Actuator

Abstract

An actuator (1) includes a motor (2) assembly, a drive coupling (113, 13, 313) assembly, and an actuator shaft (114, 14). The motor (2) assembly includes a motor housing (120, 20) having a cover (122, 22) and a base (123, 23); an electric motor (111, 11, 211, 2) including an outer stator (111, 11, 211) and an inner rotor (112, 12); and a hollow output shaft (130, 30, 330) coaxially connected to the inner rotor (112, 12) so that rotation of the inner rotor (112, 12) causes corresponding rotation of the hollow output shaft (130, 30, 330). The drive coupling (113, 13, 313) assembly includes a drive coupling housing (115, 15, 315) containing the drive coupling (113, 13, 313), wherein the drive coupling (113, 13, 313) engages a hollow output shaft (130, 30, 330) such that rotation of the hollow output shaft (130, 30, 330) causes corresponding rotation of the drive coupling (113, 13, 313). An actuator shaft (114, 14) extends through the hollow output shaft (130, 30, 330) and the inner rotor (112, 12) and engages the drive coupling (113, 13, 313) such that rotation of the drive coupling (113, 13, 313) through the hollow output shaft (130, 30, 330) causes axial movement of the actuator shaft (114, 14).

Description

Technical Field

[0001] The present invention relates to actuators such as valve actuators, and in particular to electric motor operated valve actuators. The present invention also relates to a system comprising a valve and an actuator, and an electric motor for use in such an actuator or system. Background Art

[0002] Electric valve actuators are control devices widely used in many industries, including the process control industry, to manage the flow of fluids and gases. Such actuators use electric motors to convert electrical energy into mechanical motion to operate fluid control valves.

[0003] When electric valve actuators are used to operate heavy industrial valves, it may be necessary to apply high torque to the valve. Since an electric motor that can directly provide sufficient torque for such operations may be very large, an electric motor with lower torque can be used with a gear drive system (usually a worm gear) that is configured to increase torque while reducing output speed. The use of such gears to transmit power from the electric motor to the valve increases mechanical complexity because more moving parts are involved. As a result, geared electric valve actuators may suffer from reduced efficiency due to friction losses, reduced accuracy due to gear clearance, wear / lubrication / maintenance issues, and increased noise. The drive system also takes up space in the actuator housing, resulting in a larger overall size.

[0004] Therefore, there is a need for a valve actuator including an electric motor that can be compactly packaged within a valve actuator housing and that can provide sufficient torque to operate heavy industrial valves without a large gear train.

[0005] EP 3026373 A1 (TGK CO), EP 0364308 A2 (SNEDDON) and GB 862324 A (ATOMICENERGY AUTHORITY UK) disclose motor operated valve actuators. Summary of the invention

[0006] One aspect of the present invention provides an actuator comprising a motor assembly, a drive coupling assembly, and an actuator shaft. The motor assembly comprises a motor housing having a cover and a base; an electric motor, within the motor housing, comprising an outer stator and an inner rotor; and a hollow output shaft coaxially connected to the inner rotor such that rotation of the inner rotor causes corresponding rotation of the hollow output shaft. The drive coupling assembly comprises a drive coupling housing containing a drive coupling, wherein the drive coupling engages the hollow output shaft such that rotation of the hollow output shaft causes corresponding rotation of the drive coupling; and wherein the drive coupling assembly is connected to the base of the motor housing. The actuator shaft engages the drive coupling such that rotation of the drive coupling through the hollow output shaft causes the actuator shaft to move.

[0007] The drive coupling assembly can be external to the motor housing. For example, the electric motor can be on one side of the motor housing base (inside the motor housing) and the drive coupling assembly can be on the other side of the motor housing base (outside the motor housing).

[0008] The connection between the drive coupling assembly and the motor housing may be releasable. For example, the drive coupling assembly and the motor housing may be connected to each other by at least one removable fixing element (eg, a bolt).

[0009] The hollow output shaft may be directly engaged with the drive coupling or may be engaged with the drive coupling through a gear arrangement. The gear arrangement may include a gear box, and the drive coupling assembly may be connected to the base of the motor housing through the gear box. The gear box may include a planetary gear arrangement including a sun gear and planetary gears mounted on a rotating gear carrier, wherein the sun gear is hollow and coaxial with the hollow output shaft and the actuator shaft, and the rotation of the hollow output shaft may be transmitted to the actuator shaft through the rotation of the rotating gear carrier. The planetary gear arrangement may be a multi-stage planetary gear arrangement.

[0010] The drive coupling may include an anti-backdrive coupling.

[0011] The actuator shaft may extend through the hollow output shaft and the inner rotor. In this case, rotation of the drive coupling causes the actuator shaft to move axially.

[0012] The rotation of the inner rotor can be transmitted to the drive coupling by engagement of at least one axially extending lug and at least one corresponding notch formed in corresponding portions of the hollow output shaft and the drive coupling. This engagement allows the motor assembly to be easily removed from the drive coupling assembly and the actuator shaft (e.g., for maintenance) because once the connection between the drive coupling assembly and the motor housing is released, the lug and notch can be disengaged by simply moving the motor assembly axially away from the drive coupling assembly. Furthermore, this can be accomplished without affecting the position of the actuator shaft because the actuator shaft and the motor assembly are only indirectly connected via the drive coupling assembly.

[0013] A hollow output shaft may be mounted within and extend through the inner rotor.

[0014] The cover and base of the motor housing may define an inner tube and the inner rotor may be mounted on bearings on the tube.

[0015] The cover and the base of the motor housing may be fixed in an interval arrangement by a positioning member extending between the cover and the peripheral area of ​​the base of the motor housing. In this case, bearings may be provided in the cover and the base of the motor housing to mount the inner rotor for rotation. In addition, the upper portion of the hollow output shaft may have an outer flange, and the hollow output shaft may be mounted in the inner rotor through the flange, and the upper surface of the flange engages with the bearing of the upper portion of the inner rotor.

[0016] A cover of the motor housing may extend from the base of the motor housing around the stator and the rotor.

[0017] The cover of the motor housing may have an open area, and the motor housing further includes a removable cover that can be fixed to an outer surface of the cover of the motor housing to close the open area.

[0018] The actuator may include an actuator housing in which the actuator components are fixed and defines a motor housing, on which the outer stator and inner rotor are directly mounted. Optionally, the actuator housing may define a drive coupling housing, and, for example, the actuator housing may surround the motor assembly.

[0019] The actuator may include a valve housing in which the valve member is secured, the valve housing defining a drive coupling housing.

[0020] The drive coupling may be an internally threaded drive nut, a ball screw nut or a roller screw nut that engages with threads on the exterior of the actuator shaft. The drive coupling may include an anti-backdrive coupling.

[0021] The outer stator, the inner rotor, the hollow output shaft, the drive coupling and the actuator shaft may be coaxially arranged. For example, the inner rotor, the hollow output shaft and the drive coupling may have a common axis of rotation.

[0022] The outer stator may include a stator body having a series of inwardly projecting teeth, with windings arranged around each tooth. In this case, the sides of the stator teeth may be substantially straight along the entire length of the tooth. Electric motors having this feature may also be used for other applications.

[0023] The outer stator may be secured in place by engagement with the cover and base of the motor housing.

[0024] The drive coupling housing may be fixed relative to the lower surface of the lower portion.The actuator may further include a bearing assembly located between the drive coupling and the drive coupling housing so as to allow the drive coupling to rotate relative to the drive coupling housing.

[0025] Another aspect of the invention provides a system comprising an actuator according to the first aspect and a valve connected to the actuator.

[0026] The actuator shaft can be connected directly to the valve.

[0027] Another aspect of the invention provides a system comprising an actuator according to the first aspect, wherein the actuator shaft is a threaded valve stem comprising the valve at its lower end.

[0028] Another aspect of the invention provides an electric motor for use in an actuator or system as defined above, comprising an outer stator and an inner rotor, wherein the outer stator comprises a stator body having a series of inwardly projecting teeth, a winding being arranged around each tooth; and wherein the sides of the stator teeth are substantially straight along the entire length of the tooth.

[0029] Further variations are disclosed in the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A partial cross-sectional view of an electric valve actuator is shown.

[0031] Figure 2 An exploded view of the actuation system is shown.

[0032] Figure 3 Shows Figure 2 A cross-sectional view of the assembled actuation system shown in FIG.

[0033] Figure 4 A cross-sectional view of a second actuation system is shown.

[0034] Figure 5 A cross-sectional perspective view of a second actuation system is shown at an angle.

[0035] Figure 6 The exterior of the second actuation system is shown.

[0036] Figure 7A cross-sectional view of a second actuation system is shown in a partially disassembled configuration.

[0037] Figure 8 The exterior of the second actuation system is shown in a partially disassembled configuration.

[0038] Fig. 9 Yet another valve actuation system comprising a planetary gear arrangement is shown.

[0039] Fig.10 A cross-sectional view of an electric motor designed for use with an actuation system is shown. DETAILED DESCRIPTION

[0040] Figure 1 A partial cross-sectional view of an electric valve actuator 1 is shown, which includes an electric motor 2 (e.g., a brushless DC electric motor or an AC induction motor) for electric operation of a valve (not shown); a transmission system 3, which connects the motor 2 to the valve (e.g., through a worm gear drive); a terminal box 4, which is used for power and data signal connections; an actuator control unit 5, which is used to process command signals and actuator signals to control actuator operation; a position control unit 6, which is connected to the transmission system; and a display 7 and local controls 8, which are used to locally view and configure the operation of the actuator 1. A hand wheel 8 for manually operating the valve in emergency situations (e.g., when the electric motor 2 fails or there is no main power available) may also be provided.

[0041] Figure 2 An exploded view of an actuation system 10 is shown, which can be used to replace the above-mentioned Figure 1 The electric motor 2 and transmission 3 are described. The actuation system 10 can be used to provide a compact electric valve actuator that can provide sufficient torque to operate heavy industrial valves without the need for a large transmission system / gears. Figure 2 is a simplified illustration of the actuation system 10 with components such as electronics, PCBs, and wiring omitted for clarity.

[0042] The actuation system 10 includes an electric motor, such as a brushless DC motor or a switched reluctance motor, including an outer stator 11 and an inner rotor 12; a motor housing 20; a hollow output shaft 30; a drive coupling 13 contained within a drive coupling housing 15; and an actuator shaft 14. Figure 3 As shown, all of these components are arranged on a common central axis, which is also the rotation axis of the inner rotor 12 , the hollow output shaft 30 and the drive coupling 13 .

[0043] The inner rotor 12 is hollow and has a central, axially extending bore. Figure 3As shown, the inner rotor 12 is substantially contained within the outer stator 11 such that the inner surface of the stator 11 surrounds the outer surface of the inner rotor 12 .

[0044] The outer stator 11 and the inner rotor 12 are both mounted in a generally circular motor housing 20, through which the system 10 can be located in the actuator housing. The motor housing 20 includes a base 23, a cover 22 and a hood 21, each having a central hole. The drive coupling housing 15 is located on the lower surface of the base 23 (i.e., the outer surface of the base 23 / the surface of the base 23 outside the motor enclosure of the motor housing 20). The cover 22 is fixed to the base 23 in an interval arrangement by a positioning member 25 between the cover 22 and the peripheral area of ​​the base 23, so that the stator 11 and the rotor 12 are fixed in the appropriate position in the motor housing 20. The cover 22 has an opening area 26, and the hood 21 is removably fixed to the upper surface of the cover 22 (i.e., the outer surface of the cover 22 / the surface of the cover 22 outside the motor enclosure of the motor housing 20) so as to close the opening area 26.

[0045] The locating member 25 may include a threaded rod and a nut, the threaded rod extending through clearance counterbores in the cover 22 and base 23 of the motor housing.

[0046] The shroud 21 and / or cover 22 of the motor housing 20 may provide a means of attaching components, such as electronic components and cables, to the motor housing 20 .

[0047] Bearings 27 , 28 are provided in the cover 22 and the base 23 of the motor housing 20 to enable the inner rotor 12 to rotate in the motor housing 20 .

[0048] Alternatively, the electric motors 11, 12 may be mounted directly to the actuator housing, rather than being mounted in the motor housing 20 described above, in which case bearings will be provided in the actuator housing to enable the inner rotor 12 to rotate in the actuator housing. In addition, the stator 11 will be fixed to the actuator housing by means such as heat shrinking, bonding or mechanical keying to prevent the stator 11 from rotating in the actuator housing.

[0049] The hollow output shaft 30 includes a hollow cylinder having an outer flange 31 radially protruding from the outer surface at its upper end region. The hollow output shaft 30 is mounted in the inner rotor 12 by a fixing device (e.g., bolts) between the flange 31 and the inner rotor 12 so that the hollow output shaft 30 rotates together with the inner rotor 12. The upper surface of the flange 31 engages with the bearing 27 in the upper part of the housing (e.g., the upper part 22 or the upper part of the actuator housing). The lower end of the rotor 12 engages with the bearing 28 in the lower part of the housing (e.g., the base 23 or the lower part of the actuator housing). The lower end of the shaft 30 passes through the central hole of the lower part of the housing (e.g., the base 23 or the lower part of the actuator housing).

[0050] The drive coupling housing 15 is fixed to the lower part of the motor housing 20 (i.e., the base 23) or the actuator housing around the central hole. The drive coupling 13 is mounted for rotation in the bearing 16 in the drive coupling housing 15. The hollow output shaft 30 has axially extending lugs 32a, 32b at one end (i.e., its lower end). The lugs 32a, 32b are engaged in corresponding cutouts 33a, 33b provided at one end of the drive coupling 13, so that the drive coupling 13 can rotate with the hollow output shaft 30 in the bearing 16. Alternatively, the axially extending lugs may be provided at one end of the drive coupling 13 and the corresponding cutouts may be provided at one end of the hollow output shaft 30. In this way, the rotation of the inner rotor 12 is transmitted to the drive coupling 13 by the engagement of the lugs and cutouts formed in the corresponding parts of the hollow output shaft 30 and the drive coupling 13.

[0051] The drive coupling 13 includes a drive nut having an internally threaded hole. The valve actuator shaft 14 extends through the hollow output shaft 30 and the drive coupling 13 and has an external thread that engages with the internal thread of the drive coupling 13. This engagement causes the rotation of the drive coupling 13 relative to the actuator shaft 14 to be converted into a linear motion of the shaft 14. Therefore, actuation of the rotor 12 causes the actuator shaft 14 to move axially. If a valve is provided at one end (i.e., the lower end) of the actuator shaft 14 (for example, where the actuator shaft is directly connected to the valve, or where the actuator shaft is a threaded valve stem that includes a valve at its lower end), the axial movement of the actuator shaft 14 in turn operates the valve, causing the electric motors 11, 12 to act directly on the valve. The pitch of the threads on the drive coupling and the shaft 14 determines the degree of axial movement of the shaft per rotation of the rotor 12.

[0052] As an alternative to the drive nut described above, the drive coupling 13 may be a recirculating ball screw nut or a roller screw nut. Furthermore, the actuation system 10 may include an anti-backdrive coupling.

[0053] and Figure 1 As with the actuator, a hand wheel (not shown) may be provided for manually operating the valve in emergency situations (e.g. when the electric motor fails or when no mains power is available).

[0054] Figure 4-8 An optional second actuation system 100 is shown, which may also be used in place of the above description of Figure 2-3 Describe the system. Figure 4-8 is a simplified illustration of the second actuation system 100 , with components such as electronics, PCBs, and wires omitted for clarity.

[0055] The second actuation system 100 includes an electric motor including an outer stator 111 and an inner rotor 112; a motor housing 120; a hollow output shaft 130; a drive coupling 113 contained within a drive coupling housing 115; and an actuator shaft 114, all of which are generally in the same Figure 2-3 The system shown in FIG.

[0056] In the second system, a cover 122 extends from a base 123 of the motor housing around the stator 111 and the rotor 112, defining an inner tube 122a so that the stator 111 and the rotor 112 are fixed in place within the motor housing 120. The inner rotor 112 is mounted on bearings 127, 128 on the inner tube 122a to enable the inner rotor 112 to rotate within the motor housing 120. The inner rotor 112 is also mounted on a seal 124 on the inner tube 122a and a seal 129 in a central hole in a lower portion of the housing (e.g., a lower portion of the base 123 or the actuator housing) so that components of the electric motors 111, 112 (e.g., the stator windings of the electric motors, the motor drive electronics, and the IGBT modules) are sealed, for example, from a potentially explosive environment. In addition, the cover 122 may have an opening area, and the motor housing 120 may further include a cover that is removably fixed to an upper surface of the cover 122 (i.e., an outer surface of the cover 122 / a surface of the cover 122 outside the motor enclosure of the motor housing 120) to close the opening area 26. At least one seal may be provided between the cover and the opening area.

[0057] The cover 122 and / or shroud of the motor housing 120 may provide a means of attaching components, such as electronic components and cables, to the motor housing 120 .

[0058] Similar to Figure 2-3 In the system shown in FIG. 1 , a hollow output shaft 130 has axially extending lugs 132a, 132b at one end (i.e., its lower end / end extending through a central hole in a housing lower portion (e.g., a base 123 or an actuator housing lower portion)) that engage corresponding notches 133a, 133b (see FIG. 1 ) provided at one end of the drive coupling. Figure 8 )middle.

[0059] In the above-mentioned system, the drive coupling assembly is connected to the base of the motor housing. Since the electric motor is located on one side of the motor housing base (i.e., on the inner side of the motor housing), and the drive coupling assembly is located on the other side of the base of the motor housing (i.e., on the outer side of the motor housing), the drive coupling assembly is also outside the motor housing. When the drive coupling assembly and the motor housing are connected to each other by at least one removable fixing element, the connection between the drive coupling assembly and the motor housing can be released. For example, in the compact actuation systems 10 and 100, the removable fixing elements include bolts 41, 141, which extend through clearance holes provided on flanges 42, 142 of the drive coupling housing 15, 115 and engage threaded holes in the base 23, 123 of the motor housing.

[0060] The engagement between the lugs and corresponding cutouts formed in the corresponding portions of the drive coupling (i.e., drive coupling 13 or drive coupling 113) and the hollow output shaft (i.e., shaft 30 or shaft 130) allows the motor assembly to be easily removed from the drive coupling assembly and the actuator shaft (e.g., for maintenance), such as Figure 7 and Figure 8 As shown, once the connection between the drive coupling assembly and the motor housing is released, the lug and notch can be disengaged by simply moving the motor assembly axially away from the drive coupling assembly. Furthermore, this can be done without affecting the position of the actuator shaft (i.e., shaft 14 or shaft 114) because the actuator shaft is indirectly connected to the motor assembly via the drive coupling assembly (i.e., the engagement between the lug and notch). If a valve is provided at one end of the actuator shaft (i.e., the lower end of the actuator shaft), this means that the motor assembly can be safely removed for repair or replacement without having to take the valve out of service.

[0061] The drive coupling housing (i.e., drive coupling housing 15 or drive coupling housing 115) may be connected to the valve housing, in which the valve components are fixed. Alternatively, the valve housing may define the drive coupling housing (i.e., drive coupling housing 15 or drive coupling housing 115).

[0062] Where the electric motor used with the compact actuation systems 10 and 100 is a brushless DC motor, drive electronics and IGBT (insulated gate bipolar transistor) modules may be used to switch current to the motor windings using pulse width modulation (PWM) control. The IGBT modules may be radially arranged around the motor end windings and electrically connected to the motor end winding terminations.

[0063] (or similar materials known in the art) can be used to substantially or completely encapsulate the components of the electric motor used with the compact actuation systems 10 and 100 (e.g., the stator windings of the electric motor, the motor drive electronics, and the IGBT modules at the ends of the motor end windings). For example, this can be done by using the motor housing 120 as a mold and placing the molten (or similar material) is poured into an opening of the motor housing 120 (e.g., an opening disposed between the inner rotor 112 and the base of the motor housing 123) and allowed to (or similar materials) to achieve solidification. The components of the electric motor are encapsulated in (or similar materials), the compact actuation system (i.e., the compact actuation system 10 or 100) can be made explosion-proof because (or similar materials) can be used as a barrier between a potentially explosive atmosphere and packaged components that could be a source of spark ignition (such as motor windings and drive electronics).

[0064] exist Figure 2-8 In the embodiment shown, the hollow output shaft 30, 130 directly engages the drive coupling 13, 113. In this case, the maximum torque that can be applied to the actuator shaft will depend on the size of the motor. For high torque applications, the motor size required for direct drive may be too large to be practical. In this case, a gear device can be inserted between the motor and the drive coupling. Fig. 9 One embodiment of the device is shown, which includes a gearbox 350 that houses a planetary gear arrangement including a sun gear 352 and a series of planet gears 354. The sun gear 352 is hollow and is mounted concentrically in the drive coupling housing 315 together with the hollow output shaft 330 and the drive coupling 313 (and therefore together with the actuator shaft, not shown). The sun gear 352 is mounted on a sun gear carrier 356, which is mounted in a bearing in the upper part of the gearbox 350 and has a cutout 333 to receive the lug 332 on the end of the hollow output shaft 330. The planet gears 354 are mounted on a planet gear carrier 358, which rotates with the planet gears 354 and transmits the rotation to the drive coupling 313 through the drive lug 360. The motor and gearbox can be separate units so that the motor can be removed from the gearbox. Similarly, the gearbox can be removed from the drive coupling, leaving the valve in place, as described above.

[0065] Although Fig. 9 A single-stage planetary gear system is shown, but a multi-stage planetary gear system may also be used. For example, a planet gear carrier may be connected to the hollow sun gear of a subsequent planetary gear stage. Two or more subsequent stages may be used.

[0066] As an alternative to the planetary gearbox disclosed above, the gearbox may be of the spur gear type or bevel gear type with a hollow output shaft to allow the actuator shaft to rise through the gearbox output gear. In the case of using such a spur gear or bevel gear gearbox, the actuator shaft may not rise through the hollow output shaft of the motor because the motor rotation axis may no longer be concentric with the gearbox output axis.

[0067] The direct-acting motor arrangement described above, or a direct-acting motor coupled to a gearbox, may be used in conjunction with an anti-backdrive coupling to operate a quarter-turn valve, such as a ball valve or butterfly valve. This type of quarter-turn valve does not have a rising valve stem or actuator shaft. The anti-backdrive coupling may remain attached to the valve to maintain the valve position while the motor is removed for maintenance or replacement in a manner similar to that described above.

[0068] Fig.10 A cross-sectional view of an electric motor 211, 212 that can be used with the compact actuation systems 10 and 100 described above is shown. The stator 211 consists of an outer stator body 213 having a series of inwardly projecting stator teeth 214. The sides of the stator teeth 214 are substantially straight along the entire length of each tooth. It has previously been proposed to provide a lateral extension or tip at the end of each tooth (i.e., the side extends laterally toward the adjacent tooth at the end). This is done to reduce the high flux density levels in the stator that cause excessive heat generation in use. In fact, the outer stator 211 has no stator tooth tips. In applications such as the valve actuator described above, the motor can have a low rotational output speed so that iron losses and heating are not a problem. In addition, the motor will be operated, for example, at a 25% duty cycle rather than rated for continuous operation, and the size of the outer stator 211 can be relatively large relative to the motor output power, so it has a large thermal mass to help dissipate any generated heat.

[0069] The absence of stator tooth tips on the outer stator 211 can significantly simplify the coil assembly process, as pre-wound concentrated "coil groups" can be assembled onto the stator 211 by simply sliding them onto the stator teeth, rather than having to wind the coils onto the stator 211 in situ. The process of maintaining such a stator 211 is also simplified, as the "coil groups" can be easily removed from the stator teeth by simply sliding them away from the stator teeth. In addition, it simplifies the design of the outer stator 211, making it easier to manufacture. Motors having these features, such as brushless DC motors or switched reluctance motors, can also be used in applications other than the valve actuators disclosed above. The present invention extends to such uses.

[0070] Further modifications may be made within the scope of the invention.

Claims

1. An actuator, comprising: Motor assembly, comprising: Motor housing, including: Cover, and Pedestal; An electric motor, within the motor housing, comprising: outer stator, and an inner rotor; and a hollow output shaft coaxially connected to the inner rotor such that rotation of the inner rotor causes corresponding rotation of the hollow output shaft; a drive coupling assembly connected to a base of the motor housing, the drive coupling assembly comprising a drive coupling housing containing a drive coupling, wherein the drive coupling engages the hollow output shaft such that rotation of the hollow output shaft causes corresponding rotation of the drive coupling; and an actuator shaft engaging the drive coupling such that rotation of the drive coupling through the hollow output shaft causes the actuator shaft to move, wherein the electric motor is located on one side of a base within the motor housing and the drive coupling assembly is located on another side of the base outside the motor housing; the connection between the drive coupling assembly and the motor housing being releasable such that the motor housing can be removed from and reattached to the drive coupling assembly; The actuator shaft extends through the hollow output shaft and the inner rotor, wherein rotation of the drive coupling causes the actuator shaft to move axially; and Rotation of the inner rotor is transmitted to the drive coupling through engagement of at least one axially extending lug and at least one corresponding notch formed in corresponding portions of the hollow output shaft and the drive coupling.

2. The actuator according to claim 1, wherein: The hollow output shaft directly engages the drive coupling.

3. The actuator according to claim 1, wherein: The hollow output shaft engages the drive coupling via a gear arrangement.

4. The actuator according to claim 3, wherein: The gear arrangement includes a gear box, and the drive coupling assembly is connected to a base of the motor housing through the gear box.

5. The actuator according to claim 4, wherein: The gearbox includes a planetary gear device, which includes a sun gear and planet gears mounted on a rotating gear carrier, wherein the sun gear is hollow and coaxial with the hollow output shaft and the actuator shaft, and the rotation of the hollow output shaft is transmitted to the actuator shaft through the rotation of the rotating gear carrier.

6. The actuator according to claim 5, wherein: The planetary gear device is a multi-stage planetary gear device.

7. The actuator according to claim 4, wherein: The drive coupling comprises an anti-backdrive coupling.

8. The actuator according to claim 1, wherein: A cover of the motor housing extends from a base of the motor housing around the stator and rotor.

9. The actuator according to claim 8, wherein: The cover of the motor housing defines an inner tube and the inner rotor is mounted on bearings on the tube.

10. The actuator according to any one of claims 1 to 9, wherein: The cover and base of the motor housing are secured in a spaced arrangement by a locating member extending between the cover and a peripheral region of the base of the motor housing.

11. The actuator according to claim 10, wherein: Bearings are provided in the cover and base of the motor housing to mount the inner rotor for rotation.

12. The actuator according to claim 11, wherein: The hollow output shaft has an outer flange at an upper region thereof, the hollow output shaft is mounted in the inner rotor via the flange, and an upper surface of the flange engages with a bearing in an upper portion of the housing.

13. The actuator according to claim 10, wherein: The hollow output shaft is mounted within the inner rotor and extends through the inner rotor.

14. The actuator according to any one of claims 1 to 9, wherein: The cover of the motor housing has an open area, and the motor housing further includes a removable cover that can be fixed to an outer surface of the cover of the motor housing to close the open area.

15. The actuator according to any one of claims 1 to 9, wherein: The outer stator comprises a stator body having a series of inwardly projecting teeth, around each of which a winding is arranged.

16. The actuator of claim 15, wherein: The sides of the stator teeth are substantially straight along the entire length of the teeth.

17. A system for an actuator, comprising: The actuator according to any one of claims 1 to 16, and A valve is connected to the actuator.

18. The system of claim 17, wherein: The actuator shaft is directly connected to the valve.

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