JP6032185B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine.

  2. Description of the Related Art An exhaust gas purification device for an internal combustion engine that includes a NOx purification catalyst that purifies nitrogen oxide (NOx) in exhaust gas is known. In such an exhaust purification device, for example, a reducing agent such as urea water is injected into the exhaust passage from the addition valve. The injected urea water becomes ammonia by hydrolysis by exhaust heat. This ammonia is adsorbed on the NOx purification catalyst, and NOx is reduced and purified by the adsorbed ammonia.

  Moreover, in the apparatus described in Patent Document 1, the reducing agent is injected and supplied in a pulsed manner by controlling the opening / closing operation of the addition valve so that the reducing agent is intermittently added every predetermined addition period. .

JP 2013-160127 A

  By the way, as the addition request of the reducing agent by the addition valve, not only the addition request for purifying NOx, but also the addition request for cooling the addition valve and the suppression of the precipitation of the reducing agent in the addition valve. There are a plurality of addition requests, such as addition requests. Therefore, when intermittent addition is performed based on one addition request, another addition request may occur.

  Here, another addition request occurs within the addition cycle when intermittent addition is performed based on the addition request, and the addition of the reducing agent by interruption to satisfy this another addition request There is a possibility that an appropriate amount of reducing agent according to the demand cannot be added. For example, when the opening timing of the addition valve based on such an interrupt request is the timing immediately after the addition valve is closed, or the timing immediately before the valve opening timing set separately, Due to hardware limitations, the target valve opening time cannot be ensured, and an appropriate amount of reducing agent may not be added.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an exhaust emission control device for an internal combustion engine that can appropriately add a required addition amount.

  An exhaust emission control device that solves the above problems includes an addition valve that adds a reducing agent into an exhaust passage, and a catalyst that purifies NOx in exhaust gas by the added reducing agent, and the reducing agent is added at a predetermined addition cycle. The opening / closing operation of the addition valve is controlled so as to be intermittently added every time. And when this exhaust purification apparatus produces another addition request within the addition cycle when intermittent addition is performed based on the addition request, the same addition within the addition cycle where the other addition request occurred Addition of reducing agent based on request is prohibited. In addition, the exhaust emission control device sets the reducing agent addition amount according to another prohibited addition request in the next addition cycle after the prohibited addition cycle of the reducing agent addition based on the additional addition request has elapsed. This is reflected in the amount of reducing agent added.

  According to this configuration, even if another addition request occurs within one addition cycle, addition of a reducing agent based on the other addition request is prohibited within the addition cycle. Here, if the addition of a reducing agent based on another addition request is prohibited, the other addition request cannot be satisfied. Therefore, in the same configuration, the reducing agent addition amount in another prohibited addition request is set to the reducing agent in the next addition cycle after the prohibited addition cycle of the reducing agent addition based on the other addition request has elapsed. This is reflected in the amount added. Therefore, when the reducing agent is added in the next addition cycle, the above-described prohibited addition request can be satisfied. In addition, the reducing agent addition amount in another prohibited addition request is reflected in the reducing agent addition amount in the next addition cycle. For example, the opening time of the addition valve in the next addition cycle is adjusted. It is also possible to add a reducing agent addition amount according to another prohibited addition request from the addition valve. Therefore, according to the configuration, the requested addition amount can be appropriately added.

  In the same configuration, the amount of addition required within the addition cycle in which the addition of the reducing agent based on another addition request is prohibited is integrated over time, and the integrated value is added to the reducing agent addition in the next addition cycle described above. It is preferable to reflect the amount.

  Further, in the above exhaust purification device, when a plurality of different amounts of reducing agent addition are required, the maximum addition amount of the different reducing agent addition amounts is added as a required addition amount from the addition valve, When the total required addition amount cannot be added within the cycle, it is preferable to add a part of the required addition amount within the addition cycle and reflect the remaining addition amount in the reducing agent addition amount in the next addition cycle.

  According to this configuration, when a plurality of different reducing agent addition amounts are required, the maximum addition amount is set as the required addition amount and added from the addition valve. Therefore, even when a plurality of addition requests are established at the same time, all of the plurality of addition requests can be satisfied. Further, when all of the required addition amount cannot be added within the addition cycle, a part of the required addition amount is added within the addition cycle, and the remaining addition amount is reflected in the reducing agent addition amount in the next addition cycle. I am doing so. Therefore, when the total amount of the required addition amount cannot be added within one addition cycle, the required addition amount can be appropriately added by utilizing the reducing agent addition in the next addition cycle.

BRIEF DESCRIPTION OF THE DRAWINGS Schematic which shows the internal combustion engine to which this is applied, and its periphery structure about one Embodiment of the exhaust gas purification device of an internal combustion engine. The time chart which shows the addition aspect of urea water in the embodiment. 4 is a flowchart showing a drive frequency setting processing procedure in the embodiment. 5 is a flowchart showing a procedure for calculating energization time in the embodiment. The flowchart which shows the process sequence regarding mediation of energization time and calculation of a carry-over addition amount in the embodiment.

Hereinafter, an embodiment embodying an exhaust emission control device for an internal combustion engine will be described with reference to FIGS.
FIG. 1 is a schematic configuration diagram showing a diesel engine (hereinafter simply referred to as “engine”) to which the exhaust emission control device according to the present embodiment is applied, and a peripheral configuration thereof.

  The engine 1 is provided with a plurality of cylinders # 1 to # 4. A plurality of fuel injection valves 4 a to 4 d are attached to the cylinder head 2. These fuel injection valves 4a to 4d inject fuel into the combustion chambers of the cylinders # 1 to # 4, respectively. Also, the cylinder head 2 is provided with intake ports for introducing fresh air into the cylinders and exhaust ports 6a to 6d for discharging combustion gas to the outside of the cylinders corresponding to the respective cylinders # 1 to # 4. It has been.

  The fuel injection valves 4a to 4d are connected to a common rail 9 that accumulates high-pressure fuel. The common rail 9 is connected to the supply pump 10. The supply pump 10 sucks fuel in the fuel tank and supplies high-pressure fuel to the common rail 9. The high-pressure fuel supplied to the common rail 9 is injected into the cylinder from the fuel injection valves 4a to 4d when the fuel injection valves 4a to 4d are opened.

  An intake manifold 7 is connected to the intake port. The intake manifold 7 is connected to the intake passage 3. An intake throttle valve 16 for adjusting the intake air amount is provided in the intake passage 3.

An exhaust manifold 8 is connected to the exhaust ports 6a to 6d. The exhaust manifold 8 is connected to the exhaust passage 26.
In the middle of the exhaust passage 26, there is provided a turbocharger 11 that supercharges intake air introduced into the cylinder using exhaust pressure. An intercooler 18 is provided in the intake passage 3 between the intake side compressor of the turbocharger 11 and the intake throttle valve 16. The intercooler 18 cools the intake air whose temperature has risen due to supercharging of the turbocharger 11.

  A first purification member 30 that purifies the exhaust gas is provided in the middle of the exhaust passage 26 and downstream of the exhaust side turbine of the turbocharger 11. Inside the first purification member 30, an oxidation catalyst 31 and a filter 32 are arranged in series with respect to the flow direction of the exhaust gas.

  The oxidation catalyst 31 carries a catalyst for oxidizing HC in the exhaust. The filter 32 is a filter that collects PM (particulate matter) in the exhaust gas and is made of porous ceramic, and further supports a catalyst for promoting the oxidation of PM. The PM in the exhaust gas is collected when passing through the porous wall of the filter 32.

  Further, a fuel addition valve 5 for supplying fuel as an additive to the oxidation catalyst 31 and the filter 32 is provided in the vicinity of the collecting portion of the exhaust manifold 8. The fuel addition valve 5 is connected to the supply pump 10 through a fuel supply pipe 27. The position of the fuel addition valve 5 can be changed as appropriate as long as it is in the exhaust system and upstream of the first purification member 30. Further, fuel as an additive may be supplied to the oxidation catalyst 31 and the filter 32 by adjusting the fuel injection timing and performing post injection.

  When the amount of PM collected by the filter 32 exceeds a predetermined value, the regeneration process of the filter 32 is started and fuel is injected from the fuel addition valve 5. The fuel injected from the fuel addition valve 5 is combusted when it reaches the oxidation catalyst 31, thereby increasing the exhaust temperature. The exhaust gas whose temperature has been raised by the oxidation catalyst 31 flows into the filter 32, whereby the temperature of the filter 32 is raised, whereby the PM deposited on the filter 32 is oxidized and the filter 32 is regenerated.

  A second purification member 40 that purifies the exhaust gas is provided in the middle of the exhaust passage 26 and downstream of the first purification member 30. Inside the second purification member 40, a selective reduction type NOx catalyst (hereinafter referred to as an SCR catalyst) 41 is disposed as a NOx purification catalyst that reduces and purifies NOx in the exhaust using a reducing agent.

  Further, a third purification member 50 for purifying exhaust gas is provided in the middle of the exhaust passage 26 and downstream of the second purification member 40. Inside the third purification member 50, an ammonia oxidation catalyst 51 for purifying ammonia in the exhaust is disposed.

  The engine 1 is provided with a urea water supply mechanism 200 as a reducing agent supply mechanism that supplies a reducing agent to the SCR catalyst 41. The urea water supply mechanism 200 includes a tank 210 that stores urea water, a urea addition valve 230 that injects urea water into the exhaust passage 26, a supply passage 240 that connects the urea addition valve 230 and the tank 210, and a supply passage 240. The pump 220 is provided in the middle.

  The urea addition valve 230 is provided in the exhaust passage 26 between the first purification member 30 and the second purification member 40, and the injection hole is opened toward the SCR catalyst 41. When the urea addition valve 230 is opened, urea water is injected and supplied into the exhaust passage 26 via the supply passage 240.

  The pump 220 is an electric pump, and the urea water pressure NP in the supply passage 240 is adjusted by controlling the rotational speed of the pump 220. When the pump 220 rotates forward, urea water is sent from the tank 210 toward the urea addition valve 230. On the other hand, during the reverse rotation of the pump 220, urea water is sent from the urea addition valve 230 toward the tank 210. In other words, during the reverse rotation of the pump 220, urea water is recovered from the urea addition valve 230 and the supply passage 240 and returned to the tank 210.

  A dispersion plate 60 is provided in the exhaust passage 26 between the urea addition valve 230 and the SCR catalyst 41 to promote atomization of the urea water by dispersing the urea water injected from the urea addition valve 230. It has been.

The urea water injected from the urea addition valve 230 is hydrolyzed to ammonia by the heat of the exhaust. This ammonia is stored in the SCR catalyst 41 and used for NOx reduction.
In addition, the engine 1 is provided with an exhaust gas recirculation device (hereinafter referred to as an EGR device). This EGR device is a device that reduces the combustion temperature in the cylinder by introducing a part of the exhaust gas into the intake air, thereby reducing the amount of NOx generated. This exhaust gas recirculation device includes an EGR passage 13 that connects the intake passage 3 and the exhaust manifold 8, an EGR valve 15 provided in the EGR passage 13, an EGR cooler 14, and the like. By adjusting the opening degree of the EGR valve 15, the exhaust gas recirculation amount introduced into the intake passage 3 from the exhaust passage 26, that is, the so-called external EGR amount is adjusted. Further, the temperature of the exhaust gas flowing through the EGR passage 13 is lowered by the EGR cooler 14.

  Various sensors for detecting the engine operation state are attached to the engine 1. For example, the air flow meter 19 detects the intake air amount GA in the intake passage 3. The throttle valve opening sensor 20 detects the opening of the intake throttle valve 16. The engine rotation speed sensor 21 detects the rotation speed of the crankshaft, that is, the engine rotation speed NE. The accelerator sensor 22 detects an accelerator pedal depression amount, that is, an accelerator operation amount ACCP. The pressure sensor 23 detects the urea water pressure NP in the supply passage 240. The vehicle speed sensor 24 detects the vehicle speed SPD of the vehicle on which the engine 1 is mounted. The ignition switch 25 detects a start operation and a stop operation of the engine 1 by a vehicle driver.

  The first exhaust temperature sensor 100 provided upstream of the oxidation catalyst 31 detects the first exhaust temperature TH1 that is the exhaust temperature before flowing into the oxidation catalyst 31. The differential pressure sensor 110 detects the pressure difference ΔP between the exhaust pressure upstream and downstream of the filter 32.

  A second exhaust temperature sensor 120 and a first NOx sensor 130 are provided in the exhaust passage 26 between the first purification member 30 and the second purification member 40 and upstream of the urea addition valve 230. The second exhaust temperature sensor 120 detects a second exhaust temperature TH2, which is the exhaust temperature before flowing into the SCR catalyst 41. The first NOx sensor 130 detects a first NOx concentration N1, which is the NOx concentration in the exhaust before flowing into the SCR catalyst 41. Instead of detecting the first NOx concentration N1 by the first NOx sensor 130, the first NOx concentration N1 may be estimated from the engine operating state, the exhaust temperature, and the like.

  The exhaust passage 26 downstream of the third purification member 50 is provided with a second NOx sensor 140 that detects a second NOx concentration N2 that is the NOx concentration of the exhaust purified by the SCR catalyst 41. Instead of detecting the second NOx concentration N2 by the second NOx sensor 140, the second NOx concentration N2 may be estimated from the engine operating state, the exhaust temperature, and the like.

  Outputs from these various sensors are input to the control device 80. The control device 80 includes a central processing control device (CPU), a read-only memory (ROM) that stores various programs and maps in advance, a random access memory (RAM) that temporarily stores CPU calculation results, a timer counter, an input The microcomputer is mainly configured with an interface, an output interface, and the like.

  Then, the controller 80 controls, for example, the fuel injection amount control / fuel injection timing control of the fuel injection valves 4a to 4d and the fuel addition valve 5, the discharge pressure control of the supply pump 10, and the drive amount of the actuator 17 that opens and closes the intake throttle valve 16. Various controls of the engine 1 such as control and opening control of the EGR valve 15 are performed.

The exhaust gas purification control such as the regeneration process for burning the PM collected by the filter 32 is also performed by the controller 80.
The control device 80 also performs urea water addition control by the urea addition valve 230 as one of such exhaust gas purification controls. In this addition control, the required addition amount QE of urea water necessary for reducing the NOx discharged from the engine 1 is calculated based on the engine operating state and the like, and the calculated required addition amount QE is calculated as the urea addition valve. The valve open state of the urea addition valve 230 is controlled so that the fuel is injected from 230.

  Further, the control device 80 not only adds the NOx purification addition request for purifying NOx as described above as the urea water addition request by the urea addition valve 230 but also the cooling addition for cooling the urea addition valve 230. A plurality of addition requests such as a request and an addition request for suppressing precipitation that suppresses precipitation of urea water in the urea addition valve 230 are generated.

  The required addition amount QE of urea water when an addition request for cooling is generated, and the required addition amount QE of urea water when an addition request for precipitation suppression is generated are the temperature of the urea addition valve 230 (exhaust temperature). And can be substituted) and the engine operating state. In the following, the required addition amount QE for NOx purification is referred to as “NOx addition amount QEN”, the required addition amount QE for cooling addition is referred to as “cooling addition amount QEC”, and the required addition for precipitation suppression addition The amount QE is referred to as “addition amount QES for suppressing precipitation”.

  The controller 80 controls the opening / closing operation of the urea addition valve 230 so that the urea water is intermittently added at every predetermined addition period when the urea water is added based on various requirements, whereby the urea water is injected in a pulse shape. Supplied.

  The outline of the intermittent addition of urea water will be described below. First, a drive frequency KS (unit: Hz) that is a frequency of a voltage applied to the urea addition valve 230 is set. The value of the drive frequency KS is the same value as the number of times of opening of the urea addition valve 230 in one second. An addition interval INT (unit: millisecond) is calculated based on the drive frequency KS.

As shown in FIG. 2, the addition interval INT is a value corresponding to the urea water addition cycle, and is calculated from the following equation (1).

Addition interval INT = 1000 (milliseconds) / drive frequency KS (1)

Next, a unit urea addition amount QET that is a urea addition amount required when the urea addition valve 230 is opened once is calculated based on the following equation (2).

QET = (QE / 3600) × (1 / KS) (2)
QET: Unit urea addition amount (g)
QE: Required addition amount (g / h)
KS: Drive frequency (Hz)

The value of (required addition amount QE / 3600) in equation (2) indicates the urea addition amount that needs to be added in one second. By multiplying the value of (urea addition amount QE / 3600) by (1 / drive frequency KS), that is, by dividing the value of (urea addition amount QE / 3600) by the drive frequency KS, the urea addition valve 230 is controlled. A unit urea addition amount QET, which is a urea addition amount required when the valve is opened once, is calculated.

  Here, the amount of urea water added when the urea addition valve 230 is opened varies depending on the urea water pressure NP. Therefore, based on the urea water pressure NP and the unit urea addition amount QET, the energization time TAU (unit: microsecond) when the urea addition valve 230 is opened once is calculated.

  By calculating the energization time TAU of the urea addition valve 230 in such a procedure, urea water corresponding to the unit urea addition amount QET is injected from the urea addition valve 230 within one addition interval INT. .

Next, details of a processing procedure related to drive control of the urea addition valve 230 will be described below.
FIG. 3 shows a procedure for setting the drive frequency KS. This process is executed by the control device 80 every predetermined calculation cycle (for example, every 32 ms).

  When this process is started, it is determined whether or not a precondition for setting the drive frequency KS is satisfied (S100). As preconditions in this step S100, for example, conditions that “the ignition switch 25 is“ ON ”” and “the urea water pressure NP is held at a specified value” are set.

  When the precondition is satisfied (S100: YES), it is determined whether or not it is the first addition after the engine is started (S110). In this step S110, the initial addition is performed when the initial addition flag regarding any of NOx purification addition, cooling addition, and precipitation suppression addition is “OFF” and the required addition amount QE exceeds “0”. It is determined.

  When it is determined that the addition is not the first time (S110: NO), it is determined whether or not the counter value CT is equal to or greater than “a value corresponding to the currently set drive frequency KS” (S140). . The counter value CT is a value for measuring an elapsed time after the urea addition valve 230 is opened. The “value corresponding to the currently set drive frequency KS” is the addition interval INT. Therefore, when a negative determination is made in step S140, it is determined that the calculation related to the current drive frequency KS is performed during the addition interval INT at the drive frequency KS set in the previous calculation cycle.

  When it is determined in step S140 that the counter value CT is less than “a value corresponding to the currently set drive frequency KS” (S140: NO), the counter value CT is incremented in step S150. Next, the drive frequency KS set at the previous execution of the main process is held (S160), and the process is temporarily terminated. As described above, when it is determined that the calculation related to the current drive frequency KS is performed between the addition intervals INT at the drive frequency KS set in the previous calculation cycle, it is set when the previous main process is executed. Since the drive frequency KS is maintained, the drive frequency KS is not changed during the addition interval INT.

  On the other hand, when it is determined in step S110 that it is the first addition (S110: YES), the counter value CT is greater than or equal to “a value corresponding to the currently set drive frequency KS” in step S140. (S140: YES), it is determined whether or not the SCR bed temperature, which is the temperature of the SCR catalyst 41, is equal to or higher than the threshold value A (S120). The SCR floor temperature is estimated from the exhaust temperature and the like.

When the SCR bed temperature is equal to or higher than the threshold A (S120: YES), the first frequency KS1 set based on the SCR bed temperature, the engine load, etc. is set as the drive frequency KS.
When it is determined in step S120 that the SCR bed temperature is lower than the threshold value A (S120: NO), it is determined whether or not the SCR bed temperature is lower than a value of “threshold value A−predetermined value α”. (S170). The predetermined value α is a value corresponding to hysteresis related to the temperature determination of the SCR bed temperature. When the SCR floor temperature is lower than the value of “threshold A−predetermined value α” (S170: YES), the second frequency KS2 set based on the SCR floor temperature, the engine load, etc. is set as the drive frequency KS. The The second frequency KS2 is a value smaller than the first frequency KS1. Therefore, the addition interval INT when the second frequency KS2 is set as the drive frequency KS is longer than the addition interval INT when the first frequency KS1 is set.

  In step S170, when the SCR bed temperature is equal to or higher than the value of “threshold A−predetermined value α” (S170: NO), the drive frequency KS set at the previous execution of the main process is held (S190).

  Then, after any one of the processes of step S130, step S180, and step S190 is performed, the counter value CT is cleared (S200), and this process is temporarily terminated.

Next, a process for calculating the energization time of the urea addition valve 230 will be described.
FIG. 4 shows the procedure for the energization time calculation process. This process is also executed by the control device 80 every predetermined calculation cycle (for example, every 32 ms).

  The calculation process of the energization time shown in FIG. 4 includes “NOx addition amount QEN” that is a required addition amount QE for NOx purification, “cooling addition amount QEC” that is a required addition amount QE for cooling addition, and The same process is performed for each “addition amount QES for suppressing precipitation”, which is the required addition amount QE for adding precipitation suppression.

  Therefore, in the following, calculation of the energization time TAU corresponding to the required addition amount QE (= NOx addition amount QEN) when there is an addition request for NOx purification will be described as an example. When there is a request, the energization time TAU corresponding to the required addition amount QE (= cooling addition amount QEC) is calculated. In addition, when there is an addition request for precipitation suppression, the energization time TAU corresponding to the required addition amount QE (= precipitation suppression addition amount QES) is calculated in the same manner.

  When this process is started, it is determined whether or not a precondition for calculating the energization time TAU is satisfied (S200). As preconditions in this step S200, for example, conditions that “environmental conditions such as outside temperature and exhaust temperature are established” and “urea water pressure NP is held at a specified value” are set. .

  When the precondition is satisfied (S200: YES), it is determined whether or not it is the first addition after the engine is started (S210). In this step S210, when the initial addition flag regarding NOx purification addition is “OFF” and the required addition amount QE (= NOx addition amount QEN) exceeds “0”, it is determined that the addition is the initial addition. Is done.

  When it is determined that the addition is the first time (S210: YES), the above-described equation is obtained based on the “NOx addition amount QEN” that is the required addition amount QE for NOx purification, the drive frequency KS, and the urea water pressure NP. The energization time TAU for NOx purification is calculated from (1) and equation (2).

  Next, the initial addition flag for NOx purification addition is set to “ON” (S230), and in the next step S240, the drive request flag for the urea addition valve 230 is set to “ON”, so that in step S220. The urea water addition by the calculated energization time TAU is started, and this process is temporarily ended.

  As described above, in the case of the first addition, the required addition amount QE currently calculated is directly converted into the addition amount per one valve opening, the energization time TAU is calculated, and the urea addition is executed promptly. .

  When it is determined in step S210 that the addition is not the first time (S210: NO), it is determined whether or not the counter value CT is equal to or greater than “a value corresponding to the currently set drive frequency KS”. (S250). The counter value CT is a value for measuring an elapsed time after the urea addition valve 230 is opened. The “value corresponding to the currently set drive frequency KS” is the addition interval INT.

  When it is determined in step S250 that the counter value CT is equal to or greater than “a value corresponding to the currently set drive frequency KS” (250: YES), a conversion addition amount QEH is calculated (S260). This conversion addition amount QEH is a value obtained by converting the required addition amount QE (unit: g / h) into an addition amount during the calculation cycle of this processing, that is, the unit is converted to “g / calculation cycle (for example, 32 ms)”. It is the value.

  Next, in step S270, an integrated addition amount S obtained by time-integrating the conversion addition amount QEH is calculated. In calculating the integrated addition amount S, a carry-over addition amount QK described later is also added.

  Next, the energization time TAU is calculated based on the accumulated addition amount S and urea water pressure NP updated in step S270 (S280). The calculation of the energization time TAU here is calculated in the same manner by replacing the required addition amount QE with the integrated addition amount S in the calculation of the energization time in step S220.

  When the energization time TAU based on the accumulated addition amount S is calculated in step S280, the accumulated addition amount S is cleared in step S290. Then, when the drive request flag is set to “ON” (S240), urea water addition is performed with the energization time TAU calculated in step S280, and this process is temporarily terminated.

  Thus, when it is not the first addition, the urea addition amount requested during the addition interval INT, that is, the cumulative addition amount S is converted into the addition amount per one valve opening, and the energization time TAU is calculated.

  When it is determined in step S250 that the counter value CT is less than “a value corresponding to the currently set drive frequency KS” (250: NO), a conversion addition amount QEH is calculated (S300). . The process in step S300 is the same as the process in step S260.

  Next, in step S310, an integrated addition amount S obtained by time-integrating the conversion addition amount QEH is calculated, and this process is temporarily terminated. The process in step S310 is the same as the process in step S270. Therefore, when a negative determination is made in step S250, the integrated addition amount S increases by the conversion addition amount QEH at every calculation cycle of this processing.

  If it is determined in step S200 that the precondition is not satisfied (S200: NO), the energization time TAU, the cumulative addition amount S, the drive request flag, and the initial addition flag are all cleared ( S320). As a result, the energization time TAU and the cumulative addition amount S are returned to the initial values (for example, “0”), the drive request flag and the initial addition flag are set to the initial values “OFF”, and this process is temporarily terminated. .

  The energization time calculation process described above is performed for each of the required addition amount QE for NOx purification, the required addition amount QE for cooling addition, and the required addition amount QE for precipitation suppression addition. Accordingly, the NOx purification energization time TAUN that is the energization time TAU corresponding to the NOx addition amount QEN, the cooling energization time TAUC that is the energization time TAU corresponding to the cooling addition amount QEC, and the precipitation suppression addition amount QES. The deposition suppressing energization time TAUS, which is the corresponding energization time TAU, is calculated.

Next, a description will be given of a processing procedure relating to mediation of each energization time and the calculation of the carry-over addition amount QK to cope with the case where the above-described addition requests are generated at the same time.
FIG. 5 shows a processing procedure related to the adjustment of the energization time TAU and the calculation of the carry-over addition amount QK. This process is also executed by the control device 80 every predetermined calculation cycle (for example, every 32 ms).

  When this process is started, it is first determined whether or not the integration request flag has changed from “OFF” to “ON” (S400). This integration request flag is at least one of the drive request flag set in step S240, more specifically, a drive request flag for NOx purification, a drive request flag for cooling addition, or a drive request flag for precipitation suppression. Is set to “ON” when the drive request flag is set to “ON”. On the other hand, when all of the drive request flag for NOx purification, the drive request flag for cooling addition, and the drive request flag for deposition suppression are set to “OFF”, the integration request flag is set to “OFF”.

When the integration request flag has not changed from “OFF” to “ON” (S400: NO), this process is temporarily terminated.
On the other hand, when the integration request flag changes from “OFF” to “ON” (S400: YES), the longest of the NOx purification energization time TAUN, the cooling energization time TAUC, and the deposition suppression energization time TAUS. Is set to the required energization time TAUM (S410). In the process of step S410, each energization time is adjusted, and when a plurality of different urea addition amounts are requested, the maximum addition amount is added from the urea addition valve 230.

Here, since the energization time TAU of the urea addition valve 230 has various hardware and control restrictions, a guard process for the required energization time TAU is performed.
First, in step S420, it is determined whether the required energization time TAUM is equal to or greater than a lower limit guaranteed value. The lower limit guarantee value is a minimum energization time that can guarantee the accuracy of the addition amount in controlling the amount of urea water added from the urea addition valve 230. When the required energization time TAUM is less than the lower limit guaranteed value (S420: NO), since the accuracy of the addition amount cannot be ensured, the final request that is the final required value of the energization time TAU to stop the urea addition. “0” is set in the energization time TAUF (S480). Then, the requested energization time TAUM set in step S410, that is, the requested energization time TAUM for which the current addition is stopped is set as the carry-over energization time TK (S490).

  On the other hand, when it is determined in step S420 that the required energization time TAUM is greater than or equal to the lower limit guaranteed value (S420: YES), an upper limit guard for the required energization time TAUM is performed (S430). In step S430, a value obtained by subtracting a CAN communication delay time, a calculation delay time, or the like from the addition interval INT, which is a time corresponding to the current drive frequency KS, is set as the upper limit guard value UL. When the required energization time TAUM exceeds the upper limit guard value UL, the value of the required energization time TAUM is changed to the upper limit guard value UL. On the other hand, when the required energization time TAUM is less than or equal to the upper limit guard value UL, the current required energization time TAUM is held as it is.

  When the upper limit guard for the required energization time TAUM is thus performed, the required energization time TAUM after the upper limit guard is performed is set as the final required energization time TAUF (S440). When the final required energization time TAUF is set in step S440 in this manner, the urea addition valve 230 is energized during the final required energization time TAUF. Thus, an amount of urea water corresponding to the final required energization time TAUF is added within one addition interval INT.

  Next, a value obtained by subtracting the upper limit guard value UL from the required energization time TAUM is set as the carry-over energization time TK (S450). In step S450, the energization time cut by the upper limit guard value UL, that is, the energization time TAU corresponding to the amount of urea water that could not be added within the addition interval INT is set as the carry-over energization time TK. When the value obtained by subtracting the upper limit guard value UL from the required energization time TAUM becomes a negative value, the carry-over energization time TK is set to “0”.

  When the carry-over energization time TK is set in step S450 or step S490, the carry-over addition amount QK is calculated based on the set carry-on energization time TK and the urea water pressure NP (S460). When the carryover addition amount QK is calculated based on the carryover energization time TK set in step S450, the carryover addition amount QK becomes the amount of urea water corresponding to the energization time cut by the upper limit guard value UL. . Further, when the carry-over addition amount QK is calculated based on the carry-on energization time TK set in step S490, the carry-on addition amount QK is set to the amount of urea water corresponding to the requested energization time TAUM for which the addition is stopped. Become.

  Then, all of the drive request flag for NOx purification, the drive request flag for cooling addition, and the drive request flag for precipitation suppression are set to “OFF” (S240), and this process is temporarily ended.

  The carry-over addition amount QK calculated in step S460 is added when calculating the cumulative addition amount S performed in step S270 or step S310, so that urea water corresponding to the carry-over addition amount QK is added next time. Is added in the addition cycle.

According to this embodiment described above, the following effects can be obtained.
(1) As shown in FIG. 3, when a negative determination is made in step S140, that is, the calculation related to the current drive frequency KS is performed between the addition intervals INT at the drive frequency KS set in the previous calculation cycle. If it is determined that it has been made, the drive frequency KS set at the time of the previous execution of this process is held (S160). Therefore, when it is determined that the calculation related to the current drive frequency KS is performed between the addition intervals INT at the drive frequency KS set in the previous calculation cycle, the drive frequency KS is changed between the addition intervals INT. Will not be performed. Therefore, the integrated addition amount S calculated during the addition interval INT can be suitably calculated.

  (2) As shown in FIG. 4, when it is determined that the addition is the first time (S210: YES), the energization time TAU is calculated based on the required addition amount QE at that time (S220). Therefore, the calculation of the energization time TAU at the time of the addition request is performed more quickly than the calculation of the energization time TAU based on the accumulated addition amount S that requires a certain amount of time for calculation. Therefore, urea water can be added quickly in response to the generation of the addition request.

  (3) As shown in FIG. 4, when a negative determination is made in step S250, that is, when it is determined that the calculation related to the current energization time TAU is performed between the addition intervals INT, in step S310 Although the cumulative addition amount S is calculated, the energization time TAU calculation process is temporarily terminated without calculating the energization time TAU.

  Therefore, even if another addition request occurs within one addition interval INT, only the addition amount S is calculated within the addition interval INT, and the addition of urea water based on another addition request is It is forbidden. Here, if the addition of urea water based on such another addition request is prohibited, this other addition request cannot be satisfied. In view of this, within the addition interval INT in which urea water addition based on another addition request is prohibited, the integrated addition amount S obtained by time integration of the required addition amount is calculated. Then, when an affirmative determination is made in step S250 of FIG. 4, that is, after the addition interval INT during which urea water addition based on another addition request has been prohibited has elapsed, the energization time TAU based on the cumulative addition amount S is calculated. (S280). Therefore, the urea addition amount in another prohibited addition request is reflected in the urea addition amount in the next addition interval INT after the prohibited addition interval INT of urea water addition based on the other addition request has elapsed. Will come to be. Therefore, at the time of adding urea water at the next addition interval INT, the above-described additional addition request that is prohibited can be satisfied.

  (4) Since the addition amount of urea water in another prohibited addition request is reflected in the addition amount of urea water in the next addition interval INT, the opening time of the urea addition valve 230 in the next addition interval INT The (energization time) is adjusted according to the reflected amount (integrated addition amount S). Thereby, in the addition interval INT where the addition has already been started, it is possible to appropriately set the energization time of the urea addition valve 230 as compared with the case where urea water addition according to another addition request is performed by interruption. It becomes like this. Therefore, it becomes possible to add appropriately the urea addition amount in another prohibited addition request | requirement from the urea addition valve 230, and the required addition amount can be added appropriately.

  (5) When various addition requests occur sporadically within the addition interval INT, only the instantaneous request at the calculation timing is reflected in the energization time TAU only by calculating the energization time TAU in step S220. On the other hand, in the present embodiment, since the energization time TAU is calculated using the integrated addition amount S integrated between the addition intervals INT, the required addition amount that changes sequentially is reflected in the integrated addition amount S. That is, the required addition amount of urea water based on various addition requests is reflected in the integrated addition amount S as an average amount. Therefore, it is possible to more appropriately satisfy various addition requests that change sequentially.

  (6) In step S410 shown in FIG. 5, the longest time among the NOx purification energization time TAUN, the cooling energization time TAUC, and the deposition suppression energization time TAUS is set as the required energization time TAUM. . Therefore, when a plurality of different required addition amounts QE are requested, the maximum addition amount among them is set as the required addition amount and added from the urea addition valve 230. Therefore, even when a plurality of addition requests are established at the same time, all of the plurality of addition requests can be satisfied.

  (7) In step S440 of FIG. 5, the required energization time TAUM after the upper limit guard is set is set as the final required energization time TAUF. In step S450 in FIG. 5, the energization time TAU cut by the upper limit guard is set as the carry-over energization time TK. In step S460 of FIG. 5, the amount of urea water corresponding to the energization time TAU cut by the upper limit guard is set as the carry-over addition amount QK. Then, in step S270 and step S310 in FIG. 4, this carry-over addition amount QK is added to the above-described cumulative addition amount S.

  Accordingly, when the entire required addition amount (addition amount of urea water corresponding to the required energization time TAUM set in step S410) cannot be added within the addition interval INT, a part of the required addition amount within the addition interval INT. Is added. The remaining addition amount is reflected in the addition amount of urea water in the next addition interval INT. Therefore, if the entire amount of urea water corresponding to the required energization time TAUM cannot be added within one addition interval INT, the remaining amount that could not be added is added during the addition of urea water at the next addition interval INT. Is supplemented by Therefore, the required addition amount (addition amount of urea water according to the required energization time TAUM) can be appropriately added.

In addition, the said embodiment can also be changed and implemented as follows.
The plurality of addition requests were an addition request for NOx purification, an addition request for cooling addition, and an addition request for precipitation suppression. However, other addition requirements may be used.

  Although urea water is used as the reducing agent, other reducing agents may be used.

  DESCRIPTION OF SYMBOLS 1 ... Engine, 2 ... Cylinder head, 3 ... Intake passage, 4a-4d ... Fuel injection valve, 5 ... Fuel addition valve, 6a-6d ... Exhaust port, 7 ... Intake manifold, 8 ... Exhaust manifold, 9 ... Common rail, DESCRIPTION OF SYMBOLS 10 ... Supply pump, 11 ... Turbocharger, 13 ... EGR passage, 14 ... EGR cooler, 15 ... EGR valve, 16 ... Intake throttle valve, 17 ... Actuator, 18 ... Intercooler, 19 ... Air flow meter, 20 ... Throttle valve opening Degree sensor, 21 ... Engine rotation speed sensor, 22 ... Accelerator sensor, 23 ... Pressure sensor, 24 ... Vehicle speed sensor, 25 ... Ignition switch, 26 ... Exhaust passage, 27 ... Fuel supply pipe, 30 ... First purification member, 31 ... Oxidation catalyst, 32 ... filter, 40 ... second purification member, 41 ... NOx purification catalyst (selective reduction type NOx catalyst: SCR catalyst) ), 50 ... third purification member, 51 ... ammonia oxidation catalyst, 60 ... dispersion plate, 80 ... control device, 100 ... first exhaust temperature sensor, 110 ... differential pressure sensor, 120 ... second exhaust temperature sensor, 130 ... first. DESCRIPTION OF SYMBOLS 1NOx sensor, 140 ... 2nd NOx sensor, 200 ... Urea water supply mechanism, 210 ... Tank, 220 ... Pump, 230 ... Urea addition valve, 240 ... Supply passage.

Claims (2)

An addition valve for adding a reducing agent in the exhaust passage and a catalyst for purifying NOx in the exhaust gas by the added reducing agent, and the reducing valve is added intermittently at a predetermined addition cycle. An exhaust emission control device for an internal combustion engine that controls opening and closing operations,
When another addition request occurs within the addition cycle when the intermittent addition is executed based on the addition request, the reducing agent is added based on the other addition request within the addition cycle in which the other addition request is generated And prohibit
The amount of addition of the reducing agent according to the same addition request is reflected in the amount of addition of the reducing agent in the next addition cycle after the prohibited addition cycle of addition of the reducing agent based on the other addition request has elapsed. An exhaust purification device for an internal combustion engine. When a plurality of different reducing agent addition amounts are required, the maximum addition amount of the different reducing agent addition amounts is added as the required addition amount from the addition valve, and the required addition within the addition cycle. 2. The internal combustion engine according to claim 1, wherein when the total amount cannot be added, a part of the required addition amount is added within the addition cycle, and the remaining addition amount is reflected in the reducing agent addition amount in the next addition cycle. Exhaust purification equipment.