JPH0718334B2 - Exhaust pipe structure of motorcycle - Google Patents

Description

TECHNICAL FIELD The present invention relates to an exhaust pipe of a motorcycle.

Conventional technology and its problems In a motorcycle equipped with a multi-cylinder engine, exhaust pipes are connected to the exhaust ports of the respective cylinders, and these exhaust pipes extend rearward through the outer periphery of the engine, respectively, and at the rear. It is connected to the set room.
Exhaust gas from each cylinder joins in this collecting chamber and is then discharged to the rear of the vehicle body through the muffler.

Each exhaust pipe is arranged along various routes according to the vehicle body structure so that the length of each exhaust pipe is as uniform as possible, but some exhaust pipes project to the side of the vehicle body and As a result, the bank angle of the vehicle body may be limited, or the mounting position of other members for passing the exhaust pipe may be limited.

Further, in some cases, the exhaust pipe may have to be sharply curved with a small radius of curvature. However, when such a sharp curved portion is formed in the exhaust pipe, the flow resistance of the exhaust gas flowing through the curved portion is large, so that the exhaust resistance increases and the output of the engine decreases.

Therefore, according to the present invention, the exhaust gas of a motorcycle in which a plurality of exhaust pipes respectively communicating with each cylinder of a multi-cylinder engine are collectively communicated with one collecting chamber on the downstream side in the present invention. In the pipe structure, the gathering chamber is provided at the center of the width direction of the vehicle body, and at least a part of the exhaust pipes communicates with the gathering chamber from the front through a curved portion that extends in a rearward direction. The exhaust pipes are arranged symmetrically with respect to the center line of the vehicle body, and the flow passage cross-sectional area in the curved portion is made larger than the flow passage cross-sectional areas of the other portions. Since the exhaust pipes are symmetrically arranged along the right and left sides, it is possible to set a deep bank angle on both sides of the vehicle body without a part of the exhaust pipe overhanging to the side of the vehicle body. Further, since the exhaust pipe is mounted on the vehicle body in a compact shape with left and right balance, the mounting position of other members such as pedals can be selected on the side of the vehicle body with a relatively large degree of freedom. Furthermore, it is extremely easy to make the lengths of the exhaust pipes the same.

Moreover, since the curved portion of the exhaust pipe has a larger flow passage cross-sectional area than the other portions, the flow resistance decreases due to the decrease in the flow velocity. Therefore, even if the radius of curvature of the curved portion is made small, the exhaust resistance does not increase and the output of the engine is not lowered, so that the symmetrical and compact exhaust pipe arrangement described above can be easily realized. it can.

Examples The present invention will be described below with reference to illustrated examples. FIG. 1 is a side view showing a main part of a motorcycle equipped with an exhaust pipe according to the present invention, and 1 is a head pipe. A pair of left and right main frames 2 extends rearward from the head pipe 1. The head pipe 1 also has a left and right side 1 at the bottom of the main frame 2.
A pair of down tubes 3 are fixed, and the down tubes 3 extend obliquely downward and rearward from the head pipe 1. A seat rail 4 extends rearward from an intermediate portion of the main frame 2, and a back stay 5 is provided between a rear portion of the seat rail 4 and a lower rear portion of the main frame 2. The engine 6 is mounted and mounted on the main frame 2 and the down tube 3 in the vehicle body configured as described above.

The engine 6 is a V-type four-cylinder engine, and includes a pair of left and right front cylinders 7 that project obliquely upward to the front and a pair of left and right rear cylinders 8 that project obliquely upward to the rear. Front exhaust pipes 9 are connected to the exhaust ports 7a of the left and right front cylinders 7, respectively, and these front exhaust pipes 9 descend to the front of the engine 6 and then turn to the rear, as shown in FIG. Further, the lower part of the engine 6 extends rearward in parallel with the center line L of the vehicle body, and the rear end is connected to the front end face of the collecting chamber 10 and communicates with the inside of the collecting chamber 10. Rear exhaust pipes 11 are connected to the exhaust ports 8a of the left and right rear cylinders 8, respectively, and these rear exhaust pipes 11 descend after the rear of the engine 6 and then, as shown in FIG. 2 and FIG. The front exhaust pipe 9 extends laterally and frontward, and is directed rearward through a curved portion R curved in a semicircular shape.
Is connected to the front end face of the collecting chamber 10 above.

The collecting chamber 10 is disposed on the vehicle body center line L, and the left and right front exhaust pipes 9, 9 and the rear exhaust pipes 11, 11 are arranged symmetrically with respect to the vehicle body center line L. The exhaust gases that have flowed into the collecting chamber 10 via the exhaust pipes 9, 9, 11 and 11 merge in the collecting chamber 10 and are then guided to the collecting exhaust pipe 12. The collective exhaust pipe 12 is bent to the right and upward of the vehicle body, and is directed rearward, and extends along a side portion of a rear wheel 13 (FIG. 2) provided behind the vehicle body center line L. It is connected to the muffler 14.

Next, the rear exhaust pipe 11 will be described in more detail. As shown in FIG. 3, each rear exhaust pipe 11 is provided with a rear cylinder 8 of the engine 6.
Flange 16 on the upper pipe piece 15 connected to the exhaust port 8a of
The intermediate pipe portion 17 is connected via the intermediate pipe portion 17 extending downward toward the rear of the engine 6, and the lower end portion thereof horizontally projects laterally and turns forward. ing. And, between the front end face of the intermediate pipe part 17 and the front end face of the collecting chamber 10, a curved pipe part 18 for changing the direction to a semicircle by 180 ° is connected, and the curved pipe part The curved portion R is formed by the piece 18. Left and right rear exhaust pipe 11,11
Is symmetrically formed and piped with respect to the center line of the vehicle body as described above, and thereby a balanced and compact exhaust pipe structure is obtained, but on the other hand, since the curved portion R has a large curved curvature, The flow resistance of exhaust gas passing therethrough tends to increase.

Therefore, the curved pipe portion 18 is configured as follows, so that the inner diameter of the curved portion R, that is, the cross-sectional area is increased, and the flow resistance is reduced. FIG. 4 is a top view of the curved pipe piece 18, and FIG. 5 is a cross-sectional view thereof, showing one connection port.
19 is connected to the end of the intermediate pipe piece 17, and the other connection port 20
Is connected to a pipe joint piece provided on the front end surface of the collecting chamber 10. The curved pipe piece 18, the upper and lower half portions 18a, 18b formed by press working, the flange portions 21 formed along the outer peripheral edge and the inner peripheral edge, respectively, are overlapped and fixed to each other, It has a tubular shape.
As shown in FIG. 5, the inner cross section of the curved pipe part 18 thus constructed has semi-circular cross-sections on both inner and outer sides having a radius r substantially equal to the radius of the intermediate pipe part 17.
It is formed in a shape in which an intermediate portion C having a space S is interposed between A and B, and the flow passage cross-sectional area of the curved pipe piece 18 has an intermediate pipe portion 17
It is larger than the cross-sectional area of the channel. The cross-sectional shape of the curved pipe piece 18 smoothly transitions from the shape equal to the cross-sectional shape of the intermediate pipe piece 17 at the connection port 19 to the cross-sectional shape of the intermediate portion without causing discontinuity on the inner surface of the pipe. The same can be said when going from the intermediate portion to the connection port 20.
Thus, although the curved pipe piece 18 is sharply bent by approximately 180 °, exhaust gas can pass through the curved pipe piece 18 without a great resistance, and the exhaust resistance is reduced.

The cross-sectional shape of the curved pipe part 18 is not limited to the shape shown in the above-mentioned drawings, and may be any other suitable shape larger than the cross-section of the intermediate pipe part 17. Since the curved pipe part 18 is made by joining the two half parts 18a and 18b that can be formed by press working, it is possible to form an arbitrary cross-sectional shape extremely easily.

EFFECTS OF THE INVENTION As described above, in the present invention, by bending at least a part of the exhaust pipes with a small radius of curvature, the amount of protrusion to the lateral side of the vehicle body is symmetrical with respect to the center line of the vehicle body. Can be arranged in a small and compact manner, and further, an increase in exhaust resistance due to the bent portion of the exhaust pipe can be prevented to prevent a decrease in engine output.

[Brief description of drawings]

FIG. 1 is a side view showing a main part of a motorcycle equipped with an exhaust pipe according to the present invention, FIG. 2 is a top view of the same exhaust pipe, FIG. 3 is a front view of a rear exhaust pipe, and FIG. FIG. 5 is a top view of the bent pipe part of the exhaust pipe, and FIG. 5 is a sectional view taken along the line VV of FIG. 1 ... Head pipe, 2 ... Main frame, 3 ... Down tube, 4 ... Seat rail, 5 ... Back stay, 6 ... Engine, 7 ... Front cylinder, 8 ... Rear cylinder, 9 ... Front exhaust pipe, 10 ...
Collecting chamber, 11 ... Rear exhaust pipe, 12 ... Collecting exhaust pipe, 13 ... Rear wheel, 14
... muffler, 15 ... upper pipe piece, 16 ... flange, 17 ... intermediate pipe piece, 18 ... curved pipe piece, 19 ... connection port, 20 ... connection port, 21 ...
Flange, R ... Curved section.

Claims (1)

[Claims] 1. An exhaust pipe structure for a motorcycle, wherein a plurality of exhaust pipes communicating with each cylinder of a multi-cylinder engine are made to communicate with one collecting chamber on the downstream side. The collecting chamber has a center in the width direction of a vehicle body. A plurality of exhaust pipes are provided symmetrically with respect to the center line of the vehicle body by providing the exhaust pipes at the front part and communicating at least part of the exhaust pipes from the front through a curved portion extending in a rearward direction by changing the direction. Then
An exhaust pipe structure for a motorcycle, characterized in that the flow passage cross-sectional area in the curved portion is made larger than the flow passage cross-sectional areas in other portions.