Abstract:
A sensor unit ( 2 ) for a motor vehicle or trailer is disclosed. The sensor unit comprises a sensor measuring arrangement ( 16 ) for sensing at least one physical variable, a sensor housing ( 12 ) partly or fully enclosing the sensor measuring arrangement ( 16 ) and at least two connecting lines ( 18 ). The sensor unit ( 2 ) with the sensor housing ( 12 ) is electrically connectable to a conductive part of the motor vehicle or trailer and the sensor measuring arrangement ( 16 ) is connectable to an analyzer ( 6 ) via the connecting lines ( 18 ). Related methods, a sensing and analysis device, and motor vehicles or trailers including the same are also disclosed.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the National Stage of International Application No. PCT/EP2016/000030, filed on 11 Jan. 2016, which claims priority to and all ad-vantages of German Patent Application No. 10 2015 000 380.1, filed on 13 Jan. 2015, the content of which is hereby incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention generally relates to a sensor unit and, more specifically, to a sensor unit for installation in a motor vehicle, as well as to a sensing and analysis device comprising the sensor unit and a motor vehicle or trailer therewith. The invention further relates to a method for protecting electronic components of an analyzer that is connected to the sensor unit. 
       BACKGROUND OF THE INVENTION 
       [0003]    Conventionally, sensor units in the form of revolution rate sensors in motor vehicles, for example for an antilock brake system (ABS) of an electronic brake system of a motor vehicle, are used to detect the rotation rate of a wheel and to control associated braking depending on rotary motion and the rotation rate. For this purpose, values measured by the sensor unit are transferred to an analyzer via at least two connecting lines. One such sensor unit is for example featured in DE 10 2006 021 018 B4. 
         [0004]    In the wheel area of a motor vehicle, however, electrostatic charging occurs within individual electrically isolated parts of the motor vehicle. The electrostatic charging arises for example through the friction of the tires while travelling. Because the chassis parts, in particular vehicle axles, include no conductive connection to the frame of the vehicle, electrostatic charges cannot be discharged from the vehicle axle, as a result of which there is a continuous raised potential between the vehicle axle and the frame of the vehicle. On exceeding a voltage limit, a flashover of the charge to the nearest electrically conductive part takes place. Such flashovers occur in particular in the region of connecting lines between electrical sensor units and electronic analyzers. 
         [0005]    Electric circuits with integrated components, such as those used in analyzers, in particular in control units for electronic brake systems, are however sensitive to large noise voltages that can occur because of electrostatic discharges (electrostatic discharge—ESD) in individual vehicle parts. If such overvoltages occur above an upper tolerance limit of a maximum permissible voltage of the analyzer, the analyzer can be damaged. 
         [0006]    In order to protect electrical circuits, such as analyzers in control units, against overvoltages, conventionally overvoltage protection devices, such as direct surge arresters, are used that make an electrically conductive connection between otherwise electrically decoupled vehicle parts and thereby discharge any possible electrostatic charges. 
         [0007]    DE 9412038 U1 discloses a device for connecting a sensor to a chassis of a vehicle. The sensor comprises, in addition to two conductive wires that can be connected to an analyzer, a third conductive wire that is connected to ground (GND). For this purpose, the sensor is enclosed by a covering body of non-conducting plastic from which the third conductive wire protrudes. The covering body with the protruding third conductive wire is at least partly enclosed by a further covering body of conductive plastic, wherein the sensor is attached to a wheel mounting via the further covering body such that the wheel mounting is conductively connected to ground via the third conductive wire. 
         [0008]    However, such surge arresters require a cost intensive overhead, because an additional line is provided that requires a change from standardized control units and entails greater maintenance effort for the vehicle electronics. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention provides a sensor unit, a sensing and analysis device comprising the sensor unit and analyzer, a motor vehicle or trailer comprising the sensor unit and/or the sensing and analysis device, and a method for protecting electronic components of an analyzer against excessive electrical voltages. 
         [0010]    One object of the invention is to provide an inexpensive arrangement as well as a method for safely discharging electrostatic charges in order to protect electrical circuits, in particular the analyzer of a control unit, against overvoltages at low cost. 
         [0011]    The sensor unit according to the invention is suitable for installation in a motor vehicle or trailer. The term “trailer” encompasses a dolly with a semi-trailer coupling for accepting a semi-trailer. The sensor unit comprises a sensor measuring arrangement for sensing at least one physical variable, an electrically conductive sensor housing partly or fully enclosing the sensor measuring arrangement, and at least two connecting lines. 
         [0012]    In certain embodiments, the sensor measuring arrangement comprises a part of the sensor unit that is necessary for detecting the measurement variable. In the case of a revolution rate sensor, for example, the sensor measuring arrangement may comprise a magnet for producing a magnetic flux and a coil for detecting changes of the magnetic flux. The sensor measuring arrangement of a temperature sensor may comprise a temperature-dependent resistance, for example PT100. 
         [0013]    The sensor measuring arrangement can be connected to an analyzer via the connecting lines of the sensor unit. Furthermore, the sensor unit with the sensor housing can be electrically connected to a conductive part of the motor vehicle or trailer, for example the vehicle axle. 
         [0014]    For discharging any electrostatic charge from the conductive part of the motor vehicle or trailer, the sensor unit comprises a predetermined discharge path between the electrically conductive sensor housing and a connecting line of the sensor unit or between the electrically conductive sensor housing and the sensor measuring arrangement of the sensor unit. Via the predetermined discharge path, advantageously the electrostatic charge can be output to the analyzer via the sensor measuring arrangement and/or a connecting line. In this case, the discharge path is dimensioned such that the discharge path comprises a threshold voltage that lies below the maximum permissible voltage of the analyzer that is connected to the sensor unit. Thus, the isolation voltage of the sensor unit is reduced so that the electrostatic charge can be advantageously discharged from the conductive part of the motor vehicle or trailer, for example the vehicle axle, via the analyzer without damaging the analyzer. 
         [0015]    In certain embodiments, the predetermined discharge path is implemented as a predetermined spark gap between the sensor housing and a connecting line of the sensor unit or between the sensor housing and the sensor measuring arrangement of the sensor unit. Such a spark gap can be advantageously simple to construct. 
         [0016]    In specific embodiments, the spark gap is formed by a first contact that is conductively connected to the sensor housing and by a second contact that is conductively connected to a connecting line or the sensor measuring arrangement of the sensor unit. The two contacts preferably lie opposite each other and are at a predetermined distance apart. By the design of the contacts and the spacing of the contacts from each other, the threshold voltage or breakdown voltage can advantageously be determined accurately when taking into account the medium disposed between the contacts. 
         [0017]    In other embodiments, the predetermined discharge path is implemented as a varistor between the sensor housing and a connecting line of the sensor unit or between the sensor housing and the sensor measuring arrangement of the sensor unit. A varistor is a voltage-dependent resistance that is abruptly smaller above a defined threshold voltage, i.e. in the normal mode the resistance is very large and in the event of an overvoltage is very small with almost no delay, so that advantageously the electrostatic charge can be discharged. Such a discharge path can be advantageously simple to implement as a varistor within a sensor unit. 
         [0018]    In specific embodiments including the varistor, the varistor comprises a threshold voltage that lies below the maximum permissible voltage of an analyzer that is connected to the sensor unit. The maximum permissible voltage of the analyzer is given in this case by the breakdown voltage of the weakest electrical component of the analyzer. By specifying the threshold voltage that is used, the electrostatic charge can advantageously be safely discharged from the conductive part of the motor vehicle or trailer, for example the vehicle axle, via the analyzer without damaging the analyzer in doing so. 
         [0019]    In other embodiments, the predetermined discharge path is implemented as a high-impedance resistance between the sensor housing and a connecting line of the sensor unit or between the sensor housing and the sensor measuring arrangement. Such a discharge path is advantageously also simple to construct as a high-impedance resistance. 
         [0020]    In specific embodiments including the high-impedance resistance, the high-impedance resistance between the sensor housing and a connecting line of the sensor unit comprises a resistance value of between 100 kΩ and 1000 kΩ. Owing to the high-impedance resistance, the electrostatic charge can advantageously be discharged from the conductive part of the motor vehicle or trailer, for example the vehicle axle, via the analyzer without damaging the analyzer. 
         [0021]    In yet other embodiments, the predetermined discharge path is implemented as a high-impedance casting compound between the sensor housing and a connecting line of the sensor unit or between the sensor housing and the sensor measuring arrangement of the sensor unit. The sensor measuring arrangement of the sensor unit is preferably encapsulated in a casting compound based on epoxy or polyurethane. Such a discharge path is also advantageously simple to construct as a high-impedance casting compound. 
         [0022]    In specific embodiments including the high-impedance casting compound, the high-impedance casting compound between the sensor housing and a connecting line of the sensor unit or between the sensor housing and the sensor measuring arrangement of the sensor unit comprises such a specific resistance as to produce a resistance value of the predetermined discharge path of between 100 kΩ and 1000 kΩ. For example, by enriching the casting compound with nickel particles and/or silver particles, the casting compound can be given a predetermined electrical con-ductivity. Owing to the high-impedance casting compound, the electrostatic charge can thereby advantageously be discharged from the conductive part of the motor vehicle or trailer, for example the vehicle axle, via the analyzer without damaging the analyzer. 
         [0023]    In certain embodiments, the sensor unit is a revolution rate sensor. Because electrostatic charging occurs directly in the wheel area of a vehicle and such electrostatic charge cannot be specifically discharged since the chassis parts often have no conductive connection to the frame of the vehicle, the revolution rate sensors that are attached in the wheel area and the analyzer that is connected thereto are particularly at risk of overvoltages. If the revolution rate sensor is the sensor unit according to the invention, any electrostatic charge can advantageously be discharged from the conductive part of the motor vehicle or trailer without damaging the analyzer that is connected to the revolution rate sensor. 
         [0024]    Furthermore, the present invention provides a sensing and analysis device, wherein the sensing and analysis device comprises at least one sensor unit described above and an analyzer, for example in an axle modulator of an electronic brake system. 
         [0025]    The sensing and analysis device comprises a predetermined discharge path for discharging any electrostatic charge out of a conductive part of the motor vehicle or trailer, wherein the predetermined discharge path is disposed between the sensor housing of the sensor unit and a connecting line that connects the sensor measuring arrangement of the sensor unit to the analyzer, or between the sensor housing and the sensor measuring arrangement of the sensor unit. 
         [0026]    Such a predetermined discharge path advantageously prevents the build-up of too much electrostatic charge within a conductive part of the motor vehicle or trailer that is connected to the sensor unit by reducing the electrostatic charge via the discharge path and via the analyzer. In this case, the discharge path according to the invention is designed so that the isolation voltage applied to the sensor unit is so low that the analyzer is not damaged by the charge that is being discharged. 
         [0027]    In certain embodiments, the analyzer comprises a varistor that is arranged so as to protect the electronic components that are disposed in the analyzer against damage by overvoltage. The varistor thereby advantageously acts as a protection against induced overvoltages, because it has a high resistance in the normal mode, but in the event of an overvoltage is highly conductive and thereby absorbs the voltage peak. 
         [0028]    In specific embodiments in which the analyzer comprises the varistor, the varistor is disposed in the analyzer between a connecting line to ground (GND) and a connecting line that connects the sensor measuring arrangement of the sensor unit to the analyzer. This arrangement of the varistor advantageously produces additional protection of the analyzer for the discharge path according to the invention, which is disposed in the sensor unit that is connected to the analyzer, against damage within the analyzer because of overvoltages that can arise owing to a spontaneous discharge of electrostatic charge. 
         [0029]    In other embodiments, a predetermined spark gap is disposed in the analyzer between a connecting line to ground (GND) and a connecting line that connects the sensor measuring arrangement of the sensor unit to the analyzer. This spark gap may also advantageously used as protection against induced overvoltages. The spark gap is typically formed by two mutually opposed contacts. Owing to the design and arrangement of the mutually opposed contacts, when taking into account the medium disposed between the contacts a predetermined threshold voltage or breakdown voltage at which a discharge of the applied overvoltage occurs can be determined. 
         [0030]    of the present invention further provides a motor vehicle, for example a commercial vehicle or trailer, wherein the motor vehicle or the trailer comprises at least one sensor unit as described above and/or at least one sensing and analysis device as described above. Such a motor vehicle or trailer advantageously requires fewer repairs because of faulty control units, the analyzer of which is electrically connected to at least one sensor unit, because the analyzer is advantageously protected against damage due to overvoltages via the discharge path according to the invention in the sensor unit. 
         [0031]    Finally, of the present invention provides a method for protecting electronic components of an analyzer that is connected to a sensor unit via at least two connecting lines against excessive electrical voltages. For this purpose, the sensor unit comprises a sensor measuring arrangement for sensing at least one physical variable as well as a sensor housing partly or fully enclosing the sensor measuring arrangement. The sensor unit with the sensor housing is electrically connected to a conductive part of the motor vehicle or trailer, for example the vehicle axle. 
         [0032]    The electrostatic charge present in the conductive part of the motor vehicle or trailer is advantageously discharged via a predetermined discharge path between the sensor housing and a connecting line that connects the sensor measuring arrangement of the sensor unit to the analyzer, or between the sensor housing and the sensor measuring arrangement of the sensor unit, while the measurement of the sensor itself is not affected. 
         [0033]    An overvoltage protection device in the form of a discharge path according to the invention in the sensor unit is particularly simple and inexpensive to implement, because standardized circuits or analyzers can still be used for connecting to the sensor unit. The electrostatic charge can thus be discharged from the part of the motor vehicle or trailer to which the sensor unit is attached via the connecting line and the analyzer that is connected thereto, because the analyzer usually comprises a ground line that is connected to the frame of the vehicle. As a result, the electrostatic charge can advantageously no longer build up to the extent that would cause damage to the analyzer in the event of a discharge. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0034]    The invention is described in greater detail below with reference to the accompanying figures, in which: 
           [0035]      FIG. 1  shows a sensor unit with a discharge path implemented as a predetermined spark gap and an analyzer connected to the sensor unit, 
           [0036]      FIG. 2  shows a sensor unit with a discharge path implemented as a varistor and an analyzer connected to the sensor unit, 
           [0037]      FIG. 3  shows a sensor unit with a discharge path implemented as a high-impedance resistance and an analyzer connected to the sensor unit, and 
           [0038]      FIG. 4  shows a sensor unit with a discharge path implemented as a high-impedance casting compound and an analyzer connected to the sensor unit. 
       
    
    
     DETAILED DESCRIPTION 
       [0039]    With reference to the specific embodiment of the Figures, wherein like numerals generally indicate like parts throughout the several views,  FIG. 1  shows a sensor unit  2  with a predetermined discharge path  4  and an analyzer  6  that is connected to the sensor unit  2 . 
         [0040]    Electrostatic charge is produced within a vehicle axle  10  by the friction from tires  8  while travelling, for example. Usually, however, the chassis parts of a motor vehicle or trailer, such as vehicle axles  10 , are disposed electrically separately or isolated from a frame of a vehicle  11 , which as a rule is at ground potential. As a result, electrostatic charge can arise especially in the wheel area of the motor vehicle or trailer, for example on the vehicle axle  10 , wherein such charge can be discharged when a voltage limit is exceeded by flashing over to the nearest electrically conductive part of the motor vehicle or trailer. 
         [0041]    If a sensor unit  2  is attached to the vehicle axle  10  so that there is a conductive connection  14  between a sensor housing  12  and the vehicle axle  10 , the discharge takes place via the sensor unit  2  and possibly results in damage to the sensor unit  2  and/or to an analyzer  6  that is connected to the sensor unit  2 . 
         [0042]    In order to avoid such damage to the sensor unit  2  and/or analyzer  6 , the sensor unit  2  comprises a discharge path  4  that is designed to reliably discharge an electrostatic charge present in the conductive part of the motor vehicle or trailer, for example the vehicle axle  10 . For this purpose, the predetermined discharge path  4  is disposed between the electrically conductive sensor housing  12  and a sensor measuring arrangement  16  within the sensor housing  12 . 
         [0043]    The sensor unit  2  represented in  FIG. 1  corresponds to a revolution rate sensor with a known sensor measuring arrangement  16 . The sensor measuring arrangement  16  may comprise a magnet for producing a magnetic flux and a coil for detecting a change of the magnetic flux. The invention is however not limited to the use of revolution rate sensors as the sensor unit  2 . Rather, any sensor units  2  that comprise an electrically conductive sensor housing  12  and that are connected via at least two connecting lines  18  to further electrical devices, such as an analyzer, are provided with a predetermined discharge path  4  in order to protect the electrical device that is connected via the connecting lines  18  to the sensor unit  2  against an overvoltage that was caused by an electrostatic charge, for example in the vehicle axle  10 . Thus, temperature sensors, pressure sensors, acceleration sensors, etc. may also advantageously be provided with the discharge path  4  according to the invention. 
         [0044]    The sensor unit  2  represented in  FIG. 1  comprises an electrically conductive, pot-shaped sensor housing  12  that is closed by a closure part  20 , from which the connecting lines  18  are fed out of the sensor unit  2 . The connecting lines  18  are connected to the analyzer  6  via a plug connection and are fed within the analyzer  6  to an analysis circuit  22 . 
         [0045]    In this embodiment, the analyzer  6  is connected via a further electrical line  24  to the frame of the vehicle  11  as ground potential. 
         [0046]    In order to protect the analyzer  6  in addition to the discharge path  4  against overvoltage, this can be provided with a voltage-dependent resistance  28 , also known as a varistor. For this purpose, the varistor  28  may be disposed between a ground connecting line  30  and a connecting line  32  that is connected to a connecting line  18 . 
         [0047]    In the exemplary embodiment of the invention in  FIG. 1 , the predetermined discharge path  4  is implemented as a predetermined spark gap  4 . 1 . The spark gap  4 . 1  is formed by a first contact that is conductively connected to the sensor housing  12  and a second contact that is conductively connected to a connecting line  18  of the sensor unit  2 . In this case, the contacts are disposed opposite each other and are at a predetermined distance from each other. 
         [0048]    The contacts in the sensor housing  12  are typically enclosed hermetically tight and the sensor unit  2  is filled with a gas. This has the advantage that the breakdown voltage of the spark gap  4 . 1  is independent of impurities, moisture and air pressure. Owing to the design of the contacts, the distance between the contacts and the choice of the gas disposed between the contacts, the breakdown voltage at which the electrostatic charge is discharged can advantageously be accurately determined. The breakdown voltage may be dimensioned so that the analyzer  6  is not damaged by the discharged charge. 
         [0049]      FIG. 2  shows an alternative design of the invention with which the predetermined discharge path  4  is implemented as a varistor  4 . 2  between the sensor housing  12  and a connecting line  18 . 
         [0050]    The varistor  4 . 2  is a voltage-dependent resistance that is abruptly smaller above a defined threshold voltage. In this case, the threshold voltage is typically selected so that it lies below the maximum permissible voltage of an analyzer  6  that is connected to the sensor unit  2 . The maximum permissible voltage of the analyzer  6  is dependent here on the breakdown voltage of the weakest component of the analyzer  6 . Thus, the electrostatic charge induced for example in the vehicle axle  10  can advantageously be discharged without damaging the analyzer  6 , while the measurement of the sensor is not affected. 
         [0051]      FIG. 3  shows an alternative embodiment of the invention in which the predetermined discharge path  4  between the sensor housing  12  and a connecting line  18  is in the form of a high-impedance resistance  4 . 3 . 
         [0052]    The resistance  4 . 3  typically comprises a resistance value between 100 kΩ and 1000 kΩ and is dimensioned such that the electrostatic charge that is induced in the vehicle axle  10  for example can be discharged without damaging the analyzer  6 . 
         [0053]      FIG. 4  shows an alternative embodiment of the invention in which the predetermined discharge path  4  between the sensor housing  12  and a connecting line  18  is implemented as a high-impedance casting compound  4 . 4 . 
         [0054]    The high-impedance casting compound  4 . 4  is typically implemented so as to comprise a specific resistance that forms a resistance value of the discharge path  4  of 100 kΩ to 1000 kΩ. The specific resistance is in this case dependent on enriching the casting compound  4 . 4  with conductive particles and the dimensions of the casting compound  4 . 4 . The resistance of the high-impedance casting compound  4 . 4  is generally dimensioned so that the electrostatic charge that is induced in the vehicle axle  10  for example can be discharged without damaging the analyzer  6 . 
         [0055]    The alternative embodiments of the invention according to  FIG. 1  through  FIG. 4  described above differ only in the implementation of the embodiment of the discharge path  4  according to the invention. The functions of the discharge path  4  described under  FIG. 1  thereby also apply analogously to the embodiments according to  FIG. 2  through  FIG. 4 . 
         [0056]    The discharge path  4  according to the invention can be implemented simply and inexpensively in the sensor unit  2 , so that a sensing and analysis device of such a sensor unit  2  and an analyzer  6  connected thereto have reliable overvoltage protection. 
         [0057]    All the features mentioned in the above description as well as in the claims can be combined with the features of the independent claims both individually and in any combination. The disclosure of the invention is therefore not limited to the described or claimed feature combinations. Rather, all feature combinations that are useful within the scope of the invention are to be considered as being disclosed.