JP2010236598A - Ball screw device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ball screw device having reduced size and cost. <P>SOLUTION: The ball screw nut 3 includes a nut body 12 and a pair of end caps 13. The nut body 12 is integrated with the inner ring of a bearing 6. The nut body 12 and the pair of end caps 13 are joined to each other with a screw 14 which is inserted from one end cap 13 through the nut body 12 and the other end cap 13 and screwed into the end of a hollow shaft 5. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a ball screw device, and more particularly to a ball screw device used in a form in which a nut rotates and a screw shaft linearly moves in an axial direction.

  A ball screw device including a screw shaft and a ball screw nut screwed to the screw shaft is often used for an actuator. In this case, a hollow shaft is coupled to the ball screw nut with a bolt, It is common to use this hollow shaft as a rotating shaft of a motor (Patent Document 1).

JP 2002-372117 A

  In the conventional ball screw device described above, the coupling portion between the ball screw nut and the hollow shaft is increased, and the number of parts and the number of assembling steps are increased. Thus, downsizing and cost reduction are problems.

  An object of the present invention is to provide a ball screw device that is reduced in size and cost.

  A ball screw device according to the present invention includes a screw shaft provided with a raceway groove, a ball screw nut screwed to the screw shaft via a ball, a hollow that is disposed concentrically with the screw shaft and rotates integrally with the ball screw nut. In a ball screw device including a shaft and a bearing that supports the ball screw nut, the ball screw nut includes a nut body and a pair of end caps, and the nut body and the inner ring of the bearing are integrated. The nut main body and the pair of end caps are connected by a screw member inserted from one end cap side, passing through the nut main body and the other end cap, and screwed into the end of the hollow shaft. Is.

  A ball screw nut composed of a nut body and a pair of end caps is a known one. In a conventional ball screw nut, the nut body and each end cap are coupled by end cap coupling bolts, and are hollow. Specifically, the shaft and the end cap of the ball screw nut are coupled by the hollow shaft coupling bolt at a position radially outside the end cap coupling bolt, avoiding a position where it interferes with the end cap coupling bolt. It was.

  In the ball screw device according to the present invention, the number of parts is reduced by integrating the nut body and the inner ring of the bearing. The configuration in which the hollow shaft and the end cap of the ball screw nut are coupled at the radially outer position by a hollow shaft coupling bolt different from the end cap coupling bolt is not preferable in that the coupling portion is large. In order to eliminate the problem, the end cap coupling bolt and the hollow shaft coupling bolt are made into a common screw member (bolt), and the common screw member is inserted from one end cap side so that the nut main body and the other end cap are inserted. The nut body and each end cap are coupled and the hollow shaft and the ball screw nut end cap are coupled by being threaded into the hollow shaft end. As a result, compared to the conventional one, the end cap coupling bolt is not required, the space for the hollow shaft coupling bolt is unnecessary, the coupling portion is reduced, and the number of parts and the number of bolts are reduced. Assembling man-hours are also reduced.

  The nut body and the hollow shaft are made of metal such as carbon steel (S45C, SCM, etc.), for example, and the end cap may be made of metal or synthetic resin.

  The ball screw device according to the present invention may be used as an actuator (a configuration in which a hollow shaft and a ball screw nut are rotated by a motor, whereby the screw shaft moves linearly), and a shock absorber (the screw shaft is externally provided). In this case, the hollow shaft and the ball screw nut are rotated, and the electromagnetic force generated by the motor becomes a damping force.

  In any case, the screw shaft moves linearly in a reciprocating manner, and a stopper is usually provided to prevent movement of a predetermined amount or more in the predetermined direction. The stopper can be formed, for example, by providing the screw shaft with a flange portion that contacts the housing when the screw shaft moves by a predetermined amount or more, and the stopper is formed on a member that moves linearly integrally with the screw shaft. Alternatively, it may be provided on a member that does not move linearly (a housing or a hollow shaft). Since the limit position in the forward direction of the screw shaft is defined by the stopper, the screw shaft is forcibly stopped when the limit position is reached. If the moving speed of the screw shaft at this time is fast, the nut has a large rotational inertial force when the screw shaft is suddenly stopped, so that indentations may occur in the ball screw track. In the ball screw device according to the present invention, As described above, it is possible to reduce the rotational inertia force by reducing the connecting portion, which is advantageous in terms of preventing indentation of the ball screw raceway groove.

  A spline for guiding the linear movement of the screw shaft may be provided integrally with the screw shaft. The spline in this case may be a ball spline, for example, a fitting spline such as an involute spline.

  According to the ball screw device of the present invention, the nut main body and the inner ring of the bearing are integrated, and the nut main body and the pair of end caps are inserted from one end cap side, and the nut main body and the other end cap are inserted. Since it is connected by a screw that penetrates and is screwed into the end of the hollow shaft, compared to the conventional one, the end cap coupling bolt becomes unnecessary, and the space for the hollow shaft coupling bolt becomes unnecessary, The connecting portion is reduced, and the number of parts and the number of bolts are reduced, and the number of assembling steps is also reduced. Therefore, the ball screw device can be reduced in size and cost.

FIG. 1 is a longitudinal sectional view showing an embodiment of the ball screw device of the present invention. FIG. 2 is a longitudinal sectional view showing a comparative example of the ball screw device.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows an embodiment of a ball screw device according to the present invention. In the following description, the left and right refer to the left and right in the figure.

  As shown in FIG. 1, the ball screw device (1) according to the present invention includes a steel screw shaft (2) provided with a raceway groove (2a) and a ball (2) on the raceway groove (2a) of the screw shaft (2). 4) a ball screw nut (3) screwed through, a hollow shaft (5) integrated with the ball screw nut (3), a bearing (6) supporting the ball screw nut (3), and a hollow And a bearing (7) for supporting the shaft (5).

  The screw shaft (2) and the hollow shaft (5) are concentrically arranged, and a magnet (rotor) is fixed to the outer periphery of the hollow shaft (5), so that the ball screw device (1) Using (5) as a motor shaft, the hollow shaft (5) and the ball screw nut (3) are rotated to linearly move the screw shaft (2).

  The hollow shaft (5) has a cylindrical shape with a required radial clearance between the hollow shaft (2) and a ball screw nut at the left end that is abutted against the right surface of the ball screw nut (3). A flange portion (11) used for coupling with (3) is provided.

  The ball screw nut (3) includes a cylindrical metal nut body (12) formed with a raceway groove (12a) for forming a main passage by the raceway groove (2a) of the screw shaft (2), and the nut It consists of a short cylindrical synthetic resin end cap (13) which is abutted on both the left and right sides of the main body (12). Although not shown in the drawings, the peripheral wall of the nut body (12) is formed with a return passage penetrating in the axial direction, and the end cap (13) has a groove-like shape that allows the main passage and the return passage to communicate with each other. A turning path is formed.

  The bearing (6) that supports the ball screw nut (3) is a four-point contact ball bearing, and the nut body (12) also serves as the inner ring. The bearing used to support the ball screw nut (3) is generally a double-row angular contact ball bearing, which is a four-point contact ball bearing, reducing the axial length. In addition, the number of parts is reduced because the nut main body (12) also serves as an inner ring.

  The flange portion (11) of the hollow shaft (5) is provided with a female thread portion (11a), and the nut body (12) and the pair of end caps (13) are bolts penetrating from the left side. The (screw member) (14) is coupled by being screwed into the flange portion (11).

  FIG. 2 shows a comparative example corresponding to the ball screw device (1) according to the present invention. In the following description, the same components as those in FIG.

  In FIG. 2, the bearing (20) supporting the ball screw nut (3) is a four-point contact ball bearing, and the nut body (22) also serves as the inner ring. The ball screw nut (21) includes a nut body (22) and a pair of end caps (23), which are connected by end cap coupling bolts (24). The nut body (22) has a flange portion (27) formed on a surface facing the flange portion (26) of the hollow shaft (25), and the nut portion (26) of the hollow shaft (25) and the nut The flange portion (27) of the main body (22) is coupled with a hollow shaft coupling bolt (28).

  In the case of FIG. 2, the nut body (22) and the inner ring of the bearing (20) are integrated to reduce the number of parts, but the flange portion (26) of the hollow shaft (25) and the nut body ( Since the flange portion (27) of 22) is coupled by a hollow shaft coupling bolt (28) different from the end cap coupling bolt (24), the coupling portion is large. Therefore, it is insufficient in terms of downsizing.

  Therefore, in the ball screw device (1) according to the present invention, as shown in FIG. 1, the end cap coupling bolt (24) and the hollow shaft coupling bolt (28) are replaced by a common bolt (14). The common bolt (14) connects the nut body (12) to each end cap (13) and the hollow shaft (5) to the end cap (13) of the ball screw nut (3). Yes. As a result, as compared with that shown in FIG. 2, the end cap coupling bolt (24) is not necessary, and the common bolt (14) can be disposed at the position of the hollow shaft coupling bolt (28). Therefore, the flange portion (27) of the nut body (22) in FIG. 2 is eliminated, and the overhang in the radial direction of the flange portion (26) of the hollow shaft (25) is reduced. As a result, the joint between the ball screw nut (3) and the hollow shaft (5) becomes smaller, the size is reduced, the rotational inertia force is reduced, and the number of parts and the number of bolts are reduced. Man-hours are also reduced.

  This ball screw device (1) is suitable for use as an electric actuator, for example. In this case, the rotational driving force of the motor is converted into the axial thrust of the screw shaft (2) via the ball screw nut (3), and the axial reaction force of the thrust is supported by the bearings (6) (7) and screwed. Use in a form in which the shaft (2) is linearly moved, the axial load acting on the screw shaft (2) is loaded by the ball screw nut (3), and the torque is supported by a ball spline outer cylinder (not shown), etc. It becomes. Further, the above-described ball screw device (1) can be used as an electromagnetic suspension of an automobile by arranging the screw shaft (2) in the vertical direction.

(1) Ball screw device
(2) Screw shaft
(2a) Track groove
(3) Ball screw nut
(4) Ball
(5) Hollow shaft
(6) Bearing
(11) Flange
(12) Nut body
(13) End cap
(14) Bolt (screw member)

Claims (1)

Supports a screw shaft provided with a raceway groove, a ball screw nut screwed to the screw shaft via a ball, a hollow shaft concentric with the screw shaft and rotating integrally with the ball screw nut, and a ball screw nut A ball screw device comprising:
The ball screw nut includes a nut body and a pair of end caps, and the nut body and the inner ring of the bearing are integrated, and the nut body and the pair of end caps are inserted from one end cap side and are nuts. A ball screw device, wherein the ball screw device is coupled by a screw member that passes through the main body and the other end cap and is screwed into the end portion of the hollow shaft.

Images