JP2016109140A - Bolt assembly and carburization method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent carburization to a bolt hole in which a female screw part is formed.SOLUTION: Out of a first split member 22 and a second split member 23 fixed with a fixing bolt, a seat surface 35 is formed in the first split member 22, and a male screw part 39 is formed on the inner surface of a bolt hole 38 of the second split member 23. In the second split member 23, a surface to which one end of the bolt hole 38 is opened is an inclination or curve surface 40 inclined or curved to the orthogonal direction of the bolt hole 38. In a carburization step, a movable flange part 51 of a jig 43 for carburization is closely contacted to the inclination or curve surface 40, and thereby the bolt hole 38 opened to the inclination or curve surface 40 is closed.SELECTED DRAWING: Figure 3

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, when the surface of the second divided member where one end of the bolt hole opens is an inclined / curved surface that is inclined or curved with respect to the direction perpendicular to the bolt hole, the bolt is inclined to the inclined / curved surface of the bolt hole. The head and nut cannot be seated. For this reason, there is a concern that the carburizing process is performed on the bolt hole from the opening of the bolt hole that opens to the inclined / curved surface, and the durability and reliability of the screw meshing portion are lowered.

  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. The purpose is that.

  The present invention relates to a carburizing method for a bolt assembly including a carburizing step of carburizing a surface of a bolt assembly having a first divided member and a second divided member fixed by fixing bolts.

  The first divided member and the second divided member are formed with a bolt hole through which the shaft portion of the fixing bolt is inserted, and one first divided member is a flat seat on which the head of the fixing bolt is seated. A surface is provided, and on the inner periphery of the bolt hole of the other second divided member, a female screw portion that is screwed into a male screw portion formed on the outer periphery of the shaft portion of the fixing bolt is formed, and the second In the divided member, the surface where one end of the bolt hole is opened forms an inclined / curved surface which is inclined / curved with respect to the direction perpendicular to the bolt hole.

  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. -It has the bolt hole obstruction | occlusion part which plugs up the bolt hole opened to a curved surface.

  According to the present invention, in the carburizing process, since the bolt hole opened to the inclined / curved surface is closed by the bolt hole closing portion of the carburizing jig, the carburizing of the bolt hole having the screw engagement portion is performed. Therefore, it is possible to suppress the deterioration of the toughness due to the pitch deformation and the hardness increase of the screw meshing portion.

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 jig for carburizing of the lower link of FIG. The partially broken figure which shows the movable flange part and nut part in the jig | tool for carburizing.

  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 on one divided member. 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 parts are screwed together is called the “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 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 which is screwed into a male screw portion 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. Here, the bottom surface 40 forms an inclined / curved surface that is appropriately inclined or curved so as to avoid interference with the pin boss portions 25 and 27.

  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 is inclined in a conical shape around the first bolt hole 36 so as to reduce the diameter from the flat seat surface 35 toward the first bolt hole 36. A curved taper 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 FIG.

  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. It sticks out.

  A bolt hole closing portion that closes the second bolt hole 38 that opens to the bottom surface 40, that is, the inclined / curved surface 40, is provided at the tip of the shaft portion 44 protruding from the bottom surface 40. The bolt hole closing portion has an inclined / curved surface around the second bolt hole 38 so as to close the shaft portion 44 inserted through the second bolt hole 38 and the second bolt hole 38 opened to the inclined / curved surface 40. The movable flange portion 51 is seated on 40, and a nut portion 52 that fixes the movable flange portion 51 to the shaft portion 44 is provided.

  The nut portion 52 has a cylindrical shape that is screwed to the shaft portion 44, and a female screw portion 56 that is screwed to a male screw portion 46 formed on the outer periphery of the shaft portion 44 is formed on the inner peripheral surface thereof. Further, a concave portion 54 in which the flange 53 of the movable flange portion 51 is fitted so as to be relatively rotatable around the axis is formed on one end portion in the axial direction of the nut portion 52 over the entire circumference. The concave portion 54 has a shape that is recessed in a cross-sectional channel shape radially inward from the outer peripheral surface of the nut portion 52. The movable flange portion 51 has a substantially cylindrical main body 55 having different axial dimensions along the inclined / curved surface 40, and projects from the one axial end of the main body 55 into a flange shape radially inward. 54 and a flange 53 fitted to 54.

  When performing the carburizing process, first, the carburizing jig 43 is inserted into the bolt holes 36 and 38 of the first divided member 22 and the second divided member 23 from the lower side of FIG. 3 and protrudes from the bolt holes 36 and 38. A nut portion 52 to which the movable flange portion 51 is attached is assembled to the tip portion of the shaft portion 44. Then, the nut portion 52 is rotated in the tightening direction, so that the nut portion 52 and the head portion 45 are fastened together. As a result, the movable flange portion 51 temporarily fixed to the nut portion 52 is tightened to the nut portion 52 while appropriately rotating around the axis along the inclined / curved surface 40, so that the distal end portion of the main body 55 However, the second bolt hole 38 is tightly adhered to the entire periphery of the inclined / curved surface 40 around the portion where the second bolt hole 38 opens, and the second bolt hole 38 is liquid-tightly closed. Accordingly, in the subsequent carburizing process, it is possible to prevent the carburizing process from being performed inside the bolt holes 36 and 38 in which the female screw portion 39 is formed.

  Further, 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 seating surface 35 so that the carburizing process is also performed on the seating surface 35. Yes. 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. 3, the inclined surface portion 47 is seated on the tapered 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 seat surface 35 is exposed without being blocked by the carburizing jig 43, carburization is performed, and the carburized layer 42 is also formed on the seat surface 35 as shown by a thick solid line in FIG. Will be formed.

  As described above, in the present embodiment, by using the dedicated carburizing jig 43 instead of the fixing bolt 21 during the carburizing process, the carburization of the bolt holes 36 and 38 in which the female screw portions 39 are formed can be reliably prevented. However, 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. it can. In addition, since the carburizing jig 43 can be reused many times, an increase in manufacturing cost is suppressed to a minimum.

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 part 36 ... first bolt hole 38 ... second bolt hole 39 ... internal thread part 40 ... inclined / curved surface 51 ... movable flange part (bolt hole closing part)
52 ... Nut (bolt hole closing part)

Claims (5)

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 in the second divided member, the surface on which one end of the bolt hole is opened has an inclined / curved surface that is inclined or curved with respect to the orthogonal direction of the bolt hole,
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 method for a bolt assembly, wherein the carburizing jig has a bolt hole closing portion that closes a bolt hole opened in the inclined / curved surface.   The bolt hole closing portion includes a shaft portion through which the bolt hole is inserted, a movable flange portion seated on the inclined / curved surface around the bolt hole so as to close the bolt hole opened to the inclined / curved surface, The carburizing method for a bolt assembly according to claim 1, further comprising: a nut portion that fixes the movable flange portion to the shaft portion. A taper surface that is inclined or curved in a conical shape so as to reduce the diameter from the seating surface toward the bolt hole is formed around the bolt hole in the first divided member,
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 or 2, further comprising an inclined / curved surface portion. 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 3, further comprising a control link for connecting the control shaft and the lower link.   A bolt assembly that has been carburized by the carburizing method according to claim 1.

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