Actuator

Abstract

The present invention provides a compact actuator with a simple structure. The actuator (A) comprises: an electric motor (M) having a stator (M2) and a rotor (M1); at least one cylinder (S) arranged adjacent to the electric motor (M); and a piston (P) mounted on a drive shaft (3) and arranged inside the cylinder (S); the rotor (M1) is a hollow structure, and the drive shaft (3) is received inside the rotor (M1) in a state where the axis of a part of the drive shaft (3) and a part of the rotor (M1) are aligned and screwed together, and the drive shaft (3) reciprocates along the axis (X) as the rotor (M1) rotates.

Description

Technical Field

[0001] The present invention relates to an actuator including a cylinder having a piston therein and an electric motor, wherein the piston is driven to reciprocate in accordance with the rotational drive of the electric motor. Background Art

[0002] Conventionally, as such an actuator, there is a structure shown in Patent Document 1 (see

[0011] to

[0015] ,

[0026] and Figure 1 ).

[0003] This actuator is also related to the air suspension device of the vehicle. In this device, a cylinder 5 is provided which is connected to a pair of air springs 2, and the interior of the cylinder 5 is divided into two chambers R1 and R2 by a piston 6. By displacing the piston 6, the volume of the air spring 2 changes. The driving source is an electric motor 7a, and the rotational motion of the electric motor 7a is transmitted to the piston 6 via a motion conversion mechanism 7b.

[0004] This actuator does not adjust the vehicle height by supplying or discharging compressed air from the outside, but controls the posture of the vehicle body by displacing the piston 6 of the cylinder 5 connected to each air spring 2. Therefore, it is less likely to be affected by the compressibility of air when supplying or discharging compressed air.

[0005] In addition, since no compressor or the like is used, compressed air is not released to the atmosphere from the air spring 2, so energy loss is small. Furthermore, for example, by adjusting the pressure of the left and right air springs 2 at the same time, a highly responsive vehicle body posture control can be performed.

[0006] Furthermore, since there is no need to provide a large-capacity compressor, nor is there any need to supply or discharge a large-capacity compressed air to or from the air spring 2 , the air suspension device does not increase in size, and there is no risk of impairing the mountability on the vehicle.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent Application Publication No. 2009-298170

[0010] Technical problem to be solved by the invention

[0011] In the above-mentioned conventional actuator, the rotational motion of the motor 7a is converted into the linear motion of the piston 6 via the motion conversion mechanism 7b. As the motion conversion mechanism 7b, for example, a combination of a threaded shaft provided on the outer periphery of one end of the rod 6a and a nut coupled to the motor 7a in a manner threadedly engaged with the threaded shaft, a combination of a rack formed at one end of the rod 6a and a worm gear meshed with the rack and coupled to the motor 7a, etc. are used.

[0012] However, these structures are all structures in which the motor 7a is connected to other gears, etc., and the rotation drive of the gear is transmitted to the rod 6a of the piston 6. Therefore, the arrangement of these components requires a predetermined space. In addition, in order to reliably perform the meshing transmission between the rotating shaft of the motor 7a and the rod 6a, the two need to be correctly positioned, etc., which increases the load on the structural design of the connection part and the processing of the components. Summary of the invention

[0013] As described above, conventional actuators, particularly mechanisms for converting the rotational drive of a motor into the linear drive of a piston, have various technical problems to be solved, and a compact actuator having a simple structure is desired.

[0014] Technical means for solving technical problems

[0015] (Feature Structure)

[0016] The characteristic structure of the actuator involved in the present invention is that it has:

[0017] An electric motor having a stator and a rotor;

[0018] at least one cylinder disposed adjacent to the electric motor; and

[0019] a piston mounted on the drive shaft and disposed inside the cylinder,

[0020] The rotor has a hollow structure, and the drive shaft is housed inside the rotor in a state where the axes of a part of the drive shaft and a part of the rotor coincide with each other and are screwed together.

[0021] The drive shaft reciprocates along the axis as the rotor rotates.

[0022] (Effect)

[0023] In the actuator of this structure, the drive shaft passes through the inside of the hollow rotor, and the two have a structure that overlaps along the axial direction. Generally speaking, in a mechanism with a piston, in addition to the configuration space of the cylinder that contains the piston, a reciprocating space for the drive shaft that reciprocates the piston is required, and a device frame of a specified size is required. However, with this structure, since the internal space of the rotor can be used as part of the reciprocating space of the drive shaft, it is possible to make the device size compact.

[0024] In addition, a part of the drive shaft and a part of the rotor are screwed together while keeping their axes aligned. Therefore, the rotor has the function of a component that converts its own rotational drive into the reciprocating motion of the drive shaft. Moreover, compared with a structure in which the output shaft of the motor and the drive shaft of the piston are connected in series or in parallel using another gear, the length and width of the mechanism are greatly shortened. Therefore, a compact actuator can be obtained.

[0025] (Feature Structure)

[0026] The actuator according to the present invention preferably includes two spaces formed by the cylinder and the piston.

[0027] (Effect)

[0028] The structure of the present invention in which two spaces are provided includes, for example: a structure in which two sets of cylinders and pistons are provided to form one space; and a structure in which the internal space of one cylinder is divided into two by one piston. However, in any case, the motor is one.

[0029] Therefore, if it is these structures, by reciprocating one or two drive shafts along the axis through one motor, the two spaces can be expanded or contracted alternately in different phases. Therefore, the actuator of this structure is more convenient than the driving mechanism using the increase and decrease of a pair of pressures.

[0030] (Feature Structure)

[0031] In the actuator involved in the present invention, preferably, a separate cylinder is provided as the cylinder, and the piston is configured to divide the interior of the cylinder into a first chamber and a second chamber, and an external thread portion formed on a part of the driving part is screwed with an internal thread portion formed on a part of the inner surface of the rotor, and the internal thread portion is provided at the end portion of the rotor along the axis, which is away from the cylinder.

[0032] (Effect)

[0033] In the cylinder-only actuator as in this structure, the drive shaft is mounted on the piston, and the piston often moves back and forth with the vicinity of the center of the cylinder as a reference. In this case, the external thread portion reciprocates relative to the internal thread portion, so when the piston is in the reference position, the internal thread portion is preferably located at the center of the external thread portion. The internal thread portion is formed at one end along the direction of the axis of the rotor, and the center position of the external thread portion corresponds to this position.

[0034] Therefore, when the piston is in the neutral position, the entire drive shaft is inserted far into the inner thread portion relative to the rotor. As a result, the cylinder and the motor are arranged close to each other, the length along the axis is shortened, and a more compact actuator can be obtained.

[0035] (Feature Structure)

[0036] In the actuator involved in the present invention, it is preferred that the first cylinder and the second cylinder, both of which are cup-shaped, as the cylinders are arranged in a state of being separated by the motor and opening toward the motor, the drive shaft passes through the rotor, and the first piston contained in the first cylinder and the second piston contained in the second cylinder are respectively connected to the two ends of the drive shaft.

[0037] (Effect)

[0038] The actuator of this structure is a structure in which a cylinder and a piston are arranged on both sides of the electric motor. In this structure, it is necessary to move two pistons, but the rotor drives the drive shafts of both sides that hold the first piston and the second piston, so the mechanism is not complicated.

[0039] In this structure, a cup-shaped structure is used as the first cylinder and the second cylinder. When the piston is installed, the space sandwiched by the piston and the bottom becomes a chamber, and the space on the opposite side can be open to the atmosphere.

[0040] In this case, in order to form the sealing structure of the chamber, it is sufficient to ensure the airtightness of the outer surface of the piston and the inner surface of the cylinder, and no special consideration is required for the drive shaft. Therefore, it becomes extremely easy to ensure the airtightness of the entire device, and a reasonable actuator can be obtained.

[0041] (Feature Structure)

[0042] The actuator according to the present invention may have a structure in which a ball screw is used as the screw engagement to restrict the rotation of the drive shaft around the axis.

[0043] (Effect)

[0044] By using a ball screw like this structure, the motion resistance involved in the relative rotation of the rotor and the drive shaft is reduced. Therefore, during the rotation of the rotor, the tendency of the drive shaft to rotate is alleviated, and the reciprocating movement of the restricted drive shaft becomes smooth. Therefore, an actuator with improved transmission efficiency, excellent motion responsiveness, and less vibration and noise can be obtained.

[0045] (Feature Structure)

[0046] The actuator according to the present invention may have a structure in which the two spaces are respectively connected to chambers of two air suspension devices arranged at the wheels of the vehicle.

[0047] (Effect)

[0048] According to this structure, the chambers connected to the two spaces may be chambers for the left and right wheels of the vehicle, or chambers for the front and rear wheels. In the case of the left and right wheels, the outer chamber can be pressurized and the inner chamber can be depressurized during turning to suppress changes in the rolling posture. On the other hand, in the case of the front and rear wheels, control can be performed such that when crossing a step, the chamber of the front wheel is depressurized and the chamber of the rear wheel is pressurized to suppress changes in the pitching posture.

[0049] In addition, in the case of the present structure, the thrust of the motor can be relatively small when pressurizing one side and depressurizing the other side. For example, when turning, due to the vehicle's tilt toward the outside, the height of the vehicle decreases while the outer chamber is pressurized, and the height of the vehicle increases while the inner chamber is depressurized. At this time, in order to stabilize the posture of the vehicle, the engine is driven to move the piston so that the pressure difference generated in each chamber is equal to the pressure difference between the left and right wheels. Therefore, with the present structure, the load on the motor can be reduced, and the compactness of the actuator becomes possible. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 It is an explanatory diagram showing the usage of the actuator according to the first embodiment.

[0051] Figure 2 It is a cross-sectional view showing the structure of the actuator according to the first embodiment.

[0052] Figure 3 It is a perspective view showing the structure of the actuator according to the first embodiment.

[0053] Figure 4 It is a cross-sectional view showing the structure of an actuator according to a second embodiment.

[0054] Figure 5 It is a perspective view showing the structure of an actuator according to a second embodiment.

[0055] Explanation of symbols

[0056] 1a Internal thread

[0057] 2a External thread

[0058] 3 Drive shaft

[0059] 8Ball screw

[0060] Actuator

[0061] Vehicle B

[0062] M Motor

[0063] M1 Rotor

[0064] M2 stator

[0065] P Piston

[0066] P1 first piston

[0067] P2 Second Piston

[0068] R1 Room 1

[0069] R2 Second Room

[0070] S Cylinder

[0071] S1 first cylinder

[0072] S2 Second Cylinder

[0073] T wheel

[0074] X axis. DETAILED DESCRIPTION

[0075] (First Embodiment)

[0076] (summary)

[0077] Figure 1 to Figure 3 The first embodiment of the actuator A according to the present invention is shown. The actuator A integrally includes a motor M and a cylinder S, converts the rotational motion of the motor M into reciprocating motion, and transmits the reciprocating motion to a piston P attached to the cylinder S. The actuator A is used in an air suspension device of a vehicle B, for example.

[0078] like Figure 1 As shown in one example, in a vehicle B in which the right wheel TR and the left wheel TL are supported by two chambers, namely, two air springs AS, the actuator A of the present invention is provided one for each of the left and right wheels. Figure 1 This is a diagram of vehicle B turning left as viewed along the traveling direction. A cylinder S is provided at the center of actuator A, and in a neutral state, a piston P is located at the center of cylinder S. The space inside cylinder S is divided into a first chamber R1 and a second chamber R2 on both sides of the cylinder S by piston P. The first chamber R1 is connected to the first air spring AS1 of the right wheel TR, and the second chamber R2 is connected to the second air spring AS2 of the left wheel TL.

[0079] In the case of this structure, the outer air spring AS1 can be pressurized and the inner air spring AS2 can be depressurized during turning to suppress the change of the roller posture. To this end, the lateral G is calculated based on the detection results of the vehicle speed sensor and the steering angle sensor outside the figure, and the piston P is moved in the direction of shrinking the first chamber R1 to supply air to the air spring AS1 on the outer side of the turn.

[0080] In the case of this structure, the thrust of the motor M that drives the piston P can be relatively small. For example, when turning, the vehicle B tilts outward, and the vehicle height decreases while the air spring AS1 on the outside is pressurized, and the vehicle height increases while the air spring AS2 on the inside is depressurized. At this time, in order to stabilize the posture of the vehicle B, it is sufficient to drive the motor M to move the piston P so that the pressure difference generated in each air spring AS1, AS2 is equal to the pressure difference between the left and right wheels TL, TR. Therefore, in the case of this structure, the load of the motor M can be reduced, and the actuator A can be made compact.

[0081] In addition, although not shown in the figure, the two first chambers R1 and second chambers R2 formed by the cylinder S and the piston P may be connected to the air springs AS of the front and rear wheels. In the case of the front and rear wheels, the following control can be performed: when crossing a step, the air spring AS of the front wheel is decompressed and the air spring AS of the rear wheel is pressurized to suppress the change in the pitch posture.

[0082] Thus, by controlling the roll and pitch postures of the vehicle B, the turning performance and step climbing performance of the vehicle B can be improved. In addition, the ride-on / off performance can be improved by tilting the vehicle B when parking. Furthermore, an actuator A that can be easily added to an air suspension already installed on the vehicle B and has high versatility is provided.

[0083] (Motor and travel sensor)

[0084] The motor M can adopt various structures including a stator M2 and a rotor M1. The movement amount of the piston P is determined by the rotation amount of the motor M, but in the present embodiment, the movement amount of the piston P is measured using, for example, a stroke sensor 9.

[0085] Specifically, in order to measure the movement of the external threaded shaft 2, a stroke sensor 9 is arranged over the top end of the external threaded shaft 2 and the first housing H1. If it is the stroke sensor 9, the movement of the end of the external threaded shaft 2 can be directly measured, and the position of the piston P can be easily and reliably grasped. In addition, the wiring with the motor M and the like is also easy, which can improve reliability and reduce costs. In addition, in addition to using the stroke sensor 9, it is also possible to have an encoder, a rotary transformer, etc. in advance on a part of the rotor M1, and measure the rotation speed and rotation angle of the rotor M1 to grasp the movement of the piston P.

[0086] (Control board)

[0087] The movement amount of the piston P is controlled by the control substrate 5 provided in the first housing H1. Although not shown in the figure, a vehicle speed sensor and a steering angle sensor are provided in the vehicle B. Based on the vehicle speed and steering angle data measured by these sensors, the control substrate 5 calculates the lateral G generated in the vehicle B when turning. The control substrate 5 stores a map that associates the lateral G with the stroke of the piston P, and can also perform feedforward control on the motor M.

[0088] (Cylinder, Piston)

[0089] The cylinder S is provided together with the first housing H1 in which the motor M is housed. In the present embodiment, the motor M and the cylinder S are also substantially cylindrical in shape. The piston P supported by the drive shaft is housed in the cylinder S in a reciprocating manner. In particular, the cylinder S is formed of a cylindrical member and has a through structure with both ends of the cylinder S opened, so that the cylinder S can be manufactured easily.

[0090] The interior of the cylinder S is divided into a first chamber R1 and a second chamber R2 by the piston P, and the expansion state and contraction state of each chamber are alternately changed. Figure 2 and Figure 3 As shown in FIG. 1 , as the drive shaft 3 , a first shaft 31 and a second shaft 32 are screwed and connected to the piston P. The first shaft 31 and the second shaft 32 are formed to have a length that matches the stroke of the piston P.

[0091] The cylinder S is formed into a cylindrical shape in which the piston P can slide. One end is externally inserted and fitted into the first housing H1 in which the electric motor M is installed, and the flange portion is fastened by bolts or the like in a coaxial state, and the other end is similarly externally inserted and fitted into the second housing H2, and the flange portion is fastened by bolts or the like in a coaxial state. In particular, since the bottom of one side of the cylinder S also serves as the first housing H1, the axis of the first shaft 31 and the axis of the externally threaded shaft 2 become the same axis X, and can be aligned with good accuracy.

[0092] The first shaft 31 is supported in an airtight manner by a first sealing portion s1 provided in the first housing H1, and the second shaft 32 is supported in an airtight manner by a second sealing portion s2 provided in the second housing H2. An annular piston seal SP is installed on the outer periphery of the piston P, and the piston P reciprocates while being in close contact with the inner wall of the cylinder S. A first port p1 is formed in the first chamber R1, and a second port p2 is formed in the second chamber R2, which are respectively connected to a specified air drive portion. In this structure, the internal pressures of the different air springs AS act on the two surfaces of the piston P, so that the operating force required to move the piston P becomes a left-right differential pressure. Therefore, the force borne by the motor M and the piston P, etc. becomes smaller.

[0093] As in this embodiment, by providing two spaces formed by the cylinder S and the piston P, namely, the first chamber R1 and the second chamber R2, the convenience of the actuator is improved. That is, by reciprocating one or two drive shafts 3 along the axis X by one motor M, the first chamber R1 and the second chamber R2 can be alternately expanded or contracted at different phases. Therefore, it can be widely applied to the above-mentioned air suspension device and other drive mechanisms that use the increase and decrease of a pair of pressures.

[0094] (Drive transmission)

[0095] like Figure 2 and Figure 3 As shown, at the end of the first shaft 31, an externally threaded shaft 2 having an externally threaded portion 2a is screwed and connected on the outer circumferential surface. Thus, the externally threaded shaft 2 becomes a part of the drive shaft 3. In this structure, compared with a structure in which the output shaft of the motor M and the drive shaft 3 of the piston P are connected using another gear or the like as in a general mechanism, the length of the mechanism along the axis X is greatly shortened. Therefore, a compact actuator A can be obtained.

[0096] The rotor shaft 1 has a cylindrical hollow structure. A female threaded portion 1a is formed on a portion of its inner surface to be screwed with the male threaded portion 2a. The male threaded shaft 2 is inserted into the female threaded portion 1a, and the two are screwed together with their respective axes X aligned. The male threaded shaft 2 reciprocates by the driving rotation of the rotor shaft 1.

[0097] According to this configuration, the rotor shaft 1 as a component of the electric motor M is used as a component for converting the rotational drive of the electric motor M into the reciprocating motion of the piston P, so that the mechanism can be simplified.

[0098] In addition, the externally threaded shaft 2 integrated with the drive shaft 3 penetrates the interior of the hollow rotor M1, and the two have a structure that overlaps along the direction of the axis X. Generally speaking, in a mechanism with a piston, in addition to the configuration space of the cylinder that contains the piston, a reciprocating space for the drive shaft that reciprocates the piston is required, and a device frame of a specified size is required. However, with this structure, since the internal space of the rotor M1 can be used as a part of the reciprocating space of the drive shaft 3, it is possible to make the device size compact.

[0099] Furthermore, a part of the drive shaft 3 and a part of the rotor M1 are screwed together while aligning the axis X. Therefore, the rotor M1 has a function as a component that converts its own rotational drive into the reciprocating motion of the drive shaft 3. Moreover, compared with a structure in which the output shaft of the motor and the drive shaft of the piston are connected in series or in parallel using another gear, as in a general drive transmission mechanism, the length and width of the mechanism are greatly shortened. Therefore, a compact actuator A can be obtained.

[0100] like Figure 2 and Figure 3 As shown, a rotation limiting portion 6 is provided between the end of the external threaded shaft 2 and the first housing H1 so that the external threaded shaft 2 can reciprocate without rotating relative to the first housing H1. The rotation limiting portion 6 is composed of a convex portion 6a and a groove portion 6b. At the end of the external threaded shaft 2, there is at least one convex portion 6a formed in a state of protruding in the radial direction. The groove portion 6b is formed on the inner surface of the cylindrical space of the first housing H1 as a long strip along the axis X of the external threaded portion 2a for the convex portion 6a to be inserted. The groove portion 6b is formed integrally with the first housing H1, thereby preventing an increase in the number of components and making it possible to compact the first housing H1.

[0101] The rotor shaft 1 is supported at both ends by two bearings 7 with respect to the first housing H1. The bearing 7a on the side away from the cylinder S is set to have a higher load resistance than the other bearing 7b. An internal thread portion 1a is formed on the inner surface of the bearing 7a. The internal thread portion 1a is formed in a portion along the length direction of the rotor shaft 1, but by forming it at this position, the device becomes compact.

[0102] That is, considering the stroke of the piston P, when the piston P is in a neutral state, the internal thread portion 1 a is preferably screwed into the center of the external thread portion 2 a . Figure 2 In this state, the motor M is arranged on one side of the cylinder S from the center of the length direction of the external threaded portion 2a. In this structure, since the large-diameter first housing H1 accommodating the motor M and the large-diameter cylinder S are arranged adjacent to each other, the overall length of the portion having the large diameter is shortened.

[0103] Assume that, on the contrary, in the case where the end portion close to the cylinder S of the both ends of the rotor shaft 1 is formed with an internal thread portion 1a, Figure 2 The motor M is configured to be reversed left and right based on the position of the internal thread portion 1a in the motor M. That is, the motor M and the cylinder S are configured to be separated by half the length of the external thread shaft 2. By separating the first housing H1 and the cylinder S, both of which have large diameters, the overall size of the device becomes larger, which impairs compactness.

[0104] In either case, the overall length of the device is the same, but the overall compactness will vary greatly depending on how the large diameter portion is arranged. Figure 2 The structure shown can obtain the actuator A which is excellent in mountability to the vehicle B, for example.

[0105] Furthermore, in the present structure, a ball screw 8 is used in the threaded engagement between the external thread portion 2a and the internal thread portion 1a. As a result, the relative rotation between the rotor shaft 1 and the external thread shaft 2 becomes smooth, and the movement resistance is reduced. In addition, since the external thread shaft 2 is difficult to follow the rotation of the rotor shaft 1, the sliding resistance of the external thread shaft 2 relative to the first housing H1 at the rotation limiting portion 6 is also reduced. Therefore, it is possible to obtain an actuator A with improved transmission efficiency from the rotor shaft 1 to the external thread shaft 2, excellent movement responsiveness, and less vibration and noise generation. In addition, in addition to the ball screw 8, a trapezoidal thread can also be used.

[0106] (Second Embodiment)

[0107] Figure 4 and Figure 5 1 shows an actuator A according to a second embodiment. This embodiment is an example in which a cylinder S and a piston P are provided at opposite positions to form a space across a motor M. A first cup-shaped cylinder S1 and a second cup-shaped cylinder S2 as the cylinder S are connected to a first housing H1 in which the motor M is housed.

[0108] An externally threaded shaft 2 as a drive shaft 3 is disposed through the rotor shaft 1, and a first piston P1 housed in a first cylinder S1 and a second piston P2 housed in a second cylinder S2 are mounted at both ends of the externally threaded shaft 2. The first piston P1 is connected to the externally threaded shaft 2 via a first shaft 31, and a first chamber R1 is formed by the first piston P1 and the wall of the first cylinder S1. The second piston P2 is connected to the externally threaded shaft 2 via a second shaft 32, and a second chamber R2 is formed by the second piston P2 and the wall of the second cylinder S2. The surface of the first piston P1 facing the motor M and the surface of the second piston P2 facing the motor M are open to the atmosphere. A first port p1 is provided in the first chamber R1, and a second port p2 is provided in the second chamber R2.

[0109] like Figure 4 As shown, the rotation limiting portion 6 of the external threaded shaft 2, namely the convex portion 6a and the groove portion 6b, is provided on one side of the first cylinder S1. The second housing H2 in which the rotation limiting portion 6 is incorporated is connected to the first housing H1 in which the motor M is incorporated. Furthermore, the first cylinder S1 is connected here. On the other hand, the second cylinder S2 is connected on the opposite side. The third housing H3 in which the control substrate 5 is incorporated is connected to the radially outer side of the second cylinder S2.

[0110] In this structure, the first piston P1 and the second piston P2 provided on both sides of the motor M are operated simultaneously, but the rotor M1 may only drive the externally threaded shaft 2 as the drive shaft 3 to rotate, and the mechanism will not be complicated.

[0111] The first cylinder S1 and the second cylinder S2 are cup-shaped, and the first chamber R1 or the second chamber R2 is formed only on one side of the piston P. Therefore, in order to ensure airtightness, it is sufficient to provide a piston seal SP on the outer peripheral surface of each of the first piston P1 and the second piston P2, and there is no need to provide a sliding portion that seals the first shaft 31 and the second shaft 32. Therefore, it becomes extremely easy to ensure the airtightness of the entire device, and a reasonable actuator A can be obtained.

[0112] Possibility of Industrial Application

[0113] The actuator of the present invention can be widely used as an actuator including a cylinder with a piston built therein and a motor, and the piston is reciprocated by the rotational drive of the motor.

Claims

1. An actuator comprising: An electric motor having a stator and a rotor; at least one cylinder disposed adjacent to the electric motor; and a piston mounted on the drive shaft and disposed inside the cylinder, The rotor has a hollow structure, and the drive shaft is housed inside the rotor in a state where the axes of a part of the drive shaft and a part of the rotor coincide with each other and are screwed together. The drive shaft reciprocates along the axis as the rotor rotates.

2. The actuator according to claim 1, wherein: Two spaces are provided which are formed by the cylinder and the piston.

3. The actuator according to claim 1, wherein: As the cylinder, a separate cylinder is provided, and the piston is configured to partition the interior of the cylinder into a first chamber and a second chamber. An external thread portion formed on a portion of the driving portion is threadedly engaged with an internal thread portion formed on a portion of the inner surface of the rotor. The internal thread portion is provided at an end portion of the rotor, which is located away from the cylinder, among both end portions along the axis.

4. The actuator according to claim 1, wherein: As the cylinders, the first cylinder and the second cylinder, both of which are cup-shaped, are arranged to sandwich the motor and open toward the motor. The drive shaft passes through the rotor, and a first piston housed in the first cylinder and a second piston housed in the second cylinder are connected to both ends of the drive shaft, respectively.

5. The actuator according to claim 1, wherein: The screw engagement uses a ball screw to restrict the rotation of the drive shaft around the axis.

6. The actuator according to claim 2, wherein: The two spaces are connected to chambers of two air suspension devices disposed on wheels of the vehicle, respectively.

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