JPS59689B2 - Crank chamber compression type 2-stroke engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a two-stroke engine with a crank chamber pressure.

FIG. 1 is a vertical cross-sectional partial view of a conventional two-stroke engine (corresponding to the middle part of the left half of FIG. 2). Generally speaking, when the engine rotates at high speed, a load is applied to the piston pin 30 and the piston pin boss 31. increases, causing creep in the boss portion 31 and heat generation in the piston pin 30.

When the piston pin 30 generates heat, the hardness of the piston pin 30 decreases, causing a problem that the strength of the piston pin 30 decreases. Conventionally, as a countermeasure against this problem, a lubricating oil hole 32 is provided in the boss portion 31.
However, it has not been possible to sufficiently lubricate and cool the fitting portion between the outer circumferential surface of the pin 30 and the inner circumferential surface of the boss portion 31. Furthermore, high-speed, high-output engines for racing cars and the like are required to be lighter in weight and more compact in engine size. As shown in , the cross-sectional area of the portion A extending from the crank chamber 33 to the scavenging passage 34 is
When the engine reaches near the bottom dead center, it becomes significantly restricted, which restricts the scavenging airflow and makes it difficult to produce high output. The present invention provides a solution to the above-mentioned problems and difficulties, and its purpose is to (
1) Improved cooling efficiency of the piston pin and piston pin boss, (2) Reduced engine weight and compact engine size, and (3) Increased engine output by ensuring sufficient scavenging flow.

The invention will now be explained in conjunction with the drawings. In FIG. 2, which is a longitudinal sectional view of the engine according to the first invention and the third invention, 1 is a cylinder block, 2 is a cylinder head, and 3 is a cylinder block.
is the crankcase.

A piston 5 is fitted into the cylinder working chamber 4 of the cylinder block 1 so as to move vertically, and the internal space of the piston 5 is open toward the crank chamber 6. The piston 5 has two boss portions 7 formed on the same axis.
A piston pin 8 is fitted into the inner peripheral side of the boss portion 7, and both ends of the piston pin 8 are locked by snub pins or the like to prevent the piston pin 8 from slipping out from the boss portion 1. The upper end of a connecting rod 9 is fitted into the center of the piston pin 8 in the longitudinal direction, and the lower end of the connecting rod 9 is connected to a crankshaft 10 via a crank pin 11. Of course, this crank pin 11 is offset from the axis of the crankshaft 10. 12 is a bearing.

A recess 13 recessed toward the center of the piston 5 is formed in the skirt portion of the piston 5 near both ends of the piston pin 8, and the lower end of the recess 13 opens into the crank chamber 6. .

A main scavenging passage 14 that communicates the crank chamber 6 and the cylinder working chamber 4 is carved in the peripheral wall of the cylinder block 1, and when the piston 5 is located near the bottom dead center, an intermediate part of the main scavenging passage 14 is carved. A sub-scavenging passage 15 is formed which communicates with the upper end of the inner space of the recess 13.

In addition, if the piston 5 dies before reaching the vicinity of the bottom dead center, the sub-scavenging passage 15 is connected to the intermediate part of the main scavenging passage 14 and the recess 13.
It communicates with the middle part of the inner space. The auxiliary scavenging passage 15 can be molded with a core together with the main scavenging passage 14 when the cylinder block 1 is cast, but the auxiliary scavenging passage 15 is inclined so that the main scavenging passage 14 side is located above the inner space side of the recess 13. Therefore, the cylinder block 1 can be opened by machining after casting. A groove 19 parallel to the axis of the piston pin 8 is formed in the lower end of the inner peripheral surface of the boss portion 7, and the groove 19 communicates the inner space of the recess 13 and the inner space of the piston 5.

A circular groove 19 may be formed on the outer peripheral surface of the piston pin 8. FIG. 3 is a view of the piston 5 in the direction of the arrow in FIG.
3 and grooves 19 are clearly defined.

Next, to explain the operation of the engine according to the first and third inventions, when the piston 5 starts to descend, the air-fuel mixture in the crank chamber 6 is compressed, and then when the piston 5 reaches near the bottom dead center (second state in the figure), outlet 14 of the main scavenging passage 14
a opens to the cylinder working chamber 4, and the compressed air-fuel mixture in the crank chamber 6 is supplied into the cylinder working chamber 4. During such a scavenging stroke, the compressed air-fuel mixture in the crank chamber 6 not only passes through the main scavenging passage 14 as shown by arrow B in FIG. 1
It is also supplied into the cylinder working chamber 4 through a route passing through 5. That is, a sufficient scavenging flow rate can be ensured by the recess 13 and the sub-scavenging passage 15, and the fitting portion between the pin 8 and the boss r can be forcibly cooled by the scavenging air flow passing through the space inside the recess 13. can. Furthermore, since the l portion of the air-fuel mixture in the internal space of the piston 5 flows into the internal space of the recess 13 through the groove 19, the fitting portion between the piston pin 8 and the boss portion 7 is efficiently lubricated and cooled.

Further, the groove 19 is formed over a length greater than the full width t of the fitting portion between the piston pin 8 and the boss portion 7, and furthermore, when the piston 5 is in motion, the piston pin 8 gradually moves against the boss portion 7. Because of the rotation, the oil component in the air-fuel mixture spreads over the entire area where the pin 8 and the boss r fit together, and can perform a good lubricating action. FIG. 4 is a drawing corresponding to the arrow view in FIG. 2 of the piston 5 adopted in the second invention, and apart from this FIG. is formed.

The structure of the second invention other than the rib 2:0 is the same as the structure of FIG. 2. Although the groove 19 in FIG. 2 is not shown in FIG. 4, the groove 19 may of course be made of cedar. By forming the ribs 20 in this way, it goes without saying that during the scavenging stroke, the air-fuel mixture can be rectified to smoothly pass through the space inside the recess 13 and be guided to the scavenging passage 15 (see FIG. 2). rib 2
Since the fins 0 serve as cooling fins, the boss r and the pin 8 can be cooled more efficiently. FIG. 5 is a view taken along arrow V in FIG. 4. As explained above, according to the present invention, (1) The piston pin 8 and the piston pin boss part 7 can be cooled extremely efficiently, and the creep phenomenon and strength reduction of the piston pin 8 and the boss part 7 can be prevented.

That is, in order to actively cool the piston pin 8 and the boss part r by the scavenging air flow flowing through the space inside the recess 13 and the sub-scavenge passage 15 (arrow C in FIG. 2), the heat generated by the pin 8 and the boss part 7 is reduced. It is also possible to prevent the creep phenomenon, and the engine operates well even if the engine fails at high speed and high output. In the second invention, the recess 13 is further provided with a rib 20 that guides the scavenging air flow from the crank chamber 6 to the sub-scavenging passage 15.
Not only can the scavenging air flow in the inner space be sent smoothly to the sub-scavenging passage 15, improving the filling efficiency, but also the rib 20
Since the fins serve as cooling fins, the boss r and the pin 8 can be cooled more efficiently. Also the third
In the invention, a groove 19 is formed on the inner circumferential surface of the piston boss portion 7 (or on the outer circumferential surface of the pin 8, or both) to communicate the inner space of the recess 13 and the inner space of the piston 8, so that there is no mixing during the scavenging stroke. Air will actively flow into the groove 19 from the internal space of the piston 5, so that the fitting portion between the pin 8 and the boss portion 7 can be well lubricated and cooled. (2) Good scavenging action can be performed even when the engine is made compact, making it ideal as a high-speed, high-output engine for racing cars and the like.

In other words, when the overall height of the engine is lowered, the cross-sectional area of section A in Figure 1 is significantly limited in conventional engines, making it impossible to obtain sufficient scavenging air flow, making it difficult to operate the engine at high speed and high output. was difficult. In the present invention, even when the engine is made compact, the main scavenging passage is maintained by the scavenging air flow (arrow C in Fig. 2) passing through the space inside the recess 13 and the sub-scavenging passage 15 from the beginning of the scavenging stroke to the latter half of the scavenging stroke. 1
Since the lack of scavenging air flow (arrow B in Figure 2) within the engine can be compensated for, the high speed and high output state of the engine can be maintained in good condition.

[Brief explanation of the drawing]

Figure 1 is a longitudinal cross-sectional partial view of a conventional engine, and Figure 2 is a partial longitudinal cross-sectional view of a conventional engine.
3 is a longitudinal sectional view of the engine according to the invention and the third invention, FIG. 3 is a view of the piston in the direction of the arrow in FIG. 2, FIG. Figure 5 is the fourth
It is a v arrow view of a figure. 1... Cylinder block, 4... Cylinder working chamber, 5... Piston, 6... Crank chamber, 7...
Boss portion, 8... Piston pin, 13... Recessed portion, 14
...Main scavenging passage, 15...Sub-scavenging passage, 19...
Groove, 20...rib.

Claims (1)

[Claims] 1. A main scavenging passage communicating between the crank chamber and the cylinder working chamber is provided, and the piston portion near both axial ends of the piston pin is recessed toward the center of the piston, and the lower end is connected to the crank chamber. A sub-scavenging passage is formed in the peripheral wall of the cylinder block to communicate the internal space of the recess with the middle part of the main scavenging passage, and when the piston is located near the bottom dead center, the upper end of the internal space of the recess and the main scavenging passage are formed. A crank chamber compression type two-stroke engine characterized in that an intermediate portion of a main scavenging passage is configured to communicate through a sub-scavenging passage. 2. A main scavenging passage communicating between the crank chamber and the cylinder working chamber is provided, and a recess is formed in the piston portion near both axial ends of the piston pin, which is recessed toward the center of the piston and whose lower end opens into the crank chamber. A sub-scavenging passage is formed in the peripheral wall of the cylinder block to communicate the inner space of the recess and the middle part of the main scavenging passage, and when the piston is located near the bottom dead center, the upper end of the inner space of the recess and the middle part of the main scavenging passage 1. A crank chamber compression type two-stroke engine configured to communicate via a sub-scavenging passage, and characterized in that a rib is formed in the recessed portion to guide a scavenging air flow from the crank chamber to the sub-scavenging passage. 3 A main scavenging passage communicating between the crank chamber and the cylinder working chamber is provided, and a concave portion is formed in the piston portion near both axial ends of the piston pin to be concave towards the center of the piston and whose lower end opens into the crank chamber. A sub-scavenging passage is formed in the peripheral wall of the cylinder block to communicate the inner space of the recess and the middle part of the main scavenging passage, and when the piston is located near the bottom dead center, the upper end of the inner space of the recess and the middle part of the main scavenging passage A groove is formed on either or both of the outer circumferential surface of the piston pin or the inner circumferential surface of the boss portion for the piston pin to communicate with each other via the sub-scavenging passage. A two-stroke engine with a compressed crank chamber.