JP2604158B2 - Exhaust system for motorcycle - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust device for a motorcycle equipped with a two-cycle engine near the center of a vehicle body.

(Background of the Invention) In a motorcycle equipped with a two-cycle engine, a large exhaust expansion pipe is provided to improve the engine output performance. However, since this exhaust expansion pipe is large and has a large capacity, it has been difficult to determine a preferable arrangement while avoiding interference with other equipment. For example, there is one in which this expansion tube is arranged so as to extend from the front lower part of the engine to the rear through the lower part of the engine case. However, since the length and volume of this expansion tube are directly related to the performance, in order to obtain sufficient performance, the body with the largest diameter must be located below the crankcase and rearward below the crankcase. become. In many cases, a main stand and a cushion unit are disposed below and behind the crankcase. If a trunk portion of the expansion pipe is disposed here, it is necessary to displace the trunk portion in the vehicle width direction. For this reason, when a large-diameter trunk portion is located at this position, the bank angle becomes small, and a problem arises in that the turning performance is reduced.

(Object of the Invention) The present invention has been made in view of such circumstances,
When arranging the exhaust expansion pipe so as to guide it backward through the lower part of the crankcase, the exhaust expansion pipe having a sufficiently large body can be forced without reducing the bank angle and without sacrificing length or volume. It is an object of the present invention to provide a motorcycle exhaust device that can be installed without any problem.

(Constitution of the Invention) According to the present invention, it is an object of the present invention to provide a motorcycle having a two-stroke engine mounted near the center of a vehicle body, wherein the engine is mounted such that the lower surface of a crankcase thereof is inclined downward and rearward, and the exhaust of the engine The expansion pipe is lowered upward from the front of the cylinder and bent upward so as to draw a loop when viewed from the front in front of and below the engine, and the body of the expansion pipe is positioned behind the loop and below the crankcase. The front of the body was faced so that the traveling wind passing through the loop hit the rear of the space surrounded by the loop, and the body was inclined rearward and downward along the lower surface of the crankcase. The present invention is attained by a motorcycle exhaust device characterized by that.

(Embodiment) FIG. 1 is a side view of one embodiment of the present invention, FIG. 2 is an enlarged side view of a part thereof, and FIGS. 3, 4, and 5 are a plan view, a side view, and a front view of an exhaust system, respectively. FIG. 6 shows VI in FIG.
7 is a sectional view taken along line VII-VII in FIG. 4.

1 and 2, reference numeral 10 denotes a body frame.
A pair of left and right side frames 14 (only one is shown) extending obliquely downward and rearward from the steering shaft barrel 12 are connected to each other by a castable air cleaner box 16 or another flat member (not shown). . A front fork 18 is held by the steering shaft barrel 12 so as to be rotatable left and right, and a steering front wheel 20 is provided at a lower end of the front fork 18.
The steering handlebars 22 are respectively attached to the upper ends thereof.

Reference numeral 24 denotes a driving rear wheel, which is attached to a rear end of a rear arm 28 supported by a pivot shaft 26. This rear arm 28
As shown in FIG. 2, one cushion unit 34 gives a downward return behavior via links 30 and 32. That is, the pivot end of the link 30 pivotally supported by the lower end of the frame 10 is pivotally attached to the lower end of the cushion unit 34, and the link 30 and the rear arm 28 are connected by the link 32.

36 is an air cleaner box 16 from above the pair of side frames 14.
A fuel tank disposed over the upper surface of the vehicle, 38 is an operation seat, and 40 is a rear cover. Inside the rear cover 40, a battery and a lubricating oil tank are housed.

Reference numeral 42 denotes a water-cooled single-cylinder two-stroke engine, which is mounted near the center of the vehicle body. That is, the rear upper portion of the engine 42 is rotatably supported by a support shaft 46 on a bracket 44 projecting from the frame 10 as shown in FIG.
The lower front portion is supported by a pair of left and right down tubes 48 fixed to the frame 10 via links 50 so as to be vertically movable. Pin 50 on the down tube 48 side of the support shaft 46 and link 50
A and a torsion spring using rubber are attached to a, and the return behavior of the engine 42 upward is imparted. As a result, the engine 42 can thereafter vibrate up and down around the upper support shaft 46. In the engine 42, the weight balance of each rotating part is determined such that the vibration direction generated by the reciprocating motion of the piston is substantially orthogonal to the plane connecting the support shaft 46 and the pin 50a. 52 is a carburetor and 54 is a radiator of engine cooling water.

An exhaust pipe 56 has a large-diameter expansion pipe 58 and a muffler 60. In the engine 42, the bottom surface of the crankcase 42a is strongly inclined obliquely forward and upward from the rear thereof, and the down tube 48 is similarly inclined along the lower surface of the crankcase 42a. As a result, a large space is formed below the front of the crankcase 42a between the road surface and the crankcase 42a. The expansion pipe 58 is bent upward so as to draw a loop upward after descending from the front surface of the cylinder 42b of the engine 42, and further inclined backward and downward along the lower surface of the crankcase 42a from behind this loop when viewed from the front. While extending the center in the vehicle width direction backward. Here, the front portion of the large-diameter body portion 58A of the expansion tube 58 faces behind the space surrounded by the loop when viewed from the front, and the traveling wind directly passes through the loop and hits the front portion of the body portion 58a. Making it easier. The trunk portion 58a is located below the crankcase 42a, and the tapered portion 58b is located after the diameter thereof is reduced below the crankcase 42a. The rear taper portion 58b is further connected to a silencer 60 extending from the right side of the cushion unit 34 to the right side of the rear wheel 24.

The exhaust pipe 56 is supported at three places. That is, the front end thereof is relatively rigidly connected to the exhaust port of the cylinder 42b with a leaf spring gasket and a paper gasket interposed therebetween. The rear taper portion 58b of the expansion tube 58 is attached to the rear lower portion of the crankcase 42a via a relatively hard rubber damper 62 as shown in FIG. Further, as shown in FIG. 7, the front portion of the muffler 60 is supported by a footrest bracket 64 (see FIGS. 1 and 4) fixed to the frame 10 via a rubber damper 66 which is particularly soft in the front-rear direction. As described above, the engine 42 thereafter vibrates up and down with the upper support shaft 46 as a fulcrum, whereas the exhaust pipe 56 has its expansion chamber 58 relatively rigidly supported by the cylinder 42b and the lower rear part of the crankcase 42a. Therefore, the entire exhaust pipe 56 vibrates almost integrally with the engine 42. At this time, the front portion of the muffler 60 is supported in the front-rear direction by the soft rubber damper 66, so that the rubber damper 66 does not become a major obstacle to the vibration of the entire exhaust pipe 56.

In addition, since the expansion pipe 58 is lowered downward in front of the engine and bent upward while drawing a loop when viewed from the front, and the front of the body is exposed behind the space surrounded by the loop when viewed from the front, the traveling wind Satisfactorily hits the torso through this loop. Here, the trunk is inclined rearward and downward along the lower surface of the crankcase. Therefore, the running wind easily hits the entire trunk, and the cooling performance is improved.

Further, in this embodiment, the crankcase 42a is arranged obliquely so that the front part thereof is higher, so that the loop of the expansion tube 58 and the clearance between the front part of the trunk part 58a and the road surface can be sufficiently secured, and the protrusions on the road surface can be reduced. This is particularly advantageous because the projection hardly hits the inflation tube 58 when riding over.

Although this embodiment is applied to a single cylinder engine 42, the present invention also includes an application to all or some cylinders of a multi-cylinder engine such as a two-cylinder engine. For example, in a two-cylinder engine, the present invention is applied to one of the cylinders, and one of the expansion pipes forms a loop below the front of the engine, and its body is disposed below the crankcase. It is also possible to avoid the increase in the width of the vehicle body by guiding the two expansion chambers in the front-rear direction below the vehicle body without guiding the expansion chamber without drawing.

(Effect of the Invention) As described above, according to the present invention, the expansion pipe is lowered from the front of the cylinder and bent so as to draw a loop when viewed from the front, and the trunk of the expansion pipe is provided behind the loop and below the crankcase. Since they are located, the expansion tubes can be arranged without difficulty while ensuring a sufficient length and volume. In particular, since the diameter at the lower rear of the engine can be reduced, the vehicle body width in the vicinity thereof does not increase, and the turning angle can be improved by increasing the bank angle during turning.

In addition, since the front portion of the trunk is located behind the space surrounded by the loop of the expansion tube, traveling wind easily passes through the loop and hits the trunk. Here, the trunk is inclined backward and downward along the lower surface of the crankcase, so that the traveling wind passing through the loop and the surrounding traveling wind hit the trunk well, and the cooling performance of the expansion pipe is good.

[Brief description of the drawings]

1 is a side view of one embodiment of the present invention, FIG. 2 is an enlarged side view of a part thereof, FIGS. 3, 4, and 5 are a plan view, a side view, and a front view of an exhaust system, respectively. The figure shows VI- in FIG.
FIG. 7 is a sectional view taken along line VI, and FIG. 7 is a sectional view taken along line VII-VII in FIG. 10 ... Frame, 42 ... Engine, 42a ... Crankcase, 42b ... Cylinder, 56 ... Exhaust pipe, 58 ... Expansion pipe, 58a ... Body.

Claims (1)

(57) [Claims] 1. A motorcycle having a two-stroke engine mounted near the center of a vehicle body, wherein the engine is mounted such that a lower surface of a crankcase thereof is inclined downward and a exhaust expansion pipe of the engine is lowered from a front surface of a cylinder. Bending upward so as to draw a loop when viewed from the front below the front of the engine, and positioning the body of the expansion tube behind this loop and below the crankcase,
When viewed from the front, the front of the body is facing so that the traveling wind passing through the loop hits the rear of the space surrounded by the loop, and this body is inclined backward and downward along the crankcase lower surface. An exhaust device for a motorcycle, wherein the exhaust device is a motorcycle.