JP2016180469A - Piece type ball screw and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piece-type ball screw of high reliability and a manufacturing method thereof capable of improving assembling workability of a piece member and being positioned with high accuracy without backlash of the piece member.SOLUTION: In a piece-type ball screw including a piece member 5 fitted to a circular piece window 6 formed on a barrel portion of a nut 3 and having a connection groove 5a using a rolling passage as a circumferential route on an inner periphery thereof, the piece member 5 is formed by MIM of a sintered alloy with a circular cross-section corresponding to the piece window, an outer peripheral face of the piece member 5 is provided with a flat face 8a and a knurl 10 linearly extending, a knurl 11 is formed on an inner periphery of the piece window 6 of the nut 3 correspondingly to the knurl 10, a tooth width of the knurl 10 of the piece member 5 is determined to be slightly larger than a groove width between teeth of the knurl 11 of the piece window 6, and the piece member 5 is knurl-fitted to the piece window 6.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a ball screw used in various machine tools such as an electric discharge machine and a tapping center, or an electric power steering or actuator of an automobile, and in particular, a piece type ball screw using a piece member that is a ball circulation part and It relates to the manufacturing method.

  The ball screw is composed of a screw shaft having a helical thread groove formed on the outer peripheral surface, a nut externally fitted to the screw shaft, and a spiral screw groove formed on the inner peripheral surface, and both opposing screw grooves. It is equipped with a large number of balls accommodated in the formed rolling path and a circulation mechanism having the rolling path as a circuit path, and is used as a motion conversion mechanism that linearly moves the screw shaft by rotating the nut, for example. ing.

  Generally, there are various types of ball screws having different ball circulation mechanisms, and one of them is called a piece type. This piece-type ball screw has a threaded groove connection path, and a circulation piece member with a rolling path as a circulation path is attached to the nut. The structure is relatively simple and compact. There are advantages you can do.

  A typical example of such a piece-type ball screw is shown in FIGS. This piece-type ball screw 51 includes a screw shaft 52 having a helical thread groove 52a formed on the outer peripheral surface, and a nut externally fitted to the screw shaft 52 and having a helical screw groove 53a formed on the inner peripheral surface. 53, a large number of balls 54 accommodated in a rolling path formed by the opposing screw grooves 52a and 53a, and a piece member 55 serving as a circulation member for these balls 54.

  A cylindrical window 53 having a substantially circular cross section is formed in the body of the cylindrical nut 53 so as to penetrate the inner and outer peripheral surfaces and cut out a part of the thread groove 53a. A piece member 55 serving as a circulation member for the ball 54 is fitted into the piece window 56. A connecting groove 55a for connecting adjacent one rounds of the screw groove 53a is formed inside the piece member 55.

  As shown in FIGS. 10 (a) and 10 (b), a pair of arms 55b and 55b project in opposite directions in the circumferential direction at both ends of the piece member 55 in the axial direction. The arms 55b and 55b are formed in a substantially circular cross section, and are engaged with the thread groove 53a of the nut 53 via a predetermined radial clearance, so that the positioning of the piece member 55 and the piece member 55 are arranged in the radial direction from the piece window 56. It is provided to prevent it from slipping out. Here, the portion of the thread groove 53a where the arms 55b and 55b are engaged becomes a non-ball circulating portion.

  The piece member 55 includes a body portion 55c from which arms 55b and 55b are projected, and a head portion 55d extending from the body portion 55c to the outer diameter side (the radially outer side of the nut 53). The trunk portion 55 c has a substantially circular cross section so as to correspond to the shape (circular hole) of the piece window 56 of the nut 53 and is fitted to the piece window 56.

  The head portion 55d is formed with concave portions 55e whose outer diameter surfaces are recessed relative to other portions on both sides (both sides in the circumferential direction of the nut 53), and rises from the concave portions 55e toward the outer diameter side and has a pair of arcuate circumferential surfaces. The guide walls 55f and 55f are arranged to face each other. The outer surfaces of the guide walls 55f and 55f have an R shape so as to correspond to the shape (circular hole) of the piece window 56. Further, the inner side surfaces of the guide walls 55f, 55f have an R shape that extends in an R shape around the axis of the piece member. The R-shaped portion on the inner side surface has a smaller R shape than the outer side surface, and the wall thickness of the guide walls 55f and 55f is substantially the same.

  When fixing the piece member 55, first, the piece member 55 is fitted into the piece window 56 of the nut 53 from the inner diameter side of the nut 53. Next, the arms 55 b and 55 b are engaged with the thread groove 53 a of the nut 53. In this state, a core (not shown) is put in the nut 53, and the caulking punch 57 is pushed in from the outer diameter side. The caulking punch 57 has a tapered pressure surface 57 a at the tip thereof, and the pair of guide walls 55 f and 55 f of the piece member 55 are caulked so that the tip is bent obliquely outward, and is engaged with the nut 53. It becomes a joint state.

  Here, the processed surface 57a of the caulking punch 57 first makes point contact with the end portions 55g and 55g on the inner side surfaces of the guide walls 55f and 55f, as shown in FIG. When the caulking punch 57 is pushed downward in this state, the guide walls 55f and 55f are plastically deformed in all directions as indicated by the arrows in FIG. 10B with the end portions 55g and 55g as the base points. . As described above, since the inner side surfaces of the guide walls 55f and 55f are formed in an R shape, the cross-sectional area of the guide walls 55f and 55f to be caulked is reduced, and the caulking can be fixed only by plastically deforming a smaller portion. As a result, the amount of spring back after plastic deformation due to caulking is reduced, and the backlash after caulking of the piece member 55 is reduced.

  In addition, although the processing surface 57a of the caulking punch of this example is tapered, the processing surface can be flat so as to face the guide walls 55f and 55f. Further, the machining surface 57a of the caulking punch can have an R dimension larger than the R dimension of the inner surface of the guide walls 55f and 55f. In any case, if the processed surface 57a of the caulking punch is initially in point contact with the end portions 55g and 55g of the inner surface of the guide walls 55f and 55f, when the caulking punch 57 is pushed downward, The guide walls 55f and 55f are plastically deformed in all directions as indicated by arrows in FIG. 10B with the end portions 55g and 55g as the base points. By doing so, the piece member 55 is stably fixed to the nut 53 (for example, refer to Patent Document 1).

JP 2008-057597 A

  In such a conventional piece type ball screw 51, since the inner surfaces of the guide walls 55f and 55f are formed in an R shape, the cross-sectional area of the guide walls 55f and 55f to be caulked is reduced, and only the smaller portion is caulked by plastic deformation. Can be fixed. As a result, the amount of springback after plastic deformation due to caulking is reduced, and the backlash after caulking of the piece member 55 is reduced.

  However, with this type of piece type ball screw 51, it is necessary to fit the piece member 55 into the piece window 56 of the nut 53 from the inner diameter side of the nut 53. Therefore, when the piece member 55 is small in size, assembly work is difficult. There was a fear.

  Further, as a fixing method of the piece member 55, the caulking punch 57 is pushed in from the outer diameter side, so that the posture of the piece member 55 with respect to the nut 53 is deteriorated depending on the quality of the caulking process, and between the piece member 55 and the nut 53, There was a step, which could cause rotation failure and short life.

  The present invention has been made in view of such circumstances. The positioning arm that hinders the assembling property of the piece member is abolished, and the caulking process that causes backlash of the piece member is abolished to eliminate the piece member. An object of the present invention is to provide a highly reliable piece-type ball screw capable of improving the assembly workability and capable of positioning with high accuracy without backlash of the piece member and a method for manufacturing the same.

  In order to achieve such an object, the invention according to claim 1 of the present invention includes a screw shaft having a spiral thread groove formed on the outer peripheral surface thereof, and is externally fitted to the screw shaft and spirally formed on the inner peripheral surface. A nut formed with a screw groove, a plurality of balls accommodated in a rolling path formed by the opposing screw groove, and a piece window drilled in the body of the nut, And a piece-shaped ball screw provided with a connecting groove having the rolling path as a circular path, and a knurled linearly formed knurled outer peripheral surface of the piece member. Correspondingly, a knurl is formed on the inner circumference of the piece window of the nut, and the piece member is knurl fitted to the piece window of the nut.

  Thus, in the piece-type ball screw provided with the piece member that is fitted to the piece window formed in the trunk portion of the nut and in which the connecting groove having the rolling path as the circulation path is formed on the inner periphery, the piece member A knurl extending linearly is formed on the outer peripheral surface of the knurl, a knurl is formed on the inner periphery of the nut piece window corresponding to this knurl, and the piece member is knurl fitted to the nut piece window, As in the past, the positioning arm that hinders the assembling of the piece member can be abolished, and the piece member can be mounted from the outer diameter side of the nut, improving the assembling property and eliminating the caulking process. By fitting, the posture of the piece member with respect to the nut is stable, and it is difficult for a step to be formed between the piece member and the piece window of the nut, and a highly reliable piece that can prevent positioning of the piece member and perform high-precision positioning. A ball screw can be provided.

  Preferably, as in the invention described in claim 2, when the tooth width of the knurl of the piece member is set to be slightly larger than the groove width between the teeth of the knurl of the piece window, In the process of press-fitting into the piece, it is possible to closely fit the piece member knurled or the piece window knurled while cutting, so that the play of the piece member can be further suppressed.

  Further, as in the third aspect of the invention, if a non-knurl portion that does not form the knurl is provided on a part of the inner peripheral surface of the piece window of the nut, an error may occur during assembly of the piece member. This makes it easy to match the position of the connecting groove of the piece member with respect to the screw groove of the nut, thereby improving the assembling property of the piece member.

  Further, as in the invention described in claim 4, if the piece member is a sintered metal formed by MIM, even if it has a high workability and a complicated shape, the desired shape / Can be molded to dimensions.

  According to a fifth aspect of the present invention, the piece window is formed in a circular shape, the piece member is formed in a circular shape corresponding to the piece window, and a flat surface is formed in the trunk portion. In this case, when assembling the piece member, it is possible to prevent erroneous assembly and to easily match the position of the connecting groove of the piece member with respect to the screw groove of the nut, thereby improving the assembling property of the piece member.

  Further, as in the invention described in claim 6, if a flat portion is formed at a position corresponding to the piece window in one end portion of the nut, when the piece type ball screw is assembled to the housing, the piece The position of the member can be easily identified, and the connecting groove of the piece member and the screw groove of the nut can be easily and accurately positioned.

  According to a seventh aspect of the present invention, the method invention described in claim 7 includes a screw shaft having a helical thread groove formed on the outer peripheral surface thereof, and an external fit on the screw shaft, and a helical screw groove formed on the inner peripheral surface. And a plurality of balls accommodated in a rolling path formed by the thread grooves facing each other, and a piece window drilled in a body portion of the nut, and the rolling path is disposed on the inner periphery. In the manufacturing method of a piece-type ball screw provided with a piece member formed with a connecting groove serving as a circulation path, a knurled linear knurl is formed on the outer circumferential surface of the piece member. A knurl is formed on the inner periphery of the nut piece window, and the piece member is knurl-fitted to the nut piece window so that the two knurls mesh with each other.

  As described above, the screw shaft is formed with a spiral screw groove on the outer peripheral surface, the nut is fitted on the screw shaft and the spiral screw groove is formed on the inner peripheral surface, and the opposing screw groove is formed. A plurality of balls housed in the rolling path, and a piece member fitted into a piece window drilled in the trunk of the nut and having a connecting groove formed on the inner periphery with the rolling path as a circulation path; , A knurled line is formed on the outer peripheral surface of the piece member, and a knar is formed on the inner periphery of the nut piece window corresponding to the knar. Since the piece member is knurled into the nut piece window so that both the knurles mesh, the positioning arm that hinders the assembly of the piece member can be eliminated and the piece member can be mounted from the outer diameter side of the nut. As well as improving assembly, it eliminates caulking and knurls By this fixing, the posture of the piece member with respect to the nut is stabilized, and it is difficult for a step to be generated between the piece member and the piece window 6 of the nut. A ball screw can be provided.

  The piece ball screw according to the present invention includes a screw shaft having a helical thread groove formed on the outer peripheral surface, a nut externally fitted to the screw shaft, and a spiral screw groove formed on the inner peripheral surface, A plurality of balls accommodated in a rolling path formed by the thread grooves facing each other and a piece window drilled in a body portion of the nut are fitted, and the rolling path is used as a circulation path on the inner periphery. And a piece-type ball screw provided with a connecting groove, and a knurled linear knurl is formed on the outer peripheral surface of the piece member, and an inner part of the nut piece window corresponding to the knurl. Since a knurl is formed on the circumference and the piece member is knurl-fitted to the piece window of the nut, the positioning arm that hinders the assembling property of the piece member is abolished and the piece member is nuted. It can be mounted from the outer diameter side of the tube, improving assembly and caulking By abolishing the work and fitting the knurles, the posture of the piece member with respect to the nut is stabilized, and it becomes difficult for a step to be formed between the piece member and the piece window of the nut. A highly reliable piece-type ball screw that can be provided can be provided.

  In addition, the method of manufacturing the piece-type ball screw according to the present invention includes a screw shaft having a helical thread groove formed on the outer peripheral surface, and a screw thread that is externally fitted to the screw shaft and formed on the inner peripheral surface. And a plurality of balls accommodated in a rolling path formed by the opposing thread grooves, and a piece window drilled in the body of the nut, and the rolling path on the inner periphery And a piece-shaped ball screw manufacturing method comprising a piece member having a connecting groove having a circular path, and a knurled linear knurl is formed on the outer circumferential surface of the piece member. Since a knurl is formed in the inner periphery of the nut piece window, and the piece member is knurled to the nut piece window so that both the knurles mesh with each other, positioning that hinders assembling of the piece member Can be removed from the outer diameter side of the nut It is possible to improve the verticality, and by eliminating the caulking process and fixing with the knurling, the posture of the piece member with respect to the nut is stabilized, and it becomes difficult for a step to be formed between the piece member and the piece window of the nut. Highly accurate positioning is possible with reduced sticking.

(A) is a top view which shows one Embodiment of the piece type ball screw which concerns on this invention, (b) is a longitudinal cross-sectional view same as the above. (A) is sectional drawing which shows the nut which concerns on this invention, (b) is a partial sectional view same as the above. It is a perspective view showing the piece member of the piece type ball screw concerning the present invention. It is a perspective view which shows the nut which concerns on this invention. It is explanatory drawing which shows the method of mounting | wearing with the piece member on the nut which concerns on this invention. (A) is explanatory drawing which shows the state which press-fits a piece member in the piece window of a nut, (b) is the same as the above, explanatory drawing which shows after press-fitting of a piece member, (c) is the nut of a nut and a piece member. It is a schematic diagram which shows a fitting part. (A) is a top view which shows the modification of the nut which concerns on this invention, (b) is a principal part enlarged view which shows the piece window part of (a). It is explanatory drawing which shows the post-processing method of the nut which concerns on this invention. (A) is a top view which shows the conventional piece-type ball screw, (b) is a longitudinal cross-sectional view same as the above. (A) is explanatory drawing which shows the caulking method of the piece member of FIG. 9, (b) is a schematic diagram which shows the state of the plastic deformation of the piece member of (a). It is a schematic diagram which shows the contact state of the piece member and caulking jig of Fig.10 (a).

  A screw shaft having a helical thread groove formed on the outer peripheral surface, a nut externally fitted to the screw shaft and having a spiral thread groove formed on the inner peripheral surface, and a roller formed by the opposing screw groove. A piece member fitted with a plurality of balls accommodated in the moving path and a circular piece window formed in the trunk of the nut, and having a connecting groove having the rolling path as a circulation path formed on the inner periphery. And the piece member is formed by a MIM from a sintered alloy in a circular cross section corresponding to the piece window, and a knurling that extends linearly with a flat surface is formed on the outer peripheral surface of the piece member. A knurl is formed on the inner periphery of the nut piece window corresponding to the knurl, and the tooth width of the knurl of the piece member is slightly larger than the groove width between the teeth of the knurl of the piece window. And the piece member is knurled into the piece window of the nut.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
1A and 1B show an embodiment of a piece-type ball screw according to the present invention, in which FIG. 1A is a plan view, FIG. 2B is a longitudinal sectional view, FIG. 2A is a sectional view of a nut, and FIG. FIG. 3 is a perspective view showing a piece member of the piece type ball screw according to the present invention, FIG. 4 is a perspective view showing a nut according to the present invention, and FIG. 5 is a view showing the piece member on the nut according to the present invention. FIG. 6A is an explanatory view showing a state in which the piece member is press-fitted into the piece window of the nut, FIG. 6B is an explanatory view showing the state after the piece member is press-fitted, and FIG. ) Is a schematic view showing a fitting portion of a nut and a knurled member, FIG. 7A is a plan view showing a modification of the nut according to the present invention, and FIG. 7B is a piece window portion of FIG. FIG. 8 is an explanatory view showing a post-processing method of a nut according to the present invention.

  A piece type ball screw 1 shown in FIG. 1 has a screw shaft 2 having a helical thread groove 2a formed on an outer peripheral surface thereof, and is externally fitted to the screw shaft 2 to form a helical screw groove 3a on an inner peripheral surface thereof. And a plurality of balls 4 accommodated in a rolling path formed by the opposing screw grooves 2a and 3a, and a piece member 5 serving as a circulation member for these balls 4.

  The cross-sectional shape of each thread groove 2a, 3a may be a circular arc shape or a Gothic arc shape, but here, it has a Gothic arc shape that allows a large contact angle with the ball 4 and a small axial clearance. Is formed. Thereby, the rigidity with respect to an axial load becomes high and generation | occurrence | production of a vibration can be suppressed.

  The cylindrical nut 3 has a generally circular piece window 6 having a substantially circular cross section that penetrates the inner and outer peripheral surfaces and cuts out a part of the screw groove 3a. A circular piece member 5 is fitted. A connecting groove 5a is formed on the inner side of the piece member 5 to connect adjacent ones of the screw grooves 3a, and the ball 4 rolls between the connecting groove 5a and the substantially one part of the screw groove 3a. Constitutes the road. A large number of balls 4 interposed between the inner and outer screw grooves 2a and 3a in the rolling path roll along the screw grooves 2a and 3a, are guided by the connecting grooves 5a of the piece member 5, and are screw shafts. 2 over the thread 2 and return to the adjacent screw groove 3a, and roll along the screw grooves 2a and 3a again. In addition, although the thing in which the piece window 6 and the piece member 5 were formed in the cross-sectional substantially circular shape was illustrated here, not only circular but an oval shape may be sufficient, for example.

  In this embodiment, when assembling the piece type ball screw 1 to a housing (not shown), small diameter portions 3b and 3b are formed at both ends of the outer periphery of the nut 3 so that the nut 3 can be easily fitted. A flat portion 3c is formed at one end of the nut 3 so that the position of the piece member 5 can be easily identified. Further, in order to facilitate the mounting of the piece member 5, a chamfered portion 6 a is formed in the opening on the outer diameter side of the piece window 6 of the nut 3.

  As shown in FIG. 2A, the connecting groove 5a of the piece member 5 is formed in an S-shape so as to smoothly connect the adjacent screw grooves 3a and 3a of the nut 3 to each other. The connecting groove 5a is connected to the screw groove 3a so as to coincide with the groove edge portion 7 opened to the piece window 6 of the adjacent screw groove 3a. Further, as shown in FIG. 2B, the depth of the connecting groove 5a is set to such a depth that the ball 4 can exceed the thread of the screw groove 2a in the screw shaft 2 within the connecting groove 5a.

  The piece member 5 is made of a sintered alloy obtained by adjusting a metal powder into a plastic shape and molded by an injection molding machine. In this injection molding, first, metal powder and a binder made of plastic and wax are kneaded by a kneader, and the kneaded product is granulated into pellets. The granulated pellets are molded by so-called MIM (Metal Injection Molding), which is supplied to a hopper of an injection molding machine and pushed into a mold in a heated and melted state. A sintered alloy formed by such an MIM can be easily and accurately formed into a desired shape / dimension even if it has a high workability and a complicated shape.

  As the metal powder, a material that can be subsequently carburized and hardened, for example, C (carbon) is 0.13 wt%, Ni (nickel) is 0.21 wt%, Cr (chromium) is 1.1 wt%, Cu (copper) Exemplifies SCM415 which is 0.04 wt%, Mn (manganese) is 0.76 wt%, Mo (molybdenum) is 0.19 wt%, Si (silicon) is 0.20 wt%, and the rest is Fe (iron). Can do. The piece member 5 is performed by adjusting the carburizing quenching and tempering temperatures. In addition to this, the material of the piece member 5 contains 3.0 to 10.0 wt% of Ni, and is excellent in workability and corrosion resistance (FEN8 of Japan Powder Metallurgy Industry Standard), or C is 0.1. It may be a precipitation hardening stainless steel SUS630 made of 07 wt%, Cr 17 wt%, Ni 4 wt%, Cu 4 wt%, and the rest made of Fe or the like. This SUS630 can appropriately increase the surface hardness in the range of 20 to 33 HRC by solution heat treatment, and can ensure toughness and high hardness.

  When the piece member 5 is formed of a carburized material such as SCM415, the piece member 5 is hardened by carburizing and quenching and tempering temperature adjustment or by carburizing and quenching so that the surface hardness is in the range of 30 to 40 HRC. Yes. Further, when the piece member 5 is formed of precipitation hardening stainless steel such as SUS630, the surface hardness is set to 30 HRC or more by solution heat treatment. This SUS630 has a feature that the alloy element is easily solid-solutioned by heating to a predetermined temperature and then rapidly cooling.

  In the present embodiment, as shown in FIG. 3, the piece member 5 includes a body portion 8 and a head portion 9 that extends from the body portion 8 to the outer diameter side (the radially outer side of the nut 3). The trunk portion 8 is formed in a substantially circular cross section so as to correspond to the shape (circular hole) of the piece window 6 of the nut 3, and a flat surface 8 a is formed at an opposing position on the outer periphery of the trunk portion 8. Further, the head 9 is formed with a linear recess 9a having an outer diameter surface that is recessed from the other portions, and rises from the recess 9a to the outer diameter side, and the cross section connecting the pair of flat surfaces 8a has a triangular shape. A linear protrusion 9b is formed.

  Here, a knurl (spline) 10 extending linearly from the body 8 to the head 9 on the outer peripheral surface of the piece member 5 is formed. This knurl 10 is formed on the flat surface 8a so that the position of the connecting groove 5a of the piece member 5 with respect to the screw groove 3a of the nut 3 can be easily matched when the piece member 5 is assembled. Absent.

  On the other hand, as shown in FIG. 4, the inner peripheral surface of the piece window 6 of the nut 3 also corresponds to the knurl 10 of the piece member 5 described above, from the outer diameter side to the inner diameter side excluding the chamfered portion 6 a of the piece window 6. A knurl (spline) 11 is formed extending linearly.

  And the assembly of the piece member 5 is performed from the outer diameter side with respect to the piece window 6 of the nut 3, as shown in FIG. That is, the piece member 5 is fitted to the piece window 6 in a state where the flat surface 8 a and the protruding portion 9 b of the piece member 5 are aligned with the flat portion 3 c of the nut 3. Specifically, as shown in FIG. 6A, the piece member 5 is mounted from the outer diameter side of the nut 3 toward the opening on the outer diameter side of the piece window 6 (indicated by an arrow in the figure), The knurl 10 of the piece member 5 and the knurl 11 of the piece window 6 are fitted together. Then, as shown in (b), the piece member 5 is fitted to a position slightly recessed from the opening on the outer diameter side of the piece window 6 so as not to protrude from the outer diameter surface of the nut 3.

  The incorporation of the ball 4 will be described with reference to FIG. The ball 4 is assembled by attaching the piece member 5 to the piece window 6 of the nut 3 from the outer diameter side of the nut 3 as described above, and then applying the nut 3 from the shaft end of the screw shaft 2 to The nut 3 is rotated while being sequentially inserted between the two screw grooves 2a and 3a, and the nut 3 is moved to the screw shaft 2. In addition, after the piece member 5 is mounted on the piece window 6 of the nut 3, the ball 4 may be similarly inserted using a temporary shaft.

  In the piece type ball screw according to the present invention, the knurl 10 is formed on the outer peripheral surface of the piece member 5 and the knurl 11 is formed on the piece window 6 of the nut 3 to which the piece member 5 is mounted. Since the piece member 5 is fitted to the piece window 6 so as to engage with each other, the positioning arm that obstructs the assembling property of the piece member 5 is abolished and the piece member 5 is mounted from the outer diameter side of the nut 3. As a result, it is possible to improve the assemblability and to eliminate the caulking process that causes looseness of the piece member and to fix the piece member 5 to the nut 3 by fixing with the knurles 10 and 11, so that the piece member 5 A step is less likely to occur between the piece windows 6 of the nut 3, and a highly reliable piece type ball screw capable of highly accurate positioning by suppressing the backlash of the piece member 5 can be provided.

  In addition, the knurl 10 formed on the outer peripheral surface of the piece member 5 is tightly fitted to the knurl 11 formed on the inner peripheral surface of the piece window 6 of the nut 3 by press-fitting while performing slight cutting. May be. Specifically, as shown in FIG. 6C, the tooth width W1 of the knurl 10 of the piece member 5 is slightly larger than the groove width W2 between the teeth of the knurl 11 of the piece window 6 (W1> W2). Thus, in the process of press-fitting the piece member 5 into the piece window 6, it is possible to fit closely while cutting the groove between the teeth of the knurl 10 of the piece member 5 or the knurl 11 of the piece window 6 (cross hatching in the figure). The play of the piece member 5 can be further suppressed. In this case, by providing a difference in the surface hardness of the piece member 5 and the piece window 6, it is determined whether the member to be cut is the piece member 5 or the piece window 6.

  Further, as shown in FIGS. 7A and 7B, a non-nar part 6b that does not form the nar 11 is provided on a part of the inner peripheral surface of the piece window 6 of the nut 3, and the non-nar part 6b is cut. The piece member 5 may be press-fitted and fitted, and further, although not shown, no knurl is formed at the piece window of the nut, and the inner diameter of this piece window is larger than the outer diameter of the knurled piece member. In addition to forming a small diameter and a diameter larger than the root diameter of the knurl, by forming the tip of the knurl of the piece member at the edge, the piece member is closely fitted to the piece window while being cut. May be.

  As described above, when the knurl 10 is formed on the outer peripheral surface of the piece member 5 and the piece member 5 is press-fitted at least partially into the piece window 6 of the nut 3 by press cutting, chips are generated in the piece member 5 or the nut 3. There is a fear. In this case, as shown in FIG. 8, after the piece member 5 is mounted on the nut 3, it is desirable to perform removal using a hand grinding machine 12 such as a router.

  The embodiment of the present invention has been described above, but the present invention is not limited to such an embodiment, and is merely an example, and various modifications can be made without departing from the scope of the present invention. Of course, the scope of the present invention is indicated by the description of the scope of claims, and further, the equivalent meanings described in the scope of claims and all modifications within the scope of the scope of the present invention are included. Including.

  The piece type ball screw according to the present invention can be applied to a piece type ball screw used for an electric actuator of an automobile or the like.

DESCRIPTION OF SYMBOLS 1 Piece type ball screw 2 Screw shaft 2a, 3a Thread groove 3 Nut 3b Small diameter part 3c Flat part 4 Ball 5 Piece member 5a Connecting groove 6 Piece window 6a Chamfer 6b Non-knurl part 7 Groove edge part 8 Body part 8a Flat surface 9 of the trunk portion Head portion 9a of the piece member Recessed portion 9b of the head portion Projection portions 10 and 11 of the head portion 12 Hand grinder 51 Piece type ball screw 52 Screw shaft 52a, 53a Screw groove 53 Nut 54 Ball 55 Piece Member 55a Connection groove 55b Arm 55c Body 55f Guide wall 55g End 56 Frame window 57 Caulking punch 57a Processing surface

Claims (7)

A screw shaft having a helical thread groove formed on the outer peripheral surface;
A nut externally fitted to the screw shaft and having a spiral thread groove formed on the inner peripheral surface;
A plurality of balls accommodated in a rolling path formed by the opposing thread grooves;
In a piece-type ball screw provided with a piece member fitted into a piece window drilled in the trunk portion of the nut and having a connection groove having an inner circumference as the rotation path,
A knurled line is formed on the outer peripheral surface of the piece member, and a knar is formed on the inner circumference of the piece window of the nut corresponding to the knar. Koma type ball screw characterized by being combined.   The piece-type ball screw according to claim 1, wherein a tooth width of the knurled member is set to be slightly larger than a groove width between the knurled teeth of the piece window.   The piece-type ball screw according to claim 1 or 2, wherein a non-knurl portion that does not form the knurl is provided on a part of an inner peripheral surface of the piece window of the nut.   The piece type ball screw according to claim 1, wherein the piece member is a sintered metal formed by MIM.   The piece type ball screw according to claim 1, wherein the piece window is formed in a circular shape, the piece member is formed in a circular shape corresponding to the piece window, and a flat surface is formed in the body portion.   The piece type ball screw according to claim 5, wherein a flat portion is formed at a position corresponding to the piece window in one end portion of the nut. A screw shaft having a helical thread groove formed on the outer peripheral surface;
A nut externally fitted to the screw shaft and having a spiral thread groove formed on the inner peripheral surface;
A plurality of balls accommodated in a rolling path formed by the opposing thread grooves;
A piece member fitted to a piece window drilled in a body portion of the nut and having a connecting groove having an inner circumference and the rolling path as a circulation path. ,
A knurl extending linearly is formed on the outer peripheral surface of the piece member, a knurl is formed on the inner periphery of the piece window of the nut corresponding to the knurl, and the piece member is engaged with both the knurls. A method of manufacturing a piece-type ball screw, wherein a knurled fitting is performed on the piece window of the nut.

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