JPH08121174A - Exhaust device for engine - Google Patents

Abstract

PURPOSE: To improve coolability of a changeover valve without increasing rigidity of an exhaust pipe connection part of a cylinder, hardly decrease an exhaust temperature, and prevent adhesion of foreign materials to a changeover valve. CONSTITUTION: An exhaust passage changeover valve 12 having bilateral branch passages 24, 25 and a valve body 19 is directly connected to a cylinder body 3. The left side branch passage 24 is connected to an exhaust pipe for a low speed area, while the right side branch passage 25 is connected to an exhaust pipe for a high speed area. Heat of the exhaust passage changeover valve 12 is conducted to the cylinder body 3 for cooling. Bending moment applied to an exhaust passage changeover valve installation part is small, while the cylinder body 3 can be formed thin. Exhaust gas of high pressure, high speed, and high temperature is flowed into the exhaust passage changeover valve 12, so that the exhaust temperature is hardly decreased and foreign materials are easily blown out.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine exhaust system in which an exhaust pipe having a structure for increasing the engine output by utilizing pressure waves of exhaust gas is connected to the engine.

[0002]

2. Description of the Related Art Conventionally, in order to increase the output of an engine,
The pressure wave of the exhaust gas propagating in the exhaust pipe is reflected in the expansion chamber and returned to the engine exhaust port as a negative reflected wave or a positive reflected wave, and the vicinity of the exhaust port is set to negative pressure at the beginning of the exhaust timing or at the end of the exhaust timing. It is performed as positive pressure.

In the exhaust pipe having a structure for increasing the engine output by utilizing the pressure wave of this kind of exhaust gas, if the reflected wave reflected in the expansion chamber returns to the exhaust port of the engine and the exhaust time does not match. I can't fully exercise that ability. That is, depending on the structure of the exhaust pipe, high output may be obtained only in the low rotation range or in the high rotation range.

As an exhaust system which can obtain high output by utilizing the pressure wave of exhaust gas over a wide range of engine rotation range,
For example, there is one disclosed in Japanese Utility Model Laid-Open No. 60-143125. The exhaust device disclosed in this publication has a switching valve in the exhaust passage of a single-cylinder engine that switches the flow direction of the exhaust gas to one of two directions, and one of the two outlets of the switching valve has a low rotation speed. A low-speed exhaust pipe suitable for the high speed region was connected, and a high-speed exhaust pipe suitable for the high speed region was connected to the other.

In the switching valve used in this exhaust system, an exhaust passage is formed in a valve body by forming two branch passages having a common inlet in a bifurcated shape, and a curved passage is provided at a branch portion of the exhaust passage. It was formed by rotatably fitting a rotary valve body having a. This valve body was formed into a shape in which one side of the bell was cut out, and was mounted on the valve body so that the top portion was on the downstream side. Further, the valve body is integrally formed with a valve shaft which penetrates the valve body and projects outward at the top thereof, and by rotating the valve shaft, only one of the branch passages and the other is provided. It was selected and configured to communicate. Since the passage of the valve body is greatly curved when the valve body is formed as described above, the two branch passages are formed so that their axes are substantially orthogonal to each other.

Further, this switching valve is attached to the cylinder of the engine through an exhaust pipe for connection. The connecting portion of the connecting exhaust pipe and the switching valve is such that the upstream end surface of the valve body is brought into contact with the end surface of the connecting exhaust pipe, and the upstream end portion of the valve element is radial bearing in the opening of the connecting exhaust pipe. And the valve body is fastened to the connecting exhaust pipe with bolts.

According to this exhaust system, the exhaust passage is switched by the switching valve according to the engine speed range, and when the engine speed range is in the low speed range, the exhaust gas is caused to flow through the low speed range exhaust pipe and in the high speed range. By flowing the exhaust gas through the exhaust pipe for the high rotation range at certain times, the engine output can be increased over a wide range of the engine rotation range.

[0008]

However, in the exhaust system configured as described above, there is a problem that the switching valve is likely to be inoperable. This was due to the low cooling property. That is, since the switching valve is connected to the engine through the connecting exhaust pipe, it can be cooled only by being hit by traveling wind.
This is because the valve body easily seizes on the valve body due to the high heat of the exhaust gas. It should be noted that the valve body is formed in a substantially bell shape, and the thin wall thickness and the small heat capacity are also one of the causes of easy seizure.

Further, since the switching valve is attached to the cylinder through the connecting exhaust pipe, the heavy object is supported by the cylinder in a cantilever manner, and a large bending moment is applied to the connecting exhaust pipe connecting portion of the cylinder. It will work. For this reason, the connecting exhaust pipe connecting portion must be formed with a heavy and strong structure. Moreover, since the switching valve is separated from the exhaust port of the cylinder by the pipe length of the connecting exhaust pipe, when exhaust gas flows to the downstream side exhaust pipe located on the downstream side of the switching valve, the temperature thereof tends to decrease. Therefore, when a catalyst is provided in the downstream exhaust pipe, it becomes difficult to reach the activation temperature. Moreover, since the pressure and the flow velocity of the exhaust gas discharged from the exhaust port of the cylinder reach the switching valve, the foreign matter such as carbon in the exhaust gas easily accumulates on the switching valve. In addition, since the connecting exhaust pipe is used to connect the switching valve to the engine, there is a limit in reducing the number of parts and cost.

Further, since the valve body formed in a substantially bell shape is fitted to the valve body with its top portion facing the downstream side, when the exhaust gas pushes the valve body to the downstream side, the top portion thereof is valve body. However, there is also a problem that it is likely to cause a malfunction due to the fact that it comes to bite into the valve body support hole.

Furthermore, since the angle formed between the axes of the two branch passages provided in the switching valve is approximately 90 degrees, the flow direction of the exhaust gas changes greatly within the switching valve, and the exhaust resistance increases. Will end up.

Moreover, the upstream end of the valve element of the switching valve is only rotatably fitted to the connecting exhaust pipe via the radial bearing, and the sealing material is interposed between the connecting exhaust pipe and the upstream end. Since it is not mounted, there is also a problem that, for example, tar or the like contained in the exhaust gas leaks to the outside from the switching valve mounting portion.

The present invention has been made to solve the above problems, and enhances the cooling performance of the switching valve, and
A first object of the present invention is to prevent the rigidity of the exhaust pipe connecting portion of the cylinder from increasing, and to prevent the exhaust temperature from easily lowering and prevent foreign matter from adhering to the switching valve. Also,
A second object is to enable the valve body to operate smoothly even if a large exhaust gas pressure is applied to the valve body of the exhaust passage switching valve. A third object is to reduce the resistance of the exhaust gas when passing through the exhaust passage switching valve. In addition, a fourth object is to improve the exhaust gas sealability.

[0014]

In the exhaust system for an engine according to the first aspect of the present invention, a bifurcated passage formed of two branch passages is formed in the valve body, and one of the two branch passages is selected. An exhaust passage switching valve having a rotary valve body that brings this into a communication state is provided, and one of the two branch passages is connected to a low rotation range exhaust pipe that is suitable when the engine rotation range is a low rotation range. The other is connected to the exhaust pipe for the high speed range that is suitable when the engine speed range is the high speed range, and the valve body is connected to the control device that switches the branch passage according to the engine operating state. A passage forming portion formed by forming an exhaust passage in a cylindrical body, and a valve shaft attached to an axial end portion of the passage forming portion, and freely rotatable in a valve body supporting hole formed in a valve body. In the valve body support hole The axial end surface of the portion where the road forming unit is fitted, in which the said end face a pair contact portion and the flat surface perpendicular to the axial direction of the respective valve body in the valve body.

The engine exhaust system according to the second invention is
A bifurcated passage formed of two branch passages is formed in the valve body, and an exhaust passage switching valve equipped with a rotary valve body that selects one of the two branch passages to bring them into a communication state A valve body and a valve body are connected to the exhaust port by fitting them to the opening edge of the exhaust port, and a control device that switches the branch passage by turning the valve body according to the engine operating state is connected to the valve body. Connect the branch passage to the low speed exhaust pipe that is suitable when the engine speed is low, and connect the other branch passage to the high speed exhaust pipe that is suitable when the engine speed is high. It was done.

The engine exhaust system according to the third invention is
In the exhaust system for an engine according to the first invention or the second invention, the two branch passages in the exhaust passage switching valve are formed symmetrically with respect to the axis of the valve element, and the axes of these passages have an acute angle. It is formed to intersect.

An engine exhaust system according to a fourth invention is
In the exhaust system for an engine according to any one of the first to third inventions, the inner peripheral side is axially unevenly distributed with respect to the outer peripheral side between the end surface of the valve body of the exhaust passage switching valve and the cylinder. This is an annular metal gasket interposed.

[0018]

According to the first aspect of the invention, the exhaust gas pressure applied to the valve body when the exhaust gas flows into the exhaust passage switching valve is applied from the valve body to the flat surface of the valve body support hole in the valve body. .

According to the second aspect of the invention, since the exhaust passage switching valve is directly attached to the cylinder, the heat of the exhaust passage switching valve is transferred to the cylinder by heat conduction and is cooled by the cooling means provided in the cylinder. Further, since the exhaust passage switching valve is provided integrally with the cylinder, the bending moment due to the weight of the exhaust passage switching valve can be made as small as possible. Furthermore, since the inlet of the exhaust passage switching valve coincides with the exhaust port of the cylinder, the exhaust gas flows into the exhaust passage switching valve in a state where its temperature, pressure and flow velocity are high. Moreover, when the exhaust passage switching valve is attached to the cylinder, no connecting member is required between the two, so the number of parts is reduced.

According to the third aspect of the invention, the exhaust gas passes through the exhaust passage switching valve without its flow direction changing significantly. According to the fourth aspect of the invention, the upstream end of the valve element is sealed by the metal gasket in a state in which the valve is allowed to rotate.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to FIGS. 1 is a side view of an exhaust system for an engine according to the present invention, FIG. 2 is a longitudinal sectional view showing an enlarged main part in FIG. 1, FIG. 3 is a sectional view taken along line III-III in FIG.
FIG. 4 is a sectional view taken along line IV-IV of the exhaust passage switching valve in FIG.
FIG. 5 is a front view showing a state where the valve body of the exhaust passage switching valve is viewed from the engine side.

FIG. 6 is an exploded perspective view showing a valve body portion of the exhaust passage switching valve. In the figure, the passage forming member of the valve body is cut away. FIG. 7 is a front view of the gasket for the exhaust passage switching valve,
8 is a cross-sectional view taken along the line VIII-VIII in FIG. 7, and FIG. 9 is a graph showing the relationship between the engine speed and the output of the engine equipped with the exhaust device according to the present invention.

In these figures, 1 is a water-cooled two-cycle single-cylinder engine for a motorcycle. Reference numeral 2 is a crankcase of the engine 1, 3 is a cylinder body, 4 is a cylinder head, 5 is a crankshaft, 6 is a connecting rod, 7 is a piston, and 8 is a spark plug. A reference numeral 9 provided in the vicinity of the crankshaft 5 is a crank angle sensor, which has a structure for sending a crank angle signal to the control device 10.

The control device 10 is an exhaust control valve device 1 which will be described later.
1 and the exhaust passage switching valve 12 are controlled, the engine speed is obtained based on the crank angle signal sent from the crank angle sensor 9, and the exhaust control valve device servo motor 13 and the exhaust passage switching valve servo are obtained. The motor 14 is configured to be controlled according to the engine speed.

As shown in FIG. 2, the exhaust control valve device 11 is a conventionally well-known device that changes the exhaust timing by raising and lowering substantially the upper edge of the exhaust port 15 of the cylinder body 3, and an upper wall of the exhaust passage 16. In addition, a valve body 11b having a substantially cylindrical shape and a notch surface 11a having a shape corresponding to the wall surface of the exhaust passage is rotatably mounted. Also, this valve body 11b
Includes a pulley 11c having one axial end protruding laterally from the cylinder body 3 and fixed to the protruding end as shown in FIG. 1, and two drive wires 11d connected to the pulley 11c. Via the exhaust control valve servo motor 13
It is connected to. The control device 10 controls the servo motor 13 so that the valve body 11b is closed when the engine speed is lower than a predetermined exhaust control valve drive start speed.
Is driven, and when the engine speed exceeds the exhaust control valve drive start speed, the valve body 11b is provided with the cutout surface 11a.
Is configured so as to be flush with the inner wall surface of the exhaust passage 16. That is, when the engine speed is lower than the exhaust control valve drive start speed, the exhaust timing is delayed, and when the engine speed is higher than the exhaust control valve drive start speed, the exhaust timing is advanced.

The exhaust passage switching valve 12 has a structure directly attached to the cylinder body 3 of the engine 1.
As shown in FIG. 4, a valve body 18 fixed to the cylinder body 3 by four mounting bolts 17, and a valve body 19 rotatably attached to the valve body 18.
And so on. Exhaust pipes 20 and 21, which will be described later, are connected to the engine 1 via the exhaust passage switching valve 12.

The valve body 18 has two inlets with two inlets.
A bifurcated passage that connects the two outlets is formed, and a valve body 19 is attached to a branch portion of the bifurcated passage.
The two outlets are arranged side by side, and the inlets are attached to the cylinder body 3 so that the inlets face the exhaust ports located in the vicinity of the downstream side of the exhaust port 15 in the cylinder body 3. Further, the portion of the valve body 18 attached to the cylinder body 3 has a structure in which the valve body 18 is fitted into and in close contact with the concave portion 22 forming the peripheral edge of the exhaust port. A cooling water passage 23 for flowing engine cooling water extends near the recess 22.

Reference numerals 24 and 25 denote a left branch passage and a right branch passage which form the bifurcated passage. These passages are arranged so that their axes intersect at an acute angle α as shown by the alternate long and short dash line in FIG. Has been formed. The branch passages 24 and 25 are formed symmetrically with respect to the axis C (FIG. 3) of the valve body 19.

The valve body 19 is formed by attaching a drive shaft 27 to a passage forming member 26 formed by casting. More specifically, as shown in FIG. 6, the passage forming member 26 forms a curved passage 26a, which serves as a direction changing portion of the left and right branch passages 24 and 25, in a columnar body, and a supporting plate fixing step portion 26b described later. , Screw holes 26c, pin holes 26d, etc. are formed. The passage forming member 26 is formed symmetrically with respect to the center plane hatched in FIG.

The valve body 19 is the valve body 1
8, the passage forming member 26 is provided in the valve hole 18a having a circular cross section formed in the branch portions of the left and right branch passages 24, 25.
The drive shaft 27 and the valve body 18
It is rotatably attached to the valve body 18 by being fitted into the shaft hole 18b. These valve hole 18a and shaft hole 1
8b comprises the valve body support hole which concerns on this invention. In addition,
As shown in FIG. 2, the valve hole 18a and the shaft hole 18b are formed so that the axis of the exhaust passage switching valve 12 overlaps with the axes of the left and right branch passages 24 and 25 when viewed from the side. .

As shown in FIG. 3, the valve body 19 is formed so that the end portion in the axial direction on the exhaust passage 16 side when attached to the valve body 18 projects from the valve body 18. Then, this protruding portion is fitted into the exhaust port of the cylinder body 3. A metal gasket 28 is interposed between the protruding end surface of the valve body 19 and the cylinder body 3 to prevent exhaust gas from leaking from the exhaust passage switching valve mounting portion.

This metal gasket 28 is shown in FIGS.
As shown in FIG.
It is formed such that a is unevenly distributed in the axial direction (thickness direction) with respect to the outer peripheral portion 28b. And this metal gasket 2
Of the axially opposite end faces, one end face formed by the inner peripheral portion 28a is brought into contact with the projecting end face of the valve body 19, and the other end face formed by the outer peripheral portion 28b is brought into contact with the cylinder body 3. They are in contact with each other and are interposed between these two members. When the metal gasket 28 is interposed, the valve body 19 and the cylinder body 3 clamp the metal gasket 28.

In this way, the metal gasket 28 is attached to the valve body 1
9 is provided between the cylinder body 3 and the cylinder body 3, the exhaust gas can be prevented from leaking, and the valve body 19 is urged in the direction of separating from the cylinder body 3 by the elastic force of the metal gasket 28. Body 19 is valve body 1
It is possible to prevent rattling within 8.

Exhaust gas leaks through the penetrating portion of the drive shaft 27 by fitting an annular carbon gasket 29 (FIG. 3) into the shaft hole 18b and fitting the drive shaft 27 into the carbon gasket 29. Is preventing.

The curved passage 26a has an upstream end opened at one axial end of the passage forming member 26 with an opening diameter substantially the same as the exhaust passage 16 of the cylinder body 3, and the passage forming member 26 is opened from this opening. It is curved so as to be unevenly distributed outward in the radial direction toward the other shaft end portion, and the downstream end is opened from the other shaft end surface of the passage forming member 26 to the outer peripheral surface. Moreover, this curved passage 2
As shown in FIG. 3, when the valve body 19 is fitted to the valve body 18 and the downstream end of the curved passage 26a is directed in either the left or right direction, the inner wall surface of 6a is provided in the left or right branch passage 2a.
It is formed so as to be flush with the inner wall surfaces of 4, 25.

That is, in the state shown in FIGS. 3 and 4, the curved passage 26a becomes a part of the left side branch passage 24 and communicates with the exhaust passage 16 of the cylinder body 3. By turning 19 through 180 degrees, the curved passage 26a becomes a part of the right branch passage 25 and communicates with the exhaust passage 16. In other words, the valve body 19 is configured to select either one of the two left and right branch passages 24 and 25 and bring them into the communicating state.

Further, as shown in FIG. 6, the stepped portion 26b is formed by disposing a part of the axial end surface of the passage forming member 26, which is on the downstream side of the curved passage 26a, with a step D on the axial center side. ing. Further, the formation position of the step portion 26d is formed in a substantially semicircular shape in a portion of the axial end surface of the passage forming member 26 where the downstream end portion of the curved passage 26a is not open. The screw hole 26c and the pin hole 26d are formed so as to open to the step portion 26b. That is, these holes 26c and 26d are formed in a portion of the passage forming member 26 that avoids the curved passage 26a and have a relatively large wall thickness.

The drive shaft 27 has a substantially semicircular support plate 31 welded to one end thereof, and a male screw 27a is engraved on the other end thereof to which a driven gear 32 to be described later is attached. Unlike the passage forming member 26, the drive shaft 27 and the support plate 31 are made of steel. The support plate 31 includes the step portion 2 of the passage forming member 26.
6b is formed with a thickness substantially the same as the step D, and is welded to the drive shaft 27 with the shaft end projection 27b of the drive shaft 27 fitted in the round hole 31a. The assembly formed by welding the support plate 31 to the drive shaft 27 is fixed to the passage forming member 26 by the mounting screw 33 with the support plate 31 aligned with the step portion 26b.

31b is a mounting screw 3 for the support plate 31.
The through hole 31b is formed so that the head portion 33a of the mounting screw 33, which is a countersunk screw with a cross hole, does not project to the outer surface of the support plate 31. Reference numeral 31c is a pin hole for inserting a knock pin 34 that restricts the relative rotation of the passage forming member 26 with respect to the support plate 31. The knock pin 34 penetrates the support plate 31 and is press-fitted into the pin hole 26d of the passage forming member 26.

When the drive shaft 27 is attached to the passage forming member 26 by using the support plate 31 as shown in this embodiment, the drive plate of the passage forming member 26 is moved by the support plate 31 entering the step portion 26b. Side 26e (FIG. 6) which is the axial end surface on the side and the main surface 3 of the support plate 31.
1d (FIG. 6) becomes substantially flush. Therefore, this valve body 1
In FIG. 9, the substantially end face of the passage forming member 26 on the drive shaft side is substantially flat, and therefore, as shown in FIG.
When it is mounted on the shaft 8, the axial end face of the valve hole 18a comes into surface contact with the substantially flat drive shaft side shaft end face of the passage forming member 26 over the entire surface. The axial end surface of the valve hole 18a is indicated by reference numeral 18c and hatched in FIG.

That is, the valve body 19 is pressed in the direction away from the engine 1 by the pressure of the exhaust gas during engine operation, but by adopting the configuration of this embodiment, the force acting in this axial direction is applied to the axial line. Can be received by a wide flat surface orthogonal to. In other words, when fixing the drive shaft 27 to the passage forming member 26 while preventing it from rotating, the area of the surface that receives the force in the axial direction is not narrowed by the fixing member.

The driven gear 32, which is attached to the end of the drive shaft 27 opposite to the support plate 31, meshes with the drive gear 35 as shown in FIGS. 1 and 2, and the drive gear 35 and the drive gear 35 are engaged with each other. It is connected to the exhaust passage switching valve servomotor 14 through two connected drive wires 36. The drive gear 35 is rotatably supported by the valve body 18 of the exhaust passage switching valve 12 via a pivotal support mechanism (not shown).

That is, the rotation of the exhaust passage switching valve servomotor 14 is driven by the drive gear 35 via the drive wire 36.
By rotating the drive gear 27, the drive shaft 27 is rotated together with the driven gear 32 that meshes with the drive gear 35. Therefore, by rotating the driven gear 32 at a rotation angle of 180 degrees, the exhaust passage switching valve 12 is rotated.
The left branch passage 24 and the right branch passage 25 by the valve body 19 of
Either one of them is selected and communicates.

In the control device 10 connected to the exhaust passage switching valve servomotor 14, when the engine speed is lower than a predetermined exhaust passage switching rotation speed, the left branch passage 24 is in a communicating state, and the exhaust passage switching rotation speed is set. When it is higher, the servomotor 14 is controlled so that the right side branch passage 25 is in a communicating state. The exhaust passage switching rotational speed is set to a rotational speed higher than the exhaust control valve drive starting rotational speed when the exhaust control valve device 11 is driven.

Further, this exhaust passage switching rotational speed has a hysteresis when switching from the left branch passage 24 to the right branch passage 25 and vice versa. That is,
The exhaust passage switching valve 12 is prevented from being frequently switched even if the engine speed is increased or decreased in the vicinity of the speed at which the left and right branch passages are switched. More specifically, the number of rotations when switching from the left branch passage 24 to the right branch passage 25 is
The rotation speed is set to be higher than the rotation speed when switching from the right branch passage 25 to the left branch passage 24.

Next, the structure of the exhaust pipes 20 and 21 connected to the exhaust passage switching valve 12 will be described. These exhaust pipes 20 and 21 are connected to the valve body 1 of the exhaust passage switching valve 12.
8, upstream parts 20a and 21a, expanded parts 20b and 21b having a larger diameter than the other parts and having an expansion chamber inside, and silencers 20c and 21c. The structure is such that the engine output is increased by utilizing the pressure wave of the exhaust gas discharged from the engine 1 through the exhaust passage switching valve 12. In addition, the expansion portion 2 of the exhaust pipe 20
0b is arranged on the left side of the motorcycle body (not shown), and the expansion portion 21b of the exhaust pipe 21 is arranged on the right side.

The upstream portion 20a is the left branch passage 2 of the left and right branch passages 24 and 25 of the exhaust passage switching valve 12.
4 and the upstream portion 21b is connected to the right branch passage 25. Then, the exhaust pipe 20 is configured to be suitable when the engine rotation range is a low rotation range, and the exhaust pipe 21 is configured to be compatible when the engine rotation range is a high rotation range. That is, the exhaust pipe 20 constitutes the low revolution region exhaust pipe according to the present invention, and the exhaust pipe 21 constitutes the high revolution region exhaust pipe according to the present invention.

The output characteristic of the engine 1 when the low speed exhaust pipe 20 is used is shown by a broken line in FIG. 9, and the output characteristic of the engine 1 when the high speed exhaust pipe 21 is used is shown in FIG. Is indicated by a solid line. In FIG. 9, reference symbol a indicates the exhaust control valve drive start rotational speed, b indicates the engine rotational speed when the exhaust control valve device 11 is in the fully open state, and c indicates the exhaust passage switching valve 12 on the right side of the exhaust passage. Indicates the engine speed when switching from the branch passage 25 to the left branch passage 24,
The exhaust passage switching valve 12 indicates the exhaust passage at the left branch passage 24.
Shows the engine speed when switching from to the right branch passage 25.

As shown in FIG. 9, the exhaust passage switching valve 12
The exhaust passage switching rotation speed when switching the exhaust passage is set by giving a hysteresis to the rotation speed when the output characteristic lines of both exhaust pipes 20 and 21 intersect.

Next, the operation of the exhaust device constructed as described above will be described with reference to FIG. When the engine 1 is started, the control device 10 detects the engine speed, and closes the exhaust control valve 11 until the engine speed reaches the exhaust control valve drive start speed a. When the engine speed increases to the exhaust control valve drive start speed a, the control device 10 drives the exhaust control valve device 11 to accelerate the exhaust timing. The control device 10 has an engine speed of b in FIG.
The opening degree of the exhaust control valve device 11 is changed according to the engine speed until it reaches the engine speed shown by.

Until the engine speed reaches the engine speed d, the left branch passage 24 of the exhaust passage switching valve 12 is in communication, and the exhaust gas is discharged into the atmosphere through the low speed exhaust pipe 20. At this time, the pressure wave of the exhaust gas is propagated from the engine 1 into the exhaust pipe 20, and the timing at which the reflected wave reflected by the expansion section 20b returns to the engine 1 matches the exhaust timing of the engine 1 in the low rotation range. You can get high output. That is, it is possible to perform a high output operation by utilizing the effective low speed side characteristic in the low speed region exhaust pipe 20.

When the engine speed reaches the speed d in FIG. 9, the control device 10 drives the exhaust passage switching valve 12 to bring the right side branch passage 25 into the communicating state. Therefore, the exhaust gas generated in each cylinder of the engine 1 is exhausted to the atmosphere through the exhaust pipe 21 for the high rotation range. At this time,
The pressure wave of the exhaust gas is propagated from the engine 1 into the exhaust pipe 21, and the timing at which the reflected wave reflected by the expansion section 21b returns to the engine 1 coincides with the exhaust timing of the engine 1 in the high rotation range and is high. Output is obtained. That is, it is possible to perform high-power operation by utilizing the effective high-speed side characteristics in the high-speed exhaust pipe 21.

When the engine speed drops from the high speed range to the low speed range, the right branch passage 25 is maintained in the communicating state even after the engine speed reaches the speed d in FIG. When descending to c, the right branch passage 25 is switched to the left branch passage 24.

Therefore, according to the exhaust system constructed as described above, the exhaust passage switching valve 1 is attached to the cylinder body 3.
Since 2 is directly attached, the heat of the exhaust passage switching valve 12 is transferred to the cylinder body 3 by heat conduction, and is cooled by the engine cooling device having a structure in which the engine cooling water flows through the cooling water passage 23. Also, the exhaust passage switching valve 1
Since 2 is provided integrally with the cylinder body 3, the arm length of the cantilever having the exhaust passage switching valve 12 attached to the cylinder body 3 can be minimized. Further, since the inlet of the exhaust passage switching valve 12 coincides with the exhaust outlet of the cylinder body 3, the exhaust gas flows into the exhaust passage switching valve in a state where its temperature, pressure and flow velocity are high. Moreover, when mounting the exhaust passage switching valve 12 to the cylinder body 3, it is not necessary to interpose a connecting member between the two, so the number of parts is minimized.

Further, the valve hole 18 in the valve body 18
Since the axial end surface 18c of a and the portion of the passage forming portion 26 of the valve body 19 that contacts the end surface 18c are flat surfaces that are orthogonal to the axial direction of the valve body 19, the exhaust passage switching valve 12 is not exhausted. The exhaust gas pressure applied to the valve body 19 when flowing in is applied from the valve body 19 to the flat surface. Therefore, the valve body 19 can smoothly rotate even if a large exhaust gas pressure is applied.

Moreover, the two branch passages 24 and 25 of the exhaust passage switching valve 12 are formed symmetrically with respect to the axis C of the valve body 19, and the axes of these passages 24 and 25 intersect at an acute angle α. Since the exhaust gas is formed as described above, the exhaust gas passes through the exhaust passage switching valve 12 without largely changing the flow direction, so that the exhaust passage switching valve 12 is unlikely to have exhaust resistance.

In addition, between the end surface of the valve body 19 of the exhaust passage switching valve 12 and the cylinder body 3, the inner peripheral portion 28a is axially eccentrically arranged with respect to the outer peripheral portion 28b. Since the valve is inserted, the upstream end of the valve body 19 is sealed by the metal gasket 28 in a state where the rotation is allowed. Therefore, it is possible to prevent the exhaust gas from leaking from the exhaust passage switching valve mounting portion to the outside.

In this embodiment, the example in which the 2-cycle engine is adopted as the engine 1 is shown, but it is also possible to apply it to the 4-cycle engine as shown in FIG. FIG. 10 is a cross-sectional view showing an embodiment in which the exhaust system according to the present invention is applied to a four-cycle engine. In the figure, the same or equivalent members as those described in FIGS. Detailed description is omitted.

In FIG. 10, reference numeral 41 is a water-cooled 4-cycle single-cylinder engine for a motorcycle. 42 is a cylinder body, 43 is a cylinder head, 44 is a piston, 45
Is a connecting rod, 46 is an intake valve, 47 is an exhaust valve, and 48 is a conventionally known valve operating device that drives the intake valve 46 and the exhaust valve 47. The camshaft and spark plug are omitted.

In this embodiment, the exhaust passage switching valve 12 is attached to the cylinder head 43. The mounting structure is the same as that of the above embodiment.

Further, in each of the above-mentioned embodiments, an example is shown in which the two branch passages of the exhaust passage switching valve are opened to the left and right, but these are opened vertically as shown in FIGS. 11 and 12. You can also let it.

FIG. 11 is a side view showing another embodiment in which the outlets of two branch passages are arranged vertically, and FIG. 12 is a longitudinal sectional view showing an enlarged main part in FIG. In these figures, the same or equivalent members as those described in FIGS. 1 to 10 are designated by the same reference numerals and detailed description thereof will be omitted.

The exhaust passage switching valve 12 shown in FIGS. 11 and 12 is attached to the cylinder body 3 so that the branch passages are arranged vertically. That is, the branch passage is composed of the upper branch passage 24a and the lower branch passage 25a. Then, the exhaust pipe 2 for the low rotation speed region is provided in the upper branch passage 24a.
0 is connected, and the high-speed exhaust pipe 21 is connected to the lower branch passage 25a. In the present embodiment, the low revolution range exhaust pipe 20 is arranged on the right side of the vehicle body (not shown), and the high revolution range exhaust pipe 21 is arranged on the left side.

Even with this structure, the same effect as that of each of the above-described embodiments can be obtained. Further, in the case of adopting the configuration shown in FIGS. 11 and 12, the upstream portion 20a of the low speed exhaust pipe 20
Is extended and bent forward with respect to the upstream portion 21a of the high-speed region exhaust pipe 21, so that the expansion portions 20 of both exhaust pipes
Even if b and 21b are arranged at substantially the same position in the front-rear direction, it is easy to form the low speed exhaust pipe 20 longer than the high speed exhaust pipe 21.

Further, the upstream portion 2 of the exhaust pipe 21 for high rotation range
In 1a, since the portion connected to the exhaust passage switching valve 12 is positioned behind the upstream portion 20a of the low-speed region exhaust pipe 20, the low-speed region exhaust pipe 20 blocks the traveling wind. For this reason, the frontmost portion of the upstream portion 21a is hard to be cooled by the traveling wind, so that the exhaust gas is hard to be cooled when the exhaust passage is switched to allow the exhaust gas to flow to the high-speed exhaust pipe 21. . That is, when the exhaust pipe to be used is switched from the low-speed exhaust pipe 20 to the high-speed exhaust pipe 21, the temperature change of the exhaust gas is small.

11 and 12 show an example in which the exhaust pipe 20 for the low speed region is connected to the upper branch passage 24a and the exhaust pipe 21 for the high speed region is connected to the lower branch passage 25a. The connection of the exhaust pipe to the exhaust passage switching valve 12 can be reversed. That is, the exhaust pipe 21 for the high rotation range is connected to the upper branch passage 24a, the exhaust pipe 21 for the low rotation range is connected to the lower branch passage 25a, and the valve element 19 is driven to correspond to this exhaust pipe configuration. It may be configured as follows.

When an exhaust gas purifying catalytic converter is provided in the low speed region exhaust pipe 20 with the above structure, the upstream portion 20a of the low speed region exhaust pipe 20 has exhaust air for high speed region where traveling wind is high. Since the upstream portion 21a of the pipe 21 is less likely to hit it and the temperature drop is small, it is easy to maintain the temperature of the exhaust gas flowing in the low rotation region exhaust pipe 20 at the active temperature of the catalytic converter. is there.

[0068]

As described above, in the exhaust system for a multi-cylinder engine according to the first aspect of the present invention, a bifurcated passage formed of two branch passages is formed in the valve body, and one of the two branch passages is formed. An exhaust passage switching valve having a rotary valve body that selects and puts it in a communication state is provided, and one of the two branch passages is used as an exhaust pipe for a low rotation range suitable when the engine rotation range is a low rotation range. The valve is connected to the exhaust pipe for the high speed range which is suitable when the engine speed range is the high speed range, and the valve body is connected to a control device for switching the branch passage according to the engine operating state. A body is formed of a passage forming portion formed by forming an exhaust passage in a cylindrical body and a valve shaft attached to an axial end portion of the passage forming portion, and is formed in a valve body supporting hole formed in a valve body. It is rotatably fitted and supports this valve body The exhaust gas flows into the exhaust passage switching valve because the axial end surface of the portion where the passage forming portion is fitted and the portion of the valve body that contacts the end surface are flat surfaces that are orthogonal to the axial direction of the valve body. The exhaust gas pressure sometimes applied to the valve body is applied from the valve body to the flat surface of the valve body support hole in the valve body.

Therefore, the valve body can smoothly rotate even if a large exhaust gas pressure is applied.

The engine exhaust system according to the second invention is
A bifurcated passage formed of two branch passages is formed in the valve body, and an exhaust passage switching valve equipped with a rotary valve body that selects one of the two branch passages to bring them into a communication state A valve body and a valve body are connected to the exhaust port by fitting them to the opening edge of the exhaust port, and a control device that switches the branch passage by turning the valve body according to the engine operating state is connected to the valve body. Connect the branch passage to the low speed exhaust pipe that is suitable when the engine speed is low, and connect the other branch passage to the high speed exhaust pipe that is suitable when the engine speed is high. Therefore, since the exhaust passage switching valve is directly attached to the cylinder, the heat of the exhaust passage switching valve is transferred to the cylinder by heat conduction and is cooled by the cooling means provided in the cylinder. For this reason,
It is possible to prevent the valve element from malfunctioning due to thermal distortion or the like.

Further, since the exhaust passage switching valve is provided integrally with the cylinder, the bending moment due to the weight of the exhaust passage switching valve can be made as small as possible. Therefore, it is easy to secure the rigidity in the vicinity of the exhaust port of the cylinder, and it is possible to reduce the thickness by forming the thickness of this portion to be thin.

Furthermore, since the inlet of the exhaust passage switching valve coincides with the exhaust port of the cylinder, the exhaust gas flows into the exhaust passage switching valve in a state where its temperature, pressure and flow velocity are high. Therefore, when the exhaust gas passes through the exhaust passage switching valve, there is little decrease in temperature, and when the catalyst is arranged on the downstream side of the exhaust passage, it is possible to efficiently raise the temperature by the exhaust gas. Moreover, foreign matter such as carbon contained in the exhaust gas is blown away by the exhaust gas having a high pressure and a high flow rate, and it is difficult for the foreign matter to be deposited inside the exhaust passage switching valve.

In addition, since the exhaust passage switching valve can be fixed to the cylinder without using a connecting member or support brackets, the number of parts can be reduced and the cost can be reduced.

The engine exhaust system according to the third invention is
In the exhaust system for an engine according to the first invention or the second invention, the two branch passages in the exhaust passage switching valve are formed symmetrically with respect to the axis of the valve element, and the axes of these passages have an acute angle. Since the exhaust passages are formed so as to intersect with each other, the flow direction of the exhaust gas does not change greatly when passing through the exhaust passage switching valve, so that the exhaust passage switching valve is unlikely to have exhaust resistance.

The engine exhaust system according to the fourth invention is
In the exhaust system for an engine according to any one of the first to third inventions, the inner peripheral side is axially unevenly distributed with respect to the outer peripheral side between the end surface of the valve body of the exhaust passage switching valve and the cylinder. Since the annular metal gasket thus formed is interposed, the upstream end of the valve body is sealed by the metal gasket in a state in which the rotation is allowed.

Therefore, it is possible to reliably prevent the exhaust gas, tar, etc. from leaking from the exhaust passage switching valve mounting portion while adopting the structure in which the valve body is rotatably held.

[Brief description of drawings]

FIG. 1 is a side view of an exhaust system for an engine according to the present invention.

FIG. 2 is an enlarged vertical sectional view showing a main part in FIG.

FIG. 3 is a sectional view taken along line III-III in FIG. 2;

FIG. 4 is a sectional view taken along line IV-IV of the exhaust passage switching valve in FIG.

FIG. 5 is a front view showing a state where the valve body of the exhaust passage switching valve is viewed from the engine side.

FIG. 6 is an exploded perspective view showing a valve body portion of an exhaust passage switching valve, in which the passage forming member of the valve body is cut away.

FIG. 7 is a front view of an exhaust passage switching valve gasket.

8 is a sectional view taken along line VIII-VIII in FIG.

FIG. 9 is a graph showing the relationship between engine speed and output of an engine equipped with an exhaust system according to the present invention.

FIG. 10 is a cross-sectional view showing an embodiment in which the exhaust system according to the present invention is applied to a 4-cycle engine.

FIG. 11 is a side view showing another embodiment in which the outlets of two branch passages are vertically arranged.

FIG. 12 is a vertical cross-sectional view showing an enlarged main part in FIG.

[Explanation of symbols]

1 ... Water-cooled 2-cycle engine, 3 ... Cylinder body,
10 ... Control device, 12 ... Exhaust passage switching valve, 15 ... Exhaust port, 16 ... Exhaust passage, 18 ... Valve body, 19 ... Valve body, 20, 21 ... Exhaust pipe, 20b, 21b ... Expansion part, 2
4 ... Left branch passage, 24a ... Upper branch passage, 24b ... Lower branch passage, 25 ... Right branch passage, 41 ... Water-cooled 4-cycle engine, 43 ... Cylinder head.

Claims (4)

[Claims] 1. A bifurcated passage formed by communicating one outlet with two outlets is formed in a valve body, and a branch portion of the passage is provided with one of two branch passages extending from the inlet to the two outlets. An exhaust pipe having an exhaust passage switching valve having a rotary valve body for selecting one of the two branch passages and making the two communicate with each other, and using one of the two branch passages to increase an engine output by utilizing an exhaust pressure wave. And is connected to the exhaust pipe for the low speed range that is suitable when the engine speed range is the low speed range, and the other is connected to the exhaust pipe for the high speed range that is suitable when the engine speed range is the high speed range, The valve body is connected to a control device for rotating the valve body according to the engine operating state to switch the branch passage, and the valve body is provided with a passage forming portion in which an exhaust passage is formed in a columnar body, and in this passage forming portion. Exhaust gas flow direction downstream shaft And a valve shaft attached to the end of the valve body, and is rotatably fitted into a valve body supporting hole formed in the valve body. The exhaust device for an engine, wherein an axial end surface of the valve body and a portion of the valve body that is in contact with the end surface are flat surfaces that are orthogonal to the axial direction of the valve body. 2. A bifurcated passage formed by communicating one outlet with two outlets is formed in the valve body, and a branch portion of the passage is provided with one of two branch passages extending from the inlet to the two outlets. An exhaust passage switching valve equipped with a rotary valve body that selects one of them and puts them in communication is connected to the exhaust port of the cylinder by fitting the valve body and the valve disc to the opening edge of the exhaust port. An exhaust having a structure in which a control device for rotating the valve according to an engine operating state to switch a branch passage is connected to the valve and the engine output is increased in one of the two branch passages by utilizing a pressure wave of the exhaust. Connected to the low speed exhaust pipe that is suitable when the engine speed range is low, and connected the other to a high speed range exhaust pipe that is suitable when the engine speed range is high. Exhaust system of the engine characterized by Place. 3. The exhaust system for an engine according to claim 1, wherein the two branch passages in the exhaust passage switching valve are formed symmetrically with respect to the axis of the valve body, and the axes of these passages are formed. The engine exhaust system is characterized in that the two are formed so as to intersect each other at an acute angle. 4. The exhaust system for an engine according to claim 1, wherein an inner peripheral side of the exhaust passage switching valve is axially arranged with respect to an outer peripheral side between the end surface of the valve body and the cylinder. An exhaust system for an engine, wherein an annular metal gasket, which is unevenly distributed in a certain direction, is interposed.