JPH08218847A - Exhaust gas purifying method for diesel engine - Google Patents

Abstract

PURPOSE: To reliably prevent a melt loss of a filter and to perform excellent regeneration by a method wherein in spite of the structure of a filter for collecting particulate, feedback control of a filter regeneration timing is effected through detection of an accurate filter maximum temperature during regeneration. CONSTITUTION: According to the structure of a particulate filter (filter) 5, a second temperature sensor ST2 is arranged adjacently with a part where temperature is increased to a highest value during regeneration and temperature during regeneration is monitored. An exhaust gas pressure PD right above and right below the filter 5 is measured and after a pressure loss ΔP by the filter 5 is converted into a value ΔP1 in a standard operation state, the value is averaged to determine a pressure loss ΔP2 and when the value attains to a pressure loss value ΔPr (a threshold value) during collection of a given amount of exhaust particulate, regeneration is started. The temperature Tf of the part, where temperature is increased to a highest value, of the filter 5 is continuously measured by the ST2 to determined a peak value Tfp . Through adjustment of the threshold ΔPr according to a difference between the value Tfp and a target value Tfp ', the Tfp is maintained at a value approximately equal to the Tfp '.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purifying exhaust gas from a diesel engine.

[0002]

2. Description of the Related Art Exhaust gas from diesel engines contains exhaust particulates (particulates) containing carbon as a main component, which are removed before they are released into the atmosphere to cause environmental pollution. Preferably,
Therefore, a ceramic filter for collecting particulates is arranged in the exhaust passage of the diesel engine.

When the amount of particulates trapped in the filter increases with the use of a diesel engine, exhaust resistance increases and engine performance deteriorates. Therefore, the trapped particulates are periodically burned to regenerate the filter. It is necessary.

If the filter regeneration is started at a time when the amount of collected particulates is small, not only the combustion propagation of particulates becomes insufficient and the filter is not regenerated well, but also the filter is regenerated more than necessary times. ,
The heat of combustion of particulates reduces the life of the filter. If the filter regeneration is not started until the amount of collected particulates becomes considerably large, not only the engine performance at this time will drop significantly, but also the amount of heat generated by particulate combustion during filter regeneration will become considerably large overall. , The filter may melt.

In Japanese Patent Laid-Open No. 3-18614, the pressure loss value of exhaust gas passing through the filter is used as the amount of particulate collection of the filter, and when the value reaches a set value, regeneration of the filter is started. However, when the filter temperature during regeneration deviates from the predetermined range to the upper side or the lower side, feedback control is performed to decrease or increase the set value as the actual particulate collection amount is too large or too small, and the desired amount is obtained. There is disclosed a particulate filter regenerating apparatus which starts the filter regeneration when the particulates are collected, prevents the filter from being melted and is damaged, and intends good filter regeneration.

When burning particulates during filter regeneration, the secondary air required for this combustion is supplied, and the particulates collected by the filter are burned sequentially from the upstream side of the secondary air to the downstream side. To be made. When the particulates are collected evenly in each part of the filter, the combustion heat generated in each part is almost equal, but in the axial direction, the combustion heat on the upstream side of the secondary air downstream of the filter is transferred in the axial direction. Therefore, the temperature becomes high. Further, in the radial direction, the combustion heat in the surroundings is transferred and concentrated in the radial direction toward the center of the filter, resulting in a high temperature. In the above particulate filter regenerating apparatus, since the temperature sensor is arranged in the vicinity of the central portion of the end surface on the downstream side of the secondary air, in this case, the maximum temperature of the filter during regeneration is measured.

[0007]

However, depending on the structure of the filter, the particulates are not evenly collected in each part of the filter, and the central part of the end surface of the secondary air downstream side of the filter is not the part having the highest temperature. In the above-mentioned conventional technique, the peak temperature measured by the temperature sensor is much lower than the filter maximum temperature at the time of regeneration,
If the above set value is increased accordingly, the amount of particulates collected at the start of regeneration will become too large and the engine output will drop significantly, or the amount of heat generated during regeneration will become extremely large and the filter may melt and be damaged. There is a nature.

Therefore, the object of the present invention is to irrespective of the structure of the filter for collecting particulates, by detecting the accurate maximum temperature of the filter at the time of regeneration and performing feedback control of the regeneration time of the filter, so that the filter is melted. An object of the present invention is to provide an exhaust emission control device for a diesel engine that can reliably prevent loss and realize good regeneration.

[0009]

An exhaust gas purification apparatus for a diesel engine according to the present invention regenerates a filter for collecting particulates arranged in an exhaust passage and burning the collected particulates. Regeneration time determining means for determining the regeneration time based on the particulate collection amount, and a filter having the highest temperature during regeneration determined based on the particulate collection amount distribution of the filter estimated by the structure of the filter. A temperature sensor disposed adjacent to the portion, and feedback control means for feedback-controlling the regeneration time of the filter determined by the regeneration time determination means based on the peak temperature during filter regeneration measured by the temperature sensor, It is characterized by including.

[0010]

In the exhaust emission control system of the diesel engine described above, the temperature sensor has the highest temperature during regeneration, which is determined based on the particulate collection amount distribution of the filter estimated by the structure of the particulate collection filter. Since it is arranged adjacent to the filter portion, the peak temperature during filter regeneration measured by this temperature sensor is the accurate filter maximum temperature, and the feedback control means is
The regeneration time of the filter determined by the regeneration time determining means is feedback-controlled based on this peak temperature.

[0011]

1 is a schematic view showing an exhaust emission control system for a diesel engine according to the present invention. In the figure, 1 is a diesel engine and 2 is its exhaust passage. A storage case 3 for the particulate filter 5 is arranged in the exhaust passage 2, and a bypass passage 8 for bypassing the storage case 3 is provided.
Is connected. The particulate filter 5 is a honeycomb filter having honeycomb-shaped partition walls made of a porous material. In two adjacent passages surrounded by partition walls, one is an exhaust gas upstream side and the other is an exhaust gas downstream side. Is closed by a ceramic blocking member, and is mounted in the storage case 3 via a seal member 4.

The first and second switching valves V1 and V1 are respectively provided at the branching portion and the merging portion of the bypass passage 8 in the exhaust passage 2.
V2 is arranged to allow the exhaust gas to pass through either the particulate filter 5 or the bypass passage 8. Further, in the exhaust passage 2, the first switching valve V1
And the particulate filter 5, the secondary air supply passage 6 leading to the air pump 9 is connected via the first closing valve V3, and the combustion gas discharge is performed between the second switching valve V1 and the particulate filter 5. The passage 7 is connected via the second closing valve V4.

In the figure, H is a heater mounted on the exhaust gas upstream side of the particulate filter 5, and is a switch S.
Is electrically connected to the battery 11 via. Further, SP1 and SP2 are exhaust gas pressures PU and P immediately upstream and downstream of the particulate filter 5, respectively.
First and second pressure sensors for measuring D, S
T1 is a first temperature sensor for measuring the exhaust gas temperature T immediately upstream of the particulate filter 5. ST
Reference numeral 2 denotes a second temperature sensor arranged adjacent to the end surface of the particulate filter 5 on the downstream side of the secondary air.

Reference numeral 100 denotes, for example, an analog signal input interface INa, a digital signal input interface INd, a converter A / D for converting an analog signal into a digital signal, and a central processing unit C for performing various arithmetic processing.
A PU, a random access memory RAM, a call-only memory ROM, an output circuit OUT, a bus line 111 connecting these, and the like, and the first and second switching valves V1 and V2 and the second closing valves V3 and V4 described above. Switch S,
And a control device for controlling the operation of the air pump 9, which are connected to the output circuit OUT and, in addition to the above-mentioned first and second pressure sensors SP1 and SP2 and the first and second temperature sensors ST1 and ST2, Sensor (not shown) for detecting engine speed N and intake air weight G
An intake air amount sensor (not shown) or the like for detecting a is connected to the analog signal input interface INa,
A key switch for detecting the engine start time is connected to the digital signal input interface INd.

Since the exhaust gas of the diesel engine 1 contains harmful particulates,
The first and second closing valves V3 and V4 are closed, and the first and second switching valves V1 and V2 are switched so that the exhaust gas passes through the particulate filter 5, and the particulate filter 5 exhausts the exhaust gas. It is designed to collect the particulates inside. When the diesel engine is used for a long period of time and the particulate collection amount in the particulate filter 5 reaches a predetermined amount, the exhaust resistance is considerably increased and the engine performance is significantly reduced. Therefore, the current particulate collection amount is used. Is determined, and when it reaches a predetermined amount, it is determined that it is the regeneration time of the particulate filter 5, and the control device 100 controls the first and second switching valves V1 and V2 so that the exhaust gas passes through the bypass passage 8. The first and second closing valves V3 and V4 are opened, the air pump 9 is driven, and the switch S is switched.
Is closed and the heater H is energized to generate heat.

As a result, the particulate filter 5
Since the particulates collected on the upstream side of the are heated by the heater H and the secondary air is supplied from the secondary air supply passage 6, the particulates on the upstream side start burning, and this flame is discharged to the downstream side. All the particulate matter that has propagated to the side and collected by the particulate filter 5 is burned, and the regeneration of the particulate filter 5 is completed.
The combustion gas at this time is discharged through the combustion gas discharge passage 7. In this way, when the regeneration of the particulate filter 5 is completed, the air pump 9 is stopped and the first and second switching valves V1 and V2 and the first and second closing valves V3 and V4 are set to the normal state. The exhaust gas then passes through the particulate filter 5 again.

Since the particulate combustion at the time of regeneration propagates from the upstream side of the secondary air to the downstream side, the downstream side of the secondary air of the particulate filter 5 has the combustion heat generated there as well as the combustion on the upstream side. Heat is transferred, and the temperature becomes higher in the axial direction toward the downstream side of the secondary air. On the other hand, in the radial direction, a portion having a higher temperature changes depending on the distribution of the amount of collected particulates during regeneration.
For example, in the case of a particulate filter having a uniform ventilation resistance in the radial direction, since the particulates are evenly collected in the radial direction, the combustion calorific value of each part is almost equal, but especially from the surrounding part. Since the heat transfer is concentrated in the central portion, the temperature becomes higher toward the center, and as a result, the central portion of the secondary air downstream side end surface of the particulate filter 5 is the highest temperature portion. Of course, also in the case of a particulate filter whose ventilation resistance in the central portion is smaller than that in the outer peripheral portion, similarly, the central portion of the end surface on the downstream side of the secondary air has the highest temperature. When such a particulate filter is used, as shown in FIG. 2, the second temperature sensor ST2 is arranged adjacent to the center of the end surface of the filter on the downstream air downstream side.

Further, if the particulates are collected evenly in the radial direction as described above, the temperature of the outer peripheral portion is low and the combustion propagation of the particulates becomes poor, and the particulates collected in this portion can remain unburned. In order to prevent this, there has been proposed a particulate filter that reduces the ventilation resistance of the outer peripheral portion from the central portion to collect more particulates in the outer peripheral portion and increases the combustion heat generation amount of that portion. In this case, the upper part of the outer peripheral surface of the secondary air downstream side is the highest temperature due to heat convection. When such a particulate filter is used, as shown in FIG. 3, the second temperature sensor ST2 is arranged adjacent to the outer peripheral upper end of the secondary air downstream side end surface of the filter.

As described above, since the portion having the highest temperature during regeneration differs depending on the structure of the particulate filter, in the present embodiment, the second temperature sensor ST2 is disposed adjacent to the portion having the highest temperature, and the particulate temperature is increased. During regeneration of the curate filter, the temperature of this part is monitored.

If regeneration of the particulate filter 5 is started before the amount of collected particulates reaches a predetermined amount, the flame in particulate combustion does not propagate sufficiently to the downstream side and regeneration of the particulate filter 5 becomes defective. Therefore, it is necessary to grasp the amount of particulates trapped in the particulate filter 5 and to judge that it is the regeneration time of the particulate filter 5 when it reaches a predetermined amount. ,
This judgment is executed according to the flowchart shown in FIG. This will be explained below.

This flowchart is executed for a predetermined time, for example, 5
It is executed every 0 ms. First, step 10
In step 1, it is judged whether or not the engine has just started to be started based on the time point of inputting the signal from the key switch. Only when this judgment is affirmed, the calibration of the first and second pressure sensors SP1 and SP2 is executed in step 102. Is done. Next, the routine proceeds to step 103, where it is judged whether or not the current engine operating state is a transient time. For this determination, the engine speed N detected by the rotation sensor, the intake air weight Ga detected by the intake air amount sensor, or the first temperature sensor S
The time rate of change of the exhaust gas temperature T detected by T1 is used, and when the time rate of change is equal to or more than each set value, it is determined to be a transitional time.

When the determination in step 103 is affirmative, that is, when the engine operating state is in transition, the process ends as it is, but when the determination in step 103 is negative, the process proceeds to step 104. In step 104, the exhaust gas pressure PU immediately upstream of the particulate filter 5 and the exhaust gas pressure P immediately downstream thereof measured by the first and second pressure sensors SP1 and SP2.
D, intake air weight G detected by the intake air amount sensor
a, and the exhaust gas temperature T immediately upstream of the particulate filter 5 measured by the first temperature sensor ST1 is read.

Next, at step 105, the exhaust gas pressure P immediately upstream of the particulate filter 5 is obtained.
The difference between U and the exhaust gas pressure PD on the immediate downstream side is calculated as the pressure loss value ΔP through the particulate filter 5. Since this pressure loss value ΔP is a value based on the intake air amount and the exhaust gas temperature in the current engine operating state, it is the value of the standard intake air amount and the standard exhaust gas temperature in the frequently used standard engine operating state. It is necessary to convert into the value ΔP1, and in step 106, the standard exhaust gas temperature T ′ and the current exhaust gas temperature T are added to the pressure loss value ΔP.
And the ratio between the standard intake air weight Ga ′ and the current intake air weight Ga.

Since the pressure loss value ΔP1 thus converted may be influenced by noise or the like, in step 107, the averaging process is performed, for example, about 10 times, and the pressure loss is reduced. The value ΔP2 is calculated. In the present embodiment, when the pressure loss value ΔP2 is calculated, the pressure loss value ΔP which is considerably different from the true value during the transient operation.
Since 1 is not taken in, this averaged pressure loss value ΔP2 almost accurately represents the current particulate collection amount in the particulate filter 5, and then, in step 108, It is determined whether or not this value has reached the pressure loss value ΔPr when a predetermined amount of particulates as a threshold value has been collected, and when this determination is negative, the processing ends as is, but affirmative. When it is determined that it is time to regenerate the particulate filter 5, the regeneration of the particulate filter 5 is started.

Next, in step 110, the temperature Tf of the highest temperature portion of the particulate filter 5 is continuously maintained by the second temperature sensor ST2 for a predetermined time sufficient to complete the regeneration of the particulate filter 5. After the measurement, the process proceeds to step 111, and the peak value Tfp of this temperature Tf is determined. Next, at step 112, this peak value Tfp and the estimated peak temperature of the part of the particulate filter 5 having the highest temperature at the time of regeneration when the above-mentioned predetermined amount of particulates are collected, that is, the target peak. The difference D from the temperature Tfp ′ is calculated, and in step 113, the difference D is the first positive value.
It is determined whether or not it is equal to or larger than the predetermined value A1, and when this determination is negative, the routine proceeds to step 114, where it is judged whether or not this difference D is equal to or smaller than the second negative predetermined value. When this determination is denied, the actual peak temperature Tfp and the target peak temperature Tfp ′ in the highest temperature portion of the particulate filter 5 are close to each other, and a predetermined amount of particulates is actually present at the start of regeneration this time. Since it has been collected, and the determination in step 108 described above is appropriate, the process ends.

On the other hand, when the determination in step 113 is positive, the actual peak temperature Tfp exceeds the target peak temperature Tpf 'to some extent, that is, the particulate collection amount at the start of regeneration is larger than the predetermined amount, and By repeating the process, there is a possibility that cracks due to melting loss or thermal stress may occur in the highest temperature part of the particulate filter 5. Therefore, step 1
15, the pressure loss value ΔP2 calculated in step 107 is smaller than the actual value,
The threshold value ΔPr used in the determination in step 108 can be decreased by the decrease value K1.

When the determination in step 114 is affirmative, the actual peak temperature Tfp is below the target peak temperature Tpf 'to some extent, that is, the particulate collection amount at the start of regeneration is less than the predetermined amount,
By repeating this, defective reproduction occurs or the number of times of reproduction increases. Therefore, the process proceeds to step 116, and since the pressure loss value ΔP2 calculated in step 107 is larger than the actual value, the threshold value ΔPr used in the determination in step 108 can be increased by the increase value K2. It has become. The decrease amount K1 and the increase amount K2 described above can be increased as the absolute value of the difference D is increased, whereby the actual peak temperature Tpf can be more favorably changed.
It can be maintained near pf '.

In this embodiment, the second temperature sensor ST2
In the portion of the particulate filter 5 having the highest temperature, which is arranged adjacent to each other, the particulate collection amount distribution in the radial direction of the particulate filter is estimated, and the combustion heat generation amount of each part is estimated from this particulate collection amount distribution. Then, the heat transfer amount in each direction is estimated from the combustion heat generation amount of each portion, and the temperature of each portion estimated based on the estimated heat transfer amount is compared. The estimation of the particulate collection amount distribution in the radial direction of the particulate considers the ventilation resistance distribution of the upstream and downstream exhaust passages connected to the particulate filter in addition to the radial ventilation resistance distribution of the particulate filter. It will be more accurate. Moreover, you may determine the part which becomes the highest temperature of a particulate filter by experiment.

In the present embodiment, the method of regenerating the particulate filter 5 is not limited to the one described above. For example, the heater is omitted, and the temperature of the particulate filter itself heated by the exhaust gas is utilized together with the secondary air. It is also possible to supply fuel to ignite and burn particulates. Further, in order to remove the particulates even during the regeneration of the particulate filter 5, a particulate filter may be arranged in the bypass passage.

Further, in the present embodiment, the pressure loss value is used as the means for determining the regeneration timing of the particulate filter 5, but this does not limit the present invention and, for example, the traveling distance or the like can be used. .

[0031]

As described above, according to the exhaust emission control system of the diesel engine of the present invention, the temperature sensor is determined based on the particulate trapped amount distribution of the filter estimated by the structure of the particulate trap filter. In any filter structure, the peak temperature during filter regeneration, which is measured by this temperature sensor, is the accurate maximum temperature of the filter because it is placed adjacent to the filter part that has the highest temperature during regeneration. , The peak temperature is monitored and the regeneration time of the filter determined by the regeneration time determining means is controlled so that it falls within a predetermined range. Therefore, the filter including the other parts is not melted and damaged during regeneration. It is surely prevented, and compared to the one in which the regeneration timing is feedback-controlled at a temperature other than the maximum filter temperature, melting loss For the potential it can be directly determined,
The safety factor of the threshold value can be reduced, the filter regeneration can be delayed correspondingly, and the number of regenerations can be reduced, and the life of the filter can be extended.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an exhaust emission control device for a diesel engine according to the present invention.

FIG. 2 is a diagram showing an example of a QQ section of FIG.

FIG. 3 is a diagram showing another example of a QQ cross section of FIG. 1;

FIG. 4 is a flowchart for determining the regeneration time of the particulate filter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Diesel engine 2 ... Exhaust passage 5 ... Particulate filter 6 ... Secondary air supply passage 7 ... Combustion gas discharge passage 8 ... Bypass passage 9 ... Air pump H ... Heater SP1 ... First pressure sensor SP2 ... Second pressure sensor ST1 ... First temperature sensor ST2 ... Second temperature sensor 100 ... Control device

Claims (1)

[Claims] 1. A filter for collecting particulates arranged in an exhaust passage, and a regeneration for deciding a regeneration time for burning the trapped particulates to regenerate the filter based on an amount of particulate collection. A timing determining means, a temperature sensor disposed adjacent to a filter portion having the highest temperature during regeneration, which is determined based on the particulate trapped amount distribution of the filter estimated by the structure of the filter, and the temperature sensor And a feedback control means for feedback-controlling the regeneration timing of the filter determined by the regeneration timing determining means on the basis of the peak temperature during the regeneration of the filter measured by.