WO2017179674A1

WO2017179674A1 - Exhaust gas purification device for internal combustion engine

Info

Publication number: WO2017179674A1
Application number: PCT/JP2017/015193
Authority: WO
Inventors: 大祐森山; 直水上; 泰順鈴木; 幸博川島
Original assignee: いすゞ自動車株式会社
Priority date: 2016-04-14
Filing date: 2017-04-13
Publication date: 2017-10-19
Also published as: JP2017190725A; JP6682972B2

Abstract

An exhaust gas purification device 200 for an internal combustion engine 1 is equipped with an exhaust pipe 2, an aftertreatment unit 3, and a casing 4. The aftertreatment unit is equipped with first and second catalyst casings 33, 34, a U-shaped connecting pipe 35 connecting these casings, a filter 10b provided inside the first catalyst casing, and a selective reduction NOx catalyst 10c provided inside the second catalyst casing. The exhaust gas purification device is further equipped with a detector 56 that detects the inlet exhaust temperature of the NOx catalyst, an addition valve 36 that adds urea water at an upstream end part of the connecting pipe, and a control unit 100 that controls the addition valve and executes a regeneration control for the filter. The control unit increases the amount of urea water added by the addition valve when the inlet exhaust temperature detected by the detector during the regeneration control is equal to or greater than a prescribed threshold value.

Description

Exhaust gas purification device for internal combustion engine

The present disclosure relates to an exhaust gas purification 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 typically has a filter that collects particulate matter (PM) in the exhaust, and a selective reduction that is arranged downstream of the filter to reduce and remove nitrogen oxides (NOx) in the exhaust. A type NOx catalyst (SCR) is installed.

Japanese Unexamined Patent Publication No. 2010-53847

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

On the other hand, while the filter regeneration control is being executed, the PM in the filter burns, and thus a relatively high temperature exhaust gas may be discharged from the filter. When this high-temperature exhaust gas is supplied to the NOx catalyst, the temperature of the NOx catalyst increases excessively, the deterioration of the NOx catalyst may be accelerated, and the NOx purification rate of the NOx catalyst may decrease early.

Therefore, the present disclosure has been created in view of such circumstances, and an object thereof is to provide an exhaust gas purification device for an internal combustion engine that can suppress the deterioration promotion of the NOx catalyst due to the execution of filter regeneration control.

According to one aspect of the present disclosure,
An exhaust gas purification device for an internal combustion engine,
An exhaust pipe,
A post-processing unit provided in the middle of the exhaust pipe;
A casing for housing the aftertreatment unit;
With
The post-processing unit is
A first catalyst casing;
A second catalyst casing disposed 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 the exhaust;
A selective reduction type NOx catalyst provided in the second catalyst casing and purifying nitrogen oxides in exhaust;
With
The exhaust gas purification device further includes
A detector for detecting an inlet exhaust temperature of the NOx catalyst;
An addition valve that is provided at an upstream end of the connecting pipe and adds urea water;
A control unit configured to control the addition valve and perform regeneration control to regenerate the filter;
With
The control unit is configured to increase the urea water addition amount in the addition valve when the inlet exhaust temperature detected by the detector during execution of the regeneration control becomes a predetermined threshold value or more. An exhaust gas purification apparatus for an internal combustion engine is provided.

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

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

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

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

According to a further aspect of the present disclosure, an exhaust gas purification apparatus for an internal combustion engine, comprising:
An exhaust pipe,
A post-processing unit provided in the middle of the exhaust pipe;
A casing for housing the aftertreatment unit;
With
The post-processing unit is
A first catalyst casing;
A second catalyst casing disposed 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 the exhaust;
A selective reduction type NOx catalyst provided in the second catalyst casing and purifying nitrogen oxides in exhaust;
With
The exhaust gas purification device further includes
An addition valve that is provided at an upstream end of the connecting pipe and adds urea water;
A control unit configured to control the addition valve and perform regeneration control to regenerate the filter;
With
The control unit is configured to increase the urea water addition amount for a predetermined time from the time when the condition that the regeneration control is being executed and the internal combustion engine is idling is satisfied. An exhaust gas purification device for an internal combustion engine is provided.

According to the present disclosure, it is possible to suppress the deterioration promotion of the NOx catalyst due to the execution of the filter regeneration control.

It is a schematic structure figure showing an exhaust gas purification device concerning one embodiment of this indication. It is a time chart which shows transition of each value at the time of performing filter regeneration control. It is a flowchart which shows an example of the control in this embodiment.

Hereinafter, an embodiment of the present disclosure will be described based on the accompanying drawings. FIG. 1 is a schematic configuration diagram illustrating an exhaust gas purification apparatus for an internal combustion engine according to the present embodiment.

As shown in FIG. 1, the exhaust gas purification apparatus 200 includes an exhaust pipe 2 through which exhaust gas from an internal combustion engine (engine) 1 circulates 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 a casing 4 that houses the post-processing unit 3 are provided.

The internal combustion engine 1 is a multi-cylinder compression ignition 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. Note that the types and applications 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 discharges the exhaust gas from the exhaust manifold 12 in the downstream direction (direction indicated by the arrow G) and releases it to the atmosphere.

More specifically, the exhaust pipe 2 includes an upstream exhaust pipe 21 located upstream of the post-processing unit 3 and a downstream exhaust pipe 22 located downstream of the post-processing 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 the sake of convenience, the front-rear and left-right directions of the post-processing unit 3 are the directions as shown in FIG. Such a direction is merely determined for convenience of explanation, and may or may not coincide with the front and rear and right and left directions of the vehicle. In the present embodiment, the internal combustion engine 1 is placed vertically on the vehicle, and the right direction of the post-processing unit 3 coincides with 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 provided, a second catalyst casing 34 in which at least one catalyst 10 is provided, A generally U-shaped connecting pipe 35 that connects the first catalyst casing 33 and the second catalyst casing 34 is provided. The post-processing unit 3 has a generally symmetrical structure.

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

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 the 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 the flange 32a. The flanges connected to each other are detachably fixed by an appropriate fastener such as a bolt (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 of the downstream end 33a located at the rear end. Further, the first catalyst casing 33 is formed with a first enlarged-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.

An oxidation catalyst (DOC: Diesel Oxidation Catalyst) 10a and a particulate filter (hereinafter referred to as “DPF”) are inserted into the first enlarged diameter portion 33c of the first catalyst casing 33 from the upstream side through a first heat insulating buffer 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 with heat generated during 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) contained in the exhaust gas, and corresponds to a filter in the claims. In the present embodiment, a so-called wall flow type DPF 10b is used in which openings at both ends of a honeycomb-shaped heat-resistant substrate are alternately closed in a checkered pattern. However, any type of filter that physically captures PM can be used, such as a mesh-shaped foam shape.

The DPF 10b is a so-called continuous regeneration type DPF with a catalyst in which a catalyst noble metal such as Pt is supported on its inner wall. In this case, during normal operation of the engine, HC in the exhaust gas supplied to the DPF 10b is oxidized and burned by the catalytic action, and at this time, PM deposited in the DPF 10b is burned and removed. In addition, since DPF10b has a catalyst noble metal and exhibits a catalytic action, DPF10b shall also be contained in the catalyst 10 here.

Even in such a continuous regeneration type DPF 10b, PM gradually accumulates in the DPF 10b during normal operation of the engine. In order to regenerate the DPF 10b by burning and removing the accumulated PM, filter regeneration control described later is performed. This point 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 formed with a second diameter-expanded portion 34c having a diameter larger than that of the connecting pipe 35 positioned on the upstream side and the exhaust gas outlet pipe 32 positioned on the downstream side.

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

The NOx catalyst 10c is a catalyst for purifying nitrogen oxides 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.

Ammonia oxidation catalyst 10d is to oxidize surplus ammonia not consumed in the reduction of NOx in the NOx catalyst 10c, a catalyst that generates N _2.

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

The connecting pipe 35 is disposed 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.

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. Thus, the connecting pipe 35 generally extends forward from the rear end portion of the first catalyst casing 33 and is folded back in a U shape, and then extends rearward to connect to the rear end portion 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 hence the exhaust passage length between the first catalyst casing 33 and the second catalyst casing 34, can be lengthened in a compact space. it can.

The casing 4 is made of a box-type casing using a heat-resistant material such as stainless steel, and covers the entire post-processing 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 post-processing unit 3 warm.

The front surface 45 of the casing 4 is formed with an inlet hole 46 through which the exhaust gas inlet pipe 31 is inserted with a gap S1 so that the exhaust gas inlet pipe 31 protrudes to the outside (front) of the casing 4. The gap S <b> 1 is sealed by the inlet side heat insulating seal member 6. Similarly, an outlet hole 47 through which the exhaust gas outlet pipe 32 is inserted with a gap S2 is formed in the front surface portion 45 of the casing 4 so that the exhaust gas outlet pipe 32 protrudes to the outside (front) 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 made of a material having a low heat transfer coefficient, for example, heat-resistant rubber, and minimize heat transfer from each pipe to the casing 4.

The exhaust gas purification 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 portion of the connecting pipe 35, and is particularly arranged at the bent portion L of the first portion 35a. The addition valve 36 is disposed so as to add urea water from the bent portion L toward the folded portion U of the third portion 35 c 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 side of the casing 4 toward the front side.

In addition, the exhaust gas purification apparatus 200 of the present embodiment is provided with an electronic control unit (hereinafter referred to as “ECU”) 100 that forms a control unit or a controller. 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 will be described later.

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

During normal operation of the engine, the ECU 100 detects the fuel injected from the injector 8 based on the engine operating state, particularly the engine speed detected by the rotational 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 are increased as the engine speed is higher and the accelerator opening is larger. 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 regenerate the DPF 10b by burning and removing PM accumulated in the DPF 10b during normal operation of the engine, 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, the ECU 100 determines that regeneration of the DPF 10b is necessary, causes the injector 8 to perform post injection, and supplies additional fuel into the cylinder. To do. As a result, surplus HC is combusted by the oxidation catalyst 10a, high-temperature and rich exhaust gas is supplied to the DPF 10b, and accumulated PM in the DPF 10b is combusted and removed.

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

Now, during the execution of the filter regeneration control, the PM in the DPF 10b burns, so that a relatively high temperature exhaust gas may be discharged from the DPF 10b. By supplying this high-temperature exhaust gas to the NOx catalyst 10c, the temperature of the NOx catalyst 10c excessively increases, the deterioration of the NOx catalyst 10c is accelerated, 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 maximum amount of PM accumulated and extending 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 increases, and the tendency to promote the deterioration of the NOx catalyst 10c increases.

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 called ignition idle), and the peak temperature of the exhaust gas discharged from the DPF 10b becomes As a result, the tendency to promote the deterioration of the NOx catalyst 10c increases.

Therefore, the ECU 100 according to the present embodiment increases the urea water addition amount in the addition valve 36 when the inlet exhaust temperature of the NOx catalyst 10c detected by the temperature sensor 56 becomes equal to or higher than a predetermined threshold during the execution of the filter regeneration control. It is configured to let you. According to this, on the upstream side of the NOx catalyst 10c, the increased amount of urea water can be mixed with the exhaust gas, and the exhaust temperature can be lowered. The exhaust gas whose temperature has been lowered is supplied to the NOx catalyst 10c. Therefore, even when high-temperature exhaust gas is exhausted from the DPF 10b during execution of filter regeneration control, the temperature of the exhaust gas can be lowered and supplied 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 in the NOx purification rate.

As a result, the capacity of the DPF 10b can be increased, and the regeneration interval can be extended to improve fuel efficiency. And even if it is a case where the capacity | capacitance of DPF10b is increased, it suppresses that the temperature of the exhaust gas supplied to NOx catalyst 10c resulting from ignition idle rises, and suppresses deterioration promotion of 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.

2A, line a indicates the accelerator opening degree Ac, and line b indicates the engine speed Ne. In FIG. 2B, a line c indicates the urea water addition amount Qu of a comparative example to which the present disclosure is not applied, and a line d indicates the post injection amount Qp. In FIG. 2C, 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 from time t1, and the post injection is started. The urea water addition is also executed during the filter regeneration control. Thereafter, at time t2, the accelerator opening degree Ac is zero, that is, is fully closed, the engine speed Ne is equal to or lower than a predetermined idle determination threshold value N1, and the engine operating state is shifted to the idle operating state. The idle determination threshold value N1 is set to a value slightly higher than the predetermined target idle speed Ni after engine warm-up, and is set to a value equal to, for example, the return speed when returning from the deceleration fuel cut.

After time t2, the engine is idling during execution of filter regeneration control. In this case, in the comparative example, after the start of the idle operation, the occurrence of the ignition idle causes the SCR inlet temperature T to rise rapidly and in a peak shape as indicated by the line e in FIG. 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 a 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 (reference to be described later) as shown by a virtual line c ′ in FIG. The predetermined amount ΔQu is increased from the amount Qub) to obtain a larger amount Quc. As a result, as indicated by a virtual line e ′ in FIG. 2C, it is possible to suppress an increase in the SCR inlet temperature T and to suppress deterioration of the NOx catalyst 10 c.

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 exceeding the minimum value by increasing the urea water addition amount Qu.

Alternatively, the threshold value Tth may be set to a value 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). Thereby, it can suppress more reliably that SCR entrance temperature T becomes more than the said minimum value.

As the method for increasing the urea water addition amount Qu, the following several modes are conceivable. First, regarding the first aspect, the ECU 100 increases the urea water addition amount Qu for a predetermined time Δt from the time point 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 a time equal to or longer than the time 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 t4 when the SCR inlet temperature T reaches the peak temperature in the comparative example. The The illustrated example shows the former example. The predetermined time Δt has a length of, for example, 3 seconds to 30 seconds, preferably 5 seconds to 20 seconds, and more preferably about 10 seconds. 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 suitably suppressed.

Regarding the second aspect, the ECU 100 increases the urea water addition amount Qu from the time t3 when the SCR inlet temperature T becomes equal to or higher than the threshold Tth to the time when the SCR inlet temperature T becomes lower than the threshold Tth. According to this, since 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, the SCR inlet temperature T can be suppressed with a minimum increase.

Regarding the third aspect, the ECU 100 adds the urea water addition amount for a predetermined time Δt ′ longer than the previous predetermined time Δt from the time point t2 when the filter regeneration control is being executed and the engine is idling. Increase Qu. This predetermined time Δt ′ is experimentally obtained in advance as a time from time t 2 to time t 5 when the SCR inlet temperature T once exceeds the threshold value Tth and then falls below the threshold value Tth in the comparative example, and is stored in the ECU 100. Is done. If it carries out like this, the increase in the urea water addition amount Qu can be started in advance and it can suppress more reliably that the SCR entrance temperature T rises more than the threshold value Tth. Any of the first to third aspects can be arbitrarily adopted as necessary.

Next, an example of the control in this 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 or not the filter regeneration control is being executed. If not, 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, where it is determined whether or not the engine is idling. If the idling operation is not being performed, 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 process proceeds to step S103, where it is determined whether or not the SCR inlet temperature T detected by the temperature sensor 56 is equal to or higher than a threshold value Tth. If it is 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 greater 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 that is larger than the reference amount Qub. The addition valve 36 is controlled so that the increased amount of urea water is added or injected from the addition valve 36.

If the SCR inlet temperature T once becomes equal to or higher than the threshold Tth (S103: YES), and the urea water addition amount Qu is increased, then if the SCR inlet temperature T becomes lower than the threshold Tth (S103: NO), the urea water addition amount Qu Is returned to the reference amount Qub. As described above, this flow corresponds to the second aspect described above, but it is also within the scope of those skilled in the art to construct a flowchart corresponding to the first or third aspect.

As described above, according to the present embodiment, it is possible to suppress the deterioration promotion of the NOx catalyst 10c due to the execution of the filter regeneration control.

According to the present embodiment, the aftertreatment 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. An addition valve 36 is provided. In this way, the urea water added from the addition valve 36 can be sufficiently and uniformly mixed with the exhaust gas through the relatively long passage in the connecting pipe 35. Therefore, not only can the urea water be supplied to the NOx catalyst 10c by a preferred method when the reference amount is added, but also the exhaust gas having a uniform temperature drop with little temperature unevenness can be suitably supplied to the NOx catalyst 10c when the increase amount is added. It is advantageous for suppressing temperature rise of 10c. Moreover, the passage in the long connecting pipe 35 can be realized in a relatively small space, and the post-processing unit 3 and thus the casing 4 can be made compact.

Further, since the post-processing unit 3 is accommodated in the casing 4, the post-processing unit 3 is kept warm, the post-processing unit 3 is suppressed from being cooled by 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 embodiment, 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, the ECU 100 refers to a predetermined estimated map based on the detected value (DPF outlet exhaust temperature) Td of the temperature sensor 54 at the outlet of the DPF 10b and the urea water addition amount Qu, and determines the SCR inlet temperature T. It may be estimated. In this way, the temperature sensor 56 can be omitted. The reason for considering the urea water addition amount Qu 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 a temperature drop. 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 a detector referred to in the claims. The estimated map defines a three-way relationship in which the higher the DPF outlet exhaust temperature Td and the lower the urea water addition amount Qu, the higher the SCR inlet temperature T is obtained.

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

This application is based on a Japanese patent application (Japanese Patent Application No. 2016-080782) filed on April 14, 2016, the contents of which are incorporated herein by reference.

Industrial applicability

The present disclosure is useful in that deterioration promotion of the NOx catalyst due to execution of the filter regeneration control can be suppressed.

1 Internal combustion engine
2 Exhaust pipe 3 Post-processing unit 4 Casing 10b Filter (DPF)
10c NOx catalyst 33 First catalyst casing 34 Second catalyst casing 35 Connecting pipe 36

Addition valve

54, 56 Temperature sensor 100 Electronic control unit (ECU)
200 Exhaust gas purification device

Claims

An exhaust gas purification device for an internal combustion engine,
An exhaust pipe,
A post-processing unit provided in the middle of the exhaust pipe;
A casing for housing the aftertreatment unit;
With
The post-processing unit is
A first catalyst casing;
A second catalyst casing disposed 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 the exhaust;
A selective reduction type NOx catalyst provided in the second catalyst casing and purifying nitrogen oxides in exhaust;
With
The exhaust gas purification device further includes
A detector for detecting an inlet exhaust temperature of the NOx catalyst;
An addition valve that is provided at an upstream end of the connecting pipe and adds urea water;
A control unit configured to control the addition valve and perform regeneration control to regenerate the filter;
With
The control unit is configured to increase the urea water addition amount in the addition valve when the inlet exhaust temperature detected by the detector during execution of the regeneration control becomes a predetermined threshold value or more. An exhaust gas purification apparatus for an internal combustion engine characterized by the above.
The first catalyst casing extends from the front to the rear from the upstream side toward the downstream side,
The second catalyst casing extends from the rear to the front from the upstream side toward the downstream side,
The connection pipe extends forward from a rear end portion of the first catalyst casing and is folded back in a U shape, and then extends rearward and is connected to the rear end portion of the second catalyst casing. 2. An exhaust gas purification apparatus for an internal combustion engine according to 1.
The control unit increases the urea water addition amount when the inlet exhaust temperature becomes equal to or higher than the threshold during execution of the regeneration control and idle operation of the internal combustion engine. 2. An exhaust gas purification 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 temperature becomes equal to or higher than the threshold value. Engine exhaust gas purification equipment.
The control unit increases the urea water addition amount from a time point when the inlet exhaust temperature becomes equal to or higher than the threshold value to a time point when the inlet exhaust temperature becomes lower than the threshold value. An exhaust gas purification apparatus for an internal combustion engine as described.
An exhaust gas purification device for an internal combustion engine,
An exhaust pipe,
A post-processing unit provided in the middle of the exhaust pipe;
A casing for housing the aftertreatment unit;
With
The post-processing unit is
A first catalyst casing;
A second catalyst casing disposed 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 the exhaust;
A selective reduction type NOx catalyst provided in the second catalyst casing and purifying nitrogen oxides in exhaust;
With
The exhaust gas purification device further includes
An addition valve that is provided at an upstream end of the connecting pipe and adds urea water;
A control unit configured to control the addition valve and perform regeneration control to regenerate the filter;
With
The control unit is configured to increase the urea water addition amount for a predetermined time from the time when the condition that the regeneration control is being executed and the internal combustion engine is idling is satisfied. An exhaust gas purification device for an internal combustion engine.