JP2011241746A - Exhaust emission control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To omit a labor such as replenishing urea water by eliminating the need of incidental facilities such as a urea water tank and a urea water feeding pipe by making it possible to apply a three way catalyst even in a diesel engine.SOLUTION: An exhaust emission control device has a low pressure loop 21, a high pressure loop 22, EGR valves 23, 24 (recirculation quantity controller) with which respective loops are equipped, the three-way catalyst 20 with which an exhaust pipe 4 is equipped, and a controller 27 for controlling the respective EGR valve 23, 24 so as to perform exhaust gas recirculation which is a base at an EGR rate suppressed to a degree in which black smoke is no generated when accelerating by the low pressure loop 21 and perform an additional exhaust gas recirculation to supplement of an insufficient EGR ratio by the high pressure loop 22, and suppress an air fuel ratio near a theoretical air fuel ratio, and is constituted such that the combustion can be established even near the theoretical air fuel ratio by raising the injection pressure of the fuel to the respective cylinders 19 to a predetermined height or more and by adjusting the injection hole diameter for injecting fuel such that the particles of the fuel injection can diffuse to the whole area of combustion chambers.

Description

  The present invention relates to an exhaust emission control device.

Conventionally, a three-way catalyst is known as a catalyst that is mounted on an exhaust system and simultaneously reduces HC, CO, and NOx in exhaust gas. In the reaction in the three-way catalyst, NOx O _{2 is used to} oxidize HC and CO. NOx is reduced to N ₂ , and the HC and CO are oxidized to CO ₂ and water (H ₂ O), so that harmful three components are simultaneously rendered harmless.

However, the three-way catalyst has a disadvantage that a sufficient effect cannot be exerted unless the air / fuel ratio at which O ₂ burns the fuel without excess or deficiency, that is, the stoichiometric air / fuel ratio (stoichiometry). The three-way catalyst is not used in many diesel engines, and it is actually applied to gasoline engines.

  Incidentally, in the diesel engine, even if the fuel injection amount is simply increased and the excess air ratio (λ) is about 1 (theoretical air-fuel ratio), there is a problem that the combustion in the cylinder misfires, and there is a misfire. Since there is a problem that CO and HC do not increase so much even in the previous state, it is considered impossible to simultaneously reduce HC, CO and NOx using a three-way catalyst.

  FIG. 3 shows an example of a conventional exhaust gas purification device applied to a diesel engine. In the example shown here, an exhaust pipe through which exhaust gas 3 discharged from the diesel engine 1 through the exhaust manifold 2 flows. 4 is equipped with a selective catalytic reduction catalyst 5 having the property of selectively reacting NOx with ammonia even in the presence of oxygen.

A urea water addition injector 7 (urea water addition means) for injecting urea water 6 as a reducing agent is installed in the exhaust pipe 4 upstream of the selective reduction catalyst 5 and the selective reduction catalyst. Immediately after 5, an NH ₃ slip catalyst 8 that oxidizes excess ammonia as a countermeasure against leaked ammonia is provided.

  Further, an oxidation catalyst 9 having an enhanced function of oxidizing unburned fuel in the exhaust gas 3 is provided in the exhaust pipe 4 upstream of the urea water 6 addition position by the urea water addition injector 7. In addition, immediately after the oxidation catalyst 9, the particulate filter 10 that integrally carries the oxidation catalyst is also provided.

  According to such an exhaust gas purification apparatus, urea water 6 is injected from the urea water addition injector 7 and is thermally decomposed into ammonia and carbon dioxide gas in the exhaust gas 3 and becomes active under temperature conditions equal to or higher than the activation lower limit temperature. On the selective catalytic reduction catalyst 5, the NOx in the exhaust gas 3 effectively reacts with ammonia and is favorably reduced and purified.

  Further, in the example shown here, since the particulate filter 10 is provided upstream of the selective catalytic reduction catalyst 5, the particulate filter 10 collects and removes the particulates in the exhaust gas 3. When the accumulated amount of particulates reaches a predetermined amount, if post-injection is performed at the non-ignition timing later than the compression top dead center on the diesel engine 1 side after the main injection, the exhaust gas 3 is discharged by this post-injection. An unburned fuel (mainly HC: hydrocarbon) is added to the inside, and the unburned fuel undergoes an oxidation reaction while passing through the oxidation catalyst 9, and an inflow of exhaust gas 3 heated by the reaction heat causes the downstream stage to flow. The catalyst bed temperature of the particulate filter 10 is raised, and the particulates are forcibly burned off.

  As prior art document information related to an exhaust purification device provided with a selective reduction catalyst that reduces and purifies NOx in exhaust gas using this type of urea water as a reducing agent, there is Patent Document 1 below.

JP 2004-239109 A

  However, in such a conventional exhaust purification device, it is necessary to add urea water 6 in order to perform reduction purification of NOx. Therefore, a urea water tank 11 for storing the urea water 6 and a urea water supply are provided. Ancillary facilities such as the pipe 12 and the supply pump 13 are required, and there is a problem that the equipment cost is high, and it takes time and effort to replenish the urea water 6 as needed so that the urea water tank 11 does not become empty. .

  The present invention has been made in view of the above-described circumstances, so that a three-way catalyst can be applied even in a diesel engine, and an auxiliary facility such as a urea water tank, a urea water supply pipe, and a supply pump is not required, and urea water is replenished. An object of the present invention is to provide an exhaust emission control device that can save labor.

  The present invention is an exhaust emission control device for simultaneously reducing HC, CO, and NOx in exhaust gas in a diesel engine, wherein a part of the exhaust gas is extracted from an exhaust passage downstream from a turbine of a turbocharger and the turbo A low-pressure loop that recirculates to the intake passage upstream from the compressor of the charger, a high-pressure loop that extracts a part of the exhaust gas from the exhaust manifold and recirculates it near the inlet of the intake manifold, and each of these low-pressure loop and high-pressure loop The recirculation amount adjusting means for adjusting the recirculation amount of exhaust gas, the three-way catalyst provided in the middle of the exhaust passage, and the EGR rate suppressed to the extent that black smoke is not generated during acceleration by the low pressure loop The exhaust gas recirculation is performed and additional exhaust gas recirculation is performed to supplement the insufficient EGR rate in the high pressure loop. And a control device that controls each of the recirculation amount adjusting means so that the fuel injection pressure to each cylinder of the diesel engine is increased to a predetermined value or more, and the injection hole diameter of the fuel injection By adjusting the fuel spray particles so that they can diffuse throughout the combustion chamber, the combustion can be established even in the vicinity of the theoretical air-fuel ratio.

  Thus, the exhaust gas recirculation as a base is performed on the low pressure loop side in this way, and the additional exhaust gas recirculation is performed on the high pressure loop side to supplement the shortage EGR rate. A high EGR rate is realized by the combined use of the loop and the high-pressure loop, and the air-fuel ratio can be suppressed to the stoichiometric air-fuel ratio.

  In other words, the amount of exhaust gas recirculation that must be shared on the high-pressure loop side is smaller than in the case of using the high-pressure loop alone, and there is no need to forcibly limit the exhaust gas with a variable nozzle type turbocharger. The amount of exhaust gas recirculation that should be shared on the high-pressure loop side can be realized relatively easily.

  The low-pressure loop has not been used to recirculate exhaust gas at a high EGR rate until now, when the driver depresses the accelerator and enters an acceleration state while driving. This is because black smoke is likely to be generated due to a drop, but in the present invention, exhaust gas recirculation as a base is only performed by a low-pressure loop with an EGR rate suppressed to such a level that black smoke is not generated during acceleration. Therefore, it is possible to avoid the occurrence of black smoke by immediately reducing the amount of exhaust gas recirculated on the high-pressure loop side during acceleration.

  That is, in the low-pressure loop, exhaust gas is returned to the intake passage upstream of the turbocharger compressor, but the route from here to the engine via the compressor, intercooler, and intake manifold is long, and the exhaust gas is exhausted to this long route. Since the intake air mixed with gas exists, when the fuel injection amount increases in response to accelerator depression during acceleration, even if the recirculation amount adjusting means of the low pressure loop is immediately closed, There is a disadvantage that black smoke tends to be generated because the state of low excess air rate continues until all the intake air mixed with exhaust gas is used up.

  On the other hand, in the high-pressure loop, exhaust gas is returned near the inlet of the intake manifold, so the intake air mixed with the exhaust gas exists only in the intake manifold, and even if the fuel injection amount increases during acceleration, the high-pressure loop If the loop recirculation amount adjustment means is closed, the intake air mixed with the exhaust gas in the intake manifold will be used up soon and the excess air ratio will recover quickly, so it is easy to avoid the occurrence of black smoke during acceleration. is there.

  Then, in this way, a large amount of exhaust gas is recirculated by the low pressure loop and the high pressure loop to suppress the air-fuel ratio to near the stoichiometric air-fuel ratio, and when fuel injection to each cylinder of the diesel engine is executed in such a state, By properly adjusting the injection pressure and nozzle diameter of the fuel injection, fuel spray particles diffuse throughout the combustion chamber, and the fuel is well dispersed and mixed, and combustion is performed in a state of evenly thinning. It will be established without.

  That is, by setting the injection pressure of fuel injection to a pressure that is significantly higher than the injection pressure in existing diesel engines, the power to send fuel spray farther is increased, and the injection diameter of fuel injection is made larger than the general injection diameter. By slightly increasing the size of the fuel spray, it is possible to prevent excessive atomization of the fuel spray accompanying an increase in the injection pressure and to maintain the roughness of the particles that are susceptible to injection force. It is possible to diffuse and mix well throughout the entire area.

  Even if a large amount of exhaust gas is recirculated to suppress the air-fuel ratio to near the stoichiometric air-fuel ratio, combustion can be established by appropriately adjusting the injection pressure and injection hole diameter of the fuel injection to each cylinder of the diesel engine. The facts that can be made are the facts found at the end of the inventor's earnest research, and in general, it has been proposed to simply increase the fuel injection amount and lower the excess air ratio. It is considered impossible to establish combustion in a diesel engine near the fuel ratio.

  In addition, when a large amount of exhaust gas is recirculated to suppress the air-fuel ratio to near the stoichiometric air-fuel ratio and combustion is established by appropriately adjusting the injection pressure and injection hole diameter of fuel injection to each cylinder of the diesel engine, The present inventor has also confirmed the fact that a large amount of CO and HC is produced in the gas, and it has been found that a three-way catalyst can function in a diesel engine to simultaneously reduce HC, CO, and NOx. Yes.

That is, under the condition that a large amount of exhaust gas is recirculated and the air-fuel ratio is suppressed to near the stoichiometric air-fuel ratio, the fuel injected at a predetermined injection pressure or higher is less likely to meet O ₂ , so The fuel is pyrolyzed and a large amount of HC gas is generated here. At this time, a large amount of CO ₂ having a larger mass and higher attractive force than O ₂ exists in the combustion chamber. The CO ₂ plays a role of inhibiting the reaction between HC and O ₂ , so that the oxidation reaction of HC is stagnated, and the HC remains in a large amount in the exhaust gas.

In the first reaction of HC and O ₂ , only CO is generated. Under the condition that the amount of residual oxygen is large and the amount of CO ₂ due to exhaust gas recirculation is not so large as in a normal diesel engine. The CO produced in the first reaction is connected to O ₂ one after another, and the reaction proceeds to CO _2. Under conditions where a large amount of exhaust gas is recirculated and the air-fuel ratio is suppressed to the vicinity of the stoichiometric air-fuel ratio. , The probability of encountering O ₂ is low and a large amount of CO ₂ also interferes with the reaction, so that a large amount remains in the exhaust gas in the state of CO.

Further, in the present invention, it is preferable that the three-way catalyst contains zeolite as a catalyst raw material so that NH ₃ can be adsorbed. By doing so, the air-fuel ratio becomes smaller than the stoichiometric air-fuel ratio during transient operation or the like. Te be a situation in which the NH ₃ from NOx will be generated on the three-way catalyst, can be consumed this NH ₃ it and held in the three-way catalyst as a reducing agent to reduce and purify NOx It becomes.

  Furthermore, in the present invention, it is preferable that a particulate filter is provided in the subsequent stage of the three-way catalyst, and in this way, particulates in the exhaust gas are collected and removed by the particulate filter. Moreover, when the accumulated amount of the particulates reaches a predetermined amount, if the fuel is added by performing post injection on the diesel engine side, the unburned fuel passes through the three-way catalyst. In the meantime, an oxidation reaction occurs, and the exhaust gas heated by the reaction heat inflows raises the catalyst bed temperature of the subsequent particulate filter, forcibly removing the particulates.

  According to the exhaust emission control device of the present invention described above, various excellent effects as described below can be obtained.

  (I) According to the invention described in claim 1 of the present invention, since the three-way catalyst can be applied even to a diesel engine, ancillary facilities such as a urea water tank, a urea water supply pipe, and a supply pump are provided. This eliminates the need for a significant reduction in the equipment cost, and also eliminates the trouble of supplying urea water, thereby significantly reducing the burden on the driver.

(II) According to the invention described in claim 2 of the present invention, the air-fuel ratio becomes smaller than the stoichiometric air-fuel ratio during transient operation or the like, and NH ₃ is generated from NOx on the three-way catalyst. However, since this NH ₃ can be held on the three-way catalyst and consumed as a reducing agent for reducing and purifying NOx, it is possible to prevent NH _{3 from} being discharged outside the vehicle.

  (III) According to the invention described in claim 3 of the present invention, particulates in the exhaust gas can be collected and removed by the particulate filter, and the three-way catalyst is forcibly regenerated by the particulate filter. The particulate filter can be regenerated by adding fuel as usual, instead of using an oxidation catalyst for the catalyst, and there is no need to provide a new oxidation catalyst for forced regeneration of the particulate filter. Can be made compact.

It is the schematic which shows an example of the form which implements this invention. It is a graph which shows the experimental result which confirmed combustion establishment in the theoretical air fuel ratio vicinity. It is the schematic which shows a prior art example.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 shows an example of an embodiment for carrying out the present invention, and the parts denoted by the same reference numerals as those in FIG. 3 represent the same items.

  In the example shown here, the diesel engine 1 includes a turbocharger 14, and intake air 15 guided from an air cleaner (not shown) is sent to the compressor 14 a of the turbocharger 14 through an intake pipe 16. The intake air 15 pressurized at 14 a is sent to the intercooler 17 to be cooled, and the intake air 15 is further guided from the intercooler 17 to the intake manifold 18 to be distributed to each cylinder 19 of the diesel engine 1. It has become.

  Further, the exhaust gas 3 discharged from each cylinder 19 of the diesel engine 1 is sent to the turbine 14 b of the turbocharger 14 through the exhaust manifold 2, and the exhaust gas 3 that has driven the turbine 14 b passes through the exhaust pipe 4. A three-way catalyst 20 capable of simultaneously reducing HC, CO, and NOx near the stoichiometric air-fuel ratio (stoichiometry) is disposed in the middle of the exhaust pipe 4 and the three-way catalyst. A particulate filter 10 disposed immediately after the catalyst 20 is provided.

Here, the three-way catalyst 20 contains zeolite as a catalyst raw material so that NH ₃ can be adsorbed, and the air-fuel ratio becomes smaller than the theoretical air-fuel ratio at the time of transient operation or the like, so that NOx is converted to NH on the three-way catalyst 20. This NH ₃ can be held on the three-way catalyst 20 even if ₃ is generated.

  In the diesel engine 1, a low-pressure loop 21 that extracts a part of the exhaust gas 3 from the downstream side of the particulate filter 10 and recirculates it to the intake pipe 16 upstream of the compressor 14 a of the turbocharger 14. And a high-pressure loop 22 that extracts a part of the exhaust gas 3 from the exhaust manifold 2 and recirculates it in the vicinity of the inlet of the intake manifold 18.

  In each of the low pressure loop 21 and the high pressure loop 22, EGR valves 23 and 24 (recirculation amount adjusting means) for adjusting the recirculation amount of the exhaust gas 3 and the recirculated exhaust gas 3 are cooled. EGR coolers 25 and 26 are installed, and the EGR coolers 25 and 26 exchange heat between the cooling water and the exhaust gas 3 to reduce the temperature of the exhaust gas 3 and reduce its volume, thereby reducing the diesel Generation of NOx can be effectively reduced by lowering the combustion temperature without significantly reducing the output of the engine 1.

  The opening degrees of the EGR valves 23 and 24 are controlled by opening command signals 23a and 24a from a control device 27 constituting an engine control computer (ECU: Electronic Control Unit). , The accelerator opening signal 28a from the accelerator sensor 28 (load sensor) that detects the accelerator opening as a load of the diesel engine 1, and the rotation speed from the rotation sensor 29 that detects the engine speed of the diesel engine 1 are controlled. Based on the signal 29a, it is executed as follows.

That is, the control device 27 performs exhaust gas recirculation as a base at an EGR rate (for example, about 10 to 15%) that is suppressed to a level that does not generate black smoke during acceleration by the low pressure loop 21 and is insufficient in the high pressure loop 22. Each of the EGR valves 23 and 24 according to the current operating state is controlled so that an additional exhaust gas recirculation is performed to supplement the rate (about 10 to 20%) and the air-fuel ratio can be suppressed to the vicinity of the theoretical air-fuel ratio. The opening is indicated.

  At this time, the diesel engine 1 increases the fuel injection pressure to each cylinder 19 to a predetermined value or more and adjusts the nozzle diameter of the fuel injection so that fuel spray particles can diffuse throughout the combustion chamber. Combustion can be established even in the vicinity of the fuel ratio.

  Thus, the exhaust gas recirculation as a base is performed on the low pressure loop 21 side in this way, and the additional exhaust gas recirculation is performed on the high pressure loop 22 side to supplement the insufficient EGR rate. By using the low pressure loop 21 and the high pressure loop 22 in combination, a high EGR rate is realized, and the air-fuel ratio can be suppressed to the stoichiometric air-fuel ratio.

  That is, the amount of recirculation of the exhaust gas 3 that must be shared on the high-pressure loop 22 side is smaller than in the case of using the high-pressure loop 22 alone, and it is impossible to narrow down the exhaust gas 3 with a variable nozzle type turbocharger or the like. Even if not performed, the amount of exhaust gas recirculation that should be shared on the high-pressure loop 22 side can be realized relatively easily.

  Incidentally, the low-pressure loop 21 has not been adopted so far to recirculate the exhaust gas 3 at a high EGR rate because when the accelerator is depressed by the driver during driving and the vehicle enters an acceleration state, the air is excessive. This is because black smoke is likely to be generated due to a sudden drop in the rate, but in this embodiment, the exhaust gas recirculation as a base is implemented by the low pressure loop 21 at an EGR rate that is suppressed to the extent that black smoke is not generated during acceleration. Therefore, it is possible to avoid the occurrence of black smoke by immediately reducing the recirculation amount of the exhaust gas 3 on the high-pressure loop 22 side during acceleration.

  That is, in the low-pressure loop 21, the exhaust gas 3 is returned to the intake pipe 16 upstream of the compressor 14 a of the turbocharger 14, and from here to the diesel engine 1 through the compressor 14 a, the intercooler 17, and the intake manifold 18. And the intake air mixed with the exhaust gas 3 exists in this long path. Therefore, when the fuel injection amount increases in response to the depression of the accelerator during acceleration, the EGR valve 23 of the low pressure loop 21 is Even if it closes immediately, there is a drawback that a state with a low excess air ratio continues and black smoke tends to be generated until all the intake air mixed with the exhaust gas 3 in the long path is used up.

  In contrast, in the high-pressure loop 22, the exhaust gas 3 is returned near the inlet of the intake manifold 18, so the intake air 15 mixed with the exhaust gas 3 exists only in the intake manifold 18, and the fuel injection amount during acceleration is high. If the EGR valve 24 of the high-pressure loop 22 is closed, the intake air 15 mixed with the exhaust gas 3 in the intake manifold 18 will be used up soon and the excess air ratio will be recovered quickly. There is an advantage that it is easy to avoid the occurrence.

  In this way, a large amount of the exhaust gas 3 is recirculated by the low pressure loop 21 and the high pressure loop 22 to suppress the air-fuel ratio in the vicinity of the theoretical air-fuel ratio, and in such a state, fuel is injected into each cylinder 19 of the diesel engine 1. Is performed, the fuel spray particles are diffused throughout the combustion chamber by appropriate adjustment of the injection pressure and the nozzle hole diameter of the fuel injection, and the fuel is well dispersed and mixed so that the combustion is performed in a thinned state. The combustion will be established without misfiring.

  That is, by setting the injection pressure of fuel injection to a pressure significantly higher than the injection pressure in the existing diesel engine 1, the force for sending the fuel spray further is increased, and the injection diameter of the fuel injection is changed to a general injection diameter. By making it slightly larger, it is possible to suppress the excessive atomization of the fuel spray accompanying the increase in the injection pressure and to maintain the roughness of the particles that are susceptible to the injection force. It becomes possible to diffuse and mix well by diffusing throughout the chamber.

Even if a large amount of exhaust gas 3 is recirculated and the air-fuel ratio is suppressed to near the stoichiometric air-fuel ratio, the fuel injection pressure and the injection hole diameter of each cylinder 19 of the diesel engine 1 are appropriately adjusted. The fact that combustion can be established is a fact found after the inventor's earnest research, and generally, it has been proposed only to increase the fuel injection amount and lower the excess air ratio. Although it is considered impossible to establish combustion in the diesel engine 1 near the stoichiometric air-fuel ratio, as shown in the graph of FIG. 2, the injection diameter is slightly larger than that of a normal diesel engine. The present inventors have already confirmed that if the injection pressure of fuel injection is increased to about 2000 kg / cm ² , the combustion can be established with the generation of smoke suppressed to 15% or less.

  In addition, a large amount of exhaust gas 3 is recirculated to suppress the air-fuel ratio to near the stoichiometric air-fuel ratio, and combustion is established by appropriately adjusting the injection pressure and injection hole diameter of fuel injection to each cylinder 19 of the diesel engine 1. In this case, the present inventor has also confirmed the fact that a large amount of CO and HC is generated in the exhaust gas 3, and even in the diesel engine 1, the three-way catalyst 20 is made to function to simultaneously reduce HC, CO, and NOx. It is known to get.

That is, under a condition where a large amount of exhaust gas 3 is recirculated and the air-fuel ratio is suppressed to near the stoichiometric air-fuel ratio, there is a low probability that fuel injected at an injection pressure higher than a predetermined value will meet O ₂ . It is easy to reach the wall surface, and the fuel is thermally decomposed to generate a large amount of HC gas. At this time, a large amount of CO ₂ having a larger mass and higher attractive force than O ₂ exists in the combustion chamber. As a result, the CO ₂ plays a role of inhibiting the reaction between HC and O ₂ , so that the oxidation reaction of HC stagnates and a large amount of the HC remains in the exhaust gas 3.

In the first reaction of HC and O ₂ , only CO is generated, and the amount of residual oxygen is large and the amount of CO ₂ due to exhaust gas recirculation is not so large as in a normal diesel engine 1. Then, the CO generated in the first reaction is successively combined with O ₂ and the reaction proceeds to CO ₂ , but the condition that the air-fuel ratio is suppressed to the vicinity of the theoretical air-fuel ratio by recirculating a large amount of exhaust gas 3. Below, the probability of encountering O ₂ is low and a large amount of CO ₂ also interferes with the reaction, so that it remains in the exhaust gas 3 in a large amount in the state of CO.

In the present embodiment, since the three-way catalyst 20 contains zeolite as a catalyst raw material so that NH ₃ can be adsorbed, the air-fuel ratio becomes smaller than the stoichiometric air-fuel ratio during the transient operation or the like. Even if NH ₃ is generated from NOx, it is possible to hold the NH ₃ on the three-way catalyst 20 and consume it as a reducing agent for reducing and purifying NOx.

  Further, since the particulate filter 10 is provided in the subsequent stage of the three-way catalyst 20, the particulate filter 10 collects and removes the particulates in the exhaust gas 3, and the particulates of the particulates are collected. If fuel is added, for example, by performing post injection on the diesel engine 1 side when the accumulation amount reaches a predetermined amount, the unburned fuel undergoes an oxidation reaction while passing through the three-way catalyst 20, The inflow of the exhaust gas 3 heated by the reaction heat raises the catalyst bed temperature of the particulate filter 10 at the subsequent stage, and the particulates are forcibly burned off.

  Therefore, according to the above-described embodiment, the three-way catalyst 20 can be applied even in the diesel engine 1, so that the urea water tank 11 (see FIG. 3), the urea water supply pipe 12 (see FIG. 3), Ancillary equipment such as the supply pump 13 (see FIG. 3) can be dispensed with, so that the equipment cost can be greatly reduced. Can be significantly reduced.

Even when the air-fuel ratio becomes smaller than the stoichiometric air-fuel ratio during transient operation or the like and NH ₃ is generated from NOx on the three-way catalyst 20, this NH ₃ is held on the three-way catalyst 20. And since it can be consumed as a reducing agent for reducing and purifying NOx, it is possible to prevent NH _{3 from} being discharged outside the vehicle.

  Further, particulates in the exhaust gas 3 can be collected and removed by the particulate filter 10, and the three-way catalyst 20 can be used in place of the oxidation catalyst for forced regeneration of the particulate filter 10. The particulate filter 10 can be regenerated by adding fuel as usual, and the entire configuration can be made compact by eliminating the need to provide a new oxidation catalyst for forced regeneration of the particulate filter 10.

  In particular, if a part of the exhaust gas 3 is extracted from the downstream side of the particulate filter 10 as shown in FIG. 1 and recirculated, the particulates contained in the recirculated exhaust gas 3 (proportional distribution). It is also possible to avoid contamination of the intake system (the compressor 14a, the intake pipe 16, the intercooler 17, etc.) due to.

  Note that the exhaust emission control device of the present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made without departing from the gist of the present invention.

DESCRIPTION OF SYMBOLS 1 Diesel engine 2 Exhaust manifold 3 Exhaust gas 4 Exhaust pipe 10 Particulate filter 14 Turbocharger 14a Compressor 14b Turbine 15 Intake 16 Intake pipe 18 Intake manifold 19 Cylinder 20 Three-way catalyst 21 Low pressure loop 22 High pressure loop 23 EGR valve (recirculation amount) Adjustment means)
24 EGR valve (recirculation amount adjusting means)
27 Control device

Claims (3)

  An exhaust emission control device for simultaneously reducing HC, CO, NOx in exhaust gas in a diesel engine, extracting a part of exhaust gas from an exhaust passage downstream from a turbine of a turbocharger and using a compressor of the turbocharger A low-pressure loop that recirculates to the upstream intake passage, a high-pressure loop that extracts a portion of the exhaust gas from the exhaust manifold and recirculates it near the inlet of the intake manifold, and an exhaust gas provided in each of the low-pressure loop and the high-pressure loop. The recirculation amount adjusting means for adjusting the recirculation amount of the exhaust gas, the three-way catalyst provided in the middle of the exhaust passage, and the exhaust gas serving as a base at the EGR rate that is suppressed to the extent that black smoke is not generated during acceleration by the low pressure loop Carry out recirculation and perform additional exhaust gas recirculation to supplement the shortage EGR rate in the high-pressure loop to achieve the stoichiometric air-fuel ratio And a control device that controls each of the recirculation amount adjusting means so that the ratio can be suppressed in the vicinity of the ratio. An exhaust emission control device characterized in that combustion can be established even in the vicinity of the stoichiometric air-fuel ratio by adjusting so that the particles of the particles can diffuse throughout the combustion chamber. The exhaust purification apparatus according to claim 1, wherein the three-way catalyst contains zeolite as a catalyst raw material so that NH ₃ can be adsorbed.   The exhaust emission control device according to claim 1 or 2, wherein a particulate filter is provided downstream of the three-way catalyst.

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