JP4764463B2 - Exhaust gas purification control device and exhaust gas purification system for internal combustion engine - Google Patents

Description

  The present invention provides an exhaust emission control device provided with a purification means provided in an exhaust passage of an internal combustion engine for purifying nitrogen oxides in exhaust gas, and an addition means for adding a reducing agent to the exhaust gas upstream of the purification means. The present invention relates to an exhaust gas purification control apparatus for an internal combustion engine that performs purification control of nitrogen oxides by the purification means while adjusting the amount of addition of the reducing agent based on the operation of the addition means, and an exhaust purification system including the same.

  In recent years, in-vehicle internal combustion engines (particularly diesel engines), exhaust that employs a selective catalytic reduction (SCR) that selectively purifies NOx (nitrogen oxides) in exhaust using urea water as a reducing agent. A purification system (urea SCR system) is being developed, and some have been put to practical use. In the urea SCR system, a selective reduction type NOx catalyst is provided in the exhaust pipe connected to the engine body, and urea water addition for adding urea water (urea aqueous solution) as a NOx reducing agent into the exhaust pipe is provided upstream of the exhaust gas. A valve is provided.

  In the above system, urea water is added into the exhaust pipe by the urea water addition valve, so that NOx in the exhaust gas is selectively reduced and removed on the NOx catalyst. That is, ammonia (NH 3) is generated by hydrolyzing urea water with exhaust heat, the ammonia is adsorbed to the NOx catalyst, and the reduction reaction with ammonia is performed on the NOx catalyst, whereby NOx is reduced, Purified.

By the way, when the exhaust temperature of the internal combustion engine is low, the hydrolysis efficiency from urea water to ammonia decreases, and urea thermal decomposition products such as cyanuric acid may be deposited in the exhaust passage. Therefore, conventionally, for example, as seen in Patent Document 1 below, it has also been proposed to provide a bypass passage for allowing a small amount of exhaust to pass through the exhaust passage, and to equip the bypass passage with a hydrolysis catalyst for urea water and a heater. . Thereby, when the exhaust gas temperature is low, ammonia is extracted from the urea water through the bypass passage, and this is supplied to the NOx catalyst, so that the urea thermal decomposition product is suitably prevented from depositing in the exhaust passage. Or it can be avoided.
JP 2007-327377 A

  In the above-described prior art, since hardware such as a bypass passage, a hydrolysis catalyst, and a heater is newly provided for NOx purification control in a region where the exhaust gas temperature is low, it cannot be ignored that cost performance is lowered. Furthermore, since a heater is used, there is a problem that energy consumption increases.

  The present invention has been made in order to solve the above-described problems, and an object of the present invention is to operate nitrogen controlled by the purifying means by operating an electronically controlled adding means for adding a reducing agent to the exhaust gas upstream of the purifying means. An exhaust purification control device for an internal combustion engine, which performs oxide purification control, and can suitably suppress adhesion of deposits to an exhaust passage while suppressing an increase in the number of components, and an exhaust equipped with the same It is to provide a purification system.

  Hereinafter, means for solving the above-described problems and the operation and effects thereof will be described.

The invention according to claim 1 is provided with a purifying means that is provided in an exhaust passage of the internal combustion engine and purifies nitrogen oxides in the exhaust, and an adding means that adds a reducing agent to the exhaust gas upstream of the purifying means. An exhaust gas purification control apparatus for an internal combustion engine, which is applied to an exhaust gas purification apparatus, and performs purification control of nitrogen oxides by the purification means while adjusting an addition amount of the reducing agent based on an operation of the addition means . An acquisition means for acquiring a parameter value having a correlation with the temperature of the exhaust system, and an operation mode of the addition means while grasping the temperature of the inner wall of the exhaust passage based on the exhaust temperature and the outside air temperature as the acquired parameters. Change means for changing, and the change means is configured to change the operation mode so that the deposit caused by the reducing agent is less than the upper limit temperature at which the deposits adhere to the exhaust passage. In order to reduce the amount of the reducing agent that reaches the inner wall when the temperature is lower, the one-time valve opening time of the adding means is shortened, and the one-time valve opening time is shortened. Thus, the addition frequency defined by the reciprocal of the addition interval is increased .

  The inventors have found that the shorter the valve opening time of the adding means, the less the reducing agent injected from the adding means adheres to the inner wall of the exhaust passage. In the above invention, paying attention to this point, the temperature of the inner wall of the exhaust passage is low, so that the deposit caused by the reducing agent easily adheres to the inner wall of the exhaust passage, and the time for opening the valve once is reduced. By doing so, it is possible to suitably suppress the adhesion of deposits while suppressing an increase in the number of parts.

Furthermore, in the said invention, the addition amount in a predetermined period can be made into a request | requirement addition amount irrespective of the variable setting of valve opening time. In addition, it is desirable to provide means for setting the required addition amount according to the nitrogen oxide concentration in the exhaust gas.

According to a second aspect of the invention of claim 1 Symbol placement, the internal combustion engine is an internal combustion engine, said changing means, characterized by adding the running speed of the vehicle during the changing process.

  As the traveling speed of the vehicle increases, the amount of intake air blown to the internal combustion engine per unit time increases, so the amount of heat taken from the wall surface of the exhaust passage also increases. For this reason, the traveling speed of the vehicle is a parameter having a correlation with the temperature of the inner wall of the exhaust passage. In the above invention, in view of this point, the temperature of the inner wall of the exhaust passage can be grasped with higher accuracy by including the traveling speed of the vehicle as the parameter.

According to a third aspect of the present invention, in the first or second aspect of the present invention, a swirl flow generating means for swirling the exhaust gas is provided upstream of the purifying means in the exhaust passage of the internal combustion engine.

  In the above-described invention, the reducing agent can be diffused by the swirling flow generating means, and accordingly, it is possible to suitably suppress the deposits caused by the reducing agent from adhering to the inner wall of the exhaust passage. Further, if the exhaust gas recirculation increases the amount of heat received by the inner wall of the exhaust passage, it is possible to more suitably suppress the deposits due to the reducing agent from adhering to the inner wall of the exhaust passage.

The invention according to claim 4 is the invention according to any one of claims 1 to 3 , wherein the reducing agent is urea water.

  When urea water is used as the reducing agent, it is known that a urea thermal decomposition product is deposited on the inner wall of the exhaust passage under a situation where the urea water is not sufficiently heated. For this reason, the above invention has particularly great utility value of the changing means.

An invention according to claim 5 is characterized by comprising the exhaust gas purification control device for an internal combustion engine according to any one of claims 1 to 4 and the purification means.

  Since the above invention includes the changing means, a highly reliable system is realized.

(First embodiment)
Hereinafter, a first embodiment of an exhaust gas purification control apparatus for an internal combustion engine according to the present invention will be described with reference to the drawings.

  The diesel engine 10 is an internal combustion engine having a reciprocating engine structure. An air cleaner 14 is provided upstream of the intake passage 12 of the diesel engine 10. The air cleaner 14 is provided with an intake air temperature sensor 16 that detects the intake air temperature and an air flow meter 18 that detects the intake air flow rate. A turbocharger 20 is provided downstream of the air cleaner 14. The air supercharged by the turbocharger 20 is cooled by the intercooler 22 and then supplied to the downstream side of the intake passage 12. This air is supplied to the combustion chamber 28 via a throttle valve 24 that adjusts the flow passage area of the intake passage 12, a combustion chamber 28 of the diesel engine 10, and an intake valve 26 that opens and closes the intake passage 12.

  The air thus supplied to the combustion chamber 28 is compressed together with high-pressure (for example, “several tens to 200 MPa”) fuel (for example, light oil) injected by the fuel injection valve 30 whose front end projects into the combustion chamber 28, and is combusted. Provided. The energy generated by this combustion is converted into rotational energy of the crankshaft 34 via the piston 32. Incidentally, a crank angle sensor 36 for detecting the rotation angle is provided near the crankshaft 34.

  The air and fuel used for combustion in the combustion chamber 28 are discharged into the exhaust passage 40 as exhaust gas as the exhaust valve 38 is opened. Of the exhaust passage 40, the upstream of the turbocharger 20 is connected to the intake passage 12 via the exhaust recirculation passage 42, and an exhaust recirculation valve (EGR valve 46) that adjusts the flow area of the exhaust recirculation passage 42 is opened. Depending on the degree, a part of the exhaust discharged to the exhaust passage 40 is cooled by the EGR cooler 44 and then supplied to the intake passage 12.

  A post-processing device is provided downstream of the turbocharger 20 in the exhaust passage 40. The post-treatment device includes an oxidation catalyst 50, a urea selective reduction catalyst (hereinafter referred to as urea SCR 52), and an ammonia slip catalyst 54 in order from the upstream side of the exhaust passage 40. Here, the ammonia slip catalyst 54 is used to remove ammonia that has not reacted with NOx and has been exhausted downstream of the urea SCR 52 in the urea SCR 52. The ammonia slip catalyst 54 is composed of, for example, an oxidation catalyst.

  Between the oxidation catalyst 50 and the urea SCR 52, an upstream NOx sensor 56 for detecting the NOx concentration in the exhaust gas and an exhaust temperature sensor 58 for detecting the exhaust gas temperature are provided. Further, a downstream NOx sensor 60 that detects the NOx concentration is provided between the urea SCR 52 and the ammonia slip catalyst 54. The post-treatment device further includes a diesel particulate filter (DPF) that collects particulate matter (PM) in the exhaust gas. However, this may be integrated with the oxidation catalyst 50. It may also be provided downstream thereof.

  Between the oxidation catalyst 50 and the urea SCR 52, a urea water addition valve 62 having an injection port provided downstream of the exhaust passage 40 is further provided. The urea water addition valve 62 is an electronically controlled valve body that adds urea water to exhaust gas by injecting urea water supplied from the urea water tank 64 into the exhaust passage 40. The urea water tank 64 is configured by a sealed container with a liquid supply cap, and urea water having a predetermined concentration (for example, 32.5%) is stored therein. The urea water tank 64 is connected to the urea water addition valve 62 via the urea water pipe 66, and the urea water in the urea water tank 64 is pumped up and added to the urea water addition valve 62 in the middle of the urea water pipe 66. An electronically controlled urea water pump 68 for supplying pressure (pressure feeding) is provided. A pressure sensor 70 that detects the pressure of the urea water that is pumped is provided downstream of the urea water pump 68.

  A swirling flow generating member 72 for generating a swirling flow in the exhaust gas flowing in the exhaust passage 40 is provided upstream of the urea water addition valve 62. The swirl flow generating member 72 is a member that generates a swirl flow in the exhaust by changing the cross-sectional structure of the flow path in the exhaust passage 40. FIG. 2 shows a configuration of the swirl flow generating member 72 according to the present embodiment. As shown in the drawing, the swirl flow generating member 72 includes a blade portion 72a including a plurality of blades (eight examples here). Here, the shape of the blade portion 72 a may be any shape that converts a part of the flow energy of the exhaust into the circumferential component of the exhaust passage 40. In the figure, in particular, as the shape of each wing of the blade portion 72a, an elliptical shape having a hollow inside is illustrated.

  In the urea SCR system configured to include the urea SCR 52, the urea water addition valve 62, and the like, urea water is added to the exhaust passage 40 by the urea water addition valve 62 to supply urea water together with the exhaust in the exhaust passage 40. Is supplied to the urea SCR 52. Thus, the urea SCR 52 purifies the exhaust gas by performing a NOx reduction reaction.

  Specifically, the urea water injected from the urea water addition valve 62 is hydrolyzed by the exhaust heat, and in this case, ammonia (NH3) as a reducing substance is converted by a chemical reaction expressed by the following formula (c1). Generated.

(NH2) 2CO + H2O → 2NH3 + CO2 (c1)
When the exhaust gas passes through the urea SCR 52, NOx in the exhaust gas is selectively reduced and purified by ammonia. Specifically, NOx is reduced and purified by performing a reduction reaction as shown in the following formulas (c2) to (c4).

4NO + 4NH3 + O2 → 4N2 + 6H2O (c2)
6NO2 + 8NH3 → 7N2 + 12H2O (c3)
NO + NO2 + 2NH3 → 2N2 + 3H2O (c4)
The electronic control device (ECU 80) is a control device that controls the diesel engine 10 and operates various actuators such as the fuel injection valve 30. The ECU 80 detects the detection signals of the above-described various sensors that detect the operating state of the diesel engine 10, the detection signal of the accelerator sensor 82 for detecting the accelerator operation amount by the user, and the detection of the vehicle speed sensor 84 that detects the traveling speed of the vehicle. A signal or the like is sequentially input, and the control amount (torque, exhaust characteristics, etc.) of the diesel engine 10 is controlled based on these signals.

  In particular, the ECU 80 controls the NOx purification by the urea SCR 52 by operating the urea water addition valve 62 and the urea water pump 68 to control the characteristics of the exhaust gas discharged from the exhaust passage 40 as the control amount. Here, the operation of the urea water addition valve 62 is performed by outputting a valve opening command pulse of a predetermined period to the urea water addition valve 62. That is, when the drive current flows to the drive part (solenoid part) of the urea water addition valve 62 with the pulse output, the urea water addition valve 62 is opened and urea water is added (injected).

  By the way, when the temperature of the exhaust system of the diesel engine 10 is low, the hydrolysis efficiency from urea water to ammonia decreases, and urea thermal decomposition products such as cyanuric acid may be deposited on the inner wall surface of the exhaust passage 40. is there. Therefore, in the present embodiment, when the inner wall surface temperature of the exhaust passage 40 is low, the urea water addition valve 62 is operated so as to suppress urea injected from the urea water addition valve 62 from reaching the exhaust passage 40. Change the aspect. This will be described in detail below.

  FIG. 3 is an experimental result on the relationship between the valve opening time associated with one injection of urea by the urea water addition valve 62 and the urea flight distance (penetration). As shown in the figure, the penetration increases as the valve opening time increases. For this reason, it is considered that the amount of urea reaching the inner wall surface of the exhaust passage 40 increases as the valve opening time increases. At this time, if the inner wall surface temperature of the exhaust passage 40 is low, it is considered that the deposits resulting from urea adhere to the inner wall surface.

  For this reason, in this embodiment, when the inner wall surface temperature of the exhaust passage 40 is low, the time for opening the urea water addition valve 62 once is shortened. FIG. 4 shows a processing procedure for NOx purification control according to the present embodiment. This process is repeatedly executed by the ECU 80, for example, at a predetermined cycle.

  In this series of processes, first, in step S10, it is determined whether or not the rotational speed of the diesel engine 10 is greater than a specified speed α. This process determines whether the diesel engine 10 is operating. When an affirmative determination is made in step S10, it is determined in step S12 whether or not an addition permission flag, which is a flag for permitting the addition of urea water, is on. If a negative determination is made in step S12, it is determined in step S14 whether or not the exhaust temperature TEX detected by the exhaust temperature sensor 58 is equal to or higher than the addition start temperature β. This process is for determining whether or not it is time to permit addition of urea water. Here, the addition start temperature β is set to a value as low as possible (for example, “180 ° C.”) that is equal to or higher than the lower limit temperature at which the urea SCR 52 has the NOx purification capability. If it is determined that the temperature is equal to or higher than the addition start temperature β, the addition permission flag is turned on in step S16.

  On the other hand, when an affirmative determination is made in step S12, it is determined in step S18 whether or not the exhaust gas temperature TEX is equal to or lower than a threshold temperature. This process is for determining whether or not it is time to prohibit the addition of urea. Here, the threshold temperature is set to a value lower than the addition start temperature β by a predetermined value ΔT. Here, the predetermined value ΔT is a hysteresis width provided in order to avoid a so-called hunting phenomenon in which the addition and prohibition of urea addition are frequently repeated. If an affirmative determination is made in step S18, the addition permission flag is turned off in step S20.

  On the other hand, when a negative determination is made in step S18 or when the process of step S16 is completed, the required urea amount is calculated based on the NOx emission concentration from the combustion chamber 28 in step S22. Here, the detected value of the upstream NOx sensor 56 is used as the NOx emission concentration. Specifically, the required urea amount is calculated based on the NOx emission concentration and the ammonia storage amount of the urea SCR 52. Incidentally, the ammonia storage amount is estimated by a known method. When the process of step S22 is completed, the process proceeds to step S24.

  In step S24, the temperature of the inner wall surface of the exhaust passage 40 (exhaust passage inner wall temperature TIW) is estimated based on the exhaust temperature TEX, the outside air temperature, and the vehicle speed. Here, it is considered that the higher the exhaust gas temperature TEX is, the more heat the wall surface of the exhaust passage 40 receives from the exhaust gas. Therefore, the exhaust passage inner wall temperature TIW is estimated to be higher. Further, since the amount of heat flowing out from the wall surface of the exhaust passage 40 to the outside increases as the outside air temperature is lower, the exhaust passage inner wall temperature TIW is estimated to be lower. Furthermore, since it is considered that the flow rate of the outside air blown to the wall surface of the exhaust passage 40 increases as the vehicle speed increases, the exhaust passage inner wall temperature TIW is estimated to be low. This estimation may be performed using, for example, a model related to heat transfer based on the specific heat of the wall surface of the exhaust passage 40 or the like. As the outside air temperature, in the present embodiment, the intake air temperature detected by the intake air temperature sensor 16 is used.

  When the exhaust passage inner wall temperature TIW is estimated, it is determined in step S26 whether or not the exhaust passage inner wall temperature TIW is equal to or higher than a specified temperature γ. This process is for determining whether or not there is a possibility that deposits resulting from urea adhere to the inner wall surface of the exhaust passage 40. The specified temperature γ is set to a value about the upper limit of the temperature at which urea is deposited. Then, according to whether or not the exhaust passage inner wall temperature TIW is equal to or higher than the specified temperature γ, a urea addition frequency that is the reciprocal of the urea addition interval from the urea water addition valve 62 is selected in steps S28 and S30. Here, the second addition frequency f2 selected when the exhaust passage inner wall temperature TIW is lower than the specified temperature γ is higher than the first addition frequency f1 selected when the exhaust passage inner wall temperature TIW is equal to or higher than the specified temperature γ. The This is a setting for maintaining the required addition amount calculated in step S22 even if the time for opening the urea water addition valve 62 once is shortened. That is, the amount of addition accompanying one valve opening decreases as the valve opening time for one time decreases. To make the amount added per predetermined period the same, the addition interval is shortened as the valve opening time is short. The need arises.

  When the processes in steps S28 and S30 are completed, in step S32, one opening time of the urea water addition valve 62 is calculated based on the required urea amount and the addition frequency. FIG. 5 illustrates valve opening times for each of the first addition frequency f1 and the second addition frequency f2 under the condition that the required urea amount is the same. Here, in order to make the urea addition amount per predetermined period the same, the sum of the valve opening time during the addition process at the second addition frequency f2 per the predetermined period is equal to the sum during the addition process at the first addition frequency f1. It is desirable that the valve opening time be equal to or greater than the sum per the predetermined period. The reason why these sums are not necessarily the same is that the injection rate at the subsequent timing can be larger than when the urea water addition valve 62 starts to open.

  When the process of step S32 in FIG. 4 is completed, the urea addition operation is executed by operating the urea water addition valve 62 in step S34. If a negative determination is made in steps S10 and S14, or if the processes in steps S20 and S34 are completed, this series of processes is temporarily terminated.

  FIG. 6 illustrates a urea water addition processing mode by the above processing. Specifically, FIG. 6 (a) shows the transition of the running speed of the vehicle, FIG. 6 (b) shows the transition of the outside air temperature, FIG. 6 (c) shows the transition of the exhaust temperature TEX, (D) shows the transition of the exhaust passage inner wall temperature TIW, FIG. 6 (e) shows the transition of NOx emission concentration, FIG. 6 (f) shows the transition of urea addition amount, and FIG. Shows the transition of the urea addition frequency.

  As shown in the figure, the exhaust passage inner wall temperature TIW becomes lower than the specified temperature γ even though the exhaust gas temperature is equal to or higher than the addition start temperature β and the NOx purification by the urea SCR 52 is possible. A situation may occur in which deposits due to urea adhere to the passage 40. However, in this embodiment, the adhesion of deposits can be suitably suppressed by selecting the second addition frequency f2 under such circumstances. Here, the urea polymer, which is a deposit that adheres to the wall surface of the exhaust passage 40, is vaporized by being “300 ° C.” or more, and ammonia is generated. For this reason, when deposits adhere to the exhaust passage 40, there is a possibility that the estimation accuracy of the ammonia storage amount of the urea SCR 52 is lowered, or an ammonia slip in which ammonia leaks downstream of the urea SCR 52 may occur. On the other hand, in this embodiment, such a situation can be suitably avoided by focusing on the exhaust passage inner wall temperature.

  Incidentally, even if the second addition frequency f2 is selected regardless of the exhaust passage inner wall temperature TIW, the adhesion of deposits to the exhaust passage 40 can be suppressed, but in this case, the urea water addition valve 62 Since the number of injections increases, the consumption rate of the urea water addition valve 62 increases, and there is a concern that the reliability may be lowered.

  According to the embodiment described in detail above, the following effects can be obtained.

  (1) When the temperature of the inner wall of the exhaust passage 40 is low, the time for opening the urea water addition valve 62 once is shortened. Thereby, while suppressing the increase in the number of parts, it is possible to suitably suppress the adhesion of deposits in a situation where deposits due to urea easily adhere to the inner wall of the exhaust passage 40.

  (2) The addition frequency defined by the reciprocal of the addition interval was increased as the valve opening time for one time was shortened. Thereby, the addition amount in a predetermined period can be made into a request | requirement addition amount.

  (3) The exhaust passage inner wall temperature was estimated based on the exhaust temperature TEX and the outside air temperature. Thereby, the exhaust passage inner wall temperature can be appropriately estimated.

  (4) In estimating the exhaust passage inner wall temperature, the traveling speed of the vehicle is taken into account. Thereby, the exhaust passage inner wall temperature can be estimated with higher accuracy.

  (5) A swirling flow generating member 72 that swirls exhaust is provided upstream of the urea SCR 52 in the exhaust passage 40. Thereby, urea can be diffused and by extension, it can suppress suitably that the deposit | attachment resulting from urea adheres to the inner wall of the exhaust passage 40. FIG.

(Second Embodiment)
Hereinafter, the second embodiment will be described with reference to the drawings with a focus on differences from the first embodiment.

  FIG. 7 shows a processing procedure for NOx purification control according to the present embodiment. This process is repeatedly executed by the ECU 80, for example, at a predetermined cycle. In FIG. 7, processes corresponding to the processes shown in FIG. 4 are given the same step numbers for convenience.

  In this series of processes, in step S26, the injection pressure of urea injected from the urea water addition valve 62 is variably set according to whether or not the exhaust passage inner wall temperature TIW is equal to or higher than the specified temperature γ. Specifically, the second injection pressure P2 selected when the exhaust passage inner wall temperature TIW is lower than the specified temperature γ than the first injection pressure P1 selected when the specified temperature γ is equal to or higher than the specified temperature γ (step S28a). S30a) is at a lower pressure. This is a setting for reducing the initial velocity of the urea water injected from the urea water addition valve 62 in a situation where deposits due to urea may adhere to the inner wall surface of the exhaust passage 40.

  When the processes of steps S28a and 30a are completed, the valve opening time is calculated based on the required urea amount and the injection pressure in step S32a. Here, in order to make the addition amount per predetermined period the same, the higher the injection pressure, the shorter the valve opening time may be set.

  It should be noted that adhesion of deposits to the exhaust passage 40 can also be suppressed by selecting the second injection pressure P2 regardless of the exhaust passage inner wall temperature TIW. However, the lower the injection pressure of urea water, the larger the spray particle size, and the NOx purification capacity decreases. Therefore, in the present embodiment, switching between the first injection pressure P1 and the second injection pressure P2 is performed in order to increase the NOx purification ability as much as possible while suppressing the adhesion of deposits to the inner wall of the exhaust passage 40.

  According to this embodiment described above, in addition to the effects (2) to (5) of the first embodiment, the following effects can be obtained.

  (6) When the exhaust passage inner wall temperature is low, the urea injection pressure by the urea water addition valve 62 is reduced. Thereby, while suppressing the increase in the number of parts, it is possible to suitably suppress the adhesion of deposits in a situation where deposits due to urea easily adhere to the inner wall of the exhaust passage 40.

(Other embodiments)
Each of the above embodiments may be modified as follows.

  In the first embodiment, the addition frequency is set in two ways depending on whether the exhaust passage inner wall temperature TIW is equal to or higher than the specified temperature γ, but the present invention is not limited to this. For example, as the exhaust passage inner wall temperature decreases, the addition frequency may be increased in two steps or more, or may be increased continuously.

  In the second embodiment, the injection pressure is set in two ways depending on whether the exhaust passage inner wall temperature TIW is equal to or higher than the specified temperature γ, but the present invention is not limited to this. For example, as the exhaust passage inner wall temperature decreases, the injection pressure may be decreased in two or more stages or continuously.

  In the first embodiment, when the exhaust passage inner wall temperature TIW is not more than the specified temperature γ, the injection pressure is increased to increase the addition frequency and reduce the spray particle size injected from the urea water addition valve 62. It may be raised. Since the generation of ammonia can be promoted by reducing the spray particle size in this way, the NOx purification performance can be maintained high at low temperatures when the NOx purification performance tends to be low. However, when the injection pressure of urea water is increased, the amount of urea water reaching the inner wall surface of the exhaust passage 40 may increase. For this reason, in order to avoid such a situation, it is desirable to shorten the valve opening time once by increasing the addition frequency more than the second addition frequency f2.

  In each of the above embodiments, the temperature of the inner wall surface of the exhaust passage 40 (exhaust passage inner wall temperature TIW) is estimated based on the parameter indicating the operating state of the diesel engine 10, but this is not a limitation, and dedicated hardware means are used. May be detected.

  As means for changing the operation mode of the adding means (urea water addition valve 62 and urea water pump 68) while grasping the temperature of the inner wall surface of the exhaust passage 40, the operation mode is changed based on the exhaust wall inner wall temperature TIW. Not limited to. For example, the operation mode may be changed based on the comparison between the exhaust gas temperature TEX and the threshold value, and the threshold value may be variably set according to the outside air temperature. Even in this case, it is possible to appropriately determine whether or not the temperature of the inner wall surface of the exhaust passage 40 is equal to or lower than the specified temperature. As a result, the operation mode is changed depending on whether or not the temperature is equal to or lower than the specified temperature. be able to. Note that the above determination can be made with higher accuracy if the vehicle speed is taken into account when the threshold value is variably set.

  In each of the above embodiments, the required urea amount is calculated based on the ammonia storage amount of the urea SCR 52, but the present invention is not limited to this. For example, it may be calculated based on the NOx purification rate. Here, the NOx purification rate is based on, for example, the NOx emission concentration on the upstream side of the urea SCR 52 (the amount based on the detection value of the upstream NOx sensor 56) to the NOx emission concentration on the downstream side (the detection value of the downstream NOx sensor 60). The value obtained by subtracting (amount) may be defined by a value obtained by dividing the value by the NOx emission concentration on the upstream side.

  In each of the above embodiments, the NOx emission concentration from the combustion chamber 28 is detected using the upstream side NOx sensor 56, but the present invention is not limited to this. For example, parameters indicating the operating state of the diesel engine 10 (for example, injection amount and rotation) It may be estimated based on (speed).

  In each of the above embodiments, the outside air temperature is substituted by the detected value of the intake air temperature sensor 16, but the present invention is not limited to this, and a sensor that detects the outside air temperature may be provided separately from the intake air temperature sensor 16.

  In each of the above embodiments, the exhaust temperature TEX is detected using the exhaust temperature sensor 58, but is not limited thereto. For example, the estimation may be performed based on parameters (for example, the injection amount, the rotation speed, the intake air amount, and the intake air temperature) indicating the operation state of the diesel engine 10.

  The swirl flow generating means for swirling the exhaust is not limited to that illustrated in FIG. For example, as in the swirl flow generating member 90 illustrated in FIG. 8, each blade of the blade portion 90a may be a thin plate member having an isosceles triangle shape. Further, a swirl flow generating member 92 illustrated in FIG. 9A may be used. Here, a plurality of members 92a and 92b deflected from the flow direction of the exhaust gas to a direction perpendicular thereto are provided, and the deflection angle of these members is larger than the center of the exhaust passage 40 as shown in FIG. It is set so that the outside is larger. According to such a configuration, the flow rate of the exhaust gas on the wall surface side of the exhaust passage 40 is slower than that of the central portion, so that the exhaust gas recirculation increases the amount of heat received by the exhaust passage 40. For this reason, it can suppress more suitably that the deposit | attachment resulting from urea adheres to the inner wall of the exhaust passage 40. FIG.

  Further, the swirling flow generating means is not limited to a fixed member that statically changes the cross-sectional shape of the exhaust passage 40, but may be one that rotates itself by being blown with exhaust gas like an impeller.

  -Purifying means for purifying nitrogen oxide in the exhaust is not limited to the urea SCR 52. For example, a selective reduction catalyst in which a reducing agent other than urea water is added to the exhaust on the upstream side may be used. Even in this case, the application of the present invention is effective if the deposit caused by the reducing agent may adhere when the inner wall surface temperature of the exhaust passage 40 is low.

  -The internal combustion engine is not limited to a compression ignition type internal combustion engine such as a diesel engine. For example, even in a spark ignition type internal combustion engine such as an in-cylinder injection type gasoline engine, the application of the present invention is effective when a selective reduction catalyst is used for NOx purification.

1 is a system configuration diagram according to a first embodiment. FIG. The figure which shows the structure of the swirl | vortex flow generation member concerning the embodiment. The figure for demonstrating the principle of the embodiment. The flowchart which shows the process sequence of NOx purification control concerning the embodiment. The time chart which shows the operation mode of the urea water addition valve concerning the embodiment. The time chart which illustrates the aspect of the said NOx purification control. The flowchart which shows the process sequence of NOx purification control concerning 2nd Embodiment. The figure which shows the structure of the rotational flow generation member concerning the modification of each said embodiment. The figure which shows the structure of the rotational flow generation member concerning the modification of each said embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Diesel engine, 52 ... Urea SCR (one embodiment of purification | cleaning means), 62 ... Urea water addition valve, 68 ... Urea water pump, 80 ... ECU (one embodiment of exhaust gas purification device).

Claims (5)

Applied to an exhaust gas purification device provided with a purification means that is provided in an exhaust passage of an internal combustion engine and purifies nitrogen oxides in exhaust gas, and an addition means that adds a reducing agent to the exhaust gas upstream of the purification means, In an exhaust gas purification control device for an internal combustion engine that performs purification control of nitrogen oxides by the purification means while adjusting the amount of addition of the reducing agent based on the operation of the addition means,
Obtaining means for obtaining a value of a parameter having a correlation with a temperature of an exhaust system of the internal combustion engine;
Changing means for changing the operation mode of the adding means while grasping the temperature of the inner wall of the exhaust passage based on the exhaust temperature and the outside air temperature as the acquired parameters,
The changing means is configured to change the operation mode so that the reducing agent is disposed on the inner wall when the temperature of the inner wall of the exhaust passage is lower than the upper limit temperature at which the deposit caused by the reducing agent adheres to the exhaust passage. In order to reduce the amount to reach, the one-time valve opening time of the adding means is shortened, and the addition frequency defined by the reciprocal of the addition interval is increased with the shortening of the one-time valve opening time. An exhaust gas purification control apparatus for an internal combustion engine, characterized by comprising: The internal combustion engine is an in-vehicle internal combustion engine,
The changing means, the exhaust gas purification controller according to claim 1 Symbol placement of the internal combustion engine, characterized in that considering the traveling speed of the vehicle when grasping the temperature of the inner wall of the exhaust passage during the process of changing the operation mode . The exhaust purification control apparatus for an internal combustion engine according to claim 1 or 2, further comprising a swirl flow generating means for swirling exhaust gas upstream of the purification means in the exhaust passage of the internal combustion engine. The exhaust purification control device for an internal combustion engine according to any one of claims 1 to 3 , wherein the reducing agent is urea water. An exhaust gas purification control device for an internal combustion engine according to any one of claims 1 to 4 ,
An exhaust gas purification system for an internal combustion engine comprising the purification means.