Abstract:
A driving battery of a vehicle that can be electrically driven is charged by determining a resistance value that corresponds to the size of the electrical resistance between two contacts of the charging cable, where the size of the electrical resistance specifies the current-carrying capacity of the charging cable. As a function of the determined resistance value, one of a plurality of line protection devices which are disposed on the charging device is switched into the charge current path.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the U.S. national stage of International Application No. PCT/EP2008/057064, filed Jan. 26, 2012 and claims the benefit thereof. The International Application claims the benefit of German Application No. 10 2007 032 812.7 filed on Feb. 2, 2011, both applications are incorporated by reference herein in their entirety. 
     BACKGROUND 
     Described below is a method for protecting a charging cable in a charging device for charging a traction battery of an electrically drivable vehicle and such a charging device. 
     Electrically drivable vehicles have a traction battery (rechargeable battery) which provides the electrical energy required for the vehicle operation. Discharged batteries need to be recharged by a charging device, if required. For this purpose, the traction battery of the electrically drivable vehicle and the charging device are electrically connected by a charging cable. Corresponding to the current-carrying capacity (electrical conductivity) of the charging cable, the charging cable has different line cross sections. For example, there are charging cables which have a current-carrying capacity of 13 A. Other charging cables have current-carrying capacities of 20 A, 32 A or 63 A, for example. In accordance with the standard IEC 62196-2, such charging cables are provided with electrical plugs which are configured as so-called type 2 plugs, for example. In accordance with this standard IEC 62196-2, these plugs also have the same geometric dimensions when they are intended for charging cables with different current-carrying capacities. Therefore, it is not possible to identify from the geometric dimensions of the plug the current-carrying capacity for which the charging cable connected to the plug is suitable. 
     In accordance with the standard IEC 61851-1, the current-carrying capacity of the charging cable is specified (coded) for these plugs by a resistance, which is connected between the “proximity” and “PE” contacts of the plug. In this case, a specific resistance value is associated with a specific current-carrying capacity of the charging cable. 
     SUMMARY 
     The method and device enable safe and reliable protection of the charging cable during charging. 
     The method protects a charging cable in a charging device for charging a traction battery of an electrically drivable vehicle by determining a resistance value which corresponds to the magnitude of the electrical resistance between two contacts of the charging cable and one of a plurality of line protection devices, which are arranged in the charging device and are designed for rated current intensities of different magnitudes, that is switched into the charging current path depending on the determined resistance value. In other words, each of the line protection devices is associated with a specific resistance value. In this case, the magnitude of the electrical resistance between the two contacts of the charging cable indicates the current-carrying capacity of the charging cable. 
     In this method, it is particularly advantageous that the resistance value is determined and a line protection device is switched into the charging current path automatically depending on this determined resistance value. This line protection device has, for example, a rated current intensity which corresponds to the current-carrying capacity of the charging cable, which current-carrying capacity corresponds to the resistance value. As a result, the line protection device appropriate for the current-carrying capacity of the charging cable is automatically switched into the charging current path, with the result that the charging cable is protected by the appropriate line protection device. In this case, it is particularly advantageous that, in the charging device, standard line protection devices for the respectively required rated current intensities can be used. For example, fuses for 13 A, 20 A, 32 A and 63 A can be used. Such line protection devices designed for only in each case one rated current intensity are available at very low cost. 
     The method can be configured such that the charging current is conducted via the charging current path only once the line protection device has been switched into the charging current path. This ensures that the charging cable is loaded with the charging current only when the charging cable is protected by the line protection device. 
     The method can also be configured such that a resistance value is determined which corresponds to the magnitude of the electrical resistance between two contacts of a plug of the charging cable. In this case, a resistance value is determined, for example, which corresponds to the magnitude of the electrical resistance between the “proximity” and “PE” contacts of a plug of the charging cable which is constructed in accordance with the standard IEC 62196. 
     The method can also be implemented in such a way that the charging current is additionally conducted via a residual current circuit breaker (independently of which of the line protection devices has been switched into the charging current path). Residual currents and, for example, a health risk associated therewith for people touching the charging cable can be effectively prevented by this residual current circuit breaker. 
     The charging device for charging a traction battery of an electrically drivable vehicle has:
         an interface for electrical connection to a charging cable for charging the traction battery,   a measuring device for determining a resistance value, which corresponds to the magnitude of the electrical resistance between two contacts of the charging cable, wherein the magnitude of the electrical resistance indicates the current-carrying capacity of the charging cable,   at least two line protection devices which are designed for different rated current intensities (wherein each of the line protection devices is associated with a specific resistance value),   switching device, which is designed to switch in each case one of the line protection devices into the charging current path, and   a switching actuation device, which actuates the switching device in such a way that the switching device switches in each case one of the line protection devices into the charging current path depending on the determined resistance value. This charging device is designed for implementing the method described above.       

     This charging device can have a control device, which conducts the charging current via the charging current path only once the line protection device has been switched into the charging current path. 
     Furthermore, the charging device can be configured in such a way that the measuring device is designed for determining a resistance value which corresponds to the magnitude of the electrical resistance between two contacts of a plug of the charging cable. In particular, the measuring device can be designed to determine a resistance value which corresponds to the magnitude of the electrical resistance between the “proximity” and “PE” contacts of a plug of the charging cable constructed in accordance with the standard IEC 62196. 
     The charging device can be realized in such a way that it has a residual current circuit breaker switched into the charging circuit. 
     This charging device likewise has the advantages specified above in connection with the method. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other aspects and advantages will become more apparent and more readily appreciated from the following description of an exemplary embodiment, taken in conjunction with the accompanying drawings of which: 
         FIG. 1  is a block diagram of an exemplary embodiment of a charging device and 
         FIG. 2  is a flowchart of an exemplary embodiment of the method for protecting the charging cable. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference will now be made in detail to the preferred embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. 
       FIG. 1  illustrates a charging device  1  for charging a traction battery  3  of an electrically drivable vehicle  5 . This charging device  1  is connected to an energy supply system  10  by a connection cable  8 . Electrical current is conducted from the energy supply system  10  via the connection cable  8  and a residual current circuit breaker  12  to a switch  14  of the charging device  1 . The residual current circuit breaker  12  can be designed for a current intensity of 80 A, for example. The switch  14  is actuated by a control unit  18  and can be opened or closed by this control unit  18 . Downstream of the switch  14 , the circuit branches into a plurality of line protection devices of the charging device which are connected in parallel: in the exemplary embodiment a first line protection device  20  with a rated current intensity of 13 A, a second line protection device  22  with a rated current intensity of 20 A, a third line protection device  24  with a rated current intensity of 32 A and a fourth line protection device  26  with a rated current intensity of 63 A are connected in parallel in the charging device. The four line protection devices  20 ,  22 ,  24  and  26  each realize overcurrent protection and short circuit protection. They can be configured as fuses for the current intensities 13 A, 20 A, 32 A and 63 A, for example. The inputs of these line protection devices  20 ,  22 ,  24  and  26  are connected to the switch  14 , and the outputs of the line protection devices  20 ,  22 ,  24  and  26  are connected to a switching device  30 . 
     The switching device  30  is designed in such a way that in each case only one of the four line protection devices  20 ,  22 ,  24  and  26  can be switched into the charging current path. Depending on the switch position of the switching device  30 , the output of one of the line protection devices  20 ,  22 ,  24  or  26  is electrically connected to an interface  32  (socket outlet, bush), which is arranged at the charging device  1 . This interface  32  is configured in the exemplary embodiment in such a way that it is compatible with a plug  34  of a charging cable  36 . This charging cable  36  connects the charging device  1  to the traction battery  3  of the electrically drivable vehicle  5 . 
     In the exemplary embodiment, the plug  34  is in the form of a so-called type 2 plug, which is constructed corresponding to the standard IEC 62196-2. This plug has seven electrical contacts: four contacts for transmitting three-phase alternating current, one “pilot” contact  42 , one “proximity” contact  44  and one “PE” contact  46  (standard IEC 61851-1). A resistance  40  is incorporated in the interior of the plug  34  between the “proximity” and “PE” contacts. In accordance with the standard IEC 61851-1, the rated current of the charging cable  36  is coded by this resistance component  40 . The following assignment applies here: 
     
       
         
               
               
               
             
               
               
               
               
             
           
               
                   
                   
               
               
                   
                 Charging cable 
                   
               
               
                   
                 rated current 
                 Resistance value 
               
               
                   
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 13 A 
                 1.5 
                 kΩ 
               
               
                   
                 20 A 
                 680 
                 Ω 
               
               
                   
                 32 A 
                 220 
                 Ω 
               
               
                   
                 63 A 
                 100 
                 Ω 
               
               
                   
                   
               
             
          
         
       
     
     The charging cable  36  has only 6 lines/cores since it does not have a line for the “proximity” contact. 
     When the plug  34  is plugged into the interface  32 , the “proximity” contact  44  and the “PE” contact  46  of the plug  34 , inter alia, are electrically connected to the associated contacts of the interface  32 . These contacts of the interface  32  are electrically connected to a measuring device  50  within the charging device  1 . (In addition, the “pilot” contact  42  is also connected to the measuring device  50  and therefore also to the control unit  18 ; communication between the charging device  1  and the vehicle  5  can be implemented via the “pilot” contact.) The measuring device  50  measures the electrical resistance between the “proximity” and “PE” contacts of the plug  34  when the plug  34  is plugged in and thus determines the respective resistance value between these two contacts. This resistance value is passed on to a switching actuation device  52 , which actuates the switching device  30  depending on the determined resistance value and initiates switchover of the switching device  30 . This switchover is performed in such a way that the rated current intensity of that line protection device which is switched into the charging circuit always corresponds to the current-carrying capacity of the presently used charging cable  36 . In other words, each of the line protection devices is associated with a specific resistance value. The line protection device is switched into the charging current path which is associated with the determined resistance value by the switching device  30  depending on the determined resistance value. 
     The switching actuation device  52  can be in the form of a specific hardware circuit or else in the form of a programmable logic controller (PLC). If the switching actuation device  52  is in the form of a hardware circuit, software errors can be eliminated, with the result that, advantageously, particularly reliable and safe operation can be achieved. As a result, erroneous switching operations can be avoided, with the result that safety classes (SIL classes) can be met. The measuring devices can likewise be in the form of a hardware circuit. 
     Once the corresponding line protection device (in the exemplary embodiment this is the line protection device  22 ) has been switched into the charging current path (and possibly in addition communication between the charging device  1  and the vehicle  5  has been implemented via the “pilot” contact), the control unit  18  closes the switch  14 , with the result that the charging current can only now flow via the charging current path. As a result, the charging operation is enabled or started. In the exemplary embodiment, the charging current flows from the energy supply system  10  via the connection cable  8 , the residual current circuit breaker  12 , the switch  14 , the second line protection device  22 , the switching device (changeover switch)  30 , the interface  32 , the plug  34  and the charging cable  36  to the traction battery  3  of the electrically driven vehicle  5 . This current path forms the present charging current path during charging of the traction battery  3 . (Further vehicle-internal devices such as converters, for example, are not illustrated in  FIG. 1  for reasons of clarity. Likewise not illustrated is, for example, an electrical interface of the vehicle  5 , which is electrically connected to a further electrical plug of the charging cable  36 , the further electrical plug likewise not being illustrated.) 
       FIG. 2  shows, in the form of a flowchart, an exemplary embodiment of the method. The starting point for the method is state  100 , in which the plug  34  has been plugged into the interface/socket  32  of the charging device  1 . Then, in  110 , the resistance value between the “proximity” contact  44  and the “PE” contact  46  of the plug  34  is determined. Therefore, the magnitude of the electrical resistance between the “proximity” contact  44  and the “PE” contact  46  of the plug  34  is determined, i.e. in this case the magnitude of the resistance  40 . 
     Then, in  120 , the switching device  30  is switched over depending on the determined resistance value in such a way that the line protection device associated with the determined resistance value is switched into the charging circuit. 
     Then, in  130 , the charging current is switched on. Finally, in  140 , the charging current flows via the line protection device switched into the charging current path. 
     What has been described are a method and a charging device in which the line protection is automatically matched to the respectively used charging cable. This ensures that an appropriate line protection device is automatically switched into the charging current path for each charging cable connected to the charging device. 
     A description has been provided with particular reference to preferred embodiments thereof and examples, but it will be understood that variations and modifications can be effected within the spirit and scope of the claims which may include the phrase “at least one of A, B and C” as an alternative expression that means one or more of A, B and C may be used, contrary to the holding in Superguide v. DIRECTV, 358 F3d 870, 69 USPQ2d 1865 (Fed. Cir. 2004).