JP2016188674A - Ball Screw - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ball screw which can be manufactured using a mold at low cost by eliminating restrictions on the application of the ball screw and an under-cut of screw grooves of a nut.SOLUTION: An annular salient 10 is formed at an axial center part of an inner peripheral surface of a nut 3, thread grooves 3a are formed on both sides of the annular salient 10 in an axial direction, the thread grooves 3a are undercut free grooves only on one side in which almost one quarter arc is spirally formed in one turn and two rows, balls 4 accommodated between and the thread grooves 3a and thread grooves 2a of a screw shaft 2 are configured to make angular contact in a double row outward direction while a ball circulation part 7 is provided in a part of the thread grooves 3a of the nut 3, and the ball circulation part 7 is curved in an S shape so as to smoothly connect adjacent circumferential portions of the thread grooves 2a of the screw shaft 2, and the groove depth is formed larger than that of the thread groove 3a of the nut 3.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a ball screw used for an actuator of an electric power steering of an automobile or a spool valve drive unit for switching hydraulic pressure of a transmission, and more particularly to a ball circulation type ball screw disposed between a screw shaft and a nut. .

  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. A plurality of balls accommodated in the formed rolling path and a circulation mechanism having the rolling path as a circulation path are used as, for example, a motion conversion mechanism that linearly moves the screw shaft by rotating the nut. ing.

  Among these ball screws, as a non-circular ball screw, a non-circulating retainer ball screw is known in which a ball is held by a cage so that the ball does not vary, and the ball does not circulate. In this type of ball screw, there is a problem that the contact angle cannot be increased because the screw groove becomes shallow due to the restriction of the cage space. As a solution to this problem, a ball screw as shown in FIG. 5 is known. The ball screw 51 has a screw shaft 52, a nut 53, and a ball 54. On the outer peripheral surface of the screw shaft 52, two spiral ball rolling grooves (thread grooves) 52a whose depth is slightly shallower than the radius of the ball 54 are formed.

  An annular convex portion 55 having an inner diameter slightly larger than the outer diameter of the screw shaft 52 is provided at the center of the inner peripheral surface of the nut 53. Annular ball rolling grooves 53a are formed on both sides of the annular convex portion 55 in the axial direction. A locking groove 56 is formed in the opening end portion of the nut 53 positioned on the outer side in the axial direction of the annular ball rolling groove 53a, and a thin plate ring shape revolving with respect to the screw shaft 52 together with the ball 54 in the opening end portion. After the retainer 57 is inserted, a retaining ring 58 is attached to the locking groove 56 so that the retainer 57 is positioned and fixed. In addition, a keyway 59 for fixing the nut 53 to a housing or the like is formed on the outer periphery of the nut 53.

  Here, as shown in FIG. 6, the diameter of the ball 54 is Da, the radius of curvature of the ball rolling groove 52a of the screw shaft 52 is Rs, the radius of curvature of the ball rolling groove 53a of the nut 53 is Rn, and the balls 54 are both The contact angle that makes angular contact with the ball rolling grooves 52a and 53a is α. Here, Rs = Rn = 0.52 to 0.58 Da is set.

  The center of the left and right balls 54, 54 is on the pitch circle Dp of the ball 54, and the left and right balls 54, 54 are in double-row angular contact with the ball rolling grooves 52 a, 53 a at a contact angle α, respectively The center of curvature Os, On of the ball rolling grooves 52a, 53a is located at a distance of Rs, Rn from the contact point on the contact angle line.

  The distance Ps between the left and right curvature centers Os and Os and the distance Pn between the left and right curvature centers On and On are determined. This Ps is the pitch of the ball rolling groove 52a of the screw shaft 52, and Pn is the ball of the nut 53. This is the pitch of the rolling grooves 53a. In order for the left and right balls 54 and 54 to make an angular contact outward at a contact angle α to both the ball rolling grooves 52a and 53a, a relationship of Pn> Ps is necessary.

  A total of four balls 54, two for each of the annular ball rolling grooves 53 a of the nut 53, are interposed between the ball rolling grooves 52 a, 53 a, and can be freely rolled by the cage 60. Is retained. The retainer 60 is partially different from the retainer 57 described above in that four recesses 61 are formed at equal intervals, and the balls 54 are held in contact with the recesses 61 together with the balls 54 and screw shafts. Revolve with respect to 52.

  The number of the recesses 61 depends on the number of the ball rolling grooves 52a of the screw shaft 52, and is 2 in the case of 2 and 3 in the case of 3 and this example is shown in FIG. The number of the recesses 61 is four, and the case of a four-thread screw is shown.

  In this way, the ball 54 makes double-row outward angular contact with the spiral ball rolling groove 52a of the screw shaft 52 and the annular ball rolling groove 53a of the nut 53, and the shaft of the annular ball rolling groove 53a. Plate ring-shaped retainers 57 and 60 that hold the ball 54 in a freely rolling manner and revolve with respect to the screw shaft 52 together with the ball 54 are fitted in the opening end of the nut 53 positioned on the outer side in the direction. Therefore, the gap between the outer peripheral surface of the screw shaft 52 and the inner peripheral surface of the nut 53 can be reduced. As a result, the depth of the ball rolling groove 52a of the screw shaft 52 and the ball rolling groove 53a of the nut 53 can be reduced. Can be deep. For this reason, the contact angle α at which the ball 54 makes an angular contact with both the ball rolling grooves 52a and 53a can be increased, and the rigidity against the axial load is increased (see, for example, Patent Document 1).

Japanese Patent No. 3856482

  In the conventional ball screw 51, the groove of the nut 53 (annular ball rolling groove 53a) is not used because the screw groove becomes shallow due to the restriction of the cage of the ball screw with cage. The shape is only on one side, that is, approximately one-quarter arc (four-thread), and cages 57 and 60 are arranged in a vacant space, but with respect to the spiral ball rolling groove 52a of the screw shaft 52, The ball rolling groove 53a of the nut 53 is annular, and is a non-circular ball screw 51 that moves in the axial direction while rotating relative to the screw shaft 52. Therefore, the ball rolling groove 53a is applicable only to a system in which the rotation of the nut 53 is allowed. There is a problem that a structure for receiving rotation of the nut 53 is required.

  The present invention has been made in view of such circumstances, and a circulation in which a spiral thread groove of a nut is a thread groove on only one side and a connection part of a single thread groove is an S-shaped ball circulation part. Inspired by the ball screw of the mold, there are no restrictions on the application of the ball screw, and there is no need to undercut the thread groove of the nut, and to provide a low cost ball screw that can be manufactured with a mold. It is an object.

  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. An axial direction of the inner peripheral surface of the nut in a ball screw comprising: a cylindrical nut formed with a screw groove; and a plurality of balls accommodated in a rolling path formed by the opposing screw groove An annular convex portion is formed in the central portion, and the thread groove is formed on both sides in the axial direction of the annular convex portion. This thread groove is an undercut-free groove on only one side, and a substantially one-quarter arc is spirally formed. The balls formed in one row and two rows and accommodated between the screw grooves of the screw shaft are configured to make double row outward angular contact, and the balls are formed on a part of the screw grooves of the nut. A circulation part is provided, and this ball circulation part is a thread groove of the screw shaft. The one rotation adjacent curved smoothly connected to as S-shaped, groove depth is deeper than the thread groove of the nut.

  Thus, a screw shaft having a helical thread groove formed on the outer peripheral surface, a cylindrical nut externally fitted to the screw shaft and having a helical thread groove formed on the inner peripheral surface, and an opposing screw A ball screw having a plurality of balls housed in a rolling path formed by a groove, an annular convex portion is formed at an axially central portion of an inner peripheral surface of the nut, and both axial sides of the annular convex portion A thread groove is formed on the one side, and this thread groove is an undercut-free groove on only one side. A substantially 1/4 arc is spirally formed in two rows and accommodated between the thread groove of the screw shaft. The ball is configured to make double row outward angular contact, and a ball circulation part is provided in a part of the thread groove of the nut, and this ball circulation part corresponds to one round of the screw groove of the screw shaft. Curved in an S shape to smoothly connect each other, and the thread groove of the nut Since the depth of the groove is also deep, the depth of the screw shaft screw groove and nut screw groove can be increased, and the contact angle at which the ball makes angular contact with both screw grooves can be increased to increase the axial direction. It can increase the rigidity against the load, and the ball rolling groove of the nut is annular, and it can be applied to the ball screw like a conventional non-circulating ball screw that moves in the axial direction while rotating relative to the screw shaft. It is possible to provide a ball screw that can be manufactured with a mold without any restriction, undercutting of a thread groove of a nut, and capable of being manufactured with a mold.

  Preferably, as in the invention described in claim 2, the ball circulation portion of the nut is formed to be undercut free on only one side, penetrates the inner and outer peripheral surfaces of the body portion of the nut, A holding hole is formed on the opening end side of the nut positioned on the outer side in the axial direction, and a guide member is fitted into the holding hole, and the guide member is attached to the ball circulation portion of the nut. If a holding groove made up of the other S-shaped groove to be complemented is formed, and the ball is held by the holding groove and the ball circulating portion so as to roll freely, the nut can be manufactured from a mold. In addition, the cost can be reduced, and the ball rolling on the rolling path can be stably held even if the ball circulation portion is formed to be undercut free on only one side.

  According to a third aspect of the present invention, the guide member is formed with a cylindrical fitting portion in which a tongue piece is formed at an end portion, and the holding groove is formed on one end surface of the fitting portion. A rectangular holding portion serving as a base, and a tapered counterbore portion is formed in the opening on the outer diameter side of the holding hole of the nut. The tongue piece of the guide member is plastically deformed in the counterbore portion. If the guide member is caulked and fixed to the nut in a close contact state, the guide member can be stably fixed to the nut with a simple operation, and the cost can be reduced.

  Further, as in the invention described in claim 4, if the outer peripheral surfaces of both ends of the holding portion of the guide member are formed in an arc shape along the inner diameter of the nut, the guide member is formed in the holding hole of the nut. When fitted, they are brought into contact with the inner diameter of the nut, and the guide member is stably positioned with respect to the nut without looseness, and the guide member is prevented from coming out radially outward from the holding hole. Can be prevented.

  Further, as in the invention described in claim 5, the pitch of the thread groove of the screw shaft is set to a contact angle formed between the ball and both thread grooves with respect to the pitch between the thread grooves of the nut. If the pitch is set smaller than the corresponding design pitch and a preload is applied to the ball, play of the ball screw can be suppressed and rigidity against an axial load and a moment load can be increased.

  Further, as in the invention described in claim 6, if the nut is made of sintered metal formed by MIM, the desired shape can be easily and accurately obtained even in a complicated shape with a high workability. -It can be molded into dimensions, and cost reduction can be achieved.

  Further, as in the invention described in claim 7, if the guide member is made of sintered metal formed by MIM, even if it has a high workability and a complicated shape, the desired member can be easily and accurately obtained. In addition to being molded into a shape and size, the tongue piece can be plastically deformed and crimped and fixed to the holding hole of the nut.

  A ball screw according to the present invention includes a screw shaft having a helical thread groove formed on an outer peripheral surface, and a cylindrical nut that is fitted on the screw shaft and has a spiral thread groove formed on an inner peripheral surface thereof. A plurality of balls accommodated in a rolling path formed by the opposing thread grooves, and an annular convex portion is formed at an axially central portion of the inner peripheral surface of the nut. The screw groove is formed on both axial sides of the convex portion, and this screw groove is an undercut-free groove on only one side, and is formed in one row and two rows spirally with a quarter arc. The balls accommodated between the screw grooves are configured to make double-row outward angular contact, and a ball circulation part is provided in a part of the screw groove of the nut, and the ball circulation part is Smooth contact between adjacent ones of the thread groove on the screw shaft And the groove depth is deeper than the thread groove of the nut, so that the depth of the thread groove of the screw shaft and the thread groove of the nut can be increased, The angle of contact between the screw grooves and the angular contact can be increased to increase the rigidity against the axial load, and the ball rolling groove of the nut is annular and moves in the axial direction while rotating relative to the screw shaft. Provides a low-cost ball screw that can be manufactured in a mold without the restriction of the application of the ball screw and the undercut of the screw groove of the nut as in the case of a non-circulating ball screw can do.

(A) is a longitudinal cross-sectional view which shows one Embodiment of the ball screw which concerns on this invention, (b) is a cross-sectional view along II of (a). It is a longitudinal cross-sectional view which shows the circulation part in the nut of FIG. (A) is principal part sectional drawing which shows the ball contact state of FIG. 1, (b) is principal part sectional drawing which shows the ball | bowl circulation part of FIG. The guide member which concerns on this invention is shown, (a) is a bottom view, (b) is a front view, (c) is a top view, (d), (e) is a perspective view. It is a longitudinal cross-sectional view which shows the conventional ball non-circular ball screw. FIG. 6 is a partial axial sectional view of a ball screw including a cage according to another embodiment of FIG. 5 and a design explanatory view of a ball rolling groove. It is a perspective view of the holder | retainer of FIG.

  Formed by a screw shaft having a helical thread groove formed on the outer peripheral surface, a cylindrical nut externally fitted to the screw shaft and having a spiral thread groove formed on the inner peripheral surface, and the opposing thread groove A plurality of balls accommodated in the rolling path, wherein an annular convex portion is formed at an axial central portion of the inner peripheral surface of the nut, and the annular convex portions are formed on both axial sides of the annular convex portion. A thread groove is formed, and this thread groove is an undercut-free groove on only one side, and is formed in two lines in one row and two rows spirally with a substantially 1/4 arc, and is accommodated between the thread grooves of the screw shaft. The balls are configured to make double row outward angular contact, and a ball circulation portion is provided in a part of the screw groove of the nut, and the ball circulation portion is adjacent to the screw groove of the screw shaft. Curved in an S shape to smoothly connect one circle The groove depth is deeper than the thread groove of the nut, and it is formed to be undercut free on only one side, penetrates the inner and outer peripheral surfaces of the nut body, and is located on the outer side in the axial direction of the ball circulation portion. A holding hole is formed on the opening end side of the nut, and a guide member is fitted into the holding hole. The other S-shape that complements the ball circulating portion of the nut with the guide member. A holding groove made of a groove is formed, and the ball is held by the ball circulating portion so as to roll freely.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
1A is a longitudinal sectional view showing an embodiment of a ball screw according to the present invention, FIG. 1B is a transverse sectional view taken along line II of FIG. 1A, and FIG. FIG. 3A is a cross-sectional view of the main part showing the ball contact state of FIG. 1, and FIG. 3B is a cross-sectional view of the main part showing the ball circulation part of FIG. 4 shows a guide member according to the present invention, (a) is a bottom view, (b) is a front view, (c) is a top view, and (d) and (e) are perspective views.

  A ball screw 1 shown in FIGS. 1 (a) and 1 (b) has a screw shaft 2 having a helical thread groove 2a formed on an outer peripheral surface thereof, and is externally fitted to the screw shaft 2 and has a helical shape on an inner peripheral surface thereof. A nut 3 in which a thread groove 3a is formed, a plurality of balls 4 accommodated in a rolling path formed by both opposing thread grooves 2a and 3a, and a guide member 5 serving as a holding member for these balls 4 are provided. ing.

  The cross-sectional shape of the thread groove 2a of the screw shaft 2 may be a circular arc shape or a Gothic arc shape, but here, a gothic arc shape with a large contact angle with the ball 4 and a small axial clearance can be set. Is formed. Thereby, the rigidity with respect to an axial load becomes high and generation | occurrence | production of a vibration can be suppressed.

  Here, as shown in FIG. 1A, the nut 3 is formed with an annular convex portion 10 at the center portion in the axial direction of the inner peripheral surface, and the inner diameter 10 a of the annular convex portion 10 is the outer diameter of the screw shaft 2. The diameter is set slightly larger than that. On both sides in the axial direction of the annular convex portion 10, spiral thread grooves 3a are formed. This thread groove 3a is a groove on one side only (undercut-free), and is formed by winding a substantially one-quarter arc in a spiral and in two rows. And the internal diameter 3b extended in the end surface direction from the groove bottom of the thread groove 3a is formed.

  As shown in FIG. 2, the ball circulation portion (groove) 7 of the screw groove 3 a of the nut 3 is curved in an S shape so as to smoothly connect adjacent one round of the screw groove 2 a of the screw shaft 2. The ball circulation portion 7 and a holding groove 5a of the guide member 5 described later constitute a rolling path of the ball 4.

  As shown in an enlarged view in FIG. 3 (a), the ball 4 accommodated in a freely rolling manner between the screw groove 3a of the nut 3 and the screw groove 2a of the screw shaft 2 has a contact angle θ and faces outward in a double row. It is configured to make angular contact. On the other hand, as shown in FIG. 3B, the ball circulating portion 7 is formed so that the groove depth is deeper than the thread groove 3a of the nut 3, and an inner diameter 3c extending from the groove bottom toward the end surface is formed. Yes. The plurality of balls 4 interposed between the inner and outer screw grooves 2 a and 3 a in the rolling path roll along the screw grooves 2 a and 3 a, and hold the ball circulating portion 7 of the nut 3 and the guide member 5. While being guided by the rolling path constituted by the groove 5a, it passes over the thread of the screw shaft 2, returns to the adjacent screw groove 2a, and rolls along the screw grooves 2a and 3a again. The ball 4 that rolls between the ball circulation portion 7 of the nut 3 and the holding groove 5a of the guide member 5 has an S-shaped groove of the ball circulation portion 7 of the nut 3 only on one side (undercut free). The ball circulating portion 7 and the holding groove 5a of the guide member 5 that complements the other S-shaped groove are rotatably held. Thereby, even if the ball circulation portion 7 is formed to be undercut free on only one side, the ball 4 rolling on the rolling path can be stably held.

  As shown in FIG. 1B, a holding hole 6 having a substantially circular cross section is formed in the body portion of the cylindrical nut 3 so as to penetrate the inner and outer peripheral surfaces. The holding hole 6 is formed on the opening end side of the nut 3 located on the outer side in the axial direction of the ball circulation portion 7 of the nut 3, and the guide member 5 is fitted into the holding hole 6. As shown in FIG. 4, the guide member 5 includes a fitting portion 8 having a substantially circular cross section corresponding to the holding hole 6 of the nut 3, and a holding portion 9 serving as a base portion of the fitting portion 8.

  The fitting portion 8 of the guide member 5 is formed in a columnar shape, and flat surfaces 8a and 8a are formed at opposing positions on the outer periphery. Further, in order to fix a guide member 5 to be described later to the nut 3, linear concave grooves 8b, 8b are formed at the end of the fitting portion 8, and a tongue piece 8c is formed by the concave grooves 8b, 8b. Yes.

  The holding portion 9 of the guide member 5 is formed in a bowl shape, and includes parallel flat surfaces 9a and 9a facing each other, an arcuate surface 9b connecting these flat surfaces 9a and 9a, and a holding groove 5a formed in an S shape. I have. Moreover, the outer peripheral surface 9c of the both ends by the side of the flat surface 9a among the outer peripheral surfaces by the side of the fitting part 8 is formed in circular arc shape. The radius of curvature of the outer peripheral surface 9c is set to a radius of curvature substantially the same as the inner diameter 3c of the nut 3, as shown in (b), and when the guide member 5 is fitted into the holding hole 6 of the nut 3, the nut 3 is in close contact with the inner diameter 3c of 3 (see FIG. 3B). As a result, the guide member 5 is stably positioned with no play relative to the nut 3, and the guide member 5 is prevented from coming out of the nut 3 from the holding hole 6 in the radial direction.

  As shown in FIG. 1B, a tapered counterbore 6 a is formed in the opening on the outer diameter side of the holding hole 6 of the nut 3. The tongue piece 8c of the guide member 5 is plastically deformed to the counterbore portion 6a, and the guide member 5 is crimped and fixed to the nut 3 in a close contact state. Thereby, the guide member 5 can be stably fixed to the nut 3 with a simple operation, and the cost can be reduced.

  In this embodiment, the guide 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.

  As the metal powder, a material that can be subsequently carburized and hardened, for example, C (carbon) is 0.13 wt%, Ni (nickel) is 0.21 wt%, Cr (chromium) is 1.1 wt%, Cu (copper) Exemplifies SCM415 which 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). Can do. The guide member 5 is performed by adjusting the carburizing quenching and tempering temperatures. In addition to this, the material of the guide 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 surface hardness in the range of 20 to 33 HRC by solution heat treatment, and can ensure toughness and high hardness.

  Moreover, the nut 3 is shape | molded by MIM from the sintered alloy similarly to the guide member 5 mentioned above. The nut 3 according to the present invention is suitable for molding by this type of MIM because the thread groove 3a is formed as an undercut-free groove on only one side. In addition, not only MIM but it can also form by forge processing, for example. On the other hand, the screw shaft 2 is made of medium carbon steel such as S55C or case-hardened steel such as SCM415 or SCM420, and the surface thereof is hardened in the range of 55 to 62 HRC by induction hardening or carburizing hardening.

  In the ball screw according to the present invention, the spiral thread groove 3a of the nut 3 is an undercut-free groove on only one side, and a substantially quarter arc is spirally formed in two lines in one winding. The ball 4 accommodated between the screw groove 2a is configured to make double-row outward angular contact with a contact angle θ, and the S-shaped groove is a nut made of an undercut-free groove on one side only. 3, the rolling ball 4 is held by the holding groove 5 a of the guide member 5, which is the other S-shaped groove that complements the ball circulating portion 7. The depth of the thread groove 2a of the nut 3 and the depth of the thread groove 3a of the nut 3 can be increased, and the contact angle θ with which the ball 4 is in angular contact with both the thread grooves 2a and 3a can be increased to increase the rigidity against the axial load. But The ball rolling groove of the nut is annular, and there is no restriction on the application of the ball screw as in the case of the conventional non-circulating ball screw that moves in the axial direction while rotating relative to the screw shaft, and the nut Thus, it is possible to provide a ball screw that can be manufactured with a mold by eliminating the undercut of the screw groove.

  When preload is applied to the ball screw, a ball having a diameter larger than the design dimension may be interposed depending on the amount of preload, but as shown in FIG. The pitch P2 of the screw groove 2a of the screw shaft 2 is set to be smaller than the pitch P1 corresponding to the desired contact angle θ according to the amount of preload, that is, the designed pitch at which the contact angle is θ. By setting it smaller than this, it is possible to easily apply a preload to the ball 4. Thereby, the play of the ball screw can be suppressed, and the rigidity against the axial load and moment load can be increased. In the rolling path constituted by the ball circulation portion 7 and the holding groove 5 a of the guide member 5, a clearance is formed so that the ball 4 can smoothly go over the thread of the screw shaft 2.

  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 ball screw according to the present invention can be applied to a ball screw used for an actuator of an electric power steering of an automobile, a spool valve driving unit for switching a hydraulic pressure of a transmission, or the like.

DESCRIPTION OF SYMBOLS 1 Ball screw 2 Screw shaft 2a, 3a Screw groove 3 Nut 3b, 3c Nut inner diameter 4 Ball 5 Guide member 5a Holding groove 6 Holding hole 6a Counterbore part 7 Ball circulating part 8 Fitting part 8a, 9a Flat surface 8b Concave groove 8c Tongue piece 9 Holding portion 9b Arc surface 9c Outer peripheral surface 10 Annular convex portion 10a Inner diameter of annular convex portion 51 Ball screw 52 Screw shaft 52a, 53a Ball rolling groove 53 Nut 54 Ball 55 Annular convex portion 56 Grooves 57, 60 Cage 58 Retaining ring 59 Key groove 61 Recess Da Ball diameter Dp Ball pitch circle On Nut ball rolling groove center of curvature Os Screw shaft ball rolling groove curvature center P1 Nut thread groove pitch P2 Screw Pitch of shaft screw groove Pn Pitch of ball rolling groove of nut Ps Pitch of ball rolling groove of screw shaft Rn Radius of curvature of ball rolling groove of nut Rs of screw shaft Curvature Lumpur rolling groove radius alpha, theta contact angle

Claims (7)

A screw shaft having a helical thread groove formed on the outer peripheral surface;
A cylindrical nut externally fitted to the screw shaft and having a helical thread groove formed on the inner peripheral surface;
In a ball screw comprising: a plurality of balls housed in a rolling path formed by the thread grooves facing each other;
An annular convex portion is formed at the axially central portion of the inner peripheral surface of the nut, and the thread groove is formed on both sides of the annular convex portion in the axial direction. This thread groove is an undercut-free groove on only one side. A quarter arc is formed in a spiral and in two rows, and the balls received between the screw grooves of the screw shaft are configured to make double row outward angular contact,
A ball circulation portion is provided in a part of the screw groove of the nut, and the ball circulation portion is curved in an S shape so as to smoothly connect adjacent one rounds of the screw groove of the screw shaft, and the nut A ball screw characterized in that the groove depth is formed deeper than the thread groove.   The ball circulation part of the nut is formed to be undercut free on only one side, penetrates the inner and outer peripheral surfaces of the nut body part, and on the opening end side of the nut located on the axially outer side of the ball circulation part A holding hole is formed, and a guide member is fitted into the holding hole, and a holding groove made of the other S-shaped groove that complements the ball circulating portion of the nut is provided in the guide member. The ball screw according to claim 1, wherein the ball is formed so as to be freely rollable by the holding groove and the ball circulation portion.   The guide member includes a columnar fitting portion having a tongue piece formed at an end portion, and a holding portion having a rectangular shape that forms the holding groove on one end surface and serves as a base portion of the fitting portion, A tapered spot facing portion is formed at the opening on the outer diameter side of the holding hole of the nut. The tongue piece of the guide member is plastically deformed in the spot facing portion, and the guide member is applied to the nut in a closely contacted state. The ball screw according to claim 2, which is fastened and fixed.   The ball screw according to claim 3, wherein outer peripheral surfaces of both ends of the holding portion of the guide member are formed in an arc shape along the inner diameter of the nut.   The pitch of the thread groove of the screw shaft is set to be smaller than the design pitch corresponding to the contact angle formed between the ball and both thread grooves with respect to the pitch between the thread grooves of the nut, The ball screw according to claim 1, wherein a preload is applied to the ball.   The ball screw according to claim 1, wherein the nut is made of a sintered metal formed by MIM.   The ball screw according to claim 2 or 3, wherein the guide member is made of a sintered metal formed by MIM.

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