JP2004143988A - Emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an emission control device capable of accurately grasping a catalyst floor temperature of a particulate filter, and thereby to realize an accurate and fine temperature control. <P>SOLUTION: The emission control device comprises a filter case 12 equipped in the middle of an exhaust pipe 11 in which an exhaust gas 9 from a diesel engine 1 (an internal combustion engine) circulates, a flow through type oxidation catalyst 14 stored at a front stage in the filter case 12, and a catalyst regeneration type particulate filter 13 stored at a rear stage therein. A temperature sensor 15 for detecting an exhaust temperature is provided between the oxidation catalyst 14 and the catalyst regeneration type particulate filter 13. Temperature can be accurately and finely controlled based on the detecting temperature of the temperature sensor 15. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust gas purification device.
[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, It has been considered to add fuel to the exhaust gas on the more upstream side to perform forced regeneration of the particulate filter.
[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]
A method of forcibly regenerating a particulate filter of this type is also disclosed in the following unpublished prior applications, Patent Document 1 and Patent Document 2.
[0009]
[Patent Document 1]
Japanese Patent Application No. 2001-355061 [Patent Document 2]
Japanese Patent Application No. 2002-20374 [0010]
In particular, in an exhaust gas purification device provided with a flow-through type oxidation catalyst in front of the particulate filter for the purpose of supporting the oxidation reaction of the collected particulates, the added fuel is oxidized by the oxidation catalyst in front of the particulate filter. The reaction generates reaction heat, and the exhaust gas heated by the reaction heat is introduced into the particulate filter. Therefore, the forced regeneration of the particulate filter can be realized from a lower exhaust temperature. .
[0011]
[Problems to be solved by the invention]
However, conventionally, when the particulate filter is forcibly regenerated by adding this kind of fuel, the control is performed only by the temperature detected by the temperature sensor arranged on the outlet side of the particulate filter. There was a problem that control could not be realized.
[0012]
That is, since the particulate filter has a large heat mass made of ceramics such as cordierite, the actual catalyst bed temperature of the particulate filter can be accurately determined only by detecting the exhaust gas temperature on the outlet side with poor thermal response. Could not figure out.
[0013]
In fact, the exhaust gas temperature at the particulate filter outlet side during execution of forced regeneration has a small degree of temperature rise as compared with the actual catalyst bed temperature of the particulate filter, and has a time delay. However, even if the temperature of the catalyst bed of the particulate filter has reached a high temperature that may cause melting, it is practically impossible to take control immediately by grasping this only from the exhaust gas temperature at the outlet side. Impossible.
[0014]
More specifically, the catalyst bed temperature of the particulate filter is quickly raised to a target temperature suitable for forced regeneration, and the fuel addition amount is finely adjusted so that the target temperature can be stabilized and maintained for a predetermined time, and optimum temperature control is performed. Even so, accurate and detailed temperature control cannot be realized based on the exhaust gas temperature on the outlet side with poor thermal response as described above.
[0015]
SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides an exhaust gas purifying apparatus capable of accurately grasping the catalyst bed temperature of a particulate filter, thereby realizing accurate and fine temperature control. The purpose is.
[0016]
[Means for Solving the Problems]
According to the present invention, a filter case is interposed in an exhaust pipe through which exhaust gas from an internal combustion engine flows, a flow-through type oxidation catalyst is accommodated in a front stage in the filter case, and a catalyst regeneration type In an exhaust gas purifying apparatus containing a curated filter, a temperature sensor for detecting an exhaust gas temperature is provided between an oxidation catalyst and a catalyst regeneration type particulate filter.
[0017]
Thus, when the exhaust gas flowing into the filter case passes through the oxidation catalyst in the preceding stage, the oxidation target component in the exhaust gas undergoes an oxidation reaction, thereby generating reaction heat. The temperature of the exhaust gas heated by the heat is detected by the temperature sensor at the entrance of the particulate filter.
[0018]
Since the temperature detected by this temperature sensor is the exhaust temperature immediately before the temperature has been changed by passing through the oxidation catalyst of the preceding stage and just before flowing into the particulate filter, it has a high correlation with the catalyst bed temperature of the particulate filter. Therefore, the catalyst bed temperature of the particulate filter can be accurately grasped based on the exhaust gas temperature.
[0019]
Further, when the exhaust gas purifying apparatus of the present invention is more specifically implemented, when it is necessary to regenerate the fuel addition means for adding fuel to the exhaust gas on the upstream side of the oxidation catalyst and the particulate filter. Preferably, a control device is provided for operating the fuel adding means based on the temperature detected by the temperature sensor.
[0020]
Thus, when forced regeneration of the particulate filter becomes necessary, when the fuel is added by operating the fuel adding means by the control device, the added fuel undergoes an oxidation reaction with the preceding oxidation catalyst in the filter case. As a result, heat of reaction is generated, and the temperature of the exhaust gas passing through the oxidation catalyst is significantly increased by the reaction heat. As a result, the exhaust gas heated through the oxidation catalyst is introduced into the particulate filter, and the temperature of the particulate filter increases. The entire region is heated to a high temperature, whereby the particulates are satisfactorily burned off and the particulate filter is regenerated.
[0021]
And since the control of the operation of the fuel addition means is performed by the control device based on the temperature detected by the temperature sensor, the operation control of the fuel addition means can be immediately controlled in accordance with the actual catalyst bed temperature of the particulate filter. Since it is possible to take measures such as stopping fuel addition immediately when an abnormally high temperature of exhaust gas is detected by the temperature sensor, it is possible to avoid the worst situation such as erosion of the particulate filter. It is possible to raise the catalyst bed temperature of the particulate filter to a target temperature suitable for forced regeneration at an early stage, and to precisely adjust the fuel addition amount so as to stabilize at the target temperature and maintain the fuel addition amount for a predetermined time. Control can be realized.
[0022]
If the temperature detected by the temperature sensor is abnormally high despite appropriate temperature control of the fuel addition means, it is possible to determine that an abnormality has occurred on the internal combustion engine side, and If the temperature detected by the temperature sensor does not increase despite fuel addition being performed by the fuel addition means, it is possible to determine that the oxidation catalyst in the preceding stage has deteriorated.
[0023]
Further, in the present invention, a fuel injection device for injecting fuel into each cylinder of the internal combustion engine is adopted as a fuel addition means, and the control device controls the fuel injection into the cylinder to reduce the unburned fuel component in the exhaust gas. It is advisable to add more fuel by leaving a large amount.
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0025]
1 to 3 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).
[0026]
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.
[0027]
A filter case 12 is interposed in the exhaust pipe 11, and a catalyst regeneration type particulate filter 13 integrally supporting an oxidation catalyst is provided at a subsequent stage in the filter case 12. As shown in FIG. 2 in an enlarged manner, the particulate filter 13 has a porous honeycomb structure made of ceramic, and the inlets of the flow paths 13a partitioned in a grid are alternately formed. With respect to the flow path 13a that is sealed and the inlet is not plugged, the outlet is plugged, and only the exhaust gas 9 that has passed through the porous thin wall 13b that defines each flow path 13a flows downstream. It is designed to be discharged to the side.
[0028]
Further, a flow-through type oxidation catalyst 14 having a honeycomb structure as shown in an enlarged view in FIG. 3 is accommodated in the filter case 12 immediately before the particulate filter 13.
[0029]
A temperature sensor 15 for measuring the temperature of the exhaust gas 9 as a substitute for the catalyst bed temperature is provided between the oxidation catalyst 14 and the particulate filter 13 in the filter case 12. The 15 temperature signals 15a are input to a control device 20 which forms an engine control computer (ECU: Electronic Control Unit).
[0030]
Since the control device 20 also serves as an engine control computer, the control device 20 also controls fuel injection, and more specifically, the accelerator sensor 16 (which detects the 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 18 a is output to the fuel injection valve 18.
[0031]
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.
[0032]
On the other hand, in the control device 20, 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 13. When the ignition mode is switched from the normal mode to the regeneration mode, the non-ignition timing (start timing is set to the crank angle of 90 degrees) which is later than the compression top dead center following the main fuel injection performed near the compression top dead center (crank angle 0 °) The fuel injection signal 18a for performing the post-injection in the range of {-120} is determined.
[0033]
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 13, and the heat of the reaction raises the catalyst bed temperature to burn and remove the particulates in the particulate filter 13. Will be.
[0034]
The control device 20 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, and the amount of accumulated particulates is estimated.
[0035]
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.
[0036]
Further, after the control device 20 estimates that the amount of accumulated particulates has reached a predetermined target value, based on a temperature signal 15 a from the temperature sensor 15, the exhaust temperature at the inlet of the particulate filter 13 is reduced to a predetermined temperature. After the above conditions are satisfied, the fuel injection control is switched from the normal mode to the regeneration mode, and the fuel is added to the exhaust gas 9 on the upstream side of the particulate filter 13. Is controlled so as to gradually increase the injection amount at the start according to the temperature detected by the temperature sensor 15, and after the temperature detected by the temperature sensor 15 reaches a predetermined temperature, Proportional integration control is performed so as to be maintained at a higher target temperature for a predetermined time.
[0037]
In the present embodiment, a temperature sensor 21 is also provided at the outlet of the filter case 12, and a temperature signal 21a of the temperature sensor 21 is also input to the control device 20. Reference numeral 21a is used to detect the occurrence of erosion of the particulate filter 13 by detecting an abnormally high temperature.
[0038]
When the controller 20 determines that the amount of accumulated particulates has increased and the particulate filter 13 needs to be forcibly regenerated, the temperature detected by the temperature sensor 15 is increased to a predetermined temperature. The regeneration mode is selected under the condition exceeding the above condition, the control unit 20 switches the fuel injection pattern from the normal mode to the regeneration mode, and performs the post injection at the non-ignition timing later than the compression top dead center following the main injection. As a result of adopting the injection pattern to be performed, the fuel added unburned into the exhaust gas 9 by the post-injection turns into a high-concentration hydrocarbon by thermal decomposition and is oxidized by the oxidation catalyst 14 to reduce the heat of reaction. The temperature of the exhaust gas 9 passing through the oxidation catalyst 14 is significantly increased by the reaction heat, and the exhaust gas 9 heated through the oxidation catalyst 14 is particulated. Filter 13 whole of the particulate filter 13 is high temperature by being introduced into, thereby so that it particulates are satisfactorily burned off regeneration of the particulate filter 13 is achieved.
[0039]
Here, it should be additionally described that, if the oxidation catalyst 14 is not disposed immediately before the particulate filter 13, the high-concentration hydrocarbon generated by the addition of the fuel is subjected to the particulate filter. Oxidation reaction occurs on the surface of the catalyst 13, but such substantial oxidation reaction tends to be biased toward the rear of the particulate filter 13, and only the rear of the particulate filter 13 becomes hot. Unburned particulates tend to be generated in the front part.
[0040]
On the other hand, if the oxidation catalyst 14 is arranged immediately before the particulate filter 13, even if the oxidation reaction in the oxidation catalyst 14 is biased to the rear part, the temperature of the exhaust gas 9 passing therethrough is not increased. If the temperature can be increased, the temperature of the particulate filter 13 can be increased over the entire region from the front portion to the rear portion by introducing the exhaust gas 9.
[0041]
In this embodiment, the temperature of the exhaust gas 9 heated by the reaction heat via the oxidation catalyst 14 at the preceding stage is detected by the temperature sensor 15 on the input side of the particulate filter 13. Since the temperature detected by 15 is the exhaust gas temperature immediately before the temperature of the particulate filter 13 is completely changed after passing through the oxidation catalyst 14 at the preceding stage, it is highly correlated with the catalyst bed temperature of the particulate filter 13. The catalyst bed temperature of the particulate filter 13 can be accurately grasped based on the exhaust gas temperature.
[0042]
Further, by controlling the fuel injection pattern of the fuel injection device 18 by the control device 20 based on the catalyst bed temperature of the particulate filter 13 accurately grasped in this way, it is possible to immediately respond to the actual catalyst bed temperature of the particulate filter 13. The post-injection control described above can be performed. For example, when an abnormally high temperature of the exhaust gas 9 is detected by the temperature sensor 15, it is possible to take measures such as stopping post-injection (addition of fuel) immediately. 13 can be avoided beforehand.
[0043]
Moreover, the post-injection in the regeneration mode is controlled so as to gradually increase the injection amount at the start according to the temperature detected by the temperature sensor 15 so that the catalyst bed temperature of the particulate filter 13 is set to a target suitable for forced regeneration. It is possible to realize accurate and fine temperature control such that the temperature is raised to the temperature at an early stage, and then the proportional integral control is executed so as to be stably maintained at the target temperature for a predetermined time.
[0044]
If the temperature detected by the temperature sensor 15 is abnormally high even though the fuel injection device 18 is appropriately controlled, it may be determined that an abnormality has occurred on the diesel engine 1 side. If the temperature detected by the temperature sensor 15 does not increase despite the post-injection performed by the fuel injection device 18, it is determined that the oxidation catalyst 14 in the preceding stage has deteriorated. It becomes possible.
[0045]
It should be noted that the exhaust gas purifying apparatus of the present invention is not limited to the above-described embodiment. In the above-described embodiment, the fuel injection device is adopted as the fuel adding means, and the fuel injection performed near the compression top dead center is performed. The fuel is added to the exhaust gas by performing post-injection at the timing of non-ignition later than the compression top dead center following the main injection of, but the timing of the main injection into the cylinder must be delayed from normal It is also possible to add fuel to the exhaust gas by using only means for adding fuel by controlling fuel injection into the cylinder and leaving a large amount of unburned fuel in the exhaust gas. Instead, an injector may be mounted as a fuel addition means at an appropriate position in the exhaust pipe (an exhaust manifold is also possible), and the injector may directly add fuel to the exhaust gas by adding the fuel. It is of course that various changes and modifications may be made without departing from the scope and spirit of the present invention.
[0046]
【The invention's effect】
According to the exhaust gas purification apparatus of the present invention described above, various excellent effects as described below can be obtained.
[0047]
(I) According to the first aspect of the present invention, since the catalyst bed temperature of the particulate filter can be accurately grasped, accurate and fine temperature control is performed based on the catalyst bed temperature of the particulate filter. Can be realized, and the worst situation such as erosion of the particulate filter can be avoided.
[0048]
(II) According to the second and third aspects of the present invention, when the temperature detected by the temperature sensor is abnormally high despite appropriate temperature control of the fuel addition means, the internal combustion engine If the temperature detected by the temperature sensor does not increase even though fuel addition is being performed by the fuel addition means, it is determined that an abnormality has occurred on the oxidation catalyst of the preceding stage. Can be determined to be degraded.
[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 partially cutaway perspective view showing details of the oxidation catalyst of FIG. 1;
[Explanation of symbols]
1 diesel engine (internal combustion engine)
Reference Signs List 8 cylinder 9 exhaust gas 11 exhaust pipe 12 filter case 13 particulate filter 14 oxidation catalyst 15 temperature sensor 18 fuel injection device (fuel adding means)
20 Control device

Claims (3)

A filter case is interposed in the exhaust pipe through which exhaust gas from the internal combustion engine flows. An exhaust gas purification apparatus according to claim 1, wherein a temperature sensor for detecting an exhaust gas temperature is provided between the oxidation catalyst and the catalyst regeneration type particulate filter. A fuel adding means for adding fuel to the exhaust gas on the upstream side of the oxidation catalyst, and a control device for operating the fuel adding means based on the temperature detected by the temperature sensor when it is necessary to regenerate the particulate filter. The exhaust purification device according to claim 1, further comprising: A fuel injection device that injects fuel into each cylinder of the internal combustion engine is used as fuel addition means, and the control device controls the fuel injection into the cylinders, leaving a large amount of unburned fuel in the exhaust gas to add fuel. The exhaust gas purifying apparatus according to claim 1, wherein the exhaust gas purifying apparatus is configured to execute the processing.

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