JP2012127249A - Exhaust emission control method and device - Google Patents

Abstract

A three-way catalyst can be applied to a diesel engine so that ancillary facilities such as a urea water tank and a urea water supply pipe are not required, and labor for supplying urea water can be saved.
A control device 27 controls each EGR valve 23, 24, and a low pressure loop 21 performs exhaust gas recirculation as a base at an EGR rate that is suppressed to the extent that black smoke is not generated during acceleration and a high pressure loop 22. Then, additional exhaust gas recirculation is performed to supplement the insufficient EGR rate, thereby suppressing the air-fuel ratio to near the stoichiometric air-fuel ratio and controlling the fuel injection device of the diesel engine 1 to control main injection in the diesel engine 1. By performing after injection at a timing at which ignition is possible immediately after that, the air-fuel ratio is lowered to the stoichiometric air-fuel ratio due to the increase in the amount of unburned fuel by the after-injection and the oxygen consumption by a part of the oxidation reaction. Make it work.
[Selection] Figure 1

Description

  The present invention relates to an exhaust purification method and apparatus.

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. 2 shows an example of a conventional exhaust gas purification apparatus 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. It is an object of the present invention to provide an exhaust purification method and apparatus that can save labor.

  The present invention is an exhaust purification method for simultaneously reducing HC, CO, NOx in exhaust gas using a three-way catalyst in a diesel engine, and a part of the exhaust gas is removed from an exhaust passage downstream from a turbine of a turbocharger. A low pressure loop that is extracted and recirculated to the intake passage upstream of the compressor of the turbocharger and a high pressure loop that extracts a part of the exhaust gas from the exhaust manifold and recirculates near the inlet of the intake manifold are used. The basic exhaust gas recirculation is performed at an EGR rate that suppresses black smoke during acceleration, and the air-fuel ratio is calculated by performing additional exhaust gas recirculation to supplement the insufficient EGR rate in the high-pressure loop. While suppressing to near the air-fuel ratio, after injection is performed at a timing at which ignition is possible immediately after main injection, The three-way catalyst is made to function by lowering the air-fuel ratio to the stoichiometric air-fuel ratio by increasing the amount of oxygen and consuming oxygen by a part of the oxidation reaction.

  The present invention is also 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. A low-pressure loop that recirculates to the intake passage upstream from the compressor of the turbocharger, a high-pressure loop that extracts a part of the exhaust gas from the exhaust manifold and recirculates near the inlet of the intake manifold, and each of the low-pressure loop and the high-pressure loop A recirculation amount adjusting means for adjusting a recirculation amount of exhaust gas, a three-way catalyst provided in the middle of the exhaust passage, each recirculation amount adjusting means, and a fuel injection device for the diesel engine. A control device that controls the recirculation amount adjusting means so as not to generate black smoke during acceleration in the low-pressure loop. The exhaust gas recirculation as a base is implemented at a moderate EGR rate, and the exhaust gas recirculation is performed in the high-pressure loop to supplement the insufficient EGR rate, thereby suppressing the air-fuel ratio to the theoretical air-fuel ratio. In addition, by controlling the fuel injection device and performing after injection at a timing that can be ignited immediately after main injection, the air-fuel ratio is increased due to an increase in the amount of unburned fuel by the after injection and oxygen consumption by a part of the oxidation reaction. It is also characterized in that it is configured to lower the air-fuel ratio to the stoichiometric 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 vicinity of the theoretical 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 it was easy to generate black smoke.

  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.

  In the case of the present invention, the low-pressure loop and the high-pressure loop are used in combination, and only the exhaust gas recirculation that is the base is performed by the low-pressure loop at an EGR rate that is suppressed to the extent that black smoke is not generated during acceleration. It is possible to avoid the generation of black smoke by immediately reducing the amount of exhaust gas recirculation on the high-pressure loop side during acceleration.

  Then, under such conditions that a large amount of exhaust gas is recirculated by the low-pressure loop and the high-pressure loop and the air-fuel ratio is suppressed to the vicinity of the theoretical air-fuel ratio, the after-ignition timing immediately after the main injection in the diesel engine is achieved. When the injection is carried out, the air-fuel ratio is lowered to the stoichiometric air-fuel ratio due to the increase in the unburned fuel due to the after-injection and the oxygen consumption due to a part of the oxidation reaction. , CO and NOx can be simultaneously reduced.

  Furthermore, in the present invention, it is preferable that zeolite or magnesia is contained as a catalyst raw material so that the three-way catalyst can adsorb HC, and in this way, the air-fuel ratio is temporarily reduced to the theoretical air during transient operation. Even when the fuel ratio becomes larger than the fuel ratio, it is possible to maintain the surface atmosphere of the three-way catalyst at the stoichiometric air-fuel ratio by HC adsorbed on the three-way catalyst and to continue the reaction for simultaneously reducing HC, CO, and NOx. .

  In the present invention, a fuel addition means for directly injecting fuel into the exhaust pipe upstream of the three-way catalyst is provided, and the control device can be configured to add fuel by the fuel addition means as required. It is preferable that the intake throttle means for reducing the intake air amount is further provided, and the control device is configured to be able to reduce the intake air amount by the intake throttle means as required. good.

  In this way, the air-fuel ratio can be increased by directly injecting fuel into the exhaust pipe by the fuel addition means according to the operating condition of the diesel engine to compensate for the unburned fuel, or by reducing the intake air amount by the intake throttle means. It is possible to assist the reduction of the fuel pressure, and it is possible to avoid excessive after injection by appropriately using these fuel addition means and intake throttle means together.

  Further, in the present invention, it is preferable that a particulate filter is provided after the three-way catalyst, and in this way, particulates in the exhaust gas are collected and removed by the particulate filter. In addition, if the fuel is added using the fuel addition means when the accumulated amount of the particulates reaches a predetermined amount, the unburned fuel is oxidized while passing through the three-way catalyst. The exhaust gas, which has reacted and heated by the reaction heat, raises the catalyst bed temperature of the downstream particulate filter, forcibly removing the particulates.

  According to the exhaust purification method and apparatus of the present invention described above, various excellent effects as described below can be obtained.

  (I) According to the first and second aspects of the present invention, since the three-way catalyst can function by lowering the air-fuel ratio to the stoichiometric air-fuel ratio even in a diesel engine, a urea water tank or a urea water supply pipe In addition, an auxiliary facility such as a supply pump can be dispensed with, and the cost of the facility can be greatly reduced. In addition, the labor of replenishing urea water can be saved, and the burden on the driver can be remarkably reduced. it can.

  (II) According to the invention described in claim 3 of the present invention, even if the air-fuel ratio is temporarily larger than the stoichiometric air-fuel ratio during transient operation or the like, the three-way Since the catalyst surface atmosphere is maintained at the stoichiometric air-fuel ratio, the reaction that simultaneously reduces HC, CO, and NOx can be continued, greatly increasing the continuity of the reaction that simultaneously reduces HC, CO, and NOx in the three-way catalyst. Can be improved.

  (III) According to the fourth and fifth aspects of the present invention, fuel is directly injected into the exhaust pipe by the fuel addition means according to the operating condition of the diesel engine to compensate for the unburned fuel, or the intake throttle Since the air-fuel ratio can be reduced by narrowing the intake air amount by the means, excessive after injection can be avoided by appropriately using these fuel addition means and intake throttle means together. It is possible to prevent the fuel from being mixed into the oil and diluting the oil by the after injection.

  (IV) According to the invention described in claim 6 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 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 parts denoted by the same reference numerals as those in FIG. 2 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 with a stoichiometric air-fuel ratio (stoichiometry) is provided in the middle of the exhaust pipe 4 and the three-way catalyst. The particulate filter 10 disposed immediately after the unit 20 is provided.

  Here, the three-way catalyst 20 contains zeolite, magnesia or the like as a catalyst raw material so that HC can be adsorbed, so that the HC contained in the exhaust gas 3 can be adsorbed and held on the three-way catalyst 20. Even if the air-fuel ratio temporarily becomes higher than the stoichiometric air-fuel ratio during transient operation, etc., the reaction that simultaneously reduces HC, CO, NOx by HC adsorbed on the three-way catalyst is continued. It is.

  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%) that is suppressed to the extent that black smoke is not generated during acceleration by the low pressure loop 21, and the high pressure loop 22 corresponds to the insufficient EGR rate. Depending on the current operating conditions, an additional exhaust gas recirculation is performed to supplement (for example, about 25%) so that the air-fuel ratio can be suppressed to near the stoichiometric air-fuel ratio (the excess air ratio is about 1.1). Further, the opening degree of each EGR valve 23, 24 is instructed.

  In addition, the control device 27 instructs the fuel injection device 30 of the diesel engine 1 to perform a fuel injection command based on the accelerator opening signal 28a from the accelerator sensor 28 and the rotation speed signal 29a from the rotation sensor 29. The air / fuel ratio can be controlled by the signal 30a, and the air / fuel ratio suppressed to the vicinity of the theoretical air / fuel ratio by the exhaust gas recirculation performed by the low pressure loop 21 and the high pressure loop 22 described above can be ignited immediately after the main injection. By carrying out after injection, the unburned fuel content due to the after injection and oxygen consumption due to part of the oxidation reaction are further lowered, thereby reducing the air-fuel ratio to the stoichiometric air-fuel ratio (the excess air ratio is about 1.0). Can be lowered.

  Further, in the control for lowering the air-fuel ratio to the stoichiometric air-fuel ratio, the intake valve 31 provided in the intake pipe 16 is used in combination as an intake throttle means as necessary. The intake valve 31 narrows down the amount of intake air by the signal 31a to assist the decrease in the air-fuel ratio.

  Furthermore, in this embodiment, a fuel addition valve 32 for directly injecting fuel into the exhaust pipe 4 is provided in the exhaust pipe 4 upstream of the three-way catalyst 20 as fuel addition means. Fuel is supplied to the addition valve 32 from a fuel tank (not shown) arranged at a required place, and fuel addition by the fuel addition valve 32 is performed by a fuel injection command signal 32a from the control device 27. Thus, the decrease in the air-fuel ratio is assisted.

  Here, the control of lowering the air-fuel ratio to the stoichiometric air-fuel ratio in the control device 27 is performed, for example, by dividing the operation region of the diesel engine 1 into a plurality of regions by a two-dimensional map of the total fuel injection amount and the engine speed of the diesel engine 1. The EGR valves 23, 24, the fuel injection device 30, the intake valve 31, and the fuel addition valve 32 may be controlled with the target values assigned for each of the divided operation regions.

  The reason why the air-fuel ratio is reduced by narrowing the intake air amount by the intake valve 31 and adding fuel by the fuel addition valve 32 is to prevent excessive after injection, and the piston is lowered. This is because if the after-injection is excessively performed at the stage where the operation starts, the injected fuel adheres to the cylinder wall and enters the oil, which may dilute the oil.

  If the intake air amount is narrowed by the intake valve 31 within a range in which an appropriate intake air amount can be secured, the air-fuel ratio can be reduced to the stoichiometric air-fuel ratio even if the after-injection is suppressed to the extent that fuel can be prevented from adhering to the cylinder wall. Can be lowered. However, depending on the operating condition of the diesel engine 1, when the intake air amount is narrowed by the intake valve 31, there is a possibility that the intake air amount is insufficient.

  For this reason, when there is a possibility of causing a shortage of the intake air amount, the intake air amount is narrowed by the intake valve 31 so as not to cause a shortage of the intake air amount, and fuel addition is performed by the fuel addition valve 32. The air-fuel ratio may be lowered to the stoichiometric air-fuel ratio. However, since fuel addition by the fuel addition valve 32 leads to deterioration of fuel consumption, it is of course necessary to give priority to after-injection to keep the fuel addition of the fuel addition valve 32 to the minimum necessary.

  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 vicinity of the theoretical 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.

  Until now, the low pressure loop 21 has not been used to recirculate the exhaust gas 3 at a high EGR rate because when the accelerator is depressed by the driver and the vehicle enters an acceleration state during driving, the air is excessive. This is because the rate dropped rapidly and black smoke was easily generated.

  That is, in the case of 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 reaches the diesel engine 1 from here through the compressor 14 a, the intercooler 17, and the intake manifold 18. Since the intake path mixed with the exhaust gas 3 exists in this long path, the EGR valve of the low-pressure loop 21 is increased when the fuel injection amount increases in response to the depression of the accelerator during acceleration. Even if 23 is immediately closed, there is a drawback in that a state with a low excess air ratio continues and black smoke is likely 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 the case of this embodiment, the low pressure loop 21 and the high pressure loop 22 are used in combination, and 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.

  Then, ignition can be performed immediately after the main injection in the diesel engine 1 under such conditions that a large amount of the exhaust gas 3 is recirculated by the low pressure loop 21 and the high pressure loop 22 and the air-fuel ratio is suppressed to the vicinity of the theoretical air-fuel ratio. If after-injection is performed at an appropriate timing, the air-fuel ratio is lowered to the stoichiometric air-fuel ratio due to an increase in the amount of unburned fuel due to the after-injection and oxygen consumption due to part of the oxidation reaction. It is possible to achieve simultaneous reduction of HC, CO, and NOx by making 20 function.

  In the present embodiment, since the three-way catalyst 20 contains zeolite, magnesia or the like as a catalyst raw material so that HC can be adsorbed, the air-fuel ratio temporarily becomes larger than the stoichiometric air-fuel ratio during transient operation. However, it is possible to continue the reaction of simultaneously reducing HC, CO, and NOx by the HC adsorbed on the three-way catalyst 20.

  Further, regarding the control for lowering the air-fuel ratio to the stoichiometric air-fuel ratio, in this embodiment, fuel is directly injected into the exhaust pipe 4 by the fuel addition valve 32 in accordance with the operating condition of the diesel engine 1 to compensate for the unburned fuel. Or by reducing the amount of intake air by the intake valve 31, it is possible to assist the decrease in the air-fuel ratio. Therefore, excessive after-injection can be performed by appropriately using the fuel addition valve 32 and the intake valve 31 together. It can be avoided.

  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 using the fuel addition valve 32 or the like when the deposition amount reaches a predetermined amount, the unburned fuel undergoes an oxidation reaction while passing through the three-way catalyst 20, and the reaction heat The inflow of the heated exhaust gas 3 raises the catalyst bed temperature of the particulate filter 10 at the subsequent stage, and the particulates are forcibly burned and removed.

  Therefore, according to the above embodiment, the three-way catalyst 20 can be made to function by lowering the air-fuel ratio to the stoichiometric air-fuel ratio even in the diesel engine 1, so that the urea water tank 11 (see FIG. 2) and the urea water supply pipe 12 ( 2), an auxiliary facility such as a supply pump 13 (see FIG. 2) can be eliminated, and the cost of the facility can be greatly reduced. This can significantly reduce the burden on the driver.

  Further, even when the air-fuel ratio temporarily becomes larger than the stoichiometric air-fuel ratio during transient operation or the like, the surface atmosphere of the three-way catalyst 20 is maintained at the stoichiometric air-fuel ratio by the HC adsorbed on the three-way catalyst 20. , CO and NOx can be continuously reduced, so that the continuity of the reaction of the three-way catalyst 20 simultaneously reducing HC, CO and NOx can be greatly improved.

  Further, depending on the operating condition of the diesel engine 1, the fuel addition valve 32 directly injects fuel into the exhaust pipe 4 to compensate for the unburned fuel, or the intake valve 31 narrows the intake air amount to reduce the air / fuel ratio. As the fuel addition valve 32 and the intake valve 31 are used in combination, excessive after-injection can be avoided, and fuel is mixed into the oil due to excessive after-injection. It is possible to prevent the oil from being diluted.

  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.

  The exhaust purification method and apparatus according to the present invention are not limited to the above-described embodiments. Main injection that should be performed in the vicinity of the compression top dead center is performed at a timing earlier than the compression top dead center, and then into the cylinder. Pre-mixed compression ignition that promotes pre-mixing of fuel by pre-injection of fuel and then ignites and burns may be used together to support the ability to maintain the flammability of diesel engines as well as possible In addition, a small three-way catalyst may be additionally provided in the exhaust pipe in the region where the exhaust temperature is high immediately after the exhaust manifold, and various modifications can be made without departing from the scope of the present invention. Of course.

DESCRIPTION OF SYMBOLS 1 Diesel engine 2 Exhaust manifold 3 Exhaust gas 4 Exhaust pipe 9 Oxidation catalyst 10 Particulate filter 14 Turbocharger 14a Compressor 14b Turbine 15 Intake 16 Intake pipe 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 30 Fuel Injection Device 31 Intake Valve (Intake Throttle Means)
32 Fuel addition valve (fuel addition means)

Claims (6)

  An exhaust purification method for simultaneously reducing HC, CO, NOx in exhaust gas using a three-way catalyst 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 Using a low-pressure loop that recirculates to the intake passage upstream from the compressor of the charger and 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. The exhaust gas recirculation as a base is performed at an EGR rate that is suppressed to a level that does not cause the exhaust gas, and in the high-pressure loop, additional exhaust gas recirculation is performed to supplement the insufficient EGR rate to bring the air-fuel ratio close to the theoretical air-fuel ratio. In addition, the after-injection is performed at a timing at which ignition can be performed immediately after the main injection. A method for purifying exhaust gas, wherein the three-way catalyst functions by lowering the air-fuel ratio to the stoichiometric air-fuel ratio by oxygen consumption due to part of the oxidation reaction.   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. A recirculation amount adjusting means for adjusting the recirculation amount, a three-way catalyst provided in the middle of the exhaust passage, and a control device for controlling the recirculation amount adjusting means and the fuel injection device of the diesel engine. And the control device controls the recirculation amount adjusting means to suppress the EG so as not to generate black smoke during acceleration in the low pressure loop. The exhaust gas recirculation that is the base at the R rate and the additional exhaust gas recirculation is performed to supplement the insufficient EGR rate in the high-pressure loop, thereby suppressing the air-fuel ratio in the vicinity of the theoretical air-fuel ratio, and the fuel By controlling the injection device and performing the after injection at a timing at which ignition can be performed immediately after the main injection, the air / fuel ratio is set to the stoichiometric air / fuel ratio by the increase in the unburned fuel by the after injection and the oxygen consumption by the partial oxidation reaction. An exhaust purification device configured to be lowered to   The exhaust purification apparatus according to claim 2, wherein the three-way catalyst contains zeolite or magnesia as a catalyst raw material so that HC can be adsorbed.   A fuel addition means for directly injecting fuel into the exhaust pipe upstream from the three-way catalyst is provided, and the control device is configured so that the fuel addition by the fuel addition means can be performed as necessary. The exhaust emission control device according to claim 2 or 3.   The intake air throttle means for narrowing down the intake air amount is provided, and the control device is configured such that the intake air amount can be reduced by the intake throttle means as required. 4. An exhaust emission control device according to 4.   The exhaust purification device according to any one of claims 2 to 5, wherein a particulate filter is provided in a subsequent stage of the three-way catalyst.

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