JP4508136B2 - Piston of internal combustion engine - Google Patents

Description

  The present invention relates to an improvement of a piston of an internal combustion engine, particularly a piston in which a part of a piston skirt portion is exposed from a lower edge of a cylinder bore at a piston bottom dead center position.

  As a prior art in which a piston pin and a crank pin of a reciprocating internal combustion engine are connected by a multi-link type piston crank mechanism, Patent Document 1 previously proposed by the present applicant is known. This includes an upper link connected to the piston pin of the piston, a lower link connecting the upper link and the crank pin of the crankshaft, one end supported to be swingable to the engine body side, and the other end to the lower link. A control link coupled to the link. The upper link and the lower link are rotatably connected to each other via an upper pin, and the control link and the lower link are rotatably connected to each other via a control pin.

In such a multi-link type piston crank mechanism, it is possible to adjust the amount of change in piston stroke and piston top dead center position by appropriately setting the link configuration such as the length of each link. In particular, since the lower link has a kind of “lever” action, the piston stroke can be expanded while lowering the bottom dead center position of the piston as in Patent Document 2 previously proposed by the present applicant. Is possible. In the configuration described in Patent Document 2, when the piston is near the bottom dead center, the counterweight outer peripheral portion of the crankshaft passes through the side of the pin boss of the piston.
JP 2004-116434 A JP 2005-147068 A

  For example, when the bottom dead center position of the piston is relatively downward, that is, close to the rotation center of the crankshaft as in the above-mentioned Patent Document 2, the cylinder bore is also positioned relatively downward. In addition, a notch for avoiding interference with a moving body such as a counterweight or a lower link is required. In other words, a part of the cylinder bore lower edge extending in a cylindrical shape is cut out in a slit shape along the vertical direction. As a result, when the piston is near the bottom dead center, this notch Through, a part of the piston skirt portion is exposed.

  At the bottom dead center where the direction of movement of the piston is reversed, the sliding speed of the piston temporarily becomes 0, so it is generally difficult to secure a lubricating oil film between the cylinder bore and the piston skirt, and in the first place lubrication conditions Is severe. When the piston skirt portion is exposed from the cutout portion of the cylinder bore at such a bottom dead center position, it is more difficult to ensure lubrication at this portion. In particular, since the above-mentioned notch is generally slit-shaped in the vertical direction along the piston sliding direction, a straight edge along the vertical direction is formed on the side edge, and lubrication for this edge is prevented. It is very difficult.

  Further, in the above-mentioned multi-link type piston crank mechanism, the upper link is inclined with respect to the cylinder bore center line at the bottom dead center position, so that the thrust force that the piston is pressed against the cylinder bore wall surface becomes large, and this causes wear. There is also a problem.

Accordingly, the present invention includes the piston bottom dead point position in the piston of an internal combustion engine in part from the cylinder bore lower edge of the piston skirt is exposed, at least a portion of Oite the cylinder bore lower edge to the piston bottom dead point position location As described above, a recess or a cutout is provided in the skirt portion on the surface of the piston skirt portion. In one embodiment, the recess or notch has an upper end away from the piston ring groove and a lower end terminating at a position slightly above the lower end of the piston skirt. In another embodiment, the recess is deep at the upper part of the piston and shallow at the lower part of the piston, and its upper end is separated from the piston ring groove so that the lubricating oil is accumulated in a deep part of the upper part of the piston. In this case, the concave portion may be continuous to the lowermost end of the skirt portion.

This recess or notch, Oite the bottom dead center position location, direct contact with the cylinder bore lower edge and the skirt portion surface is prevented, thereby avoiding the problem of wear due to poor lubrication.

  If it is a recessed part, the rigidity reduction of a piston is small, and if it is a notch part, the process will be comparatively easy.

  In a more specific aspect, the lower edge of the cylinder bore has a notch for avoiding interference with the moving body of the piston crank mechanism in a part in the circumferential direction, and the notch on the cylinder bore side has a notch. Correspondingly, the recess or the notch is provided.

  When the cutout portion of the lower edge of the cylinder bore has a side edge extending linearly in the cylinder vertical direction, it is desirable to provide the recess or the cutout portion corresponding to the side edge.

  The piston of the present invention can also be applied to an internal combustion engine having a normal single link type piston crank mechanism, and in particular, an upper link having one end connected to the piston via a piston pin, and the upper link. The lower link is connected to the other end of the crankshaft via an upper pin and connected to the crankpin of the crankshaft, and one end is swingably supported on the engine body side, and the other end is connected to the lower link via a control pin. It is suitable for a multi-link type piston crank mechanism comprising a control link connected together.

  Further, the multi-link type piston crank mechanism can function as a variable compression ratio mechanism by changing the swing fulcrum position of the control link on the engine body side.

  According to the present invention, for example, when a part of the piston skirt portion is exposed through the notch portion at the lower edge of the cylinder bore, direct contact of the piston skirt portion with the edge of the notch portion is avoided, and the durability thereof is improved. improves.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. First, based on FIG. 1, the structure of the whole multilink type piston crank mechanism in which the piston of this invention is used is demonstrated.

  This is particularly configured as a variable compression ratio mechanism. As shown in the figure, a piston 1 is slidably disposed in a cylinder bore 6 formed in the cylinder block 5. In addition, one end of the upper link 11 is connected through the piston pin 2 so as to be swingable. The other end of the upper link 11 is rotatably connected to one end portion of the lower link 13 via a first connecting pin 12. The lower link 13 is swingably attached to the crankpin 4 of the crankshaft 3 at the center thereof. The lower link 13 is divided into two along a split surface passing through the center of the crankpin 4 for assembly to the crankpin 4 and is integrated by a pair of bolts 14. In addition, the point shown with the code | symbol 7 is the rotation center (center of the journal part not shown) of the crankshaft 3. As shown in FIG.

  One end of a control link 15 is rotatably connected to the other end of the lower link 13 via a second connecting pin 16. The other end of the control link 15 is swingably supported by a part of the internal combustion engine body, and the position of the swing fulcrum is displaced with respect to the internal combustion engine body in order to change the compression ratio. It is possible. Specifically, a control shaft 18 extending in parallel with the crankshaft 3 and a circular eccentric cam 19 provided eccentric to the control shaft 18 are provided. The other end of the control link 15 is rotatably fitted. The control shaft 18 is rotatably supported by the cylinder block 5 via a bearing bracket (not shown).

  Therefore, when the control shaft 18 is rotationally driven by an actuator (not shown) to change the compression ratio, the center position of the eccentric cam 19 serving as the swing fulcrum of the control link 15 moves relative to the engine body. As a result, the motion restraint condition of the lower link 13 by the control link 15 changes, the stroke position of the piston 1 with respect to the crank angle changes, and consequently the engine compression ratio changes.

  Here, the lower end 6a of the cylinder bore 6 extends downward in a cylindrical shape, and in order to avoid interference with the outer periphery of the counterweight 8, the upper link 11, etc., a part of the lower edge in the circumferential direction. In addition, a notch 9 having an appropriate shape is provided. Therefore, when the piston 1 is at the bottom dead center position as illustrated, a part of the piston 1 is exposed through the notch 9.

  FIG. 2 is a side view of the piston 1 according to the present invention. Since the piston 1 has a bilaterally symmetric shape, the right half is omitted. The piston 1 is integrally cast using, for example, an aluminum alloy, and a plurality of, for example, three piston ring grooves 22 are formed on the outer peripheral surface of a piston head 21 having a relatively thick disk shape. Is formed, and a skirt portion 23 is formed in a part of the circumferential direction of the piston 8 in the thrust-anti-thrust direction so as to extend from the outer peripheral surface along the cylindrical surface. As shown in the figure, the skirt portion 23 has a substantially rectangular projection when viewed from the direction orthogonal to the piston pin 2, and the width along the piston pin axial direction is smaller than the diameter of the piston 1. The total length of the pin 2 is substantially equal. That is, the skirt portion 23 is provided in a relatively small range in the circumferential direction. A pair of pin boss portions 24 that support both ends of the piston pin 2 are formed at the center of the back surface of the piston head 21. The counterweight 8 of the crankshaft 3 passes through the space 25 on the side of the pin boss portion 24 near the bottom dead center of the piston 1.

  On the surface of the skirt portion 23, a pair of concave portions 31 are formed in a strip shape along the vertical direction. The recess 31 corresponds to, for example, the side edge positions on both sides of the notch 9 provided on the lower edge of the cylinder bore 6 so as to correspond to the upper link 11, and when the piston 1 is at the bottom dead center position, The side edges along the vertical direction of the portion 9 are in a positional relationship such that they overlap within the recess 31. Note that the lower end of the recess 31 reaches the lower end of the skirt portion 23.

  According to the configuration of such an embodiment, the side edge and the skirt portion of the notch 9 are located at the bottom dead center where the sliding speed of the piston 1 is 0, and further at the position near the bottom dead center where the thrust load is maximum. Direct contact with the 23 surface is reliably avoided. Instead of the recess 31, a slit-shaped notch having the same shape as the illustrated recess 31 may be formed in the skirt portion 23. If the cutout portion is opened at the lower end of the skirt portion 23, the processing is easy. On the other hand, if it is the recessed part 31 like the example of illustration, compared with formation of a notch part, the rigidity fall of the skirt part 23 will not be accompanied.

  FIG. 3 shows a second embodiment in which the lower end of the vertically elongated recess 32 is terminated at a position slightly above the lower end of the skirt portion 23. That is, the concave portion 32 does not reach the lower end of the skirt portion 23. According to such a configuration, the portion indicated by the reference numeral 33 below the recess 32 remains as a part of the predetermined outer peripheral surface of the skirt portion 23, so that the piston 1 is a piston compared to the first embodiment described above. This is advantageous in suppressing the collision with the wall surface of the cylinder bore 6 caused by tilting around the pin 2, that is, the slap phenomenon. In addition, as described above, instead of the recess 31, a notch may be provided in the shape of a slit having the same shape as the recess 31 shown in FIG. Even in such a case, since the slit is not open at the lower end, the rigidity reduction of the skirt portion 23 is very small.

  Next, FIG. 4 shows a third embodiment in which a concave portion 34 is provided in the lower portion of the skirt portion 23 over the entire circumferential direction. In this embodiment, when the piston 1 is at the bottom dead center position, the lower edge of the cylinder bore 6 having the notch 9 is widely included in the recess 34. Therefore, the edge of the upper edge extending in the circumferential direction of the notch 9 also overlaps the recess 34, and direct contact thereof is avoided.

  Further, FIG. 5 shows a fourth embodiment in which a recess 35 extending in the entire circumferential direction similar to that in FIG. 4 is provided at the lower portion of the skirt portion 23 and its lower end 35a is terminated at a position higher than the lower end of the skirt portion 23. Is shown. In such a configuration, the rigidity of the skirt portion 23 is higher than that of the third embodiment of FIG. 4 and is advantageous in suppressing the slap phenomenon.

  Next, FIG. 6 shows an example of a cross-sectional shape of the recess 41 when the recess 41 reaching the lower end of the skirt 23 is provided as shown in FIG. In this example, the depth of the concave portion 41 in the piston radial direction is deepest at the upper end 41a of the concave portion 41, and the depth gradually decreases to a certain intermediate point 41b, and from this intermediate point 41b to the lowermost end 41c (in other words, the skirt The depth is constant up to the bottom of the portion 23). That is, from the upper end 41a to the intermediate point 41b, it becomes a recessed part of a wedge-shaped cross section, and from the intermediate point 41b, it is a shallow recessed part. The imaginary line 42 indicates the reference outer surface position of the skirt portion 23.

  In such a configuration, the lubricating oil accumulates in a large volume portion near the upper end 41a of the recess 41, and when the piston 1 reverses at the bottom dead center and rises as indicated by an arrow, let the interior of the recess 41 advance downward. And At this time, since the depth of the recess 41 gradually decreases, the pressure increases. Accordingly, the load supporting action of the lubricating oil is increased, and the contact between the cylinder bore 6 and the surface of the skirt portion 23 is avoided, and reliable lubrication is performed. Further, the lower part from the intermediate point 41b to the lowermost end 41c is shallow in depth, is relatively close to the wall surface of the cylinder bore 6, and sufficient lubricating oil is supplied from the upper end 41a side. A large squeeze effect can be obtained, and the impact load applied to the skirt portion 23 can be reduced.

  FIG. 7 shows an example of the recesses 43 having different cross-sectional shapes. In this example, the upper portion 43a is deep and the lower portion 43b is a shallow step-like concave portion. However, the step portion 43c at the upper end of the concave portion 43 has the curvature radius as the depth of the concave portion 43 (upper portion 43a) and a reference radius. An R surface having a radius center is formed on an imaginary line 42 indicating the outer surface. In addition, the lower end of the upper portion 43a, that is, the step portion 43d serving as a boundary between the upper portion 43a and the lower portion 43b, is expressed by the relative depth of the upper portion 43a with respect to the lower portion 43b (that is, the difference in depth between the upper portion 43a and the lower portion 43b). An R surface having a radius and having a radius center at a position along the bottom surface of the upper portion 43a is formed. That is, the direction of the unevenness on the R surface is reversed between the upper step portion 43c and the lower step portion 43d. Even in this configuration, the same effect as the embodiment of FIG. 6 can be obtained. Further, in this configuration, it is possible to easily process using a cutting tool having a predetermined diameter.

Structure explanatory drawing which shows the multilink type piston crank mechanism in which the piston of this invention is used. The side view of the piston which shows 1st Example. The side view of the piston which shows 2nd Example. The side view of the piston which shows 3rd Example. The side view of the piston which shows 4th Example. Sectional drawing which shows an example of the cross-sectional shape of a recessed part. Sectional drawing which shows the example from which the cross-sectional shape of a recessed part differs.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Piston 23 ... Skirt part 31, 32, 34, 35, 41, 43 ... Recessed part

Claims (10)

In the piston of the internal combustion engine in which a part of the piston skirt portion is exposed from the lower edge of the cylinder bore at the piston bottom dead center position,
A recess is provided on the surface of the piston skirt so as to include at least a part of the lower edge of the cylinder bore at the piston bottom dead center position .
The piston of the internal combustion engine , wherein the upper end of the recess is separated from the piston ring groove, and the lower end thereof is terminated at a position slightly above the lower end of the piston skirt portion . In the piston of the internal combustion engine in which a part of the piston skirt portion is exposed from the lower edge of the cylinder bore at the piston bottom dead center position,
A notch is provided in the piston skirt so as to include at least a part of the lower edge of the cylinder bore at the piston bottom dead center position,
The notch portion has an upper end separated from the piston ring groove, and a lower end thereof is terminated at a position slightly above the lower end of the piston skirt portion . In the piston of the internal combustion engine in which a part of the piston skirt portion is exposed from the lower edge of the cylinder bore at the piston bottom dead center position,
  A recess is provided on the surface of the piston skirt so as to include at least a part of the lower edge of the cylinder bore at the piston bottom dead center position.
  The piston of the internal combustion engine, wherein the recess is deep at the upper part of the piston and shallow at the lower part of the piston, and the upper end thereof is separated from the piston ring groove so that the lubricating oil accumulates in a deep part of the upper part of the piston. The lower edge of the cylinder bore has a notch for avoiding interference with the moving body of the piston crank mechanism in a part in the circumferential direction, and the recess or the notch is provided corresponding to the notch on the cylinder bore side. The piston of the internal combustion engine according to any one of claims 1 to 3 , wherein the piston is provided. The notch portion of the lower edge of the cylinder bore has a side edge extending linearly in the cylinder vertical direction, and the recess or the notch portion is provided corresponding to the side edge. The piston of the internal combustion engine according to 4 . The piston of the internal combustion engine according to claim 3 , wherein the concave portion is continuous to the lowermost end of the skirt portion. The stepped portion that becomes the boundary between the surface of the skirt portion above the concave portion and the upper end of the concave portion has an R surface having a radius of curvature as the radius of curvature and a center of the radius at a position along the surface of the skirt portion. A piston for an internal combustion engine according to any one of claims 1 and 3-6 . The step part which becomes a boundary between the surface of the skirt part below the concave part and the lower end of the concave part has an R surface having a concave part depth as a radius of curvature and a center of the radius at a position along the bottom face of the concave part. Item 8. A piston for an internal combustion engine according to any one of Items 1 to 3-7 . An upper link having one end connected to the piston via a piston pin, a lower link connected to the other end of the upper link via an upper pin and connected to the crank pin of the crankshaft, and one end on the engine body side And a control link having the other end connected to the lower link via a control pin, and used in a multi-link type piston crank mechanism. The piston of the internal combustion engine according to any one of 8 . The piston of an internal combustion engine according to claim 9 , wherein the piston crank mechanism constitutes a variable compression ratio mechanism by changing a swing fulcrum position of the control link on the engine body side.

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