JP2011117513A - Electric actuator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric actuator carrying out cost reduction by reducing the number of parts and the number of machining manhours, and improving reliability by simplifying a ball circulation mechanism. <P>SOLUTION: A ball screw mechanism 8 is structured of: a nut 16 connected to a speed reduction mechanism 6, rotatably supported via a rolling bearing 19 attached to a housing 2, immovably in an axial direction, and formed with a spiral screw groove 16a in an inner periphery; and a screw shaft 15 inserted into the nut 16 via balls 17 and coaxial with a driving shaft 7. The screw shaft 15 is formed with one turn of a screw groove 15a on an outer periphery, and a ball circulation groove 22 meandering in an S-shape and individually forming the screw groove 15a into a closed loop. By the ball circulation groove 22, a bush 11 attached to the housing 2, and a parallel key 12 attached to the outer periphery of the screw shaft 15 and engaging with a key groove 13 formed in the housing 2, the screw shaft 15 is supported so as not to rotate with respect to the housing 2, and movably in the axial direction. <P>COPYRIGHT: (C)2011,JPO&INPIT

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 linear motion of a drive shaft via

  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 very low friction, and the ball screw shaft is easily rotated by an axial 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.

  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 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, although not shown, the ball screw 51 is configured such that the ball 59 is infinitely circulated by a known circulation member such as a return tube or a piece member having a rolling path as a circulation path. However, it is structurally difficult to provide such a circulating member on the nut 58, which not only increases the number of processing steps and increases the cost, but also increases the size of the nut 58 itself and hinders light weight and compactness. It was.

  The present invention has been made in view of such problems of the prior art, and is an electric actuator that reduces the number of parts and the number of processing steps to reduce the cost and simplifies the ball circulation mechanism to improve the reliability. The purpose is to provide.

  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. An electric actuator comprising a speed reduction mechanism and a ball screw mechanism that converts the rotational motion of the electric motor into an axial linear motion of the drive shaft via the speed reduction mechanism, wherein the ball screw mechanism is connected to the speed reduction mechanism. A nut that is rotatably supported through a rolling bearing mounted on the housing and is not axially movable, and has a spiral thread groove formed on the inner periphery, and a plurality of balls on the nut. A screw shaft that is inserted and coaxially integrated with the drive shaft is formed, and the screw shaft is formed with a screw groove corresponding to the screw groove on the outer periphery, and the screw groove is individually closed. And a ball circulation groove is formed in a meandering manner so that the downstream ball sinks to the inner diameter side, gets over the land portion of the nut and returns to the upstream side, and the ball circulation groove and the housing The screw shaft is supported by the mounted bush so as not to rotate with respect to the housing and to be movable in the axial direction.

  As described above, in the electric actuator including the speed reduction mechanism that transmits the rotational force of the electric motor and the ball screw mechanism that converts the rotational motion of the electric motor to the linear motion in the axial direction of the drive shaft via the speed reduction mechanism. A ball screw mechanism is connected to the speed reduction mechanism, is rotatably supported via a rolling bearing mounted on the housing, and is supported so as not to move in the axial direction, and a nut having a spiral thread groove formed on the inner periphery, The screw shaft is inserted into the nut through a large number of balls and is integrated with the drive shaft coaxially. The screw shaft has a screw groove corresponding to the screw groove formed on the outer periphery. A closed loop is individually formed, and a ball circulation groove is formed so that the downstream ball sinks to the inner diameter side, passes over the land portion of the nut, and returns to the upstream side. The bushing mounted on the ging supports the screw shaft so that it cannot rotate with respect to the housing and can move in the axial direction. This reduces the number of parts and man-hours, reduces costs, and circulates the ball. An electric actuator having a simplified mechanism and improved reliability can be provided.

  Preferably, as in the invention according to claim 2, the screw groove of the screw shaft is formed in one turn, and a parallel key that engages with the key groove formed in the housing is mounted on the outer periphery of the screw shaft. If this is the case, the bushing that guides and supports the screw shaft in the axial direction stabilizes the relative position of the screw shaft and the nut on the same axis, and the internal load distribution of the ball becomes uniform, ensuring the desired durability. In addition, the length of the screw shaft can be shortened, and the electric actuator can be made compact.

  Further, as in the third aspect of the invention, if the screw groove and the ball circulation groove of the screw shaft are formed by point cutting by an end mill, a predetermined shape and dimension can be finished with high accuracy.

  In addition, if the cross section of the screw groove of the screw shaft is formed in a Gothic arc shape as in the invention described in claim 4, the contact angle with the ball can be increased and the axial clearance can be set small. The rigidity with respect to the directional load is increased, and the occurrence of vibration can be suppressed.

  Further, as in the invention according to claim 5, the screw shaft is made of medium carbon steel or case-hardened steel, and is hardened in a range of 55 to 62 HRC on the surface of the screw groove and the ball circulation groove of the screw shaft by induction hardening. If the treatment is performed, a desired rolling fatigue life can be secured, wear due to the passage of the ball can be suppressed, and durability can be improved. In addition, generation of a grain boundary oxide layer on the surface layer can be suppressed, and local heating can be performed, so that the setting of the hardened layer depth can be made relatively easy.

  Further, as in the invention described in claim 6, if at least the thread groove is subjected to finish processing by shot peening after the heat treatment of the threaded shaft, the grain boundary oxidation of the scale and the surface layer adhered to the thread groove The layer can be removed, and the durability of the ball screw can be improved.

  In addition, as in the invention according to claim 7, if the nut is made of case-hardened steel and the surface is hardened by vacuum carburizing and quenching in the range of 55 to 62 HRC, the scale removal after the heat treatment is performed. Therefore, buffing for the purpose can be omitted, and cost reduction can be achieved.

  If the outer diameter of the drive shaft is set to be the same as the outer diameter of the screw shaft as in the invention described in claim 8, the outer peripheral surface can be formed centerlessly and the cost can be reduced. Can be achieved.

  Further, if the bush is made of a sintered alloy made of carburized and hardened metal powder as in the invention described in claim 9, the wear resistance is improved and the drive shaft is extended over a long period of time. Stable guidance support can be performed.

  According to a tenth aspect of the present invention, the speed reduction mechanism is engaged with the small spur gear fixed to the motor shaft and the small spur gear, and is attached to the outer periphery of the nut through a key so as not to be relatively rotatable. The large spur gear is positioned and fixed by a retaining ring through a spacer together with a rolling bearing fitted in the housing, is not relatively movable in the axial direction, and is relatively rotatable. The nuts can be standardized simply by aligning the spacers with changes in specifications such as gears, and the cost can be reduced.

  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. An electric actuator comprising a ball screw mechanism that converts the rotational motion of the motor into a linear motion in the axial direction of the drive shaft, wherein the ball screw mechanism is coupled to the speed reduction mechanism and via a rolling bearing attached to 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 large number of balls and is coaxially integrated with the drive shaft. The screw shaft is formed with a screw groove corresponding to the screw groove on the outer periphery, and each of the screw grooves is individually closed loop, and the downstream ball is placed inside. A ball circulation groove is formed which is sunk to the side, linearly meandering so as to pass over the land portion of the nut and return to the upstream side, and the ball circulation groove and the bush mounted on the housing Since the screw shaft is supported so as not to rotate and move in the axial direction with respect to the housing, the number of parts and the number of processing steps can be reduced, and the ball circulation mechanism can be simplified to improve reliability. An improved electric actuator can be provided.

It is a longitudinal cross-sectional view along the II line of FIG. 2 which shows one Embodiment of the electric actuator which concerns on this invention. It is a front view of FIG. (A) is a principal part enlarged view of FIG. 1, (b) is a cross-sectional view along the III-III line of (a). It is a longitudinal cross-sectional view which shows the conventional electric 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. An electric actuator including a ball screw mechanism that converts linear motion in an axial direction, wherein the ball screw mechanism is coupled to the speed reduction mechanism and is rotatable via a rolling bearing attached to the housing, and in an axial direction. A nut that is supported so as not to move and has a spiral thread groove formed on the inner periphery, and a screw shaft that is inserted into the nut via a large number of balls and is coaxially integrated with the drive shaft. The screw shaft is formed with a one-turn thread groove corresponding to the thread groove on the outer periphery, the thread grooves are individually closed loops, and a downstream ball is submerged to the inner diameter side, and the nut A ball circulation groove meandering in an S shape so as to pass over the land portion and return to the upstream side is formed, and the ball circulation groove, a bush attached to the housing, and an outer periphery of the screw shaft are attached, The screw shaft is supported so as to be non-rotatable and axially movable with respect to the housing by a parallel key engaged with a key groove formed in the housing.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
1 is a longitudinal sectional view taken along the line II of FIG. 2, showing an embodiment of an electric actuator according to the present invention, FIG. 2 is a front view of FIG. 1, and FIG. (B) is a cross-sectional view taken along line III-III in (a).

  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 including spur gears 4 and 5 and a ball screw mechanism 8 that converts the rotational motion of the electric motor 3 to the linear motion of the drive shaft 7 via the speed reduction mechanism 6 are provided.

  The housing 2 includes a first housing 2 a and a second housing 2 b abutted on the end surface thereof, and is fixed integrally with a fixing bolt 9. An electric motor 3 is attached to the first housing 2a. The electric motor 3 is fixed to a disk-shaped motor bracket 10 by a fixing screw 10a. The motor bracket 10 is attached so as to close the first housing 2a and the second housing 2b (see FIG. 2).

  A motor shaft 3a of the electric motor 3 protrudes from the motor bracket 10, and a small spur gear 4 is attached to the end of the motor shaft 3a so as not to be relatively rotatable by press fitting, and is rotatably supported by a bush 11 attached to the second housing 2b. ing. The large spur gear 5 is fixed to the outer diameter of a nut 16 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 15 constituting the ball screw mechanism 8 and is connected to one end portion (right end portion in the drawing) 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 11 mounted on the first housing 2a, and a parallel key 12 mounted on the outer periphery is formed in the first housing 2a. By being engaged with the formed key groove 13, it can be relatively moved in the axial direction and cannot be relatively rotated. In addition, a cup-shaped lid member 14 is fixed to the opening of the first housing 2a by a fixing screw 14a, the space between the drive shaft 7 and the first housing 2a is sealed, and dust and the like enter from the outside. Is preventing.

  The bush 11 is made of a sintered alloy, and a material that can be carburized and quenched as its metal powder, for example, C (carbon) is 0.13 wt%, Ni (nickel) is 0.21 wt%, and Cr (chromium). 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. 3, the ball screw mechanism 8 has a screw shaft 15 having a one-turn thread groove 15 a formed on the outer periphery thereof, and is opposed to the screw groove 15 a of the screw shaft 15 and has a spiral shape on the inner periphery And a plurality of balls 17 accommodated in a spiral space formed by the two screw grooves 15a and 16a so as to be freely rollable. The aforementioned large spur gear 5 is attached to the outer periphery of the nut 16 through a key 18 so as not to be relatively rotatable, and is positioned and fixed by a retaining ring 21 through a spacer 20 together with a ball bearing 19 fitted in the second housing 2b. Thus, relative movement in the axial direction is impossible, and relative rotation is possible. As a result, the nut 16 can be standardized simply by aligning the spacers in accordance with the change in the specifications of the gears and the like, and the cost can be reduced.

  The cross-sectional shape of each thread groove 15a, 16a 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 17 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 16 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 15 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 screw groove 15a of the screw shaft 15 is a closed loop, and the ball 17 accommodated in the screw groove 15a is configured to circulate infinitely. That is, a ball circulation groove 22 having a thread loop 15a of the screw shaft 15 as a closed loop is provided.

  The ball circulation groove 22 communicates and connects the upstream side and the downstream side of the thread groove 15 individually. The ball circulation groove 22 sinks the ball 17 downstream of the thread groove 15a to the inner diameter side and overcomes the land portion of the nut 16. The depth of the ball circulation groove 22 is set such that the ball 17 can get over the land portion of the thread groove 16a in the nut 16 in the ball circulation groove 22 so as to return to the upstream side. The ball circulation groove 22 is formed to meander in an S shape.

In the present embodiment, the outer diameter of the drive shaft 7 is set to the same diameter as the outer diameter of the screw shaft 15, the outer peripheral surface is formed by centerless, and the thread groove 15 a and the ball circulation groove 22 are formed by point cutting. After completion, a hardened layer is formed on the surface by heat treatment. Further, after the heat treatment, grinding processing is not performed, and finish processing (not shown) by shot peening is performed in order to remove scales and surface grain boundary oxide layers attached to the screw grooves 15a and the like by heat treatment. In this shot peening, the particle size of the steel beads was 20 to 100 μm, the injection time was about 90 seconds, the injection pressure was 1 to 3 kg / cm ² , and the distance between the injection nozzle and the surface of the workpiece was about 140 mm. By adopting such processing steps, it is possible to reduce the cost of the screw shaft 15 and improve durability.

  In the present embodiment, since the screw groove 15a is formed only once in the screw shaft 15, the length of the screw shaft 15 can be shortened, and the electric actuator 1 can be made compact. Further, it is possible to provide the electric actuator 1 in which the number of parts and the number of processing steps are reduced to reduce the cost, and the ball circulation mechanism is simplified to improve the reliability.

  When the screw groove 15a of the screw shaft 15 is a single turn, the relative positional relationship between the screw shaft 15 and the nut 16 tends to be unstable, but the screw shaft 15 is supported by the bush 11 that guides and supports the screw shaft 15 in the axial direction. The relative positions of the nut 16 and the nut 16 are stabilized on the same axis, the internal load distribution of the balls 17 becomes uniform, and desired durability can be ensured.

  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. 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 Ball screw mechanism 9 Fixing bolt 10 Motor bracket 10a, 14a Fixing screw 11 Bush 12 Parallel key 13 Key groove 14 Cover member 15 Screw shaft 15a, 16a Screw groove 16 Nut 17 Ball 18 Key 19 Ball bearing 20 Spacer 21 Retaining ring 22 Ball circulation groove 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 Nut 59 Ball 60 Housing 61, 62 Ball bearing 63 Second gear 64 Shaft 65 Solenoid 66 Receiving part

Claims (10)

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;
In the electric actuator provided with a ball screw mechanism that converts the rotational movement of the electric motor to the linear movement in the axial direction of the drive shaft through the reduction mechanism,
A nut in which the ball screw mechanism is connected to the speed reduction mechanism, is rotatably supported via a rolling bearing mounted on the housing and is not axially movable, and has a helical thread groove formed on the inner periphery And a screw shaft that is inserted into the nut via a large number of balls and is coaxially integrated with the drive shaft,
The screw shaft is formed with a screw groove corresponding to the screw groove on the outer periphery, and each screw groove is individually closed loop, the downstream ball is submerged to the inner diameter side, and the land portion of the nut is passed over the upstream side. A ball circulation groove meandering linearly so as to return to
An electric actuator characterized in that the screw shaft is supported by the ball circulation groove and a bush mounted on the housing so as not to rotate with respect to the housing and to be movable in the axial direction.   2. The electric actuator according to claim 1, wherein a screw groove of the screw shaft is formed in one turn, and a parallel key that engages with a key groove formed in the housing is mounted on an outer periphery of the screw shaft.   The electric actuator according to claim 1, wherein the thread groove of the screw shaft and the ball circulation groove are formed by point cutting with an end mill.   The electric actuator according to any one of claims 1 to 3, wherein a cross section of a screw groove of the screw shaft is formed in a Gothic arc shape.   The screw shaft is made of medium carbon steel or case-hardened steel, and the surface of the screw groove and the ball circulation groove of the screw shaft is hardened in a range of 55 to 62 HRC by induction hardening. The electric actuator described in 1.   The electric actuator according to claim 5, wherein after the heat treatment of the screw shaft, at least the screw groove is subjected to finish processing by shot peening.   2. The electric actuator according to claim 1, wherein the nut is made of case-hardened steel, and the surface thereof is hardened in a range of 55 to 62 HRC by vacuum carburizing and quenching.   The electric actuator according to claim 1, wherein an outer diameter of the drive shaft is set to be the same as an outer diameter of the screw shaft.   The electric actuator according to claim 1, wherein the bush is made of a sintered alloy made of metal powder that can be carburized and hardened.   The speed reduction mechanism includes a small spur gear fixed to the motor shaft, and a large spur gear meshed with the small spur gear and attached to the outer periphery of the nut via a key so as not to be relatively rotatable. 2. The electric actuator according to claim 1, wherein the electric actuator is positioned and fixed by a retaining ring through a spacer together with a rolling bearing fitted in the housing, is not relatively movable in the axial direction, and is relatively rotatable.

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