Method for determining the position of multiple bus subscribers in a differential two-wire bus system

Abstract

The invention relates to a method (100) for determining the position of multiple bus subscribers (12) in a differential two-wire bus system (10). Each bus subscriber (12) is designed as a master unit (14) or as a slave unit (16), wherein each bus subscriber (12) is connected to at least one adjacent bus subscriber (12) via a two-wire connection. Each bus subscriber (12) is arranged between two connection points (24) of a line of the two-wire connection. The method (100) comprises the following method steps: - carrying out (110) a first series of measurements, in which an initial voltage is provided, on a first bus subscriber, between the connection points (24) of the first bus subscriber; - carrying out (120) a second series of measurements, in which an initial voltage is provided, on a second bus subscriber, between the connection points (24) of the second bus subscriber; - determining (130) the position of the individual bus subscribers (12) on the basis of the initial voltages provided during the first series of measurements and the second series of measurements and of the measured voltages determined on the bus subscribers (12).

Description

[0001] Method for determining the position of several bus devices in a differential two-wire bus system

[0002] The present invention relates to a method for determining the position of several bus participants in a differential two-wire bus system, in particular in a CAN bus system, as well as a corresponding differential two-wire bus system.

[0003] Two-wire bus systems are generally known and are used, for example, for communication between individual bus devices in a motor vehicle. The bus devices can be configured as sensors or actuators, for example. One bus device is often configured as a master unit, with the master unit providing control functions.

[0004] In some two-wire bus systems it is desirable to determine the position of the individual bus participants within the bus system.

[0005] Various methods for determining the position of bus devices are known in the art. For example, a propagation time measurement can be used, whereby a master unit, in particular, transmits a signal that is received by the individual slave units and then sent back to the master unit. By measuring the signal propagation time, the position of the individual devices in the bus system can be determined.

[0006] The publications DE 10 2015 013 442 Al, DE 10 2007 028 928 Al, DE 10 2007 028 926 B3, DE 103 10 250 Al, DE 10 2022 210 907 B3, US 2021 / 0294771 Al and EP 4 312 408 Al describe various methods for determining individual components in a network.

[0007] While the method described above delivers reliable results for bus systems with simple topologies, it often fails for bus systems with more complex structures due to a lack of clarity in the measurement results. Based on the described problem, the object of the present invention is to provide a method for determining the position of multiple bus devices in a differential two-wire bus system.

[0008] To achieve the above object, the present invention proposes a method for determining the position of several bus subscribers in a differential two-wire bus system, in particular in a CAN bus system, wherein each bus subscriber is designed as a master unit or as a slave unit, each bus subscriber is connected to at least one adjacent bus subscriber via a two-wire connection, each bus subscriber is arranged between a connection point of a first line and a connection point of a second line of the two-wire connection, and the method comprises the following method steps:

[0009] Carrying out a first series of measurements in which an initial voltage is provided between the connection points of a first bus participant, and in which a measurement voltage recorded at each of at least all bus participants configured as slave units that are different from the first bus participant is determined;

[0010] Carrying out a second series of measurements in which an initial voltage is provided between the connection points of a second bus participant and in which a measurement voltage recorded at each of several bus participants that are different from the second bus participant is determined;

[0011] Determining the position of the individual bus devices based on the initial voltages provided during the first and second measurement series and the measured voltages determined at the bus devices. The difference between the initial voltages provided and the measured voltages determined is used as a measure of the distance between the individual bus devices during the respective measurement series. The method according to the invention makes it possible to determine the position of multiple bus devices in a two-wire bus system, even in bus systems with a complex topology. The measured voltages are evaluated for each measurement series, so that the positions of the individual bus devices within the bus system are determined step by step.

[0012] In particular, the method according to the invention can provide that the second bus participant is different from the first bus participant.

[0013] The method according to the invention can be configured to perform more than two measurement series. As explained in more detail below, the measurement series can be continued until the position of each bus participant has been determined or until each bus participant has provided an initial voltage for a measurement series.

[0014] The initial voltage according to the present invention can also be referred to as the supply voltage or primary voltage. For example, in a series of measurements, an initial voltage of 3 V, 4 V, or 5 V can be applied to the connection points of a first bus device. Subsequently, the measurement voltages measured at the other bus devices are determined and evaluated. For example, an initial voltage of 3 V can be provided at the first bus device, while the other bus devices that have not provided an initial voltage record measurement voltages of 2.8 V, 2.6 V, and 2.4 V.With such a measurement, it can be concluded that the bus device at whose connection points 2.8 V was measured is positioned in the immediate vicinity of the first bus device, while the bus device at whose connection points 2.4 V was measured is positioned furthest from the first bus device. The bus device at whose connection points 2.6 V was measured is therefore positioned between the bus devices at whose connection points 2.8 and 2.4 V were measured. In this way, the position of individual bus devices can be determined in a series of measurements. The determination of the position of the individual bus devices is therefore based on the knowledge that the initial voltage provided to the first bus device drops with increasing distance from the first bus device due to the line resistance.Thus, the bus participants that detect a smaller drop in the applied initial voltage are located closer to the first bus participant than those bus participants that detect a more significant drop in the applied initial voltage.

[0015] In particular, the invention can provide for the measurement to be initiated by a master unit. In the method according to the invention, it can therefore be provided for the first bus participant to be configured as the master unit. The master unit can be designed to initiate a series of measurements and to receive and subsequently evaluate the measurement data determined by the individual slave units. It can also be provided that all measurement voltages determined by the bus participants are communicated to the master unit, so that position determination takes place centrally in the master unit, which evaluates the voltage values ​​received from the other bus participants (predominantly or exclusively slave units).

[0016] For example, the method according to the invention can provide for the measurement to be initiated by a master unit, and for all other bus participants to be configured as slave units, each of which is configured to detect a measurement voltage and transmit a corresponding voltage value to the master unit. As explained below, some embodiments of the method according to the invention can provide for multiple master units, which are optionally also configured to detect a measurement voltage and transmit it to a master unit.

[0017] The bus participants can be, in particular, sensors, actuators, control units (also referred to as electronic control units or ECUs), or microcontrollers. In some embodiments of the method according to the invention, it can be provided that only the bus participants designed as slave units are configured to detect a measurement voltage. In further embodiments of the invention, however, it can be provided that, in addition to the slave units, one or more master units are configured to detect a measurement voltage. Accordingly, it can be provided that each bus participant is configured to detect a measurement voltage.

[0018] By carrying out two series of measurements, the present invention makes it possible to gradually determine information on the position of the individual bus participants in order to subsequently evaluate the determined information and create a map of the topology of the bus system.

[0019] The method according to the invention is based on a two-wire bus system. A two-wire bus system is generally designed such that both wires or both lines are configured to transmit a signal that differs from a (constant) reference signal. In contrast, with single-ended signal transmission, a signal is transmitted over only one line.

[0020] In some embodiments of the method according to the invention, it can be provided that the bus subscriber which is the greatest distance from the first bus subscriber is determined during the first series of measurements, wherein the bus subscriber at whose connection points the lowest measurement voltage is determined during the first series of measurements is assumed to be the bus subscriber with the greatest distance from the first bus subscriber, wherein this bus subscriber with the greatest distance from the first bus subscriber is selected as the second bus subscriber at whose connection points the initial voltage is applied during the second series of measurements. In this way, the bus subscriber which is furthest away from the first bus subscriber (also referred to as the first outer bus subscriber) can be determined. It can then be provided that an initial voltage is provided to the first outer bus subscriber during the second series of measurements.Subsequently, the bus device that is the greatest distance from the first outer bus device can be identified. This is the bus device that detects the lowest measurement voltage during the second series of measurements. This allows the outer bus devices to be clearly identified and the position of all bus devices located between the outer bus devices to be determined.

[0021] In addition, in some embodiments of the method according to the invention, it can be provided that during the second series of measurements the bus participant is determined which has the shortest distance to the second bus participant, wherein the bus participant at whose connection points the highest measurement voltage is determined during the second series of measurements is assumed to be the bus participant with the shortest distance to the second bus participant, wherein this bus participant with the shortest distance to the second bus participant is selected as the third bus participant, at whose connection points an initial voltage is applied during a third series of measurements.In this way, a total of m series of measurements can be carried out, with the bus participant with the lowest voltage and the bus participant with the highest voltage being determined alternately in each series of measurements, and the initial voltage being provided to the previously determined bus participant in the next series of measurements. Bus participants for which the lowest voltage has already been determined once are preferably ignored for the subsequent series of measurements. The series of measurements can be carried out until the positions of all bus participants in the bus system have been determined. For example, the measurement can be ended when a bus participant has the highest voltage twice in a row. The termination, i.e. the star point of a topology, is then located between this bus participant and its neighbor.The method described above enables a simple and incremental determination of the topology of a bus system. In the method according to the invention, it can be provided that the first bus participant and the second bus participant each have an identifier, and that the selection of the first bus participant for the first series of measurements and the selection of the second bus participant for the second series of measurements takes place depending on the identifiers. In particular, it can be provided that each identifier has a numeric or alphanumeric value that is designed to uniquely identify the bus participants. In particular, it can be provided that the individual bus participants are considered in sequence. The individual bus participants can, for example, be selected for the successive series of measurements in ascending or descending order depending on their identifier.In particular, the identifier can be implemented as a unique device identifier (also known as a Unique Device Identifier or UDIN).

[0022] Different implementation variants can be used within the framework of the method according to the invention. For example, the order of the bus participants can be determined by arbitration within the bus system. According to one implementation variant, all bus participants can send their UDIN, and the bus participant with the dominant voltage level prevails as the participant with the highest priority. The arbitration can then be repeated in the subsequent measurement series, whereby bus participants that have won a previous arbitration do not participate in the current arbitration again. In this way, the bus participants can be taken into account without a bus participant repeatedly participating actively in a measurement series and without generating redundant measurement results.

[0023] Furthermore, the method according to the invention can provide for the measurement series to be performed frequently enough until each bus participant has participated in a measurement series in which an initial voltage was applied to its connection points. In other words, in this embodiment of the invention, each bus participant actively participates in a measurement series exactly once. This ensures that each bus participant has actively participated in a measurement series and that all bus participants have been taken into account. This allows for the most complete reconstruction of the bus system topology possible. A local map of the bus system can then be created.

[0024] Furthermore, it can be provided that after each series of measurements the measured values ​​(i.e. the measured voltages) are transmitted to the master unit so that a map with the position of the individual bus participants can be created centrally by the master unit.

[0025] According to some embodiments of the method according to the invention, it can be provided that the bus system has a star-shaped topology, with at least one star node and at least two branches of different lengths which are adjacent to the star node, wherein during the first series of measurements the position of the bus participants within the longest branch is determined by identifying the longest branch of the bus system by evaluating the measurement voltages determined at the individual bus participants and the branch which has the bus participant with the lowest measured voltage is recognized as the longest branch;and the measurement voltages determined by the individual bus participants of the longest branch during the first series of measurements are evaluated, whereby those bus participants for which a higher voltage is measured have a shorter distance to the first bus participant and those bus participants for which a lower voltage is measured have a greater distance to the first bus participant.;

[0026] In this case, the bus participant that is arranged in the star node can preferably be selected as the first bus participant. During the first series of measurements, the longest branch of the bus system is identified, and the measured voltages are used to determine the position of all bus participants in the longest branch. As already explained above, it is not possible, or only possible to a limited extent, to clearly identify the position of the individual bus participants in a bus system with a star topology using conventional methods. The proposed embodiment makes it possible to determine the position of the individual bus participants within a first branch or a first strand during the first series of measurements. The other branches or strands of the bus system can then be evaluated until the entire bus system has been analyzed. This enables a particularly efficient analysis of the bus system orthe position of the individual bus participants is guaranteed.

[0027] Preferably, in the method according to the invention, it can be provided that during the second series of measurements the positions of the bus participants within the second longest branch are determined by again providing an initial voltage to the first bus participant, wherein at least at all bus participants designed as slave units that are different from the first bus participant, with the exception of the bus participants within the longest branch, a measurement voltage recorded at these bus participants is determined; the second longest branch of the bus system is identified by evaluating the measurement voltages recorded at the individual bus participants and the branch that has the bus participant with the lowest measured voltage is recognized as the second longest branch;and the measurement voltages determined by the individual bus participants of the second longest branch during the second series of measurements are evaluated, whereby those bus participants for which a higher voltage is measured have a shorter distance to the first bus participant and those bus participants for which a lower voltage is measured have a greater distance to the first bus participant.;

[0028] In this way, the topology of the bus system can be determined particularly efficiently, since each measurement series allows a branch of the bus system with a star topology to be fully evaluated. Therefore, only n measurement series are required to evaluate the entire topology of the bus system, where n denotes the number of branches or strands of the bus system with a star topology.

[0029] In this embodiment of the method according to the invention, the first bus participant can preferably be embodied as a master unit. For example, it can be provided that the master unit has rough information about the topology of the bus system. For example, the master unit can know that the bus system to be analyzed has a star-shaped topology with a total of n branches or strands. Accordingly, the master unit can perform n series of measurements until the position of all bus participants has been determined.

[0030] The method according to the invention can further provide for the measurement series to be repeated until the position of all bus participants within the bus system has been determined. With each measurement series, additional measurement data is provided, which can be used to supplement the information on the positions of the individual bus participants until a complete map of the bus system to be analyzed can be created.

[0031] In addition, the method according to the invention can provide for the bus system to have one or more bus participants configured as a master unit, wherein a measurement voltage present at the bus participant configured as a master unit or at the bus participants configured as master units is additionally detected. In this way, additional measurement data can be provided by the master unit(s). Preferably, it can be provided that all bus participants (i.e., all slave units and all master units) are designed to detect measurement voltages. In this case, the provided master units therefore have a dual function in that they can, on the one hand, initiate a series of measurements and, on the other hand, also actively provide measurement data.Due to their functionality, the master units according to this embodiment of the method according to the invention are also referred to as smart master units or intelligent master units. The use of smart master units can provide additional information, the evaluation of which can simplify the positioning of individual bus devices in the bus system being analyzed. This makes it possible to evaluate even particularly complex topologies.

[0032] According to some advantageous embodiments of the method according to the invention, it can be provided that at least one master unit is arranged in a node of a bus system with a star-shaped topology.

[0033] Furthermore, to achieve the object described above, a differential two-wire bus system is proposed, which is designed in particular as a CAN bus system, wherein the differential two-wire bus system has a plurality of bus subscribers; wherein each bus subscriber is designed as a master unit or as a slave unit, each bus subscriber is connected to at least one adjacent bus subscriber via a two-wire connection, and each bus subscriber is arranged between a connection point of a first line and a connection point of a second line of the two-wire connection, and wherein each bus subscriber designed as a master unit has a voltage generator designed to provide an initial voltage at its connection points;each bus participant, which is designed as a slave unit, has a voltage generator which is designed to provide an initial voltage at its connection points, as well as a voltage measuring device which is designed to detect a voltage at the connection points;at least one bus subscriber, configured as a master unit, has an evaluation unit configured to evaluate the detected voltage values ​​and to determine the position of the individual bus subscribers as a function of the detected voltage values. The differential two-wire bus system according to the invention can, in particular, be configured to carry out a first series of measurements, in which an initial voltage is provided between the connection points of a first bus subscriber at a first bus subscriber, and in which a measurement voltage detected at each of the bus subscribers configured as slave units, which are different from the first bus subscriber, is determined;to carry out a second series of measurements in which an initial voltage is provided between the connection points of a second bus participant that is different from the first bus participant, and in which a measurement voltage recorded at each of several bus participants that are different from the second bus participant is determined; to determine the position of the individual bus participants on the basis of the initial voltages provided during the first and second series of measurements and the measurement voltages recorded at the bus participants, whereby the difference between the initial voltages provided and the respective measurement voltages recorded is evaluated as a measure of the distance between the individual bus participants during the respective series of measurements;

[0034] The differential two-wire bus system can, in particular, have a terminating resistor that is optionally arranged at a star point of a bus system with a star topology or at the end points of individual branches of the bus system. After an initial voltage is applied to the connection points of a first bus participant, the voltages generated at the connection points of the other bus participants can be measured. By impressing the initial voltage and evaluating the recorded measurement voltages, the position of the individual bus participants can be determined. The provided initial voltage drops gradually from the first bus participant to the bus participant that is furthest away from the first bus participant. The voltage drop is caused by the resistors that exist between the first bus participant and the other bus participants.In particular, the line resistances of the two lines contribute to the aforementioned voltage drop. As will be explained below, resistance components can also be inserted in addition to the line resistances in order to increase the voltage drop and thereby enable simplified detection of the voltage drop. In the two-wire bus system according to the invention, it can be provided that all bus participants designed as slave units are designed to record a measurement voltage during a series of measurements. In some embodiments of the two-wire bus system according to the invention, it can also be provided that at least one bus participant designed as a master unit is also designed to record a measurement voltage during a series of measurements (so-called smart master unit).

[0035] According to some embodiments of the two-wire bus system according to the invention, the bus system can have a star-shaped topology, with at least one star node and at least two branches or strands adjacent to the star node, wherein each branch or strand has at least one bus node and a master unit is arranged in at least one star node. Furthermore, a terminating resistor can also be arranged in the star node.

[0036] According to some advantageous embodiments of the two-wire bus system according to the invention, at least one resistor, but preferably several resistors, can be arranged along one of the two lines. The resistors, which are also referred to below as (dedicated) resistor components (as opposed to the line resistances inherent in every two-wire bus system), contribute to the more pronounced voltage drops from one bus device to the neighboring bus device, making them easier to detect.The use of resistive components is particularly advantageous when the line resistances are relatively low (for example, when the line sections between the individual bus devices are relatively short) and, consequently, the voltage drops between the individual bus devices are relatively small, making it difficult to distinguish between the different positions of the individual bus devices. In other words, the deliberately introduced resistive components help ensure that the sensor units intended for detecting the measurement voltages do not require excessive precision. This allows the costs of the differential two-wire bus system according to the invention to be reduced.

[0037] Furthermore, in some embodiments of the two-wire bus system according to the invention, it can be provided that the resistance components have at least two different resistance values. In particular, it can be provided that a first resistance component in a first branch has a first resistance value and a second resistance component in a second branch has a second resistance value that is different from the first resistance value. In particular, the first resistance component and the second resistance component can be directly adjacent to a master unit. This ensures that the voltage drops in the first branch and the second branch occur differently. The asymmetric voltage drop induced in this way makes it easier to determine the topology of a bus system.

[0038] The present invention will be explained in more detail below with reference to the figures.

[0039] Fig. 1 shows a two-wire bus system according to the prior art,

[0040] Fig. 2 shows an embodiment of the method for determining the position of bus participants in a differential two-wire bus system according to the present invention,

[0041] Fig. 3 shows a first two-wire bus system that can be analyzed using the method according to the invention,

[0042] Fig. 4 shows a second two-wire bus system which can be analyzed using the method according to the invention, Fig. 5 shows a third two-wire bus system which can be analyzed using the method according to the invention,

[0043] Fig. 6 shows a fourth two-wire bus system that can be analyzed using the method according to the invention, and

[0044] Fig. 7 shows a fifth two-wire bus system that can be analyzed using the method according to the invention.

[0045] Fig. 1 shows a schematic representation of a two-wire bus system 10 according to the prior art. The two-wire bus system 10 shown in this figure includes a plurality of bus devices 12, which are labeled M and A to F. The bus device labeled M is designed as a master unit 14, while the bus devices 12 labeled A to F are designed as slave units 16. The master unit 14 is designed to initiate a position measurement and evaluate the measurement results. The slave units 16, on the other hand, are generally not designed to initiate a measurement or evaluate the measurement results. The individual bus devices 12 are arranged between a first line 18 and a second line 20, each between two connection points 24. The individual connection points 24 of a line 18, 20 are connected to one another by line sections 22.In the methods known from the prior art, it can be provided, for example, that the master unit 14 sends out a signal that is transmitted from the master unit 14 to the individual slave units 16 and then transmitted back to the master unit 14 by these slave units 16. By measuring the propagation time of a signal that propagates from the master unit 14 to a slave unit 16 and back to the master unit 14, the distance between the corresponding slave unit 16 and the master unit 14 and thus also the position of the corresponding slave unit 16 within the two-wire bus system 10 can be determined. However, this method is associated with several disadvantages. On the one hand, the approach described above does not provide reliable and unambiguous results in the case of complex topologies.On the other hand, the described method requires very precise sensors capable of resolving very short time intervals. However, such sensors are quite expensive. Therefore, it is desirable to provide a method for determining the position of bus devices in a two-wire bus system that is capable of analyzing complex topologies and is also cost-effective to implement.

[0046] An exemplary embodiment of the method 100 according to the invention is schematically illustrated in Fig. 2. In the method 100 according to the invention, a first series of measurements is carried out in a first method step 110, in which an initial voltage is provided between the connection points of a first bus participant, and in which a measurement voltage detected at each of at least all bus participants configured as slave units that are different from the first bus participant is determined.Subsequently, in a second method step 120, a second series of measurements is performed, in which an initial voltage is provided between the connection points of a second bus device, which is different from the first bus device, and in which a measurement voltage is determined at each of several bus devices, which are different from the second bus device. This provides measurement data that enables the position of the individual bus devices to be determined.Subsequently, in a third method step 130, the position of the individual bus devices in the two-wire bus system is determined based on the initial voltages provided during the first and second measurement series and the measured voltages determined at the bus devices. The difference between the provided initial voltages and the respectively determined measured voltages is evaluated as a measure of the distance between the individual bus devices during the respective measurement series. This eliminates the need to perform a time-of-flight measurement, which would require expensive sensors due to the high precision requirements. Instead, voltage sensors are used, which can be provided inexpensively.In the method according to the invention, it can preferably be provided that the first bus participant is designed as a master unit, which on the one hand is designed to initiate the series of measurements and is also set up to evaluate the measurement data provided by the individual slave units.

[0047] Fig. 3 schematically shows a first embodiment of a two-wire bus system 10 that can be analyzed using the method according to the invention. The two-wire bus system is designed as a differential two-wire bus system and has a plurality of bus participants 12, which are designated by the letters A to G and M in Fig. 3. The bus participant 12 designated by the letter M is embodied as a master unit 14, while the bus participants 12 designated by the letters A to G are embodied as slave units 16. All bus participants 12 are arranged between a first line 18 and a second line 20, with each bus participant being positioned between a connection point 24 of the first line 18 and a connection point 24 of the second line 20. The connection points 24 of a line 18, 20 are each connected to one another by line sections 22.During a first series of measurements, an initial voltage can be provided at the connection points 24 of the master unit 14. The initial voltage can be 3 V, for example. A measurement voltage can then be recorded at the connection points 24 of the slave units 16 (A to G). Due to the line resistances of the individual line sections 22, a voltage drop occurs from the connection points of the master unit 14 to the connection points 24 of the neighboring slave units 16. For example, a measurement voltage of 2.9 V can be recorded at slave units C and D, while a measurement voltage of 2.8 V is recorded at slave units B and E, a measurement voltage of 2.7 V is recorded at slave units A and F, and a measurement voltage of 2.6 V is determined at slave unit G.As can be seen from the example described above, a single series of measurements is not sufficient in this case to clearly determine the position of all bus participants 12. Therefore, for example, during the first series of measurements it can be determined that the slave unit G, for which the lowest voltage was measured during the first series of measurements, is the furthest away from the master unit M. Subsequently, during a second series of measurements, the slave unit G can be selected as the second bus participant 12, so that an initial voltage is applied to the slave unit G during the second series of measurements. During the second series of measurements, the bus participants 12 implemented as slave units 16 can determine a measurement voltage that allows the position of all bus participants 12 to be clearly determined.

[0048] Fig. 4 shows a further embodiment of a two-wire bus system 10 according to the present invention. In this embodiment, the two-wire bus system 10 has a plurality of resistors 26, each arranged between adjacent connection points 24 of the first line 18. The resistors 26 introduced into the two-wire bus system 10 in this embodiment result in a larger voltage drop from one connection point 24 to an adjacent connection point 24. This is particularly advantageous when the line sections 22 within the two-wire bus system 10 are relatively short and the voltage drop achieved without the resistors 26 is too small to be detected by conventional voltage sensors.If, for example, the available voltage sensors have a resolution of 0.1 V, but the voltage drop caused by a power section is only 0.01 V, the use of resistors 26 can help to enable the voltage-based differentiation of the position of the different bus devices 12 within the two-wire bus system. The resistors 26 can, for example, be dimensioned such that a voltage drop of 0.1 V occurs from the master unit 14 to the adjacent slave units 16, so that, for example, an initial voltage of 3.0 V can be provided at the master unit and a voltage of 2.7 V is established at bus device A and a voltage of 2.6 V at bus device G. In some embodiments of the invention, it can also be provided that the resistors used have at least two different resistance values.For example, a first resistor 26 with a first resistance value can be arranged between a connection node 24 of the master unit M and a connection node of the bus subscriber C, while a second resistor 26 with a second resistance value is provided between a connection node 24 of the master unit M and the bus subscriber D, wherein the second resistance value is different from the first resistance value. In this way, an asymmetrical voltage drop is achieved in the different branches of the two-wire bus system 10. The resistors can, for example, be dimensioned such that the first resistor causes a voltage drop of 0.1 V and the second resistor causes a voltage drop of 0.15 V.In this way, it can be achieved that when an initial voltage of 3.0 V is provided at the master unit M, voltages of 2.9 V, 2.8 V and 2.7 V are set at the bus participants C, B, A, while voltages of 2.85 V, 2.75 V, 2.65 and 2.55 V are set at the bus participants D, E, F, G. This asymmetrical voltage drop makes it possible to clearly determine the position of the individual bus participants 12 (provided the voltage sensors have a sufficiently high resolution).

[0049] Fig. 5 schematically shows a further embodiment of a two-wire bus system 10 according to the present invention. The two-wire bus system 10 shown in Fig. 5 has a star-shaped topology with a star node 28 and three branches 30, 32, 34 adjacent to the star node 28. A bus subscriber, which is designed as a master unit 14, is arranged in the star node 28. The first branch 30 has three bus subscribers (A, B, C), while the second branch 32 has four bus subscribers (D, E, F, G), and the third branch 34 has two bus subscribers (H, I). Various of the approaches described above can be used to determine the position of the individual bus subscribers. For example, the branch 30, 32, 34 with the most bus subscribers can be determined during a first series of measurements.For this purpose, an initial voltage of, for example, 3.0 V can be provided at the connection points of the master unit 14. A measurement voltage is then recorded at each of the connection points of bus devices A to I. Assuming that the voltage drop across the individual line sections is identical (constant length of the line sections and identical line properties) and is, for example, 0.1 V, a voltage drop of 0.3 V can be measured at bus device A, a voltage drop of 0.2 V at bus device I, and a voltage drop of 0.4 V at bus device G. From this, it can be concluded that the second branch 32 represents the longest branch within the star-shaped bus system 10.Subsequently, within the first series of measurements, all bus devices on the second branch 32 can be analyzed so that the position of bus devices D to G is determined and, if necessary, they can be assigned a unique address. Subsequently, within a second series of measurements, an initial voltage is again provided at the connection points of the master unit 14. Only the bus devices on the first branch 30 (A to C) and the bus devices on the third branch 34 (H and I) participate in the second series of measurements. The branch with the most bus devices is again determined. The longest branch (of the remaining branches) is determined in a similar way to the first series of measurements, although the bus devices on the second branch 32 do not participate in this series of measurements. The second series of measurements determines that the first branch 30 has more bus devices than the third branch 34.Subsequently, the position of the individual bus devices in the first branch 30 is determined. Finally, in a third series of measurements, the positions of the bus devices in the third branch 34 are determined. This enables a particularly efficient determination of the position of the individual bus devices in a bus system 10, with only three series of measurements being required to unambiguously determine the position of all bus devices in the bus system 10 with a star topology.

[0050] Fig. 6 schematically shows another embodiment of a two-wire bus system 10 with a star topology. Different approaches to determining the position of the individual bus participants described above are also suitable for analyzing this bus system 10. For example, as many measurement series as are required until an initial voltage has been applied to each bus participant and all other bus participants (at least the bus participants designed as slave units) record a measurement voltage. In this case, the number of measurement series performed is identical to the number of bus participants. In the embodiment shown in Fig. 6, a total of 14 measurement series can be performed, with the recorded measurement data (i.e., the measurement voltages) preferably being transmitted to the master unit 14, which evaluates the measurement data, after each measurement series.The master unit 14 can then determine the position of the individual bus devices within the bus system 10 based on the determined distance relationships and the determined neighborhood relationships. For example, the individual bus devices can each have a unique identifier, whereby the order of the bus devices selected for the individual measurement series can be determined according to an (ascending or descending) order of the identifiers. Optionally, it can be provided that not 14 measurement series are necessarily performed, but that the measurement series are terminated as soon as sufficient information is available to determine the position of the individual bus devices.

[0051] Fig. 7 schematically shows a further embodiment of the two-wire bus system 10 according to the invention. In this embodiment, the bus system 10 also has a star-shaped topology, wherein the bus system 10 has two star nodes 28 in which a master unit 14 is arranged. Furthermore, in the embodiment shown in Fig. 7, the master units 14, in addition to the slave units, are designed to measure voltages at their connection points. This makes it possible to provide additional information that can be evaluated when determining the position of the individual bus participants. The additional information provided can further simplify the analysis of a bus system 10, so that fewer series of measurements are required overall.

[0052] LIST OF REFERENCE SYMBOLS

[0053] Two-wire bus system Bus participant Master unit

[0054] Slave unit first line second line line section connection point resistance

[0055] Star node first branch second branch third branch inventive method first method step second method step third method step

Claims

CLAIMS 1. A method (100) for determining the position of a plurality of bus subscribers (12) in a differential two-wire bus system (10), in particular in a CAN bus system; wherein each bus subscriber (12) is designed as a master unit (14) or as a slave unit (16), each bus subscriber (12) is connected to at least one adjacent bus subscriber (12) via a two-wire connection, each bus subscriber (12) is arranged between a connection point (24) of a first line (18) and a connection point (24) of the second line (20) of the two-wire connection, and the method (100) comprises the following method steps: Carrying out (110) a first series of measurements, in which an initial voltage is provided between the connection points (24) of a first bus subscriber at a first bus subscriber, and in which a measurement voltage detected at each of the bus subscribers is determined at least at all of the bus subscribers designed as slave units (16) which are different from the first bus subscriber; Carrying out (120) a second series of measurements, in which an initial voltage is provided between the connection points (24) of a second bus subscriber at a second bus subscriber, and in which a measurement voltage detected at each of a plurality of bus subscribers that are different from the second bus subscriber is determined; Determining (130) the position of the individual bus participants (12) on the basis of the initial voltages provided during the first series of measurements and the second series of measurements and the measurement voltages determined at the bus participants (12), wherein the difference between the initial voltages provided and the respective measurement voltages determined is evaluated as a measure of the distance between the individual bus participants (12) during the respective series of measurements.

2. Method (100) according to claim 1, characterized in that during the first series of measurements the bus subscriber is determined which has the greatest distance to the first bus subscriber, wherein the bus subscriber at whose connection points (24) the lowest measurement voltage is determined during the first series of measurements is assumed to be the bus subscriber with the greatest distance to the first bus subscriber, wherein this bus subscriber with the greatest distance to the first bus subscriber is selected as the second bus subscriber at whose connection points (24) the initial voltage is applied during the second series of measurements.

3. Method (100) according to claim 2, characterized in that during the second series of measurements the bus subscriber is determined which has the shortest distance to the second bus subscriber, wherein the bus subscriber at whose connection points (24) the highest measurement voltage is determined during the second series of measurements is assumed to be the bus subscriber with the shortest distance to the second bus subscriber, wherein this bus subscriber with the shortest distance to the second bus subscriber is selected as the third bus subscriber at whose connection points (24) an initial voltage is applied during a third series of measurements.

4. Method (100) according to claim 1, characterized in that the first bus subscriber and the second bus subscriber each have an identifier, and that the selection of the first bus subscriber for the first series of measurements and the selection of the second bus subscriber for the second series of measurements takes place as a function of the identifiers.

5. Method (100) according to claim 4, characterized in that the series of measurements are carried out so frequently until each bus participant (12) has participated in a series of measurements in which an initial voltage was applied to its connection points (24).

6. The method (100) according to claim 1, characterized in that the bus system (10) has a star-shaped topology, with at least one star node (28) and at least two branches (30, 32, 34) of different lengths which adjoin the star node (28), wherein during the first series of measurements the position of the bus subscribers (12) within the longest branch (30, 32, 34) is determined by identifying the longest branch of the bus system (10) by evaluating the measurement voltages determined at the individual bus subscribers (12) and the branch which has the bus subscriber with the lowest measured voltage is recognized as the longest branch;and the measurement voltages determined by the individual bus subscribers (12) of the longest branch during the first series of measurements are evaluated, wherein those bus subscribers for which a higher voltage is measured have a shorter distance to the first bus subscriber and those bus subscribers for which a lower voltage is measured have a greater distance to the first bus subscriber; 7. The method (100) according to claim 6, characterized in that during the second series of measurements, the positions of the bus participants (12) within the second-longest branch are determined by again providing an initial voltage to the first bus participant, wherein at least at all bus participants configured as slave units (16) that are different from the first bus participant, with the exception of the bus participants within the longest branch, a measurement voltage detected at these bus participants is determined; the second-longest branch of the bus system (10) is identified by evaluating the measurement voltages determined at the individual bus participants (12), and the branch that has the bus participant (12) with the lowest measured measurement voltage is recognized as the second-longest branch; and the measuring voltages which were determined by the individual bus subscribers (12) of the second longest branch are evaluated, wherein those bus subscribers for which a higher voltage is measured have a shorter distance to the first bus subscriber and those bus subscribers for which a lower voltage is measured have a greater distance to the first bus subscriber.

8. Method (100) according to one of claims 1 to 7, characterized in that the first bus participant is designed as a master unit (14).

9. Method (100) according to one of claims 1 to 8, characterized in that the series of measurements are repeated until the position of all bus participants (12) within the bus system (10) has been determined.

10. Method (100) according to one of claims 1 to 9, characterized in that the bus system (10) has one or more bus participants (12) which are designed as a master unit (14), wherein in addition a measuring voltage applied to this bus participant (12) or to these bus participants (12) is detected at the bus participant (12) designed as a master unit (14) or at the bus participants (12) designed as master units (14).

11. Differential two-wire bus system (10) which is designed to carry out the method according to one of claims 1 to 10 and is designed in particular as a CAN bus system, comprising a plurality of bus subscribers (12); wherein each bus subscriber (12) is designed as a master unit (14) or as a slave unit (16), each bus subscriber (12) is connected to at least one adjacent bus subscriber (12) via a two-wire connection, and each bus subscriber (12) is connected between a connection point (24) of a first line (18) and a connection point of a second line (20) of the two-wire connection, and wherein each bus subscriber (12) designed as a master unit (14) has a voltage generator designed to provide an initial voltage at its connection points (24); each bus subscriber (12) designed as a slave unit (16) has a voltage generator designed to provide an initial voltage at its connection points (24), as well as a voltage measuring device designed to detect a voltage at the connection points (24); at least one bus subscriber (12) designed as a master unit (14) has an evaluation unit designed to evaluate the detected voltage values ​​and to determine the position of the individual bus subscribers (12) depending on the detected voltage values.

12. Differential two-wire bus system (10) according to claim 11, characterized in that the bus system (10) has a star-shaped topology, with at least one star node (28) and at least two branches (30, 32, 34) which are adjacent to the star node (28), wherein each branch (30, 32, 34) has at least one bus subscriber (12) and a master unit (14) is arranged in at least one star node (28).

13. Differential two-wire bus system (10) according to claim 11 or 12, characterized in that several resistors are arranged along a line (18, 20).

14. Differential two-wire bus system (10) according to claim 13, characterized in that the resistors (26) have at least two different resistance values.

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