JP2020148213A - Linear motion actuator - Google Patents

Abstract

To prevent engagement in a screw mechanism of a linear motion actuator.SOLUTION: A linear motion actuator 1 includes: a motor 2; and a motion conversion mechanism 3 which converts rotational motion of the motor 2 into linear motion. The motion conversion mechanism 3 includes: a screw shaft 7 serving as a linear motion member having a male screw part 12; a female screw part 10 which threadedly engages with the male screw part 12; and a biasing member 8 which biases the screw shaft 7. A backlash is provided between the male screw part 12 and the female screw part 10. The biasing member 8 biases the screw shaft 7 so that the male screw shaft 12 contacts with the female screw part 10.SELECTED DRAWING: Figure 1

Description

The present invention relates to a linear actuator that converts a rotary motion of a motor into a linear motion and outputs it.

In recent years, electrification has been progressing for the purpose of labor saving and fuel efficiency of vehicles and the like. For example, a system for operating an automatic transmission, a brake, a steering wheel, etc. of an automobile by the power of an electric motor such as a motor has been developed and put on the market. As an actuator used for such an application, a linear actuator having a screw mechanism for converting a rotary motion generated by driving an electric motor into a linear motion is known.

For example, in Patent Document 1, the rotational motion of a shaft driven by a motor is converted into a linear motion of a brake piston (pressing member) by a screw mechanism (power conversion member), and a brake pad (friction member) is generated by the advancing / retreating motion of the brake piston. A brake actuator that adjusts the pressing force of) is disclosed. The screw mechanism of the brake actuator is composed of a nut provided on the shaft and having a female screw, and a screw shaft (bolt) provided on the brake piston and having a male screw portion.

JP-A-2015-48850

In a conventional linear actuator, if a strong impact is applied to a screw shaft during operation, the male screw portion of the screw shaft and the female screw portion of the nut may bite each other. If the male-threaded portion and the female-threaded portion are engaged with each other, it becomes difficult for the motor to rotate the screw shaft in the opposite direction, which may cause a malfunction of the linear actuator.

The present invention has been made in view of the above circumstances, and it is a technical subject to prevent biting in the screw mechanism of the linear actuator.

The present invention is for solving the above-mentioned problems, and in a linear actuator including a motor and a motion conversion mechanism for converting the rotational motion of the motor into a linear motion, the motion conversion mechanism has a male screw portion. A screw shaft as a linear motion member, a female screw portion screwed into the male screw portion, and an urging member for urging the screw shaft are provided, and a backlash is provided between the male screw portion and the female screw portion. The urging member is characterized in that the screw shaft is urged so that the male screw portion is in contact with the female screw portion.

According to such a configuration, when an impact is applied to the screw shaft, the urging member allows the screw shaft to move within the range of the backlash and can absorb the impact by the urging force. As a result, it is possible to reliably prevent the male-threaded portion and the female-threaded portion from getting caught. Further, by urging the screw shaft with the urging member and appropriately contacting the male screw portion and the female screw portion, the rattling of the screw shaft, which is a linear motion member, is suppressed and the positioning accuracy thereof is improved. Can be done.

The urging member is composed of a compression spring, and the screw shaft can be urged so that the male screw portion comes into contact with the female screw portion by an elastic restoring force. As a result, when an impact is applied to the screw shaft, the impact can be suitably absorbed by the elastic restoring force of the compression spring.

The linear actuator according to the present invention may include a housing for accommodating the motion conversion mechanism, and the female screw portion may be formed in the housing. As a result, the number of parts of the linear actuator can be reduced as much as possible.

The urging member may be a coil spring, and the coil spring may be inserted through a part of the screw shaft. As a result, the coil spring as the urging member can be easily attached to the screw shaft.

According to the present invention, it is possible to prevent the screw mechanism from being caught in the linear actuator.

It is sectional drawing of the linear actuator which concerns on this invention. FIG. 1 is a cross-sectional view taken along the line II-II of FIG. FIG. 3 is a cross-sectional view taken along the line III-III of FIG. It is an enlarged sectional view of the main part of the screw mechanism which concerns on a linear actuator.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. 1 to 4 show an embodiment of a linear actuator according to the present invention.

As shown in FIG. 1, the linear actuator 1 includes a motor 2, a screw mechanism 3 as a motion conversion mechanism for converting the rotational motion of the motor 2 into a linear motion, and a housing 4 accommodating the motor 2 and the screw mechanism 3. To be equipped. Although the housing 4 is shown as one component in the illustrated example, it is actually composed of a plurality of components for accommodating the motor 2 and the screw mechanism 3 inside. The housing 4 includes a first accommodating portion 4a accommodating the motor 2 and a second accommodating portion 4b accommodating the screw mechanism 3.

The motor 2 has a motor body 5 fixed to the inner circumference of the housing 4 and a rotating shaft 6 protruding from the motor body 5. The motor body 5 is fixed in the first housing portion 4a of the housing 4. The motor body 5 is connected to a power source provided outside the housing 4 via wiring (not shown). The rotating shaft 6 projects from the first accommodating portion 4a of the housing 4 to the second accommodating portion 4b, and is connected to the screw mechanism 3 in the second accommodating portion 4b.

The screw mechanism 3 is configured by a sliding screw mechanism, but is not limited to this configuration. The screw mechanism 3 regulates the rotation range of the screw shaft 7 as a linear motion member driven by the rotation shaft 6 of the motor 2, the urging member 8 for urging the screw shaft 7 in the axial direction, and the screw shaft 7. It mainly includes a rotation restricting mechanism 9 and a female screw portion 10 formed inside the housing 4 and screwed into the screw shaft 7. In the following description, the operation target P side (right side in FIG. 1) is referred to as front in the axial direction, and the motor 2 side (left side in FIG. 1) is referred to as rear.

The screw shaft 7 includes an operation portion 11 for operating the operation target P, a male screw portion 12 screwed into the female screw portion 10 of the housing 4, a large diameter portion 13, a small diameter portion 14, and an insertion hole for the rotating shaft 6. It is provided with 15.

The operation portion 11 is provided at the tip end portion (front end portion) of the screw shaft 7, and a part thereof protrudes to the outside of the housing 4. The operation unit 11 can come into contact with the operation target P or move away from the operation target P by the linear movement of the screw shaft 7.

The male screw portion 12 is provided between the operation portion 11 and the large diameter portion 13. The male screw portion 12 is composed of a trapezoidal screw, but is not limited to this configuration, and may be composed of other screws such as a triangular screw. The pitch of the male screw portion 12 is preferably set larger than the pitch (coarse grade) defined in JIS B 0217-2, but is not limited to this range. When the male thread portion 12 is composed of a triangular thread, the pitch is preferably set to be larger than the pitch (coarse grade) defined in JIS B 0209-1, but is not limited to this range. .. The male threaded portion 12 includes a leading flank surface 12a in contact with the female threaded portion 10 and a trailing flank surface 12b formed on the opposite side of the advancing flank surface 12a.

The large diameter portion 13 functions as a locking portion for locking a part of the urging member 8. The large diameter portion 13 has a side surface (locking surface) 13a that contacts the end portion of the urging member 8. The large diameter portion 13 also functions as a part of the rotation regulation mechanism 9, as will be described later.

The small diameter portion 14 is integrally formed with the large diameter portion 13. The small diameter portion 14 functions as a support portion that supports the urging member 8. The small diameter portion 14 is formed at the end of the screw shaft 7 on the side opposite to the operating portion 11.

The insertion hole 15 is formed inside the screw shaft 7 in the range from the small diameter portion 14 to the male screw portion 12. The insertion hole 15 has an insertion port 15a for inserting the rotating shaft 6 of the motor 2 into the end surface of the small diameter portion 14. The inner surface of the insertion hole 15 and the outer surface of the rotating shaft 6 are connected by means such as spline fitting and key fitting. With this configuration, the screw shaft 7 and the rotating shaft 6 are configured to be movable relative to the axial direction.

The urging member 8 is composed of an elastic member, and is exemplified as a coil spring in this embodiment. The coil spring is composed of a compression spring. One end of the coil spring is inserted into the small diameter portion 14 of the screw shaft 7 and is in contact with the side surface 13a of the large diameter portion 13, and the other end is supported by the housing 4. In the compressed state, the coil spring urges the screw shaft 7 forward by its elastic restoring force.

As shown in FIGS. 2 and 3, the rotation regulation mechanism 9 includes a first locking portion 16 formed on the screw shaft 7 and a second locking portion 17 formed on the housing 4. The first locking portion 16 is composed of a protrusion that projects outward in the radial direction from the outer surface of the large diameter portion 13. The second locking portion 17 is composed of a protrusion that projects inward from the inner surface of the second accommodating portion 4b of the housing 4. The rotation regulating mechanism 9 regulates the rotation of the screw shaft 7 by contacting the first locking portion 16 and the second locking portion 17.

The female screw portion 10 is formed on the inner surface of the second accommodating portion 4b of the housing 4. The housing 4 is provided with the female screw portion 10 to have the function of a nut in the screw mechanism 3. The female thread portion 10 is composed of a trapezoidal screw, but is not limited to this structure, and may be composed of another screw such as a triangular screw. It is desirable that the specifications of the female thread portion 10 are set so as to correspond to the male thread portion 12. The female thread portion 10 includes an advancing flank surface 10a that contacts the advancing flank surface 12a of the male threaded portion 12 and a chasing flank surface 10b formed on the opposite side of the advancing flank surface 10a.

The female screw portion 10 and the male screw portion 12 are composed of right-handed screws, and when the rotating shaft 6 is viewed from the motor body 5 side (rear side) of the motor 2, the screw shaft 7 watches the rotating shaft 6. It is configured to move forward when rotated clockwise.

As shown in FIGS. 1 and 4, a backlash (gap) BL is provided between the male screw portion 12 of the screw shaft 7 and the female screw portion 10 of the housing 4. The axial dimension X of the backlash BL is preferably 0.3 mm or more, but is not limited to this numerical range, and can be appropriately set according to the size of the linear actuator 1 and the type of the operation target P. Further, the ratio (X / √L) of the axial dimension X of the backlash BL to the square root of the lead (L) is preferably 0.3 or more, but is not limited to this numerical range.

The housing 4 includes a female screw portion 10, a partition wall 18 for partitioning the first accommodating portion 4a and the second accommodating portion 4b, and a thrust bearing 19 for supporting the urging member 8. The partition wall 18 has a hole 20 through which the rotating shaft 6 of the motor 2 is inserted. The thrust bearing 19 is supported by the partition wall 18 and also supports the end portion of the urging member 8.

Hereinafter, the operation of the linear actuator 1 having the above configuration will be described.

When the rotary shaft 6 is rotated by the drive of the motor 2, the rotary motion is converted into the linear motion of the screw shaft 7 by the screw mechanism 3 (motion conversion mechanism). In this case, the urging member 8 urges the screw shaft 7 forward, and the advancing flank surface 12a of the male screw portion 12 of the screw shaft 7 is the advancing flank surface 10a of the female screw portion 10 related to the housing 4. It is in contact with. The screw shaft 7 moves (advances) toward the front operation target P while rotating together with the rotation shaft 6 by the action of screwing the male screw portion 12 and the female screw portion 10. As a result, the screw shaft 7 is operated by bringing the operation unit 11 into contact with the operation target P. When the screw shaft 7 rotates by a predetermined angle, the first locking portion 16 and the second locking portion 17 of the rotation regulating mechanism 9 come into contact with each other, and the rotation and axial movement of the screw shaft 7 are restricted.

For example, when an impact is applied to the operation target P and the impact acts on the screw shaft 7, the screw shaft 7 tends to move backward. At this time, the screw mechanism 3 can absorb this impact by the elastic restoring force of the urging member 8 that urges the screw shaft 7 forward. Depending on the degree of impact, the advancing flank surface 12a of the male threaded portion 12 may be separated from the advancing flank surface 10a of the female threaded portion 10 (indicated by the alternate long and short dash line in FIG. 4). Even in this case, the urging member 8 is further compressed and absorbs the impact by the increased elastic restoring force. After absorbing the impact, the urging member 8 moves the screw shaft 7 forward to bring the advancing flank surface 12a of the male screw portion 12 into contact with the advancing flank surface 10a of the female screw portion 10 again.

In the present embodiment, even when an impact is applied to the screw shaft 7, the follow-up flank surface 12b of the male screw portion 12 becomes the follow-up flank surface of the female screw portion 10 due to the elastic restoring force of the urging member 8 and the backlash BL. Contact with 10b is prevented. As a result, it is possible to reliably prevent the male screw portion 12 and the female screw portion 10 from being bitten.

Further, by forming the urging member 8 with a coil spring and inserting the coil spring into the small diameter portion 14 of the screw shaft 7, the second accommodating portion of the housing 4 which is a retracting space for the screw shaft 7 as a linear motion member. The urging member 8 can be suitably arranged in 4b, and the urging member 8 can be easily attached to the screw shaft 7.

Further, by forming the female screw portion 10 in the second accommodating portion 4b of the housing 4, it is not necessary to separately prepare a nut member to be screwed into the male screw portion 12 of the screw shaft 7, and the number of parts of the linear actuator 1 can be increased. It can be reduced.

The present invention is not limited to the configuration of the above-described embodiment, and is not limited to the above-mentioned action and effect. The present invention can be modified in various ways without departing from the gist of the present invention.

In the above embodiment, an example in which the rotating shaft 6 of the motor 2 and the screw shaft 7 of the screw mechanism 3 are connected so as to be relatively movable in the axial direction is shown, but the present invention is not limited to this configuration. For example, the motor body 5 is housed in the first accommodating portion 4a of the housing 4 so as to be movable in the axial direction, the rotating shaft 6 of the motor 2 is press-fitted into the insertion hole 15 of the screw shaft 7, and the screw shaft 7 and the rotating shaft are press-fitted. 6 may be configured to rotate and move in the axial direction integrally.

In this embodiment, when the rotating shaft 6 of the motor 2 rotates, the screw shaft 7 of the screw mechanism 3 rotates with the rotating shaft 6 and moves forward (or backward) by screwing the male screw portion 12 and the female screw portion 10. Advance (or evacuate). At this time, the motor main body 5 advances (or retracts) forward (or backward) together with the screw shaft 7 in the first accommodating portion 4a of the housing 4. In this embodiment, it is preferable that the first accommodating portion 4a of the housing 4 is provided with a detent mechanism that allows the motor body 5 to move in the axial direction while preventing the motor body 5 from rotating.

In the above embodiment, an example in which the urging member 8 is configured by a coil spring is shown, but the present invention is not limited to this configuration, and the urging member is urged by a spring member other than the coil spring or an elastic member other than the spring member. 8 may be configured. Further, the urging member 8 is not limited to the elastic member, and may be any member that can generate a force for urging the screw shaft 7.

In the above embodiment, the linear actuator 1 in which the female screw portion 10 which is a component of the screw mechanism 3 is formed inside the housing 4 is illustrated, but the present invention is not limited to this configuration, and the nut is provided in the housing 4. It may be arranged, or the female screw portion 10 may be formed on a member other than the housing 4.

1 Linear actuator 2 Motor 3 Screw mechanism (motion conversion mechanism)
4 Housing 7 Thread shaft 8 Biasing member 10 Female thread 12 Male thread BL backlash

Claims (4)

In a linear actuator including a motor and a motion conversion mechanism that converts the rotational motion of the motor into linear motion.
The motion conversion mechanism includes a screw shaft as a linear motion member having a male screw portion, a female screw portion screwed into the male screw portion, and an urging member for urging the screw shaft.
A backlash is provided between the male threaded portion and the female threaded portion.
The urging member is a linear actuator characterized in that the screw shaft is urged so that the male screw portion is brought into contact with the female screw portion. The linear actuator according to claim 1, wherein the urging member is composed of a compression spring and urges the screw shaft so that the male screw portion is brought into contact with the female screw portion by an elastic restoring force. A housing for accommodating the motion conversion mechanism is provided.
The linear actuator according to claim 1 or 2, wherein the female screw portion is formed in the housing. The urging member is a coil spring.
The linear actuator according to any one of claims 1 to 3, wherein the coil spring is inserted through a part of the screw shaft.

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