JP2007205474A - Piece type ball screw - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piece type ball screw which enhances reliability with lower cost by securing positioning accuracy and fixing force of a piece member to a nut. <P>SOLUTION: A piece type ball screw fitted in a piece window 6 bored in a barrel part of the nut 3 and equipped with a piece member 5 including a coupling groove 5a taking a rolling passage as a circumferential route, wherein the piece window 6 is formed in a cross-sectional substantially circular shape, the piece member 5 is correspondingly formed in a cross-sectional circular shape by a sintered alloy molded through the metal injection molding (MIM), an arm 9 is projected to both sides of the barrel part 10 and engaged with a screw groove 3a in the nut 3, a head part 11 extending to an outer diameter side from the barrel part 10 while the piece member 5 is positioned in the nut 3, a pair of guide walls 13 formed of arc-shape peripheral surfaces are arranged in the head part 11 opposite to each other and the outer peripheral surface is formed in a tapered shape gradually decreased in diameter toward the outer diameter side. By so doing, the piece member 5 can be easily fitted into the nut 3, and accurately and easily positioned and fixed. <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 having an oval shape penetrating the inner and outer peripheral surfaces, and the piece member 52 is provided in the piece member fitting opening 51. Is fitted from the inner diameter side.

  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, the ball 59 is connected when passing through the piece member 52. There is a possibility that a large stress is generated in the 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-type ball screw including a piece member having a connection groove having a circulation path as a circulation path, and a trunk portion in which the piece member is fitted and inserted into the piece window through a predetermined shimiro, and the trunk portion. A head extending from the outer diameter side to the arm, and an arm projecting from both sides of the body and engaged with a thread groove of the nut, the piece member is positioned on the nut, and the head is A pair of guide walls are arranged opposite to each other, and the tip ends of these guide walls are larger than the inner diameter of the piece window. It is formed in a diameter.

  Thus, in the piece-type ball screw provided with a piece member that is fitted to the piece window drilled in the trunk portion of the nut and has a connecting groove having a rolling path as a circulation path, the piece member is It consists of a body part that is inserted into the frame window through a predetermined shimoshiro and a head part that extends from the body part to the outer diameter side. Arms protrude from both sides of the body part and engage with the thread groove of the nut. The piece member is positioned on the nut, and a guide wall having a pair of arcuate peripheral surfaces is arranged opposite to the head, and the tip end portions of these guide walls are formed to have a smaller diameter than the inner diameter of the piece window. Therefore, the piece member can be easily fitted into the nut, and the piece member can be easily positioned and fixed with respect to the nut with high accuracy.

  Preferably, 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 2, the man-hours for processing the piece window Thus, the cost can be reduced, and the piece member can be accurately and easily positioned in the axial direction with respect to the nut, and the reliability can be improved.

  Further, as in the invention described in claim 3, if the outer periphery of the guide wall is gradually reduced in diameter toward the outer diameter side and formed into a tapered shape having a predetermined inclination angle α, the piece member can be inserted. Workability is improved.

  Further, as in the invention described in claim 4, the piece member may be formed of a sintered alloy formed by MIM, or from PEEK as in the invention described in claim 5. It may be formed. As a result, it can be used continuously at an atmospheric temperature exceeding 200 ° C., has high mechanical strength, and can be used for engine control of automobiles and peripheral devices for brakes.

  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 member includes a trunk portion that is inserted and inserted into the piece window via a predetermined shimoshiro, and a head portion that extends from the trunk portion to the outer diameter side. An arm projecting on both sides of the body and engaged with a thread groove of the nut, the piece member is positioned on the nut, and a guide wall having a pair of arcuate peripheral surfaces on the head Are arranged facing each other, and the tip ends of these guide walls are formed to have a smaller diameter than the inner diameter of the piece window. Since it is, it is possible to easily fitted the bridge member in the nut, accurately bridge member relative to the nut, and can be easily positioned and fixed.

  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 ball screw, the piece window is formed in a substantially circular cross section, the corresponding piece member is formed in a circular shape by a sintered alloy formed by MIM, and arms are formed on both sides of the trunk portion. Protruding and engaging with the thread groove of the nut, the piece member is positioned on the nut, and a head portion extending from the body portion to the outer diameter side is formed, and a pair of arcuate circumferences are formed on the head portion. The guide walls forming the surfaces are arranged opposite to each other, and the outer peripheral surfaces of these guide walls are on the outer diameter side. Towards it is formed in a gradually reduced diameter taper shape.

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 sectional perspective view of the nut, FIG. 2B is a transverse sectional view, FIG. 3A is a perspective view showing a piece member, FIG. 2B is a plan view, and FIG. FIG. 4A to FIG. 4C are explanatory views 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, 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.

  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. 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 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 through a predetermined shimiro. 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. The formed guide walls 13 are arranged to face each other. The outer circumferences of these guide walls 13 are gradually reduced in diameter toward the outer diameter side, and are formed in a tapered shape having a predetermined inclination angle α. Then, the body 10 is fitted into the piece window 6 while being elastically deformed, and the piece member 5 is fixed to the nut 3 (see FIG. 2B). The inclination angle α is preferably in the range of 2 to 8 ° in terms of the workability of inserting the piece member 5.

  Thus, since the guide wall 13 of the head 11 in the piece member 5 is formed in a taper shape and the tip portion is formed in a smaller diameter than the piece window 6, the piece member 5 can be easily inserted. Since the trunk portion 10 is fitted to the piece window 6, the piece member 5 can be fixed to the nut 3 with high accuracy. The guide wall 13 is not necessarily formed in a tapered shape, and it is sufficient that the tip end portion is formed with a smaller diameter than the inner diameter of the piece window 6. For example, the guide wall 13 may have a rounded chamfered shape. good.

  Furthermore, in this embodiment, a knob portion 14 is formed at the center of the recessed portion 12 of the head portion 11 in the piece member 5. The knob 14 has a triangular shape and is formed to protrude to the outer diameter side. However, when the piece member 5 is positioned on the piece window 6 of the nut 3, the knob 14 can be held and finely adjusted. As a result, assembly workability can be simplified. Note that the knob 14 does not necessarily have to be provided on the piece member 5, and as shown in FIG. 3C, the recess 12 of the head 16 in the piece member 15 has no knob and has a flat and simple shape. It may be formed.

  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, 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.

On the other hand, the piece member 5 may be formed of a thermoplastic synthetic resin that can be injection-molded. In this case, a repeating linear aromatic polymer of PEEK (polyetheretherketone) oxy-1,4-phenylene-oxy-phenylene-carbonyl-1,4-phenylene is preferred. This material has a glass transition temperature of 143 ° C. and sufficiently high temperature resistance. PEEK is a semi-crystalline super engineering plastic that has the highest level of chemical resistance, heat resistance, wear resistance, flame resistance and hydrolysis resistance among engineering plastics, and has both mechanical properties and functionality. Known as super heat resistant resin.
Examples of synthetic resins other than PEEK include PA (polyamide), POM (polyacetal), PBT (polybutylene terephthalate), PPS (polyphenylene sulfide), PET (polyethylene terephthalate), and the like. However, when considering application as an engine control for automobiles or peripheral devices for brakes, it is necessary to cope with 140 ° C. or higher at high temperatures. preferable.

  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 is set so that the guide wall 13 of the piece member 5 may oppose the circumferential direction of the nut 3. Alignment with the piece member 5 is performed. Then, the piece member 5 is elastically mounted from the inside of the piece window 6 as shown in FIG. Finally, as shown in (c), the body part 10 of the piece member 5 is fitted to the piece window 6 to fix the piece member 5 to the nut 3.

  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 by molding a sintered alloy by MIM or using synthetic resin. By forming by injection molding, the cross-section is formed in a substantially circular shape, and the guide wall 13 of the piece member 5 is formed in a taper shape, so that the number of processing steps of the piece window 6 can be reduced and the cost can be reduced. At the same time, the piece member 5 can be easily fitted into the nut 3. In addition, the trunk portion 10 of the piece member 5 is fitted and inserted into the piece window 6 via a predetermined shimoshiro, and arms 9 are provided at both ends of the trunk portion 10, and the arm 9 is inserted into the screw groove 3 a of the nut 3. Therefore, the piece member 5 can be positioned and fixed with respect to the nut 3 with high accuracy and easily.

  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 perspective view which shows the modification of (a). (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 ········ Balls 5 and 15 ··· Piece member 5a ·························· ... Edge 7 ... Komado Window Edge 8 ... Groove Edge 9 ... Arm 10... Body 11, 16... Head 12... Recess 13... Guide wall 14. ························································································· Nut body 51 .... Piece member 52a ... Connection groove 53 ... Internal thread groove 54 ..... Arm 55 ......... Recess 56 ...... Guide wall 57 ... Engagement step 58 ... ········· 59

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;
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 member includes a trunk portion that is fitted and inserted into the piece window via a predetermined shimiro, and a head portion that extends from the trunk portion toward the outer diameter side, and arms protrude from both sides of the trunk portion. The piece is engaged with the thread groove of the nut, the piece member is positioned on the nut, and a pair of arcuate peripheral walls are arranged opposite to the head, and the tip ends of the guide walls A piece-type ball screw characterized by being formed with a diameter smaller than the inside diameter of the piece window.   The piece-type ball screw according to claim 1, 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.   3. The piece type ball screw according to claim 1, wherein an outer periphery of the guide wall is gradually reduced in diameter toward an outer diameter side and formed into a tapered shape having a predetermined inclination angle α.   The piece type ball screw according to any one of claims 1 to 3, wherein the piece member is formed of a sintered alloy formed by MIM.   The piece type ball screw according to any one of claims 1 to 3, wherein the piece member is formed of PEEK.

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