Abstract:
Brake shoe, in particular of a drum brake for utility vehicles, includes a lining plate and a bridge unit, wherein the bridge unit is formed as a one-piece body comprising at least two bridge plates.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The present invention relates to a brake shoe, in particular a drum brake for utility vehicles, a bridge unit for a brake shoe and a drum brake. 
         [0002]    Drum brakes are still the preferred brake type in the utility vehicle segment and for trailers. Here, the basic structure comprises a rotating brake drum, against which two movably mounted brake shoes are pressed from the inside by an appropriate device, which produces the braking force. Known brake shoes normally comprise a number of parts which, for example, are joined together by welding and pressing: the lining plate, two webs, which are fixed to the lining plate at the rear, and corresponding mounting points or mounting shells which are used to mount the brake shoe. The outlay on fabrication and handling during the production of the brake shoes is correspondingly high. In addition, on account of the relatively high number of components, inaccuracies quickly arise during the joining, in particular as a consequence of the accumulating tolerances. 
         [0003]    It is therefore an object of the present invention to specify a brake shoe, a bridge unit of a brake shoe and a drum brake which are quicker, simpler and still more accurate and more economic to produce. 
       SUMMARY OF THE PRESENT INVENTION 
       [0004]    According to the invention, a brake shoe, in particular of a drum brake for utility vehicles, comprises a lining plate and a bridge unit, the bridge unit being formed as a one-piece body having at least two bridge plates. Typically, the drum brake comprises a brake drum, against which two movably mounted brake shoes, for example on a brake carrier or a brake anchor plate, are pressed from the inside by an appropriate device. The mounting of the brake shoe and the introduction of force take place via the bridge plates, which advantageously impart the necessary stiffness to the entire arrangement. Pressing on the brake shoes can be carried out directly mechanically via a camshaft, an expanding wedge or a wheel brake cylinder. In order to provide the actual braking action, an appropriate brake lining is arranged on the lining plate of the brake shoe, in particular riveted, for example. In the prior art, two mutually independent flanges or else webs are welded onto the rear side of the lining plate. These have to be positioned exactly relative to the lining plate and to each other since, as already mentioned, the mounting of the brake shoe and the introduction of force take place via the webs or bridge plates. Advantageously, the brake shoe now has the bridge unit, which is formed as a one-part or one-piece body comprising the at least two bridge plates. This configuration makes it possible to dispense with tolerances which would arise as a result of the assembly of the individual components. Since the bridge unit consists of one piece, the coordination during the mounting requires less outlay. Fabrication and mounting steps can therefore be dispensed with as compared with the prior art. The bridge unit can be fixed as a unit to the rear side of the lining plate with a form fit and/or force fit and/or an integral connection. It is preferably welded, for example. Advantageously, the bridge unit is formed from a homogeneous material. 
         [0005]    According to one embodiment, the bridge unit is a deep-drawn part, for example, the bridge unit and the lining plate preferably being connected via the welded connection. The bridge unit can also be formed from a multiplicity of deep-drawn plates, preferably two, which are adhesively bonded and/or welded to each other. Thus, the bridge unit can have a sandwich-like structure. Alternatively, the bridge unit can also be produced by forging, bending, peening, hydroforming or pressing. The bridge unit can also be folded. Alternatively, the bridge unit can also be formed as a one-piece welded construction, which is then fixed to the lining plate as a unit. The term unit or the one-piece design is in particular to be understood to mean that the bridge unit is preferably (entirely) formed from a homogeneous structure or material. Depending on the embodiment, however, it is not ruled out that this structure is interrupted, by a welded seam, for example. Instead, what is important is that the bridge unit, when it is not arranged on the lining carrier, is a (single) component, comprising at least two bridge plates, which as a rule are connected either via a transverse plate or via a connecting plate. 
         [0006]    According to one embodiment, the bridge unit has at least one connecting plate, which connects the two web surfaces. According to one embodiment, the connecting plate is oriented substantially parallel to the lining plate or replicates the orientation of the latter. Expediently, the connecting plate is arranged on an edge of the bridge plates that faces away from the lining plate. The maximum spacing of the connecting plate relative to a rear side of the lining plate in preferred embodiments is about 40-100 mm, preferably about 50-90 mm. Here, the spacing is highest in the central region of the lining carrier, since here the highest forces have to be absorbed. Expediently, the spacing of the connecting plate from the rear side of the lining carrier is highest in the center of the brake shoe and falls off on both sides along the bridge unit, that is to say along a circumferential direction of the brake drum. Therefore, a reduction in weight can advantageously be achieved. The aforementioned spacing corresponds substantially to the height of the bridge plates, which will be explained further below. The connecting plate or the connecting plates extend/s substantially along the circumferential direction. Transversely thereto, the bridge unit according to one embodiment is connected by at least one transverse plate which, so to speak, constitutes one end of the bridge unit in the circumferential direction. According to one embodiment, the bridge unit is therefore entirely closed. Bridge plates and transverse plates form a circumferential arrangement surface, via which the arrangement on the rear side of the lining plate, that is to say the side facing away from the friction lining, is carried out. This closed structure is extremely stiff and can accordingly be implemented with thin walls and light weight. In principle, it should be mentioned at this point that the material of the bridge unit and also for the lining plate is preferably a steel material. A wall thickness of the bridge unit in preferred exemplary embodiments is around 1-8 mm, particularly preferably around 2-6 mm. 
         [0007]    According to one embodiment, the connecting plate has at least one opening or a recess or forms the same. This likewise permits a further reduction in weight and can in addition be used for dissipation of heat from the bridge unit formed in one piece. The opening can be formed as a hole, in particular as a round or circular hole. However, also preferred is an elongated opening, which extends along the circumferential direction, at least in some sections. The width of the opening is dimensioned in such a way that parts of the connecting web still remain. This permits a high stiffness and low use of material, especially in the longitudinal direction/circumferential direction. According to one embodiment, a ratio of a width of the connecting plate to a width of the opening lies in a range from about 0.1-0.9, preferably around 0.2-0.8. The connecting plate in general advantageously permits an increase in the stiffness of the bridge unit and improved dissipation of heat and also heat distribution. Thus, heat differences and temperature peaks from one bridge plate to the other can easily be compensated for via the connecting plate. Via the arrangements of openings/recesses in the connecting plate or connecting plates or possibly also in the bridge plates themselves, the temperature distribution can be adapted individually. Particularly expediently, by means of two openings (for example round opening and slot) located adjacent to each other in the connecting plate, a web area is formed which forms an engagement area for a return spring to be hooked in. 
         [0008]    According to one embodiment, the bridge plates extend substantially in the form of a curve, in particular convexly, with reference to a mid-plane of the lining plate. The mid-plane is that plane which extends centrally and at right angles to the lining plate, along the longitudinal direction of the latter or along the circumferential direction. As a rule, the mid-plane is also the plane of symmetry. The curved form can be seen in particular in a plan view of the rear side of the brake shoe. Expediently, the width of the bridge unit in the center is therefore greater than at its respective ends. Expediently, a ratio of a minimum width to a maximum width lies around 0.05-0.8, preferably around 0.08-0.7. This configuration permits an optimal strength and stiffness of the brake shoe with minimal use of material. In addition, as a result of the course of the bridge plates on the rear side of the lining plate, the dissipation of heat from the lining plate is effected in the best way possible. According to one embodiment, the bridge plates also extend rectilinearly in plan view but are nevertheless aligned in such a way that they extend obliquely with reference to the mid-plane. Starting from the respective ends of the bridge unit, the bridge plates therefore describe an angle toward the center which, for example, lies in a range from about 2°-30°, preferably about 4°-25° and particularly preferably 10°-20°. Expediently, the bridge unit is designed to be symmetrical, in particular axially symmetrical, with reference to the mid-plane. 
         [0009]    According to one embodiment, the bridge plates are also inclined with respect to a mid-plane of the lining plate. In combination with the connecting plate, the result is therefore expediently a trapezoidal shape, a geometry which counteracts the forces that arise extremely well. An angle of the bridge plate (measured on the outside of the bridge unit) measured relative to the rear side of the lining plate according to one embodiment lies, for example, in a range from about 90°-130°, preferably at about 92°-105°. In particular, at their sides or edges facing the lining plate, the bridge plates can be spaced further apart from each other than at their sides or edges facing away from the lining plate. 
         [0010]    According to one embodiment, the bridge unit is designed in such a way that a stiffness of the bridge unit increases toward the center of the brake shoe. Here, toward the center means in particular toward the center “as seen in the circumferential direction”. Thus, for example, the height of the bridge plates in the central region is greater than toward the corresponding end regions, where the brake shoe is mounted or where the introduction of force takes place. The decrease in height can take place continuously or also in a stepped manner or in steps. Expediently, the minimum height of the bridge plates, which is measured in the region of the functional areas at the edge, in relation to a maximum height of the bridge plates in the center lies in a range from 0.2 to 0.8, preferably in a range from 0.3-0.7. Here, the height of the bridge plates is measured at right angles to the lining carrier. Incidentally, this also applies to the spacing of the connecting plate or plates. 
         [0011]    According to one embodiment, the brake shoe comprises two bridge units, which are connected to each other along a dividing plane, in particular welded. The dividing plane extends here substantially transversely with respect to a longitudinal direction or circumferential direction of the brake drum and the brake shoe. In particular, the dividing plane is substantially also transverse with respect to the mid-plane (however, an angle not equal to 90° is also possible). Such a configuration can be advantageous in particular with regard to the fabrication of the bridge unit, since further possibilities therefore result, such as for example folding or pressing/bending/peening from one piece of sheet metal. 
         [0012]    According to one embodiment, the bridge unit forms at least one functional area, in particular a bearing section, which in particular is formed spherically or cylindrically. In addition, a functional area can be also a force introduction area. In the prior art, the force introduction area is configured, for example, via a cam roller which is (rotatably) fixed to the webs. Advantageously, just this function is provided directly by the bridge unit as a result of the cylindrical configuration of the functional area. The mounting of the brake shoe in the prior art is carried out, for example, via a ball, which is fixed to the webs via a corresponding bearing shell/spherical shell. Advantageously, this function is provided directly by the spherical configuration of the functional area. In principle, the explicit shaping of the functional area—spherical, ball-shape, cylindrical or possibly also another geometry—is not critical. What is important is that the bridge unit itself forms this geometry or shape; this is therefore also formed by deep-drawing, forging, bending, peening, hydroforming, pressing, etc. Here, the two functional areas can be formed identically or else differently. The functional area is therefore preferably shaped together with the bridge unit and advantageously forms one unit with the latter. Alternatively, the bearing section can also be fixed to the bridge unit as a separate component by a form fit and/or force fit or integral fit or, for example, welded on. 
         [0013]    According to one embodiment, a needle bearing is arranged or provided on the functional area or bearing section. According to one embodiment, the needle bearing has a corresponding bearing cage in order to be able to be positioned with respect to the bridge unit and to match the course of a cam contour. The bearing cage is in turn expediently rotatably fixed or arranged on the functional area of the bridge unit. 
         [0014]    The invention also otherwise relates to a bridge unit which has the aforementioned advantages and features. In particular, a bridge unit which is formed as a one-piece body comprising at least two bridge plates is claimed. Expediently, the bridge unit also comprises at least one functional area, which is likewise part of the aforementioned one-piece body. 
         [0015]    The invention also relates to a drum brake comprising at least one brake shoe as claimed in one of the preceding claims, and to a cam element for actuating the at least one brake shoe, a friction-reducing layer being provided on a contact surface of the cam element. This layer can, for example, be made of an abrasion-resistant plastics material, a wear-resistant sliding lacquer or a Teflon coating. The friction-reducing layer is in particular matched to the (steel) material used for the bridge unit, since the bridge unit definitely preferably also forms the functional area directly, e.g. the bearing section and/or the force introduction area. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    Further advantages and features can be gathered from the following description of preferred embodiments of the brake shoe according to the invention and of the drum brake according to the invention, with reference to the appended figures. Here, individual features of the individual embodiments can be combined with one another within the scope of the invention. 
           [0017]      FIG. 1  shows an embodiment of a bridge unit in a perspective illustration; 
           [0018]      FIG. 2  shows the bridge unit known from  FIG. 1 , viewed along a longitudinal direction/circumferential direction; 
           [0019]      FIG. 3  shows the section A-A as sketched in  FIG. 2 ; 
           [0020]      FIG. 4  shows the section B-B as sketched in  FIG. 3 ; 
           [0021]      FIG. 5  shows a plan view of the bridge unit known from  FIG. 1 ; 
           [0022]      FIG. 6  shows a perspective illustration of an embodiment of a brake shoe; 
           [0023]      FIG. 7  shows a further perspective illustration of an embodiment of a brake shoe; 
           [0024]      FIG. 8  shows an embodiment of a cam element; 
           [0025]      FIG. 9  shows a further embodiment of a cam element, the brake shoe being provided with needle bearings; 
           [0026]      FIG. 10  shows an embodiment of a needle bearing; and 
           [0027]      FIG. 11  shows an embodiment of a bridge unit with a needle bearing arranged thereon. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0028]      FIG. 1  shows in a perspective illustration a bridge unit  40  comprising two bridge plates  42 , which are connected via transverse plates  45 . The bridge unit  40  extends along a longitudinal direction L (or along a circumferential direction of the brake drum) and, at its respective ends, respectively forms functional areas  60 , the (rear) one being formed spherically, in particular in the shape of a ball, the front one more likely cylindrically. It is possible to see clearly the one-piece configuration on the bridge unit  40 , comprising the two bridge plates  42 , the transverse plates  45  and the functional areas  60 . The bridge unit  40  forms a circumferential arrangement surface  41 , via which the arrangement and fixing on a brake lining, not illustrated here, is carried out, for example via a welded connection. Here, the great advantage of the bridge unit  40  becomes clear, specifically that only one component has to be “handled”. In addition, the decreasing height of the bridge plates  42  toward the functional areas  60  is shown clearly. The height of the bridge plates  42  is therefore greatest in the center of the bridge unit  40  and decreases steadily or continuously toward the ends. 
         [0029]      FIG. 2  shows the bridge unit  40  known from  FIG. 1 , viewed along the longitudinal direction L or in the circumferential direction. It is possible to see the substantially symmetrical or axially symmetrical configuration of the bridge unit  40  with reference to a mid-plane M. In particular, in the view illustrated here, the connection of the two bridge plates  42  via the transverse plate  45  is illustrated. The functional area  60  extends away downward from the transverse plate  45 . The sketched section A-A is illustrated in  FIG. 3 . 
         [0030]      FIG. 3  shows the section A-A as sketched in  FIG. 2 . It is possible to see in particular the course of the arrangement surface  41  and the lateral contour of the two functional areas  60 . It can also be seen that a height of the bridge unit  40  decreases toward its ends. The sketched section B-B is illustrated in  FIG. 4 . 
         [0031]      FIG. 4  shows in particular the substantially trapezoidal configuration of the cross section of the bridge unit  40 . In particular, the trapezoidal shape results from the position and orientation of the bridge plates  42  relative to the connecting plate  44 . Thus, a width b 40  of the bridge unit and a width b 44  of the connecting plate  44  result, an advantageous ratio here lying in a range from about 1.0 to 2.0, preferably 1.3 to 1.7. Indicated dashed is the orientation of a lining plate. Between the lining plate and the bridge plate  42  there is an angle α which, in preferred embodiments, for example, lies in a range from about 90° to 130°, preferably 92° to 105°. 
         [0032]      FIG. 5  shows the bridge unit to be seen in  FIG. 3  folded downward. Here, in particular the course of the bridge plates  42 , which can substantially be designated as convex, becomes clear. In this case, the bridge plates  42  enclose an angle β which, for example, lies in a range from about 2° to 30°, preferably 4° to 25° or 10° to 20°. The width ratios of the bridge unit  40  also become clear, a maximum width b max  in a central region of the bridge unit lying at about 100 mm to 120 mm, while a minimum width b min  lies in a range from about 40 mm to 50 mm. The minimum width is measured approximately in the area of the functional areas  60 . 
         [0033]      FIG. 6  shows a brake shoe  10 , comprising a lining plate  20 , to which two bridge units  40  are fixed via a welded connection. The two bridge units  40  are welded to each other along a welded connection  50  along a dividing plane T. The bridge units  40  comprise lateral bridge plates  42  and transverse plates  45 . Moreover, the bridge plates  42  are connected by connecting plates  44 , which extend in relation to the lining plate  20  in such a way that the connecting plates  44  have a greater radius of curvature than the lining plate  20 . The connecting plate  44  forms an elongated opening  46 . The bridge units  40  each comprise a functional area  60 , both being formed spherically or in a ball shape here. 
         [0034]      FIG. 7  shows a similar configuration of a brake shoe  10  as known from  FIG. 6 . The difference here resides in the fact that here only one bridge unit  40  is provided. Moreover, a right-hand functional area  60  is formed cylindrically here. 
         [0035]      FIG. 8  shows a cam element  80  which is used to actuate two brake shoes  10 , which are illustrated only in part here. The introduction of force is carried out onto the corresponding functional areas  60  of the brake shoes  10  and the bridge unit  40 . A friction-reducing layer  86 , which is arranged on the cam element  80  and which improves the frictional behavior between the cam element  80  and the functional areas  60 , is indicated. 
         [0036]      FIG. 9  substantially shows the configuration known from  FIG. 8 , here a needle bearing  62  being arranged on a functional area  60  of a brake shoe  10 . Here, too, the cam element  80  is provided with a friction-reducing layer  86 . 
         [0037]      FIG. 10  shows the needle bearing  62  in a detailed illustration. Here it is possible to see in particular a bearing cage  63 , which can be rotatably fixed to a functional area  60  of the bridge unit  40 . Indicated here is a corresponding axis of rotation D, via which ultimately the (rotatable) arrangement on the corresponding functional area of the bridge unit is carried out. 
         [0038]      FIG. 11  shows the arrangement of a needle bearing  62  with its bearing cage  63  on a bridge unit  40  and the functional area  60  of the latter. Appropriate mobility about an axis of rotation D is provided. 
       LIST OF DESIGNATIONS 
       [0000]    
       
           10  Brake shoe 
           20  Lining plate 
           40  Bridge unit 
         b 40  Width of the bridge unit 
         b min  Minimum width (of the bridge unit) 
         b max  Maximum width (of the bridge unit) 
           41  Arrangement surface 
           42  Bridge plates 
           44  Connecting plate 
           45  Transverse plate 
           46  Opening 
           50  Welded seam 
           60  Functional area, bearing section, force introduction area 
           62  Needle bearing 
           64  Bearing cage 
           80  Cam element 
           86  Friction-reducing layer 
         M Mid-plane 
         T Dividing plane 
         L Longitudinal direction 
         D Axis of rotation 
         α,β Angle