JP4978888B2 - Screw shaft of ball screw mechanism - Google Patents

Description

The present invention is, for example, or assembled in general industrial machinery or those about the screw shaft of a ball screw mechanism or is used in an automobile.

  In recent years, labor saving of vehicles and the like has progressed, and for example, a system has been developed in which a transmission, a parking brake, and the like of an automobile are performed not by hand but by the power of an electric motor. An electric actuator used for such an application may use a ball screw mechanism in order to convert the rotational motion transmitted from the electric motor into the axial motion with high efficiency.

  When the ball screw device has a narrow screw shaft outer diameter (for example, about φ10 mm), when the bearing is attached to the shaft end, the area of the bearing that receives the inner ring end surface is reduced. In particular, with specifications that increase the axial load, it is not enough to support the bearing with pressure input or a retaining ring. Therefore, it is necessary to devise a design for mounting the bearing on the screw shaft to withstand the large axial load. .

  As an example of such a design, a flange portion that is thicker than the outer diameter of the screw shaft is formed on one end side of the screw shaft, and an inner ring is brought into contact with the flange portion to increase the area that receives the end surface. Thus, a large axial load can be supported through the bearing.

  By the way, as a method of processing a screw shaft having a flange portion, it is known to process a ball groove portion by screw grinding, but it is disadvantageous in terms of manufacturing cost such as expensive processing equipment and long processing time. is there. In addition to the screw shaft, there is a method of processing and forming a flange for receiving the bearing inner ring end surface and attaching it to the screw shaft, but it is also disadvantageous in terms of manufacturing cost.

On the other hand, rolling is known as a method for forming a thread groove. As the rolling process for manufacturing the screw shaft of the ball screw mechanism, there are a through rolling method and an in-feed rolling method. The through rolling method is a method in which when a roll die is pressed against a product to be rolled, the roll die is rolled with a slight angle difference between the lead angle of the roll die and the lead angle of the material to be rolled. When the roll die or the rolled material is rotated relatively, the roll die and the rolled material are rolled while moving relative to each other due to the difference in the lead angle. When relatively rotating, rolling can be performed automatically without forcibly moving in the axial direction (see Patent Document 1).
JP-A-9-225573

  However, when the thread rolling method disclosed in Patent Document 1 is used, when a large-diameter flange portion is formed on the screw shaft, the shape of the thread rolling die and during rolling are avoided in order to avoid interference with the flange portion. In addition, considering the axial movement (step phenomenon) of the screw shaft, an incomplete thread at the end of the screw shaft is formed long, resulting in a ball screw mechanism with a short operating stroke for the entire length. is there. Therefore, it can be said that the thread rolling method of Patent Document 1 is not suitable for manufacturing a screw shaft of a ball screw mechanism in which the length of the incomplete thread portion at both ends of the screw shaft is desired to be as short as possible.

The present invention has been made in view of the problems of the prior art, and an object thereof is to provide a screw shaft of a ball screw mechanism in which an incomplete thread portion is suppressed at a low cost.

The screw shaft of the ball screw mechanism of the present invention is formed between a nut having a female screw groove, a screw shaft inserted through the nut and having a male screw groove, and a female screw groove of the nut and a male screw groove of the screw shaft. In the screw shaft of a ball screw mechanism having a ball that can roll on the rolling path,
A large-diameter portion larger than the outer diameter of the male screw groove, and a small-diameter portion disposed between the male screw groove and the large-diameter portion and having a smaller diameter than the groove bottom diameter of the male screw groove are formed. The male thread groove is formed by rolling ,
The small diameter portion has a curvature radius ρ of 0.8 (mm) or more in the axial cross section of the screw shaft,
A chamfered portion is formed at the end of the screw shaft. The chamfered portion has an axial length a, a radial length b, a screw shaft lead L, and a male screw groove depth t. A = L / 2 + 0.1-0.5 (mm) and b = t + 0.1-0.5 (mm)
The screw shaft has a concave portion on the end face with which the center shaft of the rolling device is engaged,
A flange portion having a diameter larger than the outer diameter of the male screw groove is provided adjacent to the male screw groove, and a small diameter portion having a diameter smaller than the male screw groove bottom diameter is provided between the flange portion and the male screw groove. The small-diameter portion includes a straight portion and a curved portion connected to the straight portion and having a predetermined radius of curvature in the axial cross section of the screw shaft .

According to the present invention, a large-diameter portion larger than the outer diameter of the male screw groove and a small-diameter portion disposed between the male screw groove and the large-diameter portion and having a smaller diameter than the groove bottom diameter of the male screw groove are formed. Therefore, when forming the male screw groove of the screw shaft by rolling, interference with the large diameter portion is suppressed without forming a tapered surface on the outer peripheral surface of the end of the rolling die. The male thread groove processing can be performed on the inner thread, thereby reducing the incomplete thread portion as much as possible.

  If the small diameter portion has a radius of curvature ρ of 0.8 (mm) or more in the axial cross section of the screw shaft, it is possible to suppress the bending of the screw shaft during rolling.

  A chamfered portion is formed at the end of the screw shaft. The chamfered portion has an axial length a, a radial length b, a screw shaft lead L, and a male screw groove depth t. When a = L / 2 + 0.1-0.5 (mm) and b = t + 0.1-0.5 (mm), the pre-rolling at the end of the screw shaft at the time of rolling It is possible to suppress overhang as much as possible.

  If the threaded shaft has a recess on the end face with which the center shaft of the rolling device is engaged, for example, a movable center shaft can support the material of the threaded shaft being rolled.

  In this specification, the “in-feed rolling process” is a process in which a pair of rotating rolling dies are moved closer to both sides of a cylindrical workpiece.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing an example of a ball screw mechanism using a screw shaft formed by the manufacturing method according to the present embodiment.

  A cylindrical nut 2 is arranged so as to surround the screw shaft 1 connected to a rotation shaft of a motor (not shown) and having a male screw groove 1a. The nut 2 is supported so as to be rotatable only with respect to a housing (not shown), and has a female screw groove 2a on the inner peripheral surface. A plurality of balls 3 are arranged so as to be able to roll in a spiral rolling path formed between the opposing screw grooves 1a, 2a. The nut 2 is provided with a tube 4 for returning the ball 3 from one end of the rolling path to the other end. The screw shaft 1, the nut 2, and the ball 3 constitute a ball screw mechanism.

  2 (a) is a side view of the screw shaft 1, FIG. 2 (b) is a view of the screw shaft 1 viewed in the direction of arrow IIB, and FIG. 2 (c) is a view of the screw shaft 1 shown by arrow IIC. FIG. 2D is an enlarged view showing an arrow IID portion of the screw shaft 1, and FIG. 2E is an enlarged view showing an arrow IIE portion of the screw shaft 1. FIG. 2F is an enlarged view showing an arrow IIF portion of the screw shaft 1.

  The screw shaft 1 has a flange portion (large diameter portion) 1b having a diameter larger than the outer diameter of the male screw groove 1a adjacent to the left end of the male screw groove 1a in FIG. 2A. Between the male screw groove 1a and the flange portion 1b, a small diameter portion 1c smaller in diameter than the groove bottom diameter of the male screw groove 1a is formed in contact with the flange portion 1b. As shown in FIG. 2 (f), the small-diameter portion 1c has a curved surface portion 1h having a predetermined radius of curvature in the axial section of the screw shaft 1, and a diameter increasing as it is connected to the curved surface portion 1h and away from the flange portion 1b. And a straight line portion 1j. Here, since the small diameter portion 1c has a radius of curvature ρ of 0.8 (mm) or more in the axial cross section of the screw shaft 1, the bending of the screw shaft 1 during rolling can be suppressed.

  A round shaft portion 1d is formed on the opposite side of the small diameter portion 1c with the flange portion 1b interposed therebetween. As shown in FIG. 1, an inner ring of a bearing 5 that rotatably supports the screw shaft 1 is fitted so that the end surface thereof abuts against the flange portion 1 b. As shown in FIG. 2E, a chamfered portion 1e is formed at the right end of the screw shaft 1 adjacent to the male screw groove 1a. A = L / 2 + 0.1 to 0.5 (mm) where a is the axial length of the chamfered portion, b is the radial length, L is the lead of the screw shaft, and t is the depth of the male screw groove. ) And b = t + 0.1 to 0.5 (mm), it is possible to suppress as much as possible the protrusion of the pre-wall during rolling at the end of the screw shaft 1. As shown in FIGS. 2B and 2C, circular holes (concave portions) 1f and 1g are formed on both end surfaces of the screw shaft 1. In the present embodiment, the length Δ of the incomplete screw portion (the portion not having the cross section of the male screw groove 1a) on the outer peripheral surface where the male screw groove 1a of the screw shaft 1 is formed is the lead of the male screw groove 1a. It is within the range of 1 to 1.5 times L.

  The operation of the ball screw mechanism will be described. When the screw shaft 1 is rotationally driven by a motor (not shown), the ball 3 rolls on the rolling path and circulates from one end of the rolling path to the other end via the tube 4. The rotational motion is efficiently converted into the axial motion of the nut 2.

  Next, a method for manufacturing the screw shaft will be described. FIG. 3 is a top view of the in-feed rolling device, and FIG. 4 is a side view of the in-feed rolling device, with one in-feed rolling die removed.

  3 and 4, a first center support 13 is disposed on a pair of guide rails 10 fixed to a surface plate (not shown) with a slider 12 therebetween, and is further opposed to the guide rails. A second center support 15 is mounted on 10 via a slider 14. The first center support 13 supports the penetrating first center shaft 16 so as to be rotatable and movable in the axial direction. The second center support 15 supports the second center shaft 17 so as to be rotatable and immovable in the axial direction so as to be coaxial with the first center shaft 16. The tip of the first center shaft 16 has a shape that fits into the circular hole 1 f (FIG. 2B) on the end surface of the screw shaft 1, and the tip of the second center shaft 17 is the end surface of the screw shaft 1. The circular hole 1g (FIG. 2 (c)) is fitted. The holes 1f and 1g are not circular, but may be polygonal shapes such as hexagonal shapes.

  The first center support 13 and the second center support 15 are connected via a plate member 18. Further, the end of the first center shaft 16 is urged rightward in FIGS. 3 and 4 by an air cylinder built in the urging device 19. In particular, the use of an air cylinder has the advantage that the urging force can be easily adjusted by air pressure, is relatively inexpensive, has a wide variety of shapes, sizes, and cylinder cross-sectional areas, and is easy to select. However, a spring may be used instead of the air cylinder. The urging device 19 is attached to the guide rail 10 via a slider 20.

  As shown in FIG. 3, a pair of in-feed rolling dies 30 are arranged on both sides of the guide rail 20. Each in-feed rolling die 30 has the same lead as the male screw groove 1a of the screw shaft 1 and has a corresponding cross-sectional processed screw portion 30a on the outer periphery, and is supported so as to be rotationally driven by a rotating device (not shown). Has been. In addition, as for the in-feed rolling die 30 of this Embodiment, the outer peripheral part of both ends is substantially parallel to the axis line.

  Next, the manufacturing process of the screw shaft 1 will be described. In the following explanatory drawings, the machining screw portion is omitted. First, shapes other than the male screw groove are formed on the material M of the screw shaft, which is a cylindrical shaft. As shown in FIG. 5, both ends of the material M of the thread groove are fitted into the circular hole 1f at the tip of the first center shaft 16, and the tip of the second center shaft 17 is fitted into the circular hole 1g. I support it. At this time, since the first center shaft 16 is urged by the urging device 19 toward the second center shaft 17, the material M of the screw shaft is held by the urging force and may be dropped during processing. There is no.

  Subsequently, as shown in FIG. 6, the in-feed rolling die 30 that rotates in the same direction is approached from both sides of the material M of the screw shaft, and incision by the processing screw portion 30 a is started. At this time, rotational force is transmitted from the infeed rolling die 30, but since the center shafts 16 and 17 are rotatably supported, the material M of the screw shaft is rotated and the infeed rolling die 30 is driven to rotate. This reduces the load on the device and prevents the circular holes 1f and 1g from being worn.

  Further, as the cutting by the processing screw portion 30a is performed, the material M of the screw shaft receives a force in the direction of moving in the axial direction. This is called “walking”. In the present embodiment, the center support bases 13 and 15 and the urging device 19 are supported along the guide rail 10 so as to be movable in the axial direction of the material M of the screw shaft. The movement of the material M of the screw shaft is allowed. As a result, there is no risk of galling or the like, and smooth machining can be realized.

  Furthermore, the pair of in-feed rolling dies 30 approach each other in close proximity by NC control, rotate by a predetermined rotation angle, and then rotate by the same rotation angle in the opposite direction. Repeated several times. Therefore, since the “step” of the material M of the screw shaft also reciprocates, the movement range of the center support bases 13 and 15 and the urging device 19 is limited, and the total length of the guide rail 10 can be kept short.

  In particular, referring to FIG. 2 (f), since the small-diameter portion 1c is formed in front of the flange portion 1b in the thread groove material M, interference of the corner portion of the machining screw portion 30a indicated by the dotted line is avoided. In addition, the rolling process can be performed until just before approaching the flange portion 1b by NC control, and thereby the incomplete thread portion can be reduced as much as possible. In addition, since the chamfered portion 1e is formed at the opposite end of the thread groove material M, the processing screw portion 30a can protrude the material M of the screw shaft during the rolling process. Formation of incomplete thread portions can be suppressed as much as possible.

  It should be noted that the first center support 13 and the urging device 19 can be moved relative to the second center support 15 even if the material M of the screw shaft is caused by plastic deformation during the rolling process. Therefore, this elongation can be absorbed.

  After the completion of the cutting of the male screw groove to a predetermined depth, the pair of in-feed rolling dies 30 are separated from the material M of the screw shaft as shown in FIG. As described above, the screw shaft 1 is manufactured.

  Fig.8 (a) is a figure which shows the screw shaft 1 which performed the rolling process using the infeed rolling die 30 concerning this Embodiment, FIG.8 (b) is the infeed concerning a comparative example. It is a figure showing screw axis 1 'which performed rolling processing using rolling die 30'. The in-feed rolling die 30 ′ of the comparative example has tapered portions 30 b at both ends. Therefore, when performing the rolling process using the in-feed rolling die 30 ′ of the comparative example, the range of the incomplete thread portion is inevitably increased in order to avoid interference with the flange portion 1 b. On the other hand, the in-feed rolling die 30 of the present embodiment has the outer periphery at both ends parallel to the axis and is a processed screw portion 30a up to the end, so that it can be processed until just before contacting the flange portion 1b. The incomplete thread portion can be reduced, and there is no problem even if the die length is longer than the processed portion of the material as shown.

  According to the present embodiment, even when the large-diameter flange portion 1b is formed adjacent to the male screw groove 1a on the screw shaft 1 of the ball screw mechanism, the small-diameter portion 1c having a smaller diameter than the groove bottom diameter of the male screw groove therebetween. Therefore, even if a tapered surface is not formed on the outer peripheral surface of the end portion of the rolling die, it does not interfere with the flange portion 1b, and it is inexpensive in terms of cost regardless of cutting or the like. It can be manufactured by manufacturing. Further, since the screw shaft 1 formed by the in-feed rolling process according to the present embodiment can reduce the incomplete thread portion as much as possible, resources can be saved and the apparatus using the ball screw mechanism can be made compact.

  Furthermore, the in-feed rolling device according to the present embodiment is centered to support the screw shaft material M so as to be movable in the axial direction by the center support bases 13 and 15 while being biased by the biasing device 19. Since the elongation of the material M inside is absorbed and friction between the circular holes 1f and 1g of the screw shaft 1 and the center shafts 16 and 17 can be avoided, especially when the circular holes 1f and 1g are used as processing standards in the subsequent process. Is preferable because the circular shape of the circular holes 1f and 1g can be accurately maintained.

  The present invention has been described above with reference to the embodiments. However, the present invention should not be construed as being limited to the above-described embodiments, and can be modified or improved as appropriate.

It is sectional drawing which shows an example of the ball screw mechanism using the screw shaft formed by the manufacturing method concerning this Embodiment. It is a figure which shows each part of the screw shaft. It is a top view of an in-feed rolling device. It is a side view of an infeed rolling apparatus. It is a figure which shows the process of an in-feed rolling process. It is a figure which shows the process of an in-feed rolling process. It is a figure which shows the process of an in-feed rolling process. Fig.8 (a) is a figure which shows the screw shaft 1 which performed the rolling process using the infeed rolling die 30 concerning this Embodiment, FIG.8 (b) is the infeed concerning a comparative example. It is a figure showing screw axis 1 'which performed rolling processing using rolling die 30'.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Screw shaft 1a Male thread groove 1b Flange part 1c Small diameter part 1d Round shaft part 1e Chamfer part 1f Circular hole 1g Circular hole 1h Curved part 1j Straight part 2 Nut 2a Female thread groove 3 Ball 4 Tube 5 Bearing 10 Guide rail 12 Slider 13 Center support Base 14 Slider 15 Center support base 16 Center shaft 17 Center shaft 18 Plate member 19 Biasing device 20 Slider 30 In-feed rolling die 30a Machining screw portion 30b Taper portion M Material of screw shaft

Claims (1)

It is possible to roll on a rolling path formed between a nut having a female screw groove, a screw shaft inserted through the nut and having a male screw groove, and a female screw groove of the nut and the male screw groove of the screw shaft. In a screw shaft of a ball screw mechanism having a ball,
A large-diameter portion larger than the outer diameter of the male screw groove, and a small-diameter portion disposed between the male screw groove and the large-diameter portion and having a smaller diameter than the groove bottom diameter of the male screw groove are formed. The male thread groove is formed by rolling ,
The small diameter portion has a curvature radius ρ of 0.8 (mm) or more in the axial cross section of the screw shaft,
A chamfered portion is formed at the end of the screw shaft. The chamfered portion has an axial length a, a radial length b, a screw shaft lead L, and a male screw groove depth t. A = L / 2 + 0.1-0.5 (mm) and b = t + 0.1-0.5 (mm)
The screw shaft has a concave portion on the end face with which the center shaft of the rolling device is engaged,
A flange portion having a diameter larger than the outer diameter of the male screw groove is provided adjacent to the male screw groove, and a small diameter portion having a diameter smaller than the male screw groove bottom diameter is provided between the flange portion and the male screw groove. The small-diameter portion includes a straight portion and a curved portion connected to the straight portion and having a predetermined radius of curvature in the axial cross section of the screw shaft. axis.