JP2013231364A - Exhaust emission control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain suitable purifying performance across a wide operation region by inhibiting a change of an additive concentration distribution in exhaust caused by a change of an engine operation state, when a mixer 4 for mixing an additive jetted in the exhaust with the exhaust is included on an upstream side of an exhaust emission control device (SCR catalyst 2, for example) located in an exhaust passage 1 of an internal combustion engine.SOLUTION: An exhaust emission control device includes a bypass passage 5 for bypassing a mixer 4 to provide communication between an upstream side of the bypass passage and a downstream side of an exhaust passage 1; and passage area variable means (valve plates 51, 52 and a valve plate motion mechanism 6) for varying a cross-sectional area of the bypass passage 5 so that the cross-sectional area gets larger as a flow rate of exhaust increases in the exhaust passage on the upstream side of the mixer 4 (an upstream-side exhaust pipe 10, for example).

Description

  The present invention relates to an exhaust emission control device installed in an internal combustion engine such as a diesel engine for automobiles, and particularly relates to an apparatus equipped with a mixer that promotes mixing of additive injected into an exhaust passage with exhaust gas.

  Conventionally, an internal combustion engine (hereinafter sometimes referred to as an engine) mounted on an automobile or the like has been equipped with an exhaust purification catalyst for detoxifying harmful components (for example, HC, CO, NOx, etc.) in exhaust gas. Yes. In particular, those that perform lean burn, such as diesel engines and direct-injection gasoline engines, include a catalyst for reducing NOx in exhaust gas with a high oxygen concentration.

As an example, a selective catalytic reduction (SCR catalyst) is a SCR catalyst that can be reduced to nitrogen and water by selectively reacting a reducing agent such as ammonia (NH ₃ ) with NOx. A system has been put into practical use in which urea water (additive) is injected into the exhaust on the upstream side, and the generated ammonia is supplied (a so-called urea SCR, see, for example, Patent Document 1). Some SCR catalysts selectively reduce NOx using the fuel added to the exhaust as a reducing agent.

  In order to improve the NOx purification performance by such an SCR catalyst, it is desirable to disperse the additive injected into the exhaust gas as widely and uniformly as possible. Therefore, in the conventional example, a mixer for accelerating the mixing of the injected additive with the exhaust gas is arranged in the exhaust passage upstream of the SCR catalyst.

  This mixer gives a swirl component to the flow of exhaust by a plurality of swirling blades extending radially, and sprays the additive to atomize so as to collide with the swirling blade, and toward the downstream side of the mixer The exhaust is swirled in a spiral manner and dispersed. By dispersing the atomized additive in this way, the concentration of the additive component in the exhaust gas flowing into the SCR catalyst can be made uniform.

JP 2011-111927 A

  However, in general, automobile engines are used over a wide driving range from a low load low rotation range such as idle to a high load high rotation range such as during high-speed driving. Accordingly, the flow rate of the exhaust gas changes considerably. For this reason, when the additive is widely dispersed on the swirling flow of the exhaust formed by the mixer as in the conventional example, the flow rate of the exhaust flowing through the mixer greatly varies depending on the operation region. The dispersion state of will also change greatly.

  In other words, the concentration distribution of additive components (ammonia etc.) in the exhaust gas flowing into the SCR catalyst varies greatly between the low load low rotation region where the exhaust flow rate is small and the high load high rotation region where the flow rate is large. Actually, it is difficult to obtain the desired purification performance over the operating range.

  In view of such points, an object of the present invention is to provide an exhaust gas purification apparatus having a mixer that mixes an additive injected into exhaust gas with exhaust gas, even if the operating state of the engine changes, the concentration of additive components in the exhaust gas. It is to suppress a change in distribution and obtain a suitable purification performance over a wide operation region.

  In order to achieve the above object, according to the present invention, a passage that bypasses the mixer is provided in the exhaust passage, and the change in the flow rate of the exhaust flowing through the mixer is reduced by adjusting the cross-sectional area thereof.

-Solution-
Specifically, the present invention promotes mixing of the exhaust purification catalyst disposed in the exhaust passage of the internal combustion engine and the exhaust of the additive injected into the exhaust passage upstream of the exhaust purification catalyst. And an exhaust purification device including the mixer. A bypass passage that bypasses the mixer and connects the upstream and downstream exhaust passages, and a cross-sectional area of the bypass passage, the cross-sectional area increases as the exhaust gas flow rate in the exhaust passage upstream of the mixer increases. And a passage area variable means for changing so as to increase.

  According to the exhaust purification apparatus having the above-described configuration, the additive injected into the exhaust passage during the operation of the internal combustion engine is mixed with the exhaust flow by the mixer and supplied to the downstream exhaust purification catalyst while being dispersed in the exhaust. The For example, when the flow rate of the exhaust gas is low due to low load and low rotation of the engine, the cross-sectional area of the passage that bypasses the mixer is reduced by the passage area variable means, and the flow rate of the exhaust gas flowing through the mixer is ensured. As the flow rate increases, the cross-sectional area of the bypass passage is increased, thereby suppressing an increase in the flow rate of the exhaust gas flowing through the mixer.

  In other words, even if the flow rate of the exhaust gas changes greatly due to a change in the engine operating state, the change in the flow rate of the exhaust gas flowing through the mixer is alleviated, and the additive component in the exhaust gas flowing into the exhaust purification catalyst downstream thereof Therefore, it is possible to stably obtain a suitable purification performance over a wide operation region.

  As a preferred embodiment, the passage area varying means operates by receiving a pressure of the valve plate provided in the bypass passage and the exhaust gas upstream of the mixer, and the cross-sectional area of the bypass passage is increased according to the increase in pressure. And a valve plate operating mechanism for displacing the valve plate so as to increase. In this way, it is possible to automatically adjust the cross-sectional area of the bypass passage according to an increase in the flow rate of the exhaust gas with a simple structure without using an actuator or the like.

  The bypass passage is formed between an outer peripheral portion of the mixer and a peripheral wall of the exhaust passage that surrounds and surrounds the mixer, and a support portion that supports the outer peripheral portion of the mixer on the peripheral wall of the exhaust passage is provided in a circumferential direction. A plurality of the valve plate operating mechanisms may be provided at intervals between the valve plate operating mechanisms.

  In this way, when the bypass passage is formed between the peripheral wall of the exhaust passage and the outer peripheral portion of the mixer, the additive is injected toward the mixer located on the inner peripheral side of the exhaust passage, and the additive collides with the efficiency. It can be well atomized and dispersed. Further, the mixer can be firmly supported on the peripheral wall by the plurality of support portions, and the cross-sectional area of the bypass passage can be easily ensured by disposing the valve plate operating mechanism on the support portion.

  The valve plate operating mechanism includes a piston member that receives exhaust pressure upstream from the mixer and retreats toward the downstream side, and a spring member that urges the piston member to advance toward the upstream side. The transmission member preferably includes a transmission member that transmits and moves the piston member forward and backward to the valve plate.

  In this valve plate operating mechanism, as the flow rate of the exhaust gas increases and the pressure on the upstream side of the mixer increases, the piston member retracts and stops due to balance with the biasing force from the spring member. In spite of the simple structure, the displacement amount of the valve plate can be adjusted according to the increase in the exhaust pressure, and the cross-sectional area of the bypass passage can be suitably adjusted according to the exhaust gas flow rate.

  Preferably, at least one of the outer peripheral portion of the mixer and the peripheral wall of the exhaust passage is provided with a guide portion that guides the valve plate so as to be displaced in the circumferential direction, and the transmission member is, for example, a thin leaf spring or a wire. As described above, the transmission member may be curved and disposed so as to convert the forward and backward movements of the piston member into displacements in the circumferential direction of the valve plate using a highly flexible member.

  Also, a pair of transmission members are attached to the piston member, thereby connecting the pair of valve plates, and the pair of valve plates are displaced in the circumferential direction in opposite directions in accordance with the forward and backward movement of the piston member. You may comprise as follows.

  If it carries out like this, since a pair of valve plate will be displaced to a mutually opposing direction along the outer peripheral part of a mixer according to advance and retraction operation | movement of a piston member, it is piston from each valve plate via a transmission member. Among the reaction forces applied to the members, the circumferential components of the valve plate that are displaced cancel each other. Therefore, only the reaction force in the front-rear direction acts mainly on the piston member, which is advantageous in stabilizing the operation.

  Further, the pair of valve plates may be arranged so that at least a part of them overlap each other at the last retracted position of the piston member, and in this way, when adjusting the cross-sectional area of the bypass passage to be the largest, It is easy to secure a sufficient cross-sectional area.

  According to the exhaust emission control device according to the present invention, when providing a mixer that promotes mixing of the additive with the exhaust gas in the exhaust passage of the internal combustion engine, by providing a passage that bypasses the mixer and adjusting its cross-sectional area, Changes in the exhaust flow rate flowing through the mixer can be mitigated. Thereby, the change of the concentration distribution of the additive component in the exhaust flowing into the exhaust purification catalyst over a wide engine operation region can be suppressed, and a suitable purification performance can be stably obtained.

1 is a schematic configuration diagram of an exhaust emission control device according to an embodiment of the present invention. It is explanatory drawing which shows formation of the swirl | vortex flow of the exhaust_gas | exhaustion by the mixer of the same exhaust gas purification apparatus. It is a front view showing a mixer, a bypass passage, a valve plate, etc., as viewed from the upstream side in the exhaust flow direction. FIGS. (A) to (c) are states in which the cross-sectional area of the bypass passage is minimum, intermediate, and maximum, respectively. Indicates. It is a front view which expands and shows the structure of the valve plate operating mechanism arrange | positioned at the support part of the mixer. It is sectional drawing seen from the upper direction of the valve-plate operation | movement mechanism. It is sectional drawing seen from the side of the valve plate operating mechanism. FIG. 5 is an equivalent view of FIG. 5 showing the operation of the valve plate operating mechanism, in which FIG. 5 (a) shows the state of the intermediate cross-sectional area in the middle of the valve plate being opened by the retraction of the piston member, The state of the maximum cross-sectional area where the piston member is in the last retracted position and the valve plate is fully opened is shown.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the present embodiment, as an example, a case where the present invention is applied to a diesel engine (internal combustion engine) mounted on an automobile will be described.

  FIG. 1 shows a schematic configuration of an exhaust emission control device according to an embodiment of the present invention. In FIG. 1, in the middle of an exhaust passage 1, there is a property of selectively reacting NOx with a reducing agent in exhaust gas having a high oxygen concentration. A selective catalytic reduction (SCR catalyst) 2 is provided. In the example of the figure, the SCR catalyst 2 includes a substantially cylindrical catalyst case 20 connected to an end portion on the downstream side (downstream side of the exhaust flow) of the upstream side exhaust pipe 10 constituting a part of the exhaust passage 1; It comprises a substantially cylindrical catalyst carrier 21 concentrically accommodated therein. Although not shown, a downstream exhaust pipe constituting a part of the exhaust passage 1 is connected to the downstream end of the catalyst case 20.

  In the SCR catalyst 2 shown in FIG. 1, the upstream side of the catalyst case 20 (upstream side of the exhaust flow) has a trumpet shape in which the passage sectional area gradually increases from the end of the upstream side exhaust pipe 10 toward the downstream side. The expanded portion 20a can smoothly spread the exhaust flow and guide it to the front end surface of the catalyst carrier 21. Further, a mat 22 made of an elastic body is interposed between the outer peripheral surface of the catalyst carrier 21 and the inner peripheral surface of the catalyst case 20 and is held in the catalyst case 20 while absorbing the thermal expansion of the catalyst carrier 21. .

  As an example, the catalyst carrier 21 is a monolithic type in which a large number of through holes (cells) extending in the direction in which the exhaust flows is formed, and is formed of cordierite, Fe—Cr—Al heat-resistant steel, or the like. A coating layer of a catalyst is formed on the wall surface of the cell, and for example, a zeolite-based active component (catalyst) is supported. The active component is activated by the supply of the reducing agent, and selectively reduces NOx in the exhaust.

Of the methods for treating NOx in the exhaust gas using such an SCR catalyst 2, a so-called urea SCR uses ammonia (NH ₃ ) as a reducing agent. In the present embodiment, an injection nozzle 3 for injecting urea water as an additive is disposed in the exhaust pipe 10 upstream of the SCR catalyst 2, and urea water ejected therefrom (spray is indicated by a broken line N). Hydrolysis by exhaust heat generates ammonia. Ammonia selectively reacts with NOx in the exhaust gas in the SCR catalyst 2 to generate nitrogen and water.

  The urea water is an aqueous solution of solid or powdered urea and is supplied to the injection nozzle 3 through a supply pipe from a storage tank (not shown). Preferably, compressed air may be supplied to the injection nozzle 3 together with the urea water, and the urea water may be atomized and injected from the injection port 31. Moreover, you may make it control the injection amount and injection timing of the urea water by the injection nozzle 3 according to the driving | running state of an engine.

  In the illustrated example, the upstream side exhaust pipe 10 extends generally downward from an exhaust manifold or the like of the engine (not shown), then gently curves backward and extends substantially horizontally, and is injected to the outer peripheral side of the curved part. A nozzle 3 is provided. That is, a nozzle accommodating portion 12 that is branched from the outer peripheral side of the curved portion is formed on the peripheral wall 11 of the upstream side exhaust pipe 10, and the injection nozzle 3 is attached to the outer end of the nozzle accommodating portion 12.

  The nozzle accommodating portion 12 extends substantially horizontally forward from the outer peripheral side of the curved portion so as to follow the axis m of the upstream exhaust pipe 10 on the downstream side of the curved portion, and at the outer end thereof The injection nozzle 3 is arranged with the injection port 31 facing the downstream side in the flow direction of the exhaust gas so as to inject the urea water backward substantially along the axis m. 1 indicates the flow of exhaust gas containing urea water that is atomized and dispersed, and the solid line arrow indicates the flow of exhaust gas before the urea water is added.

  A mixer 4 for dispersing the spray N of urea water in the exhaust gas is disposed immediately downstream of the injection nozzle 3 for injecting urea water (upstream in the exhaust flow direction from the SCR catalyst 2). ing. As shown in FIG. 2, the mixer 4 is provided with a plurality of (eight in the illustrated example) swirl vanes 41 extending radially from the central axis 40, and imparts a swirl component to the flow of exhaust gas passing between them. Then, an exhaust flow swirling spirally toward the downstream side is formed. Although indicated by phantom lines in FIG. 2, the outer peripheral ends of the plurality of swirl vanes 41 are respectively connected to a cylindrical outer peripheral portion 42.

  Further, the central axis 40 of the mixer 4 is positioned on the axis m of the upstream exhaust pipe 10, and the plurality of swirl vanes 41 are positioned so as to be included in the urea water injection region from the injection nozzle 3. . For this reason, the spray N of urea water from the injection nozzle 3 collides with the swirl vane 41 and the atomization thereof is promoted, and the liquid film of urea water adhering to the swirl vane 41 evaporates as described above. Dispersed by the swirling flow of the exhaust from the mixer 4 toward the downstream side.

  By the way, when the swirl flow of the exhaust gas is formed by the mixer 4 and the urea water injected into the upstream side exhaust pipe 10 is dispersed, the flow rate of the exhaust gas flowing through the mixer 4 changes greatly. The dispersion state of urea water also changes greatly. That is, in general, an automobile engine is used over a wide operation range from a low load low rotation region such as an idle to a high load high rotation region such as during high speed driving. Accordingly, the flow rate of the exhaust gas changes considerably.

  As a result, the strength and extent of the swirling flow of the exhaust gas formed by the mixer 4 as described above also change greatly. For example, when the swirling flow is weak at a small flow rate, it becomes difficult to disperse the urea water to the outer peripheral side of the exhaust passage 1, while if the swirling flow becomes too strong due to an increase in the exhaust flow rate, the urea water is now biased toward the outer peripheral side. End up. As a result, the ammonia concentration distribution in the exhaust gas flowing into the SCR catalyst 2 varies greatly depending on the operating state of the engine, and there has been a situation that high purification performance cannot be obtained over a wide operating region.

  In this embodiment, in this embodiment, an annular gap is provided between the outer peripheral portion 42 of the mixer 4 and the peripheral wall 11 of the upstream exhaust pipe 10, and the upstream and downstream exhaust passages bypass the mixer 4. In addition to functioning as a bypass passage 5 for communicating 1, the cross-sectional area of the bypass passage 5 is adjusted to mitigate changes in the flow rate of the exhaust gas flowing through the mixer 4.

  Specifically, as shown in FIGS. 3 (a) to 3 (c), in this embodiment, a support portion 43 that supports the outer peripheral portion 42 of the mixer 4 on the peripheral wall 11 of the upstream side exhaust pipe 10 is provided in the circumferential direction. A plurality (four in the illustrated example) are provided at equal intervals. Then, a pair of valve plates 51 and 52 is provided for each support portion 43 so as to open and close each opening 50 (not shown in FIG. 3A) of the bypass passage 5 divided by the support portions 43. Is provided, and is displaced from the support portion 43 to one side and the other side in the circumferential direction.

  That is, as shown in FIG. 3A, in the state where the pair of valve plates 51 and 52 for each support portion 43 is displaced most outward from the support portion 43, the valve plate of another adjacent support portion 43 is adjacent. The opening 50 is substantially closed by abutting the end edges with 52 and 51, and at this time, the cross-sectional area of the bypass passage 5 is minimized. On the other hand, as shown in FIG. 3C, in a state where the pair of valve plates 51 and 52 overlap each other in front and back and are hidden behind the support portion 43 (downstream side of the exhaust flow), each opening 50 Is fully opened, and the cross-sectional area of the bypass passage 5 is maximized.

  And as a state in between these minimum cross-sectional area and maximum cross-sectional area, a pair of valve plates 51 and 52 for each support part 43, along the outer peripheral part 42 of the mixer 4 and the peripheral wall 11 of the upstream exhaust pipe 10, By displacing in directions opposite to each other (that is, toward one side and the other side in the circumferential direction), the cross-sectional area of the bypass passage 5 becomes the minimum and maximum intermediate size as shown in FIG. That is, as will be described below, the valve plate operation mechanism 6 for each support portion 43 causes the positions of the valve plates 51 and 52 to continuously open from fully closed to fully open according to the exhaust pressure upstream of the mixer 4. To change.

  Since the valve plate operating mechanism 6 disposed in each support portion 43 is the same, the valve plate operating mechanism 6 disposed in the support portion 43 at the top of the mixer 4 will be described below with reference to FIGS. To do. In the following description, for the sake of convenience, the outer side in the radial direction in FIG. 4 centering on the axis m of the exhaust passage 1 will be referred to as the upper side and the inner side will be referred to as the lower side. The other side in the opposite circumferential direction (the clockwise side in FIG. 3) is called the right side.

  FIG. 4 is an enlarged front view (viewed from the front) showing the structure of the valve plate operating mechanism 6 disposed on the upper support portion 43 of the mixer 4, and FIGS. It is sectional drawing seen from upper direction and the right side. As shown in FIGS. 4 to 6, the valve plate operation mechanism 6 is disposed in the support portion 43 of the mixer 4, and moves forward and backward with respect to the exhaust upstream and downstream (that is, in the front-rear direction). A spring member 61 that urges the piston member 60 to move forward, and transmission members 62 and 63 that transmit the forward and backward movements of the piston member 60 to the valve plates 51 and 52 to displace them.

  As shown in FIG. 5, when viewed from above, the support portion 43 of the mixer 4 has a pair of left and right side walls 43a and a rear wall 43b formed integrally so as to connect the rear ends thereof. Eggplant. The upper ends of the left and right side walls 43 a are all fixed to the peripheral wall 11 of the upstream side exhaust pipe 10, and the lower ends are fixed to the outer peripheral portion 42 of the mixer 4. On the other hand, gaps are formed between the exhaust pipe peripheral wall 11 and the mixer outer peripheral part 42 at the upper and lower ends of the rear wall 43b of the support part 43, respectively, so as to pass through the transmission members 62 and 63 as will be described later. Become.

  A rectangular plate-shaped piston member 60 is disposed between the pair of left and right side walls 43a of the support portion 43, and the outer surfaces of the bent portions 60a extending rearward from the left and right side edges thereof are formed on the inner surface of the side wall 43a. It is in sliding contact. The piston member 60 receives the pressure of the upstream exhaust on the front surface and is pressed rearward. On the other hand, a spring member 61 (shown in the figure) is formed between the piston member 60 and the rear wall 43b of the support portion 43 which is spaced apart and opposed to the rear. In the example, it is a coil spring, but is not limited to this. Therefore, the position of the piston member 60 is determined by the balance between the force due to the exhaust pressure and the spring force.

  On the other hand, each of the pair of valve plates 51 and 52 for each support portion 43 has a substantially rectangular plate shape in which the upper edge (outer peripheral edge) and the lower edge (inner peripheral edge) draw a gentle arc. As shown in the figure, they are arranged behind each other behind the rear wall 43b of the support portion 43 so as to be displaced from each other. As an example, the valve plate 51 on one side displaced from the support 43 to the left side (one side in the circumferential direction) is disposed on the front side, and the valve plate 52 on the other side displaced to the right side (the other circumferential direction) is disposed on the rear side. Thus, they are displaced along circumferential guide grooves 42a and 11a (guide portions) formed in the outer peripheral portion 42 of the mixer 4 and the peripheral wall 11 of the upstream side exhaust pipe 10, respectively.

  Then, both of the transmission members 62 are configured such that the movement of the piston member 60 in the front-rear direction is converted into the displacement in the left-right direction (circumferential direction) of the valve plates 51, 52 to operate the valve plates 51, 52. , 63. As an example, the transmission members 62 and 63 are wires having a large flexibility and a bending rigidity necessary for transmitting force (may be thin leaf springs). When viewed from above as shown in FIG. 5, the front end portions of the pair of left and right transmission members 62, 63 are fixed to the left and right sides of the piston member 60, respectively, and the rear end portions of the transmission members 62, 63 extending rearward therefrom are respectively shown. It curves inward and is fixed to the front surface of the valve plate 51.

  Specifically, the transmission member 62 on the left side indicated by the phantom line in FIG. 5 and the solid line in FIG. 6 is fixed to the upper left side of the piston member 60 by welding or the like. After extending rearward along the left side wall 43a, it passes through the gap between the upper end of the rear wall 43b of the support portion 43 and the exhaust pipe peripheral wall 11, curves to the right side, and the one side valve plate 51 located on the left side It is fixed to the upper right part of the front by welding or the like.

  On the other hand, the right transmission member 63 indicated by the solid line in FIG. 5 and the phantom line in FIG. 6 has its front end fixed to the lower right side of the piston member 60 by welding or the like. After extending rearward along the side wall 43a of the support plate 43, it passes through a gap between the lower end of the rear wall 43b of the support portion 43 and the outer peripheral portion 42 of the mixer 4 and curves to the left side. It is fixed to the lower left part by welding or the like. Although only shown in FIG. 4, a notch 51 a is formed in the lower right portion of the valve plate 51 so that the right transmission member 63 passes.

  In the valve plate operating mechanism 6 having such a structure, as shown in FIG. 5, the backward movement of the piston member 60 at the most advanced position is transmitted to the left and right valve plates 51 and 52 by the pair of left and right transmission members 62 and 63, respectively. , Displace them in opposite directions. That is, as shown in FIG. 7 (a), as the piston member 60 moves backward, the left transmission member 62 has a shorter front part than the curved part and a right part longer than the curved part. The right part is fed from the curved part to the right side, and the left valve plate 51 to which the right end is fixed is displaced to the right.

  Similarly, also in the right transmission member 63, the front portion of the curved portion is shortened, the left portion is lengthened and the left portion is sent out to the left side, whereby the right valve plate 52 to which the left end portion is fixed is fixed. Is displaced to the left. In this manner, the pair of left and right valve plates 51, 52 are drawn into the back side of the support portion 43 from both the left and right sides, and when the piston member 60 reaches the last retracted position as shown in FIG. , 52 overlap each other in the front and rear and are hidden behind the support portion 43 (located on the rear side).

  Thus, when the pair of left and right transmission members 62 and 63 displace the valve plates 51 and 52 according to the forward and backward movements of the piston member 60, the piston member 60 is moved back and forth via the transmission members 62 and 63. In this embodiment, the opposite reaction forces acting via the pair of left and right transmission members 62 cancel each other, so that the piston member eventually becomes a force. Only the reaction force in the front-rear direction acts mainly on 60, which is advantageous for stabilizing the operation.

  Therefore, according to the exhaust gas purification apparatus of the present embodiment, first, urea water (additive) is injected from the injection nozzle 3 into the upstream exhaust pipe 10 of the exhaust passage 1 during the operation of the engine (not shown), and the swirl vane of the mixer 4 Collide with 41. As a result, the urea water in the form of minute droplets is carried on the swirling flow of the exhaust from the swirl vane 41 to the downstream side, and its evaporation is promoted while being widely dispersed. Therefore, the concentration distribution of ammonia, which is a reducing agent component, in the exhaust gas flowing into the SCR catalyst 2 on the downstream side of the mixer 4 can be made uniform.

  At that time, when the engine load and the rotational speed are low and the flow rate of the exhaust gas is relatively small, the pressure of the exhaust gas upstream of the mixer 4 is relatively low. The piston member 60 of the valve plate operating mechanism 6 is in a forward position. Therefore, the valve plates 51 and 52 project from the support portion 43 to the left and right, and the cross-sectional area of the bypass passage 5 is reduced, so that the flow rate of the exhaust gas flowing through the mixer 4 can be secured. Thus, the effect of promoting the evaporation by dispersing the urea water by the swirling flow is secured.

  On the other hand, if the engine load or rotation speed increases and the flow rate of the exhaust gas increases, the pressure of the exhaust gas upstream of the mixer 4 increases accordingly, and the piston member 60 moves backward. This backward movement is transmitted to the valve plates 51 and 52 by the transmission members 62 and 63, and the left and right valve plates 51 and 52 are drawn into the back side of the support portion 43. As a result, the cross-sectional area of the bypass passage 5 gradually increases, the flow rate of the exhaust gas that bypasses the mixer 4 increases, and the increase in the flow rate of the exhaust gas that flows through the mixer 4 is alleviated. Therefore, the swirl flow of exhaust does not become too strong.

  That is, even if the flow rate of the exhaust gas changes greatly due to a change in the operating state of the engine, the change in the flow rate of the exhaust gas flowing through the mixer 4 in the exhaust passage 1 is alleviated, and the dispersed state of urea water is always suitable. can do. Thereby, a change in the concentration distribution of ammonia in the exhaust gas flowing into the SCR catalyst 2 can be suppressed, and a suitable purification performance can be stably obtained over a wide operation region.

  In the present embodiment, in the valve plate operating mechanism 6, the piston member 60 is moved forward and backward by the balance between the exhaust pressure force and the spring force, and the valve plates 51 and 52 are mechanically displaced. Although the structure is simple, the cross-sectional area of the bypass passage 5 can be automatically adjusted according to an increase in the exhaust gas flow rate. Therefore, the cost can be reduced as compared with a sensor or an actuator.

  Further, in the present embodiment, since the bypass passage 5 is formed between the outer peripheral portion 42 of the mixer 4 and the peripheral wall 11 of the upstream side exhaust pipe 10, the urea water injected toward the vicinity of the center of the exhaust passage 1 is It can be made to collide with the mixer 4 (swivel blade 41) efficiently and the atomization can be promoted. In addition, if the bypass passage 5 on the outer periphery of the mixer 4 is closed, the flow of the exhaust gas is biased toward the inner periphery of the exhaust passage 1, so that the blowback from the outer periphery to the nozzle housing portion 12 is reduced and the injection nozzle 3 is adversely affected. There is also an effect that can be reduced.

  Furthermore, in this embodiment, valve plates 51 and 52 for opening and closing the opening 50 of the bypass passage 5 and the valve plate operating mechanism 6 are disposed on the support portion 43 of the mixer 4, and FIG. When the cross-sectional area of the bypass passage 5 is maximized as shown in (b), the valve plates 51 and 52 are hidden behind the support portion 43 in a state where they overlap each other. It can be made sufficiently large to suppress an increase in exhaust pressure loss even when the flow rate of exhaust is large.

-Other embodiments-
The configuration of the present invention is not limited to the above-described embodiment, and includes other various forms. For example, the operation of the piston member 60 of the valve plate operating mechanism 6 can be transmitted to the valve plates 51 and 52 not by the flexible transmission members 62 and 63 but by a link mechanism, a push-pull cable, or the like.

  Further, it is not necessary to configure the passage area variable means by the valve plates 51 and 52 and the mechanical valve plate operating mechanism 6. For example, the pressure and flow rate of the exhaust gas is detected by a sensor and the valve plate is operated by an actuator. Also good.

  Further, there is no need to form the bypass passage 6 on the outer periphery of the mixer 4. For example, a bypass exhaust pipe extending in parallel with the exhaust passage 1 bypasses the mixer 4 and the bypass exhaust pipe is opened and closed by a butterfly valve or the like. Also good.

  Further, in the above-described embodiment, the case where the SCR catalyst 2 is used as the exhaust purification catalyst and urea water is added has been described. However, the reducing agent (additive) is not limited to urea water, and an ammonia aqueous solution, a hydrocarbon aqueous solution, or the like. It may be applied. For example, the present invention can be applied to an NSR catalyst that supplies unburned fuel as an additive.

  Moreover, although the above-mentioned embodiment demonstrated the case where this invention was applied to the diesel engine mounted in the motor vehicle, this invention is applicable not only to this but the diesel engine mounted other than a motor vehicle. Further, the present invention is applicable not only to diesel engines but also to gasoline engines.

  INDUSTRIAL APPLICABILITY The present invention can sufficiently promote the mixing of the additive injected into the exhaust passage upstream of the exhaust purification catalyst with the mixer, and is particularly applicable to a diesel engine or the like mounted on an automobile. And has an excellent effect.

1 Exhaust passage 10 Upstream exhaust pipe (exhaust passage upstream of exhaust flow from exhaust purification catalyst)
11 peripheral wall 11a guide groove (guide part)
2 SCR catalyst (exhaust gas purification catalyst)
4 Mixer 42 Outer peripheral part of mixer 42a Guide groove (guide part)
43 Mixer Supporting Section 5 Detour Path 50 Detour Path Opening 51, 52 Valve Plate (Path Area Variable Means)
6 Valve plate operation mechanism 60 Piston member (valve plate operation mechanism, passage area variable means)
61 Spring member (valve plate operating mechanism, passage area variable means)
62, 63 Transmission member (valve plate operating mechanism, passage area variable means)

Claims (7)

An exhaust purification catalyst disposed in the exhaust passage of the internal combustion engine, and a mixer that promotes mixing of the additive exhaust injected into the exhaust passage upstream of the exhaust purification catalyst in the exhaust flow. An exhaust purification device,
A bypass passage that bypasses the mixer and connects the upstream and downstream exhaust passages;
An exhaust emission control device comprising: a passage area variable means for changing the cross-sectional area of the bypass passage so that the cross-sectional area increases as the flow rate of the exhaust gas in the exhaust passage on the upstream side of the mixer increases. The exhaust emission control device according to claim 1,
The passage area varying means operates in response to a valve plate provided in the bypass passage and an exhaust pressure upstream of the mixer, and a cross-sectional area of the bypass passage increases as the pressure increases. An exhaust purification device comprising a valve plate operating mechanism for displacing the valve plate as described above. The exhaust emission control device according to claim 2,
The bypass passage is formed between an outer peripheral portion of the mixer and a peripheral wall of an exhaust passage that surrounds and surrounds the mixer,
A plurality of support portions for supporting the outer peripheral portion of the mixer on the peripheral wall of the exhaust passage are provided at intervals in the circumferential direction, and the valve plate operating mechanism is disposed on the support portion. Purification equipment. The exhaust emission control device according to claim 3,
The valve plate operating mechanism is
A piston member that receives the pressure of the exhaust gas upstream of the mixer and moves backward toward the downstream side;
A spring member that urges the piston member to advance toward the upstream side;
An exhaust purification device comprising: a transmission member that transmits and moves forward and backward movements of the piston member to the valve plate. The exhaust emission control device according to claim 4,
At least one of the outer peripheral portion of the mixer and the peripheral wall of the exhaust passage is provided with a guide portion that guides the valve plate so as to be displaced in the circumferential direction,
The exhaust gas purification device, wherein the transmission member is flexible and is disposed so as to be curved so as to convert forward and backward movements of the piston member into a displacement in a circumferential direction of the valve plate. The exhaust emission control device according to claim 5,
A pair of valve plates are connected to the piston member by a pair of transmission members, and the pair of valve plates are configured to displace in the opposite directions in the circumferential direction in accordance with the forward and backward movement of the piston member. , Exhaust purification device. The exhaust emission control device according to claim 6,
The exhaust purification apparatus, wherein the pair of valve plates are arranged so that at least a part of the pair of valve plates overlap each other at the last retracted position of the piston member.

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