JP4844534B2 - Exhaust gas purification apparatus and method for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas purification apparatus and method for an internal combustion engine, and is particularly suitable for determining whether or not an oxidation catalyst has deteriorated.

Exhaust gas that captures or adsorbs harmful components contained in the exhaust gas or incorporates a detoxifying catalyst device in the exhaust passage of the internal combustion engine to minimize the environmental impact on the exhaust gas emitted from the internal combustion engine Purification devices are known. For example, Patent Document 1 discloses an exhaust gas purification apparatus using an oxidation catalyst, and Patent Document 2 discloses an exhaust gas purification apparatus using an NO _x catalyst.

The catalyst incorporated in such an exhaust purification device is exposed to a high temperature, the element deteriorates with time, and the catalytic function is lowered. For this reason, it is necessary to periodically perform a deterioration diagnosis of the catalyst and replace it with a new one as necessary. In Patent Document 1, post-injection is performed after main fuel injection performed near the top dead center of the compression stroke of the engine to increase unburned fuel in the exhaust, and deterioration of the oxidation catalyst is caused based on the accompanying temperature change of the oxidation catalyst. I try to make a diagnosis. In Patent Document 2, a larger amount of reducing agent than usual is added to the catalyst, and the deterioration diagnosis of the NO _x catalyst is performed based on the temperature rise of the catalyst generated thereby.

JP 2001-263048 A JP 2001-59413 A

  In the catalyst deterioration diagnosis method disclosed in Patent Document 1 or Patent Document 2, since a large amount of fuel or reducing agent is supplied to the catalyst, a part of the fuel or reducing agent passes through the catalyst as it is, Although it is only at the time of diagnosis of catalyst deterioration, there is a possibility that harmful components contained in the exhaust gas after passing through the catalyst will increase.

  An object of the present invention is to provide an exhaust purification device for an internal combustion engine and a method thereof in consideration of preventing an increase in harmful components contained in exhaust discharged into the atmosphere when determining whether or not an oxidation catalyst has deteriorated. It is in.

  According to a first aspect of the present invention, an oxidation catalyst incorporated in the middle of an exhaust passage of an internal combustion engine, a fuel addition valve for adding fuel to an exhaust passage upstream of the oxidation catalyst, and the oxidation catalyst And an exhaust gas purification device for an internal combustion engine, which incorporates an exhaust gas temperature sensor for detecting the exhaust gas temperature in the downstream exhaust gas passage, one end of which communicates with the exhaust gas passage downstream of the exhaust gas temperature sensor and the internal combustion engine. An exhaust return passage whose other end communicates with the intake passage, one end communicates with an exhaust passage downstream of one end of the exhaust return passage, and an exhaust passage upstream of the fuel addition position by the fuel addition valve. A bypass passage whose ends communicate with each other, a diversion ratio adjusting means for adjusting a ratio of exhaust from the internal combustion engine guided to the bypass passage and the oxidation catalyst, one end of the exhaust return passage, and one end of the bypass passage A passage switching means for switching between opening and closing of the exhaust passage and the exhaust return passage, and a control means for controlling the operation of the passage switching means, the fuel addition valve, and the diversion ratio adjusting means. Is.

  In the present invention, when determining whether or not the oxidation catalyst has deteriorated, the passage switching means is operated in accordance with a command from the control means to close the exhaust passage between one end of the exhaust return passage and one end of the bypass passage, and to return the exhaust. Open the passage. Further, the ratio of the exhaust gas from the internal combustion engine that is guided to the oxidation catalyst by opening the bypass passage is reduced. Further, fuel is added into the exhaust passage from the fuel addition valve. As a result, part of the exhaust from the internal combustion engine passes through the oxidation catalyst and is returned to the intake passage of the internal combustion engine by the exhaust return passage. In this state, the presence or absence of deterioration of the oxidation catalyst is determined based on the exhaust temperature detected by the exhaust temperature sensor. When it is not necessary to determine whether or not the oxidation catalyst has deteriorated, the passage switching means is operated to open the exhaust passage between one end of the exhaust return passage and one end of the bypass passage and close the exhaust return passage. Further, the bypass passage is closed to guide all exhaust from the internal combustion engine to the oxidation catalyst. In this case, the operation of the fuel addition valve is stopped, and no fuel is added into the exhaust passage.

In the exhaust gas purification apparatus for an internal combustion engine according to the first aspect of the present invention, the NO _x catalyst incorporated in the middle of the exhaust passage downstream of the one end of the bypass passage, and between the NO _x catalyst and one end of the bypass passage And a reducing agent addition valve for adding a reducing agent to the exhaust passage.

  A PM catalyst incorporated in the middle of the exhaust passage between one end of the exhaust return passage and the attachment position of the exhaust temperature sensor can further be provided.

  In the second aspect of the present invention, fuel is added to the exhaust passage upstream of the oxidation catalyst incorporated in the middle of the exhaust passage of the internal combustion engine, and the exhaust passage downstream of the oxidation catalyst that rises as a result is added. An exhaust gas purification method for an internal combustion engine that determines whether or not the oxidation catalyst has deteriorated based on an exhaust gas temperature, wherein during the addition of fuel to the exhaust passage, one of exhaust gases in an exhaust passage upstream of the fuel addition position. And a step of bypassing the exhaust gas to the exhaust passage downstream of the exhaust temperature detection position and a step of returning the exhaust gas added with fuel and passing through the oxidation catalyst to the intake passage of the internal combustion engine. Is.

  In the present invention, when determining whether or not the oxidation catalyst has deteriorated, only a part of the exhaust from the internal combustion engine is guided to the oxidation catalyst, and the exhaust that has passed through the oxidation catalyst is returned to the intake passage of the internal combustion engine. It will be.

In the exhaust purification method of the second embodiment according internal combustion engine of the present invention may further comprise the step of directing the exhaust gas to bypass the NO _X catalyst.

  The method may further include detecting the temperature of the exhaust gas that has been added with fuel and passed through the oxidation catalyst, and determining whether the oxidation catalyst has deteriorated based on the detected exhaust gas temperature.

  The method may further comprise directing all exhaust from the internal combustion engine to the oxidation catalyst during the non-addition of fuel to the exhaust passage.

  According to the present invention, during the addition of fuel to the exhaust passage, a part of the exhaust in the exhaust passage upstream from the fuel addition position is bypassed to the exhaust passage downstream from the exhaust temperature detection position. Since the exhaust gas that has been added and passed through the oxidation catalyst is returned to the intake passage of the internal combustion engine, the temperature of the exhaust gas that has been added with fuel and passed through the oxidation catalyst is detected, and based on the detected exhaust gas temperature, The presence or absence of deterioration can be determined. In addition, by introducing exhaust gas at a flow rate at which the reaction of the oxidation catalyst sufficiently proceeds to the oxidation catalyst, it is possible to prevent a problem that unreacted exhaust gas passes through the oxidation catalyst. Moreover, while determining whether the oxidation catalyst has deteriorated, it is possible to avoid a problem that harmful components contained in the added fuel are discharged into the atmosphere. Furthermore, since a part of the exhaust is led to the oxidation catalyst, the amount of fuel added can be reduced, and the amount of harmful components in the exhaust that has passed through the oxidation catalyst can be reduced absolutely. Become.

  When all the exhaust from the internal combustion engine is led to the oxidation catalyst while no fuel is added to the exhaust passage, harmful components contained in the exhaust can be reliably captured and the exhaust can be purified.

When guiding the exhaust gas to bypass the NO _X catalyst, the exhaust gas flowing through the bypass passage from the internal combustion engine when determining the presence or absence of degradation of the oxidation catalyst leads to the NO _X catalyst, that for purifying reliably exhaust it can.

  When a PM catalyst incorporated in the middle of the exhaust passage between one end of the exhaust return passage and the exhaust temperature sensor mounting position is provided, the exhaust gas that has passed through the oxidation catalyst when judging the presence or absence of deterioration of the oxidation catalyst The PM can be returned to the intake passage side while being captured by the PM catalyst, and adverse effects on the internal combustion engine can be reduced.

  An embodiment in which an exhaust gas purification apparatus for an internal combustion engine according to the present invention is applied to a vehicle equipped with a compression ignition internal combustion engine will be described in detail with reference to FIGS. Needless to say, the present invention is not limited to such an embodiment but can be applied to any other technique belonging to the spirit of the present invention.

  The concept of the engine system in this embodiment is shown in FIG. 1, and the control block in this engine system is shown in FIG. The engine 10 in this embodiment is a compression ignition type multi-cylinder internal combustion engine that spontaneously ignites by directly injecting light oil as fuel into the combustion chamber 12 in a compressed state from the fuel injection valve 11. Due to these characteristics, a single cylinder internal combustion engine may be used. The engine 10 includes an exhaust gas recirculation (EGR) device (not shown) that guides a part of the exhaust gas flowing in the exhaust passage 13 to the intake passage 14 and the combustion chamber 12 using the kinetic energy of the exhaust gas flowing in the exhaust passage 13. A turbocharger (not shown) for supercharging is installed.

  The cylinder head 17 formed with the intake port 15 and the exhaust port 16 respectively facing the combustion chamber 12 has a valve mechanism (not shown) including an intake valve 18 that opens and closes the intake port 15 and an exhaust valve 19 that opens and closes the exhaust port 16. It has been incorporated. The cylinder head 17 is provided with a fuel injection valve 11 that faces the center of the upper end of the combustion chamber 12 so as to be sandwiched between the intake valve 18 and the exhaust valve 19. The fuel injection amount and injection timing from the fuel injection valve 11 are controlled via an injection valve drive control unit 21 incorporated in the ECU 20. The valve operating mechanism in the present embodiment can change the opening / closing timings of the intake valve 18 and the exhaust valve 19 according to the operating state of the engine 10, but these opening / closing timings may be fixed. .

  The intake pipe 22 is connected to the cylinder head 17 so as to communicate with the intake port 15 and defines the intake passage 14 together with the intake port 15. An air filter (not shown) for removing dust contained in the atmosphere and guiding it to the intake passage 14 is provided on the upstream end side of the intake pipe 22 in the middle of a surge tank (not shown).

In the middle of the exhaust pipe 23 that is connected to the cylinder head 17 so as to communicate with the exhaust port 16 and defines the exhaust passage 13 together with the exhaust port 16, mainly to oxidize, that is, burn, unburned gas contained in the exhaust. an oxidation catalyst 24, DPF for harmless to capture particles contained in the exhaust (D iesel P articulate F ilter) , i.e. a PM catalyst 25 in the present invention, thereby detoxifying NO _X components in the exhaust and NO _X catalyst 26 for are incorporated in series in this order from the upstream side of the exhaust pipe 23. A fuel addition valve 27 for adding fuel into the exhaust passage 13 is provided in the middle of the exhaust pipe 23 upstream of the oxidation catalyst 24 when the deterioration of the oxidation catalyst 24 is diagnosed or when the PM catalyst 25 is regenerated. The amount and timing of addition of fuel from the fuel addition valve 27 are controlled via a fuel addition valve drive control unit 28 incorporated in the ECU 20. Further, in the middle of the exhaust pipe 23 between the PM catalyst 25 and the NO _x catalyst 26, there is a reducing agent addition valve 29 for adding a reducing agent for the NO _x catalyst 26, for example, an aqueous urea solution, into the exhaust passage 13. The amount of reducing agent added from the reducing agent addition valve 29 is controlled through a reducing agent addition valve drive control unit 30 incorporated in the ECU 20.

  The other end of the bypass pipe 31 having one end joined to the exhaust pipe 23 upstream of the fuel addition valve 27 is joined to the exhaust pipe 23 between the PM catalyst 25 and the reducing agent addition valve 29. The bypass pipe 31 has an upstream end communicating with the exhaust passage 13 upstream of the fuel addition valve 27 and a downstream end communicating with the exhaust passage 13 between the PM catalyst 25 and the reducing agent addition valve 29. A passage 32 is defined. Further, the other end of the exhaust return pipe 33 whose one end is joined to the intake pipe 22 on the downstream side of the surge tank (not shown) is joined to the exhaust pipe 23 between the PM catalyst 25 and the other end of the bypass pipe 31. Yes. The exhaust return pipe 33 has a downstream end communicating with the intake passage 14 downstream of the surge tank and an upstream end within the exhaust passage 13 downstream of the PM catalyst 25 and upstream of the downstream end of the bypass passage 32. Defines an exhaust return passage 34 that communicates with each other.

  At the upstream end of the bypass passage 32, the bypass passage 32 can be completely closed, and a part of the exhaust from the engine 10 can be led into the bypass passage 32 and the rest can be led to the oxidation catalyst 24 side. And an actuator 36 for driving the diversion valve 35 is incorporated. When the deterioration diagnosis of the oxidation catalyst 24 is performed, the flow dividing valve 35 is driven to the deterioration determination position to guide a part (for example, 80%) of the exhaust from the engine 10 into the bypass passage 32 and the remaining (for example, 20%) is oxidized. Lead to the catalyst 24 side. On the other hand, when the deterioration diagnosis of the oxidation catalyst 24 is not performed, the diversion valve 35 is driven to the steady operation position, the bypass passage 32 is completely closed, and all exhaust from the engine 10 is directed to the oxidation catalyst 24 side. It comes to lead. Such an operation of the diversion valve 35 is controlled by the diversion valve drive control unit 37 incorporated in the ECU 20 via the actuator 36. That is, the diversion valve 35 and the actuator 36 described above together with the diversion valve drive control unit 37 constitute a main part of the diversion ratio adjusting means in the present invention.

Further, at the connection portion between the exhaust return pipe 33 and the exhaust pipe 23, the opening and closing of the exhaust return passage 34 and the opening and closing of the exhaust passage 13 downstream of the connection portion between the exhaust return pipe 33 and the exhaust pipe 23 are simultaneously performed. An open / close switching valve 38 for switching is provided together with the actuator 39. When the deterioration diagnosis of the oxidation catalyst 24 is performed, the open / close switching valve 38 is driven to the deterioration determination position to open the exhaust return passage 34 and at the same time the exhaust passage 13 downstream of the connection portion between the exhaust return pipe 33 and the exhaust pipe 23. Close completely. As a result, the exhaust gas that has passed through the PM catalyst 25 can be returned into the intake passage 14 via the exhaust return passage 34, and the exhaust gas that has passed through the bypass passage 32 is guided to the NO _X catalyst 26. When the deterioration diagnosis of the oxidation catalyst 24 is not performed, the open / close switching valve 38 is driven to the steady operation position, and the exhaust return passage 34 is completely closed, and at the same time, from the connection portion between the exhaust return pipe 33 and the exhaust pipe 23. Also opens the exhaust passage 13 on the downstream side. Thereby, the exhaust gas that has passed through the PM catalyst 25 can be guided to the NO _x catalyst 26 side. The operation of the open / close switching valve 38 is controlled by the switching valve drive control unit 40 incorporated in the ECU 20 via the actuator 39. That is, the above-described opening / closing switching valve 38 and actuator 39 together with the switching valve drive control unit 40 constitute the main part of the passage switching means in the present invention.

As described above, when the shunt valve 35 is driven to the deterioration determination position, the exhaust gas that has passed through the oxidation catalyst 24 and the PM catalyst 25 is returned to the intake passage 14 side. It is possible to avoid the problem that the exhaust gas that has passed through is directly discharged into the atmosphere. Moreover, since the exhaust passing through the bypass passage 32 is guided in the NO _X catalyst 26, and finally the exhaust gas discharged into the atmosphere, since the passing through at least NO _X catalyst 26, harmful in the exhaust Ingredients can be minimized.

In a normal operation state in which deterioration diagnosis of the oxidation catalyst 24 is not performed, that is, in a steady operation state, the intake air supplied from the intake pipe 22 into the combustion chamber 12 is injected from the fuel injection valve 11 into the combustion chamber 12. And form a mixture. State and, in general burned by spontaneous ignition by compression top dead center immediately before the piston 41, the exhaust gas generated thereby passes through the oxidation catalyst 24 and PM catalyst 25 and NO _X catalyst 26 in turn, which has been purified And discharged into the atmosphere.

  In the present embodiment, the fuel setting unit 43 incorporated in the operation state determination unit 42 of the ECU 20 grasps the operation state of the engine 10 and the vehicle on which the engine 10 is mounted, and the fuel injection amount from the fuel injection valve 11 and Set the injection timing. The operation of the fuel injection valve 11 is controlled by the injection valve drive control unit 21 so that the injection amount and injection timing set by the fuel setting unit 43 can be obtained. In order to execute such control, various sensors described below, that is, an accelerator opening sensor 44, an air flow meter 45, a crank angle sensor 46, and the like are provided. The accelerator opening sensor 44 detects the amount of depression of the accelerator pedal 47 operated by the driver, and outputs this to the driving state determination unit 42 of the ECU 20. The air flow meter 45 is provided in the middle of the intake passage 14 upstream of one end of the exhaust return pipe 33, detects the amount of intake air flowing in the intake passage 14 toward the combustion chamber 12 of the engine 10, and this is detected by the ECU 20. Is output to the driving state determination unit 42. The crank angle sensor 46 attached to the cylinder block 48 detects the rotational phase of the crankshaft 50 to which the piston 41 is connected via the connecting rod 49 and outputs this to the operating state determination unit 42 of the ECU 20.

  The ECU 20 includes a microcomputer including a CPU, ROM, RAM, A / D converter, input / output interface, and the like (not shown). The ECU 20 performs predetermined arithmetic processing based on detection signals from the sensors 44 and 46 and the air flow meter 45 described above so that the engine 10 can be smoothly operated. The operation of the fuel injection valve 11, the fuel addition valve 27, the reducing agent addition valve 29, the diversion valve 35, the open / close switching valve 38, and the like is controlled according to a preset program. Further, in order to determine whether or not the oxidation catalyst 24 has deteriorated, the operating state determination unit 42 of the ECU 20 in this embodiment includes a catalyst deterioration determination unit 51. Further, an exhaust temperature sensor 52 that detects the exhaust temperature in the exhaust passage 13 downstream of the oxidation catalyst 24 and upstream of the PM catalyst 25 and outputs the detected exhaust temperature to the ECU 20 is provided. Further, a display drive control unit 53 for outputting the determination result is incorporated in the ECU 20.

  The driving state determination unit 42 determines whether or not the vehicle is in a predetermined driving state based on detection information from the sensors 44 and 46 described above. The predetermined operating state in the present embodiment is idling or warm-up operation in which the accelerator opening and the vehicle speed are 0, or steady operation in a low load region (the accelerator opening, the vehicle speed, and the engine speed are substantially constant). It is.

The catalyst deterioration determination unit 51 determines whether or not the oxidation catalyst 24 has deteriorated based on the detection signal from the exhaust temperature sensor 52 only when the driving state determination unit 42 determines that the vehicle is in a predetermined driving state. The determination of the presence or absence of this deterioration is performed only once after the ignition key switch 54 is turned on and the engine 10 is started, and before the ignition key switch 54 is turned off and the engine 10 is stopped. However, the presence or absence of deterioration may be continuously determined after the engine 10 is started. The method for determining the presence or absence of the deterioration of the oxidation catalyst 24 is well known in, for example, Patent Document 1 and is not the gist of the present invention, and therefore a detailed description thereof is omitted, but generally from the fuel addition valve 27. When the fuel is added to the exhaust gas, the fact that the exhaust gas temperature detected by the exhaust gas temperature sensor 52 differs between the state in which the oxidation catalyst 24 is deteriorated and the state in which the fuel is not deteriorated is utilized. In the present embodiment, it is determined that the exhaust gas temperature T _n detected when the addition of fuel by the exhaust temperature sensor 52 is of less than the threshold T _R, the oxidation catalyst 24 has deteriorated.

  The display drive control unit 53 is for notifying the driver that the oxidation catalyst 24 is deteriorated based on the determination result of the catalyst deterioration determination unit 51, and a warning display 55 for that purpose is provided in the vehicle interior (not shown). Is provided. The warning indicator 55 may be any device that can alert the driver of the vehicle using hearing or vision.

  A procedure for determining whether or not the oxidation catalyst 24 has deteriorated in this embodiment will be described with reference to FIG. 3. First, in step S11, it is determined whether or not a deterioration determination flag is set. Initially, since the deterioration determination flag is not set, the process proceeds to step S12 to determine whether or not the vehicle is in a predetermined driving state. Here, if it is determined that the vehicle is not in a predetermined operating state, that is, is not in an operating state in which the deterioration of the oxidation catalyst 24 can be determined, the processing after step S11 is continued again.

  When it is determined in step S12 that the vehicle is in a predetermined driving state, that is, in a driving state in which deterioration can be determined, the flow proceeds to step S13 and the deterioration of the oxidation catalyst 24 is diagnosed. Is driven to the deterioration determination position, a part of the exhaust from the engine 10 is guided into the bypass passage 32, and the rest is guided to the oxidation catalyst 24 side. At the same time, the open / close position switching valve 38 is driven to the deterioration determination position, so that the exhaust return passage 34 is fully opened and the exhaust passage 13 downstream of the connection portion between the exhaust return pipe 33 and the exhaust pipe 23 is fully closed. In step S14, fuel is added to the exhaust gas from the fuel addition valve 27, and the temperature of the oxidation catalyst 24 is raised.

Exhaust gas temperature T _n after passing through the oxidation catalyst 24 detected by the exhaust temperature sensor 52 is compared to a threshold T _R at step S15, if this is less than the threshold T _R, the oxidation catalyst 24 has deteriorated judge. In this case, the process proceeds to step S16 to drive the warning indicator 55, and then proceeds to step S17.

  When the warning indicator 55 is driven in step S16, the occupant can recognize that the oxidation catalyst 24 has deteriorated and should be replaced, so the occupant can replace the oxidation catalyst 24. For example, the vehicle may be carried into a maintenance shop and the oxidation catalyst 24 may be replaced as necessary.

On the other hand, the exhaust gas temperature T _n at S16 in step a threshold T _R above, that is, when the oxidation catalyst 24 is judged not to degrade, the process proceeds to step S17. In step S17, the diversion valve 35 is driven to the steady operation position, the bypass passage 32 is completely closed, and all exhaust from the engine 10 is guided to the oxidation catalyst 24 side. At the same time, the open / close switching valve 38 is also driven to the steady operation position, the exhaust return passage 34 is fully closed, and the exhaust passage 13 downstream of the connecting portion between the exhaust return pipe 33 and the exhaust pipe 23 is fully opened, thereby the PM catalyst. The exhaust gas having passed through 25 is guided to the NO _x catalyst 26. Then, after setting the deterioration determination flag in step S18, the steps after S11 are repeated again.

  If it is determined in step S11 that the deterioration determination flag is set, that is, it is determined that the deterioration determination of the oxidation catalyst 24 has been performed, the process proceeds to step S19, and whether or not the ignition key switch 54 is turned off. Determine. If it is determined that the ignition key switch 54 is not off, that is, the engine 10 is not stopped, the processing after step S11 is continued again without doing anything.

  If it is determined in step S19 that the ignition key switch 54 is OFF, the process proceeds to step S20, the deterioration determination flag is reset, and this flow ends. That is, when the determination routine of S13 to S15 is performed even once after the ignition key switch 54 is turned on, the determination routine of S13 to S15 is not repeated until the ignition key switch 54 is turned off. Yes.

  In the embodiment described above, the exhaust temperature sensor 52 is arranged on the downstream side of the oxidation catalyst 24. However, the exhaust temperature sensor 52 is also incorporated in the exhaust passage 13 further upstream, that is, between the fuel addition valve 27 and the oxidation catalyst 24. The presence or absence of deterioration of the oxidation catalyst 24 can be determined with higher accuracy based on the outputs from the two exhaust temperature sensors 52. It should be noted that any known method can be adopted as the method for determining the presence or absence of the deterioration of the oxidation catalyst 24 instead of the main point of the present invention.

  It should be noted that the present invention should be construed only from the matters described in the claims, and in the above-described embodiment, all the changes and modifications included in the concept of the present invention are other than those described. Is possible. That is, all matters in the above-described embodiment are not intended to limit the present invention, and include any configuration not directly related to the present invention. To get.

It is a conceptual diagram showing schematic structure of one Embodiment of the exhaust gas purification device of the internal combustion engine by this invention. FIG. 2 is a control block diagram of the embodiment shown in FIG. 1. It is a flowchart showing the procedure for determining the presence or absence of deterioration of the oxidation catalyst in embodiment shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Engine 11 Fuel injection valve 12 Combustion chamber 13 Exhaust passage 14 Intake passage 15 Intake port 16 Exhaust port 17 Cylinder head 18 Intake valve 19 Exhaust valve 20 ECU
21 exhaust pipe 24 oxidation catalyst 25 injector driving control unit 22 intake pipe 23 PM catalyst 26 NO _X catalyst 27 fuel addition valve 28 fuel addition valve drive control unit 29 reducing agent addition valve 30 reducing agent addition valve drive control section 31 bypass pipe 32 Bypass passage 33 Exhaust return pipe 34 Exhaust return passage 35 Split valve 36 Actuator 37 Split valve drive control unit 38 Open / close switching valve 39 Actuator 40 Switching valve drive control unit 41 Piston 42 Operating state determination unit 43 Fuel setting unit 44 Accelerator opening sensor 45 Air flow meter 46 Crank angle sensor 47 Accelerator pedal 48 Cylinder block 49 Connecting rod 50 Crankshaft 51 Catalyst degradation determination unit 52 Exhaust temperature sensor 53 Display drive control unit 54 Ignition key switch 55 Warning indicator _Tn detection exhaust temperature T _R degradation determination for Value

Claims (6)

An oxidation catalyst incorporated in the exhaust passage of the internal combustion engine, a fuel addition valve for adding fuel to the exhaust passage upstream of the oxidation catalyst, and an exhaust temperature of the exhaust passage downstream of the oxidation catalyst An exhaust gas purification device for an internal combustion engine, which incorporates an exhaust temperature sensor for detecting
An exhaust return passage having one end communicating with the exhaust passage downstream of the exhaust temperature sensor and the other end communicating with the intake passage of the internal combustion engine;
A bypass passage having one end communicating with an exhaust passage downstream from one end of the exhaust return passage and the other end communicating with an exhaust passage upstream of the fuel addition position by the fuel addition valve;
A diversion ratio adjusting means for adjusting the ratio of the exhaust gas from the internal combustion engine guided to the bypass passage and the oxidation catalyst;
Passage switching means for switching between opening and closing of the exhaust passage and the exhaust return passage between one end of the exhaust return passage and one end of the bypass passage;
An exhaust emission control device for an internal combustion engine, comprising: a control means for controlling the operation of the passage switching means, the fuel addition valve, and the diversion ratio adjusting means. Reducing agent for adding a reducing agent to the exhaust passage between the NO _X catalyst incorporated in the middle, and one end of the bypass passage and the NO _X catalyst on the downstream side of the exhaust passage than the one end of the bypass passage The exhaust purification device for an internal combustion engine according to claim 1, further comprising a valve.   3. The internal combustion engine according to claim 1, further comprising a PM catalyst incorporated in the middle of the exhaust passage between one end of the exhaust return passage and a position where the exhaust temperature sensor is attached. Exhaust purification device. Fuel is added to the exhaust passage upstream of the oxidation catalyst incorporated in the exhaust passage of the internal combustion engine, and the oxidation catalyst is heated based on the exhaust gas temperature in the exhaust passage downstream of the oxidation catalyst. An exhaust gas purification method for an internal combustion engine for determining the presence or absence of deterioration,
Bypassing a portion of the exhaust passage upstream of the fuel addition position to the exhaust passage downstream of the exhaust temperature detection position during addition of the fuel to the exhaust passage; and
An exhaust gas purification method for an internal combustion engine comprising the step of returning the exhaust gas added with fuel and passing through the oxidation catalyst to the intake passage of the internal combustion engine. Exhaust gas purifying method for an internal combustion engine according to claim 4, characterized in that the exhaust gas is bypassed equipped further steps leading to the NO _X catalyst.   6. The exhaust gas purification method for an internal combustion engine according to claim 4 or 5, further comprising a step of guiding all exhaust gas from the internal combustion engine to the oxidation catalyst during non-addition of fuel to the exhaust passage.

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