WO2018147369A1

WO2018147369A1 - Exhaust gas cleaning device

Info

Publication number: WO2018147369A1
Application number: PCT/JP2018/004392
Authority: WO
Inventors: 岡島　利典; 永田　誠; 伸宜奥井; 恭平山口
Original assignee: エヌ・イーケムキャット株式会社; 独立行政法人自動車技術総合機構
Priority date: 2017-02-09
Filing date: 2018-02-08
Publication date: 2018-08-16

Abstract

Provided are, inter alia, an exhaust gas cleaning device making it possible to reduce the amount of NO_x exhaust produced during a cold start. An exhaust gas cleaning device 100 is provided, in an exhaust channel 51, with a urea injection valve 83, a metal honeycomb 91, a temperature sensor S3, and an SCR catalyst 73. The exhaust gas temperature of exhaust gas passing through the metal honeycomb 91 can be elevated by the metal honeycomb 91, which can be heated electrically by control by a control unit ECU, and such temperature is detected by the temperature sensor S3. Ammonia has been adsorbed in advance onto the metal honeycomb 91 and the SCR catalyst 73 on the basis of a temperature–adsorbed ammonia quantity profile which is stored in advance in a storage unit of the control unit ECU. The metal honeycomb 91 is heated electrically during a cold start after the temperature detected by the temperature sensor S3 has fallen below 150°C.

Description

Exhaust gas purification device

The present invention relates to an exhaust gas purifying device for purifying exhaust gas discharged from an internal combustion engine such as an automobile, and more particularly, a urea SCR (Selective Catalytic Reduction) system for purifying nitrogen oxide (NOx) contained in exhaust gas of a diesel engine. The present invention relates to an exhaust gas purifying apparatus.

A urea SCR system for purifying NOx contained in exhaust gas discharged from an internal combustion engine such as an automobile has been developed. In the urea SCR system, an SCR catalyst that adsorbs ammonia generated by hydrolysis of urea is employed, and NOx is chemically reacted with ammonia on the SCR catalyst to purify into nitrogen and water.

In the urea SCR system, in order to adsorb ammonia on the SCR catalyst, it is necessary to control the temperature of the SCR catalyst so that the temperature is higher than the temperature at which urea is hydrolyzed. For this reason, attempts have been made to control the temperature of the SCR catalyst using an electrically heated heater, an electrically heated catalyst (Electrically Heated Catalyst), or the like.

For example, in Patent Document 1, the generation of deposits on the electric heater is suppressed by starting and stopping the electric heater using a periodic frequency based on the operating state of the exhaust gas treatment apparatus, or the deposit on the electric heater. A control method that eliminates the above and suppresses an increase in back pressure and deterioration in heating efficiency is disclosed. Patent Document 2 discloses a control method for improving fuel efficiency in a urea SCR system including an electric heater.

JP-T-2015-508864 International Publication No. 2013/183153

In recent years, further reduction of NOx emissions has been demanded. In particular, in the urea SCR system, urea injection is not performed under low temperature conditions in which urea does not hydrolyze due to the possibility of injector clogging. For this reason, for example, when starting cold after the engine is stopped, or when starting low load with an exhaust gas temperature of less than 150 ° C in the first half low temperature range of actual driving or WHTC (World-wide Harmonized Transient Cycle) mode (hereinafter referred to as “cold”). A large amount of NOx is discharged at the time of starting.

The present invention has been made in view of the above problems. That is, an object of the present invention is to provide a novel exhaust gas purification device and the like that can reduce the NOx emission amount generated at the cold start.

The present inventors diligently studied to solve the above problems. As a result, it has been found that the above-mentioned problems can be solved by adsorbing a predetermined amount of ammonia in advance to at least an electrically heated metal honeycomb and electrically heating the electrically heated metal honeycomb at the cold start, thereby completing the present invention. It came.

That is, the present invention provides various specific modes shown below.
(1) An exhaust passage through which exhaust gas from the engine passes, a urea injection valve for injecting urea into the exhaust passage, an SCR catalyst provided in the exhaust passage downstream of the urea injection valve, and the urea An electrically heated metal honeycomb that is provided in the exhaust passage downstream of the injection valve and upstream of the SCR catalyst and capable of raising the exhaust gas temperature, and the exhaust gas temperature of the exhaust gas that passes through the electrically heated metal honeycomb A temperature sensor for detecting the temperature, a storage unit storing a temperature-ammonia adsorption amount profile of the electrically heated metal honeycomb and the SCR catalyst, and the electrically heated metal honeycomb and the SCR based on the temperature-ammonia adsorption amount profile The urea injection amount In corresponding to the ammonia amount pre-adsorbed on the catalyst is calculated, and the calculated amount of the urea is supplied from the urea injection valve. A controller that pre-adsorbs ammonia to the electrically heated metal honeycomb and the SCR catalyst, and electrically heats the electrically heated metal honeycomb at a cold start after the exhaust gas temperature falls below 150 ° C; An exhaust gas purification device comprising at least

(2) The exhaust gas purification apparatus according to (1), wherein the control unit electrically heats the electrically heated metal honeycomb until the exhaust gas temperature is within a temperature range of a predetermined set temperature T ₁ ° C to T ₂ ° C. .
(3) The exhaust gas purification device according to (1) or (2), wherein the control unit stops the electric heating of the electric heating metal honeycomb when the exhaust gas temperature exceeds a predetermined set temperature T ₃ ° C.
(4) The exhaust gas purifying apparatus according to (3), wherein the set temperature satisfies a relationship of T ₁ <T ₃ ≦ T ₂ .

(5) The exhaust gas purifying apparatus according to any one of (1) to (4), wherein the electrically heated metal honeycomb includes at least a metal honeycomb and an SCR catalyst supported on the metal honeycomb.
(6) The electrically heated metal honeycomb includes at least a metal honeycomb and a jacket-type electric heater mounted on the metal honeycomb and / or a coil-type electric heater partially embedded in the metal honeycomb ( The exhaust gas purifying apparatus according to any one of 1) to (5).
(7) The electric heating type metal honeycomb includes at least a metal honeycomb and a heating control unit configured to energize the metal honeycomb and generate heat from the metal honeycomb according to any one of (1) to (6). Exhaust gas purification equipment.

(8) The control unit may be any one of the exhaust gas temperature at the予吸wearing performs the preheating control for raising the temperature of the exhaust gas temperature when less than the predetermined set temperature T ₁ (1) ~ (7) The exhaust gas purification apparatus according to 1.
(9) the control unit, the flue gas temperature is carried out a pre-heating control for raising the temperature of the electrical heating to the flue gas temperature the electrically heated metal honeycomb If it is less than a predetermined set temperature T ₁ of at the予吸wear ( The exhaust gas purifying apparatus according to any one of 1) to (8).
(10) The control unit reads the maximum ammonia adsorption amount Ad of the electrically heated metal honeycomb and the SCR catalyst at a predetermined set temperature Tg ° C. from the storage unit, and sets the maximum ammonia adsorption amount Ad as the injection amount In. The exhaust gas purifying apparatus according to any one of (1) to (9), wherein an amount of urea corresponding to 30 to 100% is calculated.
(11) Any one of (1) to (10), wherein the exhaust passage is provided with a heat insulating heat insulating material on the outer periphery at least downstream of the urea injection valve and upstream of the SCR catalyst. The exhaust gas purification apparatus according to 1.
(12) A second temperature sensor that detects an exhaust gas temperature of the exhaust gas flowing into the electric heating metal honeycomb is further provided upstream of the electric heating metal honeycomb, and the control unit includes the electric heating metal honeycomb. The exhaust gas according to any one of (1) to (11), wherein when the exhaust gas is electrically heated, pre-adsorption is performed by injecting the urea when the exhaust gas temperature detected by the second temperature sensor is 150 ° C. or higher. Purification equipment.

According to the present invention, it is possible to realize an exhaust gas purification device or the like that can reduce the amount of NOx emission generated at a cold start.

It is the schematic which shows the system configuration | structure of the exhaust gas purification apparatus of this embodiment. FIG. 4 is an explanatory diagram showing temperature-ammonia adsorption amount profiles of an electrically heated metal honeycomb and an SCR catalyst in the exhaust gas purification apparatus of the present embodiment, and shows a maximum ammonia adsorption amount Ad at a set temperature Tg. It is a flowchart which shows an example of the ammonia preadsorption control in the exhaust gas purification apparatus of this embodiment. It is a flowchart which shows an example of the electric heating control at the time of the cold start in the exhaust gas purification apparatus of this embodiment. It is a graph which shows the fluctuation | variation of the exhaust gas temperature in WHTC mode (reference example 1, example 1, and example 2). It is a graph which shows the fluctuation | variation of the exhaust gas temperature in WHTC mode (reference example 1, example 3, and example 4).

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The positional relationship such as up, down, left, and right is based on the positional relationship shown in the drawings unless otherwise specified. Further, the dimensional ratios in the drawings are not limited to the illustrated ratios. However, the following embodiments are examples for explaining the present invention, and the present invention is not limited to these. In this specification, for example, the description of a numerical range of “1 to 100” includes both the upper limit value “1” and the lower limit value “100”. This also applies to other numerical range notations.

FIG. 1 is a schematic diagram showing a system configuration of an exhaust gas purification apparatus 100 of the present embodiment. The exhaust gas purification apparatus 100 is connected to the engine 11, a turbocharger 21 having a compressor 21a and an exhaust turbine 21b, an intercooler IC that cools intake air, an intake passage 31 connected thereto, and the engine 11 and the exhaust turbine 21b. The

exhaust passages

41 and 51 through which the exhaust gas discharged from the engine 11 passes, the valve V1 provided in the intake passage 31 for adjusting the amount of intake air to the engine 11, drive control of the engine 11, and the exhaust gas purification device 100 A control unit ECU that performs overall control is provided.

The engine 11 used in the present embodiment is a so-called turbocharged diesel engine. The engine 11 includes an intake manifold 12 and an exhaust manifold 13. The intake manifold 12 is connected to the outlet of the compressor 21 a of the turbocharger 21 via the intake passage 31. Further, the exhaust manifold 13 is connected to an inlet of the exhaust turbine 21 b of the turbocharger 21 through an exhaust passage 41. The outlet of the exhaust turbine 21b is connected to the exhaust passage 51, and the exhaust gas from the engine 11 passes through the exhaust passage 41 and is discharged from the exhaust turbine 21b to the exhaust passage 51.

Moreover, the engine 11 of this embodiment is further equipped with an exhaust gas recirculation system. That is, an EGR (Exhaust Gas Recirculation) passage 61 serving as a bypass passage is connected between the intake passage 31 and the exhaust passage 41, and an EGR valve V2 for adjusting a bypass amount is provided in the EGR passage 61. It has been. The exhaust gas temperature can be adjusted by controlling the EGR valve V2 to bypass the EGR passage 61 and returning a part of the exhaust gas to the engine 11.

In the exhaust passage 51, a DOC (Diesel oxidation catalyst) 71 that oxidizes HC and NO contained in the exhaust gas and particulate matter contained in the exhaust gas are collected in order from the upstream side to the downstream side. DPF (Diesel particulate filter) 72, SCR catalyst (Selective Catalytic Reduction) 73 that reduces NOx in exhaust gas using ammonia as a reducing agent, and AMOX (Ammonia) that removes excess ammonia by oxidation oxidation catalyst (ammonia oxidation catalyst) 74 is provided.

In addition, the exhaust gas purification apparatus 100 of this embodiment is equipped with a urea SCR system 81. The urea SCR system 81 supplies urea into the exhaust passage 51, adsorbs ammonia generated by hydrolysis of urea to the SCR catalyst 73, and causes a chemical reaction with ammonia on the SCR catalyst 73. NOx is selectively reduced. The urea SCR system 81 includes a tank 82 for storing urea water, and a urea injection valve 83 connected to the tank 82 via a urea water supply pipe 82a and a pump P. The urea water in the tank 82 is pumped up by the pump P, supplied to the urea injection valve 83 via the urea water supply pipe 82a, and injected from the urea injection valve 83 into the exhaust passage 51. In the present embodiment, the urea injection valve 83 is connected to the exhaust passage 51 between the DPF 72 and the SCR catalyst 73.

A metal honeycomb 91 is provided in the exhaust passage 51 downstream of the urea injection valve 83 and upstream of the SCR catalyst 73. The metal honeycomb 91 used here is an EHC (Electrically-Heated-Catalyst) in which a SCR catalyst is supported on a metal honeycomb body. The metal honeycomb 91 can be electrically heated under the control of the control unit ECU, and the temperature of the exhaust gas passing through the exhaust passage 51 can be controlled by the heat generation of the metal honeycomb 91. Moreover, in this embodiment, the heat insulation heat insulating material is provided in the outer periphery of the exhaust path 51 over the full length (illustration omitted). The heat insulation and heat insulating material can be appropriately selected from those known in the art and is not particularly limited. For example, a material using cellulose fiber or rock wool is preferably used. As described above, by providing the heat insulating heat insulating material on the outer periphery of the exhaust passage 51 at least downstream of the urea injection valve 83 and upstream of the SCR catalyst 73, the temperature of the exhaust gas due to heat generation of the metal honeycomb 91 can be adjusted with high efficiency. It can be carried out.

In the present embodiment, heating of the electrically heated metal honeycomb 91 is performed by using a jacket-type electric heater attached to the outer periphery of the metal honeycomb main body and a coil-type electric heater attached so as to be partially embedded in the metal honeycomb main body. A heater is used (not shown). These electric heaters are electrically connected to an ECU and an in-vehicle power source (not shown), and the temperature of the metal honeycomb 91 and, in turn, the exhaust gas temperature in the exhaust passage 51 can be controlled by output control of these electric heaters.

The urea injected from the urea injection valve 83 into the exhaust passage 51 is hydrolyzed in the exhaust passage 51 to become ammonia. The urea and / or generated ammonia thus injected are adsorbed by the electrically heated metal honeycomb 91 which is EHC and the SCR catalyst 73 on the downstream side thereof. The reactivity of urea hydrolysis can vary depending on the urea water concentration, composition, pH, etc., but can be controlled efficiently by controlling the exhaust gas temperature in the exhaust passage 51. At this time, by controlling the heating of the electric heating-type metal honeycomb 91 described above, it is possible to perform precise control regardless of the operating state of the engine 11.

Note that the heating of the metal honeycomb 91 can also be performed by causing the metal honeycomb itself to generate heat directly by energizing the metal honeycomb body. In this case, the metal honeycomb is connected to the in-vehicle power source, and the output is controlled by the control unit ECU, thereby controlling the temperature of the metal honeycomb 91 and thus the exhaust gas temperature in the exhaust passage 51. In this case, the control unit ECU functions as a heating control unit.

The exhaust passage 51 is provided with temperature sensors, NOx sensors, and the like at various locations. In the present embodiment, the exhaust passage 51 between the DPF 72 and the urea injection valve 83 is provided with a NOx sensor S1 and a temperature sensor S2 that detect the NOx concentration and the exhaust gas temperature of the exhaust gas that has passed through the DPF 72. In addition, a temperature sensor S <b> 3 that detects the exhaust gas temperature of the exhaust gas that passes through the metal honeycomb 91 is provided in the exhaust passage 51 between the metal honeycomb 91 and the SCR catalyst 73. Further, a NOx sensor S4 that detects the NOx concentration of the exhaust gas that has passed through the AMOX 74 is provided in the exhaust passage 51 on the downstream side of the AMOX 74. These various sensors are electrically connected to the ECU, and the temperature and NOx concentration of the exhaust gas passing through the exhaust passage 51 are monitored as needed.

The control unit ECU performs drive control of the engine 11 and overall control of the exhaust gas purification device 100. The control unit ECU is a computer (not shown) including a CPU (Central Processing Unit) and a storage unit, specifically, a ROM (Read Only Memory, a RAM (Random Access Memory), etc. In this embodiment, the control unit The ECU is electrically connected to the urea injection valve 83, the pump P, the electric heater of the electrically heated metal honeycomb 91, the valve V1, the EGR valve V2, and the like, and injects into the exhaust passage 51 from the urea injection valve 83. The urea injection amount In is calculated, control is performed to inject the calculated amount of urea from the urea injection valve 83, and electric heating by the electric heater of the electrically heated metal honeycomb 91 is controlled.

Here, conventionally, the injection of urea from the urea injection valve 83 to the exhaust passage 51 avoids clogging of the injector, clogging of the catalyst, and the like due to adhesion of urea, ammonium nitrate, and reaction products of these with exhaust gas. From the viewpoint, it is performed when the temperature of the exhaust gas passing through the exhaust passage 51 is equal to or higher than the temperature at which urea can be hydrolyzed (for example, 150 to 170 ° C. or higher). Therefore, for example, at a cold start after the engine stops, or at a low load start in which the exhaust gas temperature is less than 150 ° C. in actual driving or in the first half low temperature region of the WHTC mode (hereinafter, these are collectively referred to as “cold start”). A large amount of NOx is discharged.

In contrast, in this embodiment, an ammonia pre-adsorption control system and a cold start assist heating control system are mounted in order to reduce the NOx emission amount at the cold start. This will be described in detail below.

In the storage unit of the control unit ECU of the present embodiment, the temperature-ammonia adsorption amount profiles of the metal honeycomb 91 and the SCR catalyst 73, which are the EHC described above, are stored. FIG. 2 is a graph showing an example of a temperature-ammonia adsorption amount profile. As shown in FIG. 2, the amount of ammonia adsorbed on the SCR catalyst (including the metal honeycomb 91 and the SCR catalyst 73, which is EHC) is temperature dependent, and the amount of ammonia adsorbed decreases as the temperature increases.

In the present embodiment, the control unit ECU detects the exhaust gas temperature of the exhaust gas passing through the metal honeycomb 91 from the temperature sensor S3 disposed at the same position or downstream of the metal honeycomb 91, and the detected temperature Tg. And the temperature-ammonia adsorption amount profile, the urea injection amount In corresponding to the ammonia amount to be pre-adsorbed on the metal honeycomb 91 and the SCR catalyst 73 is calculated, and the calculated amount of urea is injected from the urea injection valve 83. Then, ammonia is preadsorbed on the metal honeycomb 91 and the SCR catalyst 73. Here, urea water may be injected as it is from the urea injection valve 83, but by attaching a small ceramic heater or the like directly below the urea injection valve 83, the urea water spray injected from the urea injection valve 83 is heated. Urea or ammonia may be supplied to the metal honeycomb 91 and the SCR catalyst 73 after promoting thermal decomposition into ammonia.

The pre-adsorption of ammonia here is based on the cold start time when the exhaust gas temperature to be executed below 150 ° C. as a reference, and ammonia is adsorbed in advance on the metal honeycomb 91 and the SCR catalyst 73 at the reference time. Means. By performing such ammonia pre-adsorption, the ammonia supply at the cold start when urea injection is difficult can be supplemented, and the NOx emission amount at the cold start can be reduced. As a result, from this engine 11 The total amount of NOx discharged can be reduced. In this embodiment, the cold start determination is set to be less than 150 ° C., but the set temperature is not particularly limited to this. The cold start determination can be set as appropriate, and is preferably 120 ° C. or lower.

Here, the calculation of the urea injection amount In can be performed as follows. For example, the exhaust gas temperature of the exhaust gas passing through the metal honeycomb 91 is detected from the temperature sensor S3, and the ammonia maximum adsorption amount Ad is read based on the detected temperature Tg and the temperature-ammonia adsorption amount profile. An amount of urea corresponding to, for example, 30 to 100%, more preferably 40 to 95%, and still more preferably 50 to 90% of the maximum ammonia adsorption amount Ad is calculated as the injection amount In. The calculation of the injection amount In can be performed by various known methods, and the method is not particularly limited. For example, the method described in the prior art, specifically, the engine speed, the fuel injection amount, the intake air amount, the NOx concentration detected from the NOx sensors S1 and S4, and the like are further corrected for temperature. Then, after obtaining the amount of NOx reduced by the SCR catalyst, the amount of ammonia adsorbed on the SCR catalyst 22 is calculated, and the amount of urea corresponding to the shortage of ammonia adsorbed can be calculated. .

Further, the control unit ECU electrically heats the electrically heated metal honeycomb 91 when the exhaust gas temperature falls below 150 ° C. at the cold start after the ammonia pre-adsorption. By performing such assist heating, the rise of the exhaust gas temperature after a cold start can be made steep, and the exhaust gas temperature can be raised quickly. Moreover, the NOx reduction efficiency by ammonia can be increased by performing the assist heating in this way to quickly raise the exhaust gas temperature, thereby improving the NOx purification rate.

FIG. 3 is a flowchart showing an example of ammonia pre-adsorption control executed by the control unit ECU in the present embodiment. Here, first, the control unit ECU detects the temperature Tg (° C.) of the exhaust gas passing through the metal honeycomb 91 based on the output value from the temperature sensor S3 (step A1).

Next, the control unit ECU determines whether or not the detected temperature Tg (° C.) is within a temperature range not less than a predetermined set temperature T ₁ (° C.) and not more than T ₂ (° C.) (step A2). Here, in the present embodiment, the temperature T ₁ is set to 170 ° C. and the temperature T ₂ is set to 300 ° C., but these set temperatures can be appropriately set and are not particularly limited. In a normal use environment, the temperature T ₁ is preferably in the range of 160 to 220 ° C., more preferably in the range of 170 to 210 ° C., and the temperature T ₂ is in the range of 240 to 350 ° C. Preferably, it is in the range of 250 to 330 ° C.

If the determination in step A2 is affirmative, the control unit ECU reads the maximum ammonia adsorption amount Ad at the temperature Tg based on the temperature-ammonia adsorption amount profile as described above (step A3). Thereafter, the control unit ECU calculates an injection amount In of urea corresponding to the amount of ammonia preadsorbed on the metal honeycomb 91 and the SCR catalyst 73 based on the maximum ammonia adsorption amount Ad, and the calculated amount of urea is converted into urea. After injecting from the injection valve 83 (step A4) and performing ammonia pre-adsorption, the process is temporarily terminated.

When a negative determination is made in step A2, the control unit ECU determines whether the detected temperature Tg is lower than a predetermined set temperature T ₁ (° C.) (step A5). If a negative determination is made in step A5, it is determined that the engine 11 is in a medium to high load operating state, and the control unit ECU repeats the processes of steps A1 and A2 again, and a positive determination is made in step A2. Do not pre-adsorb ammonia until

On the other hand, in the case of an affirmative determination in step A5, it is determined that the temperature is not suitable for ammonia pre-adsorption, and the control unit ECU performs preliminary heating for increasing the exhaust gas temperature (step A6). The preheating method is not particularly limited, but electric heating of the electrically heated metal honeycomb 91, injection control for executing post injection, after injection or the like for a predetermined time, or controlling the opening degree of the intake valve V It is preferable to perform the flow rate control or the like for reducing the intake air amount. Post-injection and after-injection are sub-injections that are performed after the main injection, which is the main fuel injection. Further, the preheating is preferably performed until the metal honeycomb 91 reaches a temperature suitable for ammonia preadsorption, and is performed, for example, until the temperature falls within a temperature range from the set temperature T ₁ (° C.) to T ₂ (° C.). preferable. And after this preheating, control part ECU performs the process of step A1, A2 again, and when it becomes affirmation determination by step A2, after performing ammonia pre-adsorption (step A3, A4), a process is once performed. finish.

In the above description, an example of ammonia pre-adsorption control in the case where the metal honeycomb 91 and the SCR catalyst 73 are in a fresh state, in other words, the amount of ammonia adsorbed on the metal honeycomb 91 and the SCR catalyst 73 is shown. Here, when the ammonia pre-adsorption of the present invention has already been performed, or when the engine 11 has already been driven in a situation where the exhaust gas temperature exceeds the temperature Tg, the original ammonia adsorption of the urea SCR system has already been performed. In consideration of the amount of ammonia already adsorbed on the metal honeycomb 91 and the SCR catalyst 73, the injection amount In of urea in the ammonia pre-adsorption of the present invention may be calculated.

For example, before executing steps A1 and A2 described above, the temperature Tg of the exhaust gas passing through the metal honeycomb 91 in a state where urea injection from the urea injection valve 83 is stopped is, for example, 400 ° C. or higher, preferably 500 ° C. or higher. If the pretreatment to raise the temperature is performed and the ammonia already adsorbed on the metal honeycomb 91 and the SCR catalyst 73 is removed, the above-described steps A3 and A4 can be performed as they are. Alternatively, the amount of ammonia already adsorbed on the metal honeycomb 91 and the SCR catalyst 73 at the detected temperature Tg is calculated by a conventionally known method, and this amount is subtracted from the above-described maximum ammonia adsorption amount Ad to adsorb the deficient ammonia. The amount of urea corresponding to the shortage of ammonia adsorption amount can be calculated as the urea injection amount In executed in steps A3 and A4.

FIG. 4 is a flowchart illustrating an example of the assist heating control at the cold start executed by the control unit ECU in the present embodiment. Here, the term “cold start” includes a cold start after the engine is stopped and a low load start in which the exhaust gas temperature is relatively low in actual driving or in the first half low temperature region of the WHTC mode. In this example, the engine 11 is operated in a state where the temperature Tg (° C.) of the exhaust gas passing through the metal honeycomb 91 detected based on the output value from the temperature sensor S3 is less than 150 ° C., more preferably 120 ° C. or less. Is a cold start.

Here, first, the control unit ECU detects the temperature Tg (° C.) of the exhaust gas passing through the metal honeycomb 91 based on the output value from the temperature sensor S3 (step B1). Then, the control unit ECU determines whether or not the detected temperature Tg (° C.) is less than 150 ° C. (step B2).

If the determination in step B2 is affirmative, it is determined that the temperature condition is unfavorable for NOx purification, and the control unit ECU turns on the electric heater and adjusts the output control to electrically heat the metal honeycomb 91, that is, assist heating. (Step B3). By performing the assist heating in this way, the temperature Tg of the exhaust gas that passes through the metal honeycomb 91 is raised, thereby increasing the NOx reduction efficiency by ammonia.

The assist heating in step B3 is continued until the temperature Tg detected from the temperature sensor S3 exceeds a predetermined installation temperature T ₃ (° C.) (step B4). When the temperature Tg detected from the temperature sensor S3 exceeds a predetermined installation temperature T ₃ (° C.) (step B4), the control unit ECU turns off the electric heater and stops assist heating (step B4). B5), the process is temporarily terminated. The installation temperature T ₃ (° C.) is set to 270 ° C. in this example. However, the installation temperature T ₃ (° C.) may be appropriately set in consideration of the degree of improvement in the NOx purification rate by assist heating and the amount of electricity used for electric heating. There is no particular limitation. Specifically, the temperature is preferably in the temperature range of 200 to 300 ° C., more preferably in the temperature range of 210 to 280 ° C., and still more preferably in the temperature range of 220 to 270 ° C.

On the other hand, if a negative determination is made in step B2, the control unit ECU determines whether the detected temperature Tg (° C.) is equal to or higher than a predetermined installation temperature T ₄ (° C.) (step B6). In this step B6, when the detected temperature Tg (° C.) is lower than the predetermined installation temperature T ₄ (° C.), it is determined that the temperature condition should be adjusted to be advantageous by NOx purification. The electric heater is turned on, the output control thereof is adjusted, and assist heating of the metal honeycomb 91 is performed (step B3). Here, in this example, the set temperature T ₄ (° C.) is set to the same temperature as the set temperature T ₁ (° C.), that is, 170 ° C., but the set temperature T ₄ (° C.) depends on the desired temperature control. Although it can be appropriately set and is not particularly limited, it can be arbitrarily set between 151 and 299 ° C., for example. On the other hand, if the determination in step B6 is affirmative, the control unit ECU temporarily ends the process without turning on the electric heater.

In the above-described series of processes, the operation control for turning on the electric heater is performed in two stages of steps B2 and B6. In order to perform more precise temperature control, multistage control of three or more stages (for example, 3 to 3) is performed. (10 step control). Alternatively, when simpler temperature control is desired, step B6 can be omitted and single-step control with only step B2 can be performed. Similarly, the operation control for turning off the electric heater is not limited to the one-step control of only step B5, and may be a multi-step control of two or more steps.

The set temperature described above may be set as appropriate according to desired temperature control, and is not particularly limited, but preferably satisfies the relationship of T ₁ <T ₃ ≦ T ₂ (° C.). By setting to such a set temperature, NOx emissions during cold start can be reduced without excessively increasing power consumption and without excessively degrading fuel consumption when performing fuel injection control. Can do. As the electric power supplied to the electric heater, for example, an alternator that generates electric power by converting a part of the motive power of the engine 11, various batteries such as a nickel metal hydride battery and a lithium ion battery, and the like can be used. Is not particularly limited.

FIG. 5 is a graph showing fluctuations in exhaust gas temperature in the WHTC mode. This graph shows that the injection amount In is 30% of the maximum ammonia adsorption amount Ad when the temperature Tg is 200 ° C., the set temperature is T ₁ = 170 ° C., the set temperature T ₂ = 300 ° C., and the set temperature T ₄ = 170 ° C. The temperature change of the exhaust gas temperature is measured when each is set.

As is apparent from FIG. 5, the assist heating control is set as compared with the case where the assist heating control at the cold start is not performed (thick line of “no electric heating” in FIG. 5, hereinafter also referred to as “reference example”). When the temperature T ₃ = 230 ° C. (in FIG. 5, “Electrical heating to 230 ° C.” thin line, hereinafter also referred to as “Example 1”) and when the assist heating control is performed up to the set temperature T ₃ = 260 ° C. (In FIG. 5, the chain line “electrically heated to 260 ° C.”, hereinafter also referred to as “Example 2”) has a fast rise in exhaust gas temperature after cold start, and the time to reach 200 ° C. is about 700 seconds to about 350. It turns out that it is halved to second. When the assist heating control is performed up to the set temperature T ₃ = 230 ° C. in Example 1, the assist heating control is performed up to the set temperature T ₃ = 260 ° C. in the first half to the middle stage (50 to 900 seconds) of the WHTC mode. From the first half to the second half (50 to 1500 seconds) of the WHTC mode, an effect of improving the exhaust gas temperature by the assist heating control was recognized.

FIG. 6 is a graph showing fluctuations in exhaust gas temperature in the WHTC mode. This graph shows that the injection amount In is 100% of the maximum ammonia adsorption amount Ad when the temperature Tg is 200 ° C., the set temperature is T ₁ = 170 ° C., the set temperature T ₂ = 300 ° C., and the set temperature T ₄ = 170 ° C. The temperature change of the exhaust gas temperature is measured when each is set.

As is clear from FIG. 6, the assist heating control is set as compared with the case where the assist heating control at the cold start is not performed (thick line of “no electric heating” in FIG. 6, hereinafter also referred to as “reference example”). When the temperature T ₃ = 230 ° C. (in FIG. 6, the thin line “electric heating to 230 ° C.”, hereinafter also referred to as “Example 3”) and when the assist heating control is performed up to the set temperature T ₃ = 260 ° C. (In FIG. 6, the chain line of “electrically heated to 260 ° C.”, hereinafter also referred to as “Example 4”), the exhaust gas temperature rises quickly after a cold start, and the time to reach 200 ° C. is about 700 seconds to about 350 It turns out that it is halved to second. When the assist heating control is performed up to the set temperature T ₃ = 230 ° C. in the example 3, the assist heating control is performed up to the set temperature T ₃ = 260 ° C. in the first half to the middle stage (50 to 900 seconds) of the WHTC mode. In the first half to the second half (50 to 1500 seconds) of the WHTC mode, an effect of improving the exhaust gas temperature by the assist heating control was recognized.

Table 1 shows the NOx purification rate in the WHTC mode.

As is apparent from Table 1, it can be seen that the NOx purification rate is clearly improved by performing the ammonia pre-adsorption control of the present invention. It can also be seen that the NOx purification rate is clearly improved by performing the cold start assist heating control of the present invention. From these facts, it was confirmed that the ammonia pre-adsorption control and the cold start assist heating control according to the present invention are each independently effective in improving the NOx purification rate.

It can also be seen that the effect of improving the NOx purification rate is further enhanced by using the ammonia pre-adsorption control and the cold start assist heating control of the present invention in combination.

Then, the pre-adsorption 100% example in which the injection amount In is set to 100% of the ammonia maximum adsorption amount Ad than the examples 1 and 2 in which the injection amount In is 30% of the ammonia maximum adsorption amount Ad and 30% pre-adsorption. It was recognized that the NOx purification rate was improved in 3 and 4 respectively. Furthermore, when comparing the improvement width, the comparison between Example 2 and Example 4 is larger than the comparison between Example 1 and Example 3. From this, it was found that the greater the pre-adsorption, the greater the improvement in the NOx purification rate, that is, the higher the sensitivity.

The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific embodiments described above, and is within the scope of the gist of the present invention described in the claims. Can be modified or changed.

For example, a configuration of only the metal honeycomb 91 which is EHC in which the SCR catalyst 73 is omitted can be adopted. In this case, only the temperature-ammonia adsorption amount profile of the metal honeycomb 91 that is EHC needs to be stored in the storage unit of the control unit ECU. In addition, the present invention can employ a configuration in which a metal honeycomb 91 that does not carry an SCR catalyst, in other words, a metal honeycomb 91 that is not EHC is disposed. In this case, only the temperature-ammonia adsorption amount profile of the SCR catalyst 73 needs to be stored in the storage unit of the control unit ECU. On the other hand, a configuration in which a plurality of SCR catalysts 73 are arranged on the downstream side of the metal honeycomb 91 may be employed. In this case, in this case, the temperature-ammonia adsorption amount profiles of the metal honeycomb 91 which is EHC and the plurality of SCR catalysts 73 may be stored in the storage unit of the control unit ECU.

The ammonia pre-adsorption control according to the present invention is controlled based on a second temperature sensor (temperature sensor S2) that is provided upstream of the metal honeycomb 91 and detects the exhaust gas temperature of the exhaust gas flowing into the metal honeycomb 91. Is also possible. Specifically, when the metal honeycomb 91 is electrically heated, the control unit ECU can perform pre-adsorption by injecting urea when the exhaust gas temperature detected by the temperature sensor S2 is 150 ° C. or higher. When assist heating of the metal honeycomb 91 is performed, the exhaust gas temperature detected by the temperature sensor S3 is higher than the exhaust gas temperature detected by the temperature sensor S2. Therefore, the ammonia pre-adsorption control is appropriately performed even if such control is performed. It can be activated.

The present invention can be used widely and effectively in various internal combustion engines equipped with a urea SCR system for purifying NOx contained in exhaust gas.

11 Engine 21a Compressor 21b Exhaust turbine 21 Turbocharger 31 Intake passage 41 Exhaust passage 51 Exhaust passage 12 Intake manifold 13 Exhaust manifold 61 EGR passage 71 DOC
72 DPF
73 SCR catalyst 74 AMOX
81 Urea SCR system 82 Tank 82a Urea water supply pipe 83 Urea injection valve 91 Metal honeycomb 100 Exhaust gas purifier ECU Control unit IC Intercooler V1 valve V2 EGR valve P pump S1 NOx sensor S2 Temperature sensor S3 Temperature sensor S4 NOx sensor

Claims

An exhaust passage through which the exhaust gas of the engine passes,
A urea injection valve for injecting urea into the exhaust passage;
An SCR catalyst provided in the exhaust passage downstream of the urea injection valve;
An electrically heated metal honeycomb that is provided in the exhaust passage downstream from the urea injection valve and upstream from the SCR catalyst, and capable of raising the exhaust gas temperature;
A temperature sensor for detecting an exhaust gas temperature of exhaust gas passing through the electrically heated metal honeycomb;
A storage unit storing temperature-ammonia adsorption amount profiles of the electrically heated metal honeycomb and the SCR catalyst;
Based on the temperature-ammonia adsorption amount profile, the urea injection amount In corresponding to the ammonia amount preadsorbed on the electrically heated metal honeycomb and the SCR catalyst is calculated, and the calculated amount of the urea is injected into the urea injection A controller that pre-adsorbs ammonia to the electrically heated metal honeycomb and the SCR catalyst by injection from a valve, and electrically heats the electrically heated metal honeycomb at a cold start after the exhaust gas temperature falls below 150 ° C. And at least an exhaust gas purification device.
The exhaust gas purification device according to claim 1, wherein the control unit electrically heats the electrically heated metal honeycomb until the exhaust gas temperature falls within a temperature range of a predetermined set temperature T 1 ° C or more and T 2 ° C or less.
The exhaust gas purification device according to claim 1 or 2, wherein the control unit stops the electric heating of the electrically heated metal honeycomb when the exhaust gas temperature exceeds a predetermined set temperature T 3 ° C.
The exhaust gas purifying apparatus according to claim 3, wherein the set temperature satisfies a relationship of T 1 <T 3 ≦ T 2 (° C.).
The exhaust gas purifying apparatus according to any one of claims 1 to 4, wherein the electrically heated metal honeycomb includes at least a metal honeycomb and an SCR catalyst supported on the metal honeycomb.
The electric heating type metal honeycomb includes at least a metal honeycomb, a jacket type electric heater mounted on the metal honeycomb, and / or a coil type electric heater partially embedded in the metal honeycomb. The exhaust gas purification device according to any one of claims 5 to 6.
The exhaust gas purifying apparatus according to any one of claims 1 to 6, wherein the electrically heated metal honeycomb includes at least a metal honeycomb and a heating control unit that generates electricity by energizing the metal honeycomb.
Wherein the control unit, the exhaust gas purification according to any one of claims 1 to 7, wherein the exhaust gas temperature at the予吸wearing performs preheating control for raising the temperature of the exhaust gas temperature when less than the predetermined set temperatures T 1 apparatus.
Wherein the control unit according to claim 1 wherein the exhaust gas temperature at the予吸wearing performs preheating control for raising the temperature of the electrical heating to the flue gas temperature the electrically heated metal honeycomb If it is less than a predetermined set temperature T 1 ~ The exhaust gas purification apparatus according to any one of claims 8 to 9.
The control unit reads the ammonia maximum adsorption amount Ad of the electrically heated metal honeycomb and the SCR catalyst at a predetermined set temperature Tg ° C. from the storage unit, and 30 to 100 of the ammonia maximum adsorption amount Ad as the injection amount In The exhaust gas purification apparatus according to any one of claims 1 to 9, wherein an amount of urea corresponding to% is calculated.
The exhaust gas purification apparatus according to any one of claims 1 to 10, wherein a heat insulation heat insulating material is provided on an outer periphery of the exhaust passage at least downstream of the urea injection valve and upstream of the SCR catalyst. apparatus.
A second temperature sensor for detecting an exhaust gas temperature of the exhaust gas flowing into the electric heating metal honeycomb further upstream of the electric heating metal honeycomb;
The controller performs pre-adsorption by injecting the urea at an exhaust gas temperature detected by the second temperature sensor of 150 ° C. or higher when the electrically heated metal honeycomb is electrically heated. The exhaust gas purifying apparatus according to any one of the above.