Catalytic converter

Abstract

[Problem] To provide a catalytic converter that can stably improve the purification rate of a three-way catalyst. [Solution] Provided is a catalytic converter 2 comprising: a three-way catalyst 5 that purifies exhaust gas from an engine; a baffle plate 6 that has a plurality of holes through which the exhaust gas passes; and a case 3 that accommodates the three-way catalyst 5 and the baffle plate 6. The case 3 includes: an inflow section 31 into which flows the exhaust gas discharged from the engine; an expansion section 32 where the cross-sectional area of the flow passage for the exhaust gas flowing in from the inflow section 31 is expanded; an accommodation section 33 that accommodates the three-way catalyst 5; a reduction section 34 where the cross-sectional area of the flow passage for the exhaust gas that has passed through the three-way catalyst 5 is reduced; and an outflow section 35 out from which flows the exhaust gas that has passed through the reduction section 34. The outflow section 35 has an attachment part 351 to which is attached an oxygen sensor 4 for detecting the concentration of oxygen contained in the exhaust gas that flows through the outflow section 35. The baffle plate 6 is provided in the interior of the case 3 and between the three-way catalyst 5 and the attachment part 351.

Description

Catalytic Converter

[0001] The present invention relates to a catalytic converter for purifying exhaust gas from an engine.

[0002] Patent Document 1 discloses a catalytic converter in which a rectifying baffle plate having a plurality of holes is provided in a case. In the catalytic converter described in Patent Document 1, the catalyst carrier is housed on one side of the rectifying baffle plate in the case.

[0003] It is known that the purification rate of a three-way catalyst in which noble metals such as platinum (Pt), rhodium (Rh), and palladium (Pd) are supported on a ceramic or metal catalyst carrier as catalyst components is high in the vicinity of the theoretical air-fuel ratio (i.e., air excess ratio λ = 1). Therefore, in order to make the three-way catalyst function efficiently, keeping the air-fuel ratio of the air-fuel mixture at the theoretical air-fuel ratio is one of the important factors. Thus, a technique for performing feedback control of the fuel injection amount according to the detection signal of an oxygen sensor provided downstream of the three-way catalyst is known.

[0004] However, depending on the arrangement of the baffle plate, the exhaust gas passing through the baffle plate may not be sufficiently mixed. In this case, the measurement accuracy of the oxygen sensor may decrease, or the air-fuel ratio of the exhaust gas flowing in the vicinity of the oxygen sensor may fluctuate. As a result, precise air-fuel ratio control becomes difficult, and the purification rate of the three-way catalyst may decrease.

[0005] Japanese Unexamined Patent Application Publication No. 2007-315246

[0006] The present invention has been made in view of the above circumstances, and an object thereof is to provide a catalytic converter capable of stably improving the purification rate of a three-way catalyst.

[0007] One aspect of the present invention is a catalytic converter comprising: a three-way catalytic converter for purifying engine exhaust gas; a baffle plate provided downstream of the three-way catalytic converter in the flow of the exhaust gas and having a plurality of holes through which the exhaust gas passes; and a case housing the three-way catalytic converter and the baffle plate, wherein the case has an inlet for receiving the exhaust gas discharged from the engine; an enlargement section connected downstream of the inlet for increasing the flow path cross-sectional area of ​​the exhaust gas flowing in from the inlet; a housing section connected downstream of the enlargement section for housing the three-way catalytic converter; a reduction section connected downstream of the housing section for decreasing the flow path cross-sectional area of ​​the exhaust gas that has passed through the three-way catalytic converter; and an outlet section connected downstream of the reduction section for discharging the exhaust gas that has passed through the reduction section, wherein the outlet section has a mounting section to which an oxygen sensor for detecting the oxygen concentration contained in the exhaust gas flowing through the outlet section is attached, and the baffle plate is provided inside the case between the three-way catalytic converter and the mounting section.

[0008] According to the present invention, it is possible to provide a catalytic converter that can stably improve the purification rate of a three-way catalyst.

[0009] This is a perspective view showing the catalytic converter according to this embodiment. This is a front view showing the catalytic converter according to this embodiment. This is a cross-sectional view taken along the line A-A shown in Figure 1. This is a front view showing the baffle plate of this embodiment. This is a cross-sectional view taken along the line B-B shown in Figure 4.

[0010] Embodiments of the present invention will be described below with reference to the drawings. The embodiments described below are preferred examples of the present invention and therefore have various technically preferred limitations. However, the scope of the present invention is not limited to these embodiments unless otherwise specified in the following description. Furthermore, in each drawing, similar components are denoted by the same reference numerals, and detailed descriptions are omitted as appropriate.

[0011] Figure 1 is a perspective view showing the catalytic converter according to this embodiment. Figure 2 is a front view showing the catalytic converter according to this embodiment. Figure 3 is a cross-sectional view taken along the line A-A shown in Figure 1. Figure 4 is a front view showing the baffle plate of this embodiment. Figure 5 is a cross-sectional view taken along the line B-B shown in Figure 4.

[0012] As shown in Figures 1 to 3, the catalytic converter 2 according to this embodiment comprises a case 3, a three-way catalyst 5, and a baffle plate 6.

[0013] As shown in Figure 3, case 3 has an inlet section 31, an expansion section 32, a housing section 33, a contraction section 34, an outlet section 35, a first flange 36, and a second flange 37, and houses the three-way catalyst 5 and the baffle plate 6. Case 3 is formed from a metal material. Case 3 may be formed by joining multiple members, or it may be formed integrally by, for example, spinning. In the case 3 shown in Figure 3, the inlet section 31 and the expansion section 32 are formed integrally, and the other members (i.e., the housing section 33, the contraction section 34, the outlet section 35, the first flange 36, and the second flange 37) are formed separately.

[0014] The inlet 31 is connected to an exhaust pipe (not shown) connected to the engine's exhaust manifold via a first flange 36. As shown by arrow A1 in Figure 3, the inlet 31 allows exhaust gas discharged from the engine and passing through the exhaust manifold to flow into the case 3. In other words, arrow A1 in Figure 3 indicates the direction of the exhaust gas flow into the case 3.

[0015] The enlarged section 32 is connected to the downstream side of the inlet section 31 in the direction of exhaust gas flow. The flow path cross-sectional area of ​​the exhaust gas flowing through the enlarged section 32, that is, the flow path cross-sectional area of ​​the enlarged section 32, expands in the direction of exhaust gas flow.

[0016] The housing section 33 is connected to the downstream side of the expansion section 32 in the direction of exhaust gas flow. The housing section 33 is formed in a substantially cylindrical shape and houses the three-way catalyst 5. Specifically, as shown in Figure 3, the housing section 33 houses the three-way catalyst 5 with the support member 7 wrapped around the outer circumference of the three-way catalyst 5.

[0017] The reducing section 34 is connected to the downstream side of the housing section 33 in the direction of exhaust gas flow. The flow path cross-sectional area of ​​the exhaust gas flowing through the reducing section 34, i.e., the flow path cross-sectional area of ​​the reducing section 34, is reduced in the direction of exhaust gas flow. In other words, the reducing section 34 has a wedge shape in which the flow path cross-sectional area is reduced in the direction of exhaust gas flow. As shown in Figure 3, the reducing section 34 houses the baffle plate 6. Details of this will be described later.

[0018] The outlet section 35 is connected downstream of the constriction section 34 in the direction of exhaust gas flow. The outlet section 35 is also connected to an exhaust pipe (not shown) connected to a muffler via a second flange 37. As shown by arrow A2 in Figure 3, the outlet section 35 causes the exhaust gas that has passed through the three-way catalyst 5 and the baffle plate 6 to flow out of the case 3. In other words, arrow A2 in Figure 3 represents the direction of the exhaust gas flow out of the case 3.

[0019] As shown in Figures 1 to 3, the outlet section 35 has a mounting section 351. The mounting section 351 is located approximately in the center of the outlet section 35 in the direction of exhaust gas flow, and connects the inside and outside of the outlet section 35. The oxygen sensor 4 is attached to the mounting section 351 of the outlet section 35 and detects the oxygen concentration contained in the exhaust gas flowing through the outlet section 35. The signal regarding the oxygen concentration detected by the oxygen sensor 4 is transmitted to a control unit (not shown).

[0020] As shown in Figure 3, the three-way catalyst 5 is housed in the housing section 33 of the case 3 with the support member 7 wrapped around its outer circumference. The three-way catalyst 5 has a structure in which precious metals such as platinum (Pt), rhodium (Rh), and palladium (Pd) are supported as catalyst components on a ceramic or metal catalyst carrier.

[0021] The exhaust gas that has passed through the inlet section 31 and the expansion section 32 is purified by the catalytic action of the three-way catalyst 5 as it passes through the passages formed in the catalyst support of the three-way catalyst 5. That is, when carbon monoxide (CO), hydrocarbons (HC), and nitrogen compounds (NOx) contained in the engine exhaust gas pass through the passages in the catalyst support of the three-way catalyst 5, oxidation reactions occur for CO and HC, and reduction reactions occur for NOx. As a result, the harmful components of CO, HC, and NOx are purified by water (H ２ O), carbon dioxide (CO2) ２ ), nitrogen (N ２ ) and oxygen (O ２ It is converted into harmless components. This purifies the engine's exhaust gas.

[0022] As shown in Figure 3, the baffle plate 6 is located downstream of the three-way catalytic converter 5 in the direction of exhaust gas flow. Specifically, the baffle plate 6 is located inside the case 3 between the three-way catalytic converter 5 and the mounting portion 351 of the outlet section 35 in the direction of exhaust gas flow. More specifically, the baffle plate 6 is located inside the reduction section 34.

[0023] As shown in Figures 4 and 5, the baffle plate 6 has a first portion 61, a second portion 62, and a third portion 63. The first portion 61 is located in the center of the baffle plate 6 and is formed in the shape of a disc. The second portion 62 is located outside the first portion 61 and is connected to the outer circumference of the first portion 61, and is formed in the shape of an annular ring. The third portion 63 is located outside the second portion 62 and is connected to the outer circumference of the second portion 62, and is formed in the shape of a substantially annular ring.

[0024] The first part 61 has a plurality of first holes 611. As shown in Figure 4, the plurality of first holes 611 are arranged in a grid pattern in the first part 61, except for the central part. In other words, the first holes 611 are not formed in the central part of the first part 61, but are arranged in a grid pattern around the central part of the first part 61. In the example shown in Figure 4, there are 20 first holes 611. Also, the diameter of each of the plurality of first holes 611 is all the same. Note that the number and diameter of the first holes 611 are not particularly limited.

[0025] The second portion 62 has a plurality of second holes 621. As shown in Figure 4, the plurality of second holes 621 are arranged in the second portion 62, that is, outside the plurality of first holes 611, at approximately equal intervals in the circumferential direction. In the example shown in Figure 4, there are 18 second holes 621. The diameter of each of the plurality of second holes 621 is all the same and is larger than the diameter of the first holes 611. The total opening area of ​​all the second holes 621 is larger than the total opening area of ​​all the first holes 611. The number and diameter of the second holes 621 are not particularly limited.

[0026] The third portion 63 has a plurality of recesses 631. The recesses 631 are formed by recessing from the outer edge of the third portion 63 toward the central portion (i.e., the first portion 61). As shown in Figure 4, the plurality of recesses 631 are arranged at approximately equal intervals in the circumferential direction along the outer edge of the third portion 63. In the example shown in Figure 4, there are six recesses 631. The number of recesses 631 is not particularly limited.

[0027] As shown in Figure 5, the third portion 63 has an inclined surface 632. That is, the third portion 63 is inclined toward the upstream side of the exhaust gas flow as it moves from the center of the baffle plate 6 toward the outer edge. The inclined surface 632 corresponds to the downstream outer surface of the third portion 63. As shown in Figure 3, the inclined surface 632 of the third portion 63 is aligned with the inclined surface 341 of the reduced portion 34 of the case 3. The inclined surface 341 corresponds to the inner surface of the reduced portion 34 where the flow path cross-sectional area is reduced, that is, the inner surface of the wedge-shaped reduced portion 34.

[0028] For example, the inclined surface 632 of the third portion 63 of the baffle plate 6 is in contact with the inclined surface 341 of the reduced portion 34 of the case 3, and welding is performed to the recess 631 of the third portion 63. That is, in the baffle plate 6 shown in Figure 4, intermittent welding is performed between the inclined surface 632 of the third portion 63 of the baffle plate 6 and the inclined surface 341 of the reduced portion 34 of the case 3 at all six recesses 631 formed on the outer edge of the third portion 63. As a result, as shown in Figure 3, the baffle plate 6 is joined and fixed to the inclined surface 341 in which the flow path cross-sectional area is reduced inside the reduced portion 34.

[0029] Here, it is known from public knowledge that the purification efficiency of the three-way catalyst 5 is high in the vicinity of the stoichiometric air-fuel ratio (i.e., air excess ratio λ = 1). Therefore, in order for the three-way catalyst 5 to function efficiently, maintaining the air-fuel ratio of the air-fuel mixture at the stoichiometric air-fuel ratio is one of the important factors. Accordingly, the control unit (not shown) performs feedback control of the fuel injection amount in response to the detection signal from the oxygen sensor 4 located downstream of the three-way catalyst 5.

[0030] However, depending on the arrangement of the baffle plates, the exhaust gas that passes through the baffle plates may not be sufficiently mixed. In this case, the measurement accuracy of the oxygen sensor 4 may decrease, or the air-fuel ratio of the exhaust gas flowing near the oxygen sensor 4 may fluctuate. This can make precise air-fuel ratio control difficult, potentially reducing the purification efficiency of the three-way catalytic converter.

[0031] In contrast, the baffle plate 6 of the catalytic converter 2 according to this embodiment is provided inside the case 3 between the three-way catalyst 5 housed in the housing section 33 and the mounting section 351 for the oxygen sensor 4 provided in the outlet section 35.

[0032] As a result, the exhaust gas passes through the first hole 611 and the second hole 621 of the baffle plate 6 at a relatively high speed. This disrupts the flow of exhaust gas downstream of the baffle plate 6 (i.e., exhaust gas that has passed through the first hole 611 and the second hole 621 of the baffle plate 6), promoting the mixing of exhaust gases downstream of the baffle plate 6. This improves the measurement accuracy of the oxygen sensor 4 attached to the mounting portion 351 of the outlet section 35, and suppresses fluctuations in the air-fuel ratio of the exhaust gas flowing near the oxygen sensor 4. As a result, the control unit can perform precise and stable air-fuel ratio control. This makes it possible to stably improve the purification rate of the three-way catalyst 5.

[0033] Specifically, as described above with respect to Figure 3, the baffle plate 6 is installed inside the reduced portion 34 of the case 3. Therefore, compared to the case where the baffle plate 6 is installed immediately downstream of the three-way catalytic converter 5 (for example, in the housing portion 33), the exhaust gas passes through the first hole 611 and the second hole 621 of the baffle plate 6 at a faster speed. As a result, compared to the case where the baffle plate 6 is installed immediately downstream of the three-way catalytic converter 5, the mixing of exhaust gases downstream of the baffle plate 6 is promoted more reliably. In addition, compared to the case where the baffle plate 6 is installed immediately upstream of the mounting portion 351 of the oxygen sensor 4 (for example, in the outlet portion 35), it is possible to promote the mixing of exhaust gases downstream of the baffle plate 6 while suppressing excessively high exhaust gas pressure (i.e., back pressure) in the engine's exhaust system. As a result, it is possible to suppress a decrease in engine output and a deterioration in fuel efficiency.

[0034] Furthermore, as described above with respect to Figure 3, the baffle plate 6 is fixed to the inclined surface 341 in the reduced portion 34 of the case 3, where the flow path cross-sectional area is reduced. Specifically, the baffle plate 6 is fixed to the inclined surface 341 of the reduced portion 34 with the inclined surface 632 of the third portion 63 of the baffle plate 6 in contact with the inclined surface 341 of the reduced portion 34 of the case 3. Because the baffle plate 6 is fixed to the inner surface (i.e., the inclined surface 341) of the wedge-shaped reduced portion 34, when workers fix (for example, weld) the baffle plate 6 to the inclined surface 341 of the reduced portion 34, they can more reliably and stably install or temporarily fix the baffle plate 6 to the inclined surface 341 of the reduced portion 34, thereby improving the efficiency of the baffle plate 6 fixing work. Furthermore, since the baffle plate 6 is fixed to the inner surface (i.e., the inclined surface 341) of the wedge-shaped reduced portion 34, it is possible to suppress the formation of a gap between the outer surface of the baffle plate 6 and the inner surface of the case 3 compared to the case where the baffle plate 6 is installed in the substantially cylindrical housing portion 33. As a result, exhaust gas passes more reliably through the first hole 611 and the second hole 621 of the baffle plate 6.

[0035] Furthermore, as described above with respect to Figures 4 and 5, the baffle plate 6 has a plurality of first holes 611 and a plurality of second holes 621. The plurality of first holes 611 are arranged in a grid pattern in the first portion 61 provided in the central part of the baffle plate 6, except for the central part. The plurality of second holes 621 are arranged in a circumferential direction outside the plurality of first holes 611 in the second portion 62 connected to the outer circumference of the first portion 61. The total opening area of ​​all the second holes 621 is larger than the total opening area of ​​all the first holes 611. This makes it possible to promote the flow of exhaust gas near the inner surface of the case 3 where a pressure loss greater than the pressure loss near the central part of the exhaust gas flow occurs. In other words, the pressure loss of the exhaust gas flowing near the inner surface of the case 3 can be kept small. This makes it possible to make the velocity gradient of the exhaust gas passing through a cross section perpendicular to the direction of exhaust gas flow more uniform. Therefore, the control unit can perform more precise and stable air-fuel ratio control, and the purification rate of the three-way catalyst 5 can be improved more stably.

[0036] Embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the claims. The configurations of the above embodiments can be partially omitted or combined in any way different from those described above.

[0037] 2: Catalytic converter, 3: Case, 4: Oxygen sensor, 5: Three-way catalyst, 6: Baffle plate, 7: Support member, 31: Inlet, 32: Enlarged section, 33: Housing section, 34: Reducing section, 35: Outlet section, 36: First flange, 37: Second flange, 61: First part, 62: Second part, 63: Third part, 341: Inclined surface, 351: Mounting section, 611: First hole, 621: Second hole, 631: Recess, 632: Inclined surface

Claims

1. A catalytic converter comprising: a three-way catalytic converter for purifying engine exhaust gas; a baffle plate provided downstream of the three-way catalytic converter in the flow of the exhaust gas and having a plurality of holes through which the exhaust gas passes; and a case housing the three-way catalytic converter and the baffle plate, wherein the case has: an inlet for receiving the exhaust gas discharged from the engine; an enlargement section connected downstream of the inlet for increasing the flow path cross-sectional area of ​​the exhaust gas flowing in from the inlet; a housing section connected downstream of the enlargement section for housing the three-way catalytic converter; a reduction section connected downstream of the housing section for decreasing the flow path cross-sectional area of ​​the exhaust gas that has passed through the three-way catalytic converter; and an outlet section connected downstream of the reduction section for discharging the exhaust gas that has passed through the reduction section, wherein the outlet section has a mounting section to which an oxygen sensor for detecting the oxygen concentration contained in the exhaust gas flowing through the outlet section is attached, and the baffle plate is provided inside the case between the three-way catalytic converter and the mounting section.

2. The catalytic converter according to claim 1, characterized in that the baffle plate is provided inside the reduced portion.

3. The catalytic converter according to claim 2, characterized in that the baffle plate is fixed to an inclined surface within the reduced portion that reduces the cross-sectional area of ​​the flow path.

4. The catalytic converter according to claim 1, characterized in that the baffle plate has a plurality of first holes arranged in a grid pattern in the central part, and a plurality of second holes having a diameter larger than the diameter of the first holes and arranged in a circumferential direction outside the plurality of first holes.

5. The catalytic converter according to claim 4, characterized in that the plurality of first holes are formed in a first portion provided in the central part of the baffle plate and are arranged in a grid pattern except for the central part of the first portion.

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