JP3105513B2 - Engine exhaust system - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an exhaust device for an engine in which the downstream sides of a plurality of exhaust pipes connected to the engine are gathered in an expansion chamber.

(Background of the Invention) The downstream portion of the exhaust pipe is formed by branch pipes gathered in an expansion chamber, and the opening that opens to the downstream side of each branch pipe is rectangular in cross section, and the sides of the rectangular cross section are closely adhered to each other and welded. Have already been proposed (for example, Japanese Patent Application No. 62-228600).
No.). Here, conventionally, arc welding such as TIG welding (tungsten inert gas welding) has been used for the connection on the downstream side of each branch pipe. However, in arc welding, since the heat input is large, the sheet is melted to the back side of the sheet, and the pressure of the inert gas also acts, so that the sheet is easily melted down to the back side. For this reason, a bead (back bead) is generated on the back side (exhaust passage side) of the welded portion, and the area of the exhaust passage is reduced, so that the performance may be deteriorated.

FIG. 7C is a plan view showing a welded portion performed by the conventional technique. As shown in FIG. 7C, in the conventional TIG welding, the distance between the electrode and the welded portion must be kept substantially constant (about 5 mm). It cannot be welded to the depth of the V-shaped valley 2 formed between the two branch pipes 1a and 1b. That is, FIG. 7A is a side view showing a welded portion according to the present invention. In this figure, conventional TIG welding can be performed only in the range of A. Also, in this conventional welding, the width of the bead 3 is wide and bulges upward, so that V-shaped cuts 4a and 4b which are opened forward are formed at the joint between the bead toe 3a and the branch pipes 1a and 1b. For this reason, there is also a problem that stress is concentrated on the cuts 4a and 4b, and cracks are easily generated from the vibrations of the exhaust system.

In addition, dimensional accuracy is deteriorated due to thermal deformation, and when an exhaust control valve is provided at the junction of branch pipes, malfunction occurs, and since the amount of heat input is large, crystal grains in the welded part are coarsened and strength is reduced. And other problems.

(Object of the Invention) The present invention has been made in view of such circumstances,
When the downstream part of the exhaust pipe is formed in a rectangular cross section and gathered together, and when the adhered parts are welded, no back bead is generated inside each exhaust pipe, stress does not concentrate on the bead toe,
It is an object of the present invention to provide an exhaust device that has improved dimensional accuracy and does not cause a decrease in the strength of a welded portion.

(Constitution of the Invention) According to the present invention, it is an object of the present invention to collect a plurality of exhaust pipes having circular cross sections arranged side by side at appropriate intervals in the horizontal direction in an expansion chamber, and to exhaust the exhaust pipe facing the rear end opening of the gathering portion. In the exhaust device of an engine provided with a control valve, the downstream portion of each of the exhaust pipes is continuously changed from a circular cross section toward a downstream end to a rectangular cross section that is long in the vertical direction, and adjacent exhaust pipes are connected to the downstream side. The downstream side is brought into close contact with each other from the middle of the shape change portion in which the cross section continuously changes from circular to rectangular by gradually approaching toward, and open toward the upstream side in external appearance plan view between these adjacent exhaust pipes A V-shaped valley is formed, and the close contact surface of the adjacent exhaust pipes has a substantially arc shape in a side view that is convex toward the upstream side and the outer peripheral edge of the close contact surface facing the V-shaped valley is adjacent to each other. High energy from the rear edge that adheres This is achieved by an engine exhaust apparatus characterized in that beam welding and high-energy beam welding of the outer peripheral edge of the close contact surface of these adjacent exhaust pipes to near the depth of the V-shaped valley are performed.

(Embodiment) FIG. 1 is an exploded perspective view showing an exhaust system of a motorcycle engine according to an embodiment of the present invention, FIG. 2 is an enlarged sectional view showing a part of the exhaust system, and FIG. 4 is a sectional view taken along the line IV-IV, and FIG.
The figure is an end view taken along the line VV, FIG. 6 is a perspective view of a branch pipe assembly,
FIG. 7A is a side view showing a welded portion, and FIG. 7B is a VII B-VII thereof.
FIG. 8 is a side view of a motorcycle using this exhaust system.

In FIG. 8, reference numeral 10 denotes a four-cycle four-cylinder engine, which is mounted near the center of the vehicle body. This engine 10
Is a cylinder 14 that extends diagonally upward and forward from the crankcase 12
Having. The exhaust system includes four exhaust pipes 16 (16a) having a circular cross section extending from the front of the cylinder 14 to below the crankcase 12.
16d), an exhaust control valve device 18 connected to the rear end of the exhaust pipe 16 to collect the exhaust gas from each exhaust pipe 16,
And a collecting pipe 22 that guides exhaust gas from 18 to a silencer 20.

The exhaust control valve device 18 is, as shown in FIGS.
Four branch pipes 24 (24a to 24d) connected to the respective exhaust pipes 16 to form a part of the exhaust pipes 16; It comprises a pair of upper and lower sheet metal halves 22a, 22b sandwiching it, and a valve body 28 in the expansion chamber 26 formed between these halves 22a, 22b for controlling the area of the exhaust passage. The collecting pipe 22 is composed of these halves 22
a, 22b. As shown in FIG. 6, each of the branch pipes 24 is formed by welding upper and lower flanges of the left and right halves to each other to form a tube. The upstream portion has a circular cross section, and the downstream end thereof is elongated in the vertical direction. It is rectangular. That is, the branch pipe 24 has a cross section that continuously changes from a circular shape to a rectangular shape, and has a shape-change portion whose cross section continuously changes between a circular portion on the upstream side and a rectangular portion on the downstream side. The rectangular downstream ends of the branch pipes 24 are tightly assembled in the horizontal direction as shown in FIGS. 2 and 3, and open into the expansion chamber 26.

The valve body 28 includes a main body 30 having an arc-shaped cross section, a fan-shaped end plate 32 (32a, 32b) integrally formed at both ends of the main body 30 and extending toward the center of the arc of the main body 30, and an end plate 32. Fixed valve stem
34 (34a, 34b).

A bearing plate 36 is fixed to one side surface of the half bodies 22a and 22b,
On the other side, a ring member 38 is fixed so as to surround the circular window. A bearing plate 40 is detachably bolted to the ring member 38. The valve element 28 is inserted into the expansion chamber 26 from the window from which the bearing plate 40 has been removed, and holds the tip of the valve shaft 34b on the bearing plate 36, while the other end of the valve shaft 34b is attached to this window.
Hold at 0. In this state, the valve element 28 faces the rear end opening of the gathering portion of each branch pipe 24, and the exhaust path area can be changed by the rotation of the valve element 28.

The valve shaft 34a protrudes from the bearing plate 40, and a pulley 44 is fixed to the protruding end. The pulley 44 is rotated by a servomotor 48 via a wire 46 in accordance with the rotation speed of the engine 10, and the valve body 28 narrows the exhaust passage area in a low-medium-speed region of the engine 10 and increases the exhaust passage area in a high-speed region. Is controlled.

In FIG. 8, reference numeral 50 denotes a rear arm, the front end of which is pivotally supported by the vehicle body frame 52, and the rear wheel 54 attached to the rear end.
The spring force of the shock absorber 56 is applied to the rear arm 50 by the link mechanism 5.
Granted downward through 8, 60.

In the exhaust system, the upper end of the exhaust pipe 16 is attached to the cylinder 14, and the muffler 20
Is fixed to the vehicle body frame 52 appropriately by a bracket 62, and a pipe 63 connecting the collecting pipe 22 and the muffler 20 is suspended from a bracket 64 (FIG. 8) of the link 58 on the vehicle body frame 52 side pivotal support.

66 is a front wheel, 68 is a fuel tank, 70 is an operation seat, and 72 is a battery.

Here, the exhaust control valve device 18 is driven by a servomotor 48 so as to close in a middle speed range and open in a high speed range, for example. As a result, a negative pressure wave generated by the opening of the branch pipe 24 and returned upstream in the exhaust pipe 16 and a positive pressure wave reflected by the valve element 28 and transmitted upstream in the exhaust pipe 16 Act on the exhaust valve and cancel each other out in a certain speed range, and the sum becomes zero. At this time, the pulsation effect is canceled, and a decrease in volumetric efficiency (generation of torque valley) in this speed range can be suppressed.

Here, the branch pipes 24a to 24d are welded to each other by high-energy beam welding to form a branch pipe assembly 24A shown in FIG. In other words, the branch pipes 24a to 24d gradually approach each other toward the downstream side, and the downstream sides thereof are in close contact with each other from the middle of the shape change portion in which the cross section continuously changes from circular to rectangular, and the adjacent branch pipes 24a to 24d. A V-shaped valley is formed between the holes d. For this reason, the outer peripheral edge where the contact surface of the adjacent exhaust pipe faces the V-shaped valley has a substantially arc shape in a side view that is convex toward the upstream side (V-shaped valley side) (see FIG. 7A). In the vicinity of the V-shaped valley, a gap that opens up and down is formed between the shape change portions of the adjacent branch pipes. Therefore, by utilizing this gap, the substantially arc-shaped outer peripheral edges of the branch pipes 24a to 24d which are in close contact with each other are easily welded by high energy beam welding, for example, laser beam welding. Here, according to this beam welding, the distance between the irradiation unit 74 and the welded portion can be increased, so that
As shown in FIG. 7A, the irradiation unit 74 is moved toward the gap between the two branch pipes 24 to the depth of the V-shaped valley formed between the adjacent branch pipes 24, for example, in the range B in FIG. Welding can be performed efficiently and well along the outer peripheral edge of the contact portion. That is, there is a gap open upward or downward between the shape change portions of the adjacent branch pipes, the outer peripheral edge of the contact portion has a substantially arc shape toward the V-shaped valley, and the irradiation unit for beam welding is Separation from the weld,
By using the three conditions, it is possible to easily weld to the depth of the V-shaped valley.

As shown in FIG. 7B, the bead 76 formed by the laser beam is formed deeply between the branch pipes without protruding upward from between the two branch pipes 24, and the surface of the bead 76 has a depressed arc-shaped cross section. No back bead is generated.
Here, by gradually reducing the intensity of the laser beam toward the toe of the bead 76, the bead 76 can be smoothly reduced toward the toe. For this reason, a bead end where stress concentration occurs is not formed, and durability against vibration is improved. Further, since the range of temperature rise by beam irradiation is small, thermal deformation is small, dimensional accuracy is improved, and the heat input is small, so that the strength does not decrease due to the coarsening of crystal grains.

In the above embodiment, each branch pipe 24 is formed by welding the left and right split halves into a tubular shape, but may be processed by another processing method, or by processing the exhaust pipe 16 having a circular cross section. A portion near the rear end may have a rectangular cross section through a shape changing portion.

The high energy beam welding may use other beams such as electron beam welding in addition to laser beam welding.

(Effect of the Invention) As described above, the present invention continuously changes the downstream portion of the exhaust pipe from a circular cross section toward the downstream end to a rectangular cross section that is long in the vertical direction, and gradually moves each exhaust pipe toward the downstream side. A V-shaped valley that opens between the adjacent exhaust pipes toward the upstream side in external appearance plan view by bringing the downstream side into close contact with each other from the middle of the shape change portion where the cross section continuously changes from circular to rectangular when approaching. Is formed, and the outer peripheral edge of the contact surface where the contact surface of the adjacent exhaust pipe faces the V-shaped valley is formed into a substantially arc shape in a side view that is convex toward the upstream side. In addition to welding from the rear, when welding the outer peripheral edge of the contact surface of the adjacent exhaust pipe to the deep part (bottom) of the valley, high energy beam welding using a laser beam or the like is used. Along the outer edge of the contact surface Since welding can be easily performed and no back bead can be formed at this time, there is no problem that the area of the exhaust passage is reduced and the engine performance is reduced. Further, since the bead has an arcuate cross section depressed from the welded portion, the toe of the bead does not bulge upward, and damage due to stress concentration does not occur.
Further, the thermal deformation is small, the dimensional accuracy is improved, and the heat input is small, so that there is no reduction in strength due to a change in crystal structure. Further, since the rear edges of the adjacent exhaust pipes that are in close contact with each other are welded with high energy beams from behind, the thermal deformation of the rear edge is reduced, and the beads are formed to penetrate deeply between the adjacent exhaust pipes. . Therefore, there is little change in the interval between the exhaust control valve and the rear end edge, and even if the rear end of the exhaust pipe is cut to adjust the interval with the exhaust control valve, the beads do not disappear.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view showing an exhaust system of a motorcycle engine according to an embodiment of the present invention, FIG. 2 is an enlarged sectional view showing a part of the exhaust system, and FIG. Figure,
4 is a cross-sectional view taken along the line IV-IV, also partially omitted, FIG. 5 is an end view taken along the line VV, FIG. 6 is a perspective view of the branch pipe assembly, and FIG.
FIG. 7B is a side view showing a welded portion, FIG. 7B is an end view taken along the line VIA-VIIB, and FIG. 7C is a plan view of a portion corresponding to FIG. 7A showing a bead shape by conventional arc welding. FIG. 8 is a side view of a motorcycle using the exhaust system. 16: Exhaust pipe, 18: Exhaust control valve device, 26: Expansion chamber, 74: Laser irradiation unit, 76: Bead.

 ──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-64-78733 (JP, A) JP-A-54-25326 (JP, A) JP-A-1-73120 (JP, A) 49627 (JP, U) Michio Inagaki, Hiroshi Nakayama, "Illustration welding terminology dictionary [new edition], Nikkan Kogyo Shimbunsha, published on December 25, 1981, page 185, lines 6-18

Claims (1)

(57) [Claims] 1. An exhaust system for an engine, comprising: a plurality of exhaust pipes having a circular cross section which are juxtaposed at appropriate intervals in the horizontal direction in an expansion chamber; and an exhaust control valve opposed to a rear end opening of the gathering portion. In the above, the downstream portion of each of the exhaust pipes is continuously changed from a circular cross section toward the downstream end to a rectangular cross section that is long in the vertical direction, and the adjacent exhaust pipes are gradually approached toward the downstream side so that the cross section is The downstream side of the shape change portion that continuously changes from a circular shape to a rectangular shape is brought into close contact with each other, and a V-shaped valley that opens toward the upstream side in external plan view is formed between these adjacent exhaust pipes. The close contact surface of the exhaust pipe that faces the V-shaped valley has a substantially arc shape in a side view that is convex toward the upstream side, and the rear end edges of the adjacent exhaust pipes that contact each other are high from behind. Energy beam welding and these The high-energy beam welding of the outer peripheral edge of the contact surface of the adjacent exhaust pipe to the vicinity of the depth of the V-shaped valley.