JP2012037057A - Ball screw mechanism - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a ball screw mechanism that eliminates unnecessary machining, enhances reliability of the ball screw mechanism, and increases a degree of freedom in manufacture.SOLUTION: A circulation passage 2b is directly formed on an inner peripheral surface of a nut 2. A female screw groove 2a and the circulation passage 2b can be smoothly connected and no step is formed as shown in Fig.9. Abnormal noise or operation torque variation (hooking) can be prevented even when a ball 3 passes through a space between the female screw groove 2a and the circulation passage 2b, and reduction in the service life can be prevented.

Description

  The present invention relates to a ball screw mechanism that is assembled to a general industrial machine or used in automobiles, ships, and the like.

  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.

  However, normally, the ball screw mechanism is composed of a screw shaft, a nut, and a ball that rolls in a rolling path formed between the two. In the so-called top-type ball screw mechanism, the ball screw mechanism starts from one end of the rolling path. In order to return the ball to the other end, a top is attached to the nut (see Patent Document 1). The female thread groove of the nut can be formed by cutting the inner peripheral surface of the nut using a tap tool in which a blade is formed in a spiral shape (see Patent Document 2).

JP 11-270648 A JP 2005-69265 A

However, according to the prior art manufacturing method,
(1) On the inner peripheral surface of the nut to be processed, the internal thread groove is cut in addition to the portion where the ball is actually inserted and used, and unnecessary processing is performed.
(2) On the inner peripheral surface of the nut to be machined, the internal thread groove is also cut on the part other than the rolling path where the ball is actually inserted and used (referred to as an unused groove). In this case, if the ball is mistakenly inserted into the unused groove, the ball may be clogged, resulting in malfunction.
(3) The cutting teeth of the tap tool are tapered so that the amount of cutting gradually increases from the tip of the side that is first inserted into the nut toward the rear, so the radial and axial dimensions of the tool However, there is a problem that the processing machine and the processing method are restricted.

  The present invention has been made in view of the problems of the prior art, and provides a method of manufacturing a ball screw mechanism that eliminates processing waste, improves the reliability of the ball screw mechanism, and improves the degree of freedom in manufacturing. For the purpose.

A manufacturing method of a ball screw mechanism according to a first aspect of the present invention includes: a screw shaft having a male screw groove formed on the outer peripheral surface;
A nut disposed so as to surround the screw shaft and having an internal thread formed on an inner peripheral surface thereof;
In a manufacturing method of a ball screw mechanism having a plurality of balls arranged to roll along a rolling path formed between both screw grooves facing each other,
The female thread groove of the nut is characterized in that a tool having a cutter having a shape corresponding to the female thread groove is revolved and cut while being revolved.

A manufacturing method of a ball screw mechanism according to a second aspect of the present invention includes:
A nut disposed so as to surround the screw shaft and having an internal thread formed on an inner peripheral surface thereof;
In a manufacturing method of a ball screw mechanism having a plurality of balls arranged to roll along a rolling path formed between both screw grooves facing each other,
The nut circulation path is formed on the inner peripheral surface of the nut by plastic working.

  According to the first aspect of the present invention, the female thread groove of the nut revolves and cuts a tool having a blade having a shape corresponding to the female thread groove, so that a general tap tool is used. In comparison, cutting processing other than the female thread groove transferred by the ball can be suppressed as much as possible, so that the processing time can be shortened and wear of the blade can be suppressed. In addition, since the outer diameter of a general tap tool is larger than the inner diameter of the nut, the degree of freedom of processing is limited. However, it is sufficient to form one cutter of the present invention on the outer periphery of a relatively thin rotating shaft, for example. As a result, the degree of freedom of processing can be increased. Furthermore, when assembling, parts such as unused grooves formed by conventional tap tools can be processed without forming as much as possible. Can be avoided. Note that “the blade having a shape corresponding to the female screw groove” means that the cutting surface of the blade has a shape that matches or approximates the cross-sectional shape of the female screw groove.

  The circulation path of the nut is preferably formed on the inner peripheral surface of the nut by plastic working.

  For example, in a piece type ball screw mechanism, a piece in which a circulation groove is formed is generally assembled to a nut. However, in the top-type ball screw mechanism, it is inevitable that a step is generated between the female screw groove to which the ball is transferred and the circulation groove formed in the top, and as a result, abnormal noise, operating torque fluctuation, and life that cannot be ignored. Decrease may occur. On the other hand, according to the present invention, the circulation groove is formed directly on the inner peripheral surface of the nut without using a piece, so that a step is not formed between the circulation groove and the female screw groove, and the connection is made smoothly. Therefore, even if the ball passes between the circulation groove and the female screw groove, no abnormal noise or fluctuation in operating torque is generated, and a reduction in life can be suppressed.

  The circulation path of the nut is preferably subjected to a quenching process simultaneously with the female screw groove.

  In the top type ball screw mechanism, when the top is assembled to the nut, the top body is often plastically deformed by caulking or the like and fixed to the nut for the purpose of reducing the manufacturing cost (Japanese Patent Laid-Open No. 2001-2001). 289301). Therefore, it is necessary to lower the hardness to some extent so that the top is easily plastically deformed. On the other hand, the circulation groove formed in the top is generally considered to increase the hardness, which is good for the high-speed performance and life of the ball screw mechanism. Therefore, there is a conflicting problem that if the hardness is increased, it is difficult to crimp, and if the hardness is decreased, the high-speed performance and life of the ball screw mechanism are decreased. On the other hand, according to the present invention, the circulation groove is formed directly on the inner peripheral surface of the nut without using a top, so that when the nut body is quenched, the circulation path is simultaneously quenched. As a result, the hardness of the circulation groove to which the ball is transferred is increased, and the high-speed performance of the ball screw is enhanced and the life is improved. When induction hardening is used as the quenching process, local overheating around the top hole may occur in the nut having the top mounting hole as in the conventional case. Since there is no hole, such a problem can be avoided. There is also an advantage that the grain boundary oxide layer can be reduced.

  According to the second aspect of the present invention, since the circulation path of the nut is formed on the inner peripheral surface of the nut by plastic working, a tool having a blade having a shape corresponding to the female thread groove can be easily formed. By revolving while rotating and performing cutting together, the circulation path and the female thread groove can be connected without any step, and abnormal noise, operating torque fluctuation, life reduction, and the like can be suppressed.

It is an axial direction sectional view of the ball screw mechanism which is this embodiment. It is the figure which cut | disconnected the nut shown in FIG. 1 by the II-II line | wire, and looked at the arrow direction. 3A is a cross-sectional view of the hollow cylindrical member and the mold, FIG. 3B is a view of the configuration of FIG. 3A viewed in the direction of the arrow IIIB, and FIG. 3C is FIG. 3) is a view of the mold in the direction of arrow IIIC. 4A is a cross-sectional view in the axial direction after forging the hollow cylindrical member, and FIG. 4B is a perspective view after forging the hollow cylindrical member. Fig.5 (a) is a perspective view which shows the state of the cutting process of a hollow cylindrical member, FIG.5 (b) is the figure which looked at the hollow cylindrical member and cutting tool shown to Fig.5 (a) in the arrow VA direction. It is. FIG. 6A is an axial sectional view after the hollow cylindrical member is cut, and FIG. 6B is a perspective view after the hollow cylindrical member is cut. It is an axial direction sectional view showing the state of quenching processing of a hollow cylindrical member. It is a cross-sectional view in the direction perpendicular to the axis of the top ball screw mechanism according to the comparative example. It is the figure which cut | disconnected the structure of FIG. 8 by the IX-IX line, and looked at the arrow direction. It is the figure which cut | disconnected the structure of this Embodiment shown in FIG. 1 by the IX-IX line and looked at the arrow direction. FIG. 11A is a cross-sectional view of the hollow cylindrical member and the mold, and FIG. 11B is a view of the configuration of FIG. 11A viewed in the direction of the arrow XIB.

  Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an axial sectional view of a ball screw mechanism manufactured by the manufacturing method according to the present embodiment. FIG. 2 is a view of the nut shown in FIG. 1 taken along the line II-II and viewed in the direction of the arrow. In FIG. 1, a male screw groove 1a is formed on the outer peripheral surface of a screw shaft 1 connected to a driven member (not shown) and supported so as not to rotate but to move only in the axial direction. A cylindrical nut 2 supported so as to be rotatable only with respect to a housing (not shown) is disposed so as to surround the screw shaft 1, and has two rows of female screw grooves 2a (see FIG. 2) on the inner peripheral surface. A circulation path 2b connected to each female thread groove 2b is formed. A plurality of balls 3 are arranged so as to roll in a spiral rolling path formed between the opposing screw grooves and return via the circulation path 2b.

  Next, the manufacturing method according to this embodiment will be described. First, a circulation groove is formed on the inner peripheral surface of a hollow cylindrical member with a flange, which is a nut material. FIG. 3 is a diagram showing a process of forming a circulation groove. FIG. 3 (a) is a sectional view of a hollow cylindrical member and a mold, and FIG. 3 (b) is a configuration of FIG. 3 (a) in the direction of arrow IIIB. FIG. 3C is a view of the mold shown in FIG. 3B as viewed in the direction of arrow IIIC. Here, forging is performed using a mold M as shown in FIG. The mold M has a cylindrical shape having an outer diameter smaller than the inner diameter of the hollow cylindrical member, and two S-shaped convex portions Ma as shown in FIGS. 3B and 3C are provided on the outer surface thereof. Forming. The convex portion Ma corresponds to the shape of the circulation path 2b.

  The mold M is inserted into the hollow cylindrical member N, the convex portion Ma is brought into contact with the upper part of the inner peripheral surface thereof, and the both ends of the mold M are supported, and the hollow cylindrical member N is fixed to the mold. Press (P) toward M and perform forging. Then, as shown in FIG. 4, the convex portion Ma is transferred to the inner peripheral surface of the hollow cylindrical member N, and two recessed circulation paths 2b are formed.

  Next, a female thread groove is formed on the inner peripheral surface of the hollow cylindrical member N in which the circulation path 2b is formed. FIG. 5 is a diagram illustrating a process of forming the female thread groove. Here, cutting is performed using a cutting tool T as shown in FIG. The cutting tool T forms a blade Tb on the outer periphery of the rotation axis Ta. The cutting surface (surface facing the circumferential direction) of the blade Tb matches the shape of the female thread groove 2a. The rotation axis Ta rotates around the axis O (A in FIG. 5B), but independently revolves around the eccentric axis Q (B in FIG. 5B). As a mechanism for rotating and revolving the cutting tool T in this way, for example, a configuration in which the rotation shaft Ta is connected to a planetary gear of a planetary gear mechanism (not shown) is conceivable, but not limited thereto.

  When performing this cutting process, it is necessary to let the revolving trajectory of the rotating tool near the end surface of the hollow cylindrical member N escape from the center of the revolving track so that the rotating tool Tb does not contact the inner peripheral surface of the hollow cylindrical member N. Become. Further, as shown in FIG. 5, the rotational axis Ta of the cutting tool T is shifted radially outward at a predetermined axial position, and revolved while being sent out in the axial direction at the pitch of the female thread groove 2a, and rotated at a higher speed. By doing so, the helical female thread groove 2a of less than 360 degrees can be cut and formed on the inner peripheral surface of the hollow cylindrical member N. At this time, by aligning the axial position and phase with the circulation path 2b, as shown in FIG. 6, each circulation path 2b can be connected to both ends of the female thread groove 2a. In the cutting tool T shown in FIG. 5, in order to form the two female thread grooves 2a, the same hollow cylindrical member N is cut twice, but if two blades Tb are formed on the rotation axis Ta. It can be formed by a single cutting process.

  Next, a quenching process is performed on the inner peripheral surface of the hollow cylindrical member N in which the circulation path 2b and the female thread groove 2a are formed. FIG. 7 is a diagram illustrating a process of induction hardening. Here, as shown in FIG. 7, the coil C is disposed inside the hollow cylindrical member N, and high-frequency hardening is applied to the inner peripheral surface of the hollow cylindrical member N by flowing a high-frequency current from the high-frequency power source E to the coil C. I do. The nut 2 can be manufactured by the above process.

  According to the present embodiment, since the top mounting holes are not formed in the hollow cylindrical member N, there is no overheating heat treatment defect and the like, which is suitable for induction hardening. Further, by quenching the inner peripheral surface of the hollow cylindrical member N at a time, the female thread groove 2a and the circulation path 2b having excellent wear resistance can be formed, and in this case, grain boundary oxidation can be suppressed.

  In particular, circulating members such as tubes and pieces used in conventional ball screw mechanisms are generally not heat-treated, and thus wear when operated for a long period of time, causing poor circulation. On the other hand, according to the present embodiment, not only the female thread groove 2a but also the circulation path 2b can be quenched at the same time, so that the wear resistance can be ensured and the grain boundary oxidation can be suppressed at the same time. I can expect.

  8 is a cross-sectional view in the direction orthogonal to the axis of the top type ball screw mechanism according to the comparative example, and FIG. 9 is a view of the configuration of FIG. The dimensional depth is abolished and is shown schematically. FIG. 10 is a view of the configuration of the present embodiment shown in FIG. 1 taken along the line IX-IX and viewed in the direction of the arrow, but the three-dimensional depth is abolished and schematically shown. The comparative example shown in FIGS. 8 and 9 is different only in that the top 4 having the circulation path 4 a is assembled in the mounting hole 2 c of the nut 2.

  The transfer path formed by the male screw groove 1 a of the screw shaft 1 and the female screw groove 2 a of the nut 2 is a spiral space that is approximately approximate to the outer diameter of the ball 3. Therefore, as shown in FIG. 8, when the circulation path 4 a is formed in the top 4 and assembled to the nut 2 ′, the introduction portion of the circulation path 4 a escapes outward in the radial direction from the female thread groove 2 a of the nut 2. As a result, a step Δ is formed between the female screw groove 2a and the circulation path 4a. If the top 4 is a separate member, it is generally difficult to set the step Δ to 0. On the other hand, according to the present embodiment, the circulation path 2b is formed directly on the inner peripheral surface of the nut 2, so as shown in FIG. 9, between the female thread groove 2a and the circulation path 2b (in FIG. D portion) can be connected smoothly and no step is provided, so that even if the ball 3 passes between the female thread groove 2a and the circulation groove 2b, abnormal noise and fluctuations in operating torque (such as catching) may occur. In addition, it is possible to suppress a decrease in service life.

  Furthermore, in the configuration of the comparative example, as shown in FIG. 8, a female thread groove 2a is formed on the inner peripheral surface of the nut 2 'in the axial direction. In such a case, if the ball 3 is mistakenly assembled between the female screw groove (unnecessary groove) 2a ′ formed between the mounting holes 2c and 2c in the axial direction and the male screw groove 1a opposed to the female screw groove 2a ′, as shown by a dotted line. The ball 3 cannot be transferred and the screw shaft 1 and the nut 2 may be locked. On the other hand, according to the present embodiment, as shown in FIG. 9, since the female thread groove is not formed between the circulation grooves 2b and 2b in the axial direction, there is no room for the ball 3 to be mistakenly assembled, resulting in malfunction. There is no fear of inviting.

  FIG. 11 is a diagram illustrating a process of forming a circulation groove according to a modification. FIG. 11A is a cross-sectional view of a hollow cylindrical member and a mold, and FIG. 11B is a configuration of FIG. It is the figure seen in the arrow XIB direction. In the case of the process shown in FIG. 3, since both ends of the mold M are supported, if the press pressure P is high, the mold M may bend and the circulation groove may not be accurately transferred.

  On the other hand, in this modification, a hole Na is formed in the center of the hollow cylindrical member N, and the center of the mold M is further supported by the support column SC passing therethrough. Therefore, since the mold M is supported at three points, both ends and the center, even if the press pressure P is high, the bending of the mold M is remarkably reduced, and the circulation groove can be transferred and formed with high accuracy. Since the hollow cylindrical member N used in this modification is formed with a hole Na so as not to communicate with the two female screw grooves 2a, there is no possibility that the ball 3 will drop out. The hole Na may be shielded by a lid member (not shown) during use of the ball screw mechanism.

  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.

1 Screw shaft 2 Nut 3 Ball N Hollow cylindrical member T Cutting tool C Coil E High frequency power supply

The method of manufacturing the ball screw mechanism of the present invention includes:
A screw shaft having a male screw groove formed on the outer peripheral surface;
A nut disposed so as to surround the screw shaft and having an internal thread formed on an inner peripheral surface thereof;
In a manufacturing method of a ball screw mechanism having a plurality of balls arranged to roll along a rolling path formed between both screw grooves facing each other,
The female thread groove of the nut shifts the rotational axis of a tool having a cutter having a shape corresponding to the female thread groove radially outward at a predetermined axial position, and feeds the tool in the axial direction at the pitch of the female thread groove. The nut is formed by cutting and revolving the nut material while revolving and rotating at a higher speed .

According to the present invention, the female thread groove of the nut shifts the rotational axis of a tool having a blade having a shape corresponding to the female thread groove radially outward at a predetermined axial position, and the tool is inserted into the female thread groove. The ball is transferred as compared with the case of using a general tap tool because it is formed by cutting the material of the nut by rotating at a higher speed while revolving while feeding in the axial direction at a pitch. Since cutting other than the female thread groove can be suppressed as much as possible, the processing time can be shortened and wear of the blade can be suppressed. In addition, since the outer diameter of a general tap tool is larger than the inner diameter of the nut, the degree of freedom of processing is limited. However, it is sufficient to form one cutter of the present invention on the outer periphery of a relatively thin rotating shaft, for example. As a result, the degree of freedom of processing can be increased. Furthermore, when assembling, parts such as unused grooves formed by conventional tap tools can be processed without forming as much as possible. Can be avoided. Note that “the blade having a shape corresponding to the female screw groove” means that the cutting surface of the blade has a shape that matches or approximates the cross-sectional shape of the female screw groove.

Claims (4)

A screw shaft having a male screw groove formed on the outer peripheral surface;
A nut that is disposed so as to surround the screw shaft, and has a female screw groove formed on an inner peripheral surface thereof, and a circulation path that connects both ends of the female screw groove;
In a manufacturing method of a ball screw mechanism having a plurality of balls arranged to roll along a rolling path formed between both screw grooves facing each other,
The method of manufacturing a ball screw mechanism, wherein the female screw groove of the nut is formed by revolving and cutting a tool having a cutter having a shape corresponding to the female screw groove.   The ball screw mechanism manufacturing method according to claim 1, wherein the nut circulation path is formed on an inner peripheral surface of the nut by plastic working.   The ball screw mechanism manufacturing method according to claim 2, wherein the nut circulation path is hardened simultaneously with the female screw groove. A screw shaft having a male screw groove formed on the outer peripheral surface;
A nut disposed so as to surround the screw shaft and having an internal thread formed on an inner peripheral surface thereof;
In a manufacturing method of a ball screw mechanism having a plurality of balls arranged to roll along a rolling path formed between both screw grooves facing each other,
A method of manufacturing a ball screw mechanism, wherein the nut circulation path is formed on an inner peripheral surface of the nut by plastic working.

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