Abstract:
A safety device for a battery having battery cells that are configured to connect to poles of the battery via charging and isolating devices includes a discharge device. The discharge device is configured to connect in parallel to the battery cells. The discharge circuit can include at least one discharge resistor and an electronic valve. The electronic valve is configured to switch on and off. The discharge circuit can be configured to activate with a battery management system.

Description:
This application is a 35 U.S.C. §371 National Stage Application of PCT/EP2013/058255, filed on Apr. 22, 2013, which claims the benefit of priority to Serial No. DE 10 2012 210 603.0, filed on Jun. 22, 2012 in Germany, the disclosures of which are incorporated herein by reference in their entirety. 
     The present disclosure relates to a safety concept having a corresponding device and an associated method for batteries, in particular for traction batteries in hybrid vehicles or electric vehicles. 
     BACKGROUND AND SUMMARY 
     Batteries which are provided for use in hybrid vehicles or electric vehicles are referred to as traction batteries since they are used for feeding electrical drives. In order to obtain the power data and energy data which are required in hybrid vehicles or electric vehicles, individual battery cells are connected in series and partially additionally in parallel. In the case of electric vehicles, for example 100 cells or more are connected in series, with the result that the total voltage of the battery can be up to 340 V. Batteries which are used in hybrid vehicles also usually exceed the voltage limit of 60 V which is categorized as unproblematic in the case of touching by humans. 
       FIG. 1  illustrates the basic circuit diagram of a battery system according to the prior art. Such a battery system is described, for example, in DE-A 10 2010 027 850 with a detailed block circuit diagram. 
     In particular,  FIG. 1  shows a battery  10  with assigned integrated electronics. A multiplicity of battery cells  11  are connected in series in order to obtain a high output voltage which is desired for a respective application. Optionally, the battery cells can also be connected in parallel in order to obtain a high battery capacity. 
     A charging and isolating device  14  is connected between the positive pole of the series circuit of the battery cells  11  and a positive battery terminal  12 . In addition, an isolating device  15  is located between the negative pole of the series circuit of the battery cells  11  and a negative battery terminal  13 . The charging and isolating device  14  and the isolating device  15  each comprises a contactor  16  and  17  as isolator switches. These contactors are provided for disconnecting the battery cells  11  from the battery terminals  12 ,  13 , in order thereby to connect the battery terminals  12 ,  13  in a voltage-free fashion when required. Other switching means which are suitable for this application can also be used instead of contactors. 
     In addition, a charging contactor  18  is present in the charging and isolating device  14 . A charging resistor  19  is connected in series with the charging contactor  18 . The charging resistor  19  limits a charging current for the buffer capacitor which is connected into the DC voltage intermediate circuit of a customary battery-fed drive system when the battery is connected to the DC voltage intermediate circuit. When predefinable events occur, the battery can be activated or deactivated at one pole or two poles with the arrangement of the charging and isolating device (illustrated in  FIG. 1 ) in the positive line and the isolating device in the negative line. For this purpose a control device which is not illustrated provides corresponding signals which activate the contactors. 
     By using the charging resistor  19 , balancing currents can also be limited during the activation of the battery. In the case of an activation process, the charge switch  18  is firstly closed here in the charging and isolating device  14 , with the isolator switch  16  opened, and additionally, if desired, the isolator switch  17  in the isolating device at the negative pole of the battery system is closed. The input capacities of externally connected systems are then charged by means of the charging resistor  19 . If the voltage between the positive pole and the negative pole of the battery system differs only insignificantly from the total voltage of the battery cells, the charging process is terminated by closing the isolator switch in the charging and isolating device  14 . The battery system is then connected with low impedance to the external systems and can be operated with its specified power data. Overall, the balancing currents which occur between the external systems and the battery system when the battery system is activated, can be limited to permissible values. 
       FIG. 2  illustrates an electric drive system, known, for example, from DE-A 10 2010 027 864.5, for an electric vehicle or hybrid vehicle as a basic circuit diagram. Here, a battery  20  is connected to a DC voltage intermediate circuit which is buffered by a capacitor  21 . A pulse-controlled inverter  22 , which makes available sinusoidal voltages, which are phase-offset with respect to one another at three outputs via, in each case, two switchable semiconductor valves  22   a ,  22   b  and two diodes  22   c  and  22   d , for operating an electric drive motor  23 , for example a three phase machine, is connected to the DC voltage intermediate circuit. The capacity of the capacitor  21  has to be large enough to stabilize the voltage in the DC voltage intermediate circuit for a period of time in which one of the switchable semiconductor valves is activated. 
     The electric drive system which is known from DE-A 10 2010 027 864.5 comprises a battery  20  which has, similarly to the battery  10  illustrated in  FIG. 1 , a multiplicity of battery cells which are connected in series. A charging and isolating device is present in the positive line and an isolating device is present in the negative line, between this series circuit comprising battery cells and the positive and negative terminals of the battery  20 . By means of these isolating devices it is possible, as in the case of the battery  10  from  FIG. 1 , to disconnect the positive pole of the battery and/or the negative pole of the battery from the battery cells in the case of an accident or in the event of a malfunction when a connectable of the charger device is not operating satisfactorily, and thereby switch to a voltageless state. In particular, two-pole disconnection of the battery from the traction on-board power system is proposed in order to place the battery in a safe state. The electric charge which is stored in the battery cells is still retained in this case. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a basic circuit diagram of a battery system. 
         FIG. 2  is an electric drive system for an electric vehicle or hybrid vehicle as a basic circuit diagram. 
         FIG. 3  is an exemplary embodiment of a safety device. 
     
    
    
     DETAILED DESCRIPTION 
     A possible reaction can originate from the still-charged battery cells even after they are disconnected, if a short-circuit is triggered by certain effects. This can still occur even after a relatively long time. The advantage of the disclosure is that in a safety concept for batteries, in particular for traction batteries, the battery or the individual battery cells is/are placed in a non-critical state in which external effects or influences cannot lead to dangerous situations. 
     This advantage is achieved by placing the battery cells in a safe state after their disconnection from external connections, in particular after the disconnection from the traction on-board power system of a vehicle by discharging via discharging means so that the advantages of the disclosure are achieved, the additional discharge circuit, specified in  FIG. 3 , is added to a system, in particular a battery according to the prior art. This additional discharge circuit is actuated in a particularly advantageous way using a battery management system which outputs corresponding actuation signals. The battery management system advantageously comprises here at least one processor as well as the associated hardware and provides the required actuation signals and the switching means or contactors for the activation thereof. 
     It is particularly advantageous that the inventive discharging of the battery cells is initiated immediately after a disconnection, in particular a two-pole disconnection, of the battery cells. For this purpose, what is referred to as a clocking device, which in a further advantageous solution is implemented as a semiconductor switch or electromagnetic switch with an associated regeneration resistor is activated in an advantageous manner. In the regeneration resistor, the electrical energy which is extracted from the battery cells and which is to be destroyed is converted into thermal energy here. The inventive discharging of the battery cells advantageously functions even if other components of a traction drive which are supplied by a battery according to the disclosure, such as, for example, the inverter which generates an alternating voltage required for supplying a motor from the battery voltage, are no longer functionally capable. 
     In one development of the disclosure, additional measures can be provided which, for example, also include the inverter. In this context, parallel charging of the battery can advantageously take place via a battery-internal clocking device with discharging via the charging resistor and the charging switches as well as the power switches of the inverter. These power switches are advantageously the semiconductor valves as well as the diodes of the inverter. 
     A further advantage is provided by the possibility of carrying out additional discharging of the battery and of the battery cells by means of additional electronics for equalizing the state of charge of the battery cells. In such an arrangement, which carries out what is referred to as cell balancing, the ohmic resistors then present can advantageously be used to discharge the cells, or can additionally also be included in the discharging. 
       FIG. 3  illustrates an exemplary embodiment of the disclosure. The components as specified in  FIG. 3  correspond to the components described in more detail in  FIGS. 1 and 2  and have the same reference symbols. In addition, a discharge circuit  24  is connected parallel to the series circuit of the battery cells  11 . In the exemplary embodiment, the discharge circuit  24  is arranged inside the battery  10 , but it could also be arranged outside the battery  10 . The discharge circuit, which functions, for example, as a clocking device, comprises an electronic valve  25  which can be switched on and off as well as a resistor  26  which is connected in series with this valve  25 . The electronic valve  24  can be activated, for example, by a battery management system  27  (not illustrated in more detail). The battery management system  27  initiates here a discharge of the battery cells  11  immediately after the disconnection, in particular the two-pole disconnection. For this purpose, the battery management system transmits actuation signals to the discharge circuit as soon as it detects the disconnection of the battery cells. 
     For this purpose, the electronic valve  25  is actuated in accordance with the discharge circuit  24 , with the result that it functions as what is referred to as clocking device. In the simplest case, the electronic valve  25  is a semiconductor switch or an electromechanical switch. The regeneration resistor  26  in which the electrical energy which is to be extracted from the battery cells is converted into thermal energy completes the discharge circuit  24 . 
     The regeneration resistor  26  and the electrical or electromechanical valve  25  which can be switched on and off are configured here in such a way that the battery cells  11  can be discharged completely from the fully charged state in a predefined time. If, for example, the battery of an electric vehicle is to be discharged with an energy content of 24 kW/h within 24 hours, the clocking device must be configured for a continuous output of 1 kW. 
     The concept illustrated in  FIG. 3  functions even if other components of the traction drive, such as, for example, the inverter are no longer functionally capable. Such a traction drive is illustrated in  FIG. 2 , wherein the inverter is configured, for example, as a pulse-controlled converter. According to the disclosure it can also be included in the discharge concept for the battery cells. 
     In a development of the concept illustrated in  FIG. 3 , measures can be additionally provided which, for example, also include the inveter. In this context, a parallel discharge of the battery cells  11  can occur via the battery-internal clocking device  24  with a discharge via the charging resistor  26  and the charging switch  25  as well as the power switch of the inverter  22 . 
     As a further possibility, additional discharging of the battery and of the battery cells  11  can occur via electronics, then necessary, for equalizing the state of charge of the battery cells  11 . In such an arrangement, which carries out what is referred to as cell balancing, the ohmic resistors, which are then present, can be used to discharge the cells or can additionally also be included in the discharging. The actuation of an electronic valve, which can be switched on and off, of the discharge circuit  24  by the battery management system  27  is carried out after the single-pole or two-pole decoupling of the battery cells  11  if the battery management system  27  detects such a request on the basis of certain predefinable criteria.