Linear actuator

Abstract

To provide a linear actuator that allows easy setting of a reduction ratio and has a function for holding the positions of drive transmission members.SOLUTION: Provided is a linear actuator A comprising: an electric motor M housed in a case C and having a motor shaft m1; a planetary gear shaft p1 fixed to the motor shaft m1 and revolving about a rotational axis X; a planetary gear pg supported by the planetary gear shaft p1 and having a first external gear pg1 and a second external gear pg2 of different modules arranged from a base end side of the planetary gear shaft p1; a first internal gear rg1 meshing with the first external gear pg1 and fixed to the case C; a second internal gear rg2 meshing with the second external gear pg2 and rotating relative to the case C; a nut N rotating integrally with the second internal gear rg2 and having a female screw part nc on an inner surface thereof; and a slide shaft 1 which has a male screw part 1c screwed with the female screw part nc and is reciprocated inside the motor shaft m1 by rotation of the nut N.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a linear actuator that, for example, decelerates the driving rotation of an electric motor using a planetary gear mechanism and converts the decelerated rotation into reciprocating movement of a slide shaft via a screw member. [Background technology]

[0002] Conventionally, an example of such a linear actuator is shown in Patent Document 1 (see

[0031] to

[0033] Figs. 2, 8, and 10). This linear actuator is used, for example, as an actuator for steering the rear wheels of an automobile, and converts the rotational force of an electric motor into a moving force in the axial direction of a nut 6.

[0003] A nut 6 is supported non-rotatably but reciprocally relative to the casing 1. A thread 6a is formed on the nut 6, and a nut 41 having an internal thread is coaxially meshed with the thread 6a. Rotational drive generated by an electric motor is transmitted to the nut 41 via a planetary gear mechanism 7. The electric motor rotates the nut 41 at a significantly reduced rotational speed, but the reciprocating speed of the nut 6 is set to a speed suitable for rear wheel steering.

[0004] In the planetary gear mechanism 7, the driving rotation of the electric motor is output to gear 11a, and this driving rotation is transmitted to the first planetary gear 21 etc. The planetary gear 21 etc. is meshed with the ring gear 12 fixed to the casing 1, and the revolution of these planetary gears 21 etc. rotates the sun gear 29a that supports the planetary gears 21 etc. This performs the first stage of deceleration.

[0005] The sun gear 29a is meshed with the second-stage planetary gears 31, etc. These planetary gears 31, etc. are supported by nuts 41 while meshing with the same ring gear 12 as above. The revolution of the planetary gears 31, etc. rotates the nuts 41, thereby performing second-stage reduction. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 07-286803 Summary of the Invention [Problem to be solved by the invention]

[0007] In the above-mentioned conventional linear actuator, the use of planetary gears and a two-stage configuration allows the output of the electric motor to be significantly reduced. As a result, when a reverse input from the slide shaft of the actuator acts on the motor shaft of the electric motor, the reverse input torque acting on the motor shaft is reduced, making it easier for the electric motor to maintain its position.

[0008] However, in the above-mentioned conventional technology, since two sets of planetary gears are arranged along the longitudinal direction of the slide shaft, other gears are required to connect each set of gear units. This not only increases the number of components of the reduction unit, but also makes the overall size of the reduction unit a certain size. This also causes rattle between the gears.

[0009] Furthermore, to obtain a desired reduction ratio, the reduction ratios of the planetary gears must be added up, but because two sets of planetary gears mesh with the same ring gear, there are limitations on the tooth profile and number of teeth of each planetary gear. While these changes can be made by profile shifting the gears, the task of determining the specifications of each planetary gear to obtain a desired reduction ratio is complicated.

[0010] As described above, conventional linear actuators have various problems that need to be solved, and there has been a demand for a compact linear actuator that allows for easy setting of the reduction ratio and has excellent position-maintaining functions for components involved in drive transmission. [Means for solving the problem]

[0011] (Features and configuration) The linear actuator according to the present invention has the following characteristic configuration: an electric motor housed in a case; a motor shaft of the electric motor; a planetary gear shaft fixed to the motor shaft in parallel with the motor shaft and revolving around a rotation axis of the motor shaft; a planetary gear supported by the planetary gear shaft, the planetary gear comprising a first external gear and a second external gear having different modules, integrally formed adjacent to each other from a base end side of the planetary gear shaft along the direction of the rotation axis; a first internal gear fixed to the case while meshing with the first external gear; and a second internal gear rotating relatively to the case while meshing with the second external gear. a nut that is rotatably held by the case so as to rotate integrally with the second internal gear and has a female thread portion on its inner surface; The nut has a male threaded portion that screws into the female threaded portion, and a slide shaft that is inserted inside the motor shaft and moves back and forth along the rotation axis as the nut rotates.

[0012] 〔effect〕 By using a planetary gear mechanism as in this configuration, the reduction ratio of the output from the motor shaft can be set large and over a wide range, which makes it easy to set the reduction ratio that prevents the motor shaft from rotating due to reverse input from the slide shaft, resulting in a linear actuator with excellent position retention functions for the components involved in the drive transmission.

[0013] Furthermore, by forming the first external gear and the second external gear integrally with one planetary gear, there is no need for another gear to connect these external gears together, resulting in an extremely compact linear actuator configuration.

[0014] In particular, the first external gear and the second external gear have different modules, i.e., different tooth sizes. In other words, by appropriately setting the pitch diameters of the first internal gear and the second internal gear that mesh with these external gears, it is possible to set the difference in the number of teeth between the two internal gears relatively easily. As a result, the degree of freedom in setting the reduction ratio is increased compared to, for example, when the internal gear and the external gear are profile shifted, and a linear actuator suitable for the purpose of installation can be obtained.

[0015] (Features and configuration) In the linear actuator according to the present invention, the number of teeth of the first external gear and the number of teeth of the second external gear can be set to be equal.

[0016] 〔effect〕 If the number of teeth of the first external gear and the number of teeth of the second external gear are the same as in this configuration, the work of assembling the planetary gears to the first internal gear and the second internal gear becomes easy.

[0017] If both external gears have the same number of teeth, the first internal gear and the second internal gear must have different numbers of teeth in order for the linear actuator to obtain a predetermined reduction ratio. In this case, when the first internal gear and the second internal gear are installed in the case, the tooth phases of the two internal gears will match at some position. Also, depending on the setting of the number of teeth, the tooth phases of the respective internal gears may match at other points along the circumferential direction.

[0018] Since the tooth phases of the first external gear and the second external gear in this configuration are the same, by arranging the planetary gears in a position where the teeth of the two internal gears are aligned, the planetary gears can be easily meshed with their respective internal gears, making the assembly of each gear extremely easy.

[0019] (Features and configuration) In the linear actuator according to the present invention, The pitch circle diameter of the first external gear is set larger than the pitch circle diameter of the second external gear, and In the first internal gear, a fixing screw portion is formed between an outer peripheral surface of the first internal gear and an inner peripheral surface of the case, a first internal tooth is formed in an area of ​​the inner surface of the first internal gear close to a base end side of the planetary gear shaft, and a cylindrical inner surface having a diameter larger than the inner diameter of the first internal gear is formed in an area adjacent to the first internal tooth on the opposite side from the base end side, with a step portion sandwiched therebetween, In the second internal gear, it is preferable that a cylindrical outer surface facing the cylindrical inner surface is formed on the outer peripheral surface of the second internal gear, and that a second internal tooth is formed in an area closer to the first external gear, and that the end face of the second internal tooth is configured to face the step portion and the side surface of the first external gear.

[0020] (effect) In this configuration, the width of the members constituting the first internal gear in a direction along the rotation axis is set larger than the width of the members constituting the second internal gear in the same direction, and the first internal gear and the second internal gear are arranged so that they partially overlap in the same direction.

[0021] A fixing screw portion for fixing the first internal gear is formed between the outer peripheral surface of the first internal gear and the case, and by making the members constituting the first internal gear wider, the fastening force to the case can be increased.

[0022] Furthermore, the first internal gear has a step between the region where the internal teeth are formed and the adjacent cylindrical inner surface, and this step faces the end face of the second internal gear. As a result, when fixing the first internal gear and the second internal gear to the case, the second internal gear is first inserted into the case and the first internal gear is screwed into the case, preventing the second internal gear from coming loose. This simplifies the work of fixing both internal gears. Due to this fixation, when the motor and planetary gear are subsequently attached to the case, the first internal gear and second internal gear are already fixed to the case, making it easy to connect the motor, etc.

[0023] Furthermore, an end face of the second internal gear faces a side face of the first external gear formed on the planetary gear. Therefore, even if the planetary gear is movable along the planetary gear shaft with the planetary gear attached in a predetermined position, the side face of the first external gear can abut against the end face of the second internal gear, preventing accidental interference between the first external gear and the second internal gear.

[0024] As described above, with this configuration, the first internal gear, second internal gear, planetary gears, etc. can be easily assembled, and unexpected interference between the gears can be prevented, resulting in a durable linear actuator. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a cross-sectional view showing the structure of a linear actuator according to a first embodiment; [Figure 2] FIG. 1 is a perspective view showing a main structure of a linear actuator according to a first embodiment; [Figure 3] Schematic diagram showing the configuration of a speed reducer according to the first embodiment. [Figure 4] FIG. 1 is an explanatory diagram showing a meshing state between a planetary gear and an internal gear according to a first embodiment; [Figure 5] FIG. 1 is an explanatory diagram showing an application example of a linear actuator according to a first embodiment; DETAILED DESCRIPTION OF THE INVENTION

[0026] [First embodiment] (overview) An example of a linear actuator A (hereinafter simply referred to as "actuator A") according to the present invention is shown in Figs. 1 to 5. This actuator A reduces the rotational speed of an electric motor M and converts the rotational drive of a motor shaft m1 into reciprocating movement of a slide shaft 1. This actuator A is attached to a cross member 20 of the rear wheels of a vehicle, for example, and is used as a rear wheel steering device S.

[0027] Figure 5 shows the structure of the applied rear wheel steering device S. The rear wheel steering device S constitutes, for example, a part of a four-wheel steering system (4WS). The rear wheel steering device S is attached to both the wheel side member and the body side member of the suspension mechanism that supports the rear wheels TL and TR of the vehicle.

[0028] As shown in Figure 5, left and right wheel supports 21 are swingably connected to a cross member 20 on the vehicle body side, and these left and right wheel supports 21 are connected to a steering link 22 swingably provided on the cross member 20 via left and right tie rods 23, respectively. In the present rear wheel steering device S, a first connecting portion J1 and a second connecting portion J2 provided on both ends are connected to one end of the steering link 22 and a part of the cross member 20, respectively, and the rear wheels are steered by swinging the steering link 22 as the rear wheel steering device S expands and contracts.

[0029] A cylindrical case C extends from the second connecting part J2, and a slide shaft 1 that is capable of reciprocating motion coaxially with the rotation axis X of the case C extends from the first connecting part J1 toward the interior of the case C. A drive unit K and a speed reducer G are provided inside the case C. An electric motor M of the drive unit K is controlled by a controller 24 provided inside the case C. The internal structure of the case C is shown below.

[0030] This actuator A uses a planetary gear mechanism as a speed reducing mechanism, and is configured to exhibit high responsiveness in consideration of application to rear wheel steering of a vehicle B, for example.

[0031] The linear actuator A according to the first embodiment includes a drive unit K equipped with the electric motor M shown in FIG. 1 and the like, and a speed reducer G that outputs the drive rotation of the electric motor M while reducing the speed. These are housed inside a case C. The case C is composed of, for example, a first case c1 and a second case c2, both of which are substantially cylindrical. A bolt hole 2a for inserting a fastening bolt 2 is formed in the first case c1 by protruding therefrom, and a female bolt thread portion 2b is formed in the second case c2 by protruding therefrom at a position opposite the bolt hole 2a. The first case c1 and the second case c2 are connected such that an end of the first case c1 is inserted into an end of the second case c2.

[0032] [Drive unit] As shown in Figures 1 and 2, the driving unit K includes, for example, an electric motor M and a motor shaft m1. The rotation axis X of the motor shaft m1 serves as the reference for the rotational movement of each gear that constitutes the linear actuator A. The electric motor M may be any of various motors that include a stator ms and a rotor mr. It is particularly advantageous to include a measuring unit such as an encoder so that the rotation angle of the motor shaft m1 can be monitored.

[0033] The motor shaft m1 has a hollow structure, and a slide shaft 1 (described later) is installed inside the motor shaft m1 so that it can slide freely. A flange portion mf is formed at one end of the motor shaft m1, and a planetary gear mechanism P, which is a reduction gear G, is connected to this flange portion mf.

[0034] [Reduction section: planetary gear mechanism] 1, 2 and 4, the planetary gear mechanism P includes a planetary gear pg supported by a flange portion mf, an internal gear rg meshing with the planetary gear pg, and a nut N meshing with the planetary gear pg. Another internal gear rg is formed on the nut N. By employing the planetary gear mechanism P in this configuration, the reduction ratio of the output from the motor shaft m1 can be set over a wide range, and rotation of the motor shaft m1 due to reverse input from the slide shaft 1 is reliably prevented, thereby achieving the function of maintaining the position of the components.

[0035] (planetary gear) The planetary gear pg is journalled on a planetary gear shaft p1 fixed to the flange mf in parallel with the rotation axis X. For example, three planetary gear shafts p1 are provided, and they are evenly spaced along the circumferential direction of the flange mf.

[0036] 1, 2, and 4, the planetary gear pg includes a first external gear pg1 and a second external gear pg2 that are connected to each other along the rotation axis X. The first external gear pg1 is provided on the base end side of the planetary gear shaft p1 relative to the second external gear pg2, that is, on the side closer to the flange portion mf. By integrally forming the first external gear pg1 and the second external gear pg2 into one planetary gear pg, there is no need for another gear to connect these external gears together, and the linear actuator A has an extremely compact configuration.

[0037] In this embodiment, the pitch diameter of the first external gear pg1 is larger than the pitch diameter of the second external gear pg2, and the modules of the two gears are different. Specifically, the number of teeth of both gears is set to be the same, and the module of the first external gear pg1 is set to be larger. The module is the value obtained by dividing the pitch diameter of a gear by the number of teeth.

[0038] When forming gears with the same number of teeth but different pitch circle diameters, there are generally two ways to do it: by using profile shifting or by changing the module. In this embodiment, by changing the modules of both, the degree of freedom in setting the reduction ratio is increased. In this case, two external gears are formed on one planetary gear pg, so the difference between the pitch circle diameters of the two gears is small due to the structure.

[0039] In this embodiment, as will be described later, the pitch circle diameters of the first external gear pg1 and the internal gear rg meshing with the first external gear pg1 are both similar values ​​in order to be mounted inside the case C. As a result, if two internal gears rg are formed by profile shifting, the difference in the number of teeth between them will be small. A speed reduction unit G using such two internal gears rg will have a very large reduction ratio. Therefore, in this embodiment, internal gears rg with different modules are used so that the difference in the number of teeth between the two internal gears rg can be increased.

[0040] Furthermore, if the number of teeth of the first external gear pg1 and the number of teeth of the second external gear pg2 are the same as in this embodiment, the assembly work of the planetary gear pg to the first internal gear rg1 and the second internal gear rg2 becomes easy. If the numbers of teeth of both external gears are the same, the numbers of teeth of the first internal gear rg1 and the second internal gear rg2 must be made different in order for the actuator A to obtain a predetermined reduction ratio.

[0041] As shown in Fig. 3, the tooth phases of the first internal gear rg1 and the second internal gear rg2 are configured to match at the position where the planetary gear pg is provided. Because the tooth phases of the first external gear pg1 and the second external gear pg2 match, by disposing the planetary gear pg at a position where the teeth of the two internal gears rg match, the first external gear pg1 and the second external gear pg2 can be easily meshed with the first internal gear rg1 and the second internal gear rg2, making the assembly of each gear extremely easy.

[0042] (internal gear) As shown in FIGS. 1 and 2, the internal gear rg has an annular first internal gear rg1 fixed to the case C and a second internal gear rg2 formed on the large diameter portion na of the nut N. The outer surface of the large diameter portion na faces the cylindrical inner surface rg1b. The inner surface of the large diameter portion na is formed with the second internal gear rg2 that meshes with the second external gear pg2. The outer surface of the small diameter portion nb of the nut N is rotatably supported by the first case c1 via a bearing 3a. A female thread portion nc is formed on the inner surface of the small diameter portion nb, which meshes with a male thread portion 1c formed on the slide shaft 1, which will be described later.

[0043] 1, the first external gear pg1 meshes with the first internal gear rg1, and the second external gear pg2 meshes with the second internal gear rg2. In this embodiment, the difference in size between the pitch circle diameter of the first internal gear rg1 and the pitch circle diameter of the second internal gear rg2 is not particularly large, and as a result, the number of teeth of the second internal gear rg2 is greater than the number of teeth of the first internal gear rg1. This widens the difference in relative rotational speed between the first internal gear rg1 and the second internal gear rg2, increasing the freedom in selecting the value of the reduction ratio.

[0044] The first internal gear rg1 is fixed to the inner surface of the case C. A fixing screw portion rg1a is formed between the outer peripheral surface of the first internal gear rg1 and the inner surface of the case C, and the first internal gear rg1 is screwed and fixed to the case C. In order to increase the screwing strength, the dimension of the first internal gear rg1 in the direction along the rotation axis X is formed to be longer than the dimension of the planetary gear pg in the same direction.

[0045] On the other hand, on the inner surface of the first internal gear rg1, internal teeth are formed in a portion facing the first external gear pg1, and a simple cylindrical inner surface rg1b is formed in the adjacent region. The outer surface of the large diameter portion na of the nut N is disposed to face this cylindrical inner surface rg1b.

[0046] A step rg1c is provided between the first internal gear rg1 and the cylindrical inner surface rg1b. This step rg1c is configured to face the end face of the second internal gear rg2. As a result, when the first internal gear rg1 and the second internal gear rg2 are fixed to the case C, the second internal gear rg2 is first inserted into the bearing 3a fixed to the case C, and the first internal gear rg1 is screwed into the case C, preventing the second internal gear rg2 from coming off.

[0047] Additionally, an end face of the second internal gear rg2 faces a side face of the first external gear pg1 formed on the planetary gear pg. Therefore, even if the planetary gear pg is movable along the planetary gear shaft p1 with the planetary gear pg attached in a predetermined position, the side face of the first external gear pg1 can come into contact with the end face of the second internal gear rg2, preventing unexpected interference between the first external gear pg1 and the second internal gear rg2.

[0048] In this way, with this configuration, interference between the first internal gear rg1, the second internal gear rg2, the planetary gear pg, etc. is prevented, and a durable actuator A can be obtained.

[0049] (slide shaft) The slide shaft 1 is a roughly cylindrical rod-shaped member, and has a male threaded portion 1c that meshes with the female threaded portion nc of the nut N and is formed in a certain region along the direction of the rotation axis X. Two adjacent regions sandwiching the male threaded portion 1c have simply cylindrical surfaces. One of these cylindrical regions penetrates the interior of the motor shaft m1 of the electric motor M. The further end of this penetration portion and the opposite end sandwiching the male threaded portion 1c are supported by the slide guide portion cb of the case C.

[0050] As shown in FIG. 5, the slide guide portion cb is formed with a guide groove cc parallel to the rotation axis X. Furthermore, a restricting protrusion 1d that restricts rotation of the slide shaft 1 is formed at a portion of the slide shaft 1 facing the guide groove cc. For example, when viewed in the direction along the rotation axis X, the restricting protrusions 1d are formed at two locations on opposite sides along a radial direction passing through the rotation axis X. When the female thread portion nc of the nut N rotates, the male thread portion 1c moves back and forth along the rotation axis X with its rotation restricted by these restricting protrusions 1d and guide groove cc. It is advantageous if the male thread portion 1c and the female thread portion nc are configured with, for example, trapezoidal gears to increase the transmission strength between the teeth.

[0051] (Actuator assembly mode) In the actuator A having this configuration, predetermined components are assembled to each of the first case c1 and the second case c2, and after these are combined, they are integrated with the bolts 2.

[0052] As shown in Figures 1 and 2, first, a bearing 3a equipped with multiple ball bearings is inserted into the first case c1 to support the rotation of the nut N, and a snap ring 4 is engaged with the inner surface of the first case c1 to fix the bearing 3a. Next, the nut N is inserted into the bearing 3a starting from the small diameter portion nb side. A minute step rg1c is formed on the outer surface of the small diameter portion nb, which abuts against the inner race of the bearing 3a and determines the insertion depth of the nut N. When the nut N is inserted, the large diameter portion na faces closely against the inner surface of the first case c1.

[0053] Next, the first internal gear rg1 is inserted and screwed into the first case c1. This screwing is performed by a fixing screw portion rg1a formed between the outer surface of the first internal gear rg1 and the inner surface of the case C. The first internal gear rg1 is screwed into the case C until a predetermined torque is generated. The dimension of this fixing screw portion rg1a along the rotation axis X exceeds the width of the first external gear pg1 and extends into the area of ​​the second external gear pg2, so the first internal gear rg1 is firmly attached to the case C by applying a predetermined torque.

[0054] Meanwhile, the electric motor M is first inserted and placed in the second case c2. A stator ms is fixed to the inner surface of the case C, and a rotor mr is inserted inside the stator ms. The end of the motor shaft m1 fixedly inserted into the rotor mr is rotatably supported by the case C via a motor bearing 5. The end of the motor shaft m1 on the front side in the insertion direction is rotatably supported by the case C by a support plate 6 equipped with the motor bearing 5.

[0055] A flange portion mf is formed at the end of the motor shaft m1 protruding from the support plate 6, and the planetary gear shaft p1 is attached to this flange portion mf. Each planetary gear pg is inserted onto the planetary gear shaft p1, and no special locking mechanism is used to prevent it from coming loose. As shown in Figure 1, the end of the second external gear pg2 of the planetary gear pg faces the end face of the nut N, and this, together with the side surface of the first external gear pg1, provides a locking function.

[0056] The male threaded portion 1c of the slide shaft 1 is screwed into the nut N held in the first case c1, and the cylindrical surface of the slide shaft 1 is left protruding from the opening of the first case c1. The second case c2 is brought close to the first case c1, and the two cases C are joined together while the restricting protrusion 1d formed on the slide shaft 1 is engaged with the guide groove cc formed in the slide guide portion cb of the second case c2.

[0057] In this configuration, the inner diameter of the second internal gear rg2 is smaller than the inner diameter of the first internal gear rg1, and the outer diameter of the second external gear pg2 is smaller than the outer diameter of the first external gear pg1. Therefore, assembly of the actuator A is completed by inserting the first case c1, in which the internal gear rg is pre-arranged, and the second case c2, in which the external gear is pre-arranged, into each other, thereby streamlining the assembly man-hours. Furthermore, by combining the first case c1 and second case c2, which have been pre-assembled in this way, the drive unit K and the reduction unit G can be easily connected.

[0058] (Actuator operation mode) As the motor shaft m1 is driven to rotate, the multiple planetary gears pg revolve around the rotation axis X. At the same time, the first external gear pg1, which meshes with the first internal gear rg1, rotates around the planetary gear shaft p1 at a predetermined rotational speed. Naturally, the second external gear pg2 also rotates and revolves at the same rotational speed. In this embodiment, the number of teeth of the first external gear pg1 and the number of teeth of the second external gear pg2 are equal, but the module of the second external gear pg2 is smaller than the module of the first external gear pg1, and one tooth of the second external gear pg2 is smaller than one tooth of the first external gear pg1. The pitch circle diameter of the second external gear pg2 is also smaller.

[0059] On the other hand, with regard to the internal gear rg, one tooth of the second internal gear rg2 is smaller than one tooth of the first internal gear rg1, and the pitch circle diameter of the second internal gear rg2 is smaller than the pitch circle diameter of the first internal gear rg1. Therefore, the number of teeth of the second internal gear rg2 is smaller than the number of teeth of the first internal gear rg1.

[0060] The difference between the number of teeth of the first internal gear rg1 and the number of teeth of the second internal gear rg2 obtained by the difference in module depends on the specifications of the planetary gear pg, but is easier to make larger than the difference in the number of teeth obtained by forming the external gear and the internal gear rg by profile shifting. This increases the degree of freedom in setting the relative rotational speed between the first internal gear rg1 and the second internal gear rg2.

[0061] In this embodiment, the rotation speed of the nut N is faster when the difference in module is used than when the difference due to dislocation processing is used. In the configuration of this embodiment, the rotation speed of the motor shaft m1 is significantly reduced, but the rotation speed of the nut N has a high degree of freedom in setting, and the range of options for the reciprocating speed of the slide shaft 1 is widened.

[0062] For example, when the reduction ratio from the motor shaft m1 to the nut N is estimated, the reduction ratio in the reduction section G using a conventional profile shifted gear is about 1 / 100. However, with the actuator A configured as described above, the reduction ratio can be set within a wide range of about 1 / 11 to 1 / 70.

[0063] As described above, by providing the reduction section G of this configuration, it is possible to easily set the reduction ratio, reliably maintain the position of components involved in the drive transmission of electric motors, etc., and obtain a compact linear actuator. [Industrial Applicability]

[0064] The linear actuator of the present invention can be widely used in locations where the rotational drive of an electric motor is significantly reduced by a reduction section before being output, and where a reliable position-maintaining function of the drive transmission member is required against reverse input to the reduction section. [Explanation of symbols]

[0065] 1 Slide shaft 1c Female thread A Linear Actuator C Case M Electric motor m1 Motor shaft N nut nc Male thread p1 Planetary gear shaft pg planetary gear pg1 First external gear pg2 Second external gear rg1 First internal gear rg2 Second internal gear rg1a fixing screw part rg1b Cylindrical inner surface rg1c step part X Rotation axis

Claims

1. an electric motor housed in a case; a motor shaft of the electric motor; a planetary gear shaft fixed to the motor shaft in parallel with the motor shaft and revolving around a rotation axis of the motor shaft; a planetary gear supported by the planetary gear shaft, the planetary gear comprising a first external gear and a second external gear having different modules, integrally formed adjacent to each other from a base end side of the planetary gear shaft along the direction of the rotation axis; a first internal gear fixed to the case while meshing with the first external gear; and a second internal gear rotating relatively to the case while meshing with the second external gear. a nut that is rotatably held by the case so as to rotate integrally with the second internal gear and has a female thread portion on its inner surface; a slide shaft that has a male threaded portion that screws into the female threaded portion, is inserted inside the motor shaft, and moves back and forth along the rotation axis as the nut rotates.

2. 2. The linear actuator according to claim 1, wherein the number of teeth of the first external gear and the number of teeth of the second external gear are set equal to each other.

3. The pitch circle diameter of the first external gear is set to be larger than the pitch circle diameter of the second external gear, and In the first internal gear, a fixing screw portion is formed between an outer peripheral surface of the first internal gear and an inner peripheral surface of the case, a first internal tooth is formed in an area of ​​the inner surface of the first internal gear that is close to a base end side of the planetary gear shaft, and a cylindrical inner surface having a diameter larger than the inner diameter of the first internal gear is formed in an area adjacent to the first internal tooth on the opposite side from the base end side, with a step portion sandwiched therebetween, A linear actuator as described in claim 1 or 2, wherein the second internal gear has a cylindrical outer surface formed on its outer peripheral surface that faces the cylindrical inner surface, and a second internal tooth is formed in an area closer to the first external gear, and the end face of the second internal tooth is configured to face the step portion and the side of the first external gear.

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