JPS6385212A - Exhaust pipe of two-cycle engine for motorcycle - Google Patents

Abstract

PURPOSE:To maintain engine output excellent at all times by providing an expansion part, which is so arranged as to extend in the longitudinal direction of a motorcycle main body approximately at the center in the motorcycle width direction, a same- diameter part and a throttle part in order so as to constitute an expansion room for effectively utilizing the pulsation efficiency of exhaust gas from the engine. CONSTITUTION:This exhaust pipe 27 has an expansion chamber 28 leading to the exhaust port of an two-cycle engine and a silencer 29 connected to the rear end of this expansion chamber 28. The expansion chamber 28 is provided, in order from the upper stream side, with a connection part 31 which is projected forward and downward from an exhaust port and whose discharge end is bent rearward and an expansion part 32 which becomes larger gradually in diameter according as it comes to rear and extends in the longitudinal direction of the motorcycle body approximately at the center of the motorcycle width direction. Further it is provided with a same- diameter part 33 which is continued to this expansion part 32 and extends rearward approximately in the same diameter and a throttle part 34 which becomes smaller gradually in diameter according as it comes to rear and is bent outward in the motorcycle width direction.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an exhaust pipe for a two-stroke motorcycle engine that does not adversely affect the pulsation effect of the exhaust gas of the two-stroke engine.

(Prior Art) Generally, motorcycles are provided with an exhaust pipe connected to an exhaust boat of the engine. When the engine is a two-stroke type, an expansion chamber is formed in the middle of the exhaust pipe in order to effectively utilize the pulsation effect of the exhaust gas to improve the output of the engine.

In the above case, the expansion chamber has an expansion part whose diameter gradually increases as it moves from the exhaust boat side toward the rear of the vehicle body (hereinafter simply referred to as the rear, and the opposite direction is referred to as the front). It is composed of a same-diameter part connected to the rear end and extending rearward with substantially the same diameter, and a constricted part connected to the rear end of this same-diameter part and gradually decreasing in diameter as it goes rearward.

The exhaust pressure wave from the exhaust boat expands once in this expansion chamber, and then is reflected by the four constrictions and returns to the exhaust boat.

(Problems to be Solved by the Invention) Incidentally, in motorcycles, it is necessary to position the muffler at the rear end of the exhaust pipe on the side of the vehicle body, so the middle part of the exhaust pipe is bent. In this case, if the middle part of the exhaust pipe is simply bent, the bent part will reflect the exhaust pressure waves from the exhaust boat, adversely affecting the pulsation effect of the exhaust gas, resulting in a reduction in engine output.

(Object of the Invention) This invention was made in view of the above-mentioned circumstances, and aims to prevent the pulsation effect of the exhaust gas from being adversely affected when the middle part of the exhaust pipe in a two-stroke engine is bent. purpose.

(Structure of the Invention) A feature of the present invention for achieving the above object is that, in an exhaust pipe of a two-cycle engine for a motorcycle, an expansion portion constituting the upstream side of an expansion chamber of the exhaust pipe is arranged in the vehicle width direction. It is arranged so as to extend along the longitudinal direction of the vehicle body at approximately the center, and the same-diameter part at the midway point of the exhaust pipe is set to the vehicle width so that the constriction part constituting the downstream side of the exhaust pipe is located on the outside of the vehicle body. It is located at a point bent outward.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 2, l is a motorcycle, and a steering shaft tube 3 is provided at the front of the body frame 2, and this steering shaft tube 3 supports a front fork 4 rotatably about its axis. There is. The lower end of this front fork 4 supports the front wheel 5, and a handle 6 is attached to the upper end.

The vehicle body frame 2 also includes a pair of left and right main frames 8 extending rearward and downward from the steering shaft tube 3, and a pair of left and right down tubes connecting the front and rear ends of these amphibious frames 8 and curving downward. It has 9.

A rear arm 10 is pivotably supported by a pivot shaft 11 at the connecting portion between the rear end of the main frame 8 and the rear end of the down tube 9, so that the rear arm 10 can swing vertically.
2 is supported. Further, an engine 14 is supported within a frame between the left and right main frames 8 and the left and right down tubes 9, and this engine 14 drives the rear wheels 12. That is,
A drive chain wheel 15 driven by the engine 14 is connected to the left side of the engine 14. On the other hand, a driven chain wheel 16 that rotates together with the rear wheel 12 is provided on the left side of the rear wheel 12, and a transmission chain 17 is attached to both chain wheels 15, 16.
It is wrapped around. When the engine 14 is driven, the rear wheel 12 is rotationally driven via the transmission chain 17, and the motorcycle 1 runs.

Further, a fuel tank 19 is provided on the left and right main frames 8 above the engine 14, and a seat 20 is arranged behind the fuel tank 19. A pair of left and right footrests 2 on which the rider on this seat 20 rests his/her feet.
1 is provided. That is, a pair of left and right bracket plates 22 are provided to protrude rearward from a connecting portion between the rear end of the main frame 8 and the rear end of the down tube 9. The footrest 21 is attached to the protruding end sides of both bracket plates 22.

The engine 14 is of a two-stroke, single-cylinder type, and includes a crankcase 24 and a cylinder 25 that projects upward and forward from the crankcase 24. An exhaust boat is formed at the front of the cylinder 25, and an exhaust pipe 27 is provided for discharging the exhaust gas from the cylinder 25 to the outside from the exhaust boat.

The exhaust pipe 27 is composed of an expansion chamber 28 connected to the exhaust boat, and a muffler 29 connected to the rear end of the expansion chamber 28. Further, the middle part of the expansion chamber 28 is bent so that the muffler 29 is located on the right side of the vehicle body.

The expansion chamber 28 will be explained in detail with reference to all the figures.

The expansion chamber 28 is connected to a connecting part 31 which projects forward and downward from the exhaust boat and whose projecting end is bent backward, and is connected to the rear end of this connecting part 31, and gradually increases in diameter as it moves rearward. an inflatable part 32 and a same-diameter part 33 that is connected to the rear end of the inflatable part 32 and extends rearward with approximately the same diameter.
and a throttle part 34 which is connected to the rear end of the same diameter part 33 and whose diameter gradually decreases as it goes rearward, and the muffler 29 is connected to the rear end of this throttle part 34.

The expansion portion 32 is disposed below the crankcase 24 at approximately the center in the vehicle width direction, and extends along the longitudinal direction of the vehicle body while being bent little by little in the vertical direction. Further, the rear portion of the inflatable portion 32 is bent rearward and upward.

On the other hand, the same-diameter portion 33 has a multi-pipe structure, and includes an outer cylinder 36 and an inner cylinder 37 that fit together at a predetermined interval. A large number of through holes 37a are formed in the inner cylinder 37, and glass wool 38 is filled between the outer cylinder 36 and the inner cylinder 37. In addition, in order to avoid interference between the transmission chain 17 located on the left outer side of the vehicle body and the constricted portion 34, the middle portion of the same diameter portion 33 is arranged such that the constricted portion 34 is located on the right outer side of the vehicle body. It is bent outward due to force in the vehicle width direction.

In the above case, since the rear part of the expansion chamber 28 is bent so that the front part of the expansion chamber 28 is located approximately at the center in the vehicle width direction, and the muffler 29 is located above the footrest 21, The bank angle of this motorcycle 1 can be made almost equally large on the left and right sides.

In order to support the expansion chamber 28 on the vehicle body frame 2, a bracket 40 is provided to protrude from the throttle portion 34. This bracket 40 is a plate material extending in the longitudinal direction of the vehicle body, and its lower end is attached to the upper surface of the throttle part 34.
The upper end of 0 is the right side hoodless) 21 bracket plate 22
It is screwed on. In this case, since the bracket 40 is a plate material located above the expansion chamber 28 and extending in the longitudinal direction of the vehicle body, screwing work to the bracket plate 22 for the footrest 21 can be done from the outside of the vehicle body. , this screw fastening work can be done easily.

(Effect of the invention) The effects of this invention are as follows. That is.

In the exhaust pipe of a two-stroke motorcycle engine, an expansion chamber for effectively utilizing the pulsating effect of the engine's exhaust gas gradually increases in diameter as it progresses from the exhaust boat side of the engine toward the rear of the vehicle body. Consists of a same-diameter part that is connected to the rear end of the expansion part and extends toward the rear of the vehicle body with approximately the same diameter, and a constriction part that is connected to the rear end of this same-diameter part and gradually becomes smaller in diameter as it moves toward the rear of the vehicle body. In this case, the exhaust pressure wave expands in the expansion part and flows from the same diameter part to the constriction part, where it becomes a reflected wave and produces the desired pulsating effect. If the rear part of such an expansion chamber is to be located on the side of the vehicle body, it will be necessary to bend the middle part of this expansion chamber. Therefore, in this invention, the expansion part is arranged to extend along the longitudinal direction of the vehicle body at approximately the center in the vehicle width direction, and the same diameter part is moved outward in the vehicle width direction so that the constriction part is located on the outer side of the vehicle body. It is bent towards the other side. That is, since the expansion chamber is bent at a point where the diameter dimension is approximately constant and the reflected wave does not occur, even when the expansion chamber is bent in this way, it does not adversely affect the desired pulsation effect in the expansion chamber, and therefore, Good engine output is maintained.

[Brief explanation of the drawing]

The figures show an embodiment of the invention, and FIG. 1 is I-I in FIG.
2 is a partial cutaway side view of the entire motorcycle; FIG. 3 is a side sectional view of the exhaust pipe; FIG. 4 is a sectional view taken along the line ■-■ in FIG. 2; The figure is a sectional view taken along the line v-v in FIG. 3. 1. Motorcycle, 1411. Engine, 2711. Exhaust pipe, 28. Expansion chamber, 32. Bottle expansion section, 33. Same diameter section, 34. Fist.

Claims (1)

[Claims] The expansion chamber of the exhaust pipe connected to the exhaust boat of a 1- or 2-cycle engine has an expansion part whose diameter gradually increases as it goes from the exhaust boat side toward the rear of the vehicle body, and an expansion part that is connected to the rear end of this expansion part and extends toward the rear of the vehicle body. In an exhaust pipe for a two-cycle engine for a motorcycle, the exhaust pipe is composed of a same-diameter part that extends with approximately the same diameter, and a constricted part that is connected to the rear end of this same-diameter part and gradually becomes smaller in diameter as it moves toward the rear of the vehicle body. The expansion part is arranged so as to extend along the longitudinal direction of the vehicle body at approximately the center in the vehicle width direction,
An exhaust pipe for a two-cycle engine for a motorcycle, characterized in that a portion of the same diameter is bent outward in the vehicle width direction so that the constriction portion is located on the outer side of the vehicle body.