JP4888681B2 - Ball screw mechanism - Google Patents

Description

  The present invention relates to a ball screw mechanism that can be used for various applications such as an electric actuator.

  In recent years, labor saving of vehicles and the like has progressed, and for example, a system for operating a transmission, a parking brake, and the like of an automobile not by hand but by the power of an electric motor has been developed. An electric actuator used for such an application may use a ball screw mechanism in order to convert the rotational motion transmitted from the electric motor into the axial motion with high efficiency.

  Here, the normal ball screw mechanism consists of a screw shaft, a nut, and a ball. When the nut rotates relative to the screw shaft, the ball rolls along the rolling path in the nut, Although a smooth operation is performed, a circulation member for circulating the ball that has reached one end of the rolling path to the other end is required. As such a circulation member, a tube, a top, etc. are known.

However, for example, various techniques for fixing the top to the nut are known, but in order to easily fix the top to the nut without using other members, as described in Patent Document 1, There is a technique for fixing to a nut by plastic deformation.
Japanese Patent No. 2760455 Utility Model Registration No. 2595551 Specification

  According to Patent Document 1, a jig with a sharp tip is pressed from the outside in the radial direction of the nut against the back surface of the top mounted in the nut mounting hole, and the back surface of the top is plastically deformed. The frame is fixed by the friction holding force generated between the frame and the mounting hole. However, in the technique of Patent Document 1, the frictional holding force between the two greatly fluctuates due to variations in the dimensions of the nut mounting holes, variations in the frame dimensions, variations in the pressing force of the jig, etc., and in some cases, the fixing is insufficient. There is a risk of becoming.

  On the other hand, in Patent Document 2, a groove portion is provided in the nut mounting hole, and a jig with a sharp tip from the outside in the radial direction of the nut is pressed against the back surface of the top mounted in the mounting hole so that the back surface of the top is fixed. A technique is disclosed in which a part is plastically deformed and enters a groove portion. According to such a technique, even if there are variations in the dimensions of the nut mounting holes, variations in the frame dimensions, variations in the pressing force of the jig, etc., the dovetail groove portion absorbs them, so the frame can be fixed more reliably. Can do. However, in the technique of Patent Document 2, the shape of the dovetail portion is a tapered shape that gradually decreases in diameter as it goes outward in the radial direction of the nut. There's a problem. Further, when the piece is deformed by a jig with a strong pressing force, the circulation groove of the piece on which the ball rolls may be deformed, thereby making it impossible to smoothly circulate the ball.

  The present invention has been made in view of the problems of the prior art, and an object of the present invention is to provide a ball screw mechanism that can suppress malfunction even though it is easy to manufacture.

The ball screw mechanism of the present invention is
A screw shaft having a male screw groove formed on the outer peripheral surface;
A nut disposed so as to surround the screw shaft and having an internal thread formed on an inner peripheral surface thereof;
A plurality of balls arranged to freely roll along a rolling path formed between opposing screw grooves;
A circulation member that is attached to the attachment hole of the nut and returns the ball from one end of the rolling path to the other end;
The mounting hole has an inner peripheral surface with an enlarged portion whose size is larger in the radial inner direction than the radially outer side of the nut, and the circulating member is a claw that engages with the enlarged portion by bending. In the ball screw mechanism having a part,
The claw portion extends along the insertion direction from the surface opposite to the circulation groove of the circulation member when the circulation member is assembled, and after the circulation member is inserted into the attachment hole, It is designed to be bent outward so as to engage with the enlarged portion of the inner peripheral surface of the mounting hole,
When the circulation groove formed in the circulation member receives a force from the rolling ball , the claw portion is biased in a direction to engage with the enlarged portion,
A pair of the claw portions are provided, and the enlarged portion of the attachment hole has a pair of inclined surfaces that are close to each other as they go inward in the radial direction of the nut, and a pair of steps that are connected to the inclined surfaces and contact the tips of the claw portions. The claw portion is in contact with the inclined surface.

  According to the ball screw mechanism of the present invention, the attachment hole has an inner peripheral surface having an enlarged portion whose size is larger in the radial inner direction than in the radial outer direction, and the circulation member is bent to Since the claw portion engages with the enlarged portion, the claw portion engages with the enlarged portion only by bending the claw portion after the circulating member is loaded into the mounting hole of the nut, Thus, the circulating member can be easily assembled to the nut with a slight force. Further, even when the claw portion is bent, for example, deformation is hardly transmitted to the circulation groove in which the ball of the circulation member rolls, so that smooth rolling of the ball can be ensured.

  Furthermore, the claw portion is engaged with the enlarged portion when the circulation groove formed in the circulation member extends in a direction in which a compression force is generated when receiving force from the rolling ball. The claw portion can support the force that the circulation groove receives from the ball.

  Furthermore, a pair of the claw portions are provided, and the enlarged portion of the attachment hole has a pair of slopes that are close to each other as they go inward in the radial direction of the nut, and a pair of tips that are connected to the slopes and in contact with the tips of the claws. Therefore, if the claw portion is brought into contact with the stepped portion, even if a force directed radially outward from the ball is transmitted to the circulating member, the stepped portion The claw portion is reliably supported by the reaction force, so that the circulation member is prevented from coming off. Moreover, since the buckling of the claw portion is suppressed by the slope, the rigidity of the claw portion can be reduced, and the influence on the circulation groove of the circulation member at the time of bending can be further reduced.

  Next, embodiments of the present invention will be described with reference to the drawings. 1 is a top view of the ball screw mechanism according to the present embodiment, and FIG. 2 is a cross-sectional view of the ball screw mechanism of FIG. FIG. 3 is a cross-sectional view of the ball screw mechanism of FIG. 2 taken along line III-III and viewed in the direction of the arrow. 4-6 is the figure which cut | disconnected the nut concerning this Embodiment by the IV-IV line | wire of FIG. 1, and looked at the arrow direction, and has shown it with the top.

  1 and 2, a screw shaft 1 connected to a motor (not shown) is supported so as to be rotatable only. In the drawing, a male screw groove 1 a is formed on the outer peripheral surface of the screw shaft 1, although it is schematically shown. A substantially cylindrical nut 2 connected to a driven member (not shown) and supported so as to be movable only in the axial direction is arranged so as to surround the screw shaft 1 and has two female screws on the inner peripheral surface. Grooves 2a and 2a are formed. A plurality of balls 3 are arranged so as to be able to roll in two spiral rolling paths formed between the opposing screw grooves 1a, 2a.

  As shown in FIG. 3, on the outer periphery of the nut 2, two top mounting holes 2b, 2b are provided side by side in the axial direction so as to penetrate in the radial direction. As shown in FIG. 4, each mounting hole 2 b has an inner peripheral surface provided with enlarged portions 2 c and 2 c whose dimensions (inner width) are larger in the radial inner side than in the radial outer side of the nut 2. . Two enlarged portions 2c provided at a 180 degree phase with respect to each mounting hole 2b are a step portion connected to a slope 2d that is closer to each other as it goes inward in the radial direction of the nut 2, and a radially outer end of the slope 2d. 2e. In addition, positioning recesses 2g and 2g are formed in the vicinity of the mounting holes 2b and 2b of the nut 2, and a step 2f (one figure lower than the outer periphery) is formed between the mounting holes 2b and 2b. 2) is formed.

  The top 4 as a circulation member is provided on the outer periphery of the two cylindrical portions 4a and 4a that are fitted and disposed in each hole 2b, the plate portion 4b that connects the cylindrical portions 4a and 4a, and the cylindrical portions 4a and 4a. Positioning protrusions 4c and 4c, S-shaped circulation grooves 4d and 4d provided on the lower surface (the surface which is the inner side when assembled to the nut 2) in FIG. 2 of the cylindrical portions 4a and 4a, the cylindrical portion 4a, The claw portions 4e and 4e provided on the upper surface in FIG. 2 of 4a are integrally formed. Two claw portions 4e and 4e are provided so as to extend outward in the radial direction of the nut 2 at a phase of 180 degrees in each cylindrical portion 4a.

  The operation of the present embodiment will be described. When power from an electric motor (not shown) is transmitted to the screw shaft 1, the top 4 from one end to the other end of the rolling path formed by the male screw groove 1a and the female screw 2a. By the balls 3 circulating through the circulation grooves 4d and 4d, the rotational motion is efficiently converted into the axial motion of the nut 2, and the driven member (not shown) can be moved in the axial direction.

  A mode in which the frame 4 is assembled will be described. In the following description, only one cylindrical portion 4a will be described, but the other cylindrical portion 4a is similarly processed. In FIG. 4, when the positioning projections 4 c and 4 c of the top 4 are aligned with the recesses 2 g and 2 g of the nut 2 and the top 4 is brought close to the nut 2, the cylinder 4 is cylindrical with respect to the mounting holes 2 b and 2 b of the nut 2. Part 4a, 4a comes to fit. When the plate portion 4b of the top 4 is placed on the stepped portion 2f of the nut 2, the claw portions 4c and 4c reach positions corresponding to the enlarged portions 2c and 2c.

  Here, using a tool (not shown), a force is applied as shown by an arrow in FIG. 5, and the claws 4c and 4c are bent and spread. The claw portions 4c and 4c are thinner and less rigid than the cylindrical portion 4a, so that the claw portions 4c and 4c are easy to bend. Further, even when the claw portions 4c and 4c are bent, the claw portions 4c and 4c have the shape of the circulation groove 4d formed on the lower surface of the cylindrical portion 4a. It is designed not to affect. In such a state, the claw portions 4c and 4c extend in a direction in which the circulation groove 4d formed in the circulation member 4 generates a compressive force when receiving a force from the rolling ball 3.

  The claw portions 4c and 4c bent in the mounting hole 2b of the nut 2 bend along the inclined surfaces 2d and 2d, and the tips thereof face the step portions 2e and 2e. In this state, as shown in FIG. 6, when the thrust force F is applied to the top 4 from the ball 3 rolling in the circulation groove 4d of the top 4, the claw portions 4c and 4c come into contact with the step portions 2e and 2e. The thrust force F can be supported by receiving the reaction force F / 2. In addition, since the side surfaces of the claw portions 4c and 4c are supported by the inclined surfaces 2d and 2d, deformation such as buckling is avoided.

  The present invention has been described above with reference to the embodiments. However, the present invention should not be construed as being limited to the above-described embodiments, and can be modified or improved as appropriate. For example, before assembling, the claw portions 4c and 4c of the frame 4 are formed so that the claw portions 4c and 4c are slightly expanded. If the claw portions 4c and 4c return from elastic deformation and face the step portions 2e and 2e, it is not necessary to spread the claw portions 4c and 4c with a jig or the like, and the assembly is further simplified. Is done.

It is a top view of the ball screw mechanism which is this Embodiment. It is sectional drawing which cut | disconnected the ball screw mechanism of FIG. 1 by the II-II line | wire, and looked at the arrow direction. FIG. 3 is a cross-sectional view of the ball screw mechanism of FIG. 2 taken along line III-III and viewed in the direction of the arrow. FIG. 4 is a view of the nut according to the present embodiment taken along line IV-IV in FIG. 1 and viewed in the direction of the arrow, showing a state before the frame 4 is assembled. The nut concerning this Embodiment is the figure which cut | disconnected the IV-IV line | wire of FIG. 1, and was seen in the arrow direction, and shows the state which bent the nail | claw parts 4c and 4c of the top 4. FIG. FIG. 4 is a view of the nut according to the present embodiment taken along line IV-IV in FIG. 1 and viewed in the direction of the arrow, and shows a state in which the circulation groove 4 d receives a thrust force F from the ball 3.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Screw shaft 1a Male thread groove 2 Nut 2a Female thread groove 2b Attachment hole 2c Enlarged part 2d Slope 2e Step part 2f Step part 2g Recess 3 Ball 4 Top 4a Cylindrical part 4b Plate part 4c Claw part 4c Projection 4d Circulation groove 4e Claw part

Claims (2)

A screw shaft having a male screw groove formed on the outer peripheral surface;
A nut disposed so as to surround the screw shaft and having an internal thread formed on an inner peripheral surface thereof;
A plurality of balls arranged to freely roll along a rolling path formed between opposing screw grooves;
A circulation member that is attached to the attachment hole of the nut and returns the ball from one end of the rolling path to the other end;
The mounting hole has an inner peripheral surface with an enlarged portion whose size is larger in the radial inner direction than the radially outer side of the nut, and the circulating member is a claw that engages with the enlarged portion by bending. In the ball screw mechanism having a part,
The claw portion extends along the insertion direction from the surface opposite to the circulation groove of the circulation member when the circulation member is assembled, and after the circulation member is inserted into the attachment hole, It is designed to be bent outward so as to engage with the enlarged portion of the inner peripheral surface of the mounting hole,
When the circulation groove formed in the circulation member receives a force from the rolling ball , the claw portion is biased in a direction to engage with the enlarged portion,
A pair of the claw portions are provided, and the enlarged portion of the attachment hole has a pair of inclined surfaces that are close to each other as they go inward in the radial direction of the nut, and a pair of steps that are connected to the inclined surfaces and contact the tips of the claw portions. A ball screw mechanism , wherein the claw portion abuts along the slope . The ball screw mechanism according to claim 1 , wherein the rolling ball presses only a central portion of a circulation groove formed in the circulation member .

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