JP6194808B2 - Piston and internal combustion engine - Google Patents

Description

  The present invention relates to a piston and an internal combustion engine, and more particularly, to a piston in which a ring groove for mounting a piston ring is formed on an outer peripheral surface, and an internal combustion engine including the piston.

  Regarding a conventional piston, Japanese Patent Application Laid-Open No. 2008-14214 (Patent Document 1) discloses that the force acting on the inner peripheral surface and the outer peripheral surface of the piston ring is canceled out by the combustion chamber pressure and the crankcase pressure. A configuration for keeping the value at a predetermined value is disclosed. Japanese Patent Laying-Open No. 2004-339976 (Patent Document 2) discloses a configuration in which the tension of a piston ring is adjusted based on the pressure of oil supplied to an oil passage inside the piston.

JP 2008-14214 A JP 2004-339976 A

  In the apparatus described in Patent Document 2, since the means for pressing the piston ring from the inside of the piston toward the outer periphery of the piston is a hydraulic system, a valve and a hydraulic path for controlling the hydraulic pressure are required, There was a problem.

  The present invention has been made in view of the above problems, and a main object thereof is to provide a piston capable of adjusting the tension of the piston ring with a simple structure. Another object of the present invention is to provide an internal combustion engine including the above-described piston.

  The piston according to the present invention is a piston having a cylindrical outer peripheral surface. A ring groove extending in the circumferential direction is formed on the outer peripheral surface of the piston. A hollow space is formed inside the piston. The atmospheric pressure in the hollow space repeatedly increases and decreases periodically. The piston further includes a movable member disposed across the ring groove and the hollow space. The movable member moves in the direction toward the ring groove when the atmospheric pressure in the hollow space increases.

  Preferably, the piston includes a biasing member that biases the movable member in a direction toward the hollow space.

  Preferably, in the piston, the movable member moves in a direction toward the hollow space and blocks communication between the ring groove and the hollow space.

  Preferably, in the piston, the movable member has a groove-side end portion disposed in the ring groove and a tapered surface extending toward the groove-side end portion.

  Preferably, in the above piston, the movable member has a pressure receiving portion that slides on the inner wall surface of the hollow space in response to a change in atmospheric pressure in the hollow space.

  Preferably, in the piston, the pressure receiving portion has an elastic portion that can be elastically deformed at a peripheral edge thereof.

  In the piston, a piston ring is preferably installed in the ring groove. When the atmospheric pressure in the hollow space increases, the movable member presses the inner peripheral surface of the piston ring toward the radially outer side. The piston ring may be a second ring.

  An internal combustion engine according to the present invention includes a cylinder, a piston in any one of the above aspects that reciprocates in the cylinder, a crankshaft that converts the reciprocating motion of the piston into rotational motion, and a crankcase that houses the crankshaft. It has. The hollow space formed inside the piston communicates with the internal space of the crankcase.

  According to the piston of the present invention, the tension of the piston ring can be adjusted with a simple structure.

It is a schematic diagram of an internal combustion engine when a piston exists in the position of a bottom dead center. It is a schematic diagram of an internal combustion engine when a piston exists in the position of a top dead center. It is sectional drawing of a piston and a piston ring. It is a perspective view of a piston ring. It is sectional drawing of the movable member arrange | positioned inside a piston. It is sectional drawing which shows the state which the movable member moved to the ring groove side. It is a graph which shows the pulsation of the pressure in a crankcase. It is sectional drawing which shows the relative position of a cylinder and a piston ring when a piston exists in the position of the top dead center vicinity. It is sectional drawing which shows the relative position of a cylinder and a piston ring when a piston moves below in the vicinity of a bottom dead center.

  Embodiments of the present invention will be described below with reference to the drawings. In the following embodiments, the same or corresponding parts are denoted by the same reference numerals, and description thereof will not be repeated.

  FIG. 1 is a schematic diagram of the internal combustion engine 1 when the piston 10 is at the bottom dead center position. The internal combustion engine in the present embodiment is, for example, a diesel engine, and includes a cylinder block in which a crankcase 2 and a cylinder 3 are integrated. The cylinder 3 has a cylindrical inner peripheral surface 4. The cylinder 3 houses a piston 10 in a cylinder bore formed therein. The inner peripheral surface 4 forms a part of the inner wall surface of the cylinder bore.

  The piston 10 is provided so as to reciprocate in the cylinder 3 in the axial direction (vertical direction in FIG. 1) of the cylindrical cylinder 3. The piston 10 is made of a metal material such as aluminum or an iron-based material.

  Three piston rings are provided on the upper side of the piston 10. The piston ring includes a top ring 11, a second ring 12, and an oil ring 13. The piston ring seals the gap between the piston 10 and the inner peripheral surface 4 of the cylinder 3 to prevent gas leakage, and the excess oil adhering to the inner peripheral surface of the cylinder 3 is transferred to the crankcase 2 side. Has a function to scrape off. The top ring 11 is mainly for preventing gas leakage, and the oil ring 13 is mainly for scraping off the oil. The second ring 12 is provided to assist the gas seal function of the top ring 11 and to assist the oil scraping function of the oil ring 13.

  A crankshaft 20 that converts the reciprocating motion of the piston 10 into a rotational motion is accommodated in the crankcase 2. The crankshaft 20 and the piston 10 are connected via a connecting rod 22. The crankshaft 20 and the connecting rod 22 are connected by a crankpin 23. The piston 10 and the connecting rod 22 are connected by a piston pin 24. A counterweight 21 is attached to the crankshaft 20. The counterweight 21 is provided in order to reduce the inertia force generated by the movement of the piston 10 and the connecting rod 22.

  FIG. 2 is a schematic diagram of the internal combustion engine 1 when the piston 10 is at the top dead center position. Of the internal space of the cylinder block, the volume of the space closer to the crankcase 2 than the piston 10 changes as the piston 10 reciprocates. When the piston 10 shown in FIG. 1 is at the bottom dead center position, the volume of the space on the crankcase 2 side than the piston 10 is the smallest. The volume of the space increases as the piston 10 rises from the bottom dead center toward the top dead center, and is maximized when the piston 10 shown in FIG. 2 is at the top dead center position.

  As the piston 10 reciprocates, the pressure inside the space on the crankcase 2 side of the piston 10 changes. When the piston 10 shown in FIG. 1 is at the bottom dead center position, the internal pressure of the crankcase 2 is maximum. When the piston 10 shown in FIG. 2 is at the top dead center position, the internal pressure of the crankcase 2 is minimized. As the piston 10 repeats reciprocating motion in the cylinder 3, the pressure in the crankcase 2 also changes repeatedly. The internal pressure of the crankcase 2 pulsates as the piston 10 reciprocates.

  FIG. 3 is a cross-sectional view of the piston 10 and the piston ring. The piston 10 shown in FIGS. 1 and 2 has a piston crown 31 that constitutes the top surface of the piston 10 and a cylindrical outer peripheral surface 32. Although the piston crown 31 is shown in a flat shape in FIG. 3, the central portion of the piston crown 31 may be partially recessed to form a combustion chamber.

  Three ring grooves 33, 34 and 35 are formed on the outer peripheral surface 32 of the piston 10 in order from the side closer to the piston crown 31. Each of the ring grooves 33, 34, and 35 extends in the circumferential direction of the cylindrical outer peripheral surface 32. A top ring 11 is mounted in the ring groove 33. The second ring 12 is mounted in the ring groove 34. An oil ring 13 is mounted in the ring groove 35.

  A hollow space 36 is formed inside the piston 10. The hollow space 36 formed in the piston 10 communicates with the internal space of the crankcase 2 shown in FIGS. As described above, the air pressure in the internal space of the crankcase 2 varies as the piston 10 reciprocates. Therefore, the air pressure in the hollow space 36 inside the piston 10 also periodically increases and decreases as the piston 10 reciprocates.

  A cylindrical space 37 is formed in a part of the hollow space 36. The cylindrical space 37 is disposed radially inward with respect to the ring groove 34 in which the second ring 12 is mounted. The piston 10 further includes a movable member 50. The movable member 50 is disposed across the ring groove 34 and the cylindrical space 37 constituting a part of the hollow space 36.

  FIG. 4 is a perspective view of the second ring 12 as an example of the piston ring. As shown in FIG. 4, the second ring 12 is formed with a joint gap 12 a in which a part of a circle is cut. The second ring 12 has a C-shaped outer shape. The second ring 12 is subjected to a tension toward the radially outer side. The second ring 12 is subjected to tension in a direction to be pressed against the inner peripheral surface 4 of the cylinder 3 shown in FIGS. Due to the action of this tension, the second ring 12 is in close contact with the inner peripheral surface 4 of the cylinder 3. The shape of the second ring 12 is defined so as to have a characteristic of spreading outward in the radial direction with an optimum tension.

  FIG. 5 is a cross-sectional view of the movable member 50 disposed inside the piston 10. FIG. 5 shows the ring groove 34 in which the second ring 12 described with reference to FIGS. 1 and 2 is mounted, and the cylindrical space 37 described with reference to FIG. The movable member 50 is disposed across the ring groove 34 and the cylindrical space 37. The movable member 50 includes a pressing portion 51 provided on the ring groove 34 side, a pressure receiving portion 61 disposed in the cylindrical space 37, and a shaft portion 56 that connects the pressing portion 51 and the pressure receiving portion 61. Yes.

  The pressing portion 51 has a groove side end portion 53 disposed in the ring groove 34. The groove-side end portion 53 forms an end surface of the movable member 50 on the radially outer side (left side in FIG. 5). The groove side end portion 53 faces the inner peripheral surface 12 s of the second ring 12. The groove end 53 has a function as a pressing surface that presses the second ring 12 outward in the radial direction. The pressure receiving portion 61 includes a space side end portion 63 disposed in the cylindrical space 37. The space-side end portion 63 forms the end surface of the movable member 50 on the radially inner side (right side in FIG. 5). The space side end portion 63 is an end portion of the movable member 50 on the side away from the second ring 12. The space side end 63 has a function as a pressure receiving surface that receives the atmospheric pressure in the hollow space 36.

  The outer shape of the pressing portion 51 increases as it approaches the groove-side end portion 53. The pressing portion 51 has a tapered surface 54 having a shape that widens toward the groove-side end portion 53. The tapered surface 54 is formed in a conical shape of a cone. The groove side end portion 53 forms a part of the bottom surface of the cone. The tapered surface 54 has, for example, a conical surface shape. The pressing portion 51 is formed with a concave portion 52 in which a part of the groove side end portion 53 is recessed.

  The piston 10 is formed with a recess having a shape in which the inner peripheral surface of the ring groove 34 is recessed radially inward (right side in FIG. 5). The inner wall surface of this concave portion is formed as a tapered surface 38 that is narrowed away from the ring groove 34. The tapered surface 38 is formed in a shape corresponding to the tapered surface 54 of the movable member 50. The tapered surface 38 is formed in a conical water surface shape similar to the tapered surface 54. In the state shown in FIG. 5, the tapered surface 54 of the movable member 50 is in surface contact with the tapered surface 38 of the piston 10. Accordingly, the movable member 50 and the piston 10 are in close contact with each other without a gap, and the movable member 50 is in airtight contact with the piston 10. At this time, the ring groove 34 and the cylindrical space 37 are not in communication.

  A space extending further inward in the radial direction from the top of the tapered surface 38 is formed in the piston 10, and the shaft portion 56 of the movable member 50 is accommodated in the space. The shaft portion 56 has a rod-like shape extending in the radial direction of the piston 10. A pressing portion 51 is connected to an end portion of the shaft portion 56 on the radially outer side (left side in FIG. 5). A pressure receiving portion 61 is connected to an end portion on the radially inner side (right side in FIG. 5) of the shaft portion 56.

  The pressure receiving part 61 has a flat plate shape. One main surface of the flat plate forms a space-side end portion 63. The other main surface of the flat plate forms a facing surface 62. The pressure receiving part 61 may have a disk-shaped outer shape. An end surface 37 a and an inner peripheral surface 37 b shown in FIG. 5 are provided inside the piston 10, and the end surface 37 a and the inner peripheral surface 37 b define a cylindrical space 37. The end surface 37 a and the inner peripheral surface 37 b constitute a part of the inner wall surface of the hollow space 36 inside the piston 10.

  The end surface 37 a constitutes the end surface of the cylindrical space 37. The facing surface 62 of the pressure receiving portion 61 faces the end surface 37a. The pressure receiving portion 61 is disposed in the cylindrical space 37 so that the facing surface 62 and the end surface 37a are parallel to each other. The inner peripheral surface 37 b constitutes the inner peripheral surface of the cylindrical space 37.

  A screw hole 65 is formed in the pressure receiving portion 61. A female thread shape is formed on the inner peripheral surface of the screw hole 65. The screw hole 65 is formed along the thickness direction of the flat plate from the facing surface 62 toward the space side end portion 63. The screw hole 65 may penetrate the pressure receiving portion 61 in the thickness direction. A screw-shaped portion 55 is formed at the end of the shaft portion 56 on the pressure receiving portion 61 side. A male screw shape is formed on the outer peripheral surface of the screw-shaped portion 55. When the screw-shaped portion 55 is screwed into the screw hole 65, the shaft portion 56 and the pressure receiving portion 61 are coupled.

  An elastic portion 66 is provided on the periphery of the flat pressure receiving portion 61. The elastic part 66 has a shape surrounding the entire periphery of the pressure receiving part 61, such as an O-ring shape. The elastic portion 66 is made of an elastically deformable material such as a rubber material. The elastic part 66 is in contact with the inner peripheral surface 37 b of the cylindrical space 37. The elastic portion 66 is disposed in the cylindrical space 37 in a state where it is subjected to stress from the inner peripheral surface 37 b of the cylindrical space 37 and is slightly elastically deformed. As a result, the elastic portion 66 is in airtight contact with the inner peripheral surface 37 b of the cylindrical space 37.

  The pressure receiving portion 61 divides the cylindrical space 37 into a radially inner space (right side in FIG. 5) and a radially outer space (left side in FIG. 5). The elastic portion 66 keeps the two spaces out of communication and prevents the air flow between the two spaces.

  A spring 68 is disposed between the end surface 37 a of the cylindrical space 37 and the facing surface 62 of the pressure receiving portion 61. The spring 68 is disposed on the outer periphery of the shaft portion 56 and is supported by the shaft portion 56. The spring 68 may be a coil spring. One end of the spring 68 is in contact with the end surface 37 a of the cylindrical space 37, and the other end of the spring 68 is in contact with the facing surface 62 of the pressure receiving portion 61. As the movable member 50 moves in the radial direction of the piston 10 (left and right direction in FIG. 5), the spring 68 changes its length.

  In the state shown in FIG. 5 where the tapered surface 54 of the pressing portion 51 is in surface contact with the tapered surface 38 on the piston 10 side, the spring 68 is in a contracted state with respect to the natural length. Therefore, the spring 68 acts on the pressure receiving portion 61 with an elastic force to return to the natural length. The direction of the elastic force of the spring 68 acting on the pressure receiving portion 61 is inward in the radial direction of the piston 10. Under the elastic force of the spring 68, a force in the direction from the ring groove 34 toward the cylindrical space 37 acts on the movable member 50. The spring 68 has a function as a biasing member that biases the movable member 50 in the direction toward the hollow space 36.

  A movable member 50 shown in FIG. 5 includes a plate-like member constituting the pressure receiving portion 61 and a member in which the pressing portion 51 and the shaft portion 56 are integrated. A member in which the pressing portion 51 and the shaft portion 56 are integrated is inserted from the ring groove 34 side into a path communicating with the ring groove 34 and the hollow space 36, and the end of the shaft portion 56 is exposed in the hollow space 36. Let Thereafter, a spring 68 is attached to the end of the shaft portion 56, and the pressure receiving portion 61 is fixed. In this way, the movable member 50 is attached inside the piston 10.

  FIG. 6 is a cross-sectional view showing a state where the movable member 50 has moved to the ring groove 34 side. The atmospheric pressure in the hollow space 36 acts on the space-side end portion 63 of the pressure receiving portion 61 of the movable member 50 described above. The pressure receiving portion 61 slides with respect to the inner peripheral surface 37 b of the cylindrical space 37 in response to a change in atmospheric pressure in the hollow space 36.

  When the air pressure in the hollow space 36 increases, the air pressure in the cylindrical space 37 also increases. Due to the increased air pressure, the pressure indicated by the white arrow P in FIG. 6 acts on the space-side end 63 of the pressure receiving portion 61. In response to this pressure, the movable member 50 moves in the direction toward the ring groove 34. When the movable member 50 moves, the groove side end portion 53 of the pressing portion 51 comes into contact with the inner peripheral surface 12 s of the second ring 12. When further pressure is applied to the movable member 50, the force indicated by the arrow F in FIG. 6 acts to press the second ring 12 radially outward (left side in FIG. 6) from the movable member 50 to the second ring 12. To do. The movable member 50 presses the inner peripheral surface 12s of the second ring 12 outward in the radial direction.

  When the air pressure in the hollow space 36 decreases, the air pressure in the cylindrical space 37 also decreases. Due to the decrease in the atmospheric pressure, the pressure indicated by the white arrow P in FIG. At this time, the movable member 50 moves in the direction toward the cylindrical space 37 by the elastic force of the spring 68 described above. When the movable member 50 moves, the groove side end portion 53 of the pressing portion 51 is separated from the inner peripheral surface 12s of the second ring 12, and the movable member 50 and the second ring 12 are not in contact with each other. Thereby, the force which the movable member 50 acts on the second ring 12 is removed.

  Further, the movement of the movable member 50 toward the cylindrical space 37 results in the state shown in FIG. 5 in which the tapered surface 54 of the pressing portion 51 is in surface contact with the tapered surface 38 of the piston 10. When the taper surface 54 and the taper surface 38 are in airtight contact, the ring groove 34 and the hollow space 36 are not in communication. The movable member 50 moves in the direction toward the hollow space 36 and blocks communication between the ring groove 34 and the hollow space 36.

  A plurality of movable members 50 are provided so as to press a plurality of locations on the inner peripheral surface 12s of the substantially circular second ring 12 shown in FIG. It is desirable that the plurality of movable members 50 be arranged uniformly so that the intervals between them are equal to each other. For example, when four movable members 50 are provided, the movable member 50 may be arranged so that the extending direction of the shaft portion 56 of the adjacent movable member 50 forms an angle of 90 °.

  FIG. 7 is a graph showing the pulsation of atmospheric pressure in the crankcase 2 shown in FIGS. The horizontal axis of FIG. 7 indicates the stroke of the piston 10, TDC indicates the position of the top dead center, and BDC indicates the position of the bottom dead center. The vertical axis in FIG. 7 represents the internal pressure (unit: kPa) in the crankcase 2. In FIG. 7, the pulsation of the internal pressure of the crankcase 2 generated by the reciprocating motion from the top dead center to the bottom dead center of the piston 10 for two different types of internal combustion engines 1 is illustrated using solid lines and dotted lines. .

  Referring to FIG. 7, when piston 10 is near the top dead center, the internal pressure of crankcase 2 is relatively small. When the piston 10 is near bottom dead center, the internal pressure of the crankcase 2 is relatively large. As the piston 10 repeats reciprocating motion, the internal pressure of the crankcase 2 also repeatedly increases and decreases.

  When the piston 10 is in the vicinity of the top dead center, the air pressure in the crankcase 2 is relatively small, so that the spring 68 has a larger diameter than the pressure that presses the pressure receiving portion 61 of the movable member 50 radially outward. The elastic force that presses inward is greater. Therefore, the movable member 50 moves in the direction toward the hollow space 36 (cylindrical space 37), and the second ring 12 and the movable member 50 shown in FIG. 5 are not in contact with each other, and the tapered surface 54 is a tapered surface. 38 is brought into airtight contact with 38.

  When the piston 10 is in the vicinity of the bottom dead center, the air pressure in the crankcase 2 is relatively large, so the spring 68 causes the pressure receiving portion 61 to be more than the elastic force that presses the pressure receiving portion 61 of the movable member 50 radially inward. The pressure that presses radially outward is greater. Therefore, the movable member 50 moves in the direction toward the ring groove 34, and a force is generated that the movable member 50 presses the inner peripheral surface 12 s of the second ring 12 shown in FIG. 6 toward the radially outer side, and The tapered surface 54 and the tapered surface 38 are in a non-contact state.

  FIG. 8 is a cross-sectional view showing the relative positions of the cylinder and the piston ring when the piston 10 is in a position near the top dead center. As described above, when the piston 10 is near the top dead center, the force that the movable member 50 acts on the second ring 12 is not generated. Therefore, a radially outward tension defined by the shape of the second ring 12 itself acts on the second ring 12.

  At this time, since the tension of the second ring 12 is prevented from being excessive, it is possible to avoid an increase in the frictional resistance against the movement of the piston 10 near the top dead center. Therefore, since the power required for the reciprocating motion of the piston 10 can be reduced, the efficiency of the internal combustion engine 1 can be improved. Further, when the piston 10 rises toward the top dead center, it is possible to suppress the oil 90 adhering to the inner peripheral surface 4 of the cylinder 3 from being scraped up by the second ring 12 and reaching the combustion chamber. Therefore, the oil that has reached the combustion chamber can be avoided from being exhausted wastefully, and the amount of oil 90 consumed can be reduced.

  FIG. 9 is a cross-sectional view showing the relative positions of the cylinder and the piston ring when the piston moves downward near the bottom dead center. As described above, when the piston 10 is near the bottom dead center, a force that the movable member 50 presses the second ring 12 radially outward acts on the second ring 12. For this reason, the radially outward force acting on the second ring 12 increases, and the second ring 12 is pressed against the inner peripheral surface 4 of the cylinder 3 with a larger force.

  As a result, as shown by an arrow D in FIG. 9, when the piston 10 descends toward the bottom dead center, the oil 90 attached to the inner peripheral surface 4 of the cylinder 3 is scraped off by the second ring 12. By increasing the tension of the second ring 12 when scraping off the oil 90 and reducing the amount of oil 90 remaining on the inner peripheral surface 4 of the cylinder 3, it is possible to more reliably prevent the oil 90 from reaching the combustion chamber. The consumption of oil 90 can be effectively reduced. Since the tension acting on the second ring 12 is variable according to the increase / decrease of the air pressure in the crankcase 2, a conventional hydraulic system is not required, and the tension of the second ring 12 can be adjusted with a simple structure. Can do.

  In the piston 10 of the present embodiment, the presence or absence of an increase in the tension of the piston ring using the movable member 50 is switched when the piston 10 reaches a specific position between the top dead center and the bottom dead center. Designed optimally. For example, when the piston reaches the center position where the distance between the top dead center and the bottom dead center is equally divided, the contact with the piston ring of the movable member 50 and the non-contact are switched. Good. If the piston ring tension is increased in the vicinity of the bottom dead center and the oil is sufficiently scraped off when descending toward the bottom dead center, and the amount of oil film left behind is reduced, the oil can be scraped up when it starts to rise. It can be suppressed. Since the tension of the piston ring is reduced in the vicinity of the top dead center, the action of scooping up the oil is also reduced, and the arrival of oil to the combustion chamber can be more reliably suppressed.

  Although there are portions that partially overlap with the above description, the characteristic configurations of the present embodiment are listed below. As shown in FIG. 3, the piston 10 of the present embodiment includes a cylindrical outer peripheral surface 32, and a ring groove 34 extending in the circumferential direction is formed on the outer peripheral surface 32. A hollow space 36 is formed inside the piston 10. As shown in FIG. 7, the atmospheric pressure in the hollow space 36 periodically increases and decreases according to the reciprocating motion of the piston 10. As shown in FIGS. 3 and 5, the piston 10 further includes a movable member 50 disposed across the ring groove 34 and a cylindrical space 37 that is a part of the hollow space 36.

  When the atmospheric pressure in the hollow space 36 increases, the movable member 50 moves in the direction toward the ring groove 34 as shown in FIG. When the movable member 50 contacts the second ring 12 and acts on the stress, the tension acting on the second ring 12 is increased. When the atmospheric pressure in the hollow space 36 decreases, the movable member 50 moves in the direction toward the hollow space 36 as shown in FIG. Since the movable member 50 is not in contact with the second ring 12, the tension acting on the second ring 12 is reduced. Since the tension acting on the second ring 12 is changed by utilizing the pulsation of the internal pressure of the hollow space 36 inside the piston 10, a complicated hydraulic path as in the prior art is unnecessary, and the second ring has a simple structure. The tension of 12 can be adjusted.

  By adjusting the shape of the second ring 12, it is possible to arbitrarily set the tension with which the second ring 12 itself tends to spread outward in the radial direction. According to the present embodiment, since the tension acting on the second ring 12 can be increased using the movable member 50, the tension acting on the second ring 12 can be set small by adjusting the shape of the second ring 12 itself. As a result, the frictional resistance of the second ring 12 against the inner peripheral surface 4 of the cylinder 3 in a state where no force is received from the movable member 50 in the vicinity of the top dead center can be further reduced. Can be effectively reduced.

  Impurities such as unburned carbon contained in the fuel may flow into the ring groove 34. If impurities are deposited and fixed in the ring groove 34, the second ring 12 is fixed to the ring groove 34, and the desired gas leak performance and oil scraping performance may not be exhibited. According to the configuration of the present embodiment, the state where the second ring 12 is pressed by the movable member 50 and the state where the second ring 12 is not pressed are alternately and repeatedly formed. Thereby, the second ring 12 vibrates minutely in the radial direction. By this vibration, it is possible to suppress the accumulation of impurities in the ring groove 34, and it is possible to suppress the adhesion of impurities in the ring groove 34.

  As shown in FIGS. 5 and 6, the piston 10 includes a spring 68 as a biasing member that biases the movable member 50 in the direction toward the hollow space 36. When the atmospheric pressure in the hollow space 36 decreases and the atmospheric pressure acting on the movable member 50 falls below the elastic force of the spring 68, the movable member 50 moves in the direction toward the hollow space 36 due to the elastic force of the spring 68. . Therefore, the movable member 50 can be reliably moved according to the change in the atmospheric pressure in the hollow space 36, and the contact between the second ring 12 and the movable member 50 and the non-contact are surely switched to act on the second ring 12. The tension can be adjusted.

  Further, as shown in FIG. 5, the movable member 50 moves in the direction toward the hollow space 36 and blocks communication between the ring groove 34 and the hollow space 36. When the movable member 50 is not in contact with the second ring 12, the ring groove 34 and the hollow space 36 are disconnected from each other, so that blow-by gas leaks to the crankcase 2 via the ring groove 34 and the hollow space 36. This can be suppressed. By ensuring the gas leak prevention performance, it is possible to reliably suppress problems such as blow-by gas reducing the oil performance.

  In addition, the ring groove 34 and the hollow space 36 are mutually connected in the state which the movable member 50 moved to the direction which goes to the ring groove 34 shown in FIG. However, in this state, since the pressure in the hollow space 36 inside the piston 10 is high, the flow of gas from the ring groove 34 toward the hollow space 36 can be suppressed. Therefore, gas leak prevention performance can be ensured.

  As shown in FIG. 5, the movable member 50 has a groove side end portion 53 disposed in the ring groove 34 and a tapered surface 54 that widens toward the groove side end portion 53. In this way, when the movable member 50 moves in the direction toward the hollow space 36, the tapered surface 54 can be brought into surface contact with a part of the surface of the piston 10, and the ring groove 34 and the hollow space 36 can be communicated with each other. It can shut off more reliably.

  As shown in FIG. 6, the movable member 50 has a pressure receiving portion 61. The pressure receiving portion 61 slides on the inner peripheral surface 37 b that is the inner wall surface of the hollow space 36 in response to a change in the atmospheric pressure in the hollow space 36. When the pressure receiving portion 61 moves in response to a change in the atmospheric pressure in the hollow space 36, the tension acting on the second ring 12 can be adjusted with a simple structure using the increase or decrease in the atmospheric pressure in the hollow space 36. .

  Further, as shown in FIG. 6, the pressure receiving portion 61 has an elastic portion 66 that can be elastically deformed at the periphery thereof. In this way, since the airtightness between the pressure receiving portion 61 and the inner peripheral surface 37b can be improved, the blow-by gas leaks to the crankcase 2 side via the ring groove 34 and the hollow space 36. It can be surely suppressed.

  As shown in FIGS. 3 and 6, the second ring 12 is mounted in the ring groove 34. When the atmospheric pressure in the hollow space 36 increases, the movable member 50 presses the inner circumferential surface 12s of the second ring 12 outward in the radial direction. In this way, when the atmospheric pressure in the hollow space 36 increases, the movable member 50 can press the second ring 12 to increase the tension of the second ring 12. By adjusting the tension to be adjusted to the second ring 12 among the plurality of piston rings, it becomes easier to adjust the tension of the piston ring using the increase or decrease of the atmospheric pressure in the hollow space 36.

  As shown in FIGS. 1 and 2, the internal combustion engine 1 of the present embodiment includes a cylinder 3, a piston 10 that reciprocates in the cylinder 3, and a reciprocating motion of the piston 10 in a rotational motion. A crankshaft 20 for conversion and a crankcase 2 for housing the crankshaft 20 are provided. The hollow space 36 formed inside the piston 10 communicates with the internal space of the crankcase 2. As shown in FIG. 7, the internal pressure of the crankcase 2 periodically increases and decreases according to the reciprocating motion of the piston 10. The internal pressure of the hollow space 36 varies periodically according to the internal pressure of the crankcase 2. Therefore, the tension acting on the second ring 12 can be changed by utilizing the pulsation of the internal pressure of the crankcase 2, and the tension of the second ring 12 can be adjusted with a simple structure.

  Although the embodiment of the present invention has been described as above, the embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  DESCRIPTION OF SYMBOLS 1 Internal combustion engine, 2 Crankcase, 3 Cylinder, 4, 12s, 37b Inner peripheral surface, 10 Piston, 11 Top ring, 12 Second ring, 12a Joint gap, 13 Oil ring, 32 Outer peripheral surface, 33, 34, 35 Ring groove , 36 hollow space, 37 cylindrical space, 37a end surface, 38, 54 taper surface, 50 movable member, 51 pressing portion, 52 concave portion, 53 groove side end portion, 55 screw shape portion, 56 shaft portion, 61 pressure receiving portion, 62 Opposing surface, 63 space side end, 65 screw hole, 66 elastic part, 68 spring, 90 oil.

Claims (8)

A piston having a cylindrical outer peripheral surface,
A ring groove extending in the circumferential direction is formed on the outer peripheral surface,
A hollow space is formed inside the piston, and the atmospheric pressure in the hollow space is repeatedly increased and decreased periodically.
A movable member disposed across the ring groove and the hollow space;
The movable member moves in a direction toward the ring groove when the atmospheric pressure in the hollow space increases,
The piston further comprising a biasing member that biases the movable member in a direction toward the hollow space . 2. The piston according to claim 1, wherein the movable member moves in a direction toward the hollow space and blocks communication between the ring groove and the hollow space. The piston according to claim 2 , wherein the movable member has a groove-side end portion disposed in the ring groove and a tapered surface that extends toward the groove-side end portion. Said movable member, the receiving variation in air pressure in the hollow space having a pressure receiving portion which slides the inner wall of the hollow space, a piston according to any one of claims 1-3. The said pressure receiving part is a piston of Claim 4 which has an elastic part which can be elastically deformed in the periphery. A piston ring is mounted in the ring groove,
The said movable member is a piston of any one of Claims 1-5 which presses the internal peripheral surface of the said piston ring toward a radial direction outer side, when the atmospheric pressure in the said hollow space increases. The piston according to claim 6 , wherein the piston ring is a second ring. A cylinder,
The piston according to any one of claims 1 to 7 , which reciprocates in the cylinder,
A crankshaft for converting the reciprocating motion of the piston into a rotational motion;
A crankcase for accommodating the crankshaft,
The internal combustion engine, wherein the hollow space formed in the piston communicates with the internal space of the crankcase.

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