JP2018080776A - Electric actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric actuator which is light-weight, compact, and reliable.SOLUTION: An electric actuator 1 includes: an electric motor part A; a motion conversion mechanism part B; and a housing 8 which houses these parts and has a cylindrical shape with a closed bottom. The motion conversion mechanism part B has: a nut 92 which receives rotary motion of a rotor 52 of the electric motor part A to rotate; and a ball screw shaft 93 which moves forward and rearward in an axial direction in conjunction with rotation of the nut 92. Load reduction means M for reducing an axial load acting on an inner bottom surface of a bottom part of the housing 8 is disposed in a torque transmission path between the rotor 52 and the nut 92. As the load reduction means M, for example, a torque limiter 7 formed by a friction clutch is used.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electric actuator.

  In recent years, automobiles have been electrified in order to save labor and reduce fuel consumption. For example, a system for operating an automatic transmission, a brake, a steering, and the like with the power of an electric motor (electric motor) has been developed. Has been put on.

  As an electric actuator used in the above-mentioned system, there is one that adopts a ball screw as a motion conversion mechanism that converts a rotary motion of an electric motor into a linear motion and outputs it (for example, Patent Document 1). The ball screw is housed in a bottomed cylindrical casing together with the electric motor, and when the nut rotates around the axis of the ball screw shaft upon receiving the rotational motion of the electric motor, the output member of the actuator including the ball screw shaft The (final output member) moves back and forth in the axial direction to operate the operation target.

JP 2014-18007 A

  As the electric actuator, a push type that operates the operation target on one side in the axial direction (opposite the bottom of the casing), a pull type that operates the operation target on the other side in the axial direction (the bottom of the casing), and an operation There is a push-pull type that operates the object in both the axial direction on one side and the other side. For example, a push-type electric actuator is used for operating the piston of the hydraulic cylinder in the axial direction, such as an electric brake for automobiles. Often done. In such an application, the output of the electric actuator is used to shorten the piston and compress the hydraulic oil in the oil chamber.

  For example, when power supply to the electric motor is interrupted while the electric actuator is driven to pressurize the piston in the axial direction (the piston is shortened), it is applied to the piston. The axial pressure is lost. In this case, the final output member of the actuator including the ball screw shaft is pushed by the hydraulic pressure of the hydraulic oil in the oil chamber (under a reverse input load) and rapidly moves toward the bottom side of the casing, and the bottom of the casing It collides with the inner bottom surface. For this reason, the housing (especially the bottom) is subject to deformation of the housing, even when the axial impact load as described above is applied to the bottom of the housing. In many cases, it is formed thick so as not to cause a decrease in the thickness.

  However, when the thickness of the casing is increased, the electric actuator becomes heavier and larger. In particular, an electric actuator for an automobile is desirably as light and compact as possible from the viewpoint of promoting reduction in fuel consumption of the automobile.

  In view of the above circumstances, an object of the present invention is to provide an electric actuator in which a ball screw shaft or the like can operate with a predetermined accuracy while being lightweight and compact.

  The present invention devised to achieve the above object includes an electric motor unit, a motion conversion mechanism unit that converts the rotational motion of the rotor of the electric motor unit into a linear motion, and outputs the electric motor unit and the motion conversion mechanism. And a nut that rotates by receiving the rotational motion of the rotor, and a ball screw shaft that moves forward and backward in the axial direction as the nut rotates. The electric actuator includes a load reducing means for reducing an axial load acting on an inner bottom surface of a bottom portion of a casing in a torque transmission path between the rotor and the nut.

  If the load reducing means as described above is provided, the thickness of the casing is increased in order to increase the durability against the axial load acting on the inner bottom surface of the casing (the strength and rigidity of the casing). It is not necessary, but rather the thickness of the housing can be reduced. Further, since the load reducing means is disposed in the torque transmission path between the rotor of the electric motor unit and the nut of the motion conversion mechanism unit (ball screw), an axial load acts on the bottom of the housing. Accordingly, the reaction force input to the actuator drive side including the ball screw shaft or the like can be reduced by the load reducing means. Thereby, the possibility that the members arranged in the torque transmission path are damaged by the influence of the reaction force is reduced as much as possible. Therefore, it is possible to realize an electric actuator that is light and compact and that can stably operate with a predetermined accuracy on the driving side of the actuator including the ball screw shaft.

  As the load reducing means, for example, of two members coaxially arranged so as to be relatively rotatable, a first friction plate fixed to one side, a second friction plate fixed to the other side, and both friction plates It is possible to employ a friction clutch having an elastic member that is pressed in the axial direction.

  If the one side is a rotor of an electric motor part formed in a hollow shape and the other side is a motor part output shaft that is arranged on the inner diameter side of the rotor and outputs the rotation of the rotor, the ball screw shaft can be When it collides with a bottom part, a slip can be produced between a rotor and a motor part output shaft, and torque transmission between both can be interrupted | blocked. In this case, as compared with the case where no friction clutch is provided in the above aspect, the rotational load of the rotor is converted such that the axial load acting on the bottom of the housing is converted into a linear component at least by the motion conversion mechanism (ball screw). It is possible to reduce the amount by the amount based on the product of the moment of inertia of the member that rotates following the force and the square of the rotational speed. In addition, it is possible to prevent the ball screw from being damaged as much as possible by acting an excessive load on the ball screw.

  From the viewpoint of reducing the size of the electric actuator in the axial direction, load reducing means such as a friction clutch is disposed between a pair of bearings that are spaced apart in the axial direction in order to rotatably support the rotor with respect to the housing. It is preferable to do this.

  The electric actuator having the above configuration is further provided with a speed reducer that decelerates the rotation of the rotor of the electric motor unit and transmits it to the nut for the purpose of reducing the size of the electric motor unit and, consequently, the weight and size of the electric actuator. Can do. In particular, the traction drive type planetary speed reducer has the feature of low backlash and low noise among various speed reducers, which is advantageous in realizing a quiet and excellent electric actuator.

  In the above configuration, the nut can be disposed outside the electric motor unit in the axial direction. In this case, compared with the case where the electric motor portion and the nut are overlapped in the radial direction (for example, Patent Document 1), the electric motor portion can be made compact in the radial direction, so the electric actuator is made compact in the radial direction. be able to.

  As described above, according to the present invention, it is possible to realize an electric actuator in which the ball screw shaft (including the output member of the actuator) can be stably operated with a predetermined accuracy while being light and compact.

It is a longitudinal cross-sectional view of the electric actuator which concerns on one Embodiment of this invention, and is HH arrow directional cross-sectional view of FIG. 3 and FIG. It is a longitudinal cross-sectional view of the electric actuator which concerns on one Embodiment of this invention, and is II sectional view taken on the line of FIG. It is a left view of FIG. FIG. 2 is a cross-sectional view taken along line EE in FIG. 1. FIG. 5 is a cross-sectional view taken along line F-F in FIG. 1. FIG. 3 is a cross-sectional view taken along line GG in FIG. 2. FIG. 3 is a partially enlarged view of FIG. 2. It is the elements on larger scale near the outer-diameter end part of a reduction gear in the state before the assembly of the electric actuator shown in FIG. It is a perspective view of the electric actuator shown in FIG. It is a perspective view of the electric actuator shown in FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  1 and 2 are longitudinal sectional views of an electric actuator according to an embodiment of the present invention. More specifically, FIG. 1 is a sectional view taken along line HH in FIGS. FIG. 7 is a cross-sectional view taken along the line I-I in FIG. 6. The electric actuator of the present embodiment is a so-called linear motion type in which the output member moves forward and backward (linear motion) in the axial direction. Hereinafter, a case where the output member is used for an electric brake system of an automobile will be described as an example.

  As shown in FIGS. 1 and 2, the electric actuator 1 includes an electric motor unit A that generates a rotational driving force, a motion conversion mechanism unit B that converts the rotational motion of the electric motor unit A into a linear motion, and outputs the linear motion. And a housing 8 accommodating these.

  The casing 8 of the present embodiment is formed by coupling four casing constituent members (first casing constituent member 81 to fourth casing constituent member 84) arranged in a row in the axial direction. It has a bottomed cylindrical shape as a whole. The first casing constituent member 81 is formed in a bottomed cylindrical shape, and the second to fourth casing constituent members 82 to 84 are formed in a cylindrical shape having both ends opened in the axial direction. As shown in FIGS. 9 and 10, the first to fourth casing constituent members 81 to 84 are coupled and integrated using a bolt member 85. The fourth casing constituent member 84 has a flange portion 84a integrally therewith, and the flange portion 84a is provided with the electric actuator 1 for a device not shown (here, a hydraulic cylinder constituting an electric brake system). A through hole 84b through which a bolt member for mounting and fixing is inserted is provided.

  Of the first to fourth casing constituent members 81 to 84, the third casing constituent member 83 is formed of a ferrous metal material, and the remaining casing constituent members, that is, the first casing constituent member 81, The second casing constituent member 82 and the fourth casing constituent member 84 are formed of an aluminum alloy having a small specific gravity and a high thermal conductivity in order to reduce the weight of the electric actuator 1 and improve the cooling efficiency.

  As shown in FIGS. 1 and 3, the first casing component member 81 is provided with a terminal portion D having a connector 101, and the connector 101 protrudes outward in the axial direction of the first casing component member 81. . In the connector 101, terminals for power supply and signal lines are provided, the terminals for power supply are electrically connected to the stator coil 51c, and the terminals for signal lines are connected to a sensor (not shown) (for example, Motor rotation angle detection sensor).

  The electric motor unit A includes an electric motor 29, a motor unit output shaft 6, and a torque limiter 7 that functions as load reducing means M in the present invention. The electric motor 29 includes a stator 51 fixed to the casing 8 (first and second casing constituent members 81 and 82), and a rotor 52 disposed to face the stator 51 via a radial gap. It is a radial gap type.

  As shown in FIGS. 1, 2 and 5, the stator 51 includes a stator core 51a made of a plurality of electromagnetic steel plates laminated in the axial direction, a bobbin 51b made of an insulating material mounted on the stator core 51a, and a bobbin 51b wound around the bobbin 51b. And a rotated stator coil 51c.

  The rotor 52 includes an annular rotor core 52a, a plurality of magnets 52b attached to the rotor core 52a, and a cylindrical (hollow) rotor inner 52c fixed to the inner periphery of the rotor core 51a, and has a hollow shape as a whole. . The rotor core 52a is formed of a plurality of electromagnetic steel plates laminated in the axial direction. The rotor inner 52c has an axial dimension longer than that of the rotor core 52a, and both axial ends of the rotor inner 52c protrude outward in the axial direction of the rotor core 52a. The rotor inner 52c is rotatably supported with respect to the housing 8 by bearings 53 and 54 fixed to the outer peripheral surfaces of both end portions in the axial direction. As the bearings 53 and 54, a rolling bearing capable of supporting both a radial load and a thrust load, for example, a deep groove ball bearing is used.

  As shown in FIGS. 1 and 2, the motor unit output shaft 6 is formed in a cylindrical shape with both ends in the axial direction being opened, whereby the electric motor unit A (electric motor 29) is a hollow motor. It has a structure. The motor unit output shaft 6 is fitted into the inner periphery of the rotor inner 52c and is rotatable relative to the rotor inner 52c.

  As shown in an enlarged view in FIG. 7, an annular recess 521 having an inner diameter dimension larger than that of the other part is formed on the inner peripheral surface of the rotor inner 52 c, and the annular recess 521 is formed, for example, of the rotor inner 52 c. It is formed at the end portion on the other side in the axial direction (the left side in FIG. 1; the same applies hereinafter). An annular space is formed between the inner peripheral surface of the annular recess 521 of the rotor inner 52c facing each other and the outer peripheral surface of the motor unit output shaft 6, and the torque limiter 7 is disposed in this annular space.

  The torque limiter 7 transmits the rotational power output from the electric motor 29 to the motor unit output shaft 6. On the other hand, when an overload is applied, the torque limiter 7 interrupts torque transmission, and the rotor 52 of the electric motor 29 and the motor unit output shaft 6. Allow relative rotation. As long as it has such a function, the torque limiter 7 having an arbitrary configuration can be adopted. However, in the present embodiment, a multi-plate clutch which is a kind of friction clutch is used as the torque limiter 7.

  The configuration of the torque limiter 7 (multi-plate clutch) will be described with reference to FIGS. The multi-plate clutch as the torque limiter 7 includes a pair of first friction plates 71 and 71 that are spaced apart in the axial direction and a second friction plate 72 that is disposed between the pair of first friction plates 71 and 71. And an elastic member 73 such as a wave spring in which the first friction plate 71 and the second friction plate 72 are brought into pressure contact with each other, and a pressing plate 74. The pressing plate 74 is positioned in the axial direction by a retaining ring 75 fitted in an annular groove on the inner peripheral surface of the rotor inner 52 c, and applies a predetermined pressing force (axial load) to the elastic member 73.

  A female serration 522 extending in the axial direction is formed on the inner peripheral surface of the annular recess 521 provided in the rotor inner 52 c, and the first friction plate 71 and the pressing plate 74 are fitted to the female serration 522. A male serration 6a extending in the axial direction is formed on the outer peripheral surface of the motor unit output shaft 6, and a second friction plate 72 is fitted to the male serration 6a. A frictional force is generated between the first friction plate 71 and the second friction plate 72 by the biasing force of the elastic member 73.

  When the torque acting between the electric motor 29 and the motor unit output shaft 6 is less than the friction force acting between the friction plates 71 and 72, the friction plates 71 and 72 rotate together. Rotational power is transmitted to the motor unit output shaft 6 via both friction plates 71 and 72. Thereby, the speed reducer 20 (details will be described later) connected to the motor unit output shaft 6 and the motion conversion mechanism B connected to the output side of the speed reducer 20 are driven. On the other hand, when the torque acting between the electric motor 29 and the motor unit output shaft 6 exceeds the friction force acting between the friction plates 71 and 72, one friction plate slides with respect to the other friction plate. Torque transmission between the motor 29 and the motor unit output shaft 6 is interrupted. Thereby, relative rotation of the motor part output shaft 6 and the rotor inner 52c is permitted.

  As shown in FIGS. 1 and 2, the motion conversion mechanism portion B includes a ball screw shaft 93 having a spiral groove formed on the outer peripheral surface and disposed coaxially with the rotation center of the rotor 52 of the electric motor 29, A spiral groove is formed on the surface, and a nut 92 fitted to the outer periphery of the ball screw shaft 93, a plurality of balls 94 disposed between the spiral groove of the ball screw shaft 93 and the nut 92, and the ball screw shaft 93 And a ball screw 91 provided with a top (not shown) as a circulating member disposed between the nut 92 and the nut 92. An actuator head 100 as an operation unit C for operating an operation target (not shown) (for example, a piston of a hydraulic cylinder) is provided at one end of the ball screw shaft 93 in the axial direction. An actuator head 100 is integrally provided at one end of the screw shaft 93 in the axial direction. Therefore, the ball screw shaft 93 constitutes an output member of the electric actuator 1. The operation unit C (actuator head 100) can be provided separately from the ball screw shaft 93, and can be selected and used according to the application.

  The nut 92 is connected to an output member (motor unit output shaft 6) of the electric motor unit A and is driven to rotate. Although details will be described later, in the present embodiment, since the rotational motion of the electric motor portion A is transmitted to the nut 92 via the speed reducer 20, the carrier 24 constituting the output member of the speed reducer 20 is provided on the nut 92. It is fixed by appropriate means such as press fitting.

  The nut 92 is disposed on one side in the axial direction from the electric motor part A, and does not overlap with the rotor inner 52c of the electric motor part A and the motor part output shaft 6 in the radial direction. In this case, since the inner diameter dimension D1 of the rotor inner 52c and the inner diameter dimension D2 of the motor unit output shaft 6 can be made smaller than the outer diameter dimension D3 of the nut 92, a small electric motor 29 having a small radial dimension is used. be able to. Thereby, the electric motor part A and by extension the electric actuator 1 can be made compact in the radial direction.

  As shown in FIGS. 1 and 4, a rotation preventing mechanism for the ball screw shaft 93 is provided on the inner periphery of the hollow motor portion output shaft 6. That is, the anti-rotation mechanism for the ball screw shaft 93 is provided within the axial range of the electric motor portion A. As a result, the electric actuator 1 can be made more compact in the axial direction than in the case where the rotation prevention mechanism for the ball screw shaft 93 is provided on the outer side in the axial direction of the electric motor portion A (for example, Patent Document 1).

  The anti-rotation mechanism of this embodiment is fixed to the first casing component member 81 and penetrates the cylindrical guide member 95 disposed on the inner periphery of the motor unit output shaft 6 and the ball screw shaft 93 in the radial direction. The pin 96 is inserted through the through-hole, and has a radially outer end protruding outward in the radial direction of the ball screw shaft 93, and a guide collar 97 rotatably fitted in the protruding portion of the pin 96. . The guide member 95 has a cylindrical portion 95 a disposed between the inner peripheral surface of the motor unit output shaft 6 and the outer peripheral surface of the ball screw shaft 93. A guide groove 95b extending in the axial direction is formed on the inner diameter surface of the cylindrical portion 95a, and a guide collar 97 is fitted into the guide groove 95b. With the above configuration, the ball screw shaft 93 can smoothly move back and forth (linear motion) in the axial direction while being prevented from rotating with respect to the housing 8.

  As shown in FIGS. 1 and 2, the nut 92 is rotatably supported with respect to the housing 8 by a rolling bearing 9 having an inner ring fixed to the outer peripheral surface thereof. As the rolling bearing 9, a bearing capable of supporting both a radial load and a thrust load is used, and among them, a double row deep groove ball bearing having a particularly high load supporting ability is used. If a double-row deep groove ball bearing is used for the rolling bearing 9, the nut 92 can be a double-supported structure, so that the nut 92 is prevented from being inclined with respect to the axial direction and the rotational accuracy of the nut 92 being lowered. There is also an advantage of being able to.

  The outer ring of the rolling bearing 9 has an axial end surface on one side and the other end thereof on the shoulder surface 84c of the fourth casing component member 84 and an end surface 83a on the axial direction one side of the third casing component member 83, respectively. It is in contact. That is, the rolling bearing 9 is positioned in the axial direction by holding the outer ring between the third housing constituent member 83 and the fourth housing constituent member 84 from both axial sides. In this case, the rolling bearing 9 can be positioned and fixed at the same time as the casing 8 is assembled (the first to fourth casing constituent members 81 to 84 are coupled and integrated using the bolt member 85). Good properties. The inner ring of the rolling bearing 9 is clamped from both sides in the axial direction by a flange provided at one end of the nut 92 in the axial direction and the carrier 24 of the speed reducer 20.

  As shown in FIGS. 1 and 2, the electric actuator 1 of the present embodiment is disposed in a torque transmission path between the motor unit output shaft 6 of the electric motor unit A and the nut 92 constituting the motion conversion mechanism unit B. A reduced reduction gear 20 is provided. In this case, since the high torque rotational power decelerated by the speed reducer 20 is transmitted to the nut 92, the electric motor 29 can be reduced in size. For this reason, the electric actuator 1 can be reduced in weight and size.

  As shown in FIG. 6, the speed reducer 20 of the present embodiment is a traction drive type planetary speed reducer, and is arranged on the radially outer side of the sun roller 21, the plurality of planetary rollers 23, the carrier 24, and the planetary roller 23. And an annular traction applying member 22. In the present embodiment, the end of one side in the axial direction of the motor unit output shaft 6 is used as the sun roller 21, and the outer ring of the rolling bearing (for example, deep groove ball bearing) 25 is used as the planetary roller 23. The inner ring of each rolling bearing 25 is fixed to the outer periphery of the hollow shaft 26.

  FIG. 8 schematically shows an enlarged view of the vicinity of the outer diameter end of the speed reducer 20 in a state before the electric actuator 1 (housing 8) is assembled. As shown in FIG. 8, the traction imparting member 22 integrally includes a main body portion 22a having a U-shaped cross section and flange portions 22b provided on both axial sides of the main body portion 22a. In the state before the assembly of the housing 8, as shown by a solid line in FIG. 8, the flange portion 22 b on one axial side of the traction imparting member 22 disposed on the inner periphery of the second housing component 82 is The second casing component member 82 projects from the end surface on one side in the axial direction by a dimension t.

  Between the flange 22b on the other axial side of the traction imparting member 22 and the housing 8 (second housing component 82), an adjustment member 28 formed in an annular shape with an iron-based metal is disposed. Yes. The adjustment member 28 adjusts the dimension t before the housing 8 is assembled.

  Then, when the casing 8 is assembled (the first to fourth casing constituent members 81 to 84 are combined and integrated using the bolt member 85), the traction imparting member 22 is connected to the third casing constituent member 83. The pressure surface 83b is pressurized on the other side in the axial direction and is compressed and deformed in the axial direction. When the traction imparting member 22 is compressively deformed in the axial direction, the main body portion 22 of the traction imparting member 22 swells radially inwardly (refer to the two-dot chain line in FIG. 8; however, in FIG. 8, the degree of deformation) Is exaggerated). Accordingly, traction (radial preload) is applied to the inside of the speed reducer 20, more specifically, to the contact portion between the traction applying member 22 and the planetary roller 23, and further to the contact portion between the planetary roller 23 and the sun roller 21. Is done.

  The electric actuator 1 of the present embodiment having the above configuration operates in the following manner because the torque limiter 7 is disposed between the rotor 52 of the electric motor 29 and the motor unit output shaft 6. First, during normal times, the rotational power of the electric motor 29 is transmitted to the nut 92 of the ball screw 91 via the torque limiter 7, the motor unit output shaft 6 and the speed reducer 20, so that the nut 92 Rotate around the axis. In the present embodiment, when the nut 92 is rotated forward in response to the rotational power of the electric motor 29, the ball screw shaft 93 having the actuator head 100 moves forward in one axial direction to operate an operation target (not shown). In the embodiment, the hydraulic oil in the oil chamber is compressed by shortening the piston of the hydraulic cylinder.

  While the ball screw shaft 93 is operating the operation target (piston) in the above mode, for example, when power supply to the electric motor unit A is interrupted, the ball screw shaft 93 is applied to the piston. The axial pressure, that is, the axial compressive load applied to the hydraulic oil in the oil chamber is released. As a result, the ball screw shaft 93 is loaded with an axial load (reverse input load) that urges the ball screw shaft 93 toward the other side in the axial direction, so the ball screw shaft 93 moves rapidly toward the other side in the axial direction, The end portion on the other side in the axial direction collides with the inner bottom surface of the bottom portion of the housing 8 (first housing constituent member 81).

Here, as in the electric actuator 1 according to the present embodiment, in the torque transmission path between the rotor 52 of the electric motor 29 and the nut 92 of the ball screw 91, more specifically, the rotor inner 52c and the motor unit output shaft 6 When the torque limiter 7 (friction clutch) is not disposed between the motor 52 and the rotor 52 of the electric motor 29 continues to rotate due to inertia even when power supply to the electric motor unit A is interrupted, When the ball screw shaft 93 collides with the inner bottom surface of the bottom of the housing 8, the axial load acting on the bottom of the housing 8 is
(1) The product of the mass of the ball screw shaft 93 and the square of the moving speed, and (2) the rotor 52 of the electric motor 29 that is converted into a linear motion component by the ball screw 91 and its rotational driving force, and rotates. An axial load based on the product of the moment of inertia and the square of the rotational speed of the driven rotating member (here, the motor unit output shaft 6, the speed reducer 20, and the nut 92 of the ball screw 91);
Is the sum of

  On the other hand, if the torque limiter 7 is arranged between the rotor inner 52c and the motor unit output shaft 6 as in the electric actuator 1 according to the present embodiment, the ball screw shaft 93 collides with the bottom of the housing 8. At that moment, slip occurs between the rotor inner 52c and the motor unit output shaft 6 and the torque transmission between the two is interrupted, so that the ball screw shaft 93 collides with the bottom of the housing 8 and the housing 8 The axial load acting on the bottom of the body 8 is only the amount corresponding to the above (1) without the amount corresponding to the above (2). Therefore, the torque limiter 7 functions as a load reducing means M for reducing the axial load acting on the inner bottom surface of the bottom portion of the housing 8. In this case, in order to increase the durability (strength / rigidity) of the casing 8, it is not necessary to increase the thickness of the casing 8. Rather, the thickness of the casing 8 can be decreased. Thereby, the housing | casing 8 and by extension, the electric actuator 1 can be reduced in weight and size.

  Further, since the torque limiter 7 as the load reducing means M is arranged in the above-described manner, the ball screw shaft 93 is counteracted when the ball screw shaft 93 collides with the bottom of the housing 8 (an axial load acts on the bottom of the housing 8). Even if force is input to the drive side of the actuator 1 including the ball screw shaft 93, slippage occurs between the rotor inner 52c and the motor unit output shaft 6, and torque transmission between the two is interrupted. In addition, the possibility that an excessive load acts on the ball screw 91 and damages the ball screw 91 can be effectively reduced.

  Further, if the torque limiter 7 is provided in the above-described manner, even if the forward movement of the ball screw shaft 93 is restricted, a slip is generated between the rotor inner 52c and the motor unit output shaft 6 to generate torque. Since the transmission path can be interrupted, it is possible to prevent an excessive load from acting on the speed reducer 20 and the ball screw 91 (motion conversion mechanism part B), and to effectively reduce the possibility of damage or the like. it can.

  In addition, the torque limiter 7 serving as the load reducing means M capable of producing the effects described above is provided between the inner peripheral surface of the rotor inner 52c formed in a hollow shape and the outer peripheral surface of the motor unit output shaft 6 opposed thereto. Therefore, for example, the axial dimension of the electric motor unit A and further the electric actuator 1 can be made smaller than when the torque limiter 7 is arranged adjacent to the outside of the electric motor unit A (electric motor 29) in the axial direction. it can. In order to effectively obtain such an effect, the torque limiter 7 is provided between the pair of bearings 53 and 54 that rotatably support the rotor 52 (rotor inner 52c), more specifically, an end face on one axial side of the bearing 53. And the end face on the other axial side of the bearing 54 are preferably arranged in an axial range, and in this embodiment, the torque limiter 7 is arranged in the axial range.

  The electric actuator 1 according to the present invention combines the various functions and effects described above, and is lightweight and compact, but the drive side including the ball screw shaft 93 can stably operate with a predetermined accuracy and is reliable. It is characterized by being rich in nature.

  As mentioned above, although the electric actuator 1 which concerns on one Embodiment of this invention was demonstrated, embodiment of this invention is not restricted to this.

  For example, in the electric actuator 1 described above, a traction drive type planetary speed reducer is adopted as the speed reducer 20, but the configuration of the speed reducer 20 is arbitrary, and other speed reducers (for example, planetary gear speed reducers) are adopted. You can also Further, the reduction gear 20 is not an essential configuration, and the present invention can also be applied to the electric actuator 1 in which the reduction gear 20 is omitted.

  Further, as the electric motor 29 of the electric motor portion A, an axial gap type may be adopted instead of the radial gap type as described above.

  The present invention is not limited to the above-described embodiments, and can of course be implemented in various forms without departing from the gist of the present invention. It includes the equivalent meanings recited in the claims and the equivalents recited in the claims, and all modifications within the scope.

1 Electric Actuator 6 Motor Unit Output Shaft 7 Torque Limiter (Friction Clutch)
8 Housing 20 Reducer 29 Electric motor 52 Rotor 91 Ball screw 92 Nut 93 Ball screw shaft A Electric motor part B Motion conversion mechanism part C Operation part D Terminal part M Load reducing means

Claims (7)

An electric motor unit, a motion conversion mechanism unit that converts the rotational motion of the rotor of the electric motor unit into a linear motion and outputs the same, a bottomed cylindrical housing that houses the electric motor unit and the motion conversion mechanism unit, An electric actuator having a nut that rotates in response to the rotational motion of the rotor, and a ball screw shaft that moves forward and backward in the axial direction as the nut rotates.
An electric actuator comprising a load reducing means for reducing an axial load acting on an inner bottom surface of the bottom of the casing in a torque transmission path between the rotor and the nut.   Of the two members coaxially arranged so as to be relatively rotatable, the load reducing means presses the first friction plate fixed on one side and the second friction plate fixed on the other side in the axial direction. The electric actuator according to claim 1, wherein the electric actuator is a friction clutch.   The electric actuator according to claim 2, wherein the one side is the rotor formed in a hollow shape, and the other side is a motor unit output shaft that is disposed on an inner diameter side of the rotor and outputs rotation of the rotor. The rotor is rotatably supported with respect to the housing by a pair of bearings arranged apart in the axial direction,
The electric actuator according to claim 1, wherein the load reducing means is disposed between the pair of bearings.   The electric actuator as described in any one of Claims 1-4 further equipped with the reduction gear which decelerates rotation of the said rotor and transmits to the said nut.   The electric actuator according to claim 5, wherein the speed reducer is a traction drive type planetary speed reducer.   The electric actuator according to claim 1, wherein the nut is disposed on an outer side in the axial direction of the rotor.

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