JP2749163B2 - Exhaust system for 4-cycle engine - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust system suitable for, for example, a four-stroke engine for a motorcycle, and particularly to an exhaust system for an engine having two exhaust valves per cylinder. The present invention relates to an improvement in the connection between an exhaust port and an exhaust pipe, which can improve the exhaust efficiency of the engine and reduce the size of the cylinder head of the engine.

[Conventional technology]

The exhaust device of a four-stroke engine has a structure in which an exhaust pipe is connected to an outlet end opening formed in a front wall of a cylinder head of an exhaust port, and the exhaust pipe is bent and extended rearward, and a muffler is connected to the extended rear portion. General. And as an exhaust device in the case of having two exhaust valves per cylinder,
Conventionally, for example, as described in Japanese Utility Model Laid-Open No. 54-74816, the front opening portions of a pair of left and right exhaust ports are bent so as to be substantially parallel to the vehicle center line and connected to the openings. In some cases, the exhaust pipe is extended forward as it is so as to be substantially parallel to the vehicle center line, and then further extended backward.

In the exhaust device described in the above publication, the exhaust gas discharged from the exhaust valve opening spreads outward along the left and right exhaust ports, and then the vehicle center line near the connection between the exhaust port and the exhaust pipe. , And flows while bending backward along the shape of the exhaust pipe.

[Problems to be solved by the invention]

By the way, in order to improve the exhaust gas discharge efficiency in the exhaust system, it is necessary to reduce the flow path resistance as much as possible. From the viewpoint of reducing this resistance, it is necessary to plan the arrangement structure of the exhaust port and the exhaust pipe. Is done. Since the apparatus described in the above publication is from a different viewpoint, the discharge efficiency is not always sufficient.

Also, from the viewpoint of reducing the size of the cylinder head,
It is desirable that the cylinder head be shaped as closely as possible to the circular shape of the cylinder. However, in the conventional device described in the above publication,
As is apparent from FIG. 4, since the opening at the front end of the exhaust port is parallel to the camshaft, the outer edges of both openings form a corner, and the exhaust port conforms to the cylinder shape. The request cannot be fulfilled.

The present invention has been made in view of the above demands, and has as its object to provide an exhaust device for a four-stroke engine that can improve exhaust gas emission efficiency and reduce the size of the engine.

[Means for solving the problem]

The present invention has two exhaust valves per cylinder, and inserts and connects an exhaust pipe to each exhaust port leading out the opening of each exhaust valve to the front wall surface of the cylinder head. In an exhaust system for a four-stroke engine, which is bent toward the rear of the vehicle, then merges into one, and extends rearward of the vehicle, the two exhaust ports are linearly expanded in a C shape, and the exhaust pipes of A portion in the vicinity of a connection portion to each of the exhaust ports is extended in a C shape so as to be substantially straight with the exhaust port, and one of the exhaust pipes is divided forward and backward in the vicinity of the junction, and The invention is characterized in that the axis of the portion near the connecting portion of the exhaust pipe to the exhaust port is substantially parallel to the axis of the portion near the divided portion.

[Action]

According to the exhaust device for a four-stroke engine according to the present invention, since the exhaust port and the exhaust pipe are formed substantially linearly, the exhaust gas is discharged linearly from the exhaust valve opening. As compared with the conventional device in which the vicinity of the connection portion is bent, the flow path resistance is reduced, and accordingly, the exhaust gas discharge efficiency is improved and the engine performance can be improved.

In addition, since the exhaust pipe expands in a C-shape, the outlet end opening is substantially parallel to the tangent line of the cylinder when viewed in the cylinder axis direction, and therefore follows the shape of the cylinder accordingly, resulting in a compact cylinder head. Can contribute to

Furthermore, one of the exhaust pipes is divided into front and rear portions in the vicinity of the junction, and the axis of the portion of the one exhaust pipe near the connecting portion to the exhaust port is substantially parallel to the axis of the portion near the split portion. Therefore, assembling is easy while the exhaust pipe is expanded in a C-shape, bent backward, and merged.

That is, in assembling the exhaust device of the present invention into an engine, the connecting portion 32c of the exhaust pipe 32 is first inserted and connected to the exhaust port 29 with the exhaust pipe 31 separated, and then the connecting portion 31c of the exhaust pipe 31 is connected. Into the exhaust port 28. At this time, the exhaust pipe 3
The division on the first side is directly inserted into the division on the junction 34 side, so that the exhaust pipe 31 can be easily connected.

〔Example〕

 Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

1 to 4 are views for explaining an exhaust system of a four-stroke engine for a motorcycle according to an embodiment of the present invention, and FIG. 1 is a diagram showing a connection state between an exhaust port and an exhaust pipe. FIG. 2 is a partial sectional right side view, FIG. 3 is a sectional plan view showing the relationship between intake and exhaust valves and intake and exhaust ports, and FIG. 4 is a motorcycle employing the exhaust device. FIG. In FIG. 1, the upper side in the figure is the front side of the vehicle in the other figures, and the right side in the other figures is the front side of the vehicle.

In the drawing, reference numeral 1 denotes a motorcycle provided with the exhaust system of the present embodiment. A body frame 2 of the motorcycle 1 has a main pipe 2b and a front end of a down tube 2c welded to an upper portion and a lower portion of a head pipe 2a. It is a so-called diamond type which is connected by welding the upper end of the sheet pillar 2d to the rear end of the main pipe 2b. In addition, 2g is an underguard for protecting the crankcase, 2e is a support pipe for an engine suspension bridged between the main pipe 2b and the down tube 2c, and 2f is a seat rail.

A front fork 3 for supporting the front wheel at the lower end is supported on the head pipe 2a so as to be steerable left and right. A rear arm 5 for supporting the rear wheel 4 at the rear end is vertically mounted on the seat pillar 2d. It is pivotally supported. Also this rear arm 5
Is connected to the vicinity of the rear end of the main pipe 2b via a link mechanism (not shown) and one shock absorber 8. Reference numeral 6 denotes a fuel tank, 7 denotes a seat, 9a denotes an air scoop that covers a side surface of the tank, 9b denotes a side cover that covers a lower portion of the seat, and 9c denotes a rear cover that covers a rear portion of the vehicle.

A water-cooled 4-cycle single-cylinder 5-valve engine 10 is mounted in the body frame 2. This engine 10
It has a structure in which a cylinder body 12, a cylinder head 13, and a head cover 14 are laminated on the front upper surface of the crankcase 11 with a slight forward inclination, and the head cover 14 is suspended from the support pipe 2e via a bracket 38. Have been.

At substantially the center of the lower surface of the cylinder head 13, a combustion chamber wall surface 13a that forms a combustion chamber with a piston inserted into a cylinder liner of the cylinder body 12 is recessed. At the approximate center of the combustion chamber wall 13a, a plug hole 1 for mounting a spark plug is provided.
3b is formed, and the drain hole 13c communicates with the plug hole 13b. 13d is a cam chain room.

The left, center, and right intake valve openings 17, 18, and 19 are formed on one side of the combustion chamber wall surface 13a sandwiching the plug hole 13b, and the left and right exhaust valve openings 20, 21 are formed on the other side. Have been. The left intake valve opening 17 is led out to the rear wall of the cylinder head by a left intake port 22 extending rearward substantially in parallel with the vehicle center line A. The center and right intake valve openings 18 and 19 are located at the vehicle center line A.
The rear intake port 23a is extended rearward by a central intake port 23a extending obliquely rearward and a right intake port 23b extending substantially in parallel, and the combined intake port 23 of the two intake ports 23a, 23b is entirely rightward in the width direction. It extends diagonally.
Left and right carburetors 26 and 27 are connected to the rear end openings of the left intake port 22 and the merged intake port 23 via left and right cab joints 24 and 25, respectively.

When viewed in the cylinder axis direction, the left and right exhaust valve openings 18 and 19 extend straight from the respective openings to the front of the vehicle while extending linearly in a C-shape. Exhaust ports 28, 2
Front end opening (outlet end opening) 28a, 2 formed with slightly larger diameter of 9
9a faces both sides of the down tube 2c. The front end openings 28a and 29a are formed in the combustion chamber wall surface when viewed in the cylinder axis direction since each port is widened in a U-shape.
13a, that is, nearly parallel to the tangent to the cylinder (first
(See FIG. 3, FIG. 3).

The left and right front end openings 28a, 29a are provided with exhaust devices 3
The left and right exhaust pipes 31, 32 have connection openings 31a, 32a, which are also slightly larger in diameter, are inserted and connected, and the connection portions 31c, 32c of the left and right exhaust pipes 31, 32 are connected to the above exhaust pipes. It extends forward so as to be colinear with the ports 28 and 29. The left exhaust pipe 31 is bent downward and to the right on the left side of the down tube 2c, and is bent upward again.
The right exhaust pipe 32 extends rearward below the left exhaust pipe 31 after the right exhaust pipe 32 bends in a substantially U-shape to the right of the down tube 2c. , Right exhaust pipe 3
The rear ends of the 1,32 merge. The left exhaust pipe 31
Is divided into front and rear portions on the slightly upstream side of the junction portion 34, and the rear end portion 31b of the upstream portion is separably inserted and connected to the connection member 35 fixed to the front end of the downstream portion. And this division part is parallel to the connection part 31c. The connection member 35 and the vicinity of the junction 34 are covered with a protector 37 for protecting the legs of the occupant from heat.

A junction pipe 36 connected to the junction 34 extends rearward near the height of the upper edge of the crankcase 11, and a muffler 33 is connected to a rear end thereof. The front half of this muffler 33 is also used as a back stay for connecting the middle of the seat rail 2f and the bracket 2h fixed to the lower part of the seat pillar 2d.

 Next, the operation and effect of this embodiment will be described.

The exhaust gas generated in the combustion chamber is
From 1 left and right exhaust ports 28 and 29, left and right exhaust pipes 31 and 32,
Further, the gas is discharged through the merging pipe 36 and the muffler 33. In such exhaust gas discharge, in this embodiment, the left and right exhaust ports 28 and 29 and the connecting portions 31c and 32c of the left and right exhaust pipes 31 and 32 are formed linearly. Since the gas is discharged straight from the opening, the flow path resistance is reduced as compared with the above-described bent connection portion between the exhaust port and the exhaust pipe, and the discharge efficiency is improved accordingly.

Further, in the present embodiment, since the two exhaust ports 28, 29 are widened in a U shape, the front end openings 28a, 29a are inclined in a direction along the cylinder shape, and the cylinder head is accordingly reduced in size. Can contribute to

Furthermore, in this embodiment, the connection part 3 of the left and right exhaust pipes 31, 32 is provided.
Since the portions 1c and 32c are spread forward in the shape of a letter "C", the interval between the connecting portions 31c and 32c is widened, so that a relatively large-diameter down tube 2c can be easily arranged in the portion. In addition, the expansion of the exhaust pipe makes it easier for the traveling wind to be introduced into the cylinder head wall surface, thereby improving the cooling performance.

Further, in the present embodiment, since the left exhaust pipe 31 can be separated slightly upstream from the junction 34, the attachment work of the exhaust device 30 is easy. That is, when the exhaust pipes are formed in a U-shape as in this embodiment, the interval between the connection openings 31a and 32a becomes narrow, and this portion interferes with the down tube 2c and the like, making assembly impossible or difficult as it is. In this embodiment, the above problem can be solved by assembling the left exhaust pipe 31 in a separated state. Also, when viewed in the cylinder axis direction, the divided portion is parallel to the connection portion 31c of the left exhaust pipe 31, so that the connection opening 31a and the rear end portion 31b may be inserted directly into the mating side. It is easy to assemble from the point of view.

In the above embodiment, a single cylinder engine for a motorcycle has been described. However, the present invention is not limited to a multi-cylinder engine such as a two-cylinder engine having a cam chain chamber formed in the center, or to a motorcycle engine. It can also be applied to automobile engines and general-purpose engines.

〔The invention's effect〕

As described above, according to the exhaust device for a four-stroke engine according to the present invention, the exhaust port is formed in a straight line extending in the shape of a letter C, and the exhaust pipe is similarly connected to this straight line.
This has the effect of reducing the flow resistance of the exhaust gas, thereby improving the exhaust efficiency, and promoting the miniaturization of the cylinder head by the extent that the outlet end opening follows the cylinder shape.

Further, any one of the exhaust pipes is divided into front and rear portions in the vicinity of the merging portion, and the axis of the portion near the connection portion of the one exhaust pipe to the exhaust port and the axis of the portion near the split portion are substantially parallel to each other. Therefore, the assembling is easy while the exhaust pipe is expanded in a C-shape, bent backward, and merged.

[Brief description of the drawings]

1 to 4 are views for explaining an exhaust system of a motorcycle engine according to an embodiment of the present invention, wherein FIG. 1 is a partially sectional plan view and FIG. 2 is a partially sectional right side view. FIG. 3 is a cross-sectional plan view showing the relationship between each port and the valve, and FIG. 4 is a right side view of a motorcycle provided with the embodiment device. In the figure, 1 is a motorcycle, 2 is a body frame, 2c is a down tube (frame member), 10 is an engine, 13 is a cylinder head, 21 and 22 are left and right exhaust valve openings, and 28a and 29a are front end openings (lead-out). End openings), 31 and 32 are left and right exhaust pipes, 37 and 38
Is an exhaust valve.

Claims (1)

(57) [Claims] An exhaust pipe is inserted and connected to each exhaust port leading to the front wall surface of a cylinder head, the exhaust pipe being provided with two exhaust valves per cylinder. In a four-stroke engine exhaust device in which the two exhaust ports are bent toward the rear of the vehicle and then merged into one to extend to the rear of the vehicle, the two exhaust ports are linearly expanded in a C shape, and the exhaust pipes The portion near the connecting portion to each of the exhaust ports is extended in a C shape so as to be substantially straight with the exhaust port, and either one of the exhaust pipes is divided into front and rear portions in the vicinity of the junction, and An exhaust system for a four-stroke engine, characterized in that an axis of a portion near a connection portion of the exhaust pipe to the exhaust port is substantially parallel to an axis of a portion near the divided portion.