JP2008190357A - Piston - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem of a conventional piston that stress concentration occurs in a boundary part between a skirt part and a side wall part, and there is a possibility to have damage such as a crack depending on the degree of the load. <P>SOLUTION: The piston is provided with a pair of the side wall parts 16 having a pin boss 14 and a piston pin attachment hole 15 opened respectively, a pair of the skirt parts 17 confronting with each other while having the piston boss 14 therebetween and having a circumferential end connected to the pair of the side wall parts 16, and a stress dispersion part formed in a connection region 18 of the side wall part 16 and the skirt part 17. The stress dispersion part may include an extended part 19 formed on the pair of the side wall pars 16 on a connection end side with the skirt part 17, and protruded to be extended from the skirt part 17, and has a base end formed at least on a terminal side of the connection region 18 positioned on a head part 13 side. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a piston used in a multi-cylinder internal combustion engine in which a plurality of combustion chambers are formed adjacent to each other.

  Reducing the inertial mass of the piston is advantageous for improving the accelerator response and increasing the engine speed, and various devices have been conventionally used. For example, Patent Document 1 discloses a piston having skirt portions facing each other across a pin boss portion in which a piston pin mounting hole is formed, and sidewall portions connected to both ends of the skirt portion in the circumferential direction. In this patent document 1, the pin boss | hub part is integrally formed with a sidewall part so that a sidewall part may be penetrated, and the opposing space | interval of a sidewall part is set smaller than the outer diameter of the head part of a piston. As a result, the skirt portion and the sidewall portion form a substantially rectangular tube as a whole.

JP-A-9-242603

  In an internal combustion engine, deformation of a piston and a cylinder bore that accommodates the piston occurs due to combustion gas pressure generated due to combustion of the air-fuel mixture, thermal expansion, and the like. In particular, in a multi-cylinder internal combustion engine in which a plurality of combustion chambers are formed adjacent to each other, it is known that deformation of the cylinder bore occurs non-uniformly in the radial direction. This is because the water jacket is formed so as to sandwich the cylinder bores along the arrangement direction of the cylinder bores, whereas no water jacket is interposed between adjacent cylinder bores. That is, the deformation of the cylinder bore region facing the water jacket can occur relatively easily, whereas the deformation of the cylinder bore toward the adjacent combustion chamber is suppressed. As a result, the cylinder bore is deformed into an elliptical shape having a short axis extending along the arrangement direction of the combustion chambers and a long axis perpendicular to the short axis.

  Such uneven deformation of the cylinder bore may have various adverse effects on the thermal expansion of the piston accommodated therein. For example, in Patent Document 1 described above, elastic deformation and thermal expansion of the skirt portion facing the water jacket through the cylinder liner are relatively easily performed. This is due to the fact that deformation of the area of the cylinder bore facing the water jacket can occur relatively easily. On the other hand, elastic deformation and thermal expansion of the sidewall portion extending in the direction orthogonal to the axis of the piston pin are suppressed. This is because the deformation of the cylinder bore along the axis of the piston pin is suppressed.

  As a result, stress concentration occurs at the boundary between the skirt portion and the sidewall portion of the piston, and there is a possibility that damage such as cracks may occur depending on the degree of load. In order to prevent such a problem, it is necessary to increase the rigidity and strength of the boundary portion between the skirt portion and the sidewall portion to increase the rigidity and strength, which is a factor that hinders the weight reduction of the piston.

  An object of the present invention is to reduce stress concentration occurring in a boundary region between a skirt portion and a sidewall portion while suppressing an increase in weight in a piston used in a multi-cylinder internal combustion engine in which a plurality of combustion chambers are formed adjacent to each other. It is to provide a structure that can be relaxed.

  The piston according to the present invention has a pair of sidewall portions in which pin boss portions are formed and piston pin mounting holes respectively open, and is opposed to each other across the pin boss portions, and circumferential end portions are the pair of sidewall portions. And a pair of skirt portions connected to each other, and a stress distribution portion formed in a connection region between the sidewall portions and the skirt portions.

  In the present invention, the stress generated in these connection regions due to different thermal expansion and elastic deformation of the skirt portion and the sidewall portion is dispersed by the stress dispersion portion formed here.

  In the piston according to the present invention, the stress dispersion portion may include an extension portion that is formed on the connection end side of the pair of sidewall portions with the skirt portion and protrudes so as to extend from the skirt portion.

  Alternatively, the stress dispersion portion may include a thin portion where the thickness of the connection region is reduced.

  It is preferable that the stress dispersion portion is formed at least on the distal side of the connection region whose proximal end is located on the piston head side.

  A combustion chamber including an annular lip portion may be further provided, and a facing interval between the pair of sidewall portions may be set narrower than an inner diameter of the lip portion of the combustion chamber.

  According to the piston of the present invention, since the stress dispersion portion is formed in the connection region between the sidewall portion and the skirt portion, the stress generated in these connection regions due to different thermal expansion and elastic deformation of the skirt portion and the sidewall portion. Can be dispersed. As a result, it is possible to prevent problems such as damage due to stress concentration in the connection region between the sidewall portion and the skirt portion without impairing the weight reduction of the piston.

  When the stress distribution part includes an extension part that protrudes from the skirt part on the connection end side with the skirt part of the pair of sidewall parts, the stress generated in the connection region is pushed to the inner peripheral surface of the cylinder bore. It will be dispersed in the corresponding extension.

  When the stress dispersion portion includes a thin portion, the thin portion is easily deformed, and concentration of stress generated in the connection region can be avoided while attempting to reduce the weight of the piston.

  When the stress dispersion portion is formed at least on the terminal side of the connection region where the base end is located on the piston head side, the weight of the piston can be reduced.

  When a combustion chamber including an annular lip portion is further provided, and the facing interval between the pair of sidewall portions is set narrower than the inner diameter of the lip portion of the combustion chamber, the compression force applied to the lip portion of the combustion chamber is increased. Can be dispersed.

  Embodiments of the piston according to the present invention will be described in detail with reference to FIGS. 1 to 5, but the present invention is not limited to these embodiments, and it is possible to appropriately combine these configurations as necessary. Needless to say.

  The appearance of the first embodiment of the piston according to the present invention is shown in FIGS. The piston 10 in the present embodiment is entirely made of an alloy based on aluminum. The piston 10 has a head 13 in which a plurality of piston ring grooves 11 and oil ring grooves 12 are processed on an outer peripheral surface 13 a, a pin boss portion 14 that supports a piston pin (not shown), and a piston pin mounting hole 15. A pair of sidewall portions 16 that are open to each other, a pair of skirt portions 17 that face each other across the pin boss portion 14 and that have circumferential ends connected to the pair of sidewall portions 16, and the sidewall portions 16 and the skirt And an extension portion 19 as a stress dispersion portion of the present invention formed in a connection region 18 with the portion 17. The sidewall portion 16 and the skirt portion 17 protrude from the opposite side of the top surface 13b of the head portion 13 and have an oval cylindrical outline as a whole.

  An outer peripheral surface 17a of the skirt portion 17 that can be brought into sliding contact with an inner peripheral surface of a cylinder bore (not shown) is formed to have a diameter of several tens of micrometers smaller than the inner diameter of the cylinder bore. The aluminum alloy constituting the piston 10 generally has a higher coefficient of thermal expansion than a cylinder liner such as cast iron that defines the cylinder bore, so that the skirt portion 17 of the piston 10 is located on the inner peripheral surface of the cylinder liner during engine operation. On the other hand, it is in a sliding contact state.

  The outer peripheral surface 16a of the sidewall portion 16 is in a state of retreating toward the center side of the piston 10 with respect to the outer peripheral surface 13a of the head portion 13, and is formed by a circular arc surface having a radius sufficiently larger than the flat surface or the inner diameter of the cylinder bore. Has been. For this reason, the sidewall portion 16 is always kept in a non-contact state with respect to the inner peripheral surface of the cylinder bore.

  The pair of pin boss portions 14 formed with the piston pin mounting holes 15 penetrating is formed on the opposing end surface sides of the pair of sidewall portions 16.

  In this embodiment, the extending portion 19 as the stress dispersion portion is formed on the connection end side of the pair of sidewall portions 16 with the skirt portion 17, and protrudes so that the outer peripheral surface 19 a extends from the skirt portion 17. Yes. The outer peripheral surface 19 a of the extending part 19 has the same center of curvature and the same radius of curvature as the skirt part 17. These extending portions 19 are arranged only on the distal side of the connection region 18 whose proximal end is located on the head 13 side. As described above, since the extending portion 19 is formed on the distal end side that is more easily deformed than the proximal end side, the rigidity on the distal end side of the connection region 18 can be improved by the presence of the extending portion 19. In addition, by distributing the stress generated in the connection region 18 to the extending portion 19, it is possible to avoid the occurrence of damage such as a crack in the connection region 18 without significantly reducing the weight reduction of the piston 10.

  In the above-described embodiment, the extending portion 19 is formed only on the distal side of the connection region 18 whose base end is located on the head 13 side of the piston 10. It is also possible to form the entire region in a direction parallel to the moving direction.

  The appearance of another embodiment of the piston according to the present invention is shown in FIG. 3 in a partially broken state, and the right half of the top surface is broken and shown in FIG. In this case, the same reference numerals are used, and duplicate explanations are omitted. That is, the extending portion 19 in the present embodiment is formed over the entire length of the connection region 18 so as to cover both left and right end portions of the sidewall portion 16. For this reason, it is possible to further disperse the stress generated in the connection region 18 in the extending portion 19 as compared with the previous embodiment, and to more reliably prevent damage such as cracks from occurring in the connection region 18. .

  In addition, the piston 10 in the present embodiment includes a combustion chamber 21 including an annular lip portion 20 on the top surface 13b. Further, the interval between the pair of sidewall portions 16 is set narrower than the inner diameter of the lip portion 20 of the combustion chamber 21. That is, since the inner diameter of the combustion chamber 21 is larger than the length of the piston pin 22 press-fitted into the piston pin mounting hole 15 of the pin boss portion 14, Elastic deformation becomes easy. As a result, the stress acting on the combustion chamber 21 during the combustion of the fuel can be distributed over a wider range of the head 13 than when the facing interval of the sidewall portions 16 is increased.

  In the above-described embodiment, the extension portion 19 that protrudes from the skirt portion 17 is formed on the connection end side of the pair of sidewall portions 16 with the skirt portion 17 as a stress distribution portion. It is also possible to form a thin portion with a reduced thickness of 18 as a stress dispersion portion.

  The appearance of another embodiment of the piston according to the present invention is shown in FIG. 5, but the same reference numerals are used for the same functions as those of the previous embodiment, and duplicate explanations are omitted. . That is, a thin portion 23 having a thin thickness is formed as a stress dispersion portion of the present invention on the end side of the inner peripheral surface of the connection region 18 between the sidewall portion 16 and the skirt portion 17. By forming such a thin portion 23, the elastic deformation of the connection region 18 is facilitated, the stress generated in the connection region 18 can be dispersed, and the weight of the piston 10 can be reduced. It is also possible to form the thin portion 23 on the outer peripheral surface side of the connection region 18 between the sidewall portion 16 and the skirt portion 17.

  It should be noted that the present invention should be construed only from the matters described in the claims, and in the above-described embodiment, all the changes and modifications included in the concept of the present invention are other than those described. Is possible. That is, all matters in the above-described embodiment are not intended to limit the present invention, and include any configuration not directly related to the present invention. To get.

It is a three-dimensional projection figure showing the external appearance of one Embodiment of the piston by this invention. It is the three-dimensional projection figure of the external appearance which looked at the piston shown in FIG. 1 from the other side. It is a three-dimensional projection figure showing the appearance of other embodiments of the piston by the present invention partially fractured. FIG. 4 is a partially broken cross-sectional view showing the right half in a broken state when the piston shown in FIG. 3 is viewed from the top surface. It is a three-dimensional projection figure showing the external appearance of another embodiment of the piston by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Piston 11 Piston ring groove 12 Oil ring groove 13 Head 13a Outer peripheral surface 13b Top surface 14 Pin boss part 15 Piston pin mounting hole 16 Side wall part 16a Outer peripheral surface 17 Skirt part 17a Outer peripheral surface 18 Connection area 19 Extension part 19a Outer peripheral surface 20 Lip part 21 Combustion chamber 22 Piston pin 23 Thin part

Claims (5)

A pair of sidewall portions in which pin boss portions are formed and piston pin mounting holes respectively open;
A pair of skirt portions facing each other across the pin boss portion and having circumferential ends connected to the pair of sidewall portions,
A piston comprising: a stress dispersion portion formed in a connection region between the sidewall portion and the skirt portion.   The stress distribution portion includes an extension portion that is formed on a connection end side of the pair of sidewall portions with the skirt portion and protrudes so as to extend from the skirt portion. The piston described in 1.   The piston according to claim 1, wherein the stress dispersion portion includes a thin portion in which a thickness of the connection region is reduced.   The piston according to any one of claims 1 to 3, wherein the stress dispersion portion is formed at least at a distal end side of the connection region whose proximal end is located on the piston head side.   5. The combustion chamber according to claim 1, further comprising a combustion chamber including an annular lip portion, wherein a facing interval between the pair of sidewall portions is set narrower than an inner diameter of the lip portion of the combustion chamber. Piston in any one.

Images