Abstract:
The invention relates to an assembled undular brake disc having a hub and having two friction rings which are arranged parallel to and spaced apart from one another, which assembled undular brake disc can withstand high mechanical loads and permits good internal ventilation, wherein an insert element with arms extending radially outward in a stellate manner is arranged between the friction rings.

Description:
FIELD OF INVENTION 
     The present invention relates to an assembled axle brake disc with a hub and two friction rings which are arranged parallel to and spaced apart from one another. 
     BACKGROUND OF THE INVENTION 
     Assembled axle brake discs are used in particular for rail vehicles, and due to the built form of the axle brake discs, these can be assembled from several individual components. 
     An assembled axle brake disc is understood as being primarily an axle brake disc that is assembled from at least two components. In particular, an assembled axle brake disc is intended to describe a brake disc that comprises two friction rings that are not formed as a single piece and that share a uniform structure, for example as is known in a casting method, but which are provided individually and which are preferably assembled using further elements to form a friction ring pair using joining techniques. As a further individual part, the hub can be joined in an assembly with the friction ring pair. 
     For example, axle brake discs are known that comprise a hub, to which the two friction rings are attached parallel to and spaced apart from one another. Between the friction rings, connecting elements can be located that are designed to absorb axially acting pad contact pressure forces. In particular in the case of heavy rail vehicles, the pad contact pressure forces that are applied onto the friction ring pair by the brake linkage via the brake pads can reach very high values. For this reason, the need arises to embody axle brake discs with connecting elements that are arranged between the friction rings in a suitably stiff and mechanically highly resilient manner. 
     Furthermore, good heat removal is required, and it is frequently provided that an airflow is generated between the friction rings that for example axially flows onto the axle brake disc on the hub side and flows out radially on the outside. As a result of this air throughput, the brake disc can be cooled by heat convection between the friction rings, and the airflow is generated through the rotation of the axle brake disc around its axis of rotation. In particular in the case of cast axle brake discs, casting geometries between the friction rings are known that simulate the geometry of a radial fan, so that the corresponding air throughput results through the axle brake disc. 
     In particular, assembled axle brake discs as ceramic brake discs are known, which comprise friction rings made of a ceramic material, generally however of a material from the group of carbons. Frequently, the hub of such non-metallic brake discs is made of a steel material, and elaborate connecting geometries are required in order to avoid heat-induced distortions between the ceramic or carbon material and the metallic hub for receiving the friction rings. 
     PRIOR ART 
     From DE 195 07 922 C2, an assembled axle brake disc is known that comprises two friction rings arranged in parallel to and spaced apart from one another on a hub. Between the friction rings, a fan insert is located that serves for improving the cooling on the inside of the friction rings. In order to receive axially acting pad contact pressure forces for the braking operation, the shown fan insert is however unsuitable, and axial forces that act through the brake calliper via the brake pads onto the friction rings must be received via the connection between the friction rings and the hub. For this reason, a design of an axle brake disc that comprises a somewhat lower mechanical load capacity is obtained. 
     From DE 195 43 799 A1 a further assembled axle brake disc is known, and between friction rings made of a material from the group of carbons, connecting elements extend in order to absorb the high axially acting pad contact pressure forces. Such a construction is known for assembled axle brake discs with friction rings that are made of ceramic or a material from the group of carbons. The built form of the axle brake disc is in particular used because positively joined connections between the friction rings of a material from the group of carbons to a hub that is as a rule produced from steel cannot be used in a simple manner. As a result, screw connections or other force- or form-fit connecting techniques are used, wherein in the assembly joint between the friction rings and the hub, elements are frequently also arranged that offset the different thermal expansion between the hub made of a steel material and the friction rings made of ceramic or a material from the group of carbons, for example formed by slot nuts. 
     In particular when a rigid, highly resilient, solid connection is used between the friction rings, the disadvantage arises of a high degree of spatial filling between the friction rings, as a result of which the ventilation of the axle brake disc is in turn hindered. 
     SUMMARY OF THE INVENTION 
     It is therefore the object of the present invention to provide an assembled axle a brake disc with friction rings that can withstand high mechanical loads, and which enables good internal ventilation. 
     This object is attained by means of an assembled axle brake disc, comprising: a hub; and two friction rings which are arranged parallel and spaced apart from one another; wherein between the friction rings an insert element is arranged with arms extending radially outward in a stellate manner. 
     The invention includes the technical principle that between the friction rings, an insert element is arranged with arms extending radially outward in a stellate manner. 
     Due to the arrangement according to the invention of an insert element that comprises arms extending radially outward in a stellate manner, an axle brake disc with high mechanical resilience is provided, since the insert element can be built from a solid, preferably steel material body. If when the axle brake disc is operated pad contact pressure forces act on the friction rings, these forces can be absorbed by the solid structure of the friction rings in the packet with the insert element without significant elastic distortions. On the other hand, the insert element is designed to provide good internal ventilation despite the high axial rigidity of the axle brake disc, since the arms of the insert element that simultaneously rotate create good ventilation of the axle brake disc. 
     Furthermore, supporting bolts can be provided that are arranged additionally to the insert element between the friction rings. Here, the supporting bolts do not require a connection to the insert element, in particular to the arms of the insert element. For example, the supporting bolts can be arranged between the arms of the insert element, preferably in order to generate a tangential airflow between the friction rings in addition to a radial airflow generated by the arms. Here, the supporting bolts can for example comprise a cylindrical form, and adopt a cooling function alongside the supporting function for further absorption of pad contact pressure forces on the friction rings. 
     The friction rings can also preferably be made of a steel material, wherein however for the friction rings, a material from the group of carbons can also be used. In a particularly advantageous manner, the friction rings can be made of a heat-resistant steel material, while for the insert element, low-cost, heat-treatable steel can be selected. In order to procure simple, minimal cost and rapid production of the assembled axle brake disc, according to a further advantage of the invention, it is provided that the friction rings are soldered to the insert element. The solder can be arranged in the form of a paste or foil into the joints between the insert element and the friction rings. The soldering method can be brazing and in a particularly preferred manner, high-temperature soldering, wherein in particular the high-temperature soldering can be conducted in a vacuum or in a protective gas atmosphere. If the high-temperature soldering is conducted in a protective gas atmosphere, nitrogen can in particular be used as a protective gas. In particular, the connection between the supporting bolts and the inner sides of the friction rings can also comprise a solder connection, and the bolts can be bluntly placed on the inner surface of the friction rings without the supporting bolts having to be retained in holes in the friction rings. 
     As an alternative to the connecting technique of soldering, the connections between the insert element or the supporting bolts and the friction rings can also comprise screw connections, rivet connections or weld connections, for example. 
     With the combination of the insert element and the friction rings, a friction ring pair is created that can be handled individually without the hub. In particular, due to the friction ring pair that is provided as an individual replacement part, the advantage is created that with a hub, which for example can be mounted in a rail vehicle on an axle, an old friction ring pair can be replaced by a new friction ring pair. 
     As a further advantage, it can be provided for the connection between the friction ring pair and the hub that the connection is created between the insert element and the hub. The connection between the insert element and the hub can for example be created by several screw connections, wherein the insert element comprises an opening on the inner side, in which the hub is arranged and connected to the insert element. 
     In order to form the screw connections, the insert element can comprise several holes, and on the hub, several protrusions can be provided that are directed radially outwards, which are also designed with holes. In order to produce the screw connections, screw elements can be used that are fed through both the holes in the insert element and the holes in the protrusions in the hub. For example, on the circumference between the hub and the opening in the insert element, nine screw connections can be arranged at an equal distance from each other. 
     According to a further advantage, one, preferably several and in a particularly preferred manner, three screw connections can be provided with a sliding block in order to position the insert element with the friction rings on the hub. The sliding blocks can sit with one body part in a pocket milled into the protrusion of the hub, and with a further body part the sliding block can be inserted into a centring hole that is arranged on the insert element. Alternatively, the option advantageously also exists of inserting the slot nuts into pockets that are arranged on the inner side on the insert element. 
     Furthermore, it is advantageous when the screw connections comprise screw nuts, which are screwed to the screw elements when these are fed through the holes in the insert element and in the protrusions of the hub. It is also advantageous when a retaining ring is used, against which the screw nuts are tensioned. The retaining ring can comprise a ring form, and a number of holes are created in the ring, through which the screw elements are fed through. Finally, the screw nuts can be screwed onto the ends of the screw elements and tensioned against the retaining ring, in particular using tension plates. 
     The insert element can comprise a flat extension, and the insert element can for example be of approximately double the thickness of a friction element. In the centre of the insert element, an opening can be created, which is designed as a circle, and which extends centrally around the axis of rotation of the axle brake disc. Essentially, the insert element can be formed from a basic section, and from the basic section, the arms extend radially in an outward direction. As a result, the insert element forms a star, and the arms form the essential supporting bodies between the friction rings, in order to absorb the pad contact pressure forces that act in the axial direction on the axle brake disc. The friction rings also comprise an opening on the hub side, into which the hub is inserted. The basic section of the insert element can here comprise a maximum diameter that is smaller than the central opening in the friction rings. Thus, only the arms of the insert element extend between the friction rings. 
     For example, the insert element can comprise 6 to 30, preferably 12 to 24, and in a particularly preferred manner, 18 arms, wherein arms with a broad form and arms with a narrow form can be provided, which in particular are arranged alternately in their broad and narrow form on the basic section of the insert element. Thus, an arm with a broad form is adjoined on both sides by arms with a narrow form, and arms with the narrow form are adjoined on both sides by arms with the broad form. Thus, nine arms with the narrow form and nine arms with the broad form can be arranged on the basic section of the insert element. 
     In particular in order to improve the aeration for the interior ventilation of the axle brake disc, it is advantageous that a portion of the plurality of arms, in particular a portion of the arms with the narrow form, is separated from the basic section. Thus, only the arms with the broad form create a connection between the friction ring pair and the insert element and the hub. The separation of the arms from the basic section is achieved by removing material from the basic section, so that for example the bridges that extend between the arms and the central opening in the basic section of the insert element are removed. The removal of the bridges can be achieved for example by means of milling, but also through laser beam cutting or water jet cutting. As a result, the arms with the narrow form can extend from the outer side of the friction rings to the inner side of the friction rings, and the arms with the broad form can extend from the outer side of the friction rings to the join on the protrusions on the hub. 
     The insert element can be formed from two partial elements that adjoin each other with flat surfaces, and are in particular soldered together, so that the partial elements can comprise a base material that only comprises half the thickness of the insert element, and the partial elements can also be connected to each other by means of a brazing method or high-temperature soldering. 
     The object of the present invention is further attained by means of a method for producing an axle brake disc with a hub and two friction rings, which are arranged parallel to and spaced apart from one another. Here, the method envisages at least the steps of providing an insert element with a flat design, with arms extending radially outwards in a stellate manner and the joining of the friction rings to the flat sides of the insert element, so that the insert element is arranged between the friction rings, and further, the step of joining the insert element to the hub is envisaged. 
     The joining of the friction rings to the insert element can be conducted using a soldering procedure, preferably using brazing and in a particularly preferred manner using high-temperature soldering in a vacuum or in a protective gas atmosphere. In particular, the insert element and/or the friction rings can be heat treated, wherein the heat treatment can in particular be conducted in combination with the method step of brazing or high-temperature soldering in a vacuum or in a protective gas atmosphere. 
     First, the friction rings and/or the insert element can be cut from metal sheets using a thermal or abrasive cutting method, in particular using laser beam cutting or water jet cutting. Here, the insert element can be provided by two partial elements that share a uniform structure and that are arranged parallel to each other on the plane. Here, the partial elements can also be connected to each other by means of a soldering procedure. Alternatively, production is possible by sawing round material Ø640 to the corresponding thickness. 
     When producing the friction rings and the insert element, holes can be provided in the friction rings and in the insert element by means of laser beam cutting or water jet cutting, and when the friction rings and the insert element have been brought in contact with each other in their packet arrangement, clamping pins can be fed through the holes. As a result, a centring of the friction rings on the insert element is achieved, and after the solder has been arranged in the joints between the partial elements of the insert element and between the friction rings and the insert element, the packet consisting of the insert element and the friction rings can be placed in a vacuum furnace. This can heat the friction rings and the insert element to a soldering temperature of e.g. 1050° C. to 1070° C., and the temperature is maintained until the solder melts and a connection is formed in the respective joints. Then, the packet consisting of the insert element and the friction rings, through which now, a friction ring pair has been formed that can be handled individually, is quenched in the vacuum furnace, for example by using nitrogen, and annealed. As a result, the soldering process is accompanied by the desired process of heat treatment. Here, the entire process can take place in the vacuum furnace. Alternatively, only the soldering process can take place in the vacuum furnace, wherein subsequently, however, the friction ring pair is transferred in a separate furnace for the heat treatment, and oil can be used, for example, as the quenching medium in order to achieve a higher quenching speed, wherein the use of water, a polymer or other media is also possible. As a result, in the friction rings, but also in the insert element, a certain framework structure can be achieved, which gives the axle brake disc particularly advantageous material properties. After the soldering, or after the heat treatment, the friction ring pair can be brought to a defined thickness by machining the outer surfaces of the friction rings. The clamping pins can be of a length that is less than the thickness of the friction ring pair. Alternatively, protruding sections of the clamping pins can be milled off by machining the friction ring pair, or the clamping pins are again removed from the friction ring pair following the soldering process. 
     The insert element can comprise a basic section onto which the arms are arranged that extend outwards in a radial direction, and as a further, in particular final method step for processing the friction ring pair, it can be provided that a portion of the number of arms is separated from the basic section, in particular by machine-cutting processing of the basic section. In particular, the arms with the narrow form can be detached from the basic section by cutting out the root area of the narrow arms at the transfer point to the basic section through milling, so that the arms with the narrow form only extend radially from the outer side of the friction rings to the inner side of the friction rings. By contrast, the arms with the broad form extend radially inwards from the outer side of the friction rings to the overlap with the protrusions in the hub, in order to create the screw connections between the hub and the arms. As a result of this measure, the interior ventilation in particular of the axle brake disc is improved, since the basic section of the insert element is not hindered by an air throughput. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further measures that improve the invention will be presented in greater detail below together with the description of preferred exemplary embodiments of the invention with reference to the figures, in which: 
         FIG. 1  shows an exemplary embodiment of an axle brake disc in a perspective view with the features of the present invention 
         FIG. 2  shows a cross-section through an axle brake disc with an insert element and friction rings arranged on this 
         FIG. 3  shows a perspective view of a further exemplary embodiment of an insert element 
         FIG. 4  shows a cross-section view through the insert element and the friction rings, wherein a clamping pin is shown for positioning the friction rings on the insert element 
         FIG. 5  shows a top view onto the axle brake disc with the friction rings and the insert element before milling of the insert element, and 
         FIG. 6  shows a top view onto the axle brake disc after milling has been conducted on the insert element, and wherein the hub is connected to the insert element. 
     
    
    
     The same reference numerals from different exemplary embodiments refer to the same functional parts, with slightly different features. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows in a perspective view an exemplary embodiment of an axle brake disc  100  according to the invention, and the axle brake disc  100  is compiled from several individual parts, so that the axle brake disc  100  is designed as an assembled axle brake disc  100 . 
     The axle brake disc  100  comprises a hub  10 , and in the hub  10  a central passage is created, through which a shaft can extend on which the axle brake disc  100  is arranged. Further, the axle brake disc  100  comprises friction rings  11  and  12 , which are arranged parallel to and spaced apart from one another, and which form the friction surfaces for contact with brake pads. 
     According to the invention, an insert element  13  is inserted between the friction rings  11  and  12 , which comprises arms  14  that extend radially outwards in a stellate manner. The arms  14  are arranged at equal distances over the circumference of the axle brake disc  100 , wherein the exemplary embodiment comprises nine arms  14 . The arms  14  are designed with a length such that they end flush with the outer circumference of the friction rings  11  and  12 . 
     On the hub  10 , protrusions  20  are arranged that extend over a basic section  24  of the insert element  13  and are brought into overlap with this. Between the basic section  24  of the insert element  13  and the protrusions  20  of the hub  10 , screw connections  15  are provided that are essentially formed by screw elements  18 . Thus, the friction rings  11  and  12  are connected to the hub  10  via the insert element  13  and the friction rings  11  and  12  together with the insert element  13  form a friction ring pair, which can be arranged as an assembly that can be individually handled on the hub  10 . If for example a replacement of a worn friction ring pair on the axle brake disc  100  is required within the scope of maintenance work, it is only necessary to detach the friction ring pair from the hub  10  and replace it with a new friction ring pair. 
     Due to the stellate structure of the insert element  13  with the basic section  24  and the arms  14  that extend radially outwards from the basic section  24 , an airflow is created through the axle brake disc  100 , which flows through the axle brake disc  100  from the inside outwards, and the flow occurs between the arms  14 . 
     In a manner not shown in greater detail, cooling elements can be provided between the friction rings  11  and  12 , which are for example arranged on at least one of the inner sides of the friction rings  11  and  12 . The cooling elements can for example be arranged using stud welding, or also using a screw fitting or a solder, on the inner side of the friction rings  11  and  12 . As a result, the ventilation of the axle brake disc  100  can be further improved. 
       FIG. 2  shows a cross-sectional view through the axle brake disc  100 , of which only half the side is shown. Here, the hub  10  is shown with a protrusion  20  in cross-section, and on the protrusion  20 , the insert element  13  is arranged using a screw connection  15 . The screw connection  15  shows the screw element  18 , which extends through a hole  16  in the insert element  13  and through a hole  17  in the protrusion  20 . Adjacent to the protrusion  20 , a sliding block  21  is arranged, which sits in a form-fit manner in a pocket milled into the protrusion  20 . A further section of the sliding block  21  extends in a form-fit manner into the hole  16  in the insert element  13 , so that the insert element  13  is centred via the sliding block  21  to the hub  10 . 
     Further, the screw connection  15  comprises a screw nut  22 , which is screwed onto the free end of the screw shaft of the screw element  18 . Below the screw nut  22 , a washer  28  is arranged, together with a retaining ring  23  that surrounds the hub  10 , and in the retaining ring  23 , a number of holes are provided in order to guide the corresponding number of screw elements  18  through the retaining ring  23 . 
     On the outer side of the insert element  13 , friction rings  11  and  12  are arranged, and the insert element  13  is formed from a first partial element  13   a  and a section partial element  13   b , and the partial elements  13   a  and  13   b  are brought into contact with each other on a flat parallel. The joints  29  between the friction rings  11  and  12  and between the partial elements  13   a  and  13   b  of the insert element  13  are designed as solder joints, and the friction rings  11  and  12  are soldered with the insert element  13 , in particular also together with the partial elements  13   a  and  13   b  in a vacuum furnace using a high-temperature soldering process. The insert element  13  can also be designed as a single part, so that the joints  29  are limited to the connections between the friction rings  11  and  12  and the insert element  13 . 
       FIG. 3  shows a perspective view of an insert element  13  with a basic section  24 , from which  18  arms  14  in total extend radially outwards. In the basic section  24 , an opening  19  is created, in which the hub  10  can be arranged. 
     The arms  14  are formed by arms  14  with a broad form and arms  14  with a narrow form, which are arranged alternately in their broad and narrow form adjacent to the basic section  24  of the insert element  13 . The exemplary embodiment of the insert element  13  shows the arms  14  with forms that are curved in the lateral direction, so that the arms  14  comprise a bulged contour, and the arms  14  with the narrow form taper severely in their arm root  30  in the transfer point to the basic section  24 . By contrast, the arms  14  with the broad form comprise a correspondingly large transfer point cross-section to the basic section  24 , without tapering. 
     Further, in for example three arms  14 , holes  27  are created, via which the friction rings  11  and  12  can be positioned on the insert element  13 , as is shown in greater detail in the following  FIG. 4 . 
       FIG. 4  shows a cross-section through the friction ring pair with the friction rings  11  and  12  and the insert element  13 , which is for example formed from the two partial elements  13   a  and  13   b . In the insert element  13 , the hole  16  for guiding through the screw element  18  is shown, in order to connect the friction ring pair via the insert element  13  to the hub  10 , as has already been described in  FIG. 2 . 
     In order to centre the friction rings  11  and  12  on the insert element  13 , a hole  26  is created in each of the friction rings  11  and  12 , and the holes  26  are flush with the hole  27  in the insert element  13 . A clamping pin  25  is inserted into the holes  26  and  27 , via which the friction rings  11  and  12  are positioned on the insert element  13 . Overall, holes  27  can be created in three arms  14 , and corresponding to the holes  27  in the arms  14 , in each friction ring  11  and  12 , three holes  26  are also created. Here, the holes  26  and  27  can already be produced during production of the friction rings  11  and  12 , as well as during production of the insert element  13 , using the thermal and/or abrasive separation process. The dimensional accuracy of the holes  26  and  27  can for example already be sufficient using laser beam cutting or water jet cutting in order to ensure the required centring of the friction rings  11  and  12  on the insert element  13 . 
     In  FIG. 5 , the axle brake disc  100  is shown in a top view, and on the insert element  13 , the friction rings  11  and  12  are shown in an arranged manner. The friction rings  11  and  12  are already soldered to the insert element  13 , and the basic section  24  of the insert element  13  protrudes on the inner side from the respective central opening  31  of the friction rings  11  and  12 . The insert element  13  comprises arms  14  with a broad and a narrow form, and with one arm  14  with the narrow form, a material cut-off  32  in the basic section  24  of the insert element  13  is shown, which comprises the arm root  30  of the arm  14 . 
     The method for producing the axle brake disc  100  comprises, according to the exemplary embodiment shown, a method step in which the material cut-off  32  is removed from the basic section  24  of the insert element  13  on each arm  14  with the narrow form using a machining process. For example, the material cut-off  32  can be milled out of the basic section  24 , so that the arm  14  with the narrow form remains between the friction rings  11  and  12 . The connection to the hub  10  is thus achieved via the ends of the arms  14  with the broad form that are directed radially inwards, in which the holes  16  have been created. Here, holes  16 ′ are formed as passage holes, and the holes  16  that have a larger diameter serve to retain a section of the sliding block  21 , as shown in  FIG. 2 . 
       FIG. 6  finally shows the axle brake disc  100  in its finished form. Between the friction rings  11  and  12 , the insert element  13  is located, which is now formed from the arms  14  that extend radially between the friction rings  11  and  12 . The arms  14  with the narrow form extend from the central opening  31  of the friction rings  11  and  12  through to the outer edge, and the arms  14  with the broad form extend from the outer side of the friction rings  11  and  12  into the opening  31  in order to create an overlap with the protrusions  20  of the hub  10 . Finally, the arms  14  with the broad form with the protrusions  20  can be affixed via the screw connections  15  to the hub  10 . This provides the arrangement of the friction ring pair with the friction rings  11  and  12  via the arms  14  with the broad form with the hub  10 . The insert element  13  is shown with the material cut-offs  32  that have already been removed using a machining process, see  FIG. 5 . Following the removal of the material cut-offs  32 , the arms  14  are detached from each other, so that the basic section  24  of the insert element  13  is now limited to the ends of the arms  14  that are directed radially inwards. 
     Due to the insert element  13 , which is restricted solely to the arms  14 , the aeration of the axle brake disc  100  is further optimised, since a free airflow can be created from the inner side to the outer side between the friction rings  11  and  12 . At the same time, a high degree of rigidity in the axle brake disc  100  with a relatively low weight is achieved, since the arms  14  form a sufficiently rigid insert between the friction rings  11  and  12 . 
     The invention is not restricted in its implementation to the preferred exemplary embodiment described above. To a far greater extent, a number of variants are possible, which also use the solution presented with embodiments of a fundamentally different type. All the features and/or advantages arising from the claims, the description or the drawings, including structural details or spatial arrangements, can be essential to the invention both in their own right and in a wide range of different combinations.