Ball screw

Abstract

To suppress noise and vibration while maintaining durability of a circulation member such as an end cap, in an end cap type ball screw.SOLUTION: An elastic member 8 is provided that elastically absorbs at least one of a step formed at a boundary between a main passage 11 and a connection passage 13 and a step formed at a boundary between a return passage 12 and the connection passage 13. For example, an end cap 6 is attached to a nut body 5 via the elastic member 8, and the elastic deformation of the elastic member 8 allows relative movement between the end cap 6 and the nut body 5 in a direction perpendicular to an axial direction.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a ball screw. [Background technology]

[0002] Ball screws are installed in industrial machinery, vehicles, etc., and are used as motion conversion mechanisms that convert rotational motion into linear motion. A ball screw has a nut with a female screw groove formed on its inner periphery, a screw shaft with a male screw groove formed on its outer periphery, and a number of balls arranged between the female screw groove and the male screw groove. When one of the nut and the screw shaft is rotated by a drive source such as an electric motor, the other of the nut and the screw shaft moves linearly in the axial direction via the balls.

[0003] A ball screw is provided with a ball circulation mechanism for returning balls that have reached the end point of a main passage formed by the female screw groove and the male screw groove to the starting point. For example, a so-called end-cap type ball screw is known in which the ball circulation mechanism is formed by a pair of end caps attached to both axial ends of the nut body (see, for example, Patent Document 1 listed below). Specifically, the ball circulation path is made up of a main passage formed by the male screw groove of the screw shaft and the female screw groove of the nut, a return passage that passes through the nut body in the axial direction, and a connecting passage formed by the grooves of each end cap and the end face of the nut body facing it. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-224663 Summary of the Invention [Problem to be solved by the invention]

[0005] In an end-cap type ball screw, when a ball moves from the main passage to the connecting passage or from the connecting passage to the main passage, it passes through the joint between the nut body and the end cap. At this time, machining errors or assembly errors in the nut body and the end cap can cause a slight phase shift between the female thread groove of the nut body and the groove in the end cap, resulting in a step at this joint (i.e., the boundary between the main passage and the connecting passage). For the same reason as above, a step can also occur at the boundary between the connecting passage and the return passage. When the ball collides with this step, vibration and noise are generated.

[0006] For example, the ball screw in Patent Document 1 has end caps made of resin. In this case, when a ball collides with a step formed by the resin end cap, the step elastically deforms, reducing the step and suppressing noise and vibration. However, if the entire end cap is made of resin, wear is more likely to occur at the contact point with the ball than if it were made of metal, resulting in reduced durability.

[0007] Therefore, an object of the present invention is to suppress noise and vibration in an end cap type ball screw while maintaining the durability of circulation members such as end caps. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems, the present invention provides a ball screw having a nut including a nut body having a female screw groove formed on its inner peripheral surface and a circulation member attached to an axial end of the nut body, a threaded shaft inserted into the inner periphery of the nut and having a male screw groove formed on its outer peripheral surface, a main passage formed by the female screw groove of the nut body and the male screw groove of the threaded shaft, a return passage provided on the outer diameter side of the main passage and communicating both axial ends of the nut body, a connecting passage formed by a groove provided in the circulation member and connecting the main passage and the return passage, and a plurality of balls arranged in the main passage, the return passage, and the connecting passage, The ball screw has an elastic member that elastically absorbs at least one of a step formed at the boundary between the main passage and the connecting passage and a step formed at the boundary between the return passage and the connecting passage.

[0009] In the ball screw described above, when a ball passes through the boundary between the main passage and the connecting passage or the boundary between the return passage and the connecting passage, the elastic member absorbs and reduces the step formed at the boundary, thereby suppressing vibration and noise when the ball passes through the boundary. Furthermore, the circulation member can be made of a material stronger than the elastic member, ensuring durability.

[0010] The ball screw can be configured, for example, so that the circulation member is attached to the nut body via an elastic member, and the elastic member elastically deforms to allow relative movement between the circulation member and the nut body in a direction perpendicular to the axial direction. In this case, when a ball passes through the boundary between the main passage and the connecting passage or the boundary between the return passage and the connecting passage and hits a step formed at the boundary, the elastic member elastically deforms, causing the circulation member and the nut body to move relative to each other in a direction perpendicular to the axial direction. This reduces the step at the boundary, thereby suppressing vibration and noise when the ball passes through the step.

[0011] Furthermore, the ball screw can have an elastic member disposed at at least one of the boundary between the main passage and the connecting passage and the boundary between the return passage and the connecting passage. In this case, when a ball passes through the boundary, the ball collides with the elastic member and elastically deforms the elastic member, thereby reducing the step formed at the boundary, thereby suppressing vibration and noise when the ball passes through the step.

[0012] The elastic member may integrally include a first buffer portion disposed at the boundary between the main passage and the connecting passage and a second buffer portion disposed at the boundary between the return passage and the connecting passage. In this case, the first buffer portion can reduce the step formed at the boundary between the main passage and the connecting passage, and the second buffer portion can reduce the step formed at the boundary between the return passage and the connecting passage.

[0013] The elastic member may have an integral flat plate portion that is sandwiched and fixed between the circulation member and the nut body. In this case, by sandwiching and fixing the flat plate portion of the elastic member between the circulation member and the nut body, the elastic member can be easily fixed to the nut. [Effects of the Invention]

[0014] As described above, according to the present invention, in an end cap type ball screw, noise and vibration can be suppressed while maintaining the strength of the circulation member. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is an axial cross-sectional view of a ball screw according to a first embodiment of the present invention, in which the upper half is a cross-sectional view showing the boundary between a main passage and a connecting passage, and the lower half is a cross-sectional view showing the boundary between a return passage and a connecting passage. [Figure 2] FIG. 2 is a perspective view of an end cap of the ball screw of FIG. 1. [Figure 3] 2 is a cross-sectional view conceptually showing how a ball moves from a main passage to a connecting passage of the ball screw of FIG. 1. FIG. [Figure 4] FIG. 10 is an axial cross-sectional view of a ball screw according to a second embodiment of the present invention, in which the upper half is a cross-sectional view showing the boundary between the main passage and the connecting passage, and the lower half is a cross-sectional view showing the boundary between the return passage and the connecting passage. [Figure 5] FIG. 5 is an exploded perspective view of an end cap and an elastic member of the ball screw of FIG. 4. [Figure 6] FIG. 5 is an enlarged view of part B in FIG. [Figure 7] FIG. 5 is an enlarged view of part C in FIG. [Figure 8] 5 is a cross-sectional view conceptually showing a state in which a ball in a main passage of the ball screw of FIG. 4 collides with an elastic member. [Figure 9] 5 is a cross-sectional view conceptually showing a state in which a ball in a connection path of the ball screw in FIG. 4 collides with an elastic member. [Figure 10]FIG. 10 is an axial cross-sectional view of a ball screw according to a third embodiment of the present invention, in which the upper half is a cross-sectional view showing the boundary between the main passage and the connecting passage, and the lower half is a cross-sectional view showing the boundary between the return passage and the connecting passage. [Figure 11] FIG. 11 is a perspective view of an elastic member of the ball screw of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0017] As shown in FIG. 1, a ball screw 1 according to a first embodiment of the present invention has a screw shaft 2, a nut 3 into whose inner periphery the screw shaft 2 is inserted, and a large number of balls 4 arranged between the screw shaft 2 and the nut 3. In this embodiment, the nut 3 is a rotating member that is rotationally driven by a driving means (not shown) such as an electric motor, and the screw shaft 2 is a linearly moving member that moves linearly as the nut 3 rotates. Conversely, the nut 3 may be the linearly moving member and the screw shaft 2 may be the rotating member. In this specification, the direction parallel to the rotational axis of the rotating members of the ball screw (the axes of the screw shaft 2 and the nut 3) is referred to as the "axial direction."

[0018] The screw shaft 2 is formed into a shaft shape from metal, for example, steel. A spiral external thread groove 2a is formed on the outer peripheral surface of the screw shaft 2. The external thread groove 2a is formed, for example, by a rolling process. In this embodiment, a multi-thread (two-thread in the illustrated example) external thread groove 2a with a lead of L is formed on the outer peripheral surface of the screw shaft 2. Since the external thread grooves 2a are multi-thread in this way, the lead L of each external thread groove 2a can be made relatively large.

[0019] The nut 3 has a substantially cylindrical nut body 5 and end caps 6 as circulation members attached to the axial ends of the nut body 5. In the illustrated example, the end caps 6 are attached to both axial ends of the nut body 5.

[0020] The nut body 5 is formed into a cylindrical shape from metal, for example, steel. A spiral female screw groove 5a is formed on the inner peripheral surface of the nut body 5. In this embodiment, a multi-thread (two-thread in the illustrated example) female screw groove 5a with a lead of L is formed on the inner peripheral surface of the nut body 5. The female screw groove 5a is formed on the inner peripheral surface of the nut body 5 over the entire axial length. The male screw groove 2a of the screw shaft 2 and the female screw groove 5a of the nut body 5 radially opposed thereto form a spiral main passage 11. In this embodiment, a multi-thread (two-thread in the illustrated example) main passage 11 is formed.

[0021] A through hole 5b that penetrates the nut body 5 in the axial direction is formed on the outer diameter side of the female thread groove 5a of the nut body 5. In the illustrated example, the through hole 5b is provided in a straight line parallel to the axial direction. In the illustrated example, two through holes 5b are formed in the nut body 5. The two through holes 5b are formed at different circumferential positions, for example, at positions that are 180° out of phase with each other. The through holes 5b form a return passage 12 that communicates with both axial ends of the nut body 5.

[0022] The end caps 6 are made of metal. In this embodiment, the end caps 6 are die-cast products whose main component is zinc. Alternatively, the end caps 6 may be MIM molded products whose main component is iron.

[0023] A groove 6a is formed in the axially inner end face of the end cap 6 (the end face facing the end face of the nut body 5). This groove 6a forms a connection path 13 connecting the main passage 11 and the return passage 12. In this embodiment, the groove 6a of the end cap 6 and the flat end face 5c of the nut body 5 face each other in the axial direction, and form the connection path 13. In this embodiment, two grooves 6a are provided in the axially inner end face of each end cap 6, and two connection paths 13 are formed on each axial side of the nut body 5.

[0024] An engaging projection 6b that protrudes axially inward is formed on the axially inner end face of the end cap 6 around the outer diameter side end of the groove 6a (see FIG. 2). By engaging this engaging projection 6b with the end of the through hole 5b in the nut body 5, the phase of the end of the connecting passage 13 and the end of the return passage 12 is aligned (see FIG. 1). A guide projection 6c is formed on the inner peripheral surface of the end cap 6 in an area adjacent to the inner diameter side end of the groove 6a to smoothly guide the ball 4 picked up from the main passage 11 into the connecting passage 13 (see FIG. 2). The end cap 6 is attached to the nut body 5 with a bolt 7 as an attachment means (see FIG. 1).

[0025] A large number of balls 4 are arranged in the main passage 11, the return passage 12, and the connecting passage 13. When the nut 3 rotates, the screw shaft 2 moves linearly while the balls 4 circulate in the main passage 11, the return passage 12, and the connecting passage 13. Specifically, the balls 4 that reach the end point of the main passage 11 are returned to the start point of the main passage 11 via one connecting passage 13, the return passage 12, and the other connecting passage 13. In this embodiment, two circulation paths are formed, consisting of the main passage 11, one connecting passage 13, the return passage 12, and the other connecting passage 13.

[0026] As shown in Figure 3, when the ball 4 moves from the main passage 11 to the connecting passage 13, the ball 4 passes through the boundary between the female thread groove 5a of the nut body 5 and the groove portion 6a of the end cap 6. The female thread groove 5a of the nut body 5 and the groove portion 6a of the end cap 6 are designed to be smoothly continuous, but a slight step P may be formed at the boundary between them due to processing errors, assembly errors, etc. Note that the step P is shown exaggerated in Figure 3 and Figures 8 and 9, which will be described later.

[0027] In this embodiment, the end cap 6 is not completely fixed to the nut body 5, but is supported in a floating manner while allowing relative movement in a direction perpendicular to the axial direction (hereinafter referred to as the "axially perpendicular direction"). Specifically, as shown in FIG. 1, the end cap 6 is attached to the nut body 5 via an elastic member 8, and is locked in the axially perpendicular direction only by the elastic member 8. The elastic member 8 is formed of a material that is more elastic than the metal end cap 6 (i.e., a material with a smaller Young's modulus), and is formed of, for example, resin or rubber.

[0028] In the illustrated example, an elastic member 8 is disposed between the inner peripheral surface of an axial through-hole 6d provided in the end cap 6 and the outer peripheral surface of the shank of the bolt 7. More specifically, a washer 9 and a cylindrical bushing 10 are clamped and fixed from both axial sides between the head of the bolt 7 and the end face 5c of the nut body 5, and the elastic member 8 is disposed between the outer peripheral surface of the bushing 10 and the inner peripheral surface of the through-hole 6d of the end cap 6. In this embodiment, the elastic member 8 is press-fitted between the outer peripheral surface of the bushing 10 and the inner peripheral surface of the through-hole 6d of the end cap 6. That is, the cylindrical elastic member 8 is compressed in its radial direction and is pressed against the outer peripheral surface of the bushing 10 and the inner peripheral surface of the through-hole 6d of the end cap 6 by its own elastic force. The elastic member 8 is prevented from coming off in the axial direction by the washer 9.

[0029] As shown by arrow A in Figure 3, when ball 4 moves from main passage 11 to connecting passage 13, ball 4 collides with step P formed at the boundary between them, and load F is applied to end cap 6 in the direction perpendicular to the axis. This load F causes end cap 6, which is floatingly supported in the direction perpendicular to the axis relative to nut body 5, to move in the direction of load F relative to nut body 5 while elastically compressing elastic member 8 (see dotted line). This reduces the step P, thereby suppressing noise and vibration caused by this step P.

[0030] Even if a step occurs at the boundary between the return passage 13 and the connecting passage 13 when the ball 4 moves from the return passage 13 to the connecting passage 13, as described above, the load generated when the ball 4 hits the step causes the end cap 6 to move in a direction perpendicular to the axis, thereby reducing the step and suppressing noise and vibration caused by the step.

[0031] The present invention is not limited to the above-described embodiment. Other embodiments of the present invention will be described below, but redundant description of points similar to those of the above-described embodiment will be omitted.

[0032] 4 shows a ball screw 21 according to a second embodiment of the present invention. This ball screw 21 differs from the ball screw 1 of the first embodiment in that elastic members 8 are provided at the boundary between the main passage 11 and the connecting passage 13 and at the boundary between the return passage 12 and the connecting passage 13. In this ball screw 21, the end cap 6 and the nut body 5 are fixed with a bolt 7 in a state where they cannot move relative to each other.

[0033] The elastic member 8 has a first buffer portion 8a disposed at the boundary between the main passage 11 and the connecting passage 13, and a second buffer portion 8b disposed at the boundary between the return passage 12 and the connecting passage 13. In the illustrated example, as shown in Fig. 5, the first buffer portion 8a and the second buffer portion 8b are connected via an intermediate portion 8c, and are integrally molded from an elastic material (for example, resin or rubber). One elastic member 8 is attached to each of two grooves 6a formed in the end face of each end cap 6.

[0034] As shown in Fig. 4, a recess 14 is provided at the boundary between the female thread groove 5a that forms the main passage 11 and the groove portion 6a of the end cap 6 that forms the connection passage 13, and an elastic member 8 is fitted into this recess 14. In this embodiment, as shown enlarged in Fig. 6, the recess 14 is formed by a chamfered portion 5d formed at the end of the female thread groove 5a and a chamfered portion 6e (see Fig. 5) that is provided at the opening of the groove portion 6a on the nut body 5 side. The inner circumferential surface 8a1 of the first buffer portion 8a is designed to be smoothly continuous with the female thread groove 5a and the groove portion 6a.

[0035] As shown in Fig. 4, a recess 15 is provided at the boundary between the through hole 5b that forms the return passage 12 and the groove portion 6a of the end cap 6 that forms the connection passage 13, and the second buffer portion 8b is fitted into this recess 15. As shown enlarged in Fig. 7, the recess 15 is formed by an annular recess 5e formed at the end of the through hole 5b and a chamfered portion 6f (see Fig. 5) provided at the opening of the groove portion 6a on the nut body 5 side. An inner circumferential surface 8b1 of the second buffer portion 8b is designed to be smoothly continuous with the inner circumferential surface of the through hole 5b and the groove portion 6a.

[0036] As shown in FIG. 5, the second buffering portion 8b has an arc shape that follows the opening at the end of the through hole 5b. In the illustrated example, the second buffering portion 8b is provided in a circumferential region exceeding 180° of the opening of the through hole 5b. A tapered surface 8b2, whose diameter narrows toward the axially inner side, is provided on the axially inner side (left side in FIG. 7) of the outer peripheral surface of the second buffering portion 8b. By fitting this tapered surface 8b2 with a tapered surface 5e1 provided in the recess 5e of the nut body 5, the second buffering portion 8b is positioned relative to the nut body 5 in the direction perpendicular to the axis. A tapered surface 8b3, whose diameter narrows toward the axially outer side, is provided on the axially outer side (right side in FIG. 7). By fitting this tapered surface 8b3 with a tapered surface 6f1 provided in the chamfered portion 6f of the end cap 6, the second buffering portion 8b is positioned relative to the end cap 6 in the direction perpendicular to the axis.

[0037] As described above, by connecting the female thread groove 5a and the groove portion 6a via the first buffer portion 8a of the elastic member 8 rather than directly, noise and vibration caused by a step at the boundary between the main passage 11 and the connecting passage 13 are suppressed. For example, as shown in FIG. 8, if a step P is formed between the female thread groove 5a and the inner circumferential surface 8a1 of the first buffer portion 8a, the ball 4 collides with the step P when moving from the main passage 11 to the connecting passage 13, causing the elastic member 8 to elastically deform. This absorbs and reduces the step P, thereby suppressing noise and vibration caused by the step P (see dotted line in FIG. 8). Similarly, as shown in FIG. 9, if a step P is formed between the groove portion 6a of the end cap 6 and the inner circumferential surface 8a1 of the first buffer portion 8a, the ball 4 collides with the step P when moving from the connecting passage 13 to the main passage 11, causing the elastic member 8 to elastically deform. This absorbs and reduces the step P, thereby suppressing noise and vibration caused by the step P (see dotted line in FIG. 9).

[0038] Furthermore, as described above, by connecting the through hole 5b and the groove portion 6a via the second buffer portion 8b of the elastic member 8 rather than directly, noise and vibration caused by a step at the boundary between the return passage 12 and the connecting passage 13 are suppressed. For example, although not shown, if a step is formed between the through hole 5b and the inner circumferential surface 8b1 of the second buffer portion 8b, the ball 4 will collide with the step when moving from the return passage 12 to the connecting passage 13, causing the elastic member 8 to elastically deform. This absorbs and smooths the step, thereby suppressing noise and vibration caused by the step. Similarly, if a step is formed between the groove portion 6a of the end cap 6 and the elastic member 8, the ball 4 will collide with the step when moving from the connecting passage 13 to the return passage 12, causing the elastic member 8 to elastically deform. This absorbs and smooths the step, thereby suppressing noise and vibration caused by the step.

[0039] FIG. 10 shows a ball screw 31 according to a third embodiment of the present invention. This ball screw 31 differs from the second embodiment in that the elastic member 8 has an integral flat plate portion 8d that is sandwiched and fixed between the end cap 6 and the nut body 5. As shown in FIG. 11, the elastic member 8 of this embodiment is generally flat, and its shape conforms to the end face 5c of the nut body 5 and the end face of the end cap 6 facing it. Of this generally flat plate-shaped elastic member 8, the portion adjacent to the female thread groove 5a of the nut body 5 constitutes the first buffer portion 8a, the portion adjacent to the groove portion 6a of the end cap 6 constitutes the second buffer portion 8b, and the portion sandwiched between the end face 5c of the end cap 6 and the end face 5c of the nut body 5 constitutes the flat plate portion 8d. By tightening the bolt 7 with the flat plate portion 8d of the elastic member 8 disposed between the end face 5c of the nut body 5 and the end face of the end cap 6, the flat plate portion 8d is sandwiched and fixed between the nut body 5 and the end cap 6 from both axial sides. This allows the elastic member 8 to be assembled to the nut 3 easily and firmly.

[0040] In the illustrated example, the second buffer portion 8b of the elastic member 8 protrudes axially inward beyond the flat plate portion 8d, and a tapered surface 8b2 is provided on its outer circumferential surface. By fitting this tapered surface 8b2 into the tapered surface of a recess 5e formed in the end surface of the nut body 5, the elastic member 8 including the second buffer portion 8b is positioned relative to the nut body 5 in the direction perpendicular to the axis.

[0041] In the ball screw 21 according to the second embodiment and the ball screw 31 according to the third embodiment, as shown in FIGS. 8 and 9, if the elastic member 8 protrudes toward the center of the passage (upper side in the drawings) beyond the screw groove 5a or the groove portion 6a and the step P is formed by the elastic member 8, the ball 4 collides with the edge of the step P, elastically deforming the elastic member 8, thereby absorbing the step P. However, conversely, if the elastic member 8 recedes further from the center of the passage than the screw groove 5a or the groove portion 6a, the step P is formed by the metal nut body 5 or the end cap 6. Even if the ball 4 collides with the edge of such a metal step P, there is almost no elastic deformation, and therefore the step P cannot be alleviated. Therefore, in the ball screws 21, 31, even if there are manufacturing or assembly errors in each component (i.e., within the entire tolerance range), the inner surfaces 8a1, 8b1 of the elastic member 8 can be designed to be positioned closer to the center of the passage than the inner surfaces of the groove portion 6a and the through hole 5b, so that the step P is always formed by the elastic member 8.

[0042] Furthermore, in the above-described ball screws 21 and 31, the elastic member 8 has both the first buffer portion 8a and the second buffer portion 8b, but it may have only one of these. For example, when the ball 4 passes through the boundary between the main passage 11, which is a loaded region where the ball 4 is sandwiched between the male thread groove 2a and the female thread groove 5a, and the connecting passage 13, which is an unloaded region where the ball 4 is not sandwiched, noise and vibration are particularly likely to occur. Therefore, the elastic member 8 (first buffer portion 8a) may be disposed only at the boundary between the main passage 11 and the connecting passage 13.

[0043] In the above embodiment, the connection path 13 is formed by the flat end surface 5c of the nut body 5 and the groove portion 6a of the end cap 6, but for example, groove portions may be formed on both axial end surfaces of the nut body 5, and the connection path 13 may be formed by the groove portion 6a of the end cap 6 and the groove portion of the nut body 5.

[0044] In the above embodiment, the male screw groove 2a of the screw shaft 2 and the female screw groove 5a of the nut body 5 each have two threads, but they may each have one thread, or three or more threads. [Explanation of symbols]

[0045] 1 ball screw 2 screw shaft 2a male thread groove 3 nuts 4 balls 5 Nut body 5a female thread groove 5b Through hole 6 End cap (circulation member) 6a Groove 7 volts 8 Elastic member 8a 1st buffer section 8b 2nd buffer section 8c middle part 8d flat plate part 9 Washers 10 Bush 11 Main passage 12 Return passage 13 Connecting Road P step

Claims

1. A nut including a nut body having an internal thread groove formed on an inner peripheral surface and a circulation member attached to an axial end of the nut body; A screw shaft inserted into the inner periphery of the nut and having a male screw groove formed on its outer periphery; a main passage formed by the female screw groove of the nut body and the male screw groove of the screw shaft; a return passage provided on the outer diameter side of the main passage and communicating with both axial ends of the nut body; a connecting passage formed by a groove provided in the circulation member, the connecting passage connecting the main passage and the return passage; a ball screw having a plurality of balls arranged in the main passage, the return passage, and the connecting passage, A ball screw having an elastic member that elastically absorbs at least one of a step formed at the boundary between the main passage and the connecting passage and a step formed at the boundary between the return passage and the connecting passage.

2. The circulation member is attached to the nut body via the elastic member, 2. The ball screw according to claim 1, wherein the elastic member is elastically deformed to allow relative movement between the circulation member and the nut body in a direction perpendicular to the axial direction.

3. 2. The ball screw according to claim 1, wherein the elastic member is disposed at least at one of a boundary between the main passage and the connecting passage and a boundary between the return passage and the connecting passage.

4. 4. The ball screw according to claim 3, wherein the elastic member integrally includes a first buffer portion disposed at the boundary between the main passage and the connecting passage, and a second buffer portion disposed at the boundary between the return passage and the connecting passage.

5. 5. The ball screw according to claim 3, wherein the elastic member has integrally therewith a flat plate portion that is fixedly sandwiched between the circulation member and the nut body.

Images