JP2018115688A - Feed screw - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a feed screw capable of preventing lubricant sealed in a nut inner space from leaking, and foreign matter from entering the nut inner space from the outside, without increasing rotational resistance of a screw shaft.SOLUTION: A feed screw includes a screw shaft 1 on an outer periphery of which a male screw 5 is formed, and a cylindrical nut 2 on an inner peripheral of which a female screw 6 directly or indirectly screwed into the male screw 5 is formed. On the inner surface of the nut 2, an implanting part 16 is formed, which is obtained by implanting a plurality of fibers 17. The feed screw is, for example, a ball screw where between a screw groove 5a of the male screw 5 and a screw groove 6a of the female screw 6 a plurality of balls 3 is interposed, which rolls along the screw grooves 5a, 6a. The implanting part 16 is desirably formed within the whole circumference on the inner peripheral surface of the nut 2.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a feed screw such as a ball screw used in a power steering device of an automobile, a machine tool, and the like, and more particularly to a technique for improving a lubricant holding capability.

  Ball screws, which are a kind of feed screw, are used in various technical fields such as automobile power steering devices and machine tools. In the ball screw, a plurality of balls are movably interposed between a thread groove of a male screw formed on the outer periphery of the screw shaft and a thread groove of a female screw formed on the inner periphery of the nut. In the nut inner space formed by the gap between the screw shaft and the nut, the screw shaft and each screw groove of the nut and a lubricant for lubricating the ball are enclosed. In order to prevent the leakage of the lubricant from the inner space of the nut and the entry of foreign matter from the outside into the inner space of the nut, a seal may be provided at the axial end of the inner periphery of the nut (for example, Patent Document 1).

Japanese Patent No. 4967809

  If a seal is provided on the inner periphery of the nut as in Patent Document 1, it is possible to prevent leakage of lubricant and entry of foreign matter, but friction between the seal and the screw shaft occurs, and the rotational resistance of the screw shaft is reduced. growing. For this reason, there exists a subject that the torque of the motor which rotates a screw shaft becomes high.

  An object of the present invention is to provide a feed screw capable of preventing leakage of a lubricant enclosed in a nut inner space and entry of foreign matter from the outside into the nut inner space without increasing the rotational resistance of the screw shaft. It is to be.

  The feed screw according to the present invention includes a screw shaft having a male screw formed on the outer periphery, and a cylindrical nut having a female screw that is directly or indirectly screwed to the male screw on the inner periphery. A flocked portion formed by flocking a plurality of fibers is formed on the surface.

  According to this configuration, since the flocked portion formed on the inner peripheral surface of the cylindrical nut closes the nut inner space formed by the gap between the screw shaft and the nut, the nut is enclosed in the nut inner space. It is possible to prevent the existing lubricant from leaking outside. Specifically, the lubricant located in the vicinity of the flocked portion in the inner space of the nut is captured by the fibers of the flocked portion and held in a stable state, so that the flocked portion seals the inner space of the nut and the outside. Works and prevents lubricant leakage. Further, since the flocked portion functions as a hermetic seal, it is possible to prevent foreign matters such as dust from entering the space inside the nut from the outside.

In the present invention, the feed screw may be a ball screw in which a plurality of balls rolling along the screw grooves are interposed between the screw grooves of the male screw and the screw grooves of the female screw.
When the feed screw is a ball screw, the same operations and effects as described above can be obtained.

In this invention, it is preferable that the flocked portion is formed in the entire circumference of the inner circumferential surface of the nut.
In this case, leakage of the lubricant from the inner space of the nut and entry of foreign matter into the inner space of the nut can be prevented over the entire circumference of the inner peripheral surface of the nut.

In this invention, the said hair transplant part is good to be located in the edge part of the axial direction in the internal peripheral surface of the said nut.
If the hair transplant part is formed in the said location, since the space in a nut and the exterior are shielded by the hair transplant part at the edge part of an axial direction, the room for a foreign material to enter into the space in a nut can be decreased.

In the present invention, it is preferable that the flocked portion holds a lubricant before use.
In this case, since the sealing property between the inner space of the nut and the outside is good before the start of use, it is possible to prevent the leakage of the lubricant and the entry of foreign matter until the start of use. Moreover, since not only the lubricant enclosed in the space in the nut but also the lubricant previously held in the flocked portion is used for lubrication, the feed screw can be operated for a long time.

In this invention, the front-end | tip of the said fiber of the said hair transplant part may be contacting the screw thread of the said external thread.
When the tip of the fiber of the flocked portion is in contact with the thread of the male screw, the sealing property between the inner space of the nut and the outside is further enhanced. Since the contact between the fiber tip and the guide rail is light fiber, there is no great resistance when the screw shaft rotates.

In the present invention, the fibers are preferably made of synthetic resin, for example, polyamide.
Synthetic resins are not chemically swelled or dissolved by oil, are chemically stable, can produce a large amount of homogeneous fibers, and can be obtained at low cost, and are therefore suitable for use in flocking. Among these, polyamide is more preferable because it is excellent in impact resistance and wear resistance.

  The feed screw according to the present invention includes a screw shaft having a male screw formed on the outer periphery, and a cylindrical nut having a female screw that is directly or indirectly screwed to the male screw on the inner periphery. Since the flocked part formed by flocking multiple fibers is formed on the surface, without increasing the rotational resistance of the screw shaft, leakage of the lubricant enclosed in the inner space of the nut and from the outside to the inner space of the nut Intrusion of foreign matter can be prevented.

It is a front view of a feed screw concerning one embodiment of this invention. It is sectional drawing of the feed screw. It is a fragmentary sectional view of the nut in the feed screw. FIG. 3 is a partially enlarged view of FIG. 2. FIG. 5 is a view taken in the direction of arrow V in FIG. 4.

An embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a front view of a feed screw according to an embodiment of the present invention, and FIG. 2 is a sectional view of the feed screw. The feed screw is a ball screw and includes a screw shaft 1, a nut 2, and a plurality of balls 3.

  The screw shaft 1 has a male screw 5 formed on the outer periphery. The thread groove 5a of the male screw 5 has a substantially semicircular cross section, and the thread 5b has a flat shape with a constant outer diameter. The nut 2 has a female screw 6 formed on the inner periphery. The thread groove 6a of the female screw 6 has a substantially semicircular cross-sectional shape, and the thread 6b has a flat shape with a constant inner diameter. A rolling path 7 is constituted by the thread groove 5 a of the male screw 5 and the thread groove 6 a of the female screw 6, and the ball 3 is arranged in a row on the rolling path 7. As a result, the male screw 5 of the screw shaft 1 and the female screw 6 of the nut 2 are screwed together via the ball 3. The thread 5 b of the male screw 5 and the thread 6 b of the female screw 6 are opposed to each other with a gap 8 therebetween.

  The nut 2 includes a cylindrical nut body 11 and a plurality of piece members 12 provided on the nut body 11. The nut main body 11 has a flange portion 11a for coupling with other members at the central portion in the axial direction. Each piece member 12 is fitted into a top window 13 formed in the nut body 11.

As shown in FIG. 3, which is a partial cross-sectional view of the nut 2, the piece member 12 is provided with a connecting groove 14 that connects adjacent one rounds of the screw groove 6 a of the nut 2. As shown in FIG. 2, the depth of the connecting groove 14 is such that the ball 3 can exceed the thread 5 b of the male screw 5 of the screw shaft 1 in the connecting groove 14. In this way, the thread groove 6a is connected by the connecting groove 14, so that the rolling path 7 is a continuous circuit path of one turn.
As described above, the rolling path 7 may be a circulation path using a return tube, an end cap, a guide plate, or the like, in addition to the rolling path 7 being a circulation path by the connecting groove 14 provided in the piece member 12.

  The rolling path 7, the gap 8, and the connecting groove 14 constitute a nut inner space 15 formed by a gap between the screw shaft 1 and the nut 2. The nut inner space 15 is filled with a lubricant such as lubricating oil.

  4 is a partially enlarged view of FIG. 2, and FIG. 5 is a view taken in the direction of arrow V in FIG. On the inner peripheral surface of the nut 2, a flocked portion 16 that blocks the nut inner space 15 from the outside is formed. The flocked portion 16 is formed by flocking a plurality of fibers 17. As shown in FIG. 4, the flocked portion 16 is formed at the thread 6 b portion of the female screw 6 in the axial end portion of the inner peripheral surface of the nut 2. The flocked portion 16 is also formed at the end opposite to the end shown in FIG. Moreover, as shown in FIG. 5, the flocked part 16 is formed in the range of the perimeter in the inner peripheral surface of the nut 2. As shown in FIG. In other words, the flocked portion 16 is formed in a range of one or more rounds of the thread 6b of the female screw 6.

  The tip of the fiber 17 of the flocked portion 16 may or may not be in contact with the thread 5b of the male screw 5 of the screw shaft 1. In general, the most preferable condition is whether or not the tip of the fiber 17 is in contact with the thread 5b. In addition, it is desirable to hold the lubricant in the flocked portion 16 in a state before the start of use.

  The flocked portion 16 is formed by flocking short fibers. As a method for flocking, electrostatic flocking, electrostatic spraying flocking and the like can be employed. Electrostatic flocking is a technique in which an adhesive is applied to a processed material, an electrostatic field is created by a high voltage electrode, and short fibers are raised on the adhesive by the electrostatic attraction force. The feature of electrostatic flocking is that it can be processed easily and uniformly even in a complicated shape, and that the material of the flocking object such as metal, plastic, paper, etc. can be selected. Electrostatic spraying flocking is based on almost the same principle as electrostatic flocking, but the short fibers are tilted with respect to the substrate surface and fixed at a fixed angle by blowing the short fibers onto the adhesive layer with air. is there. Since electrostatic spraying flocking has a lower flocking density than electrostatic flocking, it can be flocked with a small amount of short fibers. For this reason, in the case of mass production, cost reduction can be expected by reducing the short fibers and shortening the time.

  The short fiber used for flocking is not particularly limited as long as it can be used as a short fiber for flocking. For example, (1) polyolefin resin such as polyethylene and polypropylene, polyamide resin such as nylon, aromatic polyamide resin, polyethylene terephthalate, Polyester resins such as polyethylene naphthalate, polyethylene succinate and polybutylene terephthalate, synthetic resin fibers such as acrylic resin, vinyl chloride and vinylon, (2) inorganic fibers such as carbon fiber and glass fiber, (3) rayon, acetate, etc. And natural fibers such as cotton, silk, hemp and wool. These may be used independently and 2 or more types may be used together. Synthetic resin fiber among these fibers for flocking is chemically stable and hardly swells or dissolves with oil, and can produce a large amount of homogeneous fibers and can be obtained at low cost. Suitable for use in. Among these, polyamide fibers are more preferable because they are excellent in impact resistance and wear resistance.

  The shape of the short fiber is not particularly limited as long as it does not interfere with other members that adversely affect the bearing function at the place where the flocked portion is formed. As a specific shape, for example, those having a length of 0.5 to 2.0 mm and a thickness of 0.5 to 50 dtex are preferable, and the density of short fibers in the flocked portion is occupied by fibers per planted area. A ratio of 1 to 30% is preferable. There are straight and bend (shape where the tip is bent) as the shape of the short fiber, and the cross-sectional shape is circular or polygonal. The bend shape can hold more oil than the straight shape. By using the short fibers having a polygonal cross section, the surface area can be made larger than that of the short fibers having a circular cross section, and the surface tension of the oil can be increased. It is preferable to select the shape of the short fiber according to each characteristic.

  Examples of the adhesive include an adhesive mainly composed of urethane resin, epoxy resin, acrylic resin, vinyl acetate resin, polyimide resin, silicone resin and the like. For example, urethane resin solvent adhesive, epoxy resin solvent adhesive, vinyl acetate resin solvent adhesive, acrylic resin emulsion adhesive, acrylic ester-vinyl acetate copolymer emulsion adhesive, vinyl acetate emulsion adhesive , Urethane resin emulsion adhesive, epoxy resin emulsion adhesive, polyester emulsion adhesive, ethylene-vinyl acetate copolymer adhesive and the like. These may be used independently and 2 or more types may be used together.

  The operation of the feed screw having the above configuration will be described. When the screw shaft 1 moves forward and backward while rotating on the inner periphery of the nut 2, the ball 3 rolls through the screw groove 5 a of the male screw 5, the screw groove 6 a of the female screw 6, and the connecting groove 14. The surfaces of the thread grooves 5a and 6a and the connecting groove 14 and the surface of the ball 3 are lubricated by a lubricant enclosed in the nut inner space 15.

  Since the nut inner space 15 and the outside are blocked by the flocked portion 16, the lubricant in the nut inner space 15 is prevented from leaking to the outside. Specifically, the lubricant located near the flocked portion 16 in the nut inner space 15 is captured by the fibers 17 of the flocked portion 16 and held in a stable state, so that the flocked portion 16 is connected to the nut inner space 15 and the outside. Acts as a hermetic seal to prevent lubricant leakage. In addition, since the flocked portion 16 functions as a hermetic seal, foreign matter such as dust can be prevented from entering the nut inner space 15 from the outside.

  When the tip of the fiber 17 of the flocked portion 16 is in contact with the thread 5b of the male screw 5 of the screw shaft 1, the sealing performance of the nut inner space 15 is further enhanced. Even if the tip of the fiber 17 is in contact with the screw thread 5b of the male screw 5, since the contact is a light fiber, there is no great resistance when the screw shaft 1 rotates. Even if the tip of the fiber 17 is not in contact with the screw thread 5b of the male screw 5, the effect of the labyrinth seal can be obtained, so that it is inferior to the case where the tip of the fiber 17 is in contact with the screw thread 5b of the male screw 5. A certain degree of sealing performance can be secured. When the tip of the fiber 17 is not in contact with the thread 5b of the male screw 5, there is an advantage that the resistance when the screw shaft 1 rotates is smaller than when the tip is in contact.

  If the lubricant is held in the flocked portion 16 before the start of use, the nut inner space 15 has a good sealing property before the start of use. Can be prevented. Moreover, since not only the lubricant enclosed in the nut inner space 15 but also the lubricant previously held in the flocked portion 16 is utilized for lubrication, the feed screw can be operated for a long time.

  If the flocked portion 16 is formed in the entire circumference of the inner peripheral surface of the nut 2 as in this embodiment, the leakage of lubricant from the nut inner space 15 and the entry of foreign matter into the nut inner space 15 are prevented. Further, it can be prevented over the entire circumference of the inner circumferential surface of the nut 2. Moreover, when the hair transplant part 16 is formed in the axial direction edge part in the inner peripheral surface of the nut 2, since the nut inner space 15 and the exterior are shielded by the hair transplant part 16 at the axial direction edge part, the nut There is less room for foreign matter to enter the inner space 15.

  Although the said embodiment shows the case where a feed screw is a ball screw, this invention is applicable also to the slide screw type feed screw which does not have a ball other than a ball screw.

  As mentioned above, although the form for implementing this invention based on embodiment was demonstrated, embodiment disclosed this time is an illustration and restrictive at no points. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 1 ... Screw shaft 2 ... Nut 3 ... Ball 5 ... Male screw 5a ... Screw groove 5b ... Screw thread 6 ... Female screw 6a ... Screw groove 6b ... Screw thread 16 ... Flocking part 17 ... Fiber

Claims (8)

A screw shaft having a male screw formed on the outer periphery, and a cylindrical nut having a female screw that is directly or indirectly screwed to the male screw on the inner periphery;
A feed screw, wherein a flocked portion formed by flocking a plurality of fibers is formed on an inner peripheral surface of the nut.   2. The feed screw according to claim 1, wherein the feed screw is a ball screw in which a plurality of balls rolling along the screw grooves are interposed between the screw grooves of the male screw and the screw grooves of the female screw.   The feed screw according to claim 1 or 2, wherein the flocked portion is formed in a range of the entire circumference on the inner circumferential surface of the nut.   The feed screw according to any one of claims 1 to 3, wherein the flocked portion is located at an end portion in an axial direction on an inner peripheral surface of the nut.   The feed screw according to any one of claims 1 to 4, wherein the flocked portion holds a lubricant before use.   The feed screw according to any one of claims 1 to 5, wherein a tip of the fiber of the flocked portion contacts a thread of the male screw.   The feed screw according to any one of claims 1 to 6, wherein the fibers are made of synthetic resin.   The feed screw according to claim 7, wherein the synthetic resin is polyamide.

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