JP2007154932A - Roller type ball screw - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a roller type ball screw, in which positioning accuracy and a fixing force of a roller member with respect to a nut are secured, and its reliability is improved at low cost. <P>SOLUTION: In the roller type ball screw 1, a roller member 5 fitted to a roller window 6 of the nut 3 is plastic-deformed and is fixed to the nut 3. A cross sectional surface of the roller window 6 is formed to be approximately circular, and a cross-sectional surface of a roller member 5 is formed to be circular corresponding to the roller window 6. Arms 9 are projected form both sides of the roller member 5, and these arms 9 are engaged with a screw groove 3a of the nut 3, so that the roller member 5 is positioned to the nut 3. A pair of guide walls 11 standing on an outer diameter side and opposed to each other are disposed to both side edges in a circumferential direction of the roller member 5, and the roller member 5 is fixed to the nut 3 by a caulking part 12 formed by plastic deformation of the guide walls 11 on edge parts 6a side of the roller window 6 within a range of 20 to 45 °. <P>COPYRIGHT: (C)2007,JPO&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 ball screw has a thread groove connecting path, and a circulation piece member having a rolling path as a circulation path is attached to the nut, so that there is an advantage that the configuration is relatively simple and can be configured compactly.

  A typical example of such a piece-type ball screw is shown in FIG. In this piece type ball screw, the nut body 50a of the rotary nut 50 is provided with a piece member fitting opening 51 penetrating the inner and outer peripheral surfaces, and the piece member 52 is fitted into the piece member fitting opening 51 from the inner diameter side. It is.

  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 caulked and fixed to the nut body 50a by plastically deforming a pair of guide walls 56 formed on the outer diameter surface thereof. Therefore, a soft material, that is, a material having ductility is required so that cracking does not occur during the caulking operation.

  On the other hand, when such a piece type ball screw is used for an electric power steering or an actuator of an automobile, a vibration load often acts on the rotating nut 50 or a screw shaft (not shown). Then, this vibration load acts as a moment load, the load distribution inside the ball screw collapses, and the revolution speed of the ball 59 in the rotary nut 50 varies. As a result, when the ball 59 passes through the piece member 52, There is a possibility that a large stress is generated in the connecting groove 52a. In such a situation, it is conceivable to increase the surface hardness of the piece member 52 and increase the strength in order to improve the durability of the piece member 52 by improving the pressure resistance and wear resistance, but as described above, It is difficult with the piece member 52 that has ductility and is fixed to the nut body 50a by plastic deformation.

  The present invention has been made in view of such circumstances, and has an object to provide a piece-type ball screw that secures positioning accuracy and fixing force of a piece member with respect to a nut and has improved reliability at a low cost. Yes.

  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-shaped ball screw in which a connecting groove having a circulation path as a circulation path is formed, and the piece member is plastically deformed and fixed to the nut, with arms projecting on both sides of the piece member, These arms are engaged with the thread grooves of the nut, the piece member is positioned on the nut, and a pair of guide walls rising to the outer diameter side are provided opposite to each other on both circumferential edges of the piece member. The guide wall is plastically deformed at a predetermined angle toward the edge of the piece window. It said bridge member by caulking portions formed Te is fixed to the nut.

  In this way, in the piece-type ball screw in which the piece member fitted to the piece window of the nut is plastically deformed and fixed to the nut, the arms protrude from both sides of the piece member, and these arms are formed in the screw grooves of the nut. Engaged, the piece member is positioned on the nut, and a pair of guide walls rising to the outer diameter side are provided on both side edges of the piece member in the circumferential direction, and the guide walls are provided on the edge side of the piece window. Since the piece member is fixed to the nut by a crimping part formed by plastic deformation at a predetermined angle, the piece type ball that secures positioning accuracy and fixing force of the piece member with respect to the nut and improves reliability at a low cost. Screws can be provided.

  Preferably, as in the invention described in claim 2, if the inclination angle of the caulking portion is set in the range of 20 to 45 °, not only the occurrence of cracking of the caulking portion is prevented, While ensuring a desired fixing force, the reliability of a crimping part 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 3, the man-hours for the piece window are 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.

  In addition, as in the invention described in claim 4, the piece member is formed of a sintered alloy formed from a carburized material by MIM, is hardened by carburizing and quenching, and has a hardness of 15 to 30 HRC by tempering. Further, as in the invention according to claim 5, the piece member is formed of a sintered alloy formed from precipitation hardening stainless steel by MIM, and is subjected to solution heat treatment. It may be hardened and the hardness may be set in a range of 15 to 30 HRC. By adopting such a configuration, even a complicated shape can be easily and accurately formed into a desired shape and size, the strength of the crimped portion can be ensured, and crimping can be performed. Occurrence of cracks and the like can sometimes be prevented.

  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 that is plastically deformed and fixed to the nut, and arms are provided on both sides of the piece member, and these arms are formed in the screw grooves of the nut. The pair of guide walls are positioned to the nut, and a pair of guide walls rising to the outer diameter side are provided opposite to the circumferential side edges of the piece member, and the guide walls are provided at the edges of the piece window. Front by a crimped part formed by plastic deformation at a predetermined angle on the part side Since the bridge member is fixed to the nut, ensuring the positioning accuracy and tightness of the bridge member relative to the nut, it is possible to provide a bridge type ball screw with improved reliability at low 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 a movement path, and a piece member fitted to a piece window drilled in a body portion of the nut and formed with a connecting groove having the rolling path as a circulation path, In a piece-type ball screw in which a piece member is plastically deformed and fixed to the nut, the piece window is formed in a substantially circular cross section, and the piece member is formed in a circular cross section corresponding to the piece window, and the piece Arms are provided on both sides of the member, these arms are engaged with the thread grooves of the nut, the piece member is positioned on the nut, and rises to the outer diameter side at both circumferential edges of the piece member. A pair of guide walls are provided facing each other, and the guide walls are connected to the piece window. The bridge member is fixed to the nut by caulking portion by plastically deforming to form the edge side in the range of 20 to 45 °.

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 the piece member, (b) is a plan view, and FIG. 4 is a caulking test result. (A) is a case where SCM415 is used for a piece member, (b) is a case where SUS630 is used for a piece member. FIGS. 5A to 5C are explanatory views showing the procedure for assembling the piece members.

  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 and a plurality of balls 4 accommodated in a rolling path formed by the opposing screw grooves 2a and 3a, and a connecting groove 5a for connecting adjacent circumferential portions of the screw groove 3a of the nut 3 are formed. A piece member 5 is provided.

  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 the vibration resulting from the clearance gap between a nut and a screw shaft 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.

  As shown in FIGS. 2A and 3B, 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 of the nut 3. ing. 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. Furthermore, the arm 9 formed in the shape of a round bar protrudes 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 can position the piece member 5 in the axial direction with respect to the nut 3, and can prevent the piece member 5 from coming out of the piece window 6 radially outward.

  Further, as shown in FIGS. 2 (b) and 3 (a), both side edges in the circumferential direction of the piece member 5 are formed as recessed portions 10 whose outer diameter surfaces are recessed as compared with other portions. A pair of guide walls 11 rising to the radial side are provided facing the circumferential direction of the piece member 5. The piece member 5 is fixed to the nut 3 by a caulking portion 12 formed by plastically deforming the guide wall 11 on the edge 6a side of the piece window 6 using a caulking jig (not shown) ( FIG. 2 (b)).

  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.

  The piece member 5 is made of a sintered alloy formed by an injection molding machine by adjusting the metal powder into a plastic shape. 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. In addition to this, it may be a precipitation hardening stainless steel SUS630 in which C is 0.07 wt%, Cr is 17 wt%, Ni is 4 wt%, Cu is 4 wt%, and the remainder is 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 12 shown in FIG. 2B, that is, the guide wall 11 shown in FIG. 3A is tempered using a high-frequency temper device so that the hardness is in the range of 15 to 30 HRC. Is set.

  Here, if the surface hardness of the hardened layer by carburizing and quenching is less than 15 HRC, the pressure resistance and wear resistance of the connecting groove 5a are insufficient, and if it exceeds 30 HRC, the heat treatment deformation of the piece member 5 increases, which is not preferable. . Further, if the hardness of the guide wall 11 by tempering is less than 15 HRC, the strength of the caulking portion is insufficient, and if it exceeds 30 HRC, cracks or the like may occur during caulking, which is not preferable. In addition to carburizing and quenching, these may be cured to a predetermined surface hardness by tempering treatment.

  On the other hand, when the piece member 5 is formed of precipitation hardening stainless steel such as SUS630, the hardness is set to 30 HRC or less by the 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.

  Since the piece member 5 is made of a sintered alloy formed by molding these carburized materials or precipitation hardened stainless steel by MIM, at least the connecting groove 5a where a large stress is generated has sufficient pressure resistance and wear resistance. Further, the toughness of the guide wall 11 serving as the caulking portion 12 is high, and the occurrence of cracks or the like can be prevented when the piece member 5 is caulked and fixed to the nut 3.

  Furthermore, the present applicant not only prevents the caulking portion 12 from being cracked when the piece member 5 is caulked and fixed to the nut 3, but also secures a desired fixing force and secures the caulking portion. In order to improve the reliability, attention was paid to the amount of caulking in the caulking portion 12. 4 (a) and 4 (b) are graphs showing the results of the caulking test of the piece member performed by the present applicant. Here, in the caulking test, in order to change the caulking amount of the caulking part 12, as shown in FIG. 2B, the caulking angle 6 is changed by changing the inclination angle θ of the edge 6a of the piece window 6. The bending amount of the tightening portion 12 was changed, and the crimping state of the piece member 5 was confirmed. Further, as the specimens, the shaft diameter of the screw shaft 2 is 16 mm, the lead is 3 mm, the ball diameter is 2.381 mm, the outer diameter of the nut 3 is 28 mm, the inner diameter is 17 mm, and the material of the piece member 5 is SCM415 and SUS630. MIM molded products were used. FIG. 4A shows the results of the caulking test using SCM415 for the piece member 5, and FIG. 4B shows the results of the caulking test using SUS630.

  As is apparent from this graph, the inclination angle θ of the edge 6a of the piece window 6 is appropriately in the range of 20 to 45 °, and if the amount of crimping increases further, the crimped portion 12 will crack. As a result, it was found that when the inclination angle θ is less than 20 °, the piece member 5 is rattled by the spring back of the caulking portion 12 and there is a problem in positioning accuracy and fixing force. By such a piece caulking test, the amount of caulking of the caulking portion 12, that is, the inclination angle θ of the edge 6 a of the frame window 6 is set in the range of 20 to 45 °, thereby causing cracking of the caulking portion 12 and the like. In addition to preventing the occurrence, it is possible to secure a desired fixing force and improve the reliability of the crimped portion.

  Next, the procedure for assembling the piece member 5 to the nut 3 will be described with reference to FIG. First, as shown to (a), the piece member 5 is arrange | positioned in the inward position of the piece window 6 of the nut 3, and the piece window 6 and the guide wall 11 of the piece member 5 are opposed to the circumferential direction of the nut 3. Alignment with the piece member 5 is performed. Then, as shown in (b), the piece member 5 is inserted into the piece window 6 from the inside. Finally, the caulking portion 12 is formed by plastically deforming the guide wall 11 of the piece member 5 toward the edge 6 a side of the piece window 6. The piece member 5 is fixed to the nut 3 by the crimping portion 12, and a desired fixing force can be secured.

  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 a piece member 5 fitted to the piece window 6 is formed in a substantially circular cross section, and both ends of the piece member 5 are formed. Since the arm 9 protrudes and is engaged with the thread groove 3a of the nut 3 via a predetermined radial clearance, the number of processing steps of the piece window 6 can be reduced, and the cost can be reduced. The piece member 5 can be easily and accurately positioned with respect to the nut 3 in the axial direction. Further, since the piece member 5 is fixed to the nut 3 by the caulking portion 12 formed by plastic deformation at a predetermined inclination angle, a predetermined fixing force is ensured and the reliability of the caulking portion is improved. be able to.

  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. (A) is a graph which shows the caulking test result when the material of the piece member is SCM415. (B) is a graph which shows the caulking test result when the material of the piece member is SUS630. (A)-(c) is explanatory drawing which shows the procedure which assembles a piece member in a nut. (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 ... Ball screw 2 ... Screw shaft 2a, 3a ... Screw groove 3 ... Nut 4 ······························ 5 ····································· 8 Arm 10 ······························································································ 50a ... Nut body 51 ········· Opening for piece member fitting 52 ··········· Piece member 52a ········ Connection groove 53 ..... Internal thread groove 54 ... Arm 55 ... Recess 6 ······· Guide wall 57 ··········· engagement step portion 58 ······················ Ball 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;
A piece member that is fitted in a piece window formed in the trunk of the nut and formed with a connecting groove having the rolling path as a circular route, and the piece member is plastically deformed and fixed to the nut. In the piece type ball screw
Arms are provided on both sides of the piece member, these arms are engaged with the thread grooves of the nut, the piece member is positioned on the nut, and the outer diameter side on both circumferential edges of the piece member A pair of guide walls that rise to the opposite are provided opposite to each other, and the piece member is fixed to the nut by a crimped portion formed by plastically deforming the guide wall on the edge side of the piece window at a predetermined angle. Koma type ball screw characterized by   The piece type ball screw according to claim 1, wherein an inclination angle of the caulking portion is set in a range of 20 to 45 °.   The piece type ball screw according to claim 1 or 2, 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.   The said piece member is formed with the sintered alloy shape | molded from a carburized material by MIM, and is hardened by carburizing and hardening, and the hardness is set to the range of 15-30 HRC by tempering. Crab type ball screw described in crab.   The said piece member is formed with the sintered alloy shape | molded from precipitation hardening type stainless steel by MIM, is hardened | cured by solution heat treatment, and the hardness is set in the range of 15-30 HRC. The piece-type ball screw described.

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