JP2016223297A - Exhaust emission control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of reducing a consumption amount of urea water.SOLUTION: An exhaust emission control device 1 for purifying exhaust gas exhausted from a diesel engine 3 of a vehicle 2 includes a selective reduction catalyst 7 for reducing and purifying NOx contained in the exhaust gas, an addition valve 10 for adding urea water A to the selective reduction catalyst 7, a target determination section 15 for determining a target urea water consumption amount on the basis of a driving state of the vehicle 2, an integrated amount calculating section 16 for calculating a urea water consumption management integrated amount for managing consumption of the urea water A by comparing an addition amount of the urea water A from the addition valve 10 with the target urea water consumption amount, and a control section 17 for controlling the addition valve 10 so as to reduce the addition amount of the urea water A from the addition valve 10 when the urea water consumption management integrated amount is equal to or more than a prescribed flag ON threshold.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an exhaust emission control device.

As a conventional exhaust purification device, for example, a device described in Patent Document 1 is known. The exhaust purification device described in Patent Document 1 includes a NOx reduction catalyst equipped in the middle of an exhaust pipe through which exhaust gas flows, an addition valve for adding urea water in a urea water tank to the upstream side of the NOx reduction catalyst, And a control device. The control device calculates an addition amount of urea water corresponding to the estimated value of the NOx generation amount, calculates a consumption amount of ammonia (NH ₃ ) corresponding to the estimated value of the NOx reduction amount, and calculates from the integrated value of the added amount of urea water. The amount of NH ₃ consumption is subtracted to estimate the amount of NH ₃ adsorbed on the NOx reduction catalyst, the amount of urea water added is corrected with a correction coefficient commensurate with the amount of NH ₃ adsorption, and the corrected urea water The addition amount of is the addition instruction value to the addition valve.

JP 2005-226504 A

However, in the above prior art, for example, in order to increase the NOx purification rate by the NOx reduction catalyst even at a cold start, it is necessary to sufficiently secure the NH ₃ adsorption amount with respect to the NOx reduction catalyst. For this reason, the consumption of urea water increases. In this case, for example, it becomes necessary for the user to regularly replenish the urea water, which causes a problem that the running cost increases.

  An object of the present invention is to provide an exhaust purification device that can reduce the consumption of urea water.

  One aspect of the present invention is an exhaust purification device that purifies exhaust gas exhausted from an engine of a vehicle. A selective reduction catalyst that reduces and purifies NOx contained in exhaust gas, and urea water is added to the selective reduction catalyst. Compare the amount of urea water added from the addition valve, the target determination unit that determines the target urea water consumption based on the driving state of the vehicle, and the amount of urea water added from the addition valve to the target urea water consumption, An integrated amount calculation unit for calculating an integrated amount of urea water consumption management for management, and when the integrated amount of urea water consumption management exceeds a predetermined threshold, the amount of urea water added from the addition valve is decreased. And a control unit for controlling the addition valve.

  In such an exhaust purification device, the target urea water consumption is determined based on the driving state of the vehicle, and the urea water consumption management integration is performed by comparing the urea water addition amount from the addition valve with the target urea water consumption. The amount is calculated, and the urea water addition amount from the addition valve is decreased when the urea water consumption management integrated amount is equal to or greater than the threshold value. Thereby, addition of excess urea water can be suppressed and consumption of urea water can be reduced.

  When the amount of urea water added from the addition valve is greater than the target urea water consumption, the integrated amount calculation unit manages the amount of urea water consumption corresponding to the difference between the amount of urea water added and the target urea water consumption. A new urea water consumption management integrated amount is calculated by adding to the integrated amount. When the amount of urea water added from the addition valve is less than the target urea water consumption, the amount of urea water added and the target urea water consumption A new urea water consumption management integrated amount may be calculated by subtracting the amount corresponding to the difference from the amount from the urea water consumption management integrated amount. When urea water is added to the selective reduction catalyst from the addition valve, ammonia is adsorbed to the selective reduction catalyst. However, when the amount of urea water added from the addition valve decreases, the amount of ammonia adsorbed to the selective reduction catalyst decreases. Become. When the amount of urea water added from the addition valve is less than the target urea water consumption, subtract the amount corresponding to the difference between the urea water addition amount and the target urea water consumption from the urea water consumption management integrated amount. Thus, the period until the urea water consumption management integrated amount reaches the threshold value becomes longer. Therefore, the period during which the desired ammonia adsorption amount is maintained for the selective reduction catalyst can be lengthened.

  The target determining unit may determine the target urea water consumption based on the vehicle speed as the driving state of the vehicle. In this case, the target urea water consumption when the vehicle travels for a unit time can be obtained with high accuracy.

  The target determination unit may determine the target urea water consumption based on the state quantity of the engine as the driving state of the vehicle. In this case, the target urea water consumption can be obtained without any vehicle speed information.

  ADVANTAGE OF THE INVENTION According to this invention, the exhaust gas purification apparatus which can reduce the consumption of urea water is provided.

1 is a schematic configuration diagram illustrating an exhaust emission control device according to a first embodiment. It is a flowchart which shows the procedure of the urea water addition control process performed by ECU shown by FIG. It is a flowchart which shows the detail of procedure S103 shown by FIG. It is a chart figure which shows the timing chart of the urea water addition control process performed with the flowchart shown by FIG. It is a schematic block diagram which shows the exhaust gas purification apparatus which concerns on 2nd Embodiment. It is a table | surface which shows the target urea water consumption map used in the urea water addition control process performed by ECU shown by FIG. It is a flowchart which shows the procedure of the urea water addition control process performed by ECU shown by FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same or equivalent elements are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a schematic configuration diagram illustrating an exhaust emission control device according to the first embodiment. In FIG. 1, an exhaust emission control device 1 of this embodiment is mounted on a vehicle 2 and purifies exhaust gas discharged from a diesel engine 3 (hereinafter simply referred to as an engine 3) of the vehicle 2. The engine 3 has an injector 4 that injects fuel into a combustion chamber (not shown).

  The exhaust gas purification apparatus 1 includes a diesel oxidation catalyst (DOC) 5, a diesel exhaust particulate removal filter (DPF) 6, a selective catalytic catalyst (SCR) 7, and an ammonia slip catalyst (ASC). Slip Catalyst) 8. The DOC 5, DPF 6, SCR 7 and ASC 8 are sequentially arranged in the exhaust passage 9 connected to the engine 3 from the upstream side toward the downstream side.

The DOC 5 oxidizes and purifies HC and CO contained in the exhaust gas. The DPF 6 removes PM from the exhaust gas by collecting particulate matter (PM) contained in the exhaust gas. The SCR 7 reduces and purifies NOx contained in the exhaust gas. The ASC 8 oxidizes ammonia (NH ₃ ) that has passed through the SCR 7.

  Further, the exhaust purification device 1 includes an addition valve 10 and a NOx sensor 11 disposed on the upstream side of the SCR 7 in the exhaust passage 9, specifically, between the DPF 6 and the SCR 7. The addition valve 10 is connected to the urea water tank 12 through the supply pipe 10a, and adds the urea water A to the SCR 7. The urea water A in the urea water tank 12 is supplied to the addition valve 10 through a supply pipe 10a by a pump (not shown). The NOx sensor 11 calculates the amount of NOx contained in the exhaust gas by detecting the NOx concentration.

When the urea water A is added to the SCR 7 by the addition valve 10, the urea water A becomes NH ₃ and is adsorbed on the SCR 7, and the NH ₃ reacts with NOx in the exhaust gas, whereby NOx is reduced.

  The exhaust emission control device 1 further includes a vehicle speed sensor 13 that detects the vehicle speed of the vehicle 2, and an ECU (Electronic Control Unit) 14 that is connected to the NOx sensor 11 and the vehicle speed sensor 13. ECU14 performs a predetermined | prescribed process based on the detected value of NOx sensor 11 and vehicle speed sensor 13, and controls addition valve 10 so that urea water A may be added from addition valve 10 according to the processing result. The ECU 14 includes a target determination unit 15, an integrated amount calculation unit 16, and a control unit 17.

  The target determination unit 15 determines the target urea water consumption based on the vehicle speed of the vehicle 2 as the driving state of the vehicle 2. The integrated amount calculation unit 16 compares the amount of urea water A added from the addition valve 10 with the target urea water consumption determined by the target determination unit 15 to manage urea water A consumption. Calculate the consumption management integrated amount. The control unit 17 adds the urea water A added from the addition valve 10 so as to decrease when the urea water consumption management integrated amount calculated by the integrated amount calculating unit 16 exceeds a predetermined threshold. The valve 10 is controlled.

  FIG. 2 is a flowchart showing a procedure of urea water addition control processing executed by the ECU 14. At the start of this process, the urea water consumption management flag is OFF, and the urea water consumption management integrated amount is zero.

In FIG. 2, the ECU 14 first inputs a detection value of the vehicle speed sensor 13 (step S101). Subsequently, the ECU 14 calculates a target urea water consumption based on the vehicle speed detected by the vehicle speed sensor 13 (step S102). Specifically, when the travelable distance of the vehicle 2 per unit volume (1 L) of the urea water A is C (for example, 1000) km / L, the specific gravity of the urea water A is 1090 g / L. The target urea water consumption when traveling for 1 hour is expressed by the following equation.
Target urea water consumption (g) = vehicle speed / (C / 1090)

  Subsequently, the ECU 14 compares the addition amount of the urea water A from the addition valve 10 (hereinafter simply referred to as the urea water addition amount) with the target urea water consumption calculated in step S102 to calculate the urea water consumption management integration. The amount is calculated (procedure S103).

The urea water addition amount is obtained from the addition amount command value sent from the ECU 14 to the addition valve 10. The addition valve 10 adds urea water A in an amount corresponding to the addition amount command value. The normal addition amount command value is an addition amount setting value corresponding to the amount necessary for purifying NOx contained in the exhaust gas, and an addition amount corresponding to the amount necessary for maintaining the NH ₃ adsorption amount for the SCR 7 at the cold start. It is an addition value with the set value. The addition amount set value corresponding to the amount necessary for NOx purification is calculated based on the NOx amount detected by the NOx sensor 11. The NOx amount may be estimated from the rotational speed of the engine 3, the load of the engine 3, and the like. An addition amount set value corresponding to the amount necessary for maintaining the NH ₃ adsorption amount for the SCR 7 is determined in advance.

The urea water consumption management integrated amount is expressed by the following equation.
Urea water consumption management integrated amount = α x (urea water addition amount-target urea water consumption amount) + previous value (A)

  The coefficient α may be a map value with the bed temperature of the SCR 7 as an argument. The coefficient α may be set using another map when the urea water addition amount is larger than the target urea water consumption amount and when the urea water addition amount is smaller than the target urea water consumption amount.

  The details of the procedure for calculating the urea water consumption management integrated amount (procedure S103) are shown in FIG. In FIG. 3, the ECU 14 first determines whether or not the urea water addition amount is larger than the target urea water consumption amount (step S201).

  When the urea water addition amount is larger than the target urea water consumption amount, the ECU 14 performs the urea water addition amount and the target urea water consumption according to the above formula (A) as shown in FIGS. 4 (a) and 4 (b). A new urea water consumption management integrated amount is calculated by adding the amount corresponding to the difference from the amount to the current urea water consumption management integrated amount obtained last time (step S202).

  When the urea water addition amount is not larger than the target urea water consumption amount, the ECU 14 determines whether or not the urea water addition amount is smaller than the target urea water consumption amount (step S203). When the urea water addition amount is smaller than the target urea water consumption amount, the ECU 14 performs the urea water addition amount and the target urea water consumption according to the above equation (A) as shown in FIGS. 4 (a) and 4 (b). A new urea water consumption management integrated amount is calculated by subtracting the amount corresponding to the difference from the current amount from the current urea water consumption management integrated amount obtained last time (step S204).

  When the urea water addition amount is not smaller than the target urea water consumption amount, that is, when the urea water addition amount is equal to the target urea water consumption amount, the ECU 14 sets the current urea water consumption management integrated amount obtained last time as a new value. The urea water consumption management integrated amount is set (step S205).

  Returning to FIG. 2, after step S103 is executed, the ECU 14 determines whether or not the urea water consumption management integrated amount is equal to or greater than a predetermined flag ON threshold (step S104). When the urea water consumption management integrated amount is not less than the flag ON threshold, the ECU 14 turns on the urea water consumption management flag as shown in FIGS. 4B and 4C (step S105).

  When the urea water consumption management integrated amount is not equal to or greater than the flag ON threshold, the ECU 14 determines whether the urea water consumption management integrated amount is equal to or less than a predetermined flag OFF threshold (step S106). The flag OFF threshold is larger than zero and smaller than the flag ON threshold. The ECU 14 turns off the urea water consumption management flag when the urea water consumption management integrated amount is equal to or less than the flag OFF threshold (step S107).

  The ECU 14 keeps the urea water consumption management flag as it is when the urea water consumption management integrated amount is not less than or equal to the flag OFF threshold, that is, when the urea water consumption management integrated amount is larger than the flag OFF threshold and smaller than the flag ON threshold. Maintain (step S108).

  After executing any one of the steps S105, 107, and S108, the ECU 14 determines whether or not the urea water consumption management flag is ON (step S109).

  When the urea water consumption management flag is ON, the ECU 14 sets the urea water addition control mode to the urea water addition amount reduction mode and decreases the urea water addition amount as shown in FIGS. 4 (c) and 4 (d). The amount command value to be added is sent to the addition valve 10 (step S110), and the procedure returns to step S101.

At this time, the ECU 14 sends an addition amount set value corresponding to the amount necessary for NOx purification to the addition valve 10 as an addition amount command value. That is, the addition amount setting value corresponding to the amount necessary for maintaining the NH ₃ adsorption amount for the SCR 7 is not included in the addition amount command value. For example, the ECU 14 sets the target urea water consumption obtained in step S102 as the addition amount command value.

When the urea water consumption management flag is OFF instead of ON, the ECU 14 sets the urea water addition control mode to the NH ₃ adsorption amount maintenance mode, as shown in FIGS. ₃ An addition amount command value that maintains the adsorption amount is sent to the addition valve 10 (step S111), and the procedure returns to step S101. That is, as described above, the ECU 14 calculates the addition value of the addition amount setting value corresponding to the amount necessary for NOx purification and the addition amount setting value corresponding to the amount necessary for maintaining the NH ₃ adsorption amount for the SCR 7. , And sent to the addition valve 10 as an addition amount command value.

  In the above, the target determination unit 15 executes steps S101 and S102. The integrated amount calculation unit 16 executes step S103. The control unit 17 executes steps S104 to S111.

  As described above, in the present embodiment, the target urea water consumption is determined based on the driving state of the vehicle 2, and the urea water consumption management integrated amount is calculated by comparing the urea water addition amount with the target urea water consumption. When the urea water consumption management integrated amount becomes equal to or greater than the flag ON threshold value, the addition valve 10 is controlled so as to decrease the urea water addition amount. Thereby, addition of excess urea water A can be suppressed and the consumption of urea water A can be reduced. As a result, since the interval for replenishing the urea water A becomes longer, the running cost can be reduced.

In this embodiment, when the urea water addition amount is larger than the target urea water consumption amount, the amount corresponding to the difference between the urea water addition amount and the target urea water consumption amount is set as the current urea water consumption management integrated amount. A new urea water consumption management integrated amount is calculated by adding, and when the urea water addition amount is smaller than the target urea water consumption amount, an amount corresponding to the difference between the urea water addition amount and the target urea water consumption amount is calculated. A new urea water consumption management integrated amount is calculated by subtracting from the current urea water consumption management integrated amount. As described above, when the urea water addition amount is smaller than the target urea water consumption amount, the amount corresponding to the difference between the urea water addition amount and the target urea water consumption amount is subtracted. The period until the threshold is reached becomes longer. Therefore, it is possible to lengthen the period for maintaining the desired NH ₃ adsorption amount with respect to the SCR 7.

  Moreover, since the target urea water consumption is determined based on the vehicle speed of the vehicle 2 as the driving state of the vehicle 2, the target urea water consumption when the vehicle 2 travels for a unit time can be obtained with high accuracy.

  FIG. 5 is a schematic configuration diagram illustrating an exhaust emission control device according to the second embodiment. In FIG. 5, the exhaust purification device 20 of the present embodiment includes an engine speed sensor 21 and an accelerator opening sensor 22 instead of the vehicle speed sensor 13 in the first embodiment.

  The engine speed sensor 21 detects the speed of the engine 3. The accelerator opening sensor 22 detects the accelerator opening as a load of the engine 3. The rotational speed of the engine 3 and the load of the engine 3 are included in the state quantity of the engine 3.

  The exhaust purification device 50 includes an ECU 23 instead of the ECU 14 in the first embodiment. The ECU 23 includes an injection amount determination unit 24 in addition to the target determination unit 15, the integrated amount calculation unit 16, and the control unit 17. The injection amount determination unit 24 determines the fuel injection amount from the injector 4 based on the detection values of the engine speed sensor 21 and the accelerator opening sensor 22. The fuel injection amount corresponds to the engine torque.

  A target urea water consumption map M as shown in FIG. 6 is stored in the target determination unit 15. The target urea water consumption map M is a map that represents the relationship among the rotational speed of the engine 3, the fuel injection amount from the injector 4, and the target urea water consumption.

  FIG. 7 is a flowchart showing a procedure of urea water addition control processing executed by the ECU 23. In this process, the same steps as those in the flowchart shown in FIG.

  In FIG. 7, the ECU 23 first inputs detection values of the engine speed sensor 21 and the accelerator opening sensor 22 (step S121). Subsequently, the ECU 23 determines the fuel from the injector 4 based on the engine speed detected by the engine speed sensor 21 and the accelerator opening (engine 3 load) detected by the accelerator opening sensor 22. An injection amount is obtained (procedure S122). Then, ECU23 calculates | requires the target urea water consumption corresponding to the rotation speed of the engine 3, and fuel injection quantity using the target urea water consumption map M shown in FIG. 6 (procedure S123). The subsequent procedure is the same as the flowchart shown in FIG.

  By the way, in vehicle development, the vehicle may be evaluated by testing the vehicle in a tabletop mode. At this time, since the passenger car can be placed on a table, various tests can be performed using the vehicle speed information. However, since a large vehicle cannot be mounted on a table, the engine of the large vehicle is mounted on the table and the engine is evaluated. In this case, a test using vehicle speed information cannot be performed.

  In this embodiment, since the target urea water consumption is determined based on the state quantity of the engine 3 as the driving state of the vehicle 2, the target urea water consumption can be obtained even if there is no vehicle speed information. As a result, it becomes easier to develop a large vehicle based on the evaluation with the engine mounted on the table.

  In the present embodiment, the target urea water consumption amount is obtained using the target urea water consumption map M that represents the relationship among the engine speed, the fuel injection amount, and the target urea water consumption. In particular, the present invention is not limited thereto, and a target urea water consumption map including the exhaust gas temperature and the like in addition to the engine speed and the fuel injection amount may be used, or in addition to the engine speed and the fuel injection amount. Alternatively, a target urea water consumption map including vehicle specifications such as gear ratio, differential ratio and tire moving radius or shift position may be used.

  As mentioned above, although embodiment of this invention has been described, this invention is not limited to the said embodiment. For example, in the above-described embodiment, the integrated amount calculation unit 16 calculates the new urea water consumption management integrated amount, and when the urea water addition amount is smaller than the target urea water consumption amount, the urea water addition amount and the target Although the amount corresponding to the difference from the urea water consumption amount is subtracted from the current urea water consumption management integrated amount, the form is not particularly limited. When the urea water addition amount is smaller than the target urea water consumption amount, the integrated amount calculation unit 16 may leave the urea water consumption management integrated amount unchanged, or the urea water addition amount may be the target urea water consumption amount. The increase rate of the urea water consumption management integrated amount may be reduced as compared with the case where the amount is larger than the above.

  Moreover, although the said embodiment is an exhaust-gas purification apparatus provided with the selective reduction catalyst (SCR) 7 arrange | positioned by the exhaust passage 9 connected to the diesel engine 3, this invention does NOx contained in exhaust gas. The present invention can be applied to any engine provided that a selective reduction catalyst for reduction is provided.

  DESCRIPTION OF SYMBOLS 1 ... Exhaust gas purification device, 3 ... Diesel engine (engine), 7 ... Selective reduction catalyst, 10 ... Addition valve, 15 ... Target determination part, 16 ... Integrated amount calculation part, 17 ... Control part, 20 ... Exhaust gas purification apparatus, A ... urea water.

Claims (4)

In an exhaust purification device that purifies exhaust gas discharged from a vehicle engine,
A selective reduction catalyst that reduces and purifies NOx contained in the exhaust gas;
An addition valve for adding urea water to the selective reduction catalyst;
A target determining unit that determines a target urea water consumption based on the driving state of the vehicle;
An integrated amount calculator that compares the amount of urea water added from the addition valve with the target urea water consumption and calculates a urea water consumption management integrated amount for managing the consumption of the urea water;
A control unit that controls the addition valve so as to reduce the addition amount of the urea water from the addition valve when the urea water consumption management integrated amount is equal to or greater than a predetermined threshold value. Exhaust purification device.   When the amount of urea water added from the addition valve is larger than the target urea water consumption, the integrated amount calculation unit determines the amount corresponding to the difference between the urea water addition amount and the target urea water consumption. Is added to the urea water consumption management integrated amount to calculate a new urea water consumption management integrated amount, and when the urea water addition amount from the addition valve is smaller than the target urea water consumption amount, the urea water consumption management integrated amount is calculated. The new urea water consumption management integrated amount is calculated by subtracting the amount corresponding to the difference between the added amount of water and the target urea water consumption amount from the urea water consumption management integrated amount. The exhaust emission control device described.   The exhaust emission control device according to claim 1 or 2, wherein the target determining unit determines the target urea water consumption based on a vehicle speed of the vehicle as an operation state of the vehicle.   The exhaust emission control device according to claim 1, wherein the target determination unit determines the target urea water consumption based on a state quantity of the engine as an operation state of the vehicle.

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