阅读说明：本技术 烧结金属制连杆 (Connecting rod made of sintered metal ) 是由 山下智典 于 2020-02-26 设计创作，主要内容包括：烧结金属制连杆(10)一体地具有大端部(11)、小端部(12)以及杆部(13)。在该烧结金属制连杆(10)中,在贯通孔(11a、12a)开口的正反一方的表面(11c～13c)中的大端部(11)与杆部(13)之间以及小端部(12)与杆部(13)之间分别形成有通过压缩成型而形成的成型模分割痕迹(14a、14b),大端部(11)与杆部(13)的密度差以及小端部(12)与杆部(13)的密度差均为4％以下。(A sintered metal connecting rod (10) integrally has a large end portion (11), a small end portion (12), and a rod portion (13). In the sintered metal connecting rod (10), mold split marks (14a, 14b) formed by compression molding are formed between the large end portion (11) and the rod portion (13) and between the small end portion (12) and the rod portion (13) on the front and back surfaces (11 c-13 c) of the openings of the through holes (11a, 12a), respectively, and the density difference between the large end portion (11) and the rod portion (13) and the density difference between the small end portion (12) and the rod portion (13) are both 4% or less.)

1. A sintered metal connecting rod, which is obtained by compression molding and sintering metal powder,

the sintered metal connecting rod integrally includes:

a large end portion and a small end portion, both of which are annular and have a through hole at an inner periphery; and

a rod portion connecting the large end portion and the small end portion,

forming die dividing marks formed by the compression molding between the large end and the rod portion and between the small end and the rod portion on the front and back surfaces of the opening of the through hole,

the density difference between the large end and the rod part and the density difference between the small end and the rod part are both less than 4%.

2. The sintered metal connecting rod as claimed in claim 1,

the parallelism between the through-holes of the large end and the small end is not more than 0.5/100.

3. A link module, comprising:

a connecting rod made of sintered metal according to claim 1 or 2; and

and a bearing raceway ring fitted to at least one of the through hole of the large end portion and the through hole of the small end portion of the sintered metal connecting rod with interference.

Technical Field

The present invention relates to a connecting rod (hereinafter, referred to as a connecting rod) for connecting a crankshaft and a piston of an engine, and more particularly to a sintered metal connecting rod.

Background

The connecting rod integrally has: a large end portion coupled to a crankshaft of an automobile engine via a bearing or the like; a small end portion connected to the piston; and a rod portion connecting the large end portion and the small end portion. As such a connecting rod, a sintered metal connecting rod that can be produced at a lower cost than other machining methods is known (for example, see patent document 1). Such a connecting rod is manufactured, for example, through a compression molding step of obtaining a green compact by compression molding a metal powder, a sintering step of sintering the green compact to obtain a sintered body, and a shaping step of performing shaping treatment on the sintered body (see, for example, patent document 2).

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2007-284769

Patent document 2: japanese laid-open patent publication No. 2017-62015

Disclosure of Invention

Problems to be solved by the invention

However, in the case where the connecting rod is formed of sintered metal as described above, there is a problem that the shape accuracy of the large end portion and the small end portion is lowered due to strain generated by sintering. Specifically, at the time of completion of the compression molding, the workpiece (green compact) is warped like a dome in the longitudinal direction thereof. The warpage (deformation) becomes more remarkable by sintering. Here, it is considered that the above-mentioned distortion can be eliminated if the shaping step after sintering described in patent document 2 is used, but in reality, it is not easy to completely or sufficiently eliminate the above-mentioned warpage. If a non-negligible amount of warping remains in the connecting rod, the parallelism between the through-holes of the large end portion and the through-holes of the small end portion located at both ends in the longitudinal direction of the connecting rod increases, which may lead to early wear due to contact of one end of a bearing used by being attached to the through-holes, or the generation of abnormal noise due to inclination of the piston.

In view of the above circumstances, a technical problem to be solved in the present specification is to provide a connecting rod that can obtain the advantage of cost reduction by sintered metal, and can suppress the occurrence of wear and abnormal noise by eliminating or suppressing warpage in the direction along the longitudinal direction of the rod portion.

Means for solving the problems

The above object is achieved by the sintered metal connecting rod of the present invention. That is, the connecting rod is formed by compression molding and sintering metal powder, and is characterized in that the sintered metal connecting rod integrally includes: a large end portion and a small end portion, both of which are annular and have a through hole at an inner periphery; and a rod portion connecting the large end portion and the small end portion, wherein a mold division mark formed by compression molding is formed between the large end portion and the rod portion and between the small end portion and the rod portion on one of the front and back surfaces of the opening of the through hole, and the density difference between the large end portion and the rod portion and the density difference between the small end portion and the rod portion are both 4% or less.

In this way, in the connecting rod of the present invention, the die-dividing marks formed by compression molding are formed between the large end portion and the rod portion and between the small end portion and the rod portion on the front and back surfaces where the through-hole opens. In the case of such a sintered metal connecting rod having a division trace formed thereon, it is known that compression molding is performed at the above-mentioned position using a divided molding die. Since the density of the sintered metal can be controlled by the relative compression amount of the raw material powder at the time of compression molding, for example, by independently adjusting the compression amount of the raw material powder at each of the rod portion, the large end portion, and the small end portion, a connecting rod having a density difference between the large end portion and the rod portion and a density difference between the small end portion and the rod portion of 4% or less can be obtained. If the density difference is 4% or less, warpage of the compression-molded body (green compact) can be suppressed, and warpage of the sintered body can be suppressed. Therefore, the parallelism between the through hole of the large end portion and the through hole of the small end portion can be reduced, and the occurrence of early wear due to the contact of one ends of the bearings attached to these through holes and the occurrence of abnormal noise due to the inclination of the piston can be prevented as much as possible.

In the sintered metal connecting rod of the present invention, the parallelism between the through hole of the large end portion and the through hole of the small end portion may be set to be equal to or less than 0.5/100.

The parallelism is defined by the following criteria. That is, the center line of each through hole is acquired from coordinates measured at a plurality of points on the inner peripheral surface of the through hole at the large end portion and the through hole at the small end portion. Assuming that a virtual center line parallel to one center line is extended by Xmm (for example, 100mm) from a state where the inner periphery of the through-hole overlaps the other center line, a virtual circle having a diameter Ymm (for example, 0.5mm) is defined in the vicinity of a point on the virtual center line at Xmm, and if a virtual circle in which the other center line is extended by Xmm is included in the virtual circle, it is defined that the parallelism between the through-hole at the large end and the through-hole at the small end is within Φ Y/X.

By setting the parallelism between the through-hole of the large end portion and the through-hole of the small end portion to be equal to or less than Φ 0.5/100 in this manner, the assembly accuracy of the components (bearings, pistons, etc.) attached to these through-holes can be ensured. Therefore, the performance of the link module in which these components are attached to the link can be ensured, and the early wear of the bearing and the generation of abnormal noise can be more reliably prevented.

In addition, the sintered metal connecting rod described above is advantageous in that it can be manufactured at low cost by sintered metal, and can suppress the occurrence of wear and abnormal noise by reducing the parallelism between the through hole of the large end portion and the through hole of the small end portion, and therefore, for example, it can be suitably provided as a connecting rod module including the sintered metal connecting rod described above and a bearing raceway ring fitted into at least one of the through hole of the large end portion and the through hole of the small end portion of the connecting rod with interference.

Effects of the invention

As described above, according to the present invention, it is possible to provide a connecting rod which can obtain the advantage of cost reduction due to the sintered metal, and which can suppress the occurrence of wear and abnormal noise by reducing the parallelism between the through hole of the large end portion and the through hole of the small end portion.

Drawings

Fig. 1 is a cross-sectional view of a link module.

Fig. 2 is a top view of the connecting rod shown in fig. 1.

Fig. 3 is a sectional view taken along line a-a of the connecting rod shown in fig. 2.

Fig. 4 is an enlarged view of a portion B of the link shown in fig. 3.

Fig. 5 is a sectional view of a molding die used in the compression molding step, which corresponds to a portion along the line C-C of the connecting rod shown in fig. 2, and which shows a state in which the raw material powder is filled.

Fig. 6 is a sectional view of a mold used in the compression molding step, which corresponds to a portion along the line C-C of the connecting rod shown in fig. 2, and which shows a state when the compression molding is completed.

Detailed Description

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

The link module 1 according to one embodiment of the present invention is incorporated in an engine, for example, a small engine (general-purpose engine) provided in a bush cutter, a blower, or the like, and having an exhaust gas volume of 100cc or less (particularly, 50cc or less). As shown in fig. 1, the link module 1 is composed of a link 10 and bearings 20 and 30.

As shown in fig. 2 and 3, the link 10 integrally has a large end portion 11, a small end portion 12, and a rod portion 13 connecting these. The large end portion 11 and the small end portion 12 are both annular, and through holes 11a and 12a are formed in the inner peripheries of the large end portion 11 and the small end portion 12. The rod portion 13 is formed with an elongated through hole 13a that is elongated in the extending direction of the rod portion 13 (the left-right direction in fig. 1 to 3). For convenience of description, the extending direction of the rod portion 13 of the link 10 (the left-right direction in fig. 1 to 3) is referred to as the longitudinal direction, the center line direction of the through hole 11a of the large end portion 11 and the small end portion 12 and the through hole 12a of the small end portion 12 (the vertical direction in fig. 1 and 3) is referred to as the thickness direction, and the direction perpendicular to the longitudinal direction and the thickness direction (the vertical direction in fig. 2) is referred to as the width direction.

The connecting rod 10 having the above-described structure is formed of a sintered metal, specifically, an iron-based sintered metal containing iron as a main component (for example, iron contained in an amount of 80 mass% or more, preferably 90 mass% or more). The iron-based sintered metal is made of, for example, nickel-molybdenum steel, and specifically, for example, a composition of 0.1 to 5 mass% (preferably 0.5 to 4 mass%) nickel, 0.1 to 3 mass% (preferably 0.3 to 2.5 mass%) molybdenum, 0.05 to 1 mass% (preferably 0.1 to 0.5 mass%) carbon, and the balance iron is given as an example. The composition of the sintered metal may be set so that the young's modulus of the connecting rod 10 is 120GPa to 180 GPa.

The density of the connecting rod 10 is set to 7.0g/cm, for example³The concentration is preferably set to 7.2g/cm³The above. On the other hand, the density of the connecting rod 10 is set to 7.8g/cm, which is an ideal density of the molten material³Hereinafter, the density of the connecting rod 10 is preferably set to 7.6g/cm in consideration of the powder pressing property during compression molding and the like³The following.

Here, the density difference between the large end portion 11 and the rod portion 13 and the density difference between the small end portion 12 and the rod portion 13 are set to 4% or less, and preferably 3% or less. In this case, the density of the large end portion 11 and the density of the small end portion 12 are preferably set to be equal as much as possible, and for example, the density of the large end portion 11 is preferably set to be 7.2g/cm³Above and 7.5g/cm³Hereinafter, the density of the small end portion 12 is set to 7.2g/cm³Above and 7.5g/cm³The following. As described above, the density of the stem portion 13 is preferably set to 7.1g/cm as long as the difference between the density of the stem portion and the density of the large end portion 11 and the small end portion 12 is 4% or less³Above and 7.5g/cm³The following.

Further, by suppressing both the density difference between the large end portion and the rod portion and the density difference between the small end portion and the rod portion to 3% or less, the warping of the connecting rod can be suppressed more effectively, and therefore the parallelism between the through hole of the large end portion and the through hole of the small end portion can be reduced more reliably. Therefore, variation per product can be suppressed, and a high-quality connecting rod can be stably provided. In addition, in the connecting rod formed so that the split trace remains, the density of the large end portion, the small end portion, and the rod portion can be easily controlled by the compression amount of the split mold, and therefore, even if the density difference is set to 3% or less, the productivity can be ensured.

In the present embodiment, the thickness direction dimension D3 of the rod portion 13 is smaller than either one of the thickness direction dimension D1 of the large end portion 11 and the thickness direction dimension D2 of the small end portion 12 (see fig. 3). In fig. 3, the upper side surface 13b of the rod portion 13 is located on the thickness direction center side (lower side in fig. 3) of the connecting rod 10 with respect to any one of the upper side surface 11b of the large end portion 11 and the upper side surface 12b of the small end portion 12, and the lower side surface 13c of the rod portion 13 is located on the thickness direction center side (upper side in fig. 3) with respect to any one of the lower side surface 11c of the large end portion 11 and the lower side surface 12c of the small end portion 12. In this case, the step difference between the upper surface 11b of the large end 11 or the upper surface 12b of the small end 12 and the upper surface 13b of the rod 13, and the step difference between the lower surface 11c of the large end 11 or the lower surface 12c of the small end 12 and the lower surface 13c of the rod 13 are each 1mm or less, for example, about 0.5 mm.

As shown in fig. 3, division marks 14a and 14b of a mold 40 (see fig. 5) formed by compression molding, which will be described later, are formed between the lower surface 11c of the large end 11 where the through hole 11a opens and the lower surface 13c of the rod portion 13, and between the lower surface 12c of the small end 12 where the through hole 12a opens and the lower surface 13c of the rod portion 13, respectively.

In the present embodiment, as shown in fig. 4 in an enlarged manner, the lower inclined surface 15b is provided continuously with the rod portion 13-side end portion of the lower surface 11c of the large end portion 11, and the flat surface 16 is provided continuously with the rod portion 13-side end portion of the lower inclined surface 15 b. The flat surface 16 extends linearly in the thickness direction, extends in an arc shape along the periphery of the large end portion 11, and is continuous at its upper end with the lower side surface 13c of the rod portion 13. The flat surface 16 constitutes a division mark 14 a. Therefore, in this case, the lower surface 11c of the large end portion 11 is continuous with the lower surface 13c of the rod portion 13 via the lower inclined surface 15b and the flat surface 16. The lower inclined surface 15b and the flat surface 16 form a step between the large end portion 11 and the rod portion 13 (see fig. 3). Although not shown, a flat surface constituting the division mark 14b is also provided between the lower inclined surface 17b on the small end portion 12 side and the lower surface 13c of the rod portion 13. Although not shown, the flat surface has the same shape as the flat surface 16 on the large end portion 11 side and is connected at its upper end to the lower side surface 13c of the rod portion 13. Therefore, in this case, the lower surface 12c of the small end portion 12 is continuous with the lower surface 13c of the lever portion 13 via the lower inclined surface 17b and the flat surface. The lower inclined surface 17b and the flat surface form a step between the small end 12 and the rod 13 (see fig. 3).

In the present embodiment, the division marks 14a and 14b are formed only on the lower surface of the connecting rod 10, and are not formed on the upper surface of the connecting rod 10. Therefore, the upper surface 11b of the large end portion 11 and the upper surface 13b of the rod portion 13 are connected via the upper inclined surface 15 a. Therefore, in this case, the step between the large end portion 11 and the rod portion 13 is formed only by the upper inclined surface 15 a. Further, the upper surface 12b of the small end portion 12 and the upper surface 13b of the rod portion 13 are connected via an upper inclined surface 17 a. Therefore, in this case, the step between the small end portion 12 and the rod portion 13 is formed only by the upper inclined surface 17 a.

The parallelism between the through-hole 11a of the large end portion 11 and the through-hole 12a of the small end portion 12 is set to be not more than φ 0.5/100, preferably not more than φ 0.3/100. On the other hand, the parallelism between the through hole 11a of the large end portion 11 and the through hole 12a of the small end portion 12 is set to be equal to or greater than 0.1/100, preferably equal to or greater than 0.2/100, depending on the manufacturing capability in the manufacturing process of the sintered metal connecting rod 10.

As shown in fig. 1, for example, the bearing 20 includes: an outer ring 21 as a bearing raceway ring having a cylindrical raceway surface 21a on an inner peripheral surface thereof; a plurality of rollers (needle rollers) 22 housed in the inner periphery of the outer ring 21; and a retainer 23 that holds the plurality of rollers 22 at equal intervals in the circumferential direction. The bearing 30 has the same structure as the bearing 20, and the bearing 30 has: an outer ring 31 as a bearing raceway ring having a cylindrical raceway surface 31a on an inner peripheral surface thereof; a plurality of rollers 32 (needle rollers) housed in the inner periphery of the outer ring 31; and a retainer 33 that holds the plurality of rollers 32 at equal intervals in the circumferential direction.

The outer rings 21 and 31 are formed in a cylindrical shape, for example, and are fitted (i.e., press-fitted) and fixed to the through hole 11a of the large end portion 11 and the through hole 12a of the small end portion 12 of the connecting rod 10 with a predetermined interference. The outer rings 21 and 31 are formed of a material having a young's modulus higher than that of the connecting rod 10, specifically, a material having a young's modulus exceeding 180 Gpa. On the other hand, if the Young's modulus of the outer ring 21, 31 is too high, the processing becomes difficult, so the Young's modulus of the outer ring 21, 31 is preferably 240GPa or less.

The connecting rod 10 is manufactured through a compression molding step S1, a sintering step S2, and a shaping step S3. Hereinafter, each step will be described in detail.

(S1) compression Molding Process

In the compression molding step S1, a raw material powder M containing a metal powder as a main component is filled into the molding die 40 (both see fig. 5) and compression molded, thereby molding a green compact 110 (see fig. 6) having substantially the same shape as the connecting rod 10. In the present embodiment, a powder obtained by adding a carbon powder (e.g., graphite powder) and a lubricant (e.g., metal soap) to an alloy powder of iron, nickel, and molybdenum is used as the raw material powder M. Here, as shown in fig. 5, the molding die 40 includes a die 41, side cores 42a and 42b, a center core (not shown), a lower punch 43, and an upper punch 44. The side cores 42a and 42b correspond to the through hole 11a of the large end portion 11 and the through hole 12a of the small end portion 12, respectively, and the center core corresponds to the through hole 13a of the rod portion 13.

The lower surface of the upper punch 44 is provided with a first molding surface 44a corresponding to the upper side surface 13b of the rod portion 13 of the connecting rod 10, a second molding surface 44b corresponding to the upper side surface 11b of the large end portion 11, and a third molding surface 44c corresponding to the upper side surface 12b of the small end portion 12. In addition, in the present embodiment, the fourth molding surface 44d and the fifth molding surface 44e corresponding to the upper inclined surfaces 15a and 17a, respectively, are provided between the first molding surface 44a and the second molding surface 44b, and between the first molding surface 44a and the third molding surface 44 c. The first molding surface 44a of the upper punch 44 is located below the second molding surface 44b and the third molding surface 44c, and these first to fifth molding surfaces 44a to 44e are integrally provided to one upper punch 44.

A first molding surface 43a corresponding to the lower side surface 13c of the rod portion 13 of the connecting rod 10, a second molding surface 43b corresponding to the lower side surface 11c of the large end portion 11, and a third molding surface 43c corresponding to the lower side surface 12c of the small end portion 12 are provided on the upper surface of the lower punch 43. In addition, in the present embodiment, the fourth molding surface 43d and the fifth molding surface 43e corresponding to the lower inclined surfaces 15b, 17b, respectively, are provided between the first molding surface 43a and the second molding surface 43b, and between the first molding surface 43a and the third molding surface 43c, and the sixth molding surface and the seventh molding surface (not shown) corresponding to the flat surface 16 on the large end portion 11 side and the flat surface (not shown) on the small end portion 12 side are provided between the fourth molding surface 43d and the first molding surface 43a, and between the fifth molding surface 43e and the first molding surface 43 a.

Here, the lower punch 43 is constituted by a first dividing punch 45 having a first molding surface 43a, a second dividing punch 46 having a second molding surface 43b and a fourth molding surface 43d, and a third dividing punch 47 having a third molding surface 43c and a fifth molding surface 43 e. These first to third dividing punches 45 to 47 can be driven independently, and the timing of lifting and lowering and the vertical position can be controlled independently. Fig. 5 shows a case where the raw material powder M is charged in a state where the first molding surface 43a is located above the vertical position of the second molding surface 43b and the third molding surface 43c at the time of completion of molding. In addition, as described above, in the case where the lower punch 43 is composed of the three split punches 45 to 47, the sixth molding surface is composed of the side surface 45a of the first split punch 45 on the second split punch 46 side, and the seventh molding surface is composed of the side surface 45b of the first split punch 45 on the third split punch 47 side.

The die 41 is provided with a first molding surface 41a corresponding to the outer periphery of the connecting rod 10 (specifically, the outer peripheral surface of the large end portion 11), a second molding surface 41b corresponding to the outer peripheral surface of the small end portion 12, and a third molding surface (not shown) corresponding to the outer side surface of the rod portion 13. In this case, the upper surface 41c of the die 41 becomes a polished surface when the raw material powder M is filled.

Next, an example of the compression molding step S1 using the mold 40 having the above-described structure will be described. First, as shown in fig. 5, a chamber defined by the die 41, the side cores 42a and 42b, the center core (not shown), and the first to third dividing punches 45 to 47 as the lower punch 43 is filled with the raw material powder M. At this time, the first molding surface 43a as the upper surface of the first dividing punch 45 is set at a position lower than the upper surface 41c of the die 41, and on the other hand, is set at a position higher than the second molding surface 43b as the upper surface of the second dividing punch 46 and the third molding surface 43c as the upper surface of the third dividing punch 47. More precisely, the first molding surface 43a is set at a position higher than the step difference between the large end portion 11 and the rod portion 13 with respect to the second molding surface 43b, and at a position higher than the step difference between the small end portion 12 and the rod portion 13 with respect to the third molding surface 43 c. In this state, the raw material powder M is filled so that the upper surface 41c of the die 41 becomes a ground surface, and thereby the region (chamber) sandwiched by the die 41, the side cores 42a and 42b, and the first to fifth molding surfaces 43a to 43e of the lower punch 43 is filled with the raw material powder M.

At this time, for example, the height positions of the respective split punches 45, 46 are set so that the ratio of the filling height of the raw material powder M on the first molding surface 43a to the thickness direction dimension D3 of the rod portion 13 to be molded by the first molding surface 43a (i.e., the compression ratio of the rod portion 13) is smaller than the ratio of the filling height of the raw material powder M on the second molding surface 43b to the thickness direction dimension D1 of the large end portion 11 to be molded by the second molding surface 43b (i.e., the compression ratio of the large end portion 11). Similarly, the height positions of the split punches 45 and 47 are set so that the compression ratio of the rod portion 13 is smaller than the ratio of the filling height of the raw material powder M in the third molding surface 43c to the thickness direction dimension D2 of the small end portion 12 to be molded by the third molding surface 43c (i.e., the compression ratio of the small end portion 12).

Then, from the state shown in fig. 5, the upper punch 44 is lowered to press the raw material powder M filled in the chamber from above. Thereby, as shown in fig. 6, the raw material powder M on the first molding surface 43a is compressed by the first molding surfaces 43a, 44a of the upper and lower punches 43, 44, and the portion of the green compact 110 corresponding to the rod 13 is molded. Further, the raw material powder M on the second molding surface 43b and the fourth molding surface 43d is compressed by the second molding surfaces 43b, 44b and the fourth molding surfaces 43d, 44d of the upper and lower punches 43, 44 to mold the portion of the compact 110 corresponding to the large end portion 11, and the raw material powder M on the third molding surface 43c and the fifth molding surface 43e is compressed by the third molding surfaces 43c, 44c and the fifth molding surfaces 43e, 44e of the upper and lower punches 43, 44 to mold the portion of the compact 110 corresponding to the small end portion 12. This completes the molding of the powder compact 110 having a shape based on the connecting rod 10.

However, as in the present embodiment, when the thickness direction dimension D3 of the stem portion 13 to be molded is smaller than the thickness direction dimension D1 of the large end portion 11 and the thickness direction dimension D2 of the small end portion 12 to be molded, the density of the portion of the green compact 110 corresponding to the stem portion 13 tends to be higher than the density of the portion corresponding to the large end portion 11 and the small end portion 12. In this regard, in the present embodiment, the compression ratio of the portion corresponding to the large end portion 11, the compression ratio of the portion corresponding to the small end portion 12, and the compression ratio of the portion corresponding to the stem portion 13 are adjusted to predetermined levels by dividing the lower punch 43 of the mold 40 and adjusting the height positions of the divided punches 45 to 47, respectively. Specifically, the height positions of the molding surfaces 43a to 43c at the time of filling and at the time of compression are adjusted so that the compression ratio of the portion corresponding to the rod portion 13 is smaller than the compression ratio of the portion corresponding to the large end portion 11 and the portion corresponding to the small end portion 12. Accordingly, the density difference between the portion corresponding to the large end 11 and the portion corresponding to the rod 13 of the green compact 110 and the density difference between the portion corresponding to the small end 12 and the portion corresponding to the rod 13 can be both suppressed to a predetermined ratio or less, specifically, 4% or less (preferably 3% or less) which is the upper limit of the allowable range. The density of the portion corresponding to the large end 11, the density of the portion corresponding to the small end 12, and the density of the portion corresponding to the stem portion 13 can be obtained by measuring the densities of the divided pieces obtained by cutting at the positions indicated by the broken lines in fig. 2, for example.

When the powder compact 110 is molded using the molding die 40 having the structure shown in fig. 5, the division mark 14a serving as the die alignment portion of the first dividing punch 45 and the second dividing punch 46 is formed between the portion of the obtained powder compact 110 corresponding to the lower surface 11c of the large end portion 11 and the portion corresponding to the lower surface 13c of the rod portion 13. Similarly, a division mark 14b serving as a die alignment portion of the first dividing punch 45 and the third dividing punch 47 is formed between a portion of the green compact 110 corresponding to the lower surface 12c of the small end portion 12 and a portion corresponding to the lower surface 13c of the rod portion 13. These division marks 14a, 14b are formed between the portions corresponding to the lower inclined surfaces 15b, 17b and the portion corresponding to the lower surface 13c of the rod portion 13 (see fig. 4).

(S2) sintering step

Next, the green compact 110 is heated at a predetermined temperature for a predetermined time to obtain a sintered body having substantially the same shape as the green compact 110. At this time, since the density difference between the portion corresponding to the large end portion 11 and the portion corresponding to the stem portion 13 of the powder compact 110 and the density difference between the portion corresponding to the small end portion 12 and the portion corresponding to the stem portion 13 are both 4% or less, it is possible to prevent the deformation such as warpage of the powder compact 110 from being promoted by sintering as much as possible. Further, during sintering, a tray may be used in order to align the green compacts 110 to be the workpieces, but if the tray has a flat surface shape, when the green compacts 110 to be the workpieces are placed on the tray, deformation such as warpage may be promoted by their own weight due to a gap generated between the tray and a portion corresponding to the stem 13. In this regard, although not shown in the drawings, for example, by using a stepped tray which can be brought into contact with a portion of the green compact 110 corresponding to the rod portion 13, it is more preferable to perform a sintering treatment by aligning the green compact 110 with a pair of stepped trays in a state of sandwiching the green compact 110 therebetween, thereby reducing the strain of the sintered body.

(S3) shaping step

Next, the sintered body is subjected to a re-compression treatment (shaping treatment) to correct the sintered body and to machine the same to a predetermined shape accuracy. Although a specific shaping die and its operation mode are not described, in the shaping step, the die head and the upper and lower punches are moved closer to each other in the vertical direction to re-compress the sintered body to correct the overall shape, two iron cores corresponding to the through holes 11a and 12a are erected, and the parts corresponding to the through holes 11a and 12a are re-molded by re-compressing as described above. Thereby, the shape accuracy, for example, roundness of the through holes 11a and 12a is processed to a predetermined accuracy. In this case, although not shown, the base end side (lower side) of each core is fixed to the jig, and the posture of the core is held more firmly than in the conventional case, thereby suppressing the inclination of the core during shaping. This can increase the correction force of the sintered body, and thus can more effectively suppress the deformation of the sintered body. Through the above steps, the connecting rod 10 shown in fig. 2 and 3 is completed.

As described above, according to the sintered metal connecting rod 10 of the present invention, the density difference between the large end portion 11 and the rod portion 13 and the density difference between the small end portion 12 and the rod portion 13 can be both made 4% or less. If the density difference is 4% or less, warpage of the green compact 110 can be suppressed, and thus warpage of the sintered body can be suppressed. Therefore, the parallelism between the through hole 11a of the large end portion 11 and the through hole 12a of the small end portion 12 can be reduced, and the occurrence of early wear due to contact of one ends of the bearings 20 and 30 attached to the through holes 11a and 12a and abnormal noise due to inclination of the piston can be prevented as much as possible.

Further, as shown in the present embodiment, in addition to the above configuration of the molding die 40 in the compression molding step S1, the sintered metal connecting rod 10 having the parallelism between the through hole 11a of the large end portion 11 and the through hole 12a of the small end portion 12 of Φ 0.5/100 or less, preferably Φ 0.3/100 or less can be obtained by using the above-described pallet in the sintering step S2 and/or the above-described re-compression mold in the shaping step S3. By setting the parallelism between the through hole 11a of the large end portion 11 and the through hole 12a of the small end portion 12 to be equal to or less than Φ 0.5/100 in this manner, it is possible to ensure the positioning accuracy of the members mounted to the through holes 11a and 12a, specifically, the bearings 20 and 30 shown in fig. 1, and the piston, the crankshaft (not shown), and the like connected to the bearings 20 and 30. Therefore, the performance of the link module 1 in which these components are attached to the link 10 can be ensured, and the early wear and the generation of abnormal noise of the bearings 20 and 30 can be more reliably prevented.

Further, as in the present embodiment, by providing the flat surface 16 linearly extending in the thickness direction and connected at the upper end thereof to the lower surface 13c of the rod portion 13 as the division mark 14a (14b), the upper surface corner portion of the second division punch 46 corresponding to the large end portion 11 (the end portion of the fourth molding surface 43d for molding the lower inclined surface 15 b) can be protected. Therefore, the life of the die can be prolonged, and the compact 110 having stable quality can be mass-produced, and the metal connecting rod 10 can be mass-produced.

While one embodiment of the present invention has been described above, the sintered metal connecting rod of the present invention is not limited to the above embodiment. Of course, any configuration can be adopted within the scope of the present invention.

For example, in the above-described embodiment, the flat surface 16 linearly extending in the thickness direction and connected at the upper end thereof to the lower surface 13c of the rod portion 13 is exemplified as the division marks 14a, 14b of the molding die 40 formed by compression molding, but the present invention is not limited thereto. The division marks 14a and 14b may take any form as long as they appear as die-aligning portions on the front and back surfaces of the finished sintered metal connecting rod 10.

In the above embodiment, the case where the height position of the first dividing punch 45 is not changed when the raw material powder M is filled (fig. 5) and when the compression molding is completed (fig. 6) has been exemplified, but the present invention is not limited to this. For example, the height position of the first dividing punch 45 during compression molding may be moved in any vertical direction as compared to the case of filling the raw material powder M. In short, the vertical position of each of the molding surfaces 43a to 43c can be arbitrarily set by filling the raw material powder M in a state where the first molding surface 43a is located above the vertical position of the first molding surface 43a with respect to the second molding surface 43b and the third molding surface 43c at the time of completion of molding.

Description of the reference symbols

1: a connecting rod module; 10: sintering a metal connecting rod; 11: a large end portion; 12: a small end portion; 11a, 12 a: a through hole; 11b, 12 b: an upper side surface; 11c, 12 c: an underside surface; 13: a rod portion; 13 a: a through hole; 13 b: an upper side surface; 13 c: an underside surface; 14a, 14 b: dividing the trace; 15a, 17 a: an upper inclined surface; 15b, 17 b: a lower inclined surface; 16: flat surface; 20. 30: a bearing; 21. 31: an outer ring; 21a, 31 a: a track surface; 22. 32: a roller; 23. 33: a holder; 40: forming a mould; 41: a die head; 42a, 42 b: a side core; 43: a lower punch; 43 a: a first molding surface (lower surface of the stem portion); 43 b: a second molding surface (lower side surface of the large end portion); 43 c: a third molding surface (lower surface of the small end portion); 43 d: a fourth molding surface (a lower inclined surface on the large end side); 43 e: a fifth molding surface (a lower inclined surface on the small end side); 44: an upper punch; 44 a: a first molding surface (upper side surface of the rod portion); 44 b: a second molding surface (upper side surface of the large end portion); 44 c: a third molding surface (upper surface of the small end portion); 44 d: a fourth molding surface (upper inclined surface on the large end side); 44e, the ratio of: a fifth molding surface (an upper inclined surface on the small end side); 45: a first dividing punch; 46: a second dividing punch; 47: a third dividing punch; 110: pressing the powder; m: raw material powder.