JP2008280901A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To control an operating valve so that unpurified exhaust gas is prevented from being emitted into the atmosphere due to delay of the operating valve when recovering fuel cut, in an exhaust emission control device for an internal combustion engine employing a catalyst bypass system. <P>SOLUTION: The opening of the operating valve is controlled according to engine speed so that a part of exhaust gas passes through an upstream catalyst in the catalyst bypass system, when not in the condition of operation at high speed and high load but in the condition of deceleration fuel cut and in the condition in which a downstream catalyst in the catalyst bypass system is not yet activated. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to an exhaust purification device that purifies exhaust gas of an internal combustion engine using a catalyst, and more particularly to an apparatus in which a plurality of catalysts are installed in series in an exhaust passage.

As an exhaust purification device for an internal combustion engine, two catalysts are installed in the exhaust passage in series, and a bypass passage that bypasses the upstream catalyst, and an on-off valve that adjusts the flow rate of the exhaust gas flowing into the bypass passage and the catalyst side passage If the catalyst temperature is lower than the predetermined temperature, exhaust gas is sent to the upstream catalyst to activate the upstream catalyst at an early stage.If the catalyst temperature is higher than the predetermined temperature, the upstream catalyst is bypassed via the bypass and exhausted directly to the downstream catalyst. That suppresses thermal deterioration of the upstream catalyst is known.

In this configuration, a technique related to control of the on-off valve at the time of fuel cut is known (for example, Patent Document 1). More specifically, when exhaust gas (air) at high temperature and high oxygen concentration flows into the catalyst, the catalyst becomes abnormally hot due to the reaction heat generated by the reaction of unreacted unreacted HC and CO with oxygen. In order to prevent this, the on-off valve is controlled so that the exhaust gas (air) bypasses the catalyst when shifting to fuel cut. In addition, in order to suppress thermal deterioration, a technique such as cooling the catalyst is also known.

In Patent Document 2, in addition to the technique disclosed in Patent Document 1, in order to desorb oxygen excessively stored in the downstream catalyst, fuel according to the cumulative amount of exhaust gas flowing into the catalyst at the time of fuel cut A technique for supplying a rich fuel at the time of cutting return is shown.

Patent Document 3 discloses a technique for controlling the on-off valve so that inflowing exhaust gas (air) bypasses the upstream catalyst in order to maintain the activation temperature of the upstream catalyst when the fuel is cut. That is, if exhaust gas (air) having a low temperature flows into the upstream catalyst after the remaining unreacted HC and CO have reacted, the upstream catalyst may be cooled and fall below the activation temperature. Because there is. In order to maintain the activation temperature of the upstream catalyst, the temperature of the exhaust gas is detected directly or indirectly to control the opening degree of the on-off valve.

JP-A-5-312031 JP 2006-144594 A JP-A-6-346724 JP 2000-282849 A

Incidentally, for example, Patent Document 4 discloses that an operation delay occurs when the on-off valve is switched. More specifically, when the fuel supply resumption switching control is performed in which the on / off valve is switched at the time of fuel cut return to switch the exhaust gas flow path from the bypass path to the catalyst side path, a delay occurs in the switching operation of the on / off valve. As a result, if the exhaust gas after combustion of the fuel unintentionally flows into the bypass passage and the downstream catalyst is not activated and the exhaust gas cannot be purified in the downstream catalyst, the unpurified exhaust gas is There is a risk of being discharged into the atmosphere.

The present invention has been made in view of the above problems, and an object of the present invention is to purify the exhaust gas of an internal combustion engine that controls the exhaust gas purification device so that the exhaust gas can be more suitably purified at the time of fuel cut recovery. Is to provide a device.

In order to achieve the above object, an exhaust gas purification apparatus for an internal combustion engine according to claim 1 is provided with an upstream catalyst side passage which is an exhaust passage having an upstream catalyst and a downstream catalyst, and an upstream catalyst disposed on an exhaust gas exhaust passage. And a bypass passage that bypasses the upstream catalyst and an on-off valve that adjusts the flow rate of exhaust gas flowing into the upstream catalyst, and controls the on-off valve when fuel supply is resumed after the deceleration fuel cut. In an exhaust gas purification apparatus for an internal combustion engine that performs switching control when resuming fuel supply so that the exhaust gas passes through the upstream catalyst side passage, according to the engine speed during the period when switching control when resuming fuel supply is performed from the start of deceleration fuel cut And controlling the flow rate of the exhaust gas flowing into the upstream catalyst.

An exhaust gas purification apparatus for an internal combustion engine according to claim 2 is the exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein when the downstream catalyst is not activated, switching control at the time of restart of fuel supply is performed from the start of the deceleration fuel cut. During this period, the flow rate of the exhaust gas flowing into the upstream catalyst is controlled according to the engine speed.

An exhaust gas purification apparatus for an internal combustion engine according to claim 2 is the exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein control is performed so that the flow rate of exhaust gas flowing into the upstream catalyst decreases as the engine speed increases. The engine speed is controlled such that the flow rate of the exhaust gas flowing into the upstream catalyst increases as the engine speed approaches the deceleration fuel cut threshold value Ne, which is the engine speed at which the engine speed returns from the deceleration fuel cut.

In the invention of claim 1, when the fuel supply is resumed after returning from the deceleration fuel cut, the exhaust gas passes through the downstream catalyst, and the unpurified exhaust gas is prevented from being discharged into the atmosphere. Exhaust gas can be purified more suitably.

In the invention of claim 2, when the fuel supply is resumed after returning from the deceleration fuel cut, the exhaust gas passes through the non-activated downstream catalyst, and the unpurified exhaust gas is discharged into the atmosphere. And the exhaust gas can be purified more suitably.

In the invention according to claim 3, when it is foreseen that the switching control at the time of resumption of fuel supply is not performed within a sufficiently short time, or when the downstream catalyst is in an activated state, the upstream catalyst is thermally deteriorated. It is possible to prevent the upstream catalyst from being cooled and below the activation temperature. On the other hand, if it can be predicted that the switching control at the time of resuming the fuel supply will be performed within a sufficiently short time, by reducing the delay in the operation of the on-off valve that occurs when the switching control at the time of restarting the fuel supply is performed, Exhaust gas can be purified more suitably.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the accompanying drawings. In order to facilitate understanding of the description, the same components in the drawings are denoted by the same reference numerals as much as possible, and redundant description will be omitted.

<Embodiment 1>
FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine to which an exhaust gas purification apparatus according to the present invention is applied and its intake and exhaust system.

The internal combustion engine shown in FIG. 1 is a four-cycle four-cylinder internal combustion engine 1. An intake branch pipe 2 is connected to the internal combustion engine 1, and each branch pipe of the intake branch pipe 2 communicates with a combustion chamber of each cylinder through an intake port (not shown).

The intake branch pipe 2 is connected to a surge tank 3, and the surge tank 3 is connected to an air cleaner box 5 via an intake pipe 4. The intake pipe 4 is provided with a throttle valve 6 that adjusts the flow rate of intake air flowing through the intake pipe 4 in conjunction with an accelerator pedal (not shown). The throttle valve 6 has an electric valve according to the opening of the throttle valve 6. A throttle position sensor 7 for outputting a signal is attached.

An air flow meter 8 that outputs an electric signal corresponding to the mass of intake air flowing in the intake pipe 4 is attached to the intake pipe 4, and an electric signal corresponding to the pressure in the surge tank 3 is output to the surge tank 3. A vacuum sensor 24 is attached.

In addition, fuel injection valves 10 a, 10 b, 10 c, and 10 d (hereinafter collectively referred to as fuel injection valves 10) are attached to the branch pipes of the intake branch pipe 2, and these fuel injection valves 10 are connected to a fuel distribution pipe 9. Connected with. The fuel distribution pipe 9 distributes fuel pumped from a fuel pump (not shown) to each fuel injection valve 10.

Each fuel injection valve 10 is provided with drive circuits 11a, 11b, 11c, and 11d (hereinafter collectively referred to as drive circuit 11), and when a drive current from these drive circuits 11 is applied to the fuel injection valve 10, The fuel injection valve 10 is opened and the fuel supplied from the fuel distribution pipe 9 is injected toward the intake port of each cylinder.

On the other hand, an exhaust branch pipe 12 is connected to the internal combustion engine 1, and each branch pipe of the exhaust branch pipe 12 communicates with a combustion chamber of each cylinder via an exhaust port (not shown). The exhaust branch pipe 12 is connected to an exhaust pipe 13, and this exhaust pipe 13 is connected downstream to a muffler (not shown).

An upstream catalyst 16, which is a three-way catalyst as a catalyst for purifying exhaust gas according to the present invention, is provided on the upstream catalyst side passage 15 in the middle of the exhaust pipe 13. The upstream catalyst side passage 15 has an exhaust inflow portion 15a and an exhaust outflow portion 15b, and the upstream catalyst 16 is located between the exhaust inflow portion 15a and the exhaust outflow portion 15b. This upstream catalyst 16 is composed of a ceramic carrier made of cordierite formed in a lattice shape so as to have a plurality of through holes along the exhaust flow direction, and a catalyst layer coated on the surface of the ceramic carrier, For example, a platinum-rhodium (Pt-Rh) noble metal catalyst material is supported on the surface of porous alumina (Al2O3) having a large number of pores.

The upstream catalyst 16 is activated when the temperature is equal to or higher than a predetermined temperature. When the air-fuel ratio of the inflowing exhaust gas is in the vicinity of the stoichiometric air-fuel ratio, the hydrocarbon (HC) and carbon monoxide (CO) contained in the exhaust gas are converted into oxygen O 2 in the exhaust gas. At the same time, NOx in the exhaust is reacted with HC and CO in the exhaust to be reduced to H2O, CO, and N2.

An upstream air-fuel ratio sensor 19 that outputs an electrical signal corresponding to the air-fuel ratio of the exhaust flowing into the upstream catalyst 16 is attached to the exhaust pipe 13 upstream of the upstream catalyst 16, and the exhaust pipe 13 downstream of the upstream catalyst 16 is connected to the exhaust pipe 13. Is provided with a downstream air-fuel ratio sensor 20 that outputs an electrical signal corresponding to the air-fuel ratio of the exhaust gas flowing out from the upstream catalyst 16.

The upstream air-fuel ratio sensor 19 and the downstream air-fuel ratio sensor 20 are, for example, a solid electrolyte portion obtained by firing zirconia (ZrO2) into a cylindrical shape, an outer platinum electrode that covers the outer surface of the solid electrolyte portion, and an inner surface of the solid electrolyte portion. When the voltage is applied between the electrodes, the oxygen concentration in the exhaust gas (when richer than the stoichiometric air-fuel ratio, the unburned gas component This sensor outputs a current having a value proportional to (concentration).

Downstream of the upstream catalyst 16, a downstream catalyst 14, which is a three-way catalyst for the purpose of exhaust purification, is provided in the same manner as the upstream catalyst 16. A bypass path 22 that bypasses the upstream catalyst 16 is connected to the exhaust pipe 13.

FIG. 4 is an enlarged view of the vicinity of the catalyst in FIG. The bypass passage 22 is provided with an opening / closing valve 17 for opening and closing the passage. The on-off valve 17 is composed of a stepper motor or the like, and an actuator 18 that opens and closes the on-off valve 17 according to the magnitude of the applied current is attached.

The on-off valve 17 illustrated in FIG. 4 is a butterfly valve, but may be a switching valve, or may be provided at the position of the exhaust inflow portion 15a or the exhaust outflow portion 15b. Although an actuator is exemplified as means for opening and closing the on-off valve 17, the power may be a hydraulic type, a mechanically switching device such as an electric motor or a gear, or a negative pressure actuator or a hydraulic actuator.

The arrangement of the exhaust inflow portion 15a and the exhaust outflow portion 15b of the upstream catalyst side passage 15 is such that the exhaust pressure in the vicinity of the exhaust inflow portion 15a and the exhaust pressure in the vicinity of the exhaust outflow portion 15b when the on-off valve 17 is fully open. The difference is set to 2 KPa or less, preferably 1 KPa or less.

The internal combustion engine 1 includes a crank position sensor 21 that outputs a pulse signal each time a crankshaft (not shown) rotates by a predetermined angle (for example, 30 degrees), and the temperature of cooling water that flows in a water jacket (not shown) of the internal combustion engine 1. A water temperature sensor 22 that outputs an electrical signal corresponding to the above is attached.

The crank position sensor 21, the water temperature sensor 22, the throttle position sensor 7, the air flow meter 8, the vacuum sensor 24, the upstream air-fuel ratio sensor 19, the downstream air-fuel ratio sensor 20, and the temperature sensor 40 are respectively connected via electric wiring. It is connected to an engine control electronic control unit (ECU) 25 so that the output signals of the sensors are input to the ECU 25.

The ECU 25 determines the operating state of the internal combustion engine 1 using the output signals from the sensors as parameters, and performs various controls such as fuel injection control, ignition timing control, and opening / closing control of the on-off valve 17 in accordance with the operating state.

2, the ECU 25 includes a CPU 27, a ROM 28, a RAM 29, a backup RAM 30, an input port 31, and an output port 32, which are connected to each other by a bidirectional bus 26. A connected A / D converter 33 is provided.

The input port 31 uses output signals from the crank position sensor 21 and the like as input signals, and transmits those output signals to the CPU 27 and the RAM 29. Further, the input port 31 outputs output signals from the throttle position sensor 7, the air flow meter 8, the upstream air-fuel ratio sensor 19, the downstream air-fuel ratio sensor 20, the water temperature sensor 22, the vacuum sensor 24, etc. via the A / D converter 33. The output signals are sent to the CPU 27 and RAM 29 as input signals.

The output port 32 transmits a control signal output from the CPU 27 to the actuator 18 and the drive circuit 11. The ROM 28 is a fuel injection amount control routine for determining the amount of fuel to be injected from each fuel injection valve 10, an air-fuel ratio feedback control routine for performing air-fuel ratio feedback control of the fuel injection amount, and fuel injection of the fuel injection valve 10. Application programs such as a fuel injection timing control routine for determining the timing, a flow path switching control routine for controlling the on-off valve 17, and various control maps are stored.

The above-mentioned various control maps are, for example, a fuel injection amount control map showing the relationship between the operating state of the internal combustion engine 1 and the fuel injection amount, and a fuel injection timing control showing the relationship between the operating state of the internal combustion engine 1 and the fuel injection timing. The map is an activity determination control map showing the relationship between the temperature of the cooling water at the start of the internal combustion engine and the time taken from the start to the activation of the upstream catalyst 16 (hereinafter referred to as catalyst activation time).

The RAM 29 stores the calculation results of the CPU 27 such as the engine speed calculated from the output signals from the sensors and the output signal of the crank position sensor 21. The output signal from each sensor, the calculation result of the CPU 27, and the like are rewritten to the latest data every time the crank position sensor 21 outputs a signal.

The backup RAM 30 is a non-volatile memory that can store data even after the operation of the internal combustion engine 1 is stopped. The CPU 27 operates in accordance with an application program stored in the ROM 28, determines the operating state of the internal combustion engine 1 from the output signals of the sensors stored in the RAM 29, and determines the fuel injection amount and the fuel injection from the operating state and each control map. The timing, the opening / closing timing of the on-off valve 17 and the like are calculated. Then, the CPU 27 controls the drive circuit 11 and the actuator 18 according to the calculated fuel injection amount, fuel injection timing, and opening / closing timing of the on-off valve 17.

For example, when executing the fuel injection control, the CPU 27 operates according to the fuel injection amount control routine, and determines the fuel injection amount (TAU) according to the following equation.
TAU = TP * FWL * (FAF + FG) * [FASE + FAE + FOTP + FDE (D)] * FFC + TAUV
(TP: Basic injection amount, FWL: Warm-up increase, FAF: Air-fuel ratio feedback correction coefficient, FG: Air-fuel ratio learning coefficient, FASE: Increase after start, FAE: Acceleration increase, FOTP: OTP increase, FDE (D): Deceleration (Increase (decrease), FFC: Correction coefficient at fuel cut return, TAUV: Invalid injection time)
At that time, the CPU 27 determines the operating state of the internal combustion engine using the output signal values of various sensors as parameters, and based on the determined engine operating state and the fuel injection amount control map in the ROM 28, the basic injection amount (TP) described above. ), Warm-up increase (FWL), post-start increase (FASE), acceleration increase (FAE), OTP increase (FOTP), deceleration increase (FDE (D)), fuel cut recovery factor (FFC), invalid injection time Calculate (TAUV) etc.

Here, the exhaust purification performance of a general catalyst will be described. As an index indicating the exhaust purification performance of the catalyst,
"Exhaust gas purification performance" = "Catalyst conversion rate" x "Gas flow rate through the catalyst"
think of. This represents the amount of gas (g) converted by the catalyst. FIG. 5 shows the exhaust purification performance of the upstream catalyst 16 and the downstream catalyst 14 with respect to the exhaust gas flow rate flowing to the upstream catalyst 16 side. Since the gas at a substantially constant flow rate flows through the downstream catalyst 14, the exhaust purification performance is substantially constant. However, since the exhaust gas is converted on the upstream catalyst 16 side when the flow rate of the gas flowing through the upstream catalyst 16 increases, the conversion efficiency of the downstream catalyst 14 decreases and the exhaust purification performance tends to decrease slightly. On the other hand, the exhaust gas purification performance on the upstream catalyst 16 side becomes larger as the flow rate increases because the flow rate becomes dominant. Accordingly, the exhaust purification performance of the upstream catalyst 16 and the downstream catalyst 14 is reversed at a certain flow rate.

Therefore, by determining the catalyst mainly performing exhaust purification based on the gas flow rate flowing into the upstream catalyst 16, and performing air-fuel ratio feedback control based on the signal of the air-fuel ratio sensor provided immediately upstream of the catalyst. The catalyst can be used effectively.

Next, an activation determination unit that determines whether the downstream catalyst 14 is in an active state or an inactive state will be described. The temperature sensor 40 is installed in the downstream catalyst 14, the catalyst temperature is measured, and it is determined whether or not the activation temperature has been reached, thereby determining the active state.

FIG. 3 is an area diagram of the fuel control in this embodiment. The vertical axis represents the load (intake pipe negative pressure), the horizontal axis represents the engine speed, and the air-fuel ratio lean setting feedback (lean F / B). Each zone of high load / high rotation increase, idle increase, deceleration fuel cut and over-rotation fuel cut (over-rev fuel cut) is shown.

In the lean F / B zone, the air-fuel ratio is made larger than the stoichiometric air-fuel ratio, and the set value is determined according to the engine speed and load. In this lean F / B zone, the basic fuel injection amount is set based on the engine speed and the intake air amount, various corrections based on the water temperature, etc. are added to it, and feedback correction based on the oxygen concentration signal is added. To the final injection amount. Then, a control pulse corresponding to this final injection amount is applied to the fuel injection valve 5, whereby the air-fuel ratio of the engine 1 is controlled to a predetermined value. Further, in the high load / high rotation increase zone and the idle increase zone, the feedback control is stopped and the required fuel increase is performed. In the deceleration fuel cut zone and the overrev fuel cut zone (for example, the engine speed is 7000 rpm or more), the fuel is increased. Supply is stopped. Further, although not shown in the above region diagram, the fuel supply is also stopped when the vehicle speed exceeds a predetermined value (for example, 180 km / h).

In this embodiment, the on-off valve 17 is closed when the temperature of the upstream catalyst 16 is lower than the heat-resistant temperature, and the on-off valve 17 is opened when the upstream catalyst 16 becomes equal to or higher than the heat-resistant temperature. I try to control it. Further, the open / close valve 17 is opened in the deceleration fuel cut zone or the overrev fuel cut zone or in a region where the vehicle speed exceeds a predetermined value.

Here, a specific description of the control of the on-off valve will be given using the flowchart of FIG. In step (denoted as S in the figure, the same applies hereinafter) 1, it is determined whether or not the vehicle is in a high speed and high load operation state. That is, when the value of the throttle position sensor 7 that outputs an electric signal corresponding to the opening degree of the throttle valve 6 is equal to or greater than a predetermined value and the engine speed is equal to or greater than the predetermined value, the driving state is high speed and high load. judge. If it is determined that the vehicle is operating at a high speed and a high load, this routine is terminated.

In step 2, it is determined whether or not a deceleration fuel cut state is present. That is, it is determined from the map in FIG. 3 based on the value of the throttle position sensor 7 (intake pipe negative pressure) and the engine speed whether the fuel is in a deceleration fuel cut state. If it is determined that the vehicle is not in the deceleration fuel cut state, this routine is terminated. If it is determined that the fuel is being decelerated, the process proceeds to step 3.

In Step 3, it is determined whether or not the downstream catalyst 14 is in an active state by the above method. When it is determined that the downstream catalyst 14 is in the active state, the routine is terminated.

If it is determined in step 3 that the downstream catalyst 14 is in an inactive state, the process proceeds to step 4 where the opening degree of the on-off valve 17 is set based on the detected engine speed as shown by the solid line in FIG. . As the engine speed that returns from the deceleration fuel cut (referred to as the deceleration fuel cut threshold value Ne) is approached, the opening of the on-off valve 17 that has been fully opened is gradually reduced, and the exhaust gas passes through the bypass passage 22. Reduce the flow rate.

The opening degree of the on-off valve 17 will be described. By defining the opening when the exhaust gas flowing through the bypass line is the largest at the fully open position as 100 and opening the opening when the smallest fully closed as 1 the opening and closing valve opening corresponds to the flow rate through the bypass path. And define it. The opening degree of the on-off valve and the flow rate flowing through the bypass path have the relationship shown in FIG. For example, when the opening degree is 50, the exhaust gas partially passes through the upstream catalyst side passage 15 and the exhaust gas passes through the bypass passage 22. When a butterfly valve is used as the on-off valve, it is as shown in FIG. 9 (c), which is an intermediate state between FIG. 9 (a), which is fully opened, and FIG. 9 (b), which is fully closed. When a switching valve is used instead of the butterfly valve, FIG. 10 (b) is half open.

When returning from deceleration fuel cut, before the exhaust gas burned by the fuel supply reaches the on-off valve, the on-off valve is controlled so that the exhaust gas passes through the upstream catalyst side passage. Ideally, the exhaust gas should be purified by the upstream catalyst by switching control. However, as described above, there is a risk that the on-off valve may be delayed in operation. The exhaust gas cannot be guided to the upstream catalyst, and there is a possibility that the exhaust gas may pass through the non-activated downstream catalyst and be exhausted to the atmosphere without being purified.

Therefore, if the control is performed as shown in FIG. 7, the delay in the operation of the on-off valve can be kept small when returning to the deceleration fuel cut. For this reason, the exhaust gas generated when the deceleration fuel cut is restored can be purified by the upstream catalyst, and the unpurified exhaust gas can be prevented from being discharged into the atmosphere.

If exhaust gas (air) with a high oxygen concentration flows into the upstream catalyst when deceleration fuel cut is performed, the reaction heat generated by the reaction of the remaining unreacted HC, CO and oxygen causes upstream The catalyst may become abnormally hot and the upstream catalyst may be thermally degraded. Further, after the remaining unreacted HC and CO have reacted, there is a problem that the activation temperature of the upstream catalyst cannot be maintained due to the flow of exhaust gas (air) having a low temperature. For this reason, it is desirable to prevent the exhaust gas (air) from flowing into the upstream catalyst as much as possible. When switching control is performed when the fuel supply is resumed when the fuel is decelerated and the downstream catalyst is in the activated state, the downstream catalyst is sufficient even if a problem due to the delay of the on-off valve occurs. Exhaust gas can be purified. Therefore, the exhaust valve (air) is not guided to the upstream catalyst, and the on-off valve is fully opened so that all the exhaust gas (air) flows into the bypass passage. That is, the opening is adjusted as shown by the broken line in FIG.

Here, it will be described that the above control is performed and the opening degree of the on-off valve is set as shown by the solid line in FIG. 8 according to the engine speed. When the engine speed is close to the deceleration fuel cut threshold value Ne, it can be regarded as a period during which it is predicted that the fuel supply restart switching control for returning from the deceleration fuel cut will be performed within a sufficiently close time. In this case, as described above, the opening degree of the on-off valve is reduced by giving priority to the problem of operation delay of the on-off valve. On the other hand, when the engine speed is sufficiently larger than the deceleration fuel cut threshold value Ne, it can be foreseen that the fixed period will not return from the deceleration fuel cut and the switching control at the time of resumption of fuel supply is not performed. . In this case, since the exhaust gas (air) is not desired to flow into the upstream catalyst as much as possible, the on-off valve is opened with a sufficiently large opening. By measuring the engine speed and comparing it with the deceleration fuel cut threshold value Ne, it is possible to more reliably foresee whether it is immediately before the fuel supply restart switching control is performed, and the range in which the thermal deterioration and temperature decrease of the upstream catalyst can be tolerated Can be stopped.

The relationship between the engine speed and the opening shown by the solid line in FIG. 8 is such that the opening / closing valve is closed at the deceleration fuel cut threshold value Ne so that the opening increases as the engine speed increases. Let it be a convex nonlinear graph. This is to prevent exhaust gas (air) from flowing into the upstream catalyst as much as possible as described above. It can be foreseen whether it is immediately before the fuel supply resumption switching control is performed, and it is possible to more suitably realize that the thermal deterioration and temperature decrease of the upstream catalyst are allowed.

As described above, in the present embodiment, when the engine speed is measured and it can be predicted that the switching control at the time of restarting the fuel supply will not be performed within a sufficiently short time, or when the downstream catalyst is in the activated state, It is foreseen that switching control at the time of resuming fuel supply will be performed within a sufficiently short time by measuring the engine speed while preventing the catalyst from thermal degradation and preventing the upstream catalyst from cooling down below the activation temperature. If possible, exhaust gas can be purified more appropriately by reducing the operation delay of the on-off valve in a timely and accurate manner.

The figure which shows schematic structure of the internal combustion engine to which the exhaust gas purification apparatus which concerns on this invention is applied. Block diagram showing internal configuration of ECU Region diagram of fuel control in one embodiment of the present invention Diagram explaining the operation of the on-off valve Comparison of exhaust purification performance of each catalyst with respect to the exhaust flow rate flowing into the upstream catalyst The figure explaining the relationship between the opening / closing valve opening and the exhaust flow rate flowing into the upstream catalyst Control flowchart of Embodiment 1 Relationship between engine speed Ne and opening / closing valve opening Diagram showing the opening of the on-off valve (butterfly valve) (a) fully open, (b) fully closed, (c) half open Figure showing the opening of the on-off valve (switching valve) (a) fully open, (b) half open

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ...... Internal combustion engine 13 ... Exhaust pipe 13a ... Upstream exhaust pipe 13b ... Downstream exhaust pipe 14 ... Downstream catalyst 15 ... Upstream catalyst side passage 15a ... Exhaust inflow part 15b ... Exhaust outlet 16 ... Upstream catalyst 17 ... On-off valve 18 ... Actuator 19 ... Upstream air-fuel ratio sensor 20 ... Downstream air-fuel ratio sensor 22 ... Bypass path 40 ... Temperature sensor

Claims (3)

An upstream catalyst and a downstream catalyst disposed on an exhaust passage of exhaust gas discharged from the internal combustion engine;
An upstream catalyst side passage which is an exhaust passage having the upstream catalyst;
A bypass that bypasses the upstream catalyst;
An on-off valve for adjusting the flow rate of the exhaust gas flowing into the upstream catalyst,
When the fuel supply is resumed after the deceleration fuel cut,
In an exhaust gas purification apparatus for an internal combustion engine that performs switching control at the time of resumption of fuel supply that changes the exhaust gas to pass through the upstream catalyst side passage by controlling the on-off valve,
An internal combustion engine that performs upstream catalyst flow rate control for controlling a flow rate of the exhaust gas flowing into the upstream catalyst according to an engine speed during a period in which the fuel supply resumption switching control is performed from the start of deceleration fuel cut Exhaust purification equipment. An activation determination means for determining that the downstream catalyst is not activated;
The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the upstream catalyst flow rate control is performed when it is determined that the downstream catalyst is not activated. Control so that the flow rate of the exhaust gas flowing into the upstream catalyst decreases as the engine speed increases,
2. The upstream catalyst flow rate control is performed, wherein the flow rate of the exhaust gas flowing into the upstream catalyst is increased as the engine speed approaches the engine speed at which the engine returns from the deceleration fuel cut. 3. An exhaust emission control device for an internal combustion engine according to claim 2.