ball screw

Abstract

To provide a ball screw that can obtain high positional accuracy and a desired seal clearance at low costs while simplifying the assembling work of a seal member to a nut.SOLUTION: In a ball screw 100, a spigot portion 70 coaxial with a screw shaft 100 is configured by an end portion inner peripheral surface of a nut 20 and a fixed portion outer peripheral surface of a seal member 50. A tongue portion 53 for deciding a phase projecting out in an outer diametrical direction is formed at only one place on an outer periphery of the seal member 50, and the tongue portion 53 is inserted in a fitting recessed portion 34 formed along an axial direction at an end portion of the nut 20, thereby fixing a position in a circumferential direction of the seal member 50 while regulated in a predetermined phase.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a ball screw having a seal member attached to the end of the nut. [Background technology]

[0002] A ball screw has a spiral screw groove on the outer circumferential surface of a screw shaft and a spiral screw groove on the inner circumferential surface of a nut, with multiple balls interposed between them. In this type of ball screw, a seal member is attached to the end of the nut (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-97668 Summary of the Invention [Problem to be solved by the invention]

[0004] In this type of ball screw, in order to prevent leakage of lubricant such as grease filled inside the nut and to prevent the intrusion of foreign matter from the outside, it is necessary to align the phase of the thread groove shape of the screw shaft with the lip portion on the inner periphery of the seal member when assembling the seal member.

[0005] In this case, if the seal member is not installed in the position that provides the desired clearance due to improper positioning, the sealing performance will decrease. Therefore, to obtain good dust-proofing and sealing performance, it is necessary to align the central axes of the screw shaft and the seal member, and to precisely adjust the phase between the lip of the seal member and the thread groove shape of the screw shaft.

[0006] Conventionally, this phase alignment work has been carried out by an assembly worker assembling the seal members by spot-matching them while visually checking the phase of each member one by one. However, with the on-site assembly method, it is difficult to simultaneously perform two adjustment tasks: aligning the central axes of the screw shaft and the seal member while accurately adjusting the phase between the lip portion of the seal member and the thread groove shape of the screw shaft. This requires a great deal of time and effort from the worker, and results in problems such as increased assembly costs and reduced productivity.

[0007] The present invention has been made in light of these problems, and has as its object to provide a ball screw that simplifies the assembly work of the seal member to the nut, while providing a seal gap with high positioning accuracy and a desired phase at low cost. [Means for solving the problem]

[0008] In order to solve the above problems, a ball screw according to one embodiment of the present invention comprises a screw shaft having a helical thread groove on its outer circumferential surface, a nut fitted onto the screw shaft and having a helical thread groove on its inner circumferential surface, a plurality of balls interposed between the thread grooves of the screw shaft and the nut, an annular sealing member that seals between the outer periphery of the screw shaft and the inner periphery of the nut along the outer circumferential shape of the screw shaft, and fixing means for fixing the sealing member to the nut, wherein at least one end of the nut forms a spigot portion where the outer circumferential surface of the sealing member and the inner circumferential surface of the end are fitted together coaxially with the screw shaft, and a tongue portion protruding in the outer diameter direction at only one location on the outer circumferential surface of the sealing member and a fitting recess formed at only one location on the inner circumferential side of the end, into which the tongue portion can be inserted along the axial direction, are formed to be located at an installation position where the seal shape of the sealing member and the outer circumferential shape of the screw shaft are aligned in phase. [Effects of the Invention]

[0009] According to the present invention, the phase of the lip portion of the seal member and the thread groove shape of the screw shaft can be set accurately and easily by simply fitting the tongue portion of the seal member into the fitting recess while aligning the central axes of the screw shaft and the seal member using the spigot portion. Therefore, the seal assembly work is simplified, and a seal gap with high positioning accuracy and the desired phase can be obtained at low cost. [Brief explanation of the drawings]

[0010] [Figure 1] 1A and 1B are explanatory diagrams of an embodiment of a ball screw according to an aspect of the present invention, in which FIG. 1A is a front view, and FIG. 1B is a cross-sectional view along the axis, with balls not shown. [Figure 2] 1A and 1B are perspective views illustrating an embodiment of a ball screw according to an aspect of the present invention, in which the screw shaft and balls are omitted and only the nut and the seal portion at its end are illustrated, and FIG. 1B is an exploded perspective view of the seal portion of FIG. 1A. [Figure 3] 2A and 2B are explanatory diagrams of an embodiment of a ball screw according to an aspect of the present invention, in which FIG. 2A is a cross-sectional view taken along the axis of the nut and the seal portion at its end in FIG. 1, and FIG. 2B is a front view seen from the seal portion side. [Figure 4] FIG. 2 is a diagram (a ZZ cross section in FIG. 1) that explains the relationship between the gap between the lip portion of the sealing member and the outer periphery of the screw shaft in response to changes in the mounting position of the sealing member, where FIG. 2(a) shows a state in which the sealing member is mounted in the correct phase, and FIG. 2(b) shows a hypothetical state in which the sealing member is mounted in the incorrect phase. [Figure 5] 10A and 10B are schematic vertical cross-sectional views illustrating a modified example of the fixing means for the sealing member. [Figure 6] 10A and 10B are schematic vertical cross-sectional views illustrating a modified example of the fixing means for the sealing member. [Figure 7] 10A and 10B are schematic vertical cross-sectional views illustrating a modified example of the fixing means for the sealing member. [Figure 8] 10A and 10B are explanatory diagrams of a modified example of the fixing means of the sealing member, in which FIG. 10A is a schematic longitudinal sectional view thereof, and FIG. 10B is a schematic front view of the fixing means. [Figure 9] 10A and 10B are schematic vertical cross-sectional views illustrating a modified example of the fixing means for the sealing member. [Figure 10] 10A and 10B are schematic vertical cross-sectional views illustrating a modified example of the fixing means for the sealing member. [Figure 11] FIG. 10 is an exploded perspective view illustrating a modified example of an embodiment of a ball screw according to an aspect of the present invention. [Figure 12]10A to 10C are schematic diagrams illustrating modified shapes of a tongue portion and a fitting recess portion and combinations thereof in a ball screw according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the drawings are schematic. Therefore, it should be noted that the relationship between thickness and planar dimensions, ratios, etc. differ from the actual ones, and the drawings also include portions where the relationship and ratio of dimensions differ from each other. Furthermore, the embodiments described below are intended to exemplify devices and methods for embodying the technical ideas of the present invention, and the technical ideas of the present invention do not limit the materials, shapes, structures, arrangements, etc. of the components to the embodiments described below.

[0012] As shown in Fig. 1, a ball screw 100 according to this embodiment has a screw shaft 10 and a nut 20 fitted onto the outer periphery of the screw shaft 10. A helical screw groove 11 is formed on the outer periphery of the screw shaft 10, and a helical screw groove 21 that faces the screw groove 11 of the screw shaft 10 is formed on the inner periphery of the nut 20. A plurality of balls 40 are interposed between these screw grooves 11, 21, and the plurality of balls 40 roll between the screw grooves 11, 21 as the screw shaft 10 and the nut 20 rotate relative to each other.

[0013] The ball screw 100 of this embodiment is an example of an internal circulation system, in which the screw shaft 10 is a single-start thread, and the inner surface of the nut 20 is configured with one or more circulation circuits, and each circulation circuit is formed with a ball reversal portion 22 consisting of an approximately S-shaped groove formed to a position deeper than the screw groove 21 of the nut 20, as shown in Figures 1 to 3. As a result, when the ball 40 that has rolled in each circulation circuit reaches the end point of the screw groove 21, it passes through the ball reversal portion 22 on the nut side and returns to the start point of the screw groove 21 in the same circulation circuit, and then rolls between the screw grooves 11 and 21 again, repeating the cycle.

[0014] The ball screw 100 of this embodiment is a suitable example for use in, for example, an electric actuator that constitutes a steering mechanism of a vehicle, and the nut 20 of this embodiment has a cylindrical portion 30 that surrounds the screw shaft 10 and extends radially outward from the axial end, and a ball rolling groove for the inner ring of a bearing that constitutes the electric actuator is integrally formed on the outer peripheral surface of this cylindrical portion 30.

[0015] In this embodiment, as shown in Figures 1 to 3, the cylindrical portion 30 is formed coaxially with the screw shaft 10 at one axial end of the nut 20. In this embodiment, the nut end face 23 on the inner diameter side of the cylindrical portion 30 is a surface perpendicular to the axial direction. An annular seal mounting groove 31 is formed on the inner surface of the cylindrical portion 30. A C-type retaining ring 60, which is a fixing means for fixing the seal member 50, is fitted axially into the seal mounting groove 31 using a dedicated tool.

[0016] The inner diameter of the seal mounting groove 31 is formed to have approximately the same dimension as the outer diameter of the fixed portion 51 of the seal member 50, and a fitting recess 34 recessed toward the outer diameter side is formed in only one location on the opening edge of the seal mounting groove 31. The seal mounting groove 31 is formed at a position deeper than the opening edge of the cylindrical portion 30 and coaxial with the screw shaft 10. An annular seal member 50 is attached to the inner periphery of the cylindrical portion 30, near the end face of the nut. The seal member 50 of this embodiment is made of elastomer, and has a fixed portion 51 and a lip portion 52 formed integrally.

[0017] More specifically, in this embodiment, as shown in FIG. 2(b), the sealing member 50 integrally comprises an annular fixing portion 51 and an approximately elliptical lip portion 52 formed on the inner surface of the fixing portion 51 and adapted to match the spiral shape of the thread groove 11 having a lead. The lip portion 52 in this embodiment is formed in an arc shape that follows the spiral shape of the thread groove 11, and is formed into a substantially elliptical shape by combining a portion that faces the interior of the thread groove 11 of the screw shaft 10 with a portion that faces the land surface 12 of the screw shaft 10 over the remaining angular range. The inside of the nut is filled with a lubricant such as grease, and when the seal member 50 is attached, the lip portion 52 faces the thread groove 11 with a small gap between them, forming a non-contact seal.

[0018] The outer peripheral surface 54 of the fixed portion 51 is a cylindrical surface having a diameter slightly smaller than or approximately the same as the inner peripheral surface of the seal mounting groove 31, and the surface of the fixed portion 51 facing the nut 20 in the axial direction is an annular surface perpendicular to the axial direction. In this embodiment, the seal mounting groove 31 of the cylindrical portion 30 and the outer peripheral surface 54 of the seal member 50 form a spigot portion 70.

[0019] 1 to 3, in this embodiment, a tongue portion 53 is formed in advance so as to protrude radially from only one location on the outer peripheral surface 54 of the fixing portion 51 of the sealing member 50. The tip of the tongue portion 53 is arc-shaped. In the seal mounting structure of this embodiment, the tongue portion 53 fits into a fitting recess 34 formed at the end portion on the inner circumferential side of the cylindrical portion 30, and the seal member 50 is positioned on the nut 20. Thereafter, the seal member 50 is fixed inside the cylindrical portion 30 with respect to the C-type retaining ring 8 by inserting the C-type retaining ring 8 into the annular fixing groove 32 in the axial direction.

[0020] 1(b), the axial dimension A is set so that the axial center position of the ball reversal portion 22 (the deepest position of the groove) is located at a position of a predetermined dimension in the axial direction, with the nut end face 23 as the reference plane. Then, using the position and phase of the ball reversal portion 22 at this axial dimension A as a reference, the axial position B (and position C from the end) of the groove center of the seal mounting groove 31, which serves as the seal mounting reference, and the phase at which the tongue portion 53 of the seal member 50 should be mounted, that is, the circumferential center position of the fitting recess 34 (the position directly above in the figure), are determined.

[0021] In this embodiment, when manufacturing the sealing member 50, the circumferential center positions of the tongue portion 53 and the mating recess 34 are formed so that the center of the tongue portion 53 is positioned at a position corresponding to a theoretical fixed angle calculated in advance.

[0022] It should be noted that manufacturing errors occur in the screw shaft 10 and the nut 20. The angle of the tongue portion 53 and the fitting recess 34 can be adjusted within the error range by adjusting the gap between the tongue portion 53 and the fitting recess 34 in the circumferential direction. Therefore, when the seal member 50 is used for a specific ball screw, the gap between the tongue portion 53 and the fitting recess 34 in the circumferential direction is set to a value that corresponds to the tolerances in manufacturing, etc. of the screw shaft 10 and the nut 20. In other words, if the tolerances in manufacturing, etc. are small, the gap is set to be narrow, and if the tolerances are large, the gap is set to be wide.

[0023] Next, a description will be given of the assembly method and effects of the seal member 50 in the ball screw 100 of this embodiment. Note that the assembly method for other components is the same as in the conventional case, and therefore the description thereof will be omitted where appropriate.

[0024] In this type of ball screw, if the seal member is not installed in the desired position due to improper positioning, the sealing performance will be reduced. Therefore, relatively high positioning accuracy and clearance management are required. Generally, the seal member is positioned by on-site assembly. In this case, to achieve good dust-proofing and sealing performance, it is necessary to align the central axes of the screw shaft and seal member, and to precisely adjust the phase of the seal member and screw shaft.

[0025] In contrast, in the ball screw 100 of this embodiment, as described above, the nut 20 has an inlay portion 70 at one end, the cylindrical portion 30, into which the outer surface 54 of the seal member 50 and the seal mounting groove 31 formed on the inner surface of the cylindrical portion 30 are fitted in a position coaxial with the screw shaft 10.

[0026] Furthermore, in the ball screw 100 of this embodiment, a tongue portion 53 protruding in the outward direction at only one location on the outer peripheral surface 54 of the sealing member 50 and a mating recess 34 formed at only one location on the inner peripheral side of the nut end face 23 of the cylindrical portion 30, into which the tongue portion 53 can be inserted along the axial direction, are formed so as to be located at an installation position where the phase of the seal shape formed by the lip portion 52 of the sealing member 50 matches the phase of the outer peripheral shape of the screw shaft 10 (Invention 1).

[0027] As a result, in the ball screw 100 of this embodiment, when attaching the seal member 50 to the nut 20, the pre-formed tongue portion 53 can be automatically attached at a predetermined fixed angle simply by fitting it axially into the mating recess 34. Therefore, when the sealing member 50 is attached to the nut 20, the circumferential position is uniquely determined to a predetermined position without the need to check the phase with the screw shaft 10, which prevents incorrect assembly, unlike positioning methods that use markings or the like to determine the assembly position visually.

[0028] If the seal is fixed by plastic deformation during assembly, it is difficult to easily determine the phase during installation, but a configuration in which the phase can be uniquely and automatically determined by fitting visible tongue portion 53 axially into fitting recess 34 even before assembly is superior. Therefore, it is preferable that tongue portion 53 is not plastically deformed, but is formed in advance in only one location in a shape that does not deform before and after assembly or that can be attached by deformation within the range of elastic deformation.

[0029] Furthermore, in the ball screw 100 of this embodiment, the seal mounting groove 31 is located further back than the opening edge of the cylindrical portion 30, and the spigot portion 70 is configured coaxially with the screw shaft 10, so not only the circumferential phase of the seal member 50 but also the position of the central axis and the position in the axial direction can be simultaneously regulated. As a result, when assembling the ball screw 100, the task of aligning the central axes of the screw shaft 10 and the seal member 50 is not required.

[0030] Furthermore, since the spigot portion 70 is configured, the central shaft is also attached to the desired position at the same time, and the inner periphery of the lip portion 52 is positioned opposite the periphery of the screw shaft 10 with a predetermined gap therebetween, as shown in Figure 4(a). Therefore, the lip portions 52 can be opposed to each other with a substantially uniform gap therebetween over the entire circumference of the screw shaft 10. As a result, the desired sealing performance can be achieved without generating excess torque or, conversely, without creating a gap larger than desired. In addition, since the mounting position of the sealing member 50 is maintained stably over time, it is possible to effectively prevent foreign matter from entering through the contact surface between the nut 20 and the sealing member 50, and it is possible to maintain the initial sealing performance for a long period of time.

[0031] As shown in Fig. 1(b), if the seal member 50 is not assembled in the intended phase (in the example shown in Fig. 1(b), the position of the tongue portion 53 is shifted 90 degrees counterclockwise), there will be areas where the seal member 50 comes into contact with the other parts, or there will be areas where the gap is larger than intended. The same applies if the central axis of the seal member 50 is shifted when it is installed.

[0032] As described above, according to the ball screw 100 of this embodiment, it is possible to extremely easily set the center axis and phase when attaching the seal member 50 and then easily fix it thereafter. In particular, in the ball screw 100 of this embodiment, one tongue portion 53 fits into one fitting recess 34 formed on the inner periphery of the cylindrical portion 30 to position the seal member 50 on the nut 20 .

[0033] That is, since the fitting recess 34 is formed only in one place on the opening edge so as to communicate with the seal mounting groove 31, the processing of the fitting recess 34 is easy, and since it cannot be assembled in any other position (phase), the risk of incorrect assembly is completely eliminated. Furthermore, it is advantageous in that the fitting state of the tongue portion 53 can be reliably confirmed visually before and after installation.

[0034] Furthermore, in the ball screw 100 of this embodiment, the multiple balls 40 are of an internal circulation type, circulating through the ball reversal portion 22 formed on the inner surface of the nut 20. Although the position of the ball reversal portion 22, which is the no-load area, cannot be determined from the outside, the tongue portion 53 of the sealing member 50 is formed based on the axial position of the ball reversal portion 22, making it easy to confirm the no-load area (Invention 2).

[0035] In other words, according to the ball screw 100 of this embodiment, if the products of the same design are mass-produced, the distance from the position of the ball reversal portion 22 to position B of the nut 20 and the screw specifications (lead and BCD) are the same, so the cross-section of the thread groove 21 in the cross-section of the nut 20 at position B will be the same for all products, and the phase of the approximately elliptical lip portion 52 of the sealing member 50 will also be maintained the same. Therefore, by determining the phase of the ball reversal portion 22 and the fitting recess 34 and providing the fitting recess 34 in the nut 20 in advance, and determining the phase of the lip portion 52 of the sealing member 50 and the position of the tongue portion 53 in advance, and combining these, it is possible to maintain the phase of the lip portion 52 the same, and the phase of the thread groove 11 of the screw shaft 10 to be incorporated into the nut 20 and the lip portion 52 the same, and it is possible to make the sealing performance the same for all products. Furthermore, even when the ball screw 100 is in its completed state, the position of the ball reversal portion 22 can be clearly determined from the position of the tongue portion 53. Therefore, if the circulation circuit is a single circuit, it becomes easier to assemble the ball screw 100 so that the unloaded region is not positioned in the phase required for the loaded region of the assembled product, and subsequent confirmation can also be easily performed. This improves the ease of assembly in the assembled product, and also contributes to improving the stability and reliability of the finished product's performance.

[0036] In particular, according to the ball screw 100 of this embodiment, the nut 20 has a cylindrical portion 30 that surrounds the screw shaft 10 and extends radially outward from the axial end, and a ball rolling groove for the inner ring of the bearing that constitutes the electric actuator is integrally formed on the outer surface of this cylindrical portion 30, making it suitable for use in an electric actuator that constitutes a steering mechanism of a vehicle (Invention 3).

[0037] That is, the ease of assembly is particularly good, making it suitable for mass production. Furthermore, with the ball screw 100 of this embodiment, the position of the ball reversal portion 22 can be determined from the position of the tongue portion 53. Therefore, it is possible to prevent incorrect assembly when assembling the ball reversal portion 22, which is the no-load area based on the tongue portion 53, into the electric actuator at the desired phase. This makes it possible to install the ball screw 100 while checking that the position of the ball reversal portion 22 does not coincide with the position of the part where stress is concentrated due to the moment load generated by the drive reaction force of the electric actuator and via the screw shaft 10.

[0038] Furthermore, the cylindrical portion 30 is formed so as to protrude radially outward from the axial end, which increases the wall thickness and improves rigidity. Because the fitting recess 34 and the seal mounting groove 31 are provided in a highly rigid portion, even if a moment load is generated by the driving reaction force of the electric actuator and is applied to the nut 20 via the screw shaft 10, deformation of the nut 20 is suppressed, the positions of the seal member 50 and the screw shaft 10 are stabilized, and sealing performance can be maintained.

[0039] The steering mechanism of the vehicle can be applied to steer-by-wire (SBW), in which the steering unit and the turning unit are electrically connected without being mechanically connected, and the steering angle of the turning unit is changed via an electrical signal, or electric power steering (EPS), in which the steering unit and the turning unit are mechanically connected. When these are incorporated into a steering mechanism, the nut 20 is connected to the drive side and rotates, and the rotation is converted into linear motion by the ball screw 100, which then linearly moves the screw shaft 10 to drive the steering mechanism, making it suitable as a rotation-to-linear motion conversion mechanism in the structure.

[0040] Furthermore, according to the ball screw 100 of this embodiment, the fixing means is a C-type retaining ring 8, and the seal member 50 can be fixed to the end of the nut 20 from the axial direction by the C-type retaining ring 8, so after the seal member 50 is attached, the C-type retaining ring 8 can be inserted into the fixing groove 32 from the same axial direction to fix the seal member 50. Therefore, according to the ball screw 100 of this embodiment, during assembly work, the seal assembly work can be performed efficiently and consecutively from the same axial side (Invention 4).

[0041] Furthermore, according to the ball screw 100 of this embodiment, the tongue portion 53 has an end portion that protrudes in the outer diameter direction and has an arc shape, so that it can be easily and efficiently machined with an end mill (Invention 5).

[0042] As described above, according to the ball screw 100 of this embodiment, the central axes of the screw shaft 10 and the seal member 50 can be automatically aligned, and the seal member 50 can be automatically attached to the screw shaft 10 in a desired phase. Therefore, the assembly work of the seal member 50 to the nut 20 is simplified, and high positioning accuracy and a desired seal gap can be obtained at low cost. Furthermore, by fitting the tongue portion 53 into the fitting recess 34, the circumferential position is reliably regulated, so the phase of the seal member 50 does not change during use, the seal gap can be maintained constant, and stable rotational torque and seal performance can be maintained for a long period of time.

[0043] The ball screw according to the present invention is not limited to the above embodiment, and various modifications are possible without departing from the spirit of the present invention. For example, in the embodiment shown in FIG. 1, the edge on the inner diameter side of the cylindrical portion 30 may be formed as an inclined or curved surface that widens outward, thereby preventing the seal member 50 from getting caught when it is fitted.

[0044] Furthermore, for example, the lip portion 52 is not limited to a non-contact type seal, but can also be a contact type seal. Of course, the planar shape of the lip portion 52 can be variously modified to match the cross section of the screw shaft 10. For example, in the case of a contact type seal, the number of sliding contact portions will change depending on how many thread grooves 11 appear in the cross section perpendicular to the axial direction of the screw shaft 10.

[0045] Furthermore, since the cross-sectional shape and phase of the screw grooves 11, 21 differ depending on the type of ball screw 100, it goes without saying that the circumferential fixing angle of the seal member 50 can be appropriately changed accordingly. From design conditions such as the cross-sectional shape and phase of the thread grooves 11, 21, it is possible to calculate a theoretical fixed angle (phase) at which the lip portion 52 of the sealing member 50 slides against the screw shaft 10 without any gaps around the entire circumference. The tongue portion 53 is formed at only one predetermined position in the circumferential direction in accordance with these conditions.

[0046] In the above embodiment, no particular mention is made of the shapes of the front and back of the seal member 50. However, if it is necessary to distinguish between the front and back of the seal member 50, various identification marks or shapes can be incorporated. Specifically, the seal member 50 can be formed to have a seal shape that matches the phase of the seal shape of the seal member 50 and the outer peripheral shape of the screw shaft 10, regardless of whether the seal member 50 is assembled from the front or back side. As a result, if the seal member 50 can be made symmetrical, it can be installed regardless of whether it is installed from the front or back side (Invention 6).

[0047] Furthermore, for example, by providing a protrusion on only one side of the seal member 50 and a protrusion fitting portion on the bottom surface of the seal mounting groove 31 of the opposing nut 20, and by configuring the protrusion and the protrusion fitting portion to fit together when the seal member 50 is attached to the seal mounting groove 31, it is possible to check the front and back of the seal member 50 in advance, and furthermore, even if it is assembled incorrectly, it is easy to visually check for incorrect assembly of the seal before attaching the screw shaft 10. 1 and 11, the axial depth of the fitting recess 34 is also formed to a position deeper than the bottom surface of the seal mounting groove 31. Regardless of this, it is preferable to provide a protruding fitting portion at a position different from the fitting recess 34 to incorporate a foolproof structure into the seal member 50 (Invention 7).

[0048] Furthermore, for example, the ball screw 100 in the above embodiment is an example of an internal circulation system in which the ball reversal portion 22 is provided on the inner periphery of the nut, but is not limited to this. For example, the ball reversal portion may be constructed in a variety of ways, including a return tube structure attached to the outer periphery of the nut, a bridge structure in which a bridge member is attached to the inner periphery of the nut and connects adjacent thread grooves with the bridge member to reverse the ball, or an end deflector structure in which the ball is reversed and transferred through a through-hole in the nut that extends axially at the end of the nut. In the case of an end deflector structure, the seal member may be integrated with the end deflector holder. Furthermore, when the ball reversal portion is constructed as a separate member, such as a return tube structure, bridge structure, or end deflector structure, the axial dimension A may be based on a portion of the outer shape of the separate member or a surface of a portion of the mounting portion where the separate member is mounted on the nut 20, with the nut end face 23 as the reference plane. Furthermore, with the seal mounting structure for the ball screw according to the present invention, the phase of the seal member 50 can be mounted at the desired phase regardless of whether or not the screw shaft 10 is present. Therefore, depending on the circulation method of the ball screw, the seal can be pre-assembled, and the assembly procedure for the ball assembly process can be changed depending on the specifications.

[0049] Furthermore, in the above embodiment, an example is shown in which one sealing member 50 is attached to one axial end of the nut 20, but this is not limited to this, and the sealing member mounting structure of the present invention can also be applied to cases in which one or more sealing members are attached in a stacked manner to each axial end of the nut.

[0050] Furthermore, the fixing means for fixing the sealing member 50 is not limited to a C-shaped retaining ring, and various modifications are possible as long as it is possible to prevent it from coming off in the axial direction. In other words, if a retaining ring other than a C-shaped retaining ring is used, a corresponding mounting structure can be provided on the end face of the nut.

[0051] Furthermore, the sealing member 50 may be made of an elastic material other than elastomer, or may be made of metal such as steel plate, or resin. Furthermore, the fixing portion 51 may be provided with a core metal to maintain the shape of the sealing member 50 and increase its strength. Below, modifications of this type are shown in Figures 5 to 10. Note that the same reference numerals are used to designate components that are similar to or correspond to those in the above embodiment, and descriptions thereof will be omitted where appropriate.

[0052] For example, in the example shown in Fig. 5, a retaining ring 60 other than a C-type retaining ring is used as the fixing means. Also, in the example shown in Fig. 6, the fixing means utilizes the elastic deformation of the seal member 50 itself to fit into the seal mounting groove 31. Therefore, it can be said that the seal mounting groove 31 also serves as the fixing groove 32. 6, the fitting gaps and axial gaps of the seal mounting grooves 31, 32 are controlled to stabilize the position and retention state of the seal member 50. Also, in the example shown in the figure, a conical surface that expands in diameter outward is provided on the guide surface 33 to facilitate insertion.

[0053] 7, the fixing means for the seal member 50 is two-shot molded by combining a substantially L-shaped seal main body portion 51b and a metal core portion (e.g., iron) 51a, and the outer surface of the metal core portion 51a is formed to form a spigot portion 70, which is press-fitted and held in the seal mounting grooves 31, (32). In the example shown in the same figure, the seal mounting grooves 31, (32) are configured with a step portion that also serves as a guide surface 33. Note that if the seal member 50 is a non-contact seal, the seal member 50 may be made of metal only, and its outer circumferential surface may be press-fitted and held in a spigot portion 70 of a similar structure.

[0054] 8, the fixing means utilizes the elastic deformation of the seal member 50 itself to fit into the spigot portion 70. In the example shown in the figure, a plurality of chrysanthemum washer-like slits 51s are provided radially in the circumferential direction, as shown in FIG. 8(b), to stabilize the elastic deformation and holding state of the seal member 50 itself. Also, in the example shown in the figure, the guide surface 33 is provided with a conical surface whose diameter expands outward to make it easier to insert the seal member 50.

[0055] 9, the fixing means is a steel seal member 50 that utilizes its own elastic deformation to fit into the spigot portion 70. In the example shown in the figure, the end portion of the seal member 50 that corresponds to the outer peripheral surface 54 is rounded into a pipe shape, and the fixing portion 51, which is the middle portion, is formed as a slope that projects diagonally outward, so that the elastic deformation and holding state of the seal member 50 itself is stable.

[0056] In the example shown in Figure 10, the fixing means is a two-color molding of the seal member 50, in which a seal main body 52, which is a core metal portion (e.g., iron), and an elastic body portion 51 (e.g., rubber) are bonded together, and a claw portion corresponding to the seal mounting groove 31 is formed on the outer surface 54 of the elastic body portion 51 to form a spigot portion 70, which is engaged and held.

[0057] Furthermore, in the above embodiment, the tongue portion 53 of the sealing member 50 is machined using an end mill or the like to have an arc-shaped end portion that protrudes in the outer diameter direction, but it goes without saying that it is not limited to machining using an end mill and may also be machined into a keyway-like shape using other tools. 11, the tongue portion 53 of the seal member 50 has a rectangular end portion. The axial depth of the fitting recess 34 may also be formed to extend deeper than the axial position of the seal mounting groove 31.

[0058] Furthermore, the shapes of the tongue portion 53 and the fitting recess 34, as well as the combination thereof, are not limited to the examples of the above embodiment and can be modified in various ways. For example, as shown in Fig. 12(a), a tongue portion 53 having an arc-shaped end may be combined with a fitting recess 34 formed of a groove penetrating in the radial direction. As shown in Fig. 1(b), a combination of a tongue portion 53 having a rectangular end and a mating recess 34 consisting of a groove penetrating in the radial direction may be used. As shown in Fig. 1(c), a combination of a tongue portion 53 having a rectangular end and a mating recess 34 consisting of an arc-shaped groove that does not penetrate in the radial direction may be used. [Explanation of symbols]

[0059] 10 Screw shaft 11 (Screw shaft) screw groove 12 Land surface 20 nuts 21 (nut) thread groove 22 Ball inversion section 23 Nut end face 30 Cylindrical part 31 Seal mounting groove 32 Fixed groove 33 Guide surface 34 Fitting recess 40 balls 50 sealing material 51 Fixed part 52 Lip 53 Tongue 54 Outer surface 60 C-type retaining ring (fixing means) 70 Inlay part 100 ball screw

Claims

1. an internal circulation type ball screw comprising: a screw shaft having a helical thread groove on its outer peripheral surface; a nut fitted onto the screw shaft and having a helical thread groove on its inner peripheral surface; a plurality of balls interposed between the thread grooves of the screw shaft and the nut; an annular sealing member that seals between the outer periphery of the screw shaft and the inner periphery of the nut along the outer periphery of the screw shaft; and fixing means for fixing the sealing member to the nut, wherein the plurality of balls circulate via a ball reversal portion formed on the inner peripheral surface of the nut, At least one end of the nut is provided with a spigot portion in which the outer peripheral surface of the sealing member and the inner peripheral surface of the end are fitted coaxially with the screw shaft, a tongue portion protruding in the outer diameter direction at only one location on the outer peripheral surface of the seal member, and a fitting recess portion formed at only one location on the inner peripheral side of the end portion, into which the tongue portion can be inserted along the axial direction, are formed so as to be located at an installation position where the seal shape of the seal member and the outer peripheral shape of the screw shaft are in phase, the mounting positions of the spigot portion and the tongue portion of the seal member are determined based on the axial position and phase of the ball reversal portion; A ball screw characterized by:

2. The ball screw is used in an electric actuator that constitutes a steering mechanism of a vehicle, The nut has a cylindrical portion that extends radially outward from the end portion, 2. The ball screw according to claim 1, wherein an inner ring ball rolling groove of a bearing constituting the electric actuator is integrally formed on the outer peripheral surface of the cylindrical portion.

3. The fixing means is a C-type retaining ring, 3. The ball screw according to claim 1, wherein the seal member is fixed to the end of the nut in the axial direction by the C-shaped retaining ring.

4. 4. The ball screw according to claim 1, wherein the tongue portion has an end portion projecting in the outer diameter direction and having a peripheral edge formed in an arc shape.

5. The ball screw according to any one of claims 1 to 3, wherein the seal shape of the seal member is formed so that the seal shape of the seal member and the outer peripheral shape of the screw shaft are in phase with each other regardless of whether the seal member is assembled from the front or back side.

6. 4. The ball screw according to claim 1, wherein the seal member is provided with a foolproof structure that makes it impossible to assemble the seal member from the opposite side thereof.

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