JP2017133669A - Ball Screw - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ball screw which can increase an allowable load capacity while suppressing an increase of a production cost.SOLUTION: In a circulation-type ball screw 1, a screw shaft 2 is inserted into a nut 3, and a plurality of balls 4 are arranged in a rolling path which is constituted of a shaft-side screw groove 2a and a nut-side screw groove 3a, the nut-side groove 3a is formed of substantially-single wound spiral step shapes which are formed at one side and the other side of an internal peripheral face in an axial direction so that the internal peripheral face and end parts of the nut 3 are expanded or contracted in diameters, the end parts displaced to the axial direction are connected to each other by a smooth curved face 3c, and formed into annular shapes. A recess 3d progressing toward the outside of the nut 3 in a radial direction is formed at the curved face which connects the spiral step-shaped end parts, and a step face having a spiral step shape is formed at a curved face which opposes the shaft-side screw groove 2a.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a ball screw. Specifically, it relates to a circulating ball screw.

  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 an outer peripheral surface and a nut supported via a plurality of balls as rolling elements. Thus, the ball screw is configured as a motion conversion mechanism in which one of the screw shaft or the nut rotates and the other linearly moves as a linear motion member. Among the ball screws configured as described above, a non-circulating ball screw in which the ball does not circulate is known. The non-circulating ball screw has an annular rolling groove formed on the inner peripheral surface of a nut and holds the ball by a cage. For example, as described in Patent Document 1.

  In the ball screw described in Patent Document 1, two spiral rolling grooves (thread grooves) are formed on the outer peripheral surface of the screw shaft, and two rows of annular rolling grooves are formed on the inner peripheral surface of the nut. Yes. The annular rolling groove is formed on both sides of the annular convex portion formed in the central portion of the inner peripheral surface of the nut. In the ball screw, two balls are disposed in each annular rolling groove, and are in angular contact with the spiral rolling groove of the screw shaft and the annular rolling groove of the nut. The two balls are rotatably held with respect to the screw shaft and the nut in a state where the positional relationship is maintained in the annular rolling groove by the cage. With this configuration, the ball screw rolls on the spiral rolling groove of the screw shaft while the ball rolls on the annular rolling groove of the nut. That is, the ball screw can convert the rotational motion into a linear motion only by forming two rows of annular rolling grooves on the inner peripheral surface of the nut in order to reduce production costs. However, in the technique described in Patent Document 1, the number of balls that can be arranged in the annular rolling groove of the nut and the position thereof are determined by the number of spiral rolling grooves on the screw shaft. For this reason, it is disadvantageous in that the allowable load capacity is limited as compared with the circulation type ball screw.

Japanese Unexamined Patent Publication No. 07-0777260

  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 capable of increasing the allowable load capacity while suppressing the production cost.

  That is, a circulating ball screw in which a screw shaft is inserted into a nut and a plurality of balls are arranged on a rolling path composed of a screw groove of the screw shaft and a screw groove of the nut, the screw groove of the nut However, from the substantially one-turn spiral step shape provided respectively on one side and the other side in the axial direction of the inner peripheral surface so as to expand or reduce the diameter of both ends in the axial direction of the inner peripheral surface of the nut. The end portions shifted in the axial direction in each of the spiral step shapes are connected with a smooth curved surface to form an annular shape, and the end portions of the spiral step shape are connected to each other. A recess is formed on the smooth curved surface toward the radially outer side of the nut, and the spiral stepped step surface is formed on a curved surface facing the screw groove of the screw shaft.

  An annular guide plate is provided in the enlarged diameter portion of the inner peripheral surface of the nut, so that the ball rolls along a smooth curved surface connecting the ends of the spiral step shape. A portion of the guide plate facing the smooth curved surface connecting the end portions of the spiral step shape is formed into a smooth curved surface along the spiral step shape.

  A part of the annular guide plate is opened so that the diameter can be reduced in the radial direction.

  The annular guide plate is engaged with a slit formed on the inner peripheral surface of the nut.

  The annular guide plate is made of a high steel wire for spring.

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

  That is, the ball screw is constituted by a nut having a thread groove having a spiral step shape that can be formed by a mold. The ball screw is formed in an annular shape with a smooth curved surface in a step shape that is a thread groove so that the ball disposed in the thread groove circulates in the thread groove of the nut. That is, the ball screw is configured as a circulation type ball screw in which a plurality of balls are continuously arranged in a thread groove of a nut that can be formed of a mold. Thereby, the allowable load capacity can be increased while suppressing the production cost.

  The ball screw is formed in an annular shape that allows the ball to circulate in a state where the screw groove of the nut is released on one side. That is, the ball screw is composed of a nut having an annular thread groove that can be formed of a mold without an undercut. Thereby, the allowable load capacity can be increased while suppressing the production cost.

  In the ball screw, a guide plate is easily incorporated in a nut, and a screw groove is formed through which the ball can circulate. Thereby, the allowable load capacity can be increased while suppressing the production cost.

The perspective view which shows the whole structure in one Embodiment of a ball screw. (A) Top view which shows whole structure in one Embodiment of ball screw. (B) A arrow sectional drawing in Fig.2 (a). The axial direction sectional view and side view of a nut in one embodiment of a ball screw. The axial direction sectional view and arrow A sectional view in the state where the guide board was provided in the nut in one embodiment of a ball screw. The axial direction sectional view and side view showing the mode of the ball which rolls the nut side thread groove of the nut in one embodiment of a ball screw. The fragmentary sectional view which shows the aspect in which ball | bowl exceeds the side wall of the axial side thread groove of a screw shaft in one Embodiment of a ball screw. The axial direction sectional view which shows the whole structure in other embodiment of a ball screw.

  Below, the ball screw 1 provided with the nut 3 which is one Embodiment of the ball screw 1 is demonstrated using FIGS. 1-4. In the present embodiment, step-shaped nut-side screw grooves 3a having diameters enlarged at both ends in the axial direction are formed on the inner peripheral surface of the nut 3 of the ball screw 1, respectively.

  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, 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 is formed with a plurality of shaft-side screw grooves 2a for rolling the balls 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 that allows a large contact angle with the ball 4 and a small axial clearance. 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.

  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 a sintered alloy prepared by adjusting a metal powder into a plastic shape and molded by an injection molding machine. The nut 3 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 pushed into a mold in a heated and melted state. 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. It is composed of SCM415 consisting of 0.04 wt%, Mn (manganese) 0.76 wt%, Mo (molybdenum) 0.19 wt%, Si (silicon) 0.20 wt%, and the rest Fe (iron) or the like. . In addition to this, the material of the nut 3 includes 3.0 to 10.0 wt% of Ni and is excellent in workability and corrosion resistance (FEN8 of Japanese Powder Metallurgy Industry Standard), or C is 0.07 wt%. %, Cr is 17 wt%, Ni is 4 wt%, Cu is 4 wt%, and the remainder is precipitation hardened stainless steel SUS630 made of Fe or the like. 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. In the present embodiment, the nut 3 is formed by MIM, but is not limited to this, and may be formed by forging.

  As shown in FIG. 2B, step-shaped nut-side thread grooves 3 a having enlarged diameters at both ends in the axial direction are formed on the inner peripheral surface of the nut 3. On the inner peripheral surface of the nut 3, a rolling surface 3 b is formed of a curved surface in which a stepped surface connecting a reduced diameter portion at the center and an enlarged diameter portion at the end gradually increases in diameter toward the respective end portions of the nut 3. Is formed. The nut-side thread groove 3a formed in each step shape is formed in a substantially clockwise clockwise spiral.

  As shown in FIG. 3, the nut-side thread grooves 3 a formed in the respective step shapes are connected by a smooth curved surface 3 c at an end portion shifted in the axial direction by the amount of the spiral lead. That is, each step shape is connected by a smooth curved surface 3c between the original end portion and the step surface moved to the adjacent position by being wound substantially spirally. Thereby, each step-shaped nut side screw groove 3a is formed in the annular | circular shape which the rolling surface 3b which is a level | step difference surface continues without interruption. In each step-shaped nut-side thread groove 3a, the smooth curved surface 3c connecting the rolling surface 3b, which is a step surface shifted in the axial direction by the spiral, is a radial direction toward the center in the circumferential direction. A concave portion 3d deeper than the groove depth of the shaft side screw groove 2a is formed toward the outside. On the inner peripheral surface of the nut 3 configured in this manner, a nut-side screw groove 3a having a circular spiral step shape connected by a smooth curved surface 3c is formed. Moreover, the nut side thread groove 3a is comprised only from the rolling surface 3b which consists of a curved surface gradually diameter-expanded as it goes to each edge part from the diameter reduction part of the center part of the nut 3. As shown in FIG. That is, the nut side screw groove 3a is configured as an undercut-free groove whose side wall is only on one side. The nut-side thread groove 3 a is formed with the same lead and pitch as the shaft-side thread groove 2 a of the screw shaft 2. As the guide plate positioning portion 3e for arranging a guide plate 5 to be described later, a stepped shape in which the end portions on both sides in the axial direction are increased in diameter along the nut-side screw groove 3a is formed in the enlarged diameter portion of the nut 3, respectively. Has been. The guide plate positioning portion 3e is formed in a substantially clockwise clockwise spiral on the opening side of the nut side screw groove 3a. Furthermore, a slit 3f for fixing the guide plate 5 is formed in the enlarged diameter portion of the nut 3 along the guide plate positioning portion 3e.

As shown in FIGS. 1, 2, and 4, an annular guide plate 5 (light ink portion in FIGS. 1, 2, and 4) is provided on the inner peripheral surface of the nut 3. The guide plate 5 holds the ball 4 as a rolling element in the nut-side screw groove 3a.
As shown in FIG. 4, the guide plate 5 is formed in a substantially clockwise spiral shape. The guide plate 5 is formed of a high steel wire rod for spring, or a steel material that has been subjected to a hardening process of about 55 to 62 HRC by induction hardening or vacuum carburizing and quenching. The guide plate 5 is connected by a smooth curved surface 5a at a portion displaced in the axial direction by the amount of the spiral lead. Furthermore, the smooth curved surface 5a of the guide plate 5 has a protruding portion 5b formed radially outward as it goes toward the center in the circumferential direction. The smooth curved surface 5a is formed to be substantially the same curved surface as the smooth curved surface 3c of the nut side screw groove 3a of the nut 3. Further, the guide plate 5 is formed in a substantially C shape by opening a portion facing the portion formed on the smooth curved surface 5a. Thereby, the guide plate 5 is configured to be capable of reducing the diameter in the radial direction by bringing both ends of the opening close to each other. Engagement portions 5 c protruding in the radial direction are formed at both ends of the opening of the guide plate 5. The guide plate 5 is fixed to the inner peripheral surface of the nut 3 by the engagement portion 5c being inserted into the slit 3f formed in the nut 3 while being positioned by the guide plate positioning portion 3e of the nut 3. The guide plate 5 is fixed at a position where the ball 4 can pass between the side wall (step surface) of the nut-side screw groove 3a. The smooth curved surface 5 a of the guide plate 5 is disposed so as to face the smooth curved surface 3 c of the nut 3. On the outer peripheral surface of the nut 3, a flange portion 3 g which is a stepped portion whose diameter is partially expanded is formed.

  As shown in FIGS. 2B and 5, the screw shaft 2 is inserted into the nut 3 so that the shaft-side screw groove 2 a and the nut-side screw groove 3 a face each other. A plurality of balls 4 that are rolling elements are housed in a space formed by the shaft-side screw groove 2a and the nut-side screw groove 3a so as to roll freely. Moreover, the nut side thread groove 3a is formed so that the smooth curved surface 3c may straddle the side wall of the shaft side thread groove 2a. As shown in FIG. 2 (b), the balls 4 accommodated so as to roll between the nut-side thread groove 3a of the nut 3 and the shaft-side thread groove 2a of the screw shaft 2 are arranged in a double row outward with a contact angle θ. It is configured to make an angular contact. Thus, the shaft side thread groove 2a and the nut side thread groove 3a constitute a rolling path on which the plurality of balls 4 roll. 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.

  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 rotation of the screw shaft 2 around the shaft is restricted by the rotation prevention mechanism, the rotational motion of the nut 3 is converted into a 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 the rotation prevention mechanism, 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 substantially wound, 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 manner of circulation of the balls 4 in the nut 3 of the ball screw 1 will be described in detail with reference to FIGS.

As shown in FIGS. 3 to 6, the nut-side thread groove 3a of the nut 3 is formed with a smooth curved surface 3c so as to straddle the side wall of the shaft-side thread groove 2a of the screw shaft 2, and the smooth curved surface 3c has a shaft. A recess 3d that is deeper than the groove depth of the side screw groove 2a is formed.
Therefore, as shown in FIGS. 5 and 6, the ball 4 that has reached the smooth curved surface 3c of the nut-side thread groove 3a gradually moves to the side wall of the shaft-side thread groove 2a by the smooth curved surface 3c of the nut-side thread groove 3a. Sent to. The ball 4 is pushed up toward the tip of the shaft side screw groove 2a along the side wall of the shaft side screw groove 2a. At this time, since the ball 4 is held by the guide plate 5 formed along the smooth curved surface 3c, the ball 4 does not fall off the rolling path. That is, even if the nut-side screw groove 3a is formed in a groove shape without an undercut on only one side, the ball 4 that attempts to cross the side wall of the shaft-side screw groove 2a can be stably held. The ball 4 moves over the side wall of the shaft-side screw groove 2a to the adjacent shaft-side screw groove 2a by the smooth curved surface 3c of the nut-side screw groove 3a, and the original screw groove position of the annular nut-side screw groove 3a. Return to. That is, the ball 4 in the rolling path moves to the adjacent shaft side thread groove 2a and circulates in the rolling path by making a round of the nut side thread groove 3a. By comprising in this way, the ball screw 1 can arrange | position the some ball | bowl 4 continuously in a rolling path.

  Moreover, as shown in FIG. 7, the ball screw 6 provided with the nut 7 from which the shape of the nut 3 differs as another embodiment of the ball screw 1 may be sufficient. In this embodiment, on the inner peripheral surface of the nut 7 of the ball screw 6, step-shaped nut-side screw grooves 7 a having diameters reduced at both ends in the axial direction are formed. In addition, the ball screw 1 which concerns on all the following embodiments is replaced with the ball screw 1 in the ball screw 1 shown in FIGS. 1-6, and the name, figure number, and symbol used in the description are used. In the following embodiments, the same points as those of the already described embodiments will be omitted, and different portions will be mainly described.

  As shown in FIG. 7, the ball screw 6 converts a rotational motion into a linear motion and outputs it. The ball screw 6 includes a screw shaft 2, a nut 7, a plurality of balls 4, and the like.

  On the inner peripheral surface of the nut 7, step-shaped nut-side screw grooves 7 a each having a reduced diameter at both ends in the axial direction are formed as nut-side screw grooves 7 a on the inner peripheral surface of the nut 7. A stepped surface connecting the reduced diameter portion of the portion and the enlarged diameter portion of the central portion is formed on the rolling surface 7 b formed of a curved surface that gradually increases in diameter toward the central portion of the nut 7. The nut 7 is divided into two at a substantially central portion of the enlarged diameter portion, and is connected via a press-fit pin 8. The connecting method of the nut 7 is not limited to the press-fit pin 8 and may be screw fastening or the like. The nut-side thread groove 7a formed in each step shape is formed in a substantially clockwise clockwise spiral. Each step-shaped nut-side thread groove 7a is connected with a smooth curved surface (not shown) at the end shifted in the axial direction by the amount of the spiral lead. On the inner peripheral surface of the nut 7 configured in this manner, a step-shaped nut-side screw groove 7a processed into a spiral of approximately one turn in a state where the nut 7 is divided is formed in a continuous annular shape without interruption. Is formed. The nut-side thread groove 7a is configured as an undercut-free groove whose side wall is only on one side. As the guide plate positioning portion 7d for arranging the guide plate 5, a stepped shape in which the diameter of the central enlarged portion is further expanded so as to follow the nut-side screw groove 7a is formed on the enlarged diameter portion of the nut 7, respectively. Yes.

  On the inner peripheral surface of the nut 7, a substantially one-turn clockwise spiral guide plate 5 is provided. The guide plate 5 holds the ball 4 as a rolling element in the nut side screw groove 7a. The guide plate 5 is configured to be able to reduce the diameter to an outer diameter smaller than the inner diameter of the reduced diameter portion of the nut 7. The guide plate 5 is fixed to the guide plate positioning portion 7 d of the nut 7 by a slit (not shown) formed on the inner peripheral surface of the nut 7.

  With the configuration as described above, the ball screws 1 and 6 have a substantially one-circular spiral spiral nut-side screw groove 3a composed only of the shaft-side screw groove 2a of the screw shaft 2 and the side wall on one side of the nuts 3 and 7. A plurality of balls 4 are arranged on the rolling path composed of 7a. In other words, the ball screws 1 and 6 have nut-side thread grooves 3a and 7a without an undercut that can be formed from a mold, are formed in an annular spiral shape, and a plurality of balls 4 are continuously arranged to be circulated. . Thereby, the ball screws 1 and 6 can increase the allowable load capacity while suppressing the production cost. The ball screws 1 and 6 are easily provided with a guide plate 5 for preventing the balls 4 from dropping off. Thereby, the allowable load capacity can be increased while suppressing the production cost.

  As described above, in the ball screws 1 and 6 as an embodiment of the ball screw, it is assumed that the nuts 3 and 7 are formed with the annular spiral nut-side screw grooves 3a and 7a on both sides in the axial direction. Although it demonstrated, it is not limited to this, What is necessary is just the structure which the nut 7 can form with a type | mold, and a ball | bowl circulates. In addition, the above-described embodiment is merely a representative form, and various modifications can be made without departing from the scope of the 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.

DESCRIPTION OF SYMBOLS 1 Ball screw 2 Screw shaft 3 Nut 3a Nut side thread groove 3c Smooth curved surface 3d Recessed part 4 Ball 5 Guide plate

Claims (5)

A circular ball screw in which a screw shaft is inserted into a nut and a plurality of balls are arranged on a rolling path composed of a screw groove of the screw shaft and a screw groove of the nut,
A substantially one-turn spiral provided in the axial direction on one side and the other side of the inner peripheral surface so that the thread grooves of the nut expand or contract the diameter of both ends in the axial direction of the inner peripheral surface of the nut. In the spiral step shape, the end portions shifted in the axial direction in each of the spiral step shapes are connected with a smooth curved surface to form an annular shape, and the end portions of the spiral step shape A circular curved surface in which a concave portion is formed on the smooth curved surface connecting the nuts radially outward of the nut, and the stepped surface of the spiral stepped shape is formed on a curved surface facing the screw groove of the screw shaft. Ball screw.   An annular guide plate is provided in the enlarged diameter portion of the inner peripheral surface of the nut, so that the ball rolls along a smooth curved surface connecting the ends of the spiral step shape. 2. The circulation according to claim 1, wherein a portion of the guide plate facing the smooth curved surface connecting the ends of the spiral step shape is formed into a smooth curved surface along the spiral step shape. Mold ball screw.   3. The circulation type ball screw according to claim 1, wherein a part of the annular guide plate is opened so that the diameter can be reduced in a radial direction.   The circulation type ball screw according to any one of claims 1 to 3, wherein the annular guide plate is engaged with a slit formed on an inner peripheral surface of the nut.   The circulation type ball screw according to any one of claims 1 to 4, wherein the annular guide plate is made of a high steel wire rod for a spring.

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