JP4822514B2 - Koma type ball screw - Google Patents

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. However, the arm 54 is loaded with all the load applied to the connecting groove 52a, that is, the pulling load with respect to the piece member 52. Such a load includes a centrifugal force generated by the revolution of the ball and a load due to a radial component force when the ball rides on the inner thread groove 53 of the nut 50 from the connecting groove 52a of the piece member 52. There was a risk that the ball would be poorly circulated due to deformation under the load of.

  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 in bridge type ball screw and a bridge member which coupling grooves are formed to circular path of Douro, the bridge member is formed by injection molding a sintered alloy comprising a metal powder, its head in the pair Guide pieces are arranged facing both sides in the circumferential direction, and the piece member is fixed to the nut by a caulking portion formed by plastically deforming these guide walls on the edge side of the piece window. The cross-sectional shape of the thread groove of the screw shaft is formed in a Gothic arc shape, Cross section on either side with a substantially circular pair of arms are projected circumferentially opposite, of the arms the diameter is set in a range of 0.7 to 0.9 of the diameter of the ball, of the pair of The arm is positioned in contact with two contact points having a predetermined span in each thread groove of the nut.

Thus, in the piece-type ball screw having the piece member that is fitted to the piece window formed in the trunk portion of the nut and has the connection groove having the rolling path as the circulation path, the piece member is made of metal powder. is formed by injection molding a sintered alloy composed of a pair of guide walls are disposed opposite to both circumferential sides to its head, it is formed by plastically deforming them guide walls on the edge side of the bridge window pressurized The piece member is fixed to the nut by the fastening portion, and the cross-sectional shape of the nut and the screw shaft is formed in a Gothic arc shape, and a pair of arms having a substantially circular cross section on both sides of the piece member are opposite in the circumferential direction. The two arms have a diameter of these arms set to a range of 0.7 to 0.9 of the diameter of the ball, and the pair of arms has a predetermined span in each thread groove of the nut. Since it is positioned in contact with a point, the piece type Without disturbing the smooth rotational movement Lumpur screws, it is possible to stably positioned and fixed bridge member in the nut, it is possible to improve the reliability of separation of the nut bridge member.

  Preferably, as in the invention described in claim 2, 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 hardened by tempering. If the piece member is fixed to the piece window by a caulking portion formed by plastically deforming the guide wall and set in a range of 15 to 30 HRC, the toughness of the guide wall serving as the caulking portion is high. Generation of cracks and the like can be prevented when the member is caulked and fixed to the nut.

  Further, as in the invention described in claim 3, if the inclination angle of the crimped portion is set in the range of 20 to 45 °, not only the occurrence of cracking of the crimped portion is prevented, but also desired As well as securing the fixing force, the reliability of the caulking portion can be improved.

  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 4, the number of processing steps of 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. in bridge type ball screw and a formed bridge member, the bridge member is formed by injection molding a sintered alloy comprising a metal powder, a pair of guide walls as a head to face the circumferential sides The piece member is fixed to the nut by a caulking portion formed by plastically deforming these guide walls to the edge side of the piece window, and the cross-sectional shape of the screw groove of the nut and the screw shaft is Gothic. A pair of arc-shaped members having a substantially circular cross section on both sides of the piece member Together with the arm is projecting circumferentially opposite, of the arms the diameter is set in a range of 0.7 to 0.9 of the diameter of the ball, to the pair of arms each thread groove of the nut Since it is positioned by contact at two contact points having a predetermined span, the piece member can be stably positioned and fixed to the nut without hindering the smooth rotational movement of the piece type ball screw, The reliability with respect to the drop-off of the piece member from the nut can be improved.

  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 a piece type ball screw in which the piece member is fixed to the piece window by a caulking portion formed by plastic deformation of the piece member, the piece window is formed in a substantially circular cross section, and the piece corresponding to the piece window The member is made of a sintered alloy having a substantially circular cross section by MIM, and a pair of arms projecting on both sides of the piece member. The diameter of these arms is 0.7 to 0.9 of the diameter of the ball. And is positioned by engaging with the thread groove 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, wherein FIG. 1A is a plan view and FIG. 1B is a longitudinal sectional view. 2 (a) is a cross-sectional perspective view of the nut, (b) is a cross-sectional view, FIG. 3 (a) is a perspective view showing a piece member, (b) is a plan view, and (c) is a side view, 4A and 4B are explanatory views showing a fixed state of the piece member.

  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 grooves 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. Here, although the cross section of the piece member 5 is exemplified from the viewpoint of workability of the piece window 6, the shape is not limited to this, 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.

  Further, as shown in FIG. 3A, the piece member 5 includes a trunk portion 10 on which arms 9 and 9 project, and an outer diameter side from the trunk portion 10 (the 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. 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.

  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, the caulking portion 14 shown in FIG. 2B, that is, the guide wall 13 shown in FIGS. 3A and 3C is tempered using a high-frequency temper device, and the hardness is in the range of 15 to 30 HRC. It is set to be.

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 2 so that the ball 4 is placed between the screw grooves 2a and 3a. The nut 3 is rotated while being sequentially inserted, 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.

  Here, in this embodiment, the diameter D of the arms 9 and 9 in the piece member 5 is set in the range of 0.7 to 0.9 of the diameter Dw of the ball 4 (0.7Dw ≦ D ≦ 0. 9Dw). 4A and 4B show the fixed state of the piece member 5. FIG. 4A shows a case where D = 0.9 Dw, and FIG. 4B shows a case where D = 0.7 Dw. As can be seen from these figures, the arm 9 and the thread groove 3a of the nut 3 are in contact at two contact points (P, P) having a predetermined span, and the piece member 5 is stably positioned and fixed to the nut 3. be able to. Therefore, the rigidity of the arm 9 in the piece member 5 can be increased, and the positioning accuracy and fixing force of the piece member 5 with respect to the nut 3 can be sufficiently secured.

  When the diameter D of the arm 9 is increased to exceed 0.9 Dw and approaches the diameter Dw of the ball 4, the rigidity of the arm 9 increases, but the processing accuracy of the thread groove 2 a of the screw shaft 2 and the piece member 5 increases. There is a possibility that the arm 9 may come into contact with the screw groove 2a of the screw shaft 2 due to an inclination of the nut 3 due to a coming shape error or a moment load. Then, the smooth rotational movement of the piece type ball screw 1 is hindered by the arm 9, which is not preferable. On the other hand, when the diameter D of the arm 9 is smaller than 0.7 Dw, not only the sectional area of the arm 9 is reduced and the rigidity is lowered, but also the thread groove 3a of the nut 3 as shown in FIG. The span of the contact points P and P with the contact point becomes narrow, and the positioning and fixing of the piece member 5 with respect to the nut 3 tends to become unstable.

  In the present embodiment, a piece window 6 having a substantially circular cross section is formed in the trunk portion of the nut 3, and the piece member 5 fitted to the piece window 6 is formed in a substantially circular cross section by molding a sintered alloy by MIM. And a pair of arms 9 projecting from both sides of the body portion 10, and the diameter D of these arms 9, 9 is set within a range of 0.7 to 0.9 of the diameter Dw of the ball 4. 3, the piece member 5 can be stably positioned and fixed to the nut 3 without hindering the smooth rotational movement of the piece type ball screw 1, and the piece member 5. The reliability with respect to the drop-off from the nut 3 can be improved.

  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 perspective view which shows the piece member which concerns on this invention. (B) is the same top view as seen from below. (C) is a side view as above. It is explanatory drawing which shows the fixed state of a piece member, (a) has shown the case where the diameter of an arm is an upper limit, (b) has shown the case where the diameter of an arm is a minimum. (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 ········ Balls 5 and 15 ······ Piece member 5a ········································ 6a ······················ 7 · Arm 10 ······· Body 11, 16 ··· Head 12 ······································· 14 ············································································································· Nut body 51 52... Piece member 52a... Connection groove 53. 4... Arm 55... Recessed portion 56... Guide wall 57. · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · ·・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Contact point θ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Inclination angle

Claims (4)

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;
In a piece-type ball screw provided with a piece member that is fitted to a piece window drilled in the trunk portion of the nut and has a connection groove having the rolling path as a circulation path,
The bridge member is formed by injection molding a sintered alloy comprising a metal powder, a pair of guide walls are disposed opposite to both circumferential sides to its head, these guide walls on the edge side of the bridge window The piece member is fixed to the nut by a caulking portion formed by plastic deformation,
The nut and the thread groove of the screw shaft are formed in a Gothic arc shape, and a pair of arms having a substantially circular cross-section are provided on both sides of the piece member so as to protrude in the opposite circumferential direction , and the diameters of these arms Is set in the range of 0.7 to 0.9 of the diameter of the ball, and the pair of arms are positioned in contact with each thread groove of the nut at two contact points having a predetermined span. Koma type ball screw characterized by   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 claim 1, wherein the piece member is fixed to the piece window by a deformed caulking portion.   The piece type ball screw according to claim 2, wherein an inclination angle of the caulking portion is set in a range of 20 to 45 °. The piece type ball screw according to any one of claims 1 to 3, 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.

Images