BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to a brake device for braking a wheel, in particular a drum brake. 
         [0002]    Brake devices for braking the wheel of a vehicle, in particular a utility vehicle, are sufficiently known in the prior art. Drum brakes comprise a brake drum which rotates together with the wheel to be braked, and a brake lining carrier which can be lined with a brake lining and is pressed against the brake drum when the brake is activated. The brake lining carrier is pivotably mounted on a brake carrier and is shifted radially outward and pressed against the inner face of the rotating brake drum by means of an actuator unit, for example an expansion wedge. 
         [0003]    In particular with respect to the monitoring of the state of movement of the vehicle, brake devices of the specified type frequently comprise a sensor for sensing or measuring the rotational speed of the wheel or of the brake drum. The sensor can be applied, in particular, in conjunction with an anti-lock brake system. A known embodiment comprises a sensor which is mounted on the brake carrier in a positionally fixed fashion, and a pole wheel which rotates together with the brake drum. The sensor comprises optical sensor means for determining the rotational speed of the pole wheel relative to the sensor. 
         [0004]    If the sensor is not arranged in a positionally accurate fashion in the provided position, faults can occur during the measurement of the rotational speed. Usually, a fault message (referred to as an ABV fault) is triggered when such a displacement of the sensor occurs. In this case it is necessary to disassemble the brake drum or the wheel hub and shift the sensor again into the provided position. In particular, owing to the necessary disassembly of the brake device, this procedure is complex and therefore cost-intensive. 
         [0005]    The invention is based on the object of specifying a brake device which permits rapid and simple adjustment of a sensor, in particular of an ABV sensor. 
       SUMMARY OF THE INVENTION 
       [0006]    According to the invention, the brake device comprises a brake drum, a brake carrier for shifting a brake lining in order to press the brake lining against the brake drum, and a sensor for sensing the rotational speed of the wheel. According to the invention, an adjustment element is provided which can be coupled to or engaged with the sensor and by means of which the sensor can be shifted or adjusted spatially. A basic concept of the invention can be considered that of coupling the sensor, in particular the housing of the sensor, to a mechanical adjustment element, with the result that the sensor can be shifted by mechanical activation or shifting of the adjustment element. In this context there is provision, in particular, that the sensor can be pressed on in the direction of a pole wheel by means of the adjustment element or transmission element. The adjustment element preferably permits a pressure force to be transmitted to the sensor, with the result that the sensor can be pressed, and as a result moved, by a pressure force transmitted via the adjustment element. The adjustment element is preferably rigid, with the result that a pressure force can be transmitted from the second end to the first end. The adjustment element preferably has a first end which is coupled to the sensor, and a second end which can be activated manually or by means of a tool. The adjustment element can be shifted altogether, in particular, without a change in shape, or without a significant change in shape, by a pressure force which is applied to the second end. By means of the adjustment element or transmission element it is possible to displace or shift the sensor back into its predefined position without disassembling the axle device, after said sensor has, under certain circumstances, moved away from the pole wheel, for example owing to vibrations on the vehicle. 
         [0007]    The adjustment element is preferably accessible from outside the brake drum. In particular, when the brake device is mounted, the adjustment element can be accessible in such a way that the sensor can be adjusted spatially by means of the adjustment element. 
         [0008]    According to one preferred embodiment of the invention, the adjustment element is embodied in the form of a hollow cylinder or sleeve. In this context, the adjustment element can, in particular, accommodate a cable element of the sensor. The cable element of the sensor preferably runs within the adjustment element here. It is particularly preferred that the cable element is led, together with the adjustment element, out of the brake device or the brake drum. The cable element can be, in particular, an electrically conductive cable or a cable wire. 
         [0009]    According to a further preferred embodiment there is provision that the adjustment element forms an integral part of a cable sleeve. The, in particular electrical, cable element, for example for connecting the sensor to a signal processing unit, runs within the cable sleeve which is configured in a rigid fashion such that pressure forces can be transmitted from one end to the end adjoining the sensor. Therefore, the cable formed by the cable sleeve and the cable element running therein can be pressed at its end lying opposite the sensor and therefore the sensor can be shifted. The adjustment element can accordingly also be referred to as a dimensionally stable or stiff cable sleeve which transmits pressure forces. 
         [0010]    A further preferred embodiment of the invention provides that the adjustment element has a length which corresponds to at least a distance of the sensor from an outer side of the brake device. The adjustment element preferably runs between the sensor and an outer side of the brake device. In this way, the adjustment element is accessible even when the brake device is mounted. 
         [0011]    It is particularly preferred that the adjustment element projects out of an interior space of the brake drum. The adjustment element preferably runs in certain sections through an interior space of the brake device or of the brake drum and out of the interior space of the brake device or of the brake drum. 
         [0012]    In a further preferred embodiment, the adjustment element is mounted in an opening in a closure plate of the brake device and/or projects through said opening. the closure plate can be, in particular, an element which bounds an interior space of the brake drum and protects it, for example, against soiling. The closure plate is preferably arranged at an open, axial end of the brake drum. Said closure plate can be a fixed element which can be embodied in an integral fashion with the brake carrier. The brake drum can be embodied here so as to be rotatable relative to the closure plate. 
         [0013]    The adjustment element can be formed, for example, from metal and/or plastic. It is crucial that the adjustment element has a hardness or stiffness which permits the sensor to be shifted by means of the adjustment element. In contrast to customary cable sleeves, the adjustment element is therefore not randomly flexible but instead at least largely dimensionally stable. In particular, a hard plastic is preferred as the plastic. 
         [0014]    Good activation of the adjustment element can be achieved if the adjustment element has a longitudinal axis which runs along a sensor longitudinal axis. The adjustment element is therefore preferably aligned with the sensor longitudinal axis. The essentially elongate and/or rotationally symmetrical adjustment element preferably runs coaxially with respect to the sensor longitudinal axis, wherein in the case of an optical sensor the sensor longitudinal axis runs, for example, in the direction of the beam path of the emitted beams. 
         [0015]    It is preferred that the sensor can be plugged axially into a sensor mount. The invention then permits the sensor to be subsequently pressed or shifted into the sensor mount by means of the adjustment element if the sensor has become partially detached from the sensor mount or has shifted within it. 
         [0016]    It is particularly preferred that the sensor can be adjusted in an axial direction, that is to say in the direction of the sensor longitudinal axis, by means of the adjustment element. In this way, there is no need for force to be diverted. The sensor can be pushed into the sensor mount, or pushed back therein, in a particularly simple manner, by pressure in the axial direction applied to the adjustment element. 
         [0017]    It is particularly advantageous here if the adjustment element can be shifted along the axial direction and/or along the direction of the sensor longitudinal axis. 
         [0018]    It is expedient if the adjustment element has indicator means, such as a mark, preferably in the region of its second end and, in particular, in the region of a part projecting out of the closure plate, by means of which indicator means the position or location of the adjustment element in the installed state can be recognized. It is therefore expediently possible to indicate visually whether the sensor or the adjustment element is in the fault position or in the operating position. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The invention will be described further below with reference to a preferred embodiment which is illustrated schematically in the appended figure. In the drawing: 
           [0020]      FIG. 1  shows a cross-sectional view of a brake device according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    The brake device  10  comprises a brake drum  20  which is rotatably mounted on an axle element  12 . The axle element  12  extends along a longitudinal axis which is characterized by the reference symbol  14  in the figure. The axle element  12  can be, for example, a fixed, that is to say non-rotating, axle of a vehicle, in particular of a utility vehicle. 
         [0022]    In order to mount the brake drum  20  in a rotating fashion relative to the axle element  12 , bearing devices  22 , for example roller bearings, are provided. A wheel hub  26  is mounted on the bearing devices  22  in such a way that it can rotate relative to the axle element  12 . The brake drum  20  is fixedly connected to the wheel hub  26 , with the result that it can rotate together with the wheel hub  26  about the axle element  12 . In order to connect the wheel hub  26  and brake drum  20  in a rotationally fixed fashion, attachment bolts  28  are provided. However, instead of the bolts  28 , other attachment devices can also be provided. 
         [0023]    The brake drum  20  is shaped in the form of a drum and comprises a drum ring  21  which extends in the axial direction and in the circumferential direction around the axle element  12  and surrounds or bounds an interior space  24  of the drum. 
         [0024]    A brake carrier  30  which is fixedly connected to the axle element  12  is arranged in the interior space  24  of the drum, that is to say inside the brake drum  20 . The brake carrier  30  bears a brake lining carrier  32  which cannot be seen in the sectional view and is indicated only schematically. The brake lining carrier  32  is provided on its face lying radially on the outside with brake linings  34  (also indicated only schematically) which, when the brake device  10  is activated, press against a circumferential face, lying on the inside, of the brake drum  20 . In order to shift the brake lining carrier  32  radially, an activation device  36  is provided, for example an expansion wedge unit. The activation device  36  can usually be operated hydraulically and can for this purpose have a hydraulic cylinder. 
         [0025]    The interior space  24  of the drum is closed off, in particular in order to protect against soiling, by a closure plate  40  which is arranged in a non-rotating fashion on the axle element  12 . The closure plate  40  is located on an axial end face of the interior space  24  of the drum, which end face is turned toward the center of the vehicle in the mounted state of the brake device  10 . The closure plate  40  can be considered to be part of the brake carrier  30  and can be embodied in an integral fashion therewith, for example as a cast part. The closure plate  40  is located, in particular, at an open end of the brake drum  20 . 
         [0026]    A pole wheel  58  is arranged on the rotating components of the brake device  10 , in particular on the wheel hub  26 . The pole wheel  58  is mounted so as to be rotatable relative to the axle element  12  and rotates together with the brake drum  20  or the wheel hub  26 . Said pole wheel  58  comprises, in a basically known fashion, a multiplicity of webs and openings in the circumferential direction which can be detected by means of a sensor  50 , in particular an optical sensor. The sensor  50  is for this purpose arranged in a positionally fixed fashion relative to the axle element  12  and is attached, for example, to the brake carrier  30 . When the brake drum  20  rotates about the axle element  12 , the sensor  50  can determine the rotational speed in a basically known fashion by measuring the speed of the grill rods and/or openings of the pole wheel  58  which pass the sensor  50 . The sensor  50  comprises a sensor housing  52  which is accommodated in a sensor mount  54 . A longitudinal axis or central axis of the sensor  50 , which axis is referred to as a sensor longitudinal axis  56 , runs in an axial direction of the axle element  12 , in particular parallel to the longitudinal axis  14 . The sensor  50  can be plugged into the sensor mount  54  along the sensor longitudinal axis  56  and can be pressed as far as a stop. The position of the sensor  50  which is illustrated in  FIG. 1  is referred to as the operating position. In this position, it is possible to measure the rotational speed of the wheel or of the brake drum  20  around the axle element  12 . 
         [0027]    A functional fault can occur as a result of undesired shifting of the sensor  50  away from the pole wheel  58 , that is to say in the direction toward the right in  FIG. 1 , and measurement of the rotational speed is therefore no longer possible. This position is referred to as fault position. In order to move the sensor  50  from its fault position to the operating position, an adjustment element  60  is provided which is connected to, or can be engaged with, the sensor  50 , in particular the sensor housing  52 . The adjustment element  60  runs out of the interior space  24  of the drum, starting from the sensor  50  arranged in the interior space  24  of the drum. In this context, said adjustment element  60  extends through the closure plate  40 , in which an opening  42  is formed for this purpose. The adjustment element  60  is embodied in the form of a sleeve or rod and is, in particular, an elongate element which extends in the axial direction of the brake device  10 , preferably parallel to the longitudinal axis  14 . An electrical or optical cable element  62  preferably runs in the adjustment element  60 , with the result that the adjustment element  60  forms a sheath of the cable element  62 . The cable element  62  can project out of the adjustment element  60  at the end lying opposite the sensor  50 . So that the sensor  50  can be pressed on in the direction of the pole wheel  58  via the adjustment element  60 , the adjustment element  60  is configured in a stiff or rigid fashion and preferably runs along a straight line, in particular coaxially with respect to the sensor longitudinal axis  56 . When the brake device  10  is mounted, the adjustment element  60  is accessible, in particular from outside the closure plate  40  which closes off the interior space  24  of the drum. For this purpose, the adjustment element preferably has a length which is greater than the distance of the sensor  50  from an axial boundary of the interior space  24  of the drum, in particular the closure plate  40 . It is particularly preferred if the adjustment element  60  projects through the closure plate  40  and projects at least  5 - 15  mm out of the latter. This ensures reliable activation and, if appropriate, also visual monitoring from the outside of the brake device  10  which is bounded by the brake drum  20  and/or the closure plate  40 . The adjustment element  60  can also be referred to as a stiff or rigid cable sleeve or additional sleeve or as a dimensionally stable or additional cable reinforcement. A fault (ABV fault) which is caused by a displacement of the sensor  50  can be eliminated with the additional sleeve or cable reinforcement without disassembling built-on parts. 
       LIST OF REFERENCE NUMBERS 
       [0028]      10  Brake device 
         [0029]      12  Axle element 
         [0030]      14  Longitudinal axis 
         [0031]      20  Brake drum 
         [0032]      21  Drum ring 
         [0033]      22  Bearing device 
         [0034]      24  Interior space of the drum 
         [0035]      26  Wheel hub 
         [0036]      28  Attachment bolt 
         [0037]      30  Brake carrier 
         [0038]      32  Brake lining carrier 
         [0039]      34  Brake lining 
         [0040]      36  Activation device 
         [0041]      40  Closure plate 
         [0042]      42  Opening 
         [0043]      50  Sensor 
         [0044]      52  Sensor housing 
         [0045]      54  Sensor mount 
         [0046]      56  Sensor longitudinal axis 
         [0047]      58  Pole wheel 
         [0048]      60  Adjustment element 
         [0049]      62  Cable element
A brake device for braking a wheel, having a brake drum, a brake carrier for shifting a brake lining in order to press the brake lining against the brake drum, a sensor for sensing a rotational speed of the wheel, and an adjustment element configured to be coupled to the sensor and to spatially adjust the sensor.