JPS5913322Y2 - 2 cycle engine piston - Google Patents

Description

[Detailed description of the invention] This invention relates to a piston used in a two-stroke engine, particularly a Schnurre scavenging type two-stroke engine in which the plane of symmetry of a pair of scavenging passages is deviated at a predetermined angle with respect to a plane perpendicular to the piston pin. It is.

When converting a conventional Schnew-scavenged two-stroke engine to a multi-cylinder engine, the plane of symmetry of the two scavenging passages is deflected at a predetermined angle with respect to the plane perpendicular to the piston pin, that is, the plane of symmetry of the two scavenging passages is deflected at a predetermined angle to the plane perpendicular to the piston pin. It may make piping easier or shorten the distance between each cylinder.

Figures 1 and 2 are the same as <II-II
FIG.

In these figures, 1 is a Schnurre scavenged two-cylinder cylinder 2.
Cycle engine, 2 is a cylinder block, 3 is a cylinder head, 4 is a crankshaft, 5 is a crank chamber 6a,
Vaporizer connected to 6b, 7a.

7b is a piston, and 8a and 8b are this piston 7a.

7b and the crankshaft 4, respectively.

Cylinder liners 9a and 9b are fitted into each cylinder of the cylinder block 2, and the cylinder liners 9a and 9b and the cylinder block 2 have a pair of scavenging passages 10a and 11a for each cylinder.

and one each of third scavenging passages 12a, 10b and llb.
, 12b, and exhaust passages 13a, 13b are open.

These scavenging passages 10a, 11a and 10b. 1
The inlets of the third scavenging passages 12a and 12b open into the lower edges of the cylinder liners 9a and 9b, and the inlets of the third scavenging passages 12a and 12b open into the crank chamber, respectively.

Therefore, in the downward stroke of the pistons 7a, 7b, the exhaust passages 13a, 13b open first, and then the pair of scavenging passages 10a, 11a, 10b, 11b open.
Then, the third scavenging passages 12a, 12b are opened, and the burned gas is smoothly sent to the exhaust passages 13a, 13b.

Note that the scavenging passages 10a, 10b, 11a, 1
1b is the scavenging passage 1 of each cylinder, as shown in Figure 2.
Each plane of symmetry 1 of 0 a and 11 a, and 10 b and 11 b
4a and 14b are provided so as not to be perpendicular to the piston pins 15a and 15b.

Further, the third scavenging passages 12a, 12b and the exhaust passage 13a
, 13b are located at symmetrical positions with respect to the center of the piston, and are provided such that their respective centers are located on the symmetry planes 14a, 14b.

That is, each passage position is generally deviated by a constant angle with respect to the piston pins 15a, 15b.

By doing this, the exhaust passages 13a, 13
By deflecting the direction b downward, it is possible to facilitate piping of the exhaust pipe 16, and the interval between each cylinder can be shortened.

Therefore, the entire engine 1 can be made compact.

Also, the piston 7a. The scavenging passage 10 is located at the lower end of 7b.
Notches 17 a, 18 a, 17 b, 18 b are provided corresponding to a, 11 a, 10 b, 11 b, and two skirts 19 a, 20 a, and 19 b, 20 b are formed on each piston 7 a, 7 b. has been done.

Here are two skirts 19a and 20a and 19b
A line connecting the circumferential centers of and 20b and the piston center coincides with the symmetry planes 14a and 14b.

In general, the positions of the piston and piston pin are as shown in Fig. 3. The piston pin 21 is not on the center line of the piston 22, and when the crankshaft rotates clockwise, it is on the right side of the piston center line, that is, on the pressure side B. Eccentric.

This type of piston is called an offset piston.

By doing this, the piston 22 during the expansion stroke
equalizes the side pressure F1 above and below the piston pin 21,
Wear of the cylinder 23 and piston slap can be reduced.

FIG. 4 is a graph showing an example of the actually measured value of the side pressure F1 when such an eccentric piston is used.

In this figure, θ is the crank angle, TDC and BDC
indicate top dead center and bottom dead center, respectively.

Even if the side pressure is reduced by using an offset piston as described above, the side pressure F1 acts on the thrust side A of the cylinder 19 for % cycles in one cycle.

FIG. 5 is a sectional view taken along the line ■-V showing the force acting on the piston 22.

In this figure, the skirts t-24, 25 of the piston 22 are not symmetrical with respect to a plane 26 orthogonal to the piston pin passing through the center of the piston.

Therefore, the resultant force F2 of the force f generated when the skirt 24 is pressed against the inner surface of the cylinder 23 does not lie on the surface 26 orthogonal to the piston pin, but faces in a direction forming an angle δ.

Therefore, it can be seen that a force F3 in the piston pin direction 21a is generated by vector combining Fl and F2.

This force F3 is applied to the large end 28 of the connecting rod 27 shown in FIG.
and acts on the bearing at the small end 29 as a thrust force.

For this reason, the large and small ends 28, 29 are twisted, which not only accelerates wear of these parts, but also may cause seizing.

Furthermore, since this F2 causes an unbalanced shape in the skirt 24, it also causes seizure of the piston 22.

This idea was devised in view of the problems that existed in conventional engines.The line connecting the circumferential center of the skirt formed at the lower end of the piston and the piston center is located closer to the center of the piston than the symmetrical plane of the scavenging passage. By deflecting the piston pin toward the perpendicular surface passing through the
We have created a two-stroke engine piston that can reduce the wear of these parts due to the thrust force acting on the bearings at the large and small ends of the connecting rod as small as possible, and prevent seizure of the piston. The purpose is to provide

FIG. 6 is a sectional view of a piston skirt showing a piston skirt according to this invention in comparison with a conventional piston skirt.

In this figure, the two skirts 2 of a conventional piston 22
The angles that lines 30 and 31 connecting the circumferential centers of pistons 4 and 25 and the piston center make with the piston pin orthogonal surface 26 passing through the piston center are indicated by a and l).

Similarly, the angles that lines 35 and 36 connecting the circumferential centers of the two skirts 33 and 34 of the piston 32 and the piston center make with the piston pin orthogonal surface 26 are c and d. is shown.

In the figure, 37 and 38 are scavenging passages, respectively.

As is clear from this figure, the piston 3 according to this invention
The skirts 33 and 34 of No. 2 are formed so that c<a and d<b.

Therefore, as shown in FIG. 5, the resultant force F2 of the force f generated when the skirt 33 is pressed against the inner surface of the cylinder is stronger than the resultant force F2 generated on the skirt 24 of the conventional screws 1 to 22. It is deflected toward the plane 26 perpendicular to the pin.

Therefore, the force F3 acting in the piston pin direction 21 a
is smaller than the conventional piston 22.

FIG. 7 and FIG. 8 each show an embodiment of this invention, and the following relationship holds between 01 to e4.

That is, θ1≧45°, 02<1.5θ1°03J4
This is the relationship of 1.

By determining θ□~& in this manner, this invention exhibits even better effects.

As is clear from FIGS. 6 to 8, according to the present invention, it is difficult to make the notch forming the skirt completely correspond to the scavenging passage as in the conventional piston;
Needless to say, it is necessary to take measures so as not to impair the scavenging function.

According to this invention configured as described above, the line connecting the circumferential center of the skirt formed on the piston and the piston center is deflected from the symmetry axis of the scavenging passage toward the plane perpendicular to the piston and pin that passes through the piston center. Because of this structure, the thrust force acting on the bearings at the large end and small end of the connecting rod can be reduced.

Therefore, wear of these bearing parts can be reduced and seizure can be prevented.

Furthermore, since the unbalanced strain generated in the piston skirt is reduced, seizure of the piston can be prevented.

[Brief explanation of the drawing]

Fig. 1 is a central vertical cross-sectional view of a Schnuelle scavenging type two-cylinder two-stroke outboard engine in which the plane of symmetry of a pair of scavenging passages is deviated at a predetermined angle from the plane orthogonal to the piston pin, and Fig.
The I-II line sectional view, Fig. 3, Fig. 4, and Fig. 5 explain the forces acting on the piston. Fig. 3 is an explanatory diagram of the lateral pressure F1, and Fig. 4 shows the actual measured value of the lateral pressure F1. The graph shown in FIG. 5 is a sectional view taken along the v-v line. FIG. 6 is a sectional view of a piston skirt showing the structure of this invention in comparison with a conventional piston, and FIGS. 7 and 8 are sectional views of a piston skirt showing an embodiment of this invention. 1... Schnuler scavenged two-cylinder two-stroke engine, 7a, 7b, 22.32--Piston, 10a. 11 a, 10 b, 11 b, 37.38--
...Scavenging passage, 14a. 14b... Symmetry axis of scavenging passage, 15a, 1
5 b, 21... Piston pin, 17 a
, 18 a, 17 b, 18 b...notch, 19 a, 20 a, 19 b, 20 b,
24.25.33゜34...Skirt, 26.
...Piston/pin orthogonal surface, 30, 31.35.
36... Line connecting the circumferential center of the skirt and the center of the piston.

Claims (1)

[Scope of utility model registration request] In a Schnüller scavenging type two-stroke engine in which the plane of symmetry of a pair of scavenging passages is deviated at a predetermined angle with respect to the plane orthogonal to the piston pin, the circumferential center of the skirt formed at the lower end of the piston by a notch that approximately corresponds to the scavenging passage. A piston for a two-stroke engine, characterized in that a line connecting the center of the piston is deflected from a plane of symmetry of the scavenging passage toward a plane orthogonal to the piston pin passing through the center of the piston.