Exhaust structure of an internal combustion engine

Abstract

The present invention provides an exhaust structure for an internal combustion engine that can improve exhaust purification performance and pressure loss while ensuring sufficient detection accuracy of the air-fuel ratio sensor. [Solution] The exhaust structure of the internal combustion engine comprises a turbine and a catalytic converter provided in the exhaust passage, a bypass passage that merges with the exhaust passage via a substantially circular port, and an air-fuel ratio sensor. The exhaust passage between the catalytic converter and the port is provided with an elliptical portion having a second elliptical cross-section similar to a hypothetical ellipse that encompasses the port and the substantially circular first cross-section of the exhaust passage between the turbine and the port, and whose major and minor axes are substantially aligned with the hypothetical ellipse, and a reducing portion that reduces the exhaust passage area toward the elliptical portion. The hypothetical ellipse has a center located on a straight line connecting the centers of the port and the first cross-section, and a major axis extending in the direction of the straight line. The air-fuel ratio sensor is provided in the elliptical portion at a position closer to one end of the minor axis of the second cross-section than to one end of the major axis of the second cross-section.

Description

Technical Field

[0001] The present invention relates to an exhaust structure of an internal combustion engine.

Background Art

[0002] Regarding the exhaust structure of an internal combustion engine, for example, Patent Document 1 describes an exhaust system of an engine equipped with a supercharger, an air-fuel ratio sensor, and a catalyst.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the exhaust passage of an internal combustion engine, when a sufficient amount of exhaust gas does not hit the tip of the air-fuel ratio sensor, the detection accuracy of the air-fuel ratio sensor decreases. For this reason, it is conceivable to form a recessed portion where the cross-sectional area of the exhaust passage becomes small and install the air-fuel ratio sensor in the recessed portion. However, in this case, the exhaust is likely to hit the inner wall of the exhaust passage, so there is a risk that the pressure loss of the exhaust passage increases and the fuel consumption deteriorates. Furthermore, in this case, since the exhaust heat diffuses from the inner wall of the exhaust passage, the downstream catalyst cannot be sufficiently warmed up and activated, and there is a risk that the purification performance of the exhaust by the catalyst deteriorates.

[0005] Therefore, the present invention has been made in view of the above problems, and an object thereof is to provide an exhaust structure of an internal combustion engine that can improve the exhaust purification performance and pressure loss while sufficiently ensuring the detection accuracy of the air-fuel ratio sensor.

Means for Solving the Problems

[0006] The exhaust structure of the internal combustion engine of the present invention comprises a supercharger having a turbine provided in the exhaust passage of the internal combustion engine, a catalytic converter provided in the exhaust passage downstream of the turbine, a bypass passage that branches off from the exhaust passage upstream of the turbine, bypasses the turbine, and merges with the exhaust passage upstream of the catalytic converter via a substantially circular port, and an air-fuel ratio sensor that detects the air-fuel ratio from the exhaust in the exhaust passage, wherein the exhaust passage between the catalytic converter and the port includes the port and the exhaust passage between the turbine and the port An elliptical portion is provided which has a second elliptical portion that is similar to a hypothetical elliptical shape encompassing the first cross section of the road, and whose major and minor axes are substantially aligned with the hypothetical elliptical shape, and a reducing portion is provided which reduces the exhaust passage area toward the elliptical portion, the hypothetical elliptical shape has a center located on a straight line connecting the centers of the port and the first cross section, and a major axis extending in the direction of the straight line, and the air-fuel ratio sensor is provided in the elliptical portion at a position closer to one end of the minor axis of the second cross section than to one end of the major axis of the second cross section.

[0007] In the exhaust structure described above, the air-fuel ratio sensor may be provided at one end of the minor axis of the second cross-section in the elliptical portion.

[0008] In the exhaust structure described above, the air-fuel ratio sensor may be provided with its tip facing the inlet of the catalytic converter. [Effects of the Invention]

[0009] According to the present invention, it is possible to improve exhaust gas purification performance and pressure loss while ensuring sufficient detection accuracy of the air-fuel ratio sensor. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 is a diagram showing an example of a vehicle system. [Figure 2] Figure 2 is a schematic cross-sectional view showing an example of an engine exhaust structure. [Figure 3]Figure 3 is a cross-sectional view of the exhaust structure along line AA in Figure 2. [Figure 4] Figure 4 is a schematic diagram showing an example of a hypothetical elliptical shape encompassing the cross-section of the exit port and the second passage, and the elliptical shape of the cross-section of the fifth passage. [Modes for carrying out the invention]

[0011] (Vehicle system configuration) Figure 1 is a diagram showing an example of a vehicle system S. The vehicle system S includes a supercharger 1 including a compressor 31 and a turbine 41, an engine 2 which is an example of an internal combustion engine, an intake passage 3, an exhaust passage 4, a bypass passage 5, an air cleaner 30, and a catalytic converter 40. Air flows through the intake passage 3 toward the cylinder (combustion chamber) of the engine 2. Exhaust gas produced by the combustion of the fuel-air mixture in the combustion chamber flows through the exhaust passage 4.

[0012] An air cleaner 30 is provided at the uppermost position of the intake passage 3. The air cleaner 30 removes dust and other particles from the air by filtering it.

[0013] A compressor 31 is provided downstream of the air cleaner 30 in the intake passage 3. The compressor 31 has an impeller 14 and a housing 15. The impeller 14 is housed in the housing 15. As the impeller 14 rotates, the compressor 31 pumps air under pressure.

[0014] A throttle valve 6 is provided downstream of the compressor 31 in the intake passage 3. The opening degree of this throttle valve 6 is controlled by, for example, the ECU (Electronic Control Unit) according to the load required on the engine 2 based on the amount of accelerator operation by the driver. This appropriately adjusts the amount of air supplied to the cylinder (intake volume).

[0015] A turbine 41 is located at the uppermost position of the exhaust passage 4. The turbine 41 has a housing 11 and an impeller 12. The impeller 12 is housed in the housing 11. The impeller 12 rotates due to the exhaust flow. The rotation axes of the impeller 12 of the turbine 41 and the impeller 14 of the compressor 31 are integrally connected by a connecting shaft 13. As a result, the impeller 12 of the turbine 41 and the impeller 14 of the compressor 31 rotate as a single unit.

[0016] A catalytic converter 40 is provided downstream of the turbine 41 in the exhaust passage 4. The catalytic converter 40 holds a catalyst support (such as palladium) that purifies the exhaust gas inside a case (not shown). The catalyst support of the catalytic converter 40 is formed, for example, from porous ceramic and forms a grid of numerous passages. The exhaust gas purified by the catalytic converter 40 is discharged outside the vehicle. Another catalytic converter (not shown) may be provided downstream of the catalytic converter 40.

[0017] In the exhaust passage 4, an air-fuel ratio sensor 42 is provided downstream of the turbine 41 and upstream of the catalytic converter 40. The air-fuel ratio sensor 42 detects the air-fuel ratio from the exhaust gas in the exhaust passage 4. An air-fuel ratio sensor 42 is provided for each cylinder (not shown) of the engine 2 and is used to determine the air-fuel ratio imbalance between cylinders.

[0018] Furthermore, a bypass passage 5 that bypasses the turbine 41 is connected to the exhaust passage 4. A wastegate valve 43 is provided downstream of the bypass passage 5. The bypass passage 5 branches off from the exhaust passage 4 upstream of the turbine 41, bypasses the turbine 41, and merges with the exhaust passage 4 upstream of the catalytic converter 40 via the outlet port 51 of the wastegate valve 43. The cross-sectional area of ​​the flow path of the bypass passage 5 changes depending on the opening of the outlet port 51 of the wastegate valve 43. Normally, the outlet port 51 is kept fully open. The exhaust flow Db that flows through the bypass passage 5 merges with the exhaust flow Da from the turbine 41 and flows into the catalytic converter 40.

[0019] FIG. 2 is a cross-sectional view schematically showing an example of the exhaust structure E of the engine 2. FIG. 2 shows a cross-section of the exhaust passage 4 along the exhaust flow. This cross-section also extends in the direction in which the tip 42a of the air-fuel ratio sensor 42 protrudes into the exhaust passage 4.

[0020] Further, FIG. 3 is a cross-sectional view of the exhaust structure E taken along the line A-A of FIG. 2. FIG. 3 shows a cross-section orthogonal to the cross-section of the exhaust passage 4 shown in FIG. 2.

[0021] The exhaust passage 4 includes a first passage 4a, a second passage 4b, a third passage 4c, a fourth passage 4d, and a fifth passage 4e having a substantially circular passage cross-section. The substantially circular shape includes, for example, a perfect circle, an ellipse, and polygons approximated to a perfect circle or an ellipse. The first passage 4a, the second passage 4b, the third passage 4c, the fourth passage 4d, and the fifth passage 4e are provided in this order from upstream to downstream.

[0022] The first passage 4a is provided between the engine 2 and the turbine 41. Exhaust flows from the engine 2 through the first passage 4a and into the turbine 41. An inlet 50 to the bypass passage 5 is provided in the middle of the first passage 4a. A part of the exhaust flows from the first passage 4a through the inlet 50 into the bypass passage 5, and the rest of the exhaust flows into the turbine 41.

[0023] The second passage 4b and the third passage 4c are integrally formed and provided on the downstream side of the turbine 41. An outlet port 51 of the waste gate valve 43 is provided in the second passage 4b. The outlet port 51 is inclined at a predetermined angle with respect to the direction in which the second passage 4b extends and is connected to the bypass passage 5. The outlet port 51 has a substantially circular shape in a front view. Here, the substantially circular shape includes, for example, a perfect circle, an ellipse, and polygons approximated to a perfect circle or an ellipse. The bypass passage 5 near the outlet port 51 is provided substantially parallel to the second passage 4b.

[0024] The exhaust gas that flows through the bypass passage 5 flows into the third passage 4c via the outlet port 51. Therefore, the exhaust gas that flows from the turbine 41 through the second passage 4b ​​flows into the third passage 4c and merges with the exhaust gas from the outlet port 51. Note that the outlet port 51 is just one example of a port.

[0025] The third passage 4c is connected to the fourth passage 4d by, for example, a clamp 7. The clamp 7 connects the third passage 4c and the fourth passage 4d by clamping from the outside the edge 4c1 that protrudes outward from the end of the third passage 4c and the edge 4d1 that protrudes outward from the end of the fourth passage 4d. The shape of the passage cross-section at the connection point between the third passage 4c and the fourth passage 4d is, for example, circular. The fourth passage 4d is formed such that the passage area expands from the exit of the third passage 4c toward the connection point with the fourth passage 4d.

[0026] The fourth passage 4d and the fifth passage 4e are integrally formed and located downstream of the third passage 4c. Exhaust gas enters the catalytic converter 40 through the fourth passage 4d and the fifth passage 4e. The fourth passage 4d is formed such that the passage area for exhaust gas decreases from the connection point with the third passage 4c toward the fifth passage 4e. The fourth passage 4d has an inner wall 4d2 formed opposite to the direction in which the exhaust gas from the third passage 4c flows.

[0027] The fifth passage 4e is provided adjacent to the inlet (input surface) 40a of the catalytic converter 40. An air-fuel ratio sensor 42 is provided in the fifth passage 4e. The air-fuel ratio sensor 42 is mounted on a mounting seat 4e1 provided on the inner wall of the fifth passage 4e. The air-fuel ratio sensor 42 is positioned so that its tip 42a faces the inlet 40a of the catalytic converter 40. The air-fuel ratio sensor 42 detects the air-fuel ratio when exhaust gas strikes the tip 42a. Therefore, the more exhaust gas that strikes the tip 42a, the higher the accuracy of the air-fuel ratio detection.

[0028] The fifth passage 4e has an elliptical cross-section Wb that is similar to the imaginary elliptical shape encompassing the outlet port 51 and the cross-section Wa of the second passage 4b. The major and minor axes of the imaginary elliptical shape are substantially aligned with the major and minor axes of the elliptical cross-section Wb. Therefore, the exhaust gas flowing out from the outlet port 51 and the second passage 4b ​​flows smoothly from cross-section Wa to cross-section Wb with little obstruction from the inner wall 4d1 of the fourth passage 4d, as indicated by the symbol F. At this time, because the fifth passage 4e is elliptical, the resistance to the exhaust gas flow is reduced compared to, for example, a rectangular passage.

[0029] Note that the fifth passage 4e is an example of an elliptical portion, and the cross-section Wa of the second passage 4b ​​is an example of the first cross-section. Here, the cross-section Wa of the second passage 4b ​​is defined as a plane parallel to the exhaust output surface of the turbine 41 and passing through the center 51c of the outlet port 51. Also, the fourth passage 4d is an example of a reduced portion, and the cross-section Wb of the fifth passage 4e is an example of the second cross-section. The cross-section Wb of the fifth passage 4e is defined as a plane passing through the mounting seat 4e1 of the air-fuel ratio sensor 42 and parallel to the inlet 40a of the catalytic converter 40.

[0030] Figure 4 is a schematic diagram showing an example of a hypothetical elliptical shape Wc encompassing the outlet port 51 and the cross-section Wa of the second passage 4b, and the elliptical shape of the cross-section Wb of the fifth passage 4e. The shapes of the outlet port 51, the cross-section Wa of the second passage 4b, and the cross-section Wb of the fifth passage 4e are shown in a front view in the direction opposite to the exhaust flow. For example, the hypothetical elliptical shape Wc is in contact with two points Pa and Pb on the outer edge of the cross-section Wb of the fifth passage 4e and with two points Pc and Pd on the outer edge of the outlet port 51.

[0031] The center Ca of the virtual ellipse Wc lies on the straight line Lc connecting the center 51c of the outlet port 51 and the center 4bc of the cross-section Wa of the second passage 4b. The major axis Mc of the virtual ellipse Wc extends in the direction of the straight line Lc between the centers 51c and 4bc. The minor axis Sc of the virtual ellipse Wc extends from the center Ca in a direction perpendicular to the major axis Mc.

[0032] The major axis Mc of the hypothetical ellipse Wc is longer than the sum of the diameter R1 of the outlet port 51 and the diameter R2 of the cross-section Wb of the fifth passage 4e. Also, the minor axis Sc of the hypothetical ellipse Wc is longer than the diameter R1 of the outlet port 51 and longer than the diameter R2 of the cross-section Wb of the fifth passage 4e.

[0033] The cross-section Wb of the fifth passage 4e is similar to the hypothetical ellipse Wc. That is, if the lengths of the major axis Mb and minor axis Sb of the ellipse in the cross-section Wb of the fifth passage 4e are L1x and L1y, respectively, and the lengths of the major axis Mc and minor axis Sc of the hypothetical ellipse Wc are L2x and L2y, respectively, then the relationship L1x / L1y = L2x / L2y, or L1x / L1y ≈ L2x / L2y, holds. There are no limitations on the relative sizes of the areas of the cross-section Wb of the fifth passage 4e and the hypothetical ellipse Wc.

[0034] Furthermore, the major axis Mb and minor axis Sb of the cross-section Wb of the fifth passage 4e are substantially aligned with the major axis Mc and minor axis Sc of the hypothetical ellipse shape Wc. That is, the major axes Mb and Mc are substantially parallel to each other, and the minor axes Sb and Sc are substantially parallel to each other. For this reason, the shapes of the exhaust inlet and outlet in the section from the second passage 4b ​​to the fifth passage 4e are similar and in the same direction. Note that the major axes Mb and Mc are perpendicular to the plane of paper in Figure 2 and parallel to the plane of paper in Figure 3. Also, the minor axes Sb and Sc are parallel to the plane of paper in Figure 2 and perpendicular to the plane of paper in Figure 3.

[0035] Thus, the cross-section Wb of the fifth passage 4e and the virtual elliptical shape Wc are similar in that their orientations are aligned. As a result, the exhaust flow F1 from the outlet port 51 and the exhaust flow F2 from the second passage 4b ​​merge and flow smoothly into the fifth passage 4e, which has a curved inner wall. This makes it possible to reduce the pressure loss and heat loss of the exhaust due to the inner wall 4d2 of the fourth passage 4d, as described above. Since the heat loss of the exhaust is reduced, the catalytic converter 40 can be sufficiently warmed up and activated by the exhaust heat, improving its purification performance.

[0036] Furthermore, the air-fuel ratio sensor 42 is located at one end E1s of the short axis of the cross-section Wb of the fifth passage 4e. Therefore, the tip 42a of the air-fuel ratio sensor 42 is positioned closer to the center Cb of the cross-section Wb than if it were located at one end E1m, E2m of the long axis Mb of the cross-section Wb. Since the exhaust flows F1 and F2 are narrowed as they pass through the fourth passage 4d, the exhaust flow rate increases closer to the center Cb of the cross-section Wb. Consequently, a sufficient amount of exhaust for detecting the air-fuel ratio hits the tip 42a of the air-fuel ratio sensor 42, making it possible to ensure sufficient detection accuracy of the air-fuel ratio sensor 42. The air-fuel ratio sensor 42 may also be located at the other end E2s of the short axis Sb.

[0037] Furthermore, the air-fuel ratio sensor 42 is not limited to one end E1s of the minor axis of the cross-section Wb of the fifth passage 4e, but may also be provided at position Px on the outer edge of the cross-section Wb between one end E2m of the major axis Mb and one end E1s of the minor axis Sb, as shown by the dashed line. Position Px is an example of a position in the elliptical shape of the cross-section Wb that is closer to one end E1s of the minor axis Sb than to one end E1m, E2m of the major axis Mb. Even in this case, the tip 42a of the air-fuel ratio sensor 42 is positioned closer to the center Cb of the cross-section Wb than when it is positioned closer to one end E1m, E2m of the major axis Mb, so it is possible to ensure sufficient detection accuracy of the air-fuel ratio sensor 42. However, it is preferable for the air-fuel ratio sensor 42 to be provided at one end E1s of the minor axis of the cross-section Wb of the fifth passage 4e, as it is closer to the center Cb of the cross-section Wb.

[0038] Furthermore, the air-fuel ratio sensor 42 is positioned with its tip 42a facing the inlet 40a of the catalytic converter. This improves the contact between the air-fuel ratio sensor 42 and the exhaust gas flowing into the catalytic converter 40. Alternatively, the air-fuel ratio sensor 42 may be positioned parallel to the inlet 40a of the catalytic converter 40.

[0039] The embodiments described above are preferred examples of the present invention. However, the invention is not limited thereto, and various modifications are possible without departing from the spirit of the invention. [Explanation of symbols]

[0040] 1 Supercharger, 2 Engine (internal combustion engine), 4 Exhaust passage, 4d 4th passage (narrowed section), 4e 5th passage (elliptical section), 5 Bypass passage, 40 Catalytic converter, 41 Turbine, 42 Air-fuel ratio sensor, 42a Tip, 51 Outlet port (port), Wa, Wb Cross-section (1st and 2nd cross-sections), Wc Virtual ellipse shape, E Exhaust structure

Claims

1. A supercharger having a turbine installed in the exhaust passage of an internal combustion engine, A catalytic converter is provided in the exhaust passage downstream of the turbine, A bypass passage that branches off from the exhaust passage upstream of the turbine, bypasses the turbine, and merges with the exhaust passage upstream of the catalytic converter via a substantially circular port, The system includes an air-fuel ratio sensor that detects the air-fuel ratio from the exhaust gas in the exhaust passage, The exhaust passage between the catalytic converter and the port is provided with an elliptical portion having a second elliptical cross-section that is similar to a hypothetical ellipse shape encompassing the port and a substantially circular first cross-section of the exhaust passage between the turbine and the port, and whose major and minor axes are substantially aligned with the hypothetical ellipse shape, and a reducing portion that reduces the exhaust passage area toward the elliptical portion. The aforementioned virtual elliptical shape has a center located on a straight line connecting the centers of the port and the first cross-section, and a major axis extending in the direction of the straight line. The air-fuel ratio sensor is provided in the elliptical portion at a position closer to one end of the minor axis of the second cross-section than to one end of the major axis of the second cross-section. Exhaust structure of an internal combustion engine.

2. The air-fuel ratio sensor is provided at one end of the minor axis of the second cross-section in the elliptical portion. The exhaust structure for an internal combustion engine according to claim 1.

3. The air-fuel ratio sensor is positioned so that its tip is facing the inlet of the catalytic converter. The exhaust structure for an internal combustion engine according to claim 1 or 2.

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