JP3685063B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust emission control device for an internal combustion engine.
[0002]
[Prior art]
NO in exhaust gas_x If a catalyst suitable for reducing the catalyst with ammonia is placed in the engine exhaust passage and the urea aqueous solution is supplied into the engine exhaust passage upstream of the catalyst, the NO generated in the exhaust gas by the ammonia generated from the urea aqueous solution._x Can be reduced. In this case, however, as the temperature of the catalyst decreases, NO_x The purification rate is low. Therefore NO corresponding to the catalyst temperature_x NO with purification rate_x An internal combustion engine in which the amount of urea necessary to reduce the amount of urea is calculated and the supply amount of the urea aqueous solution is controlled so that the calculated amount of urea is supplied is known (Japanese Utility Model Laid-Open No. 3-129712). reference).
[0003]
[Problems to be solved by the invention]
However, the NO corresponding to the catalyst temperature is_x NO with purification rate_x NO when the catalyst temperature is not so high as long as the required amount of urea is supplied_x High NO when the purification rate is low and therefore the catalyst temperature is not so high_x There is a problem that the purification rate cannot be obtained. In particular, the catalyst temperature does not become so high as in acceleration operation from a low load operation state, and NO in the exhaust gas._x NO for large quantities_x If the purification rate is low, a large amount of NO_x Is released into the atmosphere.
The object of the present invention is NO_x An object of the present invention is to provide an exhaust gas purification apparatus for an internal combustion engine that can increase the purification rate.
[0004]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, NO in exhaust gas is discharged by ammonia under an excess of oxygen._x A catalyst suitable for reducing the catalyst is disposed in the engine exhaust passage, a supply means for supplying a liquid containing an ammonia-generating compound to the catalyst, and a supply control means for controlling the supply amount of the liquid;An exhaust gas recirculation device for recirculating exhaust gas into the intake passage; andAnd the catalyst stores at least a portion of the ammonia generating compound contained in the liquid supplied to the catalyst in the catalyst and from the ammonia generating compound stored in the catalyst as the temperature of the catalyst increases. NO in exhaust gas due to ammonia released little by little._x An ammonia generating compound storage region in which the ammonia generating compound contained in the liquid supplied to the catalyst is stored in the catalyst and almost no ammonia is released from the stored ammonia generating compound. Or a means for judging whether it is an ammonia release region that releases ammonia little by little from the stored ammonia generating compound, and the supply control means is necessary when the temperature of the catalyst becomes the ammonia release region. It was determined that the temperature of the catalyst was in the ammonia generating compound storage area in order to have enough ammonia generating compound stored in the catalyst in advance to release an amount of ammonia. When supplied to the catalystWhen the determination means determines that the catalyst temperature is in the ammonia-generating compound storage region, the exhaust gas recirculation action is stopped.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows a case where the present invention is applied to a compression ignition type internal combustion engine. The present invention can also be applied to a gasoline engine.
Referring to FIG. 1, 1 is an engine body, 2 is a cylinder block, 3 is a cylinder head, 4 is a piston, 5 is a combustion chamber, 6 is an electrically controlled fuel injection valve, 7 is an intake valve, 8 is an intake port, 9 Indicates an exhaust valve, and 10 indicates an exhaust port. The intake port 8 is connected to a surge tank 12 via a corresponding intake branch pipe 11, and the surge tank 12 is connected to an air cleaner 15 via an intake duct 13 and an air flow meter 14. A throttle valve 17 driven by a step motor 16 is disposed in the intake duct 13.
[0006]
On the other hand, the exhaust port 10 is connected to an inlet portion of a first catalytic converter 20 containing a catalyst 19 via an exhaust manifold 18, and an outlet portion of the first catalytic converter 20 contains a catalyst 22 via an exhaust pipe 21. Connected to the second catalytic converter 23. In the embodiment shown in FIG. 1, the catalyst 19 comprises a catalyst having an oxidizing function, such as an oxidation catalyst or a three-way catalyst, and the catalyst 22 is NO in exhaust gas by ammonia under an excess of oxygen._x NO suitable for reducing_x It consists of a selective reduction catalyst.
[0007]
The exhaust manifold 18 and the surge tank 12 are connected to each other via an exhaust gas recirculation (hereinafter referred to as EGR) passage 24, and an electrically controlled EGR control valve 25 is disposed in the EGR passage 24. Each fuel injection valve 6 is connected to a fuel reservoir, so-called common rail 27, through a fuel supply pipe 26. Fuel is supplied into the common rail 27 from an electrically controlled fuel pump 28 with variable discharge amount, and the fuel supplied into the common rail 27 is supplied to the fuel injection valve 6 through each fuel supply pipe 26. A fuel pressure sensor 29 for detecting the fuel pressure in the common rail 27 is attached to the common rail 27, and the fuel pump 28 is configured so that the fuel pressure in the common rail 27 becomes the target fuel pressure based on the output signal of the fuel pressure sensor 29. The discharge amount is controlled.
[0008]
On the other hand, a liquid containing an ammonia-generating compound that generates ammonia is stored in the tank 30, and the liquid containing the ammonia-generating compound stored in the tank 30 is a supply conduit 31, a supply pump 32, and an electromagnetically controlled flow rate control. The gas is supplied into the exhaust pipe 21 via the valve 33.
[0009]
The electronic control unit 40 is composed of a digital computer, and is connected to each other by a bidirectional bus 41. ROM (read only memory) 42, RAM (random access memory) 43, CPU (microprocessor) 44, input port 45 and output port 46 It comprises. The air flow meter 14 generates an output voltage proportional to the amount of intake air, and this output voltage is input to the input port 45 via the corresponding AD converter 47. The output signal of the fuel pressure sensor 29 is input to the input port 45 via the corresponding AD converter 47. On the other hand, a water temperature sensor 34 for detecting the engine cooling water temperature is attached to the engine body 1, and a temperature sensor 35 for detecting the temperature of the exhaust gas flowing in the exhaust pipe 21 is disposed in the exhaust pipe 21. . The output signals of the water temperature sensor 34 and the temperature sensor 35 are input to the input port 45 via the corresponding AD converters 47, respectively.
[0010]
A load sensor 51 that generates an output voltage proportional to the depression amount L of the accelerator pedal 50 is connected to the accelerator pedal 50, and the output voltage of the load sensor 51 is input to the input port 45 via the corresponding AD converter 47. . Further, a crank angle sensor 52 that generates an output pulse every time the crankshaft rotates, for example, 30 ° is connected to the input port 45. An operation signal for the starter switch 53 is input to the input port 45. On the other hand, the output port 46 is connected to the fuel injection valve 6, the step motor 16, the EGR control valve 25, the fuel pump 28, the pump 32, and the flow rate control valve 33 through corresponding drive circuits 54.
[0011]
As described above, the liquid containing the ammonia generating compound is supplied into the exhaust pipe 21 upstream of the catalyst 22. There are various types of ammonia generating compounds capable of generating ammonia, and therefore various compounds can be used as the ammonia generating compound. In the embodiment according to the present invention, urea is used as the ammonia generating compound, and an aqueous urea solution is used as the liquid containing the ammonia generating compound. Therefore, hereinafter, the present invention will be described by taking as an example the case of supplying an aqueous urea solution into the exhaust pipe 21 upstream of the catalyst 22.
[0012]
On the other hand, as described above, the catalyst 22 is NO._x In the embodiment shown in FIG._x Catalyst V with titania as carrier as selective reduction catalyst and vanadium oxide supported on this carrier₂ O_Five / TiO₂(Hereinafter referred to as “vanadium / titania catalyst”) or a catalyst Cu / ZSM 5 (hereinafter referred to as “copper zeolite catalyst”) using zeolite as a carrier and supporting copper on this carrier is used.
[0013]
When urea aqueous solution is supplied to exhaust gas containing excess oxygen, NO contained in the exhaust gas is converted to urea CO (NH₂)₂Ammonia generated from NH_Three (Eg 2NH_Three+ 2NO + 1 / 2O² → 2N₂+ 3H₂O). In this case, NO contained in the exhaust gas_x NO in exhaust gas_x A certain amount of urea is required to completely remove NO._x The amount of urea needed to reduce and completely remove urea / NO_x This is referred to as the amount of urea having an equivalent ratio of 1. Urea / NO_x The equivalent ratio of 1 is hereinafter simply referred to as equivalent ratio = 1.
[0014]
FIG. 2 shows that the exhaust gas temperature Ti flowing into the catalyst 22 is changed while maintaining the engine speed constant, and NO in the exhaust gas is changed._x NO in the case where the urea aqueous solution is supplied so that the urea amount is equivalent ratio = 1 to the amount_x The purification rate is shown. In FIG. 2, the solid line indicates the case where a copper zeolite catalyst is used as the catalyst 22, and the broken line indicates the case where a vanadium / titania catalyst is used as the catalyst 22.
[0015]
From Fig. 2, NO in exhaust gas_x When the urea aqueous solution is supplied so that the amount of urea is equivalent to 1 with respect to the amount of NO, if the exhaust gas temperature Ti flowing into the catalyst 22 becomes 350 ° C. or higher in any catalyst 22, NO_x The purification rate is almost 100%, and NO decreases as the exhaust gas temperature Ti flowing into the catalyst 22 decreases._x It turns out that a purification rate falls.
[0016]
On the other hand, FIG. 3 shows the relationship between the elapsed time t (sec) after supplying the urea aqueous solution and the generated ammonia concentration (ppm) when the urea aqueous solution is supplied with the temperature of the catalyst 22 maintained at 400 ° C. Show. From FIG. 3, it can be seen that when the urea aqueous solution is supplied, urea is decomposed into ammonia at a stretch and ammonia is released at a stretch. As described above, when the temperature of the catalyst 22 is 400 ° C., when urea is supplied with an equivalent ratio = 1, NO_x The purification rate is almost 100%.
[0017]
Therefore, from FIG. 2 and FIG. 3, when the temperature of the catalyst 22 is approximately 350 ° C. or higher, the NO in the exhaust gas_x When the urea aqueous solution is supplied so that the urea amount becomes equivalent ratio = 1 with respect to the amount, ammonia is released at once from urea contained in the urea aqueous solution, and this ammonia causes total NO in the exhaust gas to be discharged._x It can be seen that can be reduced. In other words, when the temperature of the catalyst 22 is about 350 ° C or higher, the NO in the exhaust gas_x If the urea aqueous solution is supplied so that the urea amount is equal to 1 with respect to the amount, NO in the exhaust gas_x Can be purified almost completely.
[0018]
On the other hand, FIG. 4 shows the elapsed time t (sec) from the start of the urea aqueous solution supply when the urea aqueous solution is supplied when the temperature Tc of the catalyst 22 is 120 ° C. and then the temperature Tc of the catalyst 22 is gradually increased. The relationship with the generated ammonia concentration (ppm) is shown. As shown in FIG. 4, even when the urea aqueous solution is supplied, no ammonia is generated while the temperature Tc of the catalyst 22 is low. When the temperature Tc of the catalyst 22 starts to rise, the ammonia increases as the temperature Tc of the catalyst 22 rises. Occur little by little.
[0019]
FIG. 4 means the following two things. That is, first, when the temperature Tc of the catalyst 22 rises, ammonia is generated, which means that the supplied urea is stored in the catalyst 22. Secondly, the thermal decomposition temperature of urea is approximately 132 ° C. Therefore, assuming that ammonia is generated by thermal decomposition of urea, ammonia should be released at once when the temperature Tc of the catalyst 22 reaches approximately 132 ° C. It is. However, as shown in FIG. 4, even when the temperature Tc of the catalyst 22 reaches approximately 132 ° C., ammonia is not released all at once, which means that ammonia is not generated only by the thermal decomposition of urea. ing.
[0020]
Thus, even when the temperature Tc of the catalyst 22 reaches approximately 132 ° C., ammonia is not released at a stretch, and the ammonia is gradually released as the temperature Tc of the catalyst 22 rises due to a change in the form of urea on the catalyst 22. It is considered a thing. That is, urea changes to biuret at approximately 132 ° C, biuret changes to cyanuric acid at approximately 190 ° C, and cyanuric acid changes to cyanic acid or isocyanic acid at approximately 360 ° C. Thus, it is considered that ammonia is generated little by little in the process of shape change due to the temperature rise, and therefore ammonia is gradually released from the catalyst 22 as the temperature Tc of the catalyst 22 rises as shown in FIG. become.
[0021]
That is, when the temperature Tc of the catalyst 22 is low when the urea aqueous solution is supplied, urea contained in the urea aqueous solution is stored in the catalyst 22. Next, when the temperature Tc of the catalyst 22 rises, the urea stored in the catalyst 22 is successively transformed into another ammonia generating compound, and as a result, ammonia is gradually released from the catalyst 22.
[0022]
As described above, when the temperature Tc of the catalyst 22 is low when the urea aqueous solution is supplied, urea contained in the urea aqueous solution is stored in the catalyst 22, and this urea is maintained in a state where the temperature Tc of the catalyst 22 is low. As long as stored in the catalyst 22. On the other hand, if the urea aqueous solution is supplied when the temperature Tc of the catalyst 22 is between approximately 132 ° C. and approximately 350 ° C., the urea contained in the urea aqueous solution is once stored in the catalyst 22 also in this case. The temperature of the urea then rises, and ammonia is released from the catalyst 22 as the urea sequentially changes into another ammonia generating compound. That is, when the urea aqueous solution is supplied when the temperature Tc of the catalyst 22 is between approximately 132 ° C. and 350 ° C., the ammonia releasing action from the catalyst 22 is started after a while.
[0023]
In this way, when the urea aqueous solution is supplied when the temperature Tc of the catalyst 22 is between approximately 132 ° C. and 350 ° C., the ammonia release action from the catalyst 22 starts after a while, but the temperature Tc of the catalyst 22 If the urea aqueous solution is continuously supplied while being kept substantially constant, ammonia is continuously released from the catalyst 22. However, in this case, the urea stored in the catalyst 22 only changes its form up to the ammonia generating compound determined by the temperature Tc of the catalyst 22, so that ammonia is not generated so much. Therefore, in this case, NO in the exhaust gas_x Even if the urea aqueous solution is supplied so that the urea amount is equal to 1 with respect to the amount, all the NO in the exhaust gas by the ammonia generated from the catalyst 22_x Will not be reduced.
[0024]
In addition, when urea aqueous solution is supplied, some urea contained in the urea aqueous solution is thermally decomposed in the exhaust gas, which is considered to generate ammonia, so NO in the exhaust gas_x A part of is reduced by this ammonia. However, the amount of ammonia is not so large, so NO in the exhaust gas reduced by this ammonia_x The amount is not so much.
[0025]
Therefore, when the temperature Tc of the catalyst 22 is maintained at a substantially constant temperature between approximately 132 ° C. and approximately 350 ° C., the NO in the exhaust gas_x As shown in FIG. 2, even if the urea aqueous solution is supplied so that the urea amount is equal to the amount, the equivalent ratio = 1._x The purification rate should not be high. In this case, if the exhaust gas temperature becomes high and the temperature Tc of the catalyst 22 increases accordingly, the amount of ammonia generated from the catalyst 22 increases on the one hand, and the ammonia amount generated from urea in the urea aqueous solution in the exhaust gas on the other hand. Will also increase. Accordingly, as shown in FIG. 2, as the exhaust gas temperature Ti flowing into the catalyst 22 increases, the NO_x The purification rate is gradually increased.
[0026]
NO when the temperature Tc of the catalyst 22 is maintained at a substantially constant temperature from approximately 132 ° C to approximately 350 ° C._x In order to increase the purification rate, the amount of ammonia generated from the catalyst 22 should be increased, and the amount of ammonia generated from urea in the urea aqueous solution should be increased in the exhaust gas. To that end, the amount of urea supplied is increased. You can do that. Therefore, in the embodiment according to the present invention, when the temperature Tc of the catalyst 22 does not change so much between about 132 ° C. and about 350 ° C., the amount of urea supplied is the NO in the exhaust gas._x The supply amount of the urea aqueous solution is increased so that the equivalent amount necessary for reducing the amount of urea is 1 or more.
[0027]
In this way, when the temperature Tc of the catalyst 22 does not change so much between about 132 ° C. and about 350 ° C., NO is supplied by supplying an amount of urea equal to or higher than the equivalent ratio = 1._x The purification rate can be increased. However, for example, when the exhaust gas temperature suddenly rises during acceleration operation and the temperature Tc of the catalyst 22 suddenly rises, even if an equivalent ratio = 1 or more of urea is supplied, NO_x The purification rate cannot be increased.
[0028]
That is, when shifting from the low load operation state to the high load operation state for acceleration operation, the exhaust gas temperature rapidly rises, so the temperature Tc of the catalyst 22 also rises rapidly. On the other hand, when the engine operating state shifts to high load operation, NO in the exhaust gas_x The amount increases rapidly. However, at this time NO increased rapidly_x Even if the supply amount of the urea aqueous solution is suddenly increased so as to supply urea having an equivalent ratio of 1 or more necessary for reducing the amount of urea, ammonia will not be generated unless the urea increased rapidly as described above for a while. When actually tested, ammonia is hardly generated from urea that is rapidly increased during acceleration operation. Therefore, during acceleration operation, the amount of ammonia released from the catalyst 22 is increased._x Is significantly less than the amount of ammonia required to reduce_x The purification rate cannot be obtained.
[0029]
Therefore, in the present invention, for example, NO in the exhaust gas as in acceleration operation._x High NO when the amount increases and the temperature Tc of the catalyst 22 rises_x In order to obtain a purification rate, a large amount of urea, that is, a large amount of ammonia-generating compound is stored in the catalyst 22 before the catalyst 22 starts to rise in temperature, and when the temperature Tc of the catalyst 22 rapidly increases. A large amount of ammonia is released from the ammonia generating compound stored in the catalyst 22, and the NO in the exhaust gas is released by the released large amount of ammonia._x To reduce.
[0030]
More specifically, in the present invention, the temperature region of the catalyst 22 is an ammonia generating compound storage region in which urea in an aqueous urea solution, that is, an ammonia generating compound is stored in the catalyst 22 and ammonia is hardly released from the stored ammonia generating compound. Or an ammonia release region that releases ammonia little by little from the stored ammonia generating compound, and sufficient ammonia to release the required amount of ammonia when the temperature of the catalyst 22 reaches the ammonia release region In order to store the generated compound in the catalyst 22 in advance, a sufficient amount of aqueous urea solution is supplied to the catalyst 22 when the temperature of the catalyst 22 is determined to be in the ammonia generating compound storage region. ing.
[0031]
Here, the ammonia generating compound storage region shows a temperature region where the temperature Tc of the catalyst 22 is about 132 ° C. or less, and the ammonia release region shows a temperature region where the temperature Tc of the catalyst 22 is between about 132 ° C. and about 350 ° C. ing. When the temperature Tc of the catalyst 22 is lower than about 132 ° C., as can be seen from FIG. 4, urea in the supplied urea aqueous solution, that is, the ammonia generating compound, is stored in the catalyst 22, and from the stored ammonia generating compound, Little ammonia is generated. At this time, even if ammonia is generated from urea in the exhaust gas, the amount is extremely small. Therefore, when the urea aqueous solution is supplied when the temperature Tc of the catalyst 22 is in the ammonia generating compound storage region, the urea in the urea aqueous solution, that is, most of the ammonia generating compound is stored in the catalyst 22.
[0032]
On the other hand, when the temperature Tc of the catalyst 22 is between about 132 ° C. and about 350 ° C., that is, when the temperature Tc of the catalyst 22 is in the ammonia release region, ammonia is released from the ammonia generating compound stored in the catalyst 22. The
[0033]
In general, the temperature Tc of the catalyst 22 becomes an ammonia-generating compound storage region during engine start-up, warm-up operation, low-load operation, and deceleration operation. Therefore, in the embodiment according to the present invention, during engine start-up and warm-up operation During low-load operation and deceleration operation, a large amount of urea aqueous solution is supplied so that urea, that is, the ammonia-generating compound is stored in the catalyst 22 within a range not exceeding the maximum storage amount of the ammonia-generating compound that the catalyst 22 can store. ing. Therefore, when the acceleration operation is performed, a large amount of ammonia is released from the ammonia generating compound stored in the catalyst 22, and thus NO in the exhaust gas is discharged._x Will be purified well.
[0034]
FIG. 5 shows an example of supply control of the urea aqueous solution. FIG. 5 shows the required load L and NO in the exhaust gas discharged from the combustion chamber 5._x The change in the amount, the temperature Tc of the catalyst 22, the supply amount of the urea aqueous solution, and the storage amount of the ammonia generating compound stored in the catalyst 22 are shown. In the supply amount of the urea aqueous solution in FIG. 5, the broken line indicates NO in the exhaust gas._x The supply amount of urea aqueous solution in which the urea amount is equivalent ratio = 1 is shown, and the solid line shows the amount of urea aqueous solution actually supplied.
[0035]
In FIG. 5, an operation region I indicates an engine start time, a warm-up operation time, or a low load operation time including an idling operation. At this time, as shown in FIG._x The amount is small and the temperature Tc of the catalyst 22 is in the ammonia generating compound storage region. At this time, the urea aqueous solution is supplied so that, for example, the amount of urea supplied is 2 to 4 times the amount of urea having the equivalent ratio = 1, so that the amount of urea supplied is equal to or greater than the equivalent amount = 1. . Therefore, at this time, the storage amount of urea, that is, the ammonia generating compound stored in the catalyst 22 gradually increases.
[0036]
Next, it is assumed that the required load L is rapidly increased and the acceleration operation is performed. When the required load L is suddenly increased, NO in the exhaust gas_x The amount increases rapidly. At this time, since the exhaust gas temperature rises rapidly, the temperature Tc of the catalyst 22 also rises rapidly, and the temperature Tc of the catalyst 22 becomes the ammonia release region. At this time, a large amount of ammonia is released from the ammonia generating compound stored in the catalyst 22, and the NO released in the exhaust gas is released by the released ammonia._x Is well purified. As described above, since a large amount of ammonia is released from the ammonia generating compound at this time, the amount of the ammonia generating compound stored in the catalyst 22 rapidly decreases.
[0037]
On the other hand, the total NO in the exhaust gas is reduced by the ammonia generated from the ammonia generating compound stored in the catalyst 22._x In the exhaust gas, the remaining NO in the exhaust gas can be reduced by ammonia generated from urea in the urea aqueous solution._x In order to reduce the amount of urea, an aqueous urea solution is also supplied during acceleration operation. In the example shown in FIG. 5, when the acceleration operation is started, the supply amount of the urea aqueous solution is once decreased and then increased. Of course, NO in the exhaust gas is generated by the ammonia generated from the ammonia generating compound stored in the catalyst 22 during the acceleration operation._x If the water can be sufficiently purified, the supply of the urea aqueous solution may be stopped during the acceleration operation.
[0038]
Next, it is assumed that the steady operation is performed in the operation region II, and at this time, the temperature Tc of the catalyst 22 is maintained in the ammonia release region. At this time, in the example shown in FIG._x In order to purify the water well, the urea aqueous solution is supplied so that the supply amount of urea becomes equal to or greater than 1. Accordingly, at this time, the amount of the ammonia generating compound stored in the catalyst 22 is gradually increased.
[0039]
Next, the required load L is increased in the operation region III, and then the steady operation is performed under the high load. In the operation region III, the temperature Tc of the catalyst 22 exceeds approximately 350 ° C. and the catalyst is operated under the high load operation state. It is assumed that the temperature Tc of 22 is maintained at about 350 ° C or higher. In this case, when the temperature Tc of the catalyst 22 rises in the operation region III, the amount of ammonia released from the ammonia generating compound stored in the catalyst 22 increases, and thus the amount of the ammonia generating compound stored in the catalyst 22 Decrease. In the example shown in FIG. 5, the supply amount of the urea aqueous solution is also reduced at this time.
[0040]
On the other hand, when the temperature Tc of the catalyst 22 exceeds approximately 350 ° C., all urea in the urea aqueous solution supplied as described above is immediately pyrolyzed to ammonia, and this ammonia causes NO in the exhaust gas._x Is immediately reduced. Therefore, the amount of urea supplied at this time is the NO in the exhaust gas._x If the equivalent ratio to the amount is 1, NO in the exhaust gas_x Can be completely purified. Therefore, as shown in FIG. 5, when the temperature Tc of the catalyst 22 is approximately 350 ° C. or higher, the amount of urea supplied is the NO in the exhaust gas._x The aqueous urea solution is supplied so that the equivalent ratio = 1 with respect to the amount. At this time, no ammonia-generating compound is stored in the catalyst 22, and at this time, the amount of the ammonia compound stored in the catalyst 22 is zero as shown in FIG.
[0041]
Next, it is assumed that the deceleration operation is performed and the fuel supply is stopped. At this time, NO in the exhaust gas_x The amount becomes zero, and the temperature Tc of the catalyst 22 rapidly decreases. At this time, in the example shown in FIG. 5, the amount of urea supplied is the same as that in the operation region I._x The urea aqueous solution is supplied so that the equivalent amount is equal to or greater than 1 with respect to the amount of urea. Therefore, when the deceleration operation is started, the amount of the ammonia generating compound stored in the catalyst 22 is increased.
[0042]
When urea with an equivalent ratio of 1 or more is supplied when the temperature Tc of the catalyst 22 is approximately 350 ° C. or higher, ammonia is discharged into the atmosphere. Therefore, when the temperature Tc of the catalyst 22 becomes approximately 350 ° C. or higher, it is necessary to control the supply amount of the urea aqueous solution so that the urea amount accurately becomes the equivalent ratio = 1.
[0043]
On the other hand, even when the temperature Tc of the catalyst 22 is approximately 350 ° C. or less, if the supply amount of the urea aqueous solution is extremely increased, ammonia is discharged into the atmosphere, so that the urea aqueous solution is also prevented from being released into the atmosphere at this time. Is required to supply. According to the experiment by the present inventor, when the operating state of the engine is changed along a certain pattern, and the temperature Tc of the catalyst 22 changes between about 190 ° C. and about 350 ° C., vanadium is used as the catalyst 22. -When titania catalyst is used, ammonia is not released into the atmosphere even when urea is supplied in an amount equivalent to approximately three times the urea amount of equivalent ratio = 1, and when using a copper zeolite catalyst as catalyst 22, equivalent ratio = It has been confirmed that ammonia is not released into the atmosphere even when urea is supplied in an amount of 4 times or more the amount of 1 urea.
[0044]
The reason why the amount of ammonia discharged into the atmosphere is smaller in the case of using the copper zeolite catalyst than in the case of using the vanadium / titania catalyst is considered to be as follows. That is, on the surface of copper or vanadium, a part of the ammonia generated from the ammonia generating compound is NO in the exhaust gas._x If the excess ammonia is retained on the surface of copper or vanadium, this ammonia becomes NO (NH_Three→ NO). This NO then reacts with excess ammonia to react with N₂ (NO + NH_Three → N₂). When such a sequential reaction occurs, excess ammonia is not released into the atmosphere.
[0045]
Vanadium has a low ability to hold ammonia, and therefore it is difficult for such a sequential reaction to occur, so that ammonia is easily discharged into the atmosphere. On the other hand, copper has a high ability to hold ammonia, and therefore, such sequential reactions are likely to occur, so that ammonia is not easily discharged into the atmosphere. Accordingly, it is preferable to use a copper zeolite catalyst in order to suppress the discharge of ammonia into the atmosphere.
[0046]
Next, the first embodiment of the supply control of the urea aqueous solution according to the present invention will be described.
NO discharged from the combustion chamber 5 per unit time_x The amount increases as the engine load increases, and therefore the NO discharged from the combustion chamber 5 per unit time as shown in FIG. 6 (A)._x The amount increases as the exhaust gas temperature Ti flowing into the catalyst 22 increases. Further, as shown in FIG. 6B, NO exhausted from the combustion chamber 5 per unit time._x The amount is proportional to the intake air amount Ga. Therefore NO in exhaust gas_x The urea amount QE per unit time when the equivalent ratio = 1 with respect to the amount is a function of the exhaust gas temperature Ti and the intake air amount Qa. In the embodiment according to the present invention, the urea amount QE to be supplied per unit time = 1 is previously stored in the ROM 42 in the form of a map as shown in FIG. 6C as a function of the exhaust gas temperature Ti and the intake air amount Ga. Is stored within.
[0047]
Instead of calculating the urea amount QE based on the exhaust gas temperature Ti and the intake air amount Qa in this way, the actual NO in the exhaust gas is calculated._x This concentration is detected and this NO_x The urea amount QE can also be calculated from the concentration. In this case, NO in the exhaust pipe 21 upstream of the catalyst 22_x A concentration sensor is attached and NO_x NO detected by concentration sensor_x NO discharged from the combustion chamber 5 per unit time from the concentration and the intake air amount Ga_x The amount is sought and this NO_x NO based on quantity_x The urea amount QE per unit time with an equivalent ratio = 1 to the amount is calculated.
[0048]
On the other hand, when urea aqueous solution is supplied, a part of urea contained in the urea aqueous solution is thermally decomposed in the exhaust gas to generate ammonia. In this case, the amount of urea to be thermally decomposed increases as the exhaust gas temperature Ti flowing into the catalyst 22 increases, and therefore the urea storage ratio ST stored in the catalyst 22 when the urea aqueous solution is supplied is shown in FIG. As shown, the exhaust gas temperature Ti decreases as the exhaust gas temperature Ti increases.
[0049]
Further, during steady operation where the temperature Tc of the catalyst 22 does not change much, as described above, the amount of ammonia released from the ammonia generating compound stored in the catalyst 22 increases as the temperature Tc of the catalyst 22 increases. Therefore, the ratio NH of ammonia released per unit time from the ammonia generating compound stored in the catalyst 22 at this time_Three As shown in FIG. 8A, the temperature increases as the exhaust gas temperature Ti flowing into the catalyst 22 increases. On the other hand, as the space velocity of the exhaust gas increases, the amount of ammonia released from the ammonia generating compound stored in the catalyst 22 increases. Therefore, the ammonia generating compound stored in the catalyst 22 as shown in FIG. Percentage of ammonia released per unit time NH_Three Increases as the intake air amount Ga increases. In the embodiment according to the present invention, the ratio LE1 of ammonia released per unit time from the ammonia generating compound stored in the catalyst 22 during steady operation is shown as a function of the exhaust gas temperature Ti and the intake air amount Ga in FIG. Is stored in the ROM 42 in advance in the form of a map as shown in FIG.
[0050]
On the other hand, when the temperature of the catalyst 22 rapidly increases as in the acceleration operation, ammonia is gradually released from the ammonia generating compound stored in the catalyst 22 before the temperature of the catalyst 22 increases as described above. At this time, the ratio NH of ammonia released per unit time from the ammonia generating compound stored in the catalyst 22_Three As shown in FIG. 9 (A), it changes according to the exhaust gas temperature Ti flowing into the catalyst 22. Also in this case, as shown in FIG. 9B, the ratio NH of ammonia released per unit time from the ammonia generating compound stored in the catalyst 22_Three Increases as the intake air amount Ga increases. In the embodiment according to the present invention, when the temperature Tc of the catalyst 22 rapidly rises, the ratio LE2 of ammonia released per unit time from the ammonia generating compound stored in the catalyst 22 is the exhaust gas temperature Ti and the intake air amount. As a function of Ga, it is stored in the ROM 42 in advance in the form of a map as shown in FIG.
[0051]
FIGS. 10 to 12 show a routine for executing the first embodiment of the urea aqueous solution supply control, and this routine is executed by interruption every predetermined time.
Referring to FIG. 10, first, at step 100, it is judged if the engine is starting. When the engine is starting, the routine jumps to step 102, and when the engine is not starting, the routine proceeds to step 101. In step 101, it is determined whether or not the vehicle is decelerating. When the vehicle is decelerating, the process proceeds to step 102. In step 102, the EGR control valve 25 is closed and the supply of EGR gas is stopped. Next, the routine proceeds to step 103, where the supply control I is executed, and then the routine proceeds to step 104. This supply control I is shown in FIG.
[0052]
On the other hand, when it is judged at step 101 that the vehicle is not decelerating, the routine proceeds to step 109, where it is judged if the exhaust gas temperature Ti detected by the temperature sensor 35 is higher than a predetermined temperature, for example, 350 ° C. When Ti ≦ 350 ° C, the routine proceeds to step 110, where it is judged if acceleration operation is in progress. When it is not during acceleration operation, the routine proceeds to step 103. That is, the process proceeds to step 103 when starting and decelerating, and when Ti ≦ 350 ° C. and not during acceleration operation.
[0053]
Here, the supply control I performed in step 103 will be described with reference to FIG.
Referring to FIG. 11, first, at step 200, it is judged if the supply stop flag indicating that the supply of the urea aqueous solution should be stopped is set. When the supply stop flag is not set, the routine proceeds to step 201, where the urea amount of equivalent ratio = 1 to be supplied per unit time from the map shown in FIG. 6C based on the output signals of the air flow meter 14 and the temperature sensor 35. QE is calculated.
[0054]
Next, at step 202, the ratio of the actual supplied urea amount to the equivalent ratio = 1, that is, the urea increase ratio K is calculated. This urea increase ratio K is larger than 1.0 as shown in FIG. 13, and this urea increase ratio K becomes smaller as the inflowing exhaust gas temperature Ti to the catalyst 22 becomes higher. In the example shown in FIG. 13, when the exhaust gas temperature Ti is low, the urea increase ratio K is approximately 4.0. Next, in step 203, the urea amount QE (= K · QE) to be actually supplied per unit time is calculated by multiplying the urea amount QE of the equivalent ratio = 1 to be supplied per unit time by the urea increase ratio K. The
[0055]
Next, at step 204, the urea amount Q to be supplied per unit time is calculated by multiplying the urea amount QE by the correction coefficient C. When a 30 weight percent urea aqueous solution is used as the urea aqueous solution, the value of the correction coefficient C is (100 + 30) /30=4.3. When the supply amount Q of the urea aqueous solution per unit time is calculated, the flow rate control valve 33 is controlled so that the supply amount of the urea aqueous solution becomes Q.
[0056]
Next, at step 205, the storage ratio ST of urea is calculated from FIG. Next, at step 206, the urea amount QST (= QE · ST) stored in the catalyst 22 per unit time is calculated by multiplying the urea storage ratio ST by the urea supply amount QE. Next, at step 207, the ammonia release ratio LE1 is calculated from the map shown in FIG. Next, at step 208, the ammonia amount QLE (= ΣQS · LE1) released per unit time is calculated by multiplying the release ratio LE1 by the amount ΣQS of all ammonia generating compounds stored in the catalyst 22. Next, the routine proceeds to step 104 in FIG.
[0057]
On the other hand, when it is determined at step 200 that the supply stop flag is set, the routine proceeds to step 209, where the urea amount QST stored per unit time is made zero, and then the routine proceeds to step 207. At this time, the supply of the urea aqueous solution is stopped. Therefore, when starting or decelerating, or when Ti ≦ 350 ° C and not during acceleration operation, the urea aqueous solution is supplied so that the supply amount of urea is equal to or greater than equivalence ratio = 1 unless the supply stop flag is set. The
[0058]
In step 104 of FIG. 10, the total ammonia generating compound amount ΣQS stored in the catalyst 22 is calculated based on the following equation.
ΣQS = ΣQS + QST −QLE
Next, at step 105, it is determined whether or not the amount of ammonia generating compound ΣQS stored exceeds the maximum storage amount MAX (FIG. 5). When ΣQS> MAX, the routine proceeds to step 108 where the supply stop flag is set. . When the supply stop flag is set, the supply of the urea aqueous solution is stopped. On the other hand, when it is determined in step 105 that ΣQS ≦ MAX, the routine proceeds to step 106, where it is determined whether or not ΣQS is smaller than a certain value MIN (<MAX), and when ΣQS <MIN, the routine proceeds to step 107. Then, the supply stop flag is reset.
[0059]
On the other hand, when it is determined at step 110 that the acceleration operation is being performed, the routine proceeds to step 111 where the supply control II is executed. This supply control II is shown in FIG.
Referring to FIG. 12, first, in step 250, the total amount of ammonia-generating compounds stored in the catalyst 22 at the start of acceleration operation is the initial value ΣQS.₀ It is said. Next, at step 251, the ammonia release rate LE2 is calculated from the map shown in FIG. 9C. Next, at step 252, the initial value ΣQS of all ammonia generating compounds stored in the catalyst 22.₀ Amount of ammonia released per unit time by multiplying by the release rate LE2 QLE (= ΣQS₀ LE2) is calculated.
[0060]
Next, at step 253, NO in the exhaust gas that cannot be reduced by the ammonia released from the ammonia generating compound in the catalyst 22 is shown._x The urea amount QE required to reduce the amount is calculated. Next, at step 254, the amount Q of urea aqueous solution to be supplied per unit time is calculated by multiplying the urea amount QE by the correction coefficient C described above. When the supply amount Q of the urea aqueous solution per unit time is calculated, the flow rate control valve 33 is controlled so that the supply amount of the urea aqueous solution becomes Q.
[0061]
Next, at step 255, the storage ratio ST of urea is calculated from FIG. Next, at step 256, the urea amount QST (= QE · ST) stored in the catalyst 22 per unit time is calculated by multiplying the urea storage ratio ST by the urea supply amount QE. Next, the routine proceeds to step 105 in FIG.
[0062]
On the other hand, when it is determined in step 109 of FIG. 10 that Ti> 350 ° C., the routine proceeds to step 112, and based on the output signals of the air flow meter 14 and the temperature sensor 35, the map shown in FIG. The urea amount QE of equivalent ratio = 1 to be supplied is calculated. Next, at step 113, the urea amount Q to be supplied per unit time is calculated by multiplying the urea amount QE by the correction coefficient C described above. When the supply amount Q of the urea aqueous solution per unit time is calculated, the flow rate control valve 33 is controlled so that the supply amount of the urea aqueous solution becomes Q. Next, at step 114, the ammonia generating compound storage amount ΣQS in the catalyst 22 is made zero. In this way, when Ti> 350 ° C., the urea aqueous solution is supplied so that the supply amount of urea is equivalent ratio = 1.
[0063]
Next, a second embodiment will be described with reference to FIGS.
When the supply amount of the aqueous urea solution is small, the aqueous urea solution is dispersed in the exhaust gas. When the urea aqueous solution is dispersed in the exhaust gas, urea in the urea aqueous solution is likely to be thermally decomposed, and as a result, it becomes difficult to store the supplied urea in the catalyst 22. On the other hand, when the supply amount of the urea aqueous solution is increased, the density of urea in the exhaust gas increases, and as a result, urea is difficult to thermally decompose, so that the supplied urea can be stored in the catalyst 22. .
[0064]
Therefore, in the second embodiment, as shown in FIG. 14, the urea aqueous solution is supplied so that the equivalent amount ratio = 1 in the operation region I, the operation region II, and the amount of urea to be supplied at the time of deceleration. NO_x Then, a large amount of urea aqueous solution is supplied in a pulse manner at intervals of time so that urea in the urea aqueous solution is stored in the catalyst 22.
In the second embodiment, the routine shown in FIG. 10 is used, but the routine shown in FIG. 15 is used only for step 103 in FIG.
[0065]
Referring to FIG. 15, first, at step 300, it is judged if the supply stop flag indicating that the supply of the urea aqueous solution should be stopped is set. When the supply stop flag is not set, the routine proceeds to step 301 where the urea amount QE of the equivalent ratio to be supplied per unit time is determined from the map shown in FIG. 6C based on the output signals of the air flow meter 14 and the temperature sensor 35. Calculated. Next, at step 302, it is judged if it is a supply timing for supplying a large amount of urea aqueous solution in a short time in a pulsed manner. When it is the supply timing, the routine proceeds to step 303, where it is determined whether or not the supply time of the urea aqueous solution has elapsed. When the supply time of the urea aqueous solution has not elapsed, the routine proceeds to step 304.
[0066]
In step 304, the urea aqueous solution amount ΔQE per unit time to be supplied in a pulse manner is calculated. This urea aqueous solution amount ΔQE is determined so that the amount of urea supplied is a predetermined urea amount that is several times the equivalence ratio = 1 during low-load operation. Next, at step 306, the final urea amount QE (= QE + ΔQE) is calculated by adding the urea amount ΔQE to be added to the urea amount QE calculated at step 301. Next, at step 307, the urea amount Q to be supplied per unit time is calculated by multiplying the urea amount QE by the correction coefficient C described above. When the supply amount Q of the urea aqueous solution per unit time is calculated, the flow rate control valve 33 is controlled so that the supply amount of the urea aqueous solution becomes Q.
[0067]
Next, at step 308, the additional urea amount ΔQE is made the urea amount QST stored in the catalyst 22 per unit time. Next, at step 310, the ammonia release rate LE1 is calculated from the map shown in FIG. Next, at step 311, the amount of ammonia QLE (= ΣQS · LE1) released per unit time is calculated by multiplying the amount ΣQS of the total ammonia generating compound stored in the catalyst 22 by the release ratio LE1. Next, the routine proceeds to step 104 in FIG.
[0068]
On the other hand, when it is determined at step 302 that the supply timing is not reached, or when it is determined at step 303 that the supply time has elapsed, the routine proceeds to step 305 where the additional urea amount ΔQE is made zero, and then the routine proceeds to step 306. At this time, the amount of urea supplied is set to an equivalent ratio = 1.
[0069]
On the other hand, when it is determined at step 300 that the supply stop flag is set, the routine proceeds to step 309, where the urea amount QST stored per unit time is made zero, and then the routine proceeds to step 310. At this time, the supply of the urea aqueous solution is stopped.
[0070]
Next, a third embodiment will be described with reference to FIGS.
When exhaust gas temperature is low, NO in exhaust gas_x The amount is very small. Therefore, in this third embodiment, when the exhaust gas temperature Ti flowing into the catalyst 22 is lower than a certain value To, for example, 132 ° C., the continuous supply of the urea aqueous solution is stopped, and the operation region I and A large amount of urea aqueous solution is supplied in a pulsed manner at a time interval during deceleration to store urea in the urea aqueous solution in the catalyst 22.
The routine shown in FIG. 10 is also used in the third embodiment, but the routine shown in FIG. 17 is used only for step 103 in FIG.
[0071]
Referring to FIG. 17, first, at step 400, it is judged if the supply stop flag indicating that the supply of the urea aqueous solution should be stopped is set. When the supply stop flag is not set, the routine proceeds to step 401, where it is judged from the output signal of the temperature sensor 35 whether or not the exhaust gas temperature Ti flowing into the catalyst 22 is higher than a certain value To, for example, 132 ° C. When Ti> To, the routine proceeds to step 402, where the urea amount QE of equivalent ratio = 1 to be supplied per unit time is calculated from the map shown in FIG. 6C based on the output signals of the air flow meter 14 and the temperature sensor 35. The
[0072]
Next, at step 403, the urea increase ratio K is calculated from FIG. Next, at step 404, the urea amount QE (= K · QE) to be actually supplied per unit time is calculated by multiplying the urea amount QE of equivalent ratio = 1 to be supplied per unit time by the urea increase ratio K. The Next, at step 405, the urea amount Q to be supplied per unit time is calculated by multiplying the urea amount QE by the correction coefficient C described above. When the supply amount Q of the urea aqueous solution per unit time is calculated, the flow rate control valve 33 is controlled so that the supply amount of the urea aqueous solution becomes Q.
[0073]
Next, at step 406, the urea storage ratio ST is calculated from FIG. Next, at step 407, the urea amount QST (= QE · ST) stored in the catalyst 22 per unit time is calculated by multiplying the urea storage ratio ST by the urea supply amount QE. Next, at step 408, the ammonia release ratio LE1 is calculated from the map shown in FIG. Next, at step 409, the amount of ammonia QLE (= ΣQS · LE1) released per unit time is calculated by multiplying the amount ΣQS of the total ammonia generating compound stored in the catalyst 22 by the release rate LE1. Next, the routine proceeds to step 104 in FIG.
[0074]
On the other hand, when it is determined in step 401 that Ti ≦ To, the routine proceeds to step 410, where it is determined whether it is a supply timing for supplying a large amount of urea aqueous solution in a short time in a pulsed manner. When it is the supply timing, the routine proceeds to step 411, where it is determined whether or not the supply time of the urea aqueous solution has elapsed. When the supply time of the urea aqueous solution has not elapsed, the routine proceeds to step 412.
[0075]
In step 412, the urea amount QEE per unit time to be supplied in a pulse manner is calculated. The urea amount QEE is determined to be a predetermined urea amount that is several times the equivalence ratio = 1. Next, at step 413, the amount Q of urea aqueous solution to be supplied per unit time is calculated by multiplying the urea amount QEE by the correction coefficient C described above. When the supply amount Q of the urea aqueous solution per unit time is calculated, the flow rate control valve 33 is controlled so that the supply amount of the urea aqueous solution becomes Q. Next, at step 414, QEE is made the amount of urea QST stored in the catalyst 22 per unit time. Next, the routine proceeds to step 408.
[0076]
On the other hand, when it is judged at step 400 that the supply stop flag is set, the routine proceeds to step 415, where the urea amount QST stored per unit time is made zero, and then the routine proceeds to step 408. At this time, the supply of the urea aqueous solution is stopped.
[0077]
Note that the supply amount and supply timing of the urea aqueous solution supplied in a pulse manner in the second and third embodiments can be changed. For example, the supply amount of the urea aqueous solution at the time of deceleration can be reduced little by little every time the pulse is supplied. Further, in order to wait until the temperature Tc of the catalyst 22 sufficiently decreases, the higher the temperature Tc of the catalyst 22 at the start of deceleration, the longer the interval from the start of deceleration until the urea aqueous solution is supplied.
[0078]
Next, various examples of the catalyst 22 accommodated in the catalytic converter 23 will be described with reference to FIG. 18 and FIG.
As shown in FIG. 18A, the catalyst 22 has a honeycomb structure, and includes a large number of exhaust gas circulation holes 61 surrounded by a substrate 60 having a honeycomb structure. A catalyst layer is formed on the surface of the base material 60 forming the exhaust gas circulation hole 61. In the example shown in FIG. 18B, the catalyst layer 62 is made of titania 63. Vanadium 64 is supported on the titania 63. When the urea aqueous solution is supplied, urea contained in the urea aqueous solution, that is, an ammonia generating compound, is stored in titania 63 as a carrier. It is not always clear how the ammonia-generating compound is stored in the titania 63, but it is presumably retained in the catalyst 22 by adsorption.
[0079]
By the way, in the present invention, urea stored in the catalyst 22, that is, ammonia released little by little from the ammonia generating compound, is used for NO in the exhaust gas._x Therefore, it can be said that it is preferable to hold as much urea as possible, that is, an ammonia generating compound in the catalyst 22 when the aqueous urea solution is supplied, and to gradually release ammonia from these ammonia generating compounds. 18 (C), 18 (D), 18 (E) and FIGS. 19 (A), 19 (B) show examples in which as much ammonia-generating compound as possible is held in the catalyst 22. FIG.
[0080]
That is, in the example shown in FIG. 18C, the zeolite layer 65 is formed on the support made of titania 63. In this way, urea, that is, the ammonia generating compound is also retained in the zeolite layer 65, so that the amount of the ammonia generating compound is increased, and the ammonia generating compound retained in the zeolite layer 65 is within the carrier made of titania 63. Since it is thermally decomposed after diffusion into the ammonia, ammonia will be released slowly.
[0081]
In the example shown in FIG. 18 (D), a zeolite layer 65 is formed between the substrate 60 and the support made of titania 63. Also in this case, as in the example shown in FIG. 18C, urea, that is, the ammonia generating compound is held in the zeolite layer 65, so that the amount of the ammonia generating compound is increased and held in the zeolite layer 65. Since the ammonia generating compound is thermally decomposed after diffusing in the carrier composed of titania 64, ammonia is slowly released.
[0082]
In the example shown in FIG. 18E, the catalyst layer 62 is made of titania and zeolite, and vanadium 64 is supported on a carrier made of these titania and zeolite.
[0083]
In the example shown in FIGS. 19A and 19B, in the region X upstream of the catalyst 22, the catalyst layer 62 is made of zeolite, and in the region Y downstream of the catalyst 22, the catalyst layer 62 carries vanadium 64. It consists of 63. Also in this example, urea, that is, the ammonia generating compound is retained in the zeolite layer 65, so that the amount of the ammonia generating compound is increased, and the ammonia generating compound retained in the zeolite layer 65 is within the carrier made of titania 63. Since it is thermally decomposed after diffusion into the ammonia, ammonia will be released slowly.
[0084]
20 to 23 show other embodiments of the internal combustion engine. In the example shown in FIG. 20, another catalytic converter 70 is arranged downstream of the catalytic converter 23. As the catalyst 22 accommodated in the catalytic converter 70, any one of a copper zeolite catalyst and a vanadium / titania catalyst can be used in the same manner as the catalyst 22 accommodated in the catalytic converter 23. However, when any of these catalysts 22 is used, it is preferable that the upstream catalyst 22 in the catalytic converter 23 be a vanadium-titania catalyst and the downstream catalyst 22 in the catalytic converter 70 be a copper zeolite catalyst. This is because ammonia flowing out of the vanadium / titania catalyst can be removed on the copper zeolite catalyst.
[0085]
In the embodiment shown in FIG. 21, a pair of catalysts 22a and 22b are arranged in the catalytic converter 23 with a space therebetween. Further, in this embodiment, the exhaust pipe 21 is branched into a first exhaust passage 71a that is an inlet portion of the catalytic converter 23 and a second exhaust passage 71b that communicates between the pair of catalysts 22a and 22b. , 71b, a first exhaust control valve 72a and a second exhaust control valve 72b are arranged, respectively. In this embodiment, the urea aqueous solution is supplied into the exhaust pipe 21 upstream of the exhaust control valves 72a and 72b.
[0086]
In this embodiment, when the exhaust gas temperature detected by the temperature sensor 35 is lower than approximately 150 ° C., the first exhaust control valve 72a is fully opened and the second exhaust control valve 72b is fully closed as shown in FIG. It is done. At this time, the exhaust gas first passes through the upstream catalyst 22a and then passes through the downstream catalyst 22b. At this time, the temperatures of the catalysts 22a and 22b are in the ammonia-generating compound storage region. Therefore, most of the urea in the urea aqueous solution supplied at this time is stored in the upstream catalyst 22a.
[0087]
On the other hand, when the exhaust gas temperature detected by the temperature sensor 35 is between approximately 150 ° C. and 250 ° C., the first exhaust control valve 72a is fully closed and the second exhaust control valve 72b is fully opened. Passes through the second exhaust passage 71b and then passes through the downstream catalyst 22b. At this time, the urea stored in the upstream catalyst 22a is maintained as it is, and the exhaust gas NO in the downstream catalyst 22b is maintained by the supplied urea aqueous solution._x Is purified.
[0088]
On the other hand, when the exhaust gas temperature detected by the temperature sensor 35 becomes approximately 250 ° C. or higher, the first exhaust control valve 72a is fully opened again and the second exhaust control valve 72b is fully closed again as shown in FIG. . When the acceleration operation is performed, the exhaust gas detected by the temperature sensor 35 becomes 250 ° C. or higher. Therefore, when the acceleration operation is performed, the exhaust gas flows into the upstream catalyst 22a. At this time, ammonia is gradually released from a large amount of the ammonia generating compound stored in the upstream catalyst 22a, and this ammonia causes NO in the exhaust gas in the upstream catalyst 22a and the downstream catalyst 22b._x Is reduced.
[0089]
In the embodiment shown in FIG. 22, unlike the embodiment shown in FIG. 21, an aqueous urea solution is supplied into the first exhaust passage 71a downstream of the first exhaust control valve 72a.
In this embodiment, when the required load of the engine is lower than a predetermined set load, the first exhaust control valve 72a is fully closed and the second exhaust control valve 72b is fully opened. Through the exhaust passage 71b and then through the downstream catalyst 22b. At this time, the exhaust gas does not flow through the first exhaust passage 71a, and the temperature of the upstream catalyst 22a is in the ammonia generating compound storage region. Therefore, most of the urea in the urea aqueous solution supplied at this time is stored in the upstream catalyst 22a.
[0090]
On the other hand, when the required load of the engine becomes higher than the set load, the first exhaust control valve 72a is fully opened and the second exhaust control valve 72b is fully closed as shown in FIG. At this time, the exhaust gas first passes through the upstream catalyst 22a and then passes through the downstream catalyst 22b. Therefore, at this time, ammonia is gradually released from a large amount of the ammonia generating compound stored in the upstream catalyst 22a, and this ammonia causes NO in the exhaust gas in the upstream catalyst 22a and the downstream catalyst 22b._x Is reduced.
[0091]
In the embodiment shown in FIG. 23, an annular exhaust passage 74 that intersects the exhaust pipe 21 is provided in a flow path switching valve 73 provided in the exhaust pipe 21, and the first catalytic converter 23 and A second catalytic converter 70 is arranged in series.
[0092]
In this embodiment, when the required load of the engine is lower than a predetermined set load, the exhaust gas sent through the exhaust pipe 21 is directed in the direction of arrow A, that is, firstly the catalyst 22 in the first catalytic converter 23. The flow path control valve 73 is switched to the position indicated by the solid line in FIG. 23 so as to pass through and then pass through the catalyst 22 in the second catalytic converter 70. At this time, the urea aqueous solution is supplied to the upstream side of the second catalytic converter 70. At this time, the temperature of the catalyst 22 in the second catalytic converter 70 is lower than the temperature of the catalyst 22 in the first catalytic converter 23. Therefore, the urea in the supplied urea aqueous solution, that is, the ammonia generating compound is satisfactorily improved. It is stored in the catalyst 22 in 70.
[0093]
On the other hand, when the required load of the engine becomes higher than the set load, the exhaust gas sent through the exhaust pipe 21 passes through the catalyst 22 in the second catalytic converter 70 in the direction of arrow B, that is, first, and then the first The flow path control valve 73 is switched to the position indicated by the broken line in FIG. 23 so as to pass through the catalyst 22 in the catalytic converter 23. At this time, the temperature of the catalyst 22 in the second catalytic converter 70 becomes higher than the temperature of the catalyst 22 in the first catalytic converter 23, and thus the ammonia stored in the catalyst 22 in the second catalytic converter 70. Ammonia is released well from the generated compound.
[0094]
So far, the present invention has been described by way of an example in which an aqueous urea solution is used as a liquid containing an ammonia generating compound. In this case, as described above, a compound other than urea can be used as the ammonia generating compound, and a solvent other than water can be used as the solvent. Furthermore, ammonia water or a gas containing ammonia can be supplied into the exhaust passage together with the liquid containing the ammonia generating compound. In this case, the gas containing ammonia can be generated using solid urea.
[Brief description of the drawings]
FIG. 1 is an overall view of an internal combustion engine.
[Figure 2] NO_x It is a figure which shows a purification rate.
FIG. 3 is a graph showing the generated ammonia concentration.
FIG. 4 is a graph showing catalyst temperature and generated ammonia concentration.
[Figure 5] NO_x It is a time chart which shows a reduction process.
[Fig. 6] NO in exhaust gas_x It is a figure which shows the amount of urea of equivalence ratio = 1 required in order to reduce | restore.
FIG. 7 is a diagram showing the storage ratio of urea.
FIG. 8 is a graph showing the ammonia release rate.
FIG. 9 is a graph showing the ammonia release rate.
FIG. 10 is a flowchart for performing supply control of an aqueous urea solution.
FIG. 11 is a flowchart for executing supply control I;
FIG. 12 is a flowchart for executing supply control II.
FIG. 13 is a diagram showing a urea increase ratio.
FIG. 14 NO_x It is a time chart which shows a reduction process.
FIG. 15 is a flowchart for executing supply control I;
FIG. 16 NO_x It is a time chart which shows a reduction process.
FIG. 17 is a flowchart for executing supply control I;
FIG. 18 shows various examples of catalysts.
FIG. 19 is a view showing another example of a catalyst.
FIG. 20 is an overall view showing another embodiment of the internal combustion engine.
FIG. 21 is an overall view showing still another embodiment of the internal combustion engine.
FIG. 22 is an overall view showing still another embodiment of the internal combustion engine.
FIG. 23 is an overall view showing still another embodiment of the internal combustion engine.
[Explanation of symbols]
1 ... Engine body
5 ... Combustion chamber
6 ... Fuel injection valve
8 ... Intake port
10 ... Exhaust port
18… Exhaust manifold
20, 23 ... Catalytic converter
19,22 ... Catalyst
33 ... Flow control valve

Claims (21)

A catalyst suitable for reducing NO _x in the exhaust gas with ammonia under an excess of oxygen is disposed in the engine exhaust passage, and a supply means for supplying the catalyst with a liquid containing an ammonia-generating compound; A supply control means for controlling the supply amount of the liquid and an exhaust gas recirculation device for recirculating the exhaust gas into the intake passage , the catalyst being included in the liquid supplied to the catalyst At least a part of the generated ammonia generating compound is stored in the catalyst, and as the temperature of the catalyst rises, ammonia is gradually released from the ammonia generating compound stored in the catalyst, and the released ammonia is discharged into the exhaust gas. It has the function of reducing NO _x, further the temperature of the catalyst is, the ammonia generating compound which the ammonia generating compound contained in the liquid body, which is fed to the catalyst was stored and and stored in the catalyst A determination means for determining whether the ammonia generation compound storage area hardly releases ammonia from the ammonia generation area, or the ammonia release area for gradually releasing ammonia from the stored ammonia generation compound. In order to store enough ammonia generating compound in the catalyst in advance to release the required amount of ammonia when the temperature of the catalyst reaches the ammonia releasing region, a sufficient amount of the above liquid is required to be stored in the catalyst. When it is determined that the temperature is in the ammonia generating compound storage region, the catalyst is supplied to the catalyst. When the temperature of the catalyst is determined to be in the ammonia generating compound storage region by the determination means, the exhaust gas recirculation action is stopped. An exhaust purification device for an internal combustion engine. When the temperature representative of the temperature of the catalyst is lower than a predetermined temperature, the temperature of the catalyst is in the ammonia generating compound storage region, and the temperature representative of the temperature of the catalyst is a predetermined temperature. 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the temperature of the catalyst is determined to be in the ammonia release region when the temperature is higher than the range. The exhaust gas purification apparatus for an internal combustion engine according to claim 2, wherein a temperature representative of the temperature of the catalyst is an exhaust gas temperature flowing into the catalyst. 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the determining means determines that the temperature of the catalyst is in the ammonia-generating compound storage region when the engine is started. 2. The exhaust emission control device for an internal combustion engine according to claim 1, wherein the determination means determines that the temperature of the catalyst is in the ammonia-generating compound storage region when the required load of the engine is lower than a predetermined load. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the determination means determines that the temperature of the catalyst is in the ammonia-generating compound storage region during engine deceleration operation. 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1 , wherein the determination means determines that the temperature of the catalyst is in an ammonia release region during acceleration operation of the engine . The exhaust purification device for an internal combustion engine according to claim 1 , wherein the supply control means continuously supplies the liquid . The amount of ammonia generating compound contained in the supplied liquid is the amount of NO _x in the exhaust gas. The exhaust gas purification apparatus for an internal combustion engine according to claim 8, wherein an equivalence ratio required for reducing the fuel is 1 or more . 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1 , wherein the supply control means supplies a predetermined amount of the liquid in a pulse manner with a time interval . An estimation means for estimating the amount of the ammonia generating compound stored in the catalyst, and the supply control means is configured to provide the liquid when the estimated storage amount of the ammonia generating compound exceeds a predetermined maximum storage amount. The exhaust gas purification apparatus for an internal combustion engine according to claim 1 , wherein the supply of the engine is stopped . Estimating means for estimating the amount of ammonia generating compound stored in the catalyst and estimating the amount of ammonia released from the ammonia generating compound stored in the catalyst, the supply control means comprising: NO _{x in} exhaust gases that cannot be reduced by ammonia released from ammonia generating compounds To reduce exhaust gas control apparatus according to claim 1 for supplying a liquid in an amount that will be needed. The catalyst immediately generates ammonia from the liquid as soon as the liquid is supplied to the catalyst when the temperature of the catalyst is higher than a predetermined temperature, and the supply control means sets the temperature of the catalyst to a predetermined level. the amount of time higher than the temperature ammonia generating compound in said liquid NO _x in the exhaust gas The exhaust gas purification apparatus for an internal combustion engine according to claim 1 , wherein the supply amount of the liquid is controlled so that an equivalent ratio necessary for reducing the gas becomes 1 . The exhaust gas purification apparatus for an internal combustion engine according to claim 1 , wherein the liquid containing the ammonia generating compound is an aqueous urea solution . The exhaust gas purification apparatus for an internal combustion engine according to claim 1 , wherein the catalyst comprises a copper zeolite catalyst . 2. The exhaust emission control device for an internal combustion engine according to claim 1 , wherein the catalyst comprises a vanadium titania catalyst . 17. The exhaust emission control device for an internal combustion engine according to claim 16 , further comprising a zeolite catalyst layer in addition to the vanadium / titania catalyst layer . The exhaust purification device for an internal combustion engine according to claim 1 , wherein the catalyst is disposed in an engine exhaust passage, and the liquid is supplied into an engine exhaust passage upstream of the catalyst . The exhaust purification device for an internal combustion engine according to claim 1, wherein the catalyst is disposed in the engine exhaust passage, and another catalyst having an oxidizing function is disposed in the engine exhaust passage upstream of the catalyst . 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1 , wherein the catalyst comprises a pair of catalysts arranged in the engine exhaust passage so as to be spaced apart from each other . When the temperature of one of the pair of catalysts is in the ammonia generating compound storage region, the liquid is supplied to the one catalyst to store the ammonia generating compound contained in the liquid in the one catalyst, When the temperature of one catalyst reaches the ammonia release region, the NO _x in the exhaust gas in both catalysts is released by the ammonia released from the ammonia generating compound stored in the one catalyst. 21. The exhaust emission control device for an internal combustion engine according to claim 20 , wherein the exhaust gas is reduced .

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