JP2012039765A - Electric actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric actuator enabling the cost reduction with reduced working man-hours and improved workability in assembly.SOLUTION: The electric actuator comprises a nut 18 with a ball screw mechanism 8 supported to be rotatable relative to a housing 2 via a pair of supporting bearings 19 and be prevented from moving in the axial direction, and a spiral thread 18a on the inner circumference, and a screw shaft 16 inserted into the nut via a plurality of balls 17, integral to a driving shaft 7 having a common axis, having a spiral thread 16a on the exterior, and supported to be prevented from rotating relative to the housing 2 and be movable in the axial direction. The exterior of the nut 18 is formed to be a straight cylinder, a large spur gear 5 and the pair of supporting bearings 19 are positioned with a snap ring 22 at an exterior surface 18b, and the supporting bearings 19 comprises ball bearings identical in specifications capable of bearing the thrust load from the driving shaft 7 and the radial load from the large spur gear 5.

Description

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

  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. 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 an electric motor, or a low-efficiency thing such as a worm gear is provided as a transmission means. As a typical example, an electric actuator as shown in FIG. Are known. The electric actuator 50 includes an actuator main body 52 including a ball screw 51 that converts rotational motion into linear motion, a gear reduction mechanism 54 that transmits the rotational motion of the electric motor 53 to the actuator main body 52, and a gear reduction mechanism 54. A position holding mechanism 56 that engages with the first gear 55 and holds the position of the actuator main body 52.

  The ball screw 51 has a spiral thread groove 57a formed on the outer peripheral surface, and is externally fitted to the screw shaft 57 as an output shaft and the screw shaft 57, and a spiral thread groove 58a is formed on the inner peripheral surface. A nut 58 and a large number of balls 59 accommodated in a rolling path formed by opposing screw grooves 57a and 58a are provided.

  The actuator main body 52 includes a nut 58 rotatably supported on the inner periphery of the housing 60 via a pair of ball bearings 61 and 62, and a screw shaft 57 that cannot rotate relative to the housing 60. It is supported movably in the direction. The nut 58 is rotationally driven via the gear reduction mechanism 54, whereby the screw shaft 57 is converted into a linear motion.

  The gear reduction mechanism 54 is engaged with a first gear 55 formed of a small-diameter spur gear fixed to the motor shaft 53 a of the electric motor 53, and a large diameter integrally formed on the outer periphery of the nut 58. And a second gear 63 composed of a spur gear.

  The position holding mechanism 56 is a shaft 64 as a lock member that is detachably attached to the first gear 55, and driving means that drives the shaft 64 in a direction to be engaged with and disengaged from the first gear 55. The solenoid 65 is provided. The shaft 64 has a rod shape and is linearly driven by a solenoid 65, and its tip end portion is engaged with and disengaged from the receiving portion 66. In this way, by controlling the solenoid 65, the shaft 64 engages with the first gear 55 and is prevented from rotating. Therefore, even when a vibration load is applied, the engagement surface can be stably prevented from slipping. The position of the screw shaft 57 of the actuator body 52 can be held (see, for example, Patent Document 1).

JP 2009-156416 A

  In such a conventional electric actuator 50, the nut 58 rotates through a second gear 63 formed integrally with the outer periphery of the nut 58, and the rotational motion of the electric motor 53 is transmitted to the actuator body 52. The actuator body 52 includes a nut 58 rotatably supported on the inner periphery of the housing 60 via a pair of ball bearings 61 and 62, and a screw shaft 57 that is not rotatable relative to the housing 60. It is supported so as to be movable in the axial direction. Thus, when the nut 58 is rotationally driven, the screw shaft 57 is converted into a linear motion, and a mating member is coupled to the connecting portion provided at the tip of the screw shaft 57 to perform a desired work.

  However, if the second gear 63 is formed integrally with the outer periphery of the nut 58, the yield of the material is deteriorated and the outer peripheral surface on which the second gear 63, the thread groove 58a and the ball bearings 61 and 62 are fitted is also reduced. There is a problem that processing becomes difficult, the number of processing steps increases, and the manufacturing cost increases. Therefore, as shown in FIG. 5, a method is conceivable in which the second gear 63 ′ and the nut 58 ′ are separated and the second gear 63 ′ is fixed to the nut 58 ′ via the key 67.

  In this case, the pair of ball bearings 61 and 62 are loaded with a gear load (radial load) input from the electric motor side and a thrust load input from the connection side of the screw shaft 57. In order to apply the load, the outer peripheral surface of the nut 58 ′ has a stepped shape, and with this stepped shape, specifications such as the size of the pair of ball bearings 61 and 62 are different. That is, if the outer peripheral surface of the nut 58 'has a stepped shape, two steps of cylindrical grinding are required, which increases the number of processing steps. Furthermore, only the ball bearing 62 side that mainly receives the thrust load among the pair of ball bearings 61 and 62 requires the receiving portion 68 on the side surface of the second gear 63 'in order to suppress the change in the bearing position. As a result, the second gear 63 'becomes asymmetrical, and a confirmation operation is necessary so that the direction is not mistaken during assembly, which may reduce the assembly workability.

  The present invention has been made in view of such problems of the prior art, and an object of the present invention is to provide an electric actuator that reduces the number of processing steps and improves the assembly workability to reduce the cost.

  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 is a pair of supports attached to the housing. A nut rotatably supported through a bearing and non-movable in the axial direction and having a helical thread groove formed on the inner periphery, and inserted into the nut through a number of balls, are coaxial with the drive shaft. And a screw shaft that is supported on the outer periphery of the housing so as to be non-rotatable and movable in the axial direction. With In the electric actuator in which the speed reduction mechanism is composed of a small gear fixed to the motor shaft and a large gear meshed with the small gear and provided on the outer periphery of the nut, the outer periphery of the nut is a straight cylindrical shape The large gear is formed on the outer periphery, and the pair of support bearings are positioned and fixed on both sides of the large spur gear.

  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, and 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 An electric actuator comprising a small gear having a speed reduction mechanism fixed to the motor shaft and a large gear meshed with the small gear and provided on the outer periphery of the nut. Stre Since the outer peripheral surface of the nut is centered and ground, a large gear and a pair of support bearings on both sides of the gear are positioned and fixed. In addition, it is possible to provide an electric actuator capable of reducing the cost by improving the assembling workability.

  Preferably, as in the second aspect of the invention, the pair of support bearings can have both the thrust load from the drive shaft and the radial load loaded via the large gear. If it is comprised by this rolling bearing, the confirmation operation | work for prevention of an incorrect assembly at the time of an assembly can be simplified, and assembly workability | operativity can be improved.

  Further, as in the third aspect of the present invention, if the support bearing is constituted by a sealed deep groove ball bearing having seals attached to both ends, the lubricating grease sealed inside the bearing is exposed to the outside. A low-cost and highly durable support bearing can be provided by preventing leakage and wear powder from entering the inside of the bearing from the outside.

  Further, as in the invention according to claim 4, if the large gear is formed in a symmetrical shape and is fixed to the outer periphery of the nut via a key, a confirmation operation for preventing misassembly during assembly is performed. It can be simplified and the assembly workability can be further improved.

  Further, as in the fifth aspect of the present invention, if a retaining ring is attached to the end of the nut and the support bearing is fixed in the axial direction by the retaining ring, a thrust load is applied from the drive shaft. Even in this case, it is possible to prevent the axial displacement between the support bearing and the large gear.

  Further, as in the invention described in claim 6, if the end portion of the nut is plastically deformed radially outward and the end portion of the inner ring of the support bearing is pressed down, the crimp portion is formed. By this caulking portion, the support bearing can be fixed to the nut without any play in the axial direction.

  Further, as in the invention described in claim 7, the caulking portion may be formed at a plurality of positions in the circumferential direction in a state of being in close contact with the end face of the inner ring of the support bearing. As described in the invention, the caulking portion may be formed on the entire circumference in a state of being in close contact with the end face of the inner ring of the support bearing.

  Further, as in the invention according to claim 9, the nut is made of case-hardened steel, the surface is subjected to a hardening treatment in a range of 55 to 62HRC by vacuum carburizing and quenching except for the caulking portion, and the If the caulking part maintains the material hardness of 20 to 30 HRC without carburizing and quenching by the carburizing treatment, and the hardness is relatively lower than other parts of the hardened nut, Factors that affect durability, such as the occurrence of microcracks in the crimped portion, can be eliminated, and reliability and durability can be improved.

  Further, as in the invention according to claim 10, if the nut is hardened by vacuum carburizing and quenching and the caulking portion is lowered in hardness by induction annealing, the annealing treatment is performed by the nut. Therefore, heat treatment by general induction hardening can be performed, heat treatment work can be facilitated, and cost can be reduced.

  Further, as in the invention of claim 11, the drive shaft is slidably supported by a bush mounted on the housing, and the bush is a sintered alloy made of metal powder that can be carburized and hardened. If configured, the wear resistance can be improved, and the drive shaft can be stably guided and supported over a long period of time.

  An electric actuator according to the present invention includes 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 the electric motor via the reduction mechanism. A ball screw mechanism that converts the rotational motion of the motor into a linear motion in the axial direction of the drive shaft, and this ball screw mechanism is rotatable through a pair of support bearings 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 through a number of balls, and is integrated coaxially with the drive shaft and screwed on the outer periphery of the nut. A helical screw groove corresponding to the groove is formed, and the screw shaft is supported so as to be non-rotatable and axially movable with respect to the housing. In an electric actuator comprising a small gear fixed to a shaft and a large gear meshed with the small gear and provided on the outer periphery of the nut, the outer periphery of the nut is formed in a straight cylindrical shape, Since the large gear and the pair of support bearings are positioned and fixed on both sides of the large gear, the centerless grinding of the outer peripheral surface of the nut is possible, and the number of processing steps can be reduced. Thus, it is possible to provide an electric actuator that is improved in assembly workability and reduced in cost.

1 shows an embodiment of an electric actuator according to the present invention. It is a longitudinal cross-sectional view which shows the actuator main body of FIG. It is a longitudinal cross-sectional view which shows the modification of FIG. It is a longitudinal cross-sectional view which shows the conventional electric actuator. It is a longitudinal cross-sectional view which shows the modification of the actuator main body of FIG.

  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 the linear motion into an axial direction, and the ball screw mechanism is supported by a pair of support bearings mounted on the housing so as to be rotatable and immovable in the axial direction. A nut formed with a helical thread groove, and a helical screw that is inserted into the nut via 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 A small spur gear having a groove formed therein and a screw shaft supported so as to be non-rotatable and axially movable with respect to the housing, and the speed reduction mechanism fixed to the motor shaft, In the electric actuator configured by a large spur gear meshed with a gear and provided on the outer periphery of the nut, the outer periphery of the nut is formed in a straight cylindrical shape, the large spur gear on the outer periphery, and the pair of gears on both sides. The support bearings are positioned and fixed by retaining rings attached to both ends of the nut in a state where the large spur gears are sandwiched, and the pair of support bearings are configured to reduce the thrust load from the drive shaft and the large spur gears. It is comprised by the rolling bearing of the same specification which can load both the radial loads loaded via.

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 is a longitudinal sectional view showing an actuator body of FIG. 1, and FIG. 3 is a longitudinal sectional view showing a modification of FIG. is there.

  As shown in FIG. 1, the electric actuator 1 includes a cylindrical housing 2, an electric motor 3 attached to the housing 2, and a pair of torques transmitted from the electric motor 3 via a motor shaft 3a. A speed reduction mechanism 6 composed of spur gears 4 and 5, a ball screw mechanism 8 that converts the rotational motion of the electric motor 3 to linear motion in the axial direction of the drive shaft 7 via the speed reduction mechanism 6, and the ball screw mechanism 8 An actuator main body 9 provided, and a position holding mechanism 10 that engages with the spur gear 4 constituting the speed reduction mechanism 6 and holds the position of the actuator main body 9 are provided.

  The housing 2 includes a first housing 2a and a second housing 2b abutted on the end surface thereof, and is fixed integrally by a fixing bolt (not shown). An electric motor 3 is attached to the first housing 2a.

  The position holding mechanism 10 includes a shaft 11 as a lock member that is detachably attached to the small spur gear 4, and a solenoid as a driving unit that drives the shaft 11 in a direction to be engaged with and disengaged from the small spur gear 4. 12. The shaft 11 has a rod shape, is linearly driven by a solenoid 12, and its tip is engaged with and disengaged from the receiving portion 13.

  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 14 attached to the second housing 2b. The large spur gear 5 is fixed to the outer diameter of a nut 18 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 16 constituting the ball screw mechanism 8 and is connected to one end portion (right end portion in the figure) of the drive shaft 7, for example, a wire (not shown) of an electric parking brake mechanism. The drive shaft 7 is slidably supported by a bush 15 attached to the first housing 2a.

  The bush 15 is made of a sintered alloy, and the metal powder can be carburized and quenched, for example, C (carbon) is 0.13 wt%, Ni (nickel) is 0.21 wt%, and Cr (chromium) is used. 1.1 wt%, Cu (copper) 0.04 wt%, Mn (manganese) 0.76 wt%, Mo (molybdenum) 0.19 wt%, Si (silicon) 0.20 wt%, and the rest Fe (iron) ) And the like. Thereby, abrasion resistance can be improved and the stable guide support of the drive shaft 7 can be performed over a long period of time.

  As shown in an enlarged view in FIG. 2, the ball screw mechanism 8 includes a screw shaft 16 and a nut 18 that is externally inserted through the ball 17 to the screw shaft 17. The screw shaft 16 has a spiral thread groove 16a formed on the outer periphery thereof, and is supported so as to be axially movable and non-rotatable. On the other hand, the nut 18 is externally mounted on the screw shaft 16, and a helical screw groove 18 a corresponding to the screw groove 16 a of the screw shaft 16 is formed on the inner periphery, and a large number of screws 18 a and 18 a are provided between the nut 18. A ball 17 is housed so as to roll freely. The nut 18 is supported on a housing (not shown) via a pair of support bearings 19 and 19 so as to be rotatable and not movable in the axial direction. Reference numeral 20 denotes a piece member that constitutes a circulation member by connecting the thread groove 18a of the nut 18, and the piece member 20 can circulate a large number of balls 17 infinitely.

  The cross-sectional shape of each of the thread grooves 16a and 18a may be a circular arc shape or a Gothic arc shape, but here the Gothic arc shape can be set so that the contact angle with the ball 17 is large and the axial clearance can be set small. 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 16 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 62 HRC by induction hardening or carburizing hardening.

  Here, the large spur gear 5 constituting the speed reduction mechanism 6 is fixed to the outer peripheral surface 18b of the nut 18 via a key 21, and a pair of support bearings 19, 19 are provided on both sides of the large spur gear 5 with a predetermined shimiro. It is press-fitted through. The pair of support bearings 19 and 19 are positioned and fixed by retaining rings 22 and 22 attached to both ends of the nut 18 in a state where the large spur gear 5 is sandwiched. 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 19 and 19 and the large spur gear 5.

  Further, the pair of support bearings 19 and 19 is constituted by a deep groove ball bearing including an inner ring 19a and an outer ring 19c inserted on the inner ring 19a via rolling elements (balls) 19b. Shield plates 23 and 23 are attached to both ends of the outer ring 19c to prevent leakage of the lubricating grease sealed inside the bearing and prevent dust from entering the bearing from the outside. Further, the drive shaft 7 is composed of sealed rolling bearings of the same specification so that both a thrust load and a radial load applied via the large spur gear 5 can be applied. As a result, it is possible to provide an inexpensive and highly durable support bearing 19, and the outer peripheral surface 18b of the nut 18 can be formed into a straight cylindrical shape without being stepped, thereby enabling centerless grinding. The processing man-hour can be reduced. Here, the rolling bearings of the same specification refer to bearings having the same inner diameter, outer diameter, width dimension, rolling element size, number, bearing internal clearance, and the like.

  In addition, the pair of support bearings 19 and 19 are composed of rolling bearings of the same specification, and the large spur gear 5 is formed on the side surface, and a receiving portion for suppressing the variation of the bearing position is not required as in the prior art, and is symmetrical. Therefore, it is possible to simplify the confirmation work for preventing misassembly during assembly, and it is possible to provide an electric actuator that is improved in assembling workability and reduced in cost.

  FIG. 3 shows a modification of FIG. This embodiment is basically the same as the above-described ball screw mechanism 8 except that the configuration of the nut is partially different, and other parts and parts having the same or similar functions are denoted by the same reference numerals. The detailed explanation is omitted.

  The ball screw mechanism 24 includes a screw shaft 16 and a nut 25 that is externally inserted into the screw shaft 17 via the ball 17. The nut 25 is supported on a housing (not shown) via a pair of rolling bearings 19 and 19 so as to be rotatable and not movable in the axial direction.

  A pair of support bearings 19 and 19 are press-fitted into the outer peripheral surface 25a of the nut 25 via a predetermined squeeze. A crimping portion 26 is formed in a state where the end portion of the nut 25 is plastically deformed radially outward and the end surface of the inner ring 19a of the support bearing 19 is pressed. The support bearing 19 is fixed to the nut 25 in the axial direction without play by the caulking portion 26. The nut 25 is made of case-hardened steel such as SCM415 or SCM420, and the surface of the nut 25 is hardened in a range of 55 to 62HRC by vacuum carburizing and quenching except for the caulking portion 26. The caulking portion 26 is maintained at a material hardness of about 20 to 30 HRC without being carburized and quenched by the carbon-proof treatment, and the hardness is relatively lowered as compared with other portions of the hardened nut 25. Thereby, factors affecting durability, such as the occurrence of microcracks in the crimped portion 26, can be eliminated by crimping, and the reliability and durability can be improved. The crimping portions 26 are formed at three equal locations in the circumferential direction in close contact with the end surface of the inner ring 19a of the support bearing 19 by a crimping jig (not shown). There may be four or more locations, or the entire circumference may be plastically deformed radially outward and crimped.

  In the carburizing treatment, for example, at the time of carburizing and quenching, the end portion of the nut 25 is covered over the outer periphery with a carburizing agent (not shown), thereby preventing carburization and forming a reduced hardness region. However, only the caulking portion 26 may be partially covered with the carbon-proofing treatment. The nut 25 may be hardened by vacuum carburizing and quenching, and the caulking portion 26 may be reduced in hardness by induction annealing. In the case of vacuum carburizing and quenching, since the carburizing gas enters, the hardness cannot be lowered by the carburizing treatment, and caulking becomes impossible. Therefore, in the case of vacuum carburizing, after vacuum carburizing and quenching, the portion corresponding to the crimping portion 26 is subjected to induction annealing to reduce the hardness to 20 to 30 HRC. Since the annealing process in this case is a process on the outer diameter side of the nut 25, a heat treatment by a general induction hardening can be performed, and the heat treatment work can be facilitated and the cost can be 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 actuator according to the present invention is used in a drive unit of a general industrial electric motor, an automobile or the like, and includes a ball screw mechanism that converts rotational input from an electric motor into 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 Electric motor 3a Motor shaft 4 Small spur gear 5 Large spur gear 6 Reduction mechanism 7 Drive shaft 7a Hole 8, 24 Ball screw mechanism 9 Actuator body 10 Position holding mechanism 11 Shaft 12 Solenoid 13 Receiving part 14 Rolling bearing 15 Bush 16 Screw shaft 16a, 18a Screw groove 17 Ball 18, 25 Nut 18b, 25a Nut outer peripheral surface 19 Support bearing 19a Inner ring 19b Rolling element 19c Outer ring 20 Frame member 21 Key 22 Retaining ring 23 Shield plate 26 Caulking portion 50 Electric actuator 51 Ball screw 52 Actuator body 53 Electric motor 53a Motor shaft 54 Gear reduction mechanism 55 First gear 56 Position holding mechanism 57 Screw shaft 57a, 58a Screw groove 58, 58 'Nut 59 Ball 60 How Ring 61, 62 ball bearing 63, 63 'second gear 64 shaft 65 solenoid 66 receiving

Claims (11)

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 pair of support bearings 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, is integrated coaxially with the drive shaft, and a helical thread groove corresponding to the thread groove of the nut is formed on the outer periphery, and cannot rotate with respect to the housing. And a screw shaft supported so as to be axially movable,
In the electric actuator, in which the speed reduction mechanism is composed of a small gear fixed to the motor shaft and a large gear meshed with the small gear and provided on the outer periphery of the nut,
An electric actuator characterized in that an outer periphery of the nut is formed in a straight cylindrical shape, the large gear is disposed on the outer periphery, and the pair of support bearings are positioned and fixed on both sides of the large gear. .   The pair of support bearings are configured by rolling bearings of the same specification capable of loading both a thrust load from the drive shaft and a radial load loaded via the large gear. Electric actuator.   The electric actuator according to claim 2, wherein the support bearing is constituted by a sealed deep groove ball bearing having seals attached to both ends.   The electric actuator according to claim 1, wherein the large gear is formed in a symmetrical shape and is fixed to an outer periphery of the nut via a key.   The electric actuator according to any one of claims 1 to 4, wherein a retaining ring is attached to an end of the nut, and the support bearing is fixed in the axial direction by the retaining ring.   The electric actuator according to any one of claims 1 to 4, wherein the support bearing is fixed in an axial direction with respect to the nut by a caulking portion in which an end portion of the nut is plastically deformed radially outward.   The electric actuator according to claim 6, wherein the caulking portion is formed at a plurality of positions in the circumferential direction with a close contact with an end surface of the inner ring of the support bearing.   The electric actuator according to claim 6, wherein the caulking portion is formed on the entire circumference in a state of being in close contact with an end face of the inner ring of the support bearing.   The nut is made of case-hardened steel, and the surface is hardened in the range of 55 to 62 HRC by vacuum carburizing and quenching except for the caulking portion, and the caulking portion is not carburized and hardened by carburizing treatment. The electric actuator according to claim 6, wherein the hardness is relatively lowered than other portions of the nut that is maintained and cured at 20 to 30 HRC.   The electric actuator according to claim 6, wherein the nut is hardened by vacuum carburizing and quenching, and the caulking portion is reduced in hardness by induction annealing.   The electric actuator according to claim 1, wherein the drive shaft is slidably supported by a bush mounted on the housing, and the bush is made of a sintered alloy made of carburized and hardened metal powder.

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