JP4177007B2 - Exhaust gas purification apparatus and purification method for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas purification apparatus for an internal combustion engine capable of accurately determining and processing the purge timing of NOx in an internal combustion engine equipped with a NOx storage catalyst, and a purification method therefor.
[0002]
[Prior art]
In a lean burn internal combustion engine that burns an air-fuel mixture that is leaner than the stoichiometric air-fuel ratio, an exhaust gas purification device that uses a NOx storage catalyst is used to purify exhausted nitrogen oxides (hereinafter referred to as NOx). Yes. This exhaust gas purification device adsorbs NOx exhausted during lean burn operation of an internal combustion engine to a NOx storage catalyst and switches the air-fuel ratio to rich at every predetermined cycle to reduce the oxygen concentration in the exhaust gas, thereby reducing NOx. At the same time as NOx stored in the storage catalyst is released, a reduction process is performed to purify the exhaust gas.
[0003]
For example, Japanese Patent No. 2600492 and Japanese Patent No. 2586739 are known as disclosures of such a technique. The former discloses a technique for estimating the timing at which the air-fuel ratio is periodically switched to rich in order to release the NOx stored in the NOx storage catalyst based on the accumulated value of the load amount and the accumulated value of the rotational speed of the internal combustion engine. In the latter case, the NOx occlusion amount is estimated from the accumulated value of the load amount (surge tank pressure) of the internal combustion engine and the accumulated value of the rotational speed in the same manner as the former, and the NOx is determined by the temperature of the NOx occlusion catalyst. Has been disclosed that determines the switching timing (purge timing) in consideration of the exhaust gas temperature and the like.
[0004]
[Problems to be solved by the invention]
As described above, in the conventional NOx release reduction process, the purge amount is usually determined by estimating the stored absolute amount by adding the temperature of the NOx storage catalyst to the accumulated value of the load and rotation speed of the internal combustion engine. It was. However, the NOx storage capacity per unit time in the NOx storage catalyst varies depending on the NOx storage amount at that time, and the amount of NOx discharged from the internal combustion engine and flowing into the NOx storage catalyst is, for example, that of the internal combustion engine. Since it changes depending on the load, when the purge timing is determined by estimating only the absolute value of the NOx occlusion amount, the exhaust gas is not occluded by the NOx occlusion catalyst when the NOx amount per time exhausted is large. It could be discharged from the tube.
[0005]
FIG. 12 illustrates such a state. In FIG. 12, the horizontal axis indicates time, and the vertical axis indicates the NOx flow rate flowing into the NOx storage catalyst. Here, it is assumed that the NOx flow rate per time is a constant value. explain. (A) of FIG. 12 shows the case where the NOx flow rate flowing into the NOx storage catalyst is large, and (b) shows the case where it is small. The accumulated amount of NOx flowing into the NOx occlusion catalyst increases with time, but the range indicated by the oblique lines in the figure is the accumulated amount, that is, the NOx occlusion amount, and in FIG. 12, the NOx occlusion of (a) and (b). The state when the amount is the same is shown.
[0006]
Thus, even if the NOx occlusion amount is the same, the NOx occlusion capacity per unit time varies depending on the NOx occlusion amount, and when the flow rate of NOx flowing in is large as shown in FIG. A part of the NOx is not occluded and flows out to the downstream side, that is, the exhaust pipe. However, when the flow rate of NOx flowing in is small as shown in FIG. In addition, it is possible to continue operation by lean burn. The arrow Z in the figure indicates the amount of NOx storage catalyst that can be stored at the present time (storage capacity per unit time). Since (a) and (b) have the same NOx storage amount, The storage capacity is the same.
[0007]
Therefore, in the case of estimating only the absolute amount of NOx occluded in the NOx occlusion catalyst as in the conventional NOx release reduction process, and determining that the amount has exceeded the allowable value and switching the operating state from lean to rich, When the flow rate of NOx flowing into the NOx storage catalyst changes per hour, switching of the appropriate operating state cannot be performed, and the switching is delayed so that the exhaust gas is deteriorated or the operating state is switched quickly (rich). There was a problem of reducing the merit for fuel consumption.
[0008]
The present invention has been made to solve such a problem. The amount of NOx that can be processed by the NOx storage catalyst is calculated accurately and simply, and compared with the amount of inflowing NOx. An object of the present invention is to obtain an exhaust gas purification device and a purification method for an internal combustion engine that can prevent deterioration of exhaust gas and maintain good fuel efficiency by determining the timing of reduction (purge timing). is there.
[0009]
[Means for Solving the Problems]
  The exhaust gas purifying apparatus according to the present invention provides a NOx storage catalyst provided in an exhaust passage of an internal combustion engine, and a NOx flow rate per unit time flowing through the exhaust passage using operating conditions such as a load and a rotation speed of the internal combustion engine as parameters. The NOx storage amount estimation calculating means for estimating and calculating, the NOx storage amount estimating and calculating means for estimating and calculating the NOx storage amount stored by the NOx storage catalyst using the operating condition of the internal combustion engine as a parameter, and the noble metal carried by the NOx storage catalyst NOx reductionPer unit timeNOx reduction amountEstimated calculation as a function of the temperature of the NOx storage catalyst and the amount of reducing gas per unit time flowing into the NOx storage catalystNOx reduction amount estimation calculating means for decomposing the NOx by the noble metal supported by the NOx storage catalystPer unit timeThe amount of NOx decompositionEstimated calculation as a function of the temperature of the NOx storage catalystNOx decomposition amount estimation calculation means, NOx storage amount calculated by the NOx storage amount estimation calculation means, NOx reduction amount calculated by the NOx reduction amount estimation calculation means, and NOx decomposition amount calculated by the NOx decomposition amount estimation calculation means NOx processable amount estimation calculation means for estimating the NOx processable amount per unit time from the output of the NOx flow rate estimation calculation meansPer unit timeThe estimated value of the NOx flow rate and the NOx processable amount estimation calculating means outputPer unit timeComparing and determining means for comparing the estimated value of the NOx processable amount and determining the NOx purge timing,The comparison meansThe NOx flow rate per unit time exceeds the NOx processable amount per unit time.DeterminedThe operation of the internal combustion engine is switched to NOx purge.
[0010]
  In addition, a reduction amount estimation calculation means for estimating and calculating the reduction amount of NOx by the noble metal carried by the NOx storage catalyst, and a decomposition amount estimation calculation means for estimating and calculating the decomposition amount of NOx are provided, and a NOx processable amount estimation calculation is provided. The means calculates the NOx treatable amount per unit time from the sum of the NOx occlusion amount per unit time, the NOx reduction amount per unit time, and the NOx decomposition amount per unit time.
  In addition,NOx storage amount estimation calculation meansBut,AboveAs a function of the storage rate, which is the ratio between the maximum storage amount of the NOx storage catalyst and the current storage amount,NOx storage amountIs calculated.
[0011]
  Furthermore,AboveThe storage amount at the present time that the NOx storage amount estimation calculation means estimates isAboveNOx flow rate per unit timeAboveCompare NOx storage amount per unit time,AboveNOx flow rate per unit timeMore than the amount of NOx stored per unit timeWhen it ’s bigAboveAccumulate NOx occlusion amount per unit time,AboveNOx flow rate per unit timeLess than NOx occlusion amount per unit timeIn this case, the NOx flow rate per unit time is integrated.
[0012]
  Further, the NOx occlusion amount per unit time is calculated as a function of the occlusion rate, which is the ratio between the maximum occlusion amount of the NOx occlusion catalyst and the current occlusion amount.
[0013]
  Further, the maximum storage amount of the NOx storage catalyst is calculated as a function of the temperature of the NOx storage catalyst and the NOx flow rate per unit time flowing into the NOx storage catalyst.
[0014]
  Further, in the exhaust gas purification method according to the present invention, a NOx storage catalyst is provided in the exhaust passage of the internal combustion engine, and the NOx stored by the NOx storage catalyst is released and reduced by lowering the oxygen concentration of the exhaust gas. In NOx storage catalyst purification control, the NOx flow rate per unit time flowing in the exhaust passageAnd a unit time given as a function of the NOx occlusion amount per unit time given as a function of the NOx occlusion rate per unit time in the NOx occlusion catalyst, the temperature of the NOx occlusion catalyst, and the amount of reducing gas. The NOx reduction amount per unit time is estimated and calculated from the NOx reduction amount per unit and the NOx decomposition amount per unit time given as a function of the temperature of the NOx storage catalyst,Comparing both, the NOx flow rate per unit time isMore than the amount of NOx that can be processed per unit timeWhen it ’s bigAboveWhile reducing the oxygen concentration of the exhaust gas to release and reduce NOx, the per unit timeNOx storage amountIs calculated as a function of the storage rate, which is the ratio between the maximum storage amount of the NOx storage catalyst and the current storage amount.
[0016]
  Furthermore, the NOx treatable amount per unit time is given as a dimensionless number with respect to the storage rate of the NOx occlusion catalyst, and NOx treatment per unit time can be performed from this dimensionless number and the NOx flow rate per unit time. The amount is calculated.
  Furthermore,AboveAn upper limit and a lower limit are set for the NOx flow rate per unit time.AboveNOx flow rate per unit timeAboveWhen the upper limit or lower limit is exceededAboveThe NOx processable amount per unit time is estimated and calculated from the upper limit value or the lower limit value and the dimensionless number.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1 FIG.
1 to 9 illustrate an exhaust gas purification apparatus and purification method for an internal combustion engine according to Embodiment 1 of the present invention. FIG. 1 is a system configuration diagram of the internal combustion engine and shows one cylinder of a multi-cylinder internal combustion engine. FIG. 2 is a functional block diagram showing a schematic functional configuration of the control means, FIGS. 3 to 5 and FIG. 8 are flowcharts for explaining the exhaust gas purification operation, FIG. 6, FIG. 7, and FIG. It is characteristic explanatory drawing for demonstrating purification | cleaning of exhaust gas.
[0018]
In FIG. 1, an air flow sensor 3 and a throttle valve 4 are provided in an intake passage 2 of the internal combustion engine 1, and the intake air amount is controlled by the throttle valve 4 and introduced into the combustion chamber 5. The amount of air is measured by the air flow sensor 3. The combustion chamber 5 is provided with an injector 6 as fuel injection means and a spark plug 7 as ignition means. Fuel is injected from the injector 6 into the intake air drawn into the combustion chamber 5 to form an air-fuel mixture. The mixture is ignited by the spark plug 7 at a predetermined ignition timing.
[0019]
The piston 8 of the internal combustion engine 1 drives and rotates the crankshaft 10 via the connecting rod 9, and the rotation angle and rotation speed of the crankshaft 10 are measured by the crank angle sensor 11. Further, in the exhaust passage 12 of the internal combustion engine 1, an air-fuel ratio sensor 13 for measuring the air-fuel ratio (A / F) of the air-fuel mixture from the upstream side, and a three-way catalyst 14 for purifying the exhaust gas by oxidizing unburned gas or the like. An exhaust gas temperature sensor 15 that measures the temperature of the exhaust gas, and a NOx storage catalyst 16 that adsorbs NOx in the exhaust gas are provided. The air flow sensor 3, the air-fuel ratio sensor 13, the exhaust gas temperature sensor 15, and the crank angle are provided. A signal measured by the sensor 11 is input to a control unit 17 that controls the internal combustion engine 1, and the control unit 17 controls the internal combustion engine 1 based on an input signal from each sensor.
[0020]
The NOx storage catalyst 16 uses, for example, alumina as a carrier, and an alkali metal such as potassium (K), sodium (Na), lithium (Li), cesium (Cs), barium (Ba), calcium, for example. At least one selected from alkaline earth such as (Ca), rare earth such as lanthanum (La) and yttrium (Y), and a noble metal such as platinum (Pt) are supported. When the inflowing exhaust gas has an excessive oxygen concentration, NOx is occluded. When the oxygen concentration decreases, the NOx is released and reduced to purify the NOx in the exhaust gas.
[0021]
As shown in the block diagram of FIG. 2, for example, the control means 17 detects the rotational speed from the signal of the crank angle sensor 11, or calculates the load amount of the internal combustion engine from the signal and rotational speed of the airflow sensor 3. 18, NOx flow rate estimation calculation means 19 for estimating and calculating the NOx flow rate flowing into the NOx storage catalyst 16, as will be described later, and NOx storage amount estimation calculation means 20 for estimating and calculating the NOx storage amount stored by the NOx storage catalyst 16. NOx reduction amount estimation calculation means 21 for estimating and calculating the NOx reduction amount reduced by the noble metal of the NOx storage catalyst 16, and NOx decomposition amount estimation calculation means for estimating and calculating the NOx decomposition amount decomposed by the noble metal of the NOx storage catalyst 16 22, outputs of NOx occlusion amount estimation calculation means 20, NOx reduction amount estimation calculation means 21, and NOx decomposition amount estimation calculation means 22. Whether the NOx processable amount estimation calculation means 23 for estimating the NOx processable amount, the outputs of the NOx flow rate estimation calculation means 19 and the NOx processable amount estimation calculation means 23 are compared, and the NOx storage catalyst 16 is purified. The function is comprised from the comparison determination means 24 and the memory | storage means 25 etc. which determine whether.
[0022]
FIG. 3 is a flowchart showing the operation of the exhaust gas purifying apparatus for an internal combustion engine configured as described above. In this flowchart, in order to purify NOx stored by the NOx storage catalyst 16 during the lean operation of the internal combustion engine, the air-fuel ratio (A / F) is forcibly switched to rich and the oxygen concentration in the exhaust gas is reduced. NOx is released and reduced by the above, and is repeatedly performed at predetermined intervals. The repetition at every predetermined cycle is performed, for example, every predetermined time (10 msec) or every predetermined crank angle (180 degrees).
[0023]
First, in step 101, the signal processing means 18 reads signals from various sensors, and in step 102, the NOx flow rate estimation calculating means 19 estimates the NOx flow rate per unit time (QNOxIN) flowing into the NOx storage catalyst 16. This estimation is performed, for example, by reading a value from a map stored in advance using the rotational speed of the internal combustion engine and the load amount as parameters and correcting the value by the air-fuel ratio (A / F) detected by the air-fuel ratio sensor 13. . Subsequently, in step 103, the processable amount estimation calculating means 23 processes the current NOx storage catalyst 16 per unit time from the NOx storage amount (SUMQNOx) estimated to be stored in the NOx storage catalyst 16 by a method described later. Estimate the amount of NOx (QNOxST) possible (ie, occluded per unit time). Here, the NOx flow rate per unit time is simply referred to as NOx flow rate (QNOxIN), and the NOx processable amount per unit time is referred to as a processable NOx amount (QNOxST).
[0024]
In the subsequent step 104, the NOx storage flow rate (QNOxIN) flowing into the NOx storage catalyst 16 estimated in steps 102 and 103 and the NOx amount (QNOxST) that can be processed by the NOx storage catalyst 16 are compared by the comparison determination means 24. Then, it is determined whether or not the NOx stored in the NOx storage catalyst 16 is released. Specifically, when the NOx flow rate (QNOxIN) flowing into the NOx storage catalyst 16 is larger than the processable NOx amount (QNOxST) (YES), NOx that cannot be processed is released to the atmosphere if the lean operation is continued as it is. In step 105, NOx is released (NOx purge), and NOx occluded in the NOx occlusion catalyst 16 is released and purified.
[0025]
In step 104, if the NOx flow rate (QNOxIN) flowing into the NOx storage catalyst 16 is smaller than the processable NOx amount (QNOxST) (NO), the NOx storage catalyst 16 will change the inflow NOx even if the lean operation is continued. It is determined that sufficient processing can be performed. In this case, since the lean operation can be continued, the current routine is terminated and the process returns to the start.
[0026]
Subsequent steps 105 to 107 show the NOx purge process. First, in step 105, the operation of the internal combustion engine is switched to a preset rich air-fuel ratio (A / F), and NOx occluded in the NOx occlusion catalyst 16 is released and reduced and purified simultaneously. Subsequently, the routine proceeds to step 106, where it is determined whether or not the NOx stored in the NOx storage catalyst 16 has been sufficiently released, and when it is determined that the NOx purge has ended (YES), the routine proceeds to step 107, The NOx occlusion amount (SUMQNOx) is reset to zero and the process is terminated. If it is determined that the NOx purge is not terminated (NO), step S107 is skipped, the current routine is terminated, and the process returns to the start. .
[0027]
The NOx purge end determination is made by comparing the amount of NOx estimated to be accumulated in the NOx storage catalyst 16 during lean operation (SUMQNOx) with the amount of reducing material (HC and CO) supplied during the NOx purge period. However, if both are stoichiometrically equal, it is judged that NOx is sufficiently released and reduced. Thus, the comparison / determination means 24 determines whether or not NOx purge is possible by comparing the NOx flow rate (QNOxIN) flowing into the NOx storage catalyst 16 and the NOx amount (QNOxST) that can be processed by the NOx storage catalyst 16 at present. Then, a NOx purge execution command is output.
[0028]
As described above, the amount of NOx that can be processed (QNOxST) is a parameter necessary for exhaust gas purification, and this estimation calculation method in step 103 will be described with reference to FIGS. The amount of NOx that can be processed (QNOxST) is the sum of the amount stored in the NOx storage catalyst 16, the amount decomposed by the noble metal catalyst, and the amount reduced. Therefore, as shown in the flowchart of FIG. 4, the NOx amount that can be processed (QNOxST) estimates the amount of storage (QNOx) per hour to the NOx storage catalyst 16 in step 201 (according to the storage amount estimation calculation means 20). ), The amount of reduction (RNOx) per hour by the noble metal catalyst is estimated at step 202 (by the reduction amount estimation calculating means 21), and the amount of decomposition (DNOx) per hour by the noble metal catalyst is estimated at step 203 (decomposition). (By the quantity estimation calculation means 22), the processable quantity estimation calculation means 23 calculates the sum of these at step 204.
QNOxST = QNOx + RNOx + DNOx
Is estimated and calculated.
[0029]
Here, the storage amount per hour (QNOx) of the processable NOx amount (QNOxST) is an amount calculated as a function of the storage rate, and is estimated and calculated according to the procedure shown in the flowchart of FIG. First, the temperature (TCAT) of the NOx storage catalyst 16 is estimated in step 301 from the signal of the exhaust temperature sensor 15 and the like, and in step 302 as a function of the catalyst temperature (TCAT) and the NOx flow rate (QNOxIN) estimated in step 102. The maximum storage amount (QNOxMAX) is calculated. The relationship between the maximum storage amount (QNOxMAX) and the catalyst temperature (TCAT) is that the NOx oxidation ability of the noble metal catalyst increases with increasing temperature and the decomposition reactivity of the storage compound depends on increasing temperature. It is expressed as a function obtained by the synergistic effect of increasing relationships.
[0030]
The maximum storage amount (QNOxMAX) varies depending on the composition of the NOx storage catalyst 16. For example, in a storage catalyst containing a large amount of potassium (K), the maximum storage amount is about 400 ° C. as shown in FIG. An upward convex function is obtained as a relationship with temperature. In this storage catalyst, the maximum storage amount (QNOxMAX) depending on the inflowing NOx flow rate (QNOxIN) is quantified by the relationship shown in FIG. These relationships are stored as a map and can be obtained from the map.
[0031]
Next, at step 303, the NOx storage amount currently stored in the NOx storage catalyst 16, that is, the current storage amount (SUMQNOx) is estimated. This estimation is performed according to the procedure shown in the flowchart of FIG. In FIG. 8, in step 401, the NOx flow rate (QNOxIN) and the storage amount per hour (QNOx) are compared. If it is determined that the NOx flow rate is larger (Yes), the process proceeds to step 402, where the current storage amount is set.
SUMQNOx = SUMQNOx + QNOx
Calculate as
[0032]
If it is determined that the storage amount per hour (QNOx) is larger, the process proceeds to step 403, where it is determined that all of the amount of NOx flowing into the NOx storage catalyst 16 is stored, and the current storage amount. The
SUMQNOx = SUMQNOx + QNOxIN
Calculate as
[0033]
In step 304, the storage rate (P_NOxST) is calculated from the maximum storage amount (QNOxMAX) calculated in this way and the current storage amount (SUMQNOx).
P_NOxST = SUMQNOx / QNOxMAX
Calculate as In step 305, the storage amount per hour (QNOx) is calculated. This calculation is performed, for example, as an example of a storage catalyst containing a large amount of potassium (K) as shown in FIG. The relationship with the amount of occlusion (QNOx) is stored as a map and can be obtained from this map.
[0034]
Of the amount of NOx that can be processed (QNOxST), the reduction amount per hour (RNOx) estimated and calculated by the reduction amount estimation calculating means 21 is the NOx occlusion estimated from the signal of the exhaust temperature sensor 15 in step 301. It can be calculated as a function of the temperature (TCAT) of the catalyst 16 and the amount of reducing gas. As a method for estimating the amount of reducing gas, for example, an exhaust gas that is stored as a map using the rotational speed of the internal combustion engine and the amount of load as parameters and the value read from this map is detected by the air-fuel ratio sensor 13 is stored. Using the value corrected by the air-fuel ratio (A / F) of the exhaust gas, the consumption due to the three-way reaction by the three-way catalyst 14 provided in the exhaust passage 12 can be estimated stoichiometrically.
[0035]
Further, the NOx decomposition amount per unit time (DNOx) estimated and calculated by the NOx decomposition amount estimation calculating means 22 can be calculated as a function of the temperature (TCAT) of the NOx storage catalyst 16 estimated in step 301.
[0036]
As described above, according to the exhaust gas purification apparatus for internal combustion engine and the purification method therefor according to Embodiment 1 of the present invention, the amount of NOx that can be processed in the NOx storage catalyst 16 can be accurately estimated and calculated. Therefore, the NOx purge execution timing can be appropriately determined according to the result of comparing the amount of NOx that can be processed and the NOx flow rate flowing into the NOx storage catalyst 16. As a result, unnecessary switching of the operating state is not performed, and while the lean operation is possible, this is continued and the fuel consumption is maintained in a good state, and the NOx flow rate flowing into the NOx storage catalyst 16 can be processed. When the amount of NOx is exceeded, the air-fuel ratio is switched to rich and NOx purge is performed, so NOx is not discharged and the exhaust gas can be kept in a good state.
[0037]
Embodiment 2. FIG.
FIGS. 10 and 11 illustrate an internal combustion engine exhaust gas purification apparatus and a purification method thereof according to Embodiment 2 of the present invention. FIG. 10 is a flowchart for explaining exhaust gas purification, and FIG. 11 is an exhaust gas. It is characteristic explanatory drawing for demonstrating purification | cleaning. In this embodiment, the NOx amount that can be processed by the NOx storage catalyst 16 is given as a dimensionless function (dimensionless number), and the NOx amount that can be processed is defined as an initial value of the dimensionless number. By obtaining from the NOx flow rate flowing into the NOx storage catalyst 16, the processable NOx amount can be quickly estimated and calculated.
[0038]
This will be explained based on the flowchart of FIG. 10. First, in step 501, the dimensionless number (dQNOxST) of the processable NOx amount with respect to the storage rate is estimated. As shown in FIG. 11, the dimensionless number of the processable NOx amount is 1 when the storage rate is 0, and the processable NOx amount can be processed as the storage rate increases. The amount of NOx that can be processed is a value that depends only on decomposition and reduction when the storage rate is 1, and this relationship is stored as a map. Can be obtained from
[0039]
Next, at step 502, the NOx flow rate (QNOxIN) flowing into the NOx storage catalyst 16 is estimated. As in the case of the first embodiment, this estimation is performed by, for example, reading a value from a map stored in advance using the rotational speed of the internal combustion engine and the load amount as parameters, and detecting the air / fuel ratio (A / F) is performed by correcting.
[0040]
Subsequently, in step 503, the inflowing NOx flow rate (QNOxIN) is compared with a separately determined predetermined value (upper limit value), and if the NOx flow rate (QNOxIN) is smaller, the process proceeds to step 504, and a separately determined predetermined value (lower limit value). ), When the NOx flow rate (QNOxIN) is larger, the routine proceeds to step 505 where the processable NOx amount (QNOxST) is increased.
QNOxST = dQNOxST × QNOxIN
Calculate as
[0041]
Here, the dimensionless number (dQNOxST) is given as a value when the occlusion rate is 0, that is, an initial value. Since this initial value is 1, NOx that can be processed when the NOx flow rate (QNOxIN) is within a predetermined range. The amount (QNOxST) is given as the inflowing NOx flow rate (QNOxIN).
[0042]
When the NOx flow rate (QNOxIN) is larger in step 503, the process proceeds to step 506, and the processable NOx amount (QNOxST) is set.
QNOxST = dQNOxST × predetermined value (upper limit value)
If the NOx flow rate (QNOxIN) is smaller in step 504, the process proceeds to step S507 and the processable NOx amount (QNOxST) is calculated.
QNOxST = dQNOxST × predetermined value (lower limit value)
Calculate as
[0043]
That is, when the NOx flow rate (QNOxIN) exceeds a predetermined range, the upper limit value and the lower limit value of the range are used. Here, the predetermined values (upper limit value) and (lower limit value) separately determined are determined by, for example, the amount of the NOx storage catalyst 16, the shape, the catalyst temperature, etc., and the processing per unit time of the catalyst. The amount is determined in a range showing dependency on the NOx flow rate. Using the processable NOx amount (QNOxST) estimated and calculated in this way, the determination and the NOx purge process are performed in the same manner as in step 104 and thereafter in the first embodiment.
[0044]
By calculating by such a method, the processable NOx amount can be quickly estimated and calculated, and the NOx purge execution timing can be appropriately determined using the processable NOx amount. In addition, the non-dimensional number of NOx amount that can be processed with respect to the occlusion rate can be calculated more quickly by reading it from a pre-stored map, and the processing can be performed accurately by setting an upper limit value and a lower limit value. A possible amount of NOx can be estimated.
[0045]
【The invention's effect】
  As described above, in the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, according to the first aspect of the present invention, the NOx storage catalyst provided in the exhaust passage of the internal combustion engine, the load and the rotational speed of the internal combustion engine NOx flow rate estimation calculation means for estimating and calculating the NOx flow rate per unit time flowing in the exhaust passage using the operating conditions such as the above, and the NOx occlusion amount stored by the NOx storage catalyst is estimated using the operating conditions of the internal combustion engine as parameters. The NOx occlusion amount estimation calculating means to calculate, the NOx is reduced by the noble metal carried by the NOx occlusion catalyst.Per unit timeNOx reduction amountEstimated calculation as a function of the temperature of the NOx storage catalyst and the amount of reducing gas per unit time flowing into the NOx storage catalystNOx reduction amount estimation calculating means for decomposing the NOx by the noble metal supported by the NOx storage catalystPer unit timeThe amount of NOx decompositionEstimated calculation as a function of the temperature of the NOx storage catalystNOx decomposition amount estimation calculation means, NOx storage amount calculated by the NOx storage amount estimation calculation means, NOx reduction amount calculated by the NOx reduction amount estimation calculation means, and NOx decomposition amount calculated by the NOx decomposition amount estimation calculation means NOx processable amount estimation calculation means for estimating the NOx processable amount per unit time from the output of the NOx flow rate estimation calculation meansPer unit timeThe estimated value of the NOx flow rate and the NOx processable amount estimation calculating means outputPer unit timeComparing and determining means for comparing the estimated value of the NOx processable amount and determining the NOx purge timing,The comparison meansThe NOx flow rate per unit time exceeds the NOx processable amount per unit time.DeterminedSince the operation of the internal combustion engine is switched to NOx purge, it is possible to determine a more appropriate purge timing, and it is possible to appropriately purify exhaust gas and improve fuel efficiency by securing a lean operation time. It will be.
[0046]
  According to the invention of claim 2,The NOx processable amount estimation calculation means calculates the NOx processable amount per unit time from the sum of the NOx occlusion amount per unit time, the NOx reduction amount per unit time, and the NOx decomposition amount per unit time. DoSince it did in this way, the NOx processable amount by a NOx occlusion catalyst can be estimated and calculated accurately, and the effect of appropriate purification of exhaust gas and improvement of fuel consumption can be further enhanced.
[0047]
  Furthermore, according to the invention of claim 3, theNOx storage amount estimation calculation meansIs the ratio of the maximum storage amount of the NOx storage catalyst to the current storage amount as a function of the storage rate per unit time.NOx storage amountTherefore, the NOx processable amount can be easily calculated, and the calculation can be performed accurately and the NOx purge timing can be accurately determined.
[0048]
  Furthermore, according to the invention of claim 4, the current storage amount estimated by the NOx storage amount estimation calculating means is:AboveNOx flow rate per unit timeAboveCompare NOx storage amount per unit time,AboveNOx flow rate per unit timeMore than the amount of NOx stored per unit timeWhen it ’s bigAboveAccumulate NOx occlusion amount per unit time,AboveNOx flow rate per unit timeLess than NOx occlusion amount per unit timeIn this case, since the NOx flow rate per unit time is integrated, the amount of occlusion at the present time, that is, the NOx processable amount can be calculated with high accuracy, and the purge timing can be accurately determined.
[0049]
  According to the invention of claim 5, the NOx occlusion amount per unit time.But,AboveCalculated as a function of the storage rate, which is the ratio between the maximum storage amount of the NOx storage catalyst and the current storage amountIsThus, the NOx occlusion amount per unit time, and therefore the NOx processable amount can be calculated with high accuracy, and the purge timing can be determined accurately.
[0052]
  further,Claim 6According to the invention described inAboveMaximum storage amount of NOx storage catalystBut saidNOx storage catalyst temperature andAboveSince it is calculated as a function of the NOx flow rate per unit time flowing into the NOx storage catalyst, the maximum storage amount can be calculated accurately, and accordingly the NOx processable amount can be calculated accurately, and the purge timing can be calculated accurately. Can be determined.
[0053]
  Furthermore, in the exhaust gas purification method for an internal combustion engine of the present invention,Claim 7According to the invention described above, the NOx storage catalyst is provided in the exhaust passage of the internal combustion engine, and the NOx stored by the NOx storage catalyst is released and reduced by lowering the oxygen concentration of the exhaust gas to reduce the NOx storage catalyst. In the purifying control, the NOx flow rate per unit time flowing in the exhaust passageAnd a unit time given as a function of the NOx occlusion amount per unit time given as a function of the NOx occlusion rate per unit time in the NOx occlusion catalyst, the temperature of the NOx occlusion catalyst, and the amount of reducing gas. The NOx reduction amount per unit time is estimated and calculated from the NOx reduction amount per unit and the NOx decomposition amount per unit time given as a function of the temperature of the NOx storage catalyst,Comparing both, the NOx flow rate per unit time isMore than the amount of NOx that can be processed per unit timeWhen it ’s bigAboveWhile reducing the oxygen concentration of the exhaust gas to release and reduce NOx, the per unit timeNOx storage amountIs calculated as a function of the storage rate, which is the ratio between the maximum storage amount of the NOx storage catalyst and the current storage amount, so that a more appropriate purge timing can be determined, and the exhaust gas Purification and improvement of fuel consumption by securing lean operation time.
[0056]
  further,Claim 8According to the invention described inAbovePer unit timeThe NOx processable amount isNOx storage catalystAboveGiven as dimensionless number for storage rateIt has been, With this dimensionless numberAboveFrom the NOx flow rate per unit timeAboveNOx processable amount per unit timeButCalculationIsAs a result, the NOx processable amount can be calculated quickly and easily.
[0057]
  Furthermore,Claim 9According to the invention described above, an upper limit value and a lower limit value are set for the NOx flow rate per unit time.Has been,AboveNOx flow rate per unit timeAboveWhen the upper limit or lower limit is exceededAboveThe NOx processable amount per unit time is estimated from the upper limit value or lower limit value and the dimensionless number.Be doneThus, the NOx processable amount can be calculated with high accuracy, and the purge timing can be accurately determined.
[Brief description of the drawings]
1 is a system configuration diagram of an internal combustion engine in an exhaust gas purification apparatus for an internal combustion engine according to Embodiment 1 of the present invention;
FIG. 2 is a schematic functional configuration diagram of control means of the exhaust gas purification apparatus for an internal combustion engine according to the first embodiment of the present invention.
FIG. 3 is a flowchart illustrating the operation of the exhaust gas purification apparatus for an internal combustion engine according to the first embodiment of the present invention.
FIG. 4 is a flowchart illustrating the operation of the exhaust gas purification apparatus for an internal combustion engine according to the first embodiment of the present invention.
FIG. 5 is a flowchart illustrating the operation of the exhaust gas purification apparatus for an internal combustion engine according to the first embodiment of the present invention.
FIG. 6 is a characteristic explanatory diagram illustrating the function of the exhaust gas purifying apparatus for an internal combustion engine according to the first embodiment of the present invention.
FIG. 7 is a characteristic explanatory diagram illustrating the function of the exhaust gas purifying apparatus for an internal combustion engine according to the first embodiment of the present invention.
FIG. 8 is a flowchart illustrating the operation of the exhaust gas purification apparatus for an internal combustion engine according to the first embodiment of the present invention.
FIG. 9 is a characteristic explanatory diagram illustrating the function of the exhaust gas purifying apparatus for an internal combustion engine according to the first embodiment of the present invention.
FIG. 10 is a flowchart illustrating the operation of an exhaust gas purification apparatus for an internal combustion engine according to Embodiment 2 of the present invention.
FIG. 11 is a characteristic explanatory diagram illustrating the function of the exhaust gas purifying apparatus for an internal combustion engine according to the first embodiment of the present invention.
FIG. 12 is an explanatory diagram of a conventional exhaust gas purifying device for an internal combustion engine.
[Explanation of symbols]
1 internal combustion engine, 2 intake passage, 3 air flow sensor,
4 throttle valve, 5 combustion chamber, 6 injector,
7 Spark plug, 8 piston, 9 connecting rod,
10 crankshaft, 11 crank angle sensor, 12 exhaust passage,
13 air-fuel ratio sensor, 14 three-way catalyst, 15 exhaust temperature sensor,
16 NOx storage catalyst, 17 control means, 18 signal processing means,
19 NOx flow rate estimation calculation means, 20 NOx occlusion amount estimation calculation means,
21 NOx reduction amount estimation calculation means, 22 NOx decomposition amount estimation calculation means,
23 NOx processable amount estimation calculation means, 24 comparison determination means,
25 Storage means.

Claims (9)

A NOx occlusion catalyst provided in an exhaust passage of the internal combustion engine, NOx flow rate estimation calculation means for estimating and calculating a NOx flow rate per unit time flowing in the exhaust passage using operating conditions such as load and rotation speed of the internal combustion engine as parameters, NOx occlusion amount estimation calculation means for estimating and calculating the NOx occlusion amount occluded by the NOx occlusion catalyst using the operating condition of the internal combustion engine as a parameter , NOx reduction per unit time for reducing the NOx by the noble metal carried by the NOx occlusion catalyst NOx reduction amount estimation calculation means for estimating and calculating the amount as a function of the temperature of the NOx storage catalyst and the amount of reducing gas flowing into the NOx storage catalyst per unit time, and the noble metal carried by the NOx storage catalyst the NOx decomposition per unit decomposes time NOx, and a function of the temperature of the NOx storage catalyst NOx decomposition amount estimating calculation means for estimating Te, NOx which calculates the NOx reduction amount and the NOx decomposition amount estimating means for calculating the NOx occlusion amount and the NOx reduction amount estimating means for calculating the NOx occlusion amount estimation calculation means NOx processable amount estimation calculation means for estimating and calculating the NOx processable amount per unit time from the decomposition amount, the estimated value of NOx flow rate per unit time output from the NOx flow rate estimation calculation means and the NOx processable amount estimation Comparing and determining means for determining the NOx purge timing by comparing with the estimated value of the NOx processable amount per unit time output by the calculating means, wherein the comparing means determines the NOx flow rate per unit time as the unit time. when it is determined that exceeds the NOx processable per, characterized by switching the operation of the internal combustion engine to the NOx purging Exhaust gas purification system of an internal combustion engine to be.   The NOx processable amount estimation calculation means calculates the NOx processable amount per unit time from the sum of the NOx occlusion amount per unit time, the NOx reduction amount per unit time, and the NOx decomposition amount per unit time. The exhaust gas purifying device for an internal combustion engine according to claim 1, wherein the exhaust gas purifying device is an internal combustion engine. The NOx occlusion amount estimation calculating means calculates the NOx occlusion amount per unit time as a function of an occlusion rate that is a ratio between the maximum occlusion amount of the NOx occlusion catalyst and the current occlusion amount. Or the exhaust-gas purification apparatus of the internal combustion engine of Claim 2. The storage amount at the present time the NOx occlusion amount estimating arithmetic unit for estimating calculation compares the NOx occlusion amount per NOx flow rate and the unit time per unit time, flow rate of NOx per unit time is the unit time the NOx storage amount per when large integrates the NOx absorption amount per unit time, flow rate of NOx per unit time is when: NOx storage amount per unit time is obtained by integrating the NOx flow rate per unit time The exhaust gas purifying device for an internal combustion engine according to claim 3, wherein the exhaust gas purifying device is an internal combustion engine.   The NOx occlusion amount per unit time is calculated as a function of an occlusion rate that is a ratio between the maximum occlusion amount of the NOx occlusion catalyst and the current occlusion amount. Exhaust gas purification device for internal combustion engine.   6. The maximum storage amount of the NOx storage catalyst is calculated as a function of the temperature of the NOx storage catalyst and the NOx flow rate per unit time flowing into the NOx storage catalyst. An exhaust gas purification device for an internal combustion engine as described. A NOx storage catalyst is provided in the exhaust passage of the internal combustion engine, and the NOx storage catalyst releases and reduces the NOx stored by reducing the oxygen concentration of the exhaust gas, thereby performing purification control of the NOx storage catalyst. The NOx flow rate per unit time flowing in the exhaust passage is estimated and calculated, the NOx occlusion amount per unit time given as a function of the NOx occlusion rate per unit time in the NOx occlusion catalyst, the temperature of the NOx occlusion catalyst, and the reducing gas A NOx treatable amount per unit time is estimated from a NOx reduction amount per unit time given as a function of the amount of NOx and a NOx decomposition amount per unit time given as a function of the temperature of the NOx storage catalyst, comparing the NOx flow rate per unit time can NOx processing per unit time The ratio of together to reduce the oxygen concentration in the exhaust gas when a large emission reducing NOx, NOx storage amount per unit time is, the maximum storage amount and storage amount at the current time of the NOx storage catalyst than An exhaust gas purification method for an internal combustion engine, which is calculated as a function of the storage rate. The NOx treatable amount per unit time is given as a dimensionless number with respect to the NOx storage rate of the NOx storage catalyst. From this dimensionless number and the NOx flow rate per unit time, the amount per unit time is obtained. The exhaust gas purification method for an internal combustion engine according to claim 7 , wherein a NOx processable amount is calculated. Is set an upper limit value and the lower limit to the NOx flow rate per unit time, when the NOx flow rate per unit time exceeds the upper limit or the lower limit Mu said said upper limit value or lower limit value The exhaust gas purification method for an internal combustion engine according to claim 8 , wherein the NOx processable amount per unit time is estimated and calculated from the number of dimensions.

Images