JP2007321614A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device of an internal combustion engine capable of adding a proper quantity of unburnt fuel component to a catalyst in fuel adding control. <P>SOLUTION: An electronic control device estimates the catalyst bed temperature from a detecting value of the exhaust temperature (Step S210), and calculates the switching air volume for determining the necessity of correcting an adding quantity (Step S220). A determination is made on whether or not the detected actual air volume of suction air is larger than the switching air volume (Step S240). When the actual air volume exceeds the switching air volume, since a determination can be made that an operation state of the internal combustion engine is put in a white smoke easily generating state, a correction is made for reducing the adding quantity of fuel added from an adding valve (Step S260). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exhaust purification device for an internal combustion engine that performs fuel addition control for adding an unburned fuel component to a catalyst provided in an exhaust system of the internal combustion engine.

  2. Description of the Related Art Conventionally, as an exhaust purification device applied to an internal combustion engine such as a vehicle-mounted diesel engine, an exhaust purification device having a catalyst for purifying exhaust components such as nitrogen oxide (NOx) is known. In such an exhaust purification device, fuel addition control is performed to add an unburned fuel component as a reducing agent to a catalyst that has stored NOx, so that the unburned fuel component is oxidized in the exhaust or on the catalyst. While the catalyst bed temperature is raised and activated by the generated heat, NOx is reduced to N2, CO2, NO2, etc., thereby purifying exhaust components. Such fuel addition control is performed after a fuel injection from a fuel injection valve that contributes to the driving of the internal combustion engine, for example, during the exhaust stroke, by adding fuel from an addition valve provided upstream of the exhaust system catalyst. This is implemented by a method of adding fuel by post injection or the like, which is fuel injection in The amount of unburned fuel component added is controlled so that the catalyst is in a reducing atmosphere.

By the way, in an internal combustion engine equipped with such an exhaust purification device, when the internal combustion engine is in an accelerated state, the amount of fuel used for combustion is increased and the air-fuel ratio of the mixture of the fuel and air becomes richer than usual. Therefore, the unburned fuel components such as hydrocarbons discharged in accordance with the combustion become larger than usual. If unburned fuel components are added during such acceleration, the amount of unburned fuel components in the exhaust becomes excessive, so a large amount of unburned fuel components will be discharged without being sufficiently oxidized, A large amount of white smoke may be generated in the exhaust. In view of this, there has been proposed an exhaust emission control device that performs control to reduce the amount of unburned fuel component added or to stop adding unburned fuel component in an acceleration state of the internal combustion engine (see, for example, Patent Document 1). . By controlling the exhaust gas purification device in this way, it is possible to suppress the supply of excessive unburned fuel components in the accelerated state and suppress the generation of white smoke.
JP-A-2005-83351

  By the way, in the exhaust purification apparatus as described above, since the addition of the unburned fuel component is stopped in the acceleration state, there is a case where there is a margin in the supply of the unburned fuel component, and the temperature rise of the catalyst bed temperature is delayed. For example, the amount of unburned fuel component added may not be optimal. Further, when the catalyst bed temperature of the catalyst is low, the exhaust gas purification ability by the catalyst is lowered, so that unburned fuel components may be discharged without being sufficiently oxidized, and white smoke is generated in the exhaust gas. There is a fear. Furthermore, if the unburned fuel component is unnecessarily added in such a state that the exhaust purification capability is lowered, there is a problem that the fuel consumption is deteriorated.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an exhaust purification device for an internal combustion engine that can add an appropriate amount of unburned fuel components to a catalyst during fuel addition control. It is to provide.

  In order to achieve the above object, an invention according to claim 1 is an exhaust purification device for an internal combustion engine that performs fuel addition control for adding an unburned fuel component to a catalyst provided in an exhaust system of the internal combustion engine. Detection means for detecting the amount of air taken into the internal combustion engine, estimation means for estimating the catalyst bed temperature of the catalyst, and the fuel based on the estimated catalyst bed temperature and the detected amount of air. The gist of the invention is that it comprises correction means for correcting the addition amount of the unburned fuel component by the addition control.

  According to this configuration, in order to correct the addition amount of the unburned fuel component by the fuel addition control based on the estimated catalyst bed temperature and the detected actual air amount, purification is performed according to the exhaust purification capacity of the catalyst. The amount of unburned fuel component added can be corrected from the relationship between the amount of exhaust air that can be performed and the amount of exhaust air that actually passes through the catalyst. For this reason, it is possible to avoid a situation in which the amount of air exceeding the exhaust purification capacity of the catalyst is supplied and the unburned fuel component becomes excessive. In other words, the air-fuel ratio is richer than during normal operation, such as when an unburned fuel component is added in a large amount in a state where the catalyst bed temperature is low and the exhaust gas purification capacity is reduced, or when the internal combustion engine is accelerated when the actual air amount increases. It can suppress that an unburned fuel component is added in the state which becomes. Thereby, it can suppress that a lot of unburned fuel components are discharged | emitted outside without being fully oxidized, and generation | occurrence | production of the white smoke in exhaust_gas | exhaustion can be suppressed.

  In addition, the amount of unburned fuel component added in accordance with the exhaust gas purification capacity of the catalyst can be set by the above correction, so that the added amount becomes too small and the catalyst temperature rises too late, or the added amount becomes too large and insignificant. It is possible to suppress consumption of fuel as necessary, and it is possible to suppress deterioration of fuel consumption while purifying exhaust gas efficiently.

  According to a second aspect of the present invention, in the exhaust gas purification apparatus for an internal combustion engine according to the first aspect, the correction means is a predetermined in which the detected air amount is set according to the estimated catalyst bed temperature. The gist of the correction is to reduce the amount of unburned fuel component added by the fuel addition control when the amount of air is exceeded.

  According to this configuration, when the detected actual air amount exceeds a predetermined air amount set according to the estimated catalyst bed temperature, the amount of unburned fuel component added by the fuel addition control is reduced. to correct. When performing normal fuel addition control, the exhaust purification capacity differs depending on the catalyst used, but there is a region where the generation of white smoke in the exhaust is significant in the relationship between the actual air amount and the catalyst bed temperature. The region is located on the side where the actual air amount increases and the catalyst bed temperature decreases. For this reason, if the boundary of the region is regarded as a predetermined air amount set according to the catalyst bed temperature, it is determined that the possibility of white smoke is increased when the actual air amount exceeds the predetermined air amount. Can do. Accordingly, when the actual air amount exceeds a predetermined air amount set in accordance with the catalyst bed temperature, generation of white smoke can be suitably suppressed by performing correction to reduce the amount of unburned fuel component added. . Further, it is possible to suppress unnecessary consumption of fuel due to the reduction of the addition amount, and it is possible to suppress deterioration of fuel consumption.

  The gist of the invention according to claim 3 is that, in the exhaust gas purification apparatus for an internal combustion engine according to claim 2, the predetermined air amount is set to become smaller as the catalyst bed temperature becomes lower.

  According to this configuration, the predetermined air amount compared with the actual air amount is set so as to become smaller as the catalyst bed temperature becomes lower. Therefore, the predetermined air amount is set in a manner commensurate with the exhaust purification capacity of the catalyst. Can do. For this reason, when the catalyst bed temperature is lowered and the exhaust purification capacity is reduced, the amount of fuel added can be reduced by reducing the predetermined air amount serving as a threshold when correction for reducing the amount of unburned fuel component added is performed. Fuel addition control that suppresses an excessive state and appropriately suppresses the generation of white smoke can be performed.

  According to a fourth aspect of the present invention, in the exhaust gas purification apparatus for an internal combustion engine according to any one of the first to third aspects, the correction means includes a fuel injection amount and an engine rotational speed that contribute to driving of the internal combustion engine. The gist is to correct the addition amount by correcting an addition amount map in which the addition amount of the unburned fuel component corresponding to the above is mapped.

  According to the same configuration, the correction of the addition amount of the unburned fuel component is performed by adding an addition amount map obtained by mapping the addition amount of the unburned fuel component corresponding to the fuel injection amount contributing to the driving of the internal combustion engine and the engine rotational speed. Since the correction is performed by correction, the correction of the addition amount corresponding to the operation state of the internal combustion engine can be easily performed by using such a map. The correction using such a map includes, for example, a basic addition amount map in which the addition amount is set based on the engine speed and the fuel injection amount, and a correction in which the addition amount is set to be smaller than the basic addition amount map. The addition amount map is prepared, and when the actual air amount is relatively small, the basic addition amount map is used, and when the actual air amount is relatively large, the addition amount is obtained using the correction addition amount map. Such a method can be adopted.

  According to a fifth aspect of the present invention, in the exhaust gas purification apparatus for an internal combustion engine according to any one of the first to fourth aspects, the estimation unit is configured to detect a catalyst bed temperature based on a detection result of the exhaust temperature of the internal combustion engine. The gist of this is to estimate.

  According to this configuration, since the catalyst bed temperature is estimated based on the detection result of the exhaust temperature of the internal combustion engine, the catalyst bed temperature can be estimated with high accuracy. The catalyst bed temperature may be estimated from a value detected by another sensor, or an engine operating state quantity such as an engine speed or an engine load (for example, a fuel injection quantity).

  The invention according to claim 6 is the exhaust gas purification apparatus for an internal combustion engine according to claim 5, characterized in that the exhaust temperature is an exhaust temperature detected on the exhaust downstream side of the catalyst.

  According to this configuration, since the catalyst bed temperature is estimated based on the exhaust gas temperature detected on the exhaust gas downstream side of the catalyst, the catalyst bed temperature can be estimated more accurately by detecting the temperature of the exhaust gas that has passed through the catalyst. . For example, when detecting the exhaust gas temperature upstream of the catalyst, the catalyst bed temperature may not be estimated accurately because the temperature on the downstream side of the catalyst has not risen. There is a risk that the addition amount of the unburned fuel component based on the above relationship cannot be properly corrected. In this regard, if the catalyst bed temperature is estimated from the exhaust gas temperature downstream of the exhaust gas of the catalyst, it is possible to accurately determine the state in which the generation of white smoke becomes significant in relation to the actual air amount. The amount can be suitably corrected.

Hereinafter, an embodiment embodying an exhaust emission control device for an internal combustion engine according to the present invention will be described with reference to FIGS.
FIG. 1 is a configuration diagram of an in-vehicle internal combustion engine equipped with an exhaust purification device according to the present invention. The internal combustion engine 10 includes a combustion chamber 12 formed in each cylinder 11, an intake passage 13 for sending intake air to the combustion chamber 12, and an exhaust passage 14 for exhausting exhaust gas generated by combustion in the combustion chamber 12. ing.

  The intake passage 13 is provided with an intake throttle valve 15 whose passage area is variable, and the amount of air taken into the combustion chamber 12 is adjusted by controlling the opening degree. The air sucked into the intake passage 13 is mixed with the fuel injected from the fuel injection valve 16 provided in the combustion chamber 12 to become an air-fuel mixture, and burns in the combustion chamber 12. The intake passage 13 is provided with an air flow meter 31 for detecting the amount of air taken into the combustion chamber 12. In the exhaust passage 14, a NOx catalytic converter 17, a PM filter 18, and an oxidation catalytic converter 19 are provided in this order from the upstream side. Exhaust gas generated by combustion in the combustion chamber 12 is fed into the NOx catalytic converter 17, the PM filter 18, and the oxidation catalytic converter 19.

  The NOx catalytic converter 17 carries an NOx storage reduction catalyst. The NOx catalyst stores NOx in the exhaust when the oxygen concentration of the exhaust is high, and releases the stored NOx when the oxygen concentration of the exhaust is low. When NOx is released, the NOx catalyst reduces and purifies NOx in a reducing atmosphere in which an unburned fuel component serving as a reducing agent is present in the surrounding area.

  The PM filter 18 is made of a porous material, whereby PM in the exhaust gas is collected. Similarly to the NOx catalyst converter 17, the PM filter 18 also carries a storage reduction type NOx catalyst, and purifies NOx in the exhaust gas. Further, the collected PM is burned (oxidized) and removed by a reaction triggered by the NOx catalyst.

  The oxidation catalyst converter 19 carries an oxidation catalyst. This oxidation catalyst oxidizes and purifies hydrocarbons and carbon monoxide in the exhaust. In addition, on the exhaust upstream side and the exhaust downstream side of the PM filter 18 in the exhaust passage 14, an inlet gas temperature sensor 32 that detects an inlet gas temperature that is the temperature of the exhaust gas flowing into the PM filter 18, and after passing through the PM filter 18. An outgas temperature sensor 33 for detecting an outgas temperature that is the temperature of the exhaust gas is provided. The exhaust passage 14 is provided with a differential pressure sensor 34 that detects a differential pressure between the exhaust upstream side of the PM filter 18 and the exhaust downstream side thereof. Further, an oxygen sensor 35 for detecting the oxygen concentration in the exhaust gas is provided between the PM filter 18 and the oxidation catalyst converter 19.

  Further, the internal combustion engine 10 includes an exhaust gas recirculation device that recirculates a part of the exhaust gas to the air in the intake passage 13. The exhaust gas recirculation device includes an exhaust gas recirculation passage 20 that communicates the exhaust passage 14 and the intake passage 13. The exhaust gas recirculation passage 20 is provided with an adjustment valve 21 that adjusts the flow rate of the exhaust gas passing therethrough.

  The fuel injection valve 16 provided in the combustion chamber 12 is connected to a common rail 23 via a high-pressure fuel supply pipe 22. High pressure fuel is supplied to the common rail 23 through a fuel pump 24. The pressure of the high-pressure fuel in the common rail 23 is detected by a rail pressure sensor 25 attached to the common rail 23. Further, low pressure fuel is supplied from the fuel pump 24 to the addition valve 27 through the low pressure fuel supply pipe 26. The addition valve 27 is disposed at an exhaust port of the specific cylinder 11 and adds fuel as an unburned fuel component into the exhaust.

  Various controls of the internal combustion engine 10 are performed by the electronic control unit 40. The electronic control unit 40 includes a CPU that executes various arithmetic processes related to engine control, a ROM that stores programs and data necessary for the control, a RAM that temporarily stores arithmetic results of the CPU, and signals between the outside The input / output port for inputting / outputting is provided.

  In addition to the sensors described above, the input port of the electronic control unit 40 includes an NE sensor 36 that detects the engine speed, an accelerator sensor 37 that detects the accelerator operation amount, and an intake throttle sensor that detects the opening of the intake throttle valve 15. 38 etc. are connected. The output port of the electronic control unit 40 is connected to drive circuits such as an intake throttle valve 15, a regulating valve 21, a fuel injection valve 16, a fuel pump 24, and an addition valve 27.

  The electronic control unit 40 outputs a command signal to the drive circuit of each device connected to the output port according to the engine operating state grasped from the detection signal input from each sensor. Thus, control of the opening degree of the intake throttle valve 15, exhaust gas recirculation control based on the opening degree control of the adjusting valve 21, control of the fuel injection amount from the fuel injection valve 16, fuel injection timing, fuel injection pressure, etc. Various controls are performed by the electronic control unit 40.

  Further, as part of such control, the electronic control device 40 performs fuel addition control for adding fuel to the exhaust from the addition valve 27. This fuel addition control is performed in the following controls, that is, NOx reduction control, PM regeneration control, and S poisoning recovery control.

  The NOx reduction control is performed to reduce and release NOx stored in the NOx catalyst of the NOx catalytic converter 17 and the PM filter 18 to N2, CO2, NO2, and the like. At the time of NOx reduction control, fuel is intermittently added from the addition valve 27 to the exhaust after a certain period of time so that the exhaust around the NOx catalyst is in a state where the oxygen concentration is low and the unburned fuel component is high. Spikes are performed intermittently. Thus, NOx release from the NOx catalyst and reduction thereof are promoted to reduce and purify NOx.

  The PM regeneration control is performed to eliminate clogging of the PM filter 18 by burning and discharging the PM collected by the PM filter 18. During PM regeneration control, fuel addition from the addition valve 27 to the exhaust gas is continuously repeated to oxidize the fuel added in the exhaust gas or on the catalyst, and the catalyst bed temperature is raised by the heat generated by the oxidation reaction. In this way, PM is burned.

  The S poison recovery control is performed in order to recover the NOx occlusion ability reduced by the sulfur oxide (SOx) occluded together with NOx in the NOx catalyst. When the S poisoning recovery control is started, first, similarly to the PM regeneration control, the fuel is continuously added from the addition valve 27 to the exhaust so that the catalyst bed temperature is raised. Thereafter, in the same manner as during NOx reduction control, intermittent fuel addition from the addition valve 27 is performed, and intermittent rich spikes are performed to promote the release and reduction of SOx from the NOx catalyst, and store NOx. I am trying to restore my ability.

  As described above, the electronic control unit 40 adds the fuel to the catalyst such as the NOx catalytic converter 17 by the fuel addition control from the addition valve 27 so as to maintain the exhaust purification performance of the internal combustion engine 10. ing.

  By the way, when the fuel addition control as described above is performed, the added fuel may be exhausted through the catalyst without being sufficiently oxidized, and white smoke may be generated in the exhaust gas. FIG. 2 shows a mechanism for generating white smoke during fuel addition control. When the internal combustion engine 10 is accelerated during fuel addition control, the amount of intake air into the combustion chamber 12 increases and the amount of fuel injected from the fuel injection valve 16 increases, so that the air-fuel ratio of the air-fuel mixture becomes richer than usual. (Step S110). Further, if the catalyst bed temperature of the NOx catalytic converter 17 or the like is low during cold operation or the like, the exhaust purification capacity of the catalyst is reduced (step S120). Then, fuel is added from the addition valve 27 during operation of the internal combustion engine 10 in which the intake air amount increases and the catalyst bed temperature decreases in this way (step S130). As a result, the fuel that cannot be reacted with the catalyst passes through the catalyst due to a decrease in the exhaust purification capacity (step S140), and white smoke is generated in the exhaust gas (step S150).

  Here, FIG. 3 shows an example of a map representing the generation state of white smoke with respect to the catalyst bed temperature and the intake air amount. The vertical axis of the figure shows the actual amount of intake air detected from the air flow meter 31, and the horizontal axis shows the exhaust temperature detected by the outgas temperature sensor 33. In FIG. 3, the catalyst bed temperature is estimated from the exhaust gas temperature downstream of the PM filter 18 detected from the outgas temperature sensor 33. When fuel addition control is performed in an arbitrary operating state of the internal combustion engine 10, white smoke is generated in the state indicated by “x” in the figure, and white smoke is not generated in the state indicated by “◯”. Results are obtained. From this result, it can be seen that white smoke is generated in the region Y where the actual air amount is large and the white smoke is not generated in the other region Z with the boundary line X in the figure as the boundary. In addition, since the exhaust purification capacity decreases with a decrease in the catalyst bed temperature, the boundary line X is configured such that the value of the air amount decreases as the catalyst bed temperature decreases. Although the map as shown in FIG. 3 varies depending on the characteristics of the catalyst, the forms of the boundary line X, the region Y, and the region Z are generally common.

  Therefore, the exhaust purification apparatus of the present embodiment performs control for preventing the generation of white smoke based on the relationship between the catalyst bed temperature and the intake air amount as shown in FIG. Specifically, the intake air amount and the catalyst bed temperature are monitored at the time of fuel addition control, and when an operation state in which there is a high possibility of white smoke as shown in region Y of FIG. Corrections are made to reduce the amount of fuel added from

  FIG. 4 shows an addition amount correction routine for determining the final addition amount by executing such correction of the addition amount. This addition amount correction routine is periodically executed by the electronic control unit 40 as a scheduled interruption process at predetermined time intervals during the fuel addition control.

  When the addition amount correction routine is started, the electronic control unit 40 as the estimation means acquires the exhaust temperature on the exhaust downstream side of the PM filter 18 detected from the output gas temperature sensor 33, and from this exhaust temperature, the NOx catalytic converter is obtained. A catalyst bed temperature such as 17 is estimated (step S210). Then, a switching air amount (predetermined air amount) for determining whether the addition amount needs to be corrected is calculated from the estimated catalyst bed temperature (step S220). This switching air amount is used to determine whether the operation state of the internal combustion engine 10 is likely to generate white smoke or is difficult to generate white smoke when normal fuel addition control is performed. This is a threshold value. When the catalyst has the characteristics shown in FIG. 3, the switching air amount is obtained from the boundary line X between the region Y where white smoke is generated and the region Z where white smoke is not generated. For example, when the exhaust temperature is 200 ° C., the switching air amount can be calculated from the intersection with the boundary line X as Ag / s.

  Next, the electronic control unit 40 acquires the actual amount of intake air detected from the air flow meter 31 serving as detection means (step S230). Then, it is determined whether or not the acquired actual air amount is larger than the switching air amount set as described above (step S240). When the actual air amount is equal to or less than the switching air amount (NO in S240), it can be determined that the operating state of the internal combustion engine 10 is in a state where white smoke is difficult to be generated, for example, in the region Z of FIG. The generation of white smoke can be suppressed without correcting the addition amount. Therefore, the electronic control unit 40 obtains the fuel addition amount based on the basic addition amount map that is normally used without correcting the addition amount (step S250).

On the other hand, when the actual air amount exceeds the switching air amount (YES in S240), it can be determined that the operating state of the internal combustion engine 10 is in a state where white smoke is likely to be generated, for example, in the region Y of FIG. For this reason, the electronic control unit 40 as the correction means performs correction so as to reduce the amount of fuel added from the addition valve 27. Specifically, the fuel addition amount is obtained based on a correction addition amount map that is set to have a smaller addition amount than the basic addition amount map (step S260).
Here, the basic addition amount map and the correction addition amount map will be described with reference to FIG. FIG. 5 (a) shows a basic addition amount map, and FIG. 5 (b) shows a corrected addition amount map. As shown in the figure, each map maps the fuel injection amount from the fuel injection valve 16 controlled by the electronic control unit 40 and the addition amount corresponding to the engine rotational speed detected from the NE sensor 36. Is. That is, each map is configured such that the amount of fuel added per time added from the addition valve 27 at predetermined intervals is determined by the fuel injection amount and the engine speed. For example, in the basic addition amount map shown in FIG. 5A, when the engine speed is 2000 rpm and the fuel injection amount is 40 mm ³ / st (stroke), the fuel addition amount per time is Eij (mm ³ ). become.

The addition amount obtained in this way differs between when the basic addition amount map is used and when the correction addition amount map is used, and each addition amount obtained from the same engine speed and fuel injection amount is corrected. The value is set to be smaller when the addition amount map is used. That is, when an arbitrary addition amount Exy (mm ³ ) in the basic addition amount map is compared with an addition amount E′xy (mm ³ ) obtained from the same engine speed and fuel injection amount using the corrected addition amount map. The addition amount E′xy is set to be equal to or less than the addition amount Exy.
Since the basic addition amount map and the correction addition amount map are configured as described above, the addition amount obtained from the correction addition amount map is necessarily reduced from the addition amount obtained from the basic addition amount map. In step S260, the electronic control unit 40 uses the correction addition amount map to correct the fuel addition amount.

  The electronic control unit 40 determines the addition amount thus obtained in step S250 or step S260 as the corrected addition amount (step S270), and corrects the corrected addition amount based on the addition learning value. This is performed (step S280). The addition learning value includes, for example, the amount of deposit deposited on the addition valve 27, and the added amount after correction is corrected by the operating state of the addition valve 27 and the like. Then, the electronic control unit 40 finally determines the amount of fuel added during fuel addition control from the corrected post-correction addition amount (step S290), and ends this routine.

  In this way, the electronic control unit 40 performs correction to reduce the amount of fuel added from the addition valve 27 when the operating state of the internal combustion engine 10 is in a state where there is a high possibility that white smoke will be generated. And by performing fuel addition control based on the addition amount calculated | required by correction | amendment, it suppresses that a fuel slips through a catalyst and is discharged | emitted, and suppresses generation | occurrence | production of white smoke.

According to the exhaust gas purification apparatus for an internal combustion engine of the above embodiment, the following effects can be obtained.
(1) In the above embodiment, the NOx catalyst is used to correct the amount of fuel added from the addition valve 27 by the fuel addition control based on the catalyst bed temperature and the actual air amount based on the map as shown in FIG. The amount of fuel added can be corrected from the relationship between the amount of exhaust air that can be purified in accordance with the exhaust purification capacity of the catalyst such as the converter 17 and the actual amount of air that passes through the catalyst. For this reason, it is possible to suppress an excessive amount of fuel from the addition valve 27 from being sent due to an amount of exhaust that exceeds the exhaust purification capacity of the catalyst such as the NOx catalytic converter 17. Therefore, the air-fuel ratio becomes richer than that during normal operation, such as when a large amount of fuel is added from the addition valve 27 in a state where the catalyst bed temperature is low and the exhaust purification capability is reduced, or when the internal combustion engine 10 is accelerated. It can suppress that fuel is added from the addition valve 27 in a state. Thereby, it can suppress that the added fuel is discharged | emitted from the exhaust passage 14 without being fully oxidized, and generation | occurrence | production of the white smoke in exhaust_gas | exhaustion can be suppressed.

  (2) In the above-described embodiment, the addition amount commensurate with the exhaust purification ability of the catalyst such as the NOx catalytic converter 17 can be set by correcting the addition amount of the fuel. For this reason, it is possible to prevent the addition amount from becoming too small and delaying the temperature rise of the catalyst bed temperature, and the addition amount from becoming excessive and unnecessarily consuming fuel. Deterioration can be suppressed.

  (3) In the above embodiment, when the actual air amount exceeds the switching air amount, correction is performed to reduce the amount of fuel added from the addition valve 27, so that the possibility of white smoke increases. By reducing the addition amount in the state, it is possible to suppress the deterioration of fuel consumption while suppressing the generation of white smoke. Further, since the switching air amount is calculated based on the catalyst bed temperature and the map as shown in FIG. 3, the operating state of the internal combustion engine 10 is in a state where white smoke is likely to be generated or a state where white smoke is difficult to be generated. Can be accurately determined.

  (4) In the above embodiment, the switching air amount is set so as to become smaller as the catalyst bed temperature becomes lower as shown in FIG. 3, so the switching air amount is set in a manner commensurate with the exhaust purification capacity of the catalyst. be able to. For this reason, when the catalyst bed temperature is lowered and the exhaust purification capacity is reduced, the amount of fuel added is suppressed by reducing the switching air amount, so that the generation of white smoke is suitably suppressed. Addition control can be performed.

  (5) In the above embodiment, the correction of the fuel addition amount is performed by using each addition amount map obtained by mapping the addition amount corresponding to the fuel injection amount and the engine rotation speed. Thus, it is possible to correct the addition amount in accordance with the operating state of the internal combustion engine.

  (6) In the above embodiment, the electronic control unit 40 acquires the exhaust gas temperature on the exhaust gas downstream side of the NOx catalytic converter 17 and the PM filter 18 detected by the output gas temperature sensor 33, and the NOx catalytic converter 17 from this exhaust gas temperature. Therefore, the catalyst bed temperature can be accurately estimated by detecting the temperature of the exhaust gas that has passed through the catalyst. For this reason, it is possible to accurately obtain a state in which white smoke is easily generated in relation to the actual air amount, and it is possible to suitably correct the fuel addition amount.

In addition, you may change the said embodiment as follows.
In the above embodiment, when the actual air amount exceeds the switching air amount, correction is performed to reduce the amount of fuel added from the addition valve 27, but the actual air amount is based on the characteristics of the catalyst. Correction may be performed such that the correction amount of the addition amount is changed in accordance with the change in the amount. For example, the correction amount of the addition amount can be changed by a method of variably setting the addition amount of the basic addition amount map according to the change of the actual air amount.

  In the above embodiment, the fuel addition amount is corrected by using the basic addition amount map and the correction addition amount map, but the addition amount may be corrected without using such a map. In addition, the amount of addition may be corrected by taking into account other engine operating state quantities to such a map.

  In the above embodiment, the catalyst bed temperature is estimated from the exhaust gas temperature on the exhaust downstream side of the NOx catalytic converter 17 and the PM filter 18 detected by the output gas temperature sensor 33, but provided on the exhaust upstream side. The catalyst bed temperature may be estimated from the exhaust gas temperature detected by the inlet gas temperature sensor 32. FIG. 6 shows the exhaust temperature detected by the inlet gas temperature sensor 32 on the horizontal axis of the map shown in FIG. As shown in the figure, when the detected value by the inlet gas temperature sensor 32 is used, the region Y ′ where white smoke is generated and the region Z ′ where white smoke is not generated are expressed with the same tendency as in FIG. However, the boundary line X ′ between the region Y ′ and the region Z ′ is unclear. Thus, even if the catalyst bed temperature is estimated from the exhaust gas temperature upstream of the catalyst, the white smoke generation region can be derived with a certain degree of accuracy. However, as shown in FIG. It is preferable to estimate the catalyst bed temperature from the exhaust gas temperature.

  In the above-described embodiment, the catalyst bed temperature is estimated by detecting the exhaust temperature, but the catalyst bed temperature is estimated from the detection values by other sensors, or the engine operation state quantity such as the engine rotation speed and the engine load. You may do it.

  In the above embodiment, fuel addition control is performed by adding fuel from the addition valve 27. However, after fuel injection from the fuel injection valve 16, for example, a post that is fuel injection during the exhaust stroke You may make it implement fuel addition control by injection etc. FIG. Even when fuel addition control is performed by post injection or the like, the present invention can be applied using the same principle. Further, the fuel addition control may be performed by both the addition of the fuel from the addition valve 27 and the post injection from the fuel injection valve 16. In this case, the present invention can be applied to the addition of at least one of these fuels.

1 is a configuration diagram of an in-vehicle internal combustion engine equipped with an exhaust purification device according to the present invention. The chart which shows the mechanism in which white smoke occurs at the time of fuel addition control. The map showing the generation state of white smoke with respect to the catalyst bed temperature and the intake air amount. The flowchart of an addition amount correction routine. (A) is a basic addition amount map, and (b) is a correction addition amount map. The map showing the generation state of white smoke with respect to the catalyst bed temperature and the intake air amount.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 12 ... Combustion chamber, 13 ... Intake passage, 14 ... Exhaust passage, 15 ... Intake throttle valve, 16 ... Fuel injection valve, 17 ... NOx catalytic converter, 18 ... PM filter, 19 ... Oxidation catalytic converter, 27 DESCRIPTION OF SYMBOLS ... Addition valve, 31 ... Air flow meter, 32 ... Incoming gas temperature sensor, 33 ... Outlet gas temperature sensor, 40 ... Electronic control apparatus.

Claims (6)

In an exhaust emission control device for an internal combustion engine that performs fuel addition control for adding an unburned fuel component to a catalyst provided in an exhaust system of the internal combustion engine,
Detecting means for detecting the amount of air taken into the internal combustion engine;
Estimating means for estimating the catalyst bed temperature of the catalyst;
An exhaust emission control device for an internal combustion engine, comprising: correction means for correcting an addition amount of an unburned fuel component by the fuel addition control based on the estimated catalyst bed temperature and the detected air amount. . The exhaust gas purification apparatus for an internal combustion engine according to claim 1,
The correction means reduces the addition amount of the unburned fuel component by the fuel addition control when the detected air amount exceeds a predetermined air amount set according to the estimated catalyst bed temperature. An exhaust emission control device for an internal combustion engine, wherein The exhaust gas purification apparatus for an internal combustion engine according to claim 2,
The exhaust air purifying apparatus for an internal combustion engine, wherein the predetermined air amount is set so as to decrease as the catalyst bed temperature decreases. The exhaust gas purification apparatus for an internal combustion engine according to any one of claims 1 to 3,
The correction means corrects the addition amount by correcting an addition amount map obtained by mapping the addition amount of the unburned fuel component corresponding to the fuel injection amount contributing to driving of the internal combustion engine and the engine speed. An exhaust emission control device for an internal combustion engine. The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 4,
The exhaust gas purification apparatus for an internal combustion engine, wherein the estimation means estimates a catalyst bed temperature based on a detection result of an exhaust temperature of the internal combustion engine. The exhaust gas purification apparatus for an internal combustion engine according to claim 5,
The exhaust gas purification apparatus for an internal combustion engine, wherein the exhaust gas temperature is an exhaust gas temperature detected on an exhaust downstream side of the catalyst.

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