How to monitor a car's on-board network

Abstract

The invention relates to a method for monitoring an on-board network of a motor vehicle, comprising at least one power distributor (18), via which at least one safety-relevant consumer (16) is supplied with a supply voltage (U) and via which non-safety-relevant consumers (17) are supplied, the power distributor (18) being supplied by at least one energy store (12), and a degree of voltage (U16.n) applied to at least the safety-relevant consumer (16.n) is determined on the basis of which a safety-relevant consumer (16.n) is monitored. The present invention relates to a monitoring method in which an undervoltage (dU) at a safety-relevant consumer (16.n) is determined in dependence on a limit value (Ug), characterized in that a degree of reduction (Ir) for the disconnection or de-rating of at least one non-safety-relevant consumer (17.m), which is necessary for raising the voltage (U16.n) applied to the safety-relevant consumer (16.n), is determined in dependence on the undervoltage (dU) and a selection of the non-safety-relevant consumer (17.m) to be disconnected or de-rated is made on the basis of this degree of reduction (Ir).

Description

[Technical field]

[0001] The present invention relates to a method for monitoring an on-board network of a motor vehicle according to the field of the independent claims. [Background technology]

[0002] From DE 102018212369 A1 a method for monitoring the energy supply in a motor vehicle is known, in which at least one energy store supplies energy to a plurality of preferably safety-relevant consumers in a partial on-board network, at least one measurement value of the energy store and / or of the at least one consumer is captured and at least one cable harness model representing the partial on-board network is provided, a parameter estimator is provided for estimating at least one characteristic value of the cable harness model using the measurement value.

[0003] From DE10201821277A1, a method for monitoring the on-board network of a motor vehicle is known, in which case it is determined by simulation which safe shutdown scenarios are possible for the respective battery and on-board network states. Furthermore, corresponding measures are proposed in the on-board network and an analysis of the direct impact of these measures on the availability of various scenarios is determined.

[0004] From DE 102020212414 A1 a method is known for monitoring an on-board network of a motor vehicle, in which at least one safety-relevant consumer and possibly further consumers are supplied by an energy store and in which at least one on-board network model is provided which represents the safety-relevant consumers, corresponding wiring with an assigned wiring resistance and a connection to the energy store, comprising the following steps: providing a current or power profile which is expected to be required for a certain operation of the motor vehicle in which at least the safety-relevant consumer is involved and which may possibly include a base load of the at least one further consumer; using this current or power profile to determine a predicted characteristic of the energy store; using the current or power profile which is expected to be applied to the safety-relevant consumer, the assigned wiring resistance and the predicted characteristic of the energy store to determine a predicted characteristic of the safety-relevant consumer; evaluating the predicted characteristic of the safety-relevant consumer. Summary of the Invention

[0005] The problem on which the invention is based is to further increase the availability, in particular for on-board networks with high safety requirements, without compromising comfort too much. This problem is solved by the features of the independent claims.

[0006] In contrast, the method according to the features of claim 1 has the advantage that on the one hand an adequate voltage supply for safety-relevant consumers can be reliably guaranteed, whereby, due to a more accurate determination of the degree of curtailment, only the non-safety-relevant consumers that are actually required are degraded or switched off quite precisely, i.e. the required number of non-safety-relevant consumers is disconnected from the energy supply as few as possible. By more accurate determination of the degree of curtailment and the undervoltage, it can be precisely ensured that the measures taken effectively reduce the likewise determined undervoltage in a desired way, so that the safety-relevant consumers are then again adequately supplied. Precisely due to the individual determination of the voltage drop at the safety-relevant consumers, the tolerances for undervoltage can be better utilized, so that a potentially premature disconnection of a non-safety-relevant consumer or group of consumers is minimized, without nevertheless endangering the supply to the safety-relevant consumers. The availability of the non-safety-relevant consumers is thus increased.

[0007] In a useful variant, a disconnection time or a trigger for disconnection or deactivation of at least one of the non-safety-relevant consumers is generated if the applied voltage applied to the safety-relevant consumer falls below a limit value for a certain duration, preferably in the range between 1 ms and 500 ms. In practice, this allows a corresponding voltage requirement to be individually adapted to the respective safety-relevant consumer by a corresponding selection of limit values ​​or a corresponding duration individually tailored to the respective characteristics of the safety-relevant consumer. Precisely this corresponding time interval between 1 ms and 500 ms makes it clear that the method is not useful for line, component or part protection, which may require an overcurrent disconnection in a time range of less than 10 μs. In contrast, the selected time range takes into account the increased safety requirements for safety-relevant consumers compared to classical on-board network interventions for voltage support over 500 ms.

[0008] In one useful variant, it is provided that the degree of voltage applied to the safety-relevant consumers is determined from the supply voltage at the power distributor and the voltage drop in the wiring path between the power distributor and the safety-relevant consumers. By taking into account the voltage drop in this wiring path, a particularly precise and accurate prediction of possible undervoltages can be achieved, so that the disconnection or derating of non-safety-relevant consumers can be performed exactly and precisely to the required extent. As a tendency, non-safety-relevant consumers can be disconnected later than they would be if disconnected with the usual high safety margin.

[0009] In one useful variant, it is provided that the voltage drop in the wiring paths between the power distributor and the safety-relevant consumers is determined by the resistance of the respective wiring paths and the current flowing through the safety-relevant consumers, which allows a simple determination of the voltage drop in the safety-relevant consumers, especially since a corresponding measurement quantity of the current is generally already present in the power distributor, for example on the basis of a safety function for overcurrent disconnection or the like.

[0010] In one useful variant, the degree of reduction, and in particular the current to be reduced, is determined depending on the resistance of the wiring paths connecting the energy store and the power distributor and / or depending on the internal resistance of the energy store, again improving the accuracy of the degradation or disconnection since further characteristic quantities are taken into account, which may also vary relatively strongly over the lifetime of the energy store or the on-board network.

[0011] In one useful variant, the number of non-safety-relevant consumers to be switched off is determined depending on the extent of the reduction. In contrast to the usual case, not all non-safety-relevant consumers are switched off in the event of a supply shortage, but precisely the exact number required. This allows for an even greater comfort for the user, since unnecessary switching off of non-safety-relevant consumers can be avoided.

[0012] In one useful variant, the degree of reduction is determined so that the supply voltage is increased by at least the undervoltage. This precisely targeted increase precisely prevents an unnecessary voltage increase that is too high, which further increases comfort.

[0013] In one useful variant, the limit value varies depending on the duration for which the voltage applied to the safety-relevant consumer is below the corresponding limit value, in particular increasing the longer the duration, so that particularly critical situations involving a long fall below a sufficient supply voltage can be dealt with precisely and early.

[0014] In one useful variant, the degree of reduction is determined using the resistance of the wiring paths to the energy store and / or to the alternative energy source and / or the internal resistance of the energy store and / or depending on a predetermined degree of reduction and / or depending on the resistance of the wiring paths to the energy store and / or to the alternative energy source determined by a model or diagnostics and / or depending on the internal resistance of the energy store determined by a model or diagnostics. This can further improve the accuracy. In particular, by using a model, the aging state of the on-board network components can be predicted relatively accurately and can serve as the basis for a correspondingly more accurate determination of the degree of reduction.

[0015] A useful variant is characterized in that it is determined when the degree of voltage applied to the safety-relevant consumer reaches a limit value and, since reaching the limit value, the duration below the limit value is captured, this captured duration is compared with a duration assigned to the limit value and, once the assigned duration is reached, a trigger is generated for initiating a disconnection or degradation of at least one non-safety-relevant consumer. This allows a simple implementation of duration-dependent limits which allow easy adaptation to the respective safety-relevant consumer.

[0016] In one useful variant, it is provided that the degree of voltage applied at least to the safety-relevant consumer is determined by measuring this voltage at the safety-relevant consumer and / or by using the current flowing through the safety-relevant consumer and / or by measuring the supply voltage and / or taking into account the resistance of the wiring path between the power distributor and the safety-relevant consumer, in particular the worst-case value of the resistance or a resistance estimated by a model and / or depending on the worst-case value of the voltage drop at the resistance. On the one hand, suitable measures such as measuring the voltage at the safety-relevant consumer or measuring the current flow through the safety-relevant consumer can further improve the accuracy of the assessment. On the other hand, certain worst-case values ​​can further simplify the determination. By using a model also for the voltage determination at the safety-relevant consumer, the corresponding aging state of the on-board network components can be represented with high reliability. The accuracy of the determination is improved.

[0017] In one useful variant, it is provided that the trigger and / or undervoltage determination is performed by the safety-relevant consumer and / or that the safety-relevant consumer communicates the trigger and / or undervoltage and / or the voltage drop measured in the safety-relevant consumer to, inter alia, the power distributor. This allows a fast and accurate evaluation to be performed already in the safety-relevant consumer, which otherwise generally has high computing power, and relieves the power distributor from such a task. The amount of communication can also be reduced, since the corresponding disconnection signal is sent only if an undervoltage is imminent, precisely on target.

[0018] In a useful variant, it is provided that the selection of non-safety-relevant consumers to be disconnected or degraded is made on the basis of the current flowing through the respective non-safety-relevant consumer, in particular those non-safety-relevant consumers with a maximum current flow or a current flow above a certain limit value are disconnected or degraded. This makes it possible to ensure that the disconnected non-safety-relevant consumers actually also cause the desired voltage increase. Moreover, with the proposed measures it is achieved that only a small number of non-safety-relevant consumers that are really necessary have to be disconnected.

[0019] In one useful variant, it is provided that further non-safety-relevant consumers are switched off until the degree of reduction is reached, which results in a particularly simple implementation of the selection, which ensures that the desired voltage boost is achieved.

[0020] In one useful variant, it is provided that the current flowing through each non-safety relevant consumer is associated with a weighting factor specific to each non-safety relevant consumer, and that each associated value is used for the selection of the non-safety relevant consumer to be switched off or degraded. Particularly usefully, it is provided that each non-safety relevant consumer is assigned a weight or priority value, and that the selection of the respective consumer to be switched off or degraded is performed by optimizing the associated weight or priority value. These consumers can be given different priorities with corresponding weightings in order to keep the loss of comfort for the user as small as possible.

[0021] Further useful variants emerge from the further dependent claims and the description of the invention. [Brief description of the drawings]

[0022] [Figure 1] FIG. 1 shows an on-board network with a power distributor. [Diagram 2]FIG. 1 shows an alternative exemplary embodiment of an on-board network with a power splitter and a further splitter. [Diagram 3] FIG. 2 is a block diagram for the implementation of various sub-processes. [Figure 4] 1 is an exemplary voltage-time graph with an assigned undervoltage range. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The invention is illustrated diagrammatically on the basis of one exemplary embodiment and is explained in detail below with reference to the drawings. FIG. 1 shows a partial on-board network, in particular in a motor vehicle, including a power distributor 18. The power distributor 18 is supplied with energy via an energy store 12, in particular a battery. For this purpose, the energy store 12 is connected to a power transmission rail 14, which runs at least partially inside the power distributor 18. Between the power distributor 18 and the energy store 12, a resistance Rb is suggested, which represents the resistance in the conductor to the energy store 12, in particular the battery. For a possible redundant supply of the power distributor 18, the power transmission rail 14 of the power distributor 18 can be connected at the other inlet to a further energy supply, which is suggested in this exemplary embodiment by providing a DC voltage converter 22. The DC voltage converter 22 connects to a further partial on-board network, which may for example include a higher or lower or similar voltage level. Between the power distributor 18 and the DC voltage converter 22, a resistance Rdc is also suggested diagrammatically, which represents the resistance in the conductor from the power distributor 18 to the DC voltage converter 22.

[0024] To the power distributor 18, n safety-relevant consumers 16.1, 16.2, ..., 16.n and m non-safety-relevant consumers 17.1, 17.2, ..., 17.m are connected. These safety-relevant consumers 16.n can be secured in particular, for example against overcurrents, by switching means, which are not shown for reasons of clarity. The non-safety-relevant consumers 17.m can each be controlled, in particular by switching means 19 (19.1, 19.2, ..., 19.m), and can in particular be switched off or degraded. These switching means 19 are arranged in the power distributor 18. The switching means 19 are preferably semiconductor switches, for example Mosfet. In the power distributor 18, the voltage U at the power rail 14 is measured. Furthermore, in the power distributor 18, current measurements are carried out. In this exemplary embodiment, the respective current I16.n flowing through the respective safety-relevant consumer 16.n is captured. Optionally, the respective current I17.m flowing through the respective non-safety-relevant consumer 17.m can be captured. Optionally, the voltage U16.n respectively applied to the respective safety-relevant consumer 16.n can be measured, in particular with respect to earth or ground GND. Depending on the location of the evaluation, the determined or measured applied voltage U16.n can be sent via a communication system, for example via a bus system such as a CAN bus or similar, for example to the power distributor 18 or also to a further control device. Alternatively, the evaluation can be performed in the safety-relevant consumer 16.n itself.

[0025] Resistors R16.1, R16.2, ..., R16.n are shown between the power distributor 18 and each safety-relevant consumer 16.n, respectively, which represent the resistance of the respective wiring path between the power distributor 18 and each respective consumer 16.n. Resistors R17.1, R17.2, ..., R17.m are shown between the power distributor 18 and each respective non-safety-relevant consumer 17.m, respectively, which represent the resistance of the respective wiring path between the power distributor 18 and each respective non-safety-relevant consumer 17.m.

[0026] The energy store 12 can be equipped with sensors, not shown, preferably battery sensors, in order to capture further characteristics of the energy store 12. With said sensors, for example based on state variables of the energy store 12 and of the associated model, corresponding characteristics of the energy store 12, for example the internal resistance Ri, the state of charge SOC or the like, can be determined. Safety-relevant consumers 16 are special consumers with high demands or high protection requirements and are generally referred to as safety-relevant consumers 16. These are, for example, electric steering and / or braking systems as examples of components that absolutely must be supplied in order to ensure steering and / or braking of the vehicle in the event of a fault.

[0027] The power distributor 18 also has corresponding processing means, not shown in detail, for example a microcontroller, for storing or evaluating the captured quantities, which can also control corresponding switching means 19 (or for safety-relevant consumers 16, switching means, not shown for protecting the consumers 16). Alternatively, the evaluation can take place in a separate control device.

[0028] Consumers 16 supplied by the power distributor 18, in particular consumers 16 with high demands in terms of protection requirements, may for example include safety-relevant vehicle functions, such as braking, steering, etc. In general, safety-relevant consumers 16 are consumers which are particularly deserving of protection, for example those which are necessary for maintaining a certain level of emergency functionality. They may be not only the aforementioned functions such as steering and braking, but also functions which should, if possible, continue to function well after an accident, for example restraint systems, closing systems for opening and closing the vehicle doors, emergency call systems, for example for sending an electronic emergency call, sliding roof functions, lighting or similar functions.

[0029] The consumer device 17.m that is not related to safety is typically a comfort consumer device. The comfort consumer device 17.m can be divided into a main group and a subgroup according to its use, and thus can be grouped (see an alternative exemplary embodiment based on FIG. 2 with additional distributors 50, 52). Such consumer devices 17 feature either a low importance for safety or relatively low requirements regarding protection requirements.

[0030] The exemplary embodiment based on FIG. 2 differs from the exemplary embodiment based on FIG. 1 in that additional distributors 50, 52 are connected to the power distributor 18, and by means of these additional distributors 50, 52, additional consumer devices 16.k, 17.l, 17.j shown illustratively in the figure can be controlled respectively. The distributor 50 to which at least one safety-related consumer device 16.k is connected is supplied with a corresponding current I16.v from the power distributor 18 via a wiring having a wiring resistance R16.v. In addition, an additional distributor 52 is provided, and via the additional distributor 52, only one safety-unrelated consumer device 17.j, which is shown only as an example in this exemplary embodiment, can be supplied and can be disconnected via a corresponding switching means 19.j. This additional distributor 52 is supplied with a corresponding current I17.v from the power distributor 18 via a wiring having a wiring resistance R17.v. A current I17.j is supplied to the safety-unrelated consumer device 17.j to which it belongs.

[0031] In this respect, the sub-processes described below can be distributed to various control devices, so that the disconnection of the non-safety-relevant consumers 17.m can also be triggered in the other distributors 50, 52 via corresponding switching means 19.l, 19.j. The signal 40 for disconnecting the consumers 17.l, 17.j can be transmitted via a communication bus and can also be commanded in an independent control device, for example a so-called vehicle computer. If an undervoltage dU is present at a safety-relevant consumer 16.k, which is also supplied by a distributor 50, this distributor 50 can also propose to the power distributor 18 to disconnect the corresponding non-safety-relevant consumer 17.

[0032] By way of example, in this exemplary embodiment, a battery or accumulator is described as a possible energy store 12. However, other energy stores suitable for the task, for example inductive or capacitive based energy stores, fuel cells, capacitors or the like, can also be used instead.

[0033] The time range for the disconnection of the consumers 17 to be disconnected is in the order of magnitude between 1 ms and 500 ms. This method does not serve for line, component or part protection and is therefore not comparable to overcurrent disconnection in the time range below 10 μs. In classical on-board networks, regulating interventions of the energy management in the time range above 500 ms can be expected. In some cases, it must be ensured that the quantities to be evaluated are quickly captured and / or quickly communicated to the evaluation unit, e.g. the power distributor 18.

[0034] In Fig. 3 the different blocks 30, 34, 38 are shown diagrammatically with their input and output quantities. The undervoltage recognition 30 is fed with a number of the abovementioned quantities, which are the current I16.n through the respective safety-relevant consumer 16.n and / or the voltage U at the power transmission rail 14 and / or one or more respective resistances R16n of the respective wiring paths to the respective safety-relevant consumer 16.n and / or one or more respective resistances R17.m of the respective wiring paths to the respective non-safety-relevant consumer 17.m. On the basis of these, the undervoltage recognition 30 determines at least one trigger 32 and / or an undervoltage dU, as will be explained below. The calculations of the undervoltage recognition 30 can take place in the power distributor 18 or in the respective consumer 16.n, 17.m, in particular in the safety-relevant consumer 16.n, but also in the non-safety-relevant consumer 17.m. For the undervoltage recognition 30 the following process steps can be used, alone or in combination: The magnitude of the voltage U16.n at each safety-relevant consumer 16.n can be determined by different approaches:

[0035] In a first option, the voltage U at the power rail 14 is captured. From this voltage U at the power rail 14, a predefined voltage Uw is subtracted, which represents the worst case, in order to take into account the voltage drop due to the respective resistance R16.n of the wiring path to each safety-relevant consumer 16.n. This predefined voltage Uw is the worst-case empirical value that has to be taken into account in the worst case. Thus, the voltage U16.n at each safety-relevant consumer 16.n can be estimated as follows:

[0036] U16.n=U-Uw (1) In a further option, the measured voltage U at the transmission rail 14, the measured current I16.n through the safety-relevant consumer 16.n and a fixed resistance value R16.n_w representing the worst case are taken into account to estimate the magnitude of the voltage drop U16.n at the safety-relevant consumer 16.n. From the voltage U at the transmission rail 14, the voltage drop in the wiring path is calculated based on Ohm's law due to the worst case estimate of the wiring resistance R16.n_w and the current flow I16.n through the respective wiring.

[0037] U16.n=U-I16.n*R16.n_w (2) In a further option, the measured voltage U at the transmission rail 14, the measured current I16.n through the safety-relevant consumer 16.n and the respective line resistance R16.n_d estimated within the framework of the model are taken into account in order to estimate the extent of the voltage drop U16.n at the safety-relevant consumer 16.n. From the voltage U at the transmission rail 14, the voltage drop in the line path due to the diagnostic function of the line resistance R16.n_d (for example as described in DE 102018212369 A1 and fully linked to the disclosure thereof) and the current flow I16.n through this line are calculated.

[0038] U16.n=U-I16.n*R16.n_d (3) In a further alternative exemplary embodiment, the voltage U16n applied to the safety-relevant consumer device 16.n is measured directly at the respective consumer device 16.n itself and communicated to the power distributor 18 via a communication interface (e.g. CAN).

[0039] U16.n = U16.n via communication means (4) In a further option, the degree of the voltage U16.n applied to the safety-relevant consumer 16.n can be evaluated in the respective consumer 16.n itself. If an impending undervoltage dU is recognized, a trigger 34 and / or an undervoltage dU is transmitted to the power distributor 18 by a function integrated in the respective consumer 16.n. That is to say, the undervoltage recognition 30 is performed in the consumer 16.n instead of in the power distributor 18.

[0040] U16.n = U16.n in consumer device 16 (5) These various methods for determining the magnitude of the voltage U16.n applied to the safety-relevant consumer 16.n can be used alternatively (alone), but also for mutual likelihood checking, so that at least two, but also several alternative determination possibilities are used. In the case of a low likelihood result, corresponding warning notifications or countermeasures can be initiated.

[0041] The durations T1, T2, T3 of the applied calculated or measured voltages U16.n are important for recognizing an impending undervoltage dU and for generating a trigger signal 32 which proposes disconnecting 40 or degrading the performance of the non-safety-relevant consumer 17. According to Fig. 4, this is represented by a dynamic voltage limit Ug, i.e. the voltage limit Ug increases with increasing duration T below the voltage limit Ug. In the exemplary embodiment according to Fig. 4, the increase of the voltage limit Ug with increasing duration T is stepped. In principle, however, other relationships between the limit values ​​Ug and the maximum permissible duration T for the respective limit value Ug can also be implemented, for example a relationship in the form of a continuous, i.e. constantly rising, function. The duration T or T1, T2, T3 presents a maximum duration during which the voltage U16.n of the safety-relevant consumer 16.n must not fall below the assigned limit value Ug or Ug1, Ug2, Ug3, otherwise a supply shortage or failure of the safety-relevant consumer 16.n is imminent. From the duration T1 onwards, the limit value Ug has a first value Ug1 and remains constant until a further duration T2. ​​The duration T1 is, for example, in the range of about 0.5 ms, the further duration T2 is, for example, 10 ms. The first limit value Ug1 has a minimum value, and for a supply voltage (12 V in this exemplary embodiment), this first limit value Ug1 takes, for example, a value of about 50% of the supply voltage. In absolute terms, the first limit value Ug1 is, for example, in the range of 6 V to 7 V, in this exemplary embodiment 6.4 V. After duration T2 (for example 10 ms), the limit value Ug rises to a value Ug2 which is 70% of the supply voltage, in absolute terms, exemplarily 8.6 V as shown in FIG. 3, or in the range between 8 and 9 V. After duration T2, the second limit value Ug2 remains constant until duration T3. After duration T3 (for example 100 ms), the limit value Ug rises to a value Ug3 which is 80% of the supply voltage, in absolute terms, exemplarily 9.6 V as shown in FIG. 3, or in the range between 9 and 10 V. After duration T3, the third limit value Ug3 again remains constant.

[0042] For duration T1, the trigger 32 is generated if the established voltage U16.n is about to fall below a first limit value Ug1. For duration T2, the trigger 32 is generated if the established voltage U16.n is about to fall below a second limit value Ug2. For duration T3, the trigger 32 is generated if the established voltage U16.n is about to fall below a third limit value Ug3. If the established voltage U16.n falls below one of the limit values ​​Ug, a timer is started at this point. As soon as the duration T assigned to the limit value Ug that has been exceeded is reached, the trigger 32 is generated. For this limit value Ug that has been exceeded, an undervoltage dU is established as explained below.

[0043] Based on the determined or measured voltage U16.n at the respective safety-relevant consumer 16.n and the dynamic voltage limits Ug; Ug1, Ug2, Ug3, for example according to FIG. 3, a voltage difference or undervoltage dU is calculated (dU=Ug-U16.n), whereby the limit value Ug closest to the determined voltage drop U16.n at the safety-relevant consumer 16.n is selected. For example, if the voltage U16.n is 6 V, then the undervoltage dU for the closest limit value Ug1 (Ug1=6.4 V) is 0.4 V. If the voltage U16.n is, for example, 8 V, then the undervoltage dU for the closest limit value Ug2 (Ug2=8.6 V) is 0.6 V, etc.

[0044] This voltage difference or undervoltage dU is used as an input quantity to a block 34 for estimating the current Ir to be cut off. In the following, a process step or block 34 for estimating the degree of curtailment, e.g. the current Ir to be disconnected or reduced, is explained in more detail. In order to stabilise the voltage U (boosting by dU) and to comply with the voltage and time limits of the safety-relevant consumers 16.n, the disconnection of one or more non-safety-relevant consumers 17.m is necessary. How many non-safety-relevant consumers 17.m have to be disconnected is determined on the basis of the degree of curtailment (e.g. the current 36 to be disconnected) Ir. How much the current Ir has to be reduced to raise the supply voltage U by dU can be derived by one of the sub-processes described below.

[0045] That is, for example, as one possible option, a fixed value of the current Ir to be cut off or reduced can be implemented: if the trigger 32 is activated, the current Ir defined in this respect must be cut off.

[0046] Ir=constant (1) In a further option, the reduction degree Ir is calculated using the undervoltage dU determined by the undervoltage recognition 30, the total resistance Rb of the entire path from the energy store 12 to the inlet of the power distributor 18, and the resistance Ri relating to the internal resistance of the energy store 12, in particular the battery, up to earth or ground. The resistances Rb, Ri can be based on known resistances at the beginning of life or on corresponding estimates. If the energy store 12 is not provided as a supply source or is being charged, the current in the direction of the DC voltage converter 22 must be reduced. The current Ir to be reduced is therefore determined as follows:

[0047] Ir=dU / (Rb+Ri) or Ir=dU / Rdc (2) The reduction level, e.g., the current Ir to be interrupted, is calculated in a further alternative procedure based on the undervoltage dU calculated by the undervoltage recognition 30, the resistance Rdc_d of the cable assembly of the conductor from the DC voltage converter 22 determined by diagnosis and / or the resistance Rb_d of the cable assembly of the conductor to the energy storage 12 determined by diagnosis and / or the internal resistance Ri_d of the energy storage 12 determined by diagnosis.

[0048] Ir = dU / (Rb_d + Ri_d) or Ir = dU / Rdc_d (3) In a further option, the reduction level Ir may be set by energy management in order to correspondingly stabilize the voltage.

[0049] Ir = Ir via the communication system from the energy management (4) A further block 38 serves to select the consumer device 17.m that is not relevant for safety for interruption. For this process step 38, the trigger 32 and / or the current Ir to be interrupted from the block 34 and / or the respective current I17.m flowing through each consumer device 17.m that is not relevant for safety are fed in. That is, if the trigger 32 (from block 30) and the current Ir to be interrupted (from block 34) are known, one of the process steps described below is used to accurately determine the consumer device 17.m that is not relevant for safety for interruption. The interruption is effected via the respective interruption signals 40.1, 40.2,..., 40.m that can control the respective switching means 19m. In this case, the consumer device 17.m can be interrupted immediately or via a plurality of stages. In the case of a stepwise interruption, after the separation of the consumer device(s), a defined system response is awaited and, if necessary or in case of non-compliance with the voltage requirement, a new or further interruption of the consumer device 17.m that is not relevant for safety is carried out. The system response can be an increase in the voltage U in the power transmission rail or a signal from a system located upstream.

[0050] In one embodiment, all non-safety-relevant consumers 17.m can be switched off. When a corresponding trigger signal 36 is generated and transmitted by the undervoltage recognition 30, all non-safety-relevant consumers 17.m are switched off. The current Ir to be reduced is not required as an input quantity.

[0051] In a further alternative embodiment, this is done on the basis of just the criterion of the maximum current flowing in the respective safety-non-relevant consumer 17.m, i.e. first the safety-non-relevant consumer 17.max with the maximum current flow I17.max is switched off, until the current to be reduced Ir is reached.

[0052] In a further alternative, the current I17.m flowing through the non-safety-relevant consumer 17.m can be multiplied by a constant or dynamic weighting factor and can be cut off at least up to the current Ir to be reduced according to this weighting score. The weighting score can be determined independently of the current I17.m. This weighting allows the optimal consumer 17.m to be cut off in order to obtain the best possible condition between the current Ir to be cut off and the loss of the function of the respective non-safety-relevant consumer 17.m. For this purpose, weighting methods based on static or dynamic values ​​or on the current or state of on-board network components can be used. In this respect, the non-safety-relevant consumer 17.m to be cut off or degraded can be selected, for example, by means of an optimization method (for example an optimization problem: binary linear programming). Each consumer path is then assigned a weight, which weights the influence of the current I17.m in the respective consumer path on the system. Firstly, the condition must be fulfilled that the sum of the currents (I17.m) of the consumers 17.m to be disconnected reaches at least the reduction degree Ir. As an optimization goal for the optimized consumer disconnection, the minimum sum of the priority values ​​of the non-safety-relevant consumers 17.m can for example be taken into account (the higher the priority of the non-safety-relevant consumers 17.m, the higher the corresponding priority value), while necessarily respecting the above reduction condition.

[0053] In a further alternative, the supervised vehicle system provides, in accordance with rules, a set of disconnectable consumers 17.m which are then disconnected when performing a function. Alternatively, a corresponding group of consumers 17.m may be disconnected.

[0054] Disconnected non-safety-relevant consumers 17.m must be reconnected according to certain criteria. Different criteria can be used for this purpose. That is, in one embodiment, a reconnection attempt may be made after a defined time. If the reconnection attempt is unsuccessful, e.g. after x seconds, i.e. a new disconnection occurs, then new reconnection attempts may be made, e.g. k attempts. Instead, an error message may be sent. The reconnection attempt may be aborted.

[0055] As a further alternative criterion it is established whether the voltage U is stable for a defined time, for example if the voltage U is greater than a threshold Ug of, for example, 11 V for x seconds, then a disconnected non-safety-relevant consumer 17.m can be connected.

[0056] As a further alternative criterion, the reconnection can take place after communication with the energy management: the vehicle-wide energy management or a comparable vehicle system proposes the reconnection of the non-safety-relevant consumers 17.m via a communication system, e.g. the CAN bus. The connection can be made individually or interactively and / or in groups.

[0057] In a further alternative criterion, the disconnected consumer 17.m can be reconnected on the basis of a current reserve. This function continuously calculates the minimum current reserve required to reconnect the non-safety-relevant consumer 17.m to the energy supply. Whether the non-safety-relevant consumer 17.m is reconnected is determined on the basis of a setting by the vehicle system, for example in the context of energy management, and / or on the basis of a current value I17.m_v previously set for each consumer 17.m, and / or on the basis of a dynamically calculated value on the basis of past consumer current consumptions, and / or in a similar manner.

[0058] The above mentioned function is not limited to a certain voltage level U in the energy on-board network (e.g. 12V in this exemplary embodiment). The above mentioned method has an interface, not shown in the figures, to the energy management in order to send at least one feedback information about the disconnected non-safety consumers 17.m. In addition to this, communication or configuration from a superordinate vehicle system (e.g. the energy management as described in the attribution sub-process) is also conceivable. Due to the required execution speed (between 1ms and 500ms), the energy management cannot execute this function by itself. Therefore, the configuration parameters must be provided to the power distributor 18 before the function execution or only when reconnecting after an undervoltage event.

Claims

1. A method for monitoring an on-board network of a motor vehicle, comprising: at least one power distributor (18), via which at least one safety-relevant consumer (16) is supplied with a supply voltage (U) and via which non-safety-relevant consumer (17) is supplied, the power distributor (18) being supplied by at least one energy store (12), a degree of voltage (U16.n) applied to at least the safety-relevant consumer (16.n) is determined on the basis of which the degree of voltage (U16.n) applied to the safety-relevant consumer (16.n) is determined, A monitoring method in which an undervoltage (dU) at a safety-relevant consumer (16.n) is determined depending on a limit value (Ug), characterized in that a degree of reduction (Ir) for the disconnection or de-rating of at least one non-safety-relevant consumer (17.m) required to increase the voltage (U16.n) applied to the safety-relevant consumer (16.n) is determined depending on the undervoltage (dU) and a selection of the non-safety-relevant consumer (17.m) to be disconnected or de-rated is made based on the degree of reduction (Ir).

2. 2. The method according to claim 1, characterized in that a disconnection time or a trigger (32) for disconnection or degradation of at least one of the non-safety-relevant consumers (17.m) is generated when the voltage (U16.n) dropping across the safety-relevant consumer (16.n) reaches or is about to reach said limit value (Ug) for a certain duration (T1, T2, T3), preferably in the range between 1 ms and 500 ms.

3. 3. The method according to claim 1 or 2, characterized in that the extent of the voltage (U16.n) dropped at the safety-relevant consumer (16.n) is determined from the supply voltage (U) at the power distributor (18) and the voltage drop in the wiring path between the power distributor (18) and the safety-relevant consumer (16.n).

4. 4. The method according to claim 1, wherein the voltage drop in a wiring path between the power distributor (18) and a safety-relevant consumer (16.n) is determined by the resistance (R16.n_w, R16.n_d) of the respective wiring path and the current (I16.n) flowing through the safety-relevant consumer (16.n).

5. 5. The method according to claim 1, wherein the reduction degree (Ir) is determined depending on the resistance (Rb) of the wiring path connecting the energy store (12) and the power distributor (18) and / or depending on the internal resistance (Ri) of the energy store (12).

6. 6. The method according to claim 1, wherein the number of non-safety-relevant consumers (17.m) to be disconnected is determined in dependence on the degree of reduction (Ir).

7. 7. The method according to claim 1, wherein the degree of reduction (Ir) is determined such that the supply voltage (U) and / or the voltage (U16.n) applied to the safety-relevant consumers (16.n) is increased by at least the undervoltage (dU).

8. 8. The method according to claim 1, wherein the limit value (Ug) varies depending on the duration (Ti) during which the extent of the voltage drop (U16.n) at the safety-relevant consumer (16.n) falls below the corresponding limit value (Ug), in particular increasing as the duration (Ti) increases.

9. 9. The method according to claim 1, characterized in that the degree of reduction (Ir), in particular the current to be reduced, is determined using resistances (Rdc, Rb) of wiring paths to the energy store (12) and / or to an alternative energy source (22) and / or an internal resistance (Ri) of the energy store (12) and / or in dependence on a predetermined degree of reduction (Ir) and / or in dependence on resistances (Rdc_d, Rb_d) of wiring paths to the energy store (12) and / or to an alternative energy source (22) determined by model or diagnostics and / or in dependence on the internal resistance (Ri_d) of the energy store (12) determined by model or diagnostics and / or the degree of reduction (Ir) is preferably communicated from a further control device, in particular an energy management.

10. 10. The method according to claim 1, characterized in that the case when the extent of the voltage (U16.n) dropping at the safety-relevant consumer (16.n) reaches the limit value (Ug) is determined and, since the limit value (Ug) is reached, the duration (T) of the voltage drop below the limit value (Ug) is captured, the captured duration (T) is compared with a duration (Ti) assigned to the limit value (Ug), and, when the assigned duration (Ti) is reached, a trigger (32) is generated for initiating a disconnection or derating of at least one non-safety-relevant consumer (17.m).

11. 11. The method according to claim 1, wherein the magnitude of the voltage (U16.n) applied to at least the safety-relevant consumer (16.n) is determined by measuring the voltage at the safety-relevant consumer (16.n) and / or by using the current (I16.n) flowing through the safety-relevant consumer (16.n) and / or by measuring the supply voltage (U) and / or taking into account a resistance (R16.n) of a wiring path between a power distributor (18) and a safety-relevant consumer (16.n), in particular a worst-case value (R16.n_w) of the resistance or a model-estimated resistance (R16.n_d) of the wiring path and / or in dependence on a worst-case value (Uw) of the voltage drop across the resistance (R16.n) of the wiring path between the power distributor (18) and the safety-relevant consumer (16.n).

12. 12. The method according to claim 1, characterized in that the determination of the trigger (32) and / or the undervoltage (dU) is performed by the safety-relevant consumer (16.n) and / or the safety-relevant consumer (16.n) transmits the trigger (32) and / or the undervoltage (dU) and / or the voltage drop (U16.n) measured at the safety-relevant consumer (16.n) to, inter alia, the power distributor (18) and / or the determination of the trigger (32) is performed by various control devices.

13. 13. Method according to any one of claims 1 to 12, characterized in that the selection of non-safety relevant consumers (17.n) to be switched off or degraded is made on the basis of the current (I17.m) flowing through the respective non-safety relevant consumer (17.m), in particular non-safety relevant consumers (17.m) having a maximum current flow or a current flow above a certain limit value are switched off or degraded.

14. 14. Method according to any one of claims 1 to 13, characterized in that further non-safety relevant consumers (17.m) are switched off until said degree of reduction (Ir) is reached.

15. 15. The method according to claim 1, characterized in that the current (I17.m) flowing through each non-safety relevant consumer (17.m) is associated with a weighting factor specific to each non-safety relevant consumer (17.m), and each associated value is used for selecting the non-safety relevant consumer (17.m) to be disconnected or degraded.

16. 16. The method according to claim 1, further comprising the step of assigning a weight or priority value to each of the non-safety-related consumers (17.m) and the selection of each of the consumers (17.m) to be disconnected or degraded is performed by optimizing the associated weight or priority value.

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