Patent Application
20220212244
The present invention relates to a shaft member and a method for manufacturing a male shaft. For example, the shaft member has, on an outer peripheral surface thereof, a processing target portion for forming a male-side engagement portion such as a male screw portion. For example, in the method for manufacturing a male shaft, a male shaft is manufactured by rolling-processing a shaft member.
In a machine tool or a position adjusting device of a steering wheel, a rotational motion of a drive source such as an electric motor is converted into a linear motion by a feed screw mechanism. As the feed screw mechanism, there are a slide screw type and a ball screw type.
A feed screw mechanism of a slide screw type includes a screw shaft and a nut.
An outer peripheral surface of the screw shaft has a male screw portion in which a male screw groove having a triangular or trapezoidal cross section is spirally formed. An inner peripheral surface of the nut has a female screw portion in which a female screw groove having a triangular or trapezoidal cross section is spirally formed. The feed screw mechanism is configured by screwing the male screw groove of the screw shaft and the female screw groove of the nut.
A feed screw mechanism of a ball screw type includes a screw shaft, a nut, and a plurality of balls.
An outer peripheral surface of the screw shaft has a male screw portion in which a male screw groove having an arc-shaped cross section is spirally formed. An inner peripheral surface of the nut has a female screw portion in which a female screw groove having an arc-shaped cross section is spirally formed. The plurality of balls are rollably disposed between the male screw groove of the screw shaft and the female screw groove of the nut.
Regardless of whether the feed screw mechanism is a feed screw mechanism of a slide screw type or a feed screw mechanism of a ball screw type, the male screw portion of the screw shaft configuring the feed screw mechanism can be formed by, for example, rolling processing.
JP-A-8-318340 (Patent Literature 1) describes a rolling machine for forming a male screw portion on an outer peripheral surface of a columnar metal material (workpiece material) by rolling processing. In the rolling machine, in a state where both axial end portions of the material are rotatably supported by jigs (center) each having a conical tip end portion, the material is sandwiched between a pair of round dies, the pair of round dies are pressed while being rotated, and thus the male screw portion is rolled on the outer peripheral surface of the material.
Patent Literature 1: JP-A-8-318340
When the male screw portion is rolled on the outer peripheral surface of the material by using the rolling machine described in JP-A-8-318340, recessed holes each having a conical concave surface shape are formed in both axial end surfaces of the material. Then, it is necessary to position the material in a radial direction thereof by abutting conical tip end portions provided on the jig against inner peripheral surfaces of the recessed holes.
When the feed screw mechanism is incorporated into a structure in which another member is pressed by an axial end surface of the screw shaft, or when information for identifying a product is engraved on the axial end surface of the screw shaft, the axial end surface of the screw shaft is preferably a flat surface or a curved surface in which the recessed hole is not present. Therefore, a method of rolling a male screw portion on an outer peripheral surface of a columnar material in a state where tip end portions of a jig are abutted against inner peripheral surfaces of recessed holes formed in both axial end surfaces of the material to position the material in a radial direction thereof, and then cutting and removing an axial end portion of the material is considered.
However, when the axial end portion of the material is cut and removed, if the axial end portion of the material is cut in a state where the material is supported by gripping the male screw portion, the male screw portion may be deformed and the accuracy of the male screw portion may be reduced. That is, when the male screw portion of the screw shaft is gripped and a screw thread of the male screw portion is deformed so as to be recessed (a dent is formed), an inner surface of the screw groove is deformed so as to bulge (rise) accordingly. For example, when a feed screw mechanism of a ball screw type is configured by using a screw shaft in which such deformation occurs, the balls may ride on the bulging portion of the screw groove and the movement of the balls cannot be smoothly performed.
In order to prevent such deformation of the male screw portion, it is required to roll the male screw portion on the outer peripheral surface of the material in a state where the material is positioned in the radial direction thereof without forming recessed holes in the axial end surfaces of the material. Therefore, it is conceivable to support both axial end portions of the material by a jig having a recessed portion having a conical concave surface shape.
Specifically, as shown in
However, also in the above-described method, the following problem may occur. That is, in the method shown in
As a result, after the male screw portion is formed, an operation (processing) for removing the excess portions 104a, 104b is required, and the manufacturing cost is increased. In the example of
In view of the above-described circumstances, an object of the present invention is to provide a structure of a shaft member in which the shape accuracy of a male-side engagement portion is good and the manufacturing cost can be reduced.
The present invention can be configured, for example, as follows.
(1) A shaft member including:
The axial side surface facing the axial direction refers to an axial end surface or a step surface formed on an outer peripheral surface and connecting the small-diameter cylindrical portion and the large-diameter cylindrical portion.
According to the present invention, deformation of the male-side engagement portion can be prevented, and the manufacturing cost can be reduced.
Both of the first and second end surfaces 3a, 3b on both axial sides do not have recessed holes that is opened in the first and second end surfaces 3a, 3b.
In the present embodiment, the first end surface 3a on one axial side (a left side in
The second end surface 3b on the other axial side (a right side in
In the male screw portion 4, a male screw groove 8 having an arc-shaped cross section is formed spirally in an axially intermediate portion of the outer peripheral surface 2 of the male shaft 11.
The feed screw mechanism of a ball screw type is configured by assembling the male shaft 11, a ball nut (not shown) having a female screw portion in which a female screw groove having an arc-shaped cross section is formed spirally on an inner peripheral surface of the ball nut, and a plurality of balls (not shown). That is, the ball nut is disposed around the male screw portion 4 of the male shaft 11, and the balls are rollably disposed between the male screw groove 8 and the female screw groove of the ball nut, thereby configuring the feed screw mechanism.
The male shaft 11 is obtained by rolling a processing target portion 12 of the shaft member 1 as shown in
The processing target portion 12 is disposed at the axially intermediate portion of the outer peripheral surface 2. An outer diameter dimension of the processing target portion 12 is larger than outer diameter dimensions of portions adjacent thereto on both axial sides.
Each of the first and second chamfered portions 7a, 7b is a composite surface formed by combining three or more surfaces. In the composite surface, axially adjacent surfaces are different in an inclination angle or a curvature radius of a generatrix of the surface with respect to a central axis O of the shaft member 1.
The first and second chamfered portions 7a, 7b respectively include first and second supported surface portions 9a, 9b which are respectively disposed at axially intermediate portions of the first and second chamfered portions 7a, 7b and are each inclined radially toward as approaching the male screw portion 4 in the axial direction. In the present embodiment, each of the first and second supported surface portions 9a, 9b is a conical surface having a linear generatrix. In addition, in a cross section in the axial direction (a cross section including the central axis O of the shaft member 1), the first and second end edges 5a, 5b of the outer peripheral surface 2 and the first and second outer peripheral edges 6a, 6b of the first and second end surfaces 3a, 3b on both axial sides are located radially inward than generatrices (including an extension line of the generatrix) α, β of the first and second supported surface portions 9a, 9b. That is, in the cross section in the axial direction (the cross section including the central axis O of the shaft member 1), the first and second end edges 5a, 5b of the outer peripheral surface 2 and the first and second outer peripheral edges 6a, 6b of the first and second end surfaces 3a, 3b on both axial sides are located radially inward than tangent lines at axially intermediate portions of the first and second supported surface portions 9a, 9b.
For this reason, in the present embodiment, in the first and second chamfered portions 7a, 7b, the first chamfered portion 7a on the one axial side which is formed at the connection portion between the first end edge 5a on the one axial side of the outer peripheral surface 2 and the first outer peripheral edge 6a of the first end surface 3a on the one axial side, includes the first supported surface portion 9a and a pair of connection inclined surface portions 10a1, 10a2.
The first supported surface portion 9a is a conical surface that is disposed at an axially intermediate portion of the first chamfered portion 7a on the one axial side and has a linear generatrix inclined radially outward as approaching the other axial side. An inclination angle θa of the generatrix of the first supported surface portion 9a with respect to the central axis O of the shaft member 1 is preferably 20° or more and 60° or less, and is about 30° in the illustrated example.
In the pair of connection inclined surface portions 10a1, 10a2, the connection inclined surface portion 10a1 on the one axial side, that connects the first outer peripheral edge 6a of the first end surface 3a on the one axial side and an end edge on the one axial side of the first supported surface portion 9a, is a convex curved surface having an arc-shaped generatrix inclined radially outward as approaching the other axial side.
In the pair of connection inclined surface portions 10a1, 10a2, the connection inclined surface portion 10a2 on the other axial side, that connects an end edge on the other axial side of the first supported surface portion 9a and the first end edge 5a on the one axial side of the outer peripheral surface 2, is a convex curved surface having an arc-shaped generatrix inclined radially outward as approaching the other axial side.
Each of axial dimensions d10a1, d10a2 of the connection inclined surface portions 10a1, 10a2 is preferably 10% or more and 35% or less of an axial dimension La of the entire first chamfered portion 7a. Each of curvature radiuses of the generatrices of the connection inclined surface portions 10a1, 10a2 is preferably 1% or more and 30% or less of an outer diameter dimension of a portion of the shaft member 1 adjacent to the other axial side of the connection inclined surface portion 10a2 (an outer diameter dimension of the first end edge 5a on the one axial side of the outer peripheral surface 2).
In the first and second chamfered portions 7a, 7b, the second chamfered portion 7b on the other axial side, that connects the second end edge 5b on the other axial side of the outer peripheral surface 2 and the second outer peripheral edge 6b of the second end surface 3b on the other axial side, includes the second supported surface portion 9b and a pair of connection inclined surface portions 10b1, 10b2.
The second supported surface portion 9b is a conical surface that is disposed at an axially intermediate portion of the second chamfered portion 7b on the other axial side and has a linear generatrix inclined radially outward as approaching the one axial side. An inclination angle θb of the generatrix of the second supported surface portion 9b with respect to the central axis O of the shaft member 1 is preferably 20° or more and 60° or less, and is about 30° in the illustrated example.
In the pair of connection inclined surface portions 10a1, 10a2, the connection inclined surface portion 10b1 on the other axial side, that connects the second outer peripheral edge 6b of the second end surface 3b on the other axial side and an end edge on the other axial side of the second supported surface portion 9b, is a convex curved surface having an arc-shaped generatrix inclined radially outward as approaching the one axial side. In the pair of connection inclined surface portions 10b1, 10b2, the connection inclined surface portion 10b2 on the one axial side, that connects an end edge on the one axial side of the second supported surface portion 9b and the second end edge 5b on the other axial side of the outer peripheral surface 2, is a convex curved surface having an arc-shaped generatrix inclined radially outward as approaching the one axial side. Each of axial dimensions d10b1, d10b2 of the connection inclined surface portions 10b1, 10b2 is preferably 10% or more and 35% or less of an axial dimension Lb of the entire second chamfered portion 7b. Each of curvature radiuses of the generatrices of the connection inclined surface portions 10a1, 10a2 is preferably 1% or more and 30% or less of an outer diameter dimension of a portion of the shaft member 1 adjacent to the one axial side of the connection inclined surface portion 10b2 (an outer diameter dimension of the second end edge 5a on the other axial side of the outer peripheral surface 2).
In this way, the pair of connection inclined surface portions 10a1, 10a2 of the first end surface 3a and the pair of connection inclined surface portions 10b1, 10b2 of the second end surface 3b are each set into a gentle R shape, and thus elongation is absorbed by the connection inclined surface portions 10a1, 10a2, 10b1, 10b2 at the time of the rolling processing, and the male shaft 11 can be prevented from extending in the axial direction. The first end surface 3a and the second end surface 3b may have any shape, and can have a shape capable of absorbing the axial elongation of the male shaft 11 at the time of the rolling processing.
As to be described later, before the rolling processing (
Next, a method for manufacturing the male shaft 11 from the shaft member 1 of the present embodiment will be described with reference to
First, the columnar material is obtained by cutting a bar-shaped material, which is made of an iron-based metal such as carbon steel or chromium-molybdenum steel and has a circular cross-sectional shape, into a predetermined length. Next, cutting processing such as cutting and grinding is performed on the material, and the shaft member 1 as shown in
Next, the male shaft 11 is to be obtained by performing the rolling processing on the processing target portion 12 of the shaft member 1 and forming the male screw portion 4. For this purpose, first, as shown in
The jig 13 may be made of, for example, an iron-based metal such as high-speed steel. Alternatively, (i) a portion including at least the tapered surface 35 of the jig 13 is made of cemented carbide or polycrystalline diamond, and/or (ii) mirror finishing is performed on the tapered surface 35, thus frictional resistance with respect to the first and second supported surface portions 9a, 9b can be reduced, and wear of the tapered surface 35 can be prevented. In addition, as a method of preventing the wear of the tapered surface 35 while reducing the cost, a coating layer can also be formed on the tapered surface 35 by a chemical vapor deposition method (CVD), a high-temperature salt bath treatment method (TD method, TD-VC method), or the like. During forming of the male screw portion 4, it is preferable to supply a lubricant or air for lubrication and cooling to sliding contact portions between the tapered surfaces 35 and the first and second supported surface portions 9a, 9b. When a main body portion of the jig 13 and a portion including the tapered surface 35 are made of different materials, adhesiveness between a material forming the main body portion of the jig 13 and a material forming the portion including the tapered surface 35 can be improved by forming a vent hole in the jig 13.
As described above, in a state where both axial end portions of the shaft member 1 are supported by the pair of jigs 13, the pair of round dies 15 approach the shaft member 1 from both radial sides while being rotated. Each of the pair of round dies 15 has screw cutting teeth (not shown) formed spirally on an outer peripheral surface thereof. Therefore, as shown in
In the present embodiment, when the male screw portion 4 is formed by the rolling processing, the tapered surfaces 35 provided on the inner peripheral surfaces of the recessed portions 14 of the pair of jigs 13 are pressed against the first and second supported surface portions 9a, 9b of the first and second chamfered portions 7a, 7b so as to position the shaft member 1 in the radial direction. That is, according to the method for manufacturing the shaft member 1 of the present embodiment, unlike the case of rolling the male screw portion on the outer peripheral surface of the material using a rolling machine described in JP-A-8-318340, it is not necessary to form the recessed holes for abutting the conical tip end portions provided in the jigs against the end surfaces on both axial sides of the material. Therefore, according to the manufacturing method of the present embodiment, after the male screw portion is formed on the outer peripheral surface of the material, it is not necessary to cut and remove the axial end portions of the material in a state where the material is supported by gripping the male screw portion. In short, according to the manufacturing method of the present embodiment, the male screw portion 4 can be prevented from being deformed, and the shape accuracy of the male screw portion 4 can be satisfactorily secured.
Further, in the present embodiment, the both axial end portions of the shaft member 1 are supported by pressing the tapered surfaces 35 provided on the inner peripheral surfaces of the recessed portions 14 of the pair of jigs 13 against the first and second chamfered portions 7a, 7b respectively formed at the connection portions between the first and second end edges 5a, 5b on both axial sides of the outer peripheral surface 2 and the first and second outer peripheral edges 6a, 6b of the first and second end surfaces 3a, 3b on both axial sides. Therefore, deformation in a bending direction can be less likely to occur (buckling deformation can be less likely to occur) even when a force in the axial direction is applied, as compared with a structure in which both axial end portions of the material are supported by abutting the conical tip end portions provided in the jigs against the inner peripheral surfaces of the recessed holes formed in the both axial end surfaces of the material, as in the method described in JP-A-8-318340. From this viewpoint as well, the shape accuracy of the male screw portion 4 can be satisfactorily secured.
In the shaft member 1 of the present embodiment, the first and second end edges 5a, 5b of the outer peripheral surface 2 and the first and second outer peripheral edges 6a, 6b of the first and second end surfaces 3a, 3b are located radially inward than the generatrices α, β of the first and second supported surface portions 9a, 9b in the cross section in the axial direction. Therefore, in a state where the tapered surfaces 35 provided on the inner peripheral surfaces of the recessed portions 14 of the pair of jigs 13 are pressed against the first and second supported surface portions 9a, 9b of the first and second chamfered portions 7a, 7b, the first and second end edges 5a, 5b of the outer peripheral surface 2 of the shaft member 1 and the first and second outer peripheral edges 6a, 6b of the first and second end surfaces 3a, 3b are not in contact with the tapered surfaces 35. Therefore, even if the shaft member 1 is deformed as the tapered surfaces 35 provided on the inner peripheral surfaces of the recessed portions 14 of the jigs 13 are strongly pressed against the first and second supported surface portions 9a, 9b of the first and second chamfered portions 7a, 7b when the male screw portion 4 is rolled, the deformation can be retained in the connection inclined surface portions 10a1, 10a2, 10b1, 10b2 adjacent to the supported surface portions 9a, 9b in the axial direction. In other words, the deformation of the shaft member 1 can be reduced to such an extent that the connection inclined surface portions 10a1, 10a2, 10b1, 10b2 slightly bulge outward in the radial direction. In short, according to the manufacturing method of the present embodiment, the burr or protrusion excess portions 104a, 104b with a small thickness as shown in
In the present embodiment, the male screw portion 4 is rolled by pressing the outer peripheral surface of the shaft member 1 from both radial sides between the pair of round dies 15 having the spiral screw cutting teeth 16 (not shown in
Further, the case of carrying out the method for manufacturing the male shaft of the present invention can be configured such that, as shown in
Further, in the present embodiment, the male shaft 11 is used as a ball screw shaft configuring a feed screw mechanism of a ball screw type, and the male screw portion 4 in which the male screw groove 8 having an arc-shaped cross-sectional shape is spirally formed is formed on the outer peripheral surface 2, but the present invention is not limited to such a structure. Specifically, for example, the male shaft to which the present invention is applied can be applied to a screw shaft configuring a feed screw mechanism of a slide screw type. In this case, the male-side engagement portion provided on the outer peripheral surface is a male screw portion in which a male screw groove having a substantially trapezoidal or triangular cross-sectional shape is formed spirally. Alternatively, the male shaft to which the present invention is applied can be an inner shaft, and the male-side engagement portion can be a male spline portion or a male serration portion formed on the outer peripheral surface.
The first supported surface portion 9a is a conical surface that is disposed at an axially intermediate portion of the first chamfered portion 7c and has a linear generatrix inclined radially outward as approaching the other axial side.
In the pair of step portions 18a, 18b, the step portion 18a on the one axial side connects the first outer peripheral edge 6a of the first end surface 3a and an end edge on the one axial side of the first supported surface portion 9a. The step portion 18a includes a circular ring-shaped flat surface portion 19a that is bent radially inward from the end edge on the one axial side of the first supported surface portion 9a, and a cylindrical surface portion 20a which is bent toward the one axial side from an inner peripheral edge of the flat surface portion 19a, and whose end edge on the one axial side is connected to the first outer peripheral edge 6a of the first end surface 3a.
In the pair of step portions 18a, 18b, the step portion 18b on the other axial side connects an end edge on the other axial side of the first supported surface portion 9a and the first end edge 5a on the one axial side of the outer peripheral surface 2. The step portion 18b includes a circular ring-shaped flat surface portion 19b that is bent radially inward from the first end edge 5a on the one axial side of the outer peripheral surface 2, and a cylindrical surface portion 20b which is bent toward the one axial side from an inner peripheral edge of the flat surface portion 19b, and whose end edge on the one axial side is connected to the end edge on the other axial side of the first supported surface portion 9a.
In the present embodiment, the first end edge 5a on the one axial side of the outer peripheral surface 2 of the shaft member 1a and the first outer peripheral edge 6a of the first end surface 3a are also not in contact with the tapered surface 35 in a state where the tapered surface 35 provided on the inner peripheral surface of the recessed portion 14 of the jig 13 (see
Although the chamfered portion 7c of the present embodiment is provided at the connection portion between the first end edge 5a on the one axial side of the outer peripheral surface 2 and the first outer peripheral edge 6a of the first end surface 3a on the one axial side, the chamfered portion 7c may be provided at the connection portion between the second end edge 5b on the other axial side of the outer peripheral surface 2 and the second outer peripheral edge 6b of the second end surface 3b on the other axial side.
The supported surface portion 9c is disposed at an axially intermediate portion of the chamfered portion 7d, and is a convex curved surface having an arc-shaped generatrix inclined radially outward as approaching the other axial side.
In the pair of step portions 18c, 18d, the step portion 18c on the one axial side connects the first outer peripheral edge 6a of the first end surface 3a and an end edge on the one axial side of the first supported surface portion 9c. The step portion 18c includes a cylindrical surface portion 20c that is bent toward the other axial side from the first outer peripheral edge 6a of the first end surface 3a on the one axial side, and whose end edge on the other axial side is connected to an end edge on the one axial side of the supported surface portion 9c.
In the pair of step portions 18c, 18d, the step portion 18d on the other axial side connects an end edge on the other axial side of the supported surface portion 9c and the first end edge 5a on the one axial side of the outer peripheral surface 2. The step portion 18d on the other axial side includes a circular ring-shaped flat surface portion 19c which is bent radially inward from the first end edge 5a on the one axial side of the outer peripheral surface 2, and whose inner peripheral edge is connected to an end edge on the other axial side of the supported surface portion 9c.
In the present embodiment, the first end edge 5a on the one axial side of the outer peripheral surface 2 of the shaft member la and the first outer peripheral edge 6a of the first end surface 3a are also not in contact with the tapered surface 35 in a state where the tapered surface 35 provided on the inner peripheral surface of the recessed portion 14 of the jig 13 is pressed against the axially intermediate portion of the supported surface portion 9c of the chamfered portion 7d. Therefore, when the male screw portion 4 is rolled, deformation caused by strongly pressing the tapered surface 35 provided on the inner peripheral surface of the recessed portion 14 of the jig 13 against the axially intermediate portion of the supported surface portion 9c of the chamfered portion 7d can be retained in the step portions 18c, 18d. The configuration and the operation and effect of other portions are the same as those of the first embodiment and the second embodiment.
Although the chamfered portion 7d of the present embodiment is provided at the connection portion between the first end edge 5a on the one axial side of the outer peripheral surface 2 and the first outer peripheral edge 6a of the first end surface 3a on the one axial side, the chamfered portion 7d may be provided at the connection portion between the second end edge 5b on the other axial side of the outer peripheral surface 2 and the second outer peripheral edge 6b of the second end surface 3b on the other axial side.
The pair of supported surface portions 9d, 9e are disposed at two positions on an axially intermediate portion of the chamfered portion 7e and each are a conical surface having a linear generatrix inclined radially outward as approaching the other axial side. The pair of supported surface portions 9d and 9e exist on the same conical surface. In a cross section in the axial direction, the first end edge 5a of the outer peripheral surface 2 and the first outer peripheral edge 6a of the first end surface 3a are located radially inward than a generatrix δ of the pair of supported surface portions 9d, 9e disposed at two positions on the axially intermediate portion of the chamfered portion 7e.
Among the three step portions 18e to 18g, the step portion 18e connects the first outer peripheral edge 6a of the first end surface 3a on the one axial side and an one axial side edge of the supported surface portion 9d on the one axial side. The step portion 18e includes a circular ring-shaped flat surface portion 19d that is bent radially inward from the one axial side edge of the supported surface portion 9d on the one axial side, and a cylindrical surface portion 20d which is bent toward the one axial side from an inner peripheral edge of the flat surface portion 19d and whose one axial side edge is connected to the first outer peripheral edge 6a of the first end surface 3a on the one axial side.
Among the three step portions 18e to 18g, the step portion 18f connects the other axial side edge of the supported surface portion 9d on the one axial side and an one axial side edge of the supported surface portion 9e on the other axial side. The step portion 18f includes a circular ring-shaped flat surface portion 19e that is bent radially inward from the one axial side edge of the supported surface portion 9e on the other axial side, and a cylindrical surface portion 20e which is bent toward the one axial side from the flat surface portion 19e and whose one axial side edge is connected to the other axial side edge of the supported surface portion 9d on the one axial side.
Among the three step portions 18e to 18g, the step portion 18g connects the other axial side edge of the supported surface portion 9e on the other axial side and the first end edge 5a on the one axial side of the outer peripheral surface 2. The step portion 18g includes a circular ring-shaped flat surface portion 19f that is bent radially inward from the first end edge 5a on the one axial side of the outer peripheral surface 2, and a cylindrical surface portion 20f which is bent toward the one axial side from the flat surface portion 19f and whose one axial side edge is connected to the other axial side edge of the supported surface portion 9e on the other axial side.
According to the present embodiment, when the male screw portion 4 is formed by rolling processing, a gap can be present over an entire periphery between the tapered surface 35 and the middle step portion 18f among the three step portions 18e to 18g in a state where the tapered surface 35 provided on the inner peripheral surface of the recessed portion 14 of the jig 13 is pressed against the pair of supported surface portions 9d, 9e of the chamfered portion 7e. In present embodiment, grease can be held in such a gap, and when the male screw portion 4 is formed, the chamfered portion 7e of the shaft member 1c can be smoothly slid with respect to the tapered surface 35. Further, when the male screw portion 4 is rolled, deformation caused by strongly pressing the tapered surface 35 against the pair of supported surface portions 9d, 9e of the chamfered portion 7e can be absorbed by the middle step portion 18f to some extent, and an amount of deformation of the step portions 18e, 18g on both axial sides can be reduced. The configuration and the operation and effect of other portions are the same as those of the first embodiment and the second embodiment.
Although the chamfered portion 7e of the present embodiment is provided at the connection portion between the first end edge 5a on the one axial side of the outer peripheral surface 2 and the first outer peripheral edge 6a of the first end surface 3a on the one axial side, the chamfered portion 7e may be provided at a connection portion between the second end edge 5b on the other axial side of the outer peripheral surface 2 and the second outer peripheral edge 6b of the second end surface 3b on the other axial side.
The chamfered portion 7f is formed at a connection portion between an end edge 5c on the one axial side of the large-diameter cylindrical portion 24 and an outer peripheral edge 6c of the step surface 25. The chamfered portion 7f includes a supported surface portion 9f and a pair of connection inclined surface portions 10c1, 10c2. In the present embodiment, the supported surface portion 9f is a conical surface having a linear generatrix. Further, in a cross section in the axial direction (a cross section including the central axis O of the shaft member 1d), the end edge 5c on the one axial side of the large-diameter cylindrical portion 24 and the outer peripheral edge 6c of the step surface 25 are located radially inward than a generatrix (including an extension line of the generatrix) of the supported surface portion 9f.
The supported surface portion 9f is a conical surface that is disposed at an axially intermediate portion of the chamfered portion 7f and has a linear generatrix inclined radially outward as approaching the other axial side.
In the pair of connection inclined surface portions 10c1, 10c2, the connection inclined surface portion 10c1 on the one axial side connects the outer peripheral edge 6c of the step surface 25 and an end edge on the one axial side of the supported surface portion 9f The connection inclined surface portion 10c1 is a convex curved surface having an arc-shaped generatrix inclined radially outward as approaching the other axial side.
In the pair of connection inclined surface portions 10c1, 10c2, the connection inclined surface portion 10c2 on the other axial side connects an end edge on the other axial side of the supported surface portion 9f and the end edge 5c on the one axial side of the large-diameter cylindrical portion 24.
The connection inclined surface portion 10c2 is a convex curved surface having an arc-shaped generatrix inclined radially outward as approaching the other axial side.
Further, the shaft member 1d is provided with a recessed groove 26, which is recessed radially inward, at an end portion on the other axial side of the small-diameter cylindrical portion 23 over an entire periphery thereof.
In the present embodiment, when the male screw portion 4 is formed by the rolling processing, as shown in
When the male screw portion 4 is formed, first, in a state where an end surface on the one axial side of the jig 27 overlaps a tip end surface (an end surface on the other axial side) of the jig 13 on the one axial side in the pair of jigs 13, as shown by a two-dot chain line in
In the present embodiment, in a state where the tapered surface 28 of the jig 27 is pressed against the supported surface portion 9f of the chamfered portion 7f, the end edge 5c on the one axial side of the large-diameter cylindrical portion 24 of the shaft member 1d and the outer peripheral edge 6c of the step surface 25 are not in contact with the tapered surface 28. Therefore, even if the shaft member 1d is deformed by strongly pressing the tapered surface 28 of the jig 27 against the supported surface portion 9f of the chamfered portion 7f when the male screw portion 4 is rolled, the deformation can be retained in the connection inclined surface portions 10c1, 10c2 axially adjacent to the supported surface portion 9f
According to the present embodiment, since the axially intermediate portion can be supported in addition to the both axial end portions of the shaft member 1d, even when an axial dimension of a portion of the outer peripheral surface 2 of the shaft member 1d that is deviated from the male screw portion 4 is long to some extent, the shaft member 1d can be prevented from being bent and deformed (bucked).
Further, in the present embodiment, grease can be held in the recessed groove 26 provided in the end portion on the other axial side of the small-diameter cylindrical portion 23 of the shaft member 1d, and therefore, the chamfered portion 7f of the shaft member 1d can be smoothly slid with respect to the tapered surface 28 of the jig 27 when the male screw portion 4 is formed. The configuration and the operation and effect of other portions are the same as those of the first embodiment.
The stepped cylindrical portion 22 of the present embodiment is provided in a portion of the outer peripheral surface 2a that is deviated to the one axial side from a portion where the male screw portion 4 is formed, but the stepped cylindrical portion 22 be provided in a portion of the outer peripheral surface 2a that is deviated to the other axial side from the portion where the male screw portion 4 is formed.
In the present embodiment, when the male screw portion 4 is formed by the rolling processing, the shaft member 1e is supported by pressing the tapered surface 35 provided on the inner peripheral surface of the recessed portion 14 of the jig 13 against the first supported surface portion 9a of the first chamfered portion 7a formed on one axial end portion of the shaft member 1e, and abutting an outer peripheral surface of the tip end portion 31 provided on the jig 13b against an inner peripheral surface of the recessed hole 30 formed in the end surface 3b on the other axial side of the shaft member 1e. The configuration and the operation and effect of other portions are the same as those of the first embodiment.
The shaft member 1e of the present embodiment includes the male screw portion 4 in a range from the axially intermediate portion to the end edge on the other axial side on the outer peripheral surface 2b, but may include the male screw portion 4 in a range from the axially intermediate portion to the one axial side on the outer peripheral surface 2b. In this case, the shaft member 1e includes only the second chamfered portion 7b at the connection portion between the second end edge 5b on the other axial side of the outer peripheral surface 2b and the second outer peripheral edge 6b of the second end surface 3b on the other axial side, and includes the recessed hole 30 having a conical concave surface shape at a central portion of the first end surface 3a on the one axial side.
The structures of the first to sixth embodiments described above can be implemented in appropriate combinations as long as the embodiments do not cause a contradiction.
The shaft member of the present invention is not limited to the first to sixth embodiments described above. That is, the shaft member of the present invention can include a chamfered portion including at least one supported surface portion disposed at an axially intermediate portion thereof on at least one connection portion in connection portions between an outer peripheral surface and an axial side surface that is an axial end surface or a step surface, and can have a structure in which in a cross section in the axial direction, an axial end edge of the outer peripheral surface and an outer peripheral edge of the axial side surface are located radially inward than a tangent line at an axially intermediate portion of the supported surface portion. Specifically, for example, the shaft member of the present invention can have a structure having only the chamfered portion 7f formed at the connection portion between the large-diameter cylindrical portion 24 and the step surface 25 as in the fifth embodiment shown in
The method for manufacturing a male shaft of the present invention is not limited to the first embodiment to the sixth embodiment described above. That is, the method for manufacturing a male shaft of the present invention can includes a step of performing processing for forming the male-side engagement portion on the outer peripheral surface of the shaft member in a state where the shaft member is positioned in the radial direction by pressing at least the axially intermediate portion of the supported surface portion of the at least one chamfered portion provided on the shaft member against the tapered surface provided on the jig. Specifically, for example, the method for manufacturing the male shaft of the present invention can include a step of performing processing for forming the male-side engagement portion in a state where the axially intermediate portion of the shaft member is supported by pressing the tapered surface 28 of the jig 27 against only the chamfered portion 7f formed at the connection portion between the large-diameter cylindrical portion 24 and the step surface 25, as in the fifth embodiment shown in
In the shaft member of the present invention, for example, the chamfered portion may include a supported surface portion having an arc-shaped cross-sectional shape and a pair of connection inclined surface portions each having an arc-shaped cross-sectional shape. In this case, a curvature radius of the supported surface portion is set to be larger than a curvature radius of each of the connection inclined surface portions.
The male shaft 11 of the present invention can be applied as a screw shaft for a brake actuator.
The brake actuator 200 is used for a vehicle, and is fixed to a suspension device of a vehicle body via a bracket, a housing, or the like. The brake actuator 200 includes a ball screw 210 that is used for nut rotation, a bearing 203 that rotatably supports the ball screw 210 in a housing (not shown), a belt 205 that is connected to a motor or the like and drives a nut 211 (to be described later) of the ball screw 210, and a pressed member 207 that is pressed by the male shaft 11 of the ball screw 210. The nut 211 is not limited to being driven by the belt 205, and may be driven by a gear or the like.
The ball screw 210 includes the male shaft 11, the nut 211, a rolling path 215 formed between the male screw groove 8 on the outer peripheral surface of the male shaft 11 and a female screw groove 213 on an inner peripheral surface of the nut 211, and a plurality of balls 221 disposed in the rolling path 215. A ball circulation method of the ball screw 210 is not particularly limited, and an end cap method, a flop over method, a return tube method, a guide plate method, and the like are appropriately applied.
A recessed portion 209 is formed in a side surface of the pressed member 207. A shape of the recessed portion 209 matches the shape of the first end surface 3a of the male shaft 11. Further, the first end surface 3a of the male shaft 11 is fitted into the recessed portion 209 of the pressed member 207, and thus the pressed member 207 is fixed to the male shaft 11.
In the brake actuator 200, the nut 211 is rotationally driven by a motor or the like via the belt 205, the male shaft 11 advances toward one axial side, and the pressed member 207 is pressed toward the one axial side. Accordingly, the pressed member 207 presses a brake pad against a brake disc, and a braking force is generated on the brake disc.
As described above, the male shaft 11 of the present application can be used as a screw shaft for a brake disc actuator. In particular, the male shaft 11 of the present application is preferable as a screw shaft of a brake actuator because of good shape accuracy.
The present application is based on Japanese Patent Application No. 2019-092097 filed on May 15, 2019, and the contents thereof are incorporated herein as reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2019-092097 | May 2019 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2020/019538 | 5/15/2020 | WO | 00 |
