JP6392020B2 - Bolt assembly and its carburizing method - Google Patents

Description

  The present invention relates to a bolt assembly in which a pair of first divided members and second divided members are fixed with fixing bolts, and more particularly to a technique for performing a carburizing process on the surface of the bolt assembly.

  As described in Patent Document 1, a multi-link type piston-crank mechanism of an internal combustion engine includes a lower link rotatably attached to a crank pin of a crankshaft, an upper link connecting the lower link and the piston, A control shaft that is rotatably supported by the engine body, and a control link that connects the control shaft and the lower link are provided.

  The lower link is configured as a bolt assembly that fastens and fixes a pair of first divided member and second divided member with a fixing bolt with the crank pin interposed therebetween so that the lower link can be assembled later.

  In this type of bolt assembly, generally, one first divided member is provided with a seating surface on which the head of the fixing bolt is seated, and the bolt hole of the other second divided member is provided with a shaft portion of the fixing bolt. An internal thread portion that is screwed into an external thread portion formed on the outer periphery of the external thread is formed.

JP 2012-67758 A

  The lower link as the bolt assembly is subjected to a carburizing treatment in which carbon is added to the surface in order to ensure fatigue strength and bearing surface strength because combustion load and inertial load repeatedly act during operation of the internal combustion engine. It is desirable to perform subsequent quenching and tempering steps). In the carburized layer subjected to the carburizing treatment, the surface hardness is improved, the fatigue strength is improved, and the buckling strength is improved in the seating surface of the first divided member on which the head of the fixing bolt is seated. .

  On the other hand, when carburizing treatment is performed on the internal thread portion formed on the inner periphery of the bolt hole of the second divided member, the pitch of the screw meshing portion may be deformed, or the toughness may be reduced as the hardness increases. There is a concern that the durability and reliability of the screw-engaged portion may be reduced. Therefore, it is desirable that the bolt hole in which the female screw portion is formed is not subjected to carburizing treatment, that is, is subjected to a carbon-proofing treatment.

  As such a carburizing treatment, it is conceivable that the bolt holes are carburized by fastening and fixing a pair of divided members with fixing bolts in advance and performing the carburizing treatment in a state where the bolt holes are closed with the fixing bolts. .

  However, in this case, since the carburizing process is performed in a state where the head of the fixing bolt is seated on the seating surface of the first split member, the carburizing gas does not enter the seating surface and the carburizing process is performed. I can't. For this reason, the improvement effect of the bearing surface strength by the carburizing process which is the original purpose cannot be obtained.

  The present invention has been made in view of such circumstances, and prevents carburization of a bolt hole having a screw engaging portion, and suppresses a decrease in toughness due to a pitch deformation or an increase in hardness of the screw engaging portion. On the other hand, it is an object to improve the seating surface strength by subjecting the seating surface of the first divided member on which the head of the fixing bolt is seated to carburization.

  The present invention relates to a bolt assembly having a first divided member and a second divided member fixed by fixing bolts, and particularly relates to a technique for carburizing the surface of the bolt assembly. A bolt hole through which the shaft portion of the fixing bolt is inserted is formed through the first divided member and the second divided member. One of the first divided members is provided with a flat seat surface on which the head of the fixing bolt is seated, and the inner periphery of the bolt hole of the other second divided member has an outer periphery of the shaft portion of the fixing bolt. An internal thread portion is formed to be screwed into the external thread portion formed in the above.

  Further, the first divided member is formed with a tapered surface inclined or curved in a conical shape so as to reduce the diameter from the seat surface toward the bolt hole around the bolt hole. The carburizing process is performed in a state where the first divided member and the second divided member are fixed using a carburizing jig instead of the fixing bolt. And the said carburizing jig is comprised so that the said bolt hole may be plug | blocked, without contact | abutting to the said seat surface so that the said carved surface may also be carburized.

  According to the present invention, in the carburizing process, since the carburizing jig is configured to close the bolt hole without contacting the seating surface, the carburizing of the bolt hole having the screw engaging portion is prevented, Carving treatment is applied to the seating surface of the first divided member where the head of the fixing bolt will be seated while suppressing the deterioration of toughness due to the deformation of the pitch of the meshing portion and the increase in hardness, and the seating surface strength is increased. Can be improved.

1 is a cross-sectional view showing a multi-link piston-crank mechanism of an internal combustion engine having a lower link as an example of a bolt assembly according to a first embodiment of the present invention. Sectional drawing which expands and shows the vicinity of the lower link of FIG. Sectional drawing which expands and shows the fastening part of the fixing bolt of the lower link of FIG. Sectional drawing which shows the aspect which fitted the jig | tool for carburizing in the bolt hole in the carburizing process. Explanatory drawing which shows the seating part of the jig | tool for carburizing which concerns on 2nd Example of this invention. Explanatory drawing which shows the seating part of the jig | tool for carburizing which concerns on 3rd Example of this invention.

  Hereinafter, the present invention will be described with reference to illustrated embodiments. FIG. 1 is a sectional view showing a multi-link piston-crank mechanism of an internal combustion engine as an example of a link mechanism according to the present invention.

  This multi-link type piston-crank mechanism connects the piston 11 of the internal combustion engine and the crank pin 13 of the crankshaft 12 with a plurality of link parts, and the basic structure is the above-mentioned JP-A-2012-67758, etc. Since it is well-known as described in FIG.

  This multi-link type piston-crank mechanism is rotatable to a lower link 14 rotatably attached to a crank pin 13, an upper link 15 connecting the lower link 14 and the piston 11, and a cylinder block 10 as an engine body. And a control link 17 for connecting the control shaft 16 and the lower link 14 to each other.

  The piston 11 and the upper end of the upper link 15 are connected by a piston pin 18 so as to be relatively rotatable, and the lower end of the upper link 15 and the lower link 14 are connected by a first connecting pin 19 so as to be relatively rotatable. The upper end of the link 17 and the lower link 14 are connected to each other by a second connecting pin 20 so as to be relatively rotatable, and the lower end of the control link 17 is attached to an eccentric shaft portion 16A provided eccentric to the control shaft 16. It has been.

  Although not shown, an actuator such as a motor or a hydraulic actuator capable of changing the rotation position of the control shaft 16 is provided, and the top dead center position of the piston 11 is changed by changing the rotation position of the control shaft 16 using this actuator. Further, it is possible to change the stroke characteristics of the piston 11 including the bottom dead center position, and thus change the engine compression ratio. The operation of the actuator is controlled according to the engine operating state by a control unit (not shown).

  FIG. 2 is a cross-sectional view showing the lower link 14 as a bolt assembly according to the first embodiment of the present invention. The lower link 14 is fastened and fixed by a pair of fixing bolts 21 with the crank pin 13 interposed therebetween so that the lower link 14 can be assembled later to the crank pin 13 of the crank shaft 12 and the second divided member. A bolt assembly having a member 23 is formed, and each of the divided members 22 and 23 is formed with a half of a bearing surface 24 that rotatably supports the crank pin 13 in a half shape.

  The lower link 14 has a thin plate-like first pin boss portion to which the first connection pin 19 is fixed by press-fitting so as to sandwich the pin boss portion 25 of the upper link 15 through which the first connection pin 19 is rotatably inserted from both sides. 26 is formed in a bifurcated shape. In the cross-sectional view of FIG. 2, only one first pin boss portion 26 is drawn. After the pin boss portion 25 of the upper link 15 is disposed between the bifurcated first pin boss portion 26, the first link pin 19 is fixed to the first pin boss portion 26 of the lower link 14 by press-fitting, and the upper link The upper link 15 and the lower link 14 are connected to each other so as to be rotatable relative to each other by allowing the pin bosses 25 to penetrate through the 15 pin boss portions 25.

  Similarly, the thin plate-like second pin boss portion 28 to which the second connection pin 20 is fixed by press-fitting so as to sandwich the pin boss portion 27 of the control link 17 through which the second connection pin 20 is rotatably penetrated is bifurcated. Is formed. In the cross-sectional view of FIG. 2, only one second pin boss portion 28 is drawn. The pin boss portion 27 of the control link 17 is disposed between the bifurcated second pin boss portions 28, and the second connecting pin 20 is fixed to the pair of second pin boss portions 28 by press-fitting. The control link 17 and the lower link 14 are connected so as to be rotatable relative to each other by allowing the pin boss portion 27 to rotate therethrough.

  Of the first divided member 22 and the second divided member 23, one of the first divided members 23 and one of the second divided members 23 is connected to the first pin boss portion 26, and the other of the second divided members 23 is not concentrated. A second pin boss portion 28 is provided on the one-divided member 22.

  Next, the structure of the fastening portion by the fixing bolt 21 will be described in detail with reference to FIGS. Although there are two fixing bolts 21, the structure of both is basically the same. Therefore, here, a fixing structure of the fixing bolt 21 near the upper link 15 (right side in FIG. 2) will be described as an example. Here, for the sake of convenience, in this specification, of the pair of divided members 22 and 23, the one on which the head 33 of the fixing bolt 21 is seated is referred to as a “first divided member”, and the male screw of the shaft portion 31 of the fixing bolt 21. The direction in which the portion 32 is screwed is referred to as a “second divided member”. Therefore, when paying attention to the fastening structure of the fixing bolt 21 on the other control link 17 side, the relationship between the first divided member and the second divided member is reversed from the following description.

  The fixing bolt 21 includes a shaft portion 31 having a male screw portion 32 formed on the outer periphery, and a head portion 33 provided at one end of the shaft portion 31 and having a larger diameter than the shaft portion 31. The first divided member 22 is provided with a flat seat surface 35 on which a flat back surface 34 of the head 33 of the fixing bolt 21 is seated, and a first bolt hole 36 through which the shaft portion 31 of the fixing bolt 21 passes is penetrated. Is formed. One end of the first bolt hole 36 opens in the seat surface 35, and the other end opens in the mating surface 37 of the first divided member 22 and the second divided member 23.

  The second divided member 23 is formed with a second bolt hole 38 through which the shaft portion 31 of the fixing bolt 21 is inserted. On the inner periphery of the second bolt hole 38, a female screw portion 39 is formed that is screwed into a male screw portion 32 formed on the outer periphery of the shaft portion 31 of the fixing bolt 21. One end of the second bolt hole 38 opens to the mating surface 37 of the two divided members 22, 23, and the other end opens to the bottom surface 40 that connects the pair of first pin boss portions 26 having a bifurcated shape.

  That is, the fixing bolt 21 has a structure in which the bifurcated pin boss portions 26 and 28 are fastened to the tip end side of the shaft portion 31 in consideration of a combustion load, an inertia load, and the like. The distance from the mating surface 37 to the bottom surface 40 is relatively short. Therefore, in order to ensure the strength and rigidity of the screw fastening portion, the second bolt hole 38 has a structure that penetrates to the bottom surface 40 of the pin boss portion 26 (28), and the second bolt hole 38 in which the female screw portion 39 is formed. The length is secured sufficiently.

  As shown in FIG. 3, the first divided member 22 has a conical shape around the first bolt hole 36 so that the diameter decreases from the seat surface 35 forming a flat surface toward the first bolt hole 36. An inclined or curved tapered surface 41 is formed.

  In the carburizing process, for example, the lower link 14 is disposed in a vacuumed case, and a carburizing gas is injected and heated in the case. Thereafter, hardening is performed by quenching and tempering, and a carburized layer 42 having a high hardness is formed on the surface of the lower link 14 as shown by a thick solid line in FIGS.

  In this embodiment, in the carburizing step, the carburizing process is performed in a state where the first divided member 22 and the second divided member 23 are fixed using the carburizing jig 43 instead of the fixing bolt 21. Yes. The carburizing jig 43 has a bolt shape having a head portion 45 and a shaft portion 44 in the same manner as the fixing bolt 21 described above. The shaft portion 44 of the jig is set to be thinner and longer than the shaft portion 31 of the fixing bolt 21, penetrates the first bolt hole 36 and the second bolt hole 38, and extends from the bottom surface 40 of the pin boss portion 26. A nut (not shown) is fastened to the tip of the shaft portion 44. On the outer periphery of the shaft portion 31 of the jig, a male screw portion 46 that is screwed into a female screw portion formed on the inner periphery of the nut is formed.

  Instead of the structure using the nut as described above, the shaft portion 44 of the jig has the same thickness (diameter dimension) as the shaft portion 31 of the fixing bolt 21, and the female screw portion of the second bolt hole 38 at the tip side thereof. It is good also as a structure screwed and fastened to 39.

  The head 45 of the jig is configured to be seated on the tapered surface 41 of the first divided member 22 without contacting the seat surface 35 so that the carburizing process is also performed on the seat surface 35. Specifically, the head portion 45 of the jig is configured as an inclined surface portion 47 in which the back surface side of the shaft portion 44 is inclined in a conical shape like the tapered surface 41 formed on the first split member 22. Therefore, when the carburizing jig 43 is fastened, as shown in FIG. 4, the inclined surface portion 47 is seated on the taper surface 41 without coming into contact with the seat surface 35, and comes into strong contact. As a result, the taper surface 41 and the bolt holes 36 and 38 are closed by the carburizing jig 43 so that the carburizing process is not performed. On the other hand, since the seating surface 35 is exposed without being blocked by the carburizing jig 43, carburizing treatment is performed, and as shown by the thick solid lines in FIGS. Layer 42 will be formed.

In the present embodiment as described above, the carburizing jig 43 dedicated instead fixing bolt 21 during carburizing and Mochiiruko, while preventing carburization of bolt holes 36, 38 female thread portion 39 is formed In addition, it is possible to carburize the seat surface 35 that requires strength to form the carburized layer 42, and to improve the strength of the seat surface 35 while preventing the toughness of the screw meshing portion from being lowered. . In addition, since the carburizing jig 43 can be reused many times, an increase in manufacturing cost is suppressed to a minimum.

  FIG. 5 is an explanatory view showing a fixing structure of the carburizing jig 43 according to the second embodiment of the present invention. In the following second and third embodiments, since the basic structure is the same as that of the first embodiment, only different portions will be described here.

  When the inclination angles of the taper surface 41 and the inclined surface portion 47 are set equal, the actual seating position of the taper surface 41 and the inclined surface portion 47 is closer to the seat surface 35 than the position closer to the bolt hole 36 due to dimensional variation or the like. Between the positions of the bolt holes 36 and 38, which may impair the sealing performance of the bolt holes 36 and 38.

  Therefore, in the second embodiment of FIG. 5, the inclined surface portion 47A of the carburizing jig 43 is seated on the seat surface 35 (shaft) so that it is seated on the tapered surface 41A at the position closest to the bolt hole (lower side in the figure). The inclination angle of the inclined surface portion 47A with respect to the direction orthogonal to the axial direction of the portion is set larger than the inclination angle of the tapered surface 41A. Thus, the inclined surface portion 47A is always stably seated on the tapered surface 41 at the position closest to the bolt hole, and the bolt holes 36 and 38 can be reliably sealed.

  In the third embodiment of FIG. 5, the seat surface 35 (axis of the shaft portion) is such that the inclined surface portion 47 </ b> B of the carburizing jig 43 is seated on the tapered surface 41 </ b> B at the position closest to the seat surface (upper side in the drawing). The inclination angle of the inclined surface portion 47B with respect to the direction orthogonal to the direction is set smaller than that of the tapered surface 41B. Thus, the inclined surface portion 47B is always stably seated on the tapered surface 41B at the position closest to the seat surface, and the bolt holes 36 and 38 can be reliably sealed.

  As described above, the present invention has been described based on the specific embodiments. However, the present invention is not limited to the above-described embodiments, and includes various modifications and changes. For example, in the above embodiment, the inclined surface portion is provided on the head unit integrated with the bolt-shaped shaft portion, but the inclined surface portion may be provided on the nut side fastened to the tip of the shaft portion.

DESCRIPTION OF SYMBOLS 11 ... Piston 12 ... Crankshaft 13 ... Crankpin 14 ... Lower link 15 ... Upper link 16 ... Control shaft 17 ... Control link 19 ... 1st connection pin 20 ... 2nd connection pin 21 ... Fixing bolt 22 ... 1st division member 23 ... second divided member 33 ... head 31 ... shaft 32 ... male screw part 36 ... first bolt hole 38 ... second bolt hole 39 ... female screw part

Claims (7)

In the carburizing method of a bolt assembly including a carburizing step of carburizing the surface of a bolt assembly having a first divided member and a second divided member fixed by a fixing bolt,
A bolt hole through which the shaft portion of the fixing bolt is inserted is formed through the first divided member and the second divided member,
One of the first divided members is provided with a flat seat surface on which the head of the fixing bolt is seated, and the inner periphery of the bolt hole of the other second divided member has an outer periphery of the shaft portion of the fixing bolt. An internal thread portion that is screwed into the external thread portion formed in
And the said 1st division member is formed in the circumference | surroundings of the said bolt hole the taper surface which inclines or curves in a cone shape so that it may reduce in diameter toward the bolt hole from the said seat surface,
In the carburizing step, carburizing treatment is performed in a state where the first divided member and the second divided member are fixed using a carburizing jig instead of the fixing bolt,
The carburizing jig according to claim 1, wherein the carburizing jig is configured to close the bolt hole without contacting the seating surface so that the carburizing process is performed on the seating surface. Method. The carburizing jig is provided at one end of the shaft portion through which the bolt hole is inserted, and is inclined corresponding to the tapered surface so as to be seated on the tapered surface without contacting the seating surface. The carburizing method for a bolt assembly according to claim 1, further comprising an inclined surface portion. 3. The bolt assembly according to claim 2 , wherein the inclined surface portion is set to have an inclination angle larger than that of the tapered surface so that the inclined surface portion is seated on the tapered surface at a position near the bolt hole. Three-dimensional carburizing method. The bolt assembly according to claim 2 , wherein the inclined surface portion is set to have an inclination angle smaller than that of the tapered surface so that the inclined surface portion is seated on the tapered surface near the seat surface. Three-dimensional carburizing method. The bolt assembly is a lower link that is used in a multi-link piston-crank mechanism and is rotatably attached to a crank pin.
The multi-link piston-crank mechanism is
An upper link connecting the lower link and the piston;
A control shaft rotatably supported by the engine body,
The carburizing method for a bolt assembly according to any one of claims 1 to 4, further comprising a control link for connecting the control shaft and the lower link. In the bolt assembly having the first divided member and the second divided member fixed by the fixing bolt,
A bolt hole through which the shaft portion of the fixing bolt is inserted is formed through the first divided member and the second divided member,
One of the first divided members is provided with a flat seat surface on which the head of the fixing bolt is seated, while the inner periphery of the bolt hole of the other second divided member has an outer periphery of the shaft portion of the fixing bolt. A female screw part is formed to which the male screw part formed in
And the said 1st division member is formed in the circumference | surroundings of the said bolt hole the taper surface which inclines or curves in a cone shape so that it may reduce in diameter toward the bolt hole from the said seat surface,
A bolt assembly, wherein a carburized layer subjected to a carburizing process is formed on a surface of the first divided member including the seating surface except for the bolt holes. The bolt assembly is a lower link that is used in a multi-link piston-crank mechanism and is rotatably attached to a crank pin.
The multi-link piston-crank mechanism is
An upper link connecting the lower link and the piston;
A control shaft rotatably supported by the engine body,
The bolt assembly according to claim 6, further comprising a control link for connecting the control shaft and the lower link.

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