JP2004218713A - Ball screw device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To consistently obtain operational performance for a long time by sealing a space between a nut member 2 and a screw shaft 3 from the outside in a ball screw device 1 with a plurality of balls 4 interposed between a screw groove 21 formed on the inner circumferential surface of the nut member 2 and screw grooves 31a and 31b formed on the outer circumferential surface of the screw shaft 3. <P>SOLUTION: A cover 10 to cover a portion protruded from one end side of the axial direction of the nut member 2 in the screw shaft 3 is fitted to one end side of the axial direction of the screw shaft 3 while the nut member 2 is separated from the screw shaft 3 to a maximum. Therefore, even when the nut member 2 is separated from the screw shaft 3 to a maximum, the portion protruded from one end side of the axial direction of the nut member 2 in the screw shaft 3 is not exposed outside, and the space between the screw shaft 3 and the nut member 2 is sealed from the outside. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a ball screw device.
[0002]
[Prior art]
In a conventional ball screw device, a plurality of balls are interposed between a screw groove provided on an inner peripheral surface of a nut member and a screw groove provided on an outer peripheral surface of a screw shaft, and between the nut member and the screw shaft. The torque is converted into thrust or the thrust is converted into torque (see Patent Document 1).
[0003]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2002-257208
[Problems to be solved by the invention]
In the above-described conventional example, for example, in a situation where the nut member is moved in the axial direction by rotating the nut member by supporting the screw shaft non-rotatably and axially immovably, the nut member and the screw shaft overlap. When the nut member is separated from the screw shaft so as to minimize the region, a region extending from substantially the center in the axial direction of the screw shaft to the other end is exposed to the outside. In this state, if foreign matter (for example, dust or water) exists outside, the foreign matter may enter between the screw shaft and the nut member.
[0005]
[Means for Solving the Problems]
In a ball screw device according to the present invention, a plurality of balls are interposed between a screw groove provided on an inner peripheral surface of a nut member and a screw groove provided on an outer peripheral surface of a screw shaft, and the nut member and the screw shaft are provided. Between the torque and the thrust, or to convert the thrust into a torque, at one axial end of the screw shaft, in a state where the nut member and the screw shaft are maximally separated, the nut member of the screw shaft A cover is provided to cover a portion protruding from one end in the axial direction.
[0006]
In this case, by maximally separating the nut member and the screw shaft, the portion of the screw shaft protruding from the nut member can be covered and covered by the cover. Since the projecting portion of the screw shaft is not exposed to the outside in this manner, even when foreign matter such as dust or water exists outside, the foreign matter can be prevented from entering between the nut member and the screw shaft. .
[0007]
By the way, the cover has a mounting portion fixed to one axial end of the screw shaft, a coupling portion extending radially outward from the mounting portion, and from the coupling portion to the other axial end of the nut member. An outer cylinder portion extending in the axial direction toward the outer cylinder portion, in a state in which the nut member and the screw shaft are maximally separated from each other, while completely covering a portion of the screw shaft projecting from the nut member. The nut member may be set to have an axial length so as to cover even one end side in the axial direction of the nut member, and may be set to have an inner diameter opposed to the outer peripheral surface of the nut member via a minute gap.
[0008]
With a cover having such a simple shape, it is easy to form a pressed product of a metal plate or a molded product of a synthetic resin.
[0009]
Further, a lip that is in sliding contact with the outer peripheral surface of the nut member may be provided at an end edge of the outer cylindrical portion.
[0010]
In this case, the sealing performance of each thread groove of the nut member and the screw shaft can be further improved as compared with the above configuration.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
1 to 4 show one embodiment of the present invention. The illustrated ball screw device 1 includes a nut member 2, a screw shaft 3, and a plurality of balls 4, and is called a total ball type.
[0012]
The nut member 2 is formed with a single thread groove 21 continuous over its entire length. The screw shaft 3 is formed with two screw grooves 31a and 31b independent of each other in an axially intermediate region. Each of the thread grooves 31a and 31b has a length of less than one turn, that is, about one turn. The thread groove 21 of the nut member 2 and the thread grooves 31a and 31b of the screw shaft 3 are set to the same lead angle. The cross-sectional shape of the thread grooves 21, 31a, 31b is a Gothic arc shape, but may be a semicircular shape.
[0013]
In addition, the thread (land portion) 32 existing between the two thread grooves 31a and 31b of the screw shaft 3 is connected to the upstream side and the downstream side of the two thread grooves 31a and 31b by communicating with each other. Ball circulation grooves 33 and 34 are provided as independent closed loops. The cross-sectional shapes of the ball circulation grooves 33 and 34 are the same as the cross-sectional shapes of the screw grooves 21, 31a and 31b.
[0014]
A plurality of balls 4 are rolled and circulated in the two thread grooves 31a and 31b closed by the ball circulation grooves 33 and 34, respectively. The ball 4 that has entered the ball circulation grooves 33 and 34 once sinks to the inner diameter side, climbs over the screw thread (land portion) 22 of the nut member 2, and then floats up to the outer diameter side and exits. For this reason, in the ball circulation grooves 33 and 34, the intermediate region has a curved shape (concave shape) so as to sink inward in the radial direction, and both end regions of the ball circulation grooves 33 and 34 have the diameters. It has a curved shape (convex shape) so as to bulge outward in the direction.
[0015]
Next, the operation will be described. For example, if the screw shaft 3 is not rotated and immovable in the axial direction and the nut member 2 is rotated, the nut member 2 moves on the screw shaft 3 in the axial direction. The axial dimension of the nut member 2 is set slightly larger than that of the screw shaft 3, whereby the nut member 2 can completely cover the screw shaft 3 depending on the rotational position of the nut member 2. Has become. FIG. 1 shows a state in which the screw shaft 3 is completely covered and hidden by the nut member 2. FIG. 2 shows a state in which the nut member 2 and the screw shaft 3 are separated to the maximum. In addition, a usage pattern in which one of the nut member 2 or the screw shaft 3 is rotated to move the other in the axial direction, or a usage pattern in which one of the nut member 2 or the screw shaft 3 is moved in the axial direction to rotate the other. It can also be in the form.
[0016]
Meanwhile, a bracket 5 with a gear 6 is attached to the left end side of FIG. 1 in the nut member 2, and the nut member 2 is rotated by inputting rotational power to the gear 6.
[0017]
The bracket 5 is formed into an annular shape by pressing a thin steel plate, and includes a folded tube portion 51, a shaft end tube portion 52 that continues in one axial direction of the folded tube portion 51, and a shaft end tube portion. 52 includes a rising portion 53 that rises radially outward from the left end side in FIG. 1, and a metal core portion 54 on which the synthetic resin gear 6 is integrally formed.
[0018]
The left end side in FIG. 1 of the nut member 2 is fitted and fixed to the inner periphery of the folded tubular portion 51 of the bracket 5. In order to integrate the bracket 5 and the nut member 2 in the rotational direction, the bracket 5 is directed radially inward with respect to several circumferential points (six in the illustrated example) at the inner diameter side end of the folded tubular portion 51 of the bracket 5. While the protruding protrusion 55 is provided, the nut member 2 is provided with the concave portion 24 with which the plurality of protrusions 55 are fitted in the left end side in FIG. That is, the nut member 2 and the bracket 5 are integrated in the rotation direction by the fitting of the recess 24 and the projection 55.
[0019]
The bracket 5 is provided to stop the movement of the nut member 2 in a state where the entire screw shaft 3 is covered with the nut member 2 and the overlapping area between the screw shaft 3 and the nut member 2 is maximized. One of the protrusions 55 (referred to as a stopper protrusion) 55a is used. Specifically, the stopper projection 55a has a circumferential width and a radial length larger than those of the other projections 55, and a bent portion 56 extending in the axial direction is provided at an inner diameter end. On the other hand, a stopper groove 37 into which the stopper projection 55a enters and abuts at a predetermined position in the circumferential direction with respect to the inner diameter surface on the left end side in FIG. In other words, by moving the nut member 2 and the bracket 5 to the right side in FIG. 1 while rotating, when the stopper protrusion 55 a of the bracket 5 comes into contact with the end of the stopper groove 37 of the screw shaft 3, the nut The member 2 is forcibly stopped.
[0020]
In this embodiment, the nut member 2 and the screw shaft 3 are maximally separated from one end side in the axial direction (the right end side in FIG. 1) of the screw shaft 3 and one end side in the axial direction of the nut member 2 (in FIG. 1). A cover 10 for covering the screw shaft 3 protruding from the right end) from the outside is attached.
[0021]
The cover 10 includes an inner tubular portion 11, an outer tubular portion 12, and a coupling portion 13 that integrally connects one end side in the axial direction (the right end side in FIG. 1). The cover 10 is manufactured by, for example, pressing a thin steel plate of JIS standard SPCC or the like, but can also be manufactured of a synthetic resin or the like.
[0022]
The inner cylindrical portion 11 is fixed by press-fitting to the cylindrical outer peripheral surface at one axial end (right end in FIG. 1) where the screw shaft 3 does not have the thread grooves 31a and 31b and the ball circulation grooves 33 and 34. Have been. The axial length of the inner cylindrical portion 11 is set to a dimension necessary to secure a predetermined fixing strength, and is set shorter than that of the outer cylindrical portion 12. The inner cylindrical portion 11 corresponds to a mounting portion described in claims.
[0023]
The outer cylindrical portion 12 is set to have an inner diameter slightly larger than the outer diameter of the nut member 2, and the nut member 2 is separated from the screw shaft 3 to the maximum, that is, the nut member 2 is separated from the nut member 2. A shaft that completely covers the portion of the screw shaft 3 protruding from the nut member 2 while also minimizing the overlapping area with the screw shaft 3 and also covers one end side (the right end side in FIG. 1) of the nut member 2 in the axial direction. Direction length is set. The gap between the outer cylindrical portion 12 and the outer peripheral surface of the nut member 2 is set to be minute, but since the outer peripheral surface of the nut member 2 is polished in the first place, the clearance can be precisely controlled.
[0024]
Further, the connecting portion 13 is formed flat so as to extend in the radial direction. When the inner cylindrical portion 11 is attached to the screw shaft 3, the flat outer surface of the connecting portion 13 is connected to one end of the screw shaft 3 in the axial direction. It is positioned so as to be flush with the edge.
[0025]
With such a cover 10, as shown in FIG. 1, when the screw shaft 3 is completely covered by the nut member 2, the right side of the nut member 2 in the figure is the outer cylinder of the cover 10. It penetrates the inner diameter side of the part 12. At this time, the right end surface in the figure of the nut member 2 is in contact with the inner surface of the coupling portion 13. However, it may be in a state of facing non-contact. From this state, when the nut member 2 is moved to the left side in the figure by rotating the nut member 2, the right side part in the figure on the screw shaft 3 gradually projects from the nut member 2; As shown in FIG. 5, even when the overlapping area between the screw shaft and the nut member 2 is minimized by maximally separating the nut member 2 with respect to the screw shaft 3, the outer cylindrical portion 12 of the cover 10 The protruding part is covered and hidden.
[0026]
As described above, the portion of the screw shaft 3 protruding from the nut member 2 can be completely covered and covered by the cover 10 by maximally separating the nut member 2 from the screw shaft 3. As described above, since the projecting portion of the screw shaft 3 is not exposed to the outside, even if foreign matter such as dust or water exists outside, the foreign matter can be prevented from entering between the nut member 2 and the screw shaft 3. Become like
[0027]
Next, another embodiment of the present invention will be described with reference to FIGS. The ball screw device 1 in this embodiment is of a type in which a ball 4 is held by a retainer ring 7.
[0028]
Specifically, a single thread groove 21 that is continuous over the entire length is formed on the inner peripheral surface of the nut member 2. On the outer peripheral surface of the screw shaft 3, a single screw groove 31 that is continuous over substantially the entire length is formed. The thread groove 21 of the nut member 2 and the thread groove 31 of the screw shaft 3 have the same lead angle. The cross-sectional shape of the thread grooves 21 and 31 is a Gothic arc shape, but may be a semicircular shape.
[0029]
A plurality of balls 4 are interposed between the screw groove 21 of the nut member 2 and the screw groove 31 of the screw shaft 3. The number of the balls 4 used is such that the balls 4 are arranged within a range of three turns of the two screw grooves 21 and 31 with a predetermined gap therebetween.
[0030]
The retainer ring 7 is interposed between the nut member 2 and the screw shaft 3 so as to be in non-contact with each other, and is provided with axially long pockets 71 at several places on the circumference. The pocket 71 is set to be longer than the axial length of three turns of each of the screw grooves 21 and 31, and is arranged in a state of being shifted in the axial direction toward one circumferential direction.
[0031]
In this embodiment, the same cover 10 as in the above embodiment is used. The cover 10 is press-fitted and fixed to the outer peripheral surface of a small-diameter cylindrical portion in which the inner cylindrical portion 11 is integrally formed on one end side (right end side in the figure) of the screw shaft 3 in the axial direction. The function of the cover 10 is the same as that of the above embodiment, and the ball circulation path can be sealed from the outside.
[0032]
The operation of the ball screw device 1 in this embodiment is basically the same as in the above embodiment. During operation, the amount of axial movement of the retainer ring 7 is regulated by the protrusion 55 of the bracket 5 and the cover 10 so as not to protrude from the area where the nut member 2 and the screw shaft 3 are opposed to each other. .
[0033]
Note that the present invention is not limited to only the above-described embodiment. For example, as shown in FIG. 8 and FIG. In this case, the sealing performance of the screw grooves 21 and 31 of the nut member 2 and the screw shaft 3 can be further improved as compared with the above embodiment.
[0034]
【The invention's effect】
In the present invention, the part protruding from the one axial end of the nut member in the screw shaft by maximally separating the nut member and the screw shaft can be covered from the outside with a cover having a simple configuration. Foreign matter can be prevented from entering between the nut member. Therefore, the operating performance of the ball screw device can be stabilized for a long period of time, and this greatly contributes to the improvement of reliability.
[Brief description of the drawings]
1 is a cross-sectional view of a ball screw device according to an embodiment of the present invention; FIG. 2 is a diagram showing a state in which a nut member and a screw shaft are maximally separated in FIG. 1; FIG. 4 is a side view schematically showing the ball circulation path in FIG. 1. FIG. 5 is a cross-sectional view of a ball screw device according to another embodiment of the present invention. FIG. FIG. 7 is an exploded perspective view of the ball screw device of FIG. 5 in a state in which the screw shaft is maximally separated from the screw shaft. FIG. 8 is a sectional view of a ball screw device according to still another embodiment of the present invention. FIG. 8 shows a state in which the nut member and the screw shaft are pulled apart to the maximum.
2 nut member 21 nut member screw groove 3 screw shaft 31a, 31b screw shaft screw groove 4 ball 10 cover

Claims (3)

A plurality of balls are interposed between the screw groove provided on the inner peripheral surface of the nut member and the screw groove provided on the outer peripheral surface of the screw shaft, and a torque is applied between the nut member and the screw shaft to provide thrust. Or a ball screw device that converts thrust to torque,
A ball is provided at one axial end of the screw shaft, the cover covering a portion of the screw shaft protruding from one axial end of the nut member in a state where the nut member and the screw shaft are maximally separated from each other. Screw device. The cover has a mounting portion fixed to one end in the axial direction of the screw shaft, a coupling portion extending radially outward from the mounting portion, and from the coupling portion toward the other axial end of the nut member. An outer cylinder portion extending in the axial direction,
An axial direction in which the outer cylinder portion completely covers a portion of the screw shaft protruding from the nut member and also covers one end side of the nut member in the axial direction in a state where the nut member and the screw shaft are maximally separated from each other. 2. The ball screw device according to claim 1, wherein the ball screw device is set to have a length and an inner diameter opposed to an outer peripheral surface of the nut member via a minute gap. The ball screw device according to claim 2, wherein a lip that is in sliding contact with an outer peripheral surface of the nut member is provided at an end edge of the outer cylindrical portion.

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