JP2005264731A - Exhaust purification device control method - Google Patents

Abstract

A remaining amount of a reducing agent that remains after being stored in a selective catalytic reduction catalyst is obtained so that the amount of the reducing agent added can be appropriately controlled.
SOLUTION: A selective catalytic reduction catalyst 10 is provided in the middle of an exhaust pipe 9, and urea water 17 (reducing agent) is added upstream of the selective catalytic reduction catalyst 10 by urea water adding means 18 (reducing agent adding means). Then, regarding the control method of the exhaust gas purification apparatus for reducing and purifying NOx, the amount of NOx generated is estimated according to the operating state of the engine 1 and the scheduled addition amount of the urea water 17 corresponding to the estimated value is determined, while the urea water 17 Based on the elapsed time and the exhaust temperature (or catalyst bed temperature) after the addition of, the amount of decrease in consideration of the reaction consumption amount and the evaporation amount of the urea water 17 is calculated, and the decrease amount is actually added to the latest urea water 17 The amount of addition is subtracted from the amount, the amount of addition is subtracted from the scheduled addition amount of the next urea water 17 to determine the actual addition amount, and the actual addition amount is added to the urea water addition means 18 Use the indicated value.
[Selection] Figure 1

Description

  The present invention relates to a method for controlling an exhaust emission control device.

  Conventionally, a diesel engine is equipped with a selective reduction catalyst having a property of selectively reacting NOx with a reducing agent even in the presence of oxygen in the middle of an exhaust pipe through which exhaust gas circulates. A required amount of reducing agent is added upstream of the catalyst so that the reducing agent undergoes a reduction reaction with NOx (nitrogen oxide) in the exhaust gas on the selective catalytic reduction catalyst, thereby reducing the NOx emission concentration. There is what I did.

On the other hand, in the field of industrial flue gas denitration treatment in plants and the like, the effectiveness of a method for reducing and purifying NOx using ammonia (NH ₃ ) as a reducing agent is already widely known. Since it is difficult to ensure safety with respect to traveling with ammonia itself, in recent years, the use of non-toxic urea water as a reducing agent has been studied (for example, Patent Document 1 and Patents). Reference 2).
JP 2002-161732 A JP 2002-166130 A

  That is, if urea water is added to the exhaust gas upstream of the selective catalytic reduction catalyst, the urea water is decomposed into ammonia and carbon dioxide under a temperature condition of about 170 ° C. or higher, and the exhaust gas is exhausted on the selective catalytic reduction catalyst. The NOx contained therein is reduced and purified well by ammonia.

  However, in this type of selective reduction type catalyst, when a transient change (change in gas flow rate, change in catalyst bed temperature) of the engine operating state occurs immediately after the addition of urea water, and the catalytic activity decreases, A part of urea water (ammonia) may be stored in the selective catalytic reduction catalyst as a surplus, and thus the remaining amount of residual urea stored in the selective catalytic reduction catalyst is estimated to obtain new urea water. It has not been studied until the amount added is controlled.

  For this reason, if the amount of urea water is already stored in the selective catalytic reduction catalyst by simply increasing / decreasing the amount of urea water according to the amount of NOx generated, the amount of urea water added There is a concern that excess urea water that does not contribute to the reaction cannot be stored in the selective catalytic reduction catalyst and is discharged outside the vehicle as ammonia gas or the like.

  The present invention has been made in view of the above-described circumstances, and an exhaust purification device that can appropriately control the amount of reducing agent added by determining the remaining amount of reducing agent remaining in the selective reduction catalyst. It aims to provide a control method.

  The present invention controls an exhaust emission control device in which a selective reduction catalyst is provided in the middle of an exhaust pipe and a reducing agent is added to the upstream side of the selective reduction catalyst by a reducing agent addition means to reduce and purify NOx. In this method, the NOx generation amount is estimated according to the operating state of the engine, and the scheduled addition amount of the reducing agent corresponding to the estimated value is determined, while the elapsed time after the addition of the reducing agent and the exhaust temperature or the catalyst bed temperature Based on the above, the reduction amount considering the reaction consumption and evaporation amount of the reducing agent is calculated, and the reduction amount is subtracted from the actual addition amount of the latest reducing agent to obtain the addition residual amount. The actual addition amount is determined by subtracting from the scheduled addition amount of the reducing agent, and the actual addition amount is used as an addition instruction value to the reducing agent addition means.

  Thus, in this way, the remaining amount of the reducing agent remaining in the selective catalytic reduction catalyst in the previous addition of the reducing agent is obtained, and the remaining amount of addition is subtracted from the next scheduled reducing agent addition amount. Therefore, even if a sufficient amount of reducing agent has already been stored in the selective catalytic reduction catalyst, the residual amount of addition is determined. The reducing agent is added by the reducing agent addition means after being corrected to the actual addition amount considering the amount, and most of the reducing agent is efficiently used for the reduction and purification reaction of NOx, so that there is no surplus. A situation in which excess reducing agent that does not contribute is not stored in the selective catalytic reduction catalyst and is discharged outside the vehicle does not occur.

  Further, in the present invention, even after the engine is stopped, the reduction amount of the reducing agent is continuously calculated until the exhaust temperature around the selective catalytic reduction catalyst or the catalyst bed temperature falls to a predetermined temperature, and the reduction amount is stopped. It is preferable to update the addition remaining amount by subtracting from the immediately preceding addition remaining amount.

  In this way, taking into account the decrease that evaporates due to the residual heat remaining on the support of the selective catalytic reduction catalyst after the engine is stopped (consumption due to the reduction reaction in the high temperature range), this decrease is calculated from the remaining amount immediately before the engine is stopped. By subtracting from time to time, the addition of the reducing agent after the engine restart is executed more accurately, and the actual amount of addition is insufficient because the remaining amount of the reducing agent remaining in the selective catalytic reduction catalyst is estimated more than the actual amount. The situation will be avoided in advance.

  Further, in the present invention, the storable amount that can be stored in the selective catalytic reduction catalyst at the current exhaust temperature or catalyst bed temperature is estimated, and when the added remaining amount exceeds the estimated storable amount, It is preferable to stop the addition.

  In other words, when the remaining amount exceeds the storable amount, the possibility that the reducing agent is easily released from the selective catalytic reduction catalyst by adding a new reducing agent increases and is likely to be discharged outside the vehicle. If the addition of the reducing agent is actively stopped when the remaining amount exceeds the amount that can be stored, the reducing agent stored in the selective catalytic reduction catalyst can be used for NOx reduction and purification. The tendency to desorb the reducing agent will be suppressed.

  According to the control method of the exhaust purification apparatus of the present invention described above, various excellent effects as described below can be obtained.

  (I) Since the remaining amount of the reducing agent remaining in the selective catalytic reduction catalyst can be obtained and the amount of the reducing agent added can be appropriately controlled, most of the added reducing agent is efficiently used for NOx reduction and purification reaction. It can be used well so as not to be excessive, and it is possible to avoid a situation in which the excessive reducing agent is exhausted outside the vehicle without being stored in the selective catalytic reduction catalyst.

  (II) The remaining amount of addition can be appropriately corrected in consideration of the decrease that evaporates due to the residual heat remaining on the support of the selective catalytic reduction catalyst after the engine is stopped (consumption due to the reduction reaction in the high temperature range). A situation in which the remaining amount is estimated more than the actual amount and the actual addition amount is insufficient can be avoided in advance, and the reducing agent can be added more accurately after the engine is restarted.

  (III) Since the addition of the reducing agent is actively stopped when the remaining amount exceeds the storable amount, the reducing agent becomes excessive by selectively adding a reducing agent, and selective reduction is performed. The tendency to easily desorb from the mold catalyst can be suppressed, and the possibility that excess reducing agent is discharged outside the vehicle can be more reliably avoided.

  Embodiments of the present invention will be described below with reference to the drawings.

  1 to 5 show an example of an embodiment of the present invention. Reference numeral 1 in FIG. 1 denotes an engine that is a diesel engine. In the engine 1 shown here, a turbocharger 2 is provided. The air 4 guided from the air cleaner 3 is sent to the compressor 2a of the turbocharger 2 through the intake pipe 5, and the air 4 pressurized by the compressor 2a is further sent to the intercooler 6 to be cooled. The air 4 is guided from the intercooler 6 to an intake manifold (not shown) and introduced into each cylinder of the engine 1.

  The exhaust gas 7 discharged from each cylinder of the engine 1 is sent to the turbine 2b of the turbocharger 2 through the exhaust manifold 8, and the exhaust gas 7 that has driven the turbine 2b goes out of the vehicle through the exhaust pipe 9. It is supposed to be discharged.

  In the middle of the exhaust pipe 9 through which the exhaust gas 7 circulates, a selective catalytic reduction catalyst 10 is mounted and mounted by a casing 11, and this selective catalytic reduction catalyst 10 is a flow-through type as shown in FIG. The honeycomb structure is formed so that NOx can be selectively reacted with ammonia even in the presence of oxygen.

  Further, an electromagnetic addition valve 13 is arranged on the upstream side of the casing 11, and a urea water supply line 15 having a supply pump 16 is provided between the addition valve 13 and a urea water tank 14 provided at a required place. The urea water 17 (reducing agent) in the urea water tank 14 is driven to the upstream side of the selective catalytic reduction catalyst 10 through the addition valve 13 by driving a supply pump 16 that is connected and is provided in the middle of the urea water supply line 15. The addition valve 13, the urea water tank 14, the urea water supply line 15, and the supply pump 16 constitute urea water adding means 18 (reducing agent adding means).

  Further, a temperature sensor 19 for detecting the temperature of the exhaust gas 7 introduced into the selective catalytic reduction catalyst 10 is provided on the inlet side of the casing 11, and a detection signal 19a from the temperature sensor 19 is sent to an engine control computer ( It is input to a control device 12 constituting an ECU (Electronic Control Unit).

  On the other hand, the control device 12 outputs a valve opening command signal 13a and a drive command signal 16a to the addition valve 13 and the supply pump 16, respectively. The amount of addition of 17 is appropriately controlled, and the injection pressure required when the urea water 17 is added can be appropriately obtained by driving the supply pump 16.

FIG. 3 shows a specific control procedure in the control device 12. In step S1, the current engine 1 is determined to start based on a detection signal from a rotation sensor (not shown). If it is determined that the engine has started at a predetermined rotational speed or higher, the routine proceeds to step S2 where the exhaust temperature t is detected based on the detection signal 19a from the temperature sensor 19, and the selective reduction catalyst is detected at the current exhaust temperature t. The storage capacity q _o of urea water 17 (ammonia) that can be stored in 10 is read out and estimated from the map of the correspondence relationship between the storage capacity q _o and the exhaust gas temperature t as shown in the graph of FIG. The

Then, in step S3, than the resulting reservoir can amount q _o in the previous step S2, it is determined whether the direction of addition remaining q _r, which will be described in detail later small, the additive remaining q _r is If it exceeds the storable amount q _o , the process proceeds to step S4 and the addition of the urea water 17 is stopped. On the other hand, if it is determined that the remaining amount q _r is less than the storable amount q _o , Proceeding to S5, the NOx generation amount in the current operating state is read from the map and estimated based on detection signals from an accelerator sensor, a rotation sensor, etc. (not shown).

  Here, since the control device 12 in this embodiment also serves as an engine control computer, the rotational speed and load of the engine 1 are always monitored. It is also possible to estimate the NOx generation amount in consideration of other monitoring factors such as the fuel injection amount and the intake air amount.

Then, in step S6, it will be added a predetermined amount q _y of the urea water 17 to meet the estimated value of the NOx generation amount obtained in the previous step S5 is calculated, this time, the temperature sensor 19 at step S6 The scheduled addition amount q _y of the urea water 17 is appropriately corrected according to the exhaust gas temperature t detected by the above.

Further, in the next step S7, the next added predetermined amount q _y obtained in the previous step S6, the actual addition amount of urea water 17 by subtracting the added residual q _r used in the previous step S3 q _T is determined, and the final actual addition amount q _T of the urea water 17 is output as an addition instruction value to the urea water addition means 18.

On the other hand, the elapsed time T after the addition of the urea water 17 is elapsed by the timer function in the control device 12 in step S8, and the exhaust temperature t is detected based on the detection signal 19a from the temperature sensor 19 in step S9. The reduction coefficient k per unit time considering the reaction consumption and evaporation of the urea water 17 is read out from the map of the correspondence relationship between the reduction coefficient k and the exhaust temperature t as shown in the graph of FIG. The reduction coefficient k timed in the previous step S8 is multiplied by the elapsed time T timed in the previous step S8, thereby calculating a reduction amount q _j considering the reaction consumption amount and the evaporation amount of the urea water 17. The

Then, at step S11, reduction q _j obtained in step S10 in previously, the addition remaining q _r is subtracted from the actual addition amount q _T of the most recent urea water 17 which has been obtained in the previous step S7 This added remaining amount _qr is used in the previous step S3 or step S7 for the next addition of the urea water 17.

  The above-described control procedure from step S2 to step S11 is repeated unless stop of the engine 1 is determined based on a detection signal from a rotation sensor (not shown) in step S12. The process is terminated when it is determined that the engine 1 is stopped.

Thus, if the exhaust gas purification device is controlled by such a control device 12, the remaining amount _qr of the urea water 17 remaining in the selective catalytic reduction catalyst 10 by the previous addition of the urea water 17 is obtained. the added residual q _r to determine the actual amount q _T is subtracted from the added predetermined quantity q _y of the next urea water 17, and the said actual amount q _T and added instruction value to the urea water addition means 18 since already selective reduction as a sufficient amount of urea water 17 has been reserved in the catalyst 10, the actual amount q _T on the corrected urea water 17 is the urea water addition means in consideration of its addition remaining q _r 18 is added.

  As a result, most of the newly added urea water 17 is efficiently used for the reduction and purification reaction of NOx and does not remain, so that excess urea water 17 that does not contribute to the reaction cannot be stored in the selective catalytic reduction catalyst 10. The situation of exhausting ammonia gas etc. outside the car will not occur.

Further, particularly in the present embodiment, the storable amount q _o that can be stored in the selective catalytic reduction catalyst 10 at the current exhaust gas temperature t is estimated, and the estimated remaining storable amount q _o is used as the addition remaining amount q _r. Since the addition of the urea aqueous solution 17 is immediately stopped when it exceeds, the addition of the new aqueous urea solution 17 under the situation where the addition remaining amount q _r already exceeding the storage capacity q _o is confirmed is avoided. The

That is, when the addition remaining amount q _r exceeds the storable amount q _o , the urea water 17 is easily desorbed as ammonia gas or the like by newly adding the urea water 17 and may be discharged out of the vehicle. Therefore, if the addition of the urea water 17 is positively stopped when the addition remaining amount q _r exceeds the storable amount q _o , the NOx is reduced by the urea water 17 stored in the selective catalytic reduction catalyst 10. Reduction purification is provided and the tendency of desorption of the urea water 17 from the selective catalytic reduction catalyst 10 is suppressed.

Therefore, according to the above embodiment, the added remaining amount _qr of the urea water 17 remaining in the selective catalytic reduction catalyst 10 can be obtained and the added amount of the urea water 17 can be appropriately controlled. Most of the water 17 can be efficiently used in the reduction and purification reaction of NOx so as not to be excessive. Excess urea water 17 is not stored in the selective catalytic reduction catalyst 10 and is discharged outside the vehicle as ammonia gas or the like. Can be avoided in advance.

In addition, since the addition of the urea water 17 is actively stopped when the addition remaining amount q _r exceeds the storable amount q _o , the urea water 17 is added by newly adding the urea water 17. It is possible to suppress the tendency of excess to be easily desorbed from the selective catalytic reduction catalyst 10, and it is possible to more reliably avoid the possibility that excess urea water 17 is discharged as ammonia gas or the like outside the vehicle.

FIG. 6 shows another embodiment of the present invention. In the embodiment shown here, the stop of the engine 1 is determined in step S12 with respect to the control procedure shown in the flowchart of FIG. after proceeds to further steps S13 without exiting the control, wherein a decrease amount q _d of the urea water 17 at the current exhaust temperature t is, the reduction amount q _d as shown graphically in Figure 7 and the exhaust gas temperature t It is read out from the correspondence map of and estimated.

Here, the decrease amount q _d of the urea water 17 can be regarded mainly as an expected evaporation amount of the urea water 17, but reaction consumption can be expected even after the engine 1 is stopped in the high temperature region. The reaction consumption by the reduction reaction with NOx is also included.

Further, in the next step S14, the addition by the addition remaining q _r obtained in step S11 immediately before the engine 1 is stopped, subtracting the reduction amount q _d of the urea water 17 obtained in the previous step S13 remaining q _r is 'updated, this added the remaining amount q _r' added the remaining q _r is increasingly used in the previously described steps S3 and step S7 relates adding the next of the urea water 17.

It should be noted that the update of the remaining addition amount q _r after the engine 1 is stopped is repeated from time to time until the exhaust temperature t decreases to the predetermined temperature t ₁ in the next step S15. correspondence between the reduction amount q _d and the exhaust temperature t shown in 7 is adapted to that corresponding to the calculation cycle that is repeated this time to time.

Thus, in this way, taking into account the decrease that evaporates due to the residual heat remaining on the carrier of the selective catalytic reduction catalyst 10 after the engine 1 is stopped (consumption due to the reduction reaction in the high temperature range), this decrease is taken into account in the engine 1. By subtracting from time to time the remaining amount _qr immediately before the stop of the engine, the addition of the urea water 17 after the restart of the engine 1 is executed more accurately, and the remaining addition of the urea water 17 remaining in the selective catalytic reduction catalyst 10 is performed. a situation amount q _r the estimated actual more actual addition amount q _T is insufficient can be avoided in advance.

  In addition, the control method of the exhaust gas purification apparatus of the present invention is not limited to the above-described embodiment example, and a reducing agent other than urea water may be adopted, and selective reduction is illustrated in the illustrated example. The exhaust temperature is detected by installing a temperature sensor on the inlet side of the casing of the type catalyst, but the exhaust temperature is detected by installing a temperature sensor on the inlet side or outlet side of the selective catalytic reduction catalyst in the casing. Further, a temperature sensor may be directly inserted into the selective catalytic reduction catalyst to detect the catalyst bed temperature, and this may be used in place of the exhaust gas temperature. In addition, it does not depart from the gist of the present invention. Of course, various changes can be made within the range.

It is the schematic which shows an example of the form which implements this invention. FIG. 2 is a perspective view showing the selective catalytic reduction catalyst of FIG. It is a flowchart which shows the specific control procedure of the control apparatus of FIG. It is a graph which shows the correspondence of the amount which can be stored, and exhaust temperature. It is a graph which shows the correspondence of a reduction coefficient and exhaust temperature. It is a flowchart which shows another example of a form of this invention. It is a graph which shows the correspondence of reduction amount and exhaust gas temperature.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine 7 Exhaust gas 9 Exhaust pipe 10 Selective reduction type catalyst 17 Urea water (reducing agent)
18 Urea water addition means (reducing agent addition means)
19 Temperature sensor 19a Detection signal

Claims (3)

  A control method for an exhaust emission control device, wherein a selective reduction catalyst is installed in the middle of an exhaust pipe, and a reducing agent is added to the upstream side of the selective reduction catalyst by a reducing agent addition means to reduce and purify NOx. In addition, the amount of NOx generated is estimated according to the operating state of the engine and the planned amount of reducing agent to be added corresponding to the estimated value is determined, while the reduction is performed based on the elapsed time after addition of the reducing agent and the exhaust temperature or catalyst bed temperature. The amount of reduction taking into account the reaction consumption of the agent and the amount of evaporation is calculated, and the amount of reduction is subtracted from the actual addition amount of the latest reducing agent to determine the remaining amount of addition. A control method for an exhaust gas purification apparatus, wherein an actual addition amount is determined by subtracting from a predetermined addition amount, and the actual addition amount is used as an addition instruction value to the reducing agent addition means.   Even after the engine is stopped, the reduction amount of the reducing agent is continuously calculated until the exhaust temperature or the catalyst bed temperature around the selective catalytic reduction catalyst falls to a predetermined temperature. The control method of the exhaust emission control device according to claim 1, wherein the remaining amount of addition is updated by subtraction every moment.   Estimates the amount of storable amount that can be stored in the selective catalytic reduction catalyst at the current exhaust temperature or catalyst bed temperature, and stops adding the reducing agent when the remaining amount exceeds the estimated storable amount. The control method of the exhaust emission control device according to claim 1 or 2.

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