JP2014059042A - Actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an actuator capable of compatibly achieving operability and positioning accuracy.SOLUTION: An actuator 1 includes a screw shaft 10 having a spiral rolling groove formed in an axial direction on an outer peripheral surface, and a nut 20 which has a rolling groove corresponding to the rolling groove and formed on an inner peripheral surface and is screwed into the screw shaft 10 via a plurality of rolling elements disposed in a rolling element rolling path formed of the rolling groove and the rolling groove in the screw shaft 10. The screw shaft 10 or the nut 20 functions as a direct-acting member 2 directly acting in an axial direction by relative rotation of the screw shaft 10 and the nut 20. The direct-acting member 2 (screw shaft 10) includes an elastic member 40 abutting on an opposite member 50. The elastic member 40 has a prescribed spring coefficient.

Description

  The present invention relates to an actuator that uses a ball screw and is suitable for automobiles, motorcycles, and ships, and particularly relates to an actuator that is suitable for a brake actuator.

In recent years, labor saving of vehicles and the like has progressed, and for example, a system has been developed in which a transmission, a parking brake, and the like of an automobile are performed not by hand but by the power of an electric motor. 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. In an actuator using such a ball screw, it is required to improve the operability of the ball screw which is a conversion portion between linear motion and rotation.
A technique aimed at improving the operability of such a ball screw is disclosed in Patent Document 1. According to Patent Document 1, the elastic body is provided between the output shaft (screw shaft) and the mating member. As a result, even in applications where the stroke of the mating member is small, the screw shaft movement amount (nut rotation amount) increases, so that lubrication is achieved in the entire region and operability is improved.

JP 2002-213504 A

However, in the technique disclosed in Patent Document 1, the operability of the ball screw can be ensured, but the positioning accuracy required for many actuators using the ball screw may be lowered, and there is room for examination. It was.
Accordingly, the present invention has been made paying attention to the above-described problems, and an object thereof is to provide an actuator that can achieve both operability and positioning accuracy.

An actuator according to an embodiment for solving the above problems includes a screw shaft in which a spiral rolling groove is formed on an outer peripheral surface;
A plurality of rolling elements disposed on a rolling element rolling path formed by a rolling groove corresponding to the rolling groove on an inner peripheral surface and formed by the rolling groove and the rolling groove of the screw shaft. And a nut that is screwed onto the screw shaft, and the screw shaft and the nut rotate relative to each other, whereby the screw shaft or the nut moves directly in the axial direction. It is a functioning actuator.

And the elastic member which contact | abuts the other member which opposes the end surface of the linear motion direction of the said linear motion member is provided in the said linear motion member, and the said elastic member has a predetermined spring coefficient.
According to such a configuration, even when the ball is caught due to a nut, a screw shaft, a ball manufacturing error, and an assembly error that constitute the ball screw, the linear motion member can touch around. For this reason, smooth conversion between linear motion and rotation is possible, and operability can be improved. Further, since the linear motion member is not relatively movable in the axial direction, positioning accuracy can be ensured. Therefore, an actuator that can achieve both operability and positioning accuracy can be provided.

In addition, the force by which the linear member (for example, screw shaft) pushes the mating member during the forward operation is F, and the force by which the mating member presses the linear member (for example, the screw shaft) during the reverse operation is F. When 'is assumed, the spring coefficient k may satisfy F ′ <kx <F.
The elastic member may be wound around the outer periphery of the linear motion member (for example, a screw shaft).
Further, the elastic member may protrude toward the counterpart member from the end face in the axial direction of the linear motion member (for example, a screw shaft).

  According to the present invention, it is possible to provide an actuator that can achieve both operability and positioning accuracy.

It is a fragmentary sectional view in alignment with the axial direction which shows the structure in 1st Embodiment of the actuator of this invention, (a) is at the time of normal operation, (b) shows the time of reverse operation. It is the fragmentary sectional view which follows the axial direction which shows the structure in 2nd Embodiment of the actuator of this invention, (a) is at the time of normal operation, (b) shows the time of reverse operation.

Hereinafter, an embodiment of an actuator of the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 1 is a cross-sectional view along the axial direction showing the configuration of the actuator according to the first embodiment of the present invention.
<Configuration>
As shown in FIGS. 1A and 1B, the actuator 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 (balls) 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 10a is formed on the outer peripheral surface of the screw shaft 10 in a spiral shape in the axial direction. A thread groove 20 a is formed on the inner peripheral surface of the nut 20 so as to face the thread groove 10 a of the screw shaft 10. A rolling element 30 is arranged (or filled) so as to be able to roll on a rolling path formed by the thread groove 10a and the thread groove 20a. Then, when the screw shaft 10 and the nut 20 are relatively rotated, the screw shaft 10 or the nut 20 functions as the linear motion member 2 that linearly moves in the axial direction. In the present embodiment, a mode in which the screw shaft 10 is the linear motion member 2, that is, a mode in which the screw shaft 10 is linearly moved by rotating the nut 20 will be described.

  A small-diameter portion 11 is provided at the end of the screw shaft 10 on the side connected to the mating member 50. The mating member 50 is a member that faces the end surface of the linear motion member (in this embodiment, the screw shaft 10) in the linear motion direction. When the screw shaft 10 is pushed against the mating member 50 connected to the screw shaft 10 by the linear movement of the screw shaft 10 that is a linear motion member, the screw shaft 10 cannot be relatively moved in the axial direction and is relatively in the radial direction. A movable elastic member 40 is provided so as to protrude from the end portion toward the mating member 50 and to cover the small diameter portion 11. As this elastic member 40, FIG. As shown in (b), for example, a coil spring is preferable. Further, the spring coefficient k of the elastic member 40 is such that the force by which the linear member 2 (screw shaft 10) pushes the mating member 50 during forward operation (see FIG. 1A) is F, and during reverse operation (FIG. 1B). )), The elastic member 40 protrudes from the end portion toward the counterpart member 50 in a state where the load is not applied to the elastic member 40. Assuming that a gap (clearance between the end portion and the counterpart member 50) is x, F ′ <kx <F is satisfied. The “normal operation” refers to an operation in which the linear member presses the mating member as a result of the rotation of the rotary member to which the rotational force is transmitted being converted and the linear member being linearly moved. On the other hand, the “reverse operation” refers to an operation of rotating the rotating member by the counterpart member pressing the linear motion member and converting the linear motion generated by the pressed force by the ball screw mechanism into the rotational motion. For example, in an actuator having a configuration in which the screw shaft moves linearly when the nut rotates, the nut rotates by the rotation of the motor, and the rotated nut moves the screw shaft directly through the ball screw mechanism. The operation is “forward operation”, and when the counterpart member presses the screw shaft, the screw shaft moves directly, and the screw shaft that has moved directly rotates the nut via the ball screw mechanism is “reverse operation”.

  Here, if the ball is caught due to manufacturing errors or assembly errors of the nut, screw shaft, and ball (rolling element), the ball will be caught if the nut and the center axis of the screw shaft do not swing relatively. A big driving force is needed to escape. In other words, the screw shaft and the nut cannot move relative to a position where the ball is easy to escape from being caught. For this reason, in order for the ball to escape from catching, the ball or the part of the raceway surface where the ball is stuck, the screw shaft, and the nut must be elastically deformed. It is necessary to be loaded.

  Therefore, in the present embodiment, the elastic member 40 has a predetermined spring coefficient at the time of normal operation (see FIG. 1A) in which the screw shaft 10 moves linearly by the rotation of the nut 20 and pushes the mating member 50. The elastic member 40 is completely contracted, and the screw shaft directly presses the mating member. For this reason, positioning accuracy can be maintained. On the other hand, when the screw shaft 10 moves in a direction away from the mating member 50, or when the screw shaft 10 is pushed by the mating member 50 and the nut 20 rotates (see FIG. 1B), the elastic member 40 is moved. Extends to some extent, and the mating member 50 and the screw shaft 10 do not contact each other. For this reason, the screw shaft 10 can move in the radial direction with respect to the counterpart member 50 and can swing around the nut 20. As a result, the catch of the ball 30 can be easily released.

(Second Embodiment)
FIG. 2 is a partial cross-sectional view along the axial direction showing the configuration of the actuator according to the second embodiment of the present invention. Note that the actuator of this embodiment is different from the first embodiment described above only in the configuration of the limiting member. Therefore, the same reference numerals are given to the members that overlap or correspond to those in the first embodiment. Description is omitted. In FIG. 2, the nut 20 and the ball (rolling element) 30 are omitted.
As shown in FIG. 2, in the actuator 1 of the present embodiment, the elastic member 40 is not a coil spring but an elastic member 40 made of a cylindrical rubber or the like. The elastic member 40 may be wound around the small diameter portion 11 of the screw shaft 10 or may be partially provided.

  With such a configuration, the elastic member 40 has a predetermined spring coefficient at the time of normal operation (see FIG. 2A) in which the screw shaft 10 moves linearly by the rotation of the nut 20 and pushes the mating member 50. Therefore, the elastic member 40 is completely contracted and the screw shaft directly presses the mating member. For this reason, positioning accuracy can be maintained. On the other hand, when the screw shaft 10 moves away from the mating member 50 or when the screw shaft 10 is pushed by the mating member 50 and the nut 20 rotates (see FIG. 2B), the elastic member 40 is moved. Extends to some extent, and the mating member 50 and the screw shaft 10 do not contact each other. For this reason, the screw shaft 10 can move in the radial direction with respect to the counterpart member 50 and can swing around the nut 20. As a result, the catch of the ball 30 can be easily released.

Further, as a modification of the present embodiment, an opening that opens to the counterpart member 50 side is provided at the end of the screw shaft 10 to form a hollow screw shaft 10, and the elastic member 40 is placed in the opening to the counterpart member 50 side It may be built in so as to protrude.
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, the elastic member is provided on the screw shaft as the linear motion member, but the elastic member may be provided on the nut in the same manner as described above by using the nut as the linear motion member. That is, in the above-described embodiment, the configuration in which the screw shaft 10 is linearly moved by rotating the nut 20 has been described. However, the present invention can also be applied to a configuration in which the nut 20 is linearly moved by rotating the screw shaft 10. In this case, the first embodiment has a structure in which the elastic member 40 is provided on the nut 20, and the second embodiment has a structure in which the elastic member 40 is provided on the inner peripheral surface or the outer peripheral surface of the nut 20.

  Furthermore, the actuator 1 of this embodiment can be applied to automobiles, two wheels, and ships. In particular, when the linear motion member 2 moves in a direction away from the counterpart member 50, that is, an actuator that does not pull the counterpart member 50, such as a brake actuator, the linear motion member 2 pushes the counterpart member 50. It is suitable for an actuator in which the member 50 moves in the same direction as the linear motion member 2 or is pushed by the counterpart member 50 and the linear motion member 2 moves in that direction.

DESCRIPTION OF SYMBOLS 1 Actuator 10 Screw shaft 11 Small diameter part 12 Opening part 20 Nut 30 Rolling element 40 Elastic member 50 Counterpart member

Claims (4)

A screw shaft in which a spiral rolling groove is formed in the axial direction on the outer peripheral surface;
A plurality of rolling elements disposed on a rolling element rolling path formed by a rolling groove corresponding to the rolling groove on an inner peripheral surface and formed by the rolling groove and the rolling groove of the screw shaft. And a nut that is screwed to the screw shaft, and the screw shaft or the nut rotates relative to each other, so that the screw shaft or the nut functions as a linear motion member that linearly moves in the axial direction. An actuator that
An elastic member that abuts on a mating member facing the end surface of the linear motion member in the linear motion direction is provided on the linear motion member,
The actuator is characterized in that the elastic member has a predetermined spring coefficient. When the force that the linear member presses the counterpart member during normal operation is F, and the force that the counterpart member presses the linear member during reverse operation is F ′,
The actuator according to claim 1, wherein the spring coefficient k satisfies F ′ <kx <F.   The actuator according to claim 1, wherein the elastic member is wound around an outer periphery of the linear motion member.   2. The actuator according to claim 1, wherein the elastic member protrudes closer to the mating member than an axial end surface of the linear motion member.

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