Abstract:
A method for transmitting error information of a sensor, in a signal exchanged between the sensor and a master receiver, said signal being designed with a minimum level for supplying electric power to the sensor and carrying measurement data. One disclosed method involves identifying the error in the sensor; switching off a component of the sensor consuming electric power; and transmitting the error information at an error level lying below the minimum level.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of PCT Application PCT/EP2015/069570, filed Aug. 26, 2015, which claims priority to German Application DE 10 2014 217 834.7, filed Sep. 5, 2014. The disclosures of the above applications are incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The invention relates to transmitting an item of error information in a signal supplying a sensor with electrical energy to a control apparatus. 
       BACKGROUND 
       [0003]    DE 10 2011 080 789 A1 discloses a vehicle in which wheel speed sensors for sensing the wheel speed of the individual wheels are installed. These wheel speed sensors are active wheel speed sensors and transmit their measurement data in the form of wheel speeds to an evaluation device via a cable as the transmission path. 
         [0004]    The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. 
       BRIEF SUMMARY 
       [0005]    An object of the invention is to improve the transmission of the measurement data. 
         [0006]    A superordinate receiving device is preferably understood as meaning an external receiving device, in particular an electronic control unit or an electronic control device of a motor vehicle system or a motor vehicle control system, for example a motor vehicle brake system. 
         [0007]    According to one aspect, a method for transmitting an item of error information describing an error in a sensor in a signal, which is interchanged between the sensor and a superordinate receiving device and is set up with a minimum level for supplying electrical energy to the sensor and for carrying measurement information, comprises the steps of: detecting the error to be transmitted in the sensor, switching off a component of the sensor which consumes electrical energy, and transmitting the error with an error level below the minimum level. 
         [0008]    This is based on the consideration that, in order to comply with high safety standards, incorrect measurement information and errors in the signal processing inside the sensor need to be detected and accordingly need to be taken into account during their processing in a superordinate receiving device. The incorrect measurement information or the error in the signal processing inside the sensor could be detected in the sensor which captures the measurement information and transmits it to the superordinate receiving device. 
         [0009]    However, for reasons of costs, use is generally made of two-wire lines which both supply the sensor with electrical energy and interchange the measurement information. In order to be able to likewise include the error information describing the error in the signal, signal states outside the normal usage range would have to be defined for the error signal, which signal states would either entail an unacceptable power consumption or cannot be achieved on account of a particular basic power consumption of the functional blocks during normal operation of the sensor. The minimum level defines this basic power consumption and is therefore a basic consumption level or an energy supply level for supplying electrical energy to the sensor. If the sensor is connected to a current interface, the minimum level can be defined as a standardized normal current level, for example. 
         [0010]    Reliable measurement information can no longer be captured anyway in the event of an error in the sensor, with the result that this information actually no longer has to be transmitted on account of the fact that it cannot be used by the receiving device. For this reason, certain electronic components actually also do not need to be operated at all in the error state of the sensor and can therefore be switched off. In this manner, the power consumption of the sensor then falls, with the result that the electrical energy supply for the sensor is also safeguarded when the signal transmits the error information using signal states and therefore error levels which could not be achieved during normal operation of the sensor. 
         [0011]    Switching off at least one component of the sensor which consumes electrical energy in the event of an error makes it possible to transmit error information describing errors to the receiving device, which error information can be distinguished from the measurement information, with the result that the receiving device can then accordingly react to the error in the sensor. In this case, that component of the sensor which consumes electrical energy can be arbitrarily selected and, for example, can comprise parts of a signal processing circuit for entering the measurement information in the signal. 
         [0012]    In one development, the error is transmitted in a pulse which is kept at the error level over a predetermined length of time. Keeping the pulse at the error level means that the receiving device can clearly define this pulse as error information and can therefore distinguish it from signal fluctuations which possibly occur. 
         [0013]    In an additional development, the measurement information in the signal can be described with measurement pulses between the minimum level and a second, measurement pulse level above the minimum level. This makes it possible to transmit, for example, time-dependent measurement information, such as speeds from a speed sensor, in a particularly robust manner. The higher the speed, the more measurement pulses occur here over a predetermined reference period. In this case, the generation of the measurement pulses on the basis of the speed can be carried out in any desired manner and is not restricted to a particular measurement principle. 
         [0014]    In one particular development, the transmission of the measurement pulses is suppressed if the error to be transmitted has been detected in the sensor. A component of the sensor which consumes the electrical energy and generates the measurement pulses can then be accordingly switched off in order to reduce the electrical energy consumption of the sensor within the scope of the stated method. However, this is only one possible way of reducing the electrical energy consumption of the sensor. A further possibility would be, for example, to switch off a component of the sensor for error monitoring if no further error monitoring is considered to be necessary in the event of a detected error. 
         [0015]    However, if the transmission of the measurement pulses is suppressed in the event of an error, in one preferred development of the stated method, a check can be carried out in the event of an error in order to determine whether the error to be transmitted is still present before each transmission of a measurement pulse. The corresponding component for error monitoring should then expediently remain switched on in the event of an error. 
         [0016]    Alternatively or additionally, the sensor can be restarted after the error has been transmitted with the error level. This makes it possible to attempt to eliminate the error by re-initializing the sensor, the full range of functions then also being fully available again for error diagnosis after the restart. If the error is still present and is sensed by the error monitoring, the process can be carried out again. 
         [0017]    Yet another development, comprises the steps of: storing the error in a memory before that component of the sensor which consumes electrical energy is switched off, and interrupting an electrical energy supply for the memory in order to switch off that component of the sensor which consumes electrical energy. 
         [0018]    In this case, the memory should expediently be non-volatile. Switching off the memory makes it possible to reduce a further electrical energy consumption in order to effectively carry out the stated method. 
         [0019]    According to another aspect, a control apparatus is set up to carry out one of the methods. 
         [0020]    In one development of the control apparatus, the apparatus has a memory and a processor. In this case, one of the methods is stored in the memory in the form of a computer program and the processor is provided for the purpose of carrying out the method when the computer program is loaded into the processor from the memory. 
         [0021]    According to another aspect, a computer program comprises program code means for carrying out all steps of one of the stated methods when the computer program is executed on a computer or one of the control apparatuses. 
         [0022]    According to another aspect, a computer program product contains a program code which is stored on a computer-readable data storage medium and carries out one of the methods when it is executed on a data processing device. 
         [0023]    According to another, a sensor comprises one of the control apparatuses. 
         [0024]    In a special development, the sensor is a wheel speed sensor. 
         [0025]    According to another aspect, a vehicle comprises one of the wheel speed sensors. 
         [0026]    Other objects, features and characteristics of the present invention, as well as the methods of operation and the functions of the related elements of the structure, the combination of parts and economics of manufacture will become more apparent upon consideration of the following detailed description and appended claims with reference to the accompanying drawings, all of which form a part of this specification. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the disclosure, are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0027]    The above-described properties, features and advantages of this invention and the manner in which they are achieved become clearer and more clearly comprehensible in connection with the following description of the exemplary embodiments which are explained in more detail in connection with the drawings, in which: 
           [0028]      FIG. 1  shows a schematic view of a vehicle having a vehicle dynamics control system; 
           [0029]      FIG. 2  shows a schematic view of a wheel speed sensor in the vehicle from  FIG. 1 ; and 
           [0030]      FIG. 3  shows a graph having an output signal from the wheel speed sensor from  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0031]    In the Figures, identical technical elements are provided with identical reference symbols and are described only once. 
         [0032]    Reference is made to  FIG. 1  which shows a schematic view of a vehicle  2  having a vehicle dynamics control system which is known per se. Details of this vehicle dynamics control system can be gathered from DE 10 2011 080 789 A1, for example. 
         [0033]    The vehicle  2  comprises a chassis  4  and four wheels  6 . Each wheel  6  can be decelerated with respect to the chassis  4  via a brake  8  fastened to the chassis in a stationary manner in order to decelerate a movement of the vehicle  2  on a road (not illustrated any further). 
         [0034]    In this case, it may happen, in a manner known to a person skilled in the art, that the wheels  6  of the vehicle  2  lose their traction and the vehicle  2  even moves away from a trajectory, which is predefined using a steering wheel (not shown any further) for example, as a result of understeering or oversteering. This is avoided by means of control circuits which are known per se such as ABS (anti-lock braking system) and ESP (electronic stability program). 
         [0035]    In the present embodiment, the vehicle  2  has speed sensors  10  on the wheels  6  for this purpose, which sensors sense a speed  12  of the wheels  6 . The vehicle  2  also has an inertial sensor  14  which captures vehicle dynamics data  16  relating to the vehicle  2 , which data may comprise, for example, a pitch rate, a roll rate, a yaw rate, a transverse acceleration, a longitudinal acceleration and/or a vertical acceleration in a manner known per se to a person skilled in the art. 
         [0036]    On the basis of the sensed speeds  12  and captured vehicle dynamics data  16 , an evaluation apparatus in the form of 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 predefined trajectory mentioned above and can accordingly react to this 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 activate actuators, such as the brakes  8 , by means of actuating signals  24 , which actuators react to the sliding and the deviation from the predefined trajectory in a manner known per se. 
         [0037]    The present invention is intended to be illustrated in more detail using one of the speed sensors  10  shown in  FIG. 1  even though the present invention can be implemented on any desired sensors, for example the inertial sensor  14 . 
         [0038]    Reference is made to  FIG. 2  which shows a schematic view of one of the speed sensors  10  in the vehicle dynamics control system from  FIG. 1 . 
         [0039]    In the present embodiment, the speed sensor  10  is in the form of an active speed sensor which comprises an encoder disk  26 , which is fastened to the wheel  6  in a rotationally fixed manner, and a reading head  28  which is fastened in a stationary manner with respect to the chassis  4 . 
         [0040]    In the present embodiment, the encoder disk  26  consists of magnetic North poles  30  and magnetic South poles  32  which are strung together and together excite a transmitter magnetic field (not illustrated any further). If the encoder disk  26  fastened to the wheel  6  rotates with the latter in a direction of rotation  34 , the transmitter magnetic field accordingly concomitantly rotates in a synchronous manner. 
         [0041]    In the present embodiment, the reading head  28  is a magnetostrictive element which changes its electrical resistance on the basis of the angular position of the transmitter magnetic field excited by the encoder wheel  26 . 
         [0042]    In order to sense the speed  12 , the change in the angular position of the encoder wheel  26 , and therefore the change in the electrical resistance of the reading head  28 , is sensed. For this purpose, the reading head  28  may be connected, in a manner known per se, to a resistance measuring circuit (not illustrated any further), for example a bridge circuit known per se. A periodic output signal, called speed transmitter signal  36  below, is generated in the resistance measuring circuit on the basis of the electrical resistance of the reading head  28 . A pulse signal  40  which depends on the speed  12  and is shown in  FIG. 3  can be generated in a signal preprocessing circuit  38  downstream of the reading head  28  on the basis of the speed transmitter signal  36  and can be output to the controller  18 . With respect to this and with respect to further background information on active wheel speed sensors, reference is made to the relevant prior art, for example DE 101 46 949 A1. 
         [0043]    The generation of the pulse signal  40  in the signal preprocessing circuit  38  shall be additionally briefly explained below using  FIG. 3  in which the pulse signal  40  containing measurement pulses  42  is plotted in a signal  44 /time  46  graph. The signal  44  and therefore the pulse signal  40  may be a current signal in this case. Frequency modulation per se is already given by the measurement method in the above-mentioned speed sensor  10 , the measurement pulses  42  being able to be generated in a pulse generation device  47  of the signal preprocessing circuit  38  and being able to be modulated onto the pulse signal  40  via a mixer  49 . 
         [0044]    Starting from a particular reference signal value  48 , the measurement pulses  42  have a predetermined first height  50 . Within the scope of the frequency modulation, the number of measurement pulses  42  over time  46  is determined by the measured value to be transmitted for the speed  12 , which means that the number of measurement pulses  42  increases with increasing speed  12 . Therefore, in  FIG. 3 , the pulse signal  40  is shown in a state in which the speed  12  falls over time  46  and the number of measurement pulses  42  decreases over a particular period. 
         [0045]    Within the scope of the present embodiment, the electrical energy  50  needed to generate the measurement pulses  42  is provided by an electrical energy supply circuit  52  via a switch (yet to be described) in the form of a normally closed contact  53 . The electrical energy supply circuit  52  takes the input energy  54  required for this purpose from the pulse signal  40 , the necessary input energy  54  being fed into the pulse signal  40  by the controller  18  in a manner known per se, for example within the scope of an offset current. 
         [0046]    The signal preprocessing circuit  38  also has an error monitoring device  56 . The task of this error monitoring device  56  is to detect malfunctions and to report them to the controller  18  so that the latter can accordingly react to them. With the measurement pulses  42  from a defective speed sensor  10 , the controller  18  in the vehicle dynamics control system described using  FIG. 1  could incorrectly interpret a yaw rate which is not present, for example, and at which the vehicle  2  rotates about its vertical axis. The controller  18  would then intervene via the controller output signal  20  and would impose a yaw behavior on the vehicle  2  in order to counteract the yaw rate which is not present. Since this is highly dangerous to traffic, defective speed sensors  10  should be detected, for which the error monitoring device  56  is respectively provided. 
         [0047]    The error monitoring device  56  is also operated with electrical energy from the electrical energy supply circuit  52 . The error monitoring device  56  may be in the form of a watchdog known per se, for example, analyzes the function of the speed sensor  10  and monitors it for errors. If an error occurs, the error monitoring device  56  outputs an error pulse  58  which can likewise be modulated onto the pulse signal  40  via a mixer  49 . 
         [0048]    So that the controller  18  can also identify the error pulse  58  as such, an error pulse height  60  which differs from the height of the measurement pulses  42  must be selected for the error pulse. For good detectability by the controller  18 , the error pulse  58  should fall below the reference signal value  48  and should be held there for a predetermined period  62 . In principle, this period  62  can be held for any desired time. However, it should last until the controller  18  can also clearly distinguish the error pulse  58  from random signal value fluctuations. 
         [0049]    The problem here is that the error pulse  58  with its error pulse height  60  reduces the input energy  54 . The reference signal value  48  is expediently selected as the minimum signal value or minimum level in such a manner that a permanent electrical energy supply for all components of the speed sensor  10  and, in particular, of the signal processing circuit  38  is ensured. If the pulse signal  40  permanently falls below the reference signal value  48 , like in the error pulse  58 , the electrical energy supply for the speed sensor  10  and, in particular, for the signal processing circuit  38  can collapse. 
         [0050]    Since the metrological use of the measurement pulses  42  is doubtful in the event of an error, it is proposed within the scope of the present embodiment to reduce the electrical energy consumption of the speed sensor  10  and, in particular, of the signal processing circuit  38 . For this purpose, the normally closed contact  53  is controlled using the error pulse  58 , for example. Alternatively, however, the error monitoring device  56  can also control the normally closed contact  53  using its own signal. This interrupts the electrical energy supply  50  for the pulse generation device  47  and stops the generation of the measurement pulses  42 . The electrical energy consumption of the speed sensor  10  consequently falls and its function is still ensured by the error pulse  58  despite the pulse signal  40  which has fallen below the reference signal value  48 . 
         [0051]    On the basis of the error pulse  58 , a restart  63  of the speed sensor  10  can then also be initiated at the end of the period  62  in order to attempt to eliminate the error. With the restart  63 , the period  62  for transmitting the error pulse  58  could be automatically ended. Alternatively or additionally, the error may also be stored in a memory  64  which is only indicated in  FIG. 2 . 
         [0052]    The foregoing preferred embodiments have been shown and described for the purposes of illustrating the structural and functional principles of the present invention, as well as illustrating the methods of employing the preferred embodiments and are subject to change without departing from such principles. Therefore, this invention includes all modifications encompassed within the scope of the following claims.