JP6682972B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas purifying device for an internal combustion engine.

  In a diesel engine, it is known to provide an aftertreatment unit including a plurality of catalysts and the like in order to purify harmful substances in exhaust gas. The aftertreatment unit is typically a filter that collects particulate matter (PM) in the exhaust gas and a selective reduction that is arranged downstream of the filter and reduces and removes nitrogen oxides (NOx) in the exhaust gas. Type NOx catalyst (SCR) is installed.

JP, 2010-53847, A

  It is known to periodically perform filter regeneration control that burns and removes PM accumulated in the filter. During filter regeneration control, additional fuel is supplied by, for example, post injection.

  On the other hand, during the execution of the filter regeneration control, the PM in the filter burns, which may cause the exhaust gas of a relatively high temperature to be discharged from the filter. When this high-temperature exhaust gas is supplied to the NOx catalyst, the temperature of the NOx catalyst excessively rises, the deterioration of the NOx catalyst is accelerated, and the NOx purification rate of the NOx catalyst may decrease early.

  Therefore, the present invention has been devised in view of such circumstances, and an object thereof is to provide an exhaust gas purifying apparatus for an internal combustion engine that can suppress acceleration of deterioration of the NOx catalyst due to execution of filter regeneration control.

According to one aspect of the invention,
An exhaust gas purification apparatus for an internal combustion engine,
Exhaust pipe,
A post-treatment unit provided in the middle of the exhaust pipe,
A casing containing the post-treatment unit,
Equipped with
The post-processing unit,
A first catalyst casing,
A second catalyst casing arranged downstream of the first catalyst casing;
A U-shaped connecting pipe connecting the first catalyst casing and the second catalyst casing;
A filter provided in the first catalyst casing for collecting particulate matter in exhaust gas;
A selective reduction type NOx catalyst provided in the second catalyst casing for purifying nitrogen oxides in exhaust gas;
Equipped with
The exhaust gas purification device further includes
A detector for detecting the inlet exhaust gas temperature of the NOx catalyst,
An addition valve provided at the upstream end of the connecting pipe for adding urea water,
A control unit configured to perform a regeneration control for controlling the addition valve and regenerating the filter,
Equipped with
The control unit is configured to increase the urea water addition amount in the addition valve when the inlet exhaust gas temperature detected by the detector becomes equal to or higher than a predetermined threshold during execution of the regeneration control. An exhaust gas purifying apparatus for an internal combustion engine is provided.

Preferably, the first catalyst casing extends from the front side to the rear side from the upstream side to the downstream side,
The second catalyst casing extends from rear to front from the upstream side to the downstream side,
The connecting pipe extends forward from the rear end of the first catalyst casing and folds back in a U shape, and then extends rearward to connect to the rear end of the second catalyst casing.

  Preferably, the control unit increases the urea water addition amount when the inlet exhaust gas temperature becomes equal to or higher than the threshold value during execution of the regeneration control and during idle operation of the internal combustion engine.

  Preferably, the control unit increases the urea water addition amount for a predetermined time from the time when the inlet exhaust gas temperature becomes equal to or higher than the threshold value.

  Preferably, the control unit increases the urea water addition amount from a time point when the inlet exhaust gas temperature is equal to or higher than the threshold value to a time point when it is lower than the threshold value.

  According to the present invention, deterioration promotion of the NOx catalyst due to execution of the filter regeneration control can be suppressed.

It is a schematic block diagram which shows the exhaust gas purification apparatus which concerns on one Embodiment of this invention. It is a time chart which shows transition of each value at the time of performing filter regeneration control. It is a flow chart which shows an example of control in this embodiment.

  An embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic configuration diagram showing an exhaust gas purifying apparatus for an internal combustion engine according to this embodiment.

  As shown in FIG. 1, an exhaust gas purification device 200 has an exhaust pipe 2 for circulating exhaust gas of an internal combustion engine (engine) 1, and a plurality of catalysts 10 provided in the middle of the exhaust pipe 2 for purifying the exhaust gas. The post-processing unit 3 and the casing 4 that houses the post-processing unit 3 are provided.

  The internal combustion engine 1 is a multi-cylinder compression ignition type internal combustion engine mounted on a vehicle, that is, a diesel engine. The internal combustion engine 1 is provided with an exhaust manifold 12 that collects exhaust gas discharged from each cylinder 11. Each cylinder 11 is provided with an injector (fuel injection valve) 8 for injecting fuel into the cylinder. The types and uses of the vehicle and the internal combustion engine 1 are arbitrary.

  The exhaust pipe 2 is a pipe that is connected to the exhaust manifold 12 and causes the exhaust gas from the exhaust manifold 12 to flow in the downstream direction (the direction indicated by the arrow G) and to be released to the atmosphere.

  More specifically, the exhaust pipe 2 includes an upstream exhaust pipe 21 located upstream of the post-treatment unit 3 and a downstream exhaust pipe 22 located downstream of the post-treatment unit 3. The upstream exhaust pipe 21 has a flange 21a at its downstream end, and the downstream exhaust pipe 22 has a flange 22a at its upstream end.

  Next, the post-processing unit 3 will be described. For convenience, the front, rear, left, and right directions of the post-processing unit 3 are set as shown in FIG. It should be noted that such a direction is merely determined for convenience of description, and may or may not coincide with the front, rear, left, and right directions of the vehicle. In this embodiment, the internal combustion engine 1 is vertically installed in the vehicle, and the right direction of the post-processing unit 3 corresponds to the front direction of the vehicle.

  The aftertreatment unit 3 includes an exhaust gas inlet pipe 31, an exhaust gas outlet pipe 32, a first catalyst casing 33 in which at least one catalyst 10 is installed, and a second catalyst casing 34 in which at least one catalyst 10 is installed, The first catalyst casing 33 and the second catalyst casing 34 are provided with a generally U-shaped connecting pipe 35. The post-processing unit 3 has a substantially symmetrical structure.

  The exhaust gas inlet pipe 31 is disposed on the front end portion and the right side of the post-treatment unit 3, extends from the front side to the rear side from the upstream side to the downstream side, and the front end thereof is connected to the downstream end of the upstream side exhaust pipe 21. Further, the exhaust gas outlet pipe 32 is arranged at the front end portion and the left side of the post-treatment unit 3, extends from the rear side to the front side from the upstream side to the downstream side, and the front end thereof is connected to the upstream end of the downstream side exhaust pipe 22. It

  More specifically, a flange 31a is provided at the upstream end of the exhaust gas inlet pipe 31, and the flange 21a of the upstream exhaust pipe 21 is connected to this flange 31a. Similarly, a flange 32a is provided at the downstream end of the exhaust gas outlet pipe 32, and the flange 22a of the downstream exhaust pipe 22 is connected to this flange 32a. The flanges connected to each other are removably fixed by appropriate fasteners such as bolts (not shown).

  The first catalyst casing 33 is formed in a tubular shape, extends rearward from the exhaust gas inlet pipe 31, and has a first side hole 33b on the left side surface of the downstream end 33a located at the rear end. In addition, the first catalyst casing 33 is formed with a first expanded diameter portion 33c having a diameter larger than that of the exhaust gas inlet pipe 31 located on the upstream side and the connecting pipe 35 located on the downstream side.

  In the first expanded diameter portion 33c of the first catalyst casing 33, an oxidation catalyst (DOC: Diesel Oxidation Catalyst) 10a and a particulate filter (hereinafter referred to as “DPF”) are provided from the upstream side via a first heat insulating cushioning member (mat) 37. 10b is provided.

The oxidation catalyst 10a oxidizes and purifies unburned components (hydrocarbon HC and carbon monoxide CO) in the exhaust gas. The oxidation catalyst 10a has a function of heating and raising the temperature of exhaust gas by heat generated during the oxidation of HC and CO. The oxidation catalyst 10a oxidizes NO in the exhaust gas to NO _2, also has a function of increasing the NO ₂ concentration in the exhaust gas.

  The DPF 10b collects and removes particulate matter (PM: Particulate Matter) contained in the exhaust gas, and corresponds to the filter in the claims. In this embodiment, the DPF 10b is a so-called wall flow type in which openings at both ends of a honeycomb-shaped heat-resistant base material are alternately closed in a checkered pattern. However, any type of filter that physically collects PM can be used, such as a mesh-like foam shape.

  The DPF 10b is a so-called continuous regeneration type DPF with a catalyst having an inner wall supporting a catalytic precious metal such as Pt. In this case, during normal operation of the engine, the HC in the exhaust gas supplied to the DPF 10b is catalytically oxidized and burned, and at the same time, the PM accumulated inside the DPF 10b is burned and removed. Since the DPF 10b has a catalytic noble metal and exhibits a catalytic action, the DPF 10b is also included in the catalyst 10 here.

  Even in such a continuous regeneration type DPF 10b, PM is gradually accumulated in the DPF 10b during normal operation of the engine. Since the accumulated PM is burned and removed to regenerate the DPF 10b, the filter regeneration control described later is performed. This will be described in detail later.

  The second catalyst casing 34 is formed in a tubular shape, extends rearward from the exhaust gas outlet pipe 32, and has a second side hole 34b on the right side surface of the upstream end 34a located at the rear end. Further, the second catalyst casing 34 is provided with a second expanded diameter portion 34c having a diameter larger than that of the connecting pipe 35 located on the upstream side and the exhaust gas outlet pipe 32 located on the downstream side.

  In the second expanded diameter portion 34c of the second catalyst casing 34, the NOx catalyst 10c and the ammonia oxidation catalyst 10d are provided from the upstream side via the second heat insulating cushioning member (mat) 38.

The NOx catalyst 10c is a catalyst for purifying nitrogen oxide NOx in the exhaust gas. The NOx catalyst 10c is composed of a selective reduction type NOx catalyst (SCR: Selective Catalytic Reduction) and can continuously reduce NOx by ammonia (NH ₃ ) generated by hydrolysis of urea water.

The ammonia oxidation catalyst 10d is a catalyst that oxidizes excess ammonia that has not been consumed by the NOx catalyst 10c for NOx reduction to generate N ₂ .

  The first catalyst casing 33 and the second catalyst casing 34 are arranged parallel to each other on the right side and the left side. Further, the first side hole 33b and the second side hole 34b are arranged so as to face each other.

  The connecting pipe 35 is arranged at a position between the first catalyst casing 33 and the second catalyst casing 34 in the left-right direction. The upstream end of the connecting pipe 35 is connected to the first side hole 33b, and the downstream end of the connecting pipe 35 is connected to the second side hole 34b.

  The connecting pipe 35 has a first portion 35a extending leftward from the first side hole 33b and bent forward, and a second portion 35b extending rightward from the second side hole 34b and bent forward. The first portion 35a is a portion from X1 to X2 in the drawing, and the second portion 35b is a portion from Y1 to Y2 in the drawing.

  Further, the connecting pipe 35 has a third portion 35c that extends forward from the downstream end X2 of the first portion 35a and is folded back in a U shape, and then extends rearward and is connected to the upstream end Y2 of the second portion 35b. In this way, the connecting pipe 35 generally extends forward from the rear end of the first catalyst casing 33 and folds back in a U shape, and then extends rearward to connect to the rear end of the second catalyst casing 34.

  By forming the connecting pipe 35 in the U-shape in this way, the pipe length of the connecting pipe 35, and thus the exhaust passage length between the first catalyst casing 33 and the second catalyst casing 34, can be increased in a compact space. it can.

  The casing 4 is a box-shaped casing made of a heat-resistant material such as stainless steel, and covers the entire post-treatment unit 3 in a substantially airtight manner. A heat insulating material 5 such as glass wool is laid on almost the entire inner peripheral surface of the casing 4 to keep the heat of the post-treatment unit 3.

  An inlet hole 46 through which the exhaust gas inlet pipe 31 is inserted with a gap S1 is formed in the front surface portion 45 of the casing 4 so as to project the exhaust gas inlet pipe 31 to the outside (front side) of the casing 4. The gap S1 is sealed by the heat insulating seal member 6 on the inlet side. Similarly, the front surface portion 45 of the casing 4 is formed with an outlet hole 47 through which the exhaust gas outlet pipe 32 is inserted with a gap S2 so that the exhaust gas outlet pipe 32 projects to the outside (forward) of the casing 4. The gap S2 is sealed by the outlet side heat insulating seal member 7. These seal members 6 and 7 are formed of a material having a low heat transfer coefficient, for example, heat resistant rubber, and minimize the heat transfer from each tube to the casing 4.

  The exhaust gas purifying apparatus 200 of the present embodiment further includes an addition valve 36 that adds or injects urea water into the connecting pipe 35. The addition valve 36 is provided at the upstream end of the connecting pipe 35, and is particularly arranged at the bent portion L of the first portion 35a. The addition valve 36 is arranged so as to add urea water from the bent portion L toward the folded-back portion U of the third portion 35c from the rear to the front and along the central axis of the connecting pipe 35. The addition valve 36 is inserted and fixed in the connecting pipe 35 from the outside rear of the casing 4 toward the front.

  Further, the exhaust gas purifying apparatus 200 of the present embodiment is provided with a control unit or an electronic control unit (hereinafter referred to as “ECU”) 100 that constitutes a controller. The ECU 100 includes a CPU, a ROM, a RAM, an input / output port, a storage device, and the like. The ECU 100 is configured or programmed to control the injector 8 and the addition valve 36 as described below.

  The exhaust gas purifying apparatus 200 includes a rotation speed sensor 51 for detecting an engine rotation speed or a rotation speed (rpm), an accelerator opening sensor 52 for detecting an accelerator opening, and an inlet exhaust gas temperature of the oxidation catalyst 10a. A temperature sensor (first temperature sensor) 53 for detecting, a temperature sensor (second temperature sensor) 54 for detecting an outlet exhaust temperature of the DPF 10b, and a differential pressure sensor for detecting a differential pressure before and after the DPF 10b. 55 and a temperature sensor (third temperature sensor) 56 for detecting the inlet exhaust gas temperature of the NOx catalyst 10c. These sensors are electrically connected to the ECU 100. The temperature sensor 56 corresponds to the detector in the claims.

  During normal operation of the engine, the ECU 100 causes the fuel injected from the injector 8 based on the engine operating state, particularly the engine speed detected by the rotation speed sensor 51 and the accelerator opening detected by the accelerator opening sensor 52. The injection amount and the urea water addition amount added from the addition valve 36 are controlled. The fuel injection amount and the urea water addition amount increase as the engine speed increases and the accelerator opening increases. The urea water added from the addition valve 36 is hydrolyzed to generate ammonia, and this ammonia is supplied to the NOx catalyst 10c, whereby NOx is reduced and removed.

  Further, in order to burn off PM accumulated in the DPF 10b during normal engine operation and regenerate the DPF 10b, the ECU 100 periodically executes filter regeneration control. That is, when the differential pressure detected by the differential pressure sensor 55 exceeds a predetermined threshold value, the ECU 100 determines that the DPF 10b needs to be regenerated, causes the injector 8 to perform post injection, and supplies additional fuel into the cylinder. To do. As a result, the surplus HC is burned by the oxidation catalyst 10a, the high temperature and rich exhaust gas is supplied to the DPF 10b, and the accumulated PM in the DPF 10b is burned and removed.

  Note that the filter regeneration control can be performed by other methods including a known method. For example, instead of the post injection, the fuel may be directly supplied to the upstream side of the oxidation catalyst 10a from another fuel injection valve. The filter regeneration control corresponds to the regeneration control in the claims.

  By the way, during execution of the filter regeneration control, the PM in the DPF 10b may be burned, so that the exhaust gas having a relatively high temperature may be discharged from the DPF 10b. Then, by supplying this high-temperature exhaust gas to the NOx catalyst 10c, the temperature of the NOx catalyst 10c excessively rises, the NOx catalyst 10c is accelerated to deteriorate, and the NOx purification rate of the NOx catalyst 10c can be reduced early. is there.

  Particularly in recent years, attempts have been made to improve fuel efficiency by increasing the capacity of the DPF 10b to increase the PM maximum accumulation amount thereof and lengthening the time interval between filter regeneration controls, that is, the regeneration interval. In such a case, a large amount of accumulated PM burns at once, the peak temperature of the exhaust gas discharged from the DPF 10b rises, and the tendency of promoting the deterioration of the NOx catalyst 10c becomes stronger.

  Further, when the engine shifts to the idle operation state during the filter regeneration control, the exhaust gas passage flow rate in the DPF 10b decreases, so the accumulated PM burns at once (this is referred to as ignition idle), and the peak temperature of the exhaust gas discharged from the DPF 10b increases. The tendency is to increase and accelerate the deterioration of the NOx catalyst 10c.

  Therefore, the ECU 100 of the present embodiment increases the urea water addition amount in the addition valve 36 when the inlet exhaust gas temperature of the NOx catalyst 10c detected by the temperature sensor 56 becomes equal to or higher than a predetermined threshold during execution of the filter regeneration control. Is configured to let. According to this, on the upstream side of the NOx catalyst 10c, the increased urea water can be mixed with the exhaust gas, and the exhaust temperature can be lowered. Then, the exhaust gas whose temperature has dropped is supplied to the NOx catalyst 10c. Therefore, even when the high temperature exhaust gas is discharged from the DPF 10b during execution of the filter regeneration control, it is possible to reduce the temperature of the exhaust gas and then supply the exhaust gas to the NOx catalyst 10c. Therefore, it is possible to suppress the deterioration promotion of the NOx catalyst 10c due to the filter regeneration control and to suppress the early decrease of the NOx purification rate.

  Along with this, the capacity of the DPF 10b can be increased, the regeneration interval can be lengthened, and the fuel consumption can be improved. Even if the capacity of the DPF 10b is increased, it is possible to suppress the temperature of the exhaust gas supplied to the NOx catalyst 10c from rising due to the ignition idle, and to suppress the deterioration acceleration of the NOx catalyst 10c. it can.

  FIG. 2 is a time chart showing the transition of each value when the filter regeneration control is executed. t is time.

  In FIG. 2A, the line a indicates the accelerator opening Ac, and the line b indicates the engine speed Ne. In FIG. 2 (B), the line c shows the urea water addition amount Qu of the comparative example to which the present invention is not applied, and the line d shows the post injection amount Qp. In FIG. 2 (C), the line e indicates the inlet exhaust temperature (referred to as SCR inlet temperature) T of the NOx catalyst 10c in the comparative example.

  In the illustrated example, the filter regeneration control is started at time t1 and the post injection is started. The urea water addition is executed even during the filter regeneration control. After that, at time t2, the accelerator opening Ac becomes zero, that is, fully closed, the engine speed Ne becomes a speed equal to or lower than a predetermined idle determination threshold N1, and the engine operating state is shifted to the idle operating state. The idle determination threshold N1 is set to a value slightly higher than a predetermined target idle rotation speed Ni after engine warm-up, and is set to a value equal to the return rotation speed when returning from the deceleration fuel cut, for example.

  After time t2, the engine is idling while the filter regeneration control is being executed. In this case, in the comparative example, after the start of the idle operation, the ignition idle described above causes the SCR inlet temperature T to rise sharply and in a peak shape as shown by the line e in FIG. 2 (C). This temperature increase promotes deterioration of the NOx catalyst 10c. The time from time t2 to time t4 when the SCR inlet temperature T reaches its peak is, for example, about 100 seconds.

  However, in the present embodiment, when the SCR inlet temperature T becomes equal to or higher than the predetermined threshold value Tth, the urea water addition amount Qu is the amount of the comparative example (a reference value described later) as shown by a virtual line c ′ in FIG. The amount Quc is increased by a predetermined amount ΔQu to obtain a larger amount Quc. As a result, as shown by an imaginary line e'in FIG. 2C, it is possible to suppress the rise in the SCR inlet temperature T and suppress the deterioration of the NOx catalyst 10c.

  The threshold value Tth is experimentally obtained in advance and stored in the ECU 100. The threshold value Tth is set to the minimum value of the SCR inlet temperature T that causes excessive deterioration of the NOx catalyst 10c. In the present embodiment, it is possible to suppress the SCR inlet temperature T from becoming the minimum value or more by increasing the urea water addition amount Qu.

  Alternatively, the threshold Tth may be set to a value that is lower than the minimum value by a predetermined margin temperature (for example, a value of about several degrees Celsius to several tens of degrees Celsius). As a result, it is possible to more reliably suppress the SCR inlet temperature T from becoming the minimum value or higher.

  The following several modes can be considered as a method of increasing the urea water addition amount Qu. First, regarding the first aspect, the ECU 100 increases the urea water addition amount Qu for a predetermined time Δt from the time t3 when the SCR inlet temperature T becomes equal to or higher than the threshold value Tth. The predetermined time Δt is preferably set to be equal to or longer than the time from the time point t3 when the SCR inlet temperature T becomes the threshold value Tth or more to the time point t4 when the SCR inlet temperature T reaches the peak temperature in the comparative example. It The illustrated example shows the former example. The predetermined time Δt has a length of about 10 seconds, for example. The predetermined time Δt is also experimentally obtained in advance and stored in the ECU 100. This reliably prevents the SCR inlet temperature T from rising to the peak temperature, and the SCR inlet temperature T can be suppressed appropriately.

  Regarding the second aspect, the ECU 100 increases the urea water addition amount Qu from the time point t3 when the SCR inlet temperature T becomes equal to or higher than the threshold value Tth to the time point when it becomes less than the threshold value Tth thereafter. According to this, the urea water addition amount Qu is increased only during the period when the SCR inlet temperature T is equal to or higher than the threshold value Tth, so that the SCR inlet temperature T can be suppressed with a minimum necessary increase.

  With regard to the third aspect, the ECU 100 starts the time t2 when the two conditions, that is, executing the filter regeneration control and the idle operation of the engine, are satisfied, and then, the amount of urea water added for a predetermined time Δt ′ that is longer than the predetermined time Δt. Increase Qu. This predetermined time Δt ′ is experimentally obtained in advance as a time from time t2 to time t5 at which the SCR inlet temperature T once exceeds the threshold value Tth and then decreases below the threshold value Tth in the comparative example, and is stored in the ECU 100. To be done. In this way, the increase of the urea water addition amount Qu can be started in advance, and it is possible to more reliably suppress the SCR inlet temperature T from rising above the threshold value Tth. Any of these first to third aspects can be arbitrarily adopted as necessary.

  Next, an example of control in the present embodiment will be described based on the flowchart shown in FIG. The illustrated routine is repeatedly executed by the ECU 100 at every predetermined calculation cycle τ (for example, 10 msec).

  First, in step S101, it is determined whether the filter regeneration control is being executed. If it is not being executed, the process proceeds to step S105, and the urea water addition amount Qu is set to the reference amount Qub. The reference amount Qub is calculated using a predetermined map based on the engine operating state, that is, the engine speed Ne and the accelerator opening sensor 52 detected by the rotation speed sensor 51 and the accelerator opening sensor 52, respectively. The addition valve 36 is controlled so that the reference amount Qub of urea water is added or injected from the addition valve 36.

  If the filter regeneration control is being executed, the process proceeds to step S102, and it is determined whether or not the engine is in the idle operation. If it is not in the idle operation, the process proceeds to step S105, and the urea water addition amount Qu is set to the reference amount Qub.

  On the other hand, if the engine is idling, the routine proceeds to step S103, where it is determined whether the SCR inlet temperature T detected by the temperature sensor 56 is equal to or higher than a threshold value Tth. If not the threshold value Tth, the process proceeds to step S105, and the urea water addition amount Qu is set to the reference amount Qub.

  On the other hand, if it is equal to or more than the threshold value Tth, the process proceeds to step S104, and the urea water addition amount Qu is increased to a predetermined amount Quc larger than the reference amount Qub. Then, the addition valve 36 is controlled so that the increased urea water is added or injected from the addition valve 36.

  Even if the SCR inlet temperature T once becomes equal to or higher than the threshold value Tth (S103: Yes) and the urea water addition amount Qu is increased, but if the SCR inlet temperature T becomes lower than the threshold value Tth thereafter (S103: No), the urea water addition amount Qu. Is returned to the reference amount Qub. As described above, the present flow corresponds to the above-described second aspect, but it is within the scope of those skilled in the art to construct the flowchart corresponding to the first or third aspect.

  As described above, according to the present embodiment, acceleration of deterioration of the NOx catalyst 10c due to execution of filter regeneration control can be suppressed.

  Further, according to the present embodiment, the post-treatment unit 3 is configured as described above, the first and second catalyst casings 33 and 34 are connected by the U-shaped connecting pipe 35, and the upstream end of the connecting pipe 35 is connected. The addition valve 36 is installed. By doing so, the urea water added from the addition valve 36 can be sufficiently and homogeneously mixed with the exhaust gas in the passage in the relatively long connecting pipe 35. Therefore, not only can the urea water be supplied to the NOx catalyst 10c by a preferable method at the time of adding the reference amount, but also the exhaust gas having a uniform temperature decrease with little temperature unevenness can be suitably supplied to the NOx catalyst 10c at the time of increasing the addition amount, and the NOx catalyst 10c This is advantageous for suppressing the temperature rise of 10c. Moreover, the long passage in the connecting pipe 35 can be realized in a relatively small space, and the post-treatment unit 3 and thus the casing 4 can be made compact.

  Further, since the post-treatment unit 3 is housed in the casing 4, the post-treatment unit 3 is kept warm, the post-treatment unit 3 is prevented from being cooled by the outside air or traveling wind, and the temperature of each catalyst 10 is kept high. can do.

  It should be noted that the present invention is not limited to the above-described embodiments, and can be appropriately modified and implemented without departing from the spirit of the present invention.

  (1) In the above embodiment, the SCR inlet temperature T is directly detected by the temperature sensor 56 at the inlet of the NOx catalyst 10c. However, alternatively, based on the detected value (DPF outlet exhaust gas temperature) Td of the temperature sensor 54 at the outlet of the DPF 10b and the urea water addition amount Qu, the ECU 100 refers to a predetermined estimation map to determine the SCR inlet temperature T. It may be estimated. In this way, the temperature sensor 56 can be omitted. The reason why the urea water addition amount Qu is considered is that the exhaust gas discharged from the DPF 10b is cooled by the urea water before reaching the NOx catalyst 10c. By considering the urea water addition amount Qu, the SCR inlet temperature T can be accurately estimated in consideration of such temperature decrease. In this specification, “estimation” is also included in “detection”. In the case of this modification, the ECU 100 and the temperature sensor 54 correspond to the detector in the claims. The estimation map defines a three-way relationship in which a higher SCR inlet temperature T is obtained as the DPF outlet exhaust gas temperature Td is higher and the urea water addition amount Qu is smaller.

  (2) The engine 1 may include a turbocharger. In this case, the post-treatment unit 3 is provided on the downstream side of the turbine of the turbocharger.

1 Internal combustion engine (engine)
2 Exhaust pipe 3 Post-treatment unit 4 Casing 10b Filter (DPF)
10c NOx catalyst 33 1st catalyst casing 34 2nd catalyst casing 35 Connection pipe 36 Addition valves 54 and 56 Temperature sensor 100 Electronic control unit (ECU)
200 Exhaust gas purifier

Claims (5)

An exhaust gas purification apparatus for an internal combustion engine,
Exhaust pipe,
A post-treatment unit provided in the middle of the exhaust pipe,
A casing containing the post-treatment unit,
Equipped with
The post-processing unit,
A first catalyst casing,
A second catalyst casing arranged in parallel downstream of the first catalyst casing;
A U-shaped connecting pipe connecting the first catalyst casing and the second catalyst casing;
A filter provided in the first catalyst casing for collecting particulate matter in exhaust gas;
A selective reduction type NOx catalyst provided in the second catalyst casing for purifying nitrogen oxides in exhaust gas;
Equipped with
The exhaust gas purification device further includes
A detector for detecting the inlet exhaust gas temperature of the NOx catalyst,
An addition valve provided at the upstream end of the connecting pipe for adding urea water,
A control unit configured to perform a regeneration control for controlling the addition valve and regenerating the filter,
Equipped with
The control unit is configured to increase the urea water addition amount in the addition valve when the inlet exhaust gas temperature detected by the detector during execution of the regeneration control is equal to or higher than a predetermined threshold value ,
The first catalyst casing extends from the front side to the rear side from the upstream side to the downstream side, has a rear end surface closed, and has a first side hole on the side surface of the rear end portion,
The second catalyst casing extends from the rear side to the front side from the upstream side to the downstream side, the rear end surface is closed, and the second side hole facing the first side hole is formed on the side surface of the rear end portion. Have,
The connecting pipe extends forward from the first side hole and folds back in a U shape, and then extends rearward to connect to the second side hole,
The exhaust gas purifying apparatus for an internal combustion engine , wherein the casing covers a rear end surface of the first catalyst casing and a rear end surface of the second catalyst casing from behind . The exhaust gas purifying apparatus for an internal combustion engine according to claim 1 , wherein a heat insulating material is provided between the casing and a rear end surface of the first catalyst casing and a rear end surface of the second catalyst casing. . The control unit increases the urea water addition amount when the inlet exhaust gas temperature becomes equal to or higher than the threshold value during execution of the regeneration control and during idle operation of the internal combustion engine. 2. The exhaust gas purifying apparatus for an internal combustion engine according to 2. The internal combustion engine according to any one of claims 1 to 3, wherein the control unit increases the urea water addition amount for a predetermined time from the time when the inlet exhaust gas temperature is equal to or higher than the threshold value. Exhaust gas purification device. The control unit increases the urea water addition amount from a time point when the inlet exhaust gas temperature is equal to or higher than the threshold value to a time point when the inlet exhaust gas temperature is lower than the threshold value. An exhaust gas purifying apparatus for an internal combustion engine as described.

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