JP4619277B2 - 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 ball screw has a thread groove connecting path, and a circulation piece member having a rolling path as a circulation path is mounted on the nut. This ball screw has an advantage that the structure is relatively simple and the structure can be made compact.

  A typical example of such a piece-type ball screw is shown in FIG. This piece type ball screw 50 includes a screw shaft 51 having a helical thread groove 52 formed on the outer peripheral surface, and a nut externally fitted to the screw shaft 51 and having a helical screw groove 54 formed on the inner peripheral surface. 53, a plurality of balls 55 accommodated in a rolling path formed by opposing screw grooves 52 and 54, and a piece member 57 fitted in a piece window 56 formed in the trunk portion of the nut 53. It has. The piece member 57 is formed in an oval shape, and is provided with a connecting groove 58 for connecting adjacent one circumferential portions of the screw groove 54 of the nut 53 on the inner periphery, and is fitted into the piece window 56 from the outer diameter side of the nut 53. Yes. The thread groove 54 of the nut 53 is connected by the connection groove 58 to form a continuous circulation path of one turn.

  The outer surface of the piece member 57 is formed in a cylindrical surface, and the outer surface of the piece member 57 is substantially flush with the outer peripheral surface of the nut 53 when the piece member 57 is fitted in the piece window 56. Here, a first circumferential groove 59 is formed on the outer surface of the piece member 57, and a second circumferential groove 60 that is continuous with the first circumferential groove 59 is formed on the outer circumferential surface of the nut 53. . The first and second circumferential grooves 59 and 60 are fitted with a substantially C-shaped retaining ring 61, and the piece member 57 is pressed by the spring force of the retaining ring 61, so that the piece member 57 is turned into a nut. 53 is fixed. Thereby, even in the case of a large-diameter and thin-walled nut, the pressing and fixing force of the piece member 57 by the retaining ring 61 can be sufficiently ensured, and the cost can be reduced without impairing work efficiency and reliability. (For example, see Patent Document 1).

  Since the conventional piece type ball screw 50 is provided with the oval type piece member 57, the angle of the oval shape in the major axis direction and the angular relationship between the screw groove 54 of the nut 53 and the connecting groove 58 of the piece member 57 are matched. It has the characteristic that the piece member 57 can be uniquely positioned just by keeping it, and is applied for general purposes. However, when the piece window 56 corresponding to the oval piece member 57 is formed in the nut 53, the number of processing steps is increased, which is one factor in increasing the manufacturing cost. That is, in this type of piece window 56, a pilot hole is first drilled at one or two places, and the tool is changed to an end mill with a regular oval width and processed into a long hole shape to obtain a desired oval shape. Since it must be formed, the machining time is long, and the cycle time due to tool change is long.

  A piece type ball screw shown in FIG. 6 is known as a solution to such a workability problem. This piece type ball screw 70 is provided with a piece window 72 formed in a nut 71 so as to penetrate from an outer peripheral surface side to an inner peripheral surface side. The piece window 72 has a substantially circular cross section and is formed along the radial direction of the nut 71. The first piece member 73 is attached to the piece window 72, and the second piece member 74 is attached as a member for preventing the first piece member 73 from coming off. The first piece member 73 is formed in a substantially disk shape, and fins 73 a and 73 a for preventing rotation are formed on both sides of the nut 71 in the circumferential direction.

The 2nd piece member 74 is formed in the rectangular shape which makes the circumferential direction of the outer peripheral surface of the nut 71 a longitudinal direction, and the protrusion 75 protruded along the edge part of the longitudinal direction both sides is formed. On the other hand, a groove 76 for accommodating the second piece member 74 is formed on the outer peripheral surface of the nut 71. And the groove surface of the groove | channel 76 of the circumferential direction of the nut 71 of the groove | channel 76 each engages with the protrusion 75 of the 2nd piece member 74, and functions as a guide when inserting the 2nd piece member 74 in the nut 71. A pair of grooves 77 is formed. Thus, since the piece window 72 formed in the nut 71 has a substantially circular cross section, it is possible to form the piece window 72 by one machining of the end mill, which eliminates the need for tool change and the number of machining steps. Can be reduced and the cost can be reduced (see, for example, Patent Document 2).
JP 2004-124986 A Japanese Patent Laid-Open No. 2005-19624

  However, in this conventional piece-type ball screw 70, not only the second piece member 74 is required to prevent the first piece member 73 from coming off, but also the second piece member 74 is mounted. In addition, it is necessary to process the grooves 76 and 77 in the nut 71. Further, fins 73 a and 73 a for preventing rotation are formed on both sides of the first piece member 73, and the alignment groove (not shown) of the first piece member 73 and the screw groove 71 a of the nut 71 are aligned. However, if the processing accuracy of the fin 73a and the groove processing accuracy of the nut 71 on which the fin 73a is mounted are not strictly regulated, there is a possibility that a smooth circulating motion of the ball cannot be obtained.

  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 In a piece type ball screw provided with a piece member in which a connecting groove having a circulation path as a circulation path is formed, the piece window is formed in a substantially circular cross section, and the piece member corresponding to the piece window is sintered by MIM. A circular cross section is formed from the coupling gold, and round bar-like 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 in the same circumferential direction both side edges and the arm of the bridge member, the communication with the arm In broad to cover the grooves, guide walls that rise to the outer diameter side is provided opposite the bridge member by the caulked portion formed by plastically deformed along these guide walls inclined edge side of the bridge window Is fixed to the nut.

Thus, in the piece type ball screw in which the piece member is fitted to the nut, the piece window is formed in a substantially circular cross section, and the piece member is formed in a circular shape in cross section from the sintered alloy by MIM corresponding to this piece window. Round bar-shaped 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 on the same circumferential side edge as the arm of the piece member A caulking portion formed by plastically deforming these guide walls along the inclined edge side of the piece window, provided with a wide and wide guide wall that covers the arm and the connecting groove and rising toward the outer diameter side. Since the piece member is fixed to the nut, the man-hours for the piece window can be reduced, the cost can be reduced, and the piece member can be positioned accurately and easily in the axial direction with respect to the nut. Can be low cost It is possible to provide a desired bridge type ball screw with improved reliability of the fixing force can be ensured.

According to a second aspect of the present invention, the guide wall of the piece member has a toughness that can be plastically deformed and can secure a caulking portion strength, and at least the surface hardness of the connecting groove is 30 HRC by heat treatment. If it is set as described above, the connecting groove in which a large stress is generated has sufficient pressure resistance and wear resistance, and the guide wall serving as the crimping portion can secure desired toughness, and the piece member is fixed to the nut. It is possible to prevent cracks and the like from occurring. Accordingly, it is possible to provide a piece-type ball screw including a piece member having conflicting characteristics such as strength, durability, and toughness.

Preferably, as in the invention described in claim 3 , the piece member is formed of a carburized material, the surface is hardened by carburizing and quenching, and the surface hardness of the guide wall is 15 to 30 HRC by annealing. If it is set to, it is possible to ensure the strength of the crimped portion and to prevent the occurrence of cracks during the crimping process.

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 the piece-type ball screw provided with the formed piece member, the piece window is formed in a substantially circular cross section, and the piece member is formed in a circular shape in cross section from a sintered alloy by MIM corresponding to the piece window. Round bar-shaped 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 both sides in the same circumferential direction as the arm of the piece member the edges, a wide covering the arms and the connecting groove, the outer diameter side stand Up guide wall is provided to face, since the bridge member by the inclined edge side crimp portion formed by plastically deforming along the these guide walls the bridge window is fixed to the nut, It is possible to reduce the man-hours for the piece window and reduce the cost, and the piece member can be positioned accurately and easily in the axial direction with respect to the nut, and a desired fixing force can be obtained at a low cost. A piece-type ball screw with improved reliability that can be ensured can be provided.

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 piece comprising a plurality of balls accommodated in a movement path, and a piece member that is fitted to a piece window formed in the trunk portion of the nut and has a connecting groove having the rolling path as a circulation path. In the type ball screw, the piece window is formed in a substantially circular cross section, and the piece member is made of a sintered alloy formed into a circular shape in cross section by the MIM, and a round bar shape is formed on both sides of the piece member. arm is projected, these arms are engaged with the screw groove of the nut the bridge member is positioned in the nut, further in the same circumferential direction both side edges and the arm of the bridge member, said with the arm in broad to cover the connecting grooves, the guide wall that rises radially outwardly Provided direction, the bridge member by the caulked portion formed by plastically deformed along the inclined edge portion side of these guide walls the bridge window is fixed to 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 the piece member, (b) is a plan view, and FIGS. ) Is an explanatory view showing a 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 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.

  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. Accordingly, as shown in FIG. 2 (b), the connecting groove 5a is connected to the screw groove 3a so that the both-end piece window edge 7 matches the window piece window 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 from other portions, and from these recessed portions 10. A pair of guide walls 11 rising to the outer diameter 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 side of the piece window 6 using a caulking jig (not shown). 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 with 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 surface 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 so that the surface hardness is in the range of 30 to 40 HRC, and using a high-frequency temper device, FIG. The caulking portion 12 shown in FIG. 3B, that is, the guide wall 11 shown in FIG. 3A is annealed, and the surface hardness is set in the range of 15 to 23 HRC.

  Here, if the surface hardness of the hardened layer by carburizing and quenching is less than 30 HRC, the pressure resistance and wear resistance of the connecting groove 5a are insufficient, and if it exceeds 40 HRC, the heat treatment deformation of the piece member 5 increases, which is not preferable. . Further, if the surface hardness of the guide wall 11 by annealing is less than 15 HRC, the strength of the caulking portion is insufficient, and if it exceeds 23 HRC, cracks or the like may occur during caulking, which is not preferable.

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

  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 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. It is possible to provide the piece type ball screw 1 in which the piece member 5 can be positioned accurately and easily in the axial direction with respect to the nut 3 and the reliability is 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. 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)-(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 longitudinal cross-sectional view same as the above. It is a perspective assembly drawing which shows another piece type ball screw.

Explanation of symbols

1 ... Ball screw 2 ... Screw shaft 2a, 3a ... Screw groove 3 ... Nut 4 ··························· 5 ...... Pad window edge 8 ... Window piece window edge 9 ... Arm 10 ...・ Recess 11 ・ ・ ・ ・ ・ ・ ・ ・ ・ Guide wall 12 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Clamping section 50, 70 ・ ・ ・ ・ ・ ・ Place ball screw 51 ・ ・ ・ ・ ・ ・· Screw shafts 52, 54, 71a · · · screw grooves 53, 71 · · · nut 55 · · · · · · balls 56, 72 · · · piece window 57 · · · .... Piece member 58 ... Connection groove 59 ... First circumferential groove 0 ······· Second circumferential groove 61 ························································· ··· Fin 74 ··········· Second piece 75 ···················································

Claims (3)

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 piece window is formed in a substantially circular cross section, and the piece member is formed from a sintered alloy in a circular shape in cross section by MIM corresponding to the piece window, and round bar-shaped arms project from both sides of the piece member. The arm is engaged with the screw groove of the nut, the piece member is positioned on the nut, and the wide and outer diameter that covers the arm and the connecting groove on the same circumferential side edge as the arm of the piece member Guide walls rising to the side are provided facing each other, and the piece member is fixed to the nut by a caulking portion formed by plastically deforming these guide walls along the inclined edge side of the piece window. This is a piece-type ball screw.   2. The ball according to claim 1, wherein the guide wall of the piece member is plastically deformable and has toughness that can secure a caulking portion strength, and at least a surface hardness of the connecting groove is set to 30 HRC or more by heat treatment. screw. The ball screw according to claim 2, wherein the piece member is formed of a carburized material, the surface is hardened by carburizing and quenching, and the surface hardness of the guide wall is set in a range of 15 to 30 HRC by annealing.

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