Electric actuator

Abstract

To provide an electric actuator with high operational accuracy and durability life at low cost.SOLUTION: An electric actuator 1 includes an electric motor 2 and a screw mechanism 3. The screw mechanism 3 includes: a nut 31 supported such that it is rotatable relative to a housing 5 via rolling bearings 5, 6; and a screw shaft 32 that makes linear motion with the rotation of the nut 31. A first cover surface 8A and a second cover surface 8B are provided on members different from components of the rolling bearings 6, 7 and cover each of a one-end opening portion 64 (74) between inner and outer rings of the rolling bearing 6 (7) and another end opening portion 65 (75) with an opening area ratio of 80% or more and less than 100%. The first cover surface 8A is provided to open an inner diameter end 64a (74a) of the one-end opening portion 64 (74) and the second cover surface 8B is provided to open an outer diameter end 65a (75a) of the other end opening portion 65 (75). An opening width A of the inner diameter end-side openings of the one-end opening portions 64, 74 is larger than an opening width B of the outer diameter end-side openings of the other end opening portions 65, 75.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an electric actuator. [Background technology]

[0002] For example, Japanese Patent Application Laid-Open No. 2014-37870 (Patent Document 1) discloses an electric actuator used in an automobile's transmission mechanism, brake mechanism, etc., that includes an electric motor, a screw mechanism (ball screw mechanism) that converts the rotational motion of the electric motor transmitted via a power transmission mechanism into linear motion in the axial direction of the output shaft of the actuator, and a housing that accommodates the screw mechanism. In this electric actuator, the power transmission mechanism is composed of an input gear that rotates integrally with the rotating shaft of the electric motor, and a reduction mechanism (gear reduction mechanism) that has an output gear that meshes with the input gear and rotates integrally with a nut.

[0003] In the electric actuator, the nut is rotatably supported relative to the housing by a pair of rolling bearings (e.g., deep groove ball bearings) arranged on both axial sides of the output gear. The rolling bearings are of the so-called sealed type, in which a seal member for sealing an opening between the inner and outer rings is arranged on both axial sides of the rolling elements. This prevents the grease that lubricates the inside of the rolling bearing from leaking out and prevents foreign matter from entering the inside of the bearing (grease). The seal members are broadly divided into a contact type having a seal lip that slides against the inner or outer ring, and a non-contact type that forms a minute seal gap between the inner or outer ring. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2014-37870 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the case of a sealed rolling bearing, strict dimensional control (contact allowance control or gap width control) is required to ensure that the desired sealing performance can be adequately exhibited regardless of the type of sealing member used. Therefore, when a sealed rolling bearing is used, the cost is higher than when a so-called open rolling bearing that does not have a sealing member is used. Therefore, if the sealed rolling bearing used as a support bearing for a nut is replaced with an open rolling bearing, the cost of the electric actuator can be reduced. However, simply replacing the sealed rolling bearing with an open rolling bearing cannot prevent grease from leaking out or foreign matter from entering the bearing, and this adversely affects the bearing performance and durability of the support bearing, and ultimately the operating accuracy and durability of the output shaft of the electric actuator.

[0006] SUMMARY OF THE PRESENT EMBODIMENTS An object of the present invention is to provide an electric actuator having excellent operating accuracy and durability of an output shaft at low cost. [Means for solving the problem]

[0007] The present invention, which has been invented to achieve the above object, is an electric actuator including an electric motor, a screw mechanism that converts rotational motion of the electric motor into linear motion, and a housing that accommodates the screw mechanism, the screw mechanism including a nut that is rotatably supported with respect to the housing via a rolling bearing that is lubricated with grease, and a screw shaft that moves linearly as the nut rotates, a first cover surface that covers 80% or more and less than 100% of the one end opening in an opening area ratio with an inner diameter end of the one end opening between an inner ring and an outer ring of the rolling bearing being open, the first different member being different from a constituent member of the rolling bearing; a second cover surface is provided on a second different member different from the constituent members of the rolling bearing (and the first different member) to cover the other end opening by 80% or more and less than 100% in terms of an opening area ratio with an outer diameter end of the other end opening between the inner ring and the outer ring of the rolling bearing being open; The opening width A of the inner diameter end side opening of the one end opening is set larger than the opening width B of the outer diameter end side opening of the other end opening.

[0008] According to the above configuration, the first and second cover surfaces provided on the first and second different members, which are different from the constituent members of the rolling bearing, respectively, suppress or prevent the intrusion of foreign matter into the internal space (of the grease present therein) of the rolling bearing and the leakage of grease to the outside. Furthermore, by providing the above-mentioned first and second cover surfaces, it becomes possible to adopt an open-type rolling bearing that does not have a seal member for sealing the opening between the inner and outer rings as the rolling bearing. This makes it possible to reduce the cost of the electric actuator.

[0009] However, if the first and second cover surfaces are formed to cover the entire end faces of the inner and outer rings, there is a concern that the rolling bearing and, in turn, the operability of the electric actuator may be adversely affected. Therefore, it is preferable that the first cover surface is provided to extend from the outer diameter side to the inner diameter side of the rolling bearing so as to cover 80% or more and less than 100% of the one end opening when the inner diameter end of the one end opening between the inner and outer rings is open, and the second cover surface is provided to extend from the inner diameter side to the outer diameter side of the rolling bearing so as to cover 80% or more and less than 100% of the other end opening when the outer diameter end of the other end opening between the inner and outer rings is open. Furthermore, since grease is likely to be unevenly distributed in the outer diameter side region of the internal space due to the influence of centrifugal force during operation of the rolling bearing, if the opening between the inner and outer rings is widely opened on its outer diameter side, grease leakage may occur. Grease leakage is particularly likely to occur when low-viscosity grease suitable for high-speed rotation of rolling bearings is used. Therefore, if the opening width A of the inner diameter end opening of one end opening between the inner and outer rings is made larger than the opening width B of the outer diameter end opening of the other end opening between the inner and outer rings, grease leakage and intrusion of foreign matter through the opening between the inner and outer rings can be effectively prevented. Here, the above-mentioned opening widths (opening width A and opening width B) refer to the opening dimensions in the direction perpendicular to the bearing rotation axis (radial direction). The same applies to opening width C, which will be described later.

[0010] In the above configuration, the second different member can be provided with an annular recess that forms an outer diameter end opening of the other end opening between the inner and outer rings and communicates the bearing internal space with the bearing external space. The opening width C of this annular recess on the outer diameter side of the rolling bearing is made larger than the opening width A of the inner diameter end opening of the one end opening (and the opening width B of the outer diameter end opening of the other end opening). In this way, even if wear powder or the like is generated inside the bearing as the electric actuator is driven, the wear powder or the like can be easily discharged to the outside of the bearing via the annular recess.

[0011] In the above configuration, in order to increase the ease of discharging wear powder and the like, it is preferable to form the inner wall surface of the annular recess into an inclined surface inclined with respect to the axial direction (more specifically, an inclined surface inclined with respect to the axial direction so as to gradually expand in diameter toward the opening side of the annular recess).

[0012] The first cover surface and the second cover surface can be provided on the housing and the nut, which are essential components of the electric actuator according to the present invention, respectively, thereby making it possible to avoid an increase in the cost of the electric actuator due to an increase in the number of parts.

[0013] In addition, when the electric actuator further includes a power transmission mechanism that transmits the rotational motion of the electric motor to the nut, the second cover surface can be provided on a rotating member of the power transmission mechanism that rotates integrally with the nut. In this case, the power transmission mechanism can be a speed reduction mechanism that reduces the speed of the rotation of the electric motor and transmits it to the nut, and the rotating member can be a gear. Effect of the Invention

[0014] As described above, according to the present invention, it is possible to provide an electric actuator having excellent operating accuracy and durable life of an output shaft at low cost. [Brief description of the drawings]

[0015] [Figure 1] 1 is a vertical cross-sectional view of an electric actuator according to an embodiment of the present invention; [Diagram 2] FIG. 2 is a partially enlarged view of FIG. [Diagram 3] FIG. 11 is a partially enlarged view of an electric actuator according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] Hereinafter, an embodiment of the present invention will be described with reference to FIGS.

[0017] Fig. 1 shows a vertical cross-sectional view of an electric actuator 1 according to one embodiment of the present invention, and Fig. 2 shows a partially enlarged view of Fig. 1. The electric actuator 1 shown in Fig. 1 and Fig. 2 includes an electric motor 2 that generates rotational power, a screw mechanism 3 that converts the rotational motion of the electric motor 2 into linear motion parallel to a rotation axis 2a of the electric motor 2 and outputs the linear motion, a power transmission mechanism 4 that transmits the rotational motion (rotational power) of the electric motor 2 to the screw mechanism 3, and a housing 5 that holds these.

[0018] In this embodiment, for convenience of assembly, the housing 5 is divided into two parts in the axial direction (a direction parallel to the axis of the rotating shaft 2a of the electric motor 2). That is, the housing 5 includes a first housing 51 that holds the electric motor 2, and a second housing 52 that is axially connected to the first housing 51 by using bolt members 53.

[0019] The screw mechanism 3 is composed of a ball screw mechanism 30 including a cylindrical nut 31 that rotates around an axis X parallel to (the axis of) the rotating shaft 2a of the electric motor 2, a screw shaft 32 that is disposed on the inner periphery of the nut 31 and moves linearly in the axial direction as the nut 31 rotates, and a plurality of balls 33 interposed between a helical groove 31a provided on the inner periphery of the nut 31 and a helical groove 32a provided on the outer periphery of the screw shaft 32. The screw shaft 32 of the ball screw mechanism 30 constitutes the output shaft of the electric actuator 1.

[0020] Although not shown in the figure, the ball screw mechanism 30 further includes a circulation member for circulating the balls 33 between the two spiral grooves 31a, 32a when the nut 31 rotates. As the circulation member, a known member such as a top, an end cap, a return tube, a return plate, etc. That is, as the ball screw mechanism 30, a known member such as a so-called top type, an end cap type, a return tube type, a return plate type, etc. can be used.

[0021] A pair of anti-rotation members 34 that restrict the rotation of the screw shaft 32 (rotation around the axis X) are provided at the rear end of the screw shaft 32 (the end on the right side of the paper in FIG. 1). Each anti-rotation member 34 is formed in a round bar shape (pin shape), and is fixed to the screw shaft 32 so that a part of it protrudes radially outward from the screw shaft 32. A cylindrical guide member 35 having a pair of guide grooves 35a extending in the axial direction is accommodated in the second housing 52, and each anti-rotation member 34 (protruding part) is inserted into the corresponding guide groove 35a in a state in which it can move along the guide groove 35a. With the above configuration, when the nut 31 rotates, the screw shaft 32 moves linearly in the axial direction while being prevented from rotating.

[0022] The nut 31 is rotatably supported with respect to the housing 5 by a first rolling bearing 6 and a second rolling bearing 7 arranged on the outer periphery of one end of the nut 31 in the axial direction (the left side of the paper in FIG. 1) and the other end of the nut 31. The nut 31 in this embodiment has a flange portion 31b integral therewith, which extends radially outward from its outer periphery and is used for positioning the second rolling bearing 7 in the axial direction, etc. As shown in FIG. 2, the outer diameter end (outer periphery) of the flange portion 31b is located slightly radially inward from the inner periphery of an outer ring 72 constituting the second rolling bearing 7.

[0023] 2, the first rolling bearing 6 is configured as a ball bearing (deep groove ball bearing) including an inner ring 61 on the rotating side fitted to the outer peripheral surface of the nut 31, an outer ring 62 on the stationary side fitted to the inner peripheral surface of the first housing 51, a plurality of rolling elements (balls) 63 arranged to roll between an inner raceway surface provided on the inner ring 61 and an outer raceway surface provided on the outer ring 62, and a cage (not shown) that holds the plurality of balls 63 at intervals in the circumferential direction. The internal space of the first rolling bearing 6 (annular space formed between the outer peripheral surface of the inner ring 61 and the inner peripheral surface of the outer ring 62) is filled with grease as a lubricant. The grease that can be used has an ASTM consistency of 220 or more, specifically, grease having an ASTM consistency in the range of 220 to 250, which corresponds to JIS classification No. 3, an ASTM consistency in the range of 265 to 295, which corresponds to JIS classification No. 2, or an ASTM consistency in the range of 310 to 340, which corresponds to JIS classification No. 1. This first rolling bearing 6 is a so-called open type rolling bearing that does not have a dedicated sealing member for sealing one end opening 64 and the other end opening 65 between the inner ring 61 and the outer ring 62.

[0024] The second rolling bearing 7 is configured as an open type ball bearing (deep groove ball bearing) similar to the first rolling bearing 7, comprising an inner ring 71 on the rotating side fitted to the outer peripheral surface of the nut 31, an outer ring 72 on the stationary side fitted to the inner peripheral surface of the second housing 52, a plurality of rolling elements (balls) 73 arranged to roll freely between an inner raceway surface provided on the inner ring 71 and an outer raceway surface provided on the outer ring 72, a retainer (not shown) that holds the plurality of balls 73 at intervals in the circumferential direction, and grease filled in the internal space, but does not have a dedicated sealing member to seal the opening between the inner and outer rings.

[0025] The power transmission mechanism 4 includes a first gear 41 provided so as to be rotatable integrally with the rotating shaft 2a of the electric motor 2, and a second gear 42 meshing with the first gear 41 and provided so as to be rotatable integrally with the nut 31. The second gear 42 has a larger diameter and a larger number of teeth than the first gear 41. By the power transmission mechanism 4 configured as described above, the rotation of the rotating shaft 2a of the electric motor 2 is transmitted to the nut 31 after being decelerated. Therefore, the power transmission mechanism 4 of this embodiment also functions as a reduction mechanism.

[0026] In the electric actuator 1 according to this embodiment having the above configuration, when the rotating shaft 2a of the electric motor 2 rotates, the rotational motion is transmitted to the nut 31 via the power transmission mechanism 4 serving as a speed reducing mechanism. When the nut 31 rotates, the threaded shaft 32 serving as the output shaft moves linearly in the axial direction while being prevented from rotating. The linear movement of the threaded shaft 32 in the axial direction operates an operation target (not shown) (for example, a piston rod of a hydraulic cylinder constituting an electric brake system of an automobile).

[0027] In the electric actuator 1 described above, as mentioned above, so-called open type rolling bearings are used for the rolling bearings 6, 7 that rotatably support the nut 31 of the ball screw mechanism 30. However, since the internal space of the rolling bearings 6, 7 is filled with grease as a lubricant, unless some countermeasure is taken, the bearing performance of the rolling bearings 6, 7 and, ultimately, the operating accuracy of the ball screw mechanism 30 will be adversely affected by the leakage of grease to the outside through the opening between the inner and outer rings and the intrusion of foreign matter into the internal space of the bearing.

[0028] Therefore, in the electric actuator 1 of this embodiment, a characteristic configuration as described below is adopted for each of the rolling bearings 6, 7 that rotatably support the nut 31, thereby sealing the opening between the inner and outer rings while suppressing increases in costs.

[0029] First, the first rolling bearing 6 will be described. A first cover surface 8A is provided on the first housing 51 as the first different member M1 different from the constituent member of the first rolling bearing 6, covering 80% or more and less than 100%, preferably 90% or more and less than 100%, of the one end opening 64 of the first rolling bearing 6 (the opening on the left side of the paper in FIG. 2) in terms of an opening area ratio. This first cover surface 8A is an annular surface that extends from the outer diameter side toward the inner diameter side of the first rolling bearing 6 and is in surface contact with the entire one end face (the end face on the left side of the paper in FIG. 2) of the outer ring 62, and its inner diameter end is located within the radial range of the one end opening 64 of the rolling bearing 6. Therefore, at the inner diameter end 64a of the one end opening 64, there is an opening with a radial opening width A that is not sealed by the first cover surface 8A.

[0030] In addition, the second gear 42 as the second different member M2 different from the constituent member of the first rolling bearing 6 is provided with a second cover surface 8B that covers the other end opening 65 of the first rolling bearing 6 (the opening on the right side of the paper in FIG. 2) by 80% or more and less than 100%, preferably 90% or more and less than 100%, in terms of the opening area ratio. This second cover surface 8B is an annular surface that extends from the inner diameter side to the outer diameter side of the first rolling bearing 6 and is in surface contact with the entire other end face (the end face on the right side of the paper in FIG. 2) of the inner ring 61, and its outer diameter end portion is located within the radial range of the other end opening 65 of the rolling bearing 6. Therefore, at the outer diameter end 65a of the other end opening 65, there is an opening with a radial opening width B that is not sealed by the second cover surface 8B. The opening width B of this opening is set smaller than the opening width A of the opening existing at the inner diameter end 64a of the one end opening 64 (A>B), and the second cover surface 8B is formed so as to be able to cover the liquid surface of the grease existing on the other end opening 65 side of the internal space of the rolling bearing 6 in a stationary state.

[0031] Furthermore, as long as the required sealing performance can be ensured, a small axial gap may be provided between the first cover surface 8A and one end face of the outer ring 62, which face each other in the axial direction, and between the second cover surface 8B and the other end face of the inner ring 61.

[0032] One end face of the inner ring 61 of the first rolling bearing 6 faces the first housing 51 in the axial direction via an axial gap. This makes it possible to prevent an increase in sliding resistance (internal resistance when the electric actuator 1 is driven) when the nut 31 rotates, allowing the screw shaft 32 to move smoothly in a straight line. The above-mentioned axial gap (and the opening with opening width A) is formed by providing an annular recessed portion (annular recess) at the inner diameter end of the end face of the first housing 51 where the first cover surface 8A is provided.

[0033] In order to prevent an increase in internal resistance when the electric actuator 1 is driven, the other end surface of the outer ring 62 of the first rolling bearing 6 faces one end surface of the second gear 42 in the axial direction via an axial gap. Therefore, an annular recess 42a that forms the above-mentioned axial gap is provided on one end surface of the second gear 42. The annular recess 42a forms an opening (opening with an opening width B) on the outer diameter end 65a side of the above-mentioned other end opening 65, and is formed so as to communicate the internal space of the first rolling bearing 6 with the bearing external space (here, the space formed on the outer diameter side of the rolling bearing 6). That is, the annular recess 42a is formed so that its inner diameter end is located radially inside the outer diameter end 65a of the other end opening 65, and its outer diameter end is located radially outside the outer circumferential surface of the outer ring 62.

[0034] The opening width C of the annular recess 42a on the outer diameter side of the rolling bearing 6 is larger than the opening width A of the inner diameter end 64a side opening of the one end opening 64 (and the opening width B of the outer diameter end 65a side opening of the other end opening 65). As a result, even if wear powder or the like is generated inside the bearing due to sliding contact between the bearing components when the electric actuator 1 is driven, the wear powder or the like can be easily discharged to the outside of the bearing through the annular recess 42a. In addition, the inner peripheral wall surface of the annular recess 42a is formed as an inclined surface inclined with respect to the axial direction (strictly speaking, an inclined surface inclined in a direction that gradually increases the opening dimension of the annular recess 42a toward the rolling bearing 6). As a result, the wear powder or the like can be more easily discharged to the outside of the bearing through the annular recess 42a.

[0035] In the illustrated example, a similar annular recess 42a is provided on the other end surface of the second gear 42. This eliminates the need for a front and back surface on the second gear 42, improving the ease of fixing the second gear 42 to the outer circumferential surface of the nut 31.

[0036] Next, the second rolling bearing 7 will be described. The second housing 52 as the first different member M1 different from the constituent member of the second rolling bearing 7 is provided with a first cover surface 8A that covers 80% or more and less than 100%, preferably 90% or more and less than 100%, of the one end opening 74 of the second rolling bearing 7 (the opening on the right side of the paper in FIG. 2) in terms of an opening area ratio. This first cover surface 8A is an annular surface that extends from the outer diameter side toward the inner diameter side of the second rolling bearing 7 and is in surface contact with the entire one end face (the end face on the right side of the paper in FIG. 2) of the outer ring 72, and its inner diameter end is located within the radial range of the one end opening 74 of the rolling bearing 7. Therefore, at the inner diameter end 74a of the one end opening 74, there is a small opening with a radial opening width A that is not sealed by the first cover surface 8A.

[0037] In addition, a second cover surface 8B is provided on the flange portion 31b of the nut 31 as the second different member M2 different from the constituent member of the second rolling bearing 7, covering the other end opening 75 of the second rolling bearing 7 (the opening on the left side of the paper in FIG. 2) by 80% or more and less than 100%, preferably 90% or more and less than 100%, in terms of the opening area ratio. This second cover surface 8B is an annular surface that extends from the inner diameter side to the outer diameter side of the second rolling bearing 7 and is in surface contact with the entire other end face (the end face on the left side of the paper in FIG. 2) of the inner ring 71, and its outer diameter end portion is located within the radial range of the other end opening 75 of the rolling bearing 7. Therefore, at the outer diameter end 75a of the other end opening 75, there is a minute opening with a radial opening width B that is not sealed by the second cover surface 8B. The opening width B of this minute opening is set smaller than the opening width A of the minute opening present at the inner diameter end 74a of the one end opening 74 (A>B).

[0038] As long as the required sealing performance can be ensured, a small axial gap may be provided between the first cover surface 8A and one end face of the outer ring 72, which face each other in the axial direction, and between the second cover surface 8B and the other end face of the inner ring 71.

[0039] For the purpose of preventing an increase in internal resistance when the electric actuator 1 is driven, one end face of the inner ring 71 of the second rolling bearing 7 faces the second housing 52 in the axial direction via an axial gap, similar to the inner ring 61 of the first rolling bearing 6. This axial gap (and the minute opening with opening width A) is formed by providing an annular recess at the inner diameter end of the end face of the second housing 52 where the first cover surface 8A is provided.

[0040] In the electric actuator 1 of the present embodiment described above, the one end opening 64 and the other end opening 65 of the first rolling bearing 6 are sealed by the first cover surface 8A provided on the first housing 51 as the first different member M1 different from the constituent member of the first rolling bearing 6, and the second cover surface 8B provided on the second gear 42 as the second different member M2, and the one end opening 74 and the other end opening 75 of the second rolling bearing 7 are sealed by the first cover surface 8A provided on the second housing 52 as the first different member M1 different from the constituent member of the second rolling bearing 7, and the second cover surface 8B provided on the nut 31 as the second different member M2. As a result, even if open-type rolling bearings that do not have dedicated sealing members for sealing the one end and the other end openings are used as the rolling bearings 6, 7, it is possible to suppress or prevent the intrusion of foreign matter into (the grease present in) the internal space of the rolling bearings 6, 7 and the leakage of grease to the outside. This makes it possible to prevent as much as possible any deterioration in the bearing performance and shortening of the durability life of the rolling bearings 6, 7, and to stably maintain the operating accuracy of the screw shaft 32. Furthermore, if open-type rolling bearings can be used for the rolling bearings 6, 7, it is possible to omit strict dimensional control that is required when using sealed-type rolling bearings equipped with seal members, and therefore it is possible to reduce the cost of the electric actuator 1.

[0041] The first cover surface 8A is provided so as to cover 80% or more (preferably 90% or more) but less than 100% of the one end openings 64, 74 in terms of an opening area ratio when the inner diameter ends of the one end openings 64, 74 between the inner and outer rings are open, and the second cover surface 8B is provided so as to cover 80% or more (preferably 90% or more) but less than 100% of the other end openings 65, 75 in terms of an opening area ratio when the outer diameter ends of the other end openings 65, 75 between the inner and outer rings are open. This makes it possible to appropriately seal the openings without deteriorating the operability of the rolling bearings 6, 7, and thus the electric actuator 1.

[0042] In addition, during operation of the rolling bearings 6, 7, grease tends to be unevenly distributed in the outer diameter side region of the bearing internal space due to the influence of centrifugal force, so if the openings 65, 75 between the inner and outer rings are opened widely on the outer diameter side, grease leakage is likely to occur. In particular, when using low-viscosity grease with a consistency in the range of 310 to 340 corresponding to the high-speed rotation of the rolling bearings 6, 7, grease leakage is likely to occur. In this regard, the opening width A of the opening on the inner diameter end 64a, 74a side of the one-end opening 64, 74 of the rolling bearings 6, 7 is made larger than the opening width B of the opening on the outer diameter end 65a, 75a side of the other-end opening 65, 75 of the rolling bearings 6, 7, so that the possibility of unintended grease leakage can be reduced. Therefore, this embodiment can be suitably applied to the electric actuator 1 that employs a high-speed rotation type small motor as the electric motor 2.

[0043] As described above, the electric actuator 1 of this embodiment is characterized by being low cost and having excellent operating accuracy and durability of the output shaft (screw shaft 32).

[0044] Although the electric actuator 1 according to one embodiment of the present invention has been described above, the embodiment of the present invention is not limited to this. Fig. 3 shows a partial vertical cross-sectional view of the electric actuator 1 according to another embodiment of the present invention.

[0045] The electric actuator 1 shown in FIG. 3 differs from the electric actuator 1 shown in FIGS. 1 and 2 in the following main points: The flange portion 31b of the nut 31 is omitted, and the second gear 42 constituting the power transmission mechanism 4 is integrally provided with the nut 31; and The second gear 42 as the second different member M2 is provided with a second cover surface 8B that covers the other end opening 75 of the second rolling bearing 7 in addition to the second cover surface 8B that covers the other end opening 65 of the first rolling bearing 6, and this second cover surface 8B covers the other end opening 75 of the second rolling bearing 7 by 80% or more and less than 100% (preferably 90% or more and less than 100%) in terms of opening area ratio.

[0046] The second cover surface 8B covering the other end opening 75 of the second rolling bearing 7 is an annular surface extending from the inner diameter side to the outer diameter side of the second rolling bearing 7, similar to the second cover surface 8B covering the other end opening 65 of the first rolling bearing 6, and its outer diameter end portion is located within the radial range of the other end opening 75 of the rolling bearing 7. Therefore, at the outer diameter end 75a of the other end opening 75, there is an opening with a radial opening width B that is not sealed by the second cover surface 8B. The opening width B of this opening is set smaller than the opening width A of the opening present at the inner diameter end 74a of the one end opening 74 (A>B).

[0047] In other respects, the electric actuator 1 shown in Fig. 3 has substantially the same configuration as the electric actuator 1 shown in Fig. 1 and Fig. 2. Therefore, the electric actuator 1 shown in Fig. 3 can also provide the same operational effects as the electric actuator 1 shown in Fig. 1 and Fig. 2.

[0048] Although the electric actuator 1 according to the embodiment of the present invention has been described above, various modifications can be made to the electric actuator 1 without departing from the gist of the present invention.

[0049] For example, the screw mechanism 3 that converts the rotational motion of the electric motor 2 into linear motion may be a sliding screw mechanism in which the helical groove 31a provided on the inner peripheral surface of the nut 31 and the helical groove 32a provided on the outer peripheral surface of the screw shaft 32 are directly screwed together without using balls. In addition, the power transmission mechanism 4 is not limited to the single-stage reduction mechanism described above, and may be a multi-stage reduction mechanism. [Explanation of symbols]

[0050] 1 Electric actuator 2 Electric motor 3 Screw mechanism 4 Power transmission mechanism 5. Housing 6 First rolling bearing 7 Second rolling bearing 8A First cover surface 8B Second cover surface 30 Ball screw mechanism 31 Nut 32 Screw shaft 33 Ball 42 2nd Gear (Gear) 61,71 Inner circle 62,72 Outer ring 64,74 One end opening 65,75 Other end opening M1 1st different part M2 2nd different part

Claims

1. The electric motor includes a screw mechanism that converts the rotational motion of the electric motor into linear motion, and a housing that holds the electric motor and the screw mechanism. In the electric actuator, the screw mechanism includes a nut rotatably supported on the housing via a rolling bearing lubricated with grease, and a screw shaft that moves linearly in accordance with the rotation of the nut, a first cover surface is provided on a first member different from a constituent member of the rolling bearing, the first cover surface covering 80% or more and less than 100% of the one end opening between an inner ring and an outer ring of the rolling bearing in a state where an inner diameter end of the one end opening between the inner ring and the outer ring of the rolling bearing is open, a second cover surface is provided on a second member different from a constituent member of the rolling bearing, the second cover surface covering the other end opening by 80% or more and less than 100% in terms of an opening area ratio with an outer diameter end of the other end opening between the inner ring and the outer ring of the rolling bearing being open; an opening width A of the inner diameter end side opening of the one end opening is larger than an opening width B of the outer diameter end side opening of the other end opening.

2. an annular recess is provided in the second member to define an outer diameter end side opening of the other end opening and to communicate the outer diameter end side opening with an external space of the bearing; The electric actuator according to claim 1 , wherein an opening width C of the annular recess on an outer diameter side of the rolling bearing is larger than the opening width A.

3. 3. The electric actuator according to claim 2, wherein an inner peripheral wall surface of the annular recess is formed into an inclined surface inclined with respect to the axial direction.

4. The electric actuator according to claim 1 , wherein the first cover surface is provided on the housing.

5. The electric actuator according to claim 1 , wherein the second cover surface is provided on the nut.

6. The drive mechanism further includes a power transmission mechanism that transmits the rotational motion of the electric motor to the nut. The electric actuator according to claim 1 , wherein the second cover surface is provided on a rotating member of the power transmission mechanism which rotates integrally with the nut.

7. 7. The electric actuator according to claim 6, wherein the power transmission mechanism is a speed reducing mechanism that reduces the speed of rotation of the electric motor and transmits the reduced speed to the nut, and the rotating member is a gear.

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