JP2017020630A - Ball screw and electric actuator having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ball screw which is reduced in weight by thinning a thickness of a housing, and improved in reliability by avoiding a collision of a screw shaft, and an electric actuator having the same.SOLUTION: In an electric actuator 1 having a screw shaft 10 which is non-rotatably and movably arranged at a housing 2 in an axial direction, screw grooves 9, 16 are formed of arc-shaped screw grooves 9a, 16a and serrated screw grooves 9b, 16b, and when a tension load is applied to the screw shaft 10, a clearance is not formed between the arc-shaped screw shafts 9a, 16a and balls 19, a clearance is formed between the serrated screw grooves 9b, 16b, and the arc-shaped screw grooves 16a, 9a and the balls 19 angularly contact with each other, thus forming a ball screw state. When a reverse input is applied to the screw shaft, a clearance is formed between the arc-shaped screw grooves 16a, 9a and the balls 19, a clearance is not formed between the serrated screw grooves 16b, 9b, and there arises a trapezoidal screw state by the slide contact of the arc-shaped screw grooves and the balls.SELECTED DRAWING: Figure 2

Description

  The present invention converts a ball screw used in a drive unit of a general industrial electric motor, automobile, etc., more specifically, a rotation input from an electric motor into a linear motion of a drive shaft in an automobile transmission, a parking brake, or the like. The present invention relates to a ball screw and an electric actuator provided with the ball screw.

  In electric actuators used in various drive units, a gear mechanism such as a trapezoidal screw or a rack and pinion is generally used as a mechanism for converting the rotational motion of the electric motor into a linear motion in the axial direction. Since these conversion mechanisms involve a sliding contact portion, the power loss is large, and it is necessary to increase the size of the electric motor and increase the power consumption. Therefore, a ball screw mechanism has been adopted as a more efficient actuator.

  As a conventional electric actuator, for example, an electric motor supported by a housing can freely rotate a ball screw shaft constituting a ball screw, and an output member coupled to a nut by rotating the ball screw shaft. Displaceable in the axial direction. The ball screw mechanism has a very small frictional resistance, and the ball screw shaft is easily rotated by a thrust load acting on the output member side. Therefore, it is necessary to hold the position of the output member when the electric motor is stopped.

  In addition, when the electric actuator described above becomes uncontrollable due to a system error or the like, the ball screw shaft collides with the inner wall of the housing due to inertia force due to the load, and there is a risk of failure if the electric actuator has insufficient strength. is there. An electric actuator that solves this problem is shown in FIG. The electric actuator 51 includes a cylindrical housing 52, an electric motor (not shown) attached to the housing 52, and an intermediate gear 54 that meshes with an input gear 53 attached to a motor shaft 53a of the electric motor. A reduction mechanism 56 comprising an output gear 55 meshing with the intermediate gear 54, and a ball screw mechanism 58 for converting the rotational movement of the electric motor into the linear movement of the drive shaft 57 via the reduction mechanism 56; And an actuator body 59 having the ball screw mechanism 58.

  The housing 52 is made of an aluminum alloy, and includes a first housing 52a and a second housing 52b abutted on the end surface thereof. The first housing 52a is provided with an electric motor, and the first housing Bag holes 61 and 62 for accommodating the screw shaft 60 are formed in the abutting portion between the second housing 52b and the second housing 52b.

  The motor shaft 53a of the electric motor has an input gear 53 attached to its end portion so as not to be relatively rotatable by press fitting, and is rotatably supported by a rolling bearing 63 comprising a deep groove ball bearing mounted on the second housing 52b. . An output gear 55 that meshes with an intermediate gear 54 that is a spur gear is integrally fixed to a nut 64 that constitutes a ball screw mechanism 58 via a key 65.

  The drive shaft 57 is configured integrally with a screw shaft 60 constituting the ball screw mechanism 58, and a locking pin 66 is implanted at one end portion (right end portion in the figure) of the drive shaft 57. A steel sleeve 67 is fastened to the bag hole 62 of the second housing 52b. Then, the locking pin 66 of the screw shaft 60 is engaged with the concave grooves 67a and 67a formed in the axial direction at positions opposed to the circumferential direction of the sleeve 67, so that the screw shaft 60 cannot rotate and moves in the axial direction. Supported as possible.

  The ball screw mechanism 58 includes a screw shaft 60 and a nut 64 that is externally inserted to the screw shaft 60 via a ball 68. The screw shaft 60 has a spiral thread groove 60a formed on the outer periphery. On the other hand, the nut 64 is extrapolated to the screw shaft 60, and a helical screw groove 64a corresponding to the screw groove 60a of the screw shaft 60 is formed on the inner periphery, and a large number of nuts 64 are provided between the screw grooves 60a and 64a. A ball 68 is accommodated so as to roll freely. The nut 64 is supported by the housings 52a and 52b through two support bearings 69 and 69 so as to be rotatable and not movable in the axial direction.

  A sleeve 67 that supports the screw shaft 60 in a non-rotatable and axially movable manner is fastened to the bag hole 62 of the second housing 52b. Specifically, a female screw 62 a is formed in the bag hole 62 of the second housing 52 b, and a male screw 67 b that is screwed into the female screw 62 a is formed on the outer periphery of the sleeve 67. Then, by moving the sleeve 67 toward the bottom of the bag hole 62, the female screw 62a and the male screw 67b are engaged, and the sleeve 67 is fastened to the second housing 52b.

  The sleeve 67 is not in direct contact with the bottom of the second housing 52 b and is fastened via a cap 70. That is, the cap 70 is externally fitted to the end of the sleeve 67 and is integrally fitted to the bottom of the second housing 52b. As a result, the screw shaft 60 does not directly collide with the bag hole 62 of the second housing 52b, and damage and wear of the second housing 52b are reduced, while at the same time reducing the weight and improving the durability and strength. The reliability can be improved by increasing the reliability (see, for example, Patent Document 1).

JP 2014-43905 A

  In such a conventional electric actuator 51, the structure is improved in durability and strength so that it is safe even if the screw shaft 60 collides with the inner wall of the second housing 52b by inertia force, and the weight is reduced. However, since it is assumed that the screw shaft 60 collides, the cap 70 and the second housing 52b disposed at the end of the sleeve 67 require strength, and not only the material but also a certain level or more. Is required. This has been a hindrance to light weight and compactness.

  The present invention has been made in view of such problems of the prior art. Even when a system error occurs and control becomes impossible, the present invention focuses on a safety mechanism in which the screw shaft does not collide with the housing. An object of the present invention is to provide a ball screw and an electric actuator provided with the ball screw that are light and compact and that improve the reliability by avoiding a collision of a screw shaft.

  In order to achieve such an object, the invention according to claim 1 of the present invention includes a screw shaft having a helical thread groove formed on the outer peripheral surface thereof, and is externally fitted to the screw shaft, and the screw is formed on the inner peripheral surface thereof. In the ball screw comprising: a nut in which a spiral thread groove corresponding to the thread groove of the shaft is formed; and a plurality of balls accommodated in a rolling path formed by the opposing screw grooves, the screw shaft And the screw groove of the nut has an arcuate thread groove facing the arcuate screw groove of the screw shaft. And a serrated thread groove facing the serrated thread groove of the screw shaft.

  Thus, a screw shaft having a helical thread groove formed on the outer peripheral surface, and a nut that is fitted on the screw shaft and has a helical thread groove corresponding to the screw groove of the screw shaft formed on the inner peripheral surface. And a plurality of balls housed in a rolling path formed by opposing screw grooves, wherein the screw shaft has a circular groove and a sawtooth-shaped screw groove. And the nut thread groove is composed of an arc-shaped thread groove facing the arc-shaped thread groove of the screw shaft and a serrated thread groove facing the saw-tooth thread groove of the screw shaft. Therefore, when the screw shaft proceeds in the normal direction of travel, there is no clearance between the nut and the arc-shaped thread groove of the screw shaft and the ball, and there is no gap between the nut and the saw-tooth thread groove of the screw shaft. A clearance is generated, and the ball makes an angular contact with both arc-shaped thread grooves and the ball When the screw shaft moves in the opposite direction to the screw shaft, a clearance is generated between the nut and the arc-shaped thread groove of the screw shaft and the ball, and between the nut and the saw-tooth thread groove of the screw shaft. The gaps disappear, and both the sawtooth thread grooves come into sliding contact to form a trapezoidal screw. Therefore, it is highly efficient with respect to input load, and also acts as a brake with respect to external input. When the load is received by the saw-toothed thread groove, it becomes insensitive and cannot be controlled due to a system error, etc. In addition, it is possible to provide a ball screw that can block reverse input torque from the ball screw side.

  Preferably, as in the invention described in claim 2, the arcuate thread groove of the screw shaft is formed in a circular arc shape whose cross section is a partial arc of a quarter of the circumference, and the sawtooth The circular thread groove may be opposed to the arc-shaped thread groove in the axial direction, and the cross section may be formed in a trapezoidal shape.

  According to a third aspect of the present invention, the arc-shaped thread groove of the nut is formed in a circular arc shape whose cross section is a partial arc of a quarter of the circumference, and the sawtooth-shaped The thread groove may face the arcuate thread groove in the axial direction, and the cross section may be formed in a trapezoidal shape.

  According to a fourth aspect of the present invention, the serrated thread groove of the nut extends in a tangential direction of the arc-shaped thread groove, and is formed on a flat surface having an inclination angle of 0 ° to 20 ° with respect to the perpendicular. If it is made, the axial direction of the thread groove can be made compact.

  According to a fifth aspect of the present invention, the thread groove of the nut has a circular arc-shaped cross section, and projects radially inward from the end of the thread groove, and the cross section is formed in a trapezoidal shape. Two circular arcs having a radius of curvature larger than the radius of the ball. If it is formed in the Gothic arc shape which combined, it can hold | maintain a ball | bowl stably and can prevent rattling and can suppress generation | occurrence | production of abnormal noise and a vibration.

  According to a sixth aspect of the present invention, a housing, an electric motor attached to the housing, a reduction mechanism that transmits the rotational force of the electric motor via a motor shaft, and the reduction mechanism are provided. And a ball screw for converting the rotational motion of the electric motor into a linear motion in the axial direction of the drive shaft. The ball screw is rotatable through a support bearing mounted on the housing and cannot be moved in the axial direction. And a nut having a spiral thread groove formed on the inner periphery thereof, and a nut inserted into the nut via a number of balls, integrated with the drive shaft, and on the outer periphery thereof. And the ball screw is configured to include a screw shaft that is supported so as to be non-rotatable and axially movable with respect to the housing. When the ball screw according to any one of claims 1 to 5 is configured and a tensile load is applied to the screw shaft, there is no clearance between the nut and the arc-shaped screw groove of the screw shaft and the ball, A clearance is generated between the nut and the saw-tooth thread groove of the screw shaft, and the ball is in angular contact with both the arc-shaped thread grooves to form a ball screw, and reverse input is applied to the screw shaft. When a load is applied, a clearance is generated between the nut and the arcuate thread groove of the screw shaft and the ball, and there is no clearance between the nut and the sawtooth thread groove of the screw shaft. Both screw grooves come into sliding contact to form a trapezoidal screw.

  As described above, the housing, the electric motor attached to the housing, the reduction mechanism that transmits the rotational force of the electric motor through the motor shaft, and the rotational axis of the electric motor through the reduction mechanism are driven. The ball screw is converted to a linear motion in the axial direction of the screw, and the ball screw is supported by a support bearing mounted on the housing so as to be rotatable and non-movable in the axial direction. A nut formed with a groove, and a nut inserted into the nut through a large number of balls, integrated coaxially with the drive shaft, and formed with a helical thread groove corresponding to the thread groove of the nut on the outer periphery; An electric actuator comprising a screw shaft supported so as to be non-rotatable and axially movable, wherein the ball screw is constituted by the ball screw according to any one of claims 1 to 5. When a tensile load is applied to the screw shaft, there is no clearance between the nut and the arcuate thread groove of the screw shaft and the ball, and there is a clearance between the nut and the sawtooth thread groove of the screw shaft. When the ball is in angular contact with both arc-shaped thread grooves and a ball screw is in the state, and a reverse input is applied to the screw shaft, the clearance between the nut and the arc-shaped thread groove of the screw shaft and the ball Since there is no gap between the nut and the serrated thread groove on the screw shaft, both the sawtooth thread grooves come into sliding contact to form a trapezoidal screw, which is highly efficient for input loads. At the same time, it acts as a brake for external inputs, and when the load is received by the serrated thread groove, it becomes insensitive, and when it becomes uncontrollable due to a system error etc., the screw shaft is pushed by the load and its inertial force Even if overrun with It can be prevented from colliding with the bottom surface of the bag holes in the shaft end housing. Therefore, it is possible to provide an electric actuator that is improved in reliability by avoiding the collision of the screw shaft and reduced in weight and size by reducing the thickness of the housing.

  According to a seventh aspect of the present invention, a bag hole for accommodating the screw shaft is formed in the housing, and a steel sleeve is fastened through a threaded portion, and a shaft is formed on the inner periphery of the sleeve. If a concave groove extending in the direction is formed and a locking pin is implanted at the end of the screw shaft and engaged with the concave groove, the screw shaft cannot be rotated with respect to the housing and moved axially. It can be supported as possible.

  The ball screw according to the present invention includes a screw shaft having a helical thread groove formed on the outer peripheral surface thereof, and a helical screw groove that is fitted on the screw shaft and corresponds to the screw groove of the screw shaft on the inner peripheral surface. And a plurality of balls accommodated in a rolling path formed by opposing screw grooves, wherein the thread groove of the screw shaft has an arc-shaped cross section. And a saw-toothed thread groove, and the thread groove of the nut is opposed to the arc-shaped thread groove facing the arc-shaped thread groove of the screw shaft and the saw-tooth thread groove of the screw shaft. When the screw shaft moves in the normal direction of travel, there is no clearance between the nut and the arc-shaped thread groove of the screw shaft and the ball, and the nut and screw shaft A gap is formed between the serrated thread groove and When the ball contacts the angular contact and enters the ball screw state, and when the screw shaft moves in the opposite direction, a clearance is generated between the nut and the arc-shaped thread groove of the screw shaft and the ball, and a sawtooth shape of the nut and the screw shaft. There is no gap between the two screw grooves, and both the saw-toothed screw grooves slide and come into a trapezoidal screw state. Therefore, it is highly efficient with respect to input load, and also acts as a brake with respect to external input. When the load is received by the saw-toothed thread groove, it becomes insensitive and cannot be controlled due to a system error, etc. In addition, it is possible to provide a ball screw that can block reverse input torque from the ball screw side.

  An electric actuator according to the present invention includes a housing, an electric motor attached to the housing, a reduction mechanism that transmits the rotational force of the electric motor via a motor shaft, and the electric actuator via the reduction mechanism. A ball screw for converting the rotational motion of the motor into a linear motion in the axial direction of the drive shaft, and this ball screw is supported by a support bearing attached to the housing so as to be rotatable and not movable in the axial direction. , A nut having a helical thread groove formed on the inner periphery, and a nut inserted into the nut via a number of balls, integrated coaxially with the drive shaft, and corresponding to the thread groove of the nut on the outer periphery An electric actuator comprising a screw shaft formed with a helical screw groove and supported so as to be non-rotatable and axially movable with respect to the housing. The ball screw according to any one of claims 1 to 5, wherein when a tensile load is applied to the screw shaft, there is no clearance between the nut and the arc-shaped screw groove of the screw shaft and the ball. , A gap is generated between the nut and the sawtooth thread groove of the screw shaft, and the ball is in angular contact with both the arc-shaped screw grooves to form a ball screw, and the screw shaft is reversely input. When a load is applied, a clearance is generated between the nut and the arc-shaped thread groove of the screw shaft and the ball, and there is no clearance between the nut and the saw-tooth thread groove of the screw shaft. Since both screw grooves slide and come into a trapezoidal screw state, it is highly efficient for input loads and acts as a brake for external inputs. It becomes insensitive and When it becomes uncontrollable in such Temuera, be threaded shaft is pushed by the load is overrun by the inertia force can be prevented from colliding with the bottom surface of the bag holes in the shaft end housing of the screw shaft. Therefore, it is possible to provide an electric actuator that is improved in reliability by avoiding the collision of the screw shaft and reduced in weight and size by reducing the thickness of the housing.

It is a longitudinal section showing one embodiment of an electric actuator concerning the present invention. (A) is a longitudinal cross-sectional view which shows the ball screw mechanism of FIG. 1, (b) is the principal part enlarged view of (a). It is a principal part enlarged view which shows the intermediate | middle gear part of FIG. It is a principal part enlarged view which shows the sleeve of FIG. (A) is explanatory drawing which shows the state at the time of the load load of the screw shaft of FIG. 2, (b) is explanatory drawing which shows the state at the time of the reverse input load of a screw shaft. (A) is a principal part enlarged view which shows the modification of the nut of FIG. 2, (b) is a principal part enlarged view which shows the other modification of the nut of FIG. It is a longitudinal cross-sectional view which shows the conventional electric actuator.

An aluminum alloy housing, an electric motor attached to the housing, a reduction mechanism that transmits the rotational force of the electric motor via a motor shaft, and the rotational movement of the electric motor is driven via the reduction mechanism A ball screw mechanism for converting the shaft into a linear motion in the axial direction.The ball screw mechanism is supported by a pair of support bearings mounted on the housing so as to be rotatable and non-movable in the axial direction. A nut having a spiral thread groove formed on the circumference, and a nut corresponding to the screw groove of the nut on the outer periphery, which is inserted into the nut via a large number of balls and is coaxially integrated with the drive shaft. In the electric actuator composed of a screw shaft formed so as to be non-rotatable and axially movable with respect to the housing,
The thread groove has an arc-shaped thread groove formed in a circular arc shape whose cross section is a partial arc of a quarter of the circumference, and is opposed to the arc-shaped thread groove in the axial direction, and the cross section is trapezoidal. And when a tensile load is applied to the screw shaft, there is no clearance between the nut and the arc-shaped screw groove of the screw shaft and the ball. A clearance is generated between the nut and the saw-tooth thread groove of the screw shaft, and the ball is in angular contact with both the arc-shaped thread grooves to form a ball screw, and reverse input is applied to the screw shaft. When a load is applied, a clearance is generated between the nut and the arcuate thread groove of the screw shaft and the ball, and there is no clearance between the nut and the sawtooth thread groove of the screw shaft. Both screw grooves slide and come in trapezoidal shape The state.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
1 is a longitudinal sectional view showing an embodiment of an electric actuator according to the present invention, FIG. 2 (a) is a longitudinal sectional view showing a ball screw mechanism of FIG. 1, and FIG. 1 (b) is a main portion of FIG. FIG. 3 is an enlarged view of a main part showing the intermediate gear part of FIG. 1, FIG. 4 is an enlarged view of a main part showing the sleeve of FIG. 1, and FIG. 5 (a) is a load applied to the screw shaft of FIG. FIG. 6B is an explanatory diagram showing the state of the screw shaft during reverse input load, FIG. 6A is an enlarged view of the main part showing a modification of the nut of FIG. ) Is an enlarged view of a main part showing another modified example of the nut of FIG. 2.

  As shown in FIG. 1, the electric actuator 1 meshes with a cylindrical housing 2, an electric motor M attached to the housing 2, and an input gear 3 attached to a motor shaft 3a of the electric motor M. A reduction mechanism 6 comprising an intermediate gear 4 and an output gear 5 meshed with the intermediate gear 4, and a ball screw for converting the rotational movement of the electric motor M into the axial movement of the drive shaft 7 via the reduction mechanism 6. And a mechanism 8.

  The housing 2 is made of an aluminum alloy such as A6063TE or ADC12, and includes a first housing 2a and a second housing 2b abutted on the end face thereof, and is fixed integrally by a fixing bolt (not shown). . An electric motor M is attached to the first housing 2a, and a through hole 11 and a bag hole 12 for accommodating the screw shaft 10 are formed in the first housing 2a and the second housing 2b. .

  The motor shaft 3a of the electric motor M is rotatably supported by a rolling bearing 13 composed of a deep groove ball bearing mounted on the second housing 2b. Yes. Further, the output gear 5 that meshes with the intermediate gear 4 that is a spur gear is integrally fixed to the outer periphery of a nut 18 that constitutes a ball screw mechanism 8 described later via a key 14.

  The drive shaft 7 is formed integrally with a screw shaft 10 constituting the ball screw mechanism 8, and a locking pin 15 is implanted at one end portion (right end portion in the figure) of the drive shaft 7. A cylindrical sleeve 17 described later is fastened to the bag hole 12 of the second housing 2b. And the groove | channel 17a, 17a extended in an axial direction is formed in the position which the circumferential direction of the sleeve 17 opposes, The latching pin 15 of the screw shaft 10 is engaged with this groove 17a, 17a, and the screw shaft 10 is The housing 2 is supported so as not to rotate and to be movable in the axial direction.

  The ball screw mechanism 8 includes a screw shaft 10 and a nut 18 that is externally inserted through the ball 19 to the screw shaft 10 as shown in an enlarged view in FIG. The screw shaft 10 has a spiral thread groove 9 formed on the outer periphery. On the other hand, the nut 18 is extrapolated to the screw shaft 10, and a spiral screw groove 16 corresponding to the screw groove 16 of the screw shaft 10 is formed on the inner periphery. A ball 19 is accommodated so as to roll freely. The nut 18 is supported by the first and second housings 2a and 2b via the two support bearings 20 and 20 so as to be rotatable and non-movable in the axial direction. Reference numeral 21 denotes a piece member that constitutes a circulation member by connecting the thread groove 16 of the nut 18, and a large number of balls 19 can be infinitely circulated by the piece member 21.

  The nut 18 is formed in a cylindrical shape from case-hardened steel such as SCM415 or SCM420, and the thread groove 16 is formed by machining such as turning. And the hardening process is given to the range of 55-62HRC by the surface by vacuum carburizing hardening. Thereby, the buffing etc. for the scale removal after the heat treatment can be omitted, and the cost can be reduced. On the other hand, the screw shaft 10 is formed in a cylindrical shape from medium carbon steel such as S55C or case-hardened steel such as SCM415 or SCM420, and the screw groove 9 is formed by machining such as turning. And the hardening process is given to the range of 55-62HRC on the surface by induction hardening or carburizing hardening. Thereby, mass productivity improves and cost reduction can be achieved. The thread groove 16 of the nut 18 and the thread groove 9 of the screw shaft 10 may be formed by rolling.

  An output gear 5 constituting the speed reduction mechanism 6 is integrally fixed to the outer peripheral surface 18a of the nut 18, and two support bearings 20 and 20 are press-fitted on both sides of the output gear 5 via a predetermined shimiro. . Thereby, even if a thrust load is applied from the drive shaft 7, it is possible to prevent the axial displacement between the support bearings 20 and 20 and the output gear 5. Further, the two support bearings 20 and 20 are constituted by sealed deep groove ball bearings having shield plates 20a and 20a attached to both ends, and leakage of the lubricating grease enclosed in the bearings to the outside and from the outside This prevents wear powder from entering the bearing.

  Further, in the present embodiment, the support bearing 20 that rotatably supports the nut 18 is composed of deep groove ball bearings having the same specifications, and thus is loaded from the drive shaft 7 through the thrust load and the output gear 5 described above. Both radial loads can be applied, and confirmation work for preventing misassembly during assembly can be simplified, and assembling workability can be improved. Here, the deep groove ball bearings having the same specifications refer to bearings having the same inner diameter, outer diameter, width dimension, rolling element size, number, bearing internal clearance, and the like.

  Further, here, one (left side in the figure) of the pair of support bearings 20 and 20 is attached to the first housing 2a via a washer 27 made of a ring-shaped elastic member. This washer 27 is formed by press working from an austenitic stainless steel plate (JIS standard SUS304 type or the like) having high strength and wear resistance, or a rust-proof cold rolled steel plate (JIS standard SPCC type or the like). It consists of a wave washer. The inner diameter D is formed larger than the outer diameter d of the inner ring 20 b of the support bearing 20. As a result, the axial backlash of the pair of support bearings 20 and 20 can be eliminated, smooth rotation performance can be obtained, and the inner ring that the washer 27 abuts only on the outer ring of the support bearing 20 and becomes a rotating ring. Therefore, even if a reverse thrust load is generated and the nut 18 is pressed against the first housing 2a, the end surface of the inner ring 20b of the support bearing 20 comes into contact with the first housing 2a and the frictional force increases. Can be prevented, and the locked state can be prevented.

  As shown in FIG. 3, the intermediate gear 4 constituting the speed reduction mechanism 6 is rotatably supported on a gear shaft 22 implanted in the first and second housings 2 a and 2 b via a rolling bearing 23. . Of the end portions of the gear shaft 22, for example, when press-fitting the end portion on the first housing 2a side, the end portion on the second housing 2b side is set to be a clearance fit, thereby making misalignment (assembly error). Allowing smooth rotation performance can be ensured. In the present embodiment, the rolling bearing 23 includes an outer ring 24 made of a steel plate press-fitted into the inner diameter 4 a of the intermediate gear 4, and a plurality of needle rollers 26 accommodated in the outer ring 24 via a cage 25 so as to be freely rollable. And so-called shell-type needle roller bearings. Thereby, the availability of a bearing is high and cost reduction can be achieved.

  Moreover, ring-shaped washers 28 and 28 are mounted on both sides of the intermediate gear 4 to prevent the intermediate gear 4 from directly contacting the first and second housings 2a and 2b. Here, the width of the tooth portion 4b of the intermediate gear 4 is formed smaller than the tooth width. As a result, the contact area with the washer 28 can be reduced, and the frictional resistance during rotation can be suppressed and smooth rotation performance can be obtained. Here, the washer 28 is a flat washer formed by pressing from an austenitic stainless steel plate having high strength and high wear resistance, or a cold-rolled steel plate treated with rust prevention. In addition to this, for example, it is formed of a thermoplastic synthetic resin such as PA (polyamide) 66 filled with a predetermined amount of a fibrous reinforcing material such as brass, sintered metal, or GF (glass fiber). May be.

  Furthermore, the width of the rolling bearing 23 is set smaller than the tooth width of the intermediate gear 4. Thereby, wear and deformation of the bearing side surface due to friction can be prevented, and smooth rotation performance can be obtained.

  As shown in FIG. 4, the sleeve 17 that supports the screw shaft 10 so as not to rotate but is movable in the axial direction is fastened to the bag hole 12 of the second housing 2 b. Specifically, a female screw 12 a is formed in the bag hole 12 of the second housing 2 b, and a male screw 17 b that is screwed into the female screw 12 a is formed on the outer periphery of the sleeve 17. Then, when the sleeve 17 is screwed (advanced while rotating) toward the bottom 12b of the bag hole 12, the female screw 12a and the male screw 17b are engaged, and the sleeve 17 is fastened to the second housing 2b.

  The sleeve 17 is formed in a cylindrical shape by cold forging from medium carbon steel such as S55C or case-hardened steel such as SCM415 or SCM420, and concave grooves 17a and 17a extending in the axial direction are formed at opposing positions on the inner periphery. Has been. A metal plating such as electroless nickel plating is applied to the surface of the groove 17a. On the other hand, the surface of the locking pin 15 that engages with the concave groove 17a is also plated with metal such as hard chrome plating. Thereby, abrasion resistance improves and abrasion can be suppressed over a long period of time. In addition, examples of the metal plating include zinc plating, unichrome plating, chromate plating, nickel plating, chrome plating, and Kanigen plating. Here, the metal plating is preferably made of different materials so that the concave groove 17a and the locking pin 15 can be prevented from sticking to each other during sliding.

  Further, in the present embodiment, a plurality of concave portions 29 are formed on the end surface of the second housing 2b at equal intervals in the circumferential direction, and the outer diameter portion of the end surface of the sleeve 17 is plastically deformed toward the concave portions 29. The sleeve 17 is prevented from rotating by the crimped portion 30. Thereby, it is possible to prevent the threaded portion of the sleeve 17 from loosening due to vibration during operation, and to improve reliability.

  In the present embodiment, the female screw 12 a of the second housing 2 b and the male screw 17 b of the sleeve 17 are provided near the bottom of the bag hole 12. Thereby, in the screw fastening of the second housing 2b and the sleeve 17 each having a different linear expansion coefficient depending on the temperature rise, it is possible to suppress the change in the axial force accompanying the temperature rise.

  Further, in the operating environment of the actuator body, particularly in a high temperature region, even if the screw fastening between the second housing 2b and the sleeve 17 having different linear expansion coefficients is loose, the caulking portion 30 causes the screw to tighten. Looseness can be prevented, and reliability is improved.

  Here, in the ball screw mechanism 8 according to the present invention, as shown in FIG. 2B, the screw shaft 10 and the thread grooves 9 and 16 of the nut 18 are formed in different cross-sectional shapes on the left and right. Specifically, the screw groove 9 of the screw shaft 10 includes an arcuate screw groove 9a that forms a normal ball screw and a saw-toothed screw groove 9b that forms a trapezoidal screw. Further, the screw groove 16 of the nut 18 includes an arcuate screw groove 16a that faces the screw groove 9a of the screw shaft 10 and a sawtooth screw groove 16b that faces the sawtooth screw groove 9b.

  The thread grooves 9a and 16a forming the ball screw are formed in a circular arc shape whose cross section is a partial arc of a quarter or two of the circumference. On the other hand, the thread grooves 9b and 16b forming the trapezoidal screw are opposed to the arc-shaped thread grooves 9a and 16a in the axial direction, and a cross section formed of a flat surface having an inclination angle with respect to the perpendicular is 0 ° to 20 ° is formed in a trapezoidal shape. Has been.

  Next, the operation of the ball screw mechanism 8 will be described in detail with reference to FIG. As shown in (a), when a tensile load such as an arrow (left side in the figure) is applied to the screw shaft 10, that is, when the screw shaft 10 proceeds in a normal traveling direction, the arc-shaped thread groove 16a of the nut 18 and There is no clearance S1 between the arcuate thread groove 9a of the screw shaft 10 and the ball 19, and there is a clearance S2 between the sawtooth thread groove 16b of the nut 18 and the sawtooth thread groove 9b of the screw shaft 10. As a result, the ball 19 is in angular contact with both the arc-shaped thread grooves 16a and 9a to form a ball screw.

  On the other hand, as shown in (b), when reverse input (external input) as indicated by an arrow (rightward direction in the figure) is applied to the screw shaft 10, the arc-shaped thread groove 16a of the nut 18 and the screw shaft 10 A clearance S1 is generated between the arcuate thread groove 9a and the ball 19, and there is no clearance S2 between the sawtooth thread groove 16b of the nut 18 and the sawtooth thread groove 9b of the screw shaft 10. Both screw grooves 16b and 9b come into sliding contact to form a trapezoidal screw.

  As a result, the input load becomes highly efficient, and also acts as a brake for the external input. The screw grooves 9b and 16b are insensitive to the load, and cannot be controlled due to a system error or the like. When the load is pushed by the load and the screw shaft 10 overruns with its inertial force, the shaft end (here, the right end surface) of the screw shaft 10 collides with the bottom surface 12b of the bag hole 12 of the second housing 2b. This can be prevented (see FIG. 1). Therefore, it is possible to provide the electric actuator 1 which is improved in reliability by avoiding the collision of the screw shaft 10 and reduced in weight and size by reducing the thickness of the first housing 2b.

  FIG. 6 shows a modification of the nut 18 described above. The nut 31 shown in (a) has a spiral thread groove 32 formed on the inner periphery, and the thread groove 32 includes a thread groove 32a having an arcuate cross section forming a normal ball screw, and the thread groove 32a. A sawtooth-shaped thread groove 16b that protrudes radially inward from the end and forms a trapezoidal screw is formed. The arc-shaped thread groove 32a is formed by a semicircle having a half of the circumference, and the cross-sectional shape is formed in a Gothic arc shape combining two arcs having a radius of curvature slightly larger than the radius of the ball 19. Has been. Thereby, the ball | bowl 19 can be hold | maintained stably and shakiness can be prevented and generation | occurrence | production of abnormal noise and a vibration can be suppressed. The thread groove 32a may have a circular arc shape formed of a single arc.

  The nut 33 shown in (b) has a spiral thread groove 34 formed on the inner periphery, and the thread groove 34 is formed from a thread groove 16a having a circular arc cross section forming a normal ball screw, and the thread groove 16a. It has a sawtooth-shaped thread groove 34a that protrudes radially inward and forms a trapezoidal screw.

  The serrated thread groove 34a has one tooth surface Ff (left side in the figure) facing the arc-shaped thread groove 16a in the axial direction, and the other tooth surface Bf (right side in the figure) is the arc-shaped thread groove 16a. It extends in the tangential direction and is formed on a flat surface having an inclination angle with respect to the vertical line of 0 ° to 20 °. As a result, the axial direction of the thread groove 34 can be made compact.

  The embodiment of the present invention has been described above, but the present invention is not limited to such an embodiment, and is merely an example, and various modifications can be made without departing from the scope of the present invention. Of course, the scope of the present invention is indicated by the description of the scope of claims, and further, the equivalent meanings described in the scope of claims and all modifications within the scope of the scope of the present invention are included. Including.

  An electric actuator according to the present invention includes a ball screw mechanism that is used in a drive unit of a general industrial electric motor, an automobile, or the like, and that converts a rotational input from an electric motor into a linear motion of a drive shaft via the ball screw mechanism. Applicable to electric actuators.

DESCRIPTION OF SYMBOLS 1 Electric actuator 2 Housing 2a 1st housing 2b 2nd housing 3 Input gear 3a Motor shaft 4 Intermediate gear 4a Inner gear inner diameter 4b Tooth part 5 Output gear 6 Reduction mechanism 7 Drive shaft 8 Ball screw mechanism 9, 16, 32 , 34 Thread grooves 9a, 16a, 32a Arc-shaped thread grooves 9b, 16b, 34b Serrated thread grooves 10 Screw shaft 11 Through hole 12 Bag hole 12a Female screw 12b Bottom surface 13 of bag hole Rolling bearing 14 Key 15 Locking Pin 17 Sleeve 17a Groove 17b Male thread 18, 31, 33 Nut 18a Nut outer peripheral surface 19 Ball 20 Support bearing 20a Shield plate 20b Inner ring 21 Piece member 22 Gear shaft 24 Outer ring 25 Cage 26 Needle rollers 27, 28 Washer 29 Recess 30 Caulking portion 51 Electric actuator 52 Housing 52a First housing 52 Second housing 53 Input gear 53a Motor shaft 54 Intermediate gear 55 Output gear 56 Reduction mechanism 57 Drive shaft 58 Ball screw mechanism 59 Actuator body 60 Screw shaft 60a, 64a Screw groove 61, 62 Bag hole 62a Female screw 63 Rolling bearing 64 Nut 65 Key 66 Locking pin 67 Sleeve 67a Concave groove 67b Male thread 68 Ball 69 Support bearing 70 Cap Bf, Ff Tooth surface of serrated thread groove D Washer inner diameter d Inner ring outer diameter M of support bearing Electric motor S1 Arc-shaped thread groove Clearance between ball and ball S2 Clearance between serrated thread groove

Claims (7)

A screw shaft having a helical thread groove formed on the outer peripheral surface;
A nut externally fitted to the screw shaft and having a helical thread groove corresponding to the thread groove of the screw shaft formed on the inner peripheral surface;
In a ball screw comprising: a plurality of balls accommodated in a rolling path formed by opposing screw grooves;
The thread groove of the screw shaft is composed of an arc-shaped thread groove and a saw-toothed thread groove in cross section, and the thread groove of the nut is arc-shaped facing the arc-shaped thread groove of the screw shaft. A ball screw comprising: a thread groove; and a saw-tooth thread groove facing the saw-tooth thread groove of the screw shaft.   The arcuate screw groove of the screw shaft is formed in a circular arc shape whose cross section is a partial arc of a quarter of the circumference, and the serrated screw groove is formed with the arcuate screw groove and the shaft. The ball screw according to claim 1, which faces in a direction and has a cross section formed in a trapezoidal shape.   The arc-shaped thread groove of the nut is formed in a circular arc shape whose cross section is a partial arc of a quarter of the circumference, and the saw-tooth thread groove is axially connected to the arc-shaped thread groove The ball screw according to claim 1, which has a trapezoidal cross section.   The ball screw according to claim 3, wherein the sawtooth-shaped thread groove of the nut extends in a tangential direction of the arc-shaped thread groove, and is formed on a flat surface having an inclination angle with respect to a vertical line of 0 ° to 20 °.   The thread groove of the nut is composed of a thread groove having an arc-shaped cross section, and a sawtooth-shaped thread groove projecting radially inward from an end portion of the thread groove and having a trapezoidal cross section. The arc-shaped thread groove is formed of a semicircle having a substantially half circumference, and the cross-sectional shape thereof is formed in a Gothic arc shape combining two arcs having a radius of curvature larger than the radius of the ball. 3. A ball screw according to 3. A housing;
An electric motor attached to the housing;
A speed reduction mechanism for transmitting the rotational force of the electric motor via the motor shaft;
A ball screw for converting the rotational movement of the electric motor into a linear movement in the axial direction of the drive shaft through the reduction mechanism;
The ball screw is rotatably supported via a support bearing mounted on the housing and is not axially movable, and a nut having a helical thread groove formed on the inner periphery,
The nut is inserted through a large number of balls and is integrated coaxially with the drive shaft. A spiral screw groove corresponding to the screw groove of the nut is formed on the outer periphery, and the nut cannot rotate with respect to the housing. And an electric actuator composed of a screw shaft supported so as to be axially movable,
The ball screw is constituted by the ball screw according to any one of claims 1 to 5,
When a tensile load is applied to the screw shaft, there is no clearance between the nut and the arcuate thread groove of the screw shaft and the ball, and there is no clearance between the nut and the sawtooth thread groove of the screw shaft. Occurs, the ball is in angular contact with both the arc-shaped screw grooves and becomes a ball screw state,
When a reverse input is applied to the screw shaft, a clearance is generated between the nut and the arc-shaped thread groove of the screw shaft and the ball, and a clearance is formed between the nut and the saw-tooth thread groove of the screw shaft. The electric actuator is characterized in that both of the saw-toothed screw grooves slide and come into a trapezoidal screw state.   A bag hole for accommodating the screw shaft is formed in the housing, and a steel sleeve is fastened via a screw portion, and a concave groove extending in the axial direction is formed on the inner periphery of the sleeve. The electric actuator according to claim 6, wherein a locking pin is implanted at an end portion and engaged with the concave groove.

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