Abstract:
The invention relates to an actuating device, especially for use in a throttle device, comprising a turning spindle rotatably mounted in the device housing. Said turning spindle is functionally linked via a transmission device with a drive device to displace an actuating element that is linked with the turning spindle. The aim of the invention is to provide an improved actuating device that is secure and has a simple design and that can be telecontrolled in a simple manner without major maintenance work, without losses of functionality of the actuating device and at reduced costs. To this end, the actuating device comprises at least two separately or synchronously operated motors and the transmission device has at least one self-locking transmission unit, said transmission unit being functionally linked with the two motors for turning the turning spindle.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to an actuating device, especially for use in a throttle device, comprising a turning spindle rotatably mounted in the device housing, the turning spindle being functionally connected via a transmission device with a drive device to displace an actuating element connected with the turning spindle. 
     In practice such actuating devices are known, for instance, in the fields of maritime or terrestrial oil or gas production. The actuating device is operated either manually or hydraulically. The actuating device varies the passage of a throttle so as to reduce the pressure of, for instance, oil transported from a crude oil source. The oil exits from the crude oil source under a pressure of several hundred bar, and the corresponding throttle device reduces this pressure to less than 100 bar. 
     In an actuating device known in practice a turning spindle rotatably mounted in the device housing can be displaced in an axial direction by means of a handwheel. The turning spindle is connected with an actuating element which influences the throttling in the throttle device. Normally, a transmission device is disposed between the handwheel and the turning spindle. 
     Moreover known from practice is an actuating device whereof the turning spindle is adjusted by a hydraulically driven drive device, wherein—in this case—the turning spindle may also be designed as part of piston/cylinder unit in which a piston can be displaced inside a cylinder housing by corresponding hydraulic pressure. 
     In view of such actuating devices it should be appreciated that the same are arranged in remote and/or difficult to access regions, e.g. below the sea level. A manual actuation, therefore, involves considerable efforts, is cost-intensive and dangerous for the operator. Furthermore, the manual adjustment of the actuating device is hard to cheek, and without enough precision. A hydraulically controlled actuating device requires a plurality of hydraulic lines, corresponding connections, sealing elements, pumps and the like for forming the entire hydraulic system. The work involved is increased with each additional actuating device likewise controlled and operated via the hydraulic system. The work involved is even more increased if the actuating device is located in regions subjected to high pressures, such as below sea level. Such hydraulically controlled and operated actuating devices moreover frequently have to be checked for leakages and the like, within the scope of which the entire hydraulic system including the entirety of supply and discharge pipes, connections, pumps and the like are checked for leakages. 
     Another drawback of such hydraulic actuating devices resides in that the efforts and the expenses for the exact control of the actuating device are very high. 
     As far as the manually as well as the hydraulically operated actuating devices are concerned it finally should be noted that the same have to be provided with special safety facilities, for example, for avoiding—in connection with the throttle device—an unintended opening of the throttle and, inter alia, a pressure drop in the hydraulic system. Otherwise, the entire production system could considerably be damaged if the oil, which is subjected to a high pressure, exits without being throttled. 
     BRIEF SUMMARY OF THE PREFERRED EMBODIMENTS 
     The invention is, therefore, based on the object to improve an actuating device of the aforementioned type such that the same is secure and simple in design, and that it can be remotely controlled in a simple manner without major maintenance work and without losses of functionality of the actuating device and at reduced costs. 
     In connection with the features of the preamble of claim  1  this object is provided in that the drive device comprises at least two individually or synchronously operable electric motors and the transmission device at least one self-locking transmission unit, said transmission unit being functionally connected with the two electric motors for turning the turning spindle. 
     Due to the electrical construction of the drive device corresponding hydraulic facilities such as hydraulic lines, pumps or the like can be waived. The actuating device, especially the electric motors, are fed and controlled via an electric cable. If the electric cable is correspondingly designed, it is sensitive to pressure and temperatures. A manual actuation of the actuating device, or frequent maintenance works by maintenance staff, are no longer required. 
     The actuating device can be controlled and monitored from a station located far away, so that corresponding control facilities in the proximity of the actuating device, such as on a drilling platform or the like, are not necessary. Instead, the corresponding facilities may be located on the mainland and far away from the actuating device. 
     The drive device of the actuating device according to the invention is constructed such that the electric motors can be operated alternatively, which provides for a redundant arrangement of the drive device. If an electric motor breaks down or is insufficiently active it may be replaced by the other one. 
     According to another operating type of the drive device both electric motors can also be operated simultaneously, whereby they are synchronized in their driving activity relative to the turning spindle. Thus, higher torques can be transmitted by the drive device. 
     Separate safety measures for preventing an unintended displacement especially of the actuating element or, respectively, of the turning spindle, and thereby an unintended interference with the throttle device, are—according to the invention—no longer necessary or, respectively, feasible due to the employment of the self-locking transmission unit. The self-locking state of the transmission unit entails that the same cannot be moved even by optionally large driving torques and that the driving torque is internally blocked by proportional frictional forces. The self-locking state can be released by actuating the drive device in that said drive device transmits a corresponding release torque to the transmission unit. In view of the throttle device, normally a self-locking in the opening direction of the throttle device is sufficient. It is, however, likewise possible to adapt the transmission device to be self-locking in both moving directions. 
     For allowing an easier monitoring especially of the speed and the torque of the electric motors, and for providing highly reliable and highly efficient motors, the electric motors may be constructed as servomotors, particularly direct current servomotors. Said servomotors do normally not comprise a brush. 
     For allowing the separate, or also the synchronous operation of the electric motors, and for continuing the redundancy of the drive device towards the outside, each electric motor may be electrically connected with a separate control device. As was mentioned above, said control device may be arranged far away from the actuating device. 
     For obtaining the redundancy also for the device housing and for the corresponding connecting lines, an electric connection for each electric motor may be provided in the device housing. 
     A self-locking transmission unit can be constructed in different ways. Known are, for instance, self-locking planet gears, ratchet gears or the like. A simply structured self-locking transmission unit may be seen in a worm gear pair comprising at least a worm and a worm gear, with the worm gear being associated with the turning spindle and the worm being associated with the electric motors. 
     For simply functionally connecting the worm with the electric motors, the worm may be located on a worm shaft being functionally connected with both electric motors. In this conjunction it can be regarded as a special advantage if, for instance, the electric motors are each functionally connected with opposite shaft ends of the worm shaft. It is likewise possible that both electric motors are arranged on the same side of the worm shaft and, in the axial direction thereof, one after the other. 
     A simple drive connection in an embodiment according to the invention can be seen in that each electric motor is connected via its motor shaft with the respective shaft end in a manner secured against rotation. 
     Alternatively it is also possible that each shaft end is arranged in one of the electric motors as motor shaft in a manner secured against rotation. 
     For mounting the worm shaft in a maintenance-free manner each shaft end can be rotatably mounted by ball bearings and/or roller bearings in the device housing. 
     The worm and the worm gear moreover allow an easy gearing and a transmission of a high torque. For obtaining an even higher gearing with more reliability, high loading capacity and long service life the transmission device may moreover be provided with a ball screw formed of at least one ball nut and the turning spindle as recirculating ball screw. For allowing an even better transmission of the load by such a thread, the transmission device may comprise a roller thread formed of at least one roller nut and the turning spindle as recirculating roller spindle. 
     For being able to waive a roller recirculation in the roller thread, the roller thread may be a planetary roller thread. 
     For being able to easily accommodate the thread nut, either the ball nut or the roller nut, in the device housing, the same may be arranged in a bearing shell mounted in the device housing in a rotatable, but axially undisplaceable manner. The thread nut may be held in said bearing shell in a positive, non-positive or frictionally engaged manner. 
     For being able to transmit the driving power to the thread nut from the worm gear pair in an easy manner, an end toothing may be arranged on at least one end of the thread nut, which is engaged with a toothing of the worm gear. 
     For allowing the use of as few components as possible in this connection, and for reducing the costs, the end toothing may be formed by the worm gear, whereby the same may directly be formed on the thread nut. 
     For facilitating the fabrication in this connection, the worm gear may, however, also be formed separately and detachably especially on the thread nut. 
     Different embodiments for the worm gear and the worm are conceivable. The worm gear may, for example, be a globoid worm wheel having a substantially concavely curved toothing on its external side. A spur-toothed wheel for the worm gear is likewise conceivable. Analogously, the worm may be formed as a cylindrical worm or as enveloping worm. 
     For being able to arrange the thread nut, and correspondingly the bearing shell, in the device housing in a manner secured against load, the bearing shell may be mounted in the device housing by means of at least one axial bearing. 
     For being able to actuate the actuating device according to the invention also without any electric power supply or, if it breaks down, at least in a case of emergency, at least one electric motor may be associated with an especially manually operable actuating device. Said actuating device acts on the electric motor such that the motor shaft thereof can be turned in the desired direction. 
     An embodiment of such an emergency actuating device may comprise a pintail spring-loaded in the direction of the ready position, which can be connected with the motor shaft at its end facing the electric motor in a manner secured against rotation. In the ready position the pintail is unengaged with the motor shaft, arid only by manually actuating and pressing the pintail against the spring load is the same approximated to the motor shaft with its end and connected with the motor shaft in a manner secured against rotation. The rotation-secured connection may, for instance, take place in that the end of the motor shaft facing the pintail has a corresponding cross-section which can be grasped by said facing end of the pintail in a positive manner. 
     For being able to actuate the emergency actuating device directly manually, the pintail may be passed through a bore of an outer wall of the device housing towards the outside in a sealed manner where an actuation end is provided. This may be a handwheel or the like. For being able to protect the drive device and the transmission device in the device housing against high pressure and other negative environmental influences, the device housing may comprise a central body of metal, especially of aluminum or an aluminum alloy, in the central bore of which the thread nut is mounted and along which extends the turning spindle. The central body may have a sufficiently thick wall allowing it to withstand corresponding high pressures. For being able to substantially accommodate also the electric motors in the central body, the central body may comprise two motor openings which are open towards the outside in a radial direction, in each of which an electric motor is detachably fastened, whereby a connection opening for accommodating the worm shaft and the worm extends between the motor openings and substantially tangential to the central bore. The connection opening may be formed in that the central opening is widened in the portion of the motor openings for accommodating the worm shaft and the worm. In this case, the connection opening substantially forms a part of the central opening. 
     For being able to easily arrange the corresponding devices and particularly the transmission device in the central body, the central body can be closable with an end plate at one end in a releasable manner. 
     A simple embodiment of a central body may be seen in that the same substantially has a cylindrical shape. For being able to protect the same, and possibly additional devices arranged on the end plate, against outer influences, the central body may be arranged with its end plate in a housing shell releasably closable on one end by a cover plate. For being able, if required, to transport the actuating device with or without the throttle device a lifting journal may stand out from an external side of the cover plate. This lifting journal can be gripped by a corresponding gripping tool on a crane, an underwater vehicle or the like so that the actuating device can be transported. 
     For being able to easily determine the position of rotation of the turning spindle relative to the thread nut from a remote position, a position sensor may be arranged substantially centrally in the end plate and allocated to one end of the turning spindle. Said sensor, particularly a linear position sensor, can detect the distance between the sensor and the end of the turning spindle and transmit the same via corresponding electrical lines. 
     If the actuating device according to the invention is provided for a throttle device it may be considered favorable that the central body and/or the housing shell are detachably fastenable on a throttle housing of the throttle device, whereby they can be fixed on the throttle housing from outside by means of their fastening ends unsealed by the end plate or cover plate. 
     For fastening the central body and/or the housing shell on the throttle housing screws can, for instance, be used which are directly screwed into the throttle housing or the central body or, respectively, the housing shell. It is likewise feasible that the housing shell comprises a shoulder on its fastening end facing in a radial outward direction, which can be gripped from behind by a shoulder protruding from a fastening ring in a radial inward direction. In this case, the fastening ring is directly screwed to the throttle housing. 
     For being able to apply the actuating element of the actuating device according to the invention substantially directly in connection with the throttle device, the actuating element may protrude over the open fastening end of the central body and may be pushed in a forward direction along a throttle element bore in the throttle housing right into a throttle space, with the throttle space connecting a fluid inlet arid a fluid outlet in the throttle housing. Thus, extensions for the actuating element in the throttle housing are not necessary. It is moreover regarded as an advantage if a throttle element for varying the fluid passage in the throttle space is arranged substantially on the free end of the actuating element. In this case the actuating device according to the invention directly comprises the throttle element, and more or less forms a throttle element adjustment means varying the fluid passage between the fluid inlet and the fluid outlet in the throttle space in response to the adjustment of the throttle element, i.e. in response to the position of rotation of the turning spindle. 
     Different exemplary embodiments are conceivable for such a throttle element. For example, a perforated passage sleeve or regulating sleeve may be disposed in the throttle space, onto which a throttle sleeve may be slipped as throttle element. In response to the slip-on degree onto the passage sleeve the throttle sleeve seals the holes thereof so that more or less fluid flows from the fluid inlet via the passage sleeve to the fluid outlet. If the throttle sleeve is slipped onto the passage sleeve as far as possible, the fluid inlet is normally completely closed in the direction of the fluid outlet. 
     The perforation in the passage sleeve may be realized by radial openings formed in the case thereof in different sizes and different patterns. 
     According to another exemplary embodiment of the throttle element the same may be formed as a sealing plug variably sealing a passage bore of the fluid inlet running into the throttle space. In response to the position of rotation of the turning spindle, the sealing plug can thereby more or less be displaced by the actuating element in the direction of the fluid outlet, and correspondingly more or less covers the passage bore of the fluid inlet. A simple allocation of the actuating element and the turning spindle may be seen in that both are arranged coaxially and are releasably connected with each other at their ends facing each other. The releasable connection allows, according to need, the application of a longer or shorter actuating element with possibly differing throttle elements in respect of the actuating device. 
     It had already been pointed out above that the electric motors can be operated individually or synchronously. The synchronization of the motors may be effected, for example, mechanically. Such a mechanic synchronization, however, requires the exact observance of process tolerances. A simplified synchronization may be seen in that the electric motors are synchronized by means of software and via their control devices. 
     In order to facilitate the synchronization control in this respect, one electric motor may be connected as master and the other electric motor may be connected as slave. A master/master combination is, however, also possible, or an adjustment with one motor only in a case of emergency. 
     For electrically connecting particularly the parts contained in the central body, electrical ducts may be arranged in the end plate. 
     For being able to relatively adopt at least the interior of the housing shell to a high ambient pressure, the device housing, or particularly the space between the central body and the housing shell, can be filled with oil and compensated. The compensation in this case particularly relates to an additional supply or withdrawal of oil from the device housing, in dependence on the temperature. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Advantageous embodiments of the invention will hereinafter be explained in more detail by means of the figures shown in the drawings, wherein: 
         FIG. 1  shows a lateral view of an embodiment of an actuating device according to the invention comprising a throttle device from the side of a fluid inlet; 
         FIG. 2  shows a longitudinal section along line II-II from  FIG. 1 ; 
         FIG. 3  shows a section along line from  FIG. 1 ; 
         FIG. 4  shows a lateral view in analogy to  FIG. 1  of a second embodiment of an actuating device according to the invention, 
         FIG. 5  shows a longitudinal section along line V-V from  FIG. 4 ; 
         FIG. 6  shows a portion of a transmission device that includes a ball screw drive with a rotating ball nut and a recirculating ball screw; 
         FIG. 7  shows a portion of a transmission device that includes a roller thread drive with a rotating roller nut and a recirculating roller spindle; and 
         FIG. 8  shows a portion of a transmission device that includes a thread nut drive with a rotating thread nut and a threaded screw. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a lateral view of an embodiment of an actuating device  1  according to the invention with a connected throttle device  2  from the side of a fluid inlet  59 . The actuating device  1  is detachably fastened to a throttle housing  51  by means of a fastening ring  55  and a plurality of studs  71 . 
     A corresponding device housing  3  of the actuating device  1  is tightly and releasably sealed by a cover plate  45  on its side facing away from the throttle housing  51 . Two electrical connections  13  and  14  are provided in the cover plate  45 , which are connected with remotely disposed control facilities  1 ,  12  by means of electrical connecting lines. 
     A lifting journal  48  protrudes from an outer side  47  of the cover plate  45  by means of which at least the actuating device  1  can be removed from or approximated to the actuating device  2  by a corresponding lifting tool such as a crane, a grappler or the like. 
       FIG. 2  shows a section along line II-II from  FIG. 1 . 
     The throttle device  2  comprises in its throttle housing  51  at least one fluid inlet  59  and one fluid outlet  60 . If required, also several fluid outlets may be provided. A throttle space  58  is located between the fluid inlet  59  and the fluid outlet  60 , in which a passage sleeve  63  having a number of passage openings  85  is arranged. Opposite the fluid outlet  60  extends a throttle element bore  57  in the throttle housing  51 , in which a throttle element  62  is mounted so as to be displaceable in an axial direction. 
       FIG. 2  shows two extreme positions of the throttle element  62  formed as throttle sleeve  64 . In the position of the throttle sleeve  64  shown in the lower half of  FIG. 2  the same is withdrawn from the passage sleeve  63  as much as possible, so that all passage openings  85  are opened relative to the throttle space  58 . In the position of the throttle sleeve  64  shown in the upper half of  FIG. 2  the same is slipped onto the passage sleeve  63  as far as possible, so that—in this position—all passage openings  85  are covered and a communication between the fluid inlet  59  and the fluid outlet  60  is interrupted. 
     The throttle element  62  is detachably fastened at the free end  61  of an actuating element  6 . The actuating element  6  extends along the throttle element bore  57  to a turning spindle  4 . Ends  67 ,  68  of the turning spindle  4  and the actuating element  6  facing each other are releasably connected with each other by means of a screw  79  (also see  FIG. 5 ). An intermediate sleeve  86  is arranged in the portion of the throttle element bore  57 , through which the actuating element  6  is passed in a tight manner and in which the same is passed so as to be displaceable in an axial direction. On its side of the intermediate sleeve  86  facing the throttle space  58  the same is provided with an accommodation opening for the throttle element  62 . 
     Via its device housing  3  the actuating device  1  is detachably fastened to the throttle housing  51  on the side of the outwardly running throttle element bore  57 . The device housing  3  is formed of a central body  37  and a housing shell  46  enclosing the same. The housing shell  46  substantially is a hollow cylinder being tightly sealed by the cover plate  45  on one of its ends  44 . The connection between the cover plate and the housing shell is accomplished by corresponding studs. On its fastening end  53  facing the throttle housing  51  the housing shell  46  comprises a radially outwardly protruding shoulder  54 . In the fastening position of the actuating device  1  shown in  FIG. 2  said shoulder  54  is gripped from behind by a shoulder  56  protruding radially inwardly from the fastening ring  55 . The fastening ring  55  is detachably fastened to the throttle housing  51  by a plurality of studs  71  (also see  FIG. 1 ). 
     For correctly aligning the device housing  3  relative to the throttle housing  51  a number of positioning pins  83  are provided, which protrude from the fastening end  53  at least of the housing shell  46  in the direction of the throttle housing  51 . 
     A substantially, likewise cylindrically shaped central body  37  is disposed inside the housing shell  46 , which comprises a central bore  38  approximately in the center thereof and a fastening end  52  facing the throttle housing  51 . In the fastening state of the actuating device  1  shown in  FIG. 2  said bore  38  communicates with the throttle element bore  57 , and the turning spindle  4  can be displaced along said central bore  38  in a direction coaxial to the actuating element  6 . The displacement of the turning spindle  4  is accomplished by rotating a thread nut  25  in which the turning spindle is rotatably mounted as recirculating ball screw or recirculating roller spindle. The turning spindle  4  and the thread nut (ball nut or roller nut) form a part of a transmission device  7 , via which the actuating element  6  is functionally connected, for adjustment purposes, with a drive device  5  along the throttle element bore  57 . 
     The thread nut  25  is held in a bearing sleeve  26  in manner secured against rotation. The bearing sleeve  25  is rotatable via the axial bearing  29 , but is held in an undisplaceable manner in the axial direction of the central bore  38 . The axial fixation of the bearing sleeve  26  is effected by a threaded ring  80  (also see  FIG. 5 ). 
     At one end  27  of the thread nut  25  facing the actuating element  6  an outer toothing  28  is arranged, which is formed by a worm gear  17  detachably fastened with the thread nut  25  by means of a stud  82 . The worm gear  17  forms part of a worm gear pair  15  and engages with its toothing  28  a corresponding outer toothing of a worm  16  as additional part of the worm gear pair  15  (also see  FIG. 3 ). 
     A position sensor  49  is allocated to an end  50  of the turning spindle  4  facing away from the actuating element  6 . Said sensor  49  is arranged approximately in the center of an end plate  43 . Said end plate  43  is detachably fastened at the end  42  of the central body  37  by means of a number of screws. The end plate  43  thereby closes the central bore  38  in the direction of the cover plate  45 . The position sensor  49  is enclosed by a hood  87  being detachably fastened on one outer side of the end plate  43  and protruding into a corresponding recess on an inner side of the cover plate  45 . An electrical duct  69  is arranged in the end plate  43  in the portion of the hood  87  and is enclosed by the latter. 
       FIG. 3  illustrates a section along line III-III from  FIG. 2  or also III-III from  FIG. 5 . 
     Identical parts in  FIG. 3 , and also in the other figures, are always provided with identical reference numbers and will partially be described only in connection with the figure. 
     Fastening ring  55 , housing shell  46  and central body  37  are arranged concentrically, whereby the bearing sleeve  26 , the thread nut  25  and the turning spindle  4  are likewise concentrically arranged in the central bore  38  of the central body  37 . 
     The worm gear  17  in the exemplary embodiment according to the invention is formed by a globoid worm wheel, the outer toothing of which is engaged by a corresponding outer toothing of a cylindrical worm  16 . The worm  16  is arranged as an additional part of the worm gear pair  15  on a worm shaft  18 . The worm  16  and the worm gear  17  form a transmission unit  10  as part of the transmission device  7 —also see turning spindle  4  and thread nut  25 —whereby said transmission unit  10  forms a self-locking transmission unit. 
     By means of its two shaft ends  19 ,  20  the worm shaft  18  is releasably connected with electric motors  8 ,  9  forming a drive device  5  of the actuating device  1 . The electric motors  8 ,  9  are servomotors, especially direct current servomotors. The shaft ends  19 ,  20  form, according to one embodiment, the corresponding motor shafts  21 ,  22 . The free ends of the motor shafts  21 ,  22  protruding in the electric motors  8 ,  9  are held by nuts. 
     The electric motors  8 ,  9  are arranged in motor openings  39 ,  40  formed in the central body  37  and adapted to be open towards the outside. The motor openings  39 ,  40  are substantially arranged at both sides of the central bore  38  and outwardly offset to the same in a radial direction. A connection opening  41  is provided between the motor openings  39 ,  40  which extends approximately tangentially to the central bore  38 . 
     As can be seen in  FIG. 2  the connection opening  41  is formed radially outwardly by an expansion in the central bore  38 . 
     The worm shaft  18  is, in the portion of its shaft ends  19 ,  20  and on the side of the electric motor  9 , rotatably mounted by a ball bearing  23 , and on the side of the electric motor  8  by a roller bearing  24 . The electric motors  8 ,  9  are detachably fastened by screws or the like in the motor openings  39 ,  40 . 
     In the section according to  FIG. 3  studs  72  can be recognized in the central body  37 , which extend—according to FIG.  2 —from the end plate  43  right into the throttle housing  51  for releasably fastening the central body  37  to the throttle device  2 . 
     On the side of the electric motor  9  an emergency actuating device  30  may be arranged optionally. Said device  30  is substantially formed by a pintail  32  pushed into the ready position  31  shown in  FIG. 3  by means of a spring element. In the ready position  31  the pintail  32  is not engaged with the motor shaft  20  of the electric motor  9 . The pintail  32  is guided in a bore  34  through an outer wall  35  of the housing shell  46  in a sealed manner. A receptacle  88  for the displaceable and rotatable accommodation of the pintail  32  is disposed in said bore. Towards the outside a housing  74  is slipped onto the receptacle  88 , which encloses the pintail  32  at its outwardly protruding actuating end  36 . A bore  75  for compensating the pressure is provided in the housing  74 . 
     An end  33  of the pintail  32  facing the motor shaft is provided with pins  77  or other facilities which accommodate a correspondingly formed end of the motor shaft  22  in a positive manner or, respectively, which are brought into engagement with a blank  76  fastened at this end in a manner secured against rotation. 
       FIG. 4  shows a second exemplary embodiment of the actuating device  1  according to the invention. This substantially differs from the above-described embodiment by a connecting plate  84  fastened to the device housing  3  by means of a fastening ring  55 , and by another throttle element  62 —see particularly FIG.  5 —at the free end  61  of the actuating element  6 . 
     A throttle device  2  having a corresponding throttle housing  51  is not illustrated in  FIG. 4 . 
       FIG. 5  corresponds to a section along line V-V from  FIG. 4 . 
     For describing the actuating device  1  according to  FIG. 5  more exactly, reference is particularly made to  FIGS. 2 and 3 , with  FIG. 3  likewise corresponding to a section along line from  FIG. 5 . Only differences over the first exemplary embodiment will be explained in the following. 
     The connecting plate  84  serves to connect a non-illustrated throttle housing. Said housing comprises a passage bore  65  in the portion of the fluid inlet  59 , see the dashed illustration in  FIG. 2 . The passage bore  65  in this case replaces the passage sleeve  63 . According to the exemplary embodiment shown in  FIG. 5  a sealing plug  66  as throttle element  62  is arranged at the free end  61  of the actuating element  6  instead of a corresponding throttle sleeve  64 . For arranging said sealing plug  66 , a throttle element receptacle  78  is disposed at the free end of the actuating element  6 , in which the sealing plug  66  is releasably held. 
     In view of  FIGS. 1 and 4  it is pointed out that the emergency actuating device  30  is illustrated in FIG.  4 —see in this connection also the illustration according to FIG.  3 —while it has been omitted in the exemplary embodiment according to  FIG. 1 . It is once more pointed out that such an emergency actuating device  30  is an optional feature. 
     The operating mode of the actuating device will hereinafter be briefly explained by means of the attached figures. 
     The actuating device  1  comprises an electric drive device formed by two servomotors  8 ,  9 . Said servomotors  8 ,  9  are remotely controllable via corresponding connecting lines and their control devices  1 ,  12 . When actuating one motor or both motors in synchronous operation, said motors drive the worm shaft  18  and thus the worm  16 . Said worm  16  is engaged with the appertaining worm gear  17 . The worm and the worm gear form a self-locking worm gear pair being locked at least oppositely to the feed direction of the turning spindle  4  in the direction of the throttle device. The self-locking state of the worm gear pair can only be released by applying a release torque from the servomotors  8 ,  9 . 
     Especially in interaction with the roller thread as additional part of the transmission device  7  the worm gear pair easily results in a high gearing and allows the transmission of a high torque. The gearing can be selected, according to desire, by correspondingly selecting the worm, worm gear, thread nut and turning spindle. 
     When the thread nut  25  directly connected with the worm gear in a manner secured against rotation is rotated, the turning spindle  4  is correspondingly extended in the direction of the actuating device or is retracted in the opposite direction. Connected with the turning spindle  4  is the actuating element  6  at the free end of which a corresponding throttle element is disposed. The actuating element with the throttle element engage the throttle housing adjacent to the actuating device  1 , where they serve to vary the fluid passage between the fluid inlet and the fluid outlet. 
     An emergency actuating device may be optionally associated with at least one of the servomotors, see  FIGS. 3 and 4 .