How to limit the load current

Abstract

To provide a method for restricting load current by a supply line for supplying current to a load part.SOLUTION: There is provided a method for restricting load current by a supply line for supplying current to a first load part in an in-vehicle electric system, which includes the steps in which: a first time interval and a second time interval are regulated; the first time interval is started after a connection time point T0 of the first load part with the supply line, the second time interval is started later than the first time interval, and the load current is restricted to a first value I1 within ranges of the first time interval and the second time interval; and the load current is restricted to a second value I2 at the time of completion T3 of at least the second time interval. The second value I2 is smaller than the first value I1.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for limiting a load current in a supply line supplying a first load section. [Background technology]

[0002] In the on-board electrical system of a vehicle, electrical resistances exist, for example due to electrical lines or contacts. When a current flows through such a resistance, a voltage drop occurs across the resistance, which reduces the terminal voltage available to the power consumer or load. The voltage drop across such a resistance also increases with the magnitude of the current through the resistance. Due to the required power and the relatively low voltage in the on-board electrical system, very large currents flow, which is important for the function of the connected electrical loads, for example electrical component units. If a voltage drop across at least a portion of the supply lines causes a voltage that is too low to be applied to the connection terminals of such a component unit, it may not be possible to maintain all functions or the performance that can be achieved is limited as a result. Depending on the type of component unit and the programmed scenario, the performance of such a component unit, for example an electrically operated brake, is then reduced or a transition to a fallback level is made in the form of deactivating such a component unit and an appropriate warning is given or a transition to a fallback solution using redundant systems is made. Summary of the Invention [Problem to be solved by the invention]

[0003] To limit such voltage drops due to resistance in the supply line, systems are constructed with current limiting, which in such cases reduces the power consumption of the power consumers as a direct function of the voltage, thereby preventing in some cases a transition to the fallback level of the load itself or of a second component unit supplied by the same supply line, but this causes a reduced performance of such a component unit. [Means for solving the problem]

[0004] The present invention discloses a method, a device, a computer program and a machine-readable storage medium for limiting the load current in a supply line according to the features of the respective independent claims. Preferred embodiments are the subject of the dependent claims and the following description.

[0005] The finding on which the invention is based is that it may be more favorable for the utilization of the entire system to design a current limiting of such a nature that the additional functionality of the entire system provided by the secondarily connected component units is maintained, even if this results in a sacrifice of the performance of the primary component units. For example, the constant maintenance of the anti-lock system (ABS) during braking may be more important than the maximum braking force, since under normal conditions the brakes lock up already at 40% of the braking force.

[0006] According to one aspect, a method for limiting a load current in a supply line is disclosed, the supply line providing a current to a first load section. In one step of the method, a first time interval and a second time interval are defined, the first time interval starting after a point of connection of the first load to the supply line and the second time interval starting later than the first time interval.

[0007] In a next step, the load current is limited to a first maximum value within the first and second time intervals.

[0008] In a next step, at least at the end of the second time interval, the load current is limited to a second maximum value, the second maximum value being less than the first maximum value.

[0009] Throughout this description of the invention, the order of each method step is described so that the method can be easily understood. However, those skilled in the art will recognize that many of the method steps can be performed in a different order and still lead to the same or a corresponding result. In this sense, the order of each method step can be changed accordingly.

[0010] The advantage of limiting the load current to a first value within the first and second time intervals after the connection of the first load to the supply line is that it is possible to limit the voltage drop across at least a portion of the electrical supply line. Due to the resistance in the electrical energy inlet line to the first load, voltage drops caused by the resulting currents can occur both in the supply line itself and at the contact points. If such currents are limited, it is prevented that the terminal voltages at the first load and at the other loads can drop below the resulting voltage value, since the voltage drop across the resistance of the electrical inlet line must be subtracted from the supply voltage, e.g. coming from the power source, which would then not be available in the form of a terminal voltage, e.g. for the first load.

[0011] In this way, such a limitation of the load current can ensure that the minimum terminal voltage required by the first load to provide at least one basic functionality is not exceeded. The first load can also be understood as a system having a plurality of loads. This can be of particular importance, for example, for electrically operated vehicle brake systems, since brake systems are typically designed such that only a partial capacity is already sufficient to provide a full brake output under normal conditions. This can mean that, for example, the braked wheels are locked under such a partial capacity. By preventing the terminal voltage from falling below the minimum voltage due to the load current limit, other component units which also receive electrical energy from the supply line can also be provided with a minimum terminal voltage that ensures their functionality.

[0012] By limiting the load current to a second value smaller than the first value at least at the end of the second time interval, the load current can be further limited in a second time domain after the connection of the load to the supply line in order to provide a terminal voltage at the first load that is higher than the above-mentioned minimum terminal voltage, which can be particularly advantageous if other component units, which are also supplied with electrical energy from the supply line, require a terminal voltage higher than the minimum terminal voltage in order to be able to provide their functionality over a certain time span.

[0013] In this way, the maximum load current possibly required can be provided for example for a first load with a first magnitude during a first time interval, during which other component units as secondary loads still maintain their functionality, and the additional limitation of the load current in the second time interval ensures that the further component units maintain their functionality, albeit at the expense of the performance of the first load in the second time interval, since the current limitation to a lower value means that the first load can also only draw a lower load current from the supply line.

[0014] According to one embodiment of the method it is proposed that the second time interval immediately follows the first time interval.

[0015] Between the first and second time intervals, a time interval may be provided during which the restriction to the first value transitions to the restriction to the second value. Depending on the configuration of the system for the restriction to the first to the second value, corresponding switching times may be required. Similarly, a further time interval may be provided after the connection of the first load and after the start of the first time interval.

[0016] According to a further embodiment of the method it is proposed that the first value of the load current is determined in dependence on the terminal voltage of the first load part by means of a load current characteristic curve.

[0017] By using such a load current characteristic curve, which defines the relationship between the load current and the terminal voltage at the first load section, it can be ensured that the load current is limited to such an extent that the resulting voltage at the electrical connections of the first load section does not fall below a minimum value.

[0018] This safety measure ensures that at least other component units, which are also connected to the vehicle's electrical system, maintain their functionality, for example due to the absence of a function of the first load that would pull the entire vehicle's electrical system to too low a voltage, since an appropriate minimum voltage is maintained.

[0019] According to a further embodiment of the method, it is proposed that the terminal voltage for the load current characteristic curve is determined in the first and / or second time intervals. When the limiting of the load current to the first value continues in the second time interval, the terminal voltage must also be determined in the second time interval, and when the limiting in the second time interval is to a second value less than the first value, the limiting of the load current to the first value in the second time interval provides a fall-back solution for limiting the load current that increases the safety of the overall system.

[0020] According to another embodiment of the method, it is proposed that the terminal voltage is also determined outside the first and second time intervals, whereby a voltage value of the terminal voltage of the first load part is also provided before the connection of the first load part to the supply line, in order to achieve the limiting of the load current within a shorter time span after the connection of the first load part to the supply line.

[0021] According to another embodiment of the method, it is proposed that the first value of the load current is limited depending on the terminal voltage at the first load section or at the second load section by controlling the magnitude of the value of the load current.

[0022] According to another embodiment of the method, it is proposed that the second value of the load current is determined by a resistance value of at least a part of the supply line.

[0023] Such a resistance value of at least a portion of the supply line can be determined by an independent resistance measurement. Such a resistance can arise as a result of the resistance of the supply line itself, since in a vehicle this value can increase over the operation period of such a vehicle, for example due to corrosion. In addition to this, such a resistance arises primarily due to the contact resistance at the contacts, which can increase during operation, for example due to corrosion.

[0024] The resistance of such a supply line is understood herein, unless expressly stated otherwise, to mean all resistances resulting in a terminal voltage at the end of the supply line to which the load is connected, summed together to one value, i.e. this also includes the contact resistances and the earth connection.

[0025] If such a resistance value of the supply line is known, for example from a previous measurement, it can be determined according to Ohm's law how large the current can be at maximum in order to guarantee a corresponding minimum terminal voltage at the first load section.

[0026] Other component units or loads also connected to the supply line can maintain their functionality, for example during a period including the first and second time intervals, so that at the end of the second time interval the current is accordingly limited, thereby ensuring the minimum terminal voltage required for such component units to continue to maintain their functionality.

[0027] In this case, for example, the first time interval can be selected to be very short or this value can also define during the first time interval the value of the load current at which the current is limited in the first time interval.

[0028] According to another embodiment of the method, it is proposed that the resistance value of at least a part of the supply line is determined independently of the method for limiting the load current. Thereby, it is realized that for example the load current can be limited in a first time interval, i.e. for example immediately after the connection of a first load section to the supply line, to a determined first value of the load current.

[0029] According to one embodiment of the method, it is proposed that the load current is limited during the first and second time intervals to a second value of the load current, this second value being determined using a resistance value of at least a part of the supply line as described above.

[0030] In this way, it is achieved that some resulting minimum terminal voltage is maintained during both the first and second time intervals.

[0031] According to one embodiment of the method, it is proposed that the load current is limited to a first value at the beginning of the second time interval and to a second value within the second time interval with a predefined progression of the load current.

[0032] Such a transition can be controlled to be relatively linear, progressive, decremental, monotonically decreasing, or switched, ie, have jumps in the transition. In this way, a relatively high load current is available in the second time interval, which allows the first load to deliver a higher power output within the second time interval, for example, which may mean that for an electrically operated brake system, the brake power output within the second time interval is higher than after the end of the second time interval.

[0033] According to another embodiment of the method, it is proposed that the load current is limited within the second time interval by a predetermined target voltage curve in accordance with a control method and by a terminal voltage measured at the first load section in the first and / or second time intervals.

[0034] In this embodiment, therefore, knowledge of the resistance value is not necessary, at which a portion of the voltage may drop depending on the load current and thus provide a reduced terminal voltage. By determining the voltage, for example the terminal voltage at the first load part, a value to which the second value of the load current should be limited in comparison with the target voltage or the target voltage curve can be determined, for example by a control circuit. The target voltage curve set in this way can be adapted very closely to the target voltages possible in different time slots, so as to provide, for example, for the first load part, a maximum possible current that can take into account the current state of the on-board electrical system on the basis of the latest voltage measurements. Such a target voltage curve can set a target voltage of the magnitude of U2 at the end of the second time interval T3 in order to allow the continued operation of the second load part as explained above.

[0035] On the one hand, this means that no prior determination of the resistance of the supply line is necessary and that the load current is actually limited, both in terms of its magnitude and in terms of the available second time interval, only to the extent that is necessary to guarantee a minimum terminal voltage, i.e. the target voltage.

[0036] In this way it is realised that a maximum load current of the first load section during the second time interval can be provided under given peripheral conditions of the required terminal voltage. Such a limitation of the load current in the second time interval allows the other component units or second loads, which temporarily require the first terminal voltage or permanently require a second terminal voltage higher than the first terminal voltage, to continue to operate, but still allows a load current that allows a relatively high performance to be available for the first loads in the second time interval.

[0037] If the incoming line resistance is additionally known, this can be taken into account when determining the second value of the load current in dependence on the terminal voltage, thereby optimizing the control method for the current limiting of the load current in dependence on the terminal voltage compared to the target voltage.

[0038] According to another embodiment of the method, it is proposed that no load current limitation takes place within a start time interval which is located before the first time interval or between the first and second time intervals, during which, for example, a voltage measurement can take place or there can also be dead times of the electronic circuitry for limiting the load current.

[0039] According to another embodiment of the method, it is proposed that a parameter of the voltage control, which is related to the regulation speed, is determined using the measured first voltage value and the target voltage value and the predefined second time interval.

[0040] It is thereby realized that the determination of the second value of the load current can be optimally adapted to a given system as a function of the measured voltage, possibly also taking into account the resistance of the supply line, which may be known.

[0041] According to another embodiment of the method, it is proposed that the supply line supplies a current to a first load section and a second load section, and a second value of the load current is determined depending on a minimum terminal voltage of the second load section.

[0042] The minimum terminal voltage of the second load unit is taken into consideration, so that the second load unit can be operated at least after the end of the second time interval. If the first load unit requires a lower minimum voltage for basic functionality than the second load unit, the second load unit can continue to be operated after the end of the second time interval, and the second load unit can be configured such that the functionality of the second load unit is provided for this limited time within the first and second time intervals. After a predefined time and depending on the voltage provided at the second load section, the second load section may be set up to adjust its functionality and may only operate again through a reset process, which may require a possibly unacceptable time span. This time span or this voltage provided at the first to second load section, during which the functionality adjustment takes place, may be different for the first to second load sections. The first and / or second time interval may be defined depending on the time span during which the second load section remains functional below the second terminal voltage or depending on a time range, at the expiration of which the reset process may not yet be released.

[0043] According to another embodiment of the method it is proposed that when the magnitude of the load current reaches the first and / or the second load current value, a control signal for controlling the at least semi-automatic vehicle and / or a warning signal for warning a vehicle occupant is emitted.

[0044] According to another embodiment of the method, it is proposed that a control signal for controlling the at least semi-automatic vehicle and / or a warning signal for warning a vehicle occupant is emitted when the magnitude of the load current reaches or exceeds the first and / or second value of the load current for a specified time span, the specified time span also including the smallest possible time interval during which one exceedance occurs.

[0045] Reaching a load current magnitude according to the first and / or second value may possibly mean that the functionality of the first or second load is at least partially restricted, which may lead, in at least semi-automatic vehicles, to the inability to carry out certain driving operations or to the driver having to drive the vehicle himself again. If, due to the short duration of the restricted functionality, full functionality is subsequently available again, a warning to the vehicle driver may possibly be sufficient.

[0046] An apparatus is disclosed that is set up to perform the above described method, which allows for a fast and easy integration of the method into various larger units, which may be at least semi-automatic vehicles or driver assistance systems used in vehicles.

[0047] The above-described method for limiting the load current in the supply line can be applied in many applications, in particular in all applications where an electrohydraulic braking system is used. In this context, a vehicle is generally understood to be a motor vehicle, including at least semi-automatic vehicles or vehicles with driver assistance systems, as well as in particular motorcycles, construction machines, agricultural vehicles, etc. Alternatively, it may generally be a mobile platform, a mobile multi-sensor robot, such as a robot vacuum cleaner or lawnmower, a mobile multi-sensor monitoring system, a manufacturing machine, a personal assistant, an access control system, etc. In addition, the method can generally also be applied in non-mobile machines, for example with an electrohydraulic braking system.

[0048] A computer program is disclosed that includes instructions that, when executed by a computer, direct the computer to perform the method described above. Such a computer program allows the method to be easily incorporated into a variety of systems.

[0049] A machine-readable storage medium is disclosed having the above-described computer program product stored thereon, which allows the above-described computer program to be easily transported.

[0050] An embodiment of the present invention is shown with the aid of Figures 1 to 3 and will be explained in detail below. [Brief description of the drawings]

[0051] [Figure 1] 4 is the target voltage and time interval of the method. [Diagram 2] 4 is an illustration of a load current profile limited in a time interval of the method; [Diagram 3] 2 is an exemplary progression of a load current characteristic curve; [Figure 4] 2 is an exemplary progression of terminal voltages over a time interval; [Diagram 5] 5 is a method step for limiting a load current. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0052] In Fig. 1, the target voltage is shown by way of example at various time intervals after the connection of the load to the supply line. At time T0, the first load is connected to the supply line, which can be followed by a start time interval up to T1, possibly with no current limiting or with a current limiting that is not shown here. The start time interval can then also be omitted altogether. A first time interval starts at time T1 and can end, for example, at time T2. In Fig. 1, a second time interval follows the first time interval directly and ends at time T3. The time interval between T2' and T3 can be provided as a safety margin for the correction process or for a time interval during which the terminal voltage is controlled from U1 to U2 based on control of the current depending on the terminal voltage. The first target voltage U1 is lower than the second target voltage U2 and extends from T1 to T3, with the second target voltage U2 starting at time T3. These voltages and time intervals may be given based on technical settings and requirements for a component unit that is connected to the supply line as a second load in accordance with the first load and thus has the same supply line.

[0053] In a first embodiment, the terminal voltage of the first load is intended to be kept below the second target voltage U2 and above the first target voltage U1 during the limited time interval between T1 and T3, so that the load current in the supply line supplying the first load is limited. A first time interval from T1 to T2 and a second time interval from T2 to T3 are defined S1, the first time interval starting immediately after the connection time T1 of the first load to the supply line. Alternatively, there may be a further defined start interval between T0 and T1 between the connection time of the load and the start of the first time interval at T1. The second time interval then starts at time T2, later than the first time interval at time T1. In FIG. 1, the second time interval directly follows the first time interval at time T2.

[0054] 2 shows the course of the load current 24 limited according to the method within a first and a second time interval, for example limited S2 from a value of the load current I0 before the connection of the load to the supply line to a first value I1, where the first value I1 of the load current is determined by a load current characteristic curve 30 (FIG. 3) as a function of the terminal voltage of the first load.

[0055] 3, an exemplary load current characteristic curve for determining the required current limit is shown as a function of the terminal voltage U of the first load section. As long as the terminal voltage U of the first load section is higher than the second setpoint voltage U2, the maximum current I0 can be provided from the supply line. As soon as the measurement of the terminal voltage U determines that it is below the second setpoint voltage U2, the load current is reduced according to the characteristic curve 30, for example to the first value I1 of the load current, to ensure a terminal voltage U of the magnitude of the first setpoint voltage U1 at the first load section.

[0056] The load current in the supply line of the first load section is limited within the second time interval S3 such that at least at the end of the second time interval T3 the load current is not greater than a second value I2, the second value I2 being less than the first value I1 of the load current.

[0057] According to one embodiment, the terminal voltage U is determined in the first and / or second time interval, and the second value I2 of the load current is determined by a resistance value of at least part of the supply line. This resistance value of at least part of the supply line can be determined in a manner that is independent of the limitation of the load current. The second current I2 is then calculated from the determined or measured terminal voltage together with this resistance value according to Ohm's law. One possible progression of the terminal voltage based on a further limitation of the load current from the first value I1 to the second value I2 can result in a terminal voltage progression 46 as shown in FIG. 4. Here, the terminal voltage is progression in such a way that voltage-time regions 42, 44, which would result, for example, in the switching off of the component unit, are avoided. As a result, during the time period located after the second time interval, a terminal voltage U of the first load part occurs that is greater than the value U2, and thus other component units, which are also electrically connected to the supply line, can be operated continuously as described above.

[0058] According to another embodiment, the load current is limited in the first and second time intervals to a second value I2 determined as shown diagrammatically in FIG. 2 by the profile 22 of the load current in the supply line.

[0059] According to another embodiment, the load current can be limited to a first load current value I1 at the beginning of the second time interval T2 and within the second time interval to a second value I2 at the end of the second time interval T3 according to a predefined progression of the load current limitation. In Fig. 2, this is shown diagrammatically by the progressions 24 and 26 of the load current in the first and second time intervals, with progression 26 being selected as an example with a predominantly linear progression in the second time interval. Alternatively, the progression of the load current in the second time interval can have another shape, as is also shown diagrammatically by way of example by the jump progression 24 at the time T2.

[0060] According to another embodiment, the load current is limited to a second value I2 within a second time interval, the second value I2 being not calculated by resistance measurement as described above, but rather determined in accordance with a control method in the second time interval using a predefined target voltage, for example the first target voltage U1, and a terminal voltage U at the first load section, which is measured in the first and / or second time intervals. For this purpose, the terminal voltage U is repeatedly measured at least within the second time interval and the load current is limited to a corresponding value in accordance with the control method, so that in the second time interval the terminal voltage U at the first load section is higher than the second target voltage U1, and at the end of the second time interval the load current is limited to a second value I2, so that the terminal voltage U at the first load section is higher than the second target voltage U2.

[0061] In FIG. 5 the method steps S1 to S3 described above are shown diagrammatically. [Explanation of symbols]

[0062] S1 Method Steps S2 Method Steps S3 Method Steps T0 Connection time T3 End of the second time interval I1 First value I2 Second value

Claims

1. 1. A method for limiting a load current in a supply line supplying current to a first load and a second load, comprising the steps of: A first time interval and a second time interval are defined (S1), the first time interval starting after a connection time (T0) of the first load to the supply line, and the second time interval starting later than the first time interval; The load current is limited to a first value (I1) within the first and second time intervals (S2); the load current is limited (S3) to a second value (I2) at least at the end of the second time interval (T3), the second value (I2) being less than the first value (I1); The method wherein the second value of the load current (I2) is determined depending on a minimum terminal voltage of the second load section.

2. The first time interval and / or the second time interval may include the second 2. The method according to claim 1, wherein the load is determined depending on a time span during which the load can remain functional.

3. 2. The method of claim 1, wherein the first time interval and / or the second time interval are defined depending on a time range, at the expiration of which a reset process is not released in the second load part.

4. 4. The method according to claim 1, wherein the first value (I1) of the load current is determined in dependence on the terminal voltage of the first load part by means of a load current characteristic curve.

5. 5. The method according to claim 4, further comprising determining a minimum voltage to be maintained for the terminal voltage of the first load section during the first and / or second time intervals, and determining the first value (I1) using the minimum voltage and a load current characteristic curve.

6. 6. The method according to claim 1, wherein the second value of the load current is determined by a resistance value of at least a part of the supply line.

7. 7. The method according to claim 1, wherein the load current is limited to the first value (I1) at the beginning of the second time interval and is limited to the second value (I2) with a predefined transition within the second time interval.

8. 6. The method according to claim 1, wherein the load current is limited to the second value (I2) within the second time interval, the second value (I2) being determined using a predetermined target voltage and a terminal voltage measured at the first load section during the first and / or second time intervals.

9. 9. The method according to claim 1, wherein a control signal for controlling an at least semi-automatic vehicle and / or a warning signal for warning a vehicle occupant is emitted when the magnitude of the load current reaches the first and / or the second value (I1, I2) of the load current.

10. Apparatus set up to perform the method according to any one of claims 1 to 9.

11. A computer program comprising commands for carrying out the method according to any one of claims 1 to 9.

12. A computer readable storage medium having stored thereon the computer program according to claim 11.

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