Abstract:
A method for operating a vehicle electrical system of a motor vehicle, the vehicle electrical system having at least two onboard subsystems having different electrical voltages, and a coupling is provided which allows a flow of electrical energy between the onboard subsystems, the one onboard subsystem being connected to a generator and/or at least one electrical consumer, and the other onboard subsystem being connected to at least one electrical consumer. In the event of a fault, the voltage supplied by the generator is lowered to a value that poses no risk to persons, yet an energy flow from the onboard subsystem having the generator to the other onboard subsystem having the consumer taking place nevertheless.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a method for operating a vehicle electrical system of a motor vehicle, the vehicle electrical system having at least two onboard subsystems having different electrical voltages; furthermore, a linkage which allows a flow of electrical energy is provided between the onboard subsystems, the one onboard subsystem being connected to a generator and/or at least one electrical consumer, and the other onboard subsystem being connected to at least one electrical consumer. 
       BACKGROUND INFORMATION 
       [0002]    In motor vehicles, it is known to operate vehicle electrical systems having a plurality of onboard subsystems. This applies to hybrid vehicles, in particular, which have an onboard subsystem for an electrical drive and an onboard subsystem for electrical vehicle components which are operated at a different voltage than the electrical drive. In hybrid vehicles it is possible to operate an electrical machine either as motor for driving the motor vehicle, or as generator, which allows a battery to be charged by an internal combustion engine or energy to be supplied back to the battery when the motor vehicle is braking. A high voltage of approximately 300 V, which is supplied by a high-voltage battery, is required to operate the electrical drive. The onboard subsystems are linked to one another via a DC voltage converter, so that the voltage of the one onboard subsystem is converted and able to supply another onboard subsystem. 
         [0003]    In the event of a fault within an onboard subsystem, the onboard subsystem for the drive using a high voltage which poses a danger to persons is switched off for their protection, in that the associated battery is cut off from the onboard electrical system. Separating the battery from the onboard subsystem makes it impossible to continue the supply of electrical energy to the other onboard subsystem, so that its consumers can no longer be operated. This procedure switches off the entire motor vehicle in case of a fault. 
         [0004]    Required is an option that allows the safe operation of the motor vehicle even when a fault is occurring in the vehicle electrical system. 
       SUMMARY OF THE INVENTION 
       [0005]    According to the exemplary embodiments and/or exemplary methods of the present invention, in the event of a fault, the voltage supplied by the generator is lowered to a value that poses no risk to people; nevertheless, a flow of energy takes place from the onboard subsystem having the generator to the other onboard subsystem having the consumer. In this context it is advantageous that even in case of a fault, no shut-off of the entire vehicle electrical system takes place, but instead the system is operated in such a way that the operation does endanger people and an operation of the motor vehicle is ensured at the same time. This is achieved in that the electrical consumer continues to be supplied with electrical energy. In particular, it is provided that each of the onboard subsystems carries a DC voltage, and the coupling between the onboard subsystems takes place via a DC voltage converter. In a drop of the voltage supplied by the generator, the DC voltage converter may be adapted as well, such that the voltage in the particular onboard subsystem that is not connected to the generator experiences barely any or no change overall. Lowering the voltage supplied by the generator presupposes that the generator is a generator whose voltage is able to be regulated. It is possible to provide at least one electrical consumer in only one of the onboard subsystems. However, it is also possible to connect both the one and the other onboard subsystem to at least one electrical consumer. 
         [0006]    According to one further development of the present invention, one of the onboard subsystems is used as high-voltage onboard subsystem, and the other onboard subsystem is used as low-voltage onboard subsystem. This configuration allows the method according to the present invention to be used in a hybrid vehicle, which typically requires a high-voltage onboard subsystem for operating an electrical drive motor, while the low-voltage onboard subsystem supplies additional vehicle-typical electrical consumers. Provided as electrical consumers are, in particular, control devices for controlling drive units and safety systems. 
         [0007]    According to one further development of the present invention, the generator supplies the high-voltage onboard subsystem with electrical voltage directly. Due to the direct supply of the high-voltage onboard subsystem via the generator, a generator in the form of a high-voltage generator is able to be used. This results in an excellent energy conversion and makes it easy to supply electrical energy both to the high-voltage onboard subsystem and the low-voltage onboard subsystem. 
         [0008]    According to one further development of the present invention, at least one of the onboard subsystems, especially the low-voltage onboard subsystem, stores electrical energy in at least one battery assigned to it. The storage of the energy allows the generation of an uninterrupted, constant DC voltage within the particular onboard subsystems. A high-voltage battery may be used in the high-voltage onboard subsystem, and a low-voltage battery is used in the low-voltage onboard subsystem. 
         [0009]    According to one further development of the present invention, the fault case arises in particular when the line insulation is damaged, the insulation cover is open, and/or at least one electrical connection within the high-voltage onboard subsystem is severed. This advantageous development of the method in particular allows the use of already known detection means for detecting a fault case. For example, an insulation monitor may be used to detect damaged line insulation, an open-cover detector to detect an open insulation cover, and a pilot line monitor within the electrical connection may be used to detect a severed electrical connection. The damaged line insulation, open insulation cover, and the severed connection constitute fault cases because they allow people access to voltage-carrying lines, which thus represents a danger to people. 
         [0010]    According to one further refinement of the present invention, the fault case is detected by at least one evaluation device, and the voltage supplied by the generator is lowered in response. An evaluation device is, in particular, a control device which cooperates with corresponding means for detecting fault cases and is able to influence the generator voltage. 
         [0011]    According to one further development of the present invention, the voltage supplied by the generator is lowered when the evaluation device malfunctions. If the evaluation device itself exhibits a malfunction or failure, then the fault cause is assumed immediately and precautionally, for reasons of safety. 
         [0012]    According to one further development of the present invention, only a consumer required for the safe operation of the motor vehicle is used as consumer. Required consumers are, in particular, control devices for drive units, brake systems and other safety systems. The selective use of certain required consumers makes it possible to minimize the consumption of electrical energy within the motor vehicle. This allows the voltage of the generator to be lowered to a particularly significant extent; in addition, high personal safety and an operation of the motor vehicle are able to be provided at the same time. 
         [0013]    According to one further development of the present invention, the high-voltage onboard subsystem is operated at a voltage of approximately 300 V in normal operation. 
         [0014]    According to one further development of the present invention, the low-voltage onboard subsystem is operated at a voltage of approximately 14 V. 
         [0015]    According to one further development of the present invention, the generator supplies a voltage of approximately 60 V in the event of a fault. The voltage of 60 V within one of the onboard subsystems minimizes a safety risk for persons due to lower currents. Nevertheless, by conversion, this voltage allows the generation of sufficient energy for an onboard subsystem using low voltage, which may be 14 V. 
         [0016]    According to one further development of the present invention, a hybrid vehicle is used as motor vehicle. The use of a plurality of onboard subsystems in hybrid vehicles is encountered quite frequently, which is why the method according to the present invention is especially suitable for use in hybrid vehicles. 
         [0017]    The drawing illustrates the present invention on the basis of an exemplary embodiment. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  shows a schematic illustration of a vehicle electrical system of a motor vehicle. 
           [0019]      FIG. 2  shows a flow chart of the method according to the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]      FIG. 1  shows a vehicle electrical system  1  of a motor vehicle  2  in the form of a hybrid vehicle  3  in a schematic representation. Vehicle electrical system  1  has two onboard subsystems  4  and  5 , which are electrically connected to each other via a coupling  6  in the form of a DC voltage converter  7 . Onboard subsystem  4  is implemented as high-voltage onboard subsystem  8 , and onboard subsystem  5  is implemented as low-voltage onboard subsystem  9 . Motor vehicle  2  has an internal combustion engine  10 , which is connected to a clutch  12  via a shaft  11 . Clutch  12  leads to a gearbox  13 . From gearbox  13 , a shaft  14  leads to a differential  15 , which drives drive wheels  17  via half-shafts  16 . For reasons of clarity, only one of drive wheels  17  is shown in  FIG. 1 . Starting at differential  15 , a shaft  18  leads to a clutch  19 , which is connected to a further shaft  20  on the side facing away from shaft  18 . Shaft  20  leads to a further axle drive  21 , which in turn drives drive wheels  23  via half-shafts  22 . With respect to drive wheels  23  as well, only one of drive wheels  23  is shown for reasons of clarity. A further shaft  24  runs from differential  21 , which shaft is in operative connection with an electrical machine  25 . Disposed at internal combustion engine  10  is a generator  26  in the form of a high-voltage generator  27 . Generator  26  is in operative connection with internal combustion engine  10  via a drive connection  28 . Furthermore, a starter motor  29  is disposed at internal combustion engine  10 , which is able to be brought into operative connection with a starter pinion  30 , which is connected to shaft  11  in torsionally fixed manner. Generator  26  supplies onboard subsystem  4  with an AC voltage via a line  31 . Line  31  connects generator  26  to a rectifier  32 , which converts the AC voltage of generator  26  into a DC voltage. A high-voltage line  33  of onboard subsystem  4  extends from rectifier  32  to a node  34 . Starting at node  34 , a high-voltage line  35  runs to a battery  36  in the form of a high-voltage battery  37 , and a further high-voltage line  38  runs to a node  39 . Node  39  is electrically connected to coupling  6  via a high-voltage line  40 . In addition, a high-voltage line  41 , which supplies a pulse-controlled inverter  42  with a voltage of approximately 300 V, originates at node  39 . Pulse-controlled inverter  42  is connected to electrical machine  25  via a high-voltage line  43  and supplies it with a corresponding supply voltage. A low-voltage line  44 , which starts at coupling  6 , leads to a node  45 . Node  45  is connected via a further low-voltage line  46  to a battery  47  in the form of a low-voltage battery  48 . Furthermore, node  45  is electrically connectable to starter motor  29  via a low-voltage line  49 . Two data networks  50  and  51  are provided for controlling the individual components of motor vehicle  2 . Data network  50  is an H-CAN network  52 , and data network  51  is an A-CAN network  53 . Data network  51  has a first data line  54 , which leads from a control device (not shown) to a node  55 . Starting at node  55 , two data lines  56  and  57  run to two control devices  58 . Data line  56  connects node  55  to control device  58  in the form of a combined gearbox/clutch control device  59 , which controls and/or regulates clutch  12  as well as gearbox  13  via control paths  60  and  61 . Data line  57  of data network  51  connects node  55  to a combined motor/hybrid control device  62 . Motor/hybrid control device  62  controls and/or regulates internal combustion engine  10  via a control path  63  and additionally obtains information about an accelerator value by way of a data line  64 . Data network  50  has a data line  65 , which is connected on the one side to a gear lever  66  for specifying a gear operating mode, and connected to a node  67  on the other side. Another data line  68 , which supplies motor/hybrid control device  62  with information, starts at node  67 . Furthermore, via a data line  69 , node  67  is connected to a node  70 , which has a further data line  71 , which is connected to a control device  58  in the form of a clutch control device  72 . Via a data path  73 , clutch control device  72  is connected to clutch  19  and controls and/or regulates clutch  19 . Starting at node  70 , there is another data line  74 , which leads to a node  75 , which in turn is connected via a further data line  76  to a control device  58  in the form of an axle drive control device  77 . Axle drive control device  77  controls and/or regulates axle drive  21  via a data path  78 . Another data line  79 , which starts at node  75 , leads to a node  80 , and from node  80 , an additional data line  81  leads to a control device  58  in the form of a battery-management control device  82 , which controls and/or regulates the operation of battery  36  via a data path  83 . An additional data line  84  runs from node  80  to pulse-controlled inverter  42 , and from pulse-controlled inverter  42  an additional data line  85  leads to coupling  6 . For their electrical supply, control devices  58  are connected to onboard subsystem  5 , i.e., low-voltage onboard subsystem  9 . For reasons of clarity, the electrical connections between onboard subsystem  5  and control devices  58  are not shown. Through their connection to onboard subsystem  5 , control devices  58  and starter motor  29  are implemented as electrical consumers  86  of onboard subsystem  5 . In addition, motor vehicle  2  has an evaluation device  87 , which obtains information via a data path  88 , with the aid of which evaluation device  87  is able to detect a fault case within the vehicle electrical system. Data path  88  leads from an insulation monitor for detecting damaged line insulation, a top-open detector for detecting an open insulation cover, and a pilot-line monitor for detecting a severed electrical connection, to evaluation device  87 . With the aid of a data line  89 , evaluation device  87  is connected to generator  26  and is able to set the voltage provided by generator  26 . Through an additional data line  90 , evaluation device  87  is connected to coupling  6 , which enables it to influence the DC voltage conversion within coupling  6 . 
         [0021]    In normal operation of vehicle electrical system  1 , generator  26  supplies onboard subsystem  4  with a DC voltage of 300 V via rectifier  32 . This is fed into battery  36 , which ensures a constant supply of onboard subsystem  4 . Vehicle electrical onboard system  4  simultaneously supplies coupling  6 , via which the DC voltage of onboard subsystem  4  is converted into a DC voltage for onboard subsystem  5 . The DC voltage within onboard subsystem  5  amounts to approximately 14 V and is routed into battery  47 , which supplies onboard subsystem  5  with a constant DC voltage. Thus, it results that generator  26  supplies onboard subsystem  5  with electrical energy indirectly. During this normal operation, all electrical consumers  86  are able to be used as intended. Furthermore, it is possible to operate electrical machine  25  as motor and to charge batteries  36  and  47 . 
         [0022]    In a fault case, evaluation device  87  detects the presence of a fault based on the information it received via data path  88 , and resets the type and manner of operation of vehicle electrical system  1  accordingly. For this purpose generator  26  is controlled in such a way that it provides a voltage of approximately 60 V, which, downstream from rectifier  32 , represents a DC voltage of approximately 60 V. At the same time, battery  36  is separated from onboard subsystem  4 , so that only a voltage of 60 V prevails in onboard subsystem  4 . To allow onboard subsystem  5  to be supplied with the correct voltage, evaluation device  87  adjusts coupling  6  in such a way that the DC voltage conversion implemented by coupling  6  continues to supply a DC voltage for onboard subsystem  5  such that it suffices for the supply of onboard subsystem  5 , or such that it at least contributes to the supply. This makes it possible not to carry any voltage within onboard subsystem  4 , i.e., high-voltage onboard subsystem  8 , that poses a danger to persons and simultaneously ensures that the harmless low-voltage onboard subsystem  9  continues to be operative. Without the supply, battery  47  would be exhausted within a very short time and motor vehicle  2  would be unable to operate. It is provided, in particular, to control control devices  58  via data networks  51  and  50  in such a way that only the electrical consumers  86  required for the safe operation of motor vehicle  2  are supplied with electrical energy from low-voltage onboard subsystem  9 . This prevents motor vehicle  2  from being shut down altogether in the case of a fault and allows a safe operation of motor vehicle  2  to be maintained at least temporarily. At the same time, danger sources for persons posed by high-voltage onboard subsystem  8  are eliminated. 
         [0023]      FIG. 2  shows a flow chart  92  of the method according to the present invention. The method has a plurality of method steps  93 , which are implemented repeatedly in cyclical manner. The method is started by a first step  94 . Via an arrow  95 , the method moves to a second method step  96 . In second method step  96  it is checked whether a fault case exists. If this is the case, then a third method step  98  is initiated via an arrow  97 , in which all functions that require a supply by high-voltage onboard subsystem  8  are switched off. Then, via an arrow  99 , a move is made to a fourth method step  100  in which the voltage supplied by generator  26  is reduced down to a value of approximately 60 V which poses no danger to people. Furthermore, an operation is set in coupling  6  which enables the voltage supplied by generator  26  to be converted into the voltage required by onboard subsystem  5 . Then, via an arrow  101 , a shift to final fifth method step  102  takes place, in which not required electrical consumers  86  within onboard subsystem  5  are switched off in order to ensure the supply of required electrical consumers  86 . As a result, vehicle electrical system  1  and thus motor vehicle  2  is in emergency operation, which in a fault case ensures the safe operation of motor vehicle  2  and the safety of involved persons. Via an arrow  103 , a move back to arrow  95  takes place, and the cyclical run of the method begins anew by second method step  96 . In the event that no fault case is determined in second method step  96 , a new startup takes place directly via arrow  104 , which transitions to arrow  103  at a node  105 . 
         [0024]    It is especially advantageous if the voltage set in high-voltage onboard subsystem  9  in a fault case is non-critical with respect to endangering people by high voltage. Since battery  47  continues to be supplied with voltage via coupling  6 , vehicle  2  is able to be operated without interruption. The breakdown danger of motor vehicle  2  in critical traffic situations is thereby avoided.