JPH0588366B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a two-stroke engine for driving motorcycles and the like.

[Conventional technology]

As a two-stroke engine for motorcycles, etc.,
Generally, an exhaust port and a scavenging port are formed on the inner circumferential wall of the cylinder.

By the way, this type of two-stroke engine is configured so that the exhaust port is set slightly above the scavenging port so that residual gas is pushed out by fresh air jetted from the scavenging port. During the upward stroke of the piston, between the closing of the scavenging port and the closing of the exhaust port, a blow-by occurs in which a portion of fresh air is discharged from the exhaust port. As a result, there is a problem that the fresh air discharged causes air pollution.
Conventionally, as disclosed in Japanese Patent Publication No. 52-37130, a horizontal wall and a partition wall formed in a portion of the exhaust passage close to the exhaust port are used to prevent fresh air from flowing out.

[Problem that the invention seeks to solve]

However, in this type of conventional two-stroke engine, since the exhaust passage has a structure in which a horizontal wall and a partition are formed, the shape of the exhaust passage becomes complicated, making manufacturing difficult. Furthermore, at high speeds, the partition wall protruding into the exhaust passage generates a vortex, which increases fluid resistance. As a result, there was also the disadvantage that high-speed performance deteriorated because the exhaust gas was prevented from being discharged.

[Means for solving problems]

The present invention was made in view of the above circumstances, and it is an object of the present invention to provide a two-stroke engine that has a simple structure and can reduce fresh air blow-through without deteriorating high-speed performance. In the two-stroke engine according to the present invention, the center line of the exhaust passage is bent in the middle so as to be inclined in the cylinder axis direction with respect to the downstream side on the exhaust port side, and the exhaust port of the exhaust passage peripheral wall is bent along the center line. The upper surface of the vicinity is inclined in the direction of the cylinder axis.

[Effect]

In the present invention, by changing the flow direction of only fresh air from inside the cylinder toward a substantially horizontal direction on the upper surface of the peripheral wall of the exhaust passage that is inclined opposite to the exhaust port, the flow of fresh air can be carried out without obstructing the outflow of the exhaust gas. Prevent spills.

〔Example〕

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a longitudinal cross-sectional view showing a two-stroke engine according to the present invention. In the same figure, the reference numeral 1 indicates an air-cooled two-stroke engine, which includes a crankcase 2 and a crankcase installed above the crankcase 2. It comprises a cylinder block 4 holding a piston 3, and a cylinder head 6 covering the upper part of the cylinder block 4 to form a combustion chamber 5. A crank chamber 7 is formed in the crank case 2, and a crank shaft 8 is accommodated therein. Reference numeral 9 represents a connecting rod connecting the crankshaft 8 and the piston 3, and reference numeral 10 represents a spark plug having an electrode attached to the cylinder head 6 and facing into the combustion chamber 5.

An exhaust port 12 and a plurality of scavenging ports 13 are opened on one side of the cylinder inner circumferential wall of the cylinder head 6. These opening positions are exhaust port 12.
is set slightly above the scavenging port 13. The exhaust port 12 is open to the outside through an exhaust passage 14 extending diagonally downward from the exhaust port 12, and the scavenging port 13 is communicated with the crank chamber 7 through the scavenging passage. 15 is the exhaust port 12
At the intake port opened in the cylinder peripheral wall on the opposite side,
An intake passage 17 in which a reed valve 16 is inserted communicates with the crank chamber 7.

The exhaust passage 14 is formed such that the center line 20 is bent relatively gently in the middle.
That is, the centerline 20 is doglegged at the bend A from the exhaust port 12 so that the centerline 20 on the exhaust port 12 side is inclined in the cylinder axis direction with respect to the centerline 20 downstream of the bend A. is bent. Along this center line 20, an upper surface 14a of the peripheral wall of the exhaust passage near the exhaust port 12 is inclined in the cylinder axis direction. In other words, the exhaust passage 14 differs from the conventional exhaust passage 14 shown by the chain line 21 in that the upper surface 14a gradually bulges inward. Also,
The amount of bulge is set to be relatively small with respect to the cross-sectional area of the exhaust passage 14. On the other hand, the lower surface of the peripheral wall of the exhaust passage 14 is smoothly formed without being bent in the middle.

The cross-sectional shape of the exhaust passage 14 will be explained as follows.
As shown in FIG. 2, FIG. 3, and FIG. 4, the - line sectional view, - line sectional view, and - line sectional view of FIG. The upper surface 14a of the exhaust passage peripheral wall gradually bulges downward as it goes downstream. The amount of bulge of the upper surface 14a is maximum in the cross section including the bent portion A shown in FIG. On the downstream side, the upper surface 14a recedes to make the corners smooth, and the connection port 22 is circular in order to be connected to an exhaust pipe (not shown).

In the two-stroke engine configured in this way, when fresh air is burned and the piston 3 descends, the exhaust port 12 first opens and exhaust gas 23 is discharged, as shown in FIG. 23 flows obliquely downward in the direction of arrow E and along the surface of the upper surface 14a of the exhaust passage peripheral wall. Therefore, the upper surface 14a does not obstruct the outflow of the exhaust gas 23. This is the same even at high speeds, and since the exhaust gas 23 is guided smoothly, there is no possibility of generating vortices and causing fluid resistance as in the conventional case.

In the state shown in FIG. 6 in which the piston 3 is further lowered, fresh air 24 pre-pressurized within the crank chamber 7 is introduced into the cylinder from the scavenging port 13. Therefore, the remaining exhaust gas 23 is pushed out from the exhaust port 12 and reaches the bottom dead center in this state.

Thereafter, the piston 3 moves to an upward stroke, and the exhaust gas 23 is completely discharged just before the scavenging port 13 shown in FIG.
3 and the exhaust port 12 direction. This flow of fresh air 24 continues until the exhaust port 12 is closed, as shown in FIG. 8, and attempts to blow through the exhaust port 12.

However, the upper surface 14a of the circumferential wall of the exhaust passage is located at the exhaust port 1.
2, it is possible to prevent fresh air 24 from flowing out. That is, although the fresh air 24 heads in the substantially horizontal direction indicated by the arrow N, the direction of the flow is changed by the upper surface 14a. As a result, the energy of the fresh air 24 is attenuated,
Since the pressure inside the upper surface 14a is higher, outflow is prevented and blow-through is reduced.

〔Effect of the invention〕

As explained above, according to the present invention, the center line of the exhaust passage is bent in the middle on the exhaust port side so as to be inclined in the cylinder axis direction with respect to the downstream side, and the peripheral wall of the exhaust passage is bent along the center line. Because the top surface near the exhaust port is tilted in the direction of the cylinder axis,
By changing the flow direction of only fresh air from inside the cylinder toward a substantially horizontal direction on the upper surface of the exhaust passage surrounding wall that is inclined toward the exhaust port, it is possible to prevent the outflow of fresh air without interfering with the outflow of exhaust gas. can.

Therefore, unlike in the past, the shape of the exhaust passage is not complicated or the outflow of exhaust gas is not obstructed, so that the blow-through of fresh air can be reduced with a simple structure and without deteriorating high-speed performance.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal cross-sectional view showing a two-stroke engine according to the present invention, FIG. 2 is a cross-sectional view taken along the - line in FIG.
FIG. 3 is a sectional view taken along the same line, FIG. 4 is a sectional view taken along the same line, and FIGS. 5 to 8 are schematic diagrams for explaining the operating state. 3...Piston, 4...Cylinder block, 1
2...Exhaust port, 13...Scavenging port, 14...Exhaust passage, 14a...Top surface, 20...Center line.

Claims (1)

[Claims] 1. In a two-stroke engine having an exhaust port on the inner circumferential wall of the cylinder, the center line of the exhaust passage extending diagonally downward from the exhaust port is bent midway on the exhaust port side so as to be inclined in the cylinder axis direction with respect to the downstream side. , a two-stroke engine in which the upper surface of the peripheral wall of the exhaust passage near the exhaust port is inclined in the direction of the cylinder axis along this center line.