JP2004150416A - Regeneration method for particulate filter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To complete regeneration of a particulate filter in a short time, even in a vehicle adopting an idle stop control. <P>SOLUTION: Fuel is added to exhaust gas 9 upstream side of a catalyst regeneration type particulate filter 12 equipped in the middle of an exhaust pipe 11. Collected particulates are burnt by heat of reaction generated in oxidative reaction of the added fuel on an oxidation catalyst of the particulate filter 12 to forcibly regenerate the particulate filter 12. In the method, the forced regeneration by the addition of the fuel is performed in preference to the idle stop control for stopping a diesel engine 1, in idling stop of the vehicle. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for regenerating a particulate filter.
[0002]
[Prior art]
Particulate matter (particulate matter) discharged from the diesel engine is mainly composed of soot composed of carbonaceous material and SOF component (Soluble Organic Fraction: soluble organic component) composed of a high-boiling hydrocarbon component. Although it has a composition containing a small amount of sulfate (mist-like sulfuric acid component), as a measure to reduce this kind of particulates, it is necessary to equip a particulate filter in the middle of the exhaust pipe through which exhaust gas flows. This has been done conventionally.
[0003]
This kind of particulate filter has a porous honeycomb structure made of ceramic such as cordierite, and the inlets of the respective flow paths partitioned in a lattice are alternately plugged, and the inlets are not plugged. The outlets of the flow passages are sealed so that only the exhaust gas that has passed through the thin porous wall that defines each flow passage is discharged to the downstream side.
[0004]
Since the particulates in the exhaust gas are collected and deposited on the inner surface of the porous thin wall, the particulates are appropriately burned and removed before the exhaust resistance increases due to clogging, and the particulate filter is removed. It is necessary to regenerate, but in the normal diesel engine operating state, there is little chance of obtaining a high exhaust temperature enough for the particulates to self-combust, so for example, an appropriate amount of alumina loaded with platinum A catalyst regeneration type particulate filter integrally supporting an oxidation catalyst formed by adding a rare earth element such as cerium has been put into practical use.
[0005]
That is, if such a catalyst regeneration type particulate filter is employed, the oxidation reaction of the collected particulates is promoted, the ignition temperature is lowered, and the particulates can be burned and removed even at a lower exhaust temperature than before. It is possible.
[0006]
However, even when such a catalyst regeneration type particulate filter is employed, in the operating region where the exhaust gas temperature is low, the trapped amount exceeds the treated amount of the particulate, so that such low exhaust gas If the operating condition at the temperature continues, there is a risk that the regeneration of the particulate filter does not proceed satisfactorily and the particulate filter falls into an over-collection state, and at the stage where the accumulation amount of the particulate filter increases, Forcibly regenerating the particulate filter by adding fuel to the exhaust gas on the more upstream side has been considered.
[0007]
That is, if fuel is added upstream of 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, the regeneration of the particulate filter is achieved.
[0008]
Incidentally, a method of actively regenerating this type of particulate filter is also described in the following unpublished prior applications, Patent Document 1 and Patent Document 2, and in the descriptions in these documents, Fuel addition is performed by performing post-injection at a non-ignition timing later than the compression top dead center with respect to the fuel injection device of the engine following the main injection of the fuel performed near the compression top dead center.
[0009]
[Patent Document 1]
Japanese Patent Application No. 2001-355061 [Patent Document 2]
Japanese Patent Application No. 2002-20374 [0010]
[Problems to be solved by the invention]
However, in recent years, there has been an increase in route buses and trucks adopting idle stop control to reduce the amount of exhaust gas by automatically stopping the engine when idling is stopped for the purpose of low pollution. In a vehicle that employs a particulate filter, while the regeneration control of the particulate filter is being performed, the engine stops due to idle stop control due to a signal waiting at an intersection, etc., and exhaust gas does not flow through the exhaust pipe. As a result of the catalyst bed temperature dropping remarkably, there is a problem that it takes a long time to complete the regeneration of the particulate filter.
[0011]
The present invention has been made in view of the above circumstances, and has as its object to enable the regeneration of a particulate filter to be completed in a short time even in a vehicle employing idle stop control.
[0012]
[Means for Solving the Problems]
According to the present invention, fuel is added to exhaust gas on the upstream side of a catalyst regeneration type particulate filter provided in the middle of an exhaust pipe, and reaction heat generated when the added fuel undergoes an oxidation reaction on an oxidation catalyst of the particulate filter. A method of forcibly regenerating a particulate filter by burning collected particulates, wherein forced regeneration by fuel addition is performed prior to idle stop control for stopping an engine when the vehicle is idling and stopped. It is.
[0013]
In this way, even if the vehicle stops idling while waiting for a traffic light at an intersection or the like while the regeneration control of the particulate filter is being performed, the forced filtering of the particulate filter takes precedence over the idle stop control. Since regeneration is performed, engine stoppage is avoided and exhaust gas continues to flow through the exhaust pipe even during idling stop. As a result, the catalyst bed temperature of the particulate filter is maintained at a predetermined temperature or higher, and the catalyst activity is maintained. Thus, the forced regeneration of the particulate filter is continued without interruption by the idle stop control, and is completed within a short time.
[0014]
Further, in the present invention, it is preferable to perform fuel addition by adding post-injection at a non-ignition timing later than the compression top dead center following the main injection of the fuel performed near the compression top dead center. By doing so, unburned fuel is added to the exhaust gas by the post-injection, and the unburned fuel undergoes an oxidation reaction on the oxidation catalyst of the particulate filter. The particulates in the curated filter are forcibly burned off.
[0015]
Further, in the present invention, it is preferable to increase the injection amount per combustion main injection in order to increase the engine speed at the time of forced idling of the particulate filter in comparison with normal idling.
[0016]
In other words, when the particulate filter is forcibly regenerated while idling is stopped, since the temperature and the flow rate of the exhaust gas are too low, it is difficult to satisfactorily remove and burn the particulates. If the number of revolutions is increased from the time of normal idling by increasing the power consumption, it is possible to increase the energy input amount and raise the temperature and flow rate of the exhaust gas to levels suitable for forced regeneration.
[0017]
Further, in the present invention, the exhaust flow rate from the engine may be appropriately reduced during the forced regeneration of the particulate filter in the idling state. In this case, the exhaust flow rate is reduced and the exhaust gas on the upstream side is reduced. As the exhaust pressure rises, the exhaust temperature rises, and the exhaust resistance of the engine increases, which makes it difficult for the relatively low-temperature intake air to flow into the cylinder, and reduces the residual amount of the relatively high-temperature exhaust gas. The air in the cylinder containing a large amount of the exhaust gas having a relatively high temperature is compressed in the next compression stroke to reach the explosion stroke, so that the exhaust temperature is further increased.
[0018]
Further, in the present invention, the after-injection may be added at a timing at which combustion can be performed immediately after the main injection during the forced regeneration of the particulate filter in the idling state, so that the fuel of the after-injection is output. By burning the fuel at a timing that is difficult to convert to, the heat efficiency of the diesel engine is reduced, the amount of heat generated by the fuel that is not used for power is increased, and the exhaust temperature is further increased.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0020]
1 to 4 show an example of an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a diesel engine equipped with a turbocharger 2, and intake air 4 guided from an air cleaner 3 is used as an intake pipe 5. To the compressor 2a of the turbocharger 2, the intake air 4 pressurized by the compressor 2a is sent to the intercooler 6 where it is cooled, and the intake air 4 further flows from the intercooler 6 to the intake manifold 7. It is guided and distributed to each cylinder 8 of the diesel engine 1 (FIG. 1 illustrates the case of in-line six cylinders).
[0021]
Further, exhaust gas 9 discharged from each cylinder 8 of the diesel engine 1 is sent to a turbine 2b of the turbocharger 2 via an exhaust manifold 10, and the exhaust gas 9 driving the turbine 2b is passed through an exhaust pipe 11. It is designed to be discharged outside the vehicle.
[0022]
In the middle of the exhaust pipe 11, a catalyst regeneration type particulate filter 12 integrally supporting an oxidation catalyst is mounted and held in a filter case 13, and is shown in an enlarged scale in FIG. As described above, the particulate filter 12 has a porous honeycomb structure made of ceramic, and the inlets of the respective flow paths 12a partitioned in a lattice are alternately plugged, and the inlets are not plugged. As for 12a, the outlet thereof is plugged, and only the exhaust gas 9 that has passed through the porous thin wall 12b that defines each flow path 12a is discharged to the downstream side.
[0023]
At the outlet of the filter case 13, a temperature sensor 14 for measuring the temperature of the exhaust gas 9 passing through the particulate filter 12 as a substitute for the catalyst bed temperature is provided, and a temperature signal 14a of the temperature sensor 14 is provided. Is input to a control device 15 which forms an engine control computer (ECU: Electronic Control Unit).
[0024]
Since the control device 15 also serves as an engine control computer, it also controls fuel injection, and more specifically, an accelerator sensor 16 (which detects an accelerator opening as a load on the diesel engine 1). A fuel injection device for injecting fuel into each cylinder 8 of the diesel engine 1 based on an accelerator opening signal 16a from a load sensor) and a rotation speed signal 17a from a rotation sensor 17 for detecting the engine rotation speed of the diesel engine 1. A fuel injection signal 18a is output to the control unit 18 so that the control device 15 can always know the operating state of the diesel engine 1 when the fuel injection signal 18a is output.
[0025]
Here, the fuel injection device 18 is constituted by a plurality of injectors 19 provided for each cylinder 8, and the solenoid valves of each of the injectors 19 are appropriately opened by the fuel injection signal 18a to control the fuel injection. The injection timing (valve opening timing) and the injection amount (valve opening time) of the fuel cell are appropriately controlled.
[0026]
On the other hand, in the control device 15, while the fuel injection signal 18a in the normal mode is determined based on the accelerator opening signal 16a and the rotation speed signal 17a, it is necessary to perform the regeneration control of the particulate filter 12. In this case, the mode is switched from the normal mode to the regeneration mode, and the post-injection is performed at a non-ignition timing later than the compression top dead center following the fuel main injection performed near the compression top dead center (crank angle 0 °). The fuel injection signal 18a of the injection pattern is determined.
[0027]
That is, when the post injection is performed at the non-ignition timing later than the compression top dead center following the main injection, unburned fuel (mainly HC: hydrocarbon) is added to the exhaust gas 9 by the post injection. The unburned fuel undergoes an oxidation reaction on the oxidation catalyst on the surface of the particulate filter 12, and the heat of the reaction raises the catalyst bed temperature to burn and remove the particulates in the particulate filter 12. Will be.
[0028]
However, when the vehicle is in the idling state when the mode is switched to the regeneration mode, the main injection performed near the compression top dead center (crank angle 0 °) in order to increase the rotation speed from normal idling The injection amount is also increased.
[0029]
In other words, when the particulate filter 12 is forcibly regenerated at the time of idling stop, the temperature and flow rate of the exhaust gas 9 are too low, so that it is difficult to satisfactorily remove and burn the particulates. By increasing the injection amount, the number of revolutions is increased from that at the time of normal idling, thereby increasing the energy input amount so as to raise the temperature and the flow rate of the exhaust gas 9 to levels suitable for forced regeneration.
[0030]
Further, in addition to the control for increasing the rotation speed of the diesel engine 1, the after-injection may be performed at a combustible timing immediately after the main injection, if necessary. When the after-injection is performed at a possible timing, the fuel of the after-injection is burned at a timing that is difficult to be converted into an output, thereby lowering the thermal efficiency of the diesel engine 1 and increasing the calorific value of the calorific value of the fuel that is not used for power. Thus, it is possible to further increase the exhaust gas temperature.
[0031]
Further, the control device 15 extracts the rotation speed of the diesel engine 1 based on the rotation speed signal 17a from the rotation sensor 17, and determines the fuel injection signal 18a based on the accelerator opening signal 16a from the accelerator sensor 16. A known fuel injection amount is extracted, and a basic particulate generation amount based on the current operating state of the diesel engine 1 is estimated from a particulate generation amount map based on the rotation speed and the injection amount. The final generation amount is obtained by multiplying the basic generation amount by a correction coefficient in consideration of various conditions related to the generation of particulates and subtracting the processing amount of the particulate in the current operation state. The amount of generation is accumulated every moment to estimate the amount of accumulated particulates. Switching from the normal mode to the reproduction mode has to be done when it is estimated to have reached target value.
[0032]
Note that there are various methods of estimating the amount of accumulated particulates, and it is of course possible to estimate the amount of accumulated particulates using a method other than the estimation method exemplified here.
[0033]
Further, in addition to the accelerator sensor 16 and the rotation sensor 17 described above, a neutral switch 20 for detecting that the gear position is in the neutral position, a side brake switch 21 for detecting that the side brake is being applied, and a vehicle speed detection. The detection signals 20a, 21a and the vehicle speed signal 22a from the respective vehicle speed sensors 22 are also input to the control device 15. Based on these signals, it is determined whether or not the vehicle is in an idling state. Is to be determined.
[0034]
That is, in the control device 15, the rotation sensor 17 confirms that the rotational speed is in a relatively low predetermined speed range, the accelerator sensor 16 confirms that the accelerator is off (the load is zero), and the neutral switch 20 determines the gear position. When it is confirmed that the vehicle is in the neutral position, the side brake switch 21 confirms that the side brake is applied, and the vehicle speed sensor 22 confirms that the vehicle speed is zero, the current driving state is an idling state. Is determined.
[0035]
In determining the idling state, signals from these sensors and switches are not necessarily required. At least the rotation sensor 17, the accelerator sensor 16, the neutral switch 20, the side brake switch 21, the vehicle speed sensor, and the like. The idling determination means can be configured by a combination with any one of the above-described 22.
[0036]
At an appropriate position on the upstream side of the particulate filter 12, an exhaust brake 23 whose opening can be adjusted to narrow the flow path of the exhaust pipe 11 to an appropriate opening is provided. Although the opening is controlled by the opening command signal 23a from the controller 15, in the present embodiment, when the controller 15 selects the reproduction mode under the condition that the vehicle is in the idling state, Another operation independent of the original operation is commanded to the exhaust brake 23, so that the exhaust brake 23 can be used as exhaust throttle means for raising the exhaust temperature as described later.
[0037]
In the exhaust gas purifying apparatus in which the control device 15 is switched between the normal mode and the regeneration mode as described above, in the present embodiment, an idle stop for automatically stopping the engine when idling and stopping for the purpose of low pollution. When the control device 15 determines that the vehicle is idling by the above-mentioned idling determination means, the intake valve 24 of the intake pipe 5 is closed by an opening command signal 24a from the control device 15. The fuel injection by the fuel injection device 18 is stopped and the diesel engine 1 is stopped. However, when the regeneration mode is selected by the control device 15, the fuel is given priority over the idle stop control. Forced regeneration by addition is performed, and more specifically, FIG. While the basic control logic for the regeneration control as described above is incorporated in the control device 15, the control logic for executing the regeneration control prior to the idle stop control as shown in the flowchart in FIG. ing.
[0038]
That is, if it is confirmed in step S1 in the flowchart of FIG. 3 that the current control mode of the control device 15 is the normal mode, the accumulated amount of the particulates estimated by calculation in the control device 15 in step S2. It is determined whether or not the amount is equal to or more than a predetermined value (target value). If the amount of accumulated particulates has not reached the predetermined value, the process proceeds to “NO” and the same determination is repeated, and the accumulation of particulates is repeated. If the amount is equal to or more than the predetermined value, the process proceeds to "YES" and the mode is switched to the reproduction mode in step S3.
[0039]
Next, when the mode is switched to the regeneration mode, the process proceeds to step S4, and based on the temperature signal 14a of the temperature sensor 14, the catalyst bed temperature of the particulate filter 12 is maintained at a predetermined temperature or higher for a predetermined time (necessary for regeneration). It is determined whether or not the predetermined time has elapsed. If the predetermined time has not elapsed, the process proceeds to “NO” and the same determination is repeated. Assuming that the regeneration of the filter 12 has been completed, the process proceeds to "YES", returns to step S1, and returns to the normal mode.
[0040]
On the other hand, in the flowchart of FIG. 4, when idling stop is confirmed by the above-described idling determination means in step S11, it is determined in next step S12 whether or not the current control mode is the regeneration mode. If it has been selected, the process proceeds to "YES" and the idle stop control is invalidated in step S13. If the normal mode has been selected, the process proceeds to "NO" and the idle stop control is performed in step S14. Control is performed.
[0041]
The reason why the intake valve 24 is closed by the idle stop control is to stop the diesel engine 1 smoothly. If the fuel injection is stopped only, the intake is performed when the diesel engine 1 rotates several times by inertia. This is because the compressed air is compressed and the reaction causes the diesel engine 1 to vibrate so as to shake.
[0042]
Thus, when the control device 15 estimates that the amount of accumulated particulates has reached the predetermined target value and switches the combustion injection control by the control device 15 from the normal mode to the regeneration mode, the main injection follows the main injection. Post-injection is performed at a timing that does not ignite later than the compression top dead center, and the fuel added to the exhaust gas 9 in an unburned state by this post-injection causes an oxidation reaction on the oxidation catalyst of the particulate filter 12, and the heat As a result, the catalyst bed temperature rises, and the particulates in the particulate filter 12 are forcibly burned off.
[0043]
Even if the vehicle stops idling due to a signal at an intersection or the like while the regeneration control of the particulate filter 12 is being performed, the idle stop control is disabled according to the control logic of FIG. Exhaust gas 9 continues to flow in the exhaust pipe 11 even when the vehicle is stopped and idling is stopped, thereby keeping the catalyst bed temperature of the particulate filter 12 at a predetermined temperature or higher and maintaining the catalytic activity. The forced regeneration of No. 12 is continued without interruption by the idle stop control, and is completed in a short time.
[0044]
In addition, in the regeneration control under the idling condition, the control unit 15 increases the injection amount per main injection of the fuel injection device 18 so that the rotation speed of the diesel engine 1 is reduced during normal idling. Since the temperature becomes higher, the temperature and the flow rate of the exhaust gas 9 are raised to a level suitable for the regeneration control. Further, the exhaust flow rate is reduced by the exhaust brake 23 which receives the closing operation command from the control device 15 as the opening degree command signal 23a. Thus, the exhaust gas 9 on the upstream side is pressurized to increase the exhaust gas temperature.
[0045]
That is, the temperature T, the exhaust pressure P, and the flow rate V of the exhaust gas 9 have the following relational expression:
P · V / T = constant, it is determined that if the exhaust flow path is narrowed and the exhaust pressure P is increased to maintain the flow rate V constant, the temperature T of the exhaust gas 9 greatly increases in a predetermined operating state. become.
[0046]
Also, as the exhaust resistance of the diesel engine 1 increases, intake of relatively low-temperature intake air into the cylinder becomes difficult, and the residual amount of the relatively high-temperature exhaust gas 9 increases. Further, the exhaust gas temperature is further increased by reaching the explosion stroke by compressing the air in the cylinder containing many 9 in the next compression stroke.
[0047]
Therefore, according to the above-described embodiment, the forced regeneration by adding fuel is executed prior to the idle stop control for stopping the diesel engine 1 when the vehicle stops idling, so that the forced regeneration of the particulate filter 12 is performed in the idle mode. The control can be continued without interruption by the stop control, and the regeneration of the particulate filter 12 can be completed in a short time even in a vehicle employing the idle stop control.
[0048]
The method of regenerating the particulate filter of the present invention is not limited to the above-described embodiment. In the above-described embodiment, the regenerating method of the particulate filter is performed following the main injection of fuel near the compression top dead center. Fuel is added to the exhaust gas by performing post-injection at a timing of non-ignition later than the dead center, but fuel is added to the exhaust gas by delaying the timing of the main injection into the cylinder more than usual. In addition, the fuel injection into the cylinder is controlled in this way to leave a large amount of unburned fuel in the exhaust gas, so that not only the fuel addition is performed, but also the appropriate position of the exhaust pipe ( The injector may be inserted through the exhaust manifold, and fuel may be directly injected into the exhaust gas by the injector to be added. Further, exhaust throttle means for appropriately reducing the exhaust flow rate It is not always necessary to use an exhaust brake, an exhaust throttle valve may be separately provided in the middle of the exhaust pipe, and other various changes can be made without departing from the gist of the present invention. Of course.
[0049]
【The invention's effect】
According to the particulate filter reproducing method of the present invention described above, the following various excellent effects can be obtained.
[0050]
(I) According to the first and second aspects of the present invention, forced regeneration by fuel addition is performed prior to idle stop control for stopping the engine when the vehicle is idling and stopped. The forced regeneration of the particulate filter can be continued without interruption by the idle stop control, and the regeneration of the particulate filter can be completed in a short time even in a vehicle employing the idle stop control.
[0051]
(II) According to the invention described in claim 3 of the present invention, when idling is stopped and exhaust gas temperature and flow rate are too low and it is difficult to perform good combustion removal of particulates, one injection of main injection is performed. By increasing the injection amount, the number of revolutions can be increased and the amount of energy input can be increased from that during normal idling, so that the temperature and flow rate of the exhaust gas can be raised to levels suitable for forced regeneration.
[0052]
(III) According to the invention described in claim 4 of the present invention, the exhaust gas temperature can be further increased by narrowing the exhaust flow rate by the exhaust throttle means at the time of forced regeneration of the particulate filter in the idling state.
[0053]
(IV) According to the fifth aspect of the present invention, after-injection is added at the time of forced regeneration of the particulate filter in an idling state, and the fuel of the after-injection is burned at a timing that is difficult to convert to output. As a result, the heat efficiency of the engine is reduced, and the amount of heat generated by the fuel that is not used for power is increased, so that the exhaust gas temperature can be further increased.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an example of an embodiment for carrying out the present invention.
FIG. 2 is a sectional view showing details of the particulate filter of FIG. 1;
FIG. 3 is a flowchart showing basic control logic relating to reproduction control.
FIG. 4 is a flow sheet showing a control logic for executing regeneration control prior to idle stop control.
[Explanation of symbols]
1 Diesel engine (engine)
9 Exhaust gas 11 Exhaust pipe 12 Particulate filter 15 Control device 18 Fuel injection device 23 Exhaust brake

Claims (5)

Fuel is added to the exhaust gas on the upstream side of the catalyst regeneration type particulate filter installed in the exhaust pipe, and the collected fuel is collected by the reaction heat when the added fuel oxidizes on the oxidation catalyst of the particulate filter. In a method of forcibly regenerating a particulate filter by burning the curates, the regeneration of the particulate filter is performed by prioritizing idle stop control for stopping the engine when the vehicle is idling and stopping, and performing forced regeneration by adding fuel. Method. The fuel injection method according to claim 1, wherein the fuel addition is performed by adding a post injection at a non-ignition timing later than the compression top dead center after the main injection of the fuel performed near the compression top dead center. Curate filter regeneration method. The injection amount per main injection of combustion is increased in order to increase the number of revolutions of the engine at the time of forcible regeneration of the particulate filter in the idling state as compared with the time of normal idling. Regeneration method of particulate filter. 4. The method for regenerating a particulate filter according to claim 1, wherein an exhaust flow rate from the engine is appropriately reduced during forced regeneration of the particulate filter in an idling state. 5. The method for regenerating a particulate filter according to claim 1, wherein after-injection is added at a combustible timing immediately after the main injection during forced regeneration of the particulate filter in an idling state.

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