JPS6235014A - Cooling device of piston pin - Google Patents

Abstract

PURPOSE:To raise cooling effect of a piston pin by forming a pair of ventilation notches on the outer peripheral face of the piston to communicate both end openings of a ventilation hole passing through the piston pin to the inside of a crank case and communicating one ventilation notch to the combustion chamber side, in the scavenging stroke. CONSTITUTION:A ventilation hole 22 passing through a piston pin 17 in the axial direction is formed and both end openings 22a, 22b of the ventilation hole 22 and inside of a crank case 2 are communicated to each other by ventilation notches 24, 25 formed on the outer peripheral face of a piston 11. And the dimension h from the ventilation notch 25 to the upper end of the piston 11 is formed shorter than the dimension H of the opening 20a of a scavenging port 20 facing a cylinder hole 7. Then, a part of air mixture going to the inside of a combustion chamber 12 from the inside of the crack case 2 is introduced into the ventilation hole 22 of the piston pin 17 in the scavenging stroke and the piston pin 17 can be cooled effectively by the air mixture.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a two-stroke engine mounted on, for example, a motorcycle, and more particularly to a piston pin cooling device.

(Prior Art) A two-stroke engine is provided with a crankshaft supported by a crankcase, a piston slidably fitted into a cylinder, and a connecting rod that interlocks and connects the crankshaft and the piston.

In the above case, the piston is provided with a piston pin, and the small end of the connecting rod is rotatably connected to this piston pin (for example, Japanese Utility Model Publication No. 11694/1983).

(Problems to be Solved by the Invention) By the way, the piston becomes hot due to the combustion of fuel in the cylinder, and this heat is transferred to the piston pin marked -I-. During engine operation, this piston pin receives a high load and repeatedly rotates relative to the small end at high speed. There is a risk that the parts may cause problems such as seizure.

(Objective of the Invention) The present invention was made in view of the above-mentioned circumstances, and an object of the present invention is to effectively and sufficiently cool a piston pin with a simple configuration.

(Structure of the Invention) The feature of this invention to achieve the second object is that in the scavenging stroke of the engine, the inertia of the air-fuel mixture flowing from the crankcase to the cylinder is effectively used to generate the scavenging air. The main point is that the piston pin is cooled.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

2 is a two-cylinder two-stroke engine, and this two-stroke engine 1 is installed in, for example, a motorcycle.

Reference numeral 2 denotes a crankcase, and a crankshaft 3 is rotatably supported on the crankcase 2 by a bearing 4 about its axis. A drive gear 5 is attached to the crankshaft 3, and the drive gear 5 interlocks the rear wheels via a gear transmission (not shown) or the like.

Two cylinders 6.6 are provided on the crankcase 2. Each cylinder 6 includes a cylinder block 8 having a cylinder hole 7 whose axis is vertically oriented, and a cylinder block 8 having a cylinder hole 7 whose axis is vertically oriented.
The cylinder head 9 is mounted on the cylinder block 8 so as to cover the upper end opening of the cylinder block 8.

A piston 11 is fitted into each cylinder hole 7 so as to be slidable in the vertical direction. A space surrounded by the piston 11 and the cylinder radius 9 within the cylinder hole 7 is a combustion chamber 12.
Rad 9 is attached to the cylinder so as to face this combustion chamber 12.
A spark plug 13 is attached to the ignition plug 13. 14 is a cooling water passage.

16 is a connecting rod, and its lower large end 16a is rotatably connected to the crank pin 3a of the crankshaft 3. Further, a small end 16b at the upper end of the connecting rod 16 is connected to the piston 11.

To explain in more detail the connecting portion between the piston 11 and the small end portion 16b, the piston 11 is connected to the head portion 11a.
and a skirt portion 11b continuous to the head portion 11a. A boss portion 11C1lie is provided protrudingly at a radially symmetrical position on the inner surface of the skirt portion 11b.
A bottle hole 11d is formed on the axis extending in the radial direction of the piston 11 in each of the pistons c and llc. A piston pin 17 is provided with both ends fitted into the bottle hole lid and supported by the skirt portion 11b.

A small end 16b of the connecting rod 16 is rotatably supported on the piston pin 17 by a needle bearing 18.

An intake port (not shown) is formed in the crankcase 2 in correspondence with each cylinder 6, and a valve and a carburetor are connected to this intake port to allow the air-fuel mixture to flow into the crankcase 2. be done. Further, the cylinder block 8 is formed with a scavenging boat 20 that penetrates from the inside of the crankcase 2 into the cylinder hole 7, and the cylinder block 8 is also formed with an exhaust boat 21. 20' is another scavenging boat.

The time when the piston 11 moves up through the cylinder hole 7 is called the suction and compression stroke, and in this stroke, the reed valve is opened and the air-fuel mixture from the carburetor is supplied into the crankcase 2 through the intake port. At the same time, the air-fuel mixture in the combustion chamber 12 is compressed, and the piston 11 descends, which is considered an explosion and scavenging stroke.
At the same time, the reed valve closes, and the air-fuel mixture compressed in the crankcase 2 is transferred to the scavenging boat 20.
The combustion gas is sent to the combustion chamber lz side through the exhaust boat 21, and accordingly, the combustion gas is discharged from the exhaust boat 21.

In the above configuration, a vent hole 22 is formed in the piston pin 17 and extends through the piston pin 17 in its axial direction. The first openings 22a and 22b on both end sides of the ventilation hole 22 communicate with the inside of the crankcase 2, respectively. Second ventilation notches 24 and 25 are formed in the outer peripheral surface of the piston 11. These first and second ventilation notches 24 and 25 are both flat surfaces, and the first ventilation notch 24 extends from the opening 22a on one end of the ventilation hole 22 to the piston 11.
It extends towards the bottom edge. Further, the second ventilation notch 25
is formed to cross the other end side opening 22b of the ventilation hole 22, and its lower end extends to the lower end of the piston 11.

The above-mentioned scavenging bow]・Opening 20a where 20 faces the cylinder hole 7
The dimension (H) in the cylinder 6 axial direction is the piston 11
It is formed longer than the dimension (h) between the upper end of the outer circumferential surface and the upper edge of the second ventilation notch 25 . That is, when the piston 11 slides in the cylinder hole 7 during the scavenging stroke, the second
The -L end of the ventilation notch 25, that is, the end opposite to the crankcase 2, and the combustion chamber 12 are connected to the scavenging bow 20 opening 020a.
It is formed so that it communicates through it.

In the above case, the support span of the piston pin I7 can be shortened by increasing the depth of both ventilation notches 24, 25 and positioning the host portion Llc as close to the radial center of the piston 11 as possible, thereby increasing the rigidity of the piston pin I7. can be kept.

When the piston 11 moves down the cylinder hole 7 in the scavenging stroke, the air-fuel mixture in the crankcase 2 is sent into the combustion chamber 12 through the scavenging port 20, as described above. At this time, as shown by arrow A in FIG.
The air-fuel mixture is introduced into the vent hole 22 through the opening D 22 a at one end of the valve 1,
cooling the bearing 18. Further, after this, this air-fuel mixture flows through the other end side opening 22b of the ventilation hole 22 and the second ventilation notch 2.
5, and is further introduced into the combustion chamber 12 side through the scavenging boat 200 opening 120a.

Furthermore, when the piston 11 descends as described above,
As shown by arrow B in FIG.
The fuel is introduced into the combustion chamber 12 side through the opening 20a. At this time, this air-fuel mixture flows to the other end side of the ventilation hole 22.
bt - This air-fuel mixture flows at high speed because it flows across the radial direction and is introduced linearly into the combustion chamber 12 side. Therefore, due to the ejector effect of this air-fuel mixture, the air-fuel mixture shown by the arrow A is ejected from the inside of the ventilation hole 22 into the combustion chamber 12.
As a result, a large amount of air-fuel mixture flows through the vent hole 22, and the piston pin 17
and the needle bearing 18 are cooled more effectively.

(Effects of the Invention) According to the present invention, a vent hole is formed in the piston pin and passes through the piston pin in the axial direction, and a pair of vent notches are formed around the outer circumference of the piston to communicate each end opening of the vent hole with the inside of the crankcase. When the engine is running, the air-fuel mixture from the crankcase to the cylinder flows through the vent hole in the piston pin, so the piston pin is cooled by this air-fuel mixture.

In addition, one of the ventilation notches is formed so that it crosses one opening of the ventilation hole, and the above-mentioned ventilation notch is formed in such a manner that one of the ventilation notches crosses one opening of the ventilation hole, and through the opening of the scavenging port formed on the inner circumferential surface of the cylinder, the above-mentioned Since one of the ventilation notches is configured to communicate with the combustion chamber side in the cylinder, the air-fuel mixture inside the vent is sucked out by the ejector effect of the mixture passing through this ventilation notch, and as a result, a large amount of mixture The air will flow. Therefore, the piston pin is cooled more effectively.

Moreover, as the engine speed increases, the piston pin needs to be cooled accordingly, but the amount of air-fuel mixture flowing through the vent increases as the engine speed increases. The piston pin is effectively cooled.

Furthermore, since the cooling means for the piston pin utilizes the air-fuel mixture supplied to the engine, there is no need to provide a separate cooling medium, and therefore, the above-mentioned cooling can be achieved with a simple configuration.

[Brief explanation of drawings]

The figures show an embodiment of the present invention, in which FIG. 1 is a partial vertical cross-sectional view of the engine, FIG. 2 is an overall vertical cross-sectional view of the engine, FIG. The figure is rV- of the same figure 1.
It is a view taken along the line IV. 1--2 cycle engine, 2... crankcase, 6
φ fist cylinder, 11... piston, 16... connecting body, 1
6b--Small end, 17--Piston pin, 20--Scavenging port, 20a--Opening, 22@fist vent, 22a--
One end side opening, 22b...Other end side opening (one opening), 2
4..First ventilation notch, 25..Second ventilation notch (one ventilation notch).

Claims (1)

[Claims] 1. A piston that is slidably fitted into a cylinder has a piston pin that passes through the piston in the radial direction, and the small end of the connecting rod is rotatably connected to this piston pin. In a two-stroke engine provided with a scavenging boat that penetrates into the cylinder from above, a vent hole is formed in the piston pin in the axial direction thereof, and each end opening of the vent hole communicates with the inside of the crankcase. A ventilation notch is formed on the outer circumferential surface of the piston, one of the ventilation notches is formed so as to cross one opening of the vent hole, and a scavenging notch is formed on the inner circumferential surface of the cylinder. A cooling device for a piston pin, characterized in that one of the ventilation notches is configured to communicate with a combustion chamber in a cylinder during a scavenging stroke through an opening in the boat.