JP5564133B2 - Piston of internal combustion engine - Google Patents

Description

  The present invention relates to an improvement of a piston of an internal combustion engine which is a part of an automobile, for example.

  As is well known, the piston body of an internal combustion engine is made of an aluminum alloy material because of the demand for weight reduction. However, a large combustion pressure is applied to this piston, and the side force is set according to the angle with the connecting rod. As a result, large friction is generated between the skirt portion on the thrust side and the cylinder wall surface.

  For this reason, as in the technique described in Patent Document 1, a pair of apron portions are provided between the thrust side skirt portion and the anti-thrust side skirt portion, and the connection between the two apron portions and the both skirt portions is provided. A stress dispersion portion is provided in the region, and stress generated in the connection region due to different thermal expansion and elastic deformation of the skirt portion and the apron portion is dispersed by the stress dispersion portion.

JP 2008-190357 A

  However, in the piston of the conventional internal combustion engine, as described above, the stress acting on the skirt portion is dispersed by providing a stress dispersion portion in the connection region between each skirt portion and each apron portion. However, since the stress dispersion portion is merely constituted by the extending portion protruding outward from the lower end portion of the skirt portion, only the rigidity of the lower end portion of the skirt portion is increased and the entire skirt portion is increased. Deviation occurs in the rigidity of the. Accordingly, the surface pressure of the skirt portion against the cylinder wall surface is locally increased, and the friction cannot be reduced sufficiently.

The invention described in claim 1 includes a crown portion defining a combustion chamber, a pair of arc-shaped skirt portions provided integrally with the crown portion and sliding on the cylinder wall surface on the thrust side and the anti-thrust side, A piston of an internal combustion engine comprising a pair of apron parts connected to both side ends in the circumferential direction of each skirt part via a connection part and having pin bosses,
As for each said connection site | part, while an inner peripheral part and an outer peripheral part are formed in circular arc shape along the circumferential direction, the length of the circular arc width of the said inner peripheral part and an outer peripheral part is a lower end part side from the said crown part side. And the rate of change in the length of the arc width of the inner peripheral portion is larger than the rate of change in the length of the arc width of the outer peripheral portion. The wall thickness is gradually increased from the crown side to the lower end side in the piston axial direction.

  According to the invention according to claim 1 of the present application, both the inner peripheral portion and the outer peripheral portion of each connecting portion can be formed into an arc shape, so that the spring action can be effectively exerted, and the thickness of each connecting portion can be increased. By forming so as to gradually increase from the crown side toward the lower end side, the rigidity deviation of the skirt portion can be reduced in the piston axial direction (vertical direction).

  As a result, the bias of the surface pressure with respect to the cylinder wall surface of the skirt portion can be reduced, and the contact surface pressure can be reduced, whereby the friction can be effectively reduced.

A is a perspective view seen from the bottom side of the piston according to the first embodiment of the present invention, and B is a cross-sectional view taken along line AA of A. FIG. It is a side view of the piston. FIG. 3 is a front view showing a part of the piston in cross section. It is a bottom view of the piston. It is a perspective view which shows the outer side of a connection part by making the skirt part and apron part side of the piston into a ring. It is a perspective view which shows the inner side of a connection part by making the skirt part and apron part side of the piston into a ring. It is sectional drawing which shows the state which the piston slides on the cylinder wall surface of a cylinder block. It is a graph which compares and shows the deformation amount corresponding to the position of the thrust side skirt part of the piston of this embodiment, and the conventional piston. It is a graph which similarly compares and shows the frictional force corresponding to the crank angle of the thrust side skirt part of the piston of this embodiment, and the conventional piston. It is the perspective view seen from the bottom face side of the piston concerning a 2nd embodiment of the present invention. It is a bottom view of the piston which concerns on the 2nd Embodiment. It is the perspective view seen from the bottom face side of the piston which concerns on 3rd Embodiment of this invention. It is a longitudinal cross-sectional view of the piston of this embodiment. It is a perspective view which shows the inner side of a connection part by making the skirt part and apron part side of the piston of this embodiment into a ring.

  Hereinafter, embodiments of a piston of an internal combustion engine according to the present invention will be described in detail with reference to the drawings. The piston used in this embodiment is applied to a 4-cycle gasoline engine.

[First Embodiment]
As shown in FIG. 7, the piston 1 is slidably provided on a substantially cylindrical cylinder wall surface 3 formed in the cylinder block 2, and a combustion chamber 4 is interposed between the cylinder wall surface 3 and a cylinder head outside the figure. And is connected to a crankshaft (not shown) via a connecting rod 6 connected to the piston pin 5.

  The piston 1 is integrally cast as a whole by an AC8A Al—Si-based aluminum alloy, and is formed in a substantially cylindrical shape as shown in FIGS. 1A to 4, and defines the combustion chamber 4 on the crown surface 7 a. A crown portion 7 formed, a pair of arc-shaped thrust side skirt portion 8 and anti-thrust side skirt portion 9 provided integrally on the outer peripheral edge of the lower end of the crown portion 7, and the circumferential direction of the skirt portions 8, 9 A pair of apron portions 11 and 12 connected to each side end of each via a connecting portion 10.

  The crown portion 7 has a disk shape formed with a relatively large thickness, and a valve recess (not shown) that prevents interference with the intake / exhaust valve is formed on the crown surface 7a. Ring grooves 7b, 7c and 7d for holding three piston rings such as an oil ring are formed.

  Both the skirt portions 8 and 9 are disposed at symmetrical positions about the axis of the piston 1 and are formed in a substantially arcuate cross section. Is formed. The thrust side skirt portion 8 is adapted to be in pressure contact with the cylinder wall surface 3 while being inclined in relation to the angle of the connecting rod 6 when the piston 1 is stroked toward the bottom dead center during an expansion stroke or the like. The skirt portion 9 on the anti-thrust side comes into pressure contact with the cylinder wall surface 3 while inclining in the opposite direction when the piston 1 moves up during the compression stroke or the like. The thrust load on the cylinder wall surface 3 of each of the skirt portions 8 and 9 is larger in the thrust side skirt portion 8 that receives the combustion pressure and presses against the cylinder wall surface 3.

  The skirt portions 8 and 9 are inclined from the upper end portion 8a (9a) on the crown portion 7 side toward the lower end portion 8b (9b) as shown in FIG. 2 as viewed from the thrust side skirt portion 8 side. The lower end edge 8c (9c) is formed in a substantially horizontal shape while being formed in an enlarged diameter shape and having a vertical cross-sectional C shape.

  Each apron portion 11, 12 has an upper edge integrally joined to a lower end of the crown portion 7, and the entire circumferential direction between the connection portions 10 is larger in curvature than the skirt portions 8, 9. It is formed in a curved shape that bulges slightly outward with a radius, and like the skirt portions 8 and 9, it is formed in an inclined diameter-expanding shape from the upper end portion in the axial direction of the piston 1 to the lower end side. It is formed in a plane C shape. The curved curvature radius is set within a range of 150 mm to 300 mm, and the entire wall portion is formed relatively thick. In addition, the apron portions 11 and 12 are respectively formed with pin boss portions 13 and 14 for supporting both end portions of the piston pin 5 through pin holes 13a and 14a at substantially central positions in the circumferential direction.

  Each connecting portion 10 is formed in an arc shape along the circumferential direction from each side end of each skirt portion 8, 9 to the apron portions 11, 12, and each arc-shaped inner peripheral portion 16 and As shown by the hatched lines in FIGS. 1, 5, and 6, each outer peripheral portion 17 has a radius of curvature that gradually increases in the axial direction of the piston 1, that is, from the upper end portions 16 a and 17 a to the lower end portions 16 b and 17 b. It is formed continuously so as to be.

  That is, the respective radii of curvature of the inner peripheral portion 16 and the outer peripheral portion 17 are set in a skirt-like shape of about 10 mm to 30 mm from the small upper end portions 16a, 17a to the large lower end portions 16b, 17b, The spread increases proportionally and continuously.

  Further, the arc widths W and W1 are different in rate of change in the arc widths W and W1 in the vertical direction on the inner peripheral part 16 side and the outer peripheral part 17 side of each connecting part 10. That is, on each outer peripheral portion 17 side, the arc width length W is set to be relatively small, and the rate of change of the arc width length W from the upper end portion 17a to the lower end portion 17b is set to be small. On the other hand, the length W1 of the arc width is set relatively large on each inner peripheral portion 16 side, and the rate of change of the arc width length W1 from the upper end portion 16a to the lower end portion 16b is higher than that on the outer peripheral portion 17 side. Is also set larger.

  Thus, by setting the arc width length W1 on the inner peripheral part 16 side of the connecting part 10 to be larger and the change rate of this length W1 to be larger than that on the outer peripheral part 17 side, the thickness of the connecting part 10 can be reduced. The upper end portion on the crown portion 7 side can be gradually increased from the piston lower end portion. That is, the inner peripheral portion 16 of the connecting portion 10 is formed so that the arc surface is substantially flat, so that the circumferential and vertical rigidity of the skirt portions 8 and 9, that is, the overall rigidity is substantially uniform. Can be.

  Then, due to the arc shape and the curved shape of each of the skirt portions 8 and 9 and each of the connecting portions 10 and the apron portions 11 and 12, the overall shape seen from the bottom surface is almost elliptical as shown in FIGS. It is formed in a shape and is formed in a bowl shape as a whole.

  Further, a build-up portion 18 is locally provided at the lower end portion 16b of the inner peripheral portion 16 of each of the connecting portions 10. As shown in FIG. 1B, each of the built-up portions 18 is integrally provided on the inner side of the lower end portion 16b of the inner peripheral portion 16 of each of the connection portions 10, and the inner surface is formed in an arc shape. A lower end edge 18b below the thick lower end portion is located at the same position as the lower end edge of the inner peripheral portion 16 of the connecting portion 10. Further, the build-up portion 18 is gradually formed thinner from the thickest portion toward the upper side, and the arc-shaped upper end portion 18a is gently formed on the lower end portion 16b of the inner peripheral portion 16 of the connection portion 10. And they are connected continuously.

  Due to the presence of the build-up portion 18, the rigidity of the lower end side of the skirt portions 8 and 9 in a free state is increased, and the rigidity of the skirt portions 8 and 9 as a whole can be made more uniform.

  As described above, according to the present embodiment, since each connecting portion 10 is formed in an arc shape, the entire connecting portion 10 functions as a spring action, and thus each skirt portion at the time of the reciprocating stroke of the piston 1. Large deformation of the thrust side skirt portion 8 and the anti-thrust side skirt portion 9 can be suppressed when the outer peripheral surfaces of the cylinders 8 and 9 are in contact with the cylinder wall surface 3.

  In addition, in the present embodiment, since both the apron portions 11 and 12 are also formed in a curved shape, both the apron portions 11 and 12 also have a slight spring action due to deformation. Therefore, in combination with the spring action of each connecting portion 10, the contact area of each skirt portion 8, 9 with respect to the cylinder wall surface 3 is increased, and an increase in local surface pressure can be suppressed.

  That is, as described above, since both the skirt portions 8 and 9 and the connecting portions 10 and the apron portions 11 and 12 are substantially elliptical, the contact pressure acting on the skirt portions 8 and 9 is used. Is absorbed by the spring action of each connecting portion 10 and each apron 11, 12, thereby dispersing the surface pressure applied to each skirt 8, 9 and suppressing the generation of excessive surface pressure. It can be done.

  Further, the radii of curvature of the respective connecting portions 10 are formed so as to gradually increase from the upper end portions 16a, 17a toward the lower end portions 16b, 17b, thereby providing rigidity on both side ends of the skirt portions 8, 9. That is, the rigidity on the apron portions 11 and 12 side can be made substantially uniform in the piston axial direction. That is, since the lower end portions 16b and 17b side of each connecting portion 10 are free ends (free state), if the same thickness as the upper end portions 16a and 17b side, these stiffnesses are the upper end portions 16a, Lower than the 17a side. Therefore, by gradually increasing the thickness from the upper end portions 16a, 17a toward the lower end portions 16b, 17b, the rigidity is uniformized as a whole.

  As a result, the surface pressure of the skirt portions 8 and 9 with respect to the cylinder wall surface 3 can be made uniform to reduce the contact surface pressure, thereby effectively reducing friction.

  Further, since the built-up portion 18 is integrally provided on the inner surface of the lower end portion 16b of the inner peripheral portion 16 of each connecting portion 10, the rigidity on the lower end side of both the skirt portions 8 and 9 is increased. That is, as described above, since the lower end portion 9b of each skirt portion 8 and 9 is in a free state, the rigidity is likely to be lower than that of the upper end portion 9a. The rigidity of the lower end portion 9b is increased in combination with the increase in rigidity of the lower end portions 16b and 17b of each connecting portion 10, and the rigidity of the entire skirt portions 8 and 9 can be further uniformized.

  As a result, the contact areas of the skirt portions 8 and 9 with respect to the cylinder wall surface 3 are made uniform at the upper and lower portions, and the friction can be reduced.

  The graph shown in FIG. 8 shows the position between the upper end and the lower end of the thrust side skirt and the amount of deformation of the thrust side skirt corresponding to this position under the same load condition that contacts the cylinder wall surface 3 during the expansion stroke. The result of having compared the piston 1 (solid line) of this embodiment with the conventional piston (broken line) by experiment is shown.

  As can be seen from the above, in the conventional piston, the amount of deformation on the lower end side is larger than that on the upper end side. However, in the piston 1 of the present embodiment, the position is slightly lowered from the upper end portion or at the lowermost end side. Although the amount of deformation is slightly increased, it is clear that the amount of deformation is small as a whole.

  This is because in the present embodiment, the rigidity of the thrust side skirt portion 8 as a whole is uniformized due to the unique arc shape and thickness structure of each connecting portion 10 and the presence of the built-up portion 18. .

  FIG. 9 shows a time history of the frictional force obtained by numerical analysis of the piston 1 of the present embodiment and the conventional piston. The horizontal axis represents the crank angle, and the vertical axis represents the friction force. The greater the amplitude of the waveform, the greater the friction force.

  As is clear from this figure, the piston 1 (solid line) of the present embodiment has a lower frictional force during the stroke than the conventional piston (broken line), and this tendency is particularly prominent around the crank angle of 0 to 90 °. It has become. This is due to the unique structure of the piston 1 of the present embodiment described above.

[Second Embodiment]
10 and 11 show a second embodiment. In this embodiment, the thrust side skirt portion 8 and the anti-thrust side skirt portion 9 are formed in an asymmetric shape about the axis of the piston 1, and the anti-thrust side is shown. The circumferential length X of the skirt 9 is set to be shorter than the circumferential length X1 of the thrust side skirt portion 8. This is because the contact load on the cylinder wall surface 3 is smaller in the anti-thrust side skirt portion 9 than in the thrust side skirt portion 8, and therefore the contact area is set smaller.

  Further, the radius of curvature of each connecting portion 10 is set to be the same as that of the first embodiment on both side ends of the thrust side skirt portion 8, but each connecting portion 10 a on both side ends of the anti-thrust side skirt portion 9. In 10a, it is smaller than each connection part 10 and 10 by the side of the thrust side skirt part 8. FIG.

  Further, the build-up portion 18 is also formed in the direction of the build-up portions 18b and 18b of the anti-thrust side skirt portion 9 rather than the build-up portions 18a and 18a on the thrust side skirt portion 8 side set in the same manner as the first embodiment. However, its thickness and circumferential length are set small.

  However, the curved shapes of the two apron portions 11 and 12 are the same as those in the first embodiment.

  Therefore, according to this embodiment, the same operation effect as the first embodiment can be obtained, and the structure on the anti-thrust side is reduced according to the contact load on the cylinder wall surface 3, thereby reducing the weight of the entire piston 1. Can promote.

[Third Embodiment]
12 to 14 show a third embodiment. On the premise of the basic structure of the first and second embodiments, the apron portions 11 and 12 are slightly curved outward and the piston 1 It is formed substantially vertically without being inclined along the axial direction. In other words, unlike the first embodiment, the apron portions 11 and 12 are formed substantially in parallel, not in the shape of a bowl having a vertical cross section.

  In addition, each of the connecting portions 10 is formed substantially the same so that the radius of curvature on the outer peripheral portion 17 side does not change in the vertical direction, while the radius of curvature on the inner peripheral portion 16 side changes from the upper end portion 16a to the lower end portion 16b. It is formed so as to become gradually larger.

  Therefore, in this embodiment, the spring force is exerted by the curved shape of the apron parts 11 and 12 as in the first embodiment. The thickness of the lower end portion, which is likely to be lowered in rigidity, is sufficiently larger than the upper end portion, so that the skirt portion 8, 9 The uniformity of the rigidity of the whole can be promoted.

  Therefore, the bias of rigidity of each skirt part 8 and 9 can be suppressed by the spring action of the apron parts 11 and 12 and the spring action of each connection part 10 and the change in the thickness of each connection part 10. , 9 can be sufficiently suppressed from being biased against the cylinder wall surface 3.

  Further, the apron portions 11 and 12 can be formed in a substantially flat shape instead of a curved shape. As a result, when the skirt portions 8 and 9 are brought into pressure contact with the cylinder wall surface 3, the spring action at the apron portions 11 and 12 hardly works, and the spring action at the connection portions 10 works exclusively.

  The present invention is not limited to the configuration of the above-described embodiment. For example, the connecting portion 10 can be formed only on the thrust side skirt portion 8 side where the pressure contact load increases.

  Moreover, each said connection site | part 10 may be chamfered R shape, for example, without forming in circular arc shape.

  Moreover, it is also possible to coat the outer peripheral surfaces of the skirt portions 8 and 9 with a low friction material for reducing friction with the cylinder wall surface 3.

  Furthermore, the material of the piston is not limited to aluminum, and various metals such as iron and magnesium can be employed.

  Further, the piston of the present invention can be applied to various internal combustion engines such as a V type and a W type, and can be applied to various internal combustion engines such as a single cylinder type and a multi-cylinder type.

DESCRIPTION OF SYMBOLS 1 ... Piston 2 ... Cylinder block 3 ... Cylinder wall surface 4 ... Combustion chamber 5 ... Piston pin 7 ... Crown part 7a ... Crown surface 8 ... Thrust side skirt part 9 ... Anti-thrust side skirt part 10 (10a, 10b) ... Connection part 11 12 apron part 13 14 pin boss part 13a, 14a pin hole 16 inner peripheral part 17 outer peripheral part 18 overlaying part

Claims (2)

A crown that defines a combustion chamber; a pair of arc-shaped skirts that are provided integrally with the crown and slide on the cylinder wall surface; and a pair of arc-shaped skirts on the opposite side of the thrust side; A piston of an internal combustion engine comprising a pair of apron parts coupled to ends via a coupling part and having pin bosses,
As for each said connection site | part, while an inner peripheral part and an outer peripheral part are formed in circular arc shape along the circumferential direction, the length of the circular arc width of the said inner peripheral part and an outer peripheral part is a lower end part side from the said crown part side. And the rate of change in the length of the arc width of the inner peripheral portion is larger than the rate of change in the length of the arc width of the outer peripheral portion. a piston for an internal combustion engine, characterized in that the wall thickness is formed to be gradually thicker toward the lower end side from the crown side of the piston axis.   2. The piston of the internal combustion engine according to claim 1, wherein the pair of apron portions are formed in a curved shape that bulges outward with a larger radius of curvature than the skirt portions.

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