JP2012082921A - Electric actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric actuator that reduces frictional resistance by relaxing shock during a collision of a screw shaft and avoiding operation lock of a ball screw.SOLUTION: In this electric actuator 1, a ball screw mechanism 8 is constituted of the screw shaft 16 supported so as not to be rotatable and so as to be axially movable with respect to a housing 2, and blind holes 10a and 10b for storing the screw shaft 16 are formed in the housing 2. A cylindrical sleeve 22 including a small diameter part 22a at an end part is fitted to the blind hole 10a in the housing 2, and a snap ring 24 is fitted to an inner diameter of the small diameter part 22a of the sleeve 22. The inner diameter of the snap ring 24 is smaller than an outer diameter at a distal end part of the screw shaft 16.

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 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, by controlling the solenoid 65, the shaft 64 engages with the first gear 55 and is prevented from rotating, so that even when a vibration load is applied, the engagement surface slips. The screw shaft 57 of the actuator main body 52 can be held in a stable position.

  However, in the electric actuator 50 in which a necessary operation can be obtained by this kind of electric control, it is conceivable that the electric actuator 50 cannot be controlled when power supply cannot be performed due to a drop in battery voltage. In this case, when the solenoid 65 and the electric motor 53 become inoperable in the situation where the load on the side where the screw shaft 57 is pressed is received, the screw shaft 57 continues to rotate due to the moment of inertia around the nut 58. To do. As a result, the screw shaft 57 may collide with the inner wall of the housing 60 to be in an operation locked state, and the electric motor 53 may not be able to be restored.

  The present invention has been made in view of such problems of the prior art, and provides an electric actuator capable of reducing the frictional resistance by reducing the impact at the time of collision of the screw shaft and avoiding the operation lock of the ball screw. The purpose is to do.

  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. And a screw thread shaft that is integrally formed and has a spiral thread groove corresponding to the thread groove of the nut, and is supported so as to be non-rotatable and axially movable with respect to the housing. Said In the electric 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, and a buffer member is disposed so that the end portion of the screw shaft contacts the end portion of the sleeve. Has been.

  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 In a motor-driven actuator that includes a shaft and a bag hole that accommodates the screw shaft in the housing, a sleeve is fitted into the bag hole of the housing, and the end of the screw shaft contacts the end of the sleeve Loose Since the power supply cannot be supplied due to a drop in battery voltage and the solenoid or the electric motor becomes inoperable, the screw shaft can be moved even if the screw shaft continues to move straight due to the moment of inertia around the nut. It is possible to reduce the frictional resistance by mitigating the impact of the front end of the shock absorber against the buffer member, and to reliably prevent the screw shaft from colliding with the inner wall of the housing and being in the operation lock state.

  According to a second aspect of the present invention, the buffer member is constituted by a retaining ring, and the retaining ring is attached to the inner diameter of the small diameter portion formed at the end of the sleeve, and the retaining ring If the inner diameter of the screw shaft is smaller than the outer diameter of the tip of the screw shaft, the tip of the screw shaft reliably interferes with the retaining ring, and the screw shaft directly collides with the inner wall of the housing with a simple structure. Can be avoided. In addition, when the screw shaft interferes with the retaining ring, if there is a slight radial clearance between the retaining ring and the annular groove, it is possible to obtain a state that can rotate at the time of collision.

  According to a third aspect of the present invention, the buffer member is a ring member, and the ring member is interposed between the end of the sleeve and the bottom of the bag hole of the housing. It may be attached to.

  Preferably, as in the invention described in claim 4, if a predetermined gap is provided between the cap and the sleeve and the housing, even if the cap is elastically deformed when the screw shaft collides, And the load propagation to the housing can be suppressed.

  Further, as in the invention described in claim 5, the sleeve may include a bottom portion at one end portion, and the buffer member may be constituted by a ring member, and the ring member may be attached to the bottom portion of the sleeve. .

  Further, as in the invention described in claim 6, if the housing is formed of an aluminum alloy and the sleeve is formed of a material having higher material strength and wear resistance than the housing, durability is improved. Can be improved.

  Further, as in the invention described in claim 7, if the housing is made of an aluminum alloy and the buffer member is made of a material having higher material strength and wear resistance than the housing, durability is ensured. Can be improved.

  If the ring member is formed by pressing from a steel plate as in the invention described in claim 8, the durability can be improved and the mass productivity can be improved to reduce the cost.

  Further, if the ring member is formed of a synthetic resin filled with a fibrous reinforcing material as in the invention described in claim 9, the impact when the tip of the screw shaft collides with the ring member is reduced. It can be further relaxed.

  Moreover, if the said cap is formed from the steel plate by press work like invention of Claim 10, while improving durability, mass productivity can improve and cost reduction can be aimed at.

  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 the ball screw mechanism is rotatable via a support bearing mounted on the housing and cannot be moved in the axial direction. A nut that is supported 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 and is formed in the thread groove of the nut on the outer periphery. A corresponding helical thread groove is formed, and is configured to be supported so as to be non-rotatable and axially movable with respect to the housing. In the electric actuator in which the bag hole is formed, a sleeve is fitted into the bag hole of the housing, and a buffer member is disposed on the end of the sleeve so that the end of the screw shaft abuts. When power supply cannot be performed due to voltage drop and the solenoid or electric motor becomes inoperable, the tip of the screw shaft collides with the buffer member even if the screw shaft continues to move linearly due to the moment of inertia around the nut. The impact can be mitigated to reduce the frictional resistance, and it is possible to reliably prevent the screw shaft from colliding with the inner wall of the housing and being in the operation lock state.

It is a longitudinal section showing one embodiment of an electric actuator concerning 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 front-end | tip part of the screw shaft 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 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 a helical thread groove that is coaxially integrated with the drive shaft and corresponds to the thread groove of the nut on the outer periphery. An electric actuator 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 movable in the axial direction, and in which a bag hole for accommodating the screw shaft is formed in the housing. In the eta, a cylindrical sleeve having a small-diameter portion at the end is fitted into the bag hole of the housing, and a retaining ring is attached to the inner diameter of the small-diameter portion of the sleeve, and the inner diameter of the retaining ring is equal to that of the screw shaft. It has a smaller diameter than the outer diameter of the tip.

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 main part showing a tip portion of a screw shaft of FIG. FIG. 4A is a main part enlarged view showing a modification of FIG. 3, and FIG. 4B is a main part enlarged view showing another modification of FIG.

  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, and bag holes 10a and 10b for accommodating the screw shafts 16 are formed in the first housing 2a and the second housing 2b.

  The position holding mechanism 11 includes a shaft 11a serving as a lock member that is detachably attached to the small spur gear 4 and a solenoid serving as a driving unit that drives the shaft 11a in a direction that engages and disengages the small spur gear 4. 12. The shaft 11 a has a rod shape and 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 integrally formed with 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 second housing 2b.

  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 to the screw shaft 16 via a ball 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 with respect to a housing (not shown) via two support bearings 19 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 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.

  A large spur gear 5 constituting the speed reduction mechanism 6 is integrally formed on the outer peripheral surface 18 b of the nut 18, and two support bearings 19 and 20 are press-fitted on both sides of the large spur gear 5 via a predetermined squeeze. . 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 20 and the large spur gear 5. Further, the two support bearings 19 and 20 are constituted by sealed deep groove ball bearings having shield plates attached to both ends, 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 22 is press-fitted into the bag hole 10a of the first housing 2a. This sleeve 22 is made of a hardened high carbon chromium bearing steel such as SUJ2 or carbon steel such as S45C, and has a small diameter portion 22a at the end. Thereby, material strength and abrasion resistance become higher than the 1st housing 2a which consists of A6063TE or ADC12 at least, and durability can be improved. And the annular groove 23 is formed in the internal diameter of this small diameter part 22a, and the C-shaped retaining ring (buffer member) 24 for holes is attached. The outer diameter of the tip end portion of the screw shaft 16 is formed larger than the inner diameter of the retaining ring 24 so as to interfere with the retaining ring 24.

  By adopting such a configuration, when the power supply cannot be supplied due to a drop in the battery voltage and the solenoid 12 or the electric motor 3 becomes inoperable, the screw shaft 16 continues to move linearly due to the moment of inertia around the nut 18. The tip of the screw shaft 16 collides with the retaining ring 24 to reduce the impact and reduce the frictional resistance, and the screw shaft 16 collides with the inner wall of the first housing 2a to be in an operation locked state. Can be reliably avoided.

  FIG. 4A shows a modification of FIG. A bottomed sleeve 25 is press-fitted into the bag hole 10 a of the first housing 2 a, and a ring member (buffer member) 26 is attached to the bottom portion 25 a of the sleeve 25. A retaining ring 27 is attached to prevent the ring member 26 from moving in the axial direction or falling down. The ring member 26 is austenitic stainless steel plate (JIS standard SUS304 type or the like), ferritic stainless steel plate (JIS standard SUS430 type or the like), or rust-proofed, which has higher strength and wear resistance than the housing 2. It is formed by press working from a cold rolled steel sheet (JIS standard SPCC system or the like). Thereby, while improving durability, mass productivity can improve and cost reduction can be aimed at.

  The ring member 26 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 above-described materials. . Thereby, the impact at the time of the front-end | tip part of the screw shaft 16 colliding with this ring member 26 can be relieve | moderated further. Examples of the fibrous reinforcing material include not only GF but also CF (carbon fiber), aramid fiber, boron fiber, and the like. Further, as the material of the ring member 26, a thermoplastic synthetic resin called a so-called engineering plastic such as PPA (polyphthalamide) and PBT (polybutylene terephthalate), polyphenylene sulfide (PPS), polyether ether ketone ( Thermoplastic synthetic resins such as so-called super engineering plastics such as PEEK) and polyamideimide (PAI), or phenolic resins (PF), epoxy resins (EP), polyimide resins (PI), etc. Resin may be used.

  FIG. 4B shows another modification of FIG. Here, a bottomed sleeve 28 is press-fitted into the inner diameter portion of the first housing 2a, and a cap 29 is interposed between the sleeve 28 and the bottom portion of the bag hole 10a of the first housing 2a. . A ring member 26 is attached to the inner diameter portion of the cap 29.

  The cap 29 is formed by pressing from an austenitic stainless steel plate, a ferritic stainless steel plate, or a cold-rolled steel plate that has been rust-proofed, and has an axial direction and a diameter between the sleeve 28 and the first housing 2a. A gap in the direction is provided. As a result, even if the cap 29 is elastically deformed when the screw shaft 16 collides, it can be tolerated, and load propagation to the first housing 2a can be suppressed.

  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 Ball screw mechanism 9 Actuator main body 10a, 10b Bag hole 11 Position holding Mechanism 11a Shaft 12 Solenoid 13 Receiving part 14 Rolling bearing 15 Bush 16 Screw shaft 16a, 18a Screw groove 17 Ball 18 Nut 19, 20 Support bearing 21 Piece member 22, 25, 28 Sleeve 22a Small diameter part 23 Annular groove 24, 27 Retaining ring 25a Bottom 26 Ring member 29 Cap 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 Housing 61, 62 Ball bearing 63, 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;
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, 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 a bag hole for accommodating the screw shaft is formed in the housing,
An electric actuator characterized in that a sleeve is fitted into the bag hole of the housing, and a buffer member is disposed at an end of the sleeve so as to abut the end of the screw shaft.   The buffer member is constituted by a retaining ring, and this retaining ring is attached to the inner diameter of the small diameter portion formed at the end portion of the sleeve, and the inner diameter of the retaining ring is larger than the outer diameter of the tip end portion of the screw shaft. The electric actuator according to claim 1, which is also formed with a small diameter.   2. The electric actuator according to claim 1, wherein the buffer member is constituted by a ring member, and the ring member is attached to a cap interposed between an end portion of the sleeve and a bottom portion of the bag hole of the housing. .   The electric actuator according to claim 3, wherein a predetermined gap is provided between the cap, the sleeve, and the housing.   2. The electric actuator according to claim 1, wherein the sleeve includes a bottom portion at one end portion, the buffer member is formed of a ring member, and the ring member is attached to the bottom portion of the sleeve.   The electric 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.   The electric actuator according to any one of claims 1 to 6, wherein the housing is made of an aluminum alloy and the buffer member is made of a material having higher material strength and wear resistance than the housing.   The electric actuator according to claim 3 or 5, wherein the ring member is formed from a steel plate by pressing.   The electric actuator according to claim 3 or 5, wherein the ring member is formed of a synthetic resin filled with a fibrous reinforcing material.   The electric actuator according to claim 3 or 4, wherein the cap is formed by pressing from a steel plate.

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