JP2018197567A - Electric actuator - Google Patents

Abstract

To provide an electric actuator in which an output shaft can stably actuate and which has good reliability.SOLUTION: An electric actuator 1 includes: a drive part A having an electric motor 13; a motion conversion mechanism part B for converting rotary motion of the drive part A into linear motion; and a bottomed cylindrical housing 2 for storing these. The motion conversion mechanism part B comprises a screw shaft 41, a nut 42 rotatably fitted in an outer periphery of the screw shaft via a plurality of balls 45, and a ball screw 40. The screw shaft 41 is formed in a hollow shape in which one end is opened and the other end is closed. One end part of an inner member having an elastic part (elastic member 50) which is deformable expanding/contracting in an axial direction is positioned on the outside of an opening of the screw shaft 41, and the other end part is arranged in a hollow part of the screw shaft 41 in a state of coming into contact with a closed part 41b of the screw shaft 41.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an electric actuator.

  In recent years, various types of vehicles such as automobiles and motorcycles have been electrified to save labor and reduce fuel consumption. For example, operations of automatic transmissions, brakes, steering, and the like are performed by the power of an electric motor (electric motor). The system has been developed and put on the market. As an electric actuator used in such a system, a motion conversion mechanism that converts the rotary motion of an electric motor into a linear motion is used, a screw shaft that is arranged coaxially with the rotation center of the electric motor, and a screw through a plurality of balls. There is one that employs a ball screw including a nut that is rotatably fitted to the outer periphery of a shaft (for example, Patent Document 1). In this case, when the nut rotates around the axis of the screw shaft in response to the rotational movement of the electric motor, the screw shaft (output shaft of the electric actuator) moves linearly (back and forth) in the axial direction, and the operation target is operated in the axial direction. To do.

  In the electric actuator of Patent Document 1, the electric motor and the ball screw are accommodated in a bottomed cylindrical casing.

JP-A-2005-330942

  For example, when an electric system of the electric actuator has some trouble, the output shaft overruns when the screw shaft (output shaft) moves backward (when moving to the bottom of the housing), and the output shaft and the bottom of the housing May hit hard. As described above, when the output shaft and the bottom of the housing are strongly abutted, as shown schematically in FIG. 11, the output shaft is bent such that its axis is displaced from the rotation center of the electric motor. May occur. When such bending occurs, the ball incorporated in the ball screw comes into contact with the spiral groove 101a of the screw shaft 101 at the contact point 101c other than the predetermined contact point 101b. (The center Ob of the ball 103 has a contact point 101b between the spiral groove 101a of the screw shaft 101 and the ball 103, and a contact point 102b of the spiral groove 102a of the nut 102 and the ball 103). The ball 103 is in a so-called locked state in which the ball 103 cannot roll. When the ball screw falls into such a locked state, the rotational motion of the motor cannot be transmitted to the screw shaft 101, and the screw shaft 101 becomes inoperable.

  Therefore, in an electric actuator that uses a ball screw as the motion conversion mechanism, measures are taken to prevent the ball screw from falling into the above-mentioned locked state even when the screw shaft (output shaft) hits the bottom of the housing strongly (lock prevention) It can be said that it is preferable to take measures. However, Patent Document 1 does not mention or examine the lock prevention measures described above. However, even if measures to prevent locking are taken, measures that cause an increase in the size of the electric actuator and, in turn, a decrease in the mountability of the electric actuator to the equipment used are not preferable.

  In view of the above circumstances, the main object of the present invention is to provide a highly reliable electric actuator that is compact and capable of stably operating a screw shaft (output shaft).

  Invented to achieve the above object, the present invention includes a drive unit having an electric motor, a motion conversion mechanism unit that converts the rotational motion of the drive unit into a linear motion, and an end opening on one side in the axial direction is closed. And a housing that houses the drive unit and the motion conversion mechanism unit. The motion conversion mechanism unit includes a screw shaft disposed coaxially with the rotation center of the electric motor, and a plurality of balls. In the electric actuator having a nut rotatably fitted on the outer periphery of the screw shaft, and the screw shaft is moved forward and backward in the axial direction as the nut rotates by receiving the rotational motion of the drive unit. The shaft is formed in a hollow shape in which an end portion on one side in the axial direction is opened and an end portion on the other side in the axial direction is closed, and an inner member having an elastic portion that can expand and contract in the axial direction is provided in the axial direction. When one end is positioned outside the opening of the screw shaft In, characterized in that it is disposed in the hollow portion of the screw shaft with its and the axial end portion of the other side is abutted against the closed portion of the screw shaft.

  According to the above configuration, even if the screw shaft (the output shaft of the electric actuator including the screw shaft) moves to one side in the axial direction (the bottom side of the housing), the bottom of the housing The inner member disposed on the inner periphery of the screw shaft comes into contact with the screw shaft before the screw shaft. The inner member has an elastic part that can be expanded and contracted in the axial direction, and the end on the other side in the axial direction of the inner member is in contact with the closing part (the end on the other side in the axial direction) of the screw shaft. When the inner member comes into contact with the bottom of the housing, the screw shaft is pushed back to the other side in the axial direction by the extension deformation (elastic restoring force) of the elastic portion. As a result, it is possible to prevent the screw shaft from striking strongly against the housing and the bottom, and to prevent the screw shaft from bending such that its axis is displaced from the rotation center of the electric motor. It is possible to prevent as much as possible that the ball screw as the conversion mechanism portion falls into the locked state. Further, in the present invention, since the means for preventing the ball screw from being locked is provided on the inner periphery of the screw shaft (output shaft), it is possible to avoid an increase in the size of the electric actuator by taking a lock prevention measure. Therefore, according to the present invention, it is possible to realize a highly reliable electric actuator that is compact and capable of stably operating the screw shaft.

  The inner member is, for example, an inner shaft coupled to the screw shaft so as to be relatively movable in the axial direction with respect to the screw shaft, and an elastic member as the elastic portion interposed between the inner shaft and the closed portion of the screw shaft. It can comprise with.

  The screw shaft and the inner shaft can be connected by fitting a connecting pin so as to penetrate both in the radial direction. At this time, if the through hole of the inner shaft into which the connecting pin is fitted is formed into a long hole that allows the axial movement of the connecting pin, and the connecting pin is press-fitted into the through hole of the screw shaft, the inner shaft And the screw shaft can be coupled so as to be relatively movable in the axial direction.

  It is preferable to provide the connecting pin (the connecting portion between the screw shaft and the inner shaft) at a plurality of locations separated in the circumferential direction.

  The inner shaft is formed in a hollow shape with an end on one side in the axial direction, a guide shaft that guides the axial movement of the screw shaft in the hollow portion of the inner shaft is arranged, and the inner end of the connecting pin A rotating body externally fitted to the guide shaft may be fitted into an axial groove provided on the guide shaft. In this way, since a screw shaft detent mechanism can be provided in the hollow portion of the screw shaft, it is advantageous in realizing a compact electric actuator.

  As described above, according to the present invention, it is possible to prevent the detection accuracy of the detection device from being lowered as much as possible. Therefore, it is possible to provide an electric actuator with good operation accuracy of the screw shaft and high reliability. .

It is a longitudinal cross-sectional view of the electric actuator which concerns on one Embodiment of this invention, Comprising: It is a YY arrow directional cross-sectional view of FIG. It is a VV arrow directional cross-sectional view of FIG. It is a left view of FIG. FIG. 2 is a cross-sectional view taken along line WW in FIG. 1. FIG. 2 is a cross-sectional view taken along line XX in FIG. 1. It is the elements on larger scale of FIG. It is the elements on larger scale of Drawing 1, and is an enlarged view near the end of a screw axis. It is an enlarged view near one end of a screw shaft when an axial reverse input load is applied to the screw shaft. FIG. 2 is an exploded view of FIG. 1. It is a perspective view of the electric actuator shown in FIG. It is an enlarged view for demonstrating the problem of the conventional electric actuator.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1 is a longitudinal sectional view of an electric actuator according to an embodiment of the present invention, FIG. 2 is a sectional view taken along line VV in FIG. 1, FIG. 3 is a left side view of FIG. FIG. 5 is a sectional view taken along line XX in FIG.

  As shown in FIGS. 1 and 2, the electric actuator 1 includes a drive unit A, a motion conversion mechanism unit B, a detection unit C, and a terminal unit D, which are formed in a casing 2 having a bottomed cylindrical shape as a whole. Contained and retained.

  The casing 2 has an opening at one end in the axial direction (left side in FIG. 1 and FIG. 2; the same applies hereinafter) and the other end in the axial direction (right side in FIG. 1 and FIG. 2). From the cylindrical first casing 20, and the second casing 22 and the third casing 26 that are disposed on one side and the other side in the axial direction of the first casing 20, and are detachably connected to the first casing 20. Become. The second casing 22 and the third casing 26 are connected to the first casing 20 by an assembly bolt 27, and the end opening on one axial side of the first casing 20 is closed by the second casing 22. . Therefore, in the present embodiment, the second casing 22 constitutes the bottom of the housing 2.

  The internal space of the housing 2 includes a first storage chamber 2a that stores the drive unit A and the like, and a second storage chamber that stores the detection unit C, by a ring-shaped partition wall 21 provided integrally with the first casing 20. 2b. The second casing 22 includes a perforated disk-shaped base member 23 and a guide shaft 24 inserted through the central hole of the base member 23. The guide shaft 24 in the illustrated example is a solid flanged shaft, and is connected to the base member 23 by mounting bolts 25.

  As shown in FIGS. 1, 2, and 4, the drive unit A includes a stator 11 fixed to the inner periphery of the first casing 20 and a rotor disposed to face the inner periphery of the stator 11 via a radial gap. And a radial gap type electric motor 13. The stator 11 includes a stator core 11a, an insulating bobbin 11b attached to the stator core 11a, and a coil 11c wound around the bobbin 11b. As shown in FIG. 4, the stator core 11 a is prevented from rotating with respect to the first casing 20 by fitting a convex portion provided on the outer peripheral portion thereof to a concave portion provided on the inner peripheral surface of the first casing 20. It is fixed in the state. The rotor 12 includes a rotor core 12a, a permanent magnet 12b attached to the outer periphery of the rotor core 12a, and a cylindrical rotor inner 12c formed in a cylindrical shape and having the rotor core 12a attached to the outer periphery.

  As shown in FIGS. 1 and 10, the terminal portion D is fitted and fixed in a concave portion defined between the first casing 20 and the third casing 26, and a part thereof is radially outward of the housing 2. A protruding connector 16 and a bus bar 17 disposed between the stator 11 of the electric motor 13 and the first casing 20 are provided. A power supply terminal is provided in the connector 16, and this terminal is electrically connected to the stator coil 11 c via a terminal 17 a of the bus bar 17.

  As shown in FIGS. 1, 2, 4, and 5, the motion conversion mechanism portion B is arranged coaxially with the rotation center of the rotor 12 of the electric motor 13 and constitutes the output shaft 4 of the electric actuator 1. 41, a nut 42 rotatably fitted to the outer periphery of the screw shaft 41 via a plurality of balls 45, and provided on the outer peripheral surface of the screw shaft 41 when the screw shaft 41 moves back and forth in the axial direction. The ball screw 40 is provided with a top 46 as a circulating member for infinite circulation of the ball 45 between the spiral groove 41 c and the spiral groove 43 a provided on the inner peripheral surface of the nut 42. The top 46 is disposed inside a through hole opened in the inner peripheral surface and the outer peripheral surface of the nut 42 (the screw nut portion 43), and is fixed to the nut 42 by caulking, for example.

  The nut 42 has a spiral groove 43 a formed on the inner peripheral surface thereof, and a screw nut portion 43 disposed on the inner periphery of the rotor inner 12 c so as to be able to transmit torque with the rotor 12 of the electric motor 13, and the screw nut portion 43. A cylindrical portion 44 extending in the axial direction from one end to a position close to the second casing 22 is integrally provided. In the present embodiment, torque is directly transmitted between the rotor inner 12 c and the nut 42 by press-fitting the rotor inner 12 c into the outer periphery of the screw nut portion 43.

  In this embodiment, since the rotor inner 12c is press-fitted and fixed to the outer periphery of the screw nut portion 43 of the nut 42, the assembling property of both is good. Further, since the nut 42 and the rotor inner 12c (rotor 12) have a separate structure, for example, even when the ball screw 40 having different specifications is adopted, the rotor 12 and thus the electric motor 13 can be shared. Therefore, it is advantageous in realizing a wide variety (series) of electric actuators 1 by sharing parts.

  The inner peripheral surface 44a of the cylindrical portion 44 of the nut 42 is formed as a smooth cylindrical surface without a spiral groove, and is opposed to the outer peripheral surface of the screw shaft 41 via a radial gap. The outer peripheral surface of the cylindrical portion 44 has a relatively large-diameter large-diameter outer peripheral surface 44b and a relatively small-diameter small-diameter outer peripheral surface 44c. The inner ring of the rolling bearing 18 is fixed to the large-diameter outer peripheral surface 44b, and the rotation side (the resolver rotor 31 as a rotor ring) of the detection device 30 constituting the detection unit C is fixed to the small-diameter outer peripheral surface 44b. .

  Although not shown in detail, the ball screw 40 having the above configuration is lubricated in a radial clearance between the outer peripheral surface of the screw shaft 41 and the inner peripheral surface of the screw nut portion 43 of the nut 42 facing each other. While being filled with grease as an agent, the grease is not filled between the outer peripheral surface of the screw shaft 41 facing each other and the inner peripheral surface 44a of the cylindrical portion 44 of the nut 42, and is incorporated into the inside of the housing 2. Yes.

  The nut 42 is rotatably supported with respect to the housing 2 by rolling bearings 18 and 19 that are respectively disposed on one axial side and the other axial side of the rotor 12 of the electric motor 13. The rolling bearing 18 is press-fitted between the inner peripheral surface of the partition wall 21 of the first casing 20 and the large-diameter outer peripheral surface 44b of the cylindrical portion 44 of the nut 42, and the partition wall 21 (the flange portion thereof) and the nut 42 ( Are positioned in the axial direction by being sandwiched from both sides in the axial direction. The rolling bearing 19 is press-fitted to the inner peripheral surface of the third casing 26, and is fitted to the outer peripheral surface of the screw nut portion 43 of the nut 42. It is positioned in the axial direction by being clamped from both sides in the direction.

  In the present embodiment, both the rolling bearings 18 and 19 are constituted by sealed ball bearings (deep groove ball bearings). The details of the rolling bearing 18 will be described with reference to a representative example. As shown in FIG. 6, the rolling bearing 18 is formed between an inner ring 18a and an outer ring 18b, and an inner raceway surface of the inner ring 18a and an outer raceway surface of the outer ring 18b. A plurality of balls 18c that are movably arranged, a cage 18d that holds the plurality of balls 18c at predetermined intervals in the circumferential direction, and grease as a lubricant that is interposed in an annular space between the inner ring 18a and the outer ring 18b (not shown) ) And a pair of seal members 18e disposed on both sides in the axial direction of the cage 18d. The seal member 18e in the illustrated example is a non-contact type seal member (shield plate) in which an outer diameter end is fitted and fixed to the inner peripheral surface of the outer ring 18b, and an inner diameter end is disposed close to the outer peripheral surface of the inner ring 18a. However, a contact-type seal member in which a seal lip that comes into contact with the outer peripheral surface of the inner ring 18a is provided at the inner diameter end may be adopted. In FIG. 6, the electric motor 13 and the bus bar 17 are omitted.

  The screw shaft 41 includes a hollow shaft portion 41a in which a spiral groove 41c is formed on an outer peripheral surface and an inner peripheral surface 41d is formed in a cylindrical surface having a constant diameter, and an end opening on the other axial side of the shaft portion 41a. It consists of the hollow shaft which has integrally the obstruction | occlusion part 41b which obstruct | occludes.

  In the present embodiment, the output shaft 4 includes a screw shaft 41 and an inward member disposed in a hollow portion of the screw shaft 41. As shown in FIGS. 1 and 2, the inner member has an inner shaft 47 connected to the screw shaft 41 and an elastic portion as an elastic portion disposed between the inner shaft 47 and the closed portion 41 b of the screw shaft 41. Member 50. The inner shaft 47 includes a hollow shaft portion 47a disposed between the guide shaft 24 and the screw shaft 41 (the shaft portion 41a) constituting the second casing 22, and an end on the other axial side of the shaft portion 47a. It consists of the hollow shaft which integrally has the obstruction | occlusion part 47b which obstruct | occludes part opening. The inner shaft 47 can move relative to the screw shaft 41 and the guide shaft 24 in the axial direction.

  As shown in FIG. 7 in an enlarged manner, two through holes 47d opened at the inner peripheral surface and the outer peripheral surface of the shaft portion 47a are provided at an end of one side in the axial direction of the inner shaft 47 at a 180 ° pitch. Further, at the end portion on one side in the axial direction of the screw shaft 41, there are provided two through holes 41f opened at an inner peripheral surface 41d and an outer peripheral surface of the shaft portion 41a at a pitch of 180 °. The through holes 47d and 41f may be provided at three or more locations separated in the circumferential direction.

  The inner shaft 47 is connected to the screw shaft 41 by a connecting pin 51 having a circular cross section fitted in the through holes 47d and 41f. In order to prevent the connecting pins 51 from coming off, a ring-shaped pin cover 52 is press-fitted to the outer periphery of the connecting pins 51, and a guide roller 53 as a rotating body is externally fitted to the inner diameter end of each connecting pin 51. The guide roller 53 is rotatably fitted to the inner diameter end portion of the connecting pin 51 and is fitted to an axial guide groove 24a provided on the guide shaft 24 (see also FIGS. 4 and 5). . With such a configuration, when the electric motor 13 is driven to rotate the rotor 12 and the nut 42 rotates around the axis of the screw shaft 41, the output shaft 4 including the screw shaft 41 is prevented from rotating. To move forward and backward in the axial direction.

  The through hole 41f provided in the screw shaft 41 is formed in a perfect circle shape into which the connecting pin 51 is press-fitted, while the through hole 47d provided in the inner shaft 47 allows the connecting pin 51 to move in the axial direction. It is formed in a long hole (long hole whose longitudinal direction is the axial direction). With the above configuration, the relative movement amount of the inner shaft 47 in the axial direction with respect to the screw shaft 41 is limited within the range of the axial dimension of the through hole 47d.

  The elastic member 50 as an elastic portion is formed of an elastic material such as a rubber material, and is interposed between the closing portion 41b of the screw shaft 41 and the closing portion 47b of the inner shaft 47 in an axially compressed state. . That is, one end and the other end of the elastic member 50 are in pressure contact with the other end surface 47 c of the closing portion 47 b of the inner shaft 47 and one end surface 41 e of the closing portion 41 b of the screw shaft 41, respectively. By providing the elastic member 50 in this manner, the inner shaft 47 is urged toward one side in the axial direction, and the connecting pin 51 is connected to the other end of the through hole 47d of the inner shaft 47 as shown in FIG. Located in the department. As a result, the inner shaft 47 is restrained from both sides in the axial direction by the elastic member 50 and the connecting pin 51, so that the inner shaft 47 is prevented from rattling with respect to the screw shaft 41. As the elastic member 50, a compression coil spring can be employed in addition to the above.

  When the electric actuator 1 of the present embodiment is normally driven (for example, when the output shaft 4 moves forward in the axial direction to the other side and operates an operation target not shown in the axial direction in a predetermined manner). As shown in FIG. 7, the end on one axial side of the inner shaft 47 constituting the inner member is on the one axial side of the screw shaft 41 (on the one side in the axial direction of the screw shaft 41). It is held in a state located outside the opening).

  On the other hand, for example, when the electric power supply to the electric motor 13 is interrupted while the electric actuator 1 is being driven, a reverse input load that pressurizes the output shaft 4 in one axial direction with respect to the output shaft 4 including the screw shaft 41 is generated. When loaded, there is a possibility that the output shaft 4 rapidly moves toward one side in the axial direction and collides with the bottom of the housing 2 (second casing 22). When the output shaft 4 collides with the second casing 22, the output shaft 4 may be bent such that its axis is displaced with respect to the rotation center of the rotor 12 of the electric motor 13. When such bending occurs, as described with reference to FIG. 11, the contact state between the spiral groove 41c of the screw shaft 41 and the spiral groove 43a of the nut 42 and the ball 45 becomes a so-called three-point contact, and the ball 45 The spiral grooves 41c and 43a fall into a so-called locked state incapable of rolling. When the ball screw 40 is locked, the rotational motion of the rotor 12 of the electric motor 13 cannot be transmitted to the screw shaft 41, and the output shaft 4 becomes inoperable.

  In the electric actuator 1 of the present embodiment, since the output shaft 4 having the above-described configuration is employed, it is possible to effectively generate a serious defect that makes the output shaft 4 inoperable due to the ball screw 40 falling into a locked state. Can be prevented. The detailed reason will be described below.

  First, the inner member including the inner shaft 47 and the elastic member 50 is disposed in the hollow portion of the screw shaft 41, and usually the end portion on the one axial side of the inner shaft 47 is positioned outside the opening of the screw shaft 47. Therefore, even when the output shaft 4 rapidly moves toward one side in the axial direction, the inner shaft 47 contacts (collises) preferentially with the second casing 22. When the inner shaft 47 collides with the second casing 22, the inner shaft 47 moves relative to the screw shaft 41 in the axial direction, and is interposed between the closed portion 41 b of the screw shaft 41 and the closed portion 47 b of the inner shaft 47. The elastic member 50 is compressed in the axial direction. Since the screw shaft 41 and the inner shaft 47 are connected to each other by a connecting pin 51 fitted in the through hole 47d of the inner shaft 47 so as to be movable relative to each other, as shown in FIG. When the connecting pin 51 is positioned at one end of the through hole 47d with the movement, further relative movement of the inner shaft 47, that is, compression deformation of the elastic member 50 is restricted. After the compressive deformation is restricted, the elastic member 50 is extended and deformed in the axial direction by the elastic restoring force, and the screw shaft 41 is pressurized to the other side in the axial direction accordingly. Therefore, as the reverse input load is applied to the output shaft 4, even if the screw shaft 41 tries to collide with the second casing 22, the reverse input load is attenuated by the elastic member 50. It is possible to avoid a strong collision with the two casings 22. As described above, it is possible to effectively prevent the occurrence of a serious defect that causes the ball screw 40 to be locked and the output shaft 4 to become inoperable accordingly.

  As shown in FIGS. 1, 2, 5, and 6, the detection unit C includes a detection device 30 that detects the rotation angle of the nut 42, and the detection unit C including the detection device 30 is the second of the housing 2. It is accommodated and arranged in the accommodation chamber 2b. The detection device 30 is disposed on the outer periphery of the resolver rotor 31 via a radial gap and a resolver rotor 31 as a rotor ring that is fitted to a small-diameter outer peripheral surface 44c of a cylindrical portion 44 of the nut 42 so as to be rotatable integrally with the nut 42. It is comprised with the resolver provided with the resolver stator 32 arrange | positioned facing.

  The resolver stator 32 is fixed to the inner peripheral surface of the first casing 20 in a non-rotating state by fixing pins 35 arranged at a plurality of locations (seven locations in the present embodiment, see FIG. 5) separated in the circumferential direction. Yes. Although not shown in detail, the resolver stator 32 includes a stator core, an insulating bobbin attached to the stator core, and a coil wound around the bobbin, like the stator 11 of the electric motor 13. One end of a harness (electrical wiring) 33 including a signal line and a power supply line is electrically connected to the stator coil, and the harness 33 has a hole portion of a grommet 34 fixed to the base member 23 of the second casing 22. Through the outside of the housing 2 in the axial direction. The other end of the harness 33 drawn to the outside of the housing 2 is electrically connected to a control device and a power source not shown.

  As shown in FIG. 5, the resolver rotor 31 is prevented from rotating with respect to the cylindrical portion 44 of the nut 42 by so-called key fitting. Further, the resolver rotor 31 is sandwiched from both sides in the axial direction by a shoulder surface 44d provided on the nut 42 and positioning means arranged on one side in the axial direction of the resolver rotor 31, whereby the cylindrical portion 44 of the nut 42 is provided. Is positioned in the axial direction. In the present embodiment, the positioning means is disposed adjacent to one side in the axial direction of the resolver rotor 31 and press-fitted into the small-diameter outer peripheral surface 44c of the cylindrical portion 44 of the nut 42, and the shaft of the O-ring 36 A retaining ring 37 is disposed adjacent to one side in the direction and fitted in an annular groove provided on the small-diameter outer peripheral surface 44c of the cylindrical portion 44.

  The detection device 30 of the present embodiment has the above-described configuration, and the detection device 30 is generated by a reactance change that occurs between the resolver rotor 31 and the resolver stator 32 as the resolver rotor 31 rotates together with the nut 42. Based on the electrical signal, the rotation angle of the nut 42 is detected. The electric signal (detected value) is input to a control device (not shown) provided outside the electric actuator 1 via the harness 33, and the control device uses the screw shaft 41 (output shaft) based on the input electric signal. 4) is sent to the electric motor 13 in order to move the axial direction by a predetermined amount.

  An example of the assembly procedure of the electric actuator 1 having the above configuration will be briefly described with reference to FIG.

  First, an assembly of the screw shaft 41, the inner shaft 47 and the elastic member 50 is manufactured using the connecting pin 51 and the like, and the assembly and the plurality of balls 45 are combined with the nut 46, the rotor inner 12c, and the rolling bearing 18 assembled thereto. 42 is incorporated in the inner circumference. Thereby, a ball screw assembly including the ball screw 40 is manufactured. Next, after the stator assembly in which the bus bar 17 is assembled to the outer periphery of the stator 11 of the electric motor 13, the rotor assembly of the rotor 12 of the electric motor 13 excluding the rotor inner 12c, and the ball screw assembly are assembled in the inner periphery of the first casing 20. The third casing 26 equipped with the rolling bearing 19 is temporarily fixed to the first casing 20. As a result, an assembly arranged on the rightmost side in FIG. 9, more specifically, an assembly including the electric motor 13, the ball screw 40, the pair of rolling bearings 18, 19, the first casing 20, the third casing 26, and the like is obtained.

  Next, the resolver rotor 31 is positioned and fixed to the outer periphery of the cylindrical portion 44 of the nut 42 using the O-ring 36 and the retaining ring 37, and the resolver stator 32 is fixed to the inner periphery of the first casing 20 using the fixing pin 35. To do. Finally, the second casing 22, the first casing 20, and the third casing 26 are connected using the assembly bolts 27. Thereby, the electric actuator 1 shown by the longitudinal cross-sectional view in FIG. 1 and FIG. 2 and shown by the perspective view in FIG. 10 is obtained.

  As described above, since the electric actuator 1 according to the present embodiment can prevent the ball screw 40 from being locked as much as possible, the output shaft 4 including the screw shaft 41 can operate stably. It has the feature of being highly reliable. In particular, since the screw shaft 41 is formed in a hollow shape and means for preventing the ball screw 40 from being locked is provided in the hollow portion of the screw shaft 41, an increase in the size of the electric actuator 1 by avoiding a lock prevention measure is avoided. There is also an advantage that can be done. The electric actuator 1 of the present embodiment can further exhibit the following operational effects.

  A nut 42 constituting the ball screw 40 (motion conversion mechanism part B) has a screw groove part 43 formed with a spiral groove 43a on the inner peripheral surface and connected to the rotor 12 (rotor inner 12c) so as to be able to transmit torque, and a screw nut The part 43 has a cylindrical part 44 that extends in the axial direction from one axial end of the part 43 and has an inner peripheral surface 44a formed on a cylindrical surface without a spiral groove. In such a configuration, in order to ensure the operability of the ball screw 40, it is not necessary to interpose the grease over the entire radial clearance between the outer peripheral surface of the screw shaft 41 and the inner peripheral surface of the nut 42 that face each other. As described above, it suffices if grease is interposed in a partial region in the axial direction facing the inner peripheral surface of the screw nut portion 43 in which the spiral groove 43a is formed in the radial gap. And in the electric actuator 1 which concerns on this embodiment, the rotor ring (resolver rotor 31) of the detection apparatus 30 which detects the rotation angle of the nut 42 is fitted by the outer periphery of the cylindrical part 44 of the nut 42. FIG. In this case, even if grease is exposed (leaked) on one side of the screw nut portion 43 of the nut 42 as the screw shaft 41 moves back and forth, the grease moves (scatters) radially outward. It can be blocked by a cylindrical portion 44 provided integrally with the nut portion 43. Therefore, it is possible to effectively prevent the possibility that grease (particularly, the grease exposed on one side of the screw nut portion 43 in the axial direction) and minute foreign matters such as contamination contained in the grease will reach and adhere to the resolver rotor 31 of the detection device 30. Can be reduced.

  In particular, in the resolver rotor 31, the portion facing the resolver stator 32 disposed on the outer periphery functions as a detection unit for detecting the rotation angle of the nut 42, so that the detection unit of the resolver rotor 31 and the ball screw 40 A large separation distance from the grease filling region can be secured. Therefore, the possibility that the grease reaches and adheres to the resolver rotor 31 of the detection device 30 can be reduced more effectively.

  In this embodiment, since the nut 42 is rotatably supported by the rolling bearing 18 with a seal, there is a possibility that grease interposed in the inner space of the rolling bearing 18 adheres to the resolver rotor 31 of the detection device 30. Can be effectively reduced. Further, since the rolling bearing 18 is disposed in the vicinity of the resolver rotor 31 (supports the position in the vicinity of the resolver rotor 31 among the nuts 42), the rotation accuracy of the resolver rotor 31 and, in turn, the detection accuracy of the rotation angle of the nut 42 are detected. There is also an advantage that can be increased.

  Moreover, in this embodiment, the housing | casing 2 has the interior space, the 1st storage chamber 2a which accommodated the electric motor 13 (drive part A), and the 2nd storage chamber which accommodated the detection apparatus 30 (detection part C). Since the ring-shaped partition wall 21 divided into 2 b is provided and the rolling bearing 18 is disposed (fixed) between the inner peripheral surface of the partition wall 21 and the outer peripheral surface of the nut 42, the grease interposed in the first storage chamber 2 a Intrusion of minute foreign matters such as contamination into the second storage chamber 2 b can be effectively prevented by the partition wall 21 and the rolling bearing 18.

  In the present embodiment, since the top ball screw 40 is employed for the motion conversion mechanism B, it can be said that grease or the like is likely to be present in the first storage chamber 2a. That is, in the present embodiment in which the top-type ball screw 40 is employed, through holes opened in the inner peripheral surface and the outer peripheral surface of the nut 42 (the screw nut portion 43) are provided, and the top 46 is incorporated in the through hole. . Therefore, the grease or the like interposed in the radial gap between the screw nut portion 43 of the nut 42 and the screw shaft 41 passes through the gap between the inner wall surface of the through hole and the outer wall surface of the flange 46 facing it. Easily entering the first storage chamber 2a. As described above, even if grease or the like enters the first storage chamber 2a, if the rolling bearing 18 is fixed in the above-described manner, the grease or the like intervening in the first storage chamber 2a by the partition wall 21 and the rolling bearing 18 is changed. 2 It is possible to prevent entry into the storage chamber 2b. Therefore, it becomes easy to keep the 2nd storage chamber 2a which accommodated the detection apparatus 30 in the clean state in which grease does not exist or the amount of grease exists slightly.

  In the present embodiment, a resolver is employed for the detection device 30. Since the resolver has a feature that it has excellent environmental resistance, even if the internal temperature of the housing 2 rises due to the rotational drive of the electric motor 13 or the like, the detection accuracy of the rotation angle is hardly lowered. The resolver also has features such as the ability to detect the absolute value of the rotation angle, and the detection value does not disappear even when power supply is stopped.

  Combined with the effects described above, the electric actuator 1 of the present embodiment has a feature that the operating accuracy of the screw shaft 41 and, in turn, the output shaft 4 including the screw shaft 41 is good and reliable.

  The casing 2 constituting the electric actuator 1 of the present embodiment is arranged on the first casing 20 integrally having the partition wall 21 and on the one axial side and the other axial side of the first casing 20, respectively. The second casing 22 and the third casing 26 are detachably connected to the casing 20. If such a configuration is adopted, in addition to improving the assemblability of the electric actuator 1, for example, an abnormality occurs in the detection device 30, the electric motor 13, etc., and it becomes necessary to carry out repair / replacement work, etc. Even if it is, there exists an advantage that the operation | work can be implemented easily.

  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 embodiment described above, the rotational motion of the electric motor 13 is directly transmitted to the nut 42 by press-fitting the rotor inner 12c into the outer periphery of the screw nut portion 43 of the nut 42. Among them, a speed reducer such as a planetary gear speed reducer or a planetary roller speed reducer can be provided on the output side of the electric motor 13 and the rotational motion of the rotor 12 can be transmitted to the nut 42 via the speed reducer. Although detailed illustration is omitted, when a speed reducer is provided in the drive unit A, the input side of the speed reducer and the rotor inner 12c are connected so as to be able to transmit torque, and the output side of the speed reducer and the nut 42 are allowed to transmit torque. What is necessary is just to connect. In this case, since the rotational torque of the electric motor 13 can be increased, the electric motor 13 can be reduced in size, and the electric actuator 1 can be reduced in weight and size through this.

  Further, in the embodiment described above, the radial gap type electric motor 13 is employed, but an axial gap type electric motor may be employed.

  The present invention can also be applied to the electric actuator 1 provided with a so-called stroke detection sensor that detects the amount of movement of the screw shaft 41 (output shaft 4) in the axial direction. Although detailed illustration is omitted, when a stroke detection sensor is separately provided, for example, the guide shaft 24 is formed in a hollow shape, and a stroke detection sensor including a hall sensor is fixedly disposed in the hollow portion. It is conceivable to attach a permanent magnet as a target to the shaft portion 47a of the inner shaft 47 so as to face the stroke detection sensor via a radial gap. In this way, it is possible to avoid an increase in the size of the electric actuator 1 by separately providing a stroke detection sensor.

  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.

DESCRIPTION OF SYMBOLS 1 Electric actuator 2 Housing | casing 4 Output shaft 11 Stator 12 Rotor 12c Rotor inner 13 Electric motor 18 Rolling bearing 18e Seal member 20 First casing 21 Bulkhead 22 Second casing (bottom part of housing)
24 Guide shaft 26 Third casing 30 Detection device 40 Ball screw 41 Screw shaft 42 Nut 45 Ball 47 Inner shaft 50 Elastic member (elastic portion)
51 Connecting Pin A Drive Unit B Motion Conversion Mechanism Unit C Detection Unit D Terminal Unit

Claims (5)

A drive unit having an electric motor, a motion conversion mechanism unit that converts the rotational motion of the drive unit into a linear motion, and a bottomed cylindrical shape in which an end opening on one axial side is closed, the drive unit and the A housing housing the motion conversion mechanism, and the motion conversion mechanism can be rotated on the outer periphery of the screw shaft via a screw shaft coaxially arranged with the rotation center of the electric motor and a plurality of balls. In the electric actuator, the screw shaft is moved forward and backward in the axial direction as the nut rotates in response to the rotational movement of the drive unit,
The screw shaft is formed in a hollow shape in which an end on one side in the axial direction is opened and an end on the other side in the axial direction is closed,
An inner member having an elastic portion that can be expanded and contracted in the axial direction has an end portion on one side in the axial direction positioned outside the opening of the screw shaft, and an end portion on the other side in the axial direction on the screw shaft. An electric actuator, wherein the electric actuator is disposed in a hollow portion of the screw shaft in a state of being in contact with the closing portion.   The inner member is an inner shaft coupled to the screw shaft so as to be movable in the axial direction relative to the screw shaft, and the elastic portion interposed between the inner shaft and the closed portion of the screw shaft. The electric actuator according to claim 1, further comprising: an elastic member. The screw shaft and the inner shaft are connected by a connecting pin fitted so as to penetrate both in the radial direction,
A through hole of the inner shaft into which the connecting pin is fitted is formed as a long hole allowing the axial movement of the connecting pin, and the connecting pin is press-fitted into the through hole of the screw shaft. Item 3. The electric actuator according to Item 2.   The electric actuator according to claim 3, wherein the connecting pin is provided at a plurality of locations separated in the circumferential direction. The inner shaft is formed in a hollow shape with an end on one axial side opened,
In the hollow portion of the inner shaft, a guide shaft for guiding the axial movement of the screw shaft is disposed,
The electric actuator according to claim 3 or 4, wherein a rotating body that is rotatably fitted to an inner diameter end portion of the connecting pin is fitted in an axial groove provided in the guide shaft.

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