JP4506348B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine, and more particularly to an exhaust gas purification apparatus for an internal combustion engine including an exhaust gas purification catalyst whose exhaust gas purification performance is reduced by occluding specific components in the exhaust gas.

  2. Description of the Related Art There is known an exhaust purification device that includes an exhaust purification catalyst disposed in an exhaust passage of an internal combustion engine and purifies harmful substances in exhaust. Some of these exhaust purification catalysts absorb specific components (toxic substances) in the exhaust as they are used and store them by absorption, adsorption, etc., and the exhaust purification capacity decreases as the amount of stored poisonous substances increases.

For example, as an exhaust purification catalyst, when the inflowing exhaust air-fuel ratio is lean, it absorbs nitrogen oxide (NO _x ) in the exhaust by absorption, adsorption or both, and occludes when the inflowing exhaust air-fuel ratio becomes rich and although _the NO _X storage reduction catalyst that reduces and purifies NO _X is known the and include sulfur oxides (sO _X) in the exhaust gas, _the NO _X storage is the reduction catalyst similar to the NO _X sO _X is occluded Problems arise.

SO _X in order to form the stable sulfate in _the NO _X storage reduction catalyst, there is a case where NO _X from _the NO _X storage reduction catalyst is not released from the catalyst under conditions to be released. For this reason, the amount of the sulfur component stored in the NO _X storage reduction catalyst gradually increases, and the NO _X storage capacity decreases accordingly. That is, the NO _X storage reduction catalyst stores sulfur as a specific component in the exhaust gas, resulting in a decrease in exhaust purification capability (poisoning by sulfur).

In order to eliminate sulfur poisoning of the NO _X occluding and reducing catalyst, the poisoning recovery operation the catalyst temperature is raised to a predetermined temperature higher than the normal operation while maintaining the exhaust air-fuel ratio to the stoichiometric air-fuel ratio or a rich air-fuel ratio Is required.

  In order to raise the catalyst temperature during the poisoning elimination operation to a predetermined temperature higher than that during normal operation, a relatively large amount of hydrocarbon (HC) such as unburned fuel or CO component is supplied to the catalyst, and sufficient oxygen is supplied. It is effective to supply and burn HC and CO components on the catalyst.

  For this reason, for example, in a multi-cylinder engine, some cylinders are operated at a rich air-fuel ratio during the poisoning elimination operation, and other cylinders are operated at a lean air-fuel ratio, so that a rich HC or CO component is contained in the catalyst. By supplying the air-fuel ratio exhaust gas and the lean air-fuel ratio exhaust gas containing a large amount of oxygen and mixing them on the catalyst, a slightly rich mixed exhaust gas near the stoichiometric air-fuel ratio is formed. Thus, by forming a mixed exhaust gas containing a relatively large amount of HC, CO component and oxygen on the catalyst, the HC, CO component is combusted on the catalyst, and the catalyst temperature is raised in a slightly rich air-fuel ratio atmosphere. Can be raised.

  However, when the catalyst temperature is increased by operating some of the cylinders at the rich air-fuel ratio during the poisoning elimination operation, it is necessary to supply excess fuel to the cylinders operating at the rich air-fuel ratio. If the poison elimination operation is executed frequently, there is a problem that the fuel consumption of the engine deteriorates.

Therefore, the poisoning elimination operation is executed only when a specific engine operation state is established to prevent deterioration in engine fuel consumption due to frequent implementation of the poisoning elimination operation.
An example of this type of internal combustion engine exhaust gas purification apparatus is disclosed in Patent Document 1.

In the apparatus of Patent Document 1, as described above, the sulfur poisoning elimination operation of the NO _x storage reduction catalyst is performed by operating some cylinders of the engine at a rich air-fuel ratio and other cylinders at a lean air-fuel ratio. . In addition, the apparatus of Patent Document 1 executes the sulfur poisoning elimination operation only in a specific engine operation state, thereby preventing the poisoning elimination operation from being frequently performed and deteriorating the fuel consumption of the engine. As the SO _X storage amount of the NO _X storage reduction catalyst increases, the engine operation condition for executing the poisoning elimination operation is expanded, so that the operation in the state where the SO _X storage amount of the NO _X storage reduction catalyst increases is longer. Prevents the duration.

That is, when SO _X storage amount of the NO _X occluding and reducing catalyst is small in the apparatus of Patent Document 1, for example, _the NO _X storage reduction catalyst bed temperature is relatively unless not the engine operating conditions become hot contamination-removing operation Do not start. Further, the engine operating conditions for performing the poisoning elimination operation are expanded by starting the poisoning elimination operation even under the engine operating conditions in which the catalyst bed temperature becomes relatively low as the SO _X storage amount increases.

Thereby, in the apparatus of Patent Document 1, when the SO _X storage amount is small, the poisoning elimination operation becomes difficult to be performed, and frequent poisoning elimination operation is prevented from being performed frequently, and the SO _X storage amount is reduced. When the NO increases, the poisoning elimination operation is easily performed, and the operation is prevented from continuing for a long time in a state where the SO _X storage amount of the NO _X storage reduction catalyst is increased.

JP 2000-18025 A JP 2002-256858 A JP 11-107811 A JP 2000-303825 A JP-A-11-190209 JP 2003-155925 A

As described above, in the exhaust gas purification device of Patent Document 1, the poisoning elimination operation becomes easier to execute as the SO _X storage amount of the NO _X storage reduction catalyst increases. For this reason, for example, when the SO _X storage amount becomes large, the poisoning elimination operation is executed even when the catalyst temperature is relatively low.

However, in the poisoning elimination operation, it is necessary to raise the catalyst temperature to a predetermined recovery temperature (a temperature at which sulfur is released from the NO _x storage reduction catalyst, for example, about 870 degrees K or more). The lower the catalyst temperature is, the more energy is consumed to raise the catalyst temperature to the recovery temperature at the start of the poisoning elimination operation, resulting in a problem that the fuel consumption of the engine deteriorates.

On the contrary, in the apparatus of Patent Document 1, the poisoning elimination operation becomes difficult to be performed as the SO _X storage amount of the NO _X storage reduction catalyst is smaller. For this reason, for example, the catalyst temperature is relatively high, and the SO _X occlusion amount is low even though the energy consumed to raise the catalyst temperature to the recovery temperature at the start of the poisoning elimination operation is small. During a relatively small period, the poisoning elimination operation may not be executed.

  For this reason, the apparatus of Patent Document 1 has a problem that an increase in fuel consumption due to execution of poisoning elimination operation cannot be sufficiently suppressed.

  In view of the above-described problems of the prior art, the present invention can perform an efficient poisoning elimination operation by sufficiently suppressing an increase in engine fuel consumption when performing a poisoning elimination operation for raising the temperature of an exhaust purification catalyst. An object of the present invention is to provide an exhaust gas purification apparatus for an internal combustion engine.

According to the invention described in claim 1, it reduces and purifies NO _X exhaust is occluded NO _X components in the exhaust gas when a lean air-fuel ratio, the exhaust gas flowing is occluded when it becomes a rich air-fuel ratio flowing into And an exhaust purification catalyst that reduces the exhaust purification capacity by storing the SO _X component in the exhaust, and when the storage amount of the SO _X component of the exhaust purification catalyst increases to reach a predetermined start value, In an exhaust gas purification apparatus for an internal combustion engine that starts a poisoning elimination operation in which the temperature of the exhaust purification catalyst is raised to release the stored SO _X component from the exhaust purification catalyst, the exhaust purification catalyst temperature before the start of the poisoning elimination operation is Accordingly, there is provided an exhaust gas purification apparatus for an internal combustion engine that changes the start value so as to suppress an increase in engine fuel consumption due to execution of the poisoning elimination operation .

That is, in the first aspect of the invention, the value of the specific component storage amount for starting the poisoning elimination operation is changed according to the exhaust purification catalyst temperature.
The exhaust purification catalyst temperature before the start of the poisoning elimination operation is closely related to the amount of energy consumed in the poisoning elimination operation. For example, if the poisoning elimination operation is started with the exhaust purification catalyst temperature being high, the temperature of the catalyst can be raised with a small amount of energy. There is.

In addition, when the exhaust purification catalyst temperature is low, the amount of energy consumed for increasing the temperature of the catalyst increases, so that the energy loss is smaller when the poisoning elimination operation frequency is relatively low.
On the other hand, when the poisoning elimination operation is performed according to the specific component occlusion amount of the exhaust purification catalyst, the starting value of the occlusion amount greatly affects the execution frequency of the poisoning elimination operation.

For this reason, by changing the start value of the poisoning elimination operation according to the exhaust purification catalyst temperature, the execution frequency of the poisoning elimination operation can be changed according to the exhaust purification catalyst temperature. In addition, it is possible to set an appropriate execution frequency of the poisoning elimination operation of the exhaust purification catalyst.
Therefore, according to the present invention, it is possible to efficiently perform the poisoning elimination operation of the exhaust purification catalyst.

According to the invention described in claim 2, the poisoning elimination operation is further performed when the storage amount of the SO _X component of the exhaust purification catalyst decreases and reaches a predetermined end value during execution of the poisoning elimination operation. with ends of the in accordance with the exhaust purifying catalyst temperature before start-poisoning removing operation, the changes the pre tight Ryochi to suppress an increase in engine fuel consumption due to poisoning removing operation performed, in claim 1 An internal combustion engine exhaust gas purification apparatus is provided.

That is, according to the second aspect of the invention, in addition to the start value of the poisoning elimination operation, the end value that is the specific component occlusion amount for ending the poisoning elimination operation is changed according to the exhaust purification catalyst temperature. This makes it possible to set the poisoning elimination operation execution frequency more accurately than when only the start value is changed according to the exhaust purification catalyst temperature. In addition, the specific component release rate from the exhaust purification catalyst during the poisoning elimination operation varies according to the specific component storage amount of the exhaust purification catalyst. Therefore, by changing the end value according to the exhaust gas temperature, the range of the specific component occlusion amount of the exhaust purification catalyst in which the poisoning elimination operation is performed (that is, the poisoning elimination operation execution is performed) along with the frequency of execution of the poisoning elimination operation. The release rate of the specific component at the time) can be set.
Therefore, according to the present invention, it is possible to perform a more efficient exhaust gas elimination catalyst poisoning operation.

  According to the invention of claim 3, the value of the start value is changed so that the value of the start value becomes smaller as the exhaust purification catalyst temperature before the start of the poisoning elimination operation is higher. An internal combustion engine exhaust gas purification apparatus is provided.

  According to a fourth aspect of the present invention, the start value and the end value are set such that the higher the exhaust purification catalyst temperature before the start of the poisoning elimination operation, the smaller the start value and the end value. An exhaust emission control device for an internal combustion engine according to claim 2 is provided.

  That is, in the third and fourth aspects of the invention, both the start value and the end value are changed so that the higher the exhaust purification catalyst temperature before the start of the poisoning elimination operation, the smaller the start value and the end value. change.

  Thus, according to the third and fourth aspects of the invention, the frequency of execution of the poisoning elimination operation can be increased when the exhaust purification catalyst temperature is high, and can be set low when the exhaust purification catalyst temperature is low. Canceling operation can be performed. In the invention of claim 4, the poisoning elimination operation is executed in a region where the specific component storage amount of the exhaust purification catalyst is large (region where the release rate of the specific component is large) as the exhaust purification catalyst temperature is low. In addition, the poisoning elimination operation can be performed more efficiently.

  According to the inventions described in the respective claims, the common effect of enabling an efficient exhaust purification catalyst poisoning elimination operation by changing the frequency of performing the poisoning elimination operation according to the exhaust purification catalyst temperature. Play.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a diagram illustrating a schematic configuration of an embodiment when the present invention is applied to an automobile internal combustion engine.

  In FIG. 1, reference numeral 1 denotes an automobile internal combustion engine. In this embodiment, the engine 1 is a four-cylinder gasoline engine having four cylinders # 1 to # 4, and the fuel injection valves 111 to 114 for injecting fuel directly into the cylinders are provided for the # 1 to # 4 cylinders. Is provided. As will be described later, the internal combustion engine 1 of the present embodiment is a lean burn engine that can be operated at an air / fuel ratio that is higher (lean) than the stoichiometric air / fuel ratio.

  In the present embodiment, the cylinders # 1 to # 4 are grouped into two cylinder groups including two cylinders whose ignition timings are not continuous with each other. (For example, in the embodiment of FIG. 1, the cylinder firing order is 1-3-4-2, and the cylinders # 1 and # 4 and the cylinders # 2 and # 3 each constitute a cylinder group. In addition, the exhaust port of each cylinder is connected to an exhaust manifold for each cylinder group, and is connected to an exhaust passage for each cylinder group.

  In FIG. 1, reference numeral 21a denotes an exhaust manifold for connecting the exhaust ports of the cylinder group consisting of # 1 and # 4 cylinders to the individual exhaust passage 2a, and 21b denotes the exhaust port of the cylinder group consisting of # 2 and # 3 cylinders to the individual exhaust passage 2b. Is an exhaust manifold connected to In the present embodiment, start catalysts (hereinafter referred to as “SC”) 5a and 5b made of a three-way catalyst are disposed on the individual exhaust passages 2a and 2b, respectively. Further, the individual exhaust passages 2a and 2b merge with the common exhaust passage 2 on the downstream side of the SC.

On the common exhaust passage 2, a NO _x storage reduction catalyst 7 to be described later is disposed. In FIG. 1, 29 a and 29 b indicate upstream air-fuel ratio sensors disposed upstream of the start catalysts 5 a and 5 b of the individual exhaust passages 2 a and 2 b, and 31 indicates the converter 70 outlet of the exhaust passage 2. It is the downstream air-fuel ratio sensor arranged. The air-fuel ratio sensors 29a, 29b, and 31 are so-called linear air-fuel ratio sensors that output a voltage signal corresponding to the exhaust air-fuel ratio in a wide air-fuel ratio range, but instead of the linear air-fuel ratio sensor, oxygen in the exhaust gas It is also possible to use an O ₂ sensor having a so-called Z-type output characteristic in which the concentration is detected and the output rapidly changes with the theoretical air-fuel ratio as a boundary.

Further, an electronic control unit (ECU) of the engine 1 is indicated by 30 in FIG. In this embodiment, the ECU 30 is a microcomputer having a known configuration including a RAM, a ROM, and a CPU, and performs basic control such as ignition timing control and fuel injection control of the engine 1. Further, in the present embodiment, the ECU 30 performs the basic control as described above, and the fuel of the fuel injection valves 111 to 114 during the lean air-fuel ratio operation according to the NO _X storage state of the NO _X storage reduction catalyst 7 as described later. A rich spike operation is performed in which the injection amount is changed, the engine is operated at a rich air-fuel ratio for a short time, and the stored NO _X is released from the NO _X storage reduction catalyst 7.

Further, ECU 30 causes the release by causing the sulfur component occluded in the NO _X occluding and reducing catalyst to increase the temperature of the NO _X occluding and reducing catalyst, performs sulfur poisoning recovery operation to be described later.
In order to perform these controls, a signal corresponding to the intake pressure of the engine from an intake pressure sensor 33 provided in an engine intake manifold (not shown) and an engine crankshaft (not shown) are arranged in the input port of the ECU 30. A signal corresponding to the engine speed from the rotation speed sensor 35, a signal indicating the accelerator pedal depression amount (accelerator opening) of the driver from an accelerator opening sensor 37 disposed in the vicinity of the accelerator pedal (not shown) of the engine 1, In addition, signals representing the engine coolant temperature are input from the coolant temperature sensor 39 disposed in the coolant passage of the engine 1, respectively, and # 1, # 4 and # 2, respectively, from the air-fuel ratio sensors 29a and 29b. # exhaust air-fuel ratio from 3 cylinders, NO _X occluding and reducing catalyst 7 exhaust gas air-fuel ratio at the outlet from the air-fuel ratio sensor 31 are input respectively.

In the present embodiment, the ECU 30 calculates the intake air flow rate of the engine 1 based on the engine intake pressure detected by the intake pressure sensor 33 and the engine rotational speed detected by the rotational speed sensor 35, and calculates the stoichiometric air-fuel ratio of the engine or rich air. Controls the fuel injection amount at the time of fuel ratio operation.
Further, the ECU 30 controls the fuel injection amount during the lean air-fuel ratio operation of the engine based on the accelerator opening detected by the accelerator opening sensor 37 and the engine speed.

The output port of the ECU 30 is connected to the fuel injection valves 111 to 114 of each cylinder via a fuel injection circuit (not shown) in order to control the fuel injection amount and fuel injection timing to each cylinder.
As these fuel injection controls, any known control can be used, and a detailed description thereof will be omitted here.

Next, the NO _x storage reduction catalyst 7 of this embodiment will be described.
The NO _x storage reduction catalyst 7 of the present embodiment uses a carrier such as cordierite formed in a honeycomb shape, for example, and forms an alumina coating on the surface of the carrier. On the alumina layer, for example, potassium K, sodium Na, At least one component selected from alkali metals such as lithium Li and cesium Cs, alkaline earths such as barium Ba and calcium Ca, lanthanum La, cerium Ce and yttrium Y, and platinum Pt It carries a precious metal. When the air-fuel ratio of the exhaust gas _the NO _X storage reduction catalyst is flowing is lean, NO _X in the exhaust gas (NO _2, NO) absorbed occludes by adsorption or both, decrease the oxygen concentration in the inflowing exhaust gas then perform absorption and release action of the NO _X to release the occluded NO _X in the form of NO _2.

For example, when the engine 1 is operated at a lean air-fuel ratio and the exhaust gas flowing into the NO _X storage reduction catalyst 7 has a lean air-fuel ratio, NO _X (NO, NO ₂ ) in the exhaust is transferred to the NO _X storage reduction catalyst 7. The NO _x concentration in the exhaust gas that has been occluded and passed through the NO _x storage reduction catalyst 7 becomes almost zero.
Further, when the oxygen concentration in the inflowing exhaust gas is greatly reduced (i.e., when the air-fuel ratio of the exhaust gas becomes stoichiometric or rich air-fuel ratio), NO _X occluded in the NO _X occluding and reducing catalyst 7 Ya CO in the exhaust It is reduced by a component that functions as a reducing agent such as H ₂ or an HC component (hereinafter referred to as a reducing component) and released from the NO _x storage reduction catalyst 7 in the form of NO ₂ .

In the present embodiment, ECU 30 is operated in a short time a rich air-fuel ratio of the engine 1 every time the amount of the NO _X occluded in the NO _X occluding and reducing catalyst 7 reaches a predetermined value, the rich air-fuel ratio to the NO _X occluding and reducing catalyst Rich spike operation is performed to supply exhaust gas. Thus, NO _X occluding and reducing catalyst 7 occluded NO _X from is released in the form of NO _2, NO _X occluding and reducing catalyst can be prevented from being saturated by the absorbed NO _X.
Since any known method can be used as the rich spike operation in the present embodiment, detailed description thereof is omitted here.

However, when the NO _x storage reduction catalyst 7 as described above is used as an exhaust purification catalyst, there is a problem if a specific component such as sulfur oxide (SO _x ) is contained in the exhaust.
That is, when contains SO _X or the like during the lean air-fuel ratio exhaust, SO _X in the exhaust gas is occluded in the NO _X occluding and reducing catalyst 7 in exactly the same mechanism as the NO _X. However, since SO _x forms a compound that is much more stable than NO _{x when} it is occluded in the NO _x storage-reduction catalyst, a rich spike operation was performed simply by supplying the exhaust gas with a rich air-fuel ratio to the catalyst 7. Then, even though NO _x can be released, it is insufficient to release SO _x .

For this reason, if SO _x is contained in the exhaust gas, even if the rich spike operation is periodically performed, SO _x gradually accumulates in the catalyst 7, so that the NO _x storage reduction catalyst 7 can store NO. _The amount of _X (NO _X storage capacity) decreases by the amount of SO _X stored in the catalyst. Therefore, the amount of occluded SO _X increases, the _the NO _X storage reduction catalyst 7 will not be able to occlude NO _X in the exhaust gas, the _the NO _X storage and reduction catalyst 7 still unpurified of the NO _X is not occluded passage To come.

That is, the NO _x storage-reduction catalyst 7 causes so-called sulfur poisoning in which the exhaust purification ability is reduced by storing SO _x as a specific component in the exhaust.

_The NO _X storage and reduction catalyst 7 is occluded in the SO _X is, _the NO _X storage reduction by maintaining _the NO _X storage reduction catalyst 7 in a predetermined high-temperature state at the stoichiometric air-fuel ratio or a rich air-fuel ratio atmosphere (e.g. 870 degrees or more K) It is known to be released from the catalyst 7. For this reason, when SO _X is contained in the exhaust gas, every time the amount of SO _X stored in the NO _X storage reduction catalyst 7 increases, the NO _X storage reduction catalyst 7 is supplied with exhaust gas having a stoichiometric or rich air fuel ratio. It is necessary to carry out the poisoning elimination operation of holding the NO _x storage reduction catalyst 7 at a temperature higher than the normal operating temperature while supplying it.

  For example, in Patent Document 1 described above, exhaust gas having a lean air-fuel ratio and a rich air-fuel ratio are alternately supplied to the catalyst, and HC in the rich air-fuel ratio exhaust gas is burned on the catalyst using oxygen in the lean air-fuel ratio exhaust gas. The temperature of the catalyst is raised by this to perform the poisoning elimination operation.

  In this way, by separately supplying lean air-fuel ratio and rich air-fuel ratio exhaust gas to the catalyst to raise the temperature of the catalyst, a device for separately supplying HC or the like or secondary air to the exhaust passage upstream of the catalyst is provided. In addition, flammable components such as HC and oxygen can be easily supplied to the catalyst.

However, in the apparatus of Patent Document 1, as described above, the catalyst temperature for performing the poisoning elimination operation is changed according to the SO _X storage amount of the NO _X storage reduction catalyst 7, that is, the catalyst becomes lower as the SO _X storage amount increases. Since the poisoning elimination operation is performed from the temperature, there is a problem that the poisoning elimination operation cannot always be performed efficiently.

  In this embodiment, as described below, the above problem is solved by changing the execution frequency of the poisoning elimination operation according to the exhaust purification catalyst temperature before the start of the poisoning elimination operation.

In the present embodiment, the poisoning removing operation of the NO _X occluding and reducing catalyst 7 is performed based on the SO _X storage amount of the NO _X occluding and reducing catalyst 7. That is, in the present embodiment, the ECU 30 estimates the SO _X storage amount of the NO _X storage reduction catalyst 7 based on the engine operating state as will be described later, and when the SO _X storage amount increases to a predetermined start value. Start poisoning elimination operation regardless of catalyst temperature. While the poisoning elimination operation is being executed, the SO _X storage amount of the NO _X storage reduction catalyst 7 decreases due to the release, but in this embodiment, the SO _X storage amount of the NO _X storage reduction catalyst 7 reaches a predetermined end value. When it drops, the poisoning elimination operation is terminated.

However, in the present embodiment, the start value of the contamination-removing operation is not a constant value, depending on the contamination-removing operation before the start of the NO _X occluding and reducing catalyst 7 bed temperature, the higher the bed temperature start value is smaller Change to be.

FIG. 2 is a diagram illustrating an example of the relationship between the setting of the start value and the exhaust temperature in the present embodiment.
The vertical axis of FIG. 2 indicates the SO _X storage amount of the NO _X storage reduction catalyst 7, and the horizontal axis indicates the NO _X storage reduction catalyst 7 bed temperature (catalyst temperature) in a state before the start of the poisoning elimination operation. Also, the solid line in FIG. 2 is the SO _X storage amount (that is, the start value) at which the poisoning elimination operation is started, and the dotted line is the SO _X storage amount (the end value) at which the poisoning elimination operation is completed.

As shown in FIG. 2, in this embodiment, the start value of the poisoning elimination operation is set so as to decrease linearly as the exhaust purification catalyst temperature rises, and the end value becomes a constant value regardless of the catalyst temperature. Is set.
In the example of FIG. 2, every time the SO _X storage amount increases during the lean air-fuel ratio operation of the engine and reaches the start value (solid line), the poisoning elimination operation of the NOx storage reduction catalyst 7 is started, and the poisoning elimination operation is executed. _the NO _X storage reduction SO _X storage amount in the catalyst 7 is the end value of 2 (dotted line) poisoning removing operation of the drops SO _X until finished by the release of SO _X in.

For this reason, the interval between the start value and the end value is stored in the amount of SO _X released in one poisoning elimination operation (that is, until the next poisoning elimination operation is started after the poisoning elimination operation is completed). SO _x amount). When this amount is referred to as the processing SO _X amount per poisoning operation, as shown in FIG. 2, this processing SO _X amount becomes smaller as the temperature of the NO _X storage reduction catalyst 7 becomes higher. At times, ΔSM, and at high temperatures, ΔSH (ΔSL>ΔSM> ΔSH).

For this reason, if the storage amount per unit time of the NO _x storage reduction catalyst 7 at each temperature of the exhaust purification catalyst (the amount of SO _x generated in the engine 1) is the same, the higher the exhaust purification catalyst, the shorter the coverage. The poison elimination operation is repeated. Actually, in the operation region in which the temperature of the NO _x storage reduction catalyst 7 becomes high before the poisoning elimination operation, the exhaust temperature is high and the engine load is also increased, so the operation region in which the temperature of the NO _x storage reduction catalyst 7 is lowered (engine) since the load is also increased SO _X generation amount per unit time the engine than the exhaust temperature is low operating region) lower, the more contamination-removing operation execution interval increases further _the NO _X storage reduction catalyst 7 temperature is shortened.

As described above, in a region where the temperature of the NO _x storage reduction catalyst 7 is high, the temperature of the NO _x storage reduction catalyst 7 can be raised to a temperature necessary for elimination of poisoning with less energy. Less.

Therefore, by changing the poisoning elimination operation start value according to the exhaust temperature as shown in FIG. 2 and setting it to be a smaller value as the exhaust temperature is higher, for example, when the vehicle is traveling at high speed, In an area where the exhaust gas temperature (the temperature of the NO _X storage reduction catalyst 7) is high and an efficient poisoning elimination operation can be executed, the poisoning elimination operation is executed at short intervals in small increments, such as when the vehicle is running at a low speed. In the operation region where the exhaust gas temperature is low and the energy required for performing the poisoning elimination operation increases, it is possible to set the poisoning elimination operation execution interval longer.

  That is, according to the present embodiment, in the engine operation state in which an efficient poisoning elimination operation can be performed, the poisoning elimination operation execution frequency is set frequently, and the engine operation in which the efficient poisoning elimination operation cannot be performed. Since the frequency of performing the poisoning elimination operation can be set low in the state, it is possible to efficiently perform the poisoning elimination operation as a whole, and to suppress the deterioration of the fuel consumption of the engine.

Next, another embodiment of the present invention will be described with reference to FIGS.
FIG. 3 is a diagram showing the setting of the start value and end value of the poisoning elimination operation in the present embodiment. In the embodiment of FIG. 2, it had been changed in accordance with only the start value of the contamination-removing operation in the NO _X occluding and reducing catalyst 7 temperature, end value with start value as shown in FIG. 3 in the present embodiment is also NO _X The point which is changed according to the temperature of the storage reduction catalyst 7 is different from the embodiment of FIG.

In the present embodiment, the end value of the poisoning elimination operation is set to a smaller value as the bed temperature of the NO _X storage reduction catalyst 7 before the elimination of the poisoning elimination operation is higher, as in the case of the start value (in FIG. The end value is shown as a straight line parallel to the start value).
Thus, the poisoning elimination operation can be performed more efficiently by changing the end value of the poisoning elimination operation together with the start value in accordance with the temperature of the NO _x storage reduction catalyst 7.

That is, SO _X during the poisoning recovery operation occluding from _the NO _X storage reduction catalyst 7 of the NO _X occluding and reducing catalyst 7 is released, the release rate is _the NO _X storage reduction catalyst temperature during the poisoning recovery operation is the same If so, the larger the amount of SO _X stored by the NO _X storage reduction catalyst, the larger the amount.

4, in the case of performing contamination-removing operation at a constant temperature, NO _X from storage reduction catalyst SO _X release (desorption) rate (mg / sec) and _the NO _X storage reduction catalyst occluded the SO _X It is a figure which shows typically the relationship with quantity (mg).

As shown in FIG. 4, the SO _X release rate increases rapidly as the SO _X storage amount (retention amount) of the NO _X storage reduction catalyst increases. When the start value and the end value are set to be straight lines parallel to each other as shown in FIG. 3, the SO _X release amount (SO _X treatment) in one poisoning operation regardless of the NO _X storage reduction catalyst temperature. Amount) has the same value (FIG. 3, ΔS).

However, even when SO _X having the same amount of ΔS is released, as shown in FIG. 4, the NO _X storage reduction catalyst has a large SO _X storage amount (indicated by A in FIG. 3) and a small region (the same , B)), the release speed is significantly different, so the time required for release, that is, the time required for the poisoning elimination operation is also significantly different.

In the example of FIG. 3, since the start value and the end value are set to be straight lines parallel to each other, the SO _X processing amount in one poisoning elimination operation is the same value ΔS. However, as can be seen from FIG. 3, the poisoning removing operation of the NO _X occluding and reducing catalyst when the catalyst temperature is low is to be done in the area SO _X storage amount is large. As described above, in this region, the SO _X release speed at the time of the poisoning elimination operation is very high, so that the amount of SO _X of ΔS can be released in a shorter time compared to the region where the SO _X storage amount is small. it can. This means that in a region where the SO _X storage amount is large, the time required for the poisoning elimination operation for processing the same amount of SO _X can be shortened, and the amount of energy consumed for the poisoning elimination operation can be reduced accordingly. It means that it can be reduced.

  For this reason, not only the start value of the poisoning elimination operation as shown in FIG. 3 but also the end value is set to be smaller as the catalyst temperature is higher (larger as the catalyst temperature is lower), so that it is efficient even when the catalyst temperature is low. This makes it possible to perform a simple poisoning elimination operation.

Further, as shown in FIG. 3, when the start value and the end value are set as straight lines parallel to each other, the amount of SO _x generated in the engine becomes small in the operating state where the NO _x storage reduction catalyst temperature is low, and therefore ΔS time required for the amount of SO _X is occluded in the NO _X occluding and reducing catalyst is _the NO _X storage reduction catalyst becomes longer as compared with the case of high temperature.

Therefore, even in the example of FIG. 3, the frequency of performing the poisoning elimination operation increases as the temperature of the NO _x storage reduction catalyst 7 increases. As a result, in the present embodiment, the frequency of performing the poisoning elimination operation in the high-temperature region with high efficiency is increased, and the efficient poisoning elimination operation can be performed in the constant-temperature region with a relatively low frequency of execution. Therefore, it is possible to perform a highly efficient poisoning elimination operation as a whole.

In FIG. 3, the start value and the end value of the poisoning elimination operation are set to be parallel straight lines. For example, when the temperature of the NO _x storage reduction catalyst 7 is low, the start value is higher than when it is high. The end value is set as shown by the dotted line in FIG. 3 so that the difference between the value and the end value (that is, the SO _X processing amount in one poisoning elimination operation) becomes small, and the NO _X storage reduction catalyst temperature becomes Even when the frequency is low, it is possible to prevent the frequency of performing the poisoning elimination operation from decreasing so much. In this case, although the frequency of performing the poisoning elimination operation in the low temperature region increases, as described above, the poisoning elimination operation is performed in a state where the SO _X storage amount is large and the SO _X release rate is high in the low temperature region. Even if the execution frequency of the poisoning elimination operation increases, an increase in the fuel consumption of the engine is suppressed.

FIG. 5 is a flowchart specifically explaining the poisoning elimination operation of the present embodiment.
In the present embodiment, the operation of FIG. 5 is performed as a routine executed by the ECU 30 at regular intervals.

  When the operation starts in FIG. 5, it is determined in step 501 whether the value of the poisoning elimination operation execution flag S is set to 1. The flag S is a flag indicating whether or not the poisoning elimination operation is currently being executed. The flag S is set to 1 (execution) at the start of the poisoning elimination operation in step 513 described later, and the poisoning elimination operation in step 521. Set to 0 (not running) upon completion.

If S ≠ 1 in step 501, that is, if the poisoning elimination operation is not currently being executed, the process proceeds to step 503, where the current NO _X storage reduction catalyst 7 bed temperature is read.
The NO _x storage reduction catalyst 7 bed temperature can be directly detected by arranging a temperature sensor in the catalyst bed, but in this embodiment, the catalyst bed temperature is calculated (estimated) based on the engine operating state. .

That is, the temperature change per unit time of the NO _x storage reduction catalyst 7 is a function of the difference between the catalyst temperature and the exhaust gas temperature and the exhaust gas flow rate. Therefore, in this embodiment, the temperature difference between the catalyst and the exhaust gas and the exhaust gas flow rate are changed in advance to actually measure the catalyst temperature rise per unit time, and the temperature difference between the catalyst and the exhaust gas, the exhaust gas flow rate and the catalyst temperature rise per unit time are measured. The relationship with the width is obtained and stored in the ROM of the ECU 30 in the form of a numerical table. Further, the relationship between the engine operating state (load, rotation speed), the exhaust temperature, and the exhaust flow rate is obtained through experiments and stored in the ROM of the ECU 30 in the form of a similar numerical table.

The ECU 30 calculates the exhaust temperature and the exhaust flow rate based on the engine operating state at regular intervals from the start of the engine by a catalyst temperature calculation operation (not shown) that is separately executed, and stores the cooling water temperature at the start of the engine in the NO _X storage. As the initial value of the reduction catalyst 7 temperature, the catalyst temperature change amount per unit time is calculated from the calculated exhaust temperature, flow rate and catalyst temperature, and the current NO _X storage reduction catalyst temperature is obtained by sequentially integrating the temperature change amount. Is calculated.

In step 503, the current NO _x storage reduction catalyst 7 temperature calculated by the catalyst temperature calculation operation is read.
In step 505, the start value CSS and the end value CSE of the poisoning elimination operation are set from the relationship shown in FIG. 3 using the NO _x storage reduction catalyst 7 temperature read in the above.
Next, at step 507, the current SO _X storage amount CS of the NO _X storage reduction catalyst 7 is read.

In the present embodiment, the ECU 30 calculates (estimates) the SO _X storage amount of the NO _X storage reduction catalyst 7 by a SO _X storage amount calculation operation (not shown) that is separately executed.
The amount of SO _X stored in the NO _X storage reduction catalyst per unit time during lean air-fuel ratio operation is proportional to the amount of SO _X generated in the engine 1. On the other hand, since almost the entire amount of SO _x generated in the engine is due to the combustion of sulfur in the fuel, the amount of SO _x generated per unit time of the engine is proportional to the amount of fuel injection of the engine. Therefore, the amount of SO _X stored by the NO _X storage reduction catalyst 7 per unit time is proportional to the fuel injection amount of the engine.

Therefore, in the SO _X storage amount calculation operation, during the lean air-fuel ratio operation of the engine, the ECU 30 obtains the fuel injection amount of the engine per unit time, and the value obtained by multiplying the fuel injection amount by a coefficient obtained in advance by experiment is NO. _The amount of SO _X stored per unit time by the _X storage reduction catalyst. Accordingly, the current SO _X storage amount CS of the NO _X storage reduction catalyst is accurately calculated (estimated) by integrating the SO _X storage amount per unit time during the lean air-fuel ratio operation.
In step 507 the current SO _X storage amount calculated by the SO _X storage amount calculation operation is read.

Note that when the engine is operated at the stoichiometric air-fuel ratio or rich air-fuel ratio, SO _{X in} the exhaust is not stored in the NO _X storage reduction catalyst, so the calculation of the SO _X storage amount is performed only during lean air-fuel ratio operation. Done. Further, during the execution of the poisoning recovery operation as will be described later, SO _X storage amount in accordance with the release of SO _X is reduced.

After reading the SO _X storage amount of the NO _X storage reduction catalyst 7 as described above, in step 509, the current SO _X storage amount CS of the NO _X storage reduction catalyst 7 is equal to or greater than the poisoning elimination operation start value CSS set in step 505. It is determined whether or not.

If CS ≧ CSS in step 509, the current SO _X storage amount of the NO _X storage reduction catalyst 7 has increased beyond the start value CSS of the poisoning elimination operation elimination operation, and the process proceeds to step 511. Start poisoning elimination operation.

As described above, in this embodiment, the poisoning elimination operation is performed by operating some cylinders at a rich air-fuel ratio.
That is, when the poisoning elimination operation is started in step 511, the ECU 30 operates the # 1 and # 4 cylinders of the engine 1 with a rich air-fuel ratio and the # 2 and # 3 cylinders with a lean air-fuel ratio. The lean air-fuel ratio and the rich air-fuel ratio are selected so that the average operating air-fuel ratio of the engine 1 as a whole is slightly richer than the stoichiometric air-fuel ratio.

As a result, the NO _x storage reduction catalyst 7 has a rich air-fuel ratio exhaust from the # 1 and # 4 cylinders containing a large amount of combustible components such as unburned HC and CO, and a # 2 and # 3 cylinder containing a large amount of oxygen. The lean air-fuel ratio exhaust gas reaches the exhaust gas, and both of them are mixed on the catalyst and unburned HC and CO components are combusted, and the catalyst temperature rises due to the combustion heat.

In the poisoning elimination operation, the rich air-fuel ratio is kept while the temperature of the NO _x storage reduction catalyst 7 is brought to a predetermined temperature (about 870 ° K or higher, preferably about 900 ° K or higher) at which SO _X release occurs. Set the air-fuel ratio difference between the operating cylinder and the lean air-fuel ratio to be large (the operating air-fuel ratios of the # 1 and # 4 cylinders are very rich, and the operating air-fuel ratios of the # 2 and # 3 cylinders are very lean) However, after the temperature of the NO _x storage reduction catalyst 7 reaches the predetermined temperature, the air-fuel ratio difference is set to a relatively small value sufficient to maintain the NO _x storage reduction catalyst 7 at the predetermined temperature. Is done.

  After the poisoning elimination operation is started in step 511, the value of the aforementioned poisoning elimination operation execution flag S is set to 1 in step 513.

If the SO _X storage amount CS of the NO _X storage reduction catalyst 7 has not reached the poisoning elimination operation start value CSS in step 509, steps 511 and 513 are not executed, but immediately after step 509, this time. The execution of the operation is terminated. In this case, the poisoning elimination operation is not started and normal operation is continued.

On the other hand, if the value of the poisoning elimination operation execution flag S is set to 1 in step 513, it is determined that S = 1 (during the execution of poisoning elimination operation) in step 501 when the next main operation is executed.
In this case, step 515 is executed next, and the current SO _X storage amount CS of the NO _X storage reduction catalyst 7 is read.

As described above, in the poisoning removing operation performed for SO _X occluding from _the NO _X storage reduction catalyst 7 is released, SO _X storage amount of the NO _X occluding and reducing catalyst 7 is reduced. Further, the decrease rate is equal to the SO _X release rate from the NO _X storage reduction catalyst.

In the present embodiment, in the SO _X storage amount calculation operation separately executed by the ECU 30, the value of the SO _X storage amount CS is decreased at regular intervals during execution of the poisoning elimination operation. The weight loss per single SO _X storage amount CS is a value proportional to the SO _X release rate is determined based on the current value of SO _X storage amount CS in relation of FIG. Thus, the value of CS accurately corresponds to the actual SO _X storage amount of the NO _X storage reduction catalyst 7 even during the execution of the poisoning elimination operation.

After the SO _X storage amount CS is read in Step 515, it is determined in Step 517 whether or not the current SO _X storage amount CS has decreased to the poisoning elimination operation end value CSE set in Step 505.
If the SO _X storage amount CS has decreased to the poisoning elimination operation end value CSE in step 517 (CS ≦ CSE), then step 519 is executed to stop the poisoning elimination operation.

In this case, the ECU 30 resumes the operation at the air-fuel ratio (lean air-fuel ratio that is the same for all cylinders) before starting the poisoning elimination operation of the cylinders # 1 to # 4. Thereby, the SO _X storage amount of the NO _X storage reduction catalyst 7 starts to increase again.
If CS> CSE in step 517, the execution of this operation is terminated after step 517, and the poisoning elimination operation is continued.

Incidentally, in the case of changing in accordance with the exhaust temperature poisoning recovery operation start value only as in the example of FIG. 2, NO _X occluding and reducing on the basis of step 505, only the value of the start value CSS is the relationship of FIG. 2 It is set according to the temperature of the catalyst 7, and the end value CSE is set to an appropriate constant value.

It is a figure explaining schematic structure of an embodiment at the time of applying the present invention to an internal-combustion engine for vehicles. It is a figure which shows the example of a setting of the poisoning elimination operation start value according to a catalyst temperature. It is a figure which shows the example of a setting of the poisoning elimination operation start value and end value according to a catalyst temperature. The relationship between the SO _X release rate and SO _X storage amount from _the NO _X storage reduction catalyst is a diagram schematically illustrating. It is a flowchart explaining an example of poisoning elimination operation of this invention concretely.

Explanation of symbols

1 Engine body 2 Exhaust passage 5a, 5b Start catalyst (SC)
7 NO _X storage reduction catalyst 30 ECU (electronic control unit)

Claims (4)

With the exhaust gas flowing the occluding NO _X components in the exhaust gas when a lean air-fuel ratio, the exhaust gas flowing to reduction purification of occluded NO _X when it is rich air-fuel ratio, storing the SO _X components in the exhaust The exhaust purification catalyst has a reduced exhaust purification capability, and when the storage amount of the SO _X component of the exhaust purification catalyst increases and reaches a predetermined start value, the temperature of the exhaust purification catalyst is raised to increase the storage In the exhaust gas purification apparatus for an internal combustion engine that starts the poisoning elimination operation for releasing the released SO _X component from the exhaust gas purification catalyst,
An exhaust gas purification apparatus for an internal combustion engine that changes the start value so as to suppress an increase in engine fuel consumption due to execution of the poisoning elimination operation in accordance with an exhaust purification catalyst temperature before the poisoning elimination operation is started. Further, when the poisoning elimination operation is executed, when the storage amount of the SO _X component of the exhaust purification catalyst decreases and reaches a predetermined end value, the poisoning elimination operation is terminated and the poisoning elimination operation is started. depending on the front of the exhaust gas purifying catalyst temperature, the change of the pre-tight Ryochi to suppress an increase in engine fuel consumption due to poisoning removing operation performed, the exhaust purification system of an internal combustion engine according to claim 1.   The exhaust purification device for an internal combustion engine according to claim 1, wherein the value of the start value is changed so that the value of the start value becomes smaller as the exhaust purification catalyst temperature before the start of the poisoning elimination operation is higher.   3. The internal combustion engine according to claim 2, wherein the start value and the end value are changed so that the start value and the end value become smaller as the exhaust purification catalyst temperature before the start of the poisoning elimination operation is higher. Exhaust purification equipment.

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