JP3901526B2 - Particulate filter regeneration method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for regenerating a particulate filter.
[0002]
[Prior art]
Particulate matter (particulate matter) discharged from a diesel engine is mainly composed of soot made of carbonaceous matter and SOF content (Soluble Organic Fraction) made of high-boiling hydrocarbon components. The composition contains a small amount of sulfate (mist-like sulfuric acid component). As a measure to reduce this type of particulates, a particulate filter is installed in the middle of the exhaust pipe through which the exhaust gas flows. It has been done conventionally.
[0003]
This type of particulate filter has a porous honeycomb structure made of a ceramic such as cordierite, and the inlets of the flow paths partitioned in a lattice pattern are alternately sealed, and the inlets are not sealed. About the flow path, the exit is sealed, and only the exhaust gas which permeate | transmitted the porous thin wall which divides each flow path is discharged | emitted downstream.
[0004]
Then, the particulates in the exhaust gas are collected and deposited on the inner surface of the porous thin wall, so that the particulates are appropriately burned and removed before the exhaust resistance increases due to clogging. It is necessary to regenerate, but in normal diesel engine operating conditions, there are few opportunities to obtain exhaust temperatures that are high enough for the particulates to self-combust. For example, an appropriate amount for platinum-supported alumina A catalyst regeneration type particulate filter in which an oxidation catalyst formed by adding a rare earth element such as cerium is integrally supported is being put to practical use.
[0005]
That is, if such a catalyst regeneration type particulate filter is employed, the oxidation reaction of the collected particulates is promoted to lower the ignition temperature, and the particulates can be burned and removed even at an exhaust temperature lower than the conventional one. It becomes possible.
[0006]
However, even when such a catalyst regeneration type particulate filter is used, the trapped amount exceeds the particulate processing amount in the operation region where the exhaust temperature is low, so such a low exhaust gas. If the operation state at the temperature continues, the particulate filter may not be regenerated well, and the particulate filter may fall into an excessive collection state, and the particulate filter is in a stage where the amount of accumulated particulates has increased. It has been considered that the particulate filter is forcibly regenerated by adding fuel to the exhaust gas further upstream.
[0007]
In other words, if fuel is added upstream from the particulate filter, the added fuel undergoes an oxidation reaction on the oxidation catalyst of the particulate filter, and the heat of the reaction raises the catalyst bed temperature to burn out the particulate. Thus, regeneration of the particulate filter is achieved.
[0008]
[Problems to be solved by the invention]
However, conventionally, a target value of the amount of fuel added necessary to raise the catalyst bed temperature of the particulate filter to a predetermined temperature based on the operating state of the diesel engine is calculated, and fuel addition corresponding to the target value is executed. Although the control is considered, when the driving state in which fuel addition is restricted, for example, from the idle state, the sudden acceleration, the deceleration state, etc., to the traveling state in which fuel addition is possible, the fuel addition amount is suddenly increased. If this happens, the higher the catalyst bed temperature immediately after the start of fuel addition, the more severe the temperature drop due to fuel cooling will occur, and the added fuel will not be able to be processed on the oxidation catalyst of the particulate filter and will pass behind the particulate filter. There was a risk of producing white smoke.
[0009]
The present invention has been made in view of the above circumstances, and provides a method for regenerating a particulate filter that can reliably avoid a situation where the added fuel cannot be completely processed on the oxidation catalyst of the particulate filter. The purpose is that.
[0010]
[Means for Solving the Problems]
The present invention adds fuel to the exhaust gas upstream of the catalyst regeneration type particulate filter installed in the middle of the exhaust pipe, and reacts with the heat of reaction when the added fuel undergoes an oxidation reaction on the oxidation catalyst of the particulate filter. In the method for forcibly regenerating the particulate filter by burning the collected particulates, when the target value of the fuel addition amount determined based on the operating state increases rapidly exceeding a predetermined change amount, The fuel addition is gradually controlled so that the amount of fuel addition gradually increases to reach the target value.In addition, when executing this gradual change control, it is ensured at that temperature according to the exhaust temperature immediately after the particulate filter. all added fuel selects the upper limit value of possible fuel addition amount to oxidation treatment, to limit the fuel addition amount so as not to exceed the selected upper limit value It is an butterfly.
[0011]
Thus, in this way, even if the target value of the fuel addition amount suddenly increases beyond a predetermined change amount, it is relatively small to match the processing capacity of the particulate filter on the oxidation catalyst. The fuel addition is started from the amount, and the fuel addition is executed so that the fuel addition amount gradually increases to reach the target value. Therefore, as the fuel addition amount is increased stepwise, the catalyst bed temperature is increased by the oxidation reaction heat. The amount of fuel that increases gradually and follows the increase in the catalyst bed temperature to improve the processing capacity of the particulate filter on the oxidation catalyst, resulting in an excess amount of fuel that exceeds the processing capacity of the particulate filter on the oxidation catalyst. Addition will be avoided.
[0013]
Even if the fuel addition amount is determined from the operating state on the premise of the processing capacity when the catalyst bed temperature of the particulate filter is relatively high, it is selected according to the exhaust temperature immediately after the particulate filter. Therefore, even if the catalyst bed temperature of the particulate filter is low, an excessive amount of fuel exceeding the processing capacity is avoided.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0015]
1 to 3 show an example of an embodiment of the present invention. In the particulate filter regeneration method of this embodiment, as shown in FIG. 1, an exhaust manifold is connected from an automobile diesel engine 1 (internal combustion engine). 2 illustrates an example in which a catalyst regeneration type particulate filter 6 that integrally supports an oxidation catalyst is accommodated in a muffler 5 of an exhaust pipe 4 through which an exhaust gas 3 discharged through 2 flows. A filter case 7 that holds the particulate filter 6 forms an outer cylinder of the muffler 5.
[0016]
That is, a particulate filter 6 as shown in an enlarged view in FIG. 2 is accommodated in a filter case 7 having front and rear inlet pipes 8 and outlet pipes 9. The particulate filter 6 is made of ceramic. It has a porous honeycomb structure, and the inlets of the flow paths 6a partitioned in a lattice pattern are alternately sealed, and the outlets of the flow paths 6a that are not sealed are sealed. Only the exhaust gas 3 that has permeated through the porous thin wall 6b that partitions each flow path 6a is discharged to the downstream side.
[0017]
The outlet pipe 9 of the filter case 7 is equipped with a temperature sensor 10 for measuring the temperature of the exhaust gas 3, and the detection signal 10a of the temperature sensor 10 forms an engine control computer (ECU: Electronic Control Unit). On the other hand, in this control device 11, the fuel injection timing and the injection amount are commanded to the fuel injection device 12 that injects fuel into each cylinder of the diesel engine 1. A fuel injection signal 12a is output.
[0018]
Here, the fuel injection device 12 is composed of a plurality of injectors (not shown) provided for each cylinder, and the electromagnetic valves of these injectors are appropriately controlled to open by the fuel injection signal 12a, and the fuel is supplied. The injection timing (injection start timing and injection end timing) and the injection amount (valve opening time) are appropriately controlled.
[0019]
Further, the accelerator of the driver's seat (not shown) is provided with an accelerator sensor 13 (load sensor) that detects the accelerator opening as a load of the diesel engine 1, and the rotational speed is set at an appropriate position of the diesel engine 1. A rotation sensor 14 for detection is provided, and an accelerator opening signal 13a and a rotation speed signal 14a from the accelerator sensor 13 and the rotation sensor 14 are also input to the control device 11.
[0020]
In the control device 11, the fuel injection signal 12a based on the normal map is determined based on the accelerator opening signal 13a and the rotational speed signal 14a. On the other hand, when the particulate filter 6 is forcibly regenerated. A fuel injection signal 12a that switches from the normal map to the forced regeneration map and performs post-injection at a timing that does not ignite later than the compression top dead center following the main injection of fuel performed near the compression top dead center (crank angle 0 °). Is to be decided.
[0021]
That is, when post injection is performed at a timing that does not ignite later than the compression top dead center following main injection, unburned fuel (mainly HC: hydrocarbon) is added to the exhaust gas 3 by this post injection. As a result, the unburned fuel undergoes an oxidation reaction on the oxidation catalyst on the surface of the particulate filter 6, the catalyst bed temperature rises due to the reaction heat, and the particulates in the particulate filter 6 are naturally combusted. become.
[0022]
Here, the switching from the normal map to the forced regeneration map in the control device 11 described above estimates the accumulation amount in the particulate filter 6 based on the operating state of the diesel engine 1, and the estimated accumulation amount is a predetermined upper limit. The map should be switched when the value is exceeded.
[0023]
For example, while estimating the amount of particulate generation based on the operating state of the diesel engine 1, it is determined whether or not the processing amount of the particulate is in a regeneration region that exceeds the collected amount for the current operating state, A function of excluding the particulate generation amount while the operation state is determined to be in the regeneration region and integrating only the particulate generation amount in the non-regeneration region to obtain the accumulation amount in the particulate filter 6. It is only necessary that the control device 11 has all of them so that the control device 11 can estimate the amount of accumulated particulates.
[0024]
In this embodiment, when the controller 11 performs forced regeneration of the particulate filter 6, a specific control procedure as shown in the flowchart of FIG. 3 is taken, and the fuel to the particulate filter 6 is taken. Control of the addition amount, that is, control of post injection of the fuel injection device 12 is executed.
[0025]
With reference to the flowchart of FIG. 3, the speed of the diesel engine 1 is extracted based on the rotational speed signal 14a from the rotational sensor 14 in step S1, while the fuel based on the accelerator opening signal 13a from the accelerator sensor 13 is extracted in step S2. The fuel injection amount that is known at the time of determination of the injection signal 12a is extracted, and the post injection amount based on the operating state of the diesel engine 1 (forced regeneration) is determined in step S3 from the post injection amount map based on the rotational speed and the injection amount. The map value of the fuel addition amount) is read out.
[0026]
On the other hand, in parallel with the procedure for determining the post-injection amount map value in steps S1 to S3, the current value of the post-injection amount for gradual change is determined in the procedure described in detail below. ing.
[0027]
That is, in this embodiment, when the target value of the post injection amount suddenly increases beyond a predetermined change amount, a method is adopted in which the post injection amount gradually increases so as to reach the target value. First, in step S4, the current state is not gradually changing the post injection amount, and the value obtained by subtracting the previous value of the post injection amount from the map value of the post injection amount is a predetermined change for gradual change determination. It is determined whether or not the two conditions of exceeding the amount are satisfied at the same time.
[0028]
If it is determined in step S4 that the two conditions are satisfied at the same time, it means that a gradual change is necessary to perform the current post injection, and the process proceeds to step S5. Gradual change of the post injection amount is started, and whether or not the initial setting value of the post injection amount for gradual change is greater than the previous value of post injection amount (the amount of post injection performed immediately before) in the next step S6. Is determined.
[0029]
Here, the initial set value of the post injection amount at the time of gradual change refers to the gradual change start injection amount for gradually increasing the post injection amount to reach the target value. The amount is uniquely determined by the amount of the oxidation catalyst that can be initially treated.
[0030]
Further, when it is determined in step S6 that the initial set value is larger than the previous value of the post injection amount, the process proceeds to step S7, and the initial set value is selected as it is as the current value of the post injection amount for gradual change. It has come to be.
[0031]
If the two conditions are not satisfied at the same time in step S4, the process proceeds to step S8, where the current state is gradually changing the post injection amount, and the post injection amount is calculated from the post injection amount map value. It is determined whether or not the two conditions that the value obtained by subtracting the previous value of the amount is equal to or less than a predetermined gradual change determination change amount are simultaneously satisfied.
[0032]
If it is determined in step S8 that the two conditions are satisfied at the same time, the gradual change is not necessary to perform the current post-injection (no problem occurs even if the gradual change control is not applied). Therefore, the process proceeds to step S9 where the gradual change of the post injection amount is completed, and the process proceeds to the next step S10, where the previous value of the post injection amount is set as the current value of the gradual change post injection amount. It has come to be selected.
[0033]
Even if the previous value of the post-injection amount is equal to or greater than the initial set value in the previous step S6, the process proceeds to step S10 and the previous value of the post-injection amount is set as the current value of the post-injection amount for gradual change. It has come to be selected.
[0034]
If the two conditions are not satisfied at the same time in step S8, the process proceeds to step S11 to check whether the current state is gradually changing the post-injection amount. When it is confirmed that the gradual change is made, the process proceeds to step S12 and the gradual change is continued. In the next step S13, the current value of the gradual change post injection quantity is changed to the previous value of the post injection quantity. A value obtained by adding the increments is selected.
[0035]
Here, the counter in the control device 11 counts how many times (n-th) the current value of the post-injection amount for gradual change in step S13 is calculated.
[0036]
When it is determined in step S11 that the gradual change is not being performed, the process proceeds to step S10 so that the previous value of the post injection amount is selected as the current value of the gradual change post injection amount. It has become.
[0037]
Then, the post injection amount map value from step S3 and the current value of the post injection amount for gradual change from any of step S7, step S10, or step S13 are led to step S14, where the gradual change is in progress. If it is determined that it is not, the routine proceeds to step S15, where the post injection amount map value from step S3 is adopted as the post injection amount selection value, and if it is determined that it is gradually changing, the routine proceeds to step S16. Thus, the current value of the post-injection amount for gradual change from any one of step S7, step S10, and step S13 is adopted as the post-injection amount selection value.
[0038]
Furthermore, if the post injection amount selection value from either step S15 or step S16 is led to step S17, where it is determined that the exhaust brake is operating, the routine proceeds to step S18 and the post injection amount is selected. The current value is “0” (no post-injection amount), but if it is determined that the exhaust brake is not operating, the process proceeds to step S19, and the exhaust is performed based on the detection signal 10a from the temperature sensor 10 in step S20. The post injection amount upper limit table value read from the temperature and upper limit value table is compared with the post injection amount selection value from either step S15 or step S16, and the post injection amount selection value is equal to or greater than the upper limit table value. If so, the process proceeds to step S21, where the upper limit table value is adopted as the current value of the post injection amount.
[0039]
Here, the upper limit table value of the post-injection amount is the upper limit value of the fuel addition amount that can reliably oxidize all the added fuel at that temperature according to the exhaust temperature immediately after the particulate filter 6. This upper limit value is uniquely determined for each exhaust temperature by reading from the table.
[0040]
If the post injection amount selection value is below the upper limit table value in the previous step S19, the post injection amount selection value from either step S15 or step S16 is adopted. .
[0041]
Note that when “0” or the upper limit table value is adopted as the current value of the post injection amount, the gradual change is canceled, and the calculation of the current value of the post injection amount for gradual change in step S13 is performed (nth time). The counter in the control device 11 that counts whether or not it falls under () is reset.
[0042]
Thus, if the exhaust gas purification device is operated by such a control device 11, even if the target value of post injection by the fuel injection device 12 suddenly increases beyond a predetermined change amount, the particulate filter 6 Since the post-injection amount starts from a relatively small amount commensurate with the processing capacity of the oxidation catalyst, and the fuel addition is performed so that the post-injection amount gradually increases to reach the target value. As the injection amount increases stepwise, the catalyst bed temperature gradually rises due to the oxidation reaction heat, and the processing capacity of the particulate filter 6 on the oxidation catalyst improves following the increase in the catalyst bed temperature. An excessive amount of fuel addition exceeding the processing capacity of the curate filter 6 on the oxidation catalyst is avoided.
[0043]
Further, the upper limit value of the post injection amount is selected as the upper limit table value in accordance with the exhaust temperature immediately after the particulate filter 6, and the post injection amount is limited so as not to exceed the selected upper limit table value. Even if the post-injection amount is determined from the operating state on the premise of the processing capability when the catalyst bed temperature of the filter 6 is relatively high, the processing capability is reduced when the catalyst bed temperature of the particulate filter 6 is low. Excessive excess fuel addition will be avoided.
[0044]
Therefore, according to the above embodiment, the added fuel is processed on the oxidation catalyst of the particulate filter 6 by avoiding an excessive amount of fuel addition exceeding the processing capacity of the particulate filter 6 on the oxidation catalyst. Since it is possible to surely avoid such a situation that it cannot be exhausted, it is possible to surely prevent the generation of white smoke due to untreated added fuel, and it is also possible to suppress deterioration of fuel consumption by avoiding useless combustion addition .
[0045]
In particular, in this embodiment, the post injection amount is limited so as not to exceed the upper limit table value selected according to the exhaust gas temperature immediately after the particulate filter 6, so that the catalyst bed temperature of the particulate filter 6 is compared. Even if the post-injection amount is determined from the operating state on the premise of a high processing capacity, an excessive amount of fuel addition exceeding the processing capacity is achieved when the catalyst bed temperature of the particulate filter 6 is low. Can be avoided in advance, generation of white smoke can be prevented more reliably, and deterioration of fuel consumption can be suppressed.
[0046]
The method for regenerating a particulate filter according to the present invention is not limited to the above-described embodiment. As a means for adding fuel into the exhaust gas upstream of the particulate filter, the injection pattern of the fuel injection device is used. In this example, post-injection is performed at a timing that does not ignite later than the compression top dead center following main injection, but as this type of fuel addition means, for example, from the exhaust manifold to the exhaust pipe It is also possible to separately arrange an injector for fuel addition at any location in the exhaust flow path, and to add fuel to the exhaust gas by this injector. The control procedure is not limited to the flowchart of FIG. 3, and various other modifications are possible without departing from the scope of the present invention. To be added to is a matter of course.
[0047]
【The invention's effect】
According to the method for regenerating a particulate filter of the present invention described above, various excellent effects as described below can be obtained.
[0048]
(I) According to the invention described in claim 1 of the present invention, an excessive amount of fuel addition exceeding the processing capacity of the particulate filter on the oxidation catalyst is avoided, thereby preventing the particulate filter from being oxidized. As a result, it is possible to surely avoid the situation where the added fuel cannot be completely processed, so that the generation of white smoke due to the untreated added fuel can be surely prevented, and the fuel consumption deteriorates by avoiding unnecessary combustion addition. Can also be suppressed.
[0049]
(II) According to the invention described in claim 1 of the present invention, had so fuel addition amount is determined from the operation state assumption processing capacity when the catalyst bed temperature of the particulate filter is relatively high However, since the amount of fuel added is limited so as not to exceed the upper limit value selected according to the exhaust gas temperature immediately after the particulate filter, when the catalyst bed temperature of the particulate filter is low, the excess capacity exceeding the processing capacity is exceeded. The possibility of adding an amount of fuel can be avoided, and the generation of white smoke can be prevented more reliably and the deterioration of fuel consumption can be suppressed.
[Brief description of the drawings]
FIG. 1 is a schematic view showing an example of an embodiment for carrying out the present invention.
FIG. 2 is a cross-sectional view showing details of the particulate filter of FIG.
FIG. 3 is a flowchart showing a specific control procedure by the control device of FIG. 1;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Diesel engine 3 Exhaust gas 4 Exhaust pipe 6 Particulate filter 10 Temperature sensor 10a Detection signal 11 Control apparatus 12 Fuel injection apparatus 12a Fuel injection signal

Claims (1)

Particulates that have been collected by reaction heat when fuel is added to the exhaust gas upstream of the catalyst regeneration type particulate filter installed in the exhaust pipe and the added fuel undergoes an oxidation reaction on the oxidation catalyst of the particulate filter. In the method for forcibly regenerating the particulate filter by burning the curate, when the target value of the fuel addition amount determined based on the operating state rapidly increases beyond a predetermined change amount, the fuel addition amount is The fuel addition is controlled so as to gradually increase to reach the target value . In addition, when executing this gradual change control, all the added fuels are reliably ensured at that temperature according to the exhaust temperature immediately after the particulate filter. the selected upper limit value of the fuel addition amount which can be oxidized, and limits the amount of fuel addition so as not to exceed the selected upper limit value The method of reproduction tee particulate filter.

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