JP2007239845A - Piece type ball screw - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To inexpensively provide a piece type ball screw for improving reliability, by securing positioning accuracy and fixing force of a piece member to a nut, by enhancing rigidity of arms in the piece member. <P>SOLUTION: This piece type ball screw has the piece member 5 fitted to a piece window 6 bored in a body part of the nut 3 and forming a connecting groove 5a with a rolling passage as a revolving passage, and forms this piece member 5 of a sintered alloy by MIM. A pair of arms 9 are projected in a cross-sectional substantially circular shape corresponding to groove curvature of a screw groove 3a in the nut 3 on both sides of the pierce member 5. These arms 9 are engaged with the screw groove 3a, and the piece member 5 is positioned. A recess part 16 is formed by cutting off an outer diameter side corner part of an end surface in one arm 9 among the pair of arms 9. Since a gate 15 is arranged via this recess part 16, cost can be reduced by automatically controlling a work process by cutting the gate 15 in the shorted length only by an automatic machine. <P>COPYRIGHT: (C)2007,JPO&amp;INPIT

Description

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

  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, one of which 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 FIG. In this piece type ball screw, a piece member fitting opening 51 having an oval shape is formed in the nut main body 50a of the rotary nut 50 so as to penetrate the inner and outer peripheral surfaces, and a piece member 52 is provided on the inner diameter side of the piece member fitting opening 51. It is inserted from.

  The piece member 52 is formed with a connecting groove 52a for connecting adjacent circumferential portions of the inner screw groove 53, and engages with the inner screw groove 53 of the rotary nut 50 so that the piece member 52 is pivoted with respect to the nut body 50a. A pair of arms 54 and 54 for positioning in a direction are integrally provided. The pair of arms 54, 54 are provided at both ends of the piece member 52 in the axial direction so as to protrude opposite to each other in the circumferential direction, and are formed in a semicircular cross-sectional shape that fits into the inner screw groove 53. Here, the portion of the inner screw groove 53 with which the arm 54 is engaged becomes a non-ball circulating portion.

  Both side edges in the circumferential direction of the rotary nut 50 in the piece member 52 are recessed portions 55 whose outer diameter surfaces are recessed relative to other portions, and the side surfaces rising from these recessed portions 55 to the outer diameter side and facing the circumferential direction of the piece member 52. A pair of guide walls 56 are provided along. The opening 51 for fitting the piece member of the nut main body 50a is provided with an engaging step portion 57 at the opening edge of a pair of opposed inner side surfaces, and the width of the opening side portion is slightly wider than the engaging step portion 57. ing.

The piece member 52 is fitted into the piece member fitting opening 51 of the nut main body 50a from the inner diameter side, the pair of arms 54 is engaged with the inner screw groove 53, and the guide wall 56 is plastically deformed to deform the nut main body 50a. Fixed to. The fixing by the plastic deformation is performed by caulking and fixing the guide wall 56 to a pair of opposed inner side surfaces of the piece member fitting opening 51. Specifically, the piece wall 52 is fixed with certainty by crimping the guide wall 56 to the engagement step portion 57 to engage with each other. The piece member 52 with the arm 54 is used to prevent the piece member 52 from being detached and positioned by the arm 54, to obtain high-precision and high-strength performance, and to easily and reliably fix the piece member 52. Can do.
JP 2001-289301 A

  In such a conventional piece type ball screw, the piece member 52 is prevented from being detached and positioned by the arm 54 of the piece member 52, and a high-precision and high-strength performance can be obtained. 52 has a feature that can be fixed. Since such a piece member 52 is difficult to be processed and formed at low cost by a general cutting process or the like, a so-called MIM (Metal Injection Molding) in which a sintered alloy obtained by adjusting a metal powder into a plastic shape is formed by an injection molding machine. ). However, in this case, the gate position when the kneaded sintered alloy is injection-molded into the mold needs to be provided at a position where there is no problem in fixing the piece member 52 to the nut body 50a. Furthermore, when this gate portion is cut and separated by an automatic machine, the remaining gate cannot be avoided, and inevitably involves a step of manual repair after cutting. For this reason, the mass productivity is remarkably hindered and the manufacturing cost is increased.

  The present invention has been made in view of such circumstances, and has improved the rigidity of the arm of the piece member, and has ensured the positioning accuracy and fixing force of the piece member with respect to the nut, and has improved reliability at a low cost. It aims to provide a ball screw.

  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. And a plurality of balls accommodated in a rolling path formed by opposing screw grooves, and a piece window drilled in a body portion of the nut, and the rolling A piece-type ball screw in which a connecting groove having a circulation path as a circulation path is formed, and the piece member is formed of a sintered alloy by MIM. A pair of arms protrudes on both sides of the piece member. The piece member is positioned by engaging these arms with the thread groove of the nut, and a gate is provided at one end of the pair of arms via an escape portion.

  In this way, the piece member is provided with a piece member that is fitted to a piece window formed in the trunk portion of the nut and is formed with a connecting groove having a rolling path as a circulation route. The piece member is formed of a sintered alloy by MIM. In the piece-type ball screw, a pair of arms protrudes on both sides of the piece member, and the piece member is positioned by engaging these arms with the screw groove of the nut, and one arm of the pair of arms is positioned. Since the gate is provided at the end via the relief, the gate can be cut to the shortest length by an automatic machine while avoiding interference between the end of the arm and the cutting tool, and the gate is arm It can cut | disconnect so that it may not protrude on the outer-diameter side from the circumscribed circle diameter. In addition, the remaining amount of the gate can be made relatively large, and a step of manually repairing the gate portion after cutting is not required as in the prior art. Therefore, the piece member can be accurately formed into a desired shape and size, and the work process can be automated to reduce the cost.

  Preferably, as in the invention described in claim 2, if the relief portion is formed by cutting out an outer diameter side corner portion of the end face of the arm, interference between the end portion of the arm and the cutting tool is prevented. By avoiding this, the gate can be easily and reliably cut to the shortest length.

  According to a third aspect of the present invention, the thread groove section of the nut is formed in a Gothic arc shape, and the arm is formed in a substantially circular section corresponding to the groove curvature of the thread groove. For example, the contact area between the arm and the screw groove can be secured to reduce the surface pressure, and the contact with the arm can be made at two points having a predetermined span, so that the positioning and fixing of the piece member with respect to the nut is stabilized. .

    According to a fourth aspect of the present invention, the piece member is made of a sintered alloy made of carburized metal powder, and is hardened by carburizing and quenching, and the guide wall has a hardness of 15 by tempering. If the piece member is fixed to the piece window by a caulking part formed by plastically deforming the guide wall, the toughness of the guide wall serving as the caulking part is high. It is possible to prevent cracks and the like from occurring when caulking and fixing to the nut.

  Moreover, if the piece window is formed in a substantially circular cross section and the piece member is formed in a circular shape corresponding to the piece window as in the invention described in claim 5, the man-hour for processing the piece window is reduced. The cost can be reduced and the cost can be reduced, and the piece member can be easily and accurately positioned in the axial direction with respect to the nut, and the reliability can be improved.

  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 opposing screw grooves, and a connecting groove that is fitted to a piece window drilled in a body portion of the nut and has the rolling path as a circulation path. A piece-type ball screw formed of a sintered alloy made of MIM, and a pair of arms projecting on both sides of the piece member, and these arms are threaded grooves of the nut. The piece member is positioned by being engaged with each other, and a gate is provided at one end of the pair of arms via an escape portion, so that interference between the end of the arm and the cutting tool occurs. The gate can be cut to the shortest length by an automatic machine. And can gate is cut so as not to protrude radially outwardly from the circumscribed circle diameter of the arm. In addition, the remaining amount of the gate can be made relatively large, and a step of manually repairing the gate portion after cutting is not required as in the prior art. Therefore, the piece member can be accurately formed into a desired shape and size, and the work process can be automated to reduce the cost.

  A screw shaft having a spiral 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 both opposing screw grooves. A plurality of balls accommodated in the movement path, and a piece member fitted to a piece window drilled in the trunk portion of the nut and having a connecting groove having the rolling path as a circulation path, In the piece-type ball screw in which the piece member is formed of a sintered alloy by MIM, a pair of arms having a substantially circular cross section corresponding to the groove curvature of the screw groove in the nut are protruded on both sides of the piece member. The piece member is positioned by being engaged with the thread groove of the nut, and an outer diameter side corner portion of an end surface of one arm of the pair of arms is cut away to form a relief portion. A gate is provided.

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, wherein FIG. 1A is a plan view and FIG. 1B is a longitudinal sectional view. 2A is a cross-sectional perspective view of the nut, FIG. 2B is a cross-sectional view, FIG. 3A is a plan view showing the piece member, FIG. 2B is a bottom view, and FIG. is there.

  This piece-type ball screw 1 includes a screw shaft 2 having a helical thread groove 2a formed on the outer peripheral surface, and a nut externally fitted to the screw shaft 2 and having a helical screw groove 3a formed on the inner peripheral surface. 3, a large number of balls 4 accommodated in a rolling path formed by both opposing screw grooves 2 a and 3 a, 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 so as 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, and are guided by the connecting groove 5a of the piece member 5 to be screw shafts. 2 over the thread 2 and return to the adjacent thread groove 3a, and roll along the thread grooves 2a and 3a again. In this embodiment, the piece window 6 is formed in a substantially circular cross section, and the piece member 5 is formed in a circular shape corresponding to the piece window 6, so that the number of processing steps of the piece window 6 can be reduced and the cost can be reduced. In addition, the piece member 5 can be easily and accurately positioned in the axial direction with respect to the nut 3, and the reliability can be improved. Note that the piece window does not necessarily have a circular shape, and may be, for example, an oval shape.

  As shown in FIG. 2A, the connecting groove 5a of the piece member 5 is formed to be curved in an S shape so as to smoothly connect the adjacent screw grooves 3a, 3a of the nut 3. Therefore, as shown in FIG. 2B, the connecting window 5a is connected to the screw groove 3a so that both the frame window edges 7 and 7 are aligned with the groove edge 8 of the adjacent screw groove 3a of the nut 3. ing. The depth of the connecting groove 5a is set to a depth at which the ball 4 can exceed the thread of the screw groove 2a in the screw shaft 2 within the connecting groove 5a. Further, an arm 9 having a round bar shape with a substantially circular cross section is provided on both sides of the piece member 5 and is engaged with the thread groove 3a of the nut 3 via a predetermined radial clearance. The arm 9 positions the piece member 5 in the axial direction with respect to the nut 3, and prevents the piece member 5 from coming out of the piece window 6 radially outward. In the present embodiment, since the screw groove 3a of the nut 3 is formed in a Gothic arc shape, the contact with the arm 9 can be made at two points having a predetermined span, and the piece member with respect to the nut 3 can be contacted. Positioning and fixing 5 is stable.

  Further, as shown in FIG. 3C, the piece member 5 includes a trunk portion 10 on which the arms 9 and 9 are projected, and an outer diameter side from the trunk portion 10 (a radially outer side of the nut 3). The head 11 extends. The trunk portion 10 is formed in a circular cross section so as to correspond to the shape (circular hole) of the piece window 6 of the nut 3 and is fitted to the piece window 6. Further, the head portion 11 is formed with recessed portions 12 whose outer diameter surfaces are recessed from the other portions on both sides (both sides in the circumferential direction of the nut 3), and rises from these recessed portions 12 to the outer diameter side so that an arc-shaped circumferential surface is formed. A pair of guide walls 13, 13 are arranged so as to face each other. Then, after inserting the piece member 5 into the piece window 6 and engaging the arms 9 and 9 with the thread groove 3a of the nut 3, the guide walls 13 and 13 are tightened using a crimping jig (not shown). The piece member 5 is fixed to the nut 3 by a crimping portion 14 formed by plastic deformation on the edge 6a side of the piece window 6 (see FIG. 2B). A predetermined inclination angle θ is formed at the edge 6a of the piece window 6 and is set in a range of 20 to 45 °. If the amount of crimping further increases, cracking occurs in the crimped portion 14 and the reliability is impaired. If the inclination angle θ is less than 20 °, the piece member 5 is loose due to the springback of the crimped portion 14. This causes a problem in positioning accuracy and fixing force, which is not preferable.

  Here, the piece member 5 is made of a sintered alloy prepared by adjusting a metal powder into a plastic shape and molding it with 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. And it is formed by MIM. That is, the granulated pellets are supplied to a hopper of an injection molding machine and are molded by being pressed 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.

  In this embodiment, as the metal powder, a material that can be subsequently carburized and quenched, for example, C (carbon) is 0.13 wt%, Ni (nickel) is 0.21 wt%, and Cr (chromium) is 1.1 wt%. Cu (copper) is 0.04 wt%, Mn (manganese) is 0.76 wt%, Mo (molybdenum) is 0.19 wt%, Si (silicon) is 0.20 wt%, and the remainder is Fe (iron). The SCM 415 can be exemplified. 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 hardness 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. At the same time, using the high-frequency temper device, the caulking portion 14 shown in FIG. 2 (b), that is, the guide wall 13 shown in FIG. 3 (c) is tempered, and the hardness is set in the range of 15 to 30HRC. Has been.

  The ball 4 is assembled by attaching the piece member 5 to the piece window 6 of the nut 3 from the inner diameter side of the nut 3, and then applying the nut 3 from the shaft end of the screw shaft 1 to place the ball 4 between the screw grooves 2 a and 3 a. The nut 3 is rotated while being sequentially inserted into the screw shaft 1, and the nut 3 is moved to the screw shaft 1. 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.

  Here, in this embodiment, the gate 15 when the piece member 5 is injection-molded into the mold is formed at the end of one arm 9 of the pair of arms 9 and 9, as shown in FIG. It is provided and is formed in a cylindrical shape protruding in the horizontal direction. Furthermore, an escape portion 16 is provided at the end of the arm 9. The escape portion 16 is formed by cutting out the outer diameter side corner of the end surface of the arm 9. When the gate 15 is cut, the escape portion 16 can easily and reliably cut the gate 15 to the shortest length by avoiding interference between the end of the arm 9 and the cutting tool (two-dot chain line). Indicates a case where there is no escape portion 16). Therefore, the gate 15 can be cut so as not to protrude from the circumscribed circle diameter of the arm 9 to the outer diameter side (the side engaged with the screw groove 3a of the nut 3). That is, the gate 15 can be cut so as to be smaller inward than the circumscribed circle diameter of the arm 9 through a predetermined gap δ. Accordingly, the entire arm 9 can be brought into contact with the thread groove 3 of the nut 3, and the piece member 5 can be stably positioned and fixed. Further, since the gate 15 is formed in a predetermined shape at the end of the arm 9, the remaining amount of the gate 15 can be made relatively large, and can be cut and separated only by an automatic machine. The process of repairing the gate part manually later becomes unnecessary. Therefore, the piece member 5 can be accurately formed into a desired shape and size, and the work process can be automated to reduce the cost.

  The position of the gate 15 is not limited to this, but may be formed on the inner diameter surface side (screw shaft 2 side) of the piece member 5, but since it is close to the outer diameter of the screw shaft 2, The protrusion may interfere with the screw shaft 2 and hinder the smooth operation of the piece type ball screw 1. On the other hand, if the gate 15 is arranged on the outer diameter surface side of the piece member 5 (outer diameter surface side of the nut 3), the operation of the piece type ball screw 1 is not adversely affected, but the outer diameter surface side of the piece member 5. Is a seating surface when the piece member 5 is sintered. If there is a protrusion remaining on the gate 15, the posture during the sintering becomes unstable, and the amount of deformation of the arm 9 and the piece due to its own weight before the completion of sintering. The dimensional accuracy of the member 5 is not preferable.

  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.

(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 a cross-sectional perspective view which shows the nut which concerns on this invention. (B) is a cross-sectional view same as the above. (A) is a top view which shows the piece member which concerns on this invention. (B) is the same top view as seen from below. (C) is a front view as above. (A) is a longitudinal cross-sectional view which shows the conventional piece type | formula ball screw. (B) is a cross-sectional view of the same as above.

Explanation of symbols

1 ······ Poma type ball screw 2 ·············· Screw shafts 2a, 3a Nut 4 ... Ball 5 ... Piece member 5a ... Connection groove 6 ... Piece Window 6a ... Edge 7 ... Frame window edge 8 ... Groove edge 9 ... ··· Arm 10 ······················································································ Wall 14 ···································································································· ················································································· 5 a ... Connection groove 53 ... Internal thread groove 54 ... Arm 55 ... Recess 56 ... ··········· Guide wall 57 ····························································· Ball δ・ ・ ・ ・ ・ ・ ・ Gap θ ・ ・ ・ ・ ・ Inclination angle

Claims (5)

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 housed in a rolling path formed by opposing screw grooves;
And a piece member that is fitted in a piece window formed in the trunk portion of the nut and has a connecting groove having the rolling path as a circulation path. The piece member is made of sintered alloy by MIM. In Takoma type ball screw,
A pair of arms protrudes on both sides of the piece member, and the pieces are positioned by engaging these arms with the thread grooves of the nut, and at the end of one arm of the pair of arms. A piece-type ball screw characterized in that a gate is provided through the section.   The piece type ball screw according to claim 1, wherein the relief portion is formed by cutting an outer diameter side corner portion of an end face of the arm.   The piece type ball screw according to claim 1 or 2, wherein a cross section of the screw groove in the nut is formed in a Gothic arc shape, and the arm is formed in a substantially circular cross section corresponding to the groove curvature of the screw groove.   The piece member is made of a sintered alloy made of carburized metal powder, and is hardened by carburizing and quenching, and the guide wall is set to a hardness of 15 to 30 HRC by tempering. The piece type ball screw according to any one of claims 1 to 3, wherein the piece member is fixed to the piece window by a deformed caulking portion.   The piece type ball screw according to any one of claims 1 to 4, wherein the piece window is formed in a substantially circular cross section, and the piece member is formed in a circular shape corresponding to the piece window.

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