JP2008127998A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device of an internal combustion engine capable of realizing excellent purification performance, by sufficiently promoting diffusion of a reducing agent by agitation of exhaust gas, while preventing trouble by an increase in exhaust pressure regardless of an operation area of an engine, by making both compatible in agitation of the exhaust gas and restraint of an exhaust pressure increase. <P>SOLUTION: A low speed flow passage 35 having a low speed side fin device 43 having high diffusibility of the exhaust gas and a high speed flow passage 36 having a high speed side fin device 44 having low diffusibility, are independently formed on the upstream side of an SCR catalyst of an exhaust passage 11. The exhaust gas can be selectively made to flow by a selector valve, and is switched to the low speed flow passage 35 side in a low speed operation area of the engine 1, and is switched to the high speed flow passage 36 side in a high speed operation area. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification device for an internal combustion engine (hereinafter referred to as an engine), and more particularly to an exhaust gas purification device that provides a reducing agent supply means in an exhaust passage and supplies a reducing agent to a downstream reduction catalyst.

As an exhaust gas purification device that uses this type of reducing agent to purify harmful components in exhaust gas, for example, there is one equipped with an SCR catalyst (selective reduction type NOx catalyst), which is injected upstream of the SCR catalyst in the exhaust passage. A nozzle is arranged, and the aqueous urea solution injected from the injection nozzle is hydrolyzed by exhaust heat and water vapor in the exhaust gas, and NH ₃ (ammonia) is generated to reduce NOx in the exhaust gas on the SCR catalyst. Yes. In this type of exhaust purification device, the diffusion state of the urea aqueous solution into the exhaust gas has a great influence on the purification performance of the SCR catalyst. Therefore, a countermeasure provided with stirring means in order to stir the exhaust gas in the vicinity of the injection nozzle May be taken (see, for example, Patent Document 1).

In the technique of Patent Document 1, as shown in FIGS. 1 and 2, when a fin device including four fins is installed as an agitation means on the upstream side of the injection nozzle in the exhaust passage, and exhaust gas flows through the fin device. The swirling flow is generated by the action of the fins, thereby promoting the diffusion of the urea aqueous solution into the exhaust gas.
JP 2006-29233 A (FIGS. 1 and 2)

  The principle by which the fin device generates a swirl flow is obtained by changing the flow direction of the exhaust gas using the fins. Therefore, for example, a fin angle is set deep (with respect to the flow direction of the exhaust gas) in order to generate a strong swirl flow against the exhaust gas. As the fins are arranged at a steep angle (large angle) and the flow direction of the exhaust gas is changed abruptly, the exhaust pressure of the engine increases, and there is a trade-off between the occurrence of swirling flow and the suppression of the increase in exhaust pressure. There is a relationship.

  On the other hand, the flow rate of the exhaust gas flowing through the exhaust passage varies greatly depending on the engine operating region, and the exhaust pressure increase due to the fin device cannot be ignored in the high engine speed / high load region. Therefore, in the exhaust emission control device of Patent Document 1, for the purpose of protecting the engine from an increase in exhaust pressure in a high rotation and high load range, the fin angle must be set shallow (small angle) with respect to the exhaust gas circulation direction. The swirl flow is weakened in the middle / low rotation / medium / low load range where the exhaust gas flow rate inevitably decreases. Normally, the engine is normally used in the middle / low rotation / medium / low load range. As a result, a sufficient swirling flow cannot be obtained in the normal working region, and the problem is that satisfactory NOx purification performance cannot be achieved due to insufficient diffusion of the urea aqueous solution. there were.

  The present invention has been made in order to solve such problems. The object of the present invention is to achieve both the agitation of the exhaust gas and the suppression of the increase in the exhaust pressure so that the exhaust pressure can be reduced regardless of the engine operating region. An object of the present invention is to provide an exhaust emission control device for an internal combustion engine that can prevent a trouble due to an increase and can sufficiently promote diffusion of a reducing agent by stirring exhaust gas to achieve a good purification performance.

  In order to achieve the above object, the invention of claim 1 constitutes a part of the exhaust passage of the internal combustion engine, forms mutually independent flow paths upstream of the reduction catalyst provided in the exhaust passage, A first flow path and a second flow path communicating between the internal combustion engine side and the reduction catalyst side, and a flow path switching means for selectively flowing the exhaust gas of the internal combustion engine to the first flow path or the second flow path A reducing agent supply means for supplying a reducing agent into the exhaust passage and upstream of the reduction catalyst in the exhaust passage, and a first agitator for stirring the exhaust gas that is provided in the first flow path and circulates inside the exhaust passage. Means, a second agitation device provided in the second flow path for agitating the exhaust gas flowing through the interior, wherein the diffusibility of the exhaust gas by agitation is set lower than that of the first agitation device, and an operating region of the internal combustion engine And a control means for switching the flow path switching means based on the above.

Therefore, the flow path switching means is switched by the control means based on the operating region of the internal combustion engine, and the exhaust gas of the internal combustion engine is selectively circulated through the first flow path or the second flow path and the first agitation inside. The reducing agent supplied from the reducing agent supply means diffuses into the exhaust gas, reaches the reduction catalyst in this state, and is used for the purification action.
The principle of stirring the exhaust gas with the stirring means is obtained by changing the flow direction of the exhaust gas with the stirring means. Therefore, in order to obtain a strong stirring action (good diffusibility), the flow direction of the exhaust gas must be changed rapidly. Therefore, the exhaust pressure inevitably increases, and the stirring of the exhaust gas and the suppression of the increase in the exhaust pressure are in a trade-off relationship. The first agitation means has a characteristic in which exhaust gas agitation is prioritized and the exhaust gas diffusivity is enhanced, and the second agitation means has a characteristic in which the exhaust gas diffusibility is reduced by giving priority to suppression of increase in exhaust pressure.

  On the other hand, the exhaust gas flow rate changes according to the operating region of the internal combustion engine, and the present inventor has focused on a phenomenon in which the necessity of stirring the exhaust gas and suppressing the increase in exhaust pressure changes depending on the exhaust gas flow rate. Therefore, the first agitation unit and the second agitation unit having different diffusibility of exhaust gas are selectively applied according to the operation region of the internal combustion engine, so that the optimum agitation unit is applied to the current operation region. As a result, it is possible to achieve both agitation of exhaust gas and suppression of increase in exhaust pressure.

According to a second aspect of the present invention, in the first aspect, the control means switches the flow path switching means so that the exhaust gas flows through the first flow path when the internal combustion engine is in a predetermined low speed operation region, and the internal combustion engine is predetermined. The flow path switching means is switched so that the exhaust gas flows through the second flow path in the high-speed operation region.
Therefore, in the low-speed operation region where the exhaust gas flow rate is low, the demand for improving the diffusibility of the exhaust gas by the stirring of the stirring means increases in combination with the decrease in the exhaust gas flow rate, but the risk of increasing the exhaust pressure is low. At this time, since the exhaust gas is stirred by the first stirring means having high diffusibility of the exhaust gas by switching to the first flow path, the exhaust gas is well stirred and the diffusion of the reducing agent into the exhaust gas is promoted. At the same time, there is no problem even if the exhaust pressure is increased by the stirring of the first stirring means.

  On the other hand, in the high-speed operation region where the exhaust gas flow rate is large, the diffusibility of the exhaust gas is originally high due to the increase in the exhaust gas flow rate, and the necessity of stirring by the stirring means is not so much, but the increase in the exhaust pressure needs to be suppressed. Is expensive. At this time, since the exhaust gas is stirred by the second stirring means having low diffusibility of the exhaust gas by switching to the second flow path, an increase in exhaust pressure due to the stirring is suppressed to a minimum, and the second stirring is performed. Even with stirring by means, diffusion of the reducing agent is not insufficient.

  According to a third aspect of the present invention, there is provided a reduction catalyst provided in the exhaust passage of the internal combustion engine, a reducing agent supply means provided on the upstream side of the reduction catalyst in the exhaust passage, for supplying a reducing agent into the exhaust passage, Exhaust gas that is provided upstream of the reduction catalyst and agitates the exhaust gas and that can change the diffusibility of the exhaust gas by agitation, and controls the diffusibility of the variable agitation means based on the operating region of the internal combustion engine And a control means.

Therefore, the exhaust gas of the internal combustion engine flows through the exhaust passage and is stirred by the variable stirring means, and the reducing agent supplied from the reducing agent supply means diffuses into the exhaust gas, and reaches the reduction catalyst in this state and purifies. The diffusibility of the exhaust gas by the variable stirring means at this time is switched by the control means according to the operating state of the internal combustion engine.
The principle of stirring the exhaust gas with the stirring means is obtained by changing the flow direction of the exhaust gas with the stirring means. Therefore, in order to obtain a strong stirring action (good diffusibility), the flow direction of the exhaust gas must be changed rapidly. Therefore, the exhaust pressure inevitably increases, and the stirring of the exhaust gas and the suppression of the increase in the exhaust pressure are in a trade-off relationship. According to the variable diffusing means, by controlling the diffusibility of the exhaust gas, it is possible to give the characteristics giving priority to the stirring of the exhaust gas or to give the characteristics giving priority to the suppression of the increase in exhaust pressure.

  On the other hand, the exhaust gas flow rate changes according to the operating region of the internal combustion engine, and the present inventor has focused on a phenomenon in which the necessity of stirring the exhaust gas and suppressing the increase in exhaust pressure changes depending on the exhaust gas flow rate. Therefore, by controlling the diffusibility of the variable agitation means according to the operating range of the internal combustion engine, the optimum agitation means is applied to the current operating range, resulting in exhaust gas agitation and increased exhaust pressure. It is possible to achieve both suppression.

According to a fourth aspect of the present invention, in the third aspect, the control means controls the diffusibility of the variable agitating means to increase when the internal combustion engine is in a predetermined low speed operation region, and when the internal combustion engine is in a predetermined high speed operation region. In addition, the diffusibility of the variable stirring means is controlled to the lower side.
Therefore, in the low-speed operation region where the exhaust gas flow rate is low, the demand for improving the diffusibility of the exhaust gas by the stirring of the stirring means increases in combination with the decrease in the exhaust gas flow rate, but the risk of increasing the exhaust pressure is low. At this time, since the diffusivity of the variable stirring means is controlled to increase, the exhaust gas is well stirred to promote the diffusion of the reducing agent into the exhaust gas, and the exhaust pressure increases due to the increase in the exhaust gas diffusivity. However, there is no problem.

  On the other hand, in the high-speed operation region where the exhaust gas flow rate is large, the diffusibility of the exhaust gas is originally high due to the increase in the exhaust gas flow rate, and the necessity of stirring by the stirring means is not so much, but the increase in the exhaust pressure needs to be suppressed. Is expensive. At this time, since the diffusibility of the variable agitation means is controlled to the lower side, an increase in exhaust pressure due to agitation is suppressed to a minimum, and even if the diffusibility of the exhaust gas is reduced, the diffusion of the reducing agent is insufficient Absent.

  As described above, according to the exhaust gas purification apparatus for an internal combustion engine of the first and second aspects of the present invention, exhaust gas agitation and exhaust gas can be obtained by applying the optimum agitation means corresponding to the operating region of the internal combustion engine to the exhaust gas agitation. Concomitant with suppression of pressure increase, preventing troubles due to increased exhaust pressure regardless of the operating range of the internal combustion engine, and sufficiently purifying the diffusion of reducing agent by stirring exhaust gas Performance can be realized.

  According to the exhaust gas purification apparatus for an internal combustion engine of the third and fourth aspects of the invention, both the stirring of the exhaust gas and the suppression of the increase in the exhaust pressure are achieved by controlling the diffusibility of the variable stirring means according to the operating region of the internal combustion engine. Therefore, regardless of the operating region of the internal combustion engine, it is possible to prevent a trouble caused by an increase in exhaust pressure, and sufficiently promote the diffusion of the reducing agent by stirring the exhaust gas, thereby realizing a good purification performance. .

[First Embodiment]
Hereinafter, a first embodiment in which the present invention is embodied in an exhaust emission control device for a diesel engine will be described.
FIG. 1 is an overall configuration diagram showing an exhaust emission control device for a diesel engine according to this embodiment. The engine 1 is configured as an in-line 6-cylinder engine. Each cylinder of the engine 1 is provided with a fuel injection valve 2, and each fuel injection valve 2 is supplied with pressurized fuel from a common common rail 3 and is opened at a timing according to the operating state of the engine. The fuel is injected into the inside.

  An intake manifold 4 is mounted on the intake side of the engine 1, and the intake passage 5 connected to the intake manifold 4 is opened and closed by an air cleaner 6, a compressor 7a of the turbocharger 7, an intercooler 8, and an actuator 9a from the upstream side. An intake throttle valve 9 is provided. An exhaust manifold 10 is mounted on the exhaust side of the engine 1, and an exhaust passage 11 is connected to the exhaust manifold 10 via a turbine 7b of a turbocharger 7 connected coaxially with the compressor 7a.

  During operation of the engine 1, the intake air introduced into the intake passage 5 through the air cleaner 6 is pressurized by the compressor 7 a of the turbocharger 7, and then distributed to each cylinder through the intercooler 8, the intake throttle valve 9, and the intake manifold 4. These are introduced into the cylinder in the intake stroke of each cylinder. In the cylinder, fuel is injected from the fuel injection valve 2 at a predetermined timing and ignited and burned in the vicinity of the compression top dead center, and the exhaust gas after combustion rotates through the exhaust manifold 10 and then rotates the turbine 7b and then passes through the exhaust passage 11. It is discharged outside.

  On the other hand, the intake manifold 4 and the exhaust manifold 10 are connected by an EGR passage 17, and an EGR valve 18 and an EGR cooler 19 that are opened and closed by an actuator 18 a are provided in the EGR passage 17. During operation of the engine 1, part of the exhaust gas is recirculated as EGR gas from the exhaust manifold 10 side to the intake manifold 4 side according to the opening degree of the EGR valve 18.

The intake manifold 4 is provided with a swirl valve 20 that is driven to open and close by an actuator 20a corresponding to the intake port of each cylinder. When each swirl valve 20 is closed, a swirl flow is generated in the cylinder.
The exhaust passage 11 is provided with the exhaust purification device of the present invention. An upstream casing 32 is connected to the turbine 7b of the turbocharger 7 via a first pipe 31a. A upstream oxidation catalyst 33 is accommodated in the upstream side of the upstream casing 32, and a wall flow type is connected to the downstream side. A DPF (diesel particulate filter) 34 is accommodated. As will be described later, the DPF 34 acts to collect particulates (hereinafter referred to as PM) in the exhaust gas.

  The exhaust passage 11 on the downstream side of the upstream casing 33 branches into a low speed flow path 35 (first flow path) and a high speed flow path 36 (second flow path). Path switching means) is provided, and the upstream casing 32 is selectively connected to the low-speed flow path 35 side or the high-speed flow path 36 side according to switching of the switching valve 37. The low-speed flow path 35 and the high-speed flow path 36 form a mutually independent flow path and extend to the rear of the vehicle by a predetermined distance and then merge with each other, and the merge point is downstream via the second pipe 31b. A side casing 39 is connected. An SCR catalyst 40 (reduction catalyst) is accommodated on the upstream side in the downstream casing 39, and a post-stage oxidation catalyst 41 is accommodated on the downstream side. As will be described later, the SCR catalyst 40 acts to purify NOx in the exhaust gas. Play.

In the present embodiment, the passage cross-sectional areas of the low-speed flow path 35 and the high-speed flow path 36 are set to be the same. Since the high-speed flow path 36 used in the operation region needs to circulate a larger amount of exhaust gas, the passage cross-sectional area of the high-speed flow path 36 may be set larger than the low-speed flow path 35.
A silencer (not shown) is connected to the downstream side of the downstream casing 39 via a third pipe 31c, and the rear end of the silencer is open to the atmosphere. The second pipe 31b is provided with an injection nozzle 42 (reducing agent supply means), and the injection nozzle 42 can be arbitrarily injected into the second pipe 31b using a urea aqueous solution pumped from a tank (not shown) as a reducing agent. Has been.

  In the low-speed flow path 35 and the high-speed flow path 36, fin devices 43 and 44 (stirring means) for generating a swirling flow in the exhaust gas are respectively installed. Hereinafter, the thing in the low speed flow path 35 is called the low speed side fin apparatus 43 (1st stirring means), and the thing in the high speed flow path 36 is called the high speed side fin apparatus 44 (2nd stirring means). The fin devices 43 and 44 have different diffusibility to exhaust gas (meaning the degree of stirring of exhaust gas by the fin device), and the configuration thereof will be described in detail below.

  FIG. 2 is a perspective view showing the low-speed fin device 43, which is manufactured by press-molding a steel plate so as to form a disk shape as a whole, and is arranged and fixed in a posture in which the low-speed flow path 35 is closed. The fan-shaped regions divided into four equal parts on the low-speed fin device 43 are each punched out by press molding from the one side of the fan shape and bent toward the exhaust downstream side. As a result, the low-speed fin device 43 is formed with four flow holes 43a that allow the upstream side and the downstream side to communicate with each other, and four fins 43b are erected corresponding to the respective flow paths. The fins 43b form a predetermined angle in the same direction with respect to the flow direction of the exhaust gas, and the fin angle is set to α in the low speed side fin device 43.

FIG. 3 is a perspective view showing the high speed side fin device 44. The basic shape is not different from that of the low speed side fin device 43, but includes four flow holes 44a and fins 44b, and only the fin angle is different. Yes. That is, the fin angle of the high speed side fin device 44 is set to an angle β (<α) that is smaller than the fin angle α of the low speed side fin device 43.
On the other hand, the intake throttle valve 9, exhaust throttle valve 12, EGR valve 18, and swirl valve 20 actuators 9a, 12a, 18a, 20a, fuel injection valve 2, fuel nozzle 14, injection nozzle 42, intake air amount of the engine 1 The air flow sensor 52 that detects Qa is connected to an ECU 51 (electronic control unit), and is driven and controlled by the ECU 51 based on detection information from sensors. For example, the ECU 51 operates the engine 1 by controlling the injection amount, injection pressure, and injection timing of the fuel injection valve 2 based on the operating state of the engine 1 such as the engine speed and load, and opens the EGR valve 18 by the actuator 18a. The EGR recirculation amount is adjusted by controlling the degree, and the opening of the swirl valve 20 is controlled by the actuator 20a to adjust the swirl flow.

The ECU 51 controls post-injection for forced regeneration of the DPF 34, urea supply from the injection nozzle 38 for NOx purification by the SCR catalyst 40, and the like. The NOx purification action by the SCR catalyst 40 will be described.
The DPF 34 has an action of collecting PM in the exhaust gas. In an operation state where the exhaust gas temperature of the engine 1 is relatively high, NO ₂ is generated from NO in the exhaust gas by the oxidation action of the pre-stage oxidation catalyst 33, and the NO ₂ The PM collected in the DPF 34 by the oxidation reaction is continuously incinerated and removed, whereby the DPF 34 is regenerated. On the other hand, when such an operation state in which the continuous regeneration action cannot be obtained continues, post injection is appropriately executed after the main injection by the ECU 51, and the DPF 34 is heated by the oxidation reaction in the pre-stage oxidation catalyst 32 to incinerate PM. As a result, the DPF 34 is forcibly regenerated. Note that CO generated during PM combustion in forced regeneration is oxidized to CO ₂ by the post-stage oxidation catalyst 41.

Further, since the SCR catalyst 40 requires supply of NH ₃ (ammonia) for NOx purification, the ECU 51 determines the injection nozzle based on the operating state of the engine 1 and the temperature in the vicinity of the injection nozzle 42 detected by a temperature sensor (not shown). The injection amount of the urea aqueous solution from 42 is controlled. The injected urea aqueous solution is hydrolyzed by exhaust heat and water vapor in the exhaust gas to generate NH ₃ , and this NH ₃ reduces NOx in the exhaust gas to harmless N ₂ on the SCR catalyst 40 to purify NOx. On the other hand, surplus NH _{3 at} this time is oxidized to NO by the post-stage oxidation catalyst 41.

A hydrolysis catalyst that acts to hydrolyze urea into NH ₃ may be disposed upstream of the SCR catalyst 40, or an aqueous ammonia solution may be injected from the injection nozzle 42 instead of the aqueous urea solution. Also good.
In parallel with the urea aqueous solution injection control, the ECU 51 switches the flow path of the exhaust gas between the low-speed flow path 35 and the high-speed flow path 36 by the switching valve 37, so that an appropriate one corresponding to the operating region of the engine 1 is obtained. The swirling flow is generated in the exhaust gas by the fin devices 43 and 44, and the flow path switching control of the ECU 51 will be described below.

The ECU 51 compares the intake air amount Qa of the engine 1 detected by the air flow sensor 52 with a predetermined determination value Qa0, and when the intake air amount Qa is less than the determination value Qa0, that is, the engine 1 is in the low speed operation region. In some cases, the switching valve 37 is driven to connect the upstream casing 32 to the low-speed flow path 35 side. As a result, the exhaust gas after flowing through the upstream oxidation catalyst 33 and the DPF 34 in the upstream casing 32 is guided to the low-speed channel 35 side, and a swirling flow is generated in the exhaust gas by the low-speed fin device 43. As shown in FIG. 2, since the fin angle α of the low speed side fin device 43 is set to a large value (fin angle is deep), the exhaust gas is abruptly changed in the flow direction to generate a relatively strong swirling flow. . This swirl flow is maintained even when it reaches the second pipe 31b from the low-speed flow path 35, and during the swirl flow, an aqueous urea solution is sprayed from the injection nozzle 42 to be atomized and diffused, and as described above, the SCR catalyst 40. Above, purification of NOx using NH ₃ is performed.

  When the intake air amount Qa is greater than or equal to the determination value Qa0, that is, when the engine 1 is in the high speed operation region, the ECU 51 controls the switching valve 37 to connect the upstream casing 32 to the high speed flow path 36 side. As a result, the exhaust gas after flowing through the upstream oxidation catalyst 33 and the DPF 34 in the upstream casing 32 is guided to the high-speed flow path 36 side, and a swirling flow is generated in the exhaust gas by the high-speed fin device 44. As shown in FIG. 3, since the fin angle α of the high speed side fin device 44 is set to a small value (the fin angle is shallow), the flow direction of the exhaust gas is gradually changed to generate a relatively weak swirling flow. The urea aqueous solution is injected from the injection nozzle 42 during the swirling flow, atomized and diffused, and used for NOx purification on the SCR catalyst 40.

The selection of the fin devices 43 and 44 in accordance with the above engine operating region is based on the knowledge described below.
In the low-speed operation region of the engine 1, the exhaust gas flow rate is small. At this time, coupled with a decrease in the exhaust gas flow rate, the demand for improving the diffusibility of the exhaust gas by the swirling flow of the fin devices 43 and 44 increases, but the exhaust gas flow rate is low. Then, the possibility that the exhaust pressure of the engine 1 increases is low. On the other hand, since the exhaust gas flow rate is large in the high-speed operation region of the engine 1 and the diffusibility of the exhaust gas is originally high due to the increase in the flow rate of the exhaust gas, the diffusibility of the exhaust gas is reduced by the swirling flow of the fin devices 43 and 44. While there is not much need for improvement, in a situation where the exhaust gas flow rate is large, the exhaust pressure of the engine 1 may increase and exceed the allowable value. Thus, the necessity of both the generation of the swirl flow and the suppression of the increase in the exhaust pressure is in a trade-off relationship and varies depending on the operation region of the engine 1, and the operation region of the engine 1 is a suction that correlates with the exhaust gas flow rate. It can be determined based on the air amount Qa.

  Based on the above knowledge, in this embodiment, the low-speed side fin device 43 and the high-speed side fin device 44 are provided in the low-speed flow path 35 and the high-speed flow path 36 that are independently formed, The one of the fin devices 43 and 44 is configured to be selectable, and the switching valve 37 is driven and controlled according to the operating region (low speed operating region or high speed operating region) of the engine 1 based on the intake air amount Qa. The fin devices 43 and 44 that meet the requirements required from the region (whether emphasizing the occurrence of swirling flow or emphasizing suppression of increase in exhaust pressure) are selected.

  Therefore, since a relatively strong swirl flow is generated by the low-speed fin device 43 shown in FIG. 2 in the low-speed operation region, the diffusibility is improved in the low-speed operation region in which the diffusibility of the exhaust gas tends to decrease, and the urea aqueous solution is supplied. It can diffuse sufficiently into the exhaust gas. Further, although the exhaust pressure tends to increase in the low speed fin device 43 in which the large fin angle α is set, there is no possibility that the exhaust pressure exceeds the allowable value of the engine 1 in the low speed operation region where the exhaust gas flow rate is originally low.

  On the other hand, in the high-speed operation region, the high-speed side fin device 44 having a small fin angle β shown in FIG. 3 is applied, so that an increase in exhaust pressure due to the occurrence of the swirling flow is suppressed to a minimum and the engine 1 is allowed. The situation where the value is exceeded can be prevented beforehand. In addition, the swirl flow generated by the high speed side fin device 44 is relatively weak, but since the exhaust gas diffusibility is originally high in the high speed operation region, there is no possibility of insufficient diffusion of the urea aqueous solution into the exhaust gas. .

Therefore, according to the exhaust gas purification apparatus for the engine 1 of the present embodiment, both the generation of the swirling flow and the suppression of the increase in the exhaust pressure can be achieved, and the trouble due to the increase in the exhaust pressure can be prevented in advance regardless of the operating region of the engine 1. In addition, good NOx purification performance can be achieved by sufficiently accelerating the diffusion of the urea aqueous solution by stirring the exhaust gas.
The exhaust flow rate of the engine 1 can be estimated from the rotational speed Ne of the engine 1 and the fuel injection amount Q, in addition to determining from the intake air amount Qa. Therefore, the operating region of the engine 1 may be determined from the rotational speed Ne and the fuel injection amount Q based on a preset map, and the fin devices 43 and 44 corresponding to the determined operating region may be selected.

In the present embodiment, the switching valve 37 is provided at the branch portion between the low-speed flow path 35 and the high-speed flow path 36. However, instead of this, the switching valve 37 may be provided at the junction of both flow paths 35 and 36. .
In the present embodiment, the single injection nozzle 42 is provided in the second pipe 31b. However, the present invention is not limited to this. For example, the injection nozzle 42 is provided separately for the low-speed flow path 35 and the high-speed flow path 36 for switching. Any one of the injection nozzles 42 may be selectively operated in accordance with the switching of the valve 37. Further, when the injection nozzles 42 are individually provided in the flow paths 35 and 36 as described above, the positions of the respective injection nozzles 42 are not limited to the downstream side of the fin devices 43 and 44 and may be arranged on the upstream side.
[Second Embodiment]
Next, a second embodiment in which the present invention is embodied in another exhaust gas purification device for a diesel engine 1 will be described.

The exhaust emission control device of this embodiment has a common overall configuration as compared with that described in the first embodiment, and the difference is in the configuration of the fin device and the surrounding exhaust passage. Accordingly, parts having the same configuration are denoted by the same member numbers, description thereof is omitted, and differences are mainly described.
FIG. 4 is a partial configuration diagram showing the exhaust emission control device of the present embodiment, and the portions not shown are the same as those of the first embodiment. In the present embodiment, as in the first embodiment, the exhaust passage 11 is formed as one flow path without branching into the low speed flow path 35 and the high speed flow path 36, and a single fin device is provided. That is, the upstream casing 32 and the downstream casing 39 are directly connected by the second pipe 31b, and the variable fin device 61 (variable stirring means) is disposed along with the injection nozzle 42 on the second pipe 31b. Of course, the positional relationship between the variable fin device 61 and the injection nozzle 42 is not limited to that shown in the drawing, and both positions may be reversed.

  FIG. 5 is a perspective view showing the variable fin device 61, and the variable fin device 61 of the present embodiment is configured so that the fin angle can be changed. More specifically, a pair of support shafts 62 are arranged in the second pipe 31b so as to cross each other by 90 degrees, and both support shafts 62 are welded to each other at the central intersection. Each is welded to the inner peripheral wall of the second pipe 31b. The inside of the second pipe 31b is divided into four equal parts by the respective support shafts 62, and the exhaust gas flows through the respective fan-shaped flow paths 63 formed thereby. The base end side of the fin 64 is pivotally supported at four locations of the support shaft 62 around the intersection, and each fin 64 is formed in a square plate shape extending from the base end side toward the exhaust downstream side. The tip side can be swung around the center.

  An annular operation ring 65 is disposed in the second pipe 31 b so as to enclose all the fins 64, and the operation ring 65 is pivotable relative to the tip side of each fin 64 by a pin 66. It is supported. One end of an operation rod 67 is connected to one side of the operation ring 65, and the other end of the operation rod 67 is connected to an actuator 68 that is disposed outside through the inner peripheral wall of the second pipe 31b.

  When the operating rod 67 is operated in the axial direction by the actuator 68, the operating ring 65 is operated in the circumferential direction as indicated by an arrow, and the fins 64 are simultaneously swung in the same direction around the support shaft 62. The The movable range of the fin 64 by the actuator 68 is set so as to correspond to the fin angle α of the low-speed fin device 43 and the fin angle β of the high-speed fin device 44 described in the first embodiment. Is adjusted to an angle α at one stroke end of the actuator 68 and adjusted to an angle β at the other stroke end. It is not always necessary to set the same fin angle as in the first embodiment, but a different fin angle may be set.

The control of the fin angle by the actuator 68 is executed by the ECU 51 in the following procedure.
The control of the fin angle is executed based on the intake air amount Qa of the engine 1 as in the first embodiment. However, by taking advantage of the variable fin device 61 of this embodiment that can adjust the fin angle steplessly, the intake angle is controlled. The fin angle (actually, the operating amount of the actuator 68) corresponding to the air amount Qa is calculated, and the actuator 68 is driven and controlled based on the calculated value. Specifically, in the intake air amount Qa corresponding to the low-speed operation region, each fin is controlled to a large angle α, whereby the flow direction of the exhaust gas is rapidly changed to generate a strong swirling flow. As the intake air amount Qa increases from this operating region, the fin angle is gradually reduced, and the change in the flow direction of the exhaust gas by the fins gradually decreases accordingly, and the intake air amount Qa corresponding to the high speed operation region has a small angle. The swirling flow generated by the control of β becomes weak and the increase in exhaust pressure is suppressed.

  According to the control of the fin angle of the ECU 51 described above, the same effects as those of the first embodiment can be obtained. Although not redundantly described, the generation of the swirling flow and the suppression of the increase in the exhaust pressure are made compatible with each other. Regardless of the operation region, it is possible to prevent a trouble caused by an increase in exhaust pressure, and sufficiently promote the diffusion of the urea aqueous solution by stirring the exhaust gas to achieve a good NOx purification performance.

In addition, since the fin angle is controlled in a stepless manner, the swirling flow can always be generated with the optimum fin angle with respect to the operating region of the engine 1, so that the first generation of the swirling flow and the suppression of the increase in exhaust pressure can be achieved. It is possible to achieve both higher dimensions than in the embodiment.
When the configuration of the present embodiment is adopted, it is not always necessary to control the fin angle steplessly. For example, switching control between two positions of the angle α and the angle β may be performed as in the first embodiment. .

  This is the end of the description of the embodiment, but the aspect of the present invention is not limited to this embodiment. For example, in each of the above-described embodiments, the exhaust gas purification device of the diesel engine 1 provided with the SCR catalyst 40 for NOx purification is embodied. However, the present invention is not limited to this as long as the engine is provided with a reduction catalyst that requires supply of a reducing agent. Absent. For example, a storage-type NOx catalyst that stores NOx in exhaust gas is provided in the exhaust passage, and in order to release and reduce the stored NOx from the NOx catalyst, NOx purge is periodically performed to inject fuel into the exhaust passage as a reducing agent. It may be applied to the engine that needs it. In this case, the SCR catalyst 40 in FIG. 1 is replaced with an occlusion type NOx catalyst. However, by adopting the configuration of the fin devices 43, 44, 61, etc. of the first embodiment or the second embodiment, each implementation is performed. Similar to the mode, the effect of achieving both the promotion of the diffusion of fuel into the exhaust gas by the occurrence of the swirling flow and the suppression of the increase in the exhaust pressure can be obtained.

  Moreover, in each said embodiment, although the fin apparatus 43,44,61 which produces a swirl flow in exhaust gas as a stirring means was provided, the structure of a stirring means is not limited to this. For example, the action of stirring the exhaust gas can be obtained by arranging the baffle plate at a predetermined angle with respect to the exhaust gas circulation direction, and the stirring action of the exhaust gas and the generation state of the exhaust pressure change according to the angle of the baffle plate. Therefore, as in the first embodiment, a baffle plate having a deep angle for the low speed operation region and a baffle plate having a shallow angle for the high speed operation region are provided in separate flow paths, and are switched according to the intake air amount Qa and the like. Alternatively, as in the second embodiment, the angle of the baffle plate may be controlled according to the intake air amount Qa and the like.

1 is an overall configuration diagram illustrating an exhaust emission control device for a diesel engine according to a first embodiment. It is a perspective view which shows the low speed side fin apparatus of 1st Embodiment. It is a perspective view which shows the high speed side fin apparatus of 1st Embodiment. It is a partial block diagram which shows the exhaust gas purification apparatus of the diesel engine of 2nd Embodiment. It is a perspective view which shows the variable fin apparatus of 2nd Embodiment.

Explanation of symbols

1 engine (internal combustion engine)
11 Exhaust passage 35 Low speed flow path (first flow path)
36 High-speed channel (second channel)
37 Switching valve (flow path switching means)
40 SCR catalyst (reduction catalyst)
42 Injection nozzle (reducing agent supply means)
43 Low speed side fin device (first stirring means)
44 High-speed fin device (second stirring means)
51 ECU (control means)
61 Variable fin device (variable stirring means)

Claims (4)

A part of the exhaust passage of the internal combustion engine is formed, and an independent flow path is formed on the upstream side of the reduction catalyst provided in the exhaust passage, and the internal combustion engine side and the reduction catalyst side are communicated with each other. A first channel and a second channel;
Channel switching means for selectively circulating the exhaust gas of the internal combustion engine through the first channel or the second channel;
A reducing agent supply means provided on the upstream side of the reduction catalyst in the exhaust passage and for supplying a reducing agent into the exhaust passage;
First agitation means for agitating the exhaust gas provided in the first flow path and flowing through the interior;
Agitating the exhaust gas that is provided in the second flow path and circulates in the interior;
An exhaust purification device for an internal combustion engine, comprising: control means for switching the flow path switching means based on an operating region of the internal combustion engine.   The control means switches the flow path switching means so that the exhaust gas flows through the first flow path when the internal combustion engine is in a predetermined low speed operation region, and when the internal combustion engine is in a predetermined high speed operation region. 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the flow path switching means is switched so that the exhaust gas flows through the second flow path. A reduction catalyst provided in the exhaust passage of the internal combustion engine;
A reducing agent supply means provided on the upstream side of the reduction catalyst in the exhaust passage and for supplying a reducing agent into the exhaust passage;
Variable agitation means that is provided upstream of the reduction catalyst in the exhaust passage and that agitates the exhaust gas that circulates in the interior, and is capable of varying the diffusibility of the exhaust gas by the agitation;
An exhaust purification device for an internal combustion engine, comprising: control means for controlling the diffusibility of the variable stirring means based on an operating region of the internal combustion engine.   The control means controls the diffusibility of the variable stirring means to an increase side when the internal combustion engine is in a predetermined low speed operation region, and the diffusibility of the variable stirring means when the internal combustion engine is in a predetermined high speed operation region. 4. The exhaust gas purification apparatus for an internal combustion engine according to claim 3, wherein the exhaust gas is controlled to a lower side.

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