JP2017150307A - Engine unit and vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an engine unit capable of enhancing its exhaust emission control performance, and to provide a vehicle.SOLUTION: The engine unit includes an exhaust passage for exhaust gas to flow thereinto from a single-cylinder four-stroke engine, a main catalyst having the highest emission control ability in the exhaust passage, an upstream oxygen detection member arranged in a section of the exhaust passage from an exhaust port of the single-cylinder four-stroke engine to the upstream end of the main catalyst, at a position nearer the exhaust port than the main catalyst, and at least partly exposed to the exhaust gas exhausted only from a single combustion chamber of the single-cylinder four-stroke engine, for detecting oxygen, a downstream oxygen detection member arranged in the exhaust passage downstream of the downstream end of the main catalyst, and at least partly exposed to the exhaust gas exhausted only from the single combustion chamber of the single-cylinder four-stroke engine, for detecting oxygen, and a control part for performing combustion control of the single-cylinder four-stroke engine on the basis of the detection result of the upstream oxygen detection member and the detection result of the downstream oxygen detection member.SELECTED DRAWING: Figure 5

Description

  The present invention relates to an engine unit and a vehicle.

  There has been a technique for detecting oxygen contained in engine exhaust gas and using the detection result for engine combustion control. By controlling the air-fuel ratio, the fuel injection timing, the ignition timing, and the like by combustion control based on oxygen detection, it is possible to promote the purification of exhaust gas.

  Conventionally, there has been a proposal to attach an oxygen sensor to an engine cylinder head in order to detect oxygen in exhaust gas with high accuracy (see Patent Document 1). According to this configuration, the time from combustion to oxygen detection is shortened, and the response when the detection result is fed back and reflected in the combustion control is improved. Thereby, the purification performance of exhaust gas can be improved.

JP 2012-102662 A

  With recent maintenance and improvement of environmental standards, there is a desire to further improve exhaust gas purification performance.

  An object of the present invention is to provide an engine unit and a vehicle that can further improve exhaust gas purification performance.

An engine unit according to an aspect of the present invention (hereinafter also referred to as an engine unit of aspect 1)
A single-cylinder four-stroke engine,
An exhaust passage for flowing exhaust gas of the single-cylinder four-stroke engine;
A main catalyst disposed in the middle of the exhaust passage and having the highest purification capacity in the exhaust passage;
In the section of the exhaust passage from the exhaust port of the single-cylinder four-stroke engine to the upstream end of the main catalyst, the single-cylinder four-stroke engine is disposed at a position closer to the exhaust port than the main catalyst. An upstream oxygen detection member that at least partly is exposed to exhaust gas discharged from only the chamber and detects oxygen;
A downstream oxygen detection member that is disposed downstream of the downstream end of the main catalyst in the exhaust passage and is at least partially exposed to exhaust gas discharged from only a single combustion chamber of the single cylinder four-stroke engine to detect oxygen When,
A control unit that performs combustion control of the single-cylinder four-stroke engine based on the detection result of the upstream oxygen detection member and the detection result of the downstream oxygen detection member;
The structure provided with is taken.

  Analysis of the exhaust gas in the exhaust passage revealed the following. The exhaust gas discharged from the combustion chamber of the engine contains unburned gas. Unburned gas continues to oxidize in the exhaust passage. Since the single-cylinder four-stroke engine is configured to perform combustion once while the crankshaft rotates 720 degrees, the time interval of intermittent exhaust gas emission is longer than that of a multi-cylinder engine in which the combustion timing of each cylinder is shifted. long. For this reason, in the case of a single-cylinder four-stroke engine, compared to a multi-cylinder engine, the distance that exhaust gas moves while continuing oxidation in the exhaust passage becomes longer. If oxygen detection is performed during the oxidation, the progress of oxidation in the exhaust passage affects the oxygen detection. For this reason, there is room for improving the accuracy of oxygen detection with respect to the exhaust gas of the single-cylinder four-stroke engine.

  On the other hand, it can be considered to arrange the oxygen detection member in the downstream portion of the entire exhaust passage so that oxygen detection is performed at the stage where oxidation of the unburned gas proceeds. However, if oxygen detection is performed in the downstream part of the entire exhaust passage, the time from the combustion in the single-cylinder four-stroke engine to the oxygen detection for the exhaust gas generated by this combustion becomes longer. When the time from combustion to oxygen detection becomes longer, the response when the detection result is fed back and reflected in the combustion control is lowered.

  Therefore, in the present invention, first, the main catalyst is arranged in the middle of the exhaust passage. In the section from the exhaust port to the upstream end of the main catalyst, the upstream oxygen detection member is disposed at a position closer to the exhaust port than the main catalyst. The upstream oxygen detection member hits exhaust gas in a section closer to the exhaust port than the upstream end of the main catalyst. In this section, since the resistance action of the main catalyst is small, exhaust gas flows at a high flow rate. Therefore, the oxygen detection of the upstream oxygen detection member can shorten the time from the combustion in the single cylinder four-stroke engine to the oxygen detection of the exhaust gas generated by this combustion.

  Secondly, in the present invention, the main catalyst is disposed in the middle of the exhaust passage, and the downstream oxygen detection member is disposed downstream of the main catalyst. In the range upstream of the main catalyst and closer to the main catalyst than the exhaust port, the oxidation of the unburned gas in the exhaust gas is promoted by the resistance of the main catalyst. Further, downstream of the main catalyst, exhaust gas having a stable oxygen concentration flows through the action of the main catalyst. Further, for example, in an engine unit having a plurality of cylinders, exhaust gases discharged from a plurality of cylinders are mixed downstream of the main catalyst, and it is difficult to determine which cylinder the exhaust gas is. However, in the present invention, a single cylinder four-stroke engine is employed. For this reason, it is not clear which cylinder exhaust gas is downstream of the main catalyst. Combined with these actions, the oxygen in the exhaust gas discharged from only the single combustion chamber of the single-cylinder four-stroke engine can be detected with high accuracy by the downstream oxygen detection member.

  Thirdly, the present invention includes a control unit that performs combustion control based on the detection result of the upstream oxygen detection member and the detection result of the downstream oxygen detection member. As described above, the upstream oxygen detection member can detect the oxygen in the exhaust gas in a short time from the combustion in the single-cylinder four-stroke engine. For this reason, the response of combustion control improves by using the detection result of an upstream oxygen detection member for combustion control. Furthermore, by using the detection result of the downstream oxygen detection member for combustion control, the accuracy of the detection result of oxygen used for combustion control can be improved comprehensively. As a result, combustion control based on oxygen detection can be performed with high accuracy and high response. Therefore, according to the present invention, the exhaust gas purification performance can be further improved.

  In addition, according to the present invention, it is possible to obtain an operation capable of performing combustion control based on oxygen detection with high accuracy and high response regardless of the arrangement of the main catalyst. Therefore, the effect that the layout freedom of the main catalyst can be increased is also obtained.

The engine unit of aspect 2 is the engine unit of aspect 1,
A plurality of catalysts including the main catalyst are disposed in the exhaust passage,
The upstream oxygen detection member is disposed in the exhaust passage at a position closer to the exhaust port than the most upstream end of the plurality of catalysts in a section from the exhaust port to the most upstream end of the plurality of catalysts.
The downstream oxygen detection member is disposed downstream of the most downstream ends of the plurality of catalysts in the exhaust passage.
Take the configuration.

  According to the aspect 2, the upstream oxygen detection member is disposed at a position closer to the exhaust port than the most upstream end of the plurality of catalysts in the section of the exhaust passage from the exhaust port to the most upstream end of the plurality of catalysts. Therefore, the oxygen detection of the upstream oxygen detection member can reliably shorten the time from the combustion in the single cylinder four-stroke engine to the oxygen detection of the exhaust gas generated by this combustion. Further, the downstream oxygen detection member is disposed downstream of the most downstream ends of the plurality of catalysts in the exhaust passage. Therefore, the downstream oxygen detecting member can detect the oxygen of the exhaust gas in which the oxygen concentration is reliably stabilized through the action of the catalyst. Therefore, the oxygen detection accuracy of the downstream oxygen detection member can be reliably increased. As a result, combustion control based on oxygen detection can be performed with high accuracy and high response, and exhaust gas purification performance can be further improved.

The engine unit of aspect 3 is the engine unit of aspect 1,
A plurality of catalysts including the main catalyst are disposed in the exhaust passage,
The upstream oxygen detection member is disposed in the exhaust passage at a position closer to the exhaust port than the most upstream end of the plurality of catalysts in a section from the exhaust port to the most upstream end of the plurality of catalysts.
The downstream oxygen detection member is disposed downstream of the main catalyst in the exhaust passage.
Take the configuration.

  According to the aspect 3, the upstream oxygen detection member is disposed at a position closer to the exhaust port than the most upstream end of the plurality of catalysts in the section of the exhaust passage from the exhaust port to the most upstream end of the plurality of catalysts. Therefore, the oxygen detection of the upstream oxygen detection member can reliably shorten the time from the combustion in the single cylinder four-stroke engine to the oxygen detection of the exhaust gas generated by this combustion. Further, the downstream oxygen detection member is disposed in the exhaust passage downstream of the main catalyst. Therefore, the downstream oxygen detection member can detect oxygen in the exhaust gas having a stable oxygen concentration through the action of the main catalyst. Therefore, the oxygen detection accuracy of the downstream oxygen detection member can be increased. As a result, combustion control based on oxygen detection can be performed with high accuracy and high response, and exhaust gas purification performance can be further improved.

  The engine unit of aspect 4 is the engine unit of aspect 1, wherein the cross-sectional area perpendicular to the exhaust gas flow direction of the main catalyst is greater than the cross-sectional area orthogonal to the exhaust gas flow direction of the exhaust passage before and after the main catalyst. Take a big, configuration.

  According to the aspect 4, the cross-sectional area orthogonal to the exhaust gas flow direction of the main catalyst is larger than the cross-sectional area orthogonal to the exhaust gas flow direction of the exhaust passage before and after the main catalyst. Compared to the case, the purification capacity of the main catalyst is increased. In addition, since the number of catalysts that can be arranged upstream of the exhaust passage is increased, the activity of the main catalyst is also accelerated compared to the case where it is small. Further, such a main catalyst also has an effect that the oxidation of the unburned gas in the exhaust gas is promoted by the resistance of the catalyst upstream of the catalyst and in the range closer to the catalyst than the exhaust port.

The engine unit of aspect 5 is the engine unit of aspect 1,
The main catalyst has a porous structure for flowing exhaust gas through a plurality of holes,
Take the configuration.

  According to the aspect 5, since the catalyst has a porous structure, the oxidation of the unburned gas in the exhaust gas is promoted by the resistance of the catalyst upstream of the catalyst and in the range closer to the catalyst than the exhaust port. Is definitely obtained. Further, since the catalyst has a porous structure, the resistance of the catalyst ensures that the exhaust gas having a stable oxygen concentration flows downstream of the catalyst through the action of the catalyst. By these actions, the oxygen in the exhaust gas discharged from only the single combustion chamber of the single cylinder four-stroke engine can be detected with higher accuracy by the downstream oxygen detection member. Therefore, the combustion control based on the detection result of the downstream oxygen detection member and the detection result of the upstream oxygen detection member makes it possible to perform the combustion control based on the oxygen detection with high accuracy and high response, and to improve the exhaust gas purification performance. Can be improved.

The engine unit of aspect 6 is the engine unit of aspect 2 or aspect 3,
Each of the plurality of catalysts has a porous structure that allows exhaust gas to flow through a plurality of holes.
Take the configuration.

  According to the aspect 6, the upstream oxygen detection member is disposed at a position closer to the exhaust port than the most upstream end in the section from the most upstream end to the exhaust port of the plurality of catalysts having a porous structure. Therefore, the oxygen detection of the upstream oxygen detection member shortens the time from the combustion in the single-cylinder four-stroke engine until the oxygen detection of the exhaust gas generated by this combustion. Furthermore, the downstream oxygen detection member is disposed downstream of the most downstream ends of the plurality of catalysts having a porous structure in the exhaust passage. Therefore, the downstream oxygen detection member can detect oxygen in the exhaust gas with a stable oxygen concentration through the action of a plurality of catalysts having a porous structure. Therefore, the oxygen detection accuracy of the downstream oxygen detection member is increased. As a result, combustion control based on oxygen detection can be performed with high accuracy and high response, and exhaust gas purification performance can be further improved.

The engine unit of aspect 7 is the engine unit of aspect 1,
The main catalyst is disposed at a position where the passage length from the exhaust port of the single-cylinder four-stroke engine to the upstream end of the main catalyst is shorter than the passage length from the downstream end of the main catalyst to the discharge port facing the atmosphere. To be
Take the configuration.

  According to Aspect 7, the main catalyst is positioned such that the passage length from the exhaust port of the single-cylinder four-stroke engine to the upstream end of the main catalyst is shorter than the passage length from the downstream end of the main catalyst to the discharge port facing the atmosphere. Can be placed. Also in this main catalyst layout, combustion control based on oxygen detection can be performed with high accuracy and high response by the same operation as in the first aspect. Therefore, the exhaust gas purification performance can be further improved while realizing such a layout of the main catalyst.

The engine unit of aspect 8 is the engine unit of aspect 1,
The main catalyst is arranged at a position where the passage length from the downstream end of the main catalyst to the discharge port facing the atmosphere is shorter than the passage length from the exhaust port of the single-cylinder four-stroke engine to the upstream end of the main catalyst. To be
Take the configuration.

  According to the aspect 8, the main catalyst is positioned such that the passage length from the downstream end of the main catalyst to the discharge port facing the atmosphere is shorter than the passage length from the exhaust port of the single-cylinder four-stroke engine to the upstream end of the main catalyst. Can be placed. Also in this main catalyst layout, combustion control based on oxygen detection can be performed with high accuracy and high response by the same operation as in the first aspect. Therefore, the exhaust gas purification performance can be further improved while realizing such a layout of the main catalyst.

The engine unit of aspect 9 is the engine unit of aspect 1,
A silencer constituting a part of the exhaust passage;
An exhaust pipe for sending exhaust gas from the single-cylinder four-stroke engine to the silencer;
With
The main catalyst is disposed in the middle of the exhaust pipe,
The downstream oxygen detection member is disposed in the exhaust pipe downstream from the main catalyst.
Take the configuration.

  According to the aspect 9, the main catalyst can be arranged in the exhaust pipe between the single cylinder four-stroke engine and the silencer. Also in this main catalyst layout, combustion control based on oxygen detection can be performed with high accuracy and high response by the same operation as in the first aspect. Therefore, the exhaust gas purification performance can be further improved while realizing such a layout of the main catalyst.

The engine unit of aspect 10 is the engine unit of aspect 1,
A silencer constituting a part of the exhaust passage;
An exhaust pipe for sending exhaust gas from the single-cylinder four-stroke engine to the silencer;
With
The main catalyst is disposed in the silencer,
The downstream oxygen detection member is disposed downstream of the main catalyst in the exhaust passage of the silencer.
Take the configuration.

  According to the aspect 10, the main catalyst can be arranged in the exhaust passage of the silencer. Also in this main catalyst layout, combustion control based on oxygen detection can be performed with high accuracy and high response by the same operation as in the first aspect. Therefore, the exhaust gas purification performance can be further improved while realizing such a layout of the main catalyst.

  Aspect 11 is a vehicle including any one of the engine units according to aspects 1 to 10.

  According to the aspect 11, it is possible to provide a vehicle with further improved exhaust gas purification performance.

1 is a side view showing a motorcycle according to a first embodiment of the present invention. FIG. 3 is a side view of the motorcycle of Embodiment 1 with the body cover removed. The bottom view of the motorcycle of Embodiment 1. 1 is a block diagram showing a control system of a motorcycle according to a first embodiment. 1 is a schematic diagram showing an exhaust system of a motorcycle according to Embodiment 1. FIG. Schematic showing modified example 1 of the exhaust system Schematic showing modified example 2 of the exhaust system Schematic showing modified example 3 of the exhaust system The figure which shows the structural example 1 of the silencer to which the catalyst and the oxygen detection member were attached The figure which shows the structural example 2 of the silencer to which the catalyst and the oxygen detection member were attached The figure which shows the structural example 3 of the silencer to which the catalyst and the oxygen detection member were attached The figure which shows the structural example 4 of the silencer to which the catalyst and the oxygen detection member were attached Schematic showing modified examples 4 to 7 of the exhaust system Side view showing a motorcycle according to a second embodiment of the present invention. Bottom view of the motorcycle according to the second embodiment. Side view of the motorcycle of Embodiment 2 with the body cover removed A bottom view of the motorcycle of Embodiment 2 with the body cover removed. Side view showing a motorcycle according to a third embodiment of the present invention. The bottom view of the motorcycle of Embodiment 3. Side view of the motorcycle of Embodiment 3 with the body cover removed A bottom view of the motorcycle of Embodiment 3 with the body cover removed. Side view showing a motorcycle according to a fourth embodiment of the present invention. Bottom view of the motorcycle of the fourth embodiment. Side view of the motorcycle of Embodiment 4 with the body cover removed. Bottom view of the motorcycle of Embodiment 4 with the body cover removed.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following description, front, rear, left, and right mean front, rear, left, and right, respectively, as viewed from a motorcycle occupant. Reference numerals F, Re, L, and R attached to the drawings represent front, rear, left, and right, respectively.

(Embodiment 1)
[overall structure]
FIG. 1 is a side view showing a motorcycle according to a first embodiment of the present invention. FIG. 2 is a side view of the motorcycle according to the first embodiment with a body cover removed. FIG. 3 is a bottom view of the motorcycle according to the first embodiment.

  The vehicle of the first embodiment is a so-called underbone type motorcycle 1.

  The motorcycle 1 includes a vehicle body frame 2 composed of a plurality of frame members. The vehicle body frame 2 includes a head pipe 3, a main frame 4, and a seat rail 5. In the underbone type motorcycle 1, a recess 12 is formed behind the head pipe 3, ahead of the seat 9 and above the main frame 4 when viewed from the side of the vehicle. The portion of the main frame 4 between the seat 9 and the head pipe 3 is low. This makes it easier for the driver to straddle the main frame 4, that is, the vehicle body.

  A handle 7 is rotatably attached above the head pipe 3. A front fork 6 is supported below the head pipe 3. An axle 8 a is fixed to the lower end portion of the front fork 6. A front wheel 8 is rotatably attached to the axle 8a. Fenders 10 are provided above and behind the front wheels 8.

  The main frame 4 extends rearward and obliquely downward from the head pipe 3 in a side view. An engine 20 is disposed below the main frame 4. An air cleaner 29 is disposed above the engine 20. The air cleaner 29 is connected to the cylinder head 26 of the engine 20 via the intake pipe 30. One end of the intake pipe 30 is connected to the cylinder head 26. The intake pipe 30 extends upward from the cylinder head 26 in a side view. The other end of the intake pipe 30 is connected to an air cleaner 29. The air cleaner 29 purifies the air supplied to the engine 20. The air is purified by passing through the air cleaner 29 and supplied to the engine 20 through the intake pipe 30. A front cover 11 is provided in front of the head pipe 3, left and right sides of the air cleaner 29, and part of the engine 20 on the left and right sides.

  The seat rail 5 extends rearward and obliquely upward from the middle part of the main frame 4 in a side view. A seat 9 is disposed above the seat rail 5. The seat 9 is supported by the seat rail 5. A rear cushion unit 13 is disposed below the seat rail 5. The upper end portion of the rear cushion unit 13 is supported by the seat rail 5, and the lower end portion of the rear cushion unit 13 is supported by the rear arm 14. A pivot shaft 14 a is provided at the front portion of the rear arm 14. The rear arm 14 can swing up and down around the pivot shaft 14a. A rear wheel 15 is supported at the rear portion of the rear arm 14. The left and right sides of the main frame 4 and the seat rail 5 of the body frame 2 are covered with a body cover 16.

  As shown in FIG. 2, the main frame 4 is provided with a bracket 17. The bracket 17 extends downward from the main frame 4. The engine 20 includes a crankcase portion 18. A boss portion is formed at the upper portion of the front portion of the crankcase portion 18. The boss part of the crankcase part 18 is fixed to the bracket 17 by a bolt 18a so as not to swing. Further, the rear portion of the crankcase portion 18 is also fixed to other brackets using a bolt so as not to swing. The engine 20 is fixed to the vehicle body frame 2 so as not to swing. The crankcase portion 18 incorporates a crankshaft, a speed change mechanism, and the like.

  The motorcycle 1 includes an engine 20, an exhaust pipe 31, a catalyst unit 32, an upstream oxygen detection member 33a, a downstream oxygen detection member 33b, and a silencer 34 as an engine unit 19 (see FIG. 5). ing.

  The engine 20 is a single-cylinder four-stroke engine, and includes a cylinder part 24 extending in front of the crankcase part 18, a cylinder head part 26 fixed to the cylinder part 24, and a head cover 28 fixed to the cylinder head part 26. It has. However, any two or three of the cylinder part 24, the cylinder head part 26, and the head cover 28 may be integrated. The cylinder part 24 is disposed in front of the crankcase part 18. The cylinder part 24 may be separate from the crankcase part 18, and the cylinder part 24 may be integrated with the crankcase part 18. The cylinder part 24 is disposed below the lowest part of the upper surface of the recess 12.

  The center line of the hollow portion in which the piston moves in the cylinder portion 24, that is, the cylinder axis L1 extends forward and obliquely upward. The inclination angle of the cylinder axis L1 from the horizontal line is 35 degrees or less. The cylinder part 24 arranged in such a direction is called a horizontal cylinder.

  Details of the configuration of the exhaust system will be described later.

  FIG. 4 is a block diagram illustrating a control system of the motorcycle according to the first embodiment.

  The motorcycle 1 includes an electronic control unit 40 that performs combustion control of the single-cylinder four-stroke engine 20.

  The electronic control unit 40 includes a control unit 42, a pulse processing unit 41, an ignition drive circuit 43 that drives the ignition coil 36, an injector drive circuit 44 that drives the injector 37, and a pump drive circuit 45 that drives the fuel pump 38. And.

  The pulse processing unit 41 shapes the output signal of the crank angle sensor 35 to generate a waveform shaped crank pulse. The generated crank pulse is output to the control unit 42.

  The control unit 42 is, for example, a microcomputer. The control unit 42 receives the crank pulse output from the pulse processing unit 41, the detection result of the upstream oxygen detection member 33a, the detection result of the downstream oxygen detection member 33b, and information related to the intake pressure or the throttle opening. The control unit 42 controls the ignition drive circuit 43, the injector drive circuit 44, and the pump drive circuit 45 based on these inputs.

  The control of the control unit 42 includes drive control of the ignition coil 36 (control of ignition timing), drive control of the injector 37 (control of fuel injection timing), and drive control of the fuel pump 38 (control of fuel supply amount). It is. The control unit 42 can perform combustion control of the engine 20 so as to improve the purification degree of exhaust gas based on the oxygen detection results of the upstream oxygen detection member 33a and the downstream oxygen detection member 33b.

[Exhaust system configuration]
FIG. 5 is a schematic diagram showing an exhaust system of the motorcycle according to the first embodiment.

  The cylinder head portion 26 is provided with an intake passage P1, an exhaust gas passage P2, an intake valve V1, and an exhaust valve V2. The downstream end of the intake passage P1 is an intake port, which is opened and closed by the movement of the intake valve V1. The upstream end of the exhaust gas passage P2 is an exhaust port P2a, which is opened and closed by the movement of the exhaust valve V2. An intake passage P1 provided in the cylinder head portion 26 is an intake passage P1 provided in the engine 20. The intake passage P1 provided in the cylinder head portion 26 can be restated as the intake passage P1 of the engine 20. An exhaust gas passage P <b> 2 provided in the cylinder head portion 26 is an exhaust gas passage P <b> 2 provided in the engine 20. The exhaust gas passage P <b> 2 provided in the cylinder head portion 26 can be restated as the exhaust gas passage P <b> 2 of the engine 20.

  The exhaust pipe 31 has an upstream exhaust pipe 31A and a downstream exhaust pipe 31B. The upstream end of the upstream exhaust pipe 31A is connected to the exhaust gas passage P2 of the cylinder head portion 26, and the downstream end of the upstream exhaust pipe 31A is connected to the catalyst unit 32. The upstream end of the downstream exhaust pipe 31B is connected to the catalyst unit 32, and the downstream part of the downstream exhaust pipe 31B is connected to the silencer 34. The upstream exhaust pipe 31A flows exhaust gas from the exhaust gas passage P2 to the catalyst unit 32, and the downstream exhaust pipe 31B flows exhaust gas from the catalyst unit 32 to the silencer 34. In the upstream exhaust pipe 31A and the downstream exhaust pipe 31B, the upstream end is the end closest to the exhaust port P2a in the distance of the exhaust passage. In the upstream exhaust pipe 31A and the downstream exhaust pipe 31B, the downstream end is the end closest to the discharge port 34e of the silencer 34 at the distance of the exhaust passage.

  The catalyst unit 32 has a cylindrical casing and a main catalyst 32b. The main catalyst 32b is fixed inside the casing. The main catalyst 32b is a three-way catalyst, and purifies the exhaust gas by passing the exhaust gas. The main catalyst 32b is the catalyst having the highest purification performance in the exhaust passage. The main catalyst 32b has a porous structure provided with a plurality of passages sufficiently narrower than the passage width of the upstream exhaust pipe 31A. In the main catalyst 32b, the length c of the exhaust passage in the passage direction is longer than the maximum width W in the direction perpendicular to the passage direction. The main catalyst 32b has a sectional area in a direction perpendicular to the passage direction of the exhaust passage larger than a sectional area in a direction perpendicular to the passage direction of the exhaust passage before and after the main catalyst 32b. The porous structure is a structure in which a plurality of passages are collected in a bundle shape, and refers to a structure that is porous when a cross section perpendicular to the passage direction of the exhaust gas is viewed. An example of the porous structure is a honeycomb structure.

  The upstream oxygen detection member 33a is a sensor that detects oxygen in the exhaust gas. The upstream oxygen detection member 33a is fixed so that a part of the upstream oxygen detection member 33a is exposed to the outside of the exhaust passage and the other part is disposed in the exhaust passage and exposed to the exhaust gas. The upstream oxygen detection member 33a may be an oxygen sensor that binarizes and detects the oxygen amount or oxygen concentration, or an A / F sensor (Air Fuel) that can detect the oxygen amount or oxygen concentration in multiple stages (eg, linear). ratio sensor). The arrangement of the upstream oxygen detection member 33a will be described later.

  The downstream oxygen detection member 33b is a sensor that detects oxygen in the exhaust gas. The downstream oxygen detection member 33b is fixed such that a part thereof is exposed to the outside of the exhaust passage and the other part is disposed in the exhaust passage and exposed to the exhaust gas. The arrangement of the downstream oxygen detection member 33b will be described later.

  The silencer 34 has a resonance chamber, an expansion chamber, and a throttle portion, and reduces the volume of the exhaust sound by suppressing the pulsating wave of the exhaust gas. At the downstream end of the silencer 34, a discharge port 34e facing the atmosphere is provided. The exhaust gas that has passed through the silencer 34 is discharged to the atmosphere from the discharge port 34e.

  The exhaust passage of the first embodiment includes an exhaust gas passage P2 of the cylinder head portion 26, a passage of the upstream exhaust pipe 31A, a passage portion 32a from the upstream connection end of the catalyst unit 32 to the upstream end of the main catalyst 32b, The passage of the catalyst 32b, the passage portion 32c from the downstream end of the main catalyst 32b to the downstream connection end of the catalyst unit 32, the passage of the downstream exhaust pipe 31B, and the downstream end of the downstream exhaust pipe 31B pass through the interior of the silencer 34. And a passage (shown by an arrow e in FIG. 5) to the discharge port 34e facing the atmosphere. The upstream end of the main catalyst 32b is the end closest to the exhaust port P2a in the distance of the exhaust passage. The downstream end of the main catalyst 32b is the end of the main catalyst 32b closest to the silencer 34 by the distance of the exhaust passage.

  In FIG. 5, for the sake of simplicity, the upstream exhaust pipe 31A and the downstream exhaust pipe 31B are drawn straight, but the upstream exhaust pipe 31A and the downstream exhaust pipe 31B are not limited to a straight configuration.

  In this specification, the length of the exhaust passage when the exhaust passage is bent is defined as the length of the center line of the exhaust passage.

  The catalyst unit 32 is disposed in the middle of the exhaust passage. In the example of FIG. 5, in the catalyst unit 32, the passage length (a + b) from the exhaust port P2a to the upstream end of the main catalyst 32b is shorter than the passage length (d + e) from the downstream end of the main catalyst 32b to the discharge port 34e. Placed in position. In the example of FIG. 5, the catalyst unit 32 is disposed in the middle of the exhaust pipe 31.

  The upstream oxygen detection member 33a is disposed at a position (h1 <h2) closer to the exhaust port P2a than the upstream end of the main catalyst 32b in the section of the exhaust passage from the exhaust port P2a to the upstream end of the main catalyst 32b. In the example of FIG. 5, the upstream oxygen detection member 33a is disposed in the upstream exhaust pipe 31A. Here, “near” means that the moving distance along the exhaust passage is short.

  The downstream oxygen detection member 33b is disposed downstream of the main catalyst 32b in the exhaust passage. In the example of FIG. 5, the downstream oxygen detection member 33b is disposed in the downstream exhaust pipe 31B.

[Action of exhaust system]
The exhaust gas discharged from the combustion chamber of the engine contains unburned gas. Unburned gas continues to oxidize in the exhaust passage. Since the single-cylinder four-stroke engine 20 is configured to perform combustion once while the crankshaft rotates 720 degrees, the time interval of intermittent exhaust gas emission compared to a multiple-cylinder engine in which the combustion timing of each cylinder is shifted. Is long. Therefore, if there is no resistance in the exhaust passage, it is considered that the distance that the unburned gas travels while oxidizing is longer than in the case of the multi-cylinder engine.

  Therefore, in the first embodiment, first, the main catalyst 32b is arranged in the middle of the exhaust passage. In the section from the exhaust port P2a to the upstream end of the main catalyst 32b, the upstream oxygen detection member 33a is disposed at a position closer to the exhaust port P2a than the main catalyst 32b. Then, the upstream oxygen detection member 33a hits the exhaust gas in the section closer to the exhaust port P2a than the upstream end of the main catalyst 32b. In this section, since the resistance action of the main catalyst 32b is small, exhaust gas flows at a high flow rate. Therefore, the time from the combustion of the engine 20 to the oxygen detection of the exhaust gas generated by this combustion can be shortened by the oxygen detection of the upstream oxygen detection member 33a.

  Second, in the first embodiment, the main catalyst 32b is arranged in the middle of the exhaust passage, and the downstream oxygen detection member 33b is arranged downstream of the main catalyst 32b. In the range upstream of the main catalyst 32b and closer to the main catalyst 32b than the exhaust port P2a, the oxidation of the unburned gas in the exhaust gas is promoted by the resistance of the main catalyst 32b. Further, exhaust gas having a stable oxygen concentration flows through the action of the main catalyst 32b downstream of the main catalyst 32b. Therefore, the oxygen in the exhaust gas of the engine 20 can be detected with high accuracy by the downstream oxygen detection member 33b. Here, considering a multi-cylinder engine unit, exhaust gas discharged from a plurality of cylinders is mixed downstream of the catalyst, and it is difficult to determine which cylinder exhaust gas. However, in the first embodiment, exhaust gas is discharged only from a single combustion chamber of the single cylinder four-stroke engine 20, so that ambiguity as in the case of a plurality of cylinders does not occur. Therefore, the downstream oxygen detection member 33b disposed downstream of the main catalyst 32b can detect oxygen in the exhaust gas discharged from the single combustion chamber of the engine 20 with high accuracy.

  Third, the first embodiment includes a control unit 42 that performs combustion control based on the detection result of the upstream oxygen detection member 33a and the detection result of the downstream oxygen detection member 33b. As described above, the upstream oxygen detection member 33a can detect the oxygen in the exhaust gas in a short time from the combustion of the engine 20. For this reason, the response of combustion control improves by using the detection result of the upstream oxygen detection member 33a for combustion control. Furthermore, by using the detection result of the downstream oxygen detection member 33b for combustion control, the accuracy of the detection result of oxygen used for combustion control can be improved comprehensively. For example, the detection result with room for improvement in accuracy of the upstream oxygen detection member 33a can be corrected by the highly accurate detection result of the downstream oxygen detection member 33b, thereby improving the accuracy. Thus, the control unit 42 can perform combustion control based on oxygen detection with high accuracy and high response. Therefore, according to Embodiment 1, the exhaust gas purification performance can be further improved.

  In addition, in the first embodiment, the catalyst unit 32 is disposed closer to the exhaust port P2a than the discharge port 34e of the silencer 34 at a distance along the exhaust passage. Therefore, the catalyst unit 32 can be arranged in an appropriate space for a vehicle having an appropriate space in such a place.

(Exhaust system modification 1)
FIG. 6 is a schematic diagram showing a first modification of the exhaust system.

  The modification 1 has shown the modification of arrangement | positioning of the upstream oxygen detection member 33a. In the first modification, components similar to those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In FIG. 6, the upstream exhaust pipe 31 </ b> A and the downstream exhaust pipe 31 </ b> B are drawn straight for simplicity, but the upstream exhaust pipe 31 </ b> A and the downstream exhaust pipe 31 </ b> B are not limited to a straight configuration.

  In the first modification, the upstream oxygen detection member 33 a is provided in the cylinder head portion 26. A part of the upstream oxygen detection member 33a is disposed in the exhaust gas passage P2 and is exposed to the exhaust gas. Even in this case, the upstream oxygen detection member 33a is disposed at a position (h3 <h2) closer to the exhaust port P2a than the upstream end of the main catalyst 32b in the section of the exhaust passage from the exhaust port P2a to the upstream end of the main catalyst 32b. ing. Here, “near” means that the moving distance along the exhaust passage is short.

  As described above, even when the upstream oxygen detection member 33a is provided in the cylinder head portion 26, it is generated by the combustion from the combustion of the engine 20 by the oxygen detection of the upstream oxygen detection member 33a by the same operation as in the first embodiment. It is possible to shorten the time until oxygen detection for the exhaust gas. Therefore, by using the detection result of the upstream oxygen detection member 33a for the combustion control, the response of the combustion control is improved. Furthermore, by using the detection result of the downstream oxygen detection member 33b for combustion control, the accuracy of the detection result of oxygen used for combustion control can be improved comprehensively. Thus, the control unit 42 can perform combustion control based on oxygen detection with high accuracy and high response. Therefore, the exhaust gas purification performance can be further improved.

(Exhaust system modification 2)
FIG. 7 is a schematic diagram showing a second modification of the exhaust system.

  The modification 2 has shown the modification of arrangement | positioning of the downstream oxygen detection member 33b. In the second modification, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In FIG. 7, for the sake of simplicity, the upstream exhaust pipe 31A and the downstream exhaust pipe 31B are drawn straight, but the upstream exhaust pipe 31A and the downstream exhaust pipe 31B are not limited to a straight configuration.

  In the second modification, the downstream oxygen detection member 33 b is provided in the silencer 34. A part of the downstream oxygen detection member 33b may be disposed in the expansion chamber or the resonance chamber of the silencer 34 and exposed to the exhaust gas.

  Thus, even when the downstream oxygen detection member 33b is provided in the silencer 34, the main catalyst 32b passes around a part of the downstream oxygen detection member 33b by the same operation as in the first embodiment. Exhaust gas with a stable oxygen concentration flows. Therefore, the oxygen in the exhaust gas of the engine 20 can be detected with high accuracy by the downstream oxygen detection member 33b. Also, in the second modification, the single cylinder four-stroke engine 20 is adopted, so that the detection result of the downstream oxygen detection member 33b is the exhaust gas discharged from any cylinder as in the case of the multi-cylinder engine. It is not unclear whether this is the result of oxygen detection.

  By using the detection result of the upstream oxygen detection member 33a and the detection result of the downstream oxygen detection member 33b for combustion control, the control unit 42 performs combustion control based on oxygen detection with high accuracy and high response. It can be carried out. Therefore, the exhaust gas purification performance can be further improved.

(Exhaust system modification 3)
FIG. 8 is a schematic diagram showing a third modification of the exhaust system.

  Modification 3 shows a modification of the arrangement of the main catalyst 32b. In the third modification, components similar to those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In FIG. 8, the exhaust pipe 31 is drawn straight for simplification, but the exhaust pipe 31 is not limited to a straight configuration.

  In Modification 3, the catalyst unit 32 has a position where the passage length (a + b) from the exhaust port P2a to the upstream end of the main catalyst 32b is longer than the passage length (d + e) from the downstream end of the main catalyst 32b to the discharge port 34e. Is arranged. In the third modification, the main catalyst 32 b may be provided in the middle of the exhaust pipe 31 or may be provided in the passage of the silencer 34.

  The upstream oxygen detection member 33a is disposed at a position (h5 <h6) closer to the exhaust port P2a than the upstream end of the main catalyst 32b in the section of the exhaust passage from the exhaust port P2a to the upstream end of the main catalyst 32b. Here, “near” means that the moving distance along the exhaust passage is short.

  Thus, even if the main catalyst 32b is disposed at a distance along the exhaust passage and closer to the discharge port 34e of the silencer 34 than the exhaust port P2a, the upstream oxygen detection member is the same as in the first embodiment. High-speed exhaust gas discharged from the combustion chamber of the engine 20 flows around at least a part of the 33a. Therefore, the upstream oxygen detection member 33a can shorten the time from the combustion of the engine 20 to the oxygen detection of the exhaust gas generated by the combustion. Further, the oxygen in the exhaust gas of the engine 20 can be detected with high accuracy by the downstream oxygen detection member 33b.

  By using the detection result of the upstream oxygen detection member 33a and the detection result of the downstream oxygen detection member 33b for combustion control, the control unit 42 performs combustion control based on oxygen detection with high accuracy and high response. It can be carried out. Therefore, the exhaust gas purification performance can be further improved.

  Furthermore, in the third modification, the catalyst unit 32 is disposed closer to the discharge port 34e of the silencer 34 than the exhaust port P2a at a distance along the exhaust passage. Therefore, the catalyst unit 32 can be arranged in an appropriate space for a vehicle having an appropriate space in such a place.

  Note that several structural examples as shown below can be applied to the form in which the main catalyst 32b and the downstream oxygen detection member 33b are attached to the silencer 34.

  9 to 12 show structural examples 1 to 4 of the silencer to which the main catalyst and the downstream oxygen detection member are attached, respectively. 9 to 12, reference numerals 34a to 34d are pipes through which exhaust gas flows.

  In Structural Example 1 of FIG. 9, the catalyst unit 32 including the main catalyst 32 b is accommodated in the expansion chamber of the silencer 34. A part of the downstream oxygen detection member 33b is exposed to the outside from the side surface of the silencer 34, and the other part is disposed in the expansion chamber or the resonance chamber of the silencer 34 and exposed to the exhaust gas.

  Since the downstream oxygen detecting member 33b needs to be partly in contact with the outside air, the downstream oxygen detecting member 33b is disposed closer to the side surface than the center of the silencer 34.

  In the example of FIG. 9, the pipe 34 a downstream of the catalyst unit 32 is directed in an oblique direction (arrow M) with reference to the passage direction (arrow L) downstream of the exhaust pipe 31. And the exhaust gas sent downstream from the catalyst unit 32 is comprised so that it may spray on a part of downstream oxygen detection member 33b.

  In Structural Example 2 in FIG. 10, the catalyst unit 32 including the main catalyst 32 b is accommodated in the expansion chamber of the silencer 34. A part of the downstream oxygen detection member 33b is exposed to the outside from the side surface of the silencer 34, and a part thereof is disposed in the expansion chamber or the resonance chamber of the silencer 34 and is exposed to the exhaust gas.

  In the example of FIG. 10, the catalyst unit 32 including the main catalyst 32 b is disposed closer to the side surface than the center of the silencer 34. Thereby, the piping 34 a downstream of the catalyst unit 32 can be arranged near the side surface from the center of the silencer 34. Thereby, the exhaust gas sent downstream from the catalyst unit 32 is configured to be sprayed to a part of the downstream oxygen detection member 33b.

  In Structural Example 3 in FIG. 11, the catalyst unit 32 including the main catalyst 32 b is accommodated in the expansion chamber of the silencer 34. A part of the downstream oxygen detection member 33b is exposed to the outside from the side surface of the silencer 34, and the other part is disposed in the pipe 34a downstream of the catalyst unit 32 and exposed to the exhaust gas.

  In the example of FIG. 11, the catalyst unit 32 is disposed closer to the side surface than the center of the silencer 34, so that the pipe 34 a downstream of the catalyst unit 32 is also disposed closer to the side surface than the center of the silencer 34. Yes. Therefore, even if it arrange | positions so that a part of downstream oxygen detection member 33b may be exposed outside from the side surface of the silencer 34, the exhaust gas which passed the catalyst unit 32 flows through the other part of the downstream oxygen detection member 33b. It can be easily arranged in the pipe 34a.

  In Structural Example 4 of FIG. 12, the downstream oxygen detection member 33 b is disposed on the tail pipe 34 d of the silencer 34. Since the exhaust gas from the single-cylinder four-stroke engine 20 flows through the silencer 34, the exhaust gas that has passed through the expansion chamber or the resonance chamber may not be clear from any cylinder, unlike in the case of a multi-cylinder engine. Absent. Therefore, the oxygen detection accuracy can be increased by the downstream oxygen detection member 33b.

(Exhaust system modification 4)
FIG. 13A is a schematic diagram showing a fourth modification of the exhaust system.

  13A to 13D, the exhaust passage 201 from the combustion chamber 24A of the engine 20 to the discharge port 34e of the silencer 34 is indicated by a line.

  Modification 4 is an example in which a sub-catalyst 32s is disposed in the exhaust passage 201 and upstream of the main catalyst 32b. In the modified example 4, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the modified example 4, the sub catalyst 32s is disposed upstream of the main catalyst 32b in the exhaust passage 201.

  The sub-catalyst 32s purifies the exhaust gas by passing the exhaust gas or flowing the exhaust gas around. The sub-catalyst 32s is a catalyst whose purification capacity is lower than that of the main catalyst 32b in the exhaust passage. The sub-catalyst 32s may have a porous structure provided with a plurality of passages sufficiently narrower than the passage width of the upstream exhaust pipe 31A. The sub-catalyst 32s may have a form shorter than the maximum width in the direction perpendicular to the passage direction rather than the length in the passage direction of the exhaust passage.

  The upstream oxygen detection member 33a is provided upstream of the sub-catalyst 32s that is the most upstream catalyst. When the sub-catalyst 32s has a structure that is more resistant than the upstream exhaust pipe 31A, the upstream oxygen detection member 33a may be disposed at a distance along the exhaust passage and closer to the exhaust port P2a than the upstream end of the sub-catalyst 32s. . The most upstream may be said to be closest to the exhaust port P2a by the distance of the exhaust passage, and the upstream may be said to be close to the exhaust port P2a by the distance of the exhaust passage.

  The downstream oxygen detection member 33b is disposed downstream of the main catalyst 32b.

  According to such an arrangement, the upstream oxygen detection member 33a can detect oxygen in the exhaust gas generated by the combustion immediately after the combustion of the engine 20. Further, the downstream oxygen detection member 33b can perform oxygen detection with high accuracy for the exhaust gas that has passed through the main catalyst 32b and has a stable oxygen concentration. Therefore, by the combustion control based on these detection results, the control unit 42 can perform the combustion control based on the oxygen detection with high accuracy and high response.

(Variation 5 of exhaust system)
FIG. 13B is a schematic diagram showing a fifth modification of the exhaust system.

  The fifth modification is one example in which the sub-catalyst 32s is arranged in the exhaust passage 201 and downstream of the main catalyst 32b. In the modified example 5, the same components as those in the modified example 4 are denoted by the same reference numerals, and detailed description thereof is omitted.

  The upstream oxygen detection member 33a is disposed upstream of the main catalyst 32b which is the most upstream catalyst. Further, the upstream oxygen detection member 33a is disposed at a distance along the exhaust passage and closer to the exhaust port P2a than the upstream end of the main catalyst 32b.

  The downstream oxygen detection member 33b is disposed downstream of the main catalyst 32b and upstream of the sub catalyst 32s.

  Even with such an arrangement, the upstream oxygen detection member 33a can detect oxygen in the exhaust gas generated by the combustion immediately after the combustion of the engine 20. Further, the downstream oxygen detection member 33b can perform oxygen detection with high accuracy for the exhaust gas that has passed through the main catalyst 32b and has a stable oxygen concentration. Therefore, by the combustion control based on these detection results, the control unit 42 can perform the combustion control based on the oxygen detection with high accuracy and high response.

(Exhaust system modification 6)
FIG. 13C is a schematic diagram showing a sixth modification of the exhaust system.

  Modification 6 is one example in which the sub-catalyst 32s is disposed downstream of the main catalyst 32b in the exhaust passage 201. In the modified example 6, the same components as those in the modified example 4 are denoted by the same reference numerals, and detailed description thereof is omitted.

  The upstream oxygen detection member 33a is disposed upstream of the main catalyst 32b which is the most upstream catalyst. Further, the upstream oxygen detection member 33a is disposed at a distance along the exhaust passage and closer to the exhaust port P2a than the upstream end of the main catalyst 32b.

  The downstream oxygen detection member 33b is disposed downstream of the main catalyst 32b and downstream of the sub catalyst 32s. That is, the downstream oxygen detection member 33b is disposed downstream of the most downstream catalyst in the exhaust passage. The most downstream side may be said to be closest to the discharge port 34e, and the downstream side may be said to be close to the discharge port 34e.

  Even with such an arrangement, the upstream oxygen detection member 33a can detect oxygen in the exhaust gas generated by the combustion immediately after the combustion of the engine 20. Further, in the downstream oxygen detection member 33b, it is possible to detect oxygen with high accuracy with respect to the exhaust gas having a stable oxygen concentration by passing through the main catalyst 32b, passing through the sub-catalyst 32s, or flowing around the sub-catalyst 32s. Therefore, by the combustion control based on these detection results, the control unit 42 can perform the combustion control based on the oxygen detection with high accuracy and high response.

(Exhaust system modification 7)
FIG. 13D is a schematic diagram showing a seventh modification of the exhaust system.

  The modified example 7 is an example in which the sub-catalyst 32f with a low contribution rate for purifying exhaust gas is disposed in the exhaust passage 201. In the modification example 7, the same components as those in the modification example 4 are denoted by the same reference numerals, and detailed description thereof is omitted.

  For example, the sub-catalyst 32f of the modified example 7 is one in which a catalyst is formed on the inner wall of the exhaust pipe 31. The sub-catalyst 32f is formed by a coating method. The sub-catalyst 32 f has the same structure as the resistance of the exhaust pipe 31. The sub-catalyst 32f has a lower exhaust gas purification capability than the main catalyst 32b. The sub-catalyst 32f may be disposed on one or both of the upstream side of the main catalyst 32b and the downstream side of the main catalyst 32b. The sub-catalyst 32f may have a configuration in which a catalytic substance is added to a plate-like carrier. The plate-like carrier may have an S-shaped cross section. The sub-catalyst 32f may have a configuration in which a catalytic substance is added to one cylindrical carrier.

  In the modified example 7, the upstream oxygen detection member 33a is arranged at a distance along the exhaust passage and closer to the exhaust port P2a than the upstream end of the main catalyst 32b. The upstream oxygen detection member 33a may be disposed downstream of the sub catalyst 32f having a low purification capacity.

  The downstream oxygen detection member 33b is disposed downstream of the main catalyst 32b. The downstream oxygen detection member 33b may be disposed upstream of the sub catalyst 32f.

  Even with such an arrangement, the upstream oxygen detection member 33a can detect oxygen in the exhaust gas generated by the combustion immediately after the combustion of the engine 20. Since the sub-catalyst 32f does not have a large resistance compared to the exhaust pipe 31, the sub-catalyst 32f does not affect the moving speed of the exhaust gas. Further, the downstream oxygen detection member 33b can perform oxygen detection with high accuracy for the exhaust gas that has passed through the main catalyst 32b and has a stable oxygen concentration. Therefore, by the combustion control based on these detection results, the control unit 42 can perform the combustion control based on the oxygen detection with high accuracy and high response.

(Embodiment 2)
FIG. 14 is a side view showing a motorcycle according to the second embodiment of the present invention. FIG. 15 is a bottom view of the motorcycle according to the second embodiment. FIG. 16 is a side view of the motorcycle of Embodiment 2 with the body cover removed. FIG. 17 is a bottom view of the motorcycle according to the second embodiment with a body cover removed.

  The vehicle according to the second embodiment is a so-called street type motorcycle 50.

  The motorcycle 50 includes a fuel tank 51, a seat 52, an engine 60 that is an internal combustion engine, and a vehicle body frame 53 that supports them. A head pipe 54 is provided in front of the vehicle body frame 53, a steering shaft is supported on the head pipe 54, and a handle 55 is provided above the steering shaft. A front fork 56 is provided at the lower portion of the steering shaft. A front wheel 57 is rotatably supported at the lower end of the front fork 56. A swing arm 58 is swingably supported on the body frame 53, and a rear wheel 59 is rotatably supported on the rear end portion of the swing arm 58. The body frame 53 includes an upper main frame member 53A that extends rearward and obliquely downward from the head pipe 54, and a lower main frame member 53B.

  The engine 60 is a single-cylinder four-stroke engine, and includes a crankcase portion 61, a cylinder portion 62 that extends upward and obliquely forward from the crankcase portion 61, a cylinder head portion 63 that is connected to the upper portion of the cylinder portion 62, A head cover 64 connected to the upper portion of the cylinder head portion 63 is provided.

  The crankcase portion 61 incorporates a crankshaft, a speed change mechanism, and the like. Lubricating oil is stored in the crankcase portion 61, and the oil is conveyed by an oil pump and circulates in the engine 60.

  The cylinder head portion 63 is formed with an intake passage, an exhaust gas passage, an intake port, and an exhaust port. An intake pipe 66 is connected to the intake passage, and an exhaust pipe 67 for flowing the exhaust gas downstream is connected to the downstream end of the exhaust gas passage.

  A catalyst unit 68 for purifying exhaust gas is disposed in the middle of the exhaust pipe 67. A main catalyst is accommodated in the catalyst unit 68. The main catalyst is a three-way catalyst and purifies the exhaust gas by passing the exhaust gas. The main catalyst is the catalyst having the highest purification performance in the exhaust passage. The main catalyst has a porous structure provided with a plurality of passages sufficiently narrower than the passage width of the exhaust pipe 67. The main catalyst is longer than the maximum width in the direction perpendicular to the passage direction than the length in the passage direction of the exhaust passage. The cross section of the main catalyst in the direction perpendicular to the passage direction of the exhaust passage is larger than the cross sectional area in the direction perpendicular to the passage direction of the exhaust passage before and after the main catalyst.

  An upstream oxygen detection member 70a is disposed in the exhaust passage upstream of the main catalyst. A downstream oxygen detection member 70b is disposed in the exhaust passage downstream of the main catalyst. The upstream oxygen detection member 70a and the downstream oxygen detection member 70b detect oxygen contained in the exhaust gas discharged from only a single combustion chamber of the engine 60, and output the detection result to the electronic control unit.

  A silencer 69 is connected to the downstream portion of the exhaust pipe 67. The silencer 69 has a resonance chamber, an expansion chamber, and a throttle portion, and reduces the volume of the exhaust sound by suppressing the pulsating wave of the exhaust gas. At the downstream end of the silencer 69, a discharge port facing the atmosphere is provided. The exhaust gas that has passed through the silencer 69 is released from the discharge port to the atmosphere.

  As described above, also in the street type motorcycle 50, the catalyst unit 68, the upstream oxygen detection member 70a, and the downstream oxygen detection member 70b can be arranged so as to satisfy the arrangement condition described in the first embodiment. it can.

  Therefore, also in the motorcycle 50 of the second embodiment, the upstream oxygen detection member 70a can detect oxygen in the exhaust gas generated by this combustion immediately after the combustion of the engine 60. Further, in the downstream oxygen detection member 70b, oxygen detection can be performed with high accuracy for the exhaust gas that has passed through the main catalyst of the catalyst unit 68 and has a stable oxygen concentration. Therefore, combustion control based on oxygen detection can be performed with high accuracy and high response by the combustion control based on these detection results.

(Embodiment 3)
FIG. 18 is a side view showing a motorcycle according to the third embodiment of the present invention. FIG. 19 is a bottom view of the motorcycle according to the third embodiment. FIG. 20 is a side view of the motorcycle of Embodiment 3 with the body cover removed. FIG. 21 is a bottom view of the motorcycle of Embodiment 3 with the body cover removed.

  The vehicle of the third embodiment is a so-called scooter type motorcycle 80. The motorcycle 80 of the third embodiment shows an example of a scooter type vehicle in which the exhaust passage extends from the cylinder head portion 97 to the silencer 101 without passing between the left link member 106 and the right link member 105. . Although not particularly limited, the motorcycle 80 of the third embodiment is a forced air-cooled vehicle.

  The motorcycle 80 has a body frame 81. The body frame 81 extends in the vehicle front-rear direction as a whole. The vehicle body frame 81 includes a head frame 82 and a main frame 83 extending obliquely downward and rearward from the head frame 82. The body frame 81 also includes a pair of left and right side frames 84 that extend substantially horizontally from the lower end of the main frame 83 to the rear, and a pair of left and right rear frames 85 that extend obliquely upward and rearward from the rear end of the side frame 84. ing. The vehicle body frame 81 includes a pair of left and right seat frames 86 extending substantially horizontally rearward from the rear end of the rear frame 85.

  A front fork 88 extending downward from the handle 87 is inserted into the head frame 82. A front wheel 89 is attached to the lower end of the front fork 88. Thereby, the front wheel 89 is supported by the vehicle body frame 81 via the front fork 88. A footrest plate 90 is attached to the pair of left and right side frames 84. A pair of left and right side frames 84 constitute a footrest plate support. The footrest plate 90 is a place where a passenger sitting on a seat 91 described later places his / her foot. Therefore, the footrest plate 90 is disposed in front of the seat 91.

  The footrest plate 90 extends in the vehicle front-rear direction. The footrest plate 90 has a gently curved shape in the vehicle front-rear direction. The footrest plate 90 warps upward as it goes from the intermediate portion of the footrest plate 90 to the rear end portion.

  A storage box may be attached to the rear frame 85 and the seat frame 86. The storage box may be disposed between the left and right seat frames 86 in the vehicle left-right direction. The storage box may be formed in a box shape having an open upper surface.

  A seat 91 is attached to the seat frame 86. The seat 91 extends from the middle part of the body frame 81 to the rear end in the vehicle longitudinal direction. The storage box is disposed below the seat 91. The sheet 91 also has a function as a lid for opening and closing the opening on the upper surface of the storage box.

  Below the sheet 91, a lower space G1 (see FIG. 20) is formed as a space below the sheet 91. The storage box is disposed in the lower space G1.

  A vehicle body cover 92 is attached to the rear frame 85. The vehicle body cover 92 is configured to rise upward from the rear portion of the footrest plate 90. The vehicle body cover 92 is disposed so as to surround a part of the lower space G1 (FIG. 20) of the seat 91. The vehicle body cover 92 surrounds the storage box and the front and the left and right sides of the front end of an engine 93 to be described later.

  A unit swing type engine 93 is attached to the body frame 81. As shown in FIG. 21, the engine 93 can swing around the pivot shaft 94 with respect to the vehicle body frame 81. Specifically, a right link member 105 and a left link member 106 are provided so as to extend forward from the engine 93, and the right link member 105 and the left link member 106 rotate about the pivot shaft 94 at their respective ends. Connected as possible. The engine 93 is rotatably connected to the pivot shaft 107 on the right side and the left side.

  The engine 93 is a forced air-cooled single cylinder four-stroke engine. A front end of the engine 93 is covered with a vehicle body cover 92. The engine 93 is disposed behind the vehicle body cover 92 in the lower space G1 of the seat 91 (FIG. 20). The engine 93 includes a crankcase part 95, a cylinder part 96 extending forward from the crankcase part 95, and a cylinder head part 97 connected to the front of the cylinder part 96. The rear wheel 103 is driven by the power of the engine 93.

  The crankcase portion 95 constitutes the rear end portion of the engine 93. The crankcase portion 95 accommodates a crankshaft extending in the vehicle left-right direction. A fan 98 is connected to the right end of the crankshaft so as to be integrally rotatable. The fan 98 is driven by the rotation of the crankshaft. The fan 98 takes in air to cool the engine 93 and introduces air as cooling air.

  The cylinder head portion 97 is connected to the front portion of the cylinder portion 96 and constitutes the front end portion of the engine 93. The cylinder head portion 97 is formed with an intake passage, an exhaust gas passage, an intake port, and an exhaust port. An intake pipe is connected to the intake passage, and an exhaust pipe 99 for flowing the exhaust gas downstream is connected to the downstream end of the exhaust gas passage.

  A catalyst unit 100 for purifying exhaust gas is disposed in the middle of the exhaust pipe 99. A main catalyst is accommodated in the catalyst unit 100. The main catalyst is a three-way catalyst and purifies the exhaust gas by passing the exhaust gas. The main catalyst is the catalyst having the highest purification performance in the exhaust passage. The main catalyst has a porous structure provided with a plurality of passages sufficiently narrower than the passage width of the exhaust pipe 99. The main catalyst is longer than the maximum width in the direction perpendicular to the passage direction than the length in the passage direction of the exhaust passage. The cross section of the main catalyst in the direction perpendicular to the passage direction of the exhaust passage is larger than the cross sectional area in the direction perpendicular to the passage direction of the exhaust passage before and after the main catalyst.

  An upstream oxygen detection member 102a is disposed in the exhaust passage upstream of the main catalyst. A downstream oxygen detection member 102b is disposed in the exhaust passage downstream of the main catalyst. The upstream oxygen detection member 102a and the downstream oxygen detection member 102b detect oxygen contained in the exhaust gas discharged from only a single combustion chamber of the engine 93, and output the detection result to the electronic control unit.

  A silencer 101 is connected to the downstream portion of the exhaust pipe 99. The silencer 101 has a resonance chamber, an expansion chamber, and a throttle portion, and reduces the volume of the exhaust sound by suppressing the pulsating wave of the exhaust gas. At the downstream end of the silencer 101, a discharge port facing the atmosphere is provided. The exhaust gas that has passed through the silencer 101 is discharged from the discharge port to the atmosphere.

  As described above, even in the scooter type motorcycle 80 in which the exhaust pipe 99 does not pass between the left link member 106 and the right link member 105, the catalyst unit 100, An upstream oxygen detection member 102a and a downstream oxygen detection member 102b can be disposed.

  Therefore, also in the motorcycle 80 of the third embodiment, the upstream oxygen detection member 102a can detect oxygen in the exhaust gas generated by this combustion immediately after the combustion of the engine 93. Further, the downstream oxygen detection member 102b can perform oxygen detection with high accuracy for the exhaust gas having passed through the main catalyst of the catalyst unit 100 and having a stable oxygen concentration. Therefore, combustion control based on oxygen detection can be performed with high accuracy and high response by the combustion control based on these detection results.

(Embodiment 4)
FIG. 22 is a side view showing a motorcycle according to the fourth embodiment of the present invention. FIG. 23 is a bottom view of the motorcycle according to the fourth embodiment. FIG. 24 is a side view of the motorcycle of Embodiment 4 with the vehicle body cover removed. FIG. 25 is a bottom view of the motorcycle of Embodiment 4 with the vehicle body cover removed.

  The vehicle of the fourth embodiment is a so-called sports scooter type motorcycle 120. The motorcycle 120 of the fourth embodiment is an example of a scooter type vehicle in which an exhaust passage extends between the left link member 143 and the right link member 142 and extends from the cylinder head portion 137 to the silencer 140. Although not particularly limited, the motorcycle 120 of the fourth embodiment is a water-cooled vehicle.

  The motorcycle 120 has a handle 121 at the front thereof. The handle 121 can steer the front wheel 125 via a steering shaft 123 and a front fork 124 that are inserted through the head pipe 122. A body frame 126 is coupled to the head pipe 122.

  The upper part of the head pipe 122 is covered with a cowling 127. The entire body frame 126 is covered with a body cover 128. A seat 129 is disposed on the upper portion of the vehicle body cover 128.

  The vehicle body frame 126 includes a main frame 130. An engine 131 is attached to the main frame 130. The engine 131 is supported so as to be rotatable about the pivot shaft 132 with respect to the vehicle body frame 126. Specifically, as shown in FIG. 25, the engine 131 is rotatably connected to the pivot shaft 132 on each of the right side and the left side. Further, a right link member 142 and a left link member 143 are provided extending rearward and downward from the engine 131, and the right link member 142 and the left link member 143 can be pivoted to the pivot shaft 144 at their respective tips. It is connected to the.

  A swing arm 133 is swingably supported on the body frame 126, and a rear wheel 134 is rotatably supported at the rear end portion of the swing arm 133. Accordingly, the engine 131 can swing around the pivot shaft 132 together with the rear wheel 134.

  The engine 131 is arranged in a state where the cylinder axis is directed substantially horizontally and forward. The engine 131 is a single cylinder four-stroke engine, and includes a crankcase part 135, a cylinder part 136, and a cylinder head part 137. A crankshaft is accommodated in the crankcase portion 135. A cylinder portion 136 and a cylinder head portion 137 are sequentially stacked on the front wall of the crankcase portion 135. The crankcase part 135, the cylinder part 136, and the cylinder head part 137 are connected to each other using bolts or the like.

  The cylinder part 136 is a cylindrical member connected to the front part of the crankcase part 135. A combustion chamber is provided in the space in the cylinder portion 136, and a piston is accommodated in the combustion chamber so as to be able to reciprocate.

  The cylinder head portion 137 is formed with an intake passage, an exhaust gas passage, an intake port, and an exhaust port. An intake pipe is connected to the intake passage, and an exhaust pipe 138 for flowing the exhaust gas downstream is connected to the downstream end of the exhaust gas passage.

  A silencer 140 is connected to the downstream portion of the exhaust pipe 138. The silencer 140 has a resonance chamber, an expansion chamber, and a throttle portion, and reduces the volume of the exhaust sound by suppressing the pulsating wave of the exhaust gas. At the downstream end of the silencer 140, a discharge port facing the atmosphere is provided. The exhaust gas that has passed through the silencer 140 is discharged from the discharge port to the atmosphere.

  A catalyst unit 139 for purifying exhaust gas is disposed in the middle of the exhaust passage (in the silencer 140). A main catalyst is accommodated in the catalyst unit 139. The main catalyst is a three-way catalyst and purifies the exhaust gas by passing the exhaust gas. The main catalyst is the catalyst having the highest purification performance in the exhaust passage. The main catalyst has a porous structure provided with a plurality of passages sufficiently narrower than the passage width of the exhaust pipe 138. The main catalyst is longer than the maximum width in the direction perpendicular to the passage direction than the length in the passage direction of the exhaust passage. The cross section of the main catalyst in the direction perpendicular to the passage direction of the exhaust passage is larger than the cross sectional area in the direction perpendicular to the passage direction of the exhaust passage before and after the main catalyst.

  An upstream oxygen detection member 141a is disposed in the exhaust passage upstream of the main catalyst. A downstream oxygen detection member 141b is disposed in the exhaust passage downstream of the main catalyst. The upstream oxygen detection member 141a and the downstream oxygen detection member 141b detect oxygen contained in the exhaust gas discharged from only a single combustion chamber of the engine 131, and output the detection result to the electronic control unit.

  As described above, even in the scooter type motorcycle 120 in which the exhaust pipe 138 passes between the left link member 143 and the right link member 142, the catalyst unit 139, An upstream oxygen detection member 141a and a downstream oxygen detection member 141b can be disposed.

  Therefore, also in the motorcycle 120 of the fourth embodiment, the upstream oxygen detection member 141a can detect oxygen in the exhaust gas generated by this combustion immediately after the combustion of the engine 131. Further, the downstream oxygen detection member 141b can perform oxygen detection with high accuracy for the exhaust gas that has passed through the main catalyst of the catalyst unit 139 and has a stable oxygen concentration. Therefore, combustion control based on oxygen detection can be performed with high accuracy and high response by the combustion control based on these detection results.

  The embodiments of the present invention have been described above.

  In the above embodiment, the main catalyst has a porous structure, the length in the passage direction is longer than the maximum width in the direction perpendicular to the passage direction, and the cross-sectional area perpendicular to the passage direction is before or after the main catalyst. It has been explained that it is larger than the sectional area perpendicular to the passage direction of the exhaust passage. However, the main catalyst may not have such a structure, and may be a catalyst having the maximum exhaust gas purification capability in the exhaust passage. Further, one or more catalysts may be arranged in the exhaust passage. In a plurality of cases, the catalyst having the maximum purification ability is the main catalyst, and in one case, this catalyst is the main catalyst. In the present specification, a configuration including a catalyst substance and a support is called a catalyst. Further, the main catalyst may have a configuration in which a plurality of pieces of catalyst are arranged close to each other. Here, the proximity means an interval shorter than the exhaust gas passage length of each piece of the catalyst. The composition of the support or catalyst material of the multiple pieces of catalyst may be the same or multiple.

  In the present invention, the oxygen detection member may be a binary sensor that detects whether the oxygen amount or the oxygen concentration is higher or lower than a predetermined value, and represents the oxygen amount or the oxygen concentration in a plurality of steps or linearly. It is good also as a linear sensor (for example, A / F sensor: Air Fuel ratio sensor) which outputs a detection signal. Preferably, a binary sensor or a linear sensor oxygen detection member may be applied to the upstream oxygen detection member. Preferably, a binary sensor is applied to the downstream oxygen detection member.

  Moreover, in the said embodiment, although arrangement | positioning of the main catalyst was concretely demonstrated using drawing, the arrangement | positioning of a main catalyst is not limited to the arrangement | positioning shown by drawing. The main catalyst may be arranged in the middle of the exhaust passage.

  Moreover, in the said embodiment, although arrangement | positioning of the upstream oxygen detection member was concretely demonstrated using drawing, arrangement | positioning of an upstream oxygen detection member is not limited to the arrangement | positioning shown by drawing. The upstream oxygen detection member may be disposed at a position closer to the exhaust port than the main catalyst in the section of the exhaust passage from the exhaust port to the upstream end of the main catalyst. Here, near means that the distance along the exhaust passage is short.

  Moreover, in the said embodiment, although arrangement | positioning of the downstream oxygen detection member was demonstrated concretely using drawing, the arrangement | positioning of a downstream oxygen detection member is not limited to the arrangement | positioning shown by drawing. The downstream oxygen detection member may be disposed downstream of the downstream end of the main catalyst in the exhaust passage.

  5 to 8 and FIG. 13, the upstream exhaust pipe and the downstream exhaust pipe are drawn straight for simplification, but the upstream exhaust pipe and the downstream exhaust pipe may not be straight.

  Moreover, in the said embodiment, although the structure which has an upstream oxygen detection member and a downstream oxygen detection member was shown in the exhaust system, the structure which has three or more oxygen detection members may be employ | adopted. In the case of having three or more oxygen detection members, it is only necessary that the arrangement of the two oxygen detection members satisfies the arrangement conditions of the upstream oxygen detection member and the downstream oxygen detection member. The arrangement of the remaining oxygen detection members may not correspond to this arrangement condition.

  Moreover, in the said embodiment, the structure which a control part controls the ignition timing of an engine, the fuel injection timing, and the fuel injection quantity based on the output of an upstream oxygen detection member and a downstream oxygen detection member was shown. However, the control processing based on the outputs of the upstream oxygen detection member and the downstream oxygen detection member is not particularly limited, and one or two of the engine ignition timing, the fuel injection timing, and the fuel injection amount. May be a separate control process.

  In the above embodiment, the motorcycle is exemplified as the vehicle including the engine unit. However, any vehicle may be used as long as the vehicle moves with the power of the engine unit.

  In the present invention, in addition to the exhaust gas discharged from the combustion chamber of the engine, the secondary air injection device is used for the gas flowing around both the upstream oxygen detection member and the downstream oxygen detection member or at least a part of the latter. (AI: air injection) gas may be included. Even in this case, at least a part of the upstream oxygen detection member and the downstream oxygen detection member is exposed to the exhaust gas discharged from only a single combustion chamber to detect oxygen.

  The present invention can be embodied in many different forms. This disclosure should be regarded as providing embodiments of the principles of the invention. Many illustrated embodiments are described herein with the understanding that these embodiments are not intended to limit the invention to the preferred embodiments described and / or illustrated herein. .

  Several illustrative embodiments of the invention have been described herein. The present invention is not limited to the various preferred embodiments described herein. The present invention includes all embodiments including equivalent elements, modifications, deletions, combinations (eg, combinations of features across various embodiments), improvements, and / or changes that may be recognized by those skilled in the art based on this disclosure. Include. Claim limitations should be construed broadly based on the terms used in the claims and should not be limited to the embodiments described herein or in the process of this application. Such an embodiment should be construed as non-exclusive. For example, in this disclosure, the terms “preferably” and “good” are non-exclusive, and “preferably but not limited to” or “good but not limited thereto” "Means.

  INDUSTRIAL APPLICABILITY The present invention is useful for an engine unit that generates power for a vehicle and a vehicle that moves with the power of the engine unit.

1, 50, 80, 120 Motorcycle 2, 53, 81, 126 Body frame 3, 54, 122 Head pipe 4, 83, 130 Main frame 8, 57, 89, 125 Front wheel 15, 59, 103, 134 Rear wheel 18 61, 95, 135 Crankcase part 20, 60, 93, 131 Engine 24A Combustion chamber 26, 63, 97, 137 Cylinder head part 30, 66 Intake pipe 31, 67, 99, 138 Exhaust pipe 32, 68, 100, 139 Catalyst unit 32b Main catalyst 32s Sub catalyst 32f Sub catalyst (coating catalyst)
33a, 70a, 102a, 141a Upstream oxygen detection member 33b, 70b, 102b, 141b Downstream oxygen detection member 34, 69, 101, 140 Silencer 34e Release port 35 Crank angle sensor 36 Ignition coil 37 Injector 38 Fuel pump 40 Electronic control unit 41 Pulse processing unit 42 Control unit 43 Ignition drive circuit 44 Injector drive circuit 45 Pump drive circuit P1 Intake passage P2 Exhaust passage P2a Exhaust port 201 Exhaust passage

Claims (11)

A single-cylinder four-stroke engine,
An exhaust passage for flowing exhaust gas of the single-cylinder four-stroke engine;
A main catalyst disposed in the middle of the exhaust passage and having the highest purification capacity in the exhaust passage;
In the section of the exhaust passage from the exhaust port of the single-cylinder four-stroke engine to the upstream end of the main catalyst, the single-cylinder four-stroke engine is disposed at a position closer to the exhaust port than the main catalyst. An upstream oxygen detection member that at least partly is exposed to exhaust gas discharged from only the chamber and detects oxygen;
A downstream oxygen detection member that is disposed downstream of the downstream end of the main catalyst in the exhaust passage and is at least partially exposed to exhaust gas discharged from only a single combustion chamber of the single cylinder four-stroke engine to detect oxygen When,
A control unit that performs combustion control of the single-cylinder four-stroke engine based on the detection result of the upstream oxygen detection member and the detection result of the downstream oxygen detection member;
An engine unit comprising A plurality of catalysts including the main catalyst are disposed in the exhaust passage,
The upstream oxygen detection member is disposed in the exhaust passage at a position closer to the exhaust port than the most upstream end of the plurality of catalysts in a section from the exhaust port to the most upstream end of the plurality of catalysts.
The downstream oxygen detection member is disposed downstream of the most downstream ends of the plurality of catalysts in the exhaust passage.
The engine unit according to claim 1. A plurality of catalysts including the main catalyst are disposed in the exhaust passage,
The upstream oxygen detection member is disposed in the exhaust passage at a position closer to the exhaust port than the most upstream end of the plurality of catalysts in a section from the exhaust port to the most upstream end of the plurality of catalysts.
The downstream oxygen detection member is disposed downstream of the main catalyst in the exhaust passage.
The engine unit according to claim 1. The cross-sectional area perpendicular to the flow direction of the exhaust gas of the main catalyst is larger than the cross-sectional area orthogonal to the flow direction of the exhaust gas before and after the main catalyst,
The engine unit according to claim 1. The main catalyst has a porous structure for flowing exhaust gas through a plurality of holes,
The engine unit according to claim 1. Each of the plurality of catalysts has a porous structure that allows exhaust gas to flow through a plurality of holes.
The engine unit according to claim 2 or claim 3. The main catalyst is disposed at a position where the passage length from the exhaust port of the single-cylinder four-stroke engine to the upstream end of the main catalyst is shorter than the passage length from the downstream end of the main catalyst to the discharge port facing the atmosphere. To be
The engine unit according to claim 1. The main catalyst is arranged at a position where the passage length from the downstream end of the main catalyst to the discharge port facing the atmosphere is shorter than the passage length from the exhaust port of the single-cylinder four-stroke engine to the upstream end of the main catalyst. To be
The engine unit according to claim 1. A silencer constituting a part of the exhaust passage;
An exhaust pipe for sending exhaust gas from the single-cylinder four-stroke engine to the silencer;
With
The main catalyst is disposed in the middle of the exhaust pipe,
The downstream oxygen detection member is disposed in the exhaust pipe downstream from the main catalyst.
The engine unit according to claim 1. A silencer constituting a part of the exhaust passage;
An exhaust pipe for sending exhaust gas from the single-cylinder four-stroke engine to the silencer;
With
The main catalyst is disposed in the silencer,
The downstream oxygen detection member is disposed downstream of the main catalyst in the exhaust passage of the silencer.
The engine unit according to claim 1. A vehicle comprising the engine unit according to any one of claims 1 to 10.

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