JP2010065624A - Piston for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piston for an internal combustion engine, achieving reduction in weight while suppressing generation of hammering noise of the piston. <P>SOLUTION: A lower skirt 97 is composed of main skirts 97A, 97B of the piston 13 respectively provided on a thrust side and an anti-thrust side, a pair of auxiliary skirts 97C, 97D of the piston 13, arranged in an orthogonal direction perpendicular to thrust/anti-thrust directions, and connection skirts 97E, 97G connecting these main skirts 97A, 97B and auxiliary skirts 97C, 97D. The auxiliary skirts 97C, 97D are formed shorter in the center shaft direction of the piston 13 than the main skirts 97A, 97B. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

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

As a conventional piston for an internal combustion engine, one having a skirt portion having a constant width in the central axis direction of the piston over the entire circumference is known (for example, see Patent Document 1).
JP 2006-274861 A

FIG. 2 of Patent Document 1 will be described with reference to FIG. In addition, the code | symbol was reassigned.
FIG. 8 is a perspective view of a conventional piston for an internal combustion engine, and shows a piston 200 connected to a crankshaft 202 via a connecting rod 201.

The piston 200 is a combination of an upper piston 205 and a lower piston 206, and is connected to the small end of the connecting rod 201 via a spherical joint.
An upper skirt portion 207 having a constant vertical width is formed on the entire circumference of the upper piston 205, and a lower skirt portion 208 having a constant vertical width is formed on the entire periphery of the lower piston 206.

Since the piston 200 is connected to the connecting rod 201 by a spherical joint, it is presumed that the piston 200 is easily tilted not only in the thrust-anti-thrust direction but also in the direction orthogonal to the thrust-anti-thrust direction, and piston hitting noise is likely to be generated. The upper skirt portion 207 and the lower skirt portion 208 having a constant width in the direction of the central axis of the piston are provided on the entire circumference in order to suppress the tilting of the piston.
In such an all-around skirt structure, the piston weight increases, so that it is difficult to employ the high-rotation high-power internal combustion engine with a high engine speed.

  An object of the present invention is to provide a piston for an internal combustion engine that can be reduced in weight while suppressing generation of piston hitting sound.

  The invention according to claim 1 projects from the back surface of the crown portion, a land portion extending downward from the edge of the crown portion, an all-round skirt portion extending further downward from the land portion over the entire circumference. And a spherical joint cup portion having a concave spherical surface for forming a spherical joint with a small spherical end portion provided on the connecting rod. The main skirt portion provided on the side and the anti-thrust side, a pair of sub skirt portions arranged in a direction orthogonal to the thrust-anti-thrust direction of the piston, and a connection connecting the main skirt portion and the sub skirt portion. The skirt portion is formed, and the sub skirt portion is formed shorter than the main skirt portion in the central axis direction of the piston.

As a function, it was found that the piston connected to the connecting rod via the spherical joint is not easily tilted in the orthogonal direction perpendicular to the thrust-anti-thrust direction from the piston behavior measurement result.
This is considered to be due to the thrust-side skirt portion of the piston being in close contact with the sleeve by the side pressure in the thrust-anti-thrust direction acting on the piston, and the piston falling in the direction orthogonal to the thrust-anti-thrust direction is suppressed.

From this result, even if the sub skirt portion arranged in the orthogonal direction orthogonal to the thrust-anti-thrust direction is made shorter than the main skirt portion, it is possible to suppress piston hitting sound.
If the sub-skirt portion is shorter than the main skirt portion, the area of the skirt portion is reduced as compared with the conventional all-around skirt portion, and the piston becomes lighter.

The invention according to claim 2 is characterized in that the outer peripheral surface of the entire peripheral skirt portion has a perfect circular shape.
As an action, for example, if the outer peripheral surface of the skirt portion is elliptical, it is necessary to process the skirt portion of the piston with a lathe that does not follow a cam, etc. The skirt can be machined with an ordinary lathe.

  In the invention according to claim 1, the entire circumferential skirt portion includes a main skirt portion provided on the thrust side and the anti-thrust side of the piston, and a pair of sub skirts arranged in an orthogonal direction perpendicular to the thrust-anti-thrust direction of the piston. And a connecting skirt portion that connects each of the main skirt portion and the sub skirt portion, and the sub skirt portion is formed shorter than the main skirt portion in the central axis direction of the piston. While having the same piston striking sound suppression effect as the piston with the skirt part, the area of the skirt part can be reduced, the piston can be made lighter than before, and the internal combustion engine can be rotated at a high speed, The internal combustion engine output can be improved.

  In the invention according to claim 2, since the outer peripheral surface of the all-round skirt portion has a perfect circular shape, for example, the processing of the skirt portion is performed as compared with processing the outer peripheral surface of the skirt portion into an elliptical shape. Becomes easier and productivity can be improved.

The best mode for carrying out the present invention will be described below with reference to the accompanying drawings. The drawings are viewed in the direction of the reference numerals.
FIG. 1 is a cross-sectional view of an internal combustion engine that employs an assembly type piston structure according to the present invention. The internal combustion engine 10 includes a cylinder block 11 and a piston that is movably inserted into a cylinder bore 12 provided in the cylinder block 11. 13, a connecting rod 16 connected to the piston 13 via a spherical joint 14, and an assembly-type crank that is rotatably attached to the lower portion of the cylinder block 11 and supports the connecting rod 16 with a hollow crankpin 17 so as to be swingable. A shaft 18.

  The cylinder block 11 includes a cylinder portion 21 provided at an upper portion, a cylindrical sleeve 22 fitted inside the cylinder portion 21 and formed with a cylinder bore 12, and an upper attached to the lower portion of the cylinder portion 21. It consists of a crankcase 23.

  The connecting rod 16 includes a spherical small end portion 24 connected to the piston 13, a large end portion 25 connected to the crankpin 17, and a rod portion that connects each of the small end portion 24 and the large end portion 25. 26 is an integrally molded member, and the large end portion 25 is connected to the crank pin 17 via a slide bearing 31.

  Here, reference numeral 32 is a counterweight provided on the crankshaft 18, 33 is a cylinder head attached to the top of the cylinder block 11 via a head gasket (not shown), 34 is an intake valve, 36 is an exhaust valve, 37 Is a combustion chamber, 38 is a lower crankcase attached with a plurality of bolts 41 to the lower part of the upper crankcase 23 to form a crankcase with the upper crankcase 23, and 42 is a plurality of bolts at the lower part of the lower crankcase 38. The oil pan attached at 44.

The piston 16 is, for example, a member that is manufactured by casting a material AC8A [JIS H 5202] and subjected to machining after being subjected to T6 treatment as heat treatment.
The connecting rod 16 is preferably made of chrome steel, chrome molybdenum steel, or titanium alloy.

  FIG. 2 is a cross-sectional view of the piston and connecting rod according to the present invention. The piston 13 includes an upper piston 51 having a crown 50 for forming a combustion chamber 37 (see FIG. 1), and a small end 24 of the connecting rod 16. An upper holding member 56 disposed in a protruding portion 54 that protrudes downward from the back surface 53 of the crown portion 50 of the upper piston 51 in order to hold the upper hemispherical portion 24a slidably, and a small end portion of the connecting rod 16 The lower holding member 57 that slidably holds the lower hemispherical portion 24 b of the lower 24 and a lower piston 58 that is screwed to the upper piston 51 to hold the lower holding member 57.

  The upper piston 51 includes a crown portion 50 formed in a disc shape, a cylindrical and thick land portion 61 extending downward from the periphery of the crown portion 50, and a lower portion from the land portion 61. An upper skirt portion 62 that is formed in a cylindrical shape and is thinner than the land portion 61, and the protruding portion 54 described above are integrally formed.

The crown 50 includes a crown surface 64 that faces the combustion chamber 37 (see FIG. 1).
The land portion 61 is a portion where a top land 66, a top ring groove 67, a second land 68, a second ring groove 71, a third land 72, and an oil ring groove 73 are provided in this order from the crown surface 64 side. A top ring (not shown) is fitted into the second ring groove 71, a second ring (not shown) is fitted into the oil ring groove 73, and an oil ring (not shown) is fitted into the oil ring groove 73.

  The protrusion 54 includes a recess 75 that houses the upper holding member 56 so as to be movable in the radial direction of the piston 13, and a male screw 78 formed on the outer peripheral surface 77 of the recess 75 on the opening 76 side. Is a portion in which a small recess 82 is formed in the bottom 81.

The upper holding member 56 is made of silicon nitride ceramics having excellent heat resistance and wear resistance, and is a first spherical surface as a concave spherical surface that is slidably fitted into the upper hemisphere portion 24 a of the small end portion 24 of the connecting rod 16. 85 and a small convex portion 86 positioned in the small concave portion 82 of the upper piston 51, and the inner peripheral surface 87 of the concave portion 75 and the outer peripheral surface 88 of the upper holding member 56 have gaps C on one side, respectively. In addition, a gap C (not shown) is also provided on one side between the small concave portion 82 and the small convex portion 86.
The gap C is also provided on one side between the inner peripheral surface 87 of the recess 75 and the small end 24 of the connecting rod 16.
As the above silicon nitride ceramics, Si ₃ N ₄ (silicon nitride), BN (boron nitride), AlN (aluminum nitride), and TiN (titanium nitride) are suitable.

  The lower holding member 57 includes a second spherical surface 91 as a concave spherical surface that is slidably fitted to the lower hemispherical portion 24 b of the small end portion 24 of the connecting rod 16, and an inner portion of a cylindrical portion 95 formed at the center of the lower piston 58. An outer peripheral surface 92 fitted to the peripheral surface 102, a male tapered portion 93 fitted to the tapered portion 101 formed at the lower portion of the cylindrical portion 95, and an abutting contact with the end surface 54a of the protruding portion 54 of the upper piston 51 A member made of silicon nitride ceramics (the materials listed above are suitable) divided into four parts and having a surface 94, and a non-rotating pin (not shown) with respect to the protruding portion 54 of the upper piston 51. It is also a member that prevents the piston 13 from rotating with respect to the connecting rod 16 by preventing the rotation and providing a guided surface that is applied to the rod portion 26 of the connecting rod 16. Reference numerals 57 a to 57 d (57 c and 57 d are not shown) are four divided bodies constituting the lower holding member 57.

  The lower piston 58 includes a cylindrical portion 95 disposed so as to surround the lower portion of the projecting portion 54 of the upper piston 51 and the lower holding member 57, a plurality of ribs 96 radially extending from the cylindrical portion 95, and And a cylindrical lower skirt portion 97 connected to each end of the rib 96 is integrally formed, and the upper end surface 97a of the lower skirt portion 97 provided on the entire circumference is below the upper skirt portion 62 of the upper piston 51. It is a member applied to the end face 62a.

  The cylindrical portion 95 has a female taper portion 101 that is in close contact with the tapered portion 93 of the lower holding member 57 in the hole portion 98, and an inner periphery that fits with an outer peripheral surface 92 of the lower holding member 57 with a predetermined gap. A surface 102 and a screw 103 formed on the upper surface of the inner peripheral surface 102 so as to be screw-coupled to the male screw 78 of the upper piston 51 are provided.

By fitting the male taper portion 93 and the female taper portion 101, the axis of the lower holding member 57 is aligned with the axis of the cylindrical portion 95.
The above-described male screw 78 of the upper piston 51 and the female screw 103 of the lower piston 58 are parts constituting the screw coupling portion 104.

  The upper piston 51 and the lower piston 58 are members having substantially the same mass, and the upper holding member 56 and the lower holding member 57 have substantially the same mass. The mass of the upper piston half 105A composed of the member 56 and the mass of the lower piston half 105B composed of the lower piston 58 and the lower holding member 57 are substantially the same.

  The connecting rod 16 is a member in which hollow portions 106, 107, and 108 for weight reduction are provided inside the rod portion 26, and a hollow portion 110 for weight reduction is provided inside the small end portion 24. Oil holes 114 and 115 are provided to supply oil from the side of the portion 25 (see FIG. 1) to the sliding surface of the spherical joint 14.

The protruding portion 54, the upper holding member 56, the lower holding member 57, the cylindrical portion 95, and the small end portion 24 are portions constituting the spherical joint 14 described above.
Reference numeral 117 denotes a center point indicating the center of the spherical small end 24 and is the center of gravity of the piston 13, but the center point 117 may be substantially coincident with the center of gravity of the piston 13. Reference numeral 118 denotes an axis of the piston 13.

FIG. 3 is a first side view of the piston according to the present invention, as seen from the thrust-anti-thrust direction of the piston 13.
The lower skirt portion 97 of the lower piston 58 is provided in a direction orthogonal to the pair of main skirt portions 97A and 97B (only the reference numeral 97A on the front side) provided on the thrust side and the anti-thrust side. And a connecting skirt portion 97E to 97H (only reference numerals 97E and 97F are shown) connecting the main skirt portions 97A and 97B and the sub skirt portions 97C and 97D. It is a circumference skirt part. In addition, the code | symbol 119a, 119a, 119b, 119b in a figure is an imaginary line which shows the boundary of each skirt part.
The main skirt portions 97A and 97B are rectangular portions having a width W1 and a height H1 in a side view.

FIG. 4 is a second side view of the piston according to the present invention, as seen from a direction orthogonal to the thrust-anti-thrust direction of the piston 13.
The auxiliary skirt portions 97C and 97D (only the reference numeral 97C on the front side is shown) are rectangular portions having a width W2 and a height H2 in a side view, and the height H2 is the main skirt shown in FIG. It is smaller than the height H1 of the portions 97A and 97B.
That is, the sub skirt portions 97C and 97D are formed shorter than the main skirt portions 97A and 97B in the direction of the axis 118 (see FIG. 2) of the piston 13.

  FIG. 5 is a bottom view (partially sectional view) showing a piston and a connecting rod according to the present invention. The lower piston 58 includes a main skirt portion 97A on the thrust side and a main skirt portion 97B on the opposite thrust side. A plurality of ribs 96 that connect the skirt portions 97A and 97B and the cylindrical portion 95 are provided.

  In addition, a portion corresponding to such a rib 96 may be provided in the upper piston 51 (see FIG. 3), whereby the stress generated in the crown portion 50 (see FIG. 2) of the upper piston 51 is equally applied to each rib. The maximum value of stress generated in the upper piston 51 can be lowered.

  The connecting rod 16 is flat on the side surfaces 26a, 26a of the rod portion 26 close to the small end portion 24 (see FIG. 2), and in the direction in which the connecting rod 16 swings (oscillates in the figure). The parallel guide surfaces 26b and 26b are respectively formed, and the lower holding member 57 (the portion indicated by a thick line for easy understanding of the shape) is a rectangular shape provided for passing the connecting rod 16 therethrough. The opening 57e is provided with a guided surface 57f that is guided while hitting the guide surfaces 26b and 26b for each of the divided bodies 57a to 57d.

  As described above, the guide rods 26 b and 26 b are provided on the connecting rod 16, and the guided surfaces 57 f and 57 f guided by the guide surfaces 26 b and 26 b are provided on the lower holding member 57. Rotation around the cylinder axis can be prevented.

6A and 6B are operation diagrams showing the behavior of the piston according to the present invention.
(A) shows a state in which, when the air-fuel mixture burns in the combustion chamber 37 during operation of the internal combustion engine, the piston 13 falls to the thrust side immediately after descending from the top dead center.

That is, the upper end of the main skirt portion 97A on the thrust side (the portion of the black circle 121 in the figure) hits the cylinder bore 12, and the lower end of the main skirt portion 97B on the anti-thrust side (the portion of the black circle 122 in the drawing). ) Hits the cylinder bore 12, the posture of the piston 13 is maintained, the land portion 61 is prevented from hitting, and the occurrence of piston hitting noise is suppressed.
In the figure, since the direction orthogonal to the thrust-anti-thrust direction (T-AT direction) is, for example, the front-rear direction of the internal combustion engine, it is represented as the front (F) -rear (R) direction (FR direction).

(B) shows a state in which the exhaust stroke is finished during the operation of the internal combustion engine, and the piston 13 falls to the rear side when the piston 13 descends from the top dead center and moves to the intake stroke.
That is, the upper end of the rear side sub-skirt portion 97D (the portion of the black circle 123 in the figure) hits the cylinder bore 12, and the lower end of the thrust side main skirt portion 97A and the end in the circumferential direction (in the drawing) And the lower end of the main skirt portion 97B on the anti-thrust side in the circumferential direction (the portion of the black circle 125 in the figure) hits the cylinder bore 12, and the posture of the piston 13 is maintained. Thus, the land portion 61 is prevented from hitting, and the occurrence of piston hitting sound is suppressed.

  FIG. 7 is a graph showing the measurement results of the piston behavior and the internal combustion engine in-cylinder pressure according to the present invention. The lower side of the graph is the measurement result of the piston behavior during operation of the internal combustion engine, and the upper side of the graph is the measurement result of the in-cylinder internal cylinder pressure. Is shown. The vertical axis of the graph represents the piston tilt (unit: deg) and in-cylinder pressure, and the horizontal axis represents the crank angle. Further, in the graph of piston inclination, the broken line indicates data in the thrust-anti-thrust direction (T-AT direction) (when the inclination is positive, it falls to the anti-thrust side, and when negative, it falls to the thrust side). The solid line is data in the front-rear direction (F-R direction).

  Regarding the piston behavior, a gap sensor for measuring the distance between the piston and the sleeve is provided on the thrust side, the anti-thrust side of the entire circumferential skirt portion (having a constant width in the direction of the piston central axis), Two each are embedded on the front side and the rear side (two are arranged with a distance in the direction of the central axis of the piston), and the distance between the piston and the sleeve is set at every predetermined crank angle during operation of the internal combustion engine. The piston behavior in each stroke of the internal combustion engine is obtained by measuring and calculating the inclination of the piston from the difference between the distance data of the two gap sensors.

In the vicinity of TDC (1) (so-called “explosion top dead center”) where the crank angle is close to the crank angle at which the in-cylinder pressure is maximum, the in-cylinder pressure is reduced in the thrust-to-thrust direction (T-AT direction). As the pressure increases, the side pressure acting on the piston causes a significant change in the piston from falling to the thrust side to falling to the thrust side, and again falls to the anti-thrust side.
At this time, the inclination hardly changes in the front-rear direction (F-R direction). This is thought to be because the main skirt on the thrust side is closely attached to the cylinder bore and restrained by the side pressure.

  In addition, when the crank angle is in the vicinity of TDC (3) (so-called “exhaust top dead center”), the piston acts on the piston once it has been turned to the thrust side. The piston is tilted in the front-rear direction due to changes in the lateral pressure. However, the absolute value of the inclination is small and the change in the lateral pressure is small, so that no piston hitting sound is generated.

  As shown in FIGS. 2 to 4 above, the crown portion 50, the land portion 61 extending downward from the edge of the crown portion 50, and the entire circumferential skirt extending further downward from the land portion 61 over the entire circumference. A first spherical surface 85 as a concave spherical surface for forming the spherical joint 14 with a lower skirt portion 97 as a portion and a spherical small end portion 24 protruding from the back surface 53 of the crown portion 50 and provided on the connecting rod 16. In the internal combustion engine piston 13 including the formed upper holding member 56 and lower holding member 57 as the spherical joint cup portion, the lower skirt portion 97 is provided on the thrust side and the anti-thrust side of the piston 13. Skirt portions 97A and 97B, a pair of sub skirt portions 97C and 97D arranged in a direction orthogonal to the thrust-anti-thrust direction of the piston 13, and these main skirts 97A, 97B and the connecting skirt portions 97E to 97H (only reference numerals 97E to 97G are shown) connecting the sub skirt portions 97C and 97D. Is shorter than the main skirt portions 97A and 97B in the direction of the conventional skirt portion, so that it has the same effect of suppressing the piston hitting sound as the conventional piston having the entire peripheral skirt portion, while reducing the area of the lower skirt portion 97. In addition, the piston 13 can be made lighter, the internal combustion engine 10 (see FIG. 1) can be rotated at a higher speed, and the output of the internal combustion engine can be improved.

  2-5, since the outer peripheral surface of the lower skirt portion 97 has a perfect circle shape, for example, compared to processing the outer peripheral surface of the lower skirt portion into an elliptical shape. Thus, processing of the lower skirt portion 97 is facilitated, and productivity can be improved.

  In this embodiment, as shown in FIGS. 3 and 4, the main skirt portions 97A and 97B and the auxiliary skirt portions 97C and 97D are rectangular in side view, but the present invention is not limited to this.

  The piston for an internal combustion engine of the present invention is suitable for a high-rotation high-power internal combustion engine.

It is sectional drawing of the internal combustion engine which employ | adopted the assembly type piston structure which concerns on this invention. It is sectional drawing of the piston and connecting rod which concern on this invention. It is a 1st side view of the piston concerning the present invention. It is a 2nd side view of the piston which concerns on this invention. It is a bottom view which shows the piston and connecting rod which concern on this invention. It is an effect | action figure which shows the behavior of the piston which concerns on this invention. It is a graph which shows each measurement result of the behavior of the piston concerning this invention, and an internal combustion engine cylinder pressure. It is a perspective view of the conventional piston for internal combustion engines.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 13 ... Piston, 14 ... Spherical joint, 16 ... Connecting rod, 24 ... Small end part, 50 ... Crown part, 53 ... Back surface, 56, 57 ... Cup part for spherical joints (upper holding member, lower holding member ), 85, 91 ... concave spherical surface (first spherical surface, second spherical surface), 61 ... land portion, 97 ... full circumference skirt portion (lower skirt portion), 97A, 97B ... main skirt portion, 97C, 97D ... sub skirt portion , 97E to 97H, a connecting skirt portion, 118, a central axis of the piston (an axis of the piston).

Claims (2)

A crown part, a land part extending downward from the edge of the crown part, an entire skirt part extending further downward from the land part over the entire circumference, and protruding from the back surface of the crown part and provided on the connecting rod In a piston for an internal combustion engine comprising a spherical joint cup portion in which a concave spherical surface for forming a spherical joint is formed with a spherical small end portion,
The circumferential skirt portion includes a main skirt portion provided on the thrust side and the anti-thrust side of the piston, a pair of sub skirt portions disposed in a direction orthogonal to the thrust-anti-thrust direction of the piston, and these It consists of a connected skirt that connects each of the main skirt and sub-skirt.
The piston for an internal combustion engine, wherein the sub skirt portion is formed shorter than the main skirt portion in the central axis direction of the piston.   The piston for an internal combustion engine according to claim 1, wherein the outer peripheral surface of the all-round skirt portion has a perfect circular shape.

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