JP5982220B2 - 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.

  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 the rotation stop means as the ball screw nut 52, the problem of sliding friction and wear can be reduced and the torque can be reduced. Since 62 itself uses a rolling bearing, the cost may increase.

  The present invention has been made in view of the problems of the prior art, and provides an electric linear actuator having a simple structure and a low-cost nut rotation prevention mechanism while reducing sliding friction and wear. For the purpose.

  In order to achieve the object, the invention according to claim 1 of the present invention transmits a cylindrical housing, an electric motor attached to the housing, and a rotational force of the electric motor via a motor shaft. A reduction mechanism, and a ball screw mechanism that converts the rotational movement of the electric motor to an axial linear movement of the drive shaft via the reduction mechanism, and the ball screw mechanism includes 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 thereof, and is inserted into the nut via a large number of balls and coaxial with the drive shaft. A screw thread shaft that is integrally formed and has a spiral thread groove corresponding to the thread groove of the nut formed on the outer periphery, and is supported so as to be non-rotatable and axially movable with respect to the housing; Said In the electric linear actuator in which a bag hole for accommodating the screw shaft is formed in the wing, a sleeve is fitted into the bag hole of the housing, a guide groove extending in the axial direction is formed in the sleeve, and the screw shaft A through-hole penetrating in the radial direction is formed at the end, and a guide pin is fitted into the through-hole through a slight radial gap and engaged with the guide groove of the sleeve.

  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 In an electric linear actuator that includes a shaft and has a bag hole that accommodates a screw shaft in the housing, a sleeve is fitted into the bag hole of the housing, and a guide groove extending in the axial direction is formed in the sleeve. In addition, a through-hole penetrating in the radial direction is formed at the end of the screw shaft, and a guide pin is inserted into the through-hole through a slight radial clearance and engaged with the guide groove of the sleeve. Therefore, the guide pin can freely rotate in the through-hole, thereby reducing sliding friction and wear, and providing an electric linear actuator having a simple structure and a cost-effective nut detent mechanism.

  Preferably, as in the invention described in claim 2, if the guide pin is made of a roller of a bearing and a crowning is formed on the outer peripheral surface, the wear resistance and shear strength are high, and the availability is good and the cost is low. Can be achieved.

  Further, as in the invention described in claim 3, if the guide groove is formed so as to oppose two places in the circumferential direction, the guide pin can be stably guided.

It is preferable as defined in claim 4, if it is the hard layer in the through hole is formed, to improve the wear resistance of the through-holes, performing stable support of the guide pins for a long time be able to.

  Further, as in the fifth aspect of the present invention, the guide pin may be rotatably supported in the through hole of the screw shaft via a bush.

  Further, as in the invention described in claim 6, the bush may be formed of a sintered alloy made of a material that can be carburized and hardened as the metal powder, and the bush described in claim 7. As in the invention, the bush may be formed of a synthetic resin filled with a fibrous reinforcing material. Thereby, the wear resistance of the bush can be improved, and the guide pin can be stably supported over a long period of time.

  Further, as in the invention described in claim 8, the guide pin may be rotatably supported in the through hole of the screw shaft via a rolling bearing made of a shell-type needle roller bearing. Thereby, sliding torque, sliding friction, and wear can be further reduced.

  Further, as in the ninth aspect of the invention, if the housing is made of an aluminum alloy and the sleeve is made of a material having higher material strength and wear resistance than the housing, durability is improved. Can be improved.

  An electric linear actuator according to the present invention includes a cylindrical housing, an electric motor attached to the housing, a speed reduction mechanism that transmits the rotational force of the electric motor via a motor shaft, and the speed reduction mechanism via the speed 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. The ball screw mechanism is rotatable via a support bearing mounted on the housing and cannot move 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 a screw shaft that is supported so as to be non-rotatable and axially movable with respect to the housing. In the electric linear actuator having a bag hole for accommodating the shaft, a sleeve is fitted into the bag hole of the housing, a guide groove extending in the axial direction is formed in the sleeve, and a diameter is formed at the end of the screw shaft. A through-hole penetrating in the direction is formed, and the guide pin is inserted into the through-hole through a slight radial clearance and engaged with the guide groove of the sleeve. It is possible to provide an electric linear actuator that is rotatable, reduces sliding friction and wear, and has a simple structure and a cost-effective nut rotation prevention mechanism.

(A) is a longitudinal cross-sectional view which shows one Embodiment of the electric linear actuator which concerns on this invention, (b) is a cross-sectional view along the II line | wire of (a). It is a longitudinal cross-sectional view which shows the ball screw mechanism of FIG. It is a principal part enlarged view which shows the rotation stop part of FIG. (A) is a principal part enlarged view which shows the modification of FIG. 3, (b) is a principal part enlarged view which shows the other modification of FIG. It is a longitudinal cross-sectional view which shows the conventional electric linear actuator.

  A cylindrical 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 a rotational movement of the electric motor via the reduction mechanism. A ball screw mechanism that converts linear motion in the axial direction, and this 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. A nut formed with a plurality of balls, and is inserted into the nut through a number of balls, is coaxially integrated with the drive shaft, and has a helical thread groove corresponding to the screw groove of the nut on the outer periphery. An electric linear motor that is formed with 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, and in which a bag hole that accommodates the screw shaft is formed in the housing. In the actuator, a sleeve is fitted in the bag hole of the housing, and guide grooves extending in the axial direction are formed in the sleeve so as to face each other in the circumferential direction, and penetrate the end portion of the screw shaft in the radial direction. A through hole in which a predetermined hardened layer is formed, a guide pin having a roller bearing roller formed in the through hole, and a crowning formed on the outer peripheral surface is inserted through a slight radial clearance, It is engaged with the guide groove of the sleeve.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1A is a longitudinal sectional view showing an embodiment of an electric linear actuator according to the present invention, FIG. 1B is a transverse sectional view taken along line II of FIG. 1A, and FIG. 3 is a longitudinal sectional view showing the actuator body of FIG. 3, FIG. 3 is an enlarged view of a main part showing the rotation prevention mechanism of FIG. 1, FIG. 4 (a) is an enlarged view of a main part showing a modification of FIG. It is a principal part enlarged view which shows the other modification of FIG.

  As shown in FIG. 1A, the electric linear actuator 1 includes a cylindrical housing 2, an electric motor 3 attached to the housing 2, and the rotational force of the electric motor 3 via a motor shaft 3a. A speed reduction mechanism 6 comprising a pair of spur gears 4 and 5 for transmission, and a ball screw mechanism 8 for converting the rotational motion of the electric motor 3 into the linear motion of the drive shaft 7 via the speed reduction mechanism 6 are provided. Yes.

  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 integrally fixed by a fixing bolt (not shown). Yes. An electric motor 3 is attached to the first housing 2a, and bag holes 9 and 10 for accommodating the screw shafts 12 are formed in the first housing 2a and the second housing 2b.

  A small spur gear 4 is attached to the end of the motor shaft 3a of the electric motor 3 so as not to be relatively rotatable by press fitting, and is rotatably supported by a rolling bearing 11 attached to the second housing 2b. The large spur gear 5 is integrally formed with a nut 14 constituting a ball screw mechanism 8 described later, and meshes with the small spur gear 4. The drive shaft 7 is configured integrally with a screw shaft 12 constituting the ball screw mechanism 8.

  As shown in (b), the screw shaft 12 has a guide pin 20 inserted into its end, and a sleeve 18 is mounted in the bag hole 9 of the first housing 2a. By engaging the guide pin 20 with the groove 18a, the screw shaft 12 is prevented from rotating.

  As shown in an enlarged view in FIG. 2, the ball screw mechanism 8 includes a screw shaft 12 and a nut 14 that is externally inserted to the screw shaft 12 via a ball 13. The screw shaft 12 has a spiral thread groove 12a formed on the outer periphery thereof, and is supported so as to be movable in the axial direction and non-rotatable. On the other hand, the nut 14 is externally mounted on the screw shaft 12, and a helical screw groove 14 a corresponding to the screw groove 12 a of the screw shaft 12 is formed on the inner periphery, and a large number of screws 14 a and 14 a are formed between the nuts 14. A ball 13 is accommodated so as to roll freely. The nut 14 is supported by a housing (not shown) via two support bearings 15 and 16 so as to be rotatable and not movable in the axial direction. Reference numeral 17 denotes a piece member that constitutes a circulation member by connecting the screw grooves 14a of the nut 14, and the piece member 17 can circulate a large number of balls 13 infinitely.

  The cross-sectional shape of each thread groove 12a, 14a may be a circular arc shape or a Gothic arc shape, but here, it has a Gothic arc shape that allows a large contact angle with the ball 13 and a small axial clearance. 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 14 is made of case-hardened steel such as SCM415 or SCM420, and its surface is subjected to hardening treatment in the range of 55 to 62HRC 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 12 is made of medium carbon steel such as S55C or case-hardened steel such as SCM415 or SCM420, and the surface thereof is hardened in the range of 55 to 62HRC by induction hardening or carburizing hardening.

  A large spur gear 5 constituting the speed reduction mechanism 6 is integrally formed on the outer periphery of the nut 14, and two support bearings 15, 16 are press-fitted on both sides of the large spur gear 5 via a predetermined squeeze. As a result, even if a thrust load is applied from the drive shaft 7, it is possible to prevent the axial displacement between the support bearings 15, 16 and the large spur gear 5. Further, the two support bearings 15 and 16 are constituted by sealed deep groove ball bearings having shield plates attached to both ends thereof, leakage of lubricating grease sealed inside the bearing, wear powder from the outside, and the like. Is prevented from entering the inside of the bearing.

  Here, in this embodiment, as shown in FIG. 3, a cylindrical sleeve 18 is press-fitted into the bag hole 9 of the first housing 2a. The sleeve 18 is made of a hardened high carbon chrome bearing steel such as SUJ2 or carbon steel such as S45C, and has two guide grooves 18a and 18a extending in the axial direction that constitute a detent mechanism 21 described later in the circumferential direction. It is formed to face each other. Thereby, material strength and abrasion resistance become higher than at least the first housing 2a made of an aluminum alloy, and durability can be improved.

  On the other hand, a through hole 19 penetrating in the radial direction is formed at the end of the screw shaft 12, and a guide pin 20 is inserted into the through hole 19 through a slight radial gap. The through-hole 19 is formed with a predetermined hardened layer having a surface hardness in the range of 60 to 64 HRC by induction hardening.

  Further, the guide pin 20 is made of a roller bearing that has high wear resistance and shear strength, is readily available, and is low in cost. In particular, by using the roller of the roller bearing, the crowning is formed on the outer peripheral surface, so that edge load can be prevented in contact with the through hole 19 to reduce the contact surface pressure and improve durability. it can. The roller bearing includes needle rollers and cylindrical rollers. The guide pin 20 engages with the guide groove 18 a of the sleeve 18 to prevent rotation with the axial guide of the screw shaft 12. The guide pin 20 and the sleeve 18 having the guide groove 18a engaged with the guide pin 20 constitute a rotation preventing mechanism 21.

  Thus, since the guide pin 20 that engages with the guide groove 18a is fitted and inserted into the through hole 19 of the screw shaft 12 through a slight gap, the guide pin 20 becomes rotatable in the through hole 19, It is possible to provide an electric linear actuator that is capable of reducing sliding friction and wear and having a simple structure and a low-cost nut rotation prevention mechanism. In addition, since a predetermined hardened layer is formed in the through hole 19 by induction hardening with a surface hardness in the range of 60 to 64 HRC, even if a needle roller is used as the guide pin 20, the wear resistance of the through hole 19. The guide pin 20 can be stably supported over a long period of time.

  FIG. 4A shows a modification of FIG. This embodiment basically differs from the above-described one only in the support structure of the guide pin 20, and other parts and parts having the same parts or parts having the same functions as those of the above-described embodiments are given the same reference numerals. Therefore, detailed description is omitted.

  The anti-rotation mechanism 22 includes a guide pin 20 and a bush 23 that rotatably supports the guide pin 20. That is, a through hole 24 that penetrates in the radial direction is formed at the end of the screw shaft 12, and mounting portions 24 a and 24 a that are larger in diameter than the through hole 24 are formed at both ends of the through hole 24. And the ring-shaped bush 23 is fitted by the mounting part 24a, and the guide pin 20 is inserted by these bushes 23 and 23 and the through-hole 24 via a slight radial clearance.

  Thus, since the guide pin 20 that engages with the guide groove 18a is fitted and inserted into the through hole 24 and the bush 23 of the screw shaft 12 through a slight gap, the guide pin 20 is inserted in the same manner as in the above-described embodiment. It becomes rotatable in the through-hole 24, and sliding friction and wear can be reduced.

  Here, the bush 23 is made of a sintered alloy and can be carburized and hardened as its metal powder, for example, C (carbon) is 0.13 wt%, Ni (nickel) is 0.21 wt%, and Cr (chromium). Is 1.1 wt%, Cu (copper) is 0.04 wt%, Mn (manganese) is 0.76 wt%, Mo (molybdenum) is 0.19 wt%, Si (silicon) is 0.20 wt%, and the rest is Fe ( An example is SCM415 made of iron. Thereby, abrasion resistance can be improved and the stable support of the guide pin 20 can be performed over a long period of time.

  The material of the bush 23 may be formed of a thermoplastic synthetic resin such as PA (polyamide) 66 filled with a predetermined amount of a fibrous reinforcing material such as GF (glass fiber) other than the materials described above. good. Thereby, even if an impact load is applied to the screw shaft 12, it can be mitigated. Examples of the fibrous reinforcing material include not only GF but also CF (carbon fiber), aramid fiber, boron fiber, and the like.

  Other materials for the bushing 23 include thermoplastic synthetic resins such as so-called engineering plastics such as PPA (polyphthalamide) and PBT (polybutylene terephthalate), polyphenylene sulfide (PPS), and polyether ether ketone (PEEK). ), Thermoplastic synthetic resins called super engineering plastics such as polyamideimide (PAI), or thermosetting synthetic resins such as phenolic resin (PF), epoxy resin (EP), polyimide resin (PI), etc. It may be.

  FIG. 4B shows another modification of FIG. This embodiment basically differs from the above-described one only in the support structure of the guide pin 20, and the same parts and parts having the same functions as those of the above-described embodiments or parts and parts having the same functions are denoted by the same reference numerals. Detailed description is omitted.

  The detent mechanism 25 includes a guide pin 20 and a rolling bearing 26 that rotatably supports the guide pin 20. That is, a through hole 27 that penetrates in the radial direction is formed at the end of the screw shaft 12. A rolling bearing 26 is attached to the through hole 27. The rolling bearing 26 includes a so-called shell including an outer ring 28 made of a steel plate press-fitted into a through hole 27 and a plurality of needle rollers 30 accommodated in the outer ring 28 via a cage 29 so as to be freely rollable. It consists of a needle roller bearing of the type. Thereby, availability is high and cost reduction can be achieved.

  Thus, since the guide pin 20 engaged with the guide groove 18a is rotatably supported by the rolling bearing 26 attached to the through hole 27 of the screw shaft 12, the sliding torque is the same as in the above-described embodiment. In addition, sliding friction and wear can be further reduced.

  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 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 rotation input from an electric motor into a linear motion of a drive shaft via the ball screw mechanism. Applicable to electric linear actuators.

DESCRIPTION OF SYMBOLS 1 Electric linear actuator 2 Housing 2a 1st housing 2b 2nd housing 3 Electric motor 3a Motor shaft 4 Small spur gear 5 Large spur gear 6 Reduction mechanism 7 Drive shaft 8 Ball screw mechanism 9, 10 Bag hole 11, 26 Rolling bearing 12 Screw Shafts 12a, 14a Screw grooves 13 Balls 14 Nuts 15, 16 Support bearings 17 Frame members 18 Sleeves 18a Guide grooves 19, 24, 27 Through holes 20 Guide pins 21, 22, 25 Anti-rotation mechanism 23 Bush 24a Mounting part 28 Outer ring 29 Holding 30 Needle roller 50 Electric linear actuator 51 Ball screw shaft 51a Screw groove 52 Ball screw nut 53 Ball screw mechanism 54, 55 Housing 56, 57 Rolling bearing 58 Lid 59 Non-rotating member 60 Large diameter part 61 Flat part 62 Cam follower (Rotation) Stopping means)

Claims (9)

A cylindrical 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 a screw shaft supported so as to be axially movable,
In the electric linear actuator in which a bag hole for accommodating the screw shaft is formed in the housing,
A sleeve is fitted into the bag hole of the housing, a guide groove extending in the axial direction is formed in the sleeve, and a through hole penetrating in the radial direction is formed at an end of the screw shaft, and the guide is inserted into the through hole. An electric linear actuator characterized in that a pin is inserted and inserted through a slight radial clearance and is engaged with a guide groove of the sleeve.   The electric linear actuator according to claim 1, wherein the guide pin is made of a roller of a bearing, and a crowning is formed on an outer peripheral surface.   The electric linear actuator according to claim 1, wherein the guide groove is formed so as to face two places in the circumferential direction. Electric linear actuator according to claim 1, hard layer in the through hole is formed.   The electric linear actuator according to claim 1 or 2, wherein the guide pin is rotatably supported by a through hole of the screw shaft via a bush.   The electric linear actuator according to claim 5, wherein the bush is formed of a sintered alloy made of a material that can be carburized and quenched as the metal powder.   The electric linear actuator according to claim 5, wherein the bush is made of a synthetic resin filled with a fibrous reinforcing material.   The electric linear actuator according to claim 1 or 2, wherein the guide pin is rotatably supported in a through hole of the screw shaft via a rolling bearing formed of a shell-type needle roller bearing.   The electric linear actuator according to claim 1, wherein the housing is made of an aluminum alloy, and the sleeve is made of a material having higher material strength and wear resistance than the housing.

Images