JP2007232112A - Bearing structure of double-link piston crank - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve durability of a link connecting part and to reduce the cost. <P>SOLUTION: A lower link 13 and an upper link constituting a double link piston crank mechanism are rockably connected to each other by a first connecting pin supported in a full-float form. A first bearing part 21 of the lower link 13 is forked to support both end parts of the first connecting pin, and the upper link is interposed between both of them. A bearing hole 22 is formed and penetrated in the first bearing part, and the bearing hole 22 is not provided with the conventional crowning 107 for relaxing edge contact, so that one simple cylindrical surface is formed. This connecting part is rocked so that satisfactory oil film formation is enabled by wedge effect in a space up to the first connecting pin, and omission of the crowning can enlarge an oil film formation area to improve the lubricating state. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a piston crank mechanism of a reciprocating internal combustion engine, and more particularly to a full float type bearing structure of a link connecting portion in a multi-link type piston crank mechanism.

  For example, a piston and a connecting rod of an internal combustion engine are connected so as to be able to swing with each other via a connecting pin, that is, a piston pin, and thus can be regarded as a kind of link mechanism. In general, a piston pin having a simple cylindrical shape is used, and the piston pin is inserted between the pin boss portion on the piston side and the pin boss portion on the small end portion of the connecting rod, and both of them swing each other. Connected as possible.

  Here, as a relationship between the piston pin and each pin boss portion, a full float type configuration (for example, Patent Document 1) in which the piston pin is rotatable with respect to both the connecting rod side and the piston side pin boss portion is often employed. However, in such a configuration, the bearing hole of the bifurcated pin boss portion on the piston side that supports the piston pin is generally subjected to crowning for avoiding so-called edge contact.

  That is, as illustrated in FIG. 1, bearing holes 105 and 106 are respectively formed in the pair of pin boss portions 102 on the piston 101 side and the pin boss portion 104 on the end of the connecting rod 103 so that a piston pin (not shown) can rotate. Although supported, a crowning 107 having a relatively gentle inclined surface (tapered surface) is provided at the end of the bearing hole 105 on the piston 101 side on the connecting rod 103 side. This is because the piston pin does not rotate so much with respect to the bearing hole 105 on the piston 101 side, and an oil film due to the wedge effect is difficult to form, so that the edge of the opening edge of the bearing hole 105 is prevented from making metal contact with the outer peripheral surface of the piston pin. I am trying.

In addition, the present applicant previously used a multi-link type piston crank mechanism as a variable compression ratio mechanism of a reciprocating internal combustion engine, and changed the piston top dead center position by moving a part of the link configuration. Various mechanisms have been proposed (for example, Patent Document 2). However, in a multi-link type piston crank mechanism that constitutes this type of variable compression ratio mechanism, it is also necessary to link the links so as to be swingable with a connecting pin. is there.
Japanese Utility Model Publication No. 4-26671 JP 2004-1224776 A

  The above-mentioned crowning process takes time and cost. Further, the oil film formation area is reduced only in the crowning portion in the inner peripheral surface of the bearing hole, and the lubrication state becomes severe.

  In the present invention, at least one link connecting portion has rotational acceleration during operation, and is located between the bifurcated first bearing portion of one link member and the bifurcated first bearing portion. And a second bearing portion of the other link member, wherein the first bearing is a multi-link piston crank mechanism of an internal combustion engine configured as a full float bearing in which a connecting pin is rotatably fitted in each bearing hole. The bearing hole of the part is characterized by comprising a single cylindrical surface not provided with a crowning.

  FIG. 2A shows a general principle of oil film generation. It is generally considered that the oil film is caused by a squeeze effect and a wedge effect. Among these, the wedge effect is an effect that pressure is generated by the lubricating oil being caught between the bearing surface 112 and the shaft 111 as indicated by an arrow by the relative rotation of the shaft 111 and the bearing surface 112. It is.

  As described above, for example, in the link connecting portion between the piston 101 and the connecting rod 103, the pin boss portion 102 on the piston 101 side does not rotate but only reciprocates along the cylinder. The oil film pressure is generated only by the squeeze effect, with the relative speed with the pin being small and almost no oil film due to the wedge effect. Therefore, the oil film pressure is small and metal contact is likely to occur. For this purpose, the edge contact is reduced by providing the crowning 107 as described above. However, as shown in FIG. 2B, the oil film formation region (the region indicated by hatching) is reduced by the crowning 107.

  On the other hand, in the link connecting portion having rotational acceleration during operation, a sufficiently large relative sliding speed is ensured between the contact surfaces of the bearing hole and the connecting pin of the bifurcated first bearing portion, and the lubricating oil film due to the wedge effect is formed. It becomes easier to form. Therefore, as shown in FIG. 2 (c), by increasing the oil film forming area without providing crowning, the lubrication state is improved and the bearing durability is improved.

  The opening edge of the bearing hole that does not include the crowning may be provided with a general minimum necessary chamfer. The chamfering in this case is very small, different from crowning.

  In one aspect of the present invention, the connecting pin has a chamfered portion at the end, and the chamfering applied to the inner opening edge of the bearing hole of the pair of first bearing portions has an axial width thereof. Is smaller than the axial width of the chamfered portion of the connecting pin. Thus, by providing a sufficiently large chamfered portion on the connecting pin, the assemblability is improved without adversely affecting the lubrication performance.

  Moreover, in one aspect of the present invention, the rigidity of the first bearing portion is lowered by providing a thin portion around the bearing hole of the first bearing portion. For example, a pair of 1st bearing parts are extended along the end surface of the axial direction of a link member, and the ditch | groove part is formed in the inner surface along the circumference | surroundings of a bearing hole. Accordingly, the first bearing portion is deformed so as to be inclined in the axial direction following the bending deformation of the connecting pin, and the edge contact of the bearing hole opening edge is relaxed.

  Furthermore, in one aspect of the present invention, the pair of bearing holes in the first bearing portion are tapered so that the diameter of the bearing holes on the inside of the pair of first bearing portions is larger than the diameter on the outside. It has a shape. Thereby, the bending deformation of the connecting pin is allowed and the edge contact of the bearing hole opening edge is relaxed.

  If the surface roughness of the bearing hole of the first bearing portion is rougher than the surface roughness of the connecting pin, the amount of oil film is increased due to the wedge effect, the lubricating oil film pressure is easily generated, and the lubrication state is improved. .

  The first bearing portion may include a bushing material. Moreover, you may make it give DLC (diamond-like carbon) process to the surface of a connection pin.

  The piston crank mechanism includes, for example, an upper link having one end connected to a piston via a piston pin, and 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 a control link having one end pivotably supported on the engine body side and the other end coupled to the lower link via a control pin.

  And the bearing structure of this invention is applied to the link connection part of the said lower link and the said upper link, for example, and a lower link side is comprised in the forked shape as a 1st bearing part. Or conversely, the upper link side is formed in a bifurcated shape as the first bearing portion. In the former configuration, since the upper link side is a small bearing portion fitted into the center portion of the upper pin, the inertia weight of the entire engine is reduced, and consequently the bearing load is reduced and the bearing durability is improved. In the latter configuration, the bearing portion on the lower link side is reduced in size, and the distance between the shafts between the upper pin and the crank pin in the lower link can be reduced, resulting in a compact configuration.

  According to the present invention, a large oil film formation area of the bearing hole of the first bearing portion can be secured, the lubrication state can be improved, and the crowning processing step and processing cost can be reduced.

  Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 3 shows a variable compression ratio mechanism of an internal combustion engine using a multi-link type piston crank mechanism as an example of a piston crank mechanism to which the bearing structure according to the present invention is applied.

  As shown in the figure, a piston 1 is slidably disposed in a cylinder 6 formed in a cylinder block 5, and one end of an upper link 11 can swing on the piston 1 via a piston pin 2. It is connected to. 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. Note that the lower link 13 is actually divided into two along a split surface passing through the center of the crankpin 4 for assembly to the crankpin 4 and integrated with each other by bolts. The crankshaft 3 is rotatably supported on the cylinder block 5 by a crank bearing bracket 7.

  One end of a control link 15 is rotatably connected to the other end of the lower link 13 via a second connecting pin 14. 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 between the crank bearing bracket 7 and the control bearing bracket 8.

  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.

  In the piston crank mechanism as described above, in the link connecting portion between the lower link 13 and the upper link 11 by the first connecting pin 12, the first bearing portion on the lower link 13 side supports both ends of the first connecting pin 12. It has a bifurcated shape and is configured to sandwich the second bearing portion on the upper link 11 side in the middle. In addition, the 1st connection pin 12 is not being fixed to any link member as a full float type, and can rotate with respect to both.

  FIG. 4 shows the configuration of the pair of first bearing portions 21 of the lower link 13. As shown in the figure, the first bearing portion 21 extends along both axial end surfaces of the lower link 13. In each case, a bearing hole 22 is formed. The bearing hole 22 does not have a crowning (indicated by the imaginary line 107 for comparison), and is entirely constituted by a single cylindrical surface. In addition, the edge 22a of the opening edge is subjected to the minimum necessary chamfering (not shown) for removing burrs and the like, similarly to the edge of other portions.

  Unlike the bearing portion of the piston pin 2, the link connecting portion by the first connecting pin 12 has a large relative angular velocity with the first connecting pin 12 because the link connecting portion largely swings. Therefore, the oil film pressure due to the wedge effect is sufficiently generated. Therefore, even if no crowning is provided, the so-called edge contact in which the edge 22a of the inner opening edge makes metal contact with the first connecting pin 12 hardly occurs. In such a case, durability is improved by enlarging the oil film forming region by that amount without providing crowning.

  For example, as shown in FIG. 5, it is desirable to provide a sufficiently large chamfered portion 23 at the end portion of the first connecting pin 12, thereby improving the assembling property to the bearing hole 22 without the crowning. To do. Note that the axial width of the chamfered portion 23 is much larger than the chamfered edge 22a of the bearing hole 22 opening edge.

  FIG. 6 shows a different configuration of the first bearing portion 21 of the lower link 13. In the second embodiment, the base portion of each first bearing portion 21 that extends while branching from the main body portion of the lower link 13, particularly the inner surfaces of the pair of first bearing portions 21 that face each other, Concave grooves 25 are respectively formed along the periphery of the bearing hole 22.

  Accordingly, the axial rigidity of the first bearing portion 21 is reduced, and when the first connecting pin 12 is bent and deformed as shown in FIG. The part 21 is easily deformed so as to fall down in the axial direction. Therefore, the edge 22a of the opening edge of the bearing hole 22 that does not include the crowning is less likely to make metal contact with the outer peripheral surface of the first connecting pin 12, and durability is improved.

  Next, FIG. 8 shows a third embodiment in which the bearing hole 22 of the first bearing portion 21 is tapered. The pair of bearing holes 22 has a loosely tapered shape symmetrical to each other, and in particular, has a tapered shape such that the diameter on the inner surface of the pair of first bearing portions 21 is larger than the diameter on the outer surface. Yes. As a result, when the first connecting pin 12 is bent and deformed as shown in FIG. 7 due to the load applied from the upper link 11, the inner edge 22 a of the opening edge is less likely to make metal contact with the outer peripheral surface of the first connecting pin 12.

Explanatory drawing which shows the crowning of a general piston pin bearing part. Explanatory drawing which shows the oil film generation | occurrence | production by a wedge effect. Sectional drawing of the principal part of an internal combustion engine which shows the whole structure of a multiple link type piston crank mechanism. Sectional drawing of the lower link principal part which shows one Example of the bearing structure which concerns on this invention. The top view of the 1st connection pin provided with the chamfering part. Sectional drawing of the lower link principal part which shows 2nd Example. Explanatory drawing which shows the deformation | transformation state of a 1st connection pin. Sectional drawing of the lower link principal part which shows 3rd Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Upper link 12 ... 1st connection pin 13 ... Lower link 21 ... 1st bearing part 22 ... Bearing hole

Claims (11)

  The at least one link connecting portion has a rotational acceleration during operation, and the one link member has a bifurcated first bearing portion and the other link member located between the bifurcated first bearing portion. In a double link type piston crank mechanism of an internal combustion engine configured as a full float bearing in which a coupling pin is rotatably fitted in each bearing hole. Consists of a single cylindrical surface without crowning, and a bearing structure for a multi-link piston crank mechanism.   The connecting pin has a chamfered portion at the end, and the chamfering applied to the opening edge inside the bearing hole of the pair of first bearing portions has an axial width that is the chamfered portion of the connecting pin. The bearing structure of the multi-link type piston crank mechanism according to claim 1, wherein the bearing structure is smaller than the axial width.   The bearing structure for a multi-link piston crank mechanism according to claim 1 or 2, wherein a thin wall portion is provided around a bearing hole of the first bearing portion to reduce the rigidity of the first bearing portion.   The pair of first bearing portions extends along an end surface in the axial direction of the link member, and a concave groove portion is formed on the inner surface along the periphery of the bearing hole. The bearing structure of the double link type piston crank mechanism as described.   The pair of bearing holes of the first bearing part have a tapered shape symmetrical to each other such that the diameter of the bearing hole inside the pair of first bearing parts is larger than the diameter of the outside of the pair of first bearing parts. The bearing structure of the multilink type piston crank mechanism in any one of Claims 1-4.   The bearing structure of the multi-link type piston crank mechanism according to any one of claims 1 to 5, wherein the surface roughness of the bearing hole of the first bearing portion is rougher than the surface roughness of the connecting pin.   The bearing structure of the multi-link type piston crank mechanism according to any one of claims 1 to 6, wherein the first bearing portion is provided with a bushing material.   The bearing structure of the multi-link type piston crank mechanism according to any one of claims 1 to 7, wherein the connecting pin is subjected to DLC processing.   The piston crank mechanism includes 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. 9. A control link, one end of which is swingably supported on the engine body side and the other end is connected to the lower link via a control pin. A bearing structure for a multi-link piston crank mechanism according to claim 1.   The bearing of the multi-link type piston crank mechanism according to claim 9, wherein the bearing is applied to a link connecting portion between the lower link and the upper link, and the lower link side is formed in a bifurcated shape as the first bearing portion. Construction. The bearing of the multi-link type piston crank mechanism according to claim 9, wherein the bearing is applied to a link connecting portion between the lower link and the upper link, and the upper link side is formed in a bifurcated shape as the first bearing portion. Construction.

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