Abstract:
A method for checking the plausibility of a measurement result for an electric current by a current sensor connected to an electrical circuit, the method including: making a predetermined change to the switching state of the electrical circuit; detecting, by the current sensor, a change to the electric current resulting from the change to the switching state as a measurement result; and checking the plausibility of the measurement result by contrasting the change to the switching state and the change to the electric current.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is the U.S. National Phase Application of PCT International Application No. PCT/EP2013/068407, filed Sep. 5, 2013, which claims priority to German Patent Application No. 10 2012 215 946.0. filed Sep. 7, 2012, the contents of such applications being incorporated by reference herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to a circuit for conducting an electric current between a vehicle battery and an electrical network component which is connectable to the vehicle battery via an electrical component, and to a vehicle having the circuit. 
       SUMMARY OF THE INVENTION 
       [0003]    In order to perform measurements of an electric current output by an electrical energy source to an electrical consumer in a motor vehicle, a current sensor can be connected in series between the electrical energy source and the electrical consumer. A current sensor of this type is known, for example, from DE 10 2011 078 548 A1 being incorporated by reference herein. 
         [0004]    The problem addressed by the present invention is to improve known current measurement methods. 
         [0005]    According to one aspect of the invention, a method for checking the plausibility of a measurement result of a current sensor interconnected in an electrical circuit comprises the following steps:
       making a predetermined change to the circuit state of the electrical circuit;   detecting a change in the electric current which is brought about by the change in the circuit state; and   checking the plausibility of the measurement result of the current sensor by comparing the change in the circuit state and the change in the electric current.       
 
         [0009]    The specified method is based on the consideration that current sensors should be electrically connected in series between the electrical energy source and the electrical consumer in order to route the entire electric charge to be transported by the electric current via the current sensor. On the basis of this consideration, the specified method is based on the discovery that defects in the electrical circuit in which the current sensor is implemented, or defects in the current sensor itself, such as parasitic short circuits, for example, can lead to some of the electric current and hence some of the electric charge being conducted past the current sensor and not being able to be detected by the current sensor, which leads to an erroneous measurement by the current sensor. In order to avoid an erroneous measurement such as this, it is proposed with the specified method to transfer the electrical circuit into such a state in which the electric current is known or can at least be derived from the state. Thus, it is possible to ensure fault-free functioning of the current sensor in the electric circuit. 
         [0010]    In a development, the specified method comprises the step of connecting a known electrical consumer to the circuit in order to make the predetermined change to the circuit state of the electrical circuit. If the circuit is, for example, part of an onboard power supply system in a vehicle or is operated in a vehicle as onboard power supply system, said known electrical consumers are, for example, in the form of a heater, an air-conditioning system or the like. The development is based on the consideration that the current itself does not have to be detected, but only the change in said current which is caused by the connection of the known electrical consumer. 
         [0011]    In another development of the specified method, the current sensor has at least two parallel-connected shunts wherein, in order to make the predetermined change to the circuit state of the electrical circuit, a shunt is electrically removed from the circuit. This development is based on the consideration that the current sensor can also be monitored for fault-free functionality thereof by the individual parallel-connected shunts, the value of which must have been made known, for example, by the manufacturing process, since when a shunt is disconnected, the current in the other shunt must change in a manner known to a person skilled in the art, which can be appropriately verified. 
         [0012]    In an additional development of the specified method, the electrical circuit is in an at least quasi-static state before the electrical consumer is connected. A quasi-static state is intended to be understood below as a state in which the state of the electrical circuit within a predetermined time limit changes only within a predetermined range. In a static state, the state of the electrical circuit would not change at all. In this way, it is possible to ensure that the predetermined change in the circuit state is not superposed by an unknown change in the circuit state, as a result of which the electric current would change in an unknown manner and thus it would not be possible to check the plausibility of the measurement result using the current sensor. 
         [0013]    In yet another development of the specified method, the known current consumption of the known electrical consumer is dependent on operating conditions of the electrical circuit and/or of the electrical consumer. This development is based on the consideration that the electrical resistance of the known electrical consumer influences the electric current to be measured. Said electrical resistance is dependent on the operating conditions of the electrical circuit with the current sensor, however. Taking said operating conditions into account in the specified method therefore improves the checking of the plausibility of the measurement result. 
         [0014]    In a preferred development, the operating conditions comprise an operating voltage dropping across the known electrical consumer and/or an operating temperature of the known electrical consumer and/or of the circuit. This development is based on the consideration that not all operating conditions have an effect in the same manner on the electrical resistance of the electrical circuit. In order not to unnecessarily complicate the determination of the known current consumption, only the operating conditions which noticeably change the known current consumption, that is to say outside of particular predefinable tolerance values, should therefore have an influence on the known current consumption. 
         [0015]    In an alternative development, the specified method comprises the following steps:
       making a second predetermined change to the circuit state of the electrical circuit;   detecting a second change in the electric current which is brought about by the second change in the circuit state; and   comparing the change in the circuit state and the change in the electric current.       
 
         [0019]    This development of the specified method is based on the consideration that the first predetermined change in the circuit state could itself be erroneous, too, for example because a defective consumer is connected to the circuit to change the circuit state. The checking of the plausibility of the measurement result could then erroneously be either positive or negative. In order to prevent this case, it is proposed with the development of the specified method to directly or indirectly check the plausibility of the measurement result obtained from the first predetermined change using a further previously known change in the circuit state. 
         [0020]    In this case, according to a particular development of the specified method, the second predetermined change to the circuit state of the electrical circuit can be made after the first predetermined change in the circuit state of the electrical circuit as an alternative or in addition to said first predetermined change. 
         [0021]    According to another aspect of the invention, a control device is specified, which control device is set up to perform any of the specified methods. 
         [0022]    In a development of the invention, the specified control device has a memory and a processor. In this case, the specified method is stored in the memory in the form of a computer program and the processor is provided to execute the method if the computer program is loaded from the memory into the processor. 
         [0023]    An aspect of the invention also relates to a computer program with program code means in order to perform all of the steps of any of the specified methods if the computer program is executed on a computer or any of the specified devices. 
         [0024]    An aspect of the invention also relates to a computer program product which contains a program code which is stored on a computer-readable data carrier and which performs any of the specified methods if said program code is executed on a data processing device. 
         [0025]    According to another aspect of the invention, a vehicle battery comprises
       a battery pole for outputting an electric current to an electrical consumer,   a current sensor which is connected to the battery pole for detecting the electrical current, and   one of the specified control devices, which is connected to the current sensor, for checking the plausibility of a measurement result of the current sensor.       
 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]    The above-described properties, features and advantages of this invention and the manner in which the invention is achieved become more clearly and unambiguously understood in connection with the following description of the exemplary embodiments, which are explained in more detail in connection with the drawings, in which: 
           [0030]      FIG. 1  shows a schematic view of a current sensor between two line sections, 
           [0031]      FIG. 2  shows a schematic view of a current sensor in a circuit, 
           [0032]      FIG. 3  shows a schematic view of an alternative current sensor in a circuit, 
           [0033]      FIG. 4  shows a schematic view of a current sensor in an alternative circuit, and 
           [0034]      FIG. 5  shows a current profile graph with measurement results from a current sensor. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0035]    In the Figs., identical technical elements are provided with identical reference signs and are described only once. 
         [0036]    Reference is made to  FIG. 1 , which shows a schematic view of a current sensor  2  between two line sections  4 ,  6 . An electric current  7  which flows via the current sensor  2  through the two line sections  4 ,  6  is intended to be detected using the current sensor  2 . 
         [0037]    In the present embodiment, the current sensor  2  is embodied as passive shunt which, in a manner known to a person skilled in the art, is a simple electrical resistor with a predefined resistance value. However, the current sensor  2  can also be designed as active shunt, as known from DE 10 2011 078 548 A1, for example, or designed on the basis of a magnetic measurement principle and is not restricted in its design in any way. 
         [0038]    In the present embodiment, the current sensor  2  is accommodated in abutment between the two line sections  4 ,  6 , wherein electrical measurement lines  8 ,  10  make electrical contact at the connection points between the line sections  4 ,  6  and the current sensor  2 , which electrical measurement lines are routed to an evaluation circuit  12 . A measurement voltage  14  falls between the measurement lines  8 ,  10  in a manner known to a person skilled in the art. It is possible to deduce, in a manner known to a person skilled in the art, the current  7  to be detected from the measurement voltage  14  and the known resistance value of the current sensor  2  designed as passive shunt. 
         [0039]    However, if the current sensor  2  is bridged, for example, by a contaminant  16 , some of the current  7  to be detected does not flow via the current sensor  2  but as parasitic current  18  via said contaminant  16 , as a result of which the measurement current  20  detected by the current sensor  2  is distorted by said parasitic current  18 . Since such contaminants  16  or other defects in the current sensor itself or in a circuit containing the current sensor  2  do not emerge until during the use thereof, these should also be detected during the use thereof. Possible solutions to this are offered below. 
         [0040]    Reference is made to  FIG. 2 , which shows a schematic view of the current sensor  2  in a circuit  22 . 
         [0041]    In the present embodiment, the current sensor  2  is connected between an electrical energy source  24 , which is embodied as a battery, and an electrical consumer  26 , wherein the electric current  7  to be detected is conducted via a first battery pole  28  of the battery  24  and one of the two line sections  4  to the current sensor  2 . The current  7  to be detected is then conducted via the other of the two line sections  6  to the electrical consumer  26  and returns from the electrical consumer via a return line  30  and a second battery pole  32  to the battery  24 . 
         [0042]    The current sensor  2  is connected via measurement lines  8 ,  10  to the evaluation circuit  12 , wherein the measurement lines  8 ,  10  can transmit the voltage drop  14  across the current sensor  2  but also other signals necessary for measurement, such as a control signal, for example, by means of which the voltage drop  14  can be kept constant in the case of an active shunt. For more information in this regard, reference is made to DE 10 2011 078 548 A1. 
         [0043]    In the present embodiment, the evaluation circuit  12  outputs a state change signal  34  by means of which it can change a circuit state of the circuit  22 . The circuit state can in this case be any desired influence variable which changes the electric current  7  to be detected. Such influence variables may be, for example, the wiring of the circuit  22  or a temperature acting on the circuit  22  which change the electric current  7  to be detected. 
         [0044]    In the present embodiment, the state of the electric circuit  22  is changed by the state change signal  34  such that the electric current  7  to be detected changes in a known manner. Hence, the measurement current  20  flowing via the current sensor  2  and shown in  FIG. 1  must also change in the known manner. If it does not, some of the electric current  7  to be detected is flowing via a defect in the circuit  22 , such as the contaminant  18 , for example, as parasitic current  16 , with the result that the measurement current  20  is erroneous. Therefore, the evaluation circuit  12  can check the plausibility of the measurement current  20  detected by the current sensor  2  using the change in the circuit state via the state signal  34 . 
         [0045]    Two examples relating to this are discussed below. 
         [0046]    Reference is made to  FIG. 3 , on the basis of which a first one of the two examples is to be illustrated. 
         [0047]    In the present embodiment, the current sensor  2  is constructed from two parallel-connected individual shunts  36 ,  38 , wherein the second individual shunt  38  can be removed from the parallel circuit via a switch  40  which is controllable by the state change signal  34 . 
         [0048]    During use, the evaluation circuit detects the current  7  to be detected via the measurement current  20  firstly with the two individual shunts  36 ,  38  in the common parallel circuit and stores the value of the measurement current  20 , for example, in an internal memory which is not illustrated in more detail. Then, it isolates the second individual shunt  38  from the parallel circuit using the state change signal  34  and detects the value of the measurement current  20  again. 
         [0049]    In the fault-free case, the two detected values now depend on one another in a manner known to a person skilled in the art. If, for example, the resistance values of the two individual shunts  36 ,  38  are equal in size, the value of the measurement current  20  must be doubled after disconnection of the second individual shunt  38 . If it is not, there is a parasitic current  18  flowing. 
         [0050]    Reference is made to  FIG. 4 , on the basis of which the second one of the two examples is to be illustrated. 
         [0051]    In the second example, it is not the current sensor  2  which is changed, but the electrical consumer  26  connected to the current sensor  2 . 
         [0052]    For this purpose, the electrical consumer  26  comprises a three-phase electric motor  42 , which is supplied with electrical energy from the battery  24  via an inverter  44  in a manner known to a person skilled in the art. In this case, another single-phase current sensor  46  can be arranged in each phase in addition to the current sensor  2  which is already present, in order to perform measurements known to a person skilled in the art, such as detection of the standing magnetic field, for example. 
         [0053]    Furthermore, in the present embodiment, an electric heater  48  is connected in parallel with the inverter  44 , it being possible for said heater to be isolated from the parallel circuit via the switch  40  which is switchable by means of the state change signal  34 . 
         [0054]    During use, the evaluation device  12  can connect the electric heater  48  and measure by how much the measurement current  20  through the current sensor  2  has risen. This value must match the current consumption of the electric heater  48 . If it does not, some of the current  7  to be detected is flowing as parasitic current  18 . 
         [0055]    The individual phase current sensors  46  can in this case likewise be checked for fault-free functioning using the method presented in the present application. 
         [0056]    Reference is made to  FIG. 5 , which shows a qualitative profile  50  of the measurement current  20  over time  52 , which is associated with the arrangement shown in  FIG. 4 . 
         [0057]    Preferably, the electric heater  48  is connected as additional electrical consumer at a start instant  54  when the measurement current  20  has settled to a first static value  56 . 
         [0058]    After the start instant  54 , if the electric heater  48  is connected in parallel with the inverter  44 , the measurement current  20  increases and a settles at a second static value  58 , which can be measured, at the earliest, at an instant  60  at which said settling process is complete. The duration between said two instants is generally in the order of seconds. 
         [0059]    In a normal circuit state of the circuit  22 , the magnitude  62  of the difference between the two values  58  and  56  of the measurement current  20  should correspond to the current consumption of the electric heater.