read.

In step 22, from the intake air flow rate Qa and the engine speed Ne,
Tp = K × Qa / Ne (1)
Where K is a constant,
The basic injection pulse width Tp [ms] is calculated by the following formula.

  In steps 23 and 24, it is checked whether or not the rich spike flag = 1, and whether or not the rich spike flag = 0 was previously set. When the rich spike flag is 0 at this time, the routine proceeds to step 30, where the target equivalent ratio TFBYA is set to 1.0 in order to perform the air-fuel ratio feedback control, and the air-fuel ratio feedback correction coefficient α is calculated at step 31.

Here, based on the two outputs of the third air-fuel ratio sensor 44 and the fourth air-fuel ratio sensor 45 when the flow path switching valve 4 is closed, and when the flow path switching valve 4 is opened, the first air-fuel ratio sensor 46 and the second air-fuel ratio sensor 46 are output. Based on the two outputs of the air-fuel ratio sensor 47, the air-fuel ratio feedback correction coefficient α is calculated so that the oxygen storage amount of each catalyst (bypass catalyst, main catalyst) matches the target oxygen storage amount. An air-fuel ratio sensor is provided upstream of the three-way catalyst, and an O ₂ sensor is provided downstream. The method of calculating the air-fuel ratio feedback correction coefficient so that the oxygen storage amount of the three-way catalyst matches the target oxygen storage amount is as follows: Since it is known, the detailed description of the calculation of the air-fuel ratio feedback correction coefficient α of the present embodiment is omitted.
When the current rich spike flag = 1 and the previous rich spike flag = 0, that is, when the current rich spike flag is switched from zero to 1, the routine proceeds to step 25 and a timer is started (timer value tm = 0). . This timer is for measuring the elapsed time since the rich spike flag = 1.

In step 26, the rich spike amount A is used.
TFBYA = 1 + A (2)
The target equivalent ratio TFBYA is calculated by the following formula.

  In step 27, the air-fuel ratio feedback correction coefficient α is clamped (α = 1.0) to perform rich spike processing.

  When the current rich spike flag = 1 and the rich spike flag = 1 at the previous time in steps 23 and 24, that is, when the rich spike flag = 1 continues, the routine proceeds to step 28 where the timer value tm and the predetermined time Δt2 Compare The predetermined time Δt2 is a time for performing the rich spike processing, and is determined in advance. When the timer value tm is less than the predetermined time Δt2, the routine proceeds to steps 26 and 27 to execute the operations of steps 26 and 27 in order to continue the rich spike processing.

  Eventually, when the timer value tm becomes equal to or greater than the predetermined time Δt2 in step 28, the process proceeds to step 29 to end the rich spike process, and the rich spike flag = 0 is set. In steps 30 and 31, in order to perform air-fuel ratio feedback control again, the target equivalent ratio TFBYA is set to 1.0, and the air-fuel ratio feedback correction coefficient α is calculated.

In step 32, using the basic injection pulse width Tp, the target equivalent ratio TFBYA, and the air-fuel ratio feedback correction coefficient α,
Ti = Tp × TFBYA × (α + αm−1) × 2 + Ts (3)
Where αm is the air-fuel ratio learning value,
Ts: Invalid injection pulse width,
The fuel injection pulse width Ti [ms] is calculated by the following formula.

  The air-fuel ratio learning value αm and the invalid injection pulse width Ts in equation (3) are known. The fuel injection pulse width Ti calculated in this way is transferred to the output register, and the fuel injection valve 21 is opened during the fuel injection pulse width Ti at a predetermined injection timing.

  FIG. 10 is for performing opening / closing control of the flow path switching valve 4 and is executed at regular intervals (for example, every 10 ms).

  In step 41, it is determined whether or not the engine is cold-started. If the coolant temperature Tw detected by the coolant temperature sensor 43 is equal to or lower than a predetermined value, it is determined that the engine is cold started. Therefore, if it is not a cold start, the current process is terminated.

  When it is a cold start, the routine proceeds to step 42 where the catalyst temperature Tcat of the main catalyst 8 detected by the temperature sensor 48 and the second air-fuel ratio sensor output are read.

  In step 43, it is checked whether or not the main catalyst 8 is activated. If the catalyst temperature Tcat of the main catalyst 8 detected by the temperature sensor 48 is equal to or higher than a predetermined value, it is determined that the main catalyst 8 is activated. Therefore, if the main catalyst 8 has not been activated, the routine proceeds to step 44, where a request for closing the flow path switching valve 4 is issued.

  Eventually, when the main catalyst 8 is activated in step 43, the routine proceeds to step 45, where it is determined whether or not the second air-fuel ratio sensor output is stoichiometric. Here, when the second air-fuel ratio sensor output is within the rich-side slice bell and the lean-side slice bell, stoichiometric, when the second air-fuel ratio sensor output exceeds the rich-side slice bell, rich, the second air-fuel ratio Lean when the sensor output is less than the lean slice bell. When the second air-fuel ratio sensor output is not stoichiometric (that is, lean), the routine proceeds to step 44 and the operation of step 44 is executed.

  In the present embodiment, the rich spike process is performed before switching the flow path switching valve 4 to the open state rather than switching the flow path switching valve 4 to the open state as soon as the main catalyst is activated. Eventually, the second air-fuel ratio sensor output is switched from lean to stoichiometric. At this time, the routine proceeds from step 45 to step 46, where an opening request for the flow path switching valve 4 is issued.

  The flow path switching valve 4 is controlled to open and close by the close request and the open request issued in this way.

  Here, the effect of this embodiment is demonstrated.

  According to the first embodiment (the invention described in claim 1), the main flow path (2, 3) that is connected to the cylinder of the engine and flows exhaust gas from the cylinder, and the main flow path that is interposed in the main flow path The catalyst 8, the bypass channel (11, 14) branched from the main channel and joined upstream of the main catalyst, the bypass catalyst 18 interposed in the bypass channel, and exhaust when there is a request for closing To the bypass flow path, when there is a request to open, the flow path switching valve 4 that allows exhaust to flow only to the main flow path, the first air-fuel ratio sensor 46 interposed upstream of the main catalyst 8, and the downstream of the main catalyst 8 Request output means for issuing the closing request before the activated second air-fuel ratio sensor 47 and the main catalyst 8 are activated, and the opening request when the main catalyst is activated (step 41 in FIG. 10). 43, 44, 46) and the request output When the exhaust gas is allowed to flow only through the main flow path in response to an open request from the engine, the oxygen storage amount of the main catalyst 8 is set to the target oxygen storage amount based on the outputs of the first air-fuel ratio sensor 46 and the second air-fuel ratio sensor 47. The air-fuel ratio feedback control means (see step 31 in FIG. 9) that performs air-fuel ratio feedback control so as to match, and the second air-fuel ratio when the exhaust is flowing through the bypass flow path due to the closing request from the request output means When the sensor 47 output is not stoichiometric and an opening request is issued from the request output means, delay means for delaying giving the opening request to the flow path switching valve 4 until the second air-fuel ratio sensor 47 output switches to stoichiometry. (Refer to Steps 23 to 29 in FIG. 9 and Steps 43, 45, and 46 in FIG. 10). That is, since the main catalyst 8 is brought into the stoichiometric state and the flow path switching valve 4 is switched and the exhaust gas is allowed to flow only through the main flow paths (2, 3), the conversion rate of the main catalyst 8 can be kept high and the exhaust emission can be reduced.

  According to the first embodiment (the invention described in claim 2), the delay means (see steps 23 to 29 in FIG. 9 and steps 43, 45, and 46 in FIG. 10) is the request output means (step 41 in FIG. 10). , 43, 44, and 46), when the exhaust gas is flowing through the bypass passages (11, 14), the second air-fuel ratio sensor output is in a lean state, and the opening request is sent from the request output means. When this occurs, an air-fuel ratio enrichment process is performed, and this opening request is given to the flow path switching valve until the air-fuel ratio enrichment process switches the second air-fuel ratio sensor output from lean to stoichiometric. Delay. That is, even when the main catalyst 8 is in the lean state, the flow switching valve 4 is switched after the stoichiometric state is switched, and the exhaust gas is allowed to flow only through the main flow channels (2, 3). Emission (NOx) can be reduced.

  According to the first embodiment (the invention described in claim 3), the rich spike amount A (rich amount) in the rich spike processing is used as the fourth air-fuel ratio sensor output when exhaust is flowing in the bypass flow path. Therefore, even if there is a difference in the fourth air-fuel ratio sensor output when the exhaust gas is flowing through the bypass flow path, the optimum rich spike amount A can be given. it can.

  The above is the operation and effect when the main catalyst 8 is in the lean state with the flow path switching valve 4 closed. Next, when the main catalyst 8 is in the rich state with the flow path switching valve 4 closed. The effect will be described. That is, according to the first embodiment (the invention described in claim 6), the delay means is configured to perform the second operation when exhaust gas is allowed to flow through the bypass flow path (11, 14) in response to a closing request from the request output means. When the air-fuel ratio sensor output is in a rich state and the opening request is issued from the request output means, an air-fuel ratio leaning process is performed, and the second air-fuel ratio sensor output is rich by this air-fuel ratio leaning process. The opening request is delayed until it is switched to the stoichiometric state. That is, even if the main catalyst 8 is in a rich state, the flow switching valve 4 is switched after the stoichiometric state and the exhaust is allowed to flow only through the main flow paths (2, 3). Therefore, the conversion rate of the main catalyst 8 is kept high and the exhaust emission is maintained. (HC, CO) can be reduced.

  According to the first embodiment (the invention described in claim 7), the lean spike amount B (lean amount) in the lean spike process is used as the fourth air-fuel ratio sensor output when exhaust is flowing in the bypass flow path. Therefore, even if there is a difference in the output of the fourth air-fuel ratio sensor when exhaust gas is flowing through the bypass flow path, the optimum lean spike amount B can be given.

  11 and 12 show the second embodiment, which replaces FIGS. 5 and 6 of the first embodiment.

  In the first embodiment, as shown in FIGS. 5 and 6, the flow path switching valve 4 is in a closed state (fully closed state) in the period from t2 to t3 and t12 to t13. However, in the second embodiment, In the period from t2 to t3 and t12 to t13, the flow path switching valve is slightly opened to a predetermined opening degree.

  That is, when the main catalyst 8 is in the lean state with the flow path switching valve 4 closed, the timing (t3) at which the second air-fuel ratio sensor output is switched from lean to stoichiometric from the start timing (t2) of the rich spike processing. When the flow path switching valve 4 is opened to the predetermined opening φ during the period until, the rich atmosphere gas accompanying the rich spike process reaches the main catalyst 8 quickly. Similarly, when the main catalyst 8 is in the rich state with the flow path switching valve 4 closed, the timing at which the second air-fuel ratio sensor output is switched from rich to stoichiometric from the start timing (t12) of the lean spike processing ( When the flow path switching valve 4 is opened to a predetermined opening ψ during the period up to t13), the gas in the lean atmosphere accompanying the lean spike process reaches the main catalyst 8 quickly.

  In this case, in FIG. 11, the predetermined opening φ is made different depending on the state of the bypass catalyst 18 when the flow path switching valve 4 is closed. That is, when the predetermined opening when the bypass catalyst 18 is in a rich state is φ1, the predetermined opening when the bypass catalyst is in a stoichiometric state is φ2, and the predetermined opening when the bypass catalyst is in a lean state is φ3 , Φ1 <φ2 <φ3. In FIG. 12, the predetermined opening ψ varies depending on the state of the bypass catalyst 18 when the flow path switching valve 4 is closed. That is, when the predetermined opening when the bypass catalyst 18 is in the rich state is ψ1, the predetermined opening when the bypass catalyst is in the stoichiometric state is ψ2, and the predetermined opening when the bypass catalyst is in the lean state is ψ3. , Ψ1> ψ2> ψ3.

  According to the second embodiment (the invention described in claim 4), from the start of rich spike processing (air-fuel ratio enrichment processing) until the second air-fuel ratio sensor output is switched from lean to stoichiometric by this rich spike processing. Since the flow path switching valve 4 is opened to a predetermined opening φ during the period (t2 to t3), the time until the main catalyst 8 is in the stoichiometric state can be shortened.

  According to the second embodiment (the invention described in claim 5), the predetermined opening φ is made different according to the output of the fourth air-fuel ratio sensor when exhaust is flowing through the bypass flow path. Even if there is a difference in the output of the fourth air-fuel ratio sensor when flowing through the bypass flow path, the optimum predetermined opening φ can be given.

  The above is the effect of the second embodiment when the main catalyst 8 is in the lean state when the flow path switching valve 4 is closed. Next, the main catalyst 8 is rich when the flow path switching valve 4 is closed. The effect of 2nd Embodiment in a state is demonstrated. That is, according to the second embodiment (the invention described in claim 8), the output of the second air-fuel ratio sensor is switched from the rich to the stoichiometric by the lean spike processing from the start of the lean spike processing (air-fuel ratio leaning processing). Since the flow path switching valve 4 is opened to the predetermined opening ψ during the period until the change, the time until the main catalyst 8 is in the stoichiometric state can be shortened.

  According to the second embodiment (the invention according to claim 9), the predetermined opening ψ is made different according to the fourth air-fuel ratio sensor output when the exhaust is flowing in the bypass flow path, Even if there is a difference in the output of the fourth air-fuel ratio sensor when flowing in the bypass flow path, the optimum predetermined opening ψ can be given.

  The engine may be either a gasoline engine or a diesel engine.

The schematic diagram of the piping layout of an exhaust apparatus. The figure which shows the input-output to an engine control unit. The table | surface figure which shows that there exist nine combinations in the state of a catalyst. The timing chart which shows what happens to the exhaust emission when the bypass catalyst is lean and the main is rich. The timing chart for demonstrating the control method of this invention when a main catalyst is in a lean state in the closed state of a flow-path switching valve. The timing chart for demonstrating the control method of this invention when a main catalyst is in a rich state in the closed state of a flow-path switching valve. The flowchart for demonstrating the setting of a flag. The flowchart for demonstrating the setting of rich spike amount. The flowchart for demonstrating calculation of a fuel injection pulse width. The flowchart for demonstrating opening / closing control of a flow-path switching valve. The timing chart for demonstrating the control method of this invention when the main catalyst is in a lean state in the closed state of the flow-path switching valve of 2nd Embodiment. The timing chart for demonstrating the control method of this invention when the main catalyst is in a rich state in the closed state of the flow-path switching valve of 2nd Embodiment.

Explanation of symbols

2, 3 ... main passage (main passage)
11, 14 ... Bypass passage (bypass passage)
DESCRIPTION OF SYMBOLS 4 ... Flow path switching valve 8 ... Main catalyst 18 ... Bypass catalyst 31 ... Engine control unit 44 ... 3rd air fuel ratio sensor 45 ... 4th air fuel ratio sensor 46 ... 1st air fuel ratio sensor 47 ... 2nd air fuel ratio sensor

Claims (9)

A main flow path connected to the cylinders of the engine to flow exhaust from the cylinders;
A main catalyst interposed in the main flow path;
A bypass flow path branched from the main flow path and joined upstream of the main catalyst;
A bypass catalyst interposed in the bypass channel;
A flow path switching valve for flowing the exhaust only through the bypass flow path when there is a close request, and flowing the exhaust through the main flow path when there is a request for opening;
A first air-fuel ratio sensor interposed upstream of the main catalyst;
A second air-fuel ratio sensor interposed downstream of the main catalyst;
Request output means for issuing the closing request before the main catalyst is activated, and issuing the opening request when the main catalyst is activated;
When the exhaust is flowing through the main flow path in response to the opening request from the request output means, the oxygen storage amount of the main catalyst is determined based on the outputs of the first air-fuel ratio sensor and the second air-fuel ratio sensor. Air-fuel ratio feedback control means for performing air-fuel ratio feedback control so as to coincide with the target oxygen storage amount;
When the exhaust is flowing only through the bypass flow path due to the closing request from the request output means, when the second air-fuel ratio sensor output is not stoichiometric and the opening request is issued from the request output means, An engine exhaust system comprising: delay means for delaying the application of the opening request to the flow path switching valve until the output of the second air-fuel ratio sensor is switched to stoichiometric. The delay means is in a lean state of the second air-fuel ratio sensor output when the exhaust is flowing only through the bypass flow path in response to the closing request from the request output means, and from the request output means When an open request is issued, an air-fuel ratio enrichment process is performed, and this open request is sent to the flow path switching valve until the air-fuel ratio enrichment process switches the second air-fuel ratio sensor output from lean to stoichiometric. The engine exhaust device according to claim 1, wherein the engine exhaust device is delayed. A third air-fuel ratio sensor interposed upstream of the bypass catalyst;
A fourth air-fuel ratio sensor interposed downstream of the bypass catalyst,
3. The engine according to claim 2, wherein the enrichment amount in the enrichment process of the air-fuel ratio is made different according to the output of the fourth air-fuel ratio sensor when the exhaust is flowing through the bypass flow path. Exhaust system. The flow path switching valve flows the exhaust only through the bypass flow path when in the closed position, and flows the exhaust through the main flow path when in the open position,
The delay means advances the application of the opening request to the flow path switching valve until the air-fuel ratio enrichment processing timing, opens the flow path switching valve to a predetermined opening at this timing, and then The engine exhaust system according to claim 2 or 3, wherein the flow path switching valve is set to the open position at a timing when the output of the two air-fuel ratio sensor switches to stoichiometric.   5. The engine exhaust system according to claim 4, wherein the predetermined opening is made different in accordance with an output of the fourth air-fuel ratio sensor when the exhaust is flowing through the bypass flow path. The delay means is configured so that the second air-fuel ratio sensor output is in a rich state and the open from the request output means when the exhaust is allowed to flow only through the bypass flow path in response to the closing request from the request output means. When a request is issued, an air-fuel ratio leaning process is performed, and this opening request is given to the flow path switching valve until the air-fuel ratio leaning process switches the second air-fuel ratio sensor output from rich to stoichiometric. The engine exhaust device according to claim 1, wherein the engine exhaust device is delayed. A third air-fuel ratio sensor interposed upstream of the bypass catalyst;
A fourth air-fuel ratio sensor interposed downstream of the bypass catalyst,
The engine according to claim 6, wherein the leaning amount in the air-fuel ratio leaning process is made different according to the output of the fourth air-fuel ratio sensor when the exhaust is flowing through the bypass flow path. Exhaust system. The flow path switching valve flows the exhaust only through the bypass flow path when in the closed position, and flows the exhaust through the main flow path when in the open position,
The delay means advances the application of the opening request to the flow path switching valve until the air-fuel ratio leaning timing, opens the flow path switching valve to a predetermined opening at this timing, and then 8. The engine exhaust system according to claim 7, wherein the flow path switching valve is set to the open position at a timing when the output of the two air-fuel ratio sensor switches to stoichiometric.   9. The engine exhaust system according to claim 8, wherein the predetermined opening is made different according to an output of the fourth air-fuel ratio sensor when the exhaust is flowing through the bypass flow path.

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