Abstract:
An electromotive servo drive includes a drive motor having an external rotor and a drive train in driving relationship with the drive motor and having an output member operatively connected to a control element to be adjusted. A locking device having a brake element is movable between a release position in which the rotor is free to rotate and an operative position in which the rotor is locked in place. Operatively connected to the brake element is a reset spring for maintaining the rotor at a standstill, when the reset spring is under tension, wherein the reset spring tensioned by turning an actuating shaft by hand.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application is a continuation of prior filed copending PCT International application no. PCT/EP02/03833, filed Apr. 6, 2002, on which priority is claimed under 35 U.S.C. §120, the disclosure of which is hereby incorporated by reference. 
    
    
     This application claims the priority of German Patent Application, Serial No. 101 20 832.4, filed Apr. 27, 2001, pursuant to 35 U.S.C. 119( a )-( d ), the disclosure of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates, in general, to an electromotive servo drive for adjusting a control element. 
     Servo drives involved here are primarily used in heating, air-conditioning and ventilation systems, for opening and closing control elements such as flap valves, Hereby, the normal basic position may also be an intermediate position. Associated to the electromotive adjustment drive is a control unit. Some applications may require an opening or closing of the control element, such as in case of a danger, e.g. adjustment of the flap valve in the event of fire. 
     Conventional electromotive servo drives use drive motors having a rotor disposed within a fixed stator. The drive motor has an output journal and a pinion which is wedged on the output journal in fixed rotative engagement. The downstream drive train is hereby so configured that the rotation speed of its output member is significantly smaller than the rotation speed of the output journal of the drive motor. A locking device is provided to maintain the control element in proper end position. A drawback of conventional servo drives is the disposition of the locking device within the drive train and the considerable brake moment as a consequence of the reduced rotation speeds. 
     Many conventional servo drives are configured as so-called spring-return mechanisms, i.e. a spring assembly, for example a spiral spring, is tensioned when the motor is operated to implement the adjustment, so that the return movement of the control element is effected by the restoring force of the spring assembly. Servo drives of this type are relatively bulky, rendering their installation in some cases prohibitive because the installation space is oftentimes very narrow. 
     It would therefore be desirable and advantageous to provide an improved electromotive servo drive which obviates prior art shortcomings and is compact in structure, while still being reliable in operation. 
     SUMMARY OF THE INVENTION 
     According to one aspect of the present invention, an electromotive servo drive includes a drive motor having an external rotor, a drive train in driving relationship with the drive motor and having an output member operatively connected to a control element to be adjusted, and a locking device having a brake element movable between a release position in which the rotor is free to rotate and an operative position in which the rotor is locked in place, a reset spring operatively connected to the brake element for maintaining the rotor at a standstill, when the reset spring is under tension, and a manually-operated actuating shaft for tensioning the reset spring and moving the control element to a base position. 
     The present invention resolves prior art shortcomings by configuring the locking device to act on the rotor of the drive motor, i.e. at a location in which the respective torque of the entire drive train is the smallest so that the brake moment to be applied is minimized. In addition, the servo drive becomes hereby compact. As the rotor is held by hand when the reset spring is tensioned, the base position of the control element can be easily and precisely established. Adjustment of the base position of the control element can be implemented in a particularly simple way by attaching at least one wheel of the drive train on the actuating shaft and by tensioning the reset spring through turning of the actuating shaft, when the rotor is at a standstill. As the actuating shaft is accessible from outside, the actuating shaft becomes, in effect, a driving element that moves the following part of the drive train in order to move the control element in driving relationship with the output member of the drive train into the intended end position. The drive train is therefore configured to maintain the rotor of the drive motor and possibly the following wheels up to the actuating shaft at a standstill. Suitably, the wheel is supported on the actuating shaft via a freewheel or an overrunning clutch. In this way, the output member of the drive train and the control element can be adjusted, while the rotor stands still. In addition, the freewheel or overrunning clutch allows the rotor during return run, as realized by the reset spring, to coast, when the output member of the drive train strikes against a stop. Therefore, there is no abrupt halting that would require application of great forces. 
     According to another feature of the present invention, the actuating shaft may be supported through frictional engagement in a bushing which thus conjointly moves, when the actuating shaft is rotated, wherein stops are provided for limiting a rotation angle of the bushing in both rotation directions. 
     According to another feature of the present invention, the locking device may include a lever, which is supported by the bushing, and a reset spring, which has one end linked to the lever and another end linked to the bushing. Thus, the lever is rotated via the reset spring in a same rotation direction as the actuating shaft. As the lever is part of the locking device, the brake member stays in contact with the rotor of the motor. The rotation angle of the conjointly moved bushing is greater than the rotation angle of the lever, so that the difference between the rotation angles is commensurate with a pressing force by which the brake member is urged against the rotor via the reset spring, whereby the brake member rotates in relation to the lever. 
     According to another feature of the present invention, the brake member may be configured as a double-armed lever having first and second arms extending at an angle to one another, e.g. an acute angle. As a result, the brake member is elastic to ensure a smooth and soft bearing against the rotor of the drive motor. In addition, when the tension of the reset spring is released during reverse movement, the rotor is ensured to run freely during the start-up phase. The elasticity of the brake member can further be enhanced, when the arms of the brake member are interconnected by a spring element, preferably an annular spring element. 
     When the rotor is not decelerated, the brake member suitably strikes against a stationary stop. To maintain a sufficient distance of the contact surface of the brake member in relation to the circumferential area of the rotor, the pivoting movement of the brake member in direction toward the stop is assisted by a spring element, e.g. a spring bar. Suitably, the spring element is tensioned when the brake member is moved toward the rotor and applies the thus stored restoring force to move the brake member back to the release position. Instead of a spring bar, it is, of course, also possible to use a tension spring having one end attached to the lever of the locking device or the brake member and another end attached to a fixed component. 
     According to another feature of the present invention, a coupling element may be mounted in the connection between the actuating shaft and the rotor and so configured to allow a coasting of the rotor when rotated, as the spring element relaxes and the lever mechanism strikes against a stop, and ultimately resulting in a halting of the rotor. This coupling element may be disk-shaped and connected with a drive wheel which is associated to the drive motor. 
     Release of the locking device by hand is necessary for certain applications. Thus, according to another feature of the present invention, the actuating shaft may be provided with a spring element, e.g. a wrap spring, for urging the actuating shaft to seek a rotation in opposition to a rotation to realize a tensioning of the reset spring so as to release the locking device. Use of a wrap spring is currently preferred because the wrap spring does not lock in one direction, while acting as a catch in the other direction. Suitably, the spring element is disposed in a gap between the actuating shaft and the bushing. When releasing the locking device by suitably turning the actuating shaft, the freewheel in the drive train allows the rotor of the drive motor to freely rotate until it halts and comes to a standstill. Jerky loads are thus prevented. 
     Of course, tensioning of the reset spring may not only be realized by manually turning the actuating shaft but the use of an electric tool may also be conceivable. To prevent the reset spring from damage as a result of overrotation, the servo drive may be provided with an overload safety mechanism. The overload safety mechanism is so configured as to allow transmission of a certain torque and may include two coupling parts so constructed as to prevent movement of one coupling part, when a predetermined torque is exceeded. As interacting coupling parts, the overload safety mechanism may include a toothed disk and a spring washer having several radial spring legs with angled ends for engagement in peripheral spaces between teeth of the toothed disk. When the angled ends of the spring jump the teeth, an acoustic noise is triggered to indicate to the operator to terminate a rotation of the actuating shaft. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     Other features and advantages of the present invention will be more readily apparent upon reading the following description of currently preferred exemplified embodiments of the invention with reference to the accompanying drawing, in which: 
     FIG  1  is a vertical projection of an electromotive servo drive according to the present invention, illustrating an operative position of the locking device to halt the rotor of a drive motor; 
     FIG. 1 a  is a perspective view of the servo drive, illustrating the drive train downstream of the drive motor; 
     FIG. 2 is a vertical projection of the electromotive servo drive of FIG. 1, illustrating the locking device in a release position; and 
     FIG. 3 is a partly sectional view of an overload safety mechanism incorporated in the servo drive for protecting the reset spring from overrotation. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Throughout all the Figures, same or corresponding elements are generally indicated by same reference numerals. These depicted embodiments are to be understood as illustrative of the invention and not as limiting in any way. It should also be understood that the drawings are not necessarily to scale and that the embodiments are sometimes illustrated by graphic symbols, phantom lines, diagrammatic representations and fragmentary views. In certain instances, details which are not necessary for an understanding of the present invention or which render other details difficult to perceive may have been omitted. 
     This is one of four applications all filed on the same day. These applications deal with related inventions. They are commonly owned and have same inventive entity. These applications are unique, but incorporate the other by reference. Accordingly, the following U.S. patent applications are hereby expressly incorporated by reference: “Electromotive Adjustment Device”, and “Adjustment Device”, and “Adjustment Drive”, respectively. 
     Turning now to the drawing, and in particular to FIG. 1, there is shown a vertical projection of an electromotive servo drive according to the present invention, including a drive motor  10  having an external rotor  10   a . The drive motor  10  includes a mounting flange (not shown) for attachment within a housing of the servo drive. Drive motors  10  of this type are generally known and commercially available. When at a standstill, the rotor  10   a  is maintained at standstill by a locking device, generally designated by reference numeral  11  and described in more detail furtherbelow. 
     The servo drive further includes a reset spring  17  which can be tensioned, when a manually-operated actuating shaft  12  is turned clockwise, as indicated by arrow A. The actuating shaft  12  can be manually operated by a suitable tool to move a control element into a base position and extends in axis-parallel relationship to a rotation axis of the rotor  10   a  and has a hexagon head  13  or may also have a hexagon socket to enable attachment of a suitable tool to turn the actuating shaft  12 . 
     As shown in FIG. 1 a , the drive motor  10  has an output journal (not shown), which may be a splined output shaft with an involute gear tooth system with multiple teeth, or an output shaft with an involute gear tooth system with multiple teeth, whereby the output journal is in mesh with a helical gear wheel  3 . The helical gear wheel  3  is part of a double gear wheel assembly whose other smaller gear wheel  3   a  is in fixed rotative engagement with a gear wheel  20   a  of a double gear wheel assembly, generally designated by reference numeral  20 . The gear wheel  20   a  is supported on the actuating shaft  12 . The other gear wheel  20   b  of the double gear wheel assembly  20  has a significantly smaller number of teeth and drives a greater gear wheel  4   a  of a further double gear wheel assembly, generally designated by reference numeral  4  whose other smaller gear wheel  4   b  is in mesh with a gear wheel  5  which has a relatively high number of teeth. The gear wheel  5  represents the output member of the drive train and has a tooth segment extending about 90°. The gear wheel  5  is movable between end stops  6  (only one is visible in the illustration of FIG. 1 a ) and has a central bore for receiving a hollow shaft  7  which is restrained against rotation in the bore of the gear wheel  5  via complementary profiles. The hollow shaft  7  is provided with internal teeth  7   a  to attain a form-fitting connection with a coupling element (not shown) that is insertable therein for adjusting the control element. 
     When the drive motor  10  is idle and the reset spring  17  is relaxed, a brake member  14  of the locking device  11  bears against the rotor  10   a , without applying a significant pressing force. As soon as the actuating shaft  12  is turned to tense the reset spring  17 , the brake member  14  is urged by the reset spring  17  against the rotor  10   a . When turning the actuating shaft  12  counterclockwise, the rotor  10   a  is at a standstill because a drive wheel  8  supported on the actuating shaft  12  includes a freewheel. 
     A bushing  15  is disposed in surrounding relationship to the actuating shaft  12  and in frictional contact therewith in such a manner that a turning of the actuating shaft  12  counterclockwise conjointly moves by friction the bushing  15 . In order to limit a rotation movement by the bushing  15 , the bushing  15  includes an extension arm  15   a  which strikes against a stop  15   b . 
     In addition to the brake member  14 , the locking device  11  includes a lever  16  which supports the brake member  14  and has a bearing element  16   b  to embrace the bushing  15  from outside. The bearing element  16   b  includes a slot or recess  16   c  for passage of the extension arm  15   a  of the bushing  15 , and is formed with an extension arm  16   a  which is positioned at an angular distance to the extension arm  15   a  of the bushing  15 . Both extension arms  15   a ,  16   a  have hook-shaped ends for attachment of the ends of a reset spring  17 . As the bushing  15  is moved by the turning of the actuating shaft  12 , the lever  16  is also moved by the reset spring  17 . As a consequence, the brake member  14 , supported on the lever  16 , is moved into contact with the rotor  10   a  of the drive motor  10 . This position is shown in FIG. 1, whereby the reset spring  17  is not yet under tension. The extension arm  15   a  of the bushing  15  is hereby positioned against a stop  15   c . As soon as the actuating shaft  12  is turned slightly in the direction of arrow A, the extension arm  15   a  strikes against the stop  15   b , thereby terminating the pivoting movement of the bushing  15  and the lever  16 . Still, the actuating shaft  12  can still be turned further to tense the reset spring  17 . In view of the difference in the rotation angle, a pressing force is applied via the reset spring  17  onto the rotor  10   a . When the rotation of the actuating shaft  12  in direction of arrow A is stopped, the brake member  14  applies a sufficient braking force upon the rotor  10   a  to restrain it against rotation. 
     FIG. 2 shows the locking device  11  in release position. This position is realized by turning the actuating shaft  12  in opposition to the direction of arrow A, i.e. counterclockwise. As soon as the brake member  14  disengages from the rotor  10   a , turning of the actuating shaft  12  can stop. The brake member  14  strikes against a stationary stop  18 , and the rotor  10   a  is rotated by the reset spring  17  in direction of arrow B. The end positions of the output member  5  of the drive train are limited by stops  6 . As soon as the output member  5  has reached the end position, turning of the actuating shaft  12  is no longer possible. However, as the drive train between the actuating shaft  12  and the drive motor  10  includes a freewheel, the rotor  10   a  is able to coast until coming to a halt. As the actuating shaft  12  is turned counterclockwise, the output member  5  of the drive train pivots. Thus, the counterclockwise rotation of the actuating shaft  12  not only tensions the reset spring  17  but also moves the control element, e.g. a flap valve, that is coupled to the output member  5 . The end position of the control element that defines the base position is thus realized by turning the actuating shaft  12 . 
     A movement of the control element into the other end position, if required, is implemented by energizing the drive motor  10 . The rotor  10   a  then rotates in direction of arrow C, i.e. counterclockwise and in opposition to rotation direction B in which the rotor  10   a  is rotated back by the reset spring  17 , as the reset spring  17  relaxes. The brake member  14  disengages form the outer surface of the rotor  10   a  by the action of a spring bar  19  which is connected to the brake member  14  on the side of the bearing element  16   b  of the lever  16 . The spring bar  19  is under tension when the brake member  14  bears against the rotor  10   a . As soon as the contact is broken by the rotation of the rotor  10   a  in direction C, the spring bar  19  relaxes and the brake member  14  is able to strike against the stationary stop  18 . Of course, the provision of the spring bar  19  is shown only by way of example. Instead, it is certainly conceivable to effect the pivoting movement of the brake member  14  by a tension spring linked to the brake member  14 . 
     The drive motor  10  is operated only as long as the control element needs to move from the base position to the end positions. Once the drive motor  10  is idle, the brake member  14  is brought again into contact with the rotor  10   a . When the rotor  10   a  rotates counterclockwise in direction C, the actuating shaft  12  turns in a same direction. 
     Return of the control element may be realized by the reset spring  17  as well as by hand. When using the reset spring  17 , the actuating shaft  12  is turned in opposition to the direction A, i.e. clockwise. As a consequence, the locking device  11  is pivoted also clockwise so that the brake member  14  strikes against the stop  18  and the rotor  10   a  can coast in direction B, i.e. clockwise. The brake member  14  is further provided with a locking cam  20  which is securely mounted to the lever  16  and is able to swing clockwise about an axis  22 . An annular spring element  21  of the brake member  14  urges the locking cam  20  into the initial position so that the spring bar  19  in the form of a return spring is under tension again. The brake member  14  is thus moved in relation to the lever  16 . The lever  16  is further provided with a stop  23  which is tensioned in an area of the free end of the spring bar  19 . 
     The brake member  14  is constructed as a double-armed lever  14  with two lever arms  14   a ,  14   b  extending at an acute angle and interconnected by the annular spring element  21 . The lever arm  14   a  interacting with the rotor  10   a  is guided in a pocket of the lever  16 , whereby the pocket is formed by an angled portion. A prolongation of the longitudinal center axis of the lever arm  14  intersects the rotation axis of the rotor  10   a  or may also extend at a slight distance thereto, when the brake member  14  is in contact with the rotor  10   a . 
     Turning now to FIG. 3, there is shown an overload safety mechanism, generally designated by reference numeral  24 , for protecting the reset spring  17  against excessive turning. The overload safety mechanism  24  includes a toothed disk  24   a  and a spring washer  24   b  which has several arms radiating in a star-shaped configuration and having free angled ends for engagement in spaces between the teeth of the toothed disk  24   a . Thus, as the actuating shaft  12  is turned, a certain torque is transmitted onto the reset spring  17 . When the torque is exceeded, the angled ends deform and jump the teeth. 
     Of course, the overload safety mechanism may also be constructed in a different way. For example, it may have two disks, which are splined at their confronting sides, whereby at least one of the disks is spring-loaded so that a disk moves relative to the other disk, when the torque is exceeded. Suitably, the overload safety mechanism should be configured in such a way that an operator turning the actuating shaft  12  perceives generated noises to terminate the turning operation. 
     A relevant aspect of the present invention is thus a braking of the rotor  10   a  during tensioning of the reset spring  17  so as to prevent the rotor  10   a  from reversing the movement when, e.g., the rotation movement is momentarily interrupted. Another relevant aspect of the present invention is the fact that the reset spring drives the rotor  10   a  during a momentary rotation movement in the opposite direction. 
     The servo drive according to the present invention may also be used for adjusting control elements in case of fire. In order to ensure the operation of the servo drive even at elevated temperatures, the mentioned components are made of metal, for example, steel or non-ferrous heavy metal. 
     While the invention has been illustrated and described in connection with currently preferred embodiments shown and described in detail, it is not intended to be limited to the details shown since various modifications and structural changes may be made without departing in any way from the spirit of the present invention. The embodiments were chosen and described in order to best explain the principles of the invention and practical application to thereby enable a person skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. 
     What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims and includes equivalents of the elements recited therein: