JP5732739B2 - Ball screw device - Google Patents

Description

  The present invention relates to a ball screw device, and more particularly to a ball screw device capable of cooling a nut.

2. Description of the Related Art Conventionally, in a screw device having a screw shaft and a feed nut that is screwed into the screw shaft and is relatively rotatable, point contact or surface contact occurs during rotation. ) May be provided with cooling means.
As a technique for cooling the feed nut, there is a screw device (ball screw) disclosed in Patent Document 1. Specifically, this is a technique of passing a cooling medium through a through hole provided in the axial direction of the feed nut and cooling the feed nut.

JP 2002-310258 A

Senki Shinji (1981), Heat transfer calculation method, Engineering Books Co., Ltd.

However, the inventors have found that when cooling the nut of the screw device (ball screw) disclosed in Patent Document 1, the cooling effect varies greatly depending on the diameter of the through hole through which the coolant passes. It was estimated by the Nusselt method shown in Fig. 1, and the change in the cooling effect was confirmed by experiments.
The conclusion obtained by this experiment is that if the type and flow rate of the cooling medium are the same, the smaller the diameter of the through hole, the higher the thermal conductivity and the higher the cooling effect.

However, when the diameter of the through hole is reduced for the purpose of obtaining a high cooling effect, the following two problems may occur.
(1) Since the processing of the through hole is a small diameter and long hole processing, the processing efficiency is lowered and the cost of the ball screw device is increased.
(2) Pressure loss when passing the cooling medium increases.

  Therefore, the present invention has been made paying attention to the above-mentioned problems, and the object thereof is to provide a cooling effect in a ball screw device that performs cooling by passing a cooling medium through a through hole provided in an axial direction in a nut. It is an object of the present invention to provide a ball screw device in which the height is made as high as possible without causing excessive reduction in processing efficiency and increase in pressure loss.

  In order to solve the above-mentioned problems, the present inventors have made extensive studies and as a result, in a ball screw that cools by passing a cooling medium through a through hole provided in the axial direction of the nut, an insertion member is arranged in the through hole. By reducing the cross-sectional area of the flow path of the through hole and ensuring a large area where the cooling medium passing through the through hole is in contact with the through hole, the cooling effect is increased as much as possible and excessive processing efficiency is reduced. I found out that there was nothing.

This invention is based on the said knowledge by the present inventors, The ball screw apparatus which concerns on Claim 1 of this invention for solving the said subject is a screw shaft and the said screw | thread via several rolling elements. In a ball screw device comprising: a nut screwed into a shaft; and a cooling means for cooling the nut through a cooling medium in a through hole provided in an axial direction of the nut.
A circulating device for circulating a cooling medium in the through hole is provided in the nut;
The outer peripheral surface extending in the length direction of the through hole and facing the inner peripheral surface of the through hole forms a uniform curved surface in the length direction, and the cross-sectional shape of the flow path of the through hole is substantially circular or elliptical The insertion member is arranged in the through hole.
A ball screw device according to claim 2 of the present invention is the ball screw device according to claim 1, wherein the insertion member has a cross-sectional shape that divides the through hole into a plurality of flow paths in the length direction. It is characterized by having.

According to the ball screw device of the first aspect of the present invention, by arranging the insertion member extending in the length direction of the through hole in the through hole, a large area where the cooling medium and the through hole come into contact is ensured. However, the cross-sectional area of the flow path of the through hole can be reduced. Therefore, it is possible to provide a ball screw device that has as high a cooling effect as possible and does not cause an excessive decrease in processing efficiency.
In the ball screw device according to claim 2 of the present invention, the insertion member has a cross-sectional shape that divides the through hole into a plurality of flow paths in the length direction thereof, so that the cooling medium and the through hole are formed. Since a plurality of through-hole passages having a reduced cross-sectional area are formed while ensuring a large area in contact with each other, the flow rate of the cooling liquid is increased, and an excessive reduction in processing efficiency can be more efficiently reduced. it can.

It is a side view showing composition in one embodiment of a ball screw device concerning the present invention. It is sectional drawing which shows the structure in one Embodiment of the ball screw apparatus which concerns on this invention, (a) is sectional drawing which follows the 2a-2a line of FIG. 1, (b) is the A section enlarged view of (a). . It is a perspective view which shows the structure of the insertion member in one Embodiment of the ball screw apparatus which concerns on this invention.

Embodiments of a ball screw device according to the present invention will be described below with reference to the drawings.
FIG. 1 is a side view showing the configuration of an embodiment of a ball screw device according to the present invention. 2 is a cross-sectional view showing the configuration of the present embodiment, (a) is a cross-sectional view taken along line 2a-2a in FIG. 1, and (b) is an enlarged view of part A in (a). Moreover, Fig.3 (a)-(f) is a perspective view which shows the structure of the insertion member in this embodiment.

  As shown in FIG. 1, the ball screw device 1 of this embodiment includes a screw shaft 10 and a nut 20. The screw shaft 10 and the nut 20 are screwed together via a plurality of rolling elements 30. The nut 20 is formed in a cylindrical shape with an inner diameter larger than the outer diameter of the screw shaft 10. A screw groove 20 a is formed on the inner peripheral surface of the nut 20 so as to face the screw groove 10 a formed in a spiral shape on the outer peripheral surface of the screw shaft 10. The rolling element 30 can roll on the rolling path formed by the thread groove 10a and the thread groove 20a.

  The nut 20 is formed with through holes 20b penetrating in the axial direction (in FIG. 1, three through holes 20b are formed in the axial direction of the nut 20). The through hole 20 b is used as a passage for the cooling medium, and a circulation device (not shown) for circulating the cooling medium in the through hole 20 b is connected to the ball screw device 1. The circulation device and the through hole 20b constitute the cooling means 40. The cooling means 40 includes a pipe 41 that connects the circulation device and the through hole 20b to allow the cooling medium to flow into the through hole 20b, and a pipe 41 that allows the cooling medium to flow out of the through hole 20b. Thus, the nut 20 is cooled by circulating the cooling medium in the through hole 20b by a circulation device (not shown).

As shown in FIGS. 1 and 2A, an insertion member 50 extending in the length direction of the through hole 20b is disposed inside the through hole 20b. The cross-sectional shape of the insertion member 50 is formed so as to reduce the cross-sectional area of the flow path of the through hole 20b and to reduce the contact area with the inner peripheral surface of the through hole 20b as much as possible. Specifically, as shown in FIG. 2B, an insertion member 50 having a diamond-shaped cross-sectional shape is disposed inside the through hole 20b. The insertion member 50 having a diamond-shaped cross section extends in the length direction of the through hole 20b, and contacts the inner surface of the through hole 20b at four points in the cross section of the through hole 20b.
The shape of the insertion member 50 extends in the length direction of the through hole 20b, reduces the cross-sectional area of the flow path of the through hole 20b, and has a contact area with the inner peripheral surface of the through hole 20b as much as possible. If it is small, it will not specifically limit.

The insertion member 50 may have a cross-sectional shape that divides the through hole 20b into a plurality of flow paths in the length direction thereof.
The specific shape of the insertion member 50 is shown to Fig.3 (a)-(f).
The insertion member 50 shown in FIG. 3 (a) has a circular cross-sectional shape, extends in the length direction of the through hole 20b, and does not contact the inner surface of the through hole 20b in the cross section of the through hole 20b. It is arranged. Depending on the insertion member 50, a plurality of flow paths are not formed in the through hole 20b.

The insertion member 50 shown in FIG. 3B has a circular cross-sectional shape, extends in the length direction of the through hole 20b, and contacts the inner surface of the through hole 20b at one point in the cross section of the through hole 20b. 20b is disposed inside. Depending on the insertion member 50, a plurality of flow paths are not formed in the through hole 20b.
The insertion member 50 shown in FIG. 3C has a rectangular cross-sectional shape, extends in the length direction of the through hole 20b, and contacts the inner surface of the through hole 20b at four points in the cross section of the through hole 20b. It arrange | positions inside the through-hole 20b so that a path | route may be formed.

The insertion member 50 shown in FIG. 3 (d) has a triangular cross-sectional shape, extends in the length direction of the through hole 20b, and contacts the inner surface of the through hole 20b at three points in the cross section of the through hole 20b. It arrange | positions inside the through-hole 20b so that a path | route may be formed.
The insertion member 50 shown in FIG. 3 (e) is the insertion member 50 having the cross-sectional shape shown in FIG. 2 (b), the cross-sectional shape of which is a rhombus shape, and extends in the length direction of the through hole 20b. In the cross section of 20b, it arrange | positions inside the through-hole 20b so that four flow paths may be formed by contacting the inner surface of the through-hole 20b at four points.

The insertion member 50 shown in FIG. 3 (f) has a cross-sectional shape in which two circles are in contact with each other, extends in the length direction of the through hole 20b, and has two points on the inner surface of the through hole 20b in the cross section of the through hole 20b. It arrange | positions in the inside of the through-hole 20b so that it may contact and may form two flow paths.
Among the insertion members 50 shown in FIGS. 3A to 3F, the insertion members 50 shown in FIGS. 3C to 3F form a plurality of small cross-sectional flow paths in the through holes 20b. Therefore, there is an effect of increasing the flow rate of the coolant. However, when the circulation capacity of the circulation device (not shown) is small, the flow rate cannot be increased due to the pipe resistance by making the cross-sectional area of the insertion member 50 too large. Accordingly, it is necessary to determine the shape of the insertion member 50 (cross-sectional shape and contact area with the inner peripheral surface of the through hole 20b).

  In addition, heat exchange between the object to be cooled (nut 20) and the cooling medium in the through hole 20b is performed on the inner surface of the through hole 20b. A shape having a small number of parts in contact with is preferable. That is, the insertion member 50 having the shape shown in FIG. 3D is preferable to the insertion member 50 having the shape shown in FIGS. 3C and 3E, and the insertion member 50 having the shape shown in FIG. The insertion member 50 having the shape shown in FIG. 3B is more preferable, and the insertion member 50 having the shape shown in FIG.

Here, in general, the Reynolds number Re _m that affects the cooling effect is
u _m : Flow velocity of the cooling medium v: Kinematic viscosity of the cooling medium a: The temperature conductivity of the cooling medium is expressed by the following formula (1).

Here, the flow velocity u _m of the cooling medium is
w: Flow rate of cooling medium A: When the cross-sectional area of the through hole 20b is used, it is represented by the following formula (2).

  The cross-sectional area A of the through hole 20b is represented by the following formula (3).

When the above formulas (2) and (3) are substituted into the formula (1) and rearranged, the Reynolds number Re _m is expressed by the following formula (4).

Thus, it can be seen that the Reynolds number Re _m represented by the equation (4) is higher when the diameter D of the through hole 20b is smaller when the flow rate w of the cooling medium is constant. However, in reducing the diameter D of the through hole 20b, it must be in a range in which excessive pressure loss does not occur.
On the other hand, the heat exchange between the object to be cooled (nut 20) and the cooling medium in the through hole 20b is proportional to the contact area between the object to be cooled (nut 20) and the cooling medium in the through hole 20b.

In view of these, in order to increase the Reynolds number Re _m is to reduce the diameter D of the through hole 20b, in order to increase the contact area, the number of many it is the object to be cooled in the through hole 20b (nut 20) It can be seen that this is a method of efficiently cooling. However, forming the through holes 20b having a small cross-sectional area and increasing the number of the through holes 20b causes a reduction in processing efficiency, resulting in a significant increase in processing costs.
Therefore, in the present embodiment, the insertion member 50 is disposed inside the through hole 20b, a through hole having a small diameter is formed by the arrangement of the insertion member 50, and the contact area is increased, so that Reynolds is increased. and realize the configuration to increase the number Re _m.

By using this configuration, the diameter D of the through hole 20b is replaced with the equivalent diameter _De , and is expressed as the following formula (5). Here, in the following formula (5), the equivalent diameter D _e in the case where the cross-sectional area of the flow path of the cooling fluid is considered a circle having the same cross-sectional area refers to the diameter of the circle. That is, the greater the cross-sectional area of the inner insertion member, the equivalent diameter D _e is small, the Reynolds number Re _m obtained by substituting the D of the equivalent diameter D _e of the equation (4) is raised (cooled The effect will increase). In addition, since the through-hole diameter D provided in a nut does not change, processing efficiency is equivalent. _Ad is the cross-sectional area of the flow path. L _wet indicates a length obtained by subtracting the length of the contact portion where the insertion member is in contact with the inner surface of the through hole from the circumferential length of the through hole. That is, in the installation mode of the insertion member shown in FIGS. 3A to _3F , L _wet is equal to the circumferential length of the through hole in the mode of FIG. 3A, and FIG. , (F), L _wet is substantially equal to the circumferential length of the through hole, and in the modes of FIGS. 3C and 3E, L _wet is determined from the circumferential length of the through hole as an insertion member. Is equal to the length obtained by subtracting the length of the four contact portions that are in contact with the inner surface of the through hole. In the embodiment shown in FIG. 3 (d), L _wet is calculated based on the circumferential length of the through hole. It is equal to the length obtained by subtracting the lengths of the three contact portions in contact with the inner surface of the through hole.

  As described above, according to the ball screw device 1 of the present embodiment, since the insertion member 50 extending in the length direction of the through hole 20b is disposed in the through hole 20b, the sectional area of the flow path of the through hole 20b. The area where the cooling medium passing through the through hole 20b and the through hole come into contact can be ensured. Therefore, it is possible to provide the ball screw device 1 that has as high a cooling effect as possible and does not cause excessive reduction in processing efficiency.

  Further, in the ball screw device 1 of the present embodiment, the insertion member 50 has a cross-sectional shape that divides the through hole 20b into a plurality of flow paths in the length direction thereof, thereby increasing an area where the cooling medium and the through hole are in contact with each other. Since a plurality of flow paths of the through holes 20b having a reduced cross-sectional area are formed while ensuring, the flow rate of the coolant is increased, and an excessive reduction in processing efficiency can be more efficiently reduced.

  As mentioned above, although embodiment of this invention has been described, this invention is not limited to this, A various change and improvement can be performed. For example, in the above-described embodiment, a case where one through hole is formed in the nut and the cooling medium is cooled through the through hole has been described, but a plurality of through holes formed in the nut are connected. The ball screw device that is cooled in this manner also has an unexpected effect by applying the same configuration as described above.

DESCRIPTION OF SYMBOLS 1 Ball screw apparatus 10 Screw shaft 20 Nut 30 Rolling body 40 Cooling device 41 Pipe 50 Insertion member

Claims (2)

A ball screw device comprising: a screw shaft; a nut screwed into the screw shaft through a plurality of rolling elements; and a cooling means for cooling the nut through a cooling medium in a through hole provided in an axial direction of the nut. ,
A circulating device for circulating a cooling medium in the through hole is provided in the nut;
The outer peripheral surface extending in the length direction of the through hole and facing the inner peripheral surface of the through hole forms a uniform curved surface in the length direction, and the cross-sectional shape of the flow path of the through hole is substantially circular or elliptical A ball screw device, wherein an insertion member is disposed in the through hole.   The ball screw device according to claim 1, wherein the insertion member has a cross-sectional shape that divides the through hole into a plurality of flow paths in a length direction thereof.

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