Abstract:
A disc brake caliper for a rail vehicle comprises brake pad holders suspended—at either side of a brake disc to be braked—for movements only in a plane perpendicular to a substantially horizontal center-line of the caliper. Members of the caliper for transmitting movements from a brake unit to the brake pad holders are suspended from the vehicle via only elements of rubber-elastic material in an elastic joint allowing movements to a certain extent of said members in all directions. The elastic joint comprises at least one plate-shaped rubber-elastic element, which is substantially horizontally mounted in compression between a part for attachment to the vehicle and one of said members of the caliper.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation of pending International patent application PCT/EP2007/002978 filed on Apr. 3, 2007 which designates the United States and claims priority from Swedish patent application 0600788-4 filed on Apr. 7, 2006, the content of which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a disc brake caliper for a rail vehicle, comprising brake pad holders suspended—at either side of a brake disc to be braked—for movements only in a plane perpendicular to a substantially horisontal center-line of the caliper, wherein members of the caliper for transmitting movements from a brake unit to the brake pad holders are suspended from the vehicle via only elements of rubber-elastic material in an elastic joint allowing movements to a certain extent of said members in all directions. 
       BACKGROUND OF THE INVENTION 
       [0003]    A disc brake caliper for a rail vehicle normally comprises a brake actuator, pivotable levers for transmitting a brake force from the actuator to the levers, brake pad holders, pivotally arranged at the lever ends, and means for connecting the different members of the caliper. The brake pad holders are provided with exchangeable brake pads of a friction material for braking cooperation with a brake disc, over which the disc brake caliper is mounted astraddle. 
         [0004]    The brake actuator is normally a pneumatic brake unit, comprising a brake cylinder or brake actuator and a slack adjuster or brake regulator. The space for such a disc brake caliper in the vicinity of the brake disc in the undercarriage or bogie of the rail vehicle is very limited, and it is thus desired to keep the overall dimensions of the disc brake caliper at a minimum. 
         [0005]    An example of a measure to minimize the dimensions is to decrease the length of the pivotable levers, which means that their angular movements during operation are increased. This in turn may lead to undesirably great movements of the suspended brake pad holders in relation to the brake disc. 
         [0006]    For obtaining controlled braking, it is in principle desired to have a geometrically constant engagement of the brake pads with the brake disc irrespective of the wear of the brake pads and the disc and also of the axial position of the axially slightly movable brake disc in relation to the disc brake caliper. 
         [0007]    In order to fulfill these requirements, a basic measure is to suspend the brake pad holders in such a way that they are only movable in a plane perpendicular to a center-line of the caliper. The journaling of the brake pad holders is in principle as stiff as possible in other directions. As the brake pad holders are suspended in the described fashion, relative movements of other members of the caliper must be allowed. A disc brake caliper shown in EP-A-1 357 009 has separately suspended brake pad holders, and the remainder of the caliper is suspended via a bush containing rubber sleeves for elastically allowing certain relative movements. The design of the bush is, however, such that relative movements in the plane of the caliper center-line are not possible due to metallic contact in the bush. 
         [0008]    A disc brake caliper shown in U.S. Pat. No. 4,053,034 can be regarded as the closest prior art. Here, a rubber bushing for elastic suspension of brake levers in a disc brake caliper is shown. Two conical rubber sleeves fill compartments between a cylinder and a shaft. Hereby the stiffness is constant in all directions. These disc brake caliper designs do accordingly not fulfill the requirements set out above. 
       SUMMARY OF THE INVENTION 
       [0009]    The main object of the invention is to obtain a three-point supported disc brake caliper, which fulfills the above requirements. This is according to the invention attained in that the elastic joint comprises at least one plate-shaped rubber-elastic element, which is substantially horisontally mounted in compression between a part for attachment to the vehicle and one of the caliper members for transmitting movements from the brake unit to the brake pad holders. 
         [0010]    As desired, the stiffness in the vertical direction will hereby be substantially greater in the vertical direction than in all other directions, whereas the stiffness against torsion in the horizontal direction is as small as possible. The force transmitting capability and the useful service life will be maximized by the horizontal, prestressed rubber-elastic elements. 
         [0011]    With the prior disc brake calipers mentioned above the brake pad holders and the bush are to be suitably supported from the undercarriage or bogie of the rail vehicle. 
         [0012]    In contrast hereto a preferred embodiment of a disc brake caliper according to the invention is provided with a mounting bracket, from which the brake pad holders and the members of the caliper for transmitting movements from the brake unit to the brake pad holders are suspended and which is to be attached in the rail vehicle. In a practical embodiment of a disc brake caliper according to the invention the elastic joint is arranged between the mounting bracket and a bridge piece, to which levers for transmitting movements from the brake unit to the brake pad holders are pivotally connected. 
         [0013]    Preferably, the at least one rubber element is mounted between the mounting bracket and the bridge piece. In a practical embodiment, the bridge piece is clamped without metallic connection between the mounting bracket and a plate-shaped rubber element on the one side and a plate and a plate-shaped rubber element on the other side, the plate being attached to the mounting bracket by means of screws. It is important for the function and longevity of the rubber elements that they always work under a predetermined compression. This is obtained in that the screws are surrounded by distance sleeves determining the distance between the mounting bracket and the plate. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0014]    Brief Description of the Drawings The invention will be described in further detail below under reference to the accompanying drawings, in which: 
           [0015]      FIGS. 1 and 2  are a top view and a side view, respectively, showing very schematically and to a small scale a disc brake arrangement with a disc brake caliper according to the invention, 
           [0016]      FIG. 3  is an isometric view from the rear of the disc brake caliper according to the invention, 
           [0017]      FIG. 4  is a side view of the caliper without a brake unit, 
           [0018]      FIG. 5  is a view from the rear of the caliper without a brake unit, 
           [0019]      FIG. 6  is a sectional view from the rear to a larger scale of a joint in the caliper,  FIG. 7  is a sectional side view of the same joint along the line VII-VII in  FIG. 6 , and 
           [0020]      FIGS. 8   a - g  are very schematic illustrations of the relationship between the different members of the caliper under different conditions. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0021]    Detailed Description of Embodiments A disc brake caliper of the type shown in the drawings is primarily intended to be mounted in an undercarriage or bogie of a rail vehicle for braking engagement with a brake disc, either separately mounted on a wheel axle of the vehicle or on the rotating wheel itself, as is well known in the art. The disc brake caliper could also be used in other vehicles. The disc brake caliper shown in the drawings is intended for engagement with a separate axle-mounted brake disc, but there is no principal difference in a caliper for a wheel-mounted disc. 
         [0022]    A disc brake arrangement with an axle-mounted brake disc is very schematically illustrated in  FIGS. 1 and 2 . A brake disc BD is attached to a wheel axle A of the rail vehicle. A disc brake caliper DBC of the invention is mounted (in a way to be described below) astraddle of the brake disc BD in a portion (undercarriage or bogie) of the rail vehicle in which the wheel axle A is journalled. The brake disc BD is shown in a position in which a center-line CL of the disc brake caliper DBC is in line with a center plane of the brake disc BD and is directed towards the center of the wheel axle A. The wheel axle A with the brake disc BD is, however, normally axially movable to a limited extent, which means that the brake disc BD may be somewhat offset in relation to the disc brake caliper DBC, as will appear below. The center- line CL of the disc brake caliper DBC is perpendicular to the wheel axle A. hi the description the direction “forwards” in the caliper is towards the brake disc. Other direction or position words, such as “upper” and “lower” are related thereto. 
         [0023]    Reference is now made especially to  FIG. 3 , but also  FIGS. 4 and 5 . The disc brake caliper shown therein has a mounting bracket  1 . This bracket  1  has a number of holes  2  for its attachment to a suitable element (not shown) in the undercarriage or bogie of the rail vehicle. It is, however, important to note that a disc brake caliper according to the invention can be mounted or supported by other means, as will appear below. 
         [0024]    The bracket  1  constitutes a three-point support in the caliper. The bracket  1  is forwardly (to the left in  FIGS. 3 and 4 ) bifurcated. A suspension link  3  is pivotally suspended in each forward end of the bifurcated bracket  1 . The pivot axis is parallel with the center-line CL ( FIGS. 1 and 2 ) and the brake disc BD. At its lower end, each suspension link  3  is pivotally connected to a brake pad holder  4 . Its pivot axis is parallel with the pivot axis mentioned above and thus with the center-line CL. 
         [0025]    Each brake pad holder  4  is provided with an exchangeable brake pad  5  for frictional engagement with the brake disc (not shown). The brake pad  5  is the wear element of the disc brake and is replaced with a new one when worn out. 
         [0026]    A bridge piece  6  is connected to the mounting bracket  1  by a joint collectively numbered  7  and further described below with special reference to  FIGS. 6 and 7 . 
         [0027]    An upper lever  8  and a lower lever  9  at each side of the disc brake caliper are at their central portions pivotally attached to the bridge piece  6 . An axle  10  is provided between the two levers  8  and  9 . The forward ends of the levers  8  and  9  are pivotally attached to the brake pad holder  4  (to the left in Figs  3  and  4 ) around a pivot axis perpendicular to the center-line CL ( FIGS. 1 and 2 ). 
         [0028]    As is only shown in  FIG. 3 , a brake unit  11  is pivotally connected to and suspended by the rear ends of the brake levers  8  and  9 . A brake unit generally comprises a brake cylinder—most often a pneumatic brake cylinder—and a built-in slack adjuster or brake regulator. At the admission of air under pressure to the brake cylinder, the brake unit  11  will press the rear ends of the levers  8  and  9  apart and the forward ends thereof together for brakingly applying the brake pads  5  against the brake disc. (The term “brake unit” is not meant to exclude a plain brake actuator without a slack adjuster.) 
         [0029]    As is well known in the art, the function of the slack adjuster or brake regulator in the brake unit  11  is to keep the rest distance between the brake pads  5  and the brake disc constant irrespective of the wear of the brake pads. As a result the levers  8  and  9  will assume different pivotal rest positions depending on the wear situation for the brake pads  5 . 
         [0030]    It is well known in the art that the space allowed in the undercarriage or bogie of a rail vehicle for a disc brake caliper is very limited and that it is most desirable to minimize the volume requirement for the disc brake caliper. The present disc brake caliper is designed with this requirement in mind, which i.a. means that the levers  8  and  9  are kept as short as possible, so that the overall dimensions of the caliper are kept at a minimum and that the brake disc in operation will be close to the bridge piece  6 . This on the other hand means that the angular movements of the levers during operation are increased. The suspended brake pad holders  4  will accordingly experience undesirably great movements in relation to the brake disc. The caliper design is based on a generally firm guiding by the suspension links  3  of the brake pad holders  4  to a plane perpendicular to the center-line CL of the brake caliper and a resilient guiding of all other elements of the caliper in all directions, which is accomplished by the design of the elastic joint  7  between the mounting bracket  1  (i.e. the undercarriage or bogie in mounted condition) and the bridge piece  6 . The mounting bracket  1  and the bridge piece  6  are shown in  FIGS. 6 and 7 , to which reference is now made. These two members are connected only via generally plate-shaped rubber elements  12  and  13 . An upper rubber element  12  is arranged between the mounting bracket  1  and the bridge piece  6 , whereas a lower rubber element  13  is arranged between the bridge piece  6  and a plate  14 . The rubber elements  12  and  13  have confined positions in relation to the mounting bracket  1 , the bridge piece  6  and the plate  14 , in that these members have recesses for the rubber elements. 
         [0031]    The term “rubber” is meant to include any rubber- elastic material. The joint  7  is held together by means of screws  15 , which in the shown case engage threads in the mounting bracket  1  and pass corresponding openings in the rubber elements  12  and  13 . A fixed distance between the mounting bracket  1  and the plate  14  is created by means of distance sleeves  16  around the screws  15 . The rubber elements  12  and  13  are prestressed at mounting for ensuring that they always work under a predetermined compression. The bridge piece  6  is provided with larger holes for ensuring its freedom to move to the necessary extent in all directions in relation to the bracket  1  and the plate  14 . 
         [0032]    With the joint  7  as shown and described and with suitable choice of dimensions and material for the rubber elements  12  and  13 , it is possible to obtain linear and rotational movements with appropriate stiffnesses in all directions. The greatest stiffness is normally in the vertical direction or the direction of the screws  15 . In order to obtain a specific characteristic for the joint  7 , the portion of the bridge piece  6  in contact with the rubber elements  12  and  13  tapers slightly to the left in  FIG. 7 . This bridge piece portion is provided with a number of slots for obtaining an enhanced grip on the rubber. 
         [0033]      FIGS. 8   a - g  illustrate the relationship between the different members of the caliper under different working conditions. Only  FIG. 8   a  is provided with reference numerals for the sake of clarity. 
         [0034]    Thus, shown in  FIG. 8   a  are the bridge piece  6  with the joint  7  and the levers  8 ,  9  pivotally connected thereto. Pivotally connected to the left ends of the levers  8 ,  9  (but not shown) are the brake pad holders  4  and to the right ends the brake unit  11 .  FIG. 8   a  illustrates the caliper at the beginning of a brake application with new, unworn brake pads  5  and with a new, unworn brake disc. Further, the brake disc is centered in relation to the caliper. 
         [0035]      FIG. 8   b  is an illustration of the caliper of  FIG. 8   a  somewhat later during braking. 
         [0036]      FIG. 8   c  corresponds to  FIG. 8   a  with the difference that the brake disc is axially displaced (for example 20 mm) upwards in the Figure in relation to the caliper. 
         [0037]      FIG. 8   d  illustrates the situation when the brake pads  5  as well as the brake disc are worn, but the brake disc is centered in relation to the caliper. 
         [0038]      FIG. 8   e  corresponds to  FIG. 8   d  but illustrates the situation when the brake pads  5  have been completely worn out.  FIG. 8   f  corresponds to  FIG. 8   d  but with the brake disc axially displaced upwards in the Figure in relation to the caliper. 
         [0039]      FIG. 8   g  corresponds to  FIG. 8   e  but with the brake disc axially displaced upwards in the Figure in relation to the caliper. 
         [0040]    The shown and described disc brake caliper is provided with a mounting bracket  1 , from which all other elements of the caliper are suspended and which serves for mounting the caliper to the undercarriage or bogie of the rail vehicle. However, it is within the scope of the invention to abstain from the mounting bracket and for example suspend the suspension links  3  and the bridge piece  6  directly from the undercarriage or bogie via the elastic joint  7 . Modifications are possible within the scope of the appended claims.