Abstract:
A shoe brake assembly for a rail vehicle including a bogie connected with the rail vehicle. The assembly also includes a wheel having a wheel web and radially inward-facing surfaces on opposite sides of the wheel web. Also included are at least two brake pads adjacent respective radially inward-facing surfaces of the wheel and a pendulum suspension arrangement connecting the at least two brake pads to the bogie. The assembly further includes an operating device configured to move the at least two brake pads via the pendulum suspension essentially radially against respective radially inward-facing surfaces of the wheel.

Description:
BACKGROUND 
     The present disclosure relates to a shoe brake assembly for rail vehicles. 
     From European Patent Document EP 0 665 154 B1, a shoe brake assembly for a rail vehicle is known. The assembly comprises a brake pad which can be pressed against the tread of a rail wheel by an application device. For operating the shoe brake assembly, a suspension system is provided which permits the brake pad to carry out a certain lateral movement along with the wheels. By corresponding pressure or tension members of the suspension, the brake pads are pressed against the wheel treads for generating a frictional force. The resulting high stressing of the wheel treads is disadvantageous because the service life of the wheel is shortened and a roughening or corrugation of the wheel tread is produced. The roughening or corrugation of the wheel tread leads to a high running noise during the rolling operation of the wheel, which is why, in the case of modern rail vehicles, separate disk brakes are frequently provided which, however, are comparatively expensive. In addition, the one-sided braking load of the wheel results in high thermal stress. 
     In order to address those disadvantages, an elastic brake body is disclosed in German Patent Document DE 19840065, in the case of which a bearing body is provided with recesses into which the friction material elements are inserted. These friction material elements form a joint friction surface and are carried in an elastic manner. Although these elastic brake bodies, to a certain extent, permit a compressing and rebounding of the friction material elements when these are pressed onto the tread of the rail wheel and thereby avoid the formation of hot spots, a roughening and corrugation on the tread is not completely avoided. 
     SUMMARY 
     The present disclosure relates to a shoe brake assembly for rail vehicles. The shoe brake assembly includes a bogie connected with the rail vehicle. Also included is a wheel having a wheel web and radially inward-facing surfaces on opposite sides of the wheel web. The assembly further includes at least two brake pads adjacent respective radially inward-facing surfaces of the wheel and a pendulum suspension arrangement connecting the at least two brake pads to the bogie. The assembly also includes an operating device configured to move the at least two brake pads via the pendulum suspension essentially radially against respective radially inward-facing surfaces of the wheel. 
     If, in the case of the shoe brake assembly, for generating a braking force, at least one brake pad can be placed against a surface of the wheel facing radially toward the interior, the tread of the wheel is not stressed by this brake pad. As a result, on the one hand, temperature-caused tensions are avoided during the braking operation and, on the other hand, the above-mentioned roughening of the wheel tread by the brake pad is also avoided. The development of noise during the rolling operation of the wheel can thereby be reduced. In addition, by the arrangement of the brake pad on an inward-facing surface of the wheel, the contact pattern between the brake pad and the wheel tread can be improved. 
     According to an embodiment of the present disclosure, the at least one brake pad can be moved by way of a pendulum suspension essentially radially toward the outside against a surface of the wheel. The pendulum suspension permits a compensation of vertical movements between the bogie and the wheel, which are generated, for example, by the loading or unloading of the vehicle. 
     If at least two brake pads are provided, which are applied to the wheel at opposite sides of a wheel web, no momentum is generated at the wheel web as a result of the introduction of force since, because of the one-sided application of forces, the wheel web is only under tension. For an effective introduction of force, each brake pad is liked to or connected with two tension bows or bars which are mutually connected in an articulated manner by way of transverse lugs and can thus be displaced with respect to one another in the manner of a parallelogram. This type of suspension permits the adapting of the position of the brake pad to the frictional surface of the wheel during the compressing or rebounding of the wheel. In this case, the tension bow can be connected with the bogie in an articulated manner by way of one or several holding lugs. 
     According to another embodiment, a holding lug is linked to a tension bow in the direct proximity of the brake pad. As a result, the frictional force of the pad can be diverted at the site of its origin directly by way of the holding lug, in which case the stiffer linkage of the brake pad results in lower braking noises. In this case, the holding lug adjacent to the brake pad can be linked to a single tension bow as well as to one of two tension bows. In addition, the holding lug can be disposed on a pressure piece which acts upon the brake pad during the braking operation. 
     If a second brake pad is provided at the suspension of the brake pad assembly, the brake pad can be moved against the tread of the wheel and a particularly high braking force can be generated. This double pad arrangement, with brake pads situated on the outside and inside, is suitable for heavy rail vehicles, such as locomotives. As a result of the two-sided arrangement of brake pads, a more uniform warming-up of the wheel is also caused. 
     If the shoe brake assembly comprises two brake pads, which can be placed on one radially inward-facing surface of two adjacent wheels respectively, a caliper can be provided between the wheels for generating the force. 
     According to another embodiment of the present disclosure, the surface of the wheel and the opposite surface of the brake pad are constructed to be slightly sloped toward a wheel web. The brake pad is thus pressed to the interior toward the wheel web as a result of the slope of the braking surface during a movement radially toward the outside. By generating a braking force at a section of the wheel web as well as at the radially inward-facing surface, thermal tensions can be reduced between the wheel flange and the wheel web because a more uniform warming-up of the wheel takes place. The slope of the braking surface may also bean that the brake pads are centered and a clear assignment of the wheel surface and the frictional surface of the pad exists even when axle displacements occur. In this case, the slope is, for example, in a range between 3 and 30°. 
     Other aspects of the present disclosure will become apparent from the following descriptions when considered in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partial sectional frontal view of the shoe brake assembly, according to an embodiment of the present disclosure. 
         FIG. 2  is a lateral view of the shoe brake assembly of  FIG. 1 . 
         FIG. 3  is a lateral view of the shoe brake assembly of  FIG. 1  when the vehicle is heavily loaded. 
         FIG. 4  is a sectional frontal view of a shoe brake assembly, according to another embodiment of the present disclosure; 
         FIG. 5  is a lateral view of a shoe brake assembly, according to another embodiment of the present disclosure. 
         FIG. 6  is a lateral view of a shoe brake assembly, according to another embodiment of the present disclosure. 
         FIG. 7  is a lateral view of a shoe brake assembly, according to another embodiment of the present disclosure. 
         FIG. 8  is a lateral view of a shoe brake assembly, according to another embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The shoe brake assembly illustrated in  FIGS. 1 to 3  comprises a wheel  4  which is mounted on an axle  1  of a rail vehicle (not shown). A wheel hub  3  is fixed on the axle  1 . A wheel web  2 , which, may be thinly constructed, leads into a flange  5  of the wheel  4  and extends away from the wheel hub  3  in a radial direction. On an outward-facing side, a tread  6  is constructed which has a slight diagonal slope with respect to a horizontal line, as shown in  FIG. 1 . On the radially inward-facing side of the wheel flange  5 , surfaces  7  are constructed on both sides of the wheel web  2 , against which surfaces  7  a brake pad  8  can be placed. The brake pads  8  are each received on a holder  9  which has a bent construction and is fixed to an arm  10  of a tension bow  11 . In  FIG. 1 , the right brake pad  8  can be operated by a tension bow  11 , while the left brake pad  8  can be moved by another tension bow  12 , as indicated by the arrows. 
     A suspension arrangement for the brake pads  8  comprises two tension bows  11  which are each connected at a vertical distance via articulations  13  with the holder  9  of a brake pad  8 . In this case, the tension brows  11  are mutually connected via a first transverse lug  15  and a second transverse lug  18 . The two articulations or axes  14  of the transverse lug  15  as well as the articulations or axes  17  of the transverse lug  18  form a rectangle, which is why the tension bows  11  can be displaced in a parallelogram-type manner. An operating device, such as a tension rod  16 , is mounted on the transverse lug  15  in an articulated manner, via which tension rod  16  an operating force F can be introduced in order to press the brake pads  8  onto the braking surface  7 . 
     The upper tension bow  11  is connected by two holding lugs  19  and  21  with a bogie  80  of the rail vehicle. In this case, the holding lug  19  is mounted in an articulated manner on a suspension  20 , and the holding lug  21  is mounted in an articulated manner on a suspension  22 . In a loading case as illustrated in  FIG. 2 , center point M of the wheel  4  is at the same height as center axis C of the tension rod  16 , so that, when the force F is introduced, the brake pad  8  is arranged centrically at the wheel  4 . In this case, the wheel  4  rolls on a rail  50 , which is not shown in detail. 
     In a loading case illustrated in  FIG. 3 , the bogie  80  is slightly lowered, for example, because of its higher loading, so that the center point M of the wheel  4  is vertically offset with respect to the axis C of the force F by a distance M′. When the braking force F is introduced, the brake pad can adapt itself to a respective position of the surface  7 , the tension bows  11  are displaced via the articulations or axes  14  and  17  in a parallelogram-type manner, so that the brake pad  8  can rest against the surface  7 . 
     For initiating a braking operation, a tension force F may be applied by a caliper, which is not shown. The tension force presses the brake pad  8  onto the surface  7  via the suspension arrangement, in order to generate a desired braking torque. As a result of the introduction of the tension force F in the center of the transverse lug  15 , the two tension bows  11  can be mutually displaced when this is required by a change of a slope of the brake pad  8 , or in the case of a vertical movement of the wheel  4 . As a result of a frictionally engaged prestressing at the articulations  14  and  17 , it can be achieved in this case that, after a release of the brake, the slope of the brake pad  8  is maintained and changes only when another angle of slope is defined by a compression change of the wheel  4 . The force applied to the brake pad  8  during a braking engagement will then result in an angular change between the tension bows  11  and the transverse lugs  15  and  18 , in which case the frictionally engaged prestressing is then overcome. 
     Sintered plastic, as well as sintered gray cast iron pads, can be used for the brake pad  8 . It is also conceivable to use elastic brake pads which are formed of several individual friction material elements which are prestressed toward the braking surface. Concerning the possible construction of the brake pads, reference is made to the disclosure of German Patent Document DE 19840065. 
     In the embodiment illustrated in  FIG. 4 , a brake pad assembly is provided which has slightly modified brake pads  8 ′ held on tension bows  11  and  12  on both sides of the wheel web  2 ′ The suspension of the brake pads  8 ′ takes place as described in the preceding embodiment. 
     The brake pads  8 ′ have a friction surface which, like the surface  7 ′ on the wheel flange  5 ′, is constructed to be slightly sloped with respect to the wheel web  2 ′. When a force F is introduced via the tension bows  11  and  12 , a normal force F N  is generated which is slightly sloped with respect to the vertical and presses the brake pad  8 ′ toward the wheel web  2 ′. As a result, the brake pad  8 ′ rubs not only on the surface  7 ′ but also on a section  25 ′ of the wheel web  2 ′ to which a braking force F ax  is applied. Therefore, during a braking operation, section  25 ′ of the wheel web  2 ′ is also heated up, which reduces thermal tensions within the wheel  4 ′. In addition, as a result of the sloped construction of the surface  7 ′, a centering of the brake pads  8 ′ is caused. Since brake pads  8 ′ are provided on both sides of the wheel web  2 ′, occurring axial forces are compensated. 
     In the embodiment illustrated in  FIG. 5 , in addition to the brake pad  8 ′ situated on the inside, a brake pad  30  situated on the outside is mounted on the suspension  20 ,  22 . A mechanically, pneumatically or hydraulically acting cylinder  31  is mounted on a transverse lug  15 ′, a piston rod force of the cylinder  31  acts on the brake pad  8 ′ situated on the inside and a cylinder block reaction force acts upon the brake pad  30  situated on the outside. A pendulum suspension, including the transverse lugs  15 ′ and  18  as well as the hanging lugs  19  and  21 , takes place as in the embodiment of  FIG. 2 . As a result of the combination of a brake pad  8 ′ situated on the inside and a brake pad  30  situated on the outside, performance of the shoe brake assembly is considerably increased. The two-sided arrangement of brake pads  8 ′ and  30  provides a more uniform thermal heating of the wheel  4  during the braking operation so that thermal tensions are reduced. 
     In the embodiment illustrated in  FIG. 6 , a brake pad  8  is provided on both sides of a wheel web  2 ,  2 ′ (but not shown here). The brake pad  8  is situated on the inside and is held via two tension bows  11 . Using the embodiment of  FIGS. 1 to 3  for comparison, the holding lug  19 , which was linked to the articulation  14  of the upper tension bow  11 , is replaced by a separate holding lug  40  which is linked to one articulation  42  on the tension bow  11  and to another articulation  41  on the bogie  80 . The articulation  42  is situation in the direct proximity of the brake pad  8 , at least in the area of the wheel  4 , so that a frictional force of the pad  8  can be introduced directly forward or into the holding lug  40 . This possible stiffer linkage of the brake pad  8  will then result in lower braking noises during the operation. 
     In  FIG. 7 , a brake pad  8  is disposed on the bogie  80  via a single linkage. For this purpose, a tension bow  60  is provided on one or both sides of the wheel  4 , which tension bow  60  simultaneously forms a tension rod. The tension bow  60  is connected in an articulated manner with two holding lugs  61  and  62  which, in turn, are linked to the bogie  80 , which is not shown in detail. At the end of the tension bow  60  facing the wheel  4 , the tension bow  60  is connected via an articulation  64  with a pressure piece  65  which presses the brake pad  8  against the surface  7  of the wheel  4  during a braking operation. In this case, the holding lug  62  is linked to the tension bow  60  in the direct proximity of the brake pad  8 . 
     In the embodiment illustrated in  FIG. 8 , the shoe brake assembly is mounted on the bogie  80  via a lever linkage. For generating a braking force, the brake pad  8  is pressed via a pressure piece  74  against the surface  7  on the wheel  4 , the pressure piece  74  being movable via a tension bow  70  received at an end side in a cylinder  71 . The cylinder  71  if fixed to the bogie  80  via a plate  72  and may operate in a hydraulic or pneumatic manner or be equipped with an operating mechanism. The pressure piece  74  is connected with a holding lug  75  by way of an articulation  73 , which holding lug  75  is mounted on the bogie  80  via an articulation  76 . Also in this embodiment, the holding lug  75  is linked in the direct proximity of the brake pad  8 . 
     Features of the illustrated embodiments can be combined with one another in order to create other embodiments of the shoe brake assembly, according to the principles of the present disclosure. For example, the sloped arrangement of the braking surfaces can also be used in the embodiments of  FIGS. 5 and 6 . Furthermore, it is conceivable to design the suspension of the brake pad  8  in a different manner and to cause the operation of the brake pad  8  via a known lever mechanism. 
     Although the present disclosure has been described and illustrated in detail, it is to be clearly understood that this is done by way of illustration and example only and is not to be taken by way of limitation. The spirit and scope of the present disclosure are to be limited only by the terms of the appended claims.