Exhaust system for internal combustion engines

Abstract

An exhaust device 39 for an internal combustion engine 10 mounted in a saddle-type vehicle 10 according to one embodiment of the present invention comprises: an exhaust purification catalyst 48a provided in an exhaust passage 52 of an internal combustion engine E; and an exhaust gas sensor 46 provided in a downstream exhaust passage 52b downstream of the exhaust purification catalyst 48a. The exhaust gas sensor 46 is provided in a connecting part 70 welded to an exhaust pipe 50 that compartmentally forms the downstream exhaust passage 52b, inclined at an angle to the exhaust flow direction EF. A weld start portion B1 of a weld 70 around the connecting part 70W with respect to the exhaust pipe 50 is located non-upstream of the exhaust gas sensor 46 in the exhaust flow direction EF.

Description

Technical Field

[0001] The present invention relates to an exhaust device for an internal combustion engine mounted on a straddle-type vehicle such as a motorcycle.

Background Art

[0002] Conventionally, efforts aimed at mitigating or reducing the impact of climate change have been ongoing, and research and development related to emission improvement have been carried out to achieve this goal. For example, in internal combustion engines for vehicles including straddle-type vehicles such as motorcycles, various studies have been conducted on providing an exhaust gas sensor in an exhaust passage of the internal combustion engine to purify exhaust gas, and controlling fuel injection according to an output of the exhaust gas sensor.

[0003] For example, Patent Document 1 discloses providing a mounting portion, into which an oxygen concentration sensor is screwed, on a straight pipe portion of an exhaust manifold of an internal combustion engine of a motorcycle that is a scooter-type vehicle. The mounting portion is provided by being welded to the straight pipe portion of the exhaust manifold, and a threaded portion (female thread) corresponding to the threaded portion (male thread) of the oxygen concentration sensor is provided on an inner peripheral surface of the mounting portion. The mounting portion is obliquely welded to the straight pipe portion of the exhaust manifold, and in an attached state, the protector side (oxygen detection side) of the oxygen concentration sensor is obliquely inserted into the exhaust manifold from the upstream side toward the downstream side of exhaust gas. That is, the output signal line side (wiring side) of the oxygen concentration sensor is positioned on the cylinder head side of the engine. This reduces the flow resistance of exhaust gas in the exhaust manifold and enables accurate oxygen concentration measurement without impeding the flow of exhaust gas.

Prior Art Literature

Patent Literature

[0004]

Patent Document 1

Summary of the Invention

Problem to be Solved by the Invention

[0005] Incidentally, in improving emissions, it is desirable to further improve the detection accuracy of exhaust gas sensors such as the oxygen concentration sensor mentioned above. For example, when the mounting part for attaching the exhaust gas sensor, in other words, the connection part, is welded to the exhaust pipe, welding is performed continuously around the entire circumference of the connection part, and the welding is performed until it overlaps with the starting point of the welding. In other words, in that welding, the starting point and the ending point of the welding overlap. Therefore, the weld bead may be thicker at the starting point of the welding (i.e., the ending point of the welding) compared to other places, and thus the weld bead, or back bead, is more likely to appear on the inside of the exhaust pipe. Depending on the amount of protrusion of this back bead, the flow of exhaust gas to the exhaust gas sensor may be affected. In particular, when the exhaust gas sensor is positioned at an angle to the direction of exhaust flow, the amount of protrusion of the sensor detection part at the tip into the exhaust passage is smaller compared to when it is positioned perpendicular to the direction of exhaust flow, so the influence of such back beads on the exhaust flow may more strongly affect the detection capability.

[0006] Furthermore, the influence of such back beads on exhaust gas sensors should be given particular consideration in exhaust gas sensors located downstream of the exhaust catalytic converter in the exhaust passage of an internal combustion engine. This is because the exhaust gas velocity decreases as the exhaust gas passes through the exhaust catalytic converter, suppressing the gas flow toward the sensor detection unit. Therefore, detecting exhaust gas components with an exhaust gas sensor located downstream of the exhaust catalytic converter may be more difficult than detection with an exhaust gas sensor located upstream of the exhaust catalytic converter.

[0007] The object of the present invention is to provide a configuration that reduces the influence of the welding bead at the connection point of an exhaust gas sensor on the detection accuracy of an exhaust gas sensor when the exhaust gas sensor is installed at an angle to the exhaust passage downstream of the exhaust gas purification catalyst in an exhaust system for an internal combustion engine mounted on a saddle-type vehicle such as a motorcycle. This will ultimately contribute to mitigating or reducing the impact of climate change. [Means for solving the problem]

[0008] To achieve the above objective, one aspect of the present invention is: An exhaust system for an internal combustion engine mounted on a saddle-type vehicle, An exhaust gas purification catalyst is provided in the exhaust passage of the internal combustion engine, An exhaust gas sensor is provided in the downstream exhaust passage on the downstream side of the exhaust gas purification catalyst. Equipped with, The exhaust gas sensor is provided at a connection point welded to the exhaust pipe that partitions the downstream exhaust passage, so as to be inclined at an angle with respect to the direction of exhaust flow. The welding start point in the weld around the connection to the exhaust pipe is located on the non-upstream side of the exhaust gas sensor in the exhaust flow direction. Exhaust system characterized by To provide.

[0009] According to the above configuration, the welding start point is located on the non-upstream side of the exhaust gas sensor in the exhaust flow direction. Therefore, the welding start point is not located on the upstream side of the exhaust gas sensor, which suppresses the thickness of the weld bead on the upstream side of the exhaust gas sensor, and thus allows for a more favorable flow of exhaust gas from the exhaust gas purification catalyst to the exhaust gas sensor. Consequently, in the exhaust system of an internal combustion engine mounted on a saddle-type vehicle, it is possible to reduce the impact of the weld bead at the connection point of the exhaust gas sensor downstream of the exhaust gas purification catalyst on the detection accuracy of the exhaust gas sensor. Thus, it is possible to improve the detection accuracy of the exhaust gas sensor.

[0010] Preferably, the welding start point is located downstream in the exhaust flow direction from a virtual plane defined so as to pass through the intersection of the extended surface of the exhaust pipe and the axis of the connection point, and perpendicular to the exhaust flow direction. With this configuration, the welding start point in the weld around the connection point can be more reliably positioned on the non-upstream side of the exhaust gas sensor in the exhaust flow direction.

[0011] Preferably, the welding start portion is located within the region of the downstream width of the connection portion. With this configuration, the welding start portion in the weld around the connection portion can be more reliably positioned downstream of the exhaust gas sensor in the exhaust flow direction. This further suppresses the effect of obstruction of the exhaust gas flow by the weld bead around the connection portion, and thus the detection accuracy of the exhaust gas sensor can be further improved.

[0012] Preferably, when a virtual plane is defined passing through the intersection of the extended surface of the exhaust pipe and the axis of the connection part, and perpendicular to the exhaust flow direction, the inclination of the axis of the exhaust gas sensor with respect to the virtual plane is between 10° and 45°. With this configuration, the sensor detection part of the exhaust gas sensor can be sufficiently separated from the inner wall surface of the exhaust pipe, and the sensor detection part itself can be effectively prevented from becoming a resistance to the exhaust flow.

[0013] Preferably, the exhaust gas sensor has a sensor detection unit located in the exhaust passage and a sensor body extending outside the exhaust passage, and the sensor detection unit is located downstream of the sensor body in the exhaust flow direction. With this configuration, the sensor detection unit of the exhaust gas sensor can be arranged along the exhaust flow direction. Therefore, even if the flow velocity of the exhaust gas around the exhaust gas sensor is very high, the pressure loss of the exhaust gas due to the exhaust gas sensor can be reduced.

[0014] Preferably, the exhaust gas purification device having the exhaust gas purification catalyst inside comprises a main body on which a carrier supporting the exhaust gas purification catalyst is arranged, and a diameter-reducing portion connected downstream of the main body in the exhaust flow direction and decreasing in diameter as it approaches the downstream side in the exhaust flow direction, the connection portion being located downstream of the diameter-reducing portion in the exhaust flow direction, and the exhaust gas sensor having a sensor detection unit located in the exhaust passage and a sensor body extending outside the exhaust passage, the sensor detection unit being located downstream of the sensor body in the exhaust flow direction. With this configuration, the exhaust gas sensor can be positioned downstream of the diameter-reducing portion of the purification device, and the sensor detection unit of the exhaust gas sensor can be arranged along the exhaust flow direction. Therefore, even if the flow velocity of the exhaust gas flowing around the exhaust gas sensor after passing through the purification device is very high, the pressure loss of the exhaust gas due to the exhaust gas sensor can be reduced. [Effects of the Invention]

[0015] According to one aspect of the present invention, since the above configuration is provided, when an exhaust gas sensor is installed at an angle to the exhaust passage downstream of the exhaust gas purification catalyst in an exhaust system for an internal combustion engine mounted on a saddle-type vehicle, it is possible to reduce the influence of the welding bead at the connection part of the exhaust gas sensor on the detection accuracy of the exhaust gas sensor. [Brief explanation of the drawing]

[0016] [Figure 1] Figure 1 is a left side view of a motorcycle, which is a saddle-type vehicle according to one embodiment of the present invention. [Figure 2] Figure 2 is a front view of a portion of the motorcycle shown in Figure 1. [Figure 3] Figure 3 is a bottom view of a part of the motorcycle shown in Figure 1. [Figure 4] Figure 4 shows a modified example of the exhaust system of the internal combustion engine in the motorcycle shown in Figure 1. [Figure 5] Figure 5 is an enlarged perspective view of the exhaust gas sensor and its mounting location in the exhaust system of the internal combustion engine of the motorcycle shown in Figure 1. [Figure 6]Fig. 6 is an enlarged view of an exhaust gas sensor in an exhaust device removed from the motorcycle of Fig. 1 and the periphery of the mounting position of the exhaust gas sensor. [Figure 7] Fig. 7 is an enlarged cross-sectional view of the periphery of the exhaust gas sensor shown in Fig. 6. [Figure 8] Fig. 8 is a view of the exhaust gas sensor shown in Fig. 6 as viewed from a cut surface side, wherein an exhaust pipe is cut at a downstream side of the exhaust gas sensor. [Figure 9] Fig. 9 is a schematic cross-sectional view of a welded portion when two plate members are welded by arc welding. [Figure 10] Fig. 10 is a plan view of the periphery of a connection portion of the exhaust gas sensor shown in Fig. 6, and is a schematic diagram showing a welding start portion in a welded portion around the connection portion and a welding direction from the welding start portion. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0017] Hereinafter, a motorcycle 10 which is a straddle-type vehicle according to an embodiment of the present invention will be described with reference to the accompanying drawings. Here, the up-down, front-rear, left-right directions of the vehicle body are defined based on the line of sight of a driver riding on the motorcycle 10. In the drawings, the symbol "UP" is used for the upper side in the vertical direction, the symbol "DW" is used for the lower side, the symbol "FR" is used for the front side in the vehicle front-rear direction, the symbol "RR" is used for the rear side, the symbol "RH" is used for the right side in the vehicle width direction, and the symbol "LH" is used for the left side.

[0018] Fig. 1 shows a left side view of the motorcycle 10, that is, a side view from the right side of the vehicle body. Fig. 2 shows a partial front view of the motorcycle 10, that is, a front view. Fig. 3 shows a partial bottom view of the motorcycle 10 of Fig. 1.

[0019] The motorcycle 10 is equipped with a body frame 12 that houses the power unit and electrical components. The main tube (not shown) of the body frame 12 extends rearward from a head pipe 14 located at the front end. Behind the head pipe 14 is a fuel tank 18 that contains fuel. Behind this fuel tank 18 is a seat 20 on which the driver sits. Below the seat 20 is a footrest 22 that serves as a footrest for the driver while driving.

[0020] Near the footrest 22 on the right side of the vehicle body shown in Figure 1, a brake pedal 24 for the rear wheel WR, which is the drive wheel, is provided. The brake pedal 24 has a rear end 24r located behind the footrest 22 that is pivotally supported, and a front end 24f located in front of the footrest 22 that is provided to swing up and down. In a side view of the motorcycle 10 in Figure 1, the brake pedal 24 is shaped to first extend roughly horizontally from the rear end 24r to the front end 24f, and then to tilt slightly upward and forward. In other words, in a side view of the motorcycle 10, the brake pedal 24 extends in the front-to-back direction without tilting roughly in the up-to-down direction. The front end 24f of the brake pedal 24 functions as a pedal and is located to the right of the front end portion of the crankcase 30, which will be described later, and is also located at roughly the same height as the footrest 22, and can be operated by pressing it with the driver's foot placed on the footrest 22.

[0021] Furthermore, near the footrest 22 on the right side of the vehicle body as shown in Figure 1, a kick pedal 25 is provided, particularly above the footrest 22. The kick pedal 25 has a rear end 25r positioned roughly above the footrest 22 and a front end 25f positioned near the rear of the cylinder head 34 of the engine body 26 of the internal combustion engine E of the power unit. The kick pedal 25 extends upward first from the rear end 25r towards the front end 25f, and then curves forward. When in use, the kick pedal 25 is unfolded to extend outward in the vehicle width direction. The front end 25f of the kick pedal 25 functions as a pedal and is pressed down by the driver's foot. This pressing causes the kick pedal 25 to rotate within a predetermined range around the rear end 25r, thereby starting the internal combustion engine E.

[0022] The engine body 26 of the internal combustion engine E is suspended from the main tube of the vehicle frame 12. The engine body 26 comprises the aforementioned crankcase 30, and a cylinder block 32, cylinder head 34, and head cover 36, which are sequentially located above the crankcase 30. The cylinder block 32 is connected to the top of the crankcase 30 in a forward-tilting position. Therefore, as shown in Figure 1, the cylinder axis C of the cylinders of the engine body 26 is tilted diagonally forward from the crankshaft side of the crankcase 30 toward the cylinder head 34 side. The crankshaft extends in the vehicle width direction and is roughly perpendicular to the vertical and longitudinal directions. Figure 1 shows the rotation axis 38 of the crankshaft.

[0023] The upper (upstream) end of the exhaust pipe 40 of the exhaust system 39 of the internal combustion engine E is connected to the cylinder head 34 of the engine body 26. The exhaust gas discharged from the combustion chamber (not shown) flows through the exhaust pipe 40 and is discharged from the muffler 42 located to the right of the rear wheel WR, i.e., to the rear right side of the vehicle body. Exhaust gas sensors 44, 46 and a purification device 48 are provided at the front end, i.e., the upstream side, of the muffler 42. The exhaust port of the cylinder head 34, the exhaust pipe 40, the purification device 48, the exhaust pipe 50, and the muffler 42 are connected in this order in the direction of exhaust flow, and each partitions a part of the exhaust passage 52.

[0024] The front fork 54 is rotatably supported at the front end of the main tube via a steering shaft provided in the head pipe 14. A handlebar 56 is provided at the upper end of the steering shaft, and grips 58 are attached to both ends of the handlebar 56. The front wheel WF is rotatably supported at the lower part of the front fork 54. The upper part of the front wheel WF is partially covered by a front fender 60.

[0025] Furthermore, a rear wheel WR, to which power from the internal combustion engine E is transmitted via a swingarm, is rotatably supported behind the engine body 26. A suspension 62 is positioned between the swingarm and the vehicle frame 12 to mitigate shocks from the road surface. A rear fender 64 is positioned above and behind the rear of the rear wheel WR, and behind the seat 20.

[0026] As mentioned above, the exhaust pipe 40 of the exhaust system 39 is connected to the front wall of the cylinder head 34 of the engine body 26, and downstream there, the purification device 48 and the muffler 42 are arranged in order from the upstream side. The purification device 48 is configured to have the function of purifying exhaust gas, and in particular houses an exhaust gas purification catalyst 48a inside, that is, it has a carrier 48b that supports the catalyst 48a. Here, the carrier 48b has a honeycomb substrate in which a plurality of cells extending from the exhaust gas inlet side end face (upstream side end face) to the outlet side end face (downstream side end face) are partitioned by porous partition walls, and the catalyst 48a is supported on the partition walls of this honeycomb substrate. The catalyst 48a here is a three-way catalyst (TWC), and has the function of purifying exhaust gas by oxidizing or reducing HC to H2O and CO2, CO to CO2, and NOx to N2, respectively (i.e., three-way purification function). The support 48b consists of oxides such as alumina, silica, zirconia, titania, ceria, and zeolite, and the ternary catalyst contains precious metals such as platinum, palladium, and rhodium.

[0027] Of the exhaust passages 52, an exhaust gas sensor 44 is provided in the upstream exhaust passage 52a of the purification device 48, and an exhaust gas sensor 46 is provided in the downstream exhaust passage 52b of the purification device 48. In this case, the exhaust gas sensors 44 and 46 are oxygen (O2) sensors that output a signal according to the oxygen concentration in the exhaust gas, but they may also be LAF sensors (linear air-fuel ratio sensors), which are a type of air-fuel ratio sensor. The muffler 42 is configured to have a sound-dampening function.

[0028] As shown in Figure 1, the exhaust passage 52, which extends from the exhaust port of the cylinder head 34 of the engine body 26, extends forward of the engine body 26, then downward, and further extends backward through the lower part of the engine body 26 to the right side of the rear wheel WR. In other words, the exhaust device 39 extends from the front of the engine body 26 of the internal combustion engine E downward, and extends to the right rear through the lower right part of the engine body 26. As shown in Figures 1 to 3, the purification device 48 is located below the vehicle, on the lower right side of the engine body 26, and in particular, below the crankcase 30. In Figure 1, the purification device 48 is arranged to extend approximately horizontally on the lower side of the engine body 26. Therefore, as shown in the front view of the motorcycle 10 in Figure 2 and the bottom view of the motorcycle 10 in Figure 3, the purification device 48 is located to the right of a central virtual plane CIS that extends from the front to the rear of the motorcycle 10 in the left-right direction, and is installed on the motorcycle 10 such that the downstream portion of the purification device 48 faces slightly outward in the vehicle width direction compared to the upstream portion of the purification device 48. The central virtual plane CIS can be defined to be perpendicular to the vehicle width direction and to substantially bisect the front wheel WF and the rear wheel WR.

[0029] The exhaust pipe 50, which demarcates the downstream exhaust passage 52b extending rearward from the purification device 48, extends rearward from the downstream end of the purification device 48 on the right rear lower side of the crankcase 30 of the engine body 26. In the side view of Figure 1, the exhaust pipe 50 is provided to extend roughly along the brake pedal 24 in the longitudinal direction of the vehicle. As shown in Figures 1 to 3, the exhaust pipe 50 extends from the upstream end connected to the purification device 48, tilting slightly upward and slightly outward as it proceeds downstream in the exhaust flow direction, i.e., towards the rear of the vehicle, and connects to the muffler 42. The muffler 42 extends to the right of the rear wheel WR in the longitudinal direction of the vehicle and is positioned to tilt slightly upward as it proceeds downstream in the exhaust flow direction.

[0030] The aforementioned exhaust gas sensor (hereinafter referred to as the downstream exhaust gas sensor) 46 located downstream of the purification device 48 is installed in the exhaust pipe 50 that partitions the downstream exhaust passage 52b, which is the exhaust passage downstream of the purification device 48. Here, as shown in Figure 1, the downstream exhaust gas sensor 46 is located between the rear end 24r and the front end 24f of the brake pedal 24, closer to the rear end 24r, and is installed on the upper side of the exhaust pipe 50. Also, as shown in Figures 2 and 3, the downstream exhaust gas sensor 46 is positioned on the upper inner side of the exhaust pipe 50. Therefore, in the front view of the motorcycle 10 in Figure 2, the connection portion 70 of the downstream exhaust gas sensor 46 to the exhaust pipe 50 is hidden behind the purification device 48, and a part of the downstream exhaust gas sensor 46 is also hidden behind the purification device 48. Thus, it is possible to suitably protect the downstream exhaust gas sensor 46 from flying objects such as stones kicked up by the front wheel WF. Furthermore, as shown in Figure 1, the downstream exhaust gas sensor 46 is mounted on the exhaust pipe 50 so as to be inclined at an angle with respect to the exhaust flow direction. Therefore, in the front view of the motorcycle 10 in Figure 2, the amount of protrusion of the downstream exhaust gas sensor 46 from the exhaust pipe 50 is smaller compared to the case where it is mounted on the exhaust pipe 50 perpendicular to the exhaust flow direction. Thus, the downstream exhaust gas sensor 46 can be more effectively protected from flying objects.

[0031] Furthermore, the downstream exhaust gas sensor 46, which is positioned on the upper inner side of the exhaust pipe 50 so as to be hidden behind the purification device 48, is located behind and slightly below the footrest 22, which extends substantially parallel to the purification device 48 so as to protrude to the right outer side of the purification device 48, as shown in Figure 1. Therefore, the downstream exhaust gas sensor 46 is not affected by the driver's operation of the brake pedal 24 and is more preferably protected on the inside of the driver's foot.

[0032] Furthermore, the exhaust gas sensor 46 can be seen from the outside of the vehicle body in Figures 1 to 3, thus ensuring good ease of installation and maintenance.

[0033] Here, the aforementioned exhaust gas sensor (hereinafter referred to as the upstream exhaust gas sensor) 44, which is provided in the exhaust passage 52a upstream of the purification device 48, is attached to the cylinder head 34. The upstream exhaust gas sensor 44 can detect the oxygen concentration of the exhaust gas in the exhaust port partitioned in the cylinder head 34. However, the upstream exhaust gas sensor 44 is not limited to being provided facing the exhaust port, and may be provided in the exhaust pipe 40 as shown in Figure 4. Figure 4 is a diagram showing the exhaust pipe 40, purification device 48, and exhaust pipe 50, which each partition a part of the exhaust passage 52 extending from the engine body 26 of the internal combustion engine E, and is a modified example in which the upstream exhaust gas sensor 44 is provided in the exhaust pipe 40, unlike the exhaust system 39 of the internal combustion engine E shown in Figure 1. Thus, the upstream exhaust gas sensor 44 can be provided at any location between the exhaust port and the upstream end of the main body 48d of the purification device 48, which houses the carrier 48b that supports the exhaust gas purification catalyst 48a.

[0034] The control unit for the internal combustion engine E, or ECU (Engine Control Unit), is not shown in the diagram, but it is installed in the motorcycle 10 and has a computer-like configuration. In other words, the ECU includes a processor (e.g., CPU) and memory (e.g., ROM, RAM). The ECU receives output signals from various sensors. For example, in addition to engine load sensors such as an engine speed sensor and a throttle opening sensor, the upstream exhaust gas sensor 44 and downstream exhaust gas sensor 46 mentioned above are connected to the ECU. Based on the inputs from these sensors, the ECU analyzes the operating state and controls the operation of, for example, the fuel injector, spark plug, and throttle valve (not shown) based on the analyzed operating state. For example, based on the inputs (or outputs) from the upstream exhaust gas sensor 44 and the downstream exhaust gas sensor 46, the ECU controls fuel injection from the fuel injector so that the exhaust gas is suitably purified by the purification device 48. However, the throttle valve is not limited to being electronically controlled and may have a mechanically operated configuration.

[0035] Now, as mentioned above, the downstream exhaust gas sensor 46 is installed in the exhaust pipe 50 so as to be inclined at an angle with respect to the exhaust flow direction EF. Figure 5 shows an enlarged perspective view of the downstream exhaust gas sensor 46 and the area around its mounting location. The downstream exhaust gas sensor 46 is installed in a connection portion 70 welded to the exhaust pipe 50 that partitions the downstream exhaust passage 52b, so as to be inclined at an angle with respect to the exhaust flow direction EF. The connection portion 70 is a connecting member, or connecting holder, and more specifically, a tubular boss member, having a through hole 70h (see Figure 7) with an axis 70a, and is a slip-on weld type member. As shown in Figure 5, the connection portion 70 is connected to the mounting hole 50h of the exhaust pipe 50 by welding, in this case by arc welding. To prevent any gap from being left between the connection portion 70 and the exhaust pipe 50, a weld bead 70b is formed around the entire circumference of the connection portion 70.

[0036] Here, Figure 6 shows an enlarged view of the downstream exhaust gas sensor 46 and its mounting location in the exhaust system 39 removed from the motorcycle 10, and Figure 7 shows an enlarged cross-sectional view of the downstream exhaust gas sensor 46. However, in Figures 6 and 7, the weld bead 70b is omitted, and in Figure 7, the downstream exhaust gas sensor 46 is not shown in cross-section. Furthermore, Figure 8 shows the exhaust gas sensor 46 as seen from the cut end side after the exhaust pipe 50 has been cut at the downstream side of the downstream exhaust gas sensor 46 shown in Figure 6.

[0037] The connecting portion 70 has a threaded portion (female thread) 70c formed on its inner circumferential surface 70i, which demarcates the substantially cylindrical, straight through hole 70h, for mounting the downstream exhaust gas sensor 46. A threaded portion (male thread) 46b corresponding to this threaded portion 70c is formed on the outer circumference of the downstream exhaust gas sensor 46. Therefore, the downstream exhaust gas sensor 46 is screwed into the connecting portion 70. At this time, the annular, radially protruding contact portion 46c of the downstream exhaust gas sensor 46 abuts against the contacted portion 70d of the connecting portion 70. With the downstream exhaust gas sensor 46 attached to the connecting portion 70 in this way, the axis 46a of the downstream exhaust gas sensor 46 coincides with the axis 70a of the through hole 70h demarcated by the inner circumferential surface 70i of the connecting portion 70. In addition, these axes 46a and 70a intersect with the axis 50a of the exhaust pipe 50, which extends in the exhaust flow direction EF. Therefore, since the section of the exhaust pipe 50 where the connection section 70 is provided is generally a straight section of pipe (straight pipe section), the axis 50a of the exhaust pipe 50, the axis 70a of the connection section 70, and the axis 46a of the downstream exhaust gas sensor 46 generally extend on the same plane. Note that the axes 46a and 70a may extend without intersecting the axis 50a of the exhaust pipe 50, that is, without intersecting at a single point, but with a certain allowable distance between them.

[0038] The connecting portion 70 is welded diagonally to the exhaust pipe 50 and has a tip attachment portion 70e shaped such that its axis 70a is inclined with respect to the exhaust flow direction EF of the downstream exhaust passage 52b. The tip attachment portion 70e is curved to conform to the curved shape of the exhaust pipe 50, which has a substantially circular cross-section, and has a concave curved surface that is inclined with respect to the axis 70a. The tip attachment portion 70e is located closer to the exhaust pipe 50 than the contacted portion 70d in the direction of the axis 70a of the connecting portion 70, and is located at one end of the connecting portion 70 in the direction of the axis 70a, i.e., the tip. The other end of the connecting portion 70 in the direction of the axis 70a is the aforementioned contacted portion 70d. The connecting portion 70 is attached to the hole 50h of the exhaust pipe 50 by welding around the tip attachment portion 70e so that the connecting portion 70 does not protrude into the downstream exhaust passage 52b.

[0039] By attaching the exhaust gas sensor 46 to the connection part 70 attached to the exhaust pipe 50 in this manner, the sensor detection part 46d at its tip is located in the downstream exhaust passage 52b, and the sensor body part 46e having the aforementioned contact part 46c extends outside the downstream exhaust passage 52b. The inclination of the downstream exhaust gas sensor 46 with respect to the exhaust flow direction EF is determined such that the sensor detection part 46d is located downstream of the sensor body part 46e in the exhaust flow direction EF. This allows the sensor detection part 46d to be positioned in the downstream exhaust passage 52b of the exhaust pipe 50 so as to smoothly follow the exhaust gas flowing in the exhaust flow direction EF.

[0040] The inclination of the downstream exhaust gas sensor 46 is such that, as shown in Figure 7, when a virtual plane EIS is defined that is perpendicular to the exhaust flow direction EF, the inclination θ of the axis 46a of the downstream exhaust gas sensor 46 with respect to that virtual plane EIS is between 10° and 45°. The virtual plane EIS is preferably defined to take into account the hole 50h of the exhaust pipe 50, passing through the intersection point CP of the extended surface 50s of the surface 50s of the exhaust pipe 50 and the axis 70a of the connection part 70, and being perpendicular to the exhaust flow direction EF. By setting the inclination θ to 10° or more, the amount of protrusion of the sensor detection part 46d into the downstream exhaust passage 52b is reduced compared to when the inclination θ is less than 10°, and it is possible to suppress the sensor detection part 46d from becoming a resistance to the exhaust gas flow. Furthermore, by keeping the inclination θ within 45°, it becomes possible to ensure that the distance between the sensor detection unit 46d and the exhaust pipe 50 itself or the weld bead 70b, i.e., the back bead B described later, is greater than a predetermined distance, compared to the case where the inclination θ is at an angle greater than 45°.

[0041] Furthermore, as shown in Figure 6, the connection portion 70 is provided so as to position the sensor detection unit 46d of the downstream exhaust gas sensor 46 at a predetermined distance range (first predetermined distance range) in the exhaust flow direction EF from the downstream end 48c of the carrier 48b on which the exhaust gas purification catalyst 48a of the purification device 48 is supported. This first predetermined distance range can be defined as a range that allows the sensor detection unit 46d of the downstream exhaust gas sensor 46 to be positioned in a region where the exhaust gas that has passed through the purification device 48, i.e., the exhaust gas purification catalyst 48a, diffuses to a certain extent uniformly in the downstream exhaust passage 52b. In addition, it is preferable that this first predetermined distance range be defined so as not to affect the downstream exhaust gas sensor 46 with respect to the heat of the exhaust gas purification catalyst 48a, i.e., the carrier 48b on which the purification device 48 is supported. Here, the purification device 48 comprises a main body 48d on which a carrier 48b supporting an exhaust gas purification catalyst 48a is arranged, and a diameter-reducing section 48e connected downstream of the main body 48d in the exhaust flow direction EF, which decreases in diameter as it approaches the downstream side in the exhaust flow direction EF. Therefore, the first predetermined distance range is preferably set to a distance that positions the sensor detection section 46d of the downstream exhaust gas sensor 46 downstream of the diameter-reducing section 48e. The first predetermined distance range may be determined in relation to the average diameter of the exhaust pipe 50, but is not limited thereto, and may be determined according to, for example, the shape of the exhaust pipe 50, the size of the motorcycle 10 and / or the size of the internal combustion engine E.

[0042] Furthermore, the connection section 70 is provided so that the sensor detection unit 46d of the downstream exhaust gas sensor 46 is positioned at a distance within a second predetermined distance range in the exhaust flow direction EF from the drain hole 51h for removing condensed water from the exhaust passage 52. As shown in Figure 1, the drain hole 51h is located downstream of the downstream exhaust gas sensor 46 in the exhaust flow direction EF, and in this case, it is located near the upstream end of the muffler 42. The drain hole 51h may also be provided in the exhaust pipe 50. Since air can enter through this drain hole 51h, if the downstream exhaust gas sensor 46 is too close to the drain hole 51h, the downstream exhaust gas sensor 46 will be affected by the oxygen in the air that has entered. Therefore, the second predetermined distance range is defined to reduce this effect. This second predetermined distance range should be defined so that a compact arrangement of the downstream exhaust gas sensor 46 on the motorcycle 10 is also possible. The second predetermined distance range may be determined in relation to the average diameter of the exhaust pipe 50, but is not limited thereto, and may be determined according to, for example, the shape and / or arrangement of the exhaust pipe 50.

[0043] By the way, when arc welding is performed to connect the connection part 70 to the exhaust pipe 50, a weld bead 70b usually appears not only on the front side (outside of the exhaust pipe 50) where the electrode is located, but also on the back side (inside of the exhaust pipe 50). For example, Figure 9 shows a schematic cross-sectional view of the weld when two plate materials M1 and M2 are welded by arc welding. Figure 9 shows that the plate materials M1 and M2 are welded by arc welding, and a weld bead MB is formed between them. If the upper side MU in Figure 9 is the front side, i.e., the welding work side, then it can be seen that a weld bead MB also protrudes from the lower side MD in Figure 9, which is the opposite side.

[0044] Such a back-side weld bead, or back bead B, can also be formed during the welding of the connection portion 70 to the exhaust pipe 50. In particular, when welding a tubular connection portion 70, a continuous weld bead 70b is formed around the connection portion 70. As schematically shown in Figure 10, the weld bead 70b starts from the welding start portion B1, is formed continuously around the connection portion 70 from the welding start portion B1, and ends at the welding end portion B2 which overlaps with the welding start portion B1. In this way, since the welding start portion B1 overlaps with the welding end portion B2, the thickness of the weld bead 70b at the welding start portion B1 is greater than at other locations, and the back bead B there is also thicker than at other locations, which may increase the amount of protrusion into the exhaust pipe 50 compared to other locations. Therefore, even when the weld bead 70B is formed such that the back bead B protrudes around the connection portion 70, that is, into the inner region 50hi of the mounting hole 50h shown in Figure 8, the welding start point B1 in the weld portion 70W around the connection portion 70 to the exhaust pipe 50 is positioned on the non-upstream side of the downstream exhaust gas sensor 46 in the exhaust flow direction EF, in order to reduce the impact of the back bead B on the detection accuracy of the downstream exhaust gas sensor 46. (See Figure 10.) "Non-upstream side" refers to a side other than the upstream side of the downstream exhaust gas sensor 46 in the exhaust flow direction EF. For example, the welding start point B1 on the non-upstream side of the downstream exhaust gas sensor 46 can be positioned so that when the exhaust gas passes around the back bead at the location of the welding start point B1 in the exhaust flow direction EF, the exhaust gas does not directly reach the sensor detection unit 46d. In Figure 10, the welding direction from the welding start point B1 is shown clockwise by arrow A1, but it is not limited to this and may be counterclockwise.

[0045] Specifically, in this case, the welding start point B1 is located downstream in the exhaust flow direction EF from the virtual plane EIS (see Figure 7), which is defined to pass through the intersection point CP of the extended surface of the exhaust pipe 50 and the axis 70a of the connection point 70 and be perpendicular to the exhaust flow direction EF. In other words, in Figure 10, the welding start point B1 is located downstream of the virtual plane EIS in the exhaust flow direction EF.

[0046] Furthermore, in this embodiment, in order to more reliably prevent the influence of the back bead B at the welding start point B1, the welding start point B1 is positioned in the region within the downstream width 70r of the connection point 70. As shown in Figure 10, the region within the downstream width 70r of the connection point 70 refers to the region that extends downstream of the connection point 70 in the exhaust flow direction EF, when the length of the connection point 70 in the direction perpendicular to the exhaust flow direction EF is defined as the width of the connection point 70, i.e., the downstream width 70r.

[0047] The characteristic configuration of the exhaust system 39 of the internal combustion engine E in the motorcycle 10 having the above configuration, and its operation and effects, will be described below.

[0048] In the internal combustion engine E mounted on the motorcycle 10, which is a saddle-type vehicle, an exhaust system 39 is connected to the engine body 26. The exhaust system 39 comprises an exhaust gas purification catalyst 48a provided in the exhaust passage 52 and a downstream exhaust gas sensor 46 provided in the downstream exhaust passage 52b downstream of the exhaust gas purification catalyst 48a. The downstream exhaust gas sensor 46 is provided in a connection portion 70 welded to the downstream exhaust pipe 50 that partitions the downstream exhaust passage 52b, so as to be inclined at an angle with respect to the exhaust flow direction EF. The welding start portion B1 in the welded portion 70W around the connection portion 70 to the exhaust pipe 50 is located on the non-upstream side of the downstream exhaust gas sensor 46 in the exhaust flow direction EF. With this configuration, the welding start portion B1 is located on the non-upstream side of the downstream exhaust gas sensor 46 in the exhaust flow direction EF. Therefore, the welding start point B1 is not located upstream of the downstream exhaust gas sensor 46, and the thickness of the welding bead 70b upstream of the downstream exhaust gas sensor 46 can be suppressed, thereby maintaining a more favorable flow of exhaust gas from the exhaust gas purification catalyst 48a to the downstream exhaust gas sensor 46. Consequently, in the exhaust system 39 of the internal combustion engine E mounted on the motorcycle 10, it is possible to reduce the influence of the welding bead 70b of the connection portion 70 of the downstream exhaust gas sensor 46 downstream of the exhaust gas purification catalyst 48a on the detection accuracy of the downstream exhaust gas sensor 46. Thus, it is possible to improve the detection accuracy of the downstream exhaust gas sensor 46.

[0049] In particular, in this embodiment, the welding start point B1 is located downstream of the virtual plane EIS in the exhaust flow direction EF. With this configuration, the welding start point B1 in the welded section 70W around the connection point 70 can be more reliably positioned on the non-upstream side of the downstream exhaust gas sensor 46 in the exhaust flow direction EF, thereby providing the above-mentioned effects.

[0050] Furthermore, in this embodiment, the welding start portion B1 is positioned within the region of the downstream width 70r of the connection portion 70. With this configuration, the welding start portion B1 in the weld portion 70W around the connection portion 70 can be more reliably positioned downstream of the downstream exhaust gas sensor 46 in the exhaust flow direction EF. This further suppresses the effect of obstruction of the exhaust gas flow by the welding bead 70b, and thus the detection accuracy of the downstream exhaust gas sensor 46 can be further improved. Note that the welding start portion B1 is not limited to being positioned within the region of the downstream width 70r of the connection portion 70, but can be positioned at any location on the non-upstream side of the downstream exhaust gas sensor 46 in the exhaust flow direction EF.

[0051] Furthermore, the inclination θ of the axis 46a of the downstream exhaust gas sensor 46 with respect to the virtual plane EIS is preferably between 10° and 45°. With this configuration, the sensor detection unit 46d of the downstream exhaust gas sensor 46 can be sufficiently separated from the inner wall surface 50i of the exhaust pipe 50 (see Figure 8), and the sensor detection unit 46d itself can be effectively suppressed from becoming a resistance to the exhaust flow.

[0052] The connection section 70 is provided such that the sensor detection unit 46d of the downstream exhaust gas sensor 46 is positioned at a distance within a first predetermined distance range in the direction of exhaust flow from the downstream end 48c of the carrier 48b on which the exhaust gas purification catalyst 48a is supported. With this configuration, the downstream exhaust gas sensor 46 can be positioned at an appropriate distance from the exhaust gas purification catalyst 48a. Therefore, it becomes easier to direct the exhaust gas, which has been diffused to a certain extent uniformly within the exhaust pipe 50, to the sensor detection unit 46d, and the detection accuracy of the downstream exhaust gas sensor 46 can be substantially improved. Furthermore, with this configuration, since the exhaust gas purification catalyst 48a, i.e., the purification device 48, may have high temperatures, it becomes possible to position the downstream exhaust gas sensor 46 at an appropriate distance from the exhaust gas purification catalyst 48a, thereby enabling the maintenance of the performance of the downstream exhaust gas sensor 46 to be favorably achieved.

[0053] Furthermore, the connection section 70 is provided such that the sensor detection section 46d of the downstream exhaust gas sensor 46 is positioned at a distance within a second predetermined distance range in the exhaust flow direction from the drain hole 51h for removing condensed water from the exhaust passage 52. With this configuration, it is possible to suppress the downstream exhaust gas sensor 46 from being affected by oxygen in the atmosphere that may enter through the drain hole 51h.

[0054] Furthermore, the downstream exhaust gas sensor 46 has a sensor detection unit 46d located in the exhaust passage 52 and a sensor body 46e extending outside the exhaust passage 52. The sensor detection unit 46d is located downstream of the sensor body 46e in the exhaust flow direction EF. With this configuration, the sensor detection unit 46d of the downstream exhaust gas sensor 46 can be positioned along the exhaust flow direction EF. Therefore, even if the flow velocity of the exhaust gas around the downstream exhaust gas sensor 46 is very high, the pressure loss of the exhaust gas due to the downstream exhaust gas sensor 46 can be reduced.

[0055] Furthermore, the purification device 48, which has an exhaust gas purification catalyst 48a inside, comprises a main body 48d on which a carrier 48b supporting the exhaust gas purification catalyst 48a is arranged, and a diameter-reducing section 48e that connects to the downstream side of the main body 48d in the exhaust flow direction EF and decreases in diameter as it approaches the downstream side in the exhaust flow direction EF. The connection section 70 is located downstream of the diameter-reducing section 48e in the exhaust flow direction EF. As described above, the downstream exhaust gas sensor 46 has a sensor detection section 46d located in the exhaust passage 52 and a sensor main body 46e extending outside the exhaust passage 52, and the sensor detection section 46d is located downstream of the sensor main body 46e in the exhaust flow direction EF. With this configuration, the downstream exhaust gas sensor 46 can be positioned downstream of the diameter-reducing section 48e of the purification device 48, and the sensor detection section 46d of the downstream exhaust gas sensor 46 can be arranged along the exhaust flow direction EF. Therefore, even if the flow velocity of the exhaust gas passing through the purification device 48 and around the downstream exhaust gas sensor 46 is very high, the pressure loss of the exhaust gas due to the downstream exhaust gas sensor 46 can be reduced.

[0056] While embodiments and modifications of the present invention have been described above, the present invention is not limited thereto. Various substitutions and modifications are possible as long as they do not depart from the spirit and scope of the present invention as defined by the claims of this application.

[0057] The number of cylinders in the internal combustion engine mounted on the saddle-type vehicle to which the present invention is applied is not particularly limited; the number of cylinders in the internal combustion engine may be one, or two or more.

[0058] In the above explanation, the position of the welding start point B1 of the welded portion 70W of the connection portion 70 of the downstream exhaust gas sensor 46 was described. The above description regarding the downstream exhaust gas sensor 46, for example, the position of the welding start point B1, should also be applied to the upstream exhaust gas sensor 44. [Explanation of Symbols]

[0059] 10…Motorcycle (saddle-type vehicle) 12…Body frame 14…Head pipe 22… Footrest 24...Brake pedal 25... Kick pedal 26…Engine body 30... Crankcase 38...Axis of rotation of the crankshaft 39... Exhaust system 40…Exhaust pipe 42... Muffler 44... Exhaust gas sensor 46…Exhaust gas sensor (downstream exhaust gas sensor) 48... Purification device 48a... Exhaust gas purification catalyst 50... Exhaust pipe 70...Connection part 70b... Weld bead 70W...Welded part B1... Welding start point B2... Welding end

Claims

1. An exhaust system (39) for an internal combustion engine (E) mounted on a saddle-type vehicle (10), An exhaust gas purification catalyst (48a) is provided in the exhaust passage (52) of the internal combustion engine (E), An exhaust gas sensor (46) is provided in the downstream exhaust passage (52b) downstream of the exhaust gas purification catalyst (48a) and Equipped with, The exhaust gas sensor (46) is provided at a connection portion (70) welded to the exhaust pipe (50) that partitions the downstream exhaust passage (52b), so as to be inclined at an angle with respect to the exhaust flow direction (EF). The welding start point (B1) in the welded portion (70W) around the connection portion (70) to the exhaust pipe (50) is located on the non-upstream side of the exhaust gas sensor (46) in the exhaust flow direction (EF). The welding end portion (B2) in the welded portion (70W) around the connection portion (70) overlaps with the welding start portion (B1). An exhaust system characterized by (39).

2. The welding start portion (B1) is located downstream of the virtual plane (EIS) in the exhaust flow direction (EF) from the virtual plane (EIS), when a virtual plane (EIS) is defined to pass through the intersection (CP) of the extension plane (50s) of the surface (50s) of the exhaust pipe (50) and the axis (70a) of the connection portion (70) and to be perpendicular to the exhaust flow direction (EF). The exhaust device (39) according to feature 1.

3. The welding start portion (B1) is located within the region of the downstream width (70r) of the connection portion (70). The exhaust device (39) according to claim 1 or 2.

4. When a virtual plane (EIS) is defined so as to pass through the intersection (CP) of the extended surface (50s) of the exhaust pipe (50) and the axis (70a) of the connection portion (70), and is perpendicular to the exhaust flow direction (EF), the inclination (θ) of the axis (46a) of the exhaust gas sensor (46) with respect to the virtual plane (EIS) is between 10° and 45°. The exhaust device (39) according to feature 1.

5. The exhaust gas sensor (46) has a sensor detection unit (46d) located in the exhaust passage (52) and a sensor body (46e) extending outside the exhaust passage (52), The sensor detection unit (46d) is located downstream of the sensor body (46e) in the exhaust flow direction (EF). The exhaust device (39) according to feature 1.

6. The exhaust gas purification device (48) having the exhaust gas purification catalyst (48a) inside comprises a main body (48d) on which a carrier (48b) supporting the exhaust gas purification catalyst (48a) is arranged, and a diameter-reducing portion (48e) that is connected to the downstream side of the main body (48d) in the exhaust gas flow direction (EF) and whose diameter decreases as it approaches the downstream side in the exhaust gas flow direction (EF), The connecting portion (70) is located downstream of the reduced diameter portion (48e) in the exhaust flow direction (EF), The exhaust gas sensor (46) has a sensor detection unit (46d) located in the exhaust passage (52) and a sensor body (46e) extending outside the exhaust passage (52), The sensor detection unit (46d) is located downstream of the sensor body (46e) in the exhaust flow direction (EF). The exhaust device (39) according to feature 1.

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