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.
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.
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.
Required is an option that allows the safe operation of the motor vehicle even when a fault is occurring in the vehicle electrical system.
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.
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.
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.
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.
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.
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.
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.
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.
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.
According to one further development of the present invention, the low-voltage onboard subsystem is operated at a voltage of approximately 14 V.
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.
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.
The drawing illustrates the present invention on the basis of an exemplary embodiment.
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.
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.
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.
Number | Date | Country | Kind |
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10 2009 000 051.8 | Jan 2009 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2009/067482 | 12/18/2009 | WO | 00 | 9/15/2011 |