Abstract:
A sensor for outputting a sensor signal which is dependent on a variable to be measured, including:—a measuring pickup which is connected electrically to a data line at a connecting point, is housed in a measuring pickup housing and is set up to feed the sensor signal which is dependent on the variable to be measured into the data line, with the result that the sensor signal can be output via the data line, an installation housing which houses the measuring pickup housing and the data line at least at the connecting point and is manufactured from a flexible material, and—a fastening element which is connected fixedly to the installation housing for fastening the installation housing to a sensor holder, wherein the measuring pickup housing; and the fastening element are arranged on two sides of the installation housing which lie opposite one another.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the U.S. National Phase Application of PCT International Application No. PCT/EP2014/071587, filed Oct. 8, 2014, which claims priority to German Patent Application No. 10 2013 226 045.8, filed Dec. 16, 2013, the contents of such applications being incorporated by reference herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to a sensor for outputting a sensor signal which is dependent on a variable which is to be measured, and to a vehicle comprising the sensor. 
       BACKGROUND OF THE INVENTION 
       [0003]    WO 2010/037 810 A1, which is incorporated by reference discloses a sensor for outputting a sensor signal which is dependent on a variable which is to be measured. The sensor comprises a measurement pickup which is electrically connected to a data line at a connection point and is designed to feed the sensor signal which is dependent on the variable which is to be measured into the data line, so that the sensor signal can be output via the data line. Furthermore, an installation housing which houses the measurement pickup and the data line at least at a connection point can be formed within the scope of a plastic injection-molding process, known as “transfer molding” 
       SUMMARY OF THE INVENTION 
       [0004]    An aspect of the invention aims to improve the known sensor. 
         [0005]    According to one aspect of the invention, a sensor for outputting a sensor signal which is dependent on a variable which is to be measured comprises a measurement pickup which is electrically connected to a data line at a connection point, is housed in a measurement pickup housing and is designed to feed the sensor signal which is dependent on the variable which is to be measured into the data line, so that the sensor signal can be output via the data line, an installation housing which houses the measurement pickup housing and the data line at least at a connection point and is produced from a flexible material, and a fastening element, which is fixedly connected to the installation housing, for fastening the installation housing to a sensor receptacle, wherein the measurement pickup housing and the fastening element are arranged on two opposite sides of the installation housing. 
         [0006]    In this case, the flexible material can be a material with a specific modulus of elasticity. The flexibility of the material can also be prespecified by means of a compression set. This is the remaining deformation of the material which remains after deformation with a specific loading over a specific period of time and at a prespecified temperature. The test method used can be, for example, ASTM D395. 
         [0007]    The specified sensor is based on the consideration that the sensor, as a wheel rotation speed sensor, could be fastened to an axle body of a vehicle by means of the fastening element and the installation housing in order to measure the wheel rotation speed of a wheel which is mounted in a rotatable manner on the axle body. In this case, the material used for the installation housing could be a rigid material, such as a polyamide for example, in order to prevent the measurement pickup housing and therefore the measurement pickup from being subjected to mechanical loading and therefore outputting a sensor signal, which is incorrectly dependent on the variable which is to be measured, on account of the mechanical load. 
         [0008]    Furthermore, the specified sensor is based on the consideration that the sensor has to be fastened to such a rigid installation housing with a predetermined installation tolerance in relation to a wheel bearing in the axle body that the measurement pickup housing does not overlap with the wheel bearing and therefore mechanical stresses are applied to the installation housing, these mechanical stresses then acting on the measurement pickup. Mechanical stresses of this kind can be produced, for example, by temperature fluctuations in the other components and subject the installation housing to changes in load which can reach a number of up to two million over the service life of the housing. However, an air gap between the measurement pickup and a transmitter element is increased owing to the installation tolerance, this however increasing the tolerance range of the sensor signal and restricting a reading range of the measurement pickup at the same time. 
         [0009]    Here, the specified sensor starts with the consideration that the measurement pickup housing itself is generally produced from a rigid material. This rigid material protects the measurement pickup against the abovementioned mechanical loads. Therefore, the installation housing can be produced from a flexible material which absorbs all mechanical loads which may occur owing to the installed state of the specified sensor, for example in a vehicle, and keeps said mechanical loads away from the measurement pickup housing and therefore from the measurement pickup. Therefore, the sensor can be installed without installation tolerances, so that the abovementioned air gap can be reduced and therefore the reading range of the measurement pickup can be increased and the tolerance range of the sensor signal can be lowered. 
         [0010]    In one development of the specified sensor, the flexible material is an elastomer which can be obtained at low cost and can be mass-processed. 
         [0011]    In a particular development of the specified sensor, the elastomer has a Shore A hardness of at least 80 and is therefore suitable for providing, in addition to the abovementioned elasticity, a sufficient degree of resistance in relation to other mechanical loads. In this case, the elastomers used can particularly preferably be thermoplastic elastomers which can be plastically processed starting from a specific temperature to form the installation housing. 
         [0012]    In another development of the specified sensor, the installation housing extends from the measurement pickup housing in a direction of the data line around the data line in the manner of a rod. If the sensor is fastened, for example, to the abovementioned axle body of the vehicle, the sensor can be fastened to an outer side of the axle body of the vehicle and, owing to its rod-like design of the installation housing, can be inserted into an interior space in the axle body via an opening. 
         [0013]    In an additional development of the specified sensor, at least one bending groove is formed on the installation housing. In this case, the bending groove can be arranged in such a way that the installation housing has a preferred bending direction. In this case, the preferred bending direction should be defined such that the installation housing can absorb mechanical loads between two mounting points of the specified sensor which are situated on the fastening element and the measurement pickup housing. In this way, the preferred mechanical load absorption by the installation housing in relation to the measurement pickup housing can be further increased, as a result of which the mechanical loads on the measurement pickup housing and therefore the measurement pickup can be further reduced. In this case, two or more bending grooves are particularly preferably formed on the installation housing. 
         [0014]    In a preferred development of the specified sensor, at least two crushing ribs which are placed in an axially symmetrical manner around the data line and can be deformed by the sensor receptacle are formed on the installation housing. In this way, the elastic material on the sensor receptacle can be stiffened by pinching the sensor receptacle, as a result of which the sensor is held in a stable manner on the sensor receptacle by means of the pinched and stiffened installation housing. 
         [0015]    In a particularly preferred development of the specified sensor, the crushing rib is formed between the bending groove and the fastening element, so that it is ensured that the abovementioned mechanical loads also act on the bending groove and are kept away from the measurement pickup housing and therefore from the measurement pickup. 
         [0016]    In order to further improve the process of diverting the abovementioned mechanical loads away from the measurement pickup housing and therefore from the measurement pickup, the data line can be flexible at least in the region of the connection point in the specified sensor. 
         [0017]    In a particularly preferred development of the specified sensor, the measurement pickup housing, which is expediently designed to be rigid in the abovementioned manner, can be produced from a synthetic resin, in particular from an epoxy resin. 
         [0018]    According to a further aspect of the invention, a vehicle comprises an axle body which is fastened to a chassis, a wheel which is fastened in a rotatable manner to the axle body by means of a wheel bearing, and one of the specified sensors, the fastening element and the measurement pickup housing of said sensor correspondingly being fastened to the axle body or to an element of the wheel bearing, said element being fixed in position in relation to the axle body. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The above-described properties, features and advantages of this invention and the way in which they are achieved will become clearer and more clearly understood in connection with the following description of the exemplary embodiments which are explained in more detail in connection with the drawings, in which: 
           [0020]      FIG. 1  shows a schematic view of a vehicle having driving dynamics control, 
           [0021]      FIG. 2  shows a schematic sectional view through a wheel suspension arrangement in the vehicle of  FIG. 1 , 
           [0022]      FIG. 3  shows a schematic sectional view through a rotation speed sensor in an installed state on the wheel suspension arrangement of  FIG. 2 , 
           [0023]      FIG. 4  shows a schematic view of an alternative rotation speed sensor, and 
           [0024]      FIG. 5  shows a schematic view of a further alternative rotation speed sensor. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0025]    In the figures, identical technical elements are provided with identical reference symbols and are described only once. 
         [0026]    Reference is made to  FIG. 1  which shows a schematic view of a vehicle  2  having driving dynamics control which is known per se. Details of this driving dynamics control can be found in DE 10 2011 080 789 A1, which is incorporated by reference, for example. 
         [0027]    The vehicle  2  comprises a chassis  4  and four wheels  6  which are each held in a rotatable manner on the chassis  4  by means of a wheel suspension arrangement  5 . Each wheel  6  can be decelerated with respect to the chassis  4  by means of a brake  8  which is fastened to the chassis  4  in a fixed position, in order to decelerate a movement of the vehicle  2  on a road, not illustrated any further. 
         [0028]    In this case, in a manner known to a person skilled in the art, the wheels  6  of the vehicle  2  may lose their grip on the road and the vehicle  2  may even move away from a trajectory which is prespecified, for example, by means of a steering wheel, not shown any further, as a result of understeering or oversteering. This is avoided using control circuits such as ABS (anti-lock braking system) and ESP (electronic stability program) which are known per se. 
         [0029]    In the present embodiment, the vehicle  2  has rotation speed sensors  10  on the wheels  6  for this purpose, said rotation speed sensors detecting a rotation speed  12  of the wheels  6 . The vehicle  2  also has an inertia sensor  14  which detects driving dynamics data  16  relating to the vehicle  2 , from amongst which data a pitch rate, a roll rate, a yaw rate, a lateral acceleration, a longitudinal acceleration and/or a vertical acceleration, for example, can be output in a manner known per se to a person skilled in the art. 
         [0030]    On the basis of the detected rotation speeds  12  and driving dynamics data  16 , a controller  18  can determine, in a manner known to a person skilled in the art, whether the vehicle  2  is sliding on the road or even deviates from the abovementioned prespecified trajectory and can accordingly react thereto with a controller output signal  20  which is known per se. The controller output signal  20  can then be used by an actuating device  22  to control actuating elements, such as the brakes  8 , which react to the sliding and the deviation from the prespecified trajectory in a manner which is known per se, by means of actuating signals  24 . 
         [0031]    The controller  18  may be integrated, for example, in an engine controller of the vehicle  2  which is known per se. The controller  18  and the actuating device  22  can also be in the form of a common control device and can be optionally integrated in the abovementioned engine controller. 
         [0032]    The present invention is intended to be explained in more detail using the wheel rotation speed sensor  10  shown in  FIG. 1 , even though the present invention can be implemented in any desired electronic apparatuses and in particular in any desired sensors, such as magnetic field sensors, acceleration sensors, rate-of-rotation sensors, structure-borne sound sensors or temperature sensors. 
         [0033]    Reference is made to  FIG. 2  which shows a schematic sectional view through one of the wheel suspension arrangements  5  in the vehicle  2  of  FIG. 1 . 
         [0034]    The wheel suspension arrangement  5  has an axle body  26  which is fastened to the chassis  4  such that it is rotationally fixed in relation to the wheel  6  and possibly can be deflected by means of a steering arrangement. A receiving opening  28  is formed through the axle body  26 , the rotation speed sensor  10  which is correspondingly arranged on the wheel suspension arrangement  5  being routed through said receiving opening. Said rotation speed sensor  10  will be discussed in detail at a later point. The rotation speed sensor  10  is fastened to the axle body  26  by means of a screw  30 . 
         [0035]    The axle body  26  has an inner bore  34  which runs concentrically around a rotation axis  32  and in which a wheel bearing  36  is held. The wheel bearing  36  is designed as a second-generation wheel bearing in the present embodiment. Wheel bearings of this kind are known in a technically relevant manner, for example, from DE 195 37 808 A1, which is incorporated by reference and for this reason the functioning of said wheel bearings does not need to be discussed further in the text which follows. 
         [0036]    The wheel bearing  36  comprises an outer ring  38  which is held in the inner bore  34  of the axle body  26  in a rotationally fixed manner and comprises an inner ring  40  which is held in a rotatable manner in relation to the inner ring by means of roller elements  42 . A wheel flange  44  extends axially on the inner ring  40 , it being possible for the wheel  6  to be held on said wheel flange in a manner fastened by means of screws  30 . 
         [0037]    On that side of the wheel bearing  36  which is situated axially opposite the wheel flange  44 , the inner bore  34  of the axle body  26  is covered by a cap  48 , so that a space  50  into which the sensor  10  is inserted is formed. In the process, the rotation speed sensor  10  can be routed axially very close to the inner ring  40  which is generally fitted with an encoder  52 , shown in  FIG. 3 , which excites a magnetic transmitter field which can be evaluated for the rotation speed sensor  10 . In this case, the encoder  52  can optionally be added to the rotation speed sensor  10 . 
         [0038]    Reference is made to  FIG. 3  which shows a schematic sectional view of the rotation speed sensor  10  in an installed state on the wheel suspension arrangement  5  of  FIG. 2 . 
         [0039]    The rotation speed sensor  10  has a measurement pickup  54  and a data line  56  which, in the present embodiment, is designed as pins  58  and as a data cable  60  which is connected to the pins  58 . The data cable  60  can be connected to the controller  18 , while the pins  58  are terminated at the measurement pickup  54 , so that a rotation speed signal  62  which carries the rotation speed  12  can be conducted from the measurement pickup  54 , via the pins  58  and the data cable  60 , to the controller  18  for the abovementioned processing of the rotation speed  12 . 
         [0040]    In the present embodiment, the measurement pickup  54  is accommodated in a rigid measurement pickup housing  64  which can be produced, for example, from an epoxy resin. The pins  58  are routed out of this measurement pickup housing  64 . The pins  58 , the data cable  60  and the measurement pickup housing  64  are enclosed by an installation housing  68  at an electrical connection point  66  at which the data cable  60  is electrically connected to the pins  58 . The installation housing can be produced, for example, from a thermoplastic material by injection molding around the data cable  60  and the measurement pickup housing  64 . 
         [0041]    The thermoplastic material should have a Shore A hardness of at least  80 . 
         [0042]    This installation housing  68  has a support plate  70  through which a fastening element  72  is routed, it being possible for the screw  30  to be routed through said fastening element. At the same time, the support plate  70  can be supported on the outer side of the axle body  28  as seen from the space  50 , so that the rotation speed sensor  10  is held securely on the axle body  28  after the screw  30  has been screwed in. 
         [0043]    A rod-like projection  74  through which the data line  56  is routed extends from the connection plate  70 , through the receiving opening  28 , in the direction of the data line  56 . This rod-like projection  74  also partially encloses the measurement pickup housing  64 . In this case, the rod-like projection  74  can also extend from the connection plate  70  on a side which is situated opposite the receiving opening  28 . 
         [0044]    Bending grooves  76  are formed in the rod-like projection  74  on the side of the receiving opening  28 , said bending grooves weakening the rod-like projection  74  at this point, so that it can be bent more easily at these points. In the installed state shown in  FIGS. 2 and 3 , the rotation speed sensor  10  has two mechanical fastening points in the vehicle  2 . Firstly, the rotation speed sensor  10  is fastened to the axle body  26  by way of its connection plate  70 . Furthermore, the rotation speed sensor  10  is firmly supported on the outer ring  38  of the wheel bearing  36  by way of the measurement pickup housing  64 . If the outer ring  38  of the wheel bearing  36  moves, for example owing to thermal movements, the rotation speed sensor  10  is primarily deformed at the bending grooves  76  of the rod-like projection  74  owing to the thermal movements. The measurement pickup  54  remains largely free of mechanical stress owing to the rigid measurement pickup housing  64 . 
         [0045]    In order to firmly hold the rotation speed sensor  10  in the receiving opening  28  on the rod-like projection  74 , a collar  77  is formed on the rod-like projection  74  in the region of attachment to the connection plate  70 , said collar being axially adjoined by a plurality of crushing ribs  78  which are placed around the periphery of the rod-like projection  74 . When the rod-like projection  74  is inserted into the receiving opening  28 , the rotation speed sensor  10  is initially radially centered by the collar  77 . If the rod-like projection  74  is inserted further into the receiving opening  28 , the crushing ribs  78  are deformed by pinching, so that the rotation speed sensor  10  is firmly supported on the axle body  26  within the receiving opening  28  too. Furthermore, the crushing ribs  78  can absorb mechanical stresses from the axle body  26 , as can occur, for example, due to thermal movements of the axle body  26 , so that the overall elastic effect of the rotation speed sensor  10  is further increased. 
         [0046]    Whereas the crushing ribs  78  are routed axially on the rod-like projection  74  and can be placed around the periphery of said rod-like projection, the bending grooves  76  can be formed, for example, in a direction  80  which is directed toward the inner ring  38  and in the opposite direction in the rod-like projection  74  in order firstly to ensure a high degree of stability of the rod-like projection  74  but also to provide the rod-like projection  74  with a high degree of flexibility. 
         [0047]    By virtue of the abovementioned embodiment of the rotation speed sensor  10 , said rotation speed sensor can be fastened at different points in the vehicle  2  without thermal movements of the elements in the vehicle  2  and a resulting change in load on the rotation speed sensor  10  leading to mechanical loads on the measurement pickup  54  and corrupting the measured rotation speed  12  in the rotation speed signal  62 . 
         [0048]    Reference is made to  FIG. 4  which shows a schematic view of a rotation speed sensor  10 , which is an alternative to the rotation speed sensor  10  of  FIG. 3 , in a state in which it is not installed in the vehicle  2 . 
         [0049]    The rotation speed sensor of  FIG. 4  has six bending grooves  76  instead of four bending grooves  76 . The flexibility of the rod-like projection can be further increased in this way. 
         [0050]    Reference is made to  FIG. 5  which shows a schematic view of a further alternative rotation speed sensor  10 . 
         [0051]    The rotation speed sensor  10  of  FIG. 5  corresponds substantially to the rotation speed sensor  10  of  FIG. 4 , wherein electrical contact is made with the pins  58  by a plug receptacle  80  instead of by a cable, it being possible for a plug, which is not illustrated further, to be accommodated in said plug receptacle. Said plug can then, in turn, be connected to a corresponding data cable which leads to the controller  18 .