Abstract:
A brake shoe for braking a cable such as during speed limitation of an elevator. The brake shoe includes a shoe body supporting a brake lining facing the cable to be braked. The brake lining has at least two lining regions formed of different materials providing different effective braking properties during simultaneous contact with the cable.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a brake shoe for a brake, which brake acts on a cable of an elevator or other cable-drive conveying apparatus with a brake lining.  
           [0002]    Brake shoes of the kind used particularly in equipment for the limitation of the speed of elevator cars of high-performance elevators are known. In that case there is used as an auxiliary cable a closed cable, namely a so-termed speed limiter cable, which is simply termed cable in the following. This cable runs around a cable roller of a speed limiter mounted at the top in an elevator shaft and around a tensioning roller mounted at the bottom in the elevator shaft and it is connected with the elevator car by way of a safety brake device trigger lever. If the speed of the elevator car exceeds a certain limit speed, for example approximately 10 meters per second, then the speed limiter cable is blocked by the speed limiter, whereby the braked cable actuates the safety brake device trigger lever moving with the travelling elevator car and thus triggers the safety brake device mounted in the car.  
           [0003]    Devices for braking or blocking cables by brake shoes, which comprise a brake shoe body and a continuous brake lining fastened thereto, with an effective surface which during braking is brought into contact with the cable, are known.  
           [0004]    Brake shoes are shown in the U.S. Pat. No. 6,371,261 B1, which shoes substantially consist of a brake shoe body and of covers or linings with effective surfaces facing the cable to be braked, wherein several spaced-apart first lining regions are present, between which second lining regions of a different material are arranged; the second lining regions projecting beyond the first lining regions in such a manner that during braking only the second lining regions facing the cable contact the cable; only the second lining regions in that case form effective operative surfaces or brake surfaces, this being because they would be worn to such an extent that they would lie flush with the first lining regions.  
           [0005]    It is disadvantageous with the previously known devices of this kind or with the previously used brake shoes that on initiation of braking for the purpose of speed limitation the cable is braked in a manner which in practice is juddery. On the one hand this is very unpleasant for passengers of an elevator car and on the other hand has the consequence of transient high mechanical material loads that lead to high material wear.  
         SUMMARY OF THE INVENTION  
         [0006]    The present invention concerns a brake shoe so constructed that the brake lining thereof facing the cable consists of at least two lining regions which are formed by different materials and which are arranged adjacent to one another and so designed that during braking, i.e. when the brake shoe is disposed in its operative position, the surface regions of these lining regions together bear against the cable. In that case not only the first lining regions, i.e. the regions of the first material, but also the second lining regions, i.e. the regions of the second material, form effective operative surfaces or braking surfaces.  
           [0007]    With the brake shoe according to the present invention it is possible to simultaneously utilize the different effective properties, which are positive with respect to a desired form of braking, of the two materials. Although in the case of use of the brake shoe according to the present invention when the braking travel is generally prolonged, it is possible to not only ensure a reliable braking or a desired or prescribed speed limitation, but also to prevent a juddery, material-wearing braking. Overall, a synergy results between surface regions of the first material, which alone would intrinsically cause a juddery braking, but is durable, and surface regions of the second material, which would alone intrinsically cause a more gentle, in a given case too-gentle, braking action, but is very susceptible to wear.  
           [0008]    Performance of the braking can be optimized by appropriate dimensioning and arrangement of the lining regions of the effective surface formed by the different materials.  
           [0009]    Moreover, through appropriate shaping of the lining regions, in a given case with gaps, it can be achieved that abrasion particles arising during braking due to friction between the cable and the effective surface of the brake lining are so deflected that they do not have a disruptive effect.  
           [0010]    As already mentioned, the lining regions, which face the cable, or the surface regions, which bound them, of the brake shoe bear under pressure against the cable, which is to be braked, when the brake shoe is disposed in its operative position. The braking surfaces of all different lining regions then lie at least approximately in surfaces which are continuous in the direction of the cable and which are substantially complementary to the external surface of the cable, so that the cable is at least partly surrounded by the braking surfaces during braking. Preferably the first and the second and optionally further materials, from which the brake lining is produced, are so selected that the braking surface forms a continuous surface—optionally with small gaps—substantially complementary to the outer surface of the cable even when the brake shoe does not adopt its operative position. This means that the brake lining does not have any projecting regions even when the brake shoe is not disposed in the operative position thereof. Such projecting regions could be produced from, for example, readily compressible or otherwise readily deformable material so that the brake lining would receive a form complementary to the cable only on contact with the cable.  
           [0011]    The brake shoe according to the present invention is generally so constructed that it comprises a brake shoe body which has at least two lining regions of the brake lining.  
           [0012]    In a preferred construction of the brake shoe, the brake shoe body itself is made of one of the two materials. The brake shoe body can, however, also be made of another suitable material in the form of a block or a carrier structure.  
           [0013]    In general, the brake shoe according to the present invention is constructed so that the lining regions of one of the materials are indeed connected together, but have, at the side facing the cable, recesses in which the lining regions of the other one of the materials are received.  
           [0014]    The lining regions of the different materials can be arranged one after the other in the direction of the relative movement between cable and brake shoe and/or arranged transversely to this direction or in any desired configuration, for example in the manner of a fishbone pattern.  
           [0015]    Respectively adjacent lining regions of different materials can either directly adjoin one another or be separated from one another by gaps.  
           [0016]    In a preferred embodiment of the brake shoe a metallic material is selected as the first material, wherein, for example, bronze, particularly aluminum-bronze, has proved very satisfactory.  
           [0017]    The first material can also be a hard rubber-like or synthetic material or a plastic material, which preferably has a fiber reinforcement.  
           [0018]    It has proved particularly advantageous to select a sintered material at least for the second material.  
           [0019]    In a development of the brake shoe, the brake lining intended for contact with the cable can have at least one lining region of a further suitable material.  
           [0020]    An object of the present invention is providing an improved brake shoe which on the one hand is wear-resistant and on the other hand avoids a juddery braking. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0021]    The above, as well as other advantages of the present invention, will become readily apparent to those skilled in the art from the following detailed description of a preferred embodiment when considered in the light of the accompanying drawings in which:  
         [0022]    [0022]FIG. 1A is a transverse cross-sectional view of two brake shoes according to the present invention, in a non-actuated position, with a cable to be braked;  
         [0023]    [0023]FIG. 1B is a view similar to FIG. 1A showing the brake shoes in an actuated or operative position;  
         [0024]    [0024]FIG. 2A is a longitudinal cross-sectional view of a brake shoe according a first embodiment of the present invention;  
         [0025]    [0025]FIG. 2B is a longitudinal cross-sectional view of a brake shoe according a second embodiment of the present invention;  
         [0026]    [0026]FIG. 2C is a longitudinal cross-sectional view of a brake shoe according a third embodiment of the present invention;  
         [0027]    [0027]FIG. 3A is a front elevation view of a brake shoe according to a fourth embodiment of the present invention;  
         [0028]    [0028]FIG. 3B is a front elevation view of a brake shoe according to a fifth embodiment of the present invention;  
         [0029]    [0029]FIG. 3C is a front elevation view of a brake shoe according to a sixth embodiment of the present invention;  
         [0030]    [0030]FIG. 4 is a plan view of a speed limiter with a cable roller and a brake device for a cable to be braked, in a position in which the cable is not braked, for use with the brake shoes according to the present invention.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0031]    [0031]FIGS. 1A and 1B show a cable  10  and a brake shoe pair with two brake shoes  12 ,  13 , which are provided for braking or blocking the cable  10 . The movement of the cable  10  relative to the brake shoes  12 ,  13  is in this case perpendicular to the plane of the drawing. The brake shoes  12 ,  13  are constructed and arranged to be mirror-symmetrical in the illustrated form of embodiment. It may be noted that the number of two brake shoes and the illustrated arrangement and shaping are usual, but are not obligatory.  
         [0032]    Each of the brake shoes  12 ,  13  comprises a brake lining  14  or  15  respectively with an overall effective surface, and which is formed to be at least approximately complementary to the outer surface of the cable  10 . In the illustration according to FIG. 1A the cable  10  is not braked, the brake shoes  12  and  13  do not adopt their operative position and the effective surfaces, which are intended for contact with the cable  10 , of the brake linings  14  and  15  of the brake shoes  12  and  13  here do not contact the outer surface of the cable  10 . In the illustration according to FIG. 1B the cable  10  is braked, the brake shoes  12 ,  13  bearing under pressure against the cable  10  so that the overall effective surfaces, which are intended for contact with the cable  10 , of the brake linings  14  and  15  contact the cable  10 .  
         [0033]    In FIG. 2A there is illustrated a first embodiment single brake shoe  12   a  which is displaceable in the direction of an arrow B for performance of braking, whilst the direction of the relative movement between the cable  10  and the brake shoe  12   a  is indicated by a double arrow A.  
         [0034]    The brake shoe  12   a  illustrated in FIG. 2A comprises a brake shoe body  16   a  with a brake lining  14   a,  which is bounded by the overall effective surface intended for contact with the cable  10 . The brake lining  14   a  has several lining regions of different materials. In the part, which is illustrated in FIG. 2A, of the brake shoe  12   a,  there are visible—of the brake lining  14   a —five mutually adjacent lining regions  14 . 1  to  14 . 5 . The lining regions  14 . 1 ,  14 . 3 ,  14 . 5  are formed by a first material, namely the material of the brake shoe body  16   a  itself. The lining regions  14 . 2 ,  14 . 4  are formed by a different material; they are outer surfaces of insert parts  18   a  and  18   b  fastened in recesses  20 . 2  and  20 . 4  respectively of the brake shoe body  16   a,  wherein the recesses  20 . 2  and  20 . 4  extend from the effective surface bounding the brake lining  14   a  into the brake shoe body  16   a.    
         [0035]    The effective properties—which are positive for the intended form of braking or blocking of a speed limiter cable—of the two materials are different. Through co-operation thereof on contact with the cable  10  the specific effective braking properties of the two materials can be utilized at the same time. The kind and course of the braking can be influenced by a suitable dimensioning of the overall brake lining  14   a  and the individual lining regions  14 . 1  to  14 . 5 . The dimensions of the individual lining regions can be the same or different. In a preferred embodiment of the brake shoe a metallic material is selected as the first material, wherein, for example, bronze, particularly aluminum-bronze, has proved very satisfactory. The first material can also be a hard rubber-like or synthetic material or a plastic material, which preferably has a fiber reinforcement. It has proved particularly advantageous to select a sintered material at least for the second material, for example graphite-bronze.  
         [0036]    The fastening of the insert parts  18   a  and  18   b  in the brake shoe body  16   a  can be effected in any desired manner, in particular in a force-locking manner or a shape-locking manner; adhesives and mechanical connecting elements, such as screws or rivets, may be mentioned as examples for possible connections. There can also be used, for example, a dovetail-like profile construction as illustrated in FIG. 2A for the lower recess  20 . 4  and the insert part  18   b  received therein. A press-fit or shrink-fit is also suitable.  
         [0037]    [0037]FIG. 2B shows a second embodiment individual brake shoe  12   b  with a brake shoe body  16   b.  All lining regions  14 . 1  to  14 . 5  of a brake lining  14   b  are here formed by outer surfaces of insert parts  18   c  and  18   d  fastened to the brake shoe body  16   b.  In that case, the lining regions  14 . 1 ,  14 . 3 ,  14 . 5  are formed by the insert parts  18   c  of a first material and the lining regions  14 . 2 ,  14 . 4  by the insert parts  18   d  of a second material.  
         [0038]    A further third embodiment brake shoe  12   c  is illustrated in FIG. 2C as being of similar construction to the brake shoe  12   b  of FIG. 2B. Whilst in the case of the brake shoes of FIGS. 2A and 2B the respective adjacent lining regions directly adjoin one another, according to FIG. 2C adjacent lining regions  14 . 1  and  14 . 2 ,  14 . 2  and  14 . 3 ,  14 . 3  and  14 . 4 ,  14 . 4  and  14 . 5  are separated from one another by gaps  22 .  
         [0039]    [0039]FIGS. 3A to  3 C show, by way of example, three further variants of the subdivision of the braking surface  14  into the lining regions  14 . 1 ,  14 . 3 ,  14 . 5  formed by a first material and the lining regions  14 . 2 ,  14 . 4  formed by a second material.  
         [0040]    A fourth embodiment brake shoe  12   d  with a lining  14   d  according to FIG. 3A exhibits the two lining regions  14 . 2 ,  14 . 2 , which are formed by insert parts  18   e,  in the form of strips extending parallel to the direction of the relative movement of cable  10  and brake shoe  12   d,  i.e. in the direction of the arrow A. In this arrangement the respective length section, which is disposed between the brake shoes, of the cable is virtually continuous, but in contact with the second material of the brake lining  14   d  only by parts of its circumference.  
         [0041]    A fifth embodiment brake shoe  12   e  with a lining  14   e  according to FIG. 3B exhibits the two lining regions  14 . 2 ,  14 . 4 , which are formed by insert parts  18   f,  in the form of strips extending perpendicularly to the direction of the relative movement of cable  10  and brake shoe  12   e.  In this arrangement the respective length section, which is disposed between the brake shoes, of the cable comes into contact with the first material and the second material of the brake lining  14   e  in alternation in time, but by its entire circumference or by a substantial part of its circumference. The lining regions can also be arranged in an inclined position, for example at an angle of 45°, relative to the relative movement direction arrow A.  
         [0042]    In FIG. 3C there is illustrated a sixth embodiment brake shoe  12   f  in which the lining regions  14 . 2 ,  14 . 4  are arranged in a fishbone-like (herringbone) configuration insert part  18   g  of a brake lining  14   f.    
         [0043]    [0043]FIG. 4 shows details of a device for braking or blocking of the cable  10 , which is not illustrated, by brake shoes  12 ,  13  according to the present invention.  
         [0044]    In FIG. 4, an elevator speed limiter with a cable roller  30  for a speed limiter cable is illustrated. The cable roller  30  has two centrifugal weights  32  which co-operate with a lever  33 . Of the two brake shoes  12 ,  13  intended for braking the cable the brake shoe  12  is fixed and the brake shoe  13  is so guided by way of a parallelogram linkage with springs  34  that in the raised position it is spaced from the cable (not illustrated) and from the shoe  12 . In this raised position it is held by a lug which is formed at a first, in this case vertical, arm of the lever  33 . This setting is adopted when the speed of the speed limiter cable lies below a specific limit speed. In the case of excess speed, i.e. when the speed of the speed limiter cable exceeds the limit speed, the two centrifugal weights  32  move radially outwardly from the center axis of the cable roller  30  and in that case impinge on the second arm, which is provided with recesses, of the lever  33 . The lever  33  thereby rotates—in clockwise sense in FIG. 4—whereby the lug moves to the left and the brake shoe  13 , which is now no longer supported by it, can drop. Due to the action of the inclined parallelogram linkage with the springs  34  the brake shoe  13  is guided towards the cable and the other brake shoe  12  and entrained by the cable downwardly onto an abutment. The horizontal component of the movement has the consequence that the cable is clamped between the two brake shoes  12 ,  13 , wherein the clamping force is limited by the springs  34  of the parallelogram linkage.  
         [0045]    The brake shoe according to the present invention is particularly, but not exclusively, suitable for use in cable brakes of elevators, for example for braking a speed limiter cable or for braking the support cables of elevator car and counterweight. However, it can also find use in other cable-driven conveying means, for example cableways.  
         [0046]    In accordance with the provisions of the patent statutes, the present invention has been described in what is considered to represent its preferred embodiment. However, it should be noted that the invention can be practiced otherwise than as specifically illustrated and described without departing from its spirit or scope.