JP2005002905A - Exhaust gas purification device for internal combustion engine - Google Patents

Abstract

An NOx purification rate is optimized while suppressing deterioration of fuel consumption.
In an exhaust gas purification apparatus for an internal combustion engine having an NOx storage reduction catalyst (19) disposed in an exhaust passage (18), NOx catalyst temperature detecting means (s1 to sn) for estimating or detecting the temperature of the NOx catalyst. ), NOx storable amount estimating means for estimating the NOx storable amount (B) that can be stored in the NOx catalyst based on the temperature of the NOx catalyst estimated or detected by the NOx catalyst temperature detecting means, and after starting the internal combustion engine A temperature raising means for raising the temperature of the NOx catalyst to a target temperature; and an exhausted NOx amount detecting means (71, 72) for estimating or detecting the amount of exhausted NOx (A1) discharged from the internal combustion engine. An exhaust purification device for an internal combustion engine is provided in which the target temperature is determined so that the NOx storable amount (B) and the exhausted NOx amount (A1) are substantially equal.
[Selection] Figure 4

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust emission control device for an internal combustion engine, particularly a diesel engine.
[0002]
[Prior art]
An exhaust passage of an internal combustion engine in recent years is provided with a NOx storage reduction catalyst (hereinafter referred to as “NOx catalyst”) for purifying nitrogen oxide (hereinafter referred to as “NOx”) in exhaust gas. Yes. The NOx catalyst occludes (absorbs or adsorbs) NOx in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean, and releases the stored NOx when the air-fuel ratio of the inflowing exhaust gas is rich And has the function of reducing. Therefore, when the NOx occlusion amount of the NOx catalyst exceeds a predetermined value during operation of such an internal combustion engine, NOx in the NOx catalyst is released and reduced by appropriately forming a rich atmosphere (for example, , See Patent Document 1 to Patent Document 4.)
[Patent Document 1]
JP-A-7-189659
[Patent Document 2]
JP 11-343833 A
[Patent Document 3]
JP 2002-195080 A
[Patent Document 4]
JP 2001-152835 A
[0003]
[Problems to be solved by the invention]
In such an internal combustion engine, NOx is generated not only during normal operation but also during a cold start, particularly immediately after the cold start until the NOx in the NOx catalyst can be released. Therefore, it is desirable to store NOx generated during this time in the NOx catalyst. However, since the temperature of the NOx catalyst is low immediately after the cold start, the NOx cannot be sufficiently stored, resulting in NOx purification. The rate drops. On the other hand, in order to raise the temperature of the NOx catalyst, for example, post injection for injecting fuel after main injection, increase in idle rotation speed, or shifting the main injection timing to the retard side is performed. However, even when the temperature of the NOx catalyst is raised by any method, the fuel is excessively consumed when the temperature of the NOx catalyst is raised to a temperature higher than the temperature necessary for storing NOx. So the fuel consumption gets worse.
[0004]
The present invention has been made in view of such circumstances, and an object thereof is to provide an exhaust purification device for an internal combustion engine that optimizes the NOx purification rate while suppressing deterioration of fuel consumption.
[0005]
[Means for Solving the Problems]
In order to achieve the above-described object, according to the first aspect of the invention, in the exhaust gas purification apparatus for an internal combustion engine provided with the NOx storage reduction catalyst disposed in the exhaust passage, the temperature of the NOx catalyst is estimated or detected. NOx catalyst temperature detecting means; NOx storable amount estimating means for estimating a NOx storable amount that can be stored in the NOx catalyst based on the temperature of the NOx catalyst estimated or detected by the NOx catalyst temperature detecting means; A temperature raising means for raising the temperature of the NOx catalyst to a target temperature after starting the internal combustion engine; and an exhaust NOx amount detecting means for estimating or detecting an amount of exhausted NOx discharged from the internal combustion engine. An exhaust purification device for an internal combustion engine is provided in which the target temperature is determined so that the NOx storable amount and the exhaust NOx amount are substantially equal. That.
[0006]
That is, according to the first invention, the target temperature of the NOx catalyst is set so as to store NOx by an amount that can be stored by the NOx catalyst, so that the NOx purification rate can be optimized while suppressing the deterioration of fuel consumption. become. Note that the exhausted NOx amount in this case means the NOx amount exhausted from the internal combustion engine per unit time.
[0007]
According to the second aspect of the invention, in the exhaust gas purification apparatus for an internal combustion engine provided with the NOx storage reduction catalyst disposed in the exhaust passage, the NOx catalyst temperature detecting means for estimating or detecting the temperature of the NOx catalyst, the NOx catalyst NOx storable amount estimating means for estimating the NOx storable amount that can be stored in the NOx catalyst based on the temperature of the NOx catalyst estimated or detected by the temperature detecting means, and the NOx catalyst as a target after the internal combustion engine is started A temperature raising means for raising the temperature to a temperature, an exhaust NOx amount detecting means for estimating or detecting an exhaust NOx amount exhausted from the internal combustion engine, and a target NOx storable amount that is a target value of the NOx storable amount is exhausted. A target NOx storable amount calculating means for calculating using the NOx amount, wherein the target temperature of the temperature raising means is the NOx storable amount and the Exhaust purification system of target NOx storable amount and is almost equal as determined is as in the internal combustion engine is provided.
[0008]
That is, according to the second invention, by calculating the target NOx storable amount using the exhausted NOx amount, it is possible to further optimally control the NOx purification rate while suppressing deterioration of fuel consumption. The target NOx storable amount is calculated by multiplying a map based on the exhausted NOx amount or the exhausted NOx amount by a predetermined coefficient.
[0009]
According to a third aspect, in the first or second aspect, the apparatus further comprises a space velocity detecting means for estimating or detecting the space velocity of the NOx catalyst, and the space velocity detected by the space velocity detecting means is The larger the value, the higher the target temperature.
That is, according to the third invention, when the space velocity is high, the time for exhaust gas to pass through the NOx catalyst is shortened. Even in such a case, NOx is occluded in the NOx catalyst by setting the target temperature high. To be. The temperature raising means may be, for example, a type in which fuel is added to the NOx catalyst.
[0010]
According to a fourth invention, in any one of the second to third inventions, the temperature raising means uses the fuel of the internal combustion engine, and the target NOx storable amount is the consumption of the fuel. The amount can be adjusted to be small.
That is, according to the fourth aspect of the invention, the fuel consumption can be suppressed by adjusting the target NOx storable amount.
[0011]
According to a fifth invention, in any one of the first to fourth inventions, the NOx catalyst temperature detecting means estimates the temperature in each of the NOx catalyst regions divided into at least two in the exhaust gas flow direction. The NOx storable amount calculating means calculates the NOx storable amount from the storable NOx amount in each of the at least two regions.
That is, according to the fifth aspect of the invention, the NOx storable amount of the entire NOx catalyst is calculated from the temperatures of at least two NOx catalyst regions divided in the exhaust gas flow direction, whereby the NOx storable amount can be accurately obtained. .
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings. In the following drawings, the same members are denoted by the same reference numerals. In order to facilitate understanding, the scales of these drawings are appropriately changed.
FIG. 1 shows a four-stroke compression ignition type internal combustion engine to which the present invention is applied.
Referring to FIG. 1, 1 is an engine body, 2 is a cylinder block, 3 is a cylinder head, 4 is a piston, 5 is a combustion chamber, 6 is an electrically controlled fuel injection valve, 7 is an intake valve, 8 is an intake port, 9 Is an exhaust valve, and 10 is an exhaust port. The intake port 8 is connected to a surge tank 12 via a corresponding intake branch pipe 11, and the surge tank 12 is connected to an air cleaner 14 via an intake duct 13. A throttle valve 16 driven by a step motor 15 is disposed in the intake duct 13. On the other hand, the exhaust port 10 is connected to a catalytic converter 20 containing a catalyst 19 via an exhaust manifold 17 and an exhaust pipe 18. An air-fuel ratio sensor 21 is disposed in the exhaust pipe 18.
[0013]
Each fuel injection valve 6 is connected to a fuel reservoir, so-called common rail 26, through a fuel supply pipe 25. Fuel is supplied into the common rail 26 from an electrically controlled fuel pump 27 with variable discharge amount, and the fuel supplied into the common rail 26 is supplied to the fuel injection valve 6 through each fuel supply pipe 25. A fuel pressure sensor 28 for detecting the fuel pressure in the common rail 26 is attached to the common rail 26, and a fuel pump 27 is set so that the fuel pressure in the common rail 26 becomes a target fuel pressure based on an output signal of the fuel pressure sensor 28. The discharge amount is controlled.
[0014]
The electronic control unit 30 is composed of a digital computer, and is connected to each other by a bidirectional bus 31. A ROM (read only memory) 32, a RAM (random access memory) 33, a CPU (microprocessor) 34, an input port 35 and an output port 36. It comprises. The output signal of the air-fuel ratio sensor 21 is input to the input port 35 via the corresponding AD converter 37, and the output signal of the fuel pressure sensor 28 is also input to the input port 35 via the corresponding AD converter 37. A temperature sensor 29 for detecting the engine coolant temperature is attached to the engine body 1, and an output signal of the temperature sensor 29 is input to the input port 35 via the corresponding AD converter 37. A temperature sensor 44 for detecting the temperature of the intake air is attached in at least one intake branch pipe 11, and an output signal of the temperature sensor 44 is input to the input port 35 via the corresponding AD converter 37. Is done.
[0015]
FIG. 2 is an enlarged partial view showing the vicinity of a catalytic converter of an internal combustion engine to which the present invention is applied. In the present invention, as shown in FIG. 2, the catalyst 19 arranged in the catalytic converter 20 is virtually divided into n regions (“n” is a natural number) from c1 to cn. Assumed. In FIG. 2, the catalyst 19 has a substantially cylindrical shape extending in the exhaust gas flow direction in the exhaust pipe 18, and the region c1 to the region cn are partitioned by a plane perpendicular to the longitudinal axis of the catalyst 19 having a substantially cylindrical shape. Yes. Further, as can be seen from FIG. 2, a plurality of temperature sensors s1 to sn are provided at positions of the catalytic converter 20 corresponding to the respective regions c1 to cn of the catalyst 19. The output signals of the plurality of temperature sensors s1 to sn are input to the input port 35 through the corresponding AD converter 37.
[0016]
As shown in FIG. 2, a flow meter 61 for detecting the flow rate of exhaust gas flowing into the catalyst 19 is disposed in the exhaust pipe 18 upstream of the catalyst 19, and the catalyst is disposed in the exhaust passage downstream of the catalyst 19. A flow meter 62 for detecting the flow rate of the exhaust gas flowing out from 19 is arranged. The output signals of these flow meters 61 and 62 are also input to the input port 35 via the corresponding AD converter 37. Although not shown in FIG. 2, a NOx sensor 71 for measuring the amount of NOx in the exhaust gas flowing into the catalyst 19 is disposed in the exhaust pipe 18 upstream of the catalyst 19, and in the exhaust passage downstream of the catalyst 19. A NOx sensor 72 for detecting the amount of NOx in the exhaust gas flowing out from the catalyst 19 may be arranged. The output signals of these NOx sensors 71 and 72 (not shown) are also input to the input port 35 via the corresponding AD converter 37. As shown in FIG. 2, a temperature sensor 45 for detecting the temperature of the exhaust gas flowing into the catalyst 19 is disposed in the exhaust pipe 18 upstream of the catalyst 19, and in the exhaust passage downstream of the catalyst 19. A temperature sensor 46 for detecting the temperature of the exhaust gas flowing out from the catalyst 19 may be arranged. The output signals of these temperature sensors 45 and 46 are also input to the input port 35 via the corresponding AD converter 37.
[0017]
Referring again to FIG. 1, a load sensor 41 that generates an output voltage proportional to the depression amount L of the accelerator pedal 40 is connected to the accelerator pedal 40, and the output voltage of the load sensor 41 passes through a corresponding AD converter 37. Input to the input port 35. The input port 35 is connected to a crank angle sensor 42 that generates an output pulse every time the crankshaft rotates, for example, 30 °. Further, the output pulse of the vehicle speed sensor 43 representing the vehicle speed is input to the input port 35. On the other hand, the output port 36 is connected to the fuel injection valve 6, the electric motor 15, the fuel pump 27, the temperature sensors s1 to sn, the temperature sensors 45 and 46, the flow meters 61 and 62, and the NOx sensors 71 and 72 via the corresponding drive circuit 38. Connected to.
[0018]
As the catalyst 19, for example, an NOx storage reduction catalyst can be used. The NOx catalyst has a function of absorbing NOx when the average air-fuel ratio in the combustion chamber 5 is lean and releasing NOx when the average air-fuel ratio in the combustion chamber 5 becomes rich. This NOx catalyst has, for example, alumina as a carrier, and on this carrier, for example, alkali metal such as potassium K, sodium Na, lithium Li, cesium Cs, alkaline earth such as barium Ba, calcium Ca, lanthanum La, yttrium Y, etc. At least one selected from such rare earths and a noble metal such as platinum Pt are supported. Alternatively, the catalytic converter 20 itself may be one in which a NOx storage agent is supported on a filter that captures exhaust particulates.
[0019]
FIG. 3A is a diagram showing the relationship between the catalyst bed temperature and time when cold starting such an internal combustion engine. In FIG. 3A, the horizontal axis indicates the time after cold start, and the vertical axis indicates the temperature of the NOx catalyst. Region I in FIG. 3A shows a cold start region where the internal combustion engine is cold started, and region II shows a normal operation region after the cold start is completed. In FIG. 3A, it is assumed that the catalyst 19 is divided into three regions c1 to c3 (n = 3). Therefore, in FIG. 3A, the temperature of the region c1 of the catalyst 19 located upstream of the flow of exhaust gas in the exhaust pipe 18 is measured by the temperature sensor s1, and the temperature of the region c2 located in the middle is It is measured by the temperature sensor s2, and the temperature of the region c3 located on the downstream side is measured by the temperature sensor s3. The temperature of the catalyst 19 measured by the temperature sensors s1 to s3 is indicated by curves L1 to L3 in FIG. As shown in the cold start region I in FIG. 3 (a), the catalyst bed temperature indicated by L1 to L3 is relatively low immediately after the cold start, but increases with time. In FIG. The activation temperature of the catalyst 19 indicated by Next, when the internal combustion engine shifts to the normal operation region II, the temperature of the catalyst 19 is maintained almost constant.
[0020]
As can be seen from the curves L1 to L3 in FIG. 3A, in the normal operation region II, the temperatures of the regions c1 to c3 of the catalyst 19 are substantially equal. However, in the cold start region I, the region c1 of the catalyst 19 on the upstream side heats up relatively quickly (see “L1” in FIG. 3A), whereas it exists on the downstream side. The temperature of the region c3 of the catalyst 19 is relatively low (see “L3” in FIG. 3A). The temperature of the region c2 of the catalyst 19 at the intermediate position exists between L1 and L3. That is, the temperature of the catalyst 19 is different between the upstream side and the downstream side of the catalyst 19.
[0021]
FIG. 3B is a graph showing the relationship between the distance from the upstream end of the catalyst and the catalyst bed temperature when the internal combustion engine is cold started. In FIG. 3 (b), the vertical axis represents the catalyst bed temperature, and the horizontal axis represents the catalyst 19 from the end 19a (see FIG. 2) of the catalyst 19 located upstream of the exhaust gas flow. Shows the distance. As can be seen from FIG. 3B, at the cold start, the temperature at the upstream end 19a of the catalyst 19 is higher than the activation temperature of the catalyst 19 indicated by the one-dot chain line, but the downstream end 19b of the catalyst 19 (see FIG. 2). In the vicinity, the temperature is lower than the activation temperature. Thus, the temperature of the catalyst 19 at a certain time in the cold start region I is distributed over a relatively wide range as indicated by L1 to L3.
[0022]
FIG. 4A is a program flowchart showing the operation of the exhaust gas purification apparatus for an internal combustion engine according to the first embodiment of the present invention. The program 100 shown in FIG. 4A is executed in the electronic control unit 30. In the program 100 shown in FIG. 4A, the temperature raising action for raising the temperature of the catalyst 19 after the internal combustion engine is started, for example, post injection, idle rotation speed up or main injection timing is set to the retard side. It is premised on shifting. Further, for example, a case where fuel is added to the NOx catalyst during the temperature raising operation is also included in the temperature raising operation of the present invention. In step 101 of the program 100, the temperature of the catalyst 19 in the catalytic converter 20 provided in the exhaust pipe 18 is detected by temperature sensors s1 to sn. Since it is considered that the catalyst 19 is divided into n regions c1 to regions cn as described above with reference to FIG. 2, the temperature sensors s1 to sn corresponding to these regions c1 to cn provide the regions from the region c1. Each temperature of cn is detected. Next, the routine proceeds to step 102 where the NOx storable amount B at which the catalyst 19 can store NOx is calculated as described later based on the temperature of the catalyst 19 detected at step 101, that is, the temperatures from the region c1 to the region cn. .
[0023]
FIG. 5A is a diagram showing the relationship between the amount of NOx stored in the catalyst at a certain temperature and time, and FIG. 5B is a diagram showing the relationship between the NOx storage amount and temperature. FIG. 5C is a diagram showing a map of the NOx storable amount. The calculation of the NOx storable amount B in step 102 will be described with reference to these drawings. In FIG. 5A, a catalyst of the same shape and shape as the catalyst 19 provided in the catalytic converter 20 is arranged under a certain temperature condition. Next, by forming a rich atmosphere, NOx in the catalyst is released and reduced. Next, NOx is supplied to the catalyst at a constant amount for a predetermined time. The amount of NOx supplied to the catalyst and the amount of exhausted NOx that has passed through the catalyst are measured with a flow meter or the like, and the relationship between the time and the amount of NOx as shown in FIG. Since a part of the supplied NOx is occluded in the catalyst, the exhausted NOx amount is smaller than the supplied NOx amount as shown in FIG. Further, since the stored NOx amount decreases with the passage of time, the exhausted NOx amount gradually increases. In FIG. 5A, the area of the region III between the supplied NOx amount and the exhausted NOx amount corresponds to the NOx occlusion amount of the catalyst in the predetermined time described above.
[0024]
The NOx occlusion amount at a plurality of different temperatures is obtained by performing a similar test with different temperature conditions a plurality of times. Next, these NOx occlusion amounts are plotted with respect to temperature, and the relationship between the NOx occlusion amount and temperature as shown in FIG. 5B is obtained in advance. Further, the NOx storage time B ′ as a function of the catalyst temperature and time is mapped as shown in FIG. 5C by changing the time for supplying NOx and performing the same test several times. Is stored in the ROM 32 in advance.
[0025]
In the electronic control unit 30, the NOx storable amount corresponding to the temperature in the region c1 to the region cn detected by the temperature sensors s1 to sn described above is obtained from a map as shown in FIG. Next, the total value of the NOx storable amount B ′ in each region c1 to cn is divided by “n”. Thereby, the NOx storable amount B in the entire catalyst 19 can be calculated. As described above, in the present invention, the NOx storable amount B of the entire catalyst 19 is obtained based on the temperature of the catalyst 19 at n locations, so that it is possible to calculate a precise NOx storable amount. When “n = 1”, the temperature of the catalyst 19 is calculated from the temperatures detected by the temperature sensors 45 and 46 shown in FIG. 2 using a predetermined equation, and then shown in FIG. The NOx storable amount B may be obtained from such a map.
[0026]
Next, at step 103, the exhausted NOx amount A1 is determined. Here, the exhausted NOx amount means the NOx amount exhausted from the internal combustion engine per unit time. FIG. 6 is a view showing a map of the exhausted NOx amount A1. As shown in FIG. 6, the exhausted NOx amount A1 is stored in advance in the ROM 32 in the form of a map as a function of the load L and the engine speed N. In such a map, a plurality of types are stored in the ROM 32 according to the type of internal combustion engine, for example, an EGR engine in which exhaust gas is recirculated into the engine intake passage and a normal engine. In this way, instead of obtaining the exhausted NOx amount from the map, the exhausted NOx amount A1 may be obtained directly from the NOx sensors 71 and 72 described above. In step 103, the electronic control unit 30 determines the exhausted NOx amount A1 based on such a map or NOx sensor.
[0027]
Next, the routine proceeds to step 104, where it is determined whether or not the exhausted NOx amount A1 is larger than the NOx storable amount B. Here, FIG. 7 which is a figure which shows the relationship between time and the amount of NOx is referred. In FIG. 7, the vertical axis indicates the NOx amount, and the horizontal axis indicates time. Further, as shown in FIG. 7, the exhausted NOx amount A1 is indicated by a dotted line, and a target storable amount A2 described later is indicated by a thick solid line. Further, in FIG. 7, the NOx storable amount when it is larger than the exhausted NOx amount A1 and the target storable amount A2 is indicated by a solid line B1, and the NOx storable amount when it is smaller than the exhausted NOx amount A1 and the target storable amount A2. Is indicated by a solid line B2.
[0028]
If it is determined in step 104 that the exhausted NOx amount A1 is larger than the NOx storable amount B (corresponding to a comparison between the solid line A1 and the solid line B2 in FIG. 7), the process proceeds to step 105. When the exhausted NOx amount A1 is larger than the NOx storable amount B, a temperature raising action, for example, post injection, idle speed increase or main injection timing is set in step 105 to further increase the NOx storable amount of the catalyst 19. Promote shifting to the retard side. Such a temperature raising action is performed based on “A1−B” which is the difference between the exhausted NOx amount A1 and the NOx storable amount B, the space velocity SV in the catalyst 19, and the like. Here, the space velocity SV is obtained by dividing the amount of exhaust gas passing through the catalyst 19 per unit time by the volume of the catalyst 19, and using the flow meters 61 and 62 (see FIG. 2) described above, Calculation is performed in the control unit 30. FIG. 4B is a diagram showing a map of the target temperature determined when the temperature raising action is promoted or suppressed. As shown in FIG. 4B, the target temperature T1 in the first embodiment is a map shape as a function of A1−B, which is the difference between the exhausted NOx amount A1 and the NOx storable amount B, and the space velocity SV. Are stored in the ROM 32 in advance. Further, a similar map of A1-B and space velocity SV when other parameters such as the load L and the engine speed N are different is also stored in the ROM 32. When the space velocity is large, the time for exhaust gas to pass through the NOx catalyst is shortened, and the opportunity for the reaction of NOx with the noble metal and the storage agent of the NOx catalyst is reduced, so that NOx storage may not be performed well. However, in the map as shown in FIG. 4B, the target temperature is set relatively high so that NOx is occluded even when the space velocity is relatively small. A new target temperature T1 is determined from such a map in the electronic control unit 30, and the temperature raising action is promoted so as to reach the target temperature T1. Next, the process returns to step 101 and the illustrated steps are repeated.
[0029]
On the other hand, if it is determined in step 104 that the exhausted NOx amount A1 is not larger than the NOx storable amount B, the routine proceeds to step 106. In step 106, it is determined whether or not the exhausted NOx amount A1 is smaller than the NOx storable amount B. If it is determined in step 106 that the exhausted NOx amount A1 is smaller than the NOx storable amount B (corresponding to a comparison between the solid line A1 and the solid line B1 in FIG. 7), the routine proceeds to step 107. When the exhausted NOx amount A1 is smaller than the NOx storable amount B, in order to reduce the NOx storable amount of the catalyst 19, a temperature raising action, for example, post injection, idle speed increase or main injection timing is delayed in step 107. Suppress shifting to the corner side. As in the case described above, the target temperature T1 is determined from the map as shown in FIG. 4B based on A1-B, the space velocity SV, and the like, and the temperature raising action is suppressed so as to reach this target temperature T1. Next, the process returns to step 101 and the illustrated steps are repeated.
[0030]
As described above, according to the first embodiment of the present invention, the storable amount B is calculated based on the actual temperature of the catalyst 19, and the target storable amount B approaches the separately determined exhaust NOx amount A1. Since the temperature is determined, the NOx purification rate can be optimized. In addition, this prevents fuel from being excessively injected, thereby reducing fuel consumption.
[0031]
FIG. 8A is a program flowchart showing the operation of the exhaust gas purification apparatus for an internal combustion engine according to the second embodiment of the present invention. A program 110 shown in FIG. 8A is executed in the electronic control unit 30. As in the case of the first embodiment, in the program 110 shown in FIG. 8A, the temperature raising action for raising the temperature of the catalyst 19 after the internal combustion engine is started, for example, post injection, idle rotational speed. It is assumed that the main injection timing is shifted to the retard side or the like. Further, for example, a case where fuel is added to the NOx catalyst during the temperature raising operation is also included in the temperature raising operation of the present invention. Steps 111 to 113 of the program 110 are the same as steps 101 to 103 of the program 100, respectively, and thus description of the steps 111 to 113 is omitted.
[0032]
In step 114, the NOx target storable amount A2 is calculated from the exhausted NOx amount A1 determined in step 113. Regarding the target storable amount A2, FIG. 9 (a) showing the relationship between the fuel consumption deterioration rate and the NOx purification rate and FIG. 9 (b) showing the relationship between the fuel consumption deterioration rate and the storable amount are shown. The description will be given with reference. In FIG. 9A, the horizontal axis represents the fuel consumption deterioration rate, and the vertical axis represents the NOx purification rate. Here, the fuel consumption deterioration rate is obtained by dividing the difference between the fuel consumption amount when the temperature raising action is performed and the fuel consumption amount when the temperature raising action is not performed by the fuel consumption amount when the temperature raising action is not performed. It is. As shown in FIG. 9A, the fuel injection amount is increased in order to increase the NOx purification rate, but this also increases the fuel consumption deterioration rate. Therefore, the NOx purification rate and the fuel consumption deterioration rate are shown in FIG. Draw an S-curve as shown in (a). Here, a point K1 shown in FIG. 9A is an inflection point convex downward, and a point K2 is an inflection point convex upward. In FIG. 9A, the change in the NOx purification rate is relatively small even if the temperature is increased by increasing the fuel in the region Z1 to the left of the inflection point K1 and the region Z3 to the right of the inflection point K2. On the other hand, in the region Z2 between the inflection points K1 and K2, the change in the NOx purification rate with respect to the temperature rising action is relatively large. In particular, the inflection point K2 has the largest NOx purification effect with respect to the fuel consumption deterioration rate. Is a point.
[0033]
Next, in FIG. 9B, the horizontal axis indicates the fuel consumption deterioration rate as in FIG. 9A, and the vertical axis indicates the NOx storable amount B. As can be seen from FIG. 9B, the fuel consumption deterioration rate and the storable amount B are in a linear relationship as indicated by a straight line M, and such a relationship under various conditions is obtained in advance. In FIG. 9B, the exhausted NOx amount A1 is indicated by a dotted line. Here, when a straight line X passing through the inflection point K2 shown in FIG. 9A and the fuel consumption deterioration rate corresponding thereto is drawn as shown, the straight line X is the straight line M in FIG. 9B or Intersect at a point P2. In FIG. 9A, since the inflection point K2 is known to have the greatest NOx purification effect on the fuel consumption deterioration rate, the storable amount corresponding to this point P2 is set as the NOx target storable amount A2. As a result, the NOx purification rate relative to the fuel consumption deterioration rate can be most enhanced. Therefore, since the value of the exhausted NOx amount A1 in FIG. 9B and the target storable amount A2 obtained as described above differ by a difference α2, the exhausted NOx amount A1 is the target shown in FIG. 9B. The exhausted NOx amount A1 is corrected by the difference α2 so as to be equal to the storable amount A2. FIG. 10 is a diagram showing a map of the target storable amount A2. The target storable amount A2 obtained as described above is stored in advance in the ROM 32 in the form of a map as a function of the load L, the engine speed N, and the exhausted NOx amount A1, as shown in FIG. In step 114, the target storable amount A2 is obtained from a predetermined map as shown in FIG. Instead of using such a map, the target storable amount A2 may be calculated by multiplying the exhausted NOx amount A1 by a predetermined coefficient obtained in advance in step 114.
[0034]
9A and 9B, the target storable amount A2 is determined based on the straight line X passing through the inflection point K2. As described above, the inflection point K2 has the largest NOx purification effect on the fuel consumption deterioration rate. At the inflection point K2, the fuel consumption deterioration rate is relatively large. Accordingly, for example, a point between the point P1 where the straight line Y passing through the inflection point K1 in FIG. 9A and the corresponding fuel consumption deterioration rate intersects the straight line M in FIG. P0 may be determined, and the target storable amount A2 may be determined so as to correspond to this point P0. In this case, the target storable amount A2 is larger than the exhausted NOx amount A1 by the difference α0. In such a case, the target storable amount A2 can be set to be adjustable while the fuel consumption deterioration rate is kept relatively low, that is, so that the amount of fuel consumed to raise the temperature of the catalyst is reduced. Therefore, in the present embodiment, the fuel consumption can be suppressed by adjusting the target storable amount A2. Note that the difference α1 in FIG. 9B indicates the difference between the exhausted NOx amount A1 at the point P1 and the target storable amount A2 corresponding to the point P1.
[0035]
After calculating the target storable amount A2 in step 114 as described above, the process proceeds to step 115. In step 115, it is determined whether or not the target storable amount A2 is larger than the NOx storable amount B. If it is determined in step 115 that the target storable amount A2 is larger than the NOx storable amount B (corresponding to a comparison between the solid line A2 and the solid line B2 in FIG. 7), the process proceeds to step 116. When the target storable amount A2 is larger than the NOx storable amount B, in step 116, in order to further increase the NOx storable amount of the catalyst 19, for example, post-injection, idle speed increase or main injection timing To promote the shifting of the angle to the retard side. Such a temperature raising action is performed based on “A2−B” which is the difference between the target storable amount A2 and the NOx storable amount B, the space velocity SV described above, and the like. FIG. 8B is a diagram showing a map of the target temperature determined when the temperature raising action is promoted or suppressed. As shown in FIG. 8 (b), the target temperature T2 in the second embodiment is a function of A2-B, which is the difference between the target storable amount A2 and the NOx storable amount B, and the space velocity SV. Is stored in the ROM 32 in advance. Further, a similar map of A2-B and space velocity SV when other parameters such as the load L and the engine speed N are different is also stored in the ROM 32. As in the case described above, in the map as shown in FIG. 8B, the target temperature is set relatively high so that NOx is occluded even when the space velocity is relatively large. A new target temperature T2 is determined in the electronic control unit 30, and the temperature raising action is promoted so as to reach the target temperature T2. Next, the process returns to step 111 and the illustrated steps are repeated.
[0036]
On the other hand, if it is determined in step 115 that the target storable amount A2 is not greater than the NOx storable amount B, the process proceeds to step 117. In step 117, it is determined whether or not the target storable amount A2 is smaller than the NOx storable amount B. If it is determined in step 117 that the target storable amount A2 is smaller than the NOx storable amount B (corresponding to a comparison between the solid line A2 and the solid line B2 in FIG. 7), the process proceeds to step 118. If the target storable amount A2 is smaller than the NOx storable amount B, the temperature rise action in step 118, for example, post injection, idle speed increase or main injection timing is set to decrease the NOx storable amount of the catalyst 19. Prevent shifting to the retard side. Similarly to the case described above, the target temperature T2 is determined based on A2-B, the space velocity SV, and the like from the map as shown in FIG. 8B, and the temperature rising action is suppressed so as to reach this target temperature T2. Next, the process returns to step 111 and the illustrated steps are repeated.
[0037]
Thus, according to the second embodiment of the present invention, the storable amount B is calculated based on the actual temperature of the catalyst 19, and the target storable based on the exhausted NOx amount A1 in order to further increase the NOx purification rate. The quantity A2 is further determined. Therefore, the NOx purification rate can be further optimized as compared with the case of the first embodiment described above. Further, for example, by setting the target storable amount A2 corresponding to the fuel consumption deterioration rate between the inflection points K1 and K2 shown in FIG. 9A, it is possible to adjust the fuel consumption to be suppressed. Become.
[0038]
In the above-described embodiment, the single catalytic converter 20 is provided, but a plurality of catalytic converters supporting the NOx catalyst may be provided. In such a case, the catalyst converter 20 flows into the NOx catalyst of each catalytic converter. The amount of inflow NOx to be detected is detected. That is, when the catalytic converter 20 is single, the NOx amount discharged from the internal combustion engine is substantially equal to the NOx amount flowing into the NOx catalyst in the catalytic converter 20, but when a plurality of catalytic converters are provided. The total amount of NOx discharged from the internal combustion engine is not necessarily equal to the amount of NOx flowing into the NOx catalyst in a certain catalytic converter. Therefore, it is obvious for those skilled in the art to detect the inflow NOx amount flowing into the NOx catalyst of each catalytic converter in such a case.
[0039]
【The invention's effect】
According to each invention, it is possible to achieve a common effect that the NOx purification rate can be optimized.
[0040]
Furthermore, according to the second aspect, it is possible to achieve an effect that the NOx purification rate can be more optimally controlled.
Furthermore, according to the third aspect of the invention, even if the space velocity is large, it is possible to obtain an effect that NOx can be occluded in the NOx catalyst by setting the target temperature high.
Furthermore, according to the fourth aspect of the invention, it is possible to achieve an effect that the fuel consumption can be suppressed by adjusting the target NOx storable amount.
Furthermore, according to the fifth aspect, it is possible to obtain an effect that the NOx storable amount can be accurately obtained.
[Brief description of the drawings]
FIG. 1 is a diagram showing a four-stroke compression ignition type internal combustion engine to which the present invention is applied.
FIG. 2 is an enlarged partial view showing the vicinity of a catalytic converter of an internal combustion engine to which the present invention is applied.
FIG. 3A is a diagram showing the relationship between the catalyst bed temperature and time when the internal combustion engine is cold started.
(B) It is a figure which shows the relationship between the distance from the upstream end of a catalyst at the time of the cold start of an internal combustion engine, and a catalyst bed temperature.
FIG. 4 (a) is a flowchart showing the operation of the exhaust gas purification apparatus for an internal combustion engine according to the first embodiment of the present invention.
(B) It is a figure which shows the map of target temperature.
FIG. 5A is a diagram showing the relationship between the amount of NOx stored in a catalyst at a certain temperature and time.
(B) It is a figure which shows the relationship between NOx occlusion amount and temperature.
(C) It is a figure which shows the map of NOx occlusion possible amount.
FIG. 6 is a view showing a map of exhaust NOx amount.
FIG. 7 is a diagram showing the relationship between time and NOx amount in an internal combustion engine.
FIG. 8A is a flowchart showing the operation of the exhaust gas purification apparatus for an internal combustion engine according to the second embodiment of the present invention.
(B) It is a figure which shows the map of target temperature.
FIG. 9A is a diagram showing a relationship between a fuel consumption deterioration rate and a NOx purification rate.
(B) It is a figure which shows the relationship between a fuel consumption deterioration rate and the occlusion amount.
FIG. 10 is a diagram showing a map of a target storable amount.
[Explanation of symbols]
1 ... Engine body
6 ... Fuel injection valve
18 ... discharge pipe
19 ... Catalyst
20 ... Catalytic converter
45, 46 ... Temperature sensor
61, 62 ... Flow meter
71, 72 ... NOx sensor
s1 to sn ... temperature sensor
c1 to cn ... catalyst region
A1 ... NOx emissions
A2 ... Target storage capacity
B ... NOx storage capacity

Claims (5)

In an exhaust gas purification apparatus for an internal combustion engine provided with an NOx storage reduction catalyst disposed in an exhaust passage,
NOx catalyst temperature detecting means for estimating or detecting the temperature of the NOx catalyst;
NOx storable amount estimating means for estimating a NOx storable amount that can be stored in the NOx catalyst based on the temperature of the NOx catalyst estimated or detected by the NOx catalyst temperature detecting means;
A temperature raising means for raising the temperature of the NOx catalyst to a target temperature after starting the internal combustion engine;
An exhaust NOx amount detecting means for estimating or detecting an exhaust NOx amount exhausted from the internal combustion engine,
The exhaust gas purification apparatus for an internal combustion engine, wherein the target temperature of the temperature raising means is determined so that the NOx storable amount and the exhaust NOx amount are substantially equal. In an exhaust gas purification apparatus for an internal combustion engine provided with an NOx storage reduction catalyst disposed in an exhaust passage,
NOx catalyst temperature detecting means for estimating or detecting the temperature of the NOx catalyst;
NOx storable amount estimating means for estimating a NOx storable amount that can be stored in the NOx catalyst based on the temperature of the NOx catalyst estimated or detected by the NOx catalyst temperature detecting means;
A temperature raising means for raising the temperature of the NOx catalyst to a target temperature after starting the internal combustion engine;
An exhaust NOx amount detecting means for estimating or detecting an exhaust NOx amount exhausted from the internal combustion engine;
A target NOx storable amount calculating means for calculating a target NOx storable amount, which is a target value of the NOx storable amount, using the exhausted NOx amount;
The exhaust gas purification apparatus for an internal combustion engine, wherein the target temperature of the temperature raising means is determined so that the NOx storable amount and the target NOx storable amount are substantially equal. Furthermore, it comprises space velocity detection means for estimating or detecting the space velocity of the NOx catalyst,
The exhaust gas purification apparatus for an internal combustion engine according to claim 1 or 2, wherein the target temperature is increased as the space velocity detected by the space velocity detection means increases. The said temperature raising means uses the fuel of the said internal combustion engine, The said target NOx occlusion amount is adjustable so that the consumption amount of the said fuel may become small. Exhaust gas purification device for internal combustion engine. The NOx catalyst temperature detection means estimates the temperature in each of the NOx catalyst regions divided into at least two in the exhaust gas flow direction,
The internal combustion engine according to any one of claims 1 to 4, wherein the NOx storable amount calculating means calculates the NOx storable amount from a storable NOx amount in each of the at least two regions. Exhaust purification device.

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