JP6111038B2 - Electric linear actuator - Google Patents

Description

  The present invention relates to an electric linear actuator provided with a ball screw mechanism used in a drive unit of a general industrial electric motor or automobile, and more specifically, a rotational input from an electric motor is applied to the ball screw in an automobile transmission or a parking brake. The present invention relates to an electric linear actuator that converts a linear motion of a drive shaft through a mechanism.

  In electric linear actuators used for 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 movement of the electric motor into a linear linear movement. 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 linear actuator, for example, a ball screw shaft constituting a ball screw can be driven to rotate by an electric motor supported by a housing, and an output member coupled to a nut by rotating the ball screw shaft. Can be displaced in the axial direction. Since the ball screw mechanism has very low friction and the ball screw shaft easily rotates due to the thrust load acting on the output member side, it is necessary to hold the position of the output member when the electric motor is stopped.

  Therefore, for example, a brake means is provided in the electric motor, or a low-efficiency thing such as a worm gear is provided as a transmission means. As a typical example, an electric linear actuator as shown in FIG. It has been known. The electric linear actuator 50 includes a ball screw shaft 51 that is rotationally driven by an electric motor (not shown), and a ball screw nut 52 that is screwed onto the ball screw shaft 51 via a ball (not shown). A ball screw mechanism 53 provided is employed. When a motor shaft (not shown) of the electric motor is rotated, the ball screw shaft 51 connected to the motor shaft is rotated, and the ball screw nut 52 is moved in a linear motion (left-right direction in the figure).

  The ball screw shaft 51 is rotatably supported by cylindrical housings 54 and 55 by two rolling bearings 56 and 57. These rolling bearings 56 and 57 are fixed by a locking member 59 for preventing loosening via a fixing lid 58.

  A spiral screw groove 51a is formed on the outer periphery of the ball screw shaft 51, and a cylindrical ball screw nut 52 is screwed through the ball. A spiral screw groove 52a is formed on the inner periphery of the ball screw nut 52, and a large diameter portion 60 is formed at the end.

  A flat portion 61 is formed on the side surface of the large-diameter portion 60 and is cut so that the end surface is flat. A cam follower (rotation stop means) 62 projects from the substantially central portion of the flat portion 61 toward the outside in the radial direction. The cam follower 62 is engaged with a notch (not shown) formed in the housing 54.

  Since the cam follower 62 is thus fitted in the notch, the ball screw nut 52 does not rotate with the rotation of the ball screw shaft 51, and the cam follower 62 rotates to the notch. Since it slides, the problem of sliding friction and wear can be reduced (for example, refer to Patent Document 1).

JP 2007-333046 A

  In such a conventional electric linear actuator 50, since the cam follower 62 is used as a means for preventing the rotation of the ball screw nut 52, the problem of sliding friction and wear can be reduced and the torque can be reduced. Since the rolling bearing itself is used, the cost may increase. Further, when the housing 54 uses an aluminum material, it is necessary to take measures against wear.

  The present invention has been made in view of the above-described problems of the prior art, and provides an electric linear actuator having a simple structure and a low-cost screw shaft detent mechanism while reducing the wear of the housing. For the purpose.

In order to achieve such an object, the invention according to claim 1 of the present invention includes an aluminum alloy housing, an electric motor attached to the housing, and a rotational force of the electric motor transmitted via a motor shaft. And a ball screw mechanism that converts the rotational movement of the electric motor into a linear movement in the axial direction of the drive shaft via the reduction mechanism, and the ball screw mechanism is a support bearing mounted on the housing. And a nut that is supported so as not to move in the axial direction and has a spiral thread groove formed on the inner periphery, and is inserted into the nut via a number of balls and is coaxial with the drive shaft. And a screw shaft that is formed on the outer periphery of the screw shaft so as to correspond to the screw groove of the nut and is supported so as to be non-rotatable and axially movable with respect to the housing. Re In A the actuator is fastened through the steel sleeve external thread for detent of the screw shaft in a bag hole of the housing Rutotomoni a recess formed in an end portion of the blind bore of the housing, an end surface of the sleeve The sleeve is prevented from rotating with respect to the bag hole of the housing by a caulking portion formed by plastically deforming the outer diameter portion toward the recess .

As described above, a reduction mechanism that transmits the rotational force of the electric motor and a ball screw mechanism that converts the rotational movement of the electric motor into the linear movement in the axial direction of the drive shaft via the reduction mechanism are provided. A nut rotatably supported through a pair of support bearings mounted on the housing and not axially movable, and having a helical thread groove formed on the inner periphery, and a number of balls on the nut Screw that is interpolated and integrated coaxially with the drive shaft, has a helical thread groove corresponding to the thread groove of the nut on the outer periphery, and is supported so as to be non-rotatable and axially movable with respect to the housing the electric linear actuator which is constituted by a shaft, is fastened through the steel sleeve external thread for detent of the screw shaft in the bag holes in the housing Rutotomoni a recess formed in an end portion of the blind bore of the housing, The Because detent sleeve with respect to the bag holes in the housing is made an outer diameter of the end face of the over blanking the caulking portion formed by plastically deformed toward the recesses, the screw shaft with a simple structure While the rotation can be stopped at low cost, the wear of the housing can be reduced.

Further, as in the invention described in claim 2 , if the male screw is provided near the bottom of the bag hole, the screw connection between the housing and the sleeve, each having a different linear expansion coefficient due to the temperature rise, is accompanied by a temperature rise. A change in axial force can be suppressed.

An electric linear actuator according to the present invention includes 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 reduction mechanism. A ball screw mechanism that converts the rotational motion of the electric motor into a linear motion in the axial direction of the drive shaft, and the ball screw mechanism is rotatable through a support bearing mounted on the housing and moved in the axial direction. A nut that is unsupported and has a spiral thread groove formed on the inner periphery, and is inserted into the nut via a number of balls and integrated coaxially with the drive shaft. An electric linear actuator comprising a screw shaft that is formed with a helical screw groove corresponding to the groove and is supported so as to be non-rotatable and axially movable with respect to the housing. Oite, steel sleeve anti-rotation of the screw shaft in a bag hole of the housing is fastened via an external thread Rutotomoni a recess formed in an end portion of the blind bore of the housing, the end surface of the sleeve Since the sleeve is prevented from rotating with respect to the bag hole of the housing by a crimped portion formed by plastic deformation of the outer diameter portion toward the recess , the screw shaft can be prevented from rotating with a simple configuration. This can be done at a low cost, and the wear of the housing can be reduced.

1 is a longitudinal sectional view showing an embodiment of an electric linear actuator according to the present invention. It is a longitudinal cross-sectional view which shows the actuator main body of FIG. 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 modification of FIG. (A) is a front view which shows the fixing | fixed part of the sleeve of FIG. 1, (b) is sectional drawing along the IV-IV line of (a). 1 shows a modification of the sleeve of FIG. 1, (a) is a front view showing a fixing portion of the sleeve, and (b) is a cross-sectional view taken along line VV of (a). It is a longitudinal cross-sectional view which shows the conventional electric linear actuator.

A housing made of aluminum alloy, an electric motor attached to the housing, a reduction mechanism that transmits the rotational force of the electric motor via a motor shaft, and a rotational axis of the electric motor via the reduction mechanism A ball screw mechanism that converts the linear screw motion into an axial linear motion of the motor, and the ball screw mechanism is supported by a support bearing mounted on the housing so as to be rotatable and non-movable in the axial direction. And a helical thread groove that is inserted into the nut through a large number of balls, is coaxially integrated with the drive shaft, and corresponds to the thread groove of the nut on the outer periphery. In the electric linear actuator composed of a screw shaft that is formed so as to be non-rotatable with respect to the housing and supported so as to be axially movable,
A steel sleeve is fastened to the bag hole of the housing via a threaded portion, a concave groove extending in the axial direction is formed on the inner periphery of the sleeve, and a locking pin is implanted at the end of the threaded shaft. A plurality of recesses are formed in the end portion of the bag hole of the housing at equal intervals in the circumferential direction, and the outer diameter portion of the end surface of the sleeve is plastically deformed toward these recesses. The sleeve is prevented from rotating by the crimped portion.

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 linear actuator according to the present invention, FIG. 2 is a longitudinal sectional view showing an actuator body of FIG. 1, and FIG. 3 is a main portion showing an intermediate gear portion of FIG. 4 is an enlarged view of a main part showing a modification of FIG. 3, FIG. 5 (a) is a front view showing a fixing part of the sleeve of FIG. 1, and FIG. 4 (b) is an IV-IV of FIG. 6 is a sectional view taken along the line, FIG. 6 shows a modified example of the sleeve of FIG. 1, (a) is a front view showing a fixing portion of the sleeve, and (b) is taken along line VV of (a). FIG.

  As shown in FIG. 1, the electric linear actuator 1 includes a cylindrical housing 2, an electric motor (not shown) attached to the housing 2, and an input gear attached to a motor shaft 3a of the electric motor. 3 and an output gear 5 meshed with the intermediate gear 4, and the rotational motion of the electric motor is converted into a linear motion in the axial direction of the drive shaft 7 via the speed reduction mechanism 6. A ball screw mechanism 8 for conversion and an actuator main body 9 including the ball screw mechanism 8 are provided.

  The housing 2 is formed by die casting from an aluminum alloy such as A6061 or ADC12, and is heated to a high temperature to form a solid solution, followed by a quenching process in which it is rapidly cooled in water and subsequently kept at room temperature or at a low temperature. A so-called precipitation hardening process, in which a large lattice strain is generated in the precipitated phase and hardened by a heat treatment composed of an age hardening treatment (tempering treatment) that is heated to (100 to 200 ° C.) for precipitation, is performed. As a result, the mass productivity can be improved and the cost can be reduced. In addition, the strength can be increased to reduce the amount of aluminum used, and the weight can be reduced. The housing 2 includes a first housing 2a and a second housing 2b abutted on the end surface thereof, and is integrally fixed by a fixing bolt (not shown). An electric motor is attached to the first housing 2a, and bag holes 11 and 12 for accommodating the screw shaft 10 are formed at the abutting portions of the first housing 2a and the second housing 2b. Yes.

  The motor shaft 3a of the electric motor is rotatably supported by a rolling bearing 13 comprising a deep groove ball bearing mounted on the second housing 2b. . The output gear 5 that meshes with the intermediate gear 4 that is a spur gear is integrally fixed to 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 sleeve 17 described later is fitted into the bag hole 12 of the second housing 2b. Then, the locking pin 15 of the screw shaft 10 is engaged with the concave grooves 17a and 17a formed in the axial direction at positions facing the circumferential direction of the sleeve 17, so that the screw shaft 10 is not rotatable and moves in the axial direction. Supported as possible.

  As shown in an enlarged view in FIG. 2, the ball screw mechanism 8 includes a screw shaft 10 and a nut 18 that is externally inserted to the screw shaft 10 via a ball 19. The screw shaft 10 has a spiral thread groove 10a formed on the outer periphery. On the other hand, the nut 18 is extrapolated to the screw shaft 10, and a helical screw groove 18 a corresponding to the screw groove 10 a of the screw shaft 10 is formed on the inner periphery, and a large number of screws 18 a and 18 a are formed between these nuts 18. A ball 19 is accommodated so as to roll freely. The nut 18 is supported to the housings 2a and 2b via the two support bearings 20 and 20 so as to be rotatable and not movable in the axial direction. Reference numeral 21 denotes a piece member that constitutes a circulation member by connecting the thread grooves 18a of the nut 18, and the piece member 21 allows an infinite circulation of a large number of balls 19.

  The cross-sectional shape of each of the thread grooves 10a and 18a may be a circular arc shape or a gothic arc shape, but here, a gothic arc shape that allows a large contact angle with the ball 19 and a small axial clearance can be set. Is formed. Thereby, the rigidity with respect to an axial load becomes high and generation | occurrence | production of a vibration can be suppressed.

  The nut 18 is made of case-hardened steel such as SCM415 or SCM420, and its surface is subjected to hardening treatment in a range of 55 to 62 HRC by vacuum carburizing and quenching. 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 made of medium carbon steel such as S55C or case-hardened steel such as SCM415 or SCM420, and its surface is hardened in the range of 55 to 62 HRC by induction hardening or carburizing hardening.

  The output gear 5 constituting the speed reduction mechanism 6 is integrally fixed to the outer peripheral surface 18b 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. In addition, the rolling bearing of the same specification means a bearing having the same inner diameter, outer diameter, width dimension, rolling element size, number, bearing internal clearance, and the like.

  Also, here, one of the pair of support bearings 20, 20 is mounted on 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 inner ring outer diameter d 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 washer 27 is in contact with only the outer ring of the support bearing 20 and is an inner ring that 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 inner ring of the support bearing 20 is prevented from coming into contact with the housing 2a and the frictional force is prevented from increasing, and the locked state Can be prevented.

  Here, as shown in FIG. 3, the gear shaft 22 is implanted in the first and second housings 2 a and 2 b, and the intermediate gear 4 is rotatably supported on the gear shaft 22 via a rolling bearing 23. ing. Of the end portions of the gear shaft 22, for example, when the end portion on the first housing 2 a side is press-fitted, the end portion on the second housing 2 b side is set as a clearance fit, thereby misalignment (assembly error). And 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, availability 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.

  FIG. 4 shows a modification of FIG. The gear shaft 22 is implanted in the first and second housings 2 a and 2 b, and the intermediate gear 29 is rotatably supported on the gear shaft 22 via a slide bearing 30. In the present embodiment, the intermediate gear 29 is formed so that the width of the tooth portion 29b is the same as the tooth width, and the sliding bearing 30 is press-fitted into the inner diameter 29a of the intermediate gear 29 and added with fine graphite powder. An oil-impregnated bearing (NTN trade name; Bear Fight (registered trademark)) made of The tooth width of the intermediate gear 29 is set to be larger. This prevents the intermediate gear 29 from coming into contact with the first and second housings 2a and 2b without wearing a washer, and suppresses frictional resistance during rotation, thereby obtaining smooth rotational performance. In addition, the cost can be reduced by suppressing the increase in the number of parts. In addition, the sliding bearing 30 may be formed of, for example, a thermoplastic polyimide resin that enables injection molding.

  As shown in FIG. 1, a sleeve 17 that supports the screw shaft 10 so as not to rotate and to be movable in the axial direction is fitted in 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, by moving the sleeve 17 while rotating it toward the bottom 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. 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 it can aim at low cost.

  Further, as shown in FIGS. 5A and 5B, a plurality of recesses 31 (four in this case) are formed on the end surface of the second housing 2 b at equal intervals in the circumferential direction, and at the end surface of the sleeve 17. The sleeve 17 is prevented from rotating by a caulking portion 32 formed by plastic deformation of the outer diameter portion toward the concave portion 31.

  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 main body 9, even in a high temperature region, even if the screw fastening between the second housing 2 b and the sleeve 17 having different linear expansion coefficients is loose, the screwing portion 32 causes the screw to tighten. Can be prevented and reliability is improved.

  6A and 6B show a modification of the sleeve 17 described above. The sleeve 33 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 plurality of (in this case, four) recesses 34 are formed on the end surface of the second housing 2b ′ in the circumferential direction, and the outer diameter portion of the end surface of the sleeve 33 is plastically deformed toward the recesses 34. The sleeve 33 is prevented from rotating by the formed caulking portion 35.

  Here, a plurality of recesses 34 are formed on the end surface of the second housing 2b ′, and the caulking portion 35 of the sleeve 33 is engaged with the recesses 34, but this is not limiting and not shown. However, a plurality of recesses are formed on the end surface of the sleeve at equal intervals in the circumferential direction, and the sleeve is prevented from rotating by a caulking portion formed by plastic deformation of the inner diameter portion of the end surface of the second housing toward the recess. May be. Thereby, since the soft 2nd housing side which consists of aluminum alloys is plastically deformed, workability becomes high and workability | operativity can be improved.

  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 linear actuator according to the present invention is used in a drive unit of a general industrial electric motor, automobile, etc., and has a ball screw mechanism that converts rotational input from an electric motor into linear motion of a drive shaft via the ball screw mechanism. It can be applied to the provided electric linear actuator.

DESCRIPTION OF SYMBOLS 1 Electric linear actuator 2 Housing 2a 1st housing 2b, 2b '2nd housing 3 Input gear 3a Motor shaft 4, 29 Intermediate gear 4a, 29a Intermediate gear inner diameter 4b, 29b Tooth part 5 Output gear 6 Reduction mechanism 7 Drive Shaft 8 Ball screw mechanism 9 Actuator body 10 Screw shaft 10a, 18a Screw groove 11, 12 Bag hole 12a Female screw 13, 23 Rolling bearing 14 Key 15 Locking pin 16 Retaining ring 17, 33 Sleeve 17a Concave groove 17b Male screw 18 Nut 18b Nut Outer peripheral surface 19 ball 20 support bearing 20a shield plate 21 piece member 22 gear shaft 24 outer ring 25 cage 26 needle rollers 27 and 28 washers 30 slide bearings 31 and 34 concave portions 32 and 35 caulking portion 50 electric linear actuator 51 ball screw Shaft 51a, 52a Thread groove 52 Ball screw nut 3 the inner ring outer diameter of the ball screw mechanism 55 stopping member 60 large diameter portion 61 flat portion 62 cam follower D washer inner diameter d support bearing for the cover 59 locking the housing 56, 57 rolling bearing 58 fixed

Claims (2)

An aluminum alloy 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 mechanism that converts the rotational motion of the electric motor to linear motion in the axial direction of the drive shaft via the speed reduction mechanism;
The ball screw mechanism 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 linear actuator composed of a screw shaft supported so as to be axially movable,
Rutotomoni are fastened through steel sleeve external thread for detent of the screw shaft in a bag hole of the housing, the recess is formed at an end of the blind bore of the housing, the outer diameter of the end face of the sleeve The electric linear actuator is characterized in that the sleeve is prevented from rotating with respect to the bag hole of the housing by a caulking portion formed by plastic deformation of the sleeve toward the recess . The electric linear actuator according to claim 1, wherein the male screw is provided near the bottom of the bag hole.

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