JP2006029528A - Electric linear actuator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric linear actuator having improved product quality by suppressing vibration and noises even when vibration load or alternating load is applied to a ball screw. <P>SOLUTION: The electric linear actuator 1 comprises the ball screw 3 consisting of a screw shaft 7 coaxially connected to an electric motor 5 and having a screw groove 7a formed in the outer periphery, a nut 8 having a supporting shaft 12 on the outer periphery for supporting a link 2 at one end and having a screw groove 8a formed in the inner periphery, and a ball 9 stored between both screw grooves, for converting the rotating motion of the electric motor 5 into the axial motion to give rocking motion to the link 2 via the supporting shaft 12, and a pair of supporting bearings 10, 11 for rotatably bearing the screw shaft 7 in an axially non-movable manner. The supporting bearing 10 on the side of the electric motor 5 is formed as a double row angular contact ball bearing. Light preload is imparted to the ball screw 3 to suppress vibration and noises even when vibration load or alternating load is applied to the ball screw 3. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electric linear actuator used in a drive unit of an automobile brake, an engine, a transmission, etc., for example, and more particularly to an electric linear actuator used by converting rotation of an electric motor into linear motion through a ball screw mechanism. It is.

  In electric linear actuators used in various drive parts of vehicles such as automobiles, a gear mechanism such as a trapezoidal screw or a rack and pinion is generally used as a mechanism for converting the rotational movement of the electric motor into an axial linear movement. ing. 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.

  Conventionally, in this type of electric linear actuator, the action line on the drive side is the same as the axis of the ball screw, and a pure axial load is applied to the ball screw, but the load applied to the ball screw is not a pure axial load. In some cases, a linear guide or the like was used together so that a radial load was not directly applied to the ball screw.

  However, in general industrial equipment applications, there is a relatively large space, and there is a large degree of freedom with respect to the arrangement and size of components, but this is severely limited in the engine room of automobiles. Therefore, it has been difficult to incorporate an electric linear actuator having a structure in which only a pure axial load is applied to the ball screw.

  As a solution to these problems, an electric linear actuator as shown in FIG. 5 is known. The electric linear actuator 50 includes a pair of links 51, a ball screw 52 that swings and drives a driven member via the link 51, and an electric motor 53 that drives the ball screw 52.

  In the ball screw 52, a screw shaft 54 that is rotationally driven by an electric motor 53 and a spiral screw groove 55a that is opposed to a spiral screw groove 54a formed on the outer peripheral surface of the screw shaft 54 are formed on the inner peripheral surface. And a number of balls 56 accommodated between the screw grooves 54a and 55a (see FIG. 6). The nut 55 is provided with a support shaft 57 that rotatably supports one end portion of the link 51. The support shaft 57 passes through the center of gravity of the nut 55 and is provided at a right angle to the axis of the screw shaft 54.

  The ball screw 52 includes a return tube 58 as a circulation member that forms an infinite circulation path of the ball 56 between the spiral screw grooves 54a and 55a. The return tube 58 is attached to the nut 55, and as shown in FIG. 6, the radial direction component Fr of the load F acting on the nut 55 via the support shaft 57 acts (the upper side in the figure). It is arranged on the opposite side (lower side in the figure).

As a result, the number of balls located on the side (upper side in the figure) on which the radial direction component Fr acts is larger than the number of balls located on the opposite side (lower side in the figure) on which the radial direction component Fr acts. Accordingly, it is possible to prevent the life of the ball screw 52 from being reduced by the radial component Fr of the load F acting on the nut 55 via the support shaft 57.
JP 2004-84827 A

  However, in such a conventional electric actuator 50, a pair of deep groove ball bearings 59, 60 are provided as support bearings for rotatably supporting the screw shaft 54 of the ball screw 52. Since the ball screw 52 is loaded with a load accompanied by vibration or an alternating load as a reaction force from the point of application, problems still remain in terms of vibration and acoustics.

An object of the present invention is to solve such a conventional problem and to provide an electric linear actuator that suppresses generation of vibration and noise even when a load accompanied by vibration or an alternating load is applied to the ball screw and improves quality. And

  In order to achieve such an object, the invention according to claim 1 of the present invention includes an electric motor attached to a housing, a coaxially connected motor shaft of the electric motor, and a helical thread groove on the outer periphery. A formed screw shaft, and a nut that is extrapolated to the screw shaft, has a support shaft that supports one end of the link on the outer periphery, and is formed with a helical screw groove corresponding to the screw groove on the inner periphery A plurality of balls accommodated between the screw grooves and a ball circulation member in which an infinite circulation path of the balls is formed between the screw grooves, and converts the rotational motion of the electric motor into an axial motion. And a ball screw for swinging the link connected via the support shaft, and a pair of support bearings for supporting the screw shaft so as to be rotatable with respect to the housing and not movable in the axial direction. For electric linear actuator There are, the electric motor side of the support bearing of the support bearing and the angular ball bearing, and employs a configuration that supports the axial load applied to the screw shaft.

  As described above, since the support bearing on the electric motor side is an angular ball bearing and the axial load applied to the screw shaft is supported, the angular vibration can be suppressed to a small level, Even when an alternating load is applied, the vibration and noise of the electric linear actuator can be suppressed.

  The angular ball bearing may be a double row angular ball bearing as in the invention described in claim 2, or a four-point contact ball bearing as in the invention according to claim 3. It may be.

  Preferably, as in the invention described in claim 4, if preload is applied to the ball screw, the generation of vibration and noise is further suppressed even when a load accompanying vibration or an alternating load is applied to the ball screw. Thus, an electric linear actuator with improved quality can be provided.

  More preferably, as in the invention described in claim 5, if a ball having a large diameter is accommodated in the ball screw and a light preload is applied to the ball screw, an increase in the rotational torque of the ball screw is suppressed. In addition, the temperature rise can be prevented.

An electric linear actuator according to the present invention includes an electric motor attached to a housing, a screw shaft that is coaxially connected to a motor shaft of the electric motor, and has a spiral screw groove formed on the outer periphery thereof, and the screw shaft. A nut that is extrapolated and has a support shaft that supports one end of the link on the outer periphery, and a spiral screw groove corresponding to the screw groove formed on the inner periphery, and a large number of screws accommodated between both screw grooves It consists of a ball and a ball circulation member in which an infinite circulation path of the ball is formed between the both screw grooves. The rotary motion of the electric motor is converted into an axial motion and connected through the support shaft. An electric linear actuator comprising: a ball screw that swings a link; and a pair of support bearings that support the screw shaft so as to be rotatable with respect to the housing and not axially movable. Among them, the support bearing on the electric motor side is an angular ball bearing, and the axial load applied to the screw shaft is supported. Even when an alternating load is applied, the vibration and noise of the electric linear actuator can be suppressed.

  An electric motor attached to the housing, a screw shaft that is coaxially connected to the motor shaft of the electric motor and has a spiral screw groove formed on the outer periphery, and is externally inserted into the screw shaft, and has one end of a link on the outer periphery. A nut having a support shaft for supporting the portion, and a spiral screw groove corresponding to the screw groove formed on the inner periphery, a number of balls accommodated between the screw grooves, and the screw grooves A ball screw that forms a ball circulation member in which an infinite circulation path of the ball is formed, converts a rotational motion of the electric motor into an axial motion, and swings a link connected through the support shaft; An electric linear actuator comprising a pair of support bearings that support the screw shaft so as to be rotatable with respect to the housing and not axially movable, wherein the support bearings on the electric motor side of the support bearings are double-rowed. And angular contact ball bearings, to support the axial load applied to the screw shaft, and imparting a light preload to the ball screw.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a front view showing a cross-section of a main part of a first embodiment of an electric linear actuator according to the present invention, FIG. 2 shows a ball screw according to the present invention, (a) is a longitudinal sectional view, (b) ) Is a perspective view of the piece member.

  The electric linear actuator 1 includes a link 2, a ball screw 3 that swings and drives a driven member (not shown) via the link 2, and an electric motor 5 that drives the ball screw 3 and is attached to a housing 4. It is configured.

  The ball screw 3 is coupled to a motor shaft 5a of the electric motor 5 via a coupling 6, and as shown in FIG. 2A, the screw shaft 7 is rotationally driven by the electric motor 5, and the screw shaft 7 A nut 8 having a spiral thread groove 8a facing the spiral thread groove 7a formed on the outer peripheral surface formed on the inner peripheral surface, and a number of balls 9 accommodated between these screw grooves 7a, 8a; It has. The cross-sectional shape of each screw groove 7a, 8a may be a circular arc shape or a gothic arc shape. Here, the cross-sectional shape of each screw groove 7a, 8a has a large contact angle with the ball 9. It is formed in a Gothic arc shape with a small axial clearance. Thereby, the rigidity with respect to an axial load becomes high, and a vibration can be suppressed.

  An elliptical piece window 13 that penetrates the inner and outer peripheral surfaces and cuts out a part of the thread groove 8a is formed in the barrel portion of the cylindrical nut 8, and an elliptical piece member 14 is formed in the piece window 13. Is installed. Further, as shown in FIG. 2B, a connecting groove 15 that connects adjacent ones of the thread grooves 8a is formed inside the piece member 14, and the connection grooves 15 and the thread grooves 8a are connected to each other. A rolling path of the ball 9 is constituted by the substantially one-round portion. A large number of balls 9 interposed between the inner and outer screw grooves 7a and 8a in the rolling path roll along the screw grooves 7a and 8a, and are guided by the connecting grooves 15 of the piece member 14 to be screw shafts. 7 over the thread 7, returns to the adjacent thread groove 7 a, and rolls along the thread grooves 7 a and 8 a again.

  The connecting groove 15 of the piece member 14 is formed to be curved in an S shape so that the adjacent thread grooves 8a of the nut 8 are smoothly connected. Therefore, the connecting groove 15 of the piece member 14 is connected to the screw groove 8a so that the opening edges 16 at both ends thereof coincide with the window opening edge of the adjacent screw groove 8a of the nut 8. Further, the depth of the connecting groove 15 is set to such a depth that the ball 9 can exceed the thread of the screw groove 7 a in the screw shaft 7 in the connecting groove 15.

  The piece member 14 is made of a sintered alloy prepared by adjusting a metal powder into a plastic shape and molding it with an injection molding machine. In this injection molding, first, metal powder and a binder made of plastic and wax are kneaded with a kneader, and the kneaded product is granulated into pellets. The granulated pellet is supplied to a hopper of an injection molding machine and molded by being pushed into a mold in a heated and melted state. The metal powder is preferably a material that can be subsequently carburized and quenched. For example, C (carbon) is 0.3 wt%, Ni (nickel) is 1 to 2 wt%, and the remainder is Fe (iron). . The material of the piece member 14 is not limited to this, and may be formed of a thermoplastic resin such as PA (polyamide) 66 that can be injection molded.

  As shown in FIG. 1, the screw shaft 7 is supported so as to be rotatable with respect to the housing 4 through a support bearing 10, 11 including a pair of rolling bearings and not to move in the axial direction. On the other hand, the nut 8 has a pair of support shafts 12 protruding from the outer peripheral surface thereof. The support shaft 12 rotatably supports one end of the link 2, and protrudes at a right angle to the axis of the screw shaft 7. Therefore, the nut 8 is supported so as to be axially movable and non-rotatable.

  With such a configuration, the screw shaft 7 rotates with the rotation of the electric motor 5, and the nut 8 is moved in the axial direction (left-right direction in the drawing) by the rotation of the screw shaft 7. That is, the ball screw 3 converts the rotational movement of the motor shaft 5a into the axial movement of the nut 8 through the ball screw 3, and the link 2 connected through the support shaft 12 of the nut 8 swings. .

  Here, a predetermined light preload is applied to the ball screw 3. That is, a slightly large diameter size is selected as the ball 9 accommodated between the screw grooves 7a and 8a. Thereby, even if a load accompanied by vibration or an alternating load is applied to the ball screw 3, generation of vibration and noise can be suppressed. As a means for applying a preload to the ball screw 3, the nut 8 is composed of a pair of nuts other than accommodating the large-diameter ball 9 as described above, and the clearance between the nuts is adjusted. A so-called double nut method in which a spacer is interposed, or a method in which the lead of the screw groove 7a in the screw shaft 7 is continuously changed to apply a preload between the screw shaft 7 and the nut 8. Also good.

  Further, in the present embodiment, of the pair of support bearings 10 and 11 that rotatably support the screw shaft 7, the double-row angular contact ball bearing is provided on the support bearing 10 disposed on the electric motor 5 side, while the screw shaft 7. A deep groove ball bearing is used for the support bearing 11 disposed at the end of each. Since the support bearing 11 is constituted by a deep groove ball bearing, even if the temperature rises during operation and the screw shaft 7 expands, it can be tolerated by the internal clearance of the support bearing 11 and the outer ring is a housing. 4 is fitted with a clearance fit so that it can slide in the axial direction. Therefore, it is possible to prevent the screw shaft 7 from being excessively deformed and the rotational torque of the ball screw 3 from increasing.

  As shown in FIG. 3, the support bearing 10 has an outer ring 17 in which double-row outer rolling surfaces 17a and 17a are formed on the inner periphery, and double-row inner rolling surfaces 18a and 18a on the inner periphery. It is constituted by a double row angular ball bearing comprising an inner ring 18 and double rows of balls 20 and 20 which are accommodated so as to roll between the rolling surfaces 17a and 18a via a cage 19. This support bearing 10 has a predetermined contact angle α, has a larger load capacity than conventional deep groove ball bearings, and can suppress angular vibration to be small. Even when a load or an alternating load is applied, the vibration and noise of the electric linear actuator 1 can be suppressed in combination with the light preload of the ball screw 3 described above.

  Here, the double-row angular contact ball bearing is illustrated as the support bearing 10, but the present invention is not limited to this, and a pair of single-row angular contact ball bearings are used in combination to support the axial load applied to the screw shaft 7. You may do it.

  FIG. 4 is an enlarged view of a main part showing a second embodiment of the electric linear actuator according to the present invention. In the second embodiment, only the support bearing is basically different from the above-described embodiment, and other parts having the same parts or the same functions are denoted by the same reference numerals and detailed description thereof is omitted. .

  In the present embodiment, a four-point contact ball bearing is used for the support bearing 21 disposed on the electric motor (not shown) side, and the support is composed of a deep groove ball bearing (not shown) disposed at the end of the screw shaft 7. Along with the bearing 11, the screw shaft 7 is supported so as to be rotatable with respect to the housing 4 and not movable in the axial direction. The support bearing 21 including the four-point contact ball bearing includes an outer ring 22 having an outer rolling surface 22a formed on the inner periphery, and an inner ring 23 having an inner rolling surface 23a opposed to the outer rolling surface 22a. And a ball 24 accommodated so as to roll between the rolling surfaces 22a and 23a.

  The cross-sectional shape of the outer rolling surface 22a is formed in a so-called gothic arc shape including a pair of circular arc surfaces having a center of curvature offset at an equal distance in the axial direction with respect to the width center of the bearing. On the other hand, the inner ring 23 is composed of a pair of inner ring members 25 and 26 that are abutted with each other. , 26a are formed, and the rolling surfaces 25a, 26a cooperate with each other to form a gothic arc-shaped inner rolling surface 23a.

  The support bearing 21 in the present embodiment is a four-point contact ball bearing, and the outer rolling surface 22a and the inner rolling surface 23a are formed in a gothic arc in cross section, and therefore has a predetermined contact angle α, Although it is a row ball bearing, it can carry axial loads in both directions and can control the range of the axial clearance relative to the radial clearance of the bearing, causing vibration in the ball screw (not shown). Even when a load or an alternating load is applied, the vibration and noise of the electric linear actuator can be suppressed as in the above-described embodiment.

  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 linear actuator according to the present invention includes a ball screw that is coaxially connected to a motor shaft of an electric motor and converts rotational motion of the motor shaft into axial motion. The screw shaft in the ball screw is used as a pair of support bearings. Thus, the present invention can be applied to an electric linear actuator having a structure that is supported so as to be rotatable with respect to the housing and not movable in the axial direction.

It is a longitudinal section showing a 1st embodiment of an electric linear actuator concerning the present invention. (A) is a longitudinal cross-sectional view which shows the ball screw which concerns on this invention. (B) is a perspective view showing the same piece member. It is a principal part enlarged view of FIG. It is a principal part enlarged view which shows 2nd Embodiment of the electric linear actuator which concerns on this invention. It is the front view which carried out the cross section of a part which shows the conventional electric linear actuator. It is a longitudinal cross-sectional view which shows the ball screw of FIG.

Explanation of symbols

1 .... Electric linear actuator 2 ... Link 3 ...・ ・ ・ ・ ・ ・ ・ ・ Ball screw 4 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Housing 5 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Electric motor 5a・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Motor shaft 6 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Coupling 7 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・..... screw shafts 7a, 8a ..... screw groove 8 ..... nuts 9, 20, 24. · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · ..... Koma window 14 ........... Komabe 15 ... Connection groove 16 ... Opening edge 17, 22 ... .... Outer rings 17a, 22a ... Outer rolling surface 18 ... Inner rings 18a, 23a ...・ ・ ・ ・ ・ Inner rolling surface 19 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Cage 25, 26 ・ ・ ・ ・ ・ ・ ・ ・ Inner ring member 25a, 26a・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Rolling surface 50 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Electric linear actuator 51 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・・ Link 52 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Ball screw 53 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Electric motor 54 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・..... Screw shafts 54a, 55a ... Screws 55 ... nut 56 ... ball 57 ...・ ・ ・ Support shaft 58 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Return tube 59, 60 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Deep groove ball bearing F ・ ・ ・ ・ ・ ・・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Load Fr ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Radial direction component α ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・・ Contact angle

Claims (5)

An electric motor attached to the housing, a screw shaft that is coaxially connected to the motor shaft of the electric motor and has a spiral screw groove formed on the outer periphery, and is externally inserted into the screw shaft, and has one end of a link on the outer periphery. A nut having a support shaft for supporting the portion, and a spiral screw groove corresponding to the screw groove formed on the inner periphery, a number of balls accommodated between the screw grooves, and the screw grooves A ball screw that forms a ball circulation member in which an infinite circulation path of the ball is formed, converts a rotational motion of the electric motor into an axial motion, and swings a link connected through the support shaft; An electric linear actuator comprising a pair of support bearings that support the screw shaft so as to be rotatable with respect to the housing and not movable in the axial direction.
An electric linear actuator characterized in that the support bearing on the electric motor side among the support bearings is an angular ball bearing, and an axial load applied to the screw shaft is supported.   The electric linear actuator according to claim 1, wherein the angular ball bearing is a double-row angular ball bearing.   The electric linear actuator according to claim 1, wherein the angular ball bearing is a four-point contact ball bearing.   The electric linear actuator according to claim 1, wherein a preload is applied to the ball screw.   The electric linear actuator according to claim 4, wherein a ball having a large diameter is accommodated in the ball screw, and a light preload is applied to the ball screw.

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