Abstract:
A centrifugal brake has a rotational element, a brake drum that extends at least partially over the rotational element, at least one centrifugal shoe which is movable substantially radially between the rotational element and an inner wall of the brake drum and is located on the rotational element, and a rotational braking device provided for the rotational element and triggered when a specified rotational speed of the rotational element is exceeded.

Description:
CROSS-REFERENCE TO A RELATED APPLIACTION  
       [0001]     The invention described and claimed hereinbelow is also described in German Patent Application DE 10 2005 047 296.6 filed on Sep. 30, 2005. This German Patent Application, whose subject matter is incorporated here by reference, provides the basis for a claim of priority of invention under 35 U.S.C. 119(a)-(d).  
       BACKGROUND OF THE INVENTION  
       [0002]     The present invention relates to a centrifugal brake.  
         [0003]     More particularly, the present invention relates to a centrifugal brake with a rotational element and a brake drum that extends at least partially over the rotational element, and at least one centrifugal shoe, which is movable essentially radially between the rotational element and an inner wall of the brake drum and is located on the rotational element.  
         [0004]     Centrifugal brakes are generally known. They are not typically used to directly and greatly reduce the number of revolutions, but rather to limit them. Starting at certain drive RPMs, the centrifugal shoes begin to move radially outward from a resting position as a result of the centrifugal force. When the engagement speed is reached, the centrifugal shoes come in contact with the inner wall of the drum. Brake pads, which increase the friction, can be provided between the centrifugal shoes and the drum wall. The brake pads can be installed on the centrifugal shoes or the inner wall of the brake drum. In certain applications, however, it is desirable to bring the rotational element to a complete stop.  
       SUMMARY OF THE INVENTION  
       [0005]     The object of the present invention, therefore, is to refine a centrifugal brake of the type described initially such that the rotational element can be brought to a complete stop when necessary, particulary when the rotational element exceeds a specified rotational speed.  
         [0006]     This object is attained according to the present invention in a surprising and effective manner by providing an additional brake device for the rotational element, which is triggered when the rotational element exceeds a specified rotational speed. This means the centrifugal brake is ineffective up to the specified rotational speed. When the specified rotational speed is exceeded, the additional brake device becomes effective, thereby ensuring that the rotational element is brought to a complete halt. The rotational element can be designed as a drive shaft or a hub, or it can include one of these.  
         [0007]     With a particularly preferred embodiment, the brake drum can be a component of the additional braking device, the brake drum being positioned such that it is rotatably movable to a limited extent, and is driven by the at least one centrifugal shoe within a specified angular range when a specified rotational speed is exceeded, thereby triggering the additional braking. Although the brake drum in the related art is positioned in a non-rotatable manner, it can be moved—according to the present invention—within a specified angular range and thereby trigger the additional braking.  
         [0008]     An axially movable disk is preferably non-rotatably mounted on the brake drum. Via the axially movable disk, and in interaction with additional elements, an axial braking force can be produced. It can be provided that the disk is locked in the axial direction by a locking mechanism below the specified rotational speed, is axially unlocked above the specified rotational speed, and generates a braking force—which acts axially, in particular—to brake the rotational element. Below the specified rotational speed, the disk can therefore be held by the locking mechanism in the immediate vicinity of the brake drum, in particular in contact with the brake drum. This ensures that the disk is held at a distance away from a brake disk.  
         [0009]     When the disk is unlocked, however, i.e., when the rotational speed of the rotational element is above the specified limit, the unlocked disk can interact with at least one brake disk, which is non-rotatably connected with the rotational element and is preferably a diaphragm disk, and with a non-rotatable support bearing. In particular, due to the axial motion of the disk, the brake disk is clamped between the disk and the support bearing.  
         [0010]     The braking action can be increased when a brake pad is provided between the disk and the brake disk, and/or between the brake disk and the support bearing. Preferably, brake pads are provided at opposite points on either side of the brake disk.  
         [0011]     With a particularly preferred embodiment, several brake disks can be provided, between which plates of the support bearing engage. Friction-increasing brake pads can be provided between the brake disks and the plates. In particular, the brake disks can include brake pads, which are diametrically opposed in the axial direction.  
         [0012]     It is particularly preferred when the disk is axially preloaded by at least one axial spring. When the locking mechanism is released, the disk is automatically moved in the direction of the brake disk, and the brake disk is clamped between the disk and the support bearing. The axial spring preferably bears against the brake drum.  
         [0013]     It is particularly preferred when the preload of the at least one axial spring is adjustable. This allows the braking torque of the additional brake device to be changed and adjusted.  
         [0014]     Different embodiments of the locking mechanism are feasible. An embodiment is feasible with which the locking mechanism includes one or more bearings located in a recess when the rotational speed is below a specified limit. The bearings can hold the disk at a distance away from the support bearing and, therefore, from the brake disk located between them. When the brake drum is rotated, the bearings are displaced out of their recesses and enter a second recess, which is larger than the depth of the first recess. This permits the disk to move close to the support bearing, so that the additional braking takes place.  
         [0015]     With a preferred embodiment, the bearings can be located in a bearing cage. When the brake drum is rotated, the bearing cage can be driven, and the bearings can move out of the assigned recesses. The bearing cage is preferably positioned such that it is movable to a limited extent and is coupled with the brake drum such that it allows the rotatability of the brake drum to be limited.  
         [0016]     With a preferred embodiment of the present invention, it can be provided that the additional brake device is manually resettable. It can also be provided that the additional brake device is capable of being triggered manually or automatically when a specifiable event occurs. The additional brake device can be triggered, e.g., when it is detected that a drive is running out of true.  
         [0017]     In one embodiment, a sensor can be provided, which detects a triggering of the additional braking device and is connected with a signaling device that indicates that the additional braking device has been triggered. As a result, the triggering of the additional braking is easy to detect.  
         [0018]     Further features and advantages of the present invention result from the detailed description of exemplary embodiments of the invention presented below with reference to the figures in the drawing, which shows the details that are essential to the present invention. The individual features can be realized individually, or they can be combined in any possible manner in different variations of the present invention.  
         [0019]     Exemplary embodiments of the present invention are depicted in the schematic drawing and are described in greater detail in the description below.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]      FIG. 1  is a longitudinal sectional view through a centrifugal brake according to the present invention;  
         [0021]      FIG. 2  is a schematic depiction of a locking mechanism;  
         [0022]      FIG. 3   a  is a specific embodiment of a locking mechanism in a locked position;  FIG. 3   b  shows the embodiment of the locking mechanism in  FIG. 3   b , in an unlocked position.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]     Centrifugal brake  1  shown in  FIG. 1  includes a rotational element  2  designed as a hub, which is positioned such that it can rotate around an axis of rotation  3 . Centrifugal shoes  4  are located on rotational element  2 . They are driven by rotational element  2  when rotational element  2  rotates. Due to the centrifugal force, centrifugal shoes  4  are deflected essentially radially and preferably against a return force when rotational element  2  rotates, so that brake pads  6  of centrifugal shoes  4  come in contact with inner wall  7  of brake drum  8 . Brake drum  8  extends over portions of rotational element  2 . Ball bearings  9  are located between brake drum  8  and rotational element  2 .  
         [0024]     A disk  10  is non-rotatably located on brake drum  8 . Disk  10  is axially displaceable in certain operating states and bears against brake drum  8  via an axial spring  11 . A brake disk  13 , which is non-rotatably connected with rotational element  2 , is located between disk  10  and a non-rotatable support bearing  12 . Brake disk  13  includes brake pads  14 ,  15 , which are located at axially opposing points. Rotational element  12  is rotatably supported in support bearing  12  via ball bearing  16 . Due to the axial forces that occur, ball bearings  9 ,  16  can be designed as angular ball bearings.  
         [0025]     Below a specified rotational speed, disk  10  is held against brake drum  8  via a locking mechanism  17 . In particular, disk  10  is held at a distance away from support bearing  12  and, therefore, brake disk  13 , via bearings  18 . In the exemplary embodiment, eight bearings  18  are distributed around the circumference, bearings  18  being located in a bearing cage  19 .  
         [0026]     When rotational element  2  has reached a specified rotational speed, centrifugal shoes  4  bear with brake pads  6  against brake drum  8  and drive brake drum  8 . As a result, bearings  18  are moved out of their resting position, and disk  10  is freed to move axially. Due to preloaded axial spring  11 , disk  10  is pressed against brake pad  14  of brake disk  13 . This causes brake pad  15  to be pressed against support bearing  12 . Brake disk  13  with its brake pads  14 ,  15  is therefore clamped between disk  10  and support bearing  12 , and rotational element  2  is braked until it comes to a standstill.  
         [0027]      FIG. 2  shows a schematic depiction of locking mechanism  17 . A bearing  18  is located in its resting position, i.e., below a specified rotational speed of rotational element  2 , in a recess  25  of support bearing  12 . When brake drum  8  and disk  10  non-rotatably connected therewith rotates, bearing  18  is moved out of the resting position shown, so that it enters a recess  26 . As a result, disk  10  and support bearing  12  can move toward each other.  
         [0028]     A possible specific embodiment of locking mechanism  17  is shown in  FIG. 3a . In this case as well, bearings  18  are located in a recess  25  of support bearing  12 . As a result, it supports disk  10  and holds disk  10  away from support bearing  12 . In this case, bearing  18  is located in a bearing cage  19 . Projections  27  designed as pins, which are non-rotatably connected with disk  10  and brake drum  8 , engage in slots  28  of bearing cage  19 .  
         [0029]     If brake drum  8  or disk  10  are now rotated, projection  27  reaches lower limit  29  of slot  28 —as shown in  FIG. 3   b —and therefore drives bearing cage  19 . As a result, bearings  18  also become disengaged from recess  25  and come to rest in recess  26 . Simultaneously, projection  30 —which is designed as a pin and is non-rotatably connected with support bearing  12 —reaches the opposite limit of slot  31 . As a result, bearing cage  19  engages with projection  30  and cannot be moved further. The rotational motion of disk  10  and, therefore, brake drum  8 , are therefore also limited. Given that bearing  18  has reached recess  26 , it became possible for disk  10  to approach support bearing  12 .  
         [0030]     It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of constructions differing from the type described above.  
         [0031]     While the invention has been illustrated and described as embodied in a centrifugal brake, 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.  
         [0032]     Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, be applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.