JP2018053971A - Ball Screw - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ball screw capable of reducing rotational resistance of a nut or screw shaft occurring at the time when a ball passes through a roller member.SOLUTION: A ball screw 1 is configured such that a screw shaft 2 is inserted into a nut 3; a rolling path for balls 4 is composed of a shaft side screw groove 2a of the screw shaft 2 and a nut side screw groove 3a of the nut 3; a plurality of roller members 5 formed with a connection groove 5c with the rolling path as a circulation passage is provided in the nut 3; and a plurality of balls 4 is arranged in the rolling path constituting the circulation passage. A ball guide member 6 is provided in the roller member 5 so that the balls 4 passing through the connection groove 5c are pushed against a bottom surface of the connection groove 5c and moved.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a ball screw. Specifically, the present invention relates to a ball screw in which a circulation path is constituted by a top member.

  Conventionally, in electric actuators for general industrial motors, automobile transmissions, parking brakes, and the like, ball screws are used to convert the rotary motion of the output shaft of the electric motor into linear motion with high efficiency and output it. The ball screw is composed of a screw shaft having a thread groove formed on the outer peripheral surface and a nut having a thread groove formed on the inner peripheral surface. In the ball screw, a screw shaft is inserted into a nut, and a plurality of balls are arranged on a rolling path constituted by a screw groove of the screw shaft and a screw groove of the nut. Thus, the ball screw is configured as a motion conversion mechanism in which one of the screw shaft and the nut rotates and the other linearly moves as a linear motion member. In the ball screw configured as described above, there is known a top type ball screw in which a rolling path is configured as a circulation path by a top member provided on a nut. For example, as described in Patent Document 1.

  In the nut of the ball screw described in Patent Document 1, a rolling path is configured by a plurality of top members into a plurality of circulation paths. The ball screw is configured such that the ball passes over the thread of the screw shaft and returns to the original screw groove by the connecting groove of the top member. In addition, the ball screw suppresses elastic deformation of the top member by improving the rigidity of the top member, and reduces poor circulation of the ball due to elastic deformation of the top member. When the rotational speed of the nut is large, the ball screw configured as described above circulates in the rolling path over the thread of the screw shaft while the ball rolls in the connecting groove of the top member by centrifugal force. However, in the ball screw, when the rotation speed of the nut is small, the centrifugal force acting on the ball becomes small and the ball comes into contact with the shaft side screw groove, so that the ball does not roll smoothly in the connecting groove. For this reason, the ball screw may be disturbed in the arrangement of the balls in the rolling path, resulting in an increase in rotational resistance or abnormal noise.

JP 2006-220215 A

  The present invention has been made in view of the above situation, and an object of the present invention is to provide a ball screw that can reduce the rotational resistance of a nut or a screw shaft generated when the ball passes through a top member.

  That is, in the ball screw, the screw shaft is inserted into the nut, and the ball rolling path is constituted by the thread groove of the screw shaft and the thread groove of the nut, and the connecting groove having the rolling path as a circulation path is formed. In a ball screw in which a plurality of top members are provided on a nut and a plurality of balls are arranged on a rolling path constituting the circulation path, the ball passing through the connection groove is pressed against the bottom surface of the connection groove and moves As described above, a ball guide member is provided on the top member.

  The ball screw is configured such that the width of the opening of the coupling groove facing the bottom surface of the coupling groove is narrower than the diameter of the ball by the ball guide member.

  The ball screw is configured such that the ball guide member protrudes from the side surface of the connection groove along the bottom surface of the connection groove.

  In the ball screw, the ball guide member is formed integrally with the top member.

  As effects of the present invention, the following effects can be obtained.

  That is, the ball screw does not cause clogging due to the ball arrangement being disturbed in the connecting groove of the top member. Thereby, the rotation resistance of the nut or the screw shaft generated when the ball passes through the top member can be reduced.

  The ball screw moves in the connecting groove in a state where the ball is supported by the ball guide member. Thereby, the rotation resistance of the nut or the screw shaft generated when the ball passes through the top member can be reduced.

  The ball screw moves in the coupling groove while rolling on the ball guide member while the ball is pressed against the bottom surface of the coupling groove. Thereby, the rotation resistance of the nut or the screw shaft generated when the ball passes through the top member can be reduced.

  In the ball screw, the ball guide member is easily formed along the bottom shape of the connecting groove by integrally forming the ball guide member on the top member. Thereby, the rotation resistance of the nut or the screw shaft generated when the ball passes through the top member can be reduced.

The perspective view which shows the whole structure in one Embodiment of a ball screw. (A) The top view in one Embodiment of a ball screw, (b) A arrow directional cross-sectional view in Fig.2 (a). The expanded sectional view of the nut in one embodiment of a ball screw. (A) Sectional drawing along the groove | channel direction of the connection groove | channel of the top member in one Embodiment of a ball screw, (b) Similarly B arrow sectional drawing in Fig.4 (a). (A) Partial enlarged sectional view showing a state where the ball has reached the inlet of the top member in one embodiment of the ball screw, (b) Partial enlarged sectional view showing a state where the ball has also entered the connecting groove of the top member, (C) Partially enlarged sectional view showing a state where the ball is also supported by the ball guide member of the top member and moving in the connecting groove, (d) Similarly, a partial enlarged view showing a state where the ball has reached the escape portion of the top member Sectional drawing.

  Below, the ball screw 1 which is one Embodiment of a ball screw is demonstrated using FIGS. 1-3.

  As shown in FIGS. 1 and 2, the ball screw 1 converts a rotational motion into a linear motion and outputs it. The ball screw 1 includes a screw shaft 2, a nut 3, a plurality of balls 4, a top member 5, and the like.

  The screw shaft 2 is made of medium carbon steel such as S55C or case-hardened steel such as SCM415 or SCM420, and is subjected to a hardening process of about 55 to 62 HRC by induction hardening or vacuum carburizing and hardening. The screw shaft 2 has a one-turn shaft-side screw groove 2a for rolling the ball 4 on the outer peripheral surface thereof. The cross-sectional shape of the shaft side thread groove 2a may be a circular arc shape or a gothic arc shape. In the present embodiment, the screw shaft 2 is formed in a Gothic arc shape in which the contact angle with the ball 4 that is a rolling element can be increased and the axial clearance can be set small. Thereby, the ball screw 1 has high rigidity with respect to the axial load of the screw shaft 2 and can suppress the occurrence of vibration.

As shown in FIG. 2A, the nut 3 is formed in a hollow cylindrical shape into which the screw shaft 2 can be inserted. The nut 3 is made of case-hardened steel such as SCM415 or SCM420, and is hardened by about 55 to 62HRC by vacuum carburizing and quenching.
As shown in FIG. 2 (b), the nut side thread groove 3 a for rolling the ball 4 is formed on the inner peripheral surface of the nut 3 with the same lead and pitch as the shaft side thread groove 2 a of the screw shaft 2. Has been. The screw shaft 2 is inserted into the nut 3 such that the shaft side screw groove 2a and the nut side screw groove 3a face each other. A plurality of balls 4 are rotatably accommodated in a space formed by the shaft side screw groove 2a and the nut side screw groove 3a. That is, the shaft side thread groove 2a and the nut side thread groove 3a constitute a rolling path on which the ball 4 rolls. The nut 3 supports the screw shaft 2 through a plurality of balls 4 so as to be rotatable around the axis of the nut 3. In the present embodiment, the shaft-side thread groove 2a and the nut-side thread groove 3a are single-threaded screws, but are not limited thereto.

  The nut 3 is formed with two top windows 3b into which the top member 5 is inserted from the outer peripheral surface toward the center of the cylinder. The two top windows 3 b are formed in a substantially circular through hole extending from the outer peripheral surface of the nut 3 to the inner peripheral surface. The two top windows 3b are formed so as to cut out the adjacent nut side screw grooves 3a. That is, between the two top windows 3b, nut side thread grooves 3a corresponding to at least one round cut out by the two top windows 3b are formed.

  The top member 5 constitutes a connecting groove 5c having a rolling path composed of the shaft side thread groove 2a and the nut side thread groove 3a as a circulation path. The top member 5 is made of a sintered alloy prepared by adjusting a metal powder into a plastic shape and molded by an injection molding machine. The top member 5 is formed by MIM (Metal Injection Molding), in which a kneaded product of a metal powder and a binder made of plastic and wax is pressed into a mold in a heated and melted state by an injection molding machine. A sintered alloy formed by such MIM can be easily and accurately formed into a desired shape and size even if it has a high workability and a complicated shape.

  As a metal powder, a material that can be carburized and quenched later, for example, C (carbon) is 0.13 wt%, Ni (nickel) is 0.21 wt%, Cr (chromium) is 1.1 wt%, and Cu (copper) is used. An example of the SCM 415 is 0.04 wt%, Mn (manganese) is 0.76 wt%, Mo (molybdenum) is 0.19 wt%, Si (silicon) is 0.20 wt%, and the rest is Fe (iron). it can. The top member 5 is performed by adjusting the carburizing quenching and tempering temperatures. In addition to this, the material of the top member 5 contains 3.0 to 10.0% by weight of Ni, and is excellent in workability and corrosion resistance (FEN8 of Japanese Powder Metallurgy Industry Standard), or C is 0.07% by weight. Further, precipitation hardened stainless steel SUS630 made of 17 wt% of Cr, 4 wt% of Ni, 4 wt% of Cu, and the remainder of Fe or the like may be used. This SUS630 can appropriately increase the surface hardness in the range of 20 to 33 HRC by solution heat treatment, and can ensure toughness and high hardness.

  When the top member 5 is formed of a carburized material such as SCM415, the top member 5 is hardened by carburizing and quenching and adjusting the tempering temperature, or by carburizing and quenching so that the surface hardness is in the range of 30 to 40 HRC. At the same time, the outer peripheral portion on the outer diameter side is tempered using a high-frequency temper device, and the hardness is set to be in the range of 15 to 30 HRC. Thereby, it can prevent that a crack etc. generate | occur | produce when crimping and fixing the top member 5 to the screw shaft 2. FIG.

  As shown in FIG. 3, the top member 5 is formed with a main body portion 5a and two arm portions 5b that can be fitted into the top window 3b without any gap. The two arm portions 5b are formed so as to extend in the circumferential direction from both end portions in the axial direction of the nut 3 in the main body portion 5a. The top member 5 fits the top body portion 5a of the top member 5 into the top window 3b of the nut 3, and the two arm portions 5b are respectively fitted into the nut-side thread grooves 3a cut out by the top window 3b. Thus, the position with respect to the nut 3 is determined.

  One connecting groove 5 c is formed in the main body 5 a of the top member 5. The connecting groove 5c constitutes a part of the nut side screw groove 3a. The connecting groove 5c includes one end face of the nut side screw groove 3a in which the two arm portions 5b of the top member 5 are not fitted, and the other end face of the adjacent nut side screw grooves 3a cut out by the top window 3b. It forms so that an end surface may be connected. That is, the connecting groove 5c straddles the mountain portion (land portion) of the shaft side screw groove 2a, and is shifted by one line by turning the nut 3 from one end surface of the nut side screw groove 3a and one end surface. The other end face of the nut-side thread groove 3a is connected. The connecting groove 5c has a relief portion 5d whose bottom surface is curved (convex) toward the outer side in the radial direction of the nut 3 so that the ball 4 passing through the connecting groove 5c can get over the thread portion of the axial screw groove 2a. It is formed (see FIG. 4A). As a result, the nut 3 is configured to endlessly circulate by using the connecting groove 5c of the top member 5 with a part of the nut side screw groove 3a as a circulation path (see FIG. 2B).

  When the nut 3 is rotated, the ball screw 1 transmits a rotational force to the screw shaft 2 through a plurality of balls 4 accommodated in the rolling path. When the screw shaft 2 is restricted from rotating about its axis by a non-rotating mechanism (not shown), the rotational motion of the nut 3 is converted into the linear motion in the axial direction of the screw shaft 2 by the inclination of the shaft-side screw groove 2a. Similarly, in the ball screw 1, when the screw shaft 2 is rotated, the rotational force is transmitted to the nut 3 via the plurality of balls 4 accommodated in the rolling path. When the rotation of the nut 3 is restricted by a non-rotating mechanism (not shown), the rotational motion of the screw shaft 2 is converted into the linear motion of the nut 3 in the axial direction by the inclination of the shaft-side screw groove 2a. In the present embodiment, the shaft-side screw groove 2a and the nut-side screw groove 3a of the screw shaft 2 are wound once, but the present invention is not limited to this. In the present embodiment, the shaft-side thread groove 2a formed in the screw shaft 2 is a right-hand thread, but is not limited thereto.

  Hereinafter, the shape of the connecting groove 5c of the top member 5 and the operation thereof will be described in detail with reference to FIGS.

  As shown in FIG. 4 (a), the connecting groove 5c of the top member 5 has a relief portion 5d (light ink) curved toward the radially outer side of the nut 3 at a position facing the crest portion of the shaft side screw groove 2a. Part) is formed. The connecting groove 5c is configured such that the ball 4 rides over the shaft-side screw groove 2a without contacting the mountain portion of the shaft-side screw groove 2a by rolling the ball 4 with the bottom surface of the escape portion 5d as a rolling surface. (See FIG. 2 (b)). The connecting groove 5c is open at both end portions in the longitudinal direction as the inlet and outlet of the ball 4.

  As shown in FIG. 4B, the connecting groove 5c is open at the portion facing the bottom as an opening 5e. That is, the connecting groove 5c is formed in a groove shape from the bottom surface and two side surfaces formed at positions facing each other across the bottom surface. Further, the connecting groove 5 c is configured such that the groove width W 0 that is the distance between the two side surfaces is larger than the diameter D of the ball 4. Between the screw shaft 2 and the nut 3 of the ball screw 1 configured as described above, a space is formed that is more radially expanded than the rolling path by the escape portion 5d of the connecting groove 5c.

  The connecting groove 5c is provided with a ball guide member 6 for guiding the ball 4 so that the ball 4 moves along the bottom surface of the connecting groove 5c. The ball guide member 6 is formed in a rail shape with claw-like members protruding from both side surfaces toward the opposing side surfaces. The ball guide members 6 are respectively provided in the vicinity of the opening 5e of the connecting groove 5c and at substantially the same groove depth (distance from the bottom surface). Further, the ball guide member 6 is integrally provided continuously over the entire length from the introduction port to the discharge port of the ball 4 which is the longitudinal end portion of the connecting groove 5c. That is, the ball guide member 6 is formed in the vicinity of the opening 5e of the connection groove 5c along the bottom surface of the connection groove 5c.

  The ball guide member 6 is configured such that a position of the shaft side thread groove 2 a facing the escape portion 5 d is curved toward the radially outer side of the nut 3. The connecting groove 5 c is configured such that the guide width W 1, which is the distance between the tips of the claw-like members of the ball guide member 6, is smaller than the diameter D of the ball 4 over its entire length. That is, the connecting groove 5c is supported so that the ball 4 can enter the inside through the introduction port, and the ball 4 is supported by the ball guide member 6 so that the ball 4 does not go outside through the opening 5e. Thereby, the connecting groove 5c is configured to be able to support the ball 4 moving inside the connecting groove 5c by the ball guide member 6. The ball screw 1 can be easily formed by integrally forming the ball guide member 6 on the top member 5 so that the ball guide member 6 along the bottom shape of the connection groove 5c and the guide width W1 are set to arbitrary values. Can be provided.

In the ball screw 1 configured as described above, when the screw shaft 2 rotates, the ball 4 rolls between the bottom surface of the shaft side screw groove 2a and the bottom surface of the nut side screw groove 3a that constitute the rolling path. Move in the rolling path.
As shown in FIG. 5A, when the ball 4 reaches the connection groove 5c of the top member 5, the ball 4 enters the connection groove 5c from the introduction port which is one end of the connection groove 5c. At this time, the ball 4 is supported on the bottom surface of the shaft-side screw groove 2a. A portion of the ball guide member 6 of the connecting groove 5c adjacent to the ball 4 is between the surface of the ball 4 on the screw shaft 2 side and the shaft-side screw groove 2a, and is a predetermined distance from the surface of the ball 4. It is separated.

  As shown in FIG. 5 (b), the ball 4 moves in the connecting groove 5c by the rotation of the screw shaft 2, and reaches the escape portion 5d (thin ink portion) of the connecting groove 5c. The ball guide member 6 of the escape portion 5d is curved toward the radially outer side of the nut 3 along the bottom surface of the escape portion 5d. Accordingly, the ball 4 approaches the ball guide member 6 of the connecting groove 5c as it moves in the connecting groove 5c toward the center relief portion 5d, and the surface of the ball 4 on the screw shaft 2 side is the ball guide at a predetermined position. It contacts the member 6 (the darker ink portion). When the ball 4 further moves toward the central portion of the escape portion 5d, it rides on the ball guide member 6 and is separated from the bottom surface of the shaft-side screw groove 2a.

  As shown in FIG. 5 (c), the ball 4 is pushed by another adjacent ball 4 by the rotation of the screw shaft 2 and moves in the escape portion 5d (thin ink portion) of the connecting groove 5c. At this time, the ball 4 rolls on the ball guide member 6 in a state where it rides on the ball guide member 6 (the darker ink portion) of the connecting groove 5c. That is, the ball 4 moves in the space between the bottom surface of the connecting groove 5 c and the ball guide member 6 while being supported by the ball guide member 6.

  As shown in FIG. 5 (d), the ball 4 is urged along the bottom surface of the connection groove 5c by the ball guide member 6 (the darker black ink portion) while being pressed against the escape portion 5d (the thinner one) in the connection groove 5c. The thin ink portion is moved, and the mountain portion of the shaft side screw groove 2a is overcome without contacting the shaft side screw groove 2a.

  With the configuration as described above, the ball screw 1 smoothly gets over the shaft-side screw groove 2a while the ball 4 is pressed against the bottom surface of the connection groove 5c by the ball guide member 6, and therefore the arrangement of the balls 4 in the connection groove 5c. Is not disturbed and clogging does not occur. Further, since the ball screw 1 moves in a space sandwiched between the bottom surface of the connecting groove 5c and the ball guide member 6 in a state where the ball 4 is supported by the ball guide member 6, the ball screw 1 and the shaft 5 In the space between the side screw grooves 2a, the arrangement of the balls 4 is not disturbed and clogging does not occur. Thereby, the ball screw 1 can reduce the rotational resistance of the screw shaft 2 or the nut 3 generated when the ball 4 passes through the top member 5.

  In the present embodiment, the ball screw 1 is described with respect to the case where the screw shaft 2 is rotating. However, the present invention is not limited to this, and the ball 4 is not pressed against the nut-side screw groove 3a by centrifugal force. The nut 3 may be rotated at the rotation speed. Further, in the present embodiment, the connecting groove 5c is provided with the ball guide member 6 on both side surfaces, but the ball guide member 6 is provided only on the side surface and the guide width W1 is larger than the diameter D of the ball 4. May be configured to be smaller.

  The above-described embodiments are merely representative, and various modifications can be made without departing from the scope of one embodiment. It goes without saying that the present invention can be embodied in various forms, and the scope of the present invention is indicated by the description of the scope of claims, and the equivalent meanings of the scope of claims, and all the scopes within the scope of the claims. Includes changes.

1 Ball screw 2 Screw shaft 2a Shaft side thread groove 3 Nut 4 Ball 5 Top member 6 Ball guide member

Claims (4)

A screw shaft is inserted into the nut, a ball rolling path is constituted by the thread groove of the screw shaft and the thread groove of the nut, and a plurality of top members in which connecting grooves having the rolling path as a circulation path are formed. A ball screw in which a plurality of balls are arranged on a rolling path that constitutes the circulation path,
A ball screw in which a ball guide member is provided on the top member such that a ball passing through the connection groove moves while being pressed against the bottom surface of the connection groove.   2. The ball screw according to claim 1, wherein a width of an opening of the connection groove facing a bottom surface of the connection groove is configured to be narrower than a diameter of the ball by the ball guide member.   The ball screw according to claim 1, wherein the ball guide member is configured to protrude from a side surface of the connection groove along a bottom surface of the connection groove.   The ball screw according to any one of claims 1 to 3, wherein the ball guide member is formed integrally with the top member.

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