JPH06101759A - Piston pin lubricating structure for two-cycle engine - Google Patents

Abstract

PURPOSE:To improve the lubrication between the underside of the piston pin of a two-cycle engine and a connecting rod by using a simple means. CONSTITUTION:The center of the inner peripheral surface of a piston pin 3 is set eccentric for the center of the outer peripheral surface, and a thick part is formed on one side, and a lubricating oil hole 6 for the communication between the inner and outer peripheral surfaces of the piston pin 3 is formed on the thick part. Since, during the operation, the piston pin 3 is always applied with a force in the direction for holding the thick part downward, the lubricating oil which flows into the piston pin is supplied to the underside slidable part of the piston pin 3 from the oil feeding hole 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piston pin lubricating structure for connecting a piston and a connecting rod of a two-cycle engine.

[0002]

2. Description of the Related Art In a four-cycle engine, the upward inertial force acting on the piston in the vicinity of the top dead center of the exhaust stroke becomes larger than the downward force acting on the cylinder internal pressure. There is a period. On the other hand, in the two-cycle engine, each stroke of intake-compression-explosion-expansion-exhaust is completed while the crankshaft makes one revolution, so the piston always receives downward force regardless of the phase of the crankshaft. There is. Therefore, the piston pin is constantly pressed against the piston pin bearing of the connecting rod toward the crankshaft side, and it is difficult to supply the lubricating oil to the crankshaft side (lower side) of the piston pin, and the lubrication condition becomes severe. .

An example of a lubricating structure for a piston pin of a two-cycle engine is disclosed in Japanese Utility Model Laid-Open No. 54-9241. In the example of the publication, the width of the connecting rod small end of the two-cycle engine is made narrower on the upper side than on the lower side to reduce the radiant heat received from the piston, and on the connecting rod small end upper side, the connecting rod outer peripheral surface and inner peripheral surface are formed. A lubricating oil hole that communicates with and is provided so that the lubricating oil that scatters at the lower part of the piston and adheres to the outer peripheral surface of the connecting rod is guided to the inner peripheral surface of the connecting rod.

[0004]

However, the lubrication method disclosed in the above publication does not directly supply the lubricating oil to the lower side of the piston, but the lubricating oil adhering to the outer peripheral portion of the connecting rod is internally supplied through the lubricating oil hole. There is a problem that the lubricating oil is insufficiently supplied to the lower side of the piston pin if it is guided to the peripheral surface. To solve this problem, a forced oiling method has been devised, in which a lubricating oil supply path is provided in the connecting rod and the lubricating oil is pressure-fed to the lower side of the piston pin, but the lubricating oil supply system becomes complicated and Since it is necessary to form the lubricating oil supply passage, there is a new problem that the number of man-hours and the cost increase.

In view of the above problems, it is an object of the present invention to provide a piston pin lubrication structure for a two-cycle engine which can supply lubricating oil to the lower side of the piston pin by simple means.

[0006]

According to the present invention, in a hollow cylindrical piston pin for connecting a piston and a connecting rod of a two-cycle engine, the piston pin inner peripheral surface is eccentric with respect to the outer peripheral surface, and the piston pin is eccentric. And a lubricating oil hole that connects the inner peripheral surface and the outer peripheral surface of the piston pin are provided in the thick portion, and the piston pin lubrication of a two-cycle engine is provided. Structure is provided.

[0007]

By providing the thick portion on the piston pin, the center of gravity of the piston pin moves from the central axis toward the thick portion. Therefore, there is a distance between the point of action of the inertial force applied to the piston pin by the vertical movement of the piston (that is, the center of gravity of the piston pin) and the point of action of the reaction force applied to the piston pin from the connecting rod (that is, the point on the piston pin center axis). As a result, the moment of rotating the piston pin is generated by the inertial force.

In the vicinity of the piston top dead center, this moment acts so as to rotate the piston pin so that the thick portion is on the upper side, but in the two-cycle engine, the vicinity of the piston top dead center is in the latter half of the compression stroke or the early explosion stroke. As applicable
The piston pin does not rotate because it is pressed downward by the connecting rod bearing with a strong force. On the other hand, in the vicinity of the bottom dead center of the piston, the moment acts so as to rotate the piston pin so that the thick portion is on the lower side. In a two-cycle engine, the vicinity of the bottom dead center of the piston corresponds to the middle of the scavenging stroke, so the cylinder pressure is low and the force pressing the piston pin downward is relatively small, so the piston pin is easy to rotate.

For this reason, the piston pin rotates so that the thick portion is on the lower side, and the thick portion of the piston pin is always held on the lower side. Further, the thick-walled portion of the piston pin is provided with a lubricating oil hole that connects the inner peripheral surface and the outer peripheral surface of the piston pin, so that this lubricating oil hole is always located below the piston pin. Therefore, when the piston descends, the lubricating oil that is scraped off from the cylinder wall and flows into the piston pin is directly supplied to the sliding surface below the piston pin through the lubricating oil hole.

[0010]

1 is a sectional view of a connecting rod small end portion and a piston pin according to an embodiment of the present invention, and FIG. 2 is an enlarged sectional view taken along line II-II of FIG. In FIG. 1, 1 is a connecting rod, 1a is a small end of the connecting rod, 2 is a piston pin bearing provided on the inner peripheral surface of the connecting rod small end, and 3 is a piston pin supported by the piston pin bearing.

The piston pin 3 has a hollow cylindrical shape, and since the center of the inner peripheral surface is formed eccentrically from the center of the outer peripheral surface as will be described later, the wall thickness is not uniform, and one of the piston pins 3 with respect to the central axis is formed. The thickness of one side is thicker than the thickness of the other side. Further, as shown in FIG. 2, the diameter of the inner peripheral surface of the piston pin 3 is enlarged at the central portion in the longitudinal direction to form an oil sump 5 for retaining the lubricating oil flowing into the hollow portion of the piston pin. Reference numerals 6 in FIGS. 1 and 2 denote a plurality of lubricating oil holes that connect the oil sump 5 and the outer peripheral surface of the piston pin. The lubricating oil holes 6 are arranged at positions symmetrical with respect to the diameter passing through the portion where the thickness of the piston pin 3 is maximum (that is, the diameter passing through the center of gravity of the piston pin) in the longitudinal direction of the piston pin. , The angle formed by the lubricating oil holes on both sides (Fig. 1
Is indicated by φ) is set to be substantially equal to the swing angle of the connecting rod.

During operation of the engine, the lubricating oil splashed on the cylinder wall surface 11 and attached to the wall surface as shown in FIG.
When the piston 12 descends, it is scraped off from the cylinder wall surface 11 by the oil scraping ring of the piston, and a part thereof flows into the hollow portion of the piston pin. The lubricating oil temporarily stays in the oil sump 5 of the piston pin 3 and is supplied to the outer peripheral surface of the piston pin 3 through the lubricating oil hole 6.

In this embodiment, since the lubricating oil hole 6 is provided in the thick portion of the piston pin, the lubricating oil hole 6 is always located below the piston pin 3 and the inner circumference of the piston pin 3 is reduced. The lubricating oil that has adhered to the surface and the lubricating oil that has accumulated in the oil sump 5 are directly supplied to the piston pin bearing 3 portion below the piston pin of the connecting rod 1 through the lubricating oil hole 6, so the lubrication conditions in this portion are large. To be improved.

Next, referring to FIGS. 3 and 4, the piston pin 3 will be described.
The reason why the thick-walled portion is always held on the lower side will be described in detail. FIG. 3 is a diagram showing changes in the bearing load of the piston pin bearing 2 of the two-cycle engine with respect to the crank angle. The horizontal axis of Fig. 3 shows the crank angle, and the crank angle of 0 degrees (and ± 360 degrees) corresponds to the piston top dead center, ± 18 degrees.
0 degree corresponds to the bottom dead center of the piston. As shown in FIG. 3, the piston pin bearing load rapidly increases to a large value near the top dead center (0 degree) due to the mixture compression in the cylinder and the subsequent explosion. Further, after the top dead center, the bearing load sharply decreases due to the increase in the cylinder volume due to the piston lowering and the decrease in the cylinder internal pressure due to the exhaust valve opening, and becomes the minimum near the piston bottom dead center (180 degrees). Also at this time, the bearing load becomes a positive value due to the scavenging pressure in the cylinder and the piston inertial force. Therefore, the piston pin
It can be seen that the piston pin bearing is constantly pressed regardless of the position of the piston. Next, the action of the inertial force applied to the piston pin will be described with reference to FIG. FIG. 4 schematically shows a cross section of the piston pin 3, and a point O indicates the center of the outer diameter O ′ of the piston and a center of the inner diameter O ′. Since the center O ′ of the inner diameter is eccentric from O, a thick portion T is formed on the piston pin. Therefore, the center of gravity of the piston pin 3 is eccentric from the center O of the outer diameter toward the thick portion. In the figure, this centroid is
It shows with.

Now, FIG. 4A shows the position of the center of gravity of the piston pin at the top dead center and the bottom dead center of the piston. In this case, at the top dead center or the bottom dead center of the piston, the inertial force F acting on the center of gravity of the piston pin passes through the center of the piston pin outer diameter, so that the inertial force F does not generate a moment for rotating the piston pin. Further, as described above, in the two-cycle engine, the piston pin is always pressed downward by the bearing. Therefore, if the piston pin 3 is set in the state of FIG. Following the dynamic motion, the rocking motion is performed on both sides from the state of FIG. 4 (A). In this case, since the swing angle of the piston pin is smaller than the swing angle of the connecting rod in consideration of slippage in the bearing, if the angle formed by the lubricating oil hole 6 is made equal to the connecting rod swing angle φ, the lubricating oil hole 6 The position of does not deviate from the lower sliding surface of the piston pin bearing even by the swinging motion, and the lubricating oil can always be supplied to the sliding surface.

Next, a case where the piston pin rotates for some reason and the position of the center of gravity G moves from the state of FIG. 4A will be described. FIGS. 4B and 4C show the case where the position of the center of gravity G is displaced, FIG. 4B shows the top dead center, and FIG. 4C shows the bottom dead center. Since the inertial force applied to the piston pin acts on the center of gravity G, an upward inertial force F acts on the center of gravity G near the top dead center as shown in FIG. 4 (B).
In this case, the line of action of the inertial force F is the piston pin outer diameter center O
Since it does not pass through, the moment M that tries to rotate the piston pin so that the thick portion T is on the upper side acts on the piston pin by this inertial force F. However, as described above, in the two-cycle engine, since a large force that pushes the piston pin toward the bearing acts near the top dead center, the piston pin does not rotate due to this moment M.

Next, when the piston reaches the bottom dead center from this state, a downward inertial force F acts on the center of gravity G as shown in FIG. 4C, and this inertial force F acts on the piston pin. A moment M acts to rotate the pin so that the thick portion T is on the lower side. However, in the vicinity of the bottom dead center, the force that presses the piston pin toward the bearing is the minimum, and the piston pin easily rotates. Therefore, in the vicinity of the bottom dead center, the piston pin rotates so that the thick portion T is on the lower side, and gradually increases as the engine rotates.
It will be returned to the position of (A). Moreover, since the moment M increases as the distance between the center O of the outer diameter and the center of gravity G increases, the piston pin returns to the position shown in FIG. 4A in a short time even when the position of the center of gravity is largely deviated.

Therefore, the piston pin 3 always has the thick portion T
Is held so that it is on the lower side.

[0019]

According to the present invention, the center of the inner diameter of the piston pin is eccentric with respect to the outer diameter to form a thick portion, and a lubricating oil hole is formed in this thick portion to lubricate the lower side of the piston pin. Since the condition can be improved, there is an effect that the lubricating condition of the piston pin bearing can be improved easily and at a low cost, as compared with the case where the lubricating oil passage is bored in the connecting rod and the forced lubrication is performed.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view taken along the line II-II of FIG.

FIG. 3 is a diagram showing changes in piston pin bearing load.

FIG. 4 is a diagram for explaining the operation of the present invention.

[Explanation of symbols]

 1 ... Connecting rod 1a ... Connecting rod small end 2 ... Piston pin bearing 3 ... Piston pin 5 ... Oil sump 6 ... Lubricating oil hole 11 ... Cylinder wall surface 12 ... Piston

Claims (1)

[Claims] 1. A hollow cylindrical piston pin for connecting a piston of a two-stroke engine and a connecting rod,
The inner peripheral surface of the piston pin is eccentric with respect to the outer peripheral surface to form a thick portion with an increased thickness of the piston pin,
A piston pin lubrication structure for a two-cycle engine, characterized in that a lubricating oil hole that connects the inner peripheral surface and the outer peripheral surface of the piston pin is provided in the thick portion.