JPWO2013021789A1 - Piston structure of internal combustion engine - Google Patents

Abstract

Provided is a piston structure of an internal combustion engine that can suppress an impact sound between an inner peripheral surface of a pin hole and a piston pin by holding an oil film between the inner peripheral surface of the pin hole and the piston pin. The piston structure of the internal combustion engine (1) is formed by inserting a piston pin (7) into a pin hole (44) formed in the piston (4). A communication groove (46) that communicates the inside and the outside of (4) is provided, and the communication groove (46) is on the combustion chamber (32) side of the piston (4) in the inner peripheral surface (44a) of the pin hole (44). And it is provided only in the range on the thrust side.

Description

  The present invention relates to a piston structure for an internal combustion engine.

  In general, a piston disposed in a cylinder of an internal combustion engine has a pin hole, and is connected to a connecting rod via a piston pin attached to the pin hole. The piston pin slides with the inner peripheral surface of the pin hole as the piston moves up and down. A minute gap is provided between the piston pin and the pin hole, and oil for preventing seizure of both is supplied to the gap.

  In Patent Document 1, two communication grooves that connect the inner peripheral side and the outer peripheral side of the piston along the axial direction of the piston pin are formed at two locations on the upper half of the inner peripheral surface of the pin hole. It is disclosed. The two communication grooves are formed at symmetrical positions at an angle of 45 ° from the upper part of the pin hole. In Patent Document 1, it is assumed that the oil supply to the piston pin becomes sufficient by forming the two communication grooves at this position.

Japanese Utility Model Laid-Open No. 1-152146 (FIG. 1)

  In recent years, there has been an increasing demand for calming internal combustion engines. One of the causes of noise in the internal combustion engine is a phenomenon that a piston pin comes into contact with the inner peripheral surface of the pin hole to generate a hitting sound. As a result of studying this phenomenon, it has been found that the hitting sound increases as the oil film between the inner peripheral surface of the pin hole and the piston pin decreases. Therefore, it is required to reduce the hitting sound by holding an oil film between the inner peripheral surface of the pin hole and the piston pin.

  The present invention has been made in view of these problems, and an oil film is held between the inner peripheral surface of the pin hole and the piston pin to suppress the hitting sound between the inner peripheral surface of the pin hole and the piston pin. It is an object of the present invention to provide a piston structure for an internal combustion engine that can be used.

  As a result of observing and analyzing the movement of the piston pin and oil inside the pin hole by the inventors' earnest research, as described in Patent Document 1, when the communication groove is provided symmetrically above and below the pin hole, As the piston pin turns along the inner peripheral surface of the pin hole, oil is discharged more than necessary from the communication groove on the anti-thrust side, and the inner peripheral surface of the pin hole and the piston pin may come into contact with each other. found. Therefore, the present inventors have conceived of eliminating the communication groove on the anti-thrust side in order to suppress the unnecessary discharge of oil.

  The present invention is a piston structure of an internal combustion engine in which a piston pin is inserted into a pin hole formed in a piston, and an inner peripheral surface of the pin hole is provided with a communication groove that communicates the inside and outside of the piston, The communication groove is provided only in the combustion chamber side and thrust side range of the piston on the inner peripheral surface of the pin hole.

  According to such a configuration, the communication groove that communicates the inside and the outside of the piston is provided only in the range on the combustion chamber side and the thrust side of the piston hole on the inner peripheral surface of the pin hole. The oil discharge is suppressed compared to the case where the communication groove is provided in the piston combustion chamber side and the anti-thrust side), and the oil is suitably held in the gap between the inner peripheral surface of the pin hole and the piston pin. Is done. Therefore, the hitting sound between the inner peripheral surface of the pin hole and the piston pin can be suppressed.

  In addition, the communication groove may be provided to be biased toward the combustion chamber as the offset amount of the crankshaft rotation center with respect to the cylinder axis increases.

  According to such a configuration, as the offset amount of the crankshaft rotation center with respect to the cylinder axis increases, the communication groove is biased toward the combustion chamber so that the gap between the inner peripheral surface of the pin hole and the piston pin is increased. The flow rate of the moving oil can be reduced. Therefore, the total amount of oil discharged from the gap between the inner peripheral surface of the pin hole and the piston pin can be reduced, and a large amount of oil can be held in the gap.

  Further, the communication groove has an angle formed by a straight line connecting the axis of the pin hole and the center position in the circumferential direction of the communication groove and a straight line passing through the axis of the pin hole and perpendicular to the piston axis. It is preferable to be provided so as to be not less than 23 ° and not more than 23 °.

  According to such a configuration, oil can be suitably held between the inner peripheral surface of the pin hole and the piston pin.

  The piston includes a piston main body portion having a ring groove formed on an outer peripheral surface thereof, and a pair of pin boss portions extending downward from a lower surface of the piston main body portion and formed with the pin holes, It is preferable that the lower surface of the piston main body and the upper portion of the inner peripheral surface of the pin hole are continuous without a step.

  According to such a configuration, the lower surface of the piston main body and the upper part of the inner peripheral surface of the pin hole are smoothly continuous without a step, so that the oil adhering to the lower surface of the piston main body is retained in the pin hole. It becomes easy to flow into the peripheral surface. Therefore, the oil adhering to the lower surface of the piston main body can be suitably guided to the gap between the inner peripheral surface of the pin hole and the piston pin to maintain lubricity.

  Further, a concave groove is formed in the circumferential direction on the inner peripheral surface of the pin hole, and the concave groove is connected to the communication groove and is formed only in a range closer to the crank chamber than the communication groove. It is good to do.

  According to this configuration, since the circumferential groove is not formed in the range closer to the combustion chamber than the communication groove, oil is applied from the combustion chamber side via the groove when a load in the crank chamber direction is applied to the piston. The oil film can be held while being discharged, and the oil can be turned to the crank chamber side from the communication groove via the concave groove.

  According to the present invention, there is provided an internal combustion engine piston structure capable of holding an oil film between an inner peripheral surface of a pin hole and a piston pin and suppressing a hitting sound between the inner peripheral surface of the pin hole and the piston pin. can do.

It is sectional drawing of the piston structure of the internal combustion engine which concerns on this embodiment. It is a front view of a piston. FIG. 3 is a cross-sectional view taken along the arrow I-I in FIG. 2. (A) is an enlarged front view of a pin hole, (b) is II-II arrow sectional drawing of FIG. It is an expanded sectional view of the lower surface vicinity of the piston main-body part in FIG. It is a schematic diagram explaining the state of the piston pin and oil in the pin hole in Example 1, (a) is a state in which the piston pin is on the crank chamber side, (b) is a state in which the piston pin is on the combustion chamber side, Respectively. It is a schematic diagram explaining the state of the piston pin and oil in the pin hole in Comparative Example 1, (a) is a state where the piston pin is on the crank chamber side, (b) is a state where the piston pin is on the combustion chamber side, Respectively. It is a schematic diagram explaining the state of the piston pin and oil in the pin hole in Comparative Example 2, (a) is a state where the piston pin is on the crank chamber side, (b) is a state where the piston pin is on the combustion chamber side, Respectively. It is a graph which shows the correlation with a crank angle and the fluid velocity of the oil in a pin hole. It is a graph which shows the correlation of a communicating groove center angle and fluid velocity.

  An embodiment of the present invention will be described in detail with reference to FIGS. 1 to 5. In the description, the same elements are denoted by the same reference numerals, and redundant description is omitted. In the following description, the cylinder axis direction is referred to as “vertical direction” and the direction perpendicular to the cylinder axis is referred to as “left-right direction”.

  As shown in FIG. 1, the internal combustion engine 1 includes a cylinder block 2 having a cylinder 21 and a crank chamber 22, a cylinder head 3 that closes the upper portion of the cylinder 21, a piston 4 installed in the cylinder 21, and a crank chamber. A crankshaft 5 disposed at 22, a connecting rod 6 that connects the piston 4 and the crankshaft 5, and a piston pin 7 that connects the connecting rod 6 and the piston 4 are mainly provided.

The cylinder block 2 has an oil injection device 23 in the upper part of the crank chamber 22. The oil injection device 23 has a nozzle 23 a, and the oil injected from the nozzle 23 a is sprayed onto the piston 4. Oil adheres to the inner wall of the cylinder 21 due to, for example, scattering of the oil sprayed onto the piston 4. The oil injection device 23 is supplied with oil from an oil supply passage 24 provided in the cylinder block 2.
Note that the method of supplying oil to the cylinder 21 is not limited to this. For example, the inner wall of the cylinder 21 and the lower surface of the piston 4 are lubricated by oil scattered from the rotating crankshaft 5. Also good.

  The cylinder head 3 has an upper wall portion 31 that is recessed at a position corresponding to the cylinder 21. A space surrounded by the upper wall portion 31, the inner wall of the cylinder 21 and the upper surface of the piston 4 is a combustion chamber 32. An intake port 33 and an exhaust port 34 communicate with the upper wall portion 31. The intake port 33 and the exhaust port 34 are opened and closed by the intake valve 35 and the exhaust valve 36 at a predetermined timing.

  In the present embodiment, the crankshaft 5 rotates in the clockwise direction (see arrow y) in FIG. The axis CL of the cylinder 21 is offset by a predetermined distance L with respect to the axis 5a that is the center of rotation of the crankshaft 5 toward the side from which the crankshaft 5 is directed toward the lower fulcrum. Incidentally, such an offset state is referred to as a normal offset, and the offset to the opposite side with respect to the axis CL is referred to as a reverse offset.

  The connecting rod 6 is a member that transmits the pressing force of the piston 4 due to the expansion of the fuel gas in the combustion chamber 32 to the crankshaft 5. A lower end 6 a of the connecting rod 6 is rotatably connected to a crank pin 5 b of the crankshaft 5. An upper end portion 6 b of the connecting rod 6 is connected to the piston 4 via a piston pin 7.

The piston 4 is a substantially cylindrical member that is slidably fitted in the cylinder 21. The piston 4 reciprocates in the cylinder 21 by a pressing force due to the expansion of the fuel gas in the combustion chamber 32 and a lifting force due to the rotation of the crankshaft 5. At this time, the piston 4 is pressed against the inner wall of the cylinder 21 by the lateral force received from the connecting rod 6. More specifically, when the crankshaft 5 rotates clockwise in FIG. 1 (see arrow y), the component force of the pressing force acting in the direction of the axis CL of the cylinder 21 from the compression stroke to the expansion stroke (mainly the expansion stroke). As a result, the component force in the extending direction of the connecting rod 6 and the lateral force (thrust force) that presses the piston 4 to the left in FIG.
Here, in the piston 4, the direction in which the thrust force acts (left side in FIG. 1) is referred to as the thrust side, and the opposite direction (right side in FIG. 1) is referred to as the anti-thrust side.

  As shown in FIGS. 2 and 3, the piston 4 includes a piston body portion 41 having a circular shape in plan view, a pair of pin boss portions 42 and 42 extending in a wall shape from the lower surface of the piston body portion 41, and the piston body. It mainly has a pair of skirt parts 43 and 43 that extend downward from the part 41 and connect the ends of the pair of pin boss parts 42 and 42. A pin hole 44 for inserting the piston pin 7 is formed in the approximate center of each pin boss portion 42. A hollow portion 45 is formed at the center lower portion of the piston 4 and is opened downwardly surrounded by the pair of pin boss portions 42 and 42 and the pair of skirt portions 43 and 43. The upper end portion 6 b of the connecting rod 6 is disposed in the hollow portion 45.

  The piston main body 41 has three ring grooves 41a, 41b, 41c on the outer peripheral surface thereof. Piston rings (not shown) for preventing combustion gas leakage are fitted in the upper two ring grooves 41a and 41b. The lower ring groove 41 c is fitted with an oil ring (not shown) for adjusting the amount of oil that lubricates between the inner wall of the cylinder 21 and the piston 4. The lower ring groove 41c is formed wider than the upper two ring grooves 41a and 41b, and an oil hole 45a serving as a lubricating oil passage communicating the inside and outside of the piston 4 is provided on the bottom surface thereof. Yes. A depression 41 e is formed on the upper surface of the piston body 41. On the lower surface 41d of the piston main body 41, an arcuate recess 41d1 is formed at a position corresponding to a pin hole 44 described later. The lower surface 41d of the piston main body 41 is located below the lower oil groove 41c. The recess 41d1 is formed along the arc shape of the pin hole 44 described later.

  The pair of pin boss portions 42, 42 are wall-like portions extending downward from the lower surface 41 d of the piston main body portion 41. As shown in FIG. 3, each pin boss portion 42 is disposed at a position closer to the center than the surface of the piston main body portion 41 (recessed position).

  The pair of skirt portions 43, 43 are wall-shaped portions that extend downward from the lower surface 41 d of the piston main body portion 41 and connect both ends of the pair of pin boss portions 42, 42. The surface of each skirt portion 43 is provided flush with the surface of the piston main body portion 41.

  The pair of pin holes 44, 44 are through holes through which the piston pin 7 is inserted, and are formed at the approximate center of the pin boss portion 42. The pin hole 44 is formed in the radial direction of the piston 4 in a top view. The axial direction of the pin hole 44 coincides with the axial direction of the crankshaft 5. A communication groove 46 that communicates the surface side of the piston 4 and the hollow portion 45 and a groove 47 that is recessed in the circumferential direction are formed on the inner peripheral surface 44 a of the pin hole 44.

The communication groove 46 is a groove for guiding the oil transmitted from the inner wall of the cylinder 21 to the surface of the piston 4 into the pin hole 44. The communication groove 46 is formed in an arc shape in cross section. The communication groove 46 extends in parallel with the axial direction of the pin hole 44.
Here, as shown in FIG. 4 (a), when the pin hole 44 is viewed in the axial direction, the inner peripheral surface 44a is divided into four equal parts in the direction of the axis PL of the piston 4 and the direction perpendicular to the axis PL. The communication groove 46 is formed in a range on the combustion chamber 32 side and the thrust side of the inner peripheral surface 44a. And the groove | channel of the axial direction of the pin hole 44 is not formed in the other three ranges among the inner peripheral surfaces 44a, but it has a smooth perfect circular arc shape.
The axis PL of the piston 4 basically coincides with the axis CL (see FIG. 1) of the cylinder 21, but the piston 4 may be tilted within the cylinder 21 to be displaced from each other.

  The communication groove 46 is formed by an angle formed by a straight line L1 connecting the axis of the pin hole 44 and the center position in the circumferential direction of the communication groove 46 and a straight line L2 passing through the axis of the pin hole 44 and orthogonal to the axis PL of the piston 4. It is preferable that θ (hereinafter referred to as “communication groove center angle θ”) is provided in a range of 20 to 23 °. This will be described in detail later with reference to FIG.

  The concave groove 47 is a groove for facilitating movement of oil that has entered the pin hole 44 in the circumferential direction. As shown in FIG. 4 (b), the concave groove 47 is formed on the inner peripheral surface 44a than the communication groove 46 (more specifically, the plane P1 including the lower end of the communication groove 46 and orthogonal to the axis PL. Rather than the crank chamber 22 side. Both end portions of the concave groove 47 are connected to the communication groove 46. Thereby, the movement of the oil between the communication groove 46 and the concave groove 47 becomes smooth.

As shown in FIG. 5, the upper portion 44a1 of the inner peripheral surface 44a of the pin hole 44 is smoothly continuous with an arc-shaped recess 41d1 provided on the lower surface 41d of the piston main body 41 without any step. That is, the peripheral edge of the opening of the pin hole 44 is provided with a tapered surface 44b inclined by about 45 ° with respect to the axis of the pin hole 44, but only the vicinity of the upper part 44a1 of the inner peripheral surface of the pin hole 44 The tapered surface 44b is formed by being cut (omitted) and gently. As a result, the oil scraped off by an oil ring (not shown) attached to the ring groove 41c can easily enter the pin hole 44 and the communication groove 46 through the recess 41d1.
Note that the lower surface 41 d and the recess 41 d 1 of the piston main body 41 are inclined so as to be positioned downward toward the pin boss portion 42 so that oil can easily flow toward the pin hole 44.

  Incidentally, the upper part 44a1 of the inner peripheral surface 44a of the pin hole 44 is formed in a straight line when viewed in the direction of FIG. Further, the arc-shaped recess 41d1 is also formed in a straight line when viewed in the direction of FIG. The upper portion 44a1 of the inner peripheral surface 44a and the arc-shaped concave portion 41d1 are bent and connected at the opening of the pin hole 44 (just above the tapered surface 44b).

  As shown in FIGS. 1 and 4, the piston pin 7 is a member that is inserted into the pin hole 44 and connects the connecting rod 6 and the piston 4. The piston pin 7 is formed to have a slightly smaller diameter than the pin hole 44, and a gap S for collecting oil is provided between the inner peripheral surface 44 a of the pin hole 44 and the piston pin 7. As the crankshaft 5 rotates, the piston pin 7 turns clockwise (see the arrow x in FIG. 4) along the inner peripheral surface 44a of the pin hole 44 in the clockwise direction (the same direction as the rotation direction of the crankshaft 5).

  The piston structure of the internal combustion engine 1 according to the present embodiment is configured as described above. Next, the operation and effect of the piston structure will be described with reference to FIGS. In FIGS. 6 to 8, the locus of oil is indicated by dot-shaped hatching.

6A and 6B are schematic diagrams for explaining the state of the piston pin and oil in the pin hole in the first embodiment, where FIG. 6A is a state where the piston pin is on the crank chamber side, and FIG. 6B is a state where the piston pin is on the combustion chamber side. Each state is shown.
As shown in FIG. 6A, the pin hole 44 of the first embodiment has the communication groove 46 only in the range on the combustion chamber 32 side and the thrust side of the inner peripheral surface 44a.

  As shown in FIG. 6A, when the piston pin 7 is on the crank chamber 22 side in the pin hole 44, a gap S is formed above the piston pin 7. Further, the oil adhering to the inner wall of the cylinder 21 is scraped off by an oil ring (not shown) attached to the ring groove 41 c and flows into the clearance S and the communication groove 46 through the lower surface 41 d of the piston main body 41. . The portion of the gap S where the communication groove 46 is provided has a larger width dimension of the gap S than other portions, so that oil is likely to diffuse in the axial direction of the pin hole 44. Thereby, the oil flowing into the communication groove 46 can be sufficiently supplied in the axial direction of the pin hole 44 (to the hollow portion 45 side).

As shown in FIG. 6B, when the piston pin 7 turns and rises clockwise along the thrust side inner peripheral surface 44a of the pin hole 44 by the operation of the crankshaft 5 and the connecting rod 6, the piston pin 7 The width dimension of the upper side gap S gradually decreases, and the oil is pushed out to the anti-thrust side. At this time, the communication groove 46 is not formed in the combustion chamber 32 side and the anti-thrust side portion of the inner peripheral surface 44 a of the pin hole 44, so that oil is difficult to be discharged from the pin hole 44. Therefore, oil is suitably held in the gap S between the inner peripheral surface 44a of the pin hole 44 and the piston pin 7, and the collision noise between the two is suppressed. Further, by suppressing the collision between the inner peripheral surface 44a of the pin hole 44 and the piston pin 7, the behavior of the piston 4 in the cylinder 21 is stabilized, and the collision between the inner wall of the cylinder 21 and the piston 4 is also suppressed. .
That is, according to the pin hole 44 of the first embodiment, the amount of oil held between the inner peripheral surface 44a of the pin hole 44 and the piston pin 7 increases (the amount of oil discharged decreases). The oil film formed by this oil suppresses the hitting sound between the inner peripheral surface 44a of the pin hole 44 and the piston pin 7.

  Further, the oil pushed out to the anti-thrust side by the piston pin 7 is along a concave groove 47 formed in a circumferential direction in a portion closer to the crank chamber 22 than the communication groove 46 in the inner peripheral surface 44 a of the pin hole 44. , It moves below the pin hole 44. Thereby, oil can be sufficiently supplied also to the crank chamber 22 side of the pin hole 44. In the inner peripheral surface 44 a of the pin hole 44, the circumferential groove 47 is not provided in the portion closer to the combustion chamber 32 than the communication groove 46, so that it is difficult for oil to flow in the circumferential direction. It is possible to maintain the lubricity by lowering the flow rate of.

7A and 7B are schematic diagrams for explaining the state of the piston pin and oil in the pin hole in Comparative Example 1, wherein FIG. 7A is a state where the piston pin is on the crank chamber side, and FIG. 7B is a state where the piston pin is on the combustion chamber side. Each state is shown.
As shown in FIG. 7 (a), the pin hole 44 ′ of Comparative Example 1 has a combustion chamber 32 side and thrust side range on the inner peripheral surface 44a ′, and a combustion chamber 32 side and anti-thrust side range. A pair of communication grooves 46 'and 46' are provided.

  In the pin hole 44 ′ of Comparative Example 1, as shown in FIG. 7B, when the piston pin 7 pivots and rises clockwise, the oil in the gap S moves to the anti-thrust side, and the combustion chamber 32 side and Oil is discharged from the communication groove 46 ′ provided on the anti-thrust side. Therefore, the amount of oil retained in the gap S is reduced, and the effect of suppressing the collision noise between the pin hole 44 ′ and the piston pin 7 is reduced as compared with the first embodiment.

8A and 8B are schematic diagrams for explaining the state of the piston pin and oil in the pin hole in Comparative Example 2, wherein FIG. 8A is a state where the piston pin is on the crank chamber side, and FIG. 8B is a state where the piston pin is on the combustion chamber side. Each state is shown.
As shown in FIG. 8A, the pin hole 44 ″ of Comparative Example 2 has a communication groove 46 ″ only in the range on the combustion chamber 32 side and the anti-thrust side of the inner peripheral surface 44a ″. Since the pin hole 44 ″ of the comparative example 2 does not have the communication groove 46 ″ on the combustion chamber 32 side and the thrust side, the oil supply in the axial direction of the pin hole 44 ″ as compared with the first embodiment described above. Ability is reduced.

  Further, in the pin hole 44 ″ of Comparative Example 2, as shown in FIG. 8B, when the piston pin 7 pivots and rises clockwise, the oil in the gap S moves to the anti-thrust side, and the combustion chamber 32 Oil is discharged from the communication groove 46 "provided on the side and on the opposite side of the thrust. Therefore, the amount of oil retained in the gap S is further reduced, and the effect of suppressing the collision noise between the pin hole 44 ″ and the piston pin 7 is further reduced as compared with the first embodiment and the first comparative example.

  FIG. 9 is a graph showing the correlation between the crank angle and the fluid velocity of the oil in the pin hole. The oil fluid speed is a numerical value indicating the moving speed of the oil in the gap S, and is a value calculated by a known analysis program. The smaller the fluid velocity, the slower the moving speed of the oil in the gap S, indicating that the oil is suitably held in the gap S.

  As shown in FIG. 9, when comparing the peak values of the respective graphs, the fluid velocity of the oil in Example 1 (see the thick solid line) is 1/2 or less compared to Comparative Example 1 (see the broken line) which is a conventional structure. It has dropped to. Thereby, in Example 1, it turns out that oil can be suitably hold | maintained in the clearance gap S of the pin hole 44 and the piston pin 7 compared with the comparative example 1. FIG. As a result, in the first embodiment, the oil retained in the gap S between the inner peripheral surface 44a of the pin hole 44 and the piston pin 7 can suppress the occurrence of a hitting sound due to the collision between the two.

  On the other hand, in Comparative Example 2 (see the thin solid line), the fluid speed of the oil is almost doubled compared to Comparative Example 1. Therefore, when the communication groove 46 is provided only on the opposite side to the thrust side, the oil cannot be suitably held in the gap S, and the pin hole 44 and the piston pin 7 easily collide. From this, it is understood that the position where the communication groove 46 is formed needs to be appropriately set in consideration of the direction of the thrust force acting on the piston 4 and the turning direction of the piston pin 7.

  FIG. 10 is a graph showing the correlation between the communication groove center angle θ and the fluid velocity. Example 1 (see the thick broken line) is a case where the offset distance L (see FIG. 1) is 14 mm. Example 2 (see thick solid line) is a case where the offset distance L (see FIG. 1) is 0 mm.

  As shown in FIG. 10, in Example 1 in which the offset distance L is 14 mm, when the communication groove center angle θ is changed in the range of about 15 ° to 30 °, the fluid velocity is increased when θ = about 23 °. It turned out to be the smallest. In Example 2 where the offset distance L was 0 mm, it was found that the fluid velocity was the smallest when θ = about 20 °. Therefore, if the communication groove 46 is provided on the combustion chamber 32 side as the offset distance L is larger, the flow velocity of the oil is reduced, and the hitting sound between the inner peripheral surface 44a of the pin hole 44 and the piston pin 7 is reduced. It can be seen that it can be suppressed.

  As mentioned above, although embodiment of this invention was described in detail with reference to drawings, this invention is not limited to this, In the range which does not deviate from the main point of invention, it can change suitably.

  For example, in the present embodiment, the case where the axis line CL of the cylinder 21 is offset by a predetermined distance L from the axis 5a of the crankshaft 5 to the opposite thrust side (so-called positive offset) has been described as an example. The offset distance L may be set to 0, or may be offset by a predetermined distance L on the thrust side (so-called reverse offset).

  By the way, as a result of the experiment, if the crankshaft 5 is rotated in the clockwise direction (see arrow y) shown in FIG. It has been found that the pin hole 44 turns in the clockwise direction (see arrow x) shown in FIG. Therefore, the communication groove 46 may be provided on the combustion chamber 32 side and the thrust side as in the present embodiment.

  In the present embodiment, the concave portion 41d1 is formed in the portion corresponding to the pin hole 44 in the lower surface 41d of the piston main body 41. However, the present invention is not limited to this, and the concave portion 41d1 is omitted. The upper portion 44a1 of the inner peripheral surface 44a of the pin hole 44 and the lower surface 41d of the piston main body 41 may be directly and smoothly continuous.

  Further, in the present embodiment, the case where a so-called semi-floating method is adopted as the fixing structure of the piston pin 7 has been described as an example, but the present invention is not limited to this, for example, at both ends of the piston pin 7. A clip (C-ring) may be attached to the so-called full floating type piston structure that holds the piston pin 7 in a floating state with respect to the pin hole 44.

  In the present embodiment, the concave groove 47 is provided along the circumferential direction on the inner peripheral surface 44a of the pin hole 44. However, the present invention is not limited to this, and for example, the concave groove 47 is omitted. May be.

  Further, in the present embodiment, the case where the present invention is applied to the serial type internal combustion engine 1 has been described as an example, but the present invention is not limited to this, and other types of internal combustion engines such as a V-type engine. The present invention may be applied to.

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Cylinder block 21 Cylinder 22 Crank chamber 3 Cylinder head 32 Combustion chamber 4 Piston 41 Piston main body part 41c Ring groove 41d Lower surface 42 Pin boss part 43 Skirt part 44 Pin hole 44a Inner peripheral surface 46 Communication groove 47 Concave groove 5 Crankshaft 6 Connecting rod 7 Piston pin S Clearance

Claims (9)

A piston structure for an internal combustion engine, in which a piston pin is inserted into a pin hole formed in the piston,
A communication groove that communicates the inside and outside of the piston is provided on the inner peripheral surface of the pin hole,
The internal combustion engine piston structure according to claim 1, wherein the communication groove is provided only in a range on the combustion chamber side and the thrust side of the piston on the inner peripheral surface of the pin hole.   2. The piston structure of an internal combustion engine according to claim 1, wherein the communication groove is provided to be biased toward the combustion chamber as the amount of offset of the crankshaft rotation center with respect to the cylinder axis increases.   The communication groove has an angle formed between a straight line connecting the axis of the pin hole and the center position in the circumferential direction of the communication groove and a straight line passing through the axis of the pin hole and perpendicular to the piston axis. The piston structure for an internal combustion engine according to claim 1, wherein the piston structure is provided so as to be equal to or less than °.   The communication groove has an angle formed between a straight line connecting the axis of the pin hole and the center position in the circumferential direction of the communication groove and a straight line passing through the axis of the pin hole and perpendicular to the piston axis. 3. The piston structure for an internal combustion engine according to claim 2, wherein the piston structure is provided so as to be equal to or less than [deg.]. The piston has a piston main body portion in which a ring groove is formed on an outer peripheral surface, and a pair of pin boss portions that extend downward from the lower surface of the piston main body portion and in which the pin holes are formed,
The piston structure for an internal combustion engine according to claim 1, wherein the lower surface of the piston main body and the upper portion of the inner peripheral surface of the pin hole are continuous without a step. The piston has a piston main body portion in which a ring groove is formed on an outer peripheral surface, and a pair of pin boss portions that extend downward from the lower surface of the piston main body portion and in which the pin holes are formed,
The piston structure for an internal combustion engine according to claim 2, wherein the lower surface of the piston main body and the upper portion of the inner peripheral surface of the pin hole are continuous without a step. The piston has a piston main body portion in which a ring groove is formed on an outer peripheral surface, and a pair of pin boss portions that extend downward from the lower surface of the piston main body portion and in which the pin holes are formed,
The piston structure for an internal combustion engine according to claim 3, wherein the lower surface of the piston main body and the upper portion of the inner peripheral surface of the pin hole are continuous without a step. The piston has a piston main body portion in which a ring groove is formed on an outer peripheral surface, and a pair of pin boss portions that extend downward from the lower surface of the piston main body portion and in which the pin holes are formed,
The piston structure for an internal combustion engine according to claim 4, wherein the lower surface of the piston main body and the upper portion of the inner peripheral surface of the pin hole are continuous without a step. A concave groove is formed in the circumferential direction on the inner peripheral surface of the pin hole,
The said recessed groove is connected to the said communication groove, and is formed only in the range of the crank chamber side rather than the said communication groove, The any one of Claims 1-8 characterized by the above-mentioned. The piston structure of the internal combustion engine described.

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