JPH0326820A - Structure of cooling piston of two-cycle engine - Google Patents

Abstract

PURPOSE:To secure required amount of air-fuel mixture for cooling by a method wherein a second air scavenging passage for communicating between an inlet port and a discharge port respectively formed on a cylinder is formed on a cylinder body while a vent hole is formed on a piston skirt. CONSTITUTION:In a two-cycle engine 1, air-fuel mixture primarily compressed in a crank chamber 2c is fed from an air scavenging port 18b via a first air scavenging passage into a cylinder 18. At this time a second air scavenging passage 3b for communicating between an inlet port 18d and a discharge port 18c formed on the lower and upper sections of the cylinder 18 respectively is formed on a cylinder body 3. A vent hole 17c for communicating with the inlet port 18d at the time of air scavenging is formed on a skirt 17b of a piston 17. Thus a part of air-fuel mixture is forced to pass through inside the piston 17 and then pushed in an upper part of the piston 17 of the cylinder 18. Therefore required flow rate of air-fuel mixture for cooling can be secured while the piston 17 is securely cooled from inside to improve cooling property.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a piston cooling structure for a two-stroke engine, and particularly when a part of the air-fuel mixture is used to cool the piston from the inside. It relates to a structure that allows sufficient air-fuel mixture flow. [Prior Art] The recent increase in the output of two-stroke engines has been remarkable, and it is necessary to cool the piston more reliably to prevent seizure of the piston due to this increase in output. Water-cooling the engine is a way to improve the cooling performance of the piston. There is the use of AI materials with high thermal conductivity, etc.
These conventional methods have limitations in improving cooling performance. Therefore, a cooling structure has been proposed in which a part of the air-fuel mixture that is primarily compressed in the crank chamber is introduced into the inside of the piston to increase the cooling effect.
There is an example described in Publication No. 7094. A communication hole is formed in the middle of a scavenging passage that communicates between the crank chamber and the scavenging boat of the cylinder to communicate the passage with a portion below the scavenging port of the cylinder. The structure has a vent that communicates with the communication hole above. [Problems to be Solved by the Invention] The above-mentioned conventional cooling structure supplies a portion of the air-fuel mixture from the inside of the piston to a vent or a communication hole. The structure is such that the piston is cooled from within by flowing air through the scavenging passage. However, in the case of this conventional structure, since the flow resistance in the cooling air-fuel mixture path is greater than the resistance in the regular scavenging passage, it is difficult to secure a sufficient flow rate of the cooling air-fuel mixture, and in the end, sufficient cooling is not achieved. No effect is obtained. The present invention has been made in view of the above-mentioned conventional situation, and provides a piston cooling structure for a two-stroke engine that can secure the required cooling mixture flow rate and significantly improve the cooling performance of the pistons. The purpose is to. [Means for solving the problem] The present invention provides a first
In a two-stroke engine in which air is introduced into the cylinder through a scavenging passage, the piston cooling structure cools the piston from the inside with a part of the air-fuel mixture, and the suction is formed at the upper part of the lower part 9 of the cylinder. The present invention is characterized in that a second scavenging passage that communicates between the intake port and the discharge port is formed in the cylinder body, and a vent port that communicates with the intake port during scavenging is formed in the skirt portion of the piston. Here, the first scavenging passage in the present invention is the same as the conventional scavenging passage whose one end opens directly into the crank chamber, and the second scavenging passage is
This is a new scavenging passage different from conventional ones, with one end communicating with the crank chamber via the cylinder intake port and the piston vent. [Function] According to the piston cooling structure according to the present invention, the flow path for the cooling air-fuel mixture is from the crank chamber to the ventilation hole in the piston skirt, and the suction port at the bottom of the cylinder. Second scavenging path. The path passes through the discharge port at the top of the cylinder, and is independent from the regular scavenging passage. Therefore, in the conventional structure where a cooling mixture passage is formed by branching from the regular scavenging passage, the problem arises that the mixture flows only through the regular scavenging passage due to the large flow resistance of the cooling mixture passage. Instead, part of the air-fuel mixture is forced to pass through the inside of the piston and then into the upper part of the piston in the cylinder. The required flow rate of the air-fuel mixture for cooling the knot can be secured, and the piston can be reliably cooled from the inside to improve cooling performance. [Example] Hereinafter, an example of the present invention will be described with reference to the drawings.

1 to 4 are diagrams for explaining a piston cooling structure for a two-stroke engine according to an embodiment of the present invention.

In the figure, reference numeral 1 denotes a two-cycle motorcycle engine to which the structure of this embodiment is applied, and the engine 1 is located at the front of a crankcase 2 which is formed by integrally forming a crankshaft housing part 2a and a transmission housing part 2b. Fix the cylinder body 3 to the wall soil with stand bolts (not shown), and
The cylinder head 4 is connected to the top with a head bolt 5. -h4c! A main shaft 6 and a drive shaft 7 are arranged parallel to each other in the transmission accommodating portion 2b, and respective transmission gears 6a and 7a are meshed with each other. In addition, a shift fork 8,
9 is engaged, and this shift fork 8.9 is shift 1.
- Driven in the axial direction by rotating the cam lO.

A crankshaft 11 and a balancer shaft l2 are arranged in parallel to the main shaft 6 and the like within the crankshaft housing portion 2a. The crankshaft 1l and the balancer shaft 12 are connected by a transmission gear (not shown), and the balancer shaft 12 rotates in the opposite direction to the crankshaft 11. This balancer shaft l2 is made of iron and consists of a rotating shaft 12a at both ends and a balancer portion 12b eccentric to the rotating shaft 12a. A weight l3 made of a metal with a higher specific gravity than iron such as iron is buried. This weight 1113 is
As shown in Figure 4 tel, fdl, casting,! The leg portion 13b protrudes from the main body 13a by two structures, and this is inserted into the recess 12 formed in the balancer portion 12b.
C, and is embedded and fixed in the balancer part 12b by caulking the leg part 13b during forging. The weight 13 may have a connecting hole 13c in the main body 13a, as shown in FIG. As shown in Figure (al. Further, the crank webs l4 of the crankshaft l1 are connected to each other by a crank pin l5, and this crank web l4 portion is located in the crank chamber 2C formed in the crankshaft housing portion 2a. An intake port 2d communicating with the crank chamber 2C is formed in this crankshaft housing portion 2a, and a reed valve 19 is disposed within this intake port 2d. A guide plate 19b is disposed outside the opening of the base member 19a, which is a cylindrical body with a triangular surface, and a valve plate 19C made of a thin plate is interposed between the two.
It opens when the pressure inside C becomes negative and closes when the pressure becomes positive. In addition, the crank bin 15 has a connecting rod l6 (D large f
ta 1 6 a are connected, and the conrond 16
A piston l7 is connected to the small end 16b of the piston. This piston 17 is slidably inserted into a cylinder litchi 18 which is press-fitted into the cylinder body 3.
This cylinder liner 18 is formed with an exhaust port 18a and a scavenging boat 18b, and the exhaust boat 18a communicates with an exhaust passage 3a formed in the cylinder body 3, and the scavenging port 18b is connected to the cylinder It communicates with the crank chamber 2c via a first scavenging passage (not shown) formed in the body 3. The scavenging boat is attached to the cylinder liner 18.
A discharge port 18c is formed at the same height position as 8b,
Further, a suction port 18d is formed below the discharge port of the cylinder liner l8. The suction port 18d and the discharge port 18c communicate with each other through a second scavenging passage 3b formed in the cylinder body 3. Further, a vent hole 17c is formed in the skirt portion 17b of the piston l7, and this vent hole 17c is connected to the top wall 17a of the piston 17.
is located at the lower edge of the discharge port 18c, the suction port 1
It is formed in a position and shape that completely communicates with 8d. Next, the effects of this embodiment will be explained. In the engine of this embodiment, when the piston 17 starts descending due to the explosion of the air-fuel mixture in the combustion chamber, the air-fuel mixture in the crank chamber 2C starts to be compressed, and first, the exhaust boat 18a
begins to open, and exhaust gas begins to be discharged from the exhaust passage 3a. Next, the scavenging port 18b begins to open and the crank chamber 2C
The compressed air-fuel mixture (fresh air) is blown into the cylinder from the scavenging port 18b via the first scavenging passage, reverses itself in the combustion chamber, and pushes out the residual exhaust gas.At this time, the opening timing of the scavenging boat 18b The discharge port 18c opens in synchronization with the above, and the vent port 17c of the piston 17 communicates with the suction port 18d, thereby allowing the crank chamber 2c to flow from the inside of the piston l7 through the second scavenging passage 3b to the upper portion of the piston of the cylinder. As a result, a part of the air-fuel mixture in the combustion chamber 2c flows from the inside of the piston l7 to the vent l7c,
Inlet 18d. The air-fuel mixture is blown into the cylinder through the second scavenging passage 3b and the discharge port 18C, and then operates in the same manner as the air-fuel mixture from the first scavenging passage. At this time, a portion of the air-fuel mixture passes through the piston 17, thereby efficiently cooling the piston 17.

In this way, in this embodiment, the cooling and scavenging passage passing through the inside of the piston l7 is formed independently of the regular scavenging passage, so that a part of the air-fuel mixture reliably flows inside the seven piston l7. The cooling effect can be enhanced. In the case of the conventional structure in which the regular scavenging passage was branched, it was difficult to secure the required flow rate due to the large flow passage resistance on the branch side, but this example eliminates this problem. do not have. Further, in this embodiment, the balancer portion 1 of the balancer shaft l2
Since the weight l3 made of a metal with a large specific gravity is embedded in 2b, the required amount of unbalance can be ensured without increasing the amount of eccentricity of the balancer part 12b too much, thereby reducing the size of the balancer shaft 12 and, by extension, the entire engine. It is possible to reduce the size of the Also, when changing the unbalance amount by increasing the exhaust position, etc., the size of the salt weight should be changed. Changing the specific gravity also has the effect of eliminating the need to change the outer diameter of the balancer shaft. In the above embodiment, a case was explained in which a cooling and scavenging passage was formed in a crankcase reed-valve type engine, but the present invention is applicable to a piston valve type or a screw-in valve type engine. It can be applied to any two-cycle engine such as a reed valve combination system.

〔Effect of the invention〕

As described above, according to the piston cooling structure for a two-stroke engine according to the present invention, the suction port and the discharge port formed in the cylinder are communicated with a regular scavenging passage and a separate cooling-duty scavenging passage, and the lower suction port Since a vent is formed in the piston skirt that communicates with the piston, a portion of the air-fuel mixture can be reliably flowed through the inside of the piston, ensuring the required cooling air-fuel mixture flow rate and greatly improving piston cooling performance. There is an effect that can be improved.

[Brief explanation of drawings]

1 to 4 are diagrams for explaining a piston cooling structure of a two-stroke engine according to an embodiment of the present invention, in which FIG. 1 is a cross-sectional side view thereof, FIG. 2 is a cross-sectional side view of a piston, 3 is a cross-sectional side view of a two-stroke engine to which the structure of the embodiment is applied, FIG. 4 (al is a front view of the harness shaft, FIG. 4 (bl is a sectional view taken along the IVh-IVb line of FIG. 4 fat, Fig. 4 (C). Fig. 4 +d+ is a front view of the weight. Side view, Fig. 5 (a), and Fig. 5 fb+ are a front view, cross-sectional side view, and Fig. 5 fb+ respectively showing modified examples of the weight. Figure 6 ta
+ is a front view showing a modified example of the balancer shaft; FIG. 6 is a sectional view taken along the line v+b--b of FIG.

Claims (1)

[Claims] (1) In a two-stroke engine in which the air-fuel mixture that is primarily compressed in the crank chamber is introduced into the cylinder through the first scavenging passage, a piston cooling structure is used in which the piston is cooled from the inside with a portion of the air-fuel mixture. A second scavenging passage is formed in the cylinder body to communicate between the suction port and the discharge port formed at the bottom and top of the cylinder, respectively, and a vent that communicates with the suction port during scavenging is provided in the skirt portion of the piston. A piston cooling structure for a two-stroke engine, characterized by the following: