WO2007138454A1

WO2007138454A1 - Exhaust purification device and method of internal combustion engine

Info

Publication number: WO2007138454A1
Application number: PCT/IB2007/001409
Authority: WO
Inventors: Jun Tahara; Yukihisa Yamamoto
Original assignee: Toyota Jidosha Kabushiki Kaisha; Kabushiki Kaisha Toyota Jidoshokki
Priority date: 2006-05-31
Filing date: 2007-05-30
Publication date: 2007-12-06
Also published as: JP2007321614A

Abstract

An exhaust purification device of an internal combustion engine estimates a catalyst bed temperature from a detected value of the exhaust gas temperature (step S210), and calculates a switch amount of air that is used for determining whether or not the amount of addition of unburned fuel fraction needs to be corrected (step S220). Then, the device determines whether or not the actual amount of intake air detected is greater than the switch amount of air (step S240). If the actual amount of air exceeds the switch amount of air, it can be determined that the operation state of the engine is a state in which white smoke is likely to be produced, and therefore a correction of lessening the amount of addition of fuel provided from an fuel addition injector is performed (step S260).

Description

EXHAUST PURIFICATION DEVICEAND METHOD OF INTERNAL

COMBUSTION ENGINE

FIELD OF THE INVENTION [0001] The invention relates to an exhaust purification device and an exhaust purification method of an internal combustion engine which carry out a fuel addition control of adding an unbumed fuel fraction to a catalyst that is provided in an exhaust system of the internal combustion engine.

BACKGROUND OF THE INVENTION

[0002] An exhaust purification device applicable to an internal combustion engine, such as a vehicle-mounted diesel engine and the like, which is equipped with a catalyst for removing exhaust components, such as nitrogen oxides (NOx) and the like, is known. In such an exhaust purification device, a fuel addition control of adding an unburned fuel fraction as a reductant to a catalyst that has stored NOx is carried out, so that due to the heat produced by the oxidation of the unburned fuel fraction in exhaust gas and on the catalyst, the bed temperature of the catalyst is raised to activate the catalyst, and NOx are reduced into N₂, CO₂, NO₂, etc. Thus, exhaust components are removed. Such a fuel addition control is carried out by a technique in which fuel is added from an fuel addition injector that is provided at an upstream side of the catalyst in the exhaust system, or a technique in which fuel is added by a post-fuel injection from a fuel injector that is a'fuel injection performed after the main fuel injection that contributes to the driving of the internal combustion engine, for example, a fuel injection performed during the exhaust stroke, etc. The amount of unburned fuel fraction added is controlled so that the catalyst is surrounded by a reductive atmosphere.

[0003] When such an internal combustion engine equipped with the above-described exhaust purification device is in an accelerating state, the amount of fuel provided for combustion has been increased, and the air-fuel ratio of the mixture of fuel and air is fuel-richer than usual, so that the amount of unburned fuel fraction, including . hydrocarbon, that is discharged in accordance with the combustion is greater than usual. If the addition of unburned fuel fraction is performed during the accelerating state, the unburned fuel fraction in exhaust gas becomes excessive in amount, so that a large amount of unburned fuel fraction is let out without being sufficiently oxidized. As a result, a large amount of white smoke may be produced in exhaust gas. As solution means for this drawback, Japanese Patent Application Publication No. JP-A-2005-83351 discloses an exhaust purification device that performs a control in which the amount of unburned fuel fraction added is lessened or the addition of unburned fuel fraction is stopped during the accelerating state of the internal combustion engine. By controlling the exhaust purification device in this manner, the supply of unburned fuel fraction in excessive amount during the accelerating state is substantially prevented so as to restrain the production of white smoke.

[0004] In the exhaust purification device as described above, since the addition of unburned fuel fraction is stopped or the like during the accelerating state, the unburned fuel fraction, which is used to activate the catalyst, is not sufficiently is supplied. Namely, there are cases where the amount of unburned fuel is not optimal. Thus, problems of the temperature rise of the catalyst bed temperature being delayed can occur. If the catalyst bed temperature is low, the exhaust purification capability of the catalyst declines, so that unburned fuel fraction may be let out without being sufficiently oxidized. Thus, there is possibility of white smoke being produced in exhaust gas. Still further, if the addition of unburned fuel fraction is unnecessarily performed when the exhaust purification capability is low, the fuel economy sometimes deteriorates.

DISCLOSURE OF THE INVENTION [0005] An object of the invention is to provide an exhaust purification device and an exhaust purification method of an internal combustion engine which are able to add an appropriate amount of an unburned fuel fraction to a catalyst during the fuel addition control.

[0006] A first aspect of the invention relates to an exhaust purification device of an internal combustion engine. This exhaust purification device of the internal combustion engine caries out a fuel addition control of adding an unburned fuel fraction to a catalyst that is provided in an exhaust system of the internal combustion engine. The exhaust purification device includes detection means for detecting an amount of air taken into the internal combustion engine, estimation means for estimating a catalyst bed temperature of the catalyst, and correction means for correcting an amount of addition of the unburned fuel fraction provided by the fuel addition control based on the catalyst bed temperature estimated and the amount of air detected.

[0007] According to this construction, the amount of addition of unburned fuel fraction provided by the fuel addition control is corrected on the basis of the estimated catalyst bed temperature and the detected actual amount of air. Therefore, the amount of addition of unburned fuel fraction can be corrected from a relationship between the amount of exhaust gas that allows purification of exhaust gas in accordance with the exhaust purification capability of the catalyst and the amount of exhaust gas that actually passes through the catalyst. This avoids a situation that an amount of exhaust gas exceeding the exhaust purification capability of the catalyst is supplied so that the unburned fuel fraction becomes excessive in amount. That is, it is possible to substantially prevent unburned fuel fraction from being added in large amount when the catalyst bed temperature is low and the exhaust purification capability has declined, and also prevent unburned fuel fraction from being added when the air-fuel ratio is fuel-richer than during a normal operation, for example, at the time of acceleration of the internal combustion engine during which the actual amount of air increases, or the like. Therefore, the exhaust purification device is able to substantially prevent an event that a large amount of unburned fuel fraction is emitted to the outside without being sufficiently oxidized, and therefore restrain the production of white smoke in the exhaust gas.

[0008] Furthermore, due to the aforementioned correction, the amount of addition of unburned fuel fraction corresponding to the exhaust purification capability of the catalyst can be set. Therefore, the exhaust purification device is able to substantially prevent an event that the amount of addition is excessively small and therefore the rise of the catalyst bed temperature is delayed, or an event that the amount of addition is excessively large and therefore fuel is unnecessarily consumed, and is thus able to restrain deterioration of the fuel economy while efficiently purifying exhaust gas.

[0009] The correction means may correct the amount of addition of the unburned fuel fraction provided by the fuel addition control so that the amount of addition of the unburned fuel fraction is lessened when the detected amount of air exceeds a predetermined amount of air that is set in accordance with the estimated catalyst bed temperature.

[0010] According to this construction, when the detected actual amount of air exceeds the predetermined amount of air that is set in accordance with the estimated catalyst bed temperature, the correction is performed so as to lessen the amount of addition of the unburned fuel fraction provided by the fuel addition control. When an ordinary fuel addition control is performed, the exhaust purification capability varies depending on individual catalysts used; however, a region in which the production of white smoke in exhaust gas becomes remarkable is present in the relationship between the actual amount of air and the catalyst bed temperature. The region is located to a side of larger actual amount of air and to a side of lower catalyst bed temperature. Therefore, if a boundary of the region is seen as the predetermined amount of air that is set in accordance with the catalyst bed temperature, it can be determined that the possibility of white smoke being produced becomes high when the actual amount of air exceeds the predetermined amount of air. Hence, if the correction of lessening the amount of addition of unburned fuel fraction is performed when the actual amount of air exceeds the predetermined amount of air set in accordance with the catalyst bed temperature, the production of white smoke can be suitably restrained. Furthermore, the reduction of the amount of addition can substantially prevent unnecessary consumption of fuel, and therefore can restrain deterioration of fuel economy.

[0011] The predetermined amount of air may be set so as to become smaller as the catalyst bed temperature becomes lower.

[0012] According to this construction, since the predetermined amount of air to be compared with the actual amount of air is set so as to become smaller as the catalyst bed temperature becomes lower, the predetermined amount of air can be set in a manner corresponding to the exhaust purification capability of the catalyst. Therefore, when the catalyst bed temperature becomes low and the exhaust purification capability declines, it is possible to carry out a fuel addition control in which the predetermined amount of air used as a threshold value at the time of the correction of lessening the amount of addition of the unburned fuel fraction is made small so as to substantially prevent the state in which the amount addition of fuel is excessive and therefore suitably restrain the production of white smoke. [0013] The correction means may correct the amount of addition of the unburned fuel fraction by correcting an addition amount map in which the amount of addition of the unburned fuel fraction corresponding to an engine rotation speed and an amount of fuel injection that contributes to driving of the internal combustion engine is mapped.

[0014] According to this construction, the amount of addition of the unburned fuel fraction is corrected by correcting the addition amount map in which the amount of addition of the unburned fuel fraction corresponding to the engine rotation speed and the amount of fuel injection that contributes to the driving of the internal combustion engine is mapped. Therefore, the use of this map makes it possible to easily carry out the correction of the amount of addition of the unburned fuel fraction corresponding to the operation state of the internal combustion engine. As the correction through the use of a map, it is possible to adopt, for example, a technique in which a basic addition amount map in which the amount of addition of unburned fuel fraction is set on the basis of the engine rotation speed and the amount of fuel injection, and a corrected addition amount map in which the amount of addition is set smaller than in the basic addition amount map, and the amount of addition of the unburned fuel fraction is found by using the basic addition amount map if the actual air amount is relatively small, and by using the corrected addition amount map when the actual amount of fuel is relatively large.

[0015] The estimation means may estimate the catalyst bed temperature based on a result of detection of an exhaust gas temperature of the internal combustion engine. [0016] According to this construction, since the catalyst bed temperature is estimated on the basis of a result of detection of the exhaust gas temperature of the internal combustion engine, the catalyst bed temperature can be estimated with good accuracy. The catalyst bed temperature may also be estimated from a detection value provided by a different sensor, or from an engine operation state quantity such as the engine rotation speed, the engine load (e.g., the fuel injection amount, etc.), etc.

[0017] The exhaust gas temperature may be the exhaust gas temperature detected at the exhaust downstream side of the catalyst.

[0018] According to this construction, since the catalyst bed temperature is estimated from the exhaust gas temperature detected at the exhaust downstream side of the catalyst, the detection of exhaust gas that has passed through the catalyst makes it possible to estimate the catalyst bed temperature with good accuracy. For example, if the exhaust gas temperature at the exhaust upstream side of the catalyst is detected, it sometimes happens that the catalyst bed temperature cannot be estimated with good precision since the temperature at the downstream side of the catalyst has not risen, or the like, and therefore, there is possibility that the correction of the amount of addition of the unburned fuel fraction based on the relationship between the actual amount of air and the catalyst bed temperature cannot be performed. However, if the catalyst bed temperature is estimated from the exhaust gas temperature at the exhaust downstream side of the catalyst, a state in which the production of white smoke becomes remarkable can be found in the relationship with the actual amount of air, and therefore the correction of the amount of addition of the unburned fuel fraction can be suitably carried out.

[0019] A second aspect of the invention relates to an exhaust purification method of an internal combustion engine which carries out a fuel addition control of adding an unburned fuel fraction to a catalyst that is provided in an exhaust system of the internal combustion engine. This method includes the step of detecting an amount of air taken into the internal combustion engine, the step of estimating a catalyst bed temperature of the catalyst; and the step of correcting an amount of addition of the unburned fuel fraction provided by the fuel addition control based on the catalyst bed temperature estimated and the amount of air detected.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The foregoing and further objects, features and advantages of the invention will become apparent from the following description of preferred embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:

FIG. 1 is a construction diagram of a vehicle-mounted internal combustion engine equipped with an exhaust purification device in accordance with the invention; FIG. 2 is a chart showing a mechanism of production of white smoke at the time of a fuel addition control;

FIG. 3 is a map representing the state of production of white smoke with reference to the catalyst bed temperature and the intake air amount;

FIG. 4 is a flowchart of a fuel addition amount correction routine; FIG. 5A is a basic fuel addition amount map;

FIG. 5B is a corrected fuel addition amount map; and

FIG. 6 is a map representing the state of production of white smoke with reference to the catalyst bed temperature and the intake air amount.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0021] Embodiments of an exhaust purification device of an internal combustion engine in accordance with the invention will be described hereinafter with reference to FIGS. 1 to 5. FIG. 1 is a construction diagram of a vehicle-mounted internal combustion engine equipped with an exhaust purification device in accordance with an embodiment of the invention. An internal combustion engine 10 includes a combustion chamber 12 formed in each cylinder 11, an intake passageway 13 that feeds intake air into the combustion chamber 12, and an exhaust passageway 14 into which the exhaust gas produced by the combustion in the combustion chamber 12 is discharged.

[0022] The intake passageway 13 is provided with an intake throttle valve 15 for changing the passageway area. By controlling the degree of opening of the intake throttle valve 15, the amount of air taken into the combustion chamber 12 is adjusted. The air taken into the intake passageway 13 mixes with the fuel injected from a fuel injector 16 provided in the combustion chamber 12, thus forming a mixture. The mixture is burned in the combustion chamber 12. The intake passageway 13 is provided with an air flow meter 31 for detecting the amount of air taken into the combustion chamber 12. The exhaust passageway 14 is provided with a NOx catalytic converter 17, a PM filter 18 and an oxidation catalyic converter 19 that are disposed in that order from an upstream side. The NOx catalytic converter 17, the PM filter 18 and the oxidation catalyic converter 19 are fed with exhaust gas that is produced by combustion in the combustion chamber 12.

[0023] The NOx catalytic converter 17 is loaded with a storage reduction type NOx catalyst. The NOx catalyst stores NOx from exhaust gas when the oxygen concentration in exhaust gas is high, and releases stored NOx when the oxygen concentration in exhaust gas is low. The NOx catalyst, when releasing NOx, removes NOx by reducing it in a reductive atmosphere in which an unburned fuel fraction is present around the released NOx.

[0024] The PM filter 18 is formed of a porous material so as to trap particulate matter (PM) in exhaust gas. The PM filter 18, as in the NOx catalytic converter 17, is loaded with a storage reduction type NOx catalyst, whereby NOx in exhaust gas is removed. Furthermore, by the reactions induced by the NOx catalyst, the PM trapped as mentioned above is burned (oxidized) and thus removed.

[0025] The oxidation catalyic converter 19 is loaded with an oxidation catalyst. The oxidation catalyst removes the hydrocarbon and carbon monoxide in exhaust gas through oxidation thereof. A first gas temperature sensor 32 that detects a first gas temperature, the temperature of the exhaust gas that is to flow into the PM filter 18, and a second gas temperature sensor 33 that detects a second gas temperature, the temperature of the exhaust gas that has passed through the PM filter 18, are provided at an exhaust upstream side and an exhaust downstream side, respectively, of the PM filter 18 in the exhaust passageway 14. Furthermore, the exhaust passageway 14 is also provided with a differential pressure sensor 34 that detects the differential pressure between the exhaust upstream side and the exhaust downstream side of the PM filter 18. An oxygen sensor 35 that detects the oxygen concentration in exhaust gas is provided between the PM filter 18 and the oxidation catalyic converter 19.

[0026] The internal combustion engine 10 also has an exhaust recirculation device that recirculates a part of exhaust gas into the air in the intake passageway 13. The exhaust recirculation device includes an exhaust recirculation passageway 20 that connects the exhaust passageway 14 and the intake passageway 13 in communication. The exhaust recirculation passageway 20 is provided with a EGR valve 21 that adjusts the amount of flow of exhaust passing through the exhaust recirculation passageway 20.

[0027] The fuel injector 16 provided in each combustion chamber 12 is connected to a common rail 23 via a high-pressure injection pipe 22. The common rail 23 is supplied with high-pressure fuel via a fuel supply pump 24. The pressure of high-pressure fuel in the common rail 23 is detected by a rail pressure sensor 25 that is attached to the common rail 23. Furthermore, low-pressure fuel is supplied from the fuel supply pump 24 to an fuel addition injector 27 through a low-pressure injection pipe 26. The fuel addition injector 27 is disposed in an exhaust port of a specified cylinder 11 so as to add fuel as an unburned fuel fraction into exhaust gas. ^■ - [0028] Various controls of the internal combustion engine 10 as described above are carried out by an electronic control device 40. The electronic control device 40 includes a CPU that executes various computation processes regarding the control of the engine, a ROM in which programs and data needed for the control are stored, a RAM for temporarily storing results of computation of the CPU and the like, input and output ports for inputting and outputting signals with respect to an external device or the like, etc.

[0029] In addition to the aforementioned various sensors, an engine speed sensor 36 for detecting the engine rotation speed, an accelerator sensor 37 for detecting the accelerator operation amount, an intake throttle sensor 38 for detecting the degree of opening of the intake throttle valve 15, etc. are connected to the input port of the electronic control device 40. Drive circuits of the intake throttle valve 15, the EGR valve 21, the fuel injector 16, the fuel supply pump 24, the fuel addition injector 27, etc. are connected to the output port of the electronic control device 40.

[0030] In accordance with the engine operation state grasped from detection signals input from the aforementioned sensors, the electronic control device 40 outputs command signals to the drive circuits of various appliances and the like that are connected to the output port. In this manner, the electronic control device 40 carries out various controls, including an opening degree control of the intake throttle valve 15, an exhaust recirculation control based on an opening degree control of the EGR valve 21, controls of the amount of fuel injection from the fuel injector 16, the fuel injection timing and the fuel injection pressure, etc.

[0031] As one of such controls, the electronic control device 40 carries out a fuel addition control of adding fuel from the fuel addition injector 27 to exhaust gas. The fuel addition control is carried out at the time of the following controls: a NOx reduction control, a PM filter regeneration control, and a sulfur poisoning recovery control.

[0032] The NOx reduction control is performed in order to release the NOx stored in the NOx catalytic converter 17 and the PM filter 18 by reducing it into N₂, CO₂, NO₂, etc. During the NOx reduction control, a so-called rich spike is intermittently performed, that is, fuel is added from the fuel addition injector 27 to exhaust gas intermittently at constant time intervals so that the exhaust gas around the NOx catalyst temporarily becomes low in the oxygen concentration and rich in the unburned fuel fraction. This accelerates the release of NOx from the NOx catalyst and the reduction thereof, thus reductively removing NOx. [0033] The PM filter regeneration control is performed in order to resolve the clogging of the PM filter 18 by burning and removing the PM trapped in the PM filter 18. During the PM filter regeneration control, the fuel addition from the fuel addition injector 27 to exhaust gas is continuously repeated so that the heat produced by the oxidative reaction of the added fuel in the exhaust gas and on the catalyst raises the catalyst bed temperature high, thus burning the PM.

[0034] The sulfur poisoning recovery control is performed in order to recover the NOx storage capability that has declined due to the sulfur oxides (SOx) that are stored in the NOx catalyst together with NOx. When the sulfur poisoning recovery control is started, firstly fuel is continually added from the fuel addition injector 27 to exhaust gas as in the PM filter regeneration control to raise the catalyst bed temperature high. After that, as in the NOx reduction control, the fuel addition from the fuel addition injector 27 is intermittently performed, and therefore the rich spike is intermittently performed, so as to accelerate the release of SOx from the NOx catalyst and the reduction thereof. Thus, the NOx storage capability is recovered.

[0035] As described above, the electronic control device 40, through the control of adding fuel from the fuel addition injector 27, adds fuel to the catalysts of the NOx catalytic converter 17 and the like, thus maintaining good exhaust purification performance of the internal combustion engine 10. [0036] Incidentally, when the aforementioned fuel addition control is carried out, it sometimes happens that the added fuel passes through the catalyst without being sufficiently oxidized, and produces white smoke in exhaust gas. FIG. 2 shows a mechanism of production of white smoke at the time of the fuel addition control. If during the fuel addition control the internal combustion engine 10 becomes an accelerating state, the amount of air taken into the combustion chamber 12 increases and the amount of fuel injected from the fuel injector 16 is increased, so that the air-fuel ratio of the mixture becomes fuel-richer than usual (step SIlO). Or, if the catalyst bed temperature of the NOx catalytic converter 17 or the like is low during a cold engine operation or the like, the exhaust purification capability of the catalyst declines (step S 120). During the operation of the internal combustion engine 10 in which the amount of intake air increases and the catalyst bed temperature becomes low, fuel is added from the fuel addition injector 27 (step S130). Then, the fuel remaining unreacted due to declined exhaust purification capability passes through the catalyst (step S 140), so that smoke is produced in exhaust gas (step S 150). [0037] FIG. 3 shows an example of a map representing the state of production of white smoke with respect to the catalyst bed temperature and the intake air amount. The vertical axis in the map shows the actual amount of intake air detected from the air flow meter 31, and the horizontal axis shows the exhaust gas temperature detected from the second gas temperature sensor 33. In FIG. 3, the catalyst bed temperature is estimated from the exhaust gas temperature at the exhaust downstream side of the PM filter 18 detected from the second gas temperature sensor 33. If the fuel addition control is carried out during an arbitrary operation state of the internal combustion engine 10, results are that white smoke is produced under conditions indicated by "X" in FIG. 3, and white smoke is not produced under conditions indicated by "O". From the results, it can be seen that white smoke is produced in a region Y in which the actual air amount becomes large, and that white smoke is not produced in another region Z. Furthermore, since the exhaust purification capability declines as the catalyst bed temperature declines, a boundary line X is formed so that the lower the catalyst bed temperature the smaller the value of the air amount becomes. Incidentally, the map as shown in FIG. 3 varies depending on the characteristic of the catalyst; however, the configurations of the boundary line X, the region Y and the region Z are substantially constant.

[0038] Therefore, the exhaust purification device of this embodiment performs a control for preventing the production of white smoke on the basis of the relationship between the catalyst bed temperature and the intake air amount as shown in FIG. 3. Concretely, at the time of fuel addition control, the intake air amount and the catalyst bed temperature are monitored, and when an operation state with high possibility of production of white smoke as indicated in the region Y in FIG. 3 is detected, a correction of lessening the amount of fuel addition from the fuel addition injector 27 is performed. [0039] FIG. 4 shows a fuel addition amount correction routine of determining a final fuel addition amount by executing the correction of the fuel addition amount. This fuel addition correction routine is periodically executed as a regular time interrupt process at every predetermined time by the electronic control device 40.

[0040] When the fuel addition amount correction, routine is started, the electronic control device 40 as estimation means acquires the exhaust gas temperature at the exhaust downstream side of the PM filter 18 detected from the second gas temperature sensor 33, and estimates the catalyst bed temperature of the NOx catalytic converter 17 or the like from the exhaust gas temperature (step S210). From the estimated catalyst bed temperature, the electronic control device 40 calculates a switch air amount (predetermined air amount) that is set for determining whether or not it is necessary to correct the fuel addition amount (step S220). This switch air amount serves as a threshold value for determining whether the operation state of the internal combustion engine 10 is a state where white smoke is likely to be produced, in other words, whether the operation state is a state where white smoke is unlikely to be produced, in the case where an ordinary fuel addition control is performed. When the catalyst has a characteristic as shown in FIG. 3, the switch air amount is found from the boundary line X between the region Y in which white smoke is produced and the region Z in which white smoke is not produced. For example, when the exhaust gas temperature is 200⁰C, the switch air amount can be calculated to be B g/s from the point of intersection of the line of 200°C with the boundary line X.

[0041] Next, the electronic control device 40 acquires the actual air amount of intake air detected by the air flow meter 31 as detection means (step S230). Then, the electronic control device 40 determines whether or not the acquired actual air amount is greater than the switch air amount set as described above (step S240). If the actual air amount is less than or equal to the switch air amount (NO in S240), it can be determined that the operation state of the internal combustion engine 10 is a state in which white smoke is unlikely to be produced, for example, the region Z shown in FIG. 3. Therefore, the production of white smoke can be restrained without a need to perform correction of the fuel addition amount. Therefore, the electronic control device 40 finds the fuel addition amount on the basis of the basic addition amount map that is used under a usual condition (step S250).

[0042] On the other hand, if the actual air amount exceeds the switch air amount (YES in S240), it can be determined that the operation state of the internal combustion engine 10 is a state in which white smoke is likely to be produced, for example, the region Y shown in FIG. 3. Therefore, the electronic control device 40 as correction means performs such a correction as to lessen the amount of fuel added from the fuel addition injector 27. Concretely, the fuel addition amount is found on the basis of a corrected addition amount map in which the fuel addition amount is set less than in the basic addition amount map (step S260). With reference to FIGS. 5A and 5B, the basic addition amount map and the corrected addition amount map will be described. FIG. 5 A shows the basic addition amount map, and FIG. 5B shows the corrected addition amount map. As shown in FIGS. 5A and 5B₅ each map is provided by mapping the fuel addition amount corresponding to the fuel injection amount provided from the fuel injector 16 controlled by the electronic control device 40 and to the engine rotation speed detected from the engine speed sensor 36. That is, each map is constructed so that the fuel addition amount added from the fuel addition injector 27 in a single adding operation at predetermined intervals can be found from the amount of fuel injection and the engine rotation speed. For example, in the basic addition amount map as shown in FIG. 5A, the fuel addition amount per each operation becomes Eij (mm³) if the engine rotation speed is 2000 rpm and the amount of fuel injection is 40 mnrVst (stroke).

[0043] The thus-found fuel addition amount differs between when the basic addition amount map is used and when the corrected addition amount map is used. Specifically, these maps are set so that the corrected addition amount map provides smaller values of the fuel addition amount than the basic addition amount map if the engine rotation speed and the amount of fuel injection remain the same. That is, the maps are set so that an arbitrary addition amount Exy (mm³) in the basic addition amount map is greater than the fuel addition amount E'xy (mm³) found from the same engine rotation speed and the same fuel injection amount through the use of the corrected addition amount map. Since the basic addition amount map and the corrected addition amount map are constructed as described above, the fuel addition amount found from the corrected addition amount map is always less than the fuel addition amount found from the basic addition amount map. The electronic control device 40 performs such a correction as to lessen the fuel addition amount by using the corrected addition amount map in step S260.

[0044] The electronic control device 40 determines the fuel addition amount found in step S250 or step S260, as a post-correction fuel addition amount (step S270).

Subsequently, the electronic control device 40 performs an amendment based on a learned addition value corresponding to the post-correction fuel addition amount (step

S280). Examples of the learned addition value include the amount of deposit adhering to the fuel addition injector 27. The post-correction fuel addition amount is amended by the state of operation of the fuel addition injector 27 and the like. Then, from the amended post-correction fuel addition amount, the electronic control device 40 determines a final fuel addition amount that is to be added at the time of the fuel addition control (step S290). Then, the electronic control device 40 ends this routine.

[0045] In this manner, the electronic control device 40 performs the correction of lessening the fuel addition amount provided from the fuel addition injector 27 when the operation state of the internal combustion engine 10 is a state in which the possibility of production of white smoke is high. Then, by performing the fuel addition control on the basis of the fuel addition amount found by the correction, the electronic control device 40 restrains the discharge of fuel through the catalyst. Thus, the production of white smoke is restrained.

[0046] According to the exhaust purification device of the internal combustion engine of this embodiment, the following effects can be achieved. (1) In this embodiment, using the map as shown in FIG. 3, the amount of fuel added from the fuel addition injector 27 by the fuel addition control is corrected on the basis of the catalyst bed temperature and the actual amount of air. Therefore, the amount of fuel added can be corrected from the relationship between the amount of air in exhaust that allows purification in accordance with the exhaust purification capability of the catalyst of the NOx catalytic converter 17 and the like and the actual amount of air passing through the catalyst. This can substantially prevent an event that an amount of exhaust gas exceeding the exhaust purification capability of the catalyst of the NOx catalytic converter 17 or the like is fed and therefore the amount of fuel added from the fuel addition, injector 27 becomes excessive. Hence, this embodiment can substantially prevent an event that a large amount of fuel is added from the fuel addition injector 27 while the catalyst bed temperature is low and the exhaust purification capability has declined, and an event that fuel is added from the fuel addition injector 27 when the air-fuel ratio becomes richer than usual, for example, during acceleration of the internal combustion engine 10. Due to this, an event that fuel added is not sufficiently oxidized but is let out of the exhaust passageway 14 into the outside can be substantially prevented, and therefore the production of white smoke can be restrained.

[0047] (2) In this embodiment, through correction of the fuel addition amount, it is possible to set a fuel addition amount corresponding to the exhaust purification capability of the catalyst of the NOx catalytic converter 17 or the like. Therefore, it is possible to substantially prevent the fuel addition amount from becoming excessively small so that the rise of the catalyst bed temperature is delayed or substantially prevent the fuel addition amount from becoming excessively large so that fuel is unnecessarily consumed, and thus it is possible to restrain deterioration of the fuel economy while efficiently purifying exhaust gas.

[0048] (3) In this embodiment, if the actual air amount exceeds the switch air amount, the correction of lessening the amount of fuel added from the fuel addition injector 27 is performed. Therefore, by lessening the fuel addition amount during a state in which the possibility of production of white smoke becomes relatively high, it is possible to restrain deterioration of the fuel economy while substantially preventing production of white smoke. Furthermore, since the switch air amount is calculated on the basis of the catalyst bed temperature and the map as shown in FIG. 3, it is possible to precisely determine whether the operation state of the internal combustion engine 10 is a state in which white smoke is likely to be produced or a state in which white smoke is unlikely to be produced.

[0049] (4) In the embodiment, since the switch air amount is set so as to become smaller as the catalyst bed temperature becomes lower, as shown in FIG. 3. Therefore, the switch air amount can be set in a manner corresponding to the exhaust purification capability of the catalyst. Therefore, when the catalyst bed temperature becomes low and the exhaust purification capability declines, it is possible to carry out a fuel addition control in which the switch air amount is made small so as to substantially prevent the state in which the fuel addition amount is excessive and therefore suitably restrain the production of white smoke.

[0050] (5) In the embodiment, the fuel addition amount is corrected by using the fuel addition amount maps in which the fuel addition amount is mapped corresponding to the amount of fuel injection and the engine rotation speed. The use of these maps makes it possible to carry out a correction of the fuel addition amount corresponding to the operation state of the internal combustion engine.

[0051] (6) In the embodiment, the electronic control device 40 acquires the exhaust gas temperature at the exhaust downstream side of the NOx catalytic converter 17 and the PM filter 18 which is detected by the second gas temperature sensor 33, and estimates the catalyst bed temperature of the NOx catalytic converter 17 and the like from the acquired exhaust gas temperature. Therefore, since the temperature of the exhaust gas that has passed through the catalyst is detected, the catalyst bed temperature can be estimated with good accuracy. Hence, a state in which white smoke is likely to be produced can be accurately found in relation to the actual air amount, and the fuel addition amount can be suitably corrected. [0052] The foregoing embodiment may be modified as follows. In the foregoing embodiment, when the actual air amount exceeds the switch air amount, the correction of lessening the amount of fuel added from the fuel addition injector 27 is performed. However, in this case, it is also possible to perform a correction in which the amount of correction of the fuel addition amount is changed in accordance with changes in the actual air amount on the basis of the characteristic of the catalyst. For example, the amount of correction of the fuel addition amount can be changed by a technique in which the fuel addition amount in the basic addition amount map is variably set in accordance with changes in the actual air amount, or the like.

[0053] Although in the embodiment, the correction of the fuel addition amount is performed by using the basic addition amount map and the corrected addition amount map, the correction of the fuel addition amount may also be performed without using these maps. It is also permissible to perform the correction of the fuel addition amount by factoring in another engine operation state quantity in such maps. [0054] In the foregoing embodiment, the catalyst bed temperature is estimated from the exhaust gas temperature at the exhaust downstream side of the NOx catalytic converter 17 and the PM filter 18 which is detected by the second gas temperature sensor 33. However, the catalyst bed temperature may also be estimated from the exhaust gas temperature detected by the first gas temperature sensor 32 that is provided at the exhaust upstream side. FIG. 6 shows a map similar to the map shown in FIG. 3 in which the horizontal axis represents the exhaust gas temperature detected by the first gas temperature sensor 32. As can be seen from FIG. 6, in the case where the values detected by the first gas temperature sensor 32 are used, the region Y' in which white smoke is produced and the region Z' in which white smoke is not produced are present with a tendency similar to that in FIG. 3, but the boundary line X' between the region Y' and the region Z' is ambiguous. Thus, even in the case where the catalyst bed temperature is estimated from the exhaust gas temperature detected at the exhaust upstream side of the catalyst, a region in which white smoke is produced can be obtained with a certain degree of accuracy. However, it is preferable to estimate the catalyst bed temperature from the exhaust gas temperature detected at the exhaust downstream side of the catalyst as shown in FIG 3.

[0055] Although in the foregoing embodiment, the catalyst bed temperature is estimated by detecting the exhaust gas temperature, the catalyst bed temperature may also be estimated from a detection value provided by a different sensor, or from an engine operation state quantity such as the engine rotation speed, the engine load, etc.

[0056] Although in the foregoing embodiment, the fuel addition control is carried out by adding fuel from the fuel addition injector 27, the fuel addition control may also be carried out by a post-fuel injection that is a fuel injection performed after the main fuel injection from the fuel injector 16, for example, a fuel injection performed during the exhaust stroke, or the like. In the case where the fuel addition control is carried out by the post-fuel injection or the like, too, the invention is applicable by using the same principle as described above. Furthermore, the fuel addition control may also be carried out by both the addition of fuel from the fuel addition injector 27 and the post-injection from the fuel injector 16. In this case, the invention is applicable to at least one of the manners of adding fuel.

[0057] While the invention has been described with reference to what are considered to be preferred embodiments thereof, it is to be understood that the invention is not limited to the disclosed embodiments or constructions. On the contrary, the invention is intended to cover various modifications and equivalent arrangements^'. In addition, while the various elements of the disclosed invention are shown in various combinations and configurations, which are exemplary, other combinations and configurations, including more, less or only a single element, are also within the scope of the appended claims.

Claims

CLAIMS:

1. An exhaust purification device of an internal combustion engine which carries out a fuel addition control of adding an unburned fuel fraction to a catalyst that is provided in an exhaust system of the internal combustion engine, comprising: detection means for detecting an amount of air taken into the internal combustion engine; estimation means for estimating a catalyst bed temperature of the catalyst; and correction means for correcting an amount of addition of the unburned fuel fraction provided by the fuel addition control based on the catalyst bed temperature estimated and the amount of air detected.

2. The exhaust purification device of the internal combustion engine according to claim I₅ wherein the correction means corrects the amount of addition of the unburned fuel fraction provided by the fuel addition control so that the amount of addition of the unburned fuel fraction is lessened when the detected amount of air exceeds a predetermined amount of air that is set in accordance with the estimated catalyst bed temperature.

3. The exhaust purification device of the internal combustion engine according to claim 2, wherein the predetermined amount of air is set so as to become smaller as the catalyst bed temperature becomes lower.

4. The exhaust purification device of the internal combustion engine according to any one of claims 1 to 3, wherein the correction means corrects the amount of addition of the unburned fuel fraction by correcting an addition amount map in which the amount of addition of the unburned fuel fraction corresponding to an engine rotation speed and an amount of fuel injection that contributes to driving of the internal combustion engine is mapped.

5. The exhaust purification device of the internal combustion engine according to any one of claims 1 to 4, wherein the estimation means estimates the catalyst bed temperature based on a result of detection of an exhaust gas temperature of the internal combustion engine.

6. The exhaust purification device of the internal combustion engine according to claim 5, wherein the estimation means includes exhaust gas temperature detection means provided at an exhaust downstream side of the catalyst,

7. An exhaust purification method of an internal combustion engine which carries out a fuel addition control of adding an unburned fuel fraction to a catalyst that is provided in an exhaust system of the internal combustion engine, comprising: detecting an amount of air taken into the internal combustion engine; estimating a catalyst bed temperature of the catalyst; and correcting an amount of addition of the unburned fuel fraction provided by the fuel addition control based on the catalyst bed temperature estimated and the amount of air detected.

8. An exhaust purification device of an internal combustion engine, comprising: a fuel adding device that adds an unburned fuel fraction to a catalyst that is provided in an exhaust system of the internal combustion engine; a detector that detects an amount of air taken into the internal combustion engine; an estimation device that estimates a catalyst bed temperature of the catalyst; and a correction device that corrects an amount of addition of the unburned fuel fraction provided by the fuel addition control based on the catalyst bed temperature estimated and the amount of air detected.