JP2002227641A - Exhaust emission control device for motorcycle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To arrange a secondary air filter for a device of controlling exhaust emission by introducing the secondary air, a control unit therefore and a piping therebetween by effectively and reasonably utilizing the dead space of a vehicle body in a motorcycle having restriction in the space to arrange the instruments concerned. SOLUTION: The secondary air filter 85 is set in a space 13a between a housing box 12 and a fuel tank 11 both disposed at the vehicular side opposed to the side at which the control unit 100 is provided. Further, there is provided the piping for the secondary air connecting to the control unit 100 and air filter 85 while crossing the space between the housing box 12 and the fuel tank 11 from one side of the vehicular body to the other side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle such as a motorcycle having a forced air-cooled engine, and more particularly to an apparatus for purifying unburned components contained in exhaust gas of the engine, and more particularly to an apparatus for purifying unburned components contained in exhaust gas of the engine. This is related to the arrangement of the secondary air filter and the control unit (secondary air intake valve unit; the same applies hereinafter), which can be rationally arranged by effectively utilizing the dead space around the storage box. It is.

[0002]

2. Description of the Related Art Recently, exhaust gas regulations have been tightened even for motorcycles having a small exhaust gas amount per vehicle. For this reason, in some motorcycles, secondary air is introduced into an exhaust system of an engine, and HC and C contained in exhaust gas are introduced.
Exhaust gas purification measures for burning unburned components such as O are employed. When purifying exhaust gas using this secondary air, it is important to mix secondary air with unburned components contained in the exhaust gas. That is, it is desirable that the fuel be injected immediately after the exhaust valve so as to face the flow of the exhaust gas. For this reason, the introduction pipe for introducing secondary air is
It is directly connected to a cylinder head having an exhaust valve.

[0003] In a scooter-type motorcycle, a space between a front fork and a seat is occupied as a space for accommodating a driver's feet, and an engine and its accessories are installed between the front fork and a seat. Is extremely difficult. For this reason, the engine is integrated with the rear wheel and the V-belt transmission that drives the rear wheel, and is disposed below the seat. This type of motorcycle employs a so-called forced air-cooled engine that forcibly blows cooling air around these cylinder blocks and cylinder heads because the engine enters a deep position below the seat. I have. In this engine, the cylinder block and cylinder head are covered with an air shroud, and cooling air is forcibly blown into the air guide passage inside this air shroud via a fan directly connected to the crankshaft. Has become.

[0004]

However, when secondary air is introduced into the exhaust system of the forced air-cooled engine and the secondary air introduction pipe is connected to the cylinder head as described above, the introduction pipe is formed. The pipe will be provided in the air guide passage inside the air shroud. Then, since the introduction pipe penetrates the air shroud, it is necessary to remove the introduction pipe from the air shroud every time maintenance and inspection of the engine is performed, which requires a great deal of work. Moreover,
Since the introduction pipe is located in the air guide passage, the flow of the cooling air in the air guide passage may be hindered by the presence of the introduction pipe. Therefore, there arises a problem that the flow resistance of the cooling air increases and the cooling efficiency around the cylinder head decreases. In addition, since the introduction pipe is heated by the high-temperature exhaust gas, the heat generated from the introduction pipe is also large, which has a large thermal effect on the cooling air flowing through the air guide passage including the air shroud. . From this, especially when the rotation speed of the fan is low, such as during idling operation, since the amount of cooling air flowing through the air guide passage is small, the inside of the air shroud becomes hot due to the influence of heat from the introduction pipe, There arises a problem that the cooling performance of the engine deteriorates. In addition, for motorcycles where the space for installing related equipment is limited, the placement of secondary air filters and control units for exhaust gas purification devices by introducing secondary air, and how to make dead space effective in piping between them The problem is how to arrange them rationally while using them.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an exhaust gas purifying apparatus for a vehicle by introducing secondary air, in which a secondary air filter and a control unit are rationally arranged by effectively utilizing dead space, and piping of the exhaust gas is imposed. It is to devise these arrangements so that they can be performed rationally.

[0006]

Means taken to solve the above problem is that an exhaust gas purifying apparatus for a motorcycle is constructed as follows. A fuel tank is provided on the main pipe of the vehicle body and a storage box having a substantially circular peripheral surface is provided at the rear thereof.The engine extends below the main pipe and extends rearward from one side of the crankcase of the engine. A power unit having a transmission case on which a rear wheel is supported is provided.A front part of the power unit is pivotably supported on the vehicle body, and a rear wheel is sandwiched between the transmission case and the rear of a crankcase of the power unit. In a motorcycle in which the exhaust silencer of the engine is located on the opposite side, the engine has a cylinder block that is tilted forward to a horizontal or nearly horizontal angle, and is opened downward in front of the cylinder block. Exhaust passage,
At the open end of this exhaust passage, an exhaust pipe connected to a rear exhaust silencer through a position lower than the cylinder block is connected, and an exhaust system of the engine from the exhaust passage to the exhaust pipe is provided with an exhaust gas. A secondary air introduction pipe for introducing secondary air for burning the contained unburned components is connected, and the secondary air introduction pipe is connected to a reed valve that opens and closes in response to exhaust pulsation and to the exhaust system during deceleration operation. A control unit including a normally open type cut valve that shuts off the flow of secondary air is provided, and the control unit is provided in a space between the storage box and the fuel tank on the other side of the vehicle body on the side opposite to the side where the control unit is provided. An air filter for the secondary air is provided, and a gap between the storage box and the fuel tank is traversed from one side of the vehicle body to the other side, and the secondary unit is connected to the control unit and the air filter. To the provision of care piping.

[0007]

Since the storage box has a substantially circular peripheral surface, there is a space between the storage box and the fuel tank on the outer side of the vehicle body. In a motorcycle having a small space, the air filter for the secondary air can be reasonably arranged without difficulty by effectively utilizing the space. In addition, a pipe connecting the control unit and the air filter can be easily piped through a gap between the storage box and the fuel tank. Further, by effectively utilizing the space and the gap between the storage box and the fuel tank, the air filter is disposed, and piping is provided between the air filter and the control unit, so that a motorcycle is provided. The arrangement of various devices can be made compact. The “motorcycle” also means a vehicle such as a motorcycle.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a first embodiment of the present invention will be described with reference to FIGS.
Description will be made based on 0. FIG. 10 shows a scooter-type motorcycle. In the figure, reference numeral 1 denotes a frame constituting the vehicle body, 2 denotes a front fork, and 3 denotes a front wheel. The frame 1 includes a pair of left and right main pipes 4a and 4b. The main pipes 4a and 4b include a horizontal portion 5 extending substantially horizontally in the front-rear direction behind the front wheel 3, an upright portion 6 rising from the rear end of the horizontal portion 5, and a support portion extending rearward from the upper end of the upright portion 6. 7 are provided. Support part 7
Has a slanted portion 7a that is slanted rearward and upward. The rear ends of the inclined portions 7a of the main pipes 4a, 4b are integrally connected by a substantially U-shaped connecting portion 8, and the upper surface of the rear end of the inclined portion 7a is an auxiliary projecting above the connecting portion 8. Pipe 9 is welded. The horizontal portion 5 of the main pipes 4a and 4b is provided with a step board 10 on which a driver's foot rests.

As shown in FIGS. 1 and 2, a fuel tank 11 and a storage box 12 for storing a helmet and the like are supported side by side on the support portion 7 of the main pipes 4a and 4b. The fuel tank 11 has a box shape having a tapered front portion, and is located on the front half of the support portion 7. The storage box 12 has a substantially circular opening 12 a on the upper surface, and is located on the rear half of the support 7. And the peripheral wall 12b of the storage box 12
Are curved in an arc shape along the opening shape of the opening 12a. From this, as shown in FIG. 1, on both left and right sides between the storage box 12 and the fuel tank 11,
A space 13a shaped to expand as it progresses to the side,
13b is formed. A seat 14 is disposed above the fuel tank 11 and the storage box 12. The seat 14 covers the fuel tank 11 and the storage box 12 from above. When the seat 14 is turned upward with the front end as a pivot point, the opening 12a of the fuel tank 11 and the storage box 12 is exposed. Has become.

A unit swing type power unit 16 is disposed below the support 7 of the main pipes 4a and 4b. As shown in FIG. 7, the power unit 16 includes a four-cycle engine 17 and a transmission case 19 extending rearward from a left side of a crankcase 18 of the engine 17. And this power unit 16
, I.e., the upper part of the crankcase 18 is pivotally supported via a pivot shaft 21 to an engine bracket 20 welded to the support portion 7 of the main pipes 4a and 4b. The rear of the transmission case 19 and the crankcase 18
Between the auxiliary arm 22 extending rearward from the right side of the
The rear wheel 23 is supported. The rear part of the transmission case 19 and the rear part of the auxiliary arm 22 are connected to the main pipes 4a, 4b.
Are suspended via a pair of shock absorbers 24a and 24b provided between the shock absorbers 24a and 24b. Therefore, when the rear wheel 23 gets over the unevenness, the entire power unit 16 including the engine 17 swings up and down around the pivot shaft 21, and the transmission case 19 functions as a rear arm. Also serves as. The left side surface of the transmission case 19 is covered with a case cover 25. A transmission chamber 26 is formed between the transmission case 19 and the case cover 25. In the transmission chamber 26, the crankshaft 2 of the engine 17 is provided.
A V-belt automatic transmission 28 for interlocking the rear wheel 7 with the rear wheel 23 is accommodated.

As shown in FIG. 7, the engine 17 includes a cylinder block 30 extending substantially horizontally from the front end of the crankcase 18 toward the front. The cylinder block 30, the axis X ₁ of the cylinder 30a are largely tilted forward to a nearly horizontal angle, the piston 31 is accommodated in the cylinder 30a. The piston 31
The cylinder block 30 is connected to the crankshaft 27 via a connecting rod 32, and a large number of cooling fins 33 are formed on the outer peripheral surface of the cylinder block 30.

A cylinder head 34 is connected to the front end face of the cylinder block 30. The cylinder head 34 is located immediately after the step board 10 due to the forward inclination of the cylinder 30a. As shown in FIG. 9, an intake passage 36 and an exhaust passage 37 connected to the combustion chamber 35 are formed inside the cylinder head 34. The intake passage 36 and the exhaust passage 37 are provided with an intake port 36a and an exhaust port 37a that open to the combustion chamber 35. The intake port 36a and the exhaust port 37a are individually opened and closed by an intake valve 38 and an exhaust valve 39. It has become so. A valve chamber 41 is formed inside the cylinder head 34. A camshaft 42 for opening and closing the intake valve 38 and the exhaust valve 39 is housed in the valve operating chamber 41.
2 is the crankshaft 27 via the timing chain 43
It is linked to.

The intake passage 36 extends out of the cylinder head 34 as shown in FIG.
The upstream end of 6 is opened rearward. An intake pipe 45 is connected to an upstream open end of the intake passage 36.
As shown in FIGS. 1 and 2, the intake pipe 45 extends rearward above the cylinder block 30, and a carburetor 46 is connected to an upstream end of the intake pipe 45. The vaporizer 46 is connected to an air cleaner 48 via a joint 47. The air cleaner 48 is provided in the transmission case 1.
9 and is attached to the upper surface of the air cleaner 48.
A series of intake systems from to the intake pipe 45 are swung together with the power unit 16.

The exhaust passage 37 is provided in the cylinder head 3.
4 is open on the lower surface. An exhaust pipe 50 is connected to an open end of the exhaust passage 37. As shown in FIG. 2, the exhaust pipe 50 is guided rearward from below the cylinder block 30 through the lower side of the crankcase 18. A muffler 51 is connected to a rear end of the exhaust pipe 50. The silencer 51 is located immediately after the right side of the crankcase 18 and is bolted to the crankcase 18 and the auxiliary arm 22. Therefore, a series of exhaust systems from the exhaust passage 37 to the muffler 51 are also swung together with the power unit 16. In the case of the present embodiment, the rear surface of the right side portion of the crankcase 18 is curved in an arc shape centering on the crankshaft 27, and the front surface of the silencer 51 facing the rear surface advances upward. And is inclined so as to be located rearward. From this, the crankcase 18 and the silencer 51
A dead space 52 having a shape that expands as it goes upward is present between.

As shown in FIGS. 7 and 8, the engine 1
7 is surrounded by an air shroud 5.
5 is covered. An air guide passage 55a is formed between the air shroud 55 and the cylinder block 30. At the right end of the air shroud 55, a fan cover 56 is provided continuously. An axial fan 57 is disposed inside the fan cover 56, and the fan 57 is located on the right side of the cylinder block 30. The rotation shaft 58 of the fan 57
Is supported by a boss portion 60 of a support stay 59 extending from the crankcase 18 via a bearing 61, and a driven pulley 62 is mounted on the rotating shaft 58.

The fan cover 56 also integrally covers a flywheel magnet 63 fixed to the right end of the crankshaft 27. The flywheel magnet 63 includes a drive pulley 64 that rotates integrally with the flywheel magnet 63. A V-belt 65 is provided between the drive pulley 64 and the driven pulley 62.
Is wound. For this reason, the fan 57 is driven to be accelerated by the power transmission from the crankshaft 27. When the fan 57 is driven to rotate, the outside air is sucked through the suction port 66 on the right side of the fan cover 56. Then, the outside air is forcibly blown as cooling air to the wind guide passage 55 a inside the air shroud 55.

The left end of the air shroud 55
As shown in FIG. 8, a downwardly opening discharge port 67 is provided, and the cooling air blown into the air guide passage 55a through the discharge port 67 is discharged to the outside. The engine 17 of this embodiment has a cylinder head 34 of a water-cooled type.
Most of 4 is not covered with the air shroud 55,
It is exposed to the outside as it is. Inside the cylinder head 34, a cooling water passage 70 is provided around the combustion chamber 35.
Is provided. The cooling water passage 70 is connected to a radiator 71 via a pipe (not shown). Radiator 7
1 is installed outside the suction port 66 of the fan cover 56. For this reason, the radiator 71 is located in the intake path of the engine cooling air, and the cooling air is always guided to the radiator 71 during the operation of the engine.

A radiator 71 is mounted on the cylinder head 34.
A cooling water pump 72 is provided to guide the cooling water subjected to the heat exchange to the cooling water passage 70, and the cooling water pump 72 is driven by the cam shaft 42. The periphery of the engine 17 to the periphery of the fuel tank 11 and the storage box 12 is covered with a cover 73. Cover 73
Is connected to the seat 14, and a tail lamp 74 is incorporated in the rear surface of the cover 73. A rear fender 75 is provided continuously below the tail lamp 74. The rear fender 75 covers a range from the rear to the rear of the rear wheel 23. Rear fender 7
The upper part of 5 extends between the inclined parts 7a of the main pipes 4a, 4b and extends forward along the inclined parts 7a, covering the storage box 12 from below.

By the way, the power unit 16 includes:
A secondary air introduction device 80 for burning unburned components such as HC and CO contained in the exhaust gas of the engine 17 is provided. The secondary air introduction device 80 includes a secondary air introduction pipe 81 as shown in FIGS. The secondary air introduction pipe 81 is a first pipe 81a made of a metal pipe.
And a second pipe 81b formed of a flexible pipe such as a rubber hose. First piping 81
A connection fitting 82 is provided at the distal end of “a”. The connection fitting 82 is screwed into a mounting opening 83 of the cylinder head 34 as shown in FIG. The mounting port 83 is exposed outside without being covered by the air shroud 55, and the mounting port 83 is located on the lower surface of the cylinder head 34 adjacent to the open end of the exhaust passage 37. The mounting opening 83 is open to the exhaust passage 37, and the opening end of the mounting opening 83 to the exhaust passage 37 is connected to the exhaust opening 37a.
Is provided at a position immediately opposite to the exhaust gas flow direction. As shown in FIG. 2, the first pipe 81 a connected to the cylinder head 34 is bent downward toward the rear after being led out below the cylinder head 34, and is bent rearward along the exhaust pipe 50 as it is. You are being led.

The rear portion of the first pipe 81a is provided with a radiator 7
Behind 1 is bent upward. As shown in FIGS. 1 to 3, the second pipe 81 b connected to the first pipe 81 a is guided to the upper part of the muffler 51 through the right side of the crankcase 18 and from there to the right main pipe 4 b. The fuel tank 1 through the inside
It is guided to a gap between the storage box 1 and the storage box 12, and crosses this gap from right to left. And the second
The leading end of the pipe 81b is guided to a left space 13a formed between the fuel tank 11 and the storage box 12. In this space 13a, an air filter 85 dedicated to secondary air is arranged. As shown in FIGS. 3 and 4, the air filter 85 includes a tubular filter case 86 that is vertically long in the vertical direction. Filter case 86
Has a triangular shape that expands as it goes to the side as viewed in plan, and is efficiently stored in the space 13a.

A secondary air inlet 87 is formed at the lower part of the peripheral surface of the filter case 86, and a secondary air inlet 87 at a position higher than the inlet 87 is provided at the center of the upper surface of the filter case 86. An air outlet 88 is formed. An element 89 is housed inside the filter case 86. The element 89 has a hollow cylindrical shape with a closed bottom surface, and has an inflow passage 89a for filtered secondary air inside. The element 89 is pressed upward by a spring 90 interposed between the element 89 and the bottom plate 86 a of the filter case 86, and the upper end of the inflow passage 89 a of the element 89 is fitted and held in the outlet 88 by this pressing. Have been. The outlet 88 extends upward, and the second pipe 81b is connected to an open end of the outlet 88. Such an air filter 85 is located on the left main pipe 4a as shown in FIGS. In this case, brackets 90a, 90 extending upward to support the fuel tank 11 and the seat 14 are provided on the left and right main pipes 4a, 4b.
b is welded, and a tongue piece 91 projecting from the upper surface of the filter case 86 is provided on the inner surface of the left bracket 90a.
Are bolted.

A suction pipe 93 for secondary air is connected to an inlet 87 of the filter case 86. The suction pipe 93 is
For example, it is composed of a flexible pipe such as a rubber hose. The suction pipe 93 extends from the left to the right through the gap between the fuel tank 11 and the storage box 12 under the second pipe 81b. The distal end of the suction pipe 93 penetrates the right bracket 90b, and is guided rearward along the right side surface of the storage box 12. That is, as shown in FIGS. 1 and 3, the suction pipe 93 is guided rearward from the front surface of the storage box 12 along the right side surface.
It is located above the rear end of the right main pipe 4b.
At the rear end of the suction pipe 93, a suction port 9 that is bent downward is provided.
4 is inserted. The sucker 94 is covered with a damper 95 having air permeability such as a sponge. The suction port 94 covered with the damper 95 is connected to the cover 7.
3. It is pushed into the gap surrounded by the right main pipe 4b, the auxiliary pipe 9 and the upper part of the rear fender 75, so that the damper 95 is held on the upper surface side of the main pipe 4b.

The second pipe 81b of the secondary air introduction pipe 81
Is divided into a first half 98a and a second half 98b.
A control unit 1 for supplying secondary air to the exhaust passage 37 of the engine 17 is provided in the second pipe 81b divided portion.
00 is provided. The control unit 100 includes a box-shaped main body case 101 as shown in FIG. The main body case 101 has an inlet 102 and an outlet 103 for secondary air. These inlet 102 and outlet 1
03 is opened to the air chamber 104 in the main body case 101. The inlet 102 has a second half 9 of the second pipe 81b.
8b is connected and the outlet 103 is connected to the second
The first half 98a of the pipe 81b is connected.

A reed valve 105 is provided in the air chamber 104 of the main body case 101. The reed valve 105 is opened and closed in accordance with the pulsating pressure of the exhaust gas. When a negative pressure in the exhaust passage 37 acts on the air chamber 104 via the secondary air introduction pipe 81, the reed valve 105 is opened and the reed valve 105 is opened. 102 and the outlet 103 are communicated.

The main body case 101 contains the engine 1
7, a cut valve 108 for obtaining an appropriate amount of secondary air according to the operation state, and an actuator 109 for driving the cut valve 108 are incorporated. Cut valve 1
08 is an opening 1 of the inlet 102 to the air chamber 104.
The valve body 110 includes a valve body 110 that comes in contact with and separates from the valve body 02a, and a valve shaft 111 that supports the valve body 110. Actuator 109
Is provided with a cover 112 covered on the main body case 101, and a diaphragm 11 is provided inside the cover 112.
3 are accommodated. The diaphragm 113 is a cover 1
12 is divided into a negative pressure chamber 114 and an atmospheric pressure chamber 115. The negative pressure chamber 114 is connected to the intake pipe 45 via a negative pressure guide hose 116.
During the operation of the engine, the intake negative pressure in the intake pipe 45 is introduced.

The valve shaft 111 of the cut valve 108 is slidably penetrated through the main body case 101 and connected to the diaphragm 113. The diaphragm 113 includes the spring 11
7, the valve body 110 is pressed toward the atmospheric pressure chamber 115, and the valve body 110 is
, And the cut valve 108 is maintained in the normally open state.

The control unit 100 is supported by the crankcase 18 together with the front end of the silencer 51. Therefore, the control unit 100 has just the silencer 5
The power unit 16 is housed in a dead space 52 generated between the power unit 1 and the crankcase 18 and swings integrally with the power unit 16. Next, the operation of the above configuration will be described.

During the operation of the engine, exhaust pulsation occurs in the exhaust passage 37, and the negative pressure in the exhaust passage 37 is applied to the reed valve 1 of the control unit 100 through the secondary air introduction pipe 81.
05, the reed valve 105 is opened.
Then, the suction port 94 located below the rear end of the seat 14
From outside air is sucked in as secondary air. The secondary air is guided to an air filter 85 through a suction pipe 93, and dust and the like are filtered while passing through the element 89. The clean secondary air filtered by the air filter 85 is
Injected into the exhaust passage 37 via the secondary air introduction pipe 81,
The exhaust gas is mixed with the exhaust gas flowing through the exhaust passage 37. Therefore, unburned components in the exhaust gas are burned in an exhaust system such as the exhaust passage 37 and the exhaust pipe 50, and the purification of the exhaust gas is promoted.

On the other hand, at the time of deceleration operation such as when the throttle valve of the carburetor 46 is suddenly closed, the venturi passage of the carburetor 46 is throttled, the flow speed of the intake air increases, and the amount of fuel suction increases. Then, the air-fuel mixture becomes temporarily rich, and a misfire may occur in the combustion chamber 35, so that a large amount of the unburned air-fuel mixture is discharged into the exhaust passage 37. At this time, when the secondary air is injected into the exhaust passage 37, a so-called afterburn occurs in which the unburned air-fuel mixture explosively burns with an appropriate air-fuel ratio by mixing with the secondary air.

However, in the above configuration, since the negative pressure chamber 114 of the control unit 100 and the intake pipe 45 are communicated with each other through the negative pressure introducing hose 116, the negative pressure in the intake pipe 45 increases during the deceleration operation. Then, the diaphragm 113
Is deformed toward the negative pressure chamber 114 against the urging force of the spring 117. Due to this deformation, the valve body 110 of the cut valve 108 causes the secondary air from the air filter 85 to transfer the secondary air from the air chamber 1.
The entrance 102 leading to 04 is closed. As a result, during the deceleration operation, the supply of the secondary air to the exhaust passage 37 is stopped,
The occurrence of afterburn is prevented.

Incidentally, the forced air-cooled engine 17
In this case, the cylinder head 34 is led out of the air shroud 55, and a secondary air introduction pipe 81 laid along the exhaust pipe 50 is connected to the leading part. For this reason, the secondary air introduction pipe 81 does not penetrate the air shroud 55, and it is not necessary to remove the secondary air introduction pipe 81 from the air shroud 55 every time maintenance and inspection is performed around the cylinder head 34 and the cylinder block 30. . Therefore, even if the secondary air introduction device 80 is attached to the forced air-cooled engine 17, the maintainability is not impaired.

The secondary air introduction pipe 81 is connected to the air guide passage 55.
Therefore, the flow of the cooling air in the air guide passage 55a is not blocked or obstructed by the secondary air introduction pipe 81, and the flow of the cooling air is smoothed accordingly. At the same time, during the operation of the engine, the secondary air introduction pipe 81, which becomes hot due to the inflow of the exhaust gas, is directly exposed to the outside of the air shroud 55, so that the heat of the secondary air introduction pipe 81 is released to the atmosphere. Will be naturally radiated,
The thermal influence on the wind guide passage 55a and the cooling air flowing therethrough is reduced.

In addition, since the cylinder block 30 is largely inclined forward, the cylinder head 34 is located immediately behind the step board 10, and the cylinder head 34 itself moves forward along the lower surface of the step board 10. Is exposed to the flow of traveling wind flowing from For this reason, even if the cylinder head 34 is drawn out without being covered with the air shroud 55, the cooling performance of the cylinder head 34 can be sufficiently ensured, and the flow of the cooling air can be smoothed. In addition to reducing the thermal influence on the wind guide passage 55a, the entire engine 17 can be efficiently cooled.

In the first embodiment, the cylinder head of the engine is of a water-cooled type. However, the present invention is not limited to this, and the cylinder head 130 may be replaced with a cylinder head as in the second embodiment of the present invention shown in FIG. It may be air-cooled. That is, also in the second embodiment, as shown in FIG.
The entire cylinder head 130 is led out without being covered with the air shroud 55, and cooling fins 131 for heat radiation protrude from the outer peripheral surface of the cylinder head 130. In the second embodiment, a mounting port 83 to which the secondary air introduction pipe 81 is connected is provided on a side surface of the cylinder head 130, and is located between the intake passage 36 and the exhaust passage 37. I have.

The intake passage 36 extending upward from the upper surface of the cylinder head 130 is curved laterally as it goes upward to avoid interference with the air shroud 55. In each of the above embodiments, the entire cylinder head is led out of the air shroud. However, the present invention is not limited to this. For example, only the vicinity of the opening end of the exhaust passage in the cylinder head is partially removed. And a mounting port to which a secondary air introduction pipe is connected may be provided. Further, in the first embodiment, only the secondary air is introduced into the exhaust system, but a catalyst for purifying exhaust gas may be provided in the exhaust system.

[0036]

According to the present invention described in detail above, it is not necessary to remove the secondary air introduction pipe from the air shroud every time maintenance and inspection is performed around the cylinder head and the cylinder block. Even if secondary air is introduced, the maintainability is not impaired. Further, since the secondary air introduction pipe is separated from the air guide passage, the flow of the cooling air in the air guide passage is not interrupted or obstructed by the secondary air introduction pipe, and the cooling air flow is accordingly reduced. The flow becomes smooth. At the same time, the secondary air introduction pipe itself is directly exposed to the outside of the air shroud, and the heat of the secondary air introduction pipe is naturally radiated into the atmosphere. Thermal effects are reduced. Moreover,
When the cylinder block is tilted forward, the cylinder head itself is exposed to the flow of the traveling wind flowing from the front, so that the cooling performance of the cylinder head can be sufficiently ensured. Therefore, the whole engine can be efficiently cooled, in addition to the smooth flow of the cooling air and the reduction of the thermal influence on the wind guide passage.

Further, the storage box 12 having a substantially circular peripheral surface.
By effectively utilizing the space 13a remaining between the fuel tank 11 and the fuel tank 11, the secondary air air filter 85 can be reasonably arranged without difficulty. In addition, a pipe connecting the control unit 100 and the air filter 85 can be easily piped through a gap between the storage box 12 and the fuel tank 11.
a and the gap between the storage box 12 and the fuel tank 11 is used effectively to form a pipe between the air filter 85 and the control unit 100, so that the secondary air air filter 85 of the motorcycle The control unit 100 and the piping between them can be stored reasonably and compactly in a small space.

[Brief description of the drawings]

FIG. 1 shows a power unit according to a first embodiment of the present invention;
It is a top view showing the layout of a secondary air introduction device to a fuel tank and a storage box.

FIG. 2 is a side view showing a state where a secondary air introduction device is incorporated in the power unit.

FIG. 3 is a plan view showing a layout of a secondary air introduction device with respect to a frame.

FIG. 4 is a view as viewed in the direction of the arrow A in FIG. 3;

FIG. 5 is a cross-sectional view showing a positional relationship of a suction end of secondary air with respect to a frame and a cover.

FIG. 6 is a cross-sectional view schematically showing an overall configuration of a secondary air introduction device.

FIG. 7 is a sectional view of the power unit around the engine.

FIG. 8 is a sectional view showing a positional relationship between a cylinder block, a fan, and an air shroud.

FIG. 9 is a sectional view of a cylinder head.

FIG. 10 is a side view of the scooter type motorcycle.

FIG. 11A is a side view of a cylinder head according to a second embodiment of the present invention, and FIG. 11B is a front view of the cylinder head.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Body (frame) 13a, 13b ... Space 17 ... Engine 33 ... Cooling fin 34 ... Cylinder head 37 ... Exhaust passage 55 ... Air shroud 55a ... Wind guide Passage 57: Fan 81: Secondary air introduction pipe 83: Mounting port 85: Air filter for secondary air 100: Control unit

Claims (1)

[Claims] 1. A fuel tank is provided on a main pipe of a vehicle body and a storage box having a substantially circular peripheral surface is provided at a rear portion thereof. An engine extends below the main pipe and extends rearward from one side of a crankcase of the engine. A power unit having a transmission case in which a rear wheel is supported at a rear end thereof is provided.A front portion of the power unit is pivotably supported on a vehicle body, and the power transmission case and the transmission case are provided behind a crankcase of the power unit. Is a motorcycle in which the exhaust muffler of the engine is located on the opposite side of the rear wheel, wherein the engine has a cylinder block that is tilted forward to a horizontal or nearly horizontal angle, and a front of the cylinder block. At the open end of the exhaust passage, at the open end of the exhaust passage, through a position lower than the cylinder block, A secondary air inlet for connecting an exhaust pipe connected to the gas silencer and for introducing secondary air for burning unburned components contained in the exhaust gas into an exhaust system of the engine from the exhaust passage to the exhaust pipe. A control unit including a reed valve that opens and closes in response to exhaust pulsation and a normally-open cut valve that shuts off the flow of secondary air to the exhaust system during deceleration operation is provided on the secondary air introduction pipe. An air filter for the secondary air is provided in a space between the storage box and the fuel tank on the other side of the vehicle body on the side opposite to the side on which the control unit is provided, and between the storage box and the fuel tank. And a secondary air pipe connected to the control unit and the air filter so as to extend from one side of the vehicle body to the other side of the vehicle body.