JP3812197B2 - Engine NOx reduction device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an engine NOx reduction device, and more particularly to an engine NOx reduction device suitable for a diesel engine or a lean burn gasoline engine.
[0002]
[Prior art]
In general, in a diesel engine or lean burn (lean combustion) gasoline engine, combustion is performed in an excess air state, and exhaust gas is not stoichiometric, so NOx purification by a three-way catalyst cannot be performed. However, in recent years, a zeolite-based NOx catalyst carrying a transition metal has emerged, and NOx can be reduced in the presence of a reducing agent such as HC. No. 265414, JP-A-8-312336, etc.).
[0003]
The characteristics of this NOx catalyst are that the active temperature range where NOx purification treatment can be performed is relatively narrow, that the NOx purification rate has a peak within this temperature range, and that the temperature range shifts to the high temperature side due to deterioration (change over time). And so on (see FIG. 9).
[0004]
Further, as previously described in Japanese Patent Application No. 10-72335 by the present applicant, for example, a specific type of NOx catalyst containing Ir (iridium) has an activation phenomenon, and once deteriorated, the activation temperature region is on the high temperature side. A phenomenon occurs in which the material that has shifted to is activated and shifted again to the low temperature side while being used. For this reason, in this prior application, the reducing agent addition map is switched in accordance with the shift of the active temperature region, and the temperature at which the reducing agent addition is started is switched, so that the optimum reducing agent addition according to the shift state, that is, the NOx purification process is performed. I was trying to do it.
[0005]
[Problems to be solved by the invention]
However, the control of the prior application merely switches the map following the deterioration / activation of the catalyst, the deterioration itself cannot be suppressed, and the activation is only performed secondary to the stage of use. Since the normal catalyst usually adjusts the active temperature region in the initial state to the exhaust gas temperature region where purification is most desired, if the active temperature region shifts due to deterioration, naturally the desired performance cannot be obtained, and the NOx emission amount increases from the initial schedule. In addition, since activation is performed secondary or passively, it takes a relatively long time for activation, resulting in an increase in usage time in a deteriorated state, which also contributes to an increase in NOx emissions.
[0006]
[Means for Solving the Problems]
The present invention is a NOx reduction device for an engine in which a NOx catalyst is provided in an exhaust path of the engine, and a reducing agent is added to the exhaust gas within a predetermined exhaust gas temperature range to reduce NOx in the exhaust gas. An activation treatment means for activating the NOx catalyst is provided by adding a reducing agent to the exhaust gas within a predetermined exhaust gas temperature range lower or higher than the exhaust gas temperature region.
[0007]
According to this, since the NOx catalyst can be activated at times other than during the NOx purification treatment, the NOx catalyst can be actively activated, and the initial performance can be maintained.
[0008]
Here, it is preferable that the activation processing means executes the activation processing every predetermined engine operation time.
[0009]
The activation processing means cumulatively calculates the engine operation time while performing weighting according to the exhaust gas temperature during engine operation, and executes the activation processing when the calculated value becomes a predetermined value. Is preferred.
[0010]
Moreover, it is preferable that the said activation process means performs the said activation process for every predetermined | prescribed vehicle travel distance.
[0011]
Preferably, the activation processing means performs the addition of the reducing agent by fuel sub-injection into the engine cylinder, and determines the sub-injection amount for each engine speed based on a predetermined map.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
[0013]
FIG. 8 shows a NOx reduction device for an engine according to the present invention. The engine 1 here is a diesel engine, and an exhaust path of the engine 1 is formed by an exhaust pipe 2, and a NOx catalyst 3 is provided in the middle of the exhaust pipe 2.
[0014]
As the NOx catalyst 3, one that causes an activation phenomenon is used, and here contains Ir as an active metal species. However, the NOx catalyst 3 may be anything as long as it can be activated. The presence of a reducing agent is necessary for activation. Therefore, the fuel of the engine 1, that is, light oil, is used as the reducing agent. HC contained in light oil plays a role as a substantial reducing agent.
[0015]
The engine 1 is electronically controlled by an electronic control unit (hereinafter referred to as ECU) 4. That is, the predetermined ECU4 is adapted to calculate a current crank angle and the engine rotational speed N _E based on the output of the crank angle sensor 5, and calculates the current engine load Q based on the output of the engine load sensor 6, from these values The target fuel injection amount and the target injection timing are determined according to the injection amount map and the injection timing map, and the injection amount control and the injection timing control are executed based on these.
[0016]
In particular, as shown in the frame of the figure, apart from the main injection for the combustion stroke performed near the compression top dead center, a small amount of sub-injection is also performed near the exhaust top dead center and reduced into the exhaust gas. Light oil as an agent is added and mixed. In this way, it is not necessary to provide a separate nozzle device dedicated to the addition of the reducing agent, and simplification and cost reduction can be achieved. The sub-injection will be described in detail later.
[0017]
The method for adding the reducing agent is not limited to the sub-injection near the exhaust top dead center. The addition timing may be an expansion stroke or an exhaust stroke, or the addition may be directly performed in the exhaust path on the upstream side of the NOx catalyst 3 using a dedicated nozzle.
[0018]
An exhaust gas temperature sensor 7 for detecting an exhaust gas temperature at the catalyst inlet (hereinafter referred to as catalyst inlet temperature) T _IN is provided near and upstream of the inlet of the NOx catalyst 3. The ECU 4 determines whether or not the sub-injection can be executed based on the output of the sensor 7 as described later. A catalyst temperature sensor 8 is embedded in the NOx catalyst 3. The ECU 4 calculates a temperature difference based on the output of the sensor 8 and the output of the exhaust gas temperature sensor 7, and determines the deterioration state of the NOx catalyst 3 (see Japanese Patent Laid-Open No. 8-312336 etc.). A NOx sensor 9 is provided on the downstream side of the NOx catalyst 3, and the ECU 4 detects the NOx concentration in the exhaust gas based on the output of the sensor 9.
[0019]
The NOx catalyst 3 exhibits a purification characteristic as shown in FIG. That is, in the initial state shown by the solid line, the catalyst inlet temperature T _IN activity start temperature T _ST (here 350 ° C.) was activated at or over, gradually increasing the NOx purification rate as the increase in the catalyst inlet temperature T _IN after peaked NOx purification rate temperature T _P, gradually reducing the NOx purification rate at higher temperatures. Therefore, in this apparatus, sub-injection is executed in the temperature range T _{Z that} is higher than the temperature T _ON on the lower temperature side and lower than the temperature T _OFF on the higher temperature side than the peak temperature T _P, and reduces the reducing agent into the exhaust gas. The NOx reduction process or the purification process is executed by adding the NOx. T _ON purification starting temperature, T _OFF purification stop temperature, the T _ON or T _OFF following temperature range T _Z that purification temperature region. Here, T _ON = 400 ° C. and T _OFF = 500 ° C.
[0020]
As indicated by the broken line, the NOx catalyst 3 can also purify HC and CO when the catalyst inlet temperature T _IN is _{equal to} or higher than the activation start temperature T _ST . That is, a reduction / oxidation reaction is performed between NOx, HC, and CO so that HC and CO can also be purified. As the purification characteristics of HC and CO, when the catalyst inlet temperature T _IN becomes a value slightly lower than the activation start temperature T _ST , the purification rate starts to rise relatively rapidly and reaches a maximum at a predetermined temperature slightly lower than T _ON. The value is reached and the maximum value is maintained thereafter.
[0021]
The above are the initial characteristics of the NOx catalyst 3. When the NOx catalyst 3 deteriorates (changes with time), the entire NOx purification curve and the entire HC and CO purification curves shift to the high temperature side, as shown by the one-dot chain line. Therefore, T _ON , T _OFF , and T _Z are shifted by map switching in accordance with this in the prior application. Although it is possible to perform the same control in this apparatus, the following description will be made on the assumption that the catalyst is in the initial state without touching it.
[0022]
In the purification temperature region _TZ , the sub-injection is executed according to the portion Z in the sub-injection amount map shown in FIG. That is, this sub-injection amount map is created in advance by experiments or the like and stored in the ECU 4, and is used for uniquely determining the sub-injection amount based on the engine speed _NE and the engine load Q. On this map, when the engine rotational speed _NE and the engine load Q are on the lower right line written T _ON and T _OFF , the catalyst inlet temperature T _IN becomes T _ON and T _OFF . Thus the portion Z sandwiched between these corresponding to the purification temperature region T _Z, each moiety Z in each engine rotational speed N _E, for each engine load Q, i.e. sub-injection amount for each mesh is defined.
[0023]
Next, FIG. 5 shows a control flow of the NOx purification process. This control is an interrupt process executed by the ECU 4 every predetermined control time (several tens of milliseconds). First, the ECU 4 reads the current catalyst inlet temperature T _IN , the engine speed _NE and the engine load Q in step 31. In step 32, it is determined whether or not T _ON ≦ T _IN ≦ T _OFF , that is, whether or not the current catalyst inlet temperature T _IN is within the purification temperature region T _Z. When it is determined that T _ON ≦ T _IN ≦ T _OFF , the routine proceeds to step 33, where the target sub-injection amount is calculated from the sub-injection amount map, and at step 34, sub-injection according to the target sub-injection amount is executed, and this control Exit. On the other hand, if it is determined in step 32 that T _ON ≦ T _IN ≦ T _OFF, this control is immediately terminated. At this time, NOx purification processing is not performed.
[0024]
In the course of the NOx purification treatment as described above, the NOx catalyst 3 may be activated by the addition of a reducing agent during catalyst activity. However, this is only secondary or passive, not aggressive. Therefore, in this apparatus, an activation processing means for activating the NOx catalyst 3 is provided so as to actively activate the NOx catalyst 3. The contents will be described below.
[0025]
As shown in FIG. 6, in the sub injection amount map, a part FK is defined in addition to the part Z. This portion FK in a portion used for the activation treatment, and the sub injection amount is defined for each engine rotational speed N _E. That mesh cutting maps made only with respect to the engine rotational speed N _E, not been made with respect to the engine load Q. The portion FK is a region adjacent to the portion Z on the lower temperature side and the higher temperature side. That is, on the map, when the engine speed _NE and the engine load Q are on the line written as T _L , the catalyst inlet temperature T _IN becomes T _L = T _ST (here, 350 ° C.). Therefore, on the low temperature side, the activation process is executed in the temperature range of T _L ≦ T _IN ≦ T _ON . This temperature region is referred to as a low temperature side activation temperature region. On the map, the T _L line is a parallel translation of the T _ON line to the low load side. In the low temperature side activation temperature region, the NOx catalyst 3 is in an active state.
[0026]
On the other hand, on the high temperature side, the activation process is executed within a temperature range of T _IN ≧ T _OFF . This temperature region is referred to as a high temperature side activation temperature region.
[0027]
The main flow of this activation process control is shown in FIG. This flow is an interrupt process that is repeatedly executed every predetermined control time. First, the ECU 4 determines whether or not a predetermined activation process execution time has come in step 41, and when it is determined that the time has come, executes the activation process in step 42 and ends this flow. If it is determined in step 41 that it is not the time, this flow is immediately terminated. That is, the activation process here is executed at predetermined intervals. The detailed contents will be described below.
[0028]
2 and 3 show a sub-flow for determining the activation process execution time. Here, both of the determination method based on the engine operation time (FIG. 2) and the determination method based on the travel distance of the vehicle in which the present apparatus is mounted (FIG. 3) are used in combination. That is, the flow of FIG. 2 and FIG. 3 proceeds in parallel, and when it is determined that the execution time has come, the activation process is executed. These flows are also interrupt processes that are repeatedly executed every predetermined control time t.
[0029]
The engine operation time is cumulatively calculated by the built-in timer of the ECU 4. Here, during the calculation, the time is weighted according to the catalyst inlet temperature T _IN , that is, the weight calculation is performed, and the degree of deterioration of the catalyst is taken into consideration. ing.
[0030]
FIG. 7 is a diagram showing a conversion method for converting the engine operation time into the timer count value. According to the catalyst inlet temperature T _IN , it is divided into four regions A, B, C, and D, the region where T _IN <T _H1 is A, the region where T _H1 ≦ T _IN <T _H2 is B, and T _H2 ≦ T _The region where _IN <T _H3 is C, and the region where T _H3 ≦ T _IN is D. Here, the values of T _H1 , T _H2 , and T _H3 are 500 ° C., 600 ° C., and 700 ° C., respectively, and particularly, T _H1 = T _OFF . In each of the areas A, B, C, and D, the actual engine operation time is 0, 1, 5 and 10 times, respectively, as the timer count value. For example, when the catalyst inlet temperature T _IN is 650 ° C., the region C is entered. Therefore, the actual engine operation time of 1 second is set to 1 × 5 = 5 seconds, and this is used as the timer count value.
[0031]
A region, ie, T _IN <500 ° C., 0 times (no count) corresponds to the previous purification temperature region T _Z if T _IN ≧ 400 ° C. and the reducing agent is added. This is based on the reason that the activation process has been executed and the catalyst is considered to be activated or not deteriorated, and that if T _IN <400 ° C., the catalyst temperature is low, so that there is no deterioration.
[0032]
Thus, B, C, and the total of each _{T Σ B, T Σ C,} T Σ D of the calculated timer count value in each region of the D to. And the sum of these is T _Σ = And _{T Σ B + T Σ C +} T Σ D.
[0033]
Now, the activation process execution time determination method shown in FIG. 2 will be described below. At the beginning of this flow, T _Σ The initial value of _{T Σ B, T Σ C,} T Σ D is 0. The ECU 4 reads the catalyst inlet temperature T _IN in the first step 51, and determines whether or not T _IN ≧ T _H1 in the next step 52. When T _IN ≧ T _H1 (Y), the process proceeds to step 53, and when T _IN <T _H1 (N), this flow ends. In step 53, it is determined whether T _IN ≧ T _H2 or not. When T _IN ≧ T _H2 (Y), the _routine proceeds to step 54, and when T _IN <T _H2 (N), the _routine proceeds to step 55. In step 54, it is determined whether or not T _IN ≧ T _H3 . When T _IN ≧ T _H3 (Y), the _routine proceeds to step 57, and when T _IN <T _H3 (N), the _routine proceeds to step 56.
[0034]
At step 55 computes the T _{sigma B.} That is, a value obtained by adding the control time t from the previous time to the current time as it is to the value of T _{Σ B} at the previous control is set as a new T _{Σ B.} Similarly, to calculate in step _56,57 T Σ _C, T Σ _D, respectively. That is, the values obtained by adding the control times t 5 times and 10 times to T _{Σ C} and T _{Σ D} at the previous control are set as new T _{Σ C} and T _{Σ D} , respectively.
[0035]
When _{T Σ B, T Σ C,} T Σ D is calculated in step 55 or 57, T _sigma proceeds to step 58 = Calculating the _{T Σ B + T Σ C +} T Σ D. At step 59, T _Σ It is determined whether ≧ D ₁ or not. D ₁ is a predetermined time (index time) determined in advance, and here, 20 hours is set. T _Σ When ≧ D ₁ (Y), the routine proceeds to step 60, the activation process flag FLG _{FK is set} to 1 (ON), and an activation process described later is started, and at step 61, T _Σ The _{T Σ B, T Σ C,} T Σ D as the initial value 0, the flow ends. In step 59, T _Σ If <D ₁ (N), this flow is immediately terminated.
[0036]
By repeating this flow, the engine operating time (T _Σ ) is weighted according to the exhaust gas temperature (T _IN ). ) Is cumulatively calculated. And when this becomes a predetermined value (D ₁ ), the activation process is executed. That is the activation process for each predetermined engine operating time D ₁ is performed.
[0037]
Next, an activation process execution time determination method based on the vehicle travel distance shown in FIG. 3 will be described. Here, the trip meter of the vehicle is connected to the ECU 4, and a distance counter built in the ECU 4 is incremented every time the trip distance of the trip meter increases. Therefore, the ECU 4 first determines the distance count value L _Σ in the first step 71. And the distance count value L _{Σ in the} next step 72 It is compared with a predetermined constant distance (index distance) D ₂ a. Here, D ₂ = 1000 km. L _Σ If D ₂ (N), this flow ends and L _Σ If ≧ D ₂ (Y), the routine proceeds to step 73, where the activation process flag FLG _{FK is set} to 1 (ON), and an activation process described later is started. After this, at step 74, _LΣ = 0 and distance count value L _Σ Is returned to the initial value, and this flow ends. Thus it becomes activation treatment is performed for each predetermined vehicle travel distance D _2.
[0038]
Next, the specific execution contents of the activation process will be described with reference to the flowchart shown in FIG.
[0039]
The starting condition of this flow is that the activation process flag FLG _FK is 1 (ON). This flow is also interrupt processing that is repeatedly executed every predetermined control time t _FK . The ECU 4 reads the catalyst inlet temperature T _IN in the first step 81, and in the next step 82, the T _IN is in the range of T _L ≦ T _IN ≦ T _ON or T _IN ≧ T _H1 (= T _OFF ). When it is not within these temperature ranges (N), this flow is terminated, and when it is within the temperature range (Y), the routine proceeds to step 83 where the engine speed _NE is read. Thereafter, in step 84, the target sub-injection amount for the activation process is calculated from the partial FK in the sub-injection amount map shown in FIG. 6, and in step 85, the sub-injection corresponding to the amount is executed. In step 86, the control time t _FK minute counts up the timer count value T _{sigma FK} by ECU4 the built-in timer. In the next step 87, the timer count value T _sigma predetermined value _FK (activating treatment end time) is compared with T Σ _FKEND. Here _T Σ _FKEND is set to about 15~20min. If T _{Σ FK} <T _{Σ FKEND} (N), this flow is terminated. If T _{Σ FK} ≧ T _{Σ FKEND} (Y), the _routine proceeds to step 88 where T _{Σ FK} is reset to the initial value 0 and the activation processing flag FLG _FK Is set to 0 (OFF), and this flow ends.
[0040]
As a result, the activation process can be executed for a certain time (T _{Σ FKEND} ) within the exhaust gas temperature range of T _L ≦ T _IN ≦ T _ON or T _IN ≧ T _H1 (= T _OFF ).
[0041]
As described above, according to the present apparatus, the NOx catalyst can be actively activated when it is not during the NOx purification treatment, so that the deterioration of the NOx catalyst is suppressed as much as possible and its initial performance is maintained for as long as possible. In addition, an increase in NOx emission can be prevented. In particular, this apparatus does not wait for activation of a once deteriorated NOx catalyst as in the prior application (Japanese Patent Application No. 10-72335), but takes measures to prevent deterioration as much as possible before deterioration. Therefore, the initial performance can be maintained for a longer time than before, the active temperature range of the catalyst can be stopped for a long time in the exhaust gas temperature range where purification is most desired, and the most effective usage can be achieved. In addition, the progress of the deterioration can be minimized.
[0042]
Further, as indicated by the one-dot chain line in FIG. 9, as the NOx catalyst 3 deteriorates, the purification rate also decreases. Therefore, the use in the deteriorated state increases the emission amount of NOx, HC and CO. However, since the deterioration is difficult to progress in this apparatus, such increase is minimized.
[0043]
Further, when the NOx catalyst 3 deteriorates, the substantial activation temperature region shifts from the initial T _Z to T _ZX . However, since the sub-injection (addition of the reducing agent) is performed at T _Z , the sub-injection is performed in the low-temperature exhaust gas temperature region ΔT that deviates from the active temperature region due to the deviation, although the purification is not performed. This causes HC and fuel consumption deterioration due to useless injection. In this device, such a shift in the active temperature region can be suppressed for a long time, and as a result, HC and fuel consumption can be improved.
[0044]
As described above, the embodiment of the present invention is not limited to the above. For example, in the present embodiment, the activation process is performed in both the low temperature range and the high temperature range than the purification temperature range T _Z , but it may be performed in either the low temperature range or the high temperature range. . The present invention can be applied not only to a diesel engine but also to a lean burn gasoline engine. The contents of the prior application may be combined with the present invention, and the sub-injection amount map may be switched following the deterioration / activation of the catalyst. In this embodiment, regarding the determination of the activation process execution time, the engine operation time and the vehicle travel distance are in a parallel relationship, and the activation process is executed when one of the times comes. Since the other may arrive immediately after that, a delay of a predetermined time may be performed or the latter may be canceled in order to prevent useless continuous activation processing.
[0045]
【The invention's effect】
The present invention exhibits the following excellent effects.
[0046]
(1) Deterioration of the NOx catalyst can be suppressed and its initial performance can be maintained for a long time.
[0047]
(2) Increase in NOx emissions can be prevented.
[Brief description of the drawings]
FIG. 1 is a flowchart showing execution contents of an activation process according to an embodiment of the present invention.
FIG. 2 is a flowchart showing an activation processing execution time determination method according to an embodiment of the present invention.
FIG. 3 is a flowchart showing an activation processing execution time determination method according to the embodiment of the present invention.
FIG. 4 is a flowchart showing a main flow of activation processing control according to the embodiment of the present invention.
FIG. 5 is a flowchart showing a NOx purification processing method according to an embodiment of the present invention.
FIG. 6 shows a sub-injection map used for NOx purification processing and activation processing.
FIG. 7 is a graph showing the relationship between catalyst inlet temperature and timer count value in activation processing execution time determination.
FIG. 8 is a configuration diagram showing a NOx reduction device for an engine according to an embodiment of the present invention.
FIG. 9 is a graph showing the purification characteristics of a NOx catalyst.
[Explanation of symbols]
1 Engine 3 NOx catalyst _TZ purification temperature region _NE Engine speed

Claims (5)

An NOx reduction device for an engine in which a NOx catalyst is provided in an exhaust path of an engine, and a reducing agent is added to the exhaust gas within a predetermined exhaust gas temperature range to reduce NOx in the exhaust gas. A NOx reduction device for an engine, comprising an activation treatment means for activating the NOx catalyst by adding a reducing agent to the exhaust gas within a predetermined exhaust gas temperature range at a lower temperature or a higher temperature. The engine NOx reduction device according to claim 1, wherein the activation processing means executes the activation processing every predetermined engine operating time. 3. The activation processing means performs cumulative calculation of engine operation time while performing weighting according to exhaust gas temperature during engine operation, and executes the activation processing when the calculated value reaches a predetermined value. The engine NOx reduction device as described. The engine NOx reduction device according to any one of claims 1 to 3, wherein the activation processing means executes the activation processing for each predetermined vehicle travel distance. 5. The activation processing means performs the addition of the reducing agent by fuel sub-injection into the engine cylinder, and determines the sub-injection amount for each engine speed based on a predetermined map. An NOx reduction device for an engine as described in 1.

Images