JP5053134B2 - Exhaust purification device - Google Patents

Description

  The present invention relates to an exhaust purification device for reducing NOx in exhaust gas.

  Conventionally, a diesel engine is equipped with a selective reduction catalyst having a property of selectively reacting NOx with a reducing agent even in the presence of oxygen in the middle of an exhaust pipe through which exhaust gas flows, and the selective reduction catalyst A required amount of a reducing agent is added to the upstream side of the catalyst so that the reducing agent undergoes a reduction reaction with NOx (nitrogen oxide) in the exhaust gas on the selective catalytic reduction catalyst, thereby reducing the NOx emission concentration. There is what I did.

On the other hand, in the field of industrial flue gas denitration treatment in plants and the like, the effectiveness of a method for reducing and purifying NOx using NH ₃ (ammonia) as a reducing agent is already widely known. Since it is difficult to ensure safety with respect to traveling with a toxic substance such as NH ₃ , in recent years, the use of non-toxic urea water as a reducing agent has been studied (for example, , See Patent Document 1).

That is, when urea water is added to the exhaust gas upstream of the selective catalytic reduction catalyst, the urea water is decomposed into NH ₃ and CO ₂ (carbon dioxide) in the exhaust gas, and the exhaust gas is exhausted on the selective catalytic reduction catalyst. The inside NOx is reduced and purified well by NH ₃ .

  However, in the exhaust gas purification apparatus using the selective catalytic reduction catalyst using urea water as a reducing agent in this way, a urea water tank for storing urea water must be newly added. As a result, there is a problem that it is difficult to secure the installation space for the vehicle, and that it is unavoidable that the rise in cost is unavoidable, and that the infrastructure must be improved so that the driver can easily obtain urea water. It also caused a serious problem.

Therefore, the present inventor has arranged a three-way catalyst having NOx and NH ₃ adsorption capacity in the middle of the exhaust pipe of a diesel engine, and has an excess air ratio deeply to about 0.7 when the accelerator is off during engine operation. In addition, premixed compression ignition is performed with a diesel engine so that smokeless combustion can be maintained even at a low excess air ratio, and NH ₃ is generated from NOx and H ₂ in the exhaust gas by the three-way catalyst. It came to invent a new system of collecting.

In other words, if NH ₃ is generated and stored in the three-way catalyst when the accelerator is off while the engine is running, the accelerator off state is canceled and the accelerator is depressed, and when the vehicle shifts to the normal driving state, The excess air ratio is returned to the normal state of about 1.6 or more, the surroundings of the three-way catalyst become aerobic, and NOx already adsorbed on the three-way catalyst and newly adsorbed NOx are turned off. Sometimes it is reduced and purified to N ₂ by NH ₃ accumulated.

As a result, it becomes possible to eliminate the urea water tank for storing the urea water, eliminate the problems related to securing the mounting space of the urea water tank and the cost increase, and the driver can easily It is possible to eliminate the need for infrastructure that can be obtained.
JP 2002-161732 A

However, if the condition of constant speed or acceleration operation at a medium or high load that continues to climb a long uphill continues for a long time, the accelerator off state does not occur easily, so NH ₃ is generated and stored by a three-way catalyst. There is a possibility that NOx may not be reduced from the point where the adsorption amount of NOx by the three-way catalyst exceeds the allowable amount because only the NOx adsorption proceeds without obtaining an opportunity.

The present invention has been made in view of the above circumstances, and applies a three-way catalyst having NOx and NH ₃ adsorption capability to a diesel engine, and generates NH ₃ from NOx when the accelerator is off while the engine is running. An exhaust gas purification device that adsorbs and accumulates on a three-way catalyst and uses this NH ₃ to reduce and purify NOx in the exhaust gas, even during medium and high load constant speed or acceleration operation where the accelerator off state hardly occurs The object is to ensure that NOx can be reduced and purified.

The present invention is provided in the middle of the exhaust pipe of a diesel engine and has a three-way catalyst capable of adsorbing NOx and NH ₃ , and when the accelerator is off while the engine is operating, the excess air ratio is lowered to about 0.7 and low. An exhaust emission control device including a control device for causing the diesel engine to perform premixed compression ignition so that smokeless combustion can be maintained even in an excess air ratio, wherein an exhaust pipe upstream of the three-way catalyst has a fuel in the exhaust pipe. A fuel addition means is provided so that the engine can be directly injected, and the accelerator that is operating the engine during constant-speed or acceleration operation at medium or high load under the condition that the NOx adsorption amount by the three-way catalyst is determined to exceed the allowable amount The excess air ratio is lowered shallower than when the engine is turned off, and fuel is supplementally added in the middle of the exhaust pipe by the fuel addition means so that the excess air ratio on the inlet side of the three-way catalyst is reduced to about 1.0. The control device is configured as described above.

Thus, in this way, when the accelerator is off while the engine is running, the control unit can reduce the excess air ratio to about 0.7 , and premixing can maintain smokeless combustion even at the low excess air ratio. As a result of compression ignition being performed in the diesel engine, N (denoted as N because it is a reaction) is generated in the reaction process of the three-way catalyst , and is not allowed to react with O due to a low excess air ratio. NH ₃ is produced in combination with H), and is adsorbed and stored in the three-way catalyst.

Then, the accelerator-off state is released and the accelerator travels to a normal driving state, the excess air ratio is returned to a normal state of about 1.6 or more, and the three-way catalyst is in an aerobic state. As a result, NOx already adsorbed on the three-way catalyst and newly adsorbed NOx are reduced and purified to N ₂ by NH ₃ stored when the accelerator is off.

  Furthermore, the control device determines that the NOx adsorption amount on the three-way catalyst exceeds the allowable amount, and under that condition, when the medium speed operation is accelerated or accelerated, it is shallower than when the accelerator is off while the engine is running. The excess air ratio is lowered, and fuel is supplementally added in the middle of the exhaust pipe by the fuel addition means, so that the excess air ratio on the inlet side of the three-way catalyst is about 1.0 (about 1.1 to 0.9). ).

As a result, the excess air ratio of the exhaust gas flowing around the three-way catalyst becomes around 1.0, and an environment in which CO and HC oxidation and NOx reduction in the exhaust gas can be performed at the same time is prepared and applied to gasoline vehicles. The purification characteristics that are the same as in the above case are exhibited, and the three harmful gas components (CO, HC, NOx) in the exhaust gas are purified to harmless CO ₂ , H ₂ O, and N ₂ .

  When reducing the excess air ratio on the inlet side of the three-way catalyst to about 1.0, on the diesel engine side, the excess air ratio is within a range that can maintain smokeless combustion without generating black smoke (a large amount of soot). What is necessary is just to make it the operation | use which is not overreasonable about 1.4-1.2, and to make up the remaining 0.5-0.1 lowering shortage by the fuel addition by the fuel addition means in the middle of an exhaust pipe.

  In this case, the control device may be configured to add after-injection at a timing at which ignition is possible after main injection. In this case, the control device is likely to be generated by reducing the excess air ratio. The portion is surely burnt down by the combustion of the after injection.

  In the present invention, it is preferable that a particulate filter is provided immediately after the three-way catalyst so that fuel can be added to the exhaust gas upstream of the three-way catalyst. For example, the oxidation of a three-way catalyst exposed to exhaust gas with a large amount of residual oxygen in a diesel engine is activated, and high-concentration HC generated from the added fuel is well oxidized by the three-way catalyst. The inflow of the heated exhaust gas further raises the bed temperature of the particulate filter immediately after that, so that the particulates are efficiently incinerated in a short time.

  Moreover, in the present invention, since premixed compression ignition is performed with a deep excess of the air excess ratio when the accelerator is off while the engine is running, the fuel injection of the diesel engine is stopped especially when the accelerator is off at the time of deceleration while traveling. As a result, low-temperature intake air does not flow directly into the three-way catalyst and the particulate filter without going through the combustion stroke, and the problem that these three-way catalyst and the particulate filter are rapidly deprived of heat is avoided. In addition, since the high temperature exhaust gas flows into the three-way catalyst and the particulate filter, the temperature rises rather positively, so the time required for completing the regeneration of the particulate filter is greatly reduced. .

  In addition, when the accelerator is off when idling while the vehicle is stopped, the exhaust temperature can be significantly increased compared to the conventional extremely low exhaust temperature. It is possible to complete the warm-up of the filter within a short time, and the time required for completing the regeneration of the particulate filter is greatly reduced.

  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, a three-way catalyst having NOx and NH ₃ adsorption capacity is applied to a diesel engine, and NH ₃ is removed from NOx when the accelerator is off while the engine is running. This is an exhaust gas purification device that is generated and adsorbed on a three-way catalyst and stored, and this NO ₃ is used to reduce and purify NOx in the exhaust gas. Even during operation, when the control device determines that the NOx adsorption amount on the three-way catalyst exceeds the allowable amount, the control device lowers the excess air ratio more shallowly than when the accelerator is off while the engine is running, and The fuel addition means supplementarily adds fuel in the middle of the exhaust pipe to lower the excess air ratio on the inlet side of the three-way catalyst to about 1.0, and the three-way catalyst reduces the CO and HC in the exhaust gas. Oxidation and reduction of NOx It is possible to clean the NOx in the exhaust gas together with CO and HC by preparing an environment that can sometimes be performed, and avoid the possibility that NOx cannot be reduced at the constant speed or acceleration operation at medium and high loads. be able to.

  (II) According to the invention described in claim 2 of the present invention, at the time of medium-high load constant speed or acceleration operation under the condition where the NOx adsorption amount on the three-way catalyst is determined to exceed the allowable amount, After injection is added at the timing when ignition is possible after main injection, soot that has become easy to occur by lowering the excess air ratio can be burned off by combustion of after injection, and black smoke ( The occurrence of 回避) can be avoided more reliably.

  (III) According to the invention described in claim 3 of the present invention, when the accelerator is off during engine operation, the bed temperature of the three-way catalyst and the particulate filter tends to be low, the excess air ratio is deeply reduced and the premix compression is performed. By performing ignition, high-temperature exhaust gas can be sent from the diesel engine to raise the bed temperature of the three-way catalyst and particulate filter, so the excess air ratio was returned to the normal vicinity and the process shifted to forced regeneration by adding fuel. At this time, the particulate filter can be regenerated more efficiently and quickly than before, and the time taken to complete the regeneration of the particulate filter can be greatly reduced.

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

  FIG. 1 and FIG. 2 show an example of an embodiment for carrying out the present invention. In FIG. 1, 1 shows a diesel engine equipped with a turbocharger 2, and intake air 4 guided from an air cleaner 3 passes through an intake pipe 5. The intake air 4 sent to the compressor 2 a of the turbocharger 2 and pressurized by the compressor 2 a is sent to the intercooler 6 to be cooled, and the intake air 4 is further guided from the intercooler 6 to the intake manifold 7. Thus, the fuel is distributed to each cylinder 8 of the diesel engine 1 (in FIG. 1, the case of in-line 6 cylinders is illustrated).

  Further, the exhaust gas 9 discharged from each cylinder 8 of the diesel engine 1 is sent to the turbine 2b of the turbocharger 2 through the exhaust manifold 10, and the exhaust gas 9 driving the turbine 2b is discharged to the exhaust pipe 11 (exhaust gas). It is designed to be discharged out of the vehicle through the flow path).

  In the middle of the exhaust pipe 11, a filter case 12 is interposed, and a catalyst regeneration type particulate filter 13 that integrally supports an oxidation catalyst is accommodated on the rear stage side in the filter case 12. Has been.

  In other words, this particulate filter 13 has a porous honeycomb structure made of ceramic, and the inlets of the respective flow paths partitioned in a lattice pattern are alternately sealed, and the flow paths in which the inlets are not sealed are used. The outlet is sealed, and only the exhaust gas 9 that has permeated through the porous thin wall defining each flow path is discharged to the downstream side.

In addition, a flow-through type three-way catalyst 14 having NOx and NH ₃ adsorption ability is provided in the preceding stage of the particulate filter 13 in the filter case 12, and more specifically, conventionally known. Zeolite catalyst (for example, Cu / zeolite catalyst or Fe / zeolite) having excellent ability to physically adsorb NOx and NH ₃ in the exhaust gas 9 to a three-way catalyst composed of Pt, Pd, Rh, ZeO, CeO, etc. A three-way catalyst 14 in which a catalyst or the like is coated, or this type of zeolitic catalyst is mixed and supported together from the raw material stage is applied.

Here, the conventionally known three-way catalyst simultaneously performs oxidation of CO and HC in the exhaust gas 9 and reduction of NOx, and removes the three harmful gas components in the exhaust gas 9 as harmless CO ₂ , H ₂ O, N it is intended to purify the _2, but in which the excess air ratio of 1.0 works only effective in the vicinity of the stoichiometric air-fuel ratio before and after, in a diesel engine air excess ratio is also 1.6 or more under normal running state The remaining oxygen amount in the exhaust gas 9 is too large to effectively use the three-way catalyst, and there has been a history of being applied only to gasoline vehicles so far.

  Note that the purification characteristics of the conventionally known three-way catalyst greatly change depending on the excess air ratio (air-fuel ratio), and when the excess air ratio is high (when the air-fuel ratio is low), the amount of residual oxygen in the exhaust gas 9 is large. Therefore, it is known that when the excess air ratio is low (when the air-fuel ratio is high), the reduction action becomes active and the oxidation action becomes inactive when the oxidation action becomes active and the reduction action becomes inactive. Yes.

  Zeolite, on the other hand, is an alumina silicate porous crystal material, characterized by having uniform molecular level pores regularly oriented in the crystal, through which various molecules are hollow or In addition to these properties, it has the property of adsorbing inside pores, and has the function of molecular sieving based on the uniform pores (adsorbs only molecules smaller than the pore diameter), crystal structure It also has the property of strongly adsorbing polar substances by the action of the cations and anions therein and the property of having a catalytic action.

Also, this type of zeolite is classified into various types based on the type of its backbone structure, the ability to adsorb NOx and NH ₃ into the pores, and the ability to promote the reaction between NOx and NH _3, What is necessary is just to select suitably the thing excellent in high heat resistance and high durability, and it is also possible to select from the zeolite related compounds provided with the same property.

Further, a fuel addition valve 15 for directly injecting fuel into the exhaust pipe 11 is provided in the exhaust pipe 11 upstream of the three-way catalyst 14 having the NOx and NH ₃ adsorption capability in this way. A fuel addition line 17 led from a fuel tank 16 disposed at a required place is connected to the fuel addition valve 15, and a pump 18 provided in the middle of the fuel addition line 17 is provided as an addition means. As a result, the fuel in the fuel tank 16 is extracted and supplied to the fuel addition valve 15.

Further, the diesel engine 1 is equipped with a fuel injection device 19 composed of an injector (not shown) provided for each cylinder 8, and an electromagnetic valve of each injector in the fuel injection device 19 is connected to an engine control computer (ECU). : The control device 20 forming the Electronic Control Unit) appropriately controls the injection timing and the injection amount (valve opening time) based on the load and the rotational speed. When the accelerator is off while the engine is running, Premixed compression ignition is performed so that the excess air ratio (λ) is lowered to about 0.7 and smokeless combustion can be maintained even at the low excess air ratio.

  However, when the accelerator is off while the engine is running, the engine output is not particularly required, such as when the vehicle is decelerating or when the vehicle is idling, so simply increase the fuel injection amount to increase the excess air ratio. In addition to reducing the air intake, the air throttle (which may reduce the intake air amount by reducing the turbine efficiency by using the turbocharger 2 as a variable geometry turbocharger) is used in combination to reduce the air excess rate. To avoid unnecessary engine power.

In addition, the premixed compression ignition used in this case is that the main injection that should normally be performed in the vicinity of the compression top dead center is performed at a timing earlier than the compression top dead center, and the fuel is put into the cylinder 8 in advance. Refers to a combustion method that promotes premixing of fuel and then performs ignition and combustion, and is conventionally known as a combustion method for suppressing the generation of NOx However, NOx is more easily generated by lowering the excess air ratio deeply, and by using this NOx, NH ₃ can be generated and adsorbed on the three-way catalyst 14 as described later.

  Moreover, in the control device 20, it is determined whether or not the amount of NOx adsorbed by the three-way catalyst 14 exceeds the allowable amount, and the amount of NOx adsorbed exceeds the allowable amount. During constant speed or acceleration operation at medium and high loads under the determined conditions, the excess air ratio is lowered more shallowly than when the accelerator is off while the engine is operating, and fuel is supplementally supplied in the middle of the exhaust pipe 11 by the fuel addition valve 15. Addition is performed so that the excess air ratio on the inlet side of the three-way catalyst 14 is reduced to about 1.0.

  That is, the specific control procedure will be described below with reference to the flowchart of FIG. 2. First, in step S1, it is determined whether or not the NOx adsorption amount in the three-way catalyst 14 exceeds the allowable amount. However, here, the adsorption amount of NOx at the three-way catalyst 14 is obtained by calculation based on the operating state of the diesel engine 1, and is the calculated adsorption amount exceeding the allowable amount? Whether or not is determined.

  Here, the allowable amount of NOx that can be adsorbed by the three-way catalyst 14 basically depends on the amount of the zeolite-based catalyst supported, but the temperature and flow rate of the exhaust gas 9 (the amount that can be continuously adsorbed as the temperature and flow rate increase). If all of these are taken into consideration, the allowable amount under the current operating conditions is determined by the control device 20.

  On the other hand, since the amount of NOx generated can be calculated based on the load and rotation speed of the diesel engine 1 ascertained by the control device 20, what percentage of these (a numerical value already known as the initial condition) is the three-way catalyst. 14 is calculated as the amount adsorbed by NO.14, the total amount of NOx adsorbed is obtained, and if this is compared with the above-mentioned allowable amount, the NOx adsorbed amount at the three-way catalyst 14 exceeds the allowable amount. Can be determined.

  However, even if it is not strictly determined so far, the amount of NOx adsorbed on the three-way catalyst 14 exceeds the allowable amount when the elapsed time from the previous accelerator off time is measured with a timer and the specified time or more has elapsed. Furthermore, when the NOx concentration is measured by the NOx sensor before and after the three-way catalyst 14 and the NOx adsorption capacity of the three-way catalyst 14 falls below a specified level, the NOx at the three-way catalyst 14 is reduced. It is also possible to determine that the amount of adsorbed exceeds the allowable amount.

  If it is determined in step S1 that the amount of NOx adsorbed by the three-way catalyst 14 exceeds the allowable amount, the process proceeds to step S2 to determine whether the current operation state is a medium or high load constant speed or acceleration operation state. If it is not determined and the vehicle is not in a medium-high load constant speed or acceleration operation state, the control for reducing the excess air ratio and performing premixed compression ignition on the diesel engine at the time of accelerator off described earlier in step S3 is selected. However, when the vehicle is in a medium-high load constant speed or acceleration operation state, the process proceeds to step S4 and step S5, and the following control is executed.

  That is, in step S4, the main injection in the diesel engine 1 is reduced, and the reduced amount is added as after-injection at a timing at which ignition is possible after the main injection, and the air throttle (turbo turbo) for reducing the opening of the intake valve 21 The charger 2 can be used as a variable geometry turbocharger to reduce the turbine efficiency to reduce the intake air amount. It is executed continuously.

  In step S5, the fuel addition valve 15 supplementarily adds fuel in the middle of the exhaust pipe 11 to reduce the excess air ratio on the inlet side of the three-way catalyst 14 to about 1.0 at a specified time. Continuously executed.

  In addition, in this embodiment, when it is necessary to perform forced regeneration of the particulate filter 13, the main injection of fuel performed near the compression top dead center (crank angle 0 °) is followed by the compression top dead center. Post-injection is added at a late non-ignition timing (starting time is in the range of crank angle 90 ° to 120 °).

  That is, unburned fuel is added to the exhaust gas 9 by this post injection, and high-concentration HC generated from the unburned fuel undergoes an oxidation reaction while passing through the three-way catalyst 14, The inflow of the exhaust gas 9 raised in temperature by the reaction heat raises the bed temperature of the particulate filter 13 immediately after that to burn out the particulate filter 13 so that the particulate filter 13 can be regenerated.

  In FIG. 1, reference numeral 22 denotes an exhaust brake provided near the outlet of the turbine 2b in the exhaust pipe 11, 23 denotes an EGR line for recirculating the exhaust gas 9 from the exhaust side to the intake side, and 24 denotes the recirculation. A water-cooled EGR cooler 25 for cooling a part of the exhaust gas 9 to be circulated, and 25 respectively indicate EGR valves.

Thus, when the accelerator is off while the engine is running, the fuel injection device 19 and the intake valve 21 are controlled by the control device 20 so that the excess air ratio is deeply reduced , and smokeless combustion can be maintained even at the low excess air ratio. Yo When the HCCI accounted performed diesel engine 1, N generated in the reaction process of the three-way catalyst 14 (since story in the reaction referred to as N) is, surplus unable react with O by low air excess ratio NH ₃ is produced in combination with H (denoted as H because it is a reaction) and is adsorbed and stored in the three-way catalyst as it is.

That is, when premixed compression ignition is performed with the air excess ratio lowered deeply, the ratio of the fuel input amount to the unit air amount increases to a combustion temperature of 2000 K or more, and the moisture (H ₂ O) in the intake air is H ₂ , O ₂ , which decomposes thermally into OH and H and reacts with the originally stable N ₂ to generate NOx, but the NOx reduction reaction is promoted by the active reduction action of the three-way catalyst 14, and this N generated during the reduction reaction reacts with excess H in the exhaust gas 9 to generate NH ₃ .

  At this time, it is preferable to reduce the excess air ratio deeply to about 0.7. However, even if the excess air ratio is lowered so far, the pre-mixed compression ignition improves the combustibility significantly. It is possible to keep smokeless combustion without generating a large amount of soot).

  That is, according to this type of premixed compression ignition, the main injection of fuel that should be performed in the vicinity of the compression top dead center in a normal case is performed at a timing earlier than the compression top dead center, and the fuel is first introduced into the cylinder. Since the premixing of the fuel is promoted by this, ignition combustion is performed, so that the fuel is well dispersed and mixed, and combustion is performed by simultaneous global ignition in a state where the fuel is evenly diluted, and the combustibility is remarkably improved. .

  However, when the accelerator is off while the engine is running, the engine output is not particularly required, such as when the vehicle is decelerating or when the vehicle is idling, so simply increase the fuel injection amount to increase the excess air ratio. Not only lowering, but also using an air throttle as appropriate, the excess air ratio is lowered to prevent unnecessary engine output.

  In addition, you may make it use together control of the recirculation amount of the exhaust gas 9 by the EGR line 23 for adjustment of the excess air ratio at the time of such an accelerator off, and adjustment of the ignition timing of premixed compression ignition.

Then, the accelerator-off state is released and the vehicle is shifted to a normal driving state where the accelerator is depressed, the excess air ratio is returned to a normal state of about 1.6 or more, and the three-way catalyst 14 is in an aerobic state. Then, NOx already adsorbed on the three-way catalyst 14 and newly adsorbed NOx are reduced and purified to N ₂ by NH ₃ stored when the accelerator is off.

  Further, the control device 20 determines that the amount of NOx adsorbed by the three-way catalyst 14 exceeds an allowable amount, and when the medium-high load constant speed or acceleration operation is performed under the circumstances, the accelerator off during engine operation described above is performed. The excess air ratio is lowered shallower than the time, and fuel is supplementally added in the middle of the exhaust pipe 11 by the fuel addition valve 15 so that the excess air ratio on the inlet side of the three-way catalyst 14 is about 1.0 (1 .About 0.9 to 0.9).

As a result, the excess air ratio of the exhaust gas 9 flowing around the three-way catalyst 14 becomes around 1.0, and an environment in which CO and HC oxidation and NOx reduction in the exhaust gas 9 can be performed simultaneously is prepared. The purification characteristics that are the same as when applied to a vehicle are exhibited, and the three harmful gas components (CO, HC, NOx) in the exhaust gas 9 are purified to harmless CO ₂ , H ₂ O, and N ₂ .

  In reducing the excess air ratio on the inlet side of the three-way catalyst 14 to about 1.0, the diesel engine 1 side has excess air within a range that can maintain smokeless combustion without generating black smoke (a large amount of soot). Keep the operation at a reasonable rate of 1.4 to 1.2, and make up for the remaining shortage of 0.5 to 0.1 by adding fuel with the fuel addition valve 15 in the middle of the exhaust pipe 11. To do.

  At this time, in this embodiment, after injection is added at the timing when ignition is possible after main injection, the apportionment that is likely to occur by lowering the excess air ratio is surely caused by the combustion of after injection. Will be burned down.

  In addition, when it is necessary to perform forced regeneration on the particulate filter 13, if the control device 20 performs fuel addition by post-injection in the fuel injection device 19 and starts forced regeneration, a large amount of oxygen remains in the diesel engine 1. The oxidation action of the three-way catalyst 14 exposed to the exhaust gas 9 is activated, and the high-concentration HC generated from the added fuel is oxidized well by the three-way catalyst 14, and the exhaust gas 9 heated by the reaction heat is heated. The bed temperature immediately after the particulate filter 13 is further raised by the inflow, and the particulates are efficiently incinerated in a short time.

  At this time, a part of the fuel of the main injection is distributed as after-injection at a combustible timing immediately after the main injection, and burned at a slightly later timing to lower the thermal efficiency of the diesel engine 1, The amount of heat not used for power may be increased to further increase the exhaust gas temperature.

  In addition, when the particulate filter 13 is forcibly regenerated, an air throttle that throttles the opening of the intake valve 21 can be used together. In this way, the intake 4 is throttled by the intake valve 21, and the diesel engine 1 The amount of generated exhaust gas 9 due to combustion of the gas decreases with respect to the amount of input heat, so that the exhaust temperature can be further increased.

  In addition, when the particulate filter 13 is forcibly regenerated, an exhaust throttle that narrows the opening of the exhaust brake 22 can be used together. In this way, the exhaust is throttled when the accelerator is off, and the exhaust on the upstream side of this is throttled. By increasing the pressure of the gas 9, the exhaust temperature is raised, and the exhaust resistance of the engine is increased, so that the intake air 4 having a relatively low temperature does not easily flow into the cylinder 8 and the exhaust gas having a relatively high temperature is exhausted. The exhaust gas temperature can be further increased by increasing the amount of residual gas 9 and the air in the cylinder 8 containing a large amount of the relatively high-temperature exhaust gas 9 being compressed in the next compression stroke to reach the explosion stroke.

  Further, in the present embodiment, since premixed compression ignition is performed in which the excess air ratio is deeply reduced when the accelerator is off while the engine is operating, the fuel injection of the diesel engine 1 is performed particularly when the accelerator is off during deceleration during traveling. The low-temperature intake air does not flow into the three-way catalyst 14 and the particulate filter 13 without going through the combustion stroke, and the three-way catalyst 14 and the particulate filter 13 are suddenly deprived of heat. In addition, since the high temperature exhaust gas 9 flows into the three-way catalyst 14 and the particulate filter 13 to increase the temperature actively, the regeneration of the particulate filter 13 is completed. The time it takes to be significantly reduced.

  In addition, when the accelerator is off when idling while the vehicle is stopped, the exhaust temperature can be significantly increased compared to the conventional extremely low exhaust temperature. It is possible to complete the warm-up in a short time, and the time required for the regeneration of the particulate filter 13 to be completed is greatly reduced.

Therefore, according to the above embodiment, the three-way catalyst 14 having the ability to adsorb NOx and NH ₃ is applied to the diesel engine 1, and NH ₃ is generated from NOx when the accelerator is turned off while the engine is operating to produce the three-way catalyst. 14, the exhaust gas purifying apparatus which adsorbs and accumulates the NOx in the exhaust gas 9 by using this NH ₃ to reduce and purify the exhaust gas 9, even during a medium and high load constant speed or acceleration operation where the accelerator off state hardly occurs. Under the situation where the control device 20 determines that the NOx adsorption amount at the three-way catalyst 14 exceeds the allowable amount, the control device 20 reduces the excess air ratio more shallowly than when the accelerator is off while the engine is running, and A fuel addition valve 15 supplementarily adds fuel in the middle of the exhaust pipe 11 to reduce the excess air ratio on the inlet side of the three-way catalyst 14 to about 1.0. CO and H It is possible to clean the NOx in the exhaust gas 9 together with CO and HC by preparing an environment in which C oxidation and NOx reduction can be performed at the same time, making it impossible to reduce NOx during medium and high load constant speed or acceleration operation. It is possible to avoid the fear that it will occur.

  Furthermore, in the present embodiment, the timing at which ignition is possible after main injection during constant-speed or acceleration operation at a medium to high load in a situation where the NOx adsorption amount at the three-way catalyst 14 is determined to exceed the allowable amount Since after-injection is added, the soot that was easily generated by lowering the excess air ratio can be burned down by the after-injection combustion, and the generation of black smoke (a large amount of soot) is more reliable. Can be avoided.

  Further, when the accelerator is off while the engine is operating, the bed temperature of the three-way catalyst 14 and the particulate filter 13 tends to be low, the exhaust air at a high temperature is exhausted from the diesel engine 1 by performing premixed compression ignition with the excess air ratio lowered deeply. Since the gas 9 can be fed and the bed temperature of the three-way catalyst 14 and the particulate filter 13 can be raised, the particulate filter 13 is used when the excess air ratio is returned to the normal vicinity and the forced regeneration is performed by adding fuel. It is possible to regenerate more efficiently and quickly, and the time taken to complete the regeneration of the particulate filter 13 can be greatly reduced.

  Note that the exhaust emission control device of the present invention is not limited to the above-described embodiment. When adding fuel at the time of forced regeneration, instead of post-injection at the diesel engine side, Direct injection can also be adopted, and both post injection and direct injection in the middle of the exhaust pipe may be used together as appropriate, and various other modifications may be made without departing from the scope of the present invention. Of course.

It is the schematic which shows an example of the form which implements this invention. It is a flowchart which shows the control procedure in the control apparatus of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Diesel engine 9 Exhaust gas 11 Exhaust pipe 13 Particulate filter 14 Three-way catalyst 15 Fuel addition valve (fuel addition means)
20 Control device

Claims (3)

A three-way catalyst is installed in the middle exhaust pipe of a diesel engine having an adsorption ability of the NOx and NH _3, even deeper down and the lower the excess air ratio of the excess air ratio to about 0.7 near the time of accelerator pedal during engine operation An exhaust emission control device including a control device that performs premixed compression ignition on the diesel engine so as to maintain smokeless combustion, and directly injects fuel into the exhaust pipe upstream of the three-way catalyst. The fuel addition means is provided so that the amount of NOx adsorbed on the three-way catalyst is determined to exceed the allowable amount than when the accelerator is off while the engine is operating during medium-high load constant speed or acceleration operation. The control is performed such that the excess air ratio is shallowly lowered and fuel is supplementally added in the middle of the exhaust pipe by the fuel addition means to reduce the excess air ratio on the inlet side of the three-way catalyst to about 1.0. An exhaust emission control device comprising an apparatus.   Control to add after-injection at the timing when ignition is possible after main injection during medium- and high-load constant speed or acceleration operation under the condition that the amount of NOx adsorbed by the three-way catalyst exceeds the allowable amount The exhaust emission control device according to claim 1, wherein the device is configured.   The exhaust gas purification according to claim 1 or 2, wherein a particulate filter is disposed immediately after the three-way catalyst so that fuel can be added to the exhaust gas upstream of the three-way catalyst. apparatus.

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