JP5195283B2 - Engine exhaust purification system - Google Patents

Description

  The present invention relates to an engine exhaust purification system in which a liquid reducing agent stored in a storage tank is supplied to a selective reduction type NOx purification catalyst provided on an exhaust passage of the engine to promote a reduction reaction. About.

  Conventionally, as shown, for example, in Patent Document 1 below, a selective reduction type NOx purification catalyst (SCR catalyst) provided on an exhaust passage of an engine, a reducing agent solution tank for storing a liquid reducing agent, And a nozzle provided in the exhaust passage upstream of the NOx purification catalyst, and the reducing agent pumped from the pump through a predetermined pipe is added from the nozzle into the exhaust passage. There is known an exhaust gas purification device that promotes a specific exhaust gas purification reaction in the NOx purification catalyst by supplying the same.

In particular, in the technique of Patent Document 1, a concentration sensor for detecting the concentration of the reducing agent is provided in the reducing agent solution tank, and when the concentration of the reducing agent detected by the concentration sensor is outside a specified value, an alarm is issued. The machine is operated to notify the driver of the abnormality, and control is performed to reduce the engine output.
JP 2002-371831 A

  According to the configuration of Patent Document 1 described above, the concentration of the reducing agent is monitored using the concentration sensor, thereby preventing the NOx purification rate from deteriorating when an irregular reducing agent outside the specified concentration is used. There are advantages. However, since the concentration sensor for detecting the concentration of the reducing agent (for example, urea water) is quite expensive, there is a problem that the initial cost of the exhaust gas purification device is greatly increased in the configuration of Patent Document 1 described above.

  The present invention has been made in view of the above circumstances, and is an engine exhaust capable of detecting an abnormal concentration of a reducing agent supplied to a selective reduction type NOx purification catalyst with a lower cost configuration. An object is to provide a purification device.

In order to solve the above problems, the present invention provides a selective reduction type NOx purification catalyst provided on the exhaust passage of an engine by supplying a liquid reducing agent stored in a storage tank to perform a reduction reaction. An engine exhaust gas purification apparatus that is promoted, the first parameter value detection means for detecting a parameter value related to the NOx purification rate purified by the NOx purification catalyst, and the temperature of the NOx purification catalyst Second parameter value detection means for detecting the parameter value to be performed, and control means for controlling each part of the exhaust purification device based on the detection values of both of the detection means, wherein the control means comprises the first parameter value detection means A purification rate calculation unit for calculating an actual NOx purification rate based on the detected value of the NOx, and a temperature of the NOx purification catalyst based on the detected value of the second parameter value detecting means A target setting unit for setting a target NOx purification rate, and a storage unit for storing a target achievement rate comprising a ratio of the target NOx purification rate and the actual NOx purification rate obtained by the target setting unit and the purification rate calculation unit; A replenishment detection unit for detecting that the reductant has been replenished in the storage tank based on a liquid level of the reductant in the storage tank, and the control means uses the replenishment detection unit to reduce the reductant. When replenishment is detected, the target achievement rate stored in the storage unit before and after the replenishment is compared to detect a concentration abnormality of the reducing agent , and the control means further includes the storage unit. The deterioration of the NOx purification catalyst is detected on the basis of the target achievement rate stored in the table, and when the deterioration is detected, the detection of the abnormal concentration of the reducing agent is prohibited (claim). Term ).

  According to the present invention, the storage unit sequentially stores a target achievement rate that is a ratio of the target NOx purification rate according to the temperature of the NOx purification catalyst and the actual NOx purification rate calculated based on the NOx concentration upstream and downstream of the catalyst. Since the urea water concentration abnormality is detected by comparing the target achievement rates stored in the storage unit before and after the replenishment of urea water to the storage tank, Thus, even if a concentration sensor for detecting the concentration of urea water is not provided, it is possible to properly detect the concentration of urea water, and to lower the performance of the NOx purification catalyst due to the concentration abnormality at a lower cost. There is an advantage that it can be effectively prevented with a simple configuration.

In the present invention, since the deterioration of the NOx purification catalyst is detected based on the target achievement rate, the deterioration of the NOx purification catalyst is determined based on the target achievement rate that changes according to the degree of deterioration of the NOx purification catalyst. There is an advantage that it can be detected accurately.

Further, in the present invention, when the deterioration of the NOx purification catalyst is detected, the detection of the abnormal concentration of the reducing agent is prohibited. Therefore, when the target achievement rate rapidly decreases due to the deterioration of the NOx purification catalyst, etc. It is possible to effectively prevent this from being erroneously determined as an abnormal concentration of urea water, and there is an advantage that it is possible to appropriately ensure the detection accuracy regarding the abnormal concentration of urea water.

  As a preferred embodiment of the present invention, the first parameter value detecting means detects the NOx concentration downstream of the NOx purification catalyst and estimates or detects the NOx concentration upstream of the NOx purification catalyst, The purification rate calculation unit of the control means calculates the actual NOx purification rate based on the NOx concentrations upstream and downstream of the catalyst estimated or detected by the first parameter value detection means (claim 2).

  According to this configuration, there is an advantage that the actual NOx purification rate can be accurately calculated based on the NOx concentration detected or estimated on the upstream side and the downstream side of the NOx purification catalyst.

  As a preferred embodiment of the present invention, when the concentration abnormality of the reducing agent is detected, the control means activates a predetermined alarm device to notify the abnormality (Claim 3).

  According to this configuration, it is possible to reliably notify the occupant or maintenance worker that the concentration of urea water is abnormal, and necessary measures such as replenishing the occupant with appropriate concentration of urea water, for example. Can be properly encouraged to adopt.

  As described above, according to the present invention, it is possible to detect an abnormal concentration of the reducing agent supplied to the selective reduction type NOx purification catalyst with a lower cost configuration.

  FIG. 1 is a schematic view showing an exhaust emission control device for an engine according to an embodiment of the present invention. The exhaust gas purification apparatus shown in this figure purifies exhaust gas discharged from an engine other than the figure such as a diesel engine, for example, and, as its basic component, the exhaust passage 1 through which the exhaust gas flows is provided. A NOx purification catalyst 3 provided in the middle part and an addition valve 5 for adding urea water as a reducing agent into the pipe 1a upstream of the NOx purification catalyst 3 in the exhaust passage 1 are provided. . That is, the exhaust gas purification apparatus shown in FIG. 1 adds (injects) urea water into the exhaust passage 1 from the addition valve 5 in accordance with the operating state, and performs a reduction reaction at the downstream side NOx purification catalyst 3. It is provided as a purifying device for a so-called urea SCR (Selective Catalytic Reduction) system that can purify NOx in exhaust gas with a high purification rate by promoting it by the action of the urea water.

  Specifically, when urea water is added to the exhaust gas from the addition valve 5, hydrolysis is performed by the heat of the exhaust gas to generate ammonia. Then, the produced ammonia is adsorbed to the downstream side NOx purification catalyst 3, and the denitration reaction occurs between the adsorbed ammonia and NOx in the exhaust gas, so that the reduction of NOx is promoted. It has become.

  The addition valve 5 has substantially the same structure as an existing fuel injection valve (injector), and is constituted by, for example, an electromagnetic open / close needle valve. Then, when the addition valve 5 is opened or closed based on a control signal from the ECU 21 described later, urea water is injected into the exhaust passage 1 through the nozzle at the tip thereof, or the injection is stopped. It is like that.

  Next, a urea water supply system that supplies urea water to the addition valve 5 will be described. That is, urea water is sequentially supplied from the storage tank 9 to the addition valve 5 through the supply pipe 13, and urea water stored in the storage tank 9 is provided in the middle of the supply pipe 13. An electric pump 7 is disposed for pumping up and pumping the fuel to the addition valve 5. The electric pump 7 is composed of, for example, a three-phase AC motor, and its driving is controlled according to a control signal from the ECU 21 described later.

  The storage tank 9 is composed of a sealed container in which a predetermined concentration of urea water is accommodated, and urea water can be replenished as needed from a liquid supply cap (not shown) provided at the predetermined portion. Yes. In addition, as a measure for preventing the urea water in the storage tank 9 from freezing when it is cold, the storage tank 9 is provided with a heater, a heat insulating material, or the like as necessary.

  A filter 11 for filtering urea water is provided in the storage tank 9 so as to be immersed in the urea water. One end of the supply pipe 13 is connected to the filter 11. . On the other hand, the other end of the supply pipe 13 is connected to the addition valve 5, and urea water filtered by the filter 11 is added through the supply pipe 13 in response to the driving of the electric pump 7. 5 is supplied.

  A pressure control valve 17 for adjusting the pressure of the urea water inside the supply pipe 13 is provided in the middle of the supply pipe 13. Specifically, the pressure control valve 17 returns the excess urea water to the storage tank 9 and maintains the pressure in the supply pipe 13 at a predetermined pressure. That is, a return pipe 15 extending from the storage tank 9 is connected to the pressure control valve 17, and the pressure control valve 17 is opened when the pressure of the urea water in the supply pipe 13 exceeds a predetermined pressure. Then, the excess urea water is returned from the return pipe 15 to the storage tank 9 and, when the pressure in the supply pipe 13 falls below a predetermined pressure, the pressure control valve 17 is closed and the return pipe 15 is closed. By stopping the flow from the storage tank 9 to the storage tank 9, the pressure of the urea water in the supply pipe 13 is maintained at a predetermined pressure.

  Next, the control system of the exhaust emission control device will be described. The exhaust purification apparatus of the present embodiment has an ECU 21 (corresponding to the control means according to the present invention) comprising a conventionally known CPU, various memories, and the like. The operation of each part is controlled centrally.

  Various sensors are electrically connected to the ECU 21. Specifically, the ECU 21 includes a temperature sensor 25 provided in the NOx purification catalyst 3, a first NOx concentration sensor 26 provided in the pipe 1a upstream of the NOx purification catalyst 3 in the exhaust passage 1, and a NOx purification. The second NOx concentration sensor 27 provided in the pipe 1b on the downstream side of the catalyst 3 and the liquid level sensor 28 provided in the storage tank 9 are electrically connected. In this embodiment, the temperature sensor 25 provided in the NOx purification catalyst 3 corresponds to the first parameter value detecting means according to the present invention, and the first is provided on the upstream side and the downstream side of the NOx purification catalyst. The first and second NOx concentration sensors 26 and 27 correspond to the second parameter value detecting means according to the present invention.

  The temperature of the NOx purification catalyst 3 detected by the temperature sensor 25, the NOx concentration in the exhaust gas detected by the first and second NOx concentration sensors 26, 27, and the liquid level sensor 28 are detected. The level of the urea aqueous solution is input to the ECU 21 as an electrical signal, and the ECU 21 is configured to execute various arithmetic processing for control using the input value. Hereinafter, the temperature of the NOx purification catalyst 3 detected by the temperature sensor 25 is detected by Ts, the NOx concentration upstream of the catalyst detected by the first NOx concentration sensor 26 is detected by Dnf, and the second NOx concentration sensor 27 detects the NOx concentration. The NOx concentration on the downstream side of the catalyst is represented by Dnr, and the liquid level of urea water in the storage tank 9 detected by the liquid level sensor 28 is represented by L.

  Further, the ECU 21 is electrically provided with an alarm device 31 comprising a warning lamp or the like for notifying the occupant or the maintenance worker when the deterioration of the NOx purification catalyst 3 or the abnormal concentration of urea water is detected. It is connected to the. Note that how to detect the deterioration of the NOx purification catalyst 3 and the abnormal concentration of urea water will be described in detail in a flowchart described later.

  The ECU 21 configured as described above executes various calculations based on the detection values (Dnf, Dnr, Ts, L) input from the various sensors 25 to 28, thereby enabling each part of the exhaust gas purification apparatus to perform various operations. Control the overall operation. For example, the ECU 21 determines the urea water to be added from the addition valve 5 based on the catalyst temperature Ts detected by the temperature sensor 25, the NOx concentration Dnf on the upstream side of the catalyst detected by the first NOx concentration sensor 26, and the like. The amount is calculated, and the opening / closing operation of the addition valve 5 is controlled so that the calculated amount of urea water is actually added into the exhaust passage 1. Then, by adding urea water from the addition valve 5 in this way, a predetermined amount of urea water is supplied to the downstream NOx purification catalyst 3, and by the action of this urea water, the reduction reaction at the NOx purification catalyst. Has been promoted.

  The function of the ECU 21 will be described in more detail. The ECU 21 includes a purification rate calculation unit 21a, a target setting unit 21b, a storage unit 21c, and a replenishment detection unit 21d as functional elements.

  The purification rate calculation unit 21a determines the NOx actually purified by the NOx purification catalyst 3 based on the NOx concentrations Dnf and Dnr upstream and downstream of the catalyst detected by the first and second NOx concentration sensors 26 and 27. The ratio (hereinafter, this is referred to as the actual NOx purification rate Ra) is calculated.

  Based on the temperature Ts of the NOx purification catalyst 3 detected by the temperature sensor 25, the target setting unit 21b sets the ratio of NOx that can be ideally purified by the NOx purification catalyst 3 to a target NOx purification rate. (Hereinafter, this is referred to as a target NOx purification rate Rt).

  The target NOx purification rate Rt will be described in more detail. The effect of promoting the reduction reaction by adding urea water from the addition valve 5 varies depending on the temperature Ts of the NOx purification catalyst 3, and the active state of the catalyst is also the temperature. It varies depending on Ts. Therefore, the target NOx purification rate Rt, which is an ideal value of the NOx purification rate, varies according to the catalyst temperature Ts as shown in FIG. Therefore, the target setting unit 21b shows the current catalyst temperature Ts input from the temperature sensor 25 to appropriately set the target NOx purification rate Rt that changes in accordance with the catalyst temperature Ts as shown in FIG. The target NOx purification rate Rt to be targeted at the present time is sequentially set based on the characteristic data. Note that the temperature Tsq in FIG. 2 represents the lower limit value of the catalyst temperature Ts at which the urea water from the addition valve 5 can be added. That is, when the catalyst temperature Ts is lower than the lower limit temperature Tsq, the urea water is not sufficiently hydrolyzed (that is, ammonia for promoting the reduction reaction is not sufficiently generated). There is no addition.

  The storage unit 21c stores the ratio of the actual NOx purification rate Ra to the target NOx purification rate Rt (hereinafter referred to as the target achievement rate X) while sequentially updating it. That is, the ECU 21 executes an operation of dividing the actual NOx purification rate Ra calculated by the purification rate calculation unit 21a by the target NOx purification rate Rt set by the target setting unit 21b, and the ratio Ra / Rt obtained as a result Are sequentially stored in the storage unit 21c as the target achievement rate X. The storage unit 21c stores, for example, map-format data corresponding to the relationship between the catalyst temperature Ts and the target NOx purification rate Ra (FIG. 2) as other various control data.

  The replenishment detector 21d detects that urea water has been replenished in the storage tank 9 based on the liquid level L of urea water in the storage tank 9 detected by the liquid level sensor 28.

  Next, a specific procedure of the control operation performed by the ECU 21 will be described using the flowchart of FIG. 3 and the time chart of FIG. When the engine is started and the flowchart of FIG. 3 is started, the ECU 21 detects the temperature Ts of the NOx purification catalyst 3 from the temperature sensor 25, the first NOx concentration sensor 26, the second NOx concentration sensor 27, and the liquid level sensor 28, and the upstream side of the catalyst. The control for acquiring the NOx concentration Dnf, the NOx concentration Dnr on the downstream side of purification, and the urea water liquid level L in the storage tank 9 is executed (step S1).

  Next, the ECU 21 executes control for determining whether or not the temperature Ts of the NOx purification catalyst 3 acquired in step S1 is equal to or higher than the lower limit value Tsq of the catalyst temperature shown in FIG. 2 (step S2). And after it determines with YES here and it is confirmed that the catalyst temperature Ts rose to temperature Tsq which can add the urea water from the addition valve 5, it transfers to the process of following step S3.

  When the process proceeds to step S3, the ECU 21 executes a control for setting the current target NOx purification rate Rt based on the catalyst temperature Ts acquired in step S1 under the calculation process by the target setting unit 21b ( Step S3). That is, the target setting unit 21b compares the current catalyst temperature Ts detected by the temperature sensor 25 with the characteristic data (see FIG. 2) stored in the storage unit 21c in advance, so that the catalyst temperature Ts. The target NOx purification rate Rt corresponding to is specified, and the value is set as the target NOx purification rate Rt that should be the current target.

  Next, the ECU 21 performs control to calculate the current actual NOx purification rate Ra based on the NOx concentrations Dnf and Dnr upstream and downstream of the catalyst acquired in step S1 under the calculation process by the purification rate calculation unit 21a. Execute (step S4). That is, the purification rate calculation unit 21a performs an operation of dividing the difference between the upstream and downstream NOx concentrations Dnf and Dnr of the NOx purification catalyst 3 by the upstream NOx concentration Dnf, and the obtained ratio (Dnf−Dnr). / Dnf is acquired as the actual NOx purification rate Ra, which is the ratio of NOx actually purified by the NOx purification catalyst 3.

  When the current target NOx purification rate Rt and the actual NOx purification rate Ra are calculated as described above, the ECU 21 calculates the target achievement rate X composed of the ratio Ra / Rt of both, and stores this in the storage unit 21c. The stored control is executed (step S5). For example, when the target NOx purification rate Rt is 80% and the actual NOx purification rate Ra is 70%, the ratio Ra / Rt = 0.875 of both, so the target achievement rate X is 87.5% become.

  FIG. 5 shows a data group accumulated in the storage unit 21c by repeating the process of step S5. As shown in the figure, the storage unit 21c stores a plurality of data groups in which the target achievement rate X is accumulated over a predetermined period, and in response to obtaining a new data group, The memory is updated sequentially. For example, as shown in the figure, when data groups 1 and 2 consisting of data of the target achievement rate X in two periods are stored in the storage unit 21c, when the third data group 3 is obtained, By erasing the previously stored data group 1, a new data group is constantly updated and stored in the storage unit 21c.

  When the process for storing the target achievement rate X is completed in this way, the ECU 21 executes control for determining whether or not the stored target achievement rate X is equal to or less than a predetermined threshold value α (step S6). As shown in FIG. 4B, the threshold value α is set to a predetermined value smaller than 1, and is used to determine whether or not the NOx purification catalyst 3 has deteriorated. That is, the purification performance gradually decreases due to the deterioration of the NOx purification catalyst 3 over time, so the target achievement rate X also gradually decreases with time. Therefore, when the target achievement rate X, which is an indicator of the degree of deterioration of the NOx purification catalyst 3, is reduced and the value is equal to or less than the threshold value α, it is determined that the NOx purification catalyst 3 has deteriorated.

  When it is determined YES in step S6 and it is confirmed that the target achievement rate X ≦ α, the ECU 21 determines that the NOx purification catalyst 3 has deteriorated (step S7) and activates the alarm device 31. Then, control for notifying the occupant and the like of the deterioration of the NOx purification catalyst 3 is executed (step S8).

  On the other hand, when it is determined NO in step S6 and it is confirmed that the NOx purification catalyst 3 has not deteriorated, the ECU 21 supplies urea water to the storage tank 9 under the arithmetic processing by the replenishment detection unit 21d. Control to determine whether or not there is is executed (step S9). That is, when the urea water is replenished in the storage tank 9, the liquid level L of the urea water temporarily rises, for example, as shown at time t1 or t2 in FIG. Determines whether or not the liquid level L of the urea water has risen by a predetermined amount or more based on the detection value of the liquid level sensor 28 acquired in step S1, and if it is confirmed that the liquid level L has risen, Judge that water has been replenished.

  When it is determined YES in step S9 and the supply of urea water is confirmed, the ECU 21 executes control for comparing the absolute value of the difference in the target achievement rate X before and after the supply of urea water with a predetermined threshold value β. (Step S10). Specifically, the data group of the target achievement rate X (see FIG. 5) is read from the storage unit 21c, and the data group is averaged before and after replenishment. The absolute value of the difference between the target achievement rates X in (1) is calculated, and it is determined whether or not the value is equal to or greater than a predetermined threshold value β.

  If the determination in step S10 is YES, it can be determined that the concentration of urea water is abnormal. For example, when the replenished urea water has a prescribed concentration, there is no effect on the performance of the NOx purification catalyst 3, and therefore, as shown at time t1 in FIG. Thus, the target achievement rate X does not change. On the other hand, if the supplied urea water is non-standard, for example, its concentration is abnormally low, the effect of promoting the reduction reaction due to the addition of urea water is reduced, and the performance of the NOx purification catalyst 3 is adversely affected. Therefore, as shown at time t2 in FIG. 4 (b), the target achievement rate X greatly decreases before and after the urea water supply. Therefore, the concentration of urea water is detected by comparing the target achievement rates X before and after replenishment and determining whether or not the absolute value of the difference between them is equal to or greater than a predetermined threshold value β. Note that the absolute value of the difference in the target achievement rate X is calculated in this calculation even when the target achievement rate X suddenly rises due to abnormally high-concentration urea water replenished exceeding the specified value. This is because it can be detected as an abnormal concentration.

  Incidentally, the supply of urea water to the storage tank 9 is not necessarily performed during operation of the engine, but may be performed while the engine is stopped. In such a case, in step S10, for example, the average value of the target achievement rate X stored immediately before the engine is stopped, and the average value of the target achievement rate X that is acquired first after the engine is restarted. Is performed, and the concentration abnormality of the urea water is determined according to the result.

  If it is determined YES in step S10 as described above, and | X before replenishment-X after replenishment X | ≧ β is confirmed, ECU 21 determines that the concentration of the urea water is equal to or higher (step S10). S11), the alarm device 31 is operated to execute a control for notifying the passenger or the like of the abnormal concentration of urea water (step S12). At this time, for example, when the alarm device 31 is composed of a warning lamp, the warning lamp is operated in a manner different from that in step S8 in order to distinguish it from the notification of the deterioration of the NOx purification catalyst 3 in the previous step S8. It is preferable. Specifically, it is conceivable to turn on the warning lamp when notifying the deterioration of the catalyst in step S8 and blinking the warning lamp when notifying the concentration abnormality of urea water in step S12.

  On the other hand, when it is determined NO in step 10, the ECU 21 determines that the concentration of urea water is normal (step S13), and then returns.

  As described above, the engine exhaust purification apparatus according to the present embodiment stores the selective reduction type NOx purification catalyst 3 provided on the exhaust passage 1 of the engine and the urea water supplied to the NOx purification catalyst 3. Storage tank 9, first and second NOx concentration sensors 26 and 27 for detecting NOx concentrations Dnf and Dnr upstream and downstream of the NOx purification catalyst 3, and a temperature Ts of the NOx purification catalyst 3. A temperature sensor 25 to be detected, and an ECU 21 as control means for controlling each part of the exhaust gas purification apparatus based on detection values of these various sensors are provided. The ECU 21 has, as functional elements, a purification rate calculation unit 21a that calculates an actual NOx purification rate Ra based on the detection values Dnf and Dnr of the NOx concentration sensors 26 and 27, and a detection value of the temperature sensor 25. A target setting unit 21b for setting a target NOx purification rate Rt according to the temperature Ts of the NOx purification catalyst 3, and the target NOx purification rate Rt and the actual NOx obtained by the target setting unit 21b and the purification rate calculation unit 21a. Based on the storage unit 21c that stores the target achievement rate X, which is a ratio with the purification rate Ra, and the liquid level L of the urea water in the storage tank 9, it is detected that urea water has been replenished in the storage tank 9. Further, the ECU 21 detects the supply of urea water before and after the supply when the supply detection unit 21d detects the supply of urea water. By comparing the Target% X stored respectively in 憶部 21c, and is configured to detect the concentration abnormality of the urea aqueous solution. According to such a configuration, there is an advantage that an abnormal concentration of urea water supplied to the NOx purification catalyst 3 can be detected with a lower cost configuration.

  That is, in the above embodiment, the ratio (Ra / Rt) between the target NOx purification rate Rt corresponding to the temperature Ts of the NOx purification catalyst 3 and the actual NOx purification rate Ra calculated based on the NOx concentrations Dnf and Dnr upstream and downstream of the catalyst. ) Is sequentially stored in the storage unit 21c (step S5), and when the urea water is replenished to the storage tank 9 (YES in step S9), the above-mentioned memory is stored before and after the replenishment. Since the urea water concentration abnormality is detected by comparing the target achievement rate X stored in the unit 21c (steps S10 and S11), a concentration sensor for detecting the urea water concentration is provided as in the prior art. Even if it is not, it is possible to properly detect the concentration abnormality of the urea water, and it is possible to effectively prevent the deterioration of the performance of the NOx purification catalyst 3 due to the concentration abnormality with a lower cost configuration. There is an advantage to say.

  Of course, in the case of the above configuration, the temperature sensor 25 for detecting the catalyst temperature Ts and the concentration sensors 26 and 27 for detecting the NOx concentrations Dnf and Dnr are necessary, but these various sensors determine the amount of urea water added. Or a sensor that is originally necessary for judging deterioration of the NOx purification catalyst 3 or the like, and is a sensor that is inherently provided in the exhaust purification device regardless of whether or not an abnormal concentration of urea water is detected. Therefore, according to the above configuration in which the abnormal concentration of urea water is detected using the detection values of these inherently provided sensors, the performance of the NOx purification catalyst 3 can be improved without causing unnecessary cost increase. There is an advantage that it can be secured properly.

  Further, in the above embodiment, when the urea water concentration abnormality is detected, the alarm device 31 including, for example, a warning lamp is operated to notify the abnormality (step S12), so the urea water concentration is abnormal. This can be surely notified to the occupant or the maintenance worker, and the occupant or the like can be appropriately urged to take necessary measures such as replenishing an appropriate concentration of urea water.

  In the above embodiment, the deterioration of the NOx purification catalyst 3 is detected by comparing the target achievement rate X stored in the storage unit 21c with a predetermined threshold value α (steps S6 and S7). There is an advantage that the deterioration of the NOx purification catalyst 3 can be accurately detected based on the target achievement rate X that changes in accordance with the degree of deterioration of the NOx purification catalyst 3.

  Further, in the above embodiment, when the deterioration of the NOx purification catalyst 3 is detected (in the case of YES at step S6), the alarm device 31 is actuated to immediately return to detect the urea water concentration abnormality. Since the execution of the control (steps S10 to S13) is prohibited, when the target achievement rate X suddenly decreases due to the deterioration of the NOx purification catalyst 3, this is mistaken as an abnormal concentration of urea water. Determination can be effectively prevented, and there is an advantage that it is possible to appropriately ensure the detection accuracy regarding the abnormal concentration of urea water.

  In the above embodiment, the catalyst temperature Ts is directly detected by the temperature sensor 25 provided in the NOx purification catalyst 3. For example, the temperature of the exhaust gas flowing upstream from the NOx purification catalyst 3 by a predetermined distance is set. The temperature Ts of the NOx purification catalyst 3 may be obtained by detecting and multiplying the detected temperature by a predetermined correction coefficient. Further, the temperature Ts of the NOx purification catalyst 3 may be estimated based on the operating state of the engine determined from the engine load and the rotational speed, the duration in the operating state, and the like. In any case, in order to examine the temperature Ts of the NOx purification catalyst 3, it is only necessary to detect some parameter value related to the temperature Ts, and there is no particular limitation as to what state quantity is specifically detected.

  Similarly, in the above embodiment, the NOx concentrations Dnf and Dnr on the upstream side and the downstream side of the NOx purification catalyst 3 are detected by the first and second NOx concentration sensors 26 and 27 and detected by these sensors. Based on the NOx concentrations Dnf and Dnr, the actual NOx purification rate Ra, which is the ratio of NOx actually purified by the NOx purification catalyst 3, is calculated. Any parameter value related to the purification rate may be detected, and the NOx concentrations Dnf and Dnr upstream and downstream of the catalyst are not necessarily detected directly. In particular, the NOx concentration Dnf on the upstream side of the NOx purification catalyst 3 can be estimated relatively easily from, for example, the operating state of the engine, and the NOx concentration Dnf is thus obtained by estimation. Since the first NOx concentration sensor 26 in the above embodiment can be omitted, there is an advantage that the cost of the apparatus can be further reduced.

  In the above embodiment, urea water is used as the reducing agent for promoting the reduction reaction in the NOx purification catalyst 3, but the present invention is not limited to this as long as the same effect can be obtained. For example, the NOx purification catalyst 3 Depending on the type, ammonia water or alcohols may be used as the reducing agent.

1 is a schematic view showing an exhaust emission control device for an engine according to an embodiment of the present invention. It is a graph which shows the relationship between catalyst temperature and target NOx purification rate. It is a flowchart for demonstrating control operation | movement of the said exhaust gas purification apparatus. It is a time chart for demonstrating control operation | movement of the said exhaust gas purification apparatus. It is a figure for demonstrating the specific procedure at the time of memorize | storing data of a real NOx purification rate in a memory | storage part.

DESCRIPTION OF SYMBOLS 1 Exhaust passage 3 NOx purification catalyst 9 Storage tank 21 ECU (control means)
21a Purification rate calculation unit 21b Target setting unit 21c Storage unit 21d Replenishment detection unit 25 Temperature sensor (second parameter value detection means)
26, 27 NOx concentration sensor (first parameter value detecting means)
31 alarm device Rt target NOx purification rate Ra actual NOx purification rate X target achievement rate Dnf (upstream of catalyst) NOx concentration Dnr (downstream of catalyst) NOx concentration L (reducing agent) liquid level

Claims (3)

An engine exhaust gas purification apparatus that promotes a reduction reaction by supplying a liquid reducing agent stored in a storage tank to a selective reduction type NOx purification catalyst provided on an exhaust passage of an engine,
First parameter value detecting means for detecting a parameter value related to the purification rate of NOx purified by the NOx purification catalyst;
Second parameter value detection means for detecting a parameter value related to the temperature of the NOx purification catalyst;
Control means for controlling each part of the exhaust gas purification device based on the detection values of both the detection means,
The control means includes a purification rate calculation unit that calculates an actual NOx purification rate based on the detection value of the first parameter value detection means, and a temperature of the NOx purification catalyst based on the detection value of the second parameter value detection means. A target setting unit that sets a target NOx purification rate according to the target, and a storage that stores a target achievement rate that is a ratio of the target NOx purification rate and the actual NOx purification rate obtained by the target setting unit and the purification rate calculation unit And a replenishment detection unit for detecting that the reductant is replenished in the storage tank based on the liquid level of the reductant in the storage tank,
In addition, when the replenishment detection unit detects the replenishment of the reducing agent, the control means compares the target achievement rates stored in the storage unit before and after the replenishment, thereby comparing the concentration of the reducing agent. Detect anomalies ,
Furthermore, the control means detects the deterioration of the NOx purification catalyst based on the target achievement rate stored in the storage unit, and prohibits the detection of the concentration abnormality of the reducing agent when the deterioration is detected. An exhaust emission control device for an engine characterized by comprising: The exhaust emission control device for an engine according to claim 1,
The first parameter value detecting means detects the NOx concentration downstream of the NOx purification catalyst and estimates or detects the NOx concentration upstream of the NOx purification catalyst,
A purification rate calculation unit of the control unit calculates the actual NOx purification rate based on each NOx concentration upstream or downstream of the catalyst estimated or detected by the first parameter value detection unit. apparatus. The engine exhaust gas purification apparatus according to claim 1 or 2,
The engine exhaust purification apparatus according to claim 1, wherein when the reducing agent concentration abnormality is detected, the control means activates a predetermined alarm device to notify the abnormality.

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