JP3622624B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust emission control device for an internal combustion engine.
[0002]
[Prior art]
Conventionally, a particulate filter for collecting particulates in exhaust gas is placed in the engine exhaust passage, and when the particulate filter is to be regenerated, the particulate filter is heated to burn the collected particulates. An exhaust gas purification apparatus for an internal combustion engine that is damped is known.
[0003]
However, if the temperature of the particulate filter becomes excessively high during the regeneration operation, the particulate filter may melt. Therefore, an exhaust emission control device for an internal combustion engine is known in which the rate of change of the temperature of the particulate filter during the regeneration operation is detected, and the regeneration operation is weakened when this rate of change is greater than a predetermined set rate of change. (See JP-A-5-240025).
[0004]
If the rate of change of the particulate filter temperature is large when the particulate filter temperature is high, the particulate filter temperature may then become excessively high and the particulate filter may melt. Therefore, if the regeneration action is weakened at this time, the particulate filter can be prevented from being melted.
[0005]
[Problems to be solved by the invention]
However, if the regenerating action is weakened when the temperature of the particulate filter is low enough to prevent melting, simply because the temperature change rate is high, the temperature of the particulate filter cannot be quickly raised and There is a problem that it takes a long time to complete the action. That is, the regeneration action should be weakened only when the temperature of the particulate filter may be melted. Then, it is necessary to accurately determine whether or not the particulate filter may be melted.
[0006]
SUMMARY OF THE INVENTION An object of the present invention is to provide an exhaust emission control device for an internal combustion engine that can accurately determine whether or not a particulate filter may be melted.
[0008]
[Means for Solving the Problems]
SUMMARY OF THE INVENTION In order to solve the above SL problem, a particulate filter for collecting particulates in exhaust is disposed in the engine exhaust passage, the particulate on when to play the particulate filter in the exhaust purification system of an internal combustion engine which is adapted allowed to burn the particulates captured by heating the filter to detect a representative temperature representing the temperature of the particulate filter during regeneration action, the rate of change of the representative temperature, The regeneration action is weakened when the rate of change is larger than a preset change rate so as to decrease as the representative temperature increases . That is, in the first invention, it is determined whether there is a possibility that the particulate filter may be melted based on the change rate of the representative temperature and the set change rate determined according to the representative temperature. It is accurately determined whether or not.
[0009]
Further, according to the second invention to solve the above problems, to place the particulate filter for collecting particulates in exhaust into the engine exhaust passage, patties when to play the particulate filter In an exhaust gas purification apparatus for an internal combustion engine that heats a curative filter to burn collected particulates, a representative temperature representative of the temperature of the particulate filter during regeneration is detected, and the representative temperature is determined in advance. When the change rate of the representative temperature is higher than the predetermined first set change rate and the change rate of the representative temperature change rate is larger than the predetermined second set change rate. The regenerative action is weakened. That is, in the second invention, a representative temperature, and the rate of change of the representative temperature, whether or not there is a possibility that the particulate filter is melting on the basis of the rate of change of the rate of change of the representative temperature is determined, thus the regenerative action It is accurately determined whether or not to weaken.
[0011]
Further, according to the third invention for solving the above problems, to place the particulate filter for collecting particulates in exhaust into the engine exhaust passage, patties when to play the particulate filter In an exhaust gas purification apparatus for an internal combustion engine that heats a particulate filter and burns the collected particulates, a representative temperature representative of the temperature of the particulate filter during regeneration and the exhaust gas flowing out of the particulate filter When the representative temperature is higher than the predetermined set temperature and the oxygen concentration is lower than the predetermined set concentration so as to increase as the representative temperature increases , the regeneration action is weakened. I am doing so. That is, in the third invention, a representative temperature, particulate particulate filter on the basis of the oxygen concentration which represents the combustion state of being judged whether there is a risk of erosion and hence whether to weaken the playback action Accurately judged.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a case where the present invention is applied to a diesel engine. However, the present invention can also be applied to a spark ignition gasoline engine.
Referring to FIG. 1, 1 is an engine body, 2 is a piston, 3 is a combustion chamber, 4 is an intake port, 5 is an intake valve, 6 is an exhaust port, 7 is an exhaust valve, and 8 is disposed in the combustion chamber 3. Each fuel injection valve is shown. The intake port 4 is connected to a surge tank 10 via a corresponding intake branch pipe 9, and the surge tank 10 is connected to an air cleaner 12 via an intake duct 11. A throttle valve 13 is disposed in the intake duct 11. The fuel injection valve 8 is connected to the discharge side of a fuel pump (not shown) via a fuel accumulator chamber (not shown), so that fuel injection can be performed a plurality of times in one combustion cycle.
[0013]
On the other hand, the exhaust port 6 is connected to a casing 17 containing a catalyst 16 via an exhaust manifold 14 and an exhaust pipe 15, and the casing 17 is connected to an exhaust pipe 18. A diesel particulate filter (hereinafter referred to as DPF) 19 is accommodated in the exhaust manifold 14.
The electronic control unit (ECU) 30 is a digital computer, and is connected to each other via a bidirectional bus 31. A ROM (read only memory) 32, a RAM (random access memory) 33, a CPU (microprocessor) 34, and a constant time. A B-RAM (backup RAM) 35 connected to a power source, an input port 36, and an output port 37 are provided. A pressure sensor 38 that generates an output voltage proportional to the intake pressure in the surge tank 10 is disposed in the surge tank 10. A temperature sensor 39 that generates an output voltage proportional to the temperature of the exhaust gas flowing out from the DPF 19 is disposed in the exhaust manifold 14 downstream of the DPF 19. A depression amount sensor 40 that generates an output voltage proportional to the depression amount is attached to an accelerator pedal (not shown). The output voltages of these sensors 38, 39, and 40 are input to the input port 36 via corresponding AD converters 41, respectively. Further, a rotational speed sensor 42 that generates an output pulse representing the engine rotational speed is connected to the input port 36. On the other hand, the output port 37 is connected to each fuel injection valve 8 via a corresponding drive circuit 43.
[0014]
Note that the exhaust temperature detected by the temperature sensor 39 represents the temperature of the DPF 19. Therefore, hereinafter, this exhaust temperature is referred to as the DPF temperature. Further, the DPF temperature is read at regular time intervals, and the DPF temperature read at the i-th time is represented by T (i).
The DPF 19 is for collecting particulates contained in the exhaust discharged from the engine, and is made of a porous material such as ceramic. In the present embodiment, the DPF 19 carries an oxidation catalyst.
[0015]
As time passes, the amount of particulates collected by the DPF 19 increases, and as a result, the flow path resistance by the DPF 19 increases. Therefore, it is necessary to regenerate the DPF 19 by removing the collected particulates.
There are various methods for regenerating the DPF 19, but in this embodiment, when the DPF 19 is to be regenerated, the sub-injection is performed from the fuel injection valve 8 in the expansion stroke or exhaust stroke after the completion of the main injection. That is, when secondary fuel by sub-injection reaches the DPF 19, it is burned by the oxidation catalyst, and as a result, the DPF temperature is raised. As a result, the collected particulates burn and are removed from the DPF 19, and thus the DPF 19 is regenerated.
[0016]
Such a regeneration operation of the DPF 19 is started when the start condition is satisfied, and is stopped when the completion condition is satisfied. In the present embodiment, the particulate amount collected by the DPF 19 is estimated, and it is determined that the start condition is satisfied when the estimated particulate amount becomes larger than a predetermined threshold value. The collected particulate amount can be estimated based on, for example, the integrated fuel injection amount, the differential pressure across the DPF 19, and the like. On the other hand, after the start of the regeneration action, it is determined that the completion condition is satisfied when a predetermined set time has elapsed since the collected particulates started to burn. This set time can be the time required to burn almost all of the collected particulates.
[0017]
By the way, as mentioned at the beginning, the DPF temperature during the regeneration operation is preferably as high as possible for the regeneration operation, but it is necessary to prevent the DPF 19 from being melted. Therefore, it is determined whether or not there is a possibility that the DPF 19 may be melted. When there is a possibility that the DPF 19 may be melted, the regeneration action is weakened. This is the basic idea of the present invention.
[0018]
In this embodiment, when the regeneration action is to be weakened, the sub-injection is stopped, that is, the regeneration action is stopped. In this way, it is possible to reliably prevent the DPF 19 from being melted. However, it is possible to continue the sub-injection while reducing the amount of fuel to be injected, or to cool the DPF 19 by supplying secondary air to the DPF 19, for example.
[0019]
Next, a method for determining whether or not the DPF 19 may be melted will be described. In this embodiment, the determination is made based on both the DPF temperature and the change rate of the DPF temperature. Specifically, referring to FIG. 2, it is first determined whether or not the DPF temperature T (k-1) in the previous detection cycle is higher than a predetermined set temperature T1, for example. If T (k-1)> T1, then the DPF temperature change rate DT (k) (= T (k) -T (k-1)) is greater than a predetermined set change rate D1, for example. Is judged. When DT (k)> D1, that is, when T (k-1)> T1 and DT (k)> D1, the regeneration action is stopped.
[0020]
That is, when the DPF temperature is high and the DPF temperature change rate is large, it is determined that the DPF 19 may be melted, and the regeneration action is stopped. As a result, it is possible to prevent the DPF 19 from being melted. On the other hand, when the DPF temperature is low, the regeneration action is continued regardless of the DPF temperature change rate, and therefore the DPF temperature can be quickly increased. Further, even when the DPF temperature is high, when the DPF temperature change rate is small, the regeneration operation is continued, so that the DPF temperature can be further increased.
[0021]
FIG. 3 shows a routine for executing the first embodiment described above. This routine is executed by interruption every predetermined time.
Referring to FIG. 3, first, at step 100, the parameter i is incremented by one. In the subsequent step 101, the DPF temperature T (i) at this time is read. In the following step 102, it is determined whether or not the current regenerating operation is in progress. If it is not during the current regenerating operation, the routine proceeds to step 103 where it is determined whether or not a start condition is satisfied. When the start condition is not satisfied, the processing cycle is then terminated. When the start condition is satisfied, the routine proceeds to step 104 where the regeneration action is started.
[0022]
On the other hand, when the current regenerating action is in step 102, the routine proceeds to step 105 where it is determined whether or not a completion condition is satisfied. When the completion condition is satisfied, the routine proceeds to step 106 where the regeneration action is stopped. When the completion condition is not satisfied, the process proceeds to a regeneration action control subroutine at step 107. This subroutine is shown in FIG.
[0023]
Referring to FIG. 4, first, at step 110, it is judged if the DPF temperature T (i-1) in the previous processing cycle is higher than the set temperature T1. When T (i-1)> T1, the routine proceeds to step 111 where the DPF temperature change rate DT (i) is calculated (DT (i) = T (i) -T (i-1)). In the following step 112, it is determined whether or not the DPF temperature change rate DT (i) is larger than the set change rate D1. When DT (i)> D1, that is, when T (i-1)> T1 and DT (i)> D1, the routine proceeds to step 113 where the regeneration action is stopped. On the other hand, when T (i−1) ≦ T1 in step 110, or when DT (i) ≦ D1 in step 112, the processing cycle is then terminated. That is, the regeneration action is continued.
[0024]
Next, another embodiment will be described.
In the present embodiment, it is determined whether or not there is a possibility that the DPF 19 may be melted based on the DPF temperature change rate DT (i) and the set change rate D2 determined according to the DPF temperature T (i). That is, as shown in FIG. 5, when the set change rate D2 is set so as to decrease as the DPF temperature T (i) becomes higher, and the DPF temperature change rate DT (i) is larger than the set change rate D2. The regeneration action is stopped.
[0025]
In this way, when the DPF temperature change rate DT (i) increases when the DPF temperature T (i) is high, the regeneration action is stopped, but when the DPF temperature T (i) is low, it is not stopped. Therefore, it is possible to quickly increase the DPF temperature while preventing the DPF 19 from being melted. The setting change rate D2 is stored in advance in the ROM 32 in the form of a map shown in FIG.
[0026]
FIG. 6 shows a regeneration action control subroutine according to this embodiment. Note that the routine shown in FIG. 3 is also executed in this embodiment.
Referring to FIG. 6, first, at step 120, the DPF temperature change rate DT (i) is calculated. In the following step 121, the setting change rate D2 is calculated from the map of FIG. In the following step 122, it is determined whether or not the DPF temperature change rate DT (i) is larger than the set change rate D2. When DT (i)> D2, the routine proceeds to step 123 where the regeneration action is stopped. On the other hand, when DT (i) ≦ D2, the processing cycle is then terminated. That is, the regeneration action is continued.
[0027]
Next, still another embodiment will be described. In this embodiment, it is determined whether or not there is a possibility that the DPF 19 may be melted based on the DPF temperature, the DPF temperature change rate, and the change rate of the DPF temperature change rate. More specifically, referring to FIG. 7, it is first determined whether or not the DPF temperature T (k-2) in the last detection cycle is higher than a predetermined set temperature T3, for example. When T (k−2)> T3, it is next determined whether or not the DPF temperature change rate DT (k−1) in the previous detection cycle is larger than a predetermined set change rate D3, for example. When DT (k−1)> D3, the rate of change DDT (k) (= DT (k) −DT (k−1)) of the DPF temperature change rate is then set to a predetermined set value DD3, for example. It is determined whether or not it is larger. When DDT (k)> DD3, that is, when T (k-2)> T3, DT (k-1)> D3, and DDT (k) > DD3 , the regenerating action is stopped.
[0028]
That is, when the DPF temperature is high, the DPF temperature change rate is large, and the DPF temperature change rate is large, it is determined that the DPF 19 may be melted, and the regeneration operation is stopped. When the set value DD3 is, for example, zero, the time-dependent change curve of the DPF temperature is a convex curve downward mathematically, and at this time, it can be said that the DPF temperature rises extremely rapidly. In such a case, the regeneration action is stopped, and therefore it is possible to prevent the DPF 19 from being melted.
[0029]
On the other hand, when the DPF temperature is low, or when the DPF temperature change rate is small even when the DPF temperature is high, or when the DPF temperature change rate is small even when the DPF temperature is high and the DPF temperature change rate is large, the regeneration action is achieved. Will continue. Therefore, the DPF temperature can be quickly increased, or the DPF temperature can be further increased.
FIG. 8 shows a regeneration action control subroutine according to this embodiment. Note that the routine shown in FIG. 3 is also executed in this embodiment.
[0030]
Referring to FIG. 8, first, at step 130, it is judged if the DPF temperature T (i-2) in the last processing cycle is higher than the set temperature T3. When T (i-2)> T3, the routine proceeds to step 131 where the DPF temperature change rate DT (i-1) in the previous processing cycle is calculated. In the following step 132, it is determined whether or not the DPF temperature change rate DT (i-1) is larger than the set change rate D3. When DT (i-1)> D3, the routine proceeds to step 133, where the DPF temperature change rate DT (i) in the current processing cycle is calculated. In the following step 134, the change rate DDT (i) of the DPF temperature change rate is calculated. In the following step 135, it is determined whether or not the change rate DDT (i) of the DPF temperature change rate is larger than the set value DD3. When DDT (i)> DD3, the routine proceeds to step 136 where the regeneration action is stopped. On the other hand, when T (i−2) ≦ T3 in step 130, or when DT (i−1) ≦ D3 in step 132, or when DDT (i) ≦ DD3 in step 135, the processing cycle is then terminated. To do. That is, the regeneration action is continued.
[0031]
Next, still another embodiment will be described.
In the present embodiment, the DPF temperature after a predetermined set time is predicted based on the change history of the DPF temperature, and it is determined whether there is a possibility that the DPF 19 may be melted based on the predicted DPF temperature. Specifically, based on a plurality of DPF temperature detection results T (i), T (i−1), T (i−2)..., A predicted DPF temperature ET (i + 1) that is a DPF temperature in the next detection cycle. And the regenerating action is stopped when the predicted DPF temperature ET (i + 1) is higher than a predetermined set temperature T4, for example.
[0032]
In this way, the DPF temperature is prevented from becoming higher than the set temperature T4, and the regeneration action is continued as long as the DPF temperature is lower than the set temperature T4. For this reason, the set temperature T4 can be set to a temperature at which the DPF 19 starts to melt, and at this time, the DPF temperature can be considerably increased while preventing the DPF 19 from being melted.
[0033]
Any method may be used to obtain the predicted DPF temperature ET (i + 1). For example, as shown in FIG. 9A, a DPF temperature change curve with time is approximated using a plurality of DPF temperature detection results T (k), T (k-1), T (k-2). The predicted DPF temperature ET (k + 1) can be calculated using this approximate result. Alternatively, as shown in FIG. 9B, the DPF temperature change rate DT (k) in the current detection cycle is calculated, and the DPF temperature change rate is assumed to be constant while maintaining this DT (k). The temperature ET (k + 1) can also be calculated.
[0034]
FIG. 10 shows a regeneration action control subroutine according to this embodiment. Note that the routine shown in FIG. 3 is also executed in this embodiment.
Referring to FIG. 10, first, at step 140, the predicted DPF temperature ET (i + 1) in the next processing cycle is calculated. In the following step 141, it is determined whether or not the predicted DPF temperature ET (i + 1) is higher than the set temperature T4. When ET (i + 1)> T4, the routine proceeds to step 142 where the regeneration action is stopped. On the other hand, when ET (i + 1) ≦ T4, the processing cycle is then terminated. That is, the regeneration action is continued.
[0035]
FIG. 11 shows yet another embodiment.
Referring to FIG. 11, an oxygen concentration sensor 44 that generates an output voltage representing the oxygen concentration in the exhaust gas flowing out from the DPF 19 is disposed in the exhaust manifold 14 downstream of the DPF 19. The output voltage of the oxygen concentration sensor 44 is input to the input port 36 via the corresponding AD converter 41.
[0036]
In this embodiment, it is determined whether or not there is a possibility that the DPF 19 may be melted based on the DPF temperature T (i) and the oxygen concentration COX (i) in the exhaust gas flowing out from the DPF 19. Specifically, the regeneration action is performed when the DPF temperature T (i) is higher than a predetermined set temperature T5, for example, and the oxygen concentration V (i) is lower than a predetermined set temperature C5, for example. Is stopped. Note that the set concentration C5 can be set so as to increase as the DPF temperature T (i) increases.
[0037]
That is, when the DPF temperature is high and the oxygen concentration is low, it is determined that the DPF 19 may be melted, and the regeneration action is stopped. As a result, it is possible to prevent the DPF 19 from being melted. On the other hand, when the DPF temperature is low, the regeneration action is continued, and therefore the DPF temperature can be quickly raised. Further, even if the DPF temperature is high, the regeneration action is continued when the oxygen concentration is high, and therefore the DPF temperature can be further increased.
[0038]
Here, the oxygen concentration is taken into account because the oxygen concentration represents the combustion state of the particulates in the DPF 19. More specifically, the particulates burn while consuming oxygen in the exhaust gas. Therefore, when the amount of the burning particulates increases, the oxygen concentration in the exhaust gas flowing out from the DPF 19 decreases. For this reason, when the DPF temperature is high and the oxygen concentration is low, it can be determined that the DPF 19 may be melted.
[0039]
FIG. 12 shows a regeneration action control subroutine according to this embodiment. Note that the routine shown in FIG. 3 is also executed in this embodiment.
Referring to FIG. 12, first, at step 150, it is judged if the DPF temperature T (i) is higher than the set temperature T5. When T (i)> T5, the routine proceeds to step 151 where the oxygen concentration COX (i) is read. In the following step 152, it is determined whether or not the oxygen concentration COX (i) is lower than the set concentration C5. When COX (i) <C5, that is, when T (i)> T5 and COX (i) <C5, the routine proceeds to step 153 where the regeneration action is stopped. On the other hand, when T (i) ≦ T5 in step 150, or when COX (i) ≧ C5 in step 152, the processing cycle is then terminated. That is, the regeneration action is continued.
[0040]
In the embodiments described so far, the temperature of the exhaust gas flowing out from the DPF is used as the representative temperature of the DPF. However, the temperature of the exhaust gas flowing into the DPF can be used as the representative temperature, or the DPF temperature obtained by directly attaching the temperature sensor to the DPF can be used.
[0041]
【The invention's effect】
Since it is possible to accurately determine whether or not the particulate filter may be melted, the regeneration operation can be completed quickly while preventing the particulate filter from being melted.
[Brief description of the drawings]
FIG. 1 is an overall view of an internal combustion engine.
FIG. 2 is a diagram for explaining regeneration action control;
FIG. 3 is a flowchart showing a routine for controlling the regeneration action.
FIG. 4 is a flowchart showing a regeneration action control subroutine.
FIG. 5 is a diagram showing a setting change rate D2.
FIG. 6 is a flowchart showing a regeneration action control subroutine in another embodiment.
FIG. 7 is a diagram for explaining regeneration action control in still another embodiment.
FIG. 8 is a flowchart showing a regenerative action control subroutine in still another embodiment.
FIG. 9 is a diagram for explaining regeneration action control in still another embodiment.
FIG. 10 is a flowchart showing a regeneration operation control subroutine in still another embodiment.
FIG. 11 is an overall view of an internal combustion engine in still another embodiment.
FIG. 12 is a flowchart showing a regeneration operation control subroutine in still another embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Entire engine 14 ... Exhaust manifold 19 ... Particulate filter 39 ... Temperature sensor

Claims (3)

A particulate filter for collecting particulates in the exhaust is disposed in the engine exhaust passage, and when the particulate filter is to be regenerated, the particulate filter is heated to burn the collected particulates. in the exhaust purification system of an internal combustion engine which is adapted to detect a representative temperature representing the temperature of the particulate filter during regeneration action, the surrogate table temperature rate of change, preset to be smaller as surrogate table temperature increases An exhaust emission control device for an internal combustion engine, wherein the regeneration action is weakened when the rate of change is larger than a set change rate. A particulate filter for collecting particulates in the exhaust is disposed in the engine exhaust passage, and when the particulate filter is to be regenerated, the particulate filter is heated to burn the collected particulates. In the exhaust gas purification apparatus for an internal combustion engine thus configured, a representative temperature representative of the temperature of the particulate filter during the regeneration operation is detected, the representative temperature is higher than a preset set temperature, and the rate of change of the representative temperature is Exhaust gas from an internal combustion engine in which the regeneration action is weakened when the change rate of the representative temperature change rate is larger than the predetermined first set change rate and the representative temperature change rate is higher than the predetermined second set change rate. Purification equipment. A particulate filter for collecting particulates in the exhaust is disposed in the engine exhaust passage, and when the particulate filter is to be regenerated, the particulate filter is heated to burn the collected particulates. In the exhaust gas purification apparatus for an internal combustion engine thus configured, the representative temperature representative of the temperature of the particulate filter during the regeneration operation and the oxygen concentration in the exhaust gas flowing out of the particulate filter are detected, and the representative temperature is determined in advance. An exhaust purification device for an internal combustion engine that weakens the regenerating action when the oxygen concentration is lower than a preset concentration that is higher than the preset temperature and the oxygen concentration becomes higher as the representative temperature becomes higher .

Images