JP2016196827A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine, capable of suppressing a drop in the temperature of a dispersion plate at its site where urea water collides.SOLUTION: The exhaust emission control device for an engine 1 includes a urea water addition valve 230 provided in an exhaust passage 26 for injecting urea water, a dispersion plate 60 provided on the exhaust downstream side of the urea water addition valve 230, and a control device 80 for executing the injection of the urea water by the urea water addition valve 230 in time synchronization based on a predetermined certain time period. The control device 80 calculates a peak timing when a discharge pressure at the arrangement position of the urea water addition valve 230 arranged in the exhaust passage 26 is maximized by exhaust pulsation, from an engine speed. Then, when the temperature of the dispersion plate 60 is lower than a predetermined temperature, the control device 80 executes processing for changing a timing for injecting the urea water from the time synchronization based on the certain time period into engine-speed synchronization, that is, synchronization with the peak timing.SELECTED DRAWING: Figure 1

Description

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

There is known an exhaust purification device for an internal combustion engine including a catalyst for purifying nitrogen oxide (NOx) in exhaust using urea water added to exhaust (for example, Patent Document 1).
In such an exhaust purification device, an addition valve for injecting urea water is provided in the exhaust passage, and the urea water injected from the addition valve is hydrolyzed by the heat of the exhaust gas and converted into ammonia. This ammonia is adsorbed by a catalyst prepared for NOx purification, and NOx in the exhaust is reduced and purified by the adsorbed ammonia.

  In addition, in the exhaust passage provided with such an exhaust purification device, a dispersion plate that collides urea water injected from the addition valve is provided downstream of the addition valve. By causing urea water to collide with the dispersion plate, vaporization or atomization of urea water is promoted, thereby promoting generation of ammonia by hydrolysis of urea water.

JP 2010-71255 A

By the way, the exhaust emission control device described in Patent Document 1 performs the urea water injection by the addition valve in time synchronization with a predetermined time period.
If urea water injection continues to be performed in time synchronization with such a constant time period, a state in which urea water injected from the addition valve continues to collide with the same portion of the dispersion plate is likely to occur. If the urea water continues to collide with the same part of the dispersion plate in this way, the temperature of the collision part decreases, so the urea water adheres without vaporization at the collision part, There is a risk of depositing at the collision site.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an exhaust purification device for an internal combustion engine that can suppress a temperature drop in a portion where urea water collides in a dispersion plate.

  An exhaust gas purification apparatus for an internal combustion engine that solves the above-described problems includes an addition valve that is provided in an exhaust passage of the internal combustion engine and injects urea water, a dispersion plate that is provided downstream of the exhaust passage of the addition valve, and the addition valve. A catalyst that purifies NOx in exhaust gas by using ammonia generated from the injected urea water as a reducing agent, and the urea water injection by the addition valve is executed in a time-synchronized manner with a predetermined fixed time period. An exhaust gas purification apparatus for an internal combustion engine, comprising: a control unit; a temperature calculation unit that calculates a temperature of the dispersion plate based on an exhaust gas temperature; and an exhaust gas at an installation position of the addition valve provided in the exhaust passage. A peak timing calculation unit that calculates a peak timing at which the pressure becomes maximum due to exhaust pulsation from the engine speed. When the temperature of the dispersion plate calculated by the temperature calculation unit is lower than a predetermined temperature, the control unit determines the injection timing of the urea water from the time synchronization and the peak calculated by the peak timing calculation unit. Execute processing to change to synchronized with the time.

  According to this configuration, when the temperature of the dispersion plate is lower than the predetermined temperature and there is a concern about a temperature drop due to urea water, the exhaust pressure at the position where the addition valve disposed in the exhaust passage is maximized by the exhaust pulsation. The urea water is injected at the peak time. When urea water is injected at the peak time, the injected urea water is sufficiently diffused by the exhaust gas. Accordingly, it is possible to suppress the urea water from continuously colliding with the same part of the dispersion plate, and thereby it is possible to suppress the temperature drop of the part of the dispersion plate where the urea water collides.

1 is a schematic diagram showing an internal combustion engine to which an exhaust emission control device of a first embodiment is applied and its peripheral configuration. In the embodiment, the time chart which shows the operation state of the urea addition valve by time synchronization. In the same embodiment, the schematic diagram which shows the direction of spraying of the urea water injected from a urea addition valve. In the same embodiment, the timing chart which shows the setting aspect of the injection timing of urea water using exhaust pulsation. The flowchart which shows the procedure of the injection process of urea water in the embodiment. The graph which shows the relationship between the urea addition amount and temperature determination value in the embodiment. In the same embodiment, the conceptual diagram which shows the relationship between an engine speed, urea addition amount, and the number of injection divisions. The flowchart which shows the procedure of the injection process of the urea water in 2nd Embodiment. The table | surface which shows the setting aspect of the object cylinder by the engine speed in the same embodiment. The flowchart which shows the part about the procedure of the injection process of urea water in 3rd Embodiment. The timing chart which shows the injection aspect of the urea water in the same embodiment.

(First embodiment)
Hereinafter, a first 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 first cylinder # 1, a second cylinder # 2, a third cylinder # 3, and a fourth cylinder # 4 side by side in order in the longitudinal direction of the cylinder block. 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 order of fuel injection in the engine 1 is as follows: first cylinder # 1, third cylinder # 3, fourth cylinder # 4, second cylinder # 2.

  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.

  The intake port is provided with an intake valve that opens and closes in synchronization with the rotation of the crankshaft that is the output shaft of the engine 1. 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.

  The exhaust ports 6 a to 6 d are provided with exhaust valves that open and close in synchronization with the rotation of the crankshaft that is the output shaft of the engine 1. 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 adding fuel to the exhaust 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 may be changed as appropriate as long as it is in the exhaust system and upstream of the first purification member 30. Further, the fuel may be added to the exhaust by adjusting the fuel injection timing and performing the 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, whereby fuel is injected from the fuel addition valve 5 toward the exhaust in the exhaust manifold 8. The fuel added to the exhaust gas from the fuel addition valve 5 is oxidized when it reaches the oxidation catalyst 31, thereby increasing the exhaust gas 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 SCR catalyst) 41 as a NOx purification catalyst for reducing and purifying NOx in exhaust gas using ammonia generated from urea water is disposed. ing.

  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. An ammonia oxidation catalyst 51 that oxidizes and purifies ammonia in the exhaust is disposed inside the third purification member 50.

  The engine 1 is provided with a urea water supply mechanism 200 as an addition mechanism for adding urea water to the exhaust gas. 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 urea water supply passage 240 that connects the urea addition valve 230 and the tank 210, and urea water supply. The pump 220 is provided in the middle of the passage 240.

  The urea addition valve 230 is provided at a curved portion of the exhaust passage 26 between the first purification member 30 and the second purification member 40, and its injection hole is directed downstream of the exhaust. When the urea addition valve 230 is opened, urea water is injected and supplied into the exhaust passage 26 via the urea water supply passage 240.

  The pump 220 is an electric pump, and its rotation speed is controlled so that the injection pressure P of urea water becomes a predetermined target pressure. During the forward rotation of the pump 220, urea water is fed 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. That is, during reverse rotation of the pump 220, urea water is recovered from the urea addition valve 230 and the urea water supply passage 240 and returned to the tank 210.

  A dispersion plate 60 is provided in the exhaust passage 26 between the exhaust passage downstream of the urea addition valve 230 and the exhaust passage upstream of the SCR catalyst 41 to cause the urea water injected from the urea addition valve 230 to collide. .

  The urea water added to the exhaust from the urea addition valve 230 is hydrolyzed to ammonia by the heat of the exhaust. Moreover, since urea water is vaporized and atomized by colliding the urea water with the dispersion plate 60, generation of ammonia by hydrolysis of the urea water is promoted. When such ammonia derived from aqueous urea reaches the SCR catalyst 41, it is adsorbed by the SCR catalyst 41. Then, NOx in the exhaust is reduced and purified using ammonia adsorbed on the SCR catalyst 41.

  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 lowers the combustion temperature of the air-fuel mixture in the cylinder by returning a part of the exhaust gas to the intake passage, thereby reducing the amount of NOx generated from the engine 1. This EGR device includes an EGR passage 13 that communicates an intake manifold 7 that constitutes a part of an intake passage and an exhaust manifold 8, an EGR valve 15 that is provided in the EGR passage 13, and an EGR that is provided in the middle of the EGR passage 13. The cooler 14 is configured. By adjusting the opening degree of the EGR valve 15 according to the engine operating state, the EGR amount that is the amount of exhaust gas that is returned from the exhaust passage 26 to the intake passage 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 crank angle sensor 21 detects a crank angle that is a rotation angle of the crankshaft. The engine speed NE is calculated based on the detected crank angle. The accelerator sensor 22 detects an accelerator operation amount ACCP, which is an accelerator pedal depression amount. The vehicle speed sensor 24 detects the vehicle speed SPD of the vehicle on which the engine 1 is mounted. The outside air temperature sensor 25 detects the outside air temperature THout. Further, the pressure sensor 260 provided in the vicinity of the connection portion between the urea addition valve 230 and the urea water supply passage 240 detects the urea pressure NP that is the pressure of the urea water in the vicinity of the urea addition valve 230.

  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 of these various sensors and the like are input to a control device 80 as a control unit. 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.

  As shown in FIG. 2, when there is a request for addition of urea water, the control device 80 repeatedly injects urea water from the urea addition valve 230 by a predetermined time period, that is, time synchronization by the injection period PR. Thus, the urea water injection timing is set, and urea water injection by the urea addition valve 230 is executed.

The outline of this urea water injection will be described below.
First, the drive frequency KS (unit: Hz), which is the frequency of the voltage applied to the urea addition valve 230, is set based on the temperature of the SCR catalyst 41 and the like. The value of the drive frequency KS is the same value as the number of injections of the urea addition valve 230 in one second, and the injection cycle PR (unit: millisecond) is calculated from the following equation (1) based on the drive frequency KS. The

Injection cycle PR = 1000 (milliseconds) / drive frequency KS (1)

For example, as shown in FIG. 2, when the drive frequency KS is 3 Hz, the urea addition valve 230 is opened and closed three times in one second, and the injection period PR at this time is about 333 milliseconds. .

Next, a unit urea addition amount QET which is a urea addition amount required in one injection cycle PR is calculated based on the following equation (2).

QET = (QE / 3600) / 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 dividing the value of (requested addition amount QE / 3600) by the drive frequency KS, a unit urea addition amount QET, which is a urea addition amount required when the urea addition valve 230 is opened once, is calculated. The

  Here, the amount of urea water added when the urea addition valve 230 is opened varies depending on the urea pressure NP. Therefore, based on the urea pressure NP and the unit urea addition amount QET, the valve opening time KT when the urea addition valve 230 is opened once is calculated.

  By calculating the valve opening time KT 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 injection cycle PR. The Further, the urea water is intermittently added in a pulsed manner by repeatedly opening and closing the urea addition valve 230 every injection cycle PR.

  By the way, if the urea water injection is continued in time synchronization by the injection cycle PR, which is a constant time cycle, the urea water injected from the urea addition valve 230 is placed in the same portion of the dispersion plate 60 as shown in FIG. It becomes easy to happen that the collision continues continuously. If the urea water continues to collide with the same part of the dispersion plate 60 in this way, the temperature of the collision part decreases, so that the urea water adheres without vaporizing at the collision part, and the adhered urea water May be deposited at the collision site.

  On the other hand, in the exhaust passage 26, exhaust pulsation is generated by the opening and closing operations of the exhaust valves provided in the cylinders # 1 to # 4. Therefore, the urea addition valve 230 provided in the exhaust passage 26 is provided. The exhaust pressure at the position of the exhaust gas (the pressure of the exhaust gas in the exhaust passage 26) periodically fluctuates due to such exhaust pulsation.

  As shown in FIG. 4, the exhaust pressure at the position where the urea addition valve 230 is disposed fluctuates periodically according to the scavenging timing of each cylinder, that is, the opening timing of the exhaust valve provided in each cylinder. For example, the engine 1 is a four-cylinder engine, and the order of fuel injection is first cylinder # 1 → third cylinder # 3 → fourth cylinder # 4 → second cylinder # 2. Therefore, a time when the exhaust pressure at the position where the urea addition valve 230 is disposed becomes the highest due to exhaust pulsation (hereinafter, this time is referred to as a peak time) appears every time the crank angle advances by 180 °.

  When the urea water is injected at such peak time, the injected urea water is sufficiently diffused by the exhaust gas, so that it is possible to suppress the urea water from continuing to collide with the same part of the dispersion plate 60. . Therefore, in this embodiment, not only the time synchronization described above but also the urea injection synchronized with the peak time due to the exhaust pulsation is performed.

Hereinafter, the urea water injection process in the present embodiment will be described with reference to FIGS.
FIG. 5 shows the procedure of urea water injection processing in the present embodiment. In addition, this injection process is repeatedly performed by the control apparatus 80 for every period shorter than the injection period PR mentioned above.

  When this process is started, it is determined whether there is a request for urea water injection in time synchronization (S100). In this step S100, an affirmative determination is made when there is an injection request due to the arrival of the injection period PR. Then, when there is no time-synchronized urea water injection request (S100: NO), this process ends.

  On the other hand, when there is a time-synchronized urea water injection request (S100: YES), it is determined whether the dispersion plate temperature THD is lower than the temperature determination value TH (S110). The dispersion plate temperature THD is a second exhaust temperature TH2 that is an exhaust temperature upstream of the dispersion plate 60, a heat transfer rate TR that is a transfer rate of heat transferred from the exhaust to the dispersion plate 60, and a second exhaust temperature TH2. Based on the heat release amount HR of the exhaust between the measurement position and the dispersion plate 60, it is calculated from the following equation (3).

Dispersion plate temperature THD = second exhaust temperature TH2 × heat transfer coefficient TR−heat radiation amount HR (3)

The heat transfer rate TR is set based on the exhaust flow rate and the exhaust temperature. More specifically, the heat transfer rate TR is set to a higher value as the exhaust gas flow rate increases. Further, the heat transfer coefficient TR is set to a higher value as the exhaust gas temperature is higher. The exhaust flow rate can be obtained from the engine operating state and the intake air amount GA. Further, it is preferable to use the second exhaust temperature TH2 as the exhaust temperature.

  The heat release amount HR is set based on the temperature difference between the outside air temperature THout and the second exhaust temperature TH2, the exhaust flow rate, the urea addition amount, and the vehicle speed SPD. More specifically, the heat release amount HR is set to a larger value as the temperature difference between the outside air temperature THout and the second exhaust temperature TH2 is larger. Further, the heat release amount HR is set to a larger value as the exhaust gas flow rate increases. Further, the larger the heat release amount HR and the urea addition amount, the larger the value is set. The heat dissipation amount HR is set to a larger value as the vehicle speed SPD is higher. Further, as the temperature judgment value TH, based on the fact that the dispersion plate temperature THD is lower than the temperature judgment value TH, the present value is such that the depositing is caused by the temperature drop of the dispersion plate 60 due to the urea water collision. The value is variably set based on the urea addition amount so that it can be accurately determined that the temperature of the dispersion plate 60 is low.

  As shown in FIG. 6, the temperature determination value TH is variably set so as to increase as the required addition amount QE increases. Such variable setting of the temperature determination value TH is performed because the temperature of the dispersion plate 60 is likely to decrease as the required addition amount QE increases.

  When the dispersion plate temperature THD is equal to or higher than the temperature determination value TH (S110: NO), the urea water injection by the time synchronization described above is immediately executed (S140). Then, this process ends.

On the other hand, when the dispersion plate temperature THD is lower than the temperature determination value TH (S110: YES), the injection division number DN is set based on the urea addition amount and the engine speed NE (S120).
This injection division number DN is the division number when the unit urea addition amount QET described above is divided and injected, and is set based on the following reasons.

  That is, when urea water is injected at the peak time, the injected urea water is diffused by the exhaust gas, but the time during which the diffusion effect is obtained at one peak time is a relatively short time. Therefore, if the urea addition amount, more specifically, the greater the unit urea addition amount QET described above, the more the urea water injection division number DN is increased and the urea water is injected at more peak times, the injection The total amount of the urea water thus made can be sufficiently diffused.

  Further, the time during which the diffusion effect is obtained at one peak time becomes shorter as the engine speed NE becomes higher. Therefore, if the urea water injection number DN is increased and the urea water is injected at more peak times as the engine rotational speed NE becomes higher, the entire amount of the injected urea water can be sufficiently diffused. Can do.

  Therefore, the time during which the diffusion effect is obtained at one peak time is defined as the unit diffusion time TMK, and the unit diffusion time TMK is calculated so that the unit diffusion time TMK becomes shorter as the engine speed NE is higher. Then, the amount of urea that can be injected within this unit diffusion time TMK is calculated, and the unit urea addition amount QET is divided by the calculated urea amount, thereby calculating the injection division number DN.

  Accordingly, as shown in FIG. 7, the injection division number DN increases as the engine speed NE is higher and the unit diffusion time TMK is shorter. Further, the injection division number DN increases as the unit urea addition amount QET increases. In addition, you may build the map which sets the injection division number DN based on the engine speed NE and the unit urea addition amount QET, without calculating as mentioned above.

  Next, instead of the urea water injection by time synchronization, the urea water injection synchronized with the peak time due to the exhaust pulsation described above is executed (S130), and this process ends. In this step S130, it is the time from when the exhaust valve of one cylinder is opened until the exhaust pressure at the arrangement site of the urea addition valve 230 is maximized by the exhaust discharged from that one cylinder. The exhaust pressure synchronization time HDT is calculated based on the engine speed NE. The exhaust pressure synchronization time HDT is set to a shorter time as the engine speed NE is higher. Then, the time when the exhaust pressure synchronization time HDT has elapsed from the opening timing of the exhaust valve that opens first after calculating the exhaust pressure synchronization time HDT is set as the above peak time, and in accordance with the arrival of the peak time Urea water is injected.

  When the injection division number DN is “2”, after calculating the exhaust pressure synchronization time HDT, the timing at which the exhaust pressure synchronization time HDT has elapsed from the opening timing of the exhaust valve that opens second is shown. The second peak time is set, and the second urea water injection is executed in accordance with the arrival of the second peak time. That is, when the injection division number DN is “n”, after calculating the exhaust pressure synchronization time HDT, the same exhaust pressure synchronization time HDT has elapsed from the opening timing of the exhaust valve that is opened first to nth. Each time is set as a peak time, and n times of urea water injection is executed in accordance with the arrival of each peak time. For example, when the injection division number DN is “5” and the exhaust valve that is first opened after calculating the exhaust pressure synchronization time HDT is the exhaust valve of the first cylinder # 1, Urea water is dividedly injected at peak times corresponding to each cylinder in the order of 1 cylinder # 1, 3rd cylinder # 3, 4th cylinder # 4, 2nd cylinder # 2, 1st cylinder # 1.

  Incidentally, the calculation of each peak time may be performed in consideration of fluctuations in exhaust pressure due to exhaust pulsation, and can be changed as appropriate. For example, in the case of a four-cylinder engine 1, the peak timing shift between the cylinders is approximately 180 ° CA. Therefore, instead of setting each peak time described above, the following setting can be performed.

  That is, for example, when the injection division number DN is “3”, the peak time initially calculated in the above mode is set as the reference peak time, and “180 ° CA” is added to the crank angle at the reference peak time. Set the crank angle as the second peak time. Then, a crank angle obtained by adding “180 ° CA” to the crank angle at the second peak time may be set as the third peak time. That is, when the injection division number DN is “n”, the time when the exhaust pressure synchronization time HDT has elapsed from the opening timing of the exhaust valve that opens first after calculating the exhaust pressure synchronization time HDT is the reference peak. It is time. Then, by adding “180 ° CA” to the crank angle at the reference peak time by a necessary amount, the crank angle at each peak time when the urea water is dividedly injected is obtained, and each of the obtained crank angles is obtained. By injecting urea water at the corner, the urea water may be dividedly injected in accordance with a plurality of continuous peak times.

  It should be noted that the exhaust pressure at the position where the temperature calculation unit for calculating the temperature of the dispersion plate 60 and the urea addition valve 230 provided in the exhaust passage 26 is maximized by the exhaust pulsation by the control device 80 that performs the injection process. A peak time calculation unit for calculating the peak time from the engine speed is configured.

Next, the effect | action by the said injection process is demonstrated.
When the dispersion plate temperature THD is lower than the temperature judgment value TH and there is a concern about the temperature drop of the dispersion plate 60 due to urea water, the exhaust pressure at the position where the urea addition valve 230 disposed in the exhaust passage 26 is disposed is exhaust pulsation. As a result, urea water is injected at the maximum peak time. When urea water is injected at the peak time, the injected urea water is sufficiently diffused by the exhaust gas.

According to this embodiment described above, the following effects can be obtained.
(1) When the dispersion plate temperature THD is lower than the temperature judgment value TH, urea is synchronized with the peak time at which the exhaust pressure at the position where the urea addition valve 230 disposed in the exhaust passage 26 is maximized due to exhaust pulsation. Water is jetted. When urea water is injected at the peak time, the injected urea water is sufficiently diffused by the exhaust gas. Accordingly, it is possible to suppress the urea water from continuing to collide with the same part of the dispersion plate 60, thereby suppressing the temperature drop of the part of the dispersion plate 60 where the urea water collides. As a result, for example, it is possible to suppress the deposition of urea water attached to the dispersion plate 60.

(2) Since the temperature determination value TH for determining the dispersion plate temperature THD is variably set according to the urea addition amount, the temperature decrease of the dispersion plate 60 can be more appropriately determined.
(3) The injection division number DN of urea water is set based on the unit urea addition amount QET and the engine speed NE. Therefore, even if the unit urea addition amount QET and the engine rotational speed NE are different, the injected urea water can be appropriately diffused.

(Second Embodiment)
Next, a second embodiment that embodies an exhaust emission control device for an internal combustion engine will be described with reference to FIGS.

  In the case of injecting urea water in accordance with a plurality of peak times, the time interval of each peak time becomes shorter as the engine speed increases, so the urea water injection cycle becomes shorter. When the urea water injection cycle is shortened in this way, the drive cycle of the urea addition valve 230 is shortened, and the mechanical load increases.

  For example, when the urea addition valve 230 is not energized, the temperature of the urea addition valve 230 that has generated heat due to the energization decreases. However, if the drive cycle of the urea addition valve 230 is shortened, the temperature reduction time of the urea addition valve 230 due to de-energization cannot be secured sufficiently, and the mechanical load that the temperature of the urea addition valve 230 becomes excessive increases. As a result, the life of the urea addition valve 230 is shortened.

  Therefore, in the present embodiment, the number of cylinders that synchronize urea water injection (hereinafter, this cylinder is referred to as a target cylinder) is made variable to prevent the injection cycle from becoming excessively short.

  The urea water injection process in the present embodiment is performed by changing a part of the injection process described with reference to FIG. Therefore, in the following, the procedure of the injection process in the present embodiment will be described focusing on the differences from the injection process described in FIG.

FIG. 8 shows the procedure of the injection process in the present embodiment.
In the present embodiment, when the injection division number DN is set in step S120 shown in FIG. 5, it is determined whether or not the current engine speed NE is equal to or higher than the first determination speed NE1 (S200). . As the first determination speed NE1, it is accurately determined that the driving period of the urea addition valve 230 becomes excessively short based on the engine speed NE being equal to or higher than the first determination speed NE1. Its value is set so that it can.

When the engine speed NE is equal to or higher than the first determination speed NE1 (S200: YES), the number of target cylinders to be synchronized is changed based on the engine speed NE (S210).
As shown in FIG. 9, when the engine speed NE is equal to or higher than the first determination speed NE1 and lower than the second determination speed NE2 set to a speed higher than the first determination speed NE1, the target cylinder is selected. The two cylinders, the first cylinder # 1 and the fourth cylinder # 4, are selected. Instead of selecting the first cylinder # 1 and the fourth cylinder # 4, the second cylinder # 2 and the third cylinder # 3 may be selected.

  Further, when the engine rotational speed NE is equal to or higher than the second determination speed NE2 and lower than the third determination speed NE3 set to a speed higher than the second determination speed NE2, only one cylinder is selected as a target cylinder. Selected. In the present embodiment, the first cylinder # 1 is selected as this one cylinder, but the second cylinder # 2, the third cylinder # 3, the fourth cylinder # 3, or the like is selected. 4 may be selected.

  When the target cylinder is selected in this manner, urea water injection synchronized with the peak time due to the exhaust pulsation described above is executed in a state where two cylinders are the target cylinders or one cylinder is the target cylinder. (S130), the process is terminated.

  On the other hand, when it is determined in step S200 that the engine rotational speed NE is lower than the first determination speed NE1 (S200: NO), the target cylinder is not limited as shown in FIG. In a state where all the cylinders are the target cylinders, urea water injection synchronized with the peak time due to the exhaust pulsation described above is executed (S130), and this process ends.

According to this embodiment described above, the following operational effects can be obtained in addition to the effects of the first embodiment described above.
(4) Since the number of cylinders that synchronize urea water injection is reduced as the engine rotational speed NE is higher, urea is added as the engine rotational speed NE increases when urea water is injected at the peak time. It can suppress that the drive period of the valve 230 becomes short. Therefore, an increase in the mechanical load of the urea addition valve 230 can be suppressed.

(Third embodiment)
Next, a third embodiment that embodies an exhaust emission control device for an internal combustion engine will be described with reference to FIGS. 10 and 11.

In the second embodiment, the number of cylinders that synchronize urea water injection is made variable in order to suppress the drive cycle of the urea addition valve 230 from becoming shorter as the engine rotational speed NE increases.
Here, when the engine rotational speed NE becomes very high, the time interval of the peak time becomes very short even if only one target cylinder is used. It becomes difficult to inject the urea water in synchronism with the peak time.

  Therefore, in the present embodiment, when the dispersion plate temperature THD is lower than the temperature determination value TH, the peak is obtained when the engine rotation speed is high enough that the driving of the urea addition valve 230 cannot follow the time interval of the peak timing. The urea water injection synchronized with the timing is stopped, and the urea water injection according to another aspect is executed.

  The urea water injection process in the present embodiment is performed by changing a part of the injection process described with reference to FIG. Therefore, in the following, the procedure of the injection process in the present embodiment will be described focusing on the differences from the injection process described in FIG.

In FIG. 10, the procedure of the injection process in this embodiment is shown.
In the present embodiment, when the injection division number DN is set in step S120 shown in FIG. 8, the process of step S200 described above is executed, so that the current engine speed NE is changed to the first determination speed NE1. It is determined whether or not this is the case.

  When the engine rotation speed NE is lower than the first determination speed NE1 (S200: NO), the target cylinder is not limited and all the cylinders are set as the target cylinders, and the peak timing due to the exhaust pulsation described above. The urea water injection synchronized with is executed (S130), and this process is terminated.

  On the other hand, when the engine rotational speed NE is equal to or higher than the first determination speed NE1 (S200: YES), it is determined whether or not the engine rotational speed NE is equal to or higher than the above-described third determination speed NE3 (S300).

  When the engine rotational speed NE is lower than the third determination speed NE3 (S300: NO), the number of target cylinders is changed based on the engine rotational speed NE by executing the process of step S210 described above. . Then, when the target cylinder is selected, urea water injection synchronized with the peak timing due to exhaust pulsation in a state where two cylinders are the target cylinders or a state where one cylinder is the target cylinder as described above. Is executed (S130), and this process is terminated.

  On the other hand, when the engine rotational speed NE is equal to or higher than the third determination speed NE3 (S300: YES), the urea water injection synchronized with the peak time is stopped by executing the processes of steps S310 to S330. The urea water injection according to another aspect is executed.

  First, in step S310, the number N of injections is set based on the currently calculated unit urea addition amount QET and the minimum injection amount QEmin that can be injected by the urea addition valve 230. More specifically, by dividing the unit urea addition amount QET by the minimum injection amount QEmin (N = QET / QEmin), in order to secure the unit urea addition amount QET when injecting urea water at the minimum injection amount QEmin A required number of injections N is calculated.

  Next, in step S320, the injection cycle RC when performing urea water injection of the number of injections N at the minimum injection amount QEmin is set. This injection cycle RC is set to the following time.

  That is, the temperature of the dispersion plate 60 decreases during the period in which the urea water is being injected. On the other hand, during the period when urea water injection is not performed, the temperature of the dispersion plate 60 that has decreased increases due to the heat of the exhaust gas. Therefore, if the period during which urea water is not injected, that is, the valve closing period of the urea addition valve 230 is appropriately set, the temperature of the dispersion plate 60 that has been lowered can be increased. Therefore, an optimal valve closing time of the urea addition valve 230 for increasing the temperature of the dispersion plate 60 is obtained in advance, and the urea addition valve 230 necessary for injecting the valve closing time and the minimum injection amount QEmin is opened. The time obtained by adding the time is set as the injection cycle RC. Note that the optimal valve closing time of the urea addition valve 230 for increasing the temperature of the dispersion plate 60 may be a fixed value, but may be variably set based on the exhaust temperature passing through the dispersion plate 60 or the like. .

Next, in step S330, urea water injection with the minimum injection amount QEmin is executed for the number N of injections in the set injection cycle RC (S330), and this process is terminated.
According to this embodiment described above, the following operational effects can be obtained in addition to the effects of the second embodiment described above.

  (5) When the engine rotational speed is high enough that the driving of the urea addition valve 230 cannot follow the time interval of the peak time when the dispersion plate temperature THD is lower than the temperature judgment value TH (S300: YES). The urea water is injected with the minimum injection amount QEmin every injection cycle RC.

  As shown in FIG. 11, in the urea water injection with such a minimum injection amount QEmin, the amount of urea water injected from the urea addition valve 230 is small, so the amount of urea water reaching the dispersion plate 60 is also very small. Therefore, the temperature drop of the dispersion plate 60 due to urea water can be suppressed.

  Further, as shown in FIG. 11, since the urea water injection interval is set to the injection cycle RC, the temperature of the dispersion plate 60 rises during the valve closing period of the urea addition valve 230. Therefore, the temperature drop of the dispersion plate 60 can also be suppressed by this.

In addition, each said embodiment can also be changed and implemented as follows.
Although the temperature determination value TH is variably set based on the required addition amount QE, for simplicity, the temperature determination value TH may be a fixed value.

  In the second embodiment, the number of target cylinders is variably set based on the engine rotational speed NE, but the number of target cylinders is always fixed to two cylinders regardless of the engine rotational speed, or one cylinder It may be fixed to.

  The engine 1 is an in-line four-cylinder engine, but may be an engine having another number of cylinders or a cylinder arrangement.

  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, 10 DESCRIPTION OF SYMBOLS ... 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 DESCRIPTION OF SYMBOLS 21 ... Crank angle sensor, 22 ... Accelerator sensor, 24 ... Vehicle speed sensor, 25 ... Outside air temperature sensor, 26 ... Exhaust passage, 27 ... Fuel supply pipe, 30 ... 1st purification member, 31 ... Oxidation catalyst, 32 ... Filter 40 ... 2nd purification member, 41 ... NOx purification catalyst (selective reduction type NOx catalyst: SCR catalyst), 50 ... 3rd purification member, 5 DESCRIPTION OF SYMBOLS ... Ammonia oxidation catalyst, 60 ... Dispersion plate, 80 ... Control apparatus, 100 ... First exhaust temperature sensor, 110 ... Differential pressure sensor, 120 ... Second exhaust temperature sensor, 130 ... First NOx sensor, 140 ... Second NOx sensor, 200 ... urea water supply mechanism, 210 ... tank, 220 ... pump, 230 ... urea addition valve, 240 ... supply passage, 260 ... pressure sensor.

Claims (1)

An addition valve provided in the exhaust passage of the internal combustion engine for injecting urea water;
A dispersion plate provided downstream of the exhaust passage of the addition valve;
A catalyst that purifies NOx in the exhaust by using ammonia generated from urea water injected by the addition valve as a reducing agent;
An exhaust gas purification apparatus for an internal combustion engine, comprising: a control unit that executes urea water injection by the addition valve in a time-synchronized manner with a predetermined time period;
A temperature calculator that calculates the temperature of the dispersion plate based on the exhaust temperature;
A peak timing calculation unit that calculates the peak timing at which the exhaust pressure at the position where the addition valve disposed in the exhaust passage is maximized due to exhaust pulsation from the engine rotation speed;
When the temperature of the dispersion plate calculated by the temperature calculation unit is lower than a predetermined temperature, the control unit determines the injection timing of the urea water as the peak timing calculated by the peak timing calculation unit from the time synchronization. An exhaust purification device for an internal combustion engine that executes processing to be changed in synchronization with the engine.