Ball screw and seal member for ball screw

Abstract

The present invention can prevent leakage of a lubricant during normal use, can easily discharge old lubricant when lubricant is supplied, prevents damage to a seal, and can maintain a good lubrication state. A ball screw (10) comprises: a screw shaft (20), in the outer peripheral surface of which is formed a screw groove (21); a nut (30), in the inner peripheral surface of which is formed a screw groove (31); a plurality of balls (22) which roll in a load track that is constituted by the screw groove (21) of the screw shaft (20) and the screw groove (31) of the nut (30); and a seal member (50) which is attached to an axial end part of the nut (30) and which seals a gap (12) between the screw shaft (20) and the nut (30). The seal member (50) has a lubricant discharge part (13). The lubricant discharge part (13) is closed in a state where the pressure inside the nut (30) and the pressure outside the ball screw (10) are the same, and opens to allow passage therethrough the axial direction of the screw shaft (20) when the pressure inside the nut (30) increases.

Description

Ball screw and seal member for ball screw

[0001] The present invention relates to a ball screw and a seal member used for the ball screw.

[0002] Conventionally, a ball screw that converts rotational motion into linear motion generally includes a screw shaft having a spiral thread groove formed on its outer peripheral surface and a nut having a spiral thread groove formed on its inner peripheral surface. Between the thread grooves of both the screw shaft and the nut, a large number of balls that roll as the screw shaft or the nut rotates are loaded. Further, a seal member is usually attached to the end of the nut of the ball screw. The seal member has two functions: a function of suppressing grease leakage from inside the nut and a function of preventing foreign matter from entering the nut. For this purpose, the seal member is provided such that a minute gap is provided between the inner peripheral portion and the outer peripheral surface of the screw shaft, or it is provided to be in sliding contact with the outer peripheral surface of the screw shaft with a predetermined tightening allowance.

[0003] By the way, in a ball screw used in a large machine such as an injection molding machine, a method of supplying new grease at regular intervals by an automatic greasing device is common. At this time, the old grease is pushed out from between the inner peripheral portion of the seal and the screw shaft by the supplied new grease. However, if the space between the screw shaft and the nut is sealed by a seal, it becomes difficult to discharge the old grease. Therefore, the old grease remains in the nut and is mixed with the supplied new grease, and the performance of the new grease cannot be fully exhibited. Also, there was a risk that the seal member would come off the nut due to the pressure of the grease or the seal member would be damaged.

[0004] Therefore, Patent Document 1 proposes a ball screw that can easily discharge grease while attaching a seal. The above ball screw is provided with a grease supply port as a through hole extending from the outer peripheral surface of the nut to the spiral groove, and a grease discharge port is provided at the edge of the seal.

[0005] Furthermore, Patent Document 2 discloses a ball screw device that can prevent the internal pressure inside the nut from increasing when lubricant is supplied into the nut, and can also prevent foreign matter from entering from outside the nut. The ball screw device has a lubricant supply port for supplying lubricant into the nut, and the seal is placed in recesses provided at both ends of the nut, with a radial gap formed between the outer circumference of the seal and the inner circumference of the recess. The gap is also sized such that when lubricant is supplied from the lubricant supply port provided in the nut, the lubricant leaks out of the gap.

[0006] Furthermore, Patent Document 3 discloses a rolling device that, in addition to being less prone to internal pressure increases, is less likely to allow foreign matter to enter the interior from the outside and less likely to cause excessive leakage of internal lubricant. The ball screw described in Patent Document 3 has a sealing device, which includes a discharge hole with a labyrinth structure that releases air from inside the ball screw to the outside when lubricant is supplied to the inside of the ball screw through the lubrication hole.

[0007] Japanese Patent Publication No. 2007-225033, Japanese Patent Publication No. 2011-133049, Japanese Patent Publication No. 2013-024319

[0008] However, in the ball screw described in Patent Document 1, the grease discharge passage is always open, so there is a risk of grease leaking or foreign matter entering from the outside even when grease is not being replenished. Furthermore, although the ball screw devices described in Patent Documents 2 and 3 have a structure that makes it difficult for foreign matter to enter from the outside, it is difficult to prevent lubricant leakage or promote lubricant discharge as needed.

[0009] The present invention has been made in view of the above problems, and aims to provide a ball screw and a ball screw sealing member that can prevent leakage of lubricant during normal use and can easily discharge old lubricant when supplying lubricant, thereby preventing damage to the seal and maintaining a good lubrication state.

[0010] The above object of the present invention is achieved by the following configuration: [1] A ball screw comprising: a screw shaft having a helical screw groove formed on its outer circumference; a nut having a helical screw groove formed on its inner circumference; a plurality of balls that roll in a load trajectory formed by the screw groove of the screw shaft and the screw groove of the nut; and a sealing member attached to the axial end of the nut to seal the gap between the screw shaft and the nut, wherein the sealing member has a lubricant discharge portion, the lubricant discharge portion is closed when the pressure inside the nut is equal to the pressure outside the ball screw, and opens to penetrate the screw shaft in the axial direction when the pressure inside the nut increases.

[0011] According to the present invention, since the sealing member is provided with a lubricant discharge section that can be opened and closed as needed, leakage of lubricant can be prevented during normal use, and old lubricant can be easily discharged when supplying lubricant, thereby preventing damage to the seal and maintaining an excellent lubrication state of the ball screw.

[0012] Figure 1 is a side view showing a ball screw according to the first embodiment of the present invention. Figure 2 is a partial cross-sectional view showing an enlarged portion of the ball screw shown in Figure 1. Figure 3 is a front view showing a sealing member attached to the ball screw according to the first embodiment. Figure 4 is a front view and a cross-sectional view showing the faceplate of the sealing member according to the first embodiment. Figure 5 is a front view and a cross-sectional view showing the sealing plate of the sealing member according to the first embodiment. Figure 6 is a cross-sectional view showing the lubricant discharge section when the pressure inside the nut rises. Figure 7 is a front view and a cross-sectional view showing the sealing plate in the second embodiment of the present invention. Figure 8 is a schematic cross-sectional view showing an enlarged portion A in Figure 7.

[0013] [Ball Screw] <First Embodiment> Hereinafter, a ball screw according to the first embodiment of the present invention will be described in detail with reference to the drawings. Figure 1 is a side view showing a ball screw according to the first embodiment of the present invention. Figure 2 is a partial cross-sectional view showing an enlarged portion of the ball screw shown in Figure 1. Figure 3 is a front view showing a sealing member attached to the ball screw according to the first embodiment.

[0014] The ball screw 10 according to the first embodiment comprises a screw shaft 20 extending axially and having a helical screw groove 21 on its outer circumference, a nut 30 having a helical screw groove 31 on its inner circumference corresponding to the screw groove 21 of the screw shaft 20, a plurality of balls 22 that roll along a load trajectory formed by the screw groove 21 of the screw shaft 20 and the screw groove 31 of the nut 30, and a sealing member 50 that seals the gap between the screw shaft 20 and the nut 30.

[0015] Multiple return passages (not shown) are provided on the outer circumferential surface of the nut 30, each having a scooping portion that scoops up the balls and penetrates the nut 30 so that both ends advance into the load track. The return passages are a means of connecting one end and the other end of the load track to allow the balls to circulate indefinitely. For example, a method in which the return passages are arranged on the outside of the nut, such as a tube type, or a method in which the return passages are arranged inside the nut, such as a spindle type, end cap type, end deflector type, or S groove type, can be appropriately selected. As a result, the balls scooped up at one end of the load track pass through the return passages and are returned to the other end of the load track, thereby forming an infinite circulation path. In normal use, a lubricant (not shown), such as grease, is placed in the gap 12 between the screw shaft 20 and the nut 30, etc., in order to allow the balls 22 to roll smoothly in this infinite circulation path. In addition, a lubricant supply hole 11 is formed in the axial center of the nut 30, penetrating from the outer circumferential surface to the inner circumferential surface of the nut 30.

[0016] A flange portion 32 is formed on one axial end of the nut 30. This flange portion 32 is fixed to a movable table or the like of a machine device (not shown) with mounting bolts or the like. In addition, circular recesses 33, which have an inner diameter larger than the largest outer surface of the screw shaft 20, are formed concentrically with the screw shaft 20 at both axial ends of the nut 30. Furthermore, sealing members 50 are attached to both ends of the nut 30.

[0017] The sealing member 50 comprises a ring-shaped faceplate 60 and a ring-shaped sealing plate 40 having an inner surface that contacts the outer surface of the screw shaft 20. The sealing plate 40 is made of an elastic material and is positioned in circular recesses 33 formed at both axial ends of the nut 30. The faceplate 60 is fastened to the nut 30 from the axially outer side of the nut 30 by fixing members 61 such as bolts and retaining rings, thereby holding the sealing plate 40. In other words, the sealing plate 40 is fixed to both axial ends of the nut 30 in a state that is deformed in the thickness direction by being pressed against the faceplate 60.

[0018] The sealing member 50 according to the first embodiment will be described in detail below. Figure 4 is a front view and a cross-sectional view showing the faceplate of the sealing member according to the first embodiment, and Figure 5 is a front view and a cross-sectional view showing the sealing plate of the sealing member according to the first embodiment.

[0019] As shown in Figure 4, the faceplate 60 has a faceplate hole 60a in the center in a plan view through which the screw shaft 20 is inserted, and the diameter of the faceplate hole 60a is larger than the diameter of the screw shaft 20. The faceplate 60 also has screw holes 62 around the faceplate hole 60a at approximately equal intervals in the circumferential direction through which the fixing member 61 is inserted. Furthermore, the faceplate 60 has a circular lubricant discharge hole 51 that penetrates in the axial direction of the screw shaft 20. As the material constituting the faceplate 60, the same steel material as the nut 30 or rubber that is harder than the seal plate 40 can be appropriately selected.

[0020] As shown in Figure 5, the seal plate 40 has a seal plate hole 40a near the center in a plan view, and three screw holes 42 are formed so as to coincide with the positions of the screw holes 62 of the faceplate 60 when the faceplate 60 and the seal plate 40 are superimposed. The seal plate hole 40a has a shape similar to the cross-sectional shape perpendicular to the axial direction of the screw shaft 20, and its size is formed to be smaller than the cross-sectional shape of the screw shaft 20. Therefore, when the screw shaft 20 is inserted through the seal plate hole 40a, the inner circumferential surface of the seal plate 40 contacts the outer circumferential surface of the screw shaft 20. For this reason, the radial length from the inner circumferential surface of the seal plate 40 to the outer circumferential surface of the seal plate 40 is not constant, and the radial length in the region where the inner circumferential surface of the seal plate 40 slides against the screw groove 21 of the screw shaft 20 is longer than the length in other regions.

[0021] Furthermore, when the seal plate 40 is superimposed on the faceplate 60, it has a lubricant discharge slit 52 at a position that coincides with the lubricant discharge hole 51 in the faceplate 60. The lubricant discharge slit 52 is formed to penetrate in the axial direction of the screw shaft 20 and has, for example, an X shape formed by two intersecting straight lines. A movable part 55 is formed in the region sandwiched between the lubricant discharge slit 52. In this embodiment, the lubricant discharge section 13 is formed by the lubricant discharge slit 52 of the seal plate 40 in the seal member 50 and the lubricant discharge hole 51 of the faceplate 60.

[0022] In the ball screw 10 configured as described above, for example, by rotating the screw shaft 20, the multiple balls 22 roll in a circulation path consisting of a load path and a return path, moving the nut 30 in the axial direction of the screw shaft 20. At this time, the gap 12 between the screw shaft 20 and the nut 30 is sealed by the sealing members 50 attached to both axial ends of the nut 30. Under normal use, the pressure inside the nut 30 is equal to the pressure outside the ball screw 10, and as shown in Figure 2, the lubricant discharge slit 52 is closed. Therefore, under normal use, it is possible to prevent lubricant leakage and to prevent foreign matter from entering the inside of the nut 30 from outside the ball screw 10.

[0023] Furthermore, when the lubricant pre-placed inside the ball screw 10 deteriorates, lubricant such as grease is supplied into the gap 12 from the lubricant supply hole 11 by an automatic lubrication device or grease gun. Figure 6 is a cross-sectional view showing the state of the lubricant discharge section 13 when the pressure inside the nut 30 rises. When lubricant is supplied inside the nut 30 and the pressure inside the nut 30 rises, the movable part 55 bends outward. In this embodiment, since the lubricant discharge hole 51 is formed in the faceplate 60 at a position corresponding to the lubricant discharge slit 52, the area around the lubricant discharge slit 52 is fixed by the faceplate 60, which is harder than the seal plate 40. Therefore, only the movable part 55 is easily bent outward, and an opening 53 that penetrates in the axial direction of the screw shaft is formed. Also, when the supply of lubricant is stopped and the pressure inside the nut 30 decreases, the movable part 55 returns to its original shape due to the restoring force of the elastic material, and the lubricant discharge slit 52 closes.

[0024] Furthermore, since the nut 30 of the ball screw 10 reciprocates relative to the screw shaft 20, the lubricant sealed inside the nut 30 is easily pushed out towards the end of the nut 30. As a result, deteriorated lubricant with reduced lubricating effect tends to accumulate at the end of the nut. In other words, deteriorated lubricant accumulates on the back side (nut 30 side) of the seal member 50 located at the axial end of the nut 30. As described above, when the internal pressure of the nut 30 increases and the opening 53 is formed, the deteriorated lubricant can be efficiently and easily discharged to the outside. As a result, damage to the seal due to the increase in internal pressure of the ball screw 10 can be prevented, and new lubricant can be retained inside the nut 30, maintaining good lubrication of the balls 22, etc.

[0025] The position of the lubricant discharge portion 13 in the sealing member 50 is not particularly limited, but it is preferable that it be formed in a position where the lubricant can be easily discharged. For example, near the end of the nut 30, there is no ball 22 between the screw groove 21 of the screw shaft 20 and the screw groove 31 of the nut 30, and a space is formed, in which deteriorated lubricant tends to accumulate. Therefore, if a lubricant discharge slit 52 that can communicate with the above space is formed near the region where the outer surface of the sealing plate 40 contacts the screw groove 21 of the screw shaft 20, deteriorated lubricant can be discharged to the outside more efficiently.

[0026] <Second Embodiment> Next, a ball screw according to the second embodiment of the present invention will be described. Figure 7 is a front view and a cross-sectional view showing a seal plate in the second embodiment of the present invention. Figure 8 is a schematic cross-sectional view showing an enlarged view of part A in Figure 7. The only difference between the second embodiment and the first embodiment is the portion of the seal plate that constitutes the lubricant discharge section. Therefore, the second embodiment will be described below assuming that the seal plate shown in Figure 7 is applied to the ball screw 10 shown in Figure 1. In Figure 7, the same reference numerals are used for parts identical to the seal plate 40 shown in Figure 5, and their detailed descriptions are omitted or simplified.

[0027] As shown in Figures 7 and 8, the seal plate 45 in the second embodiment, like the first embodiment, has a seal plate hole 45a through which the screw shaft 20 is inserted, and also has an X-shaped lubricant discharge slit 52. The seal plate 45 also has a circular notch 54 around the lubricant discharge slit 52. This notch 54 is formed to a depth that does not penetrate the seal plate 45 in the thickness direction (axial direction of the screw shaft) from the nut-side surface 45b to the faceplate-side surface 45c.

[0028] In this second embodiment, the movable part 55, which becomes bendable due to the formation of the lubricant discharge slit 52, becomes more easily bent starting from the notch 54. Therefore, when the pressure inside the nut 30 increases during lubricant supply and pressure is applied from the nut-side surface 45b, the movable part 55 easily bends towards the faceplate 40, allowing for smooth discharge of the lubricant. When the supply of new lubricant is finished and the air and lubricant inside the nut 30 are discharged, the pressure inside the nut 30 becomes equal to the pressure outside the ball screw 10. At this time, since the notch 54 is formed to a depth that does not penetrate the thickness direction of the seal plate 45, a force acts to return it to its original shape as the pressure inside the nut 30 decreases, and the lubricant discharge slit 52 is closed. Therefore, during normal use, leakage of lubricant and contamination of the nut 30 with foreign matter can be prevented, and when lubricant is supplied, deteriorated lubricant can be discharged even more easily.

[0029] The ball screw according to the present invention has been described above with reference to the first and second embodiments, but the present invention is not limited to the configurations of the above embodiments. For example, the sealing member may have a lubricant discharge portion, and this lubricant discharge portion may have a structure that opens and closes based on changes in the pressure inside the nut. Specifically, the sealing member does not need to be composed of a sealing plate and a faceplate, and may consist only of a sealing plate having an openable and closable lubricant discharge portion. When the sealing member consists only of a sealing plate, the lubricant discharge portion may be formed by a lubricant discharge slit formed to penetrate axially in at least a part of the sealing plate. In this case as well, it is preferable that a notch is formed as shown in Figures 7 and 8. The notch may have a depth that does not penetrate axially from the nut-side surface of the sealing plate toward the outside of the ball screw.

[0030] Furthermore, the shape of the lubricant discharge slit formed in the seal plate 40 is not particularly limited, and it is sufficient to have a movable part that opens and closes based on changes in the pressure inside the nut. For example, in addition to the X-shape shown in the first and second embodiments above, there may also be slits that extend radially in three or five or more directions from a single point, or V-shaped or U-shaped slits.

[0031] Furthermore, as shown in the second embodiment, when the seal plate 45 has a notch 54, it is preferable that the notch 54 is formed around the lubricant discharge slit 52, surrounding it. For example, it is preferable that the notch 54 is formed in the region that forms the base of the movable part, connecting the ends of the slit. Alternatively, the notch 54 may be formed only in at least a part of the periphery of the lubricant discharge slit 52. In terms of the shape of the notch 54 in plan view, it may be circular, polygonal, or, in the case of a V-shaped or U-shaped slit, a notch consisting only of a line segment can be used. As for the cross-sectional shape of the notch 54, it may not only be a single notch formed in the thickness direction of the seal plate 45, but also a notch formed so that the cross-section is V-shaped or U-shaped.

[0032] The shape of the lubricant discharge hole 51 formed in the faceplate 60 is not particularly limited, and any shape that can hold the area around the lubricant discharge slit 52 formed in the seal plate 40 is acceptable. The shape of the lubricant discharge hole 51 may be, for example, a polygon, similar to the shape of the notch 54 in the second embodiment.

[0033] The seal plate is preferably made of an elastic material. Elastic materials include elastically deformable materials such as rubber and resin, and examples include thermoplastic elastomers (polyester elastomers, urethane elastomers, etc.) and rubber (acrylic rubber, nitrile rubber, fluororubber, etc.). Alternatively, a metal material may be used as the material for the seal plate as long as it is flexible. When the seal plate is made of an elastic material, the lubricant discharge slit can be opened and closed flexibly in response to changes in pressure, and the peripheral edge of the seal plate can be brought into close contact with the outer surface of the screw shaft 20, thereby improving the sealing performance.

[0034] Depending on the type of elastic material used for the seal plate and its thickness (dimensions), the elastic force may be too strong, making it difficult to open the lubricant discharge slit 52. In such cases, the depth and shape of the cut portion 54 can be appropriately adjusted to obtain an elastic force suitable for lubricant discharge.

[0035] [Sealing Member for Ball Screw] The sealing member for the ball screw according to this embodiment is used in the ball screw 10 according to this embodiment. Details of the sealing member are as described above.

[0036] It should be noted that the present invention is not limited to the embodiments described above, and can be modified, improved, and so on as appropriate.

[0037] As described above, the following matters are disclosed in this specification:

[0038] (1) A ball screw comprising: a screw shaft having a helical screw groove formed on its outer circumference; a nut having a helical screw groove formed on its inner circumference; a plurality of balls that roll along a load track formed by the screw groove of the screw shaft and the screw groove of the nut; and a sealing member attached to the axial end of the nut to seal the gap between the screw shaft and the nut, wherein the sealing member has a lubricant discharge section, the lubricant discharge section is closed when the internal pressure of the nut is equal to the external pressure of the ball screw, and opens to penetrate the screw shaft in the axial direction when the internal pressure of the nut increases. With this configuration, leakage of lubricant and contamination of foreign matter can be prevented during normal use, and when new lubricant is supplied to the inside of the nut, deteriorated lubricant can be easily and efficiently discharged through the lubricant discharge section, thereby preventing damage to the seal.

[0039] (2) The ball screw according to (1), wherein the sealing member is arranged at the axial end of the nut and has a ring-shaped sealing plate having an inner surface that contacts the outer surface of the screw shaft, and the lubricant discharge portion is made up of a lubricant discharge slit formed in at least a part of the sealing plate so as to penetrate in the axial direction. With this configuration, a lubricant discharge portion that can be opened and closed based on changes in pressure inside the nut can be obtained with a simpler structure.

[0040] (3) The ball screw according to (2), wherein the seal plate has a notch in at least a part of the periphery of the lubricant discharge slit, and the notch is formed from the nut-side surface of the seal plate toward the outside of the ball screw to a depth that does not penetrate in the axial direction. With this configuration, the lubricant discharge slit and the notch make it easier to open the lubricant discharge section, and deteriorated lubricant can be discharged even more easily.

[0041] (4) The ball screw according to (2), wherein the sealing plate is made of an elastic material. According to this configuration, the lubricant discharge slit can be flexibly opened and closed based on a change in pressure, and the peripheral edge of the sealing plate can be brought into close contact with the outer peripheral surface of the screw shaft, so that the sealing performance can be improved.

[0042] (5) The ball screw according to (1), wherein the sealing member includes a ring-shaped sealing plate disposed at an axial end portion of the nut and having an inner peripheral surface that contacts the outer peripheral surface of the screw shaft, and a ring-shaped face plate that holds the sealing plate. The face plate has a lubricant discharge hole that penetrates in the axial direction. The sealing plate has a lubricant discharge slit that penetrates in the axial direction at a position corresponding to the lubricant discharge hole in the face plate. The lubricant discharge hole and the lubricant discharge slit constitute the lubricant discharge portion. According to this configuration, a lubricant discharge portion that can be easily opened and closed based on a change in pressure inside the nut can be obtained with a simple structure, and the sealing plate can be fixed by the face plate.

[0043] (6) The ball screw according to (5), wherein the sealing plate has a cut portion at at least a part of the periphery of the lubricant discharge slit. The cut portion is formed to a depth that does not penetrate in the axial direction from the surface of the sealing plate on the nut side toward the surface on the face plate side. According to this configuration, the lubricant discharge slit and the cut portion facilitate the opening of the lubricant discharge portion, and the deteriorated lubricant can be discharged more easily.

[0044] (7) The ball screw according to (5), wherein the sealing plate is made of an elastic material. According to this configuration, the lubricant discharge slit can be flexibly opened and closed based on a change in pressure, and the peripheral edge of the sealing plate can be brought into close contact with the outer peripheral surface of the screw shaft, so that the sealing performance can be improved.

[0045] (8) A ball screw sealing member characterized by being used in any one of the ball screws described in (1) to (7). With this configuration, leakage of lubricant and contamination of foreign matter can be prevented, and deteriorated lubricant can be efficiently discharged.

[0046] Although various embodiments have been described above with reference to the drawings, it goes without saying that the present invention is not limited to these examples. It is clear to those skilled in the art that various modifications or alterations can be conceived within the scope of the claims, and these will naturally also fall within the technical scope of the present invention. Furthermore, the components of the above embodiments may be combined in any way without departing from the spirit of the invention.

[0047] This application is based on the Japanese Patent Application No. 2024-201020 filed on November 18, 2024, the contents of which are incorporated herein by reference.

[0048] 10 Ball screw 11 Lubricant supply hole 13 Lubricant discharge section 20 Screw shaft 21, 31 Screw groove 22 Ball 30 Nut 40, 45 Seal plate 50 Seal member 51 Lubricant discharge hole 52 Lubricant discharge slit 53 Opening 54 Notch 60 Face plate 61 Fixing member

Claims

1. A ball screw comprising: a screw shaft having a helical screw groove formed on its outer circumference; a nut having a helical screw groove formed on its inner circumference; a plurality of balls that roll along a load track formed by the screw groove of the screw shaft and the screw groove of the nut; and a sealing member attached to the axial end of the nut to seal the gap between the screw shaft and the nut, wherein the sealing member has a lubricant discharge portion, and the lubricant discharge portion is closed when the internal pressure of the nut is equal to the external pressure of the ball screw, and opens to penetrate the screw shaft in the axial direction when the internal pressure of the nut increases.

2. The ball screw according to claim 1, characterized in that the sealing member is disposed at the axial end of the nut and has a ring-shaped sealing plate having an inner surface that contacts the outer surface of the screw shaft, and the lubricant discharge portion is made up of a lubricant discharge slit formed in at least a part of the sealing plate so as to penetrate in the axial direction.

3. The ball screw according to claim 2, wherein the seal plate has a notch in at least a portion of the area surrounding the lubricant discharge slit, and the notch is formed to a depth that does not penetrate in the axial direction from the nut-side surface of the seal plate toward the outside of the ball screw.

4. The ball screw according to claim 2, characterized in that the sealing plate is made of an elastic material.

5. The ball screw according to claim 1, wherein the sealing member comprises a ring-shaped sealing plate positioned at the axial end of the nut and having an inner surface that contacts the outer surface of the screw shaft, and a ring-shaped faceplate that holds the sealing plate, the faceplate having a lubricant discharge hole that penetrates in the axial direction, and the sealing plate having a lubricant discharge slit that penetrates in the axial direction at a position corresponding to the lubricant discharge hole in the faceplate, and the lubricant discharge portion is formed by the lubricant discharge hole and the lubricant discharge slit.

6. The ball screw according to claim 5, wherein the seal plate has a notch in at least a portion of the area surrounding the lubricant discharge slit, and the notch is formed to a depth that does not penetrate in the axial direction from the nut-side surface of the seal plate toward the faceplate-side surface.

7. The ball screw according to claim 5, characterized in that the sealing plate is made of an elastic material.

8. A ball screw sealing member, characterized in that it is used for a ball screw according to any one of claims 1 to 7.

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