Control unit circuit for a motor vehicle, motor vehicle and method for operating a control unit circuit

Abstract

The invention relates to a control unit circuit (22) for a motor vehicle (10), wherein the control unit circuit (22) comprises a control unit (12) and an electrical energy storage device (14) for emergency power supply outside the housing of the control unit (12). It is provided that, in order to form a circuit (22') for emergency power supply, both poles (P+, P-) of the energy storage device (14) are connected to the control unit (12) via a cable (19) and one of the two poles (P+, P-) is connected to a ground potential (17) of a vehicle electrical system (11) via a switching element (24) and at least one measuring circuit (27) couples each of the poles (P+, P-) to the ground potential (17) and is set to generate a voltage-dependent measurement signal (32). In the event that the respective measurement signal (32) indicates that the respective voltage is greater than a predetermined threshold value, the switching element (24) is switched to a non-conductive state.

Description

Technical Field

[0001] This invention relates to a circuit in which a control unit and an energy storage device are interconnected for emergency power supply to the control unit. This circuit is referred to herein as a control unit circuit. The invention also includes a motor vehicle equipped with the control unit circuit and a method for operating the control unit circuit. Background Technology

[0002] To ensure that control units in a motor vehicle remain operational even after an accident (collision) and a failure of the vehicle's onboard electrical system, an additional energy supply can be provided through an energy storage device. An example of such a control unit is a so-called electronic call module, used for emergency calls after a collision. If the connection to the positive line of the onboard electrical system (so-called terminal 30 line, KL30) is interrupted, this electronic call service is continuously supplied via a backup battery. A suitable backup battery can be implemented using a lithium-ion battery.

[0003] For space reasons, it can be stipulated here that a backup battery or general energy storage device is located outside the control unit and connected to the control unit via a cable. However, this presents the possibility that if the cable is damaged, one of its power supply lines or wires will come into electrical contact with the vehicle's electrical system, i.e., short-circuit with the positive terminal of the vehicle's electrical system or ground potential. While the vehicle's electrical system typically has a rated voltage of 12 volts, the energy storage device used for emergency power supply to the control unit operates at a rated voltage of less than 12 volts (e.g., 4 volts). In this case, the negative terminal of the energy storage device remains electrically connected to the vehicle's ground potential to prevent phase drift between the two circuits. For example, if the cable of the energy storage device is damaged and its positive terminal comes into contact with the positive terminal of the vehicle's electrical system, the vehicle's electrical system voltage (i.e., 12 volts) is also applied to the energy storage device, which could damage the energy storage device due to overvoltage or excessive charging current, such as overheating and / or degassing. However, in general, the reaction is unpredictable. Thus, the operation of the control unit after a collision is no longer guaranteed.

[0004] For example, a control unit circuit is known from DE 196 33 202C1, which includes a control unit and an energy storage device for emergency power supply. In the event of insufficient voltage, the emergency operation circuit switches the control unit from the vehicle's onboard electrical system to the energy storage device. Summary of the Invention

[0005] The purpose of this invention is to prevent the control unit in the control unit circuit from operating even if the electrical connection between one pole of the emergency power supply energy storage device and the live components of the vehicle's onboard electrical system is damaged due to overvoltage and / or excessive charging current. The control unit circuit has a control unit and an associated emergency power supply connected via a cable.

[0006] This objective is achieved by a control unit circuit for a motor vehicle, a motor vehicle, and a method for operating the control unit circuit. Advantageous embodiments of the invention are described by way of other examples, the following description, and the accompanying drawings.

[0007] This invention provides a control unit circuit for a motor vehicle. In this context, "control unit circuit" refers to the combination of a control unit for providing vehicle functions and an energy storage device disposed outside the housing of the control unit for emergency power supply to the control unit. An example of vehicle functions that can be provided by the control unit is the already described electronic call function. The energy storage device can be an electric or electrochemical battery, such as a lithium-ion battery. This energy storage device differs from the energy storage device of the motor vehicle's onboard electrical system and, in particular, can provide a rated voltage lower than, especially less than half the rated voltage of, the onboard electrical system. This invention is based on the assumption that the energy storage device for emergency power supply is configured to supply electrical energy to the control unit in the absence of a power supply current from the motor vehicle's onboard electrical system. The switching from the power supply current of the onboard electrical system to the energy storage device can be performed in a manner known in the prior art.

[0008] To allow the energy storage device to be installed at a distance from the control unit within a motor vehicle, the two poles (positive and negative) of the energy storage device are connected to the control unit via cables. The cables can provide a power supply line or wire for each pole for electrical connection. Each power supply line can be implemented using stranded wire or Litz wire.

[0009] To prevent potential drift between an emergency power supply circuit (with an energy storage device) and the vehicle's onboard electrical system, one of these two poles is connected to the ground potential of the onboard electrical system via a switching element. This pole is preferably the negative pole. In this case, the switching element can be located in the control unit, the energy storage device, or on the cable. This is because it may be sufficient if one pole of the energy storage device is "indirectly" connected to the ground potential of the control unit via a cable. Another name for the ground potential of the onboard electrical system is "vehicle ground," which can be provided, for example, in the vehicle panel, vehicle bracket, or chassis. The ground potential is typically provided in the vehicle through structural components. Because electrical connections to both poles of the energy storage device exist in the control unit, in the cable, and on the energy storage device itself, the switching element can be located at one of these locations. For example, a semiconductor switch (e.g., a transistor) can be provided as the switching element.

[0010] In the control unit circuit according to the invention, at least one measuring circuit is provided that couples each pole (positive or negative) of the energy storage device to ground potential and is configured to generate a measuring signal that is related to or depends on the voltage drop between the respective pole of the energy storage device and the ground potential. Therefore, such a measuring circuit can be used to measure which voltage exists between the respective pole and the ground potential, or, if only a threshold comparison is performed, whether the voltage is greater than or less than a predetermined threshold. Thus, the measuring signal only needs to be related to the voltage within a range indicating whether the voltage is greater than or less than a threshold. However, the measuring signal can also be voltage-matched or represent a scaled variant of the voltage, for example, by a voltage divider. Like switching elements, the measuring circuit can be connected to the pole in the control unit, on a cable, or directly on the energy storage device.

[0011] The control circuit for the switching element (which connects one pole of the energy storage device to the ground potential of the vehicle electrical system) is configured to: maintain the switching element in a conductive state during normal operation of the control unit (when a power supply current is available from the vehicle electrical system); and switch the switching element to a non-conductive state at least if a corresponding measurement signal from at least one measuring circuit indicates that the corresponding voltage (between the pole and the ground potential monitored by the measuring circuit) is greater than a predetermined threshold, thereby suppressing or interrupting the coupling between the cable and the ground potential caused by the electrical switching element. Therefore, the potential of this previously coupled pole and the ground potential are now decoupled or separated.

[0012] If a short circuit occurs between one pole of the vehicle electrical system and the energy storage device (e.g., due to a bent and contacting pin on the relevant cable connector, or a worn-out cable insulation), this pole is led to the potential of the vehicle electrical system line, in the case of the positive pole of the vehicle electrical system, for example, to 12 volts or normally to the vehicle electrical system voltage. Typically, it is necessary to protect the energy storage device from fault currents that could overload it and cause the described undesirable reactions. However, the measuring circuit for this pole can then detect a change in voltage between this pole and the vehicle electrical system's ground potential. If the voltage exceeds the threshold, another electrical coupling between the ground potential and the cable (specifically caused by a switching element) is interrupted or suppressed. This leaves only one short-circuit location as the sole electrical connection between the emergency power supply circuit on one side and the vehicle electrical system on the other. The circuit is then raised to the potential of the vehicle electrical system, where no current can flow because the second electrical coupling via the switching element is interrupted. However, this allows the emergency power supply circuit to continue operating, even if, for example, a plug failure or damage to the electrical insulation of the cable causes electrical contact between one pole of the energy storage device and the positive wire of the vehicle's electrical system.

[0013] The present invention also covers embodiments that provide additional advantages.

[0014] In one embodiment, the control circuit has a signal input for receiving a switching signal and is configured to switch the switching element to a non-conductive state according to the switching signal. In addition to the at least one measuring circuit, the signal input can also be used to cause the control circuit to switch the switching element to a non-conductive state. Therefore, for example, a microcontroller can be used to control the coupling between the cable and ground potential caused by the switching element. The signal input can be implemented as an electrical contact or a pin.

[0015] In one embodiment, this connection specifies that the control unit is configured to execute a test procedure for checking the insulation resistance of the cable, and to generate a switching signal at the control input of the control circuit at the start of the test procedure. Therefore, the test procedure can be executed even if the electrical coupling between the cable and ground potential is interrupted. This has the advantage that the test routine can include detecting ground fault current. This can only be detected if the electrical coupling caused by the switching element is suppressed. If current still flows (e.g., via an insulation fault), this can be detected as a fault current because of the difference in current intensity between the cable's power supply lines. By measuring the current intensity in the two power supply lines of the cable at the poles of the energy storage device, an insulation fault or insulation resistance in the cable can be detected if the difference in current intensity is greater than a threshold. The control unit can now control the electrical coupling of the test procedure, caused by the switching element, via the signal input. Alternatively, a load test can be performed on the energy storage device, wherein a predetermined load resistor is connected to the energy storage device to generate current flow.

[0016] In one embodiment, during the load test, the current of the energy storage device is routed via a load resistor connected between the poles of the energy storage device, and during this process, the switching element remains in the non-conductive state by the switching signal, and since one of these poles or one of these power lines is connected to the charging circuit of the control unit circuit, the corresponding voltages of the two poles of the energy storage device (14) relative to the ground potential of the cable are set to positive values. Then, advantageously, the voltage between these poles can also be measured using the voltage measurement input of a microcontroller that can only measure positive voltages (e.g., using an analog-to-digital converter). In this case, the microcontroller can use the ground potential as ground.

[0017] In one embodiment, each measurement circuit includes a series circuit consisting of a Zener diode and a resistive element. The respective terminals are connected to ground potential via said series circuit. Current flows through this series connection only when the breakdown voltage of the Zener diode is exceeded. The breakdown voltage of the Zener diode thus defines the threshold voltage that must be exceeded between the terminal and ground potential for the control circuit to switch the switching element to a non-conductive state. The described series circuit consisting of a Zener diode and a resistive element has proven particularly advantageous in terms of response time when switching the switching element.

[0018] In one embodiment, a Zener diode is positioned on the electrode side of a series circuit (i.e., towards the energy storage device) and a resistive element is positioned on the ground potential side of the series circuit (i.e., towards ground potential). Therefore, when the voltage between the electrode and ground potential is below a threshold, the electrical connection point between the Zener diode and the resistive element has a ground potential. If the Zener diode subsequently breaks down due to a voltage exceeding the threshold, the voltage at the connection point also increases. Therefore, a tap at the connection point can be used to generate a switching signal.

[0019] In one embodiment, each measuring circuit (connected to each pole) has a resistance greater than 1 kΩ, particularly greater than 5 kΩ, between its respective pole and ground potential. This has the advantage that the measuring circuit itself generates only a small measuring current between the emergency power supply circuit and the vehicle's electrical system.

[0020] In one embodiment, the switching element is an N-channel MOSFET with its source electrode connected to ground. Control circuitry controlling the switching element provides a positive voltage connection between the gate electrode of the N-channel MOSFET and the control unit via a pull-up resistor. A positive voltage from the energy storage device can also be routed to the gate electrode via a pull-up resistor. With this circuit arrangement, the switching element switches to a conducting state when a positive voltage is present. This means no active switching process is required. To now allow for rapid turn-off, i.e., switching the switching element to a non-conductive state, a corresponding measurement circuit is connected to the control input of the corresponding switching transistor, which connects its gate electrode to ground. Thus, when the gate electrode is connected to a positive voltage via a pull-up resistor, another interconnect exists between the gate electrode and ground. However, this interconnect is switched to a non-conductive state by the switching transistor. The measurement circuit can generate its measurement signal at the control input of the switching transistor (i.e., its gate or base), resulting in the measurement circuit being able to directly switch the switching transistor to a conducting state. For example, an MPN bipolar transistor can be used as the switching transistor. If the switching transistor is switched to a conducting state, the potential of the gate electrode drops to ground, resulting in the switching element being switched to a non-conductive state. Therefore, each measurement circuit can directly switch its switching element to a non-conductive state via its own switching transistor.

[0021] In one embodiment, at least one additional switching transistor connects the described gate electrode to ground potential. Therefore, independent of the measurement circuitry, the switching element can also be switched to a non-conductive state via a corresponding additional switching transistor. For example, the signal input (through which the microcontroller should be able to control the switching element) can be connected to the control input of such an additional switching transistor. If a switching signal is generated at the signal input, the additional switching transistor can thus be switched to a conductive state, and the switching element can thus be switched to a non-conductive state.

[0022] As already described, a measurement circuit can be provided for each pole (positive and negative) of the energy storage device. This means that the positive pole can be connected to ground potential via the measurement circuit and / or the negative pole can be connected to ground potential via the measurement circuit. In one embodiment, a measurement circuit is provided for each of these two poles. The measurement circuit connected to the same pole, which is also connected to ground potential via a switching element, cannot actually establish a voltage that may exceed a threshold because the switching element provides electrical coupling to ground potential. However, if a short circuit occurs on the positive line of the vehicle electrical system, the current flowing through this pole and the switching element becomes so large that the voltage drop across the switching element exceeds a threshold. This can then be detected using the measurement circuit, and the switching element can be switched to a non-conductive state.

[0023] If two measuring circuits are provided, one for each pole, one embodiment specifies that these measuring circuits provide different resistance values ​​between each pole and ground potential. Because each pole has a different potential (since the two poles are offset from each other by the supply voltage of the energy storage device), the different resistance values ​​at ground potential ensure that the generated measuring signals are at the same level. Regardless of which pole each measuring circuit is connected to, there is no need to individually adjust the switching elements in the control circuitry to process the individual measuring signals from these circuits.

[0024] The cable connecting the energy storage device to the control unit can, in a known manner, have power supply lines (wires), each power supply line connecting one pole of the energy storage device to the control unit. Thus, each pole is connected to the control unit via its own power supply line. In one embodiment, the cable additionally provides corresponding measuring lines for one or two of these poles to connect that pole to the control unit while bypassing the power supply lines. The cable thus has three or more wires. Two of these wires are power supply lines, through which the actual load current or power used to power the control unit is transmitted. One or more measuring lines are then reserved, and the control unit is configured to detect the voltage of the corresponding pole to which the measuring line is routed and / or the voltage of a thermistor, which may be provided on the energy storage device for temperature measurement via the at least one measuring line. This ensures that the current flowing through the power supply lines and the associated voltage drop on the power supply lines do not distort the measurement results at the pole.

[0025] As previously mentioned, a control unit with emergency power supply is particularly advantageous when the control unit provides electronic emergency call functionality as a vehicle function. Therefore, this is explicitly provided as a vehicle function in one embodiment of the invention.

[0026] The invention also includes a motor vehicle in which an embodiment of the described control unit circuit is provided. In the motor vehicle, the control unit circuit can operate advantageously even when there is an electrical short circuit between one pole of the energy storage device of the control unit circuit and the vehicle's onboard electrical system (i.e., an electrical connection is established between them (e.g., due to a plug failure or insulation failure)). If the measuring circuit provided at or for that pole for monitoring the voltage between that pole and the vehicle's ground potential, the switching element can be switched to a non-conductive state in the event of a short circuit. The emergency power supply circuit can then continue to operate.

[0027] The operation of the control unit circuit according to the invention produces a method, which is also part of the invention. In the method for operating the control unit circuit, a control unit for providing vehicle functions is provided, and an energy storage device located outside the housing of the control unit for emergency power supply to the control unit, wherein the energy storage device supplies electrical energy to the control unit in the absence of a power supply current from the vehicle's on-board electrical system, wherein two poles of the energy storage device are connected to the control unit via cables, and one of these poles is connected to the ground potential of the on-board electrical system via a switching element, and at least one measuring circuit couples each of these poles to the ground potential and generates a measuring signal relating to the voltage drop between the respective pole and the ground potential, and a control circuit of the switching element keeps the switching element in a conductive state during normal operation of the control unit, and switches the switching element to a non-conductive state and thereby interrupts the electrical coupling to the ground potential at least when the corresponding measuring signal of the at least one measuring circuit indicates that the corresponding voltage is greater than a predetermined threshold.

[0028] The present invention also includes embodiments of the method according to the invention, which have features already described in conjunction with the development of the control unit circuit according to the invention. Therefore, corresponding embodiments of the method according to the invention will not be described again here.

[0029] The present invention also includes combinations of features of the described embodiments. Attached Figure Description

[0030] Exemplary embodiments of the present invention are described below. In this respect:

[0031] Figure 1 A schematic diagram of an embodiment of the control unit circuit according to the present invention is shown;

[0032] Figure 2 A schematic circuit diagram for implementing the control unit circuit according to the invention is shown; and

[0033] Figure 3A schematic circuit diagram of an alternative configuration of the control unit circuit according to the present invention is shown.

[0034] The exemplary embodiments described below are preferred embodiments of the present invention. In these exemplary embodiments, each of the described components represents a separate feature of the invention, which should be considered independently of each other and each also independently develops the invention, and therefore can be considered part of the invention individually or in combinations other than those shown. Furthermore, the described embodiments may be supplemented by other features of the invention already described.

[0035] In the accompanying drawings, elements with the same function are each given the same reference numerals. Detailed Implementation

[0036] Figure 1 A motor vehicle 10 is shown, which may be an automobile, particularly a passenger car or a truck. An onboard electrical system 11 may be provided in the motor vehicle 10, to which a control unit 12 may be connected. For example, the control unit 12 may be an electronic call control unit. In the event of a failure of the power supply current 13 from the onboard electrical system 11, the control unit 12 may be equipped with an additional energy storage device 14, which may include, for example, a lithium-ion battery 15. The energy storage device 14 provides emergency power to the control unit 12 and thus represents a backup battery (BUB).

[0037] exist Figure 1 In this configuration, the circuit 16 formed by the vehicle electrical system 11 is represented by a positive line 16' and a ground potential 17. The ground potential 17 can be provided, for example, by the supporting metal structure of the vehicle 10 in a manner known per se. An energy storage device 14 for emergency power supply to the control unit 12 can be connected to the control unit 12, as the energy storage device 14 is disposed on the exterior of the housing 18 of the control unit 12 and connected to the control unit 12 via a cable 19. Power supply lines 20, 20' are provided by the cable 19; for example, power supply line 20 can represent the positive line, and power supply line 20' can represent the negative line. Figure 1 In the diagram, the resistance values ​​of the line resistances 21 of the power supply lines 20 and 20' are symbolically represented by resistive elements. The energy storage device 14 can provide potential at the poles P+ and P-, resulting in an emergency supply voltage Un between the poles P+ and P- as a potential difference. The energy storage device 14 provides two poles P+ and P-, and the emergency supply voltage Un is generated between these two poles by the energy storage device 14. The control unit 12 is connected to these poles P+ and P- via cable 19, so that the emergency supply voltage Un can be provided within the housing 18 of the control unit 12.

[0038] The control unit 12, energy storage device 14, and cable 19 thus collectively form circuit 22, through which the control unit 12 can still draw power from the energy storage device 14 and thus continue to operate, even without the supply current 13. This may be relevant to situations involving electronic emergency call functionality, such as after a collision with the motor vehicle 10. Circuit 22 as a whole represents control unit circuit 22'.

[0039] For normal operation, the on-board electrical system 11 can provide an on-board electrical system voltage Ub. The on-board electrical system voltage Ub can be greater than the emergency power supply voltage Un. For example, the on-board electrical system voltage Ub can have a rated voltage of 12 volts, and the emergency power supply voltage Un can have a rated voltage of less than 6 volts, such as 4 volts.

[0040] To achieve potential matching between the ground potential 17 of the vehicle electrical system 11 and the power supply line 20' (negative line), an electrical coupling 23 can be provided, via which the power supply line 20' can be connected to the ground potential 17, thereby matching the potential of the ground potential 17 with that of the power supply line 20'. The electrical coupling 23 can be designed to be switchable via a switching element 24, which can be a transistor, such as, in particular, a semiconductor power switch, such as a MOSFET, for example, an N-channel MOSFET.

[0041] The circuit 22 can be protected by the switching element 24 to prevent overvoltage and / or charging current at the energy storage device in the event of an electrical connection or short circuit 25 between the positive line 16 and one of the poles P+ and P-.

[0042] Such an electrical connection or short circuit 25' may also exist between the positive line 16' and the negative power supply line 20'. Such a short circuit 25, 25' may be caused, for example, by insulation damage to the cable 19 and / or by a plug failure of the cable 19. As an alternative to the short circuit 25, 25', a creepage current may also exist between the positive line 16' and one of the power supply lines 20, 20' via the leakage resistor 26, which also results in an electrical connection 22 from the circuit to the positive line 16'.

[0043] If a short circuit 25' or a creepage current occurs in the leakage resistor 26, the vehicle electrical system voltage Ub drops through the electrical connection and coupling 23 (which is performed via the energy storage device 14), thus the energy storage device experiences a voltage higher than the voltage supplied according to the emergency power supply voltage Un. This could potentially damage the energy storage device 14. If a short circuit 25' occurs, the vehicle electrical system voltage Ub drops across the switching element 24, and the vehicle electrical system 11 is short-circuited except for the resistance of the switching element 24 and the line resistance 21.

[0044] To account for these fault scenarios, the motor vehicle 10 may specify that at least one or both of the poles P+ and P- are connected to ground potential 17 via measuring circuit 27 in their respective cases. In this case, measuring circuit 27 may be provided directly at the corresponding pole P+ or P- or in cable 19, or as... Figure 1 As shown, it is provided in control unit 12. This variant is possible because the line resistance 21 is low enough.

[0045] The measuring circuit 27 can be designed, for example, as a series circuit 28, in which a Zener diode 29 and a resistive element 30 are connected in series between the respective terminals P+, P- and ground potential 17. A measuring signal 32 can be tapped at the connection point 31, indicating whether the corresponding voltage between one terminal P+, P- and the other terminal ground potential 17 is greater than the breakdown voltage of the Zener diode 29. If this is the case, a switching process occurs at the switching element 24. In normal operation, when the measured voltage is lower than the breakdown voltage of the Zener diode 29, the switching element 24 switches to a conductive state, resulting in coupling 23. If the voltage exceeds the breakdown voltage of the corresponding Zener diode 29, the switching element 24 switches to a non-conductive state, resulting in the suppression or interruption of coupling 23. Even in the event of a single short circuit 25, 25' or creepage current, the energy storage device 14 can still be used by the control unit 12 for further operation or emergency power supply. Thus, such a separate fault associated with short circuit 25 or 25' or creepage current is compensated for.

[0046] exist Figure 1 The switching logic described herein is only symbolically represented by control circuit 12'. Control circuit 12' may additionally provide a signal input terminal 33, through which the switching element 24 can also be switched by a microcontroller 34 using a switching signal 33'. This switching signal can be provided for performing insulation tests or general test routines 35. Therefore, the provision of switching element 24 does not hinder self-testing in control unit 12.

[0047] Figure 2 and Figure 3 A possible implementation of the control circuit 12' is shown.

[0048] according to Figure 2 The switching element 24 is a power semiconductor switch in the form of a MOSFET, with its source electrode S connected to ground potential 17 and its gate electrode D connected to a positive voltage P, which can be, for example, the vehicle electrical system voltage Ub. The control unit 12 can be used to receive the vehicle electrical system voltage Ub, the voltage at terminal P+, the ground potential 17 (denoted as ground GND), and the potential at the input terminal P-. In this context, Figure 2The diagram shows a plug 36 for the cable 19 used in the control unit 12. Electrical contact pins or pins 1, 2, 3, 4 can be provided in the plug 32 with the following assignment: terminal 30 (positive wire of the vehicle electrical system 11).

[0049] 3GND Vehicle ground (ground potential 17),

[0050] 2. The P+ pole of the energy storage device

[0051] 4. The P- pole of the energy storage device.

[0052] According to the control circuit 12', the potential of the gate G is pulled up to a positive voltage P via the pull-up resistor 38, resulting in the switching element 24 remaining in a conductive state. The control circuit can provide switching transistors 39 for each power supply line 20, 20', which are distinguished here by reference numerals T1011 and T1024. Each switching transistor 39 can receive one of the measurement signals 32 from the measurement circuit 27 via the control input terminal 40, resulting in the switching transistor 39 switching to a conductive state according to the corresponding measurement signal 32. If the voltage between one of the power supply lines 20, 20' now exceeds the threshold specified by the corresponding Zener diode 29, the associated switching transistor 39 is switched to a conductive state and the potential of the gate electrode G of the switching element 24 is thus pulled up to ground potential 17, resulting in the switching element 24 switching to a non-conductive state. The switching speed of this solution is so fast that if a short circuit 25, 25' or leakage current (creep current) occurs, the electrical coupling 23 is interrupted before it may cause damage to the energy storage device 14, cable 19, or control unit 12.

[0053] Figure 3 This demonstrates how the measurement circuit 27 can also be implemented as a voltage divider 40'. Figure 3 It also demonstrates that the measurement circuit 27 can have different resistance values ​​overall, so that the level of the measurement signal 32 can remain the same even though the potentials of the poles P+ and P- are different. Figure 3 It shows how one or more resistive elements can be used for this purpose. It also shows how the charging circuit 41 can be turned on via switch 41' so as to recharge the energy storage device 14 with electrical energy.

[0054] In addition to power supply lines 20, 20', cable 19 may have at least one measuring line 42 via which voltage measurements can be provided from control unit 12 at corresponding poles P+, P-, wherein the current intensity in measuring line 42 is kept lower than the current intensity in power supply lines 20, 20'. In this way, load tests or stress tests can be performed, for example, via load resistor 43 and switch 44 on energy storage device 14, and during this process, the emergency power supply voltage Un provided by energy storage device 14 can be measured, and measuring line 42 can be used for this purpose.

[0055] The voltage drop across the thermistor T (which may be mechanically connected to the energy storage device 14) can also be measured via the measuring line 42, thereby enabling the detection of the temperature of the energy storage device. For this purpose, a test voltage can be generated by a circuit of the voltage source 45 (as is known per se), which can be switched on by means of the switching element 46 of the switchable voltage divider 47 to generate a temperature signal 48 when the resistance value is known.

[0056] The type of energy storage device 14 currently installed in the motor vehicle 10 can be indicated by an coded resistor 49, which is generated by applying a test voltage 50, which can be implemented using a circuit known in itself of the voltage source, and can be turned on, read out, or checked by a switching element 51 on the coded resistor 49.

[0057] The various aspects of the invention are summarized again below in particularly preferred embodiments.

[0058] If a positive overvoltage (KL3O) or excessive leakage current (via contact resistance to KL30) is fed into the positive or negative backup battery feed line or power supply line 20, 20', the negative connection (or both connections) from the backup battery (energy storage device 14) to the control unit 12 is disconnected from the unit ground via a switch (switching element 24, particularly a FET). Alternatively, the grounding wire can be disconnected via software using the switch signal 33' (BATF_OFF) to enable cyclic monitoring of the ground fault current.

[0059] This provides backup battery protection against overvoltage and leakage current on both power lines. No additional electronics are required in the backup battery module. High accuracy in backup battery measurement can also be achieved by using 3-wire or 4-wire technology to measure the backup battery voltage through equalized line resistance. Compared to "smart backup batteries," this represents a more cost-effective solution.

[0060] This can be used for uninterrupted power supply to automotive electronic devices, such as for rechargeable solar cells.

[0061] exist Figure 2In the circuit diagram, the backup battery protection electronics are connected to the P+ and P- terminals of the backup battery via BATT_P (pin 2) and BATT_N (pin 4). The gate switching voltage is generated by Ub (+10V) from the control unit voltage source. FET T1008 switches BATT_N to GND. A fault voltage at BATT_N > 5V or BATT_P > 7V switches the collector of transistor T1011 or T1024 to GND, thereby switching the gate voltage of T1008 to 0V. FET T1008 disconnects, and the backup battery ground connection is broken.

[0062] Figure 3 A backup battery protection circuit with temperature measurement and code checking is shown. This protection circuit allows GND to be disconnected via software (BATT_N_OFF at signal input 33). It also enables more complex measurements of the backup battery (health test / load test, charging voltage), 3-wire or 4-wire measurement of the backup battery voltage between P+ and P-, and can read existing coded resistors (identifying battery type) and a temperature sensor with a thermistor T via the same measurement line, all at a low cost.

[0063] In summary, the examples illustrate how the present invention can provide overvoltage protection for backup batteries.

Claims

1. A control unit circuit (22) for a motor vehicle (10), wherein the control unit circuit (22) includes a control unit (12) for providing vehicle functions (F) and an energy storage device (14) for emergency power supply to the control unit (12) is included outside the housing (18) of the control unit (12), wherein the energy storage device (14) is configured to supply electrical energy to the control unit (12) in the absence of a power supply current (13) from the on-board electrical system (11) of the motor vehicle (10), Its features are, To form the circuit (22') for the emergency power supply, the two electrodes (P+, P-) of the energy storage device (14) are connected to the control unit (12) via cable (19), and in the control unit (12), or in the energy storage device (14), or on the cable (19), one of the two electrodes (P+, P-) is connected to the ground potential (17) of the vehicle electrical system (11) via a switching element (24), and At least one measurement circuit (27) is coupled to one of these electrodes (P+, P-) to the ground potential (17) and configured to generate a measurement signal (32) relating to the voltage drop between the respective electrode (P+, P-) and the ground potential (17), and The control circuit (12') of the switching element (24) is configured to keep the switching element (24) switched to conductive during normal operation of the control unit (12), and to switch the switching element (24) to electrically cut off at least in response to a signal (32) from the corresponding measurement signal (32) of the at least one measurement circuit (27) indicating that the corresponding voltage is greater than a predetermined threshold, thereby canceling the electrical coupling (23) between the circuit (22) and the ground potential (17) caused by the switching element (24).

2. The control unit circuit (22) as claimed in claim 1, wherein the control circuit (12') has a signal input terminal (33) for receiving a switch signal (33') and is configured to switch the switch element (24) to electrical cutoff according to the switch signal (33').

3. The control unit circuit (22) as claimed in claim 2, wherein the control unit (12) is configured to perform a test routine for checking the insulation resistance of the cable (19) and / or perform a load test for the energy storage device (14), and generate the switching signal (33') at the signal input (33) when the test routine and / or the load test begins.

4. The control unit circuit (22) as claimed in claim 3, wherein during the load test, the current of the energy storage device (14) is routed via a load resistor (43) connected between the electrodes (P+, P-) of the energy storage device (14), and here, the switching element (24) is kept switched to electrical off by the switching signal (33'), and by connecting one of these electrodes (P+, P-) or the power supply line (20, 20') of the cable (19) to the charging circuit (41) of the control unit circuit (22), the corresponding voltages of the two electrodes (P+, P-) of the energy storage device (14) relative to the ground potential (17) of the cable (19) are set to positive values.

5. The control unit circuit (22) as claimed in any one of claims 1 to 4, wherein the at least one measurement circuit (27) comprises a series circuit (28) consisting of a Zener diode (29) and a resistive element (30), with the respective electrodes (P+, P-) connected to the ground potential (17) via the series circuit, wherein the threshold is defined by the breakdown voltage of the Zener diode (29).

6. The control unit circuit (22) as claimed in claim 5, wherein in the series circuit (28), the Zener diode (29) is arranged on the electrode side and the resistive element (30) is arranged on the ground potential side.

7. The control unit circuit (22) as claimed in any one of claims 1 to 4, wherein each measuring circuit (27) between the respective electrode (P+, P-) and the ground potential (17) has a resistance value greater than 1 kΩ.

8. The control unit circuit (22) as claimed in any one of claims 1 to 4, wherein the switching element (24) is an N-channel MOSFET whose source electrode (S) is connected to the ground potential (17), and the control circuit (12') provides a connection via a pull-up resistor (38) to the positive voltage (P) of the gate electrode (G) of the N-channel MOSFET and the control unit (12) and / or the energy storage device (14), and a corresponding measurement circuit (27) is connected to the control input terminal (40) of a corresponding switching transistor (39) that connects the gate electrode (G) to the ground potential (17).

9. The control unit circuit (22) of claim 8, wherein at least one additional switching transistor (32) connects the gate electrode (G) to the ground potential (17).

10. The control unit circuit (22) as claimed in any one of claims 1 to 4, wherein measurement circuits (27) are provided for the two electrodes (P+, P-) respectively.

11. The control unit circuit (22) of claim 10, wherein the measurement circuit (27) provides different resistance values ​​between the respective electrodes (P+, P-) and the ground potential (17).

12. The control unit circuit (22) as claimed in any one of claims 1 to 4, wherein the cable (19) includes power supply lines (20, 20'), each of which connects one of the electrodes (P+, P-) to the control unit (12), and additionally provides a corresponding measuring line (42) for connecting one or both of the electrodes (P+, P-) to the control unit (12) while bypassing the power supply lines (20, 20'), and the control unit (12) is configured to detect the voltage of the electrode (P+, P-) and / or the voltage of the thermistor (T) on the energy storage device (14) via the at least one measuring line (42).

13. The control unit circuit (22) as claimed in any one of claims 1 to 4, wherein the control unit (12) provides an electronic emergency call function as a vehicle function (F).

14. A motor vehicle (10) including a control unit circuit (22) as described in any one of claims 1 to 13.

15. A method for operating a control unit circuit (22), the control unit circuit providing a control unit (12) for providing vehicle functions (F) and an energy storage device (14) provided outside a housing (18) of the control unit (12) for emergency power supply to the control unit (12), wherein the energy storage device (14) supplies electrical energy to the control unit (12) in the absence of a power supply current (13) from the on-board electrical system (11) of the motor vehicle (10), Its features are, The two electrodes (P+, P-) of the energy storage device (14) are connected to the control unit (12) via cable (19), and one of these two electrodes (P+, P-) is connected to the ground potential (17) of the vehicle electrical system via a switching element (24). At least one measurement circuit (27) couples one of these electrodes (P+, P-) to the ground potential (17) and generates a measurement signal (32) that is correlated with the voltage drop between the corresponding electrode (P+, P-) and the ground potential (17), and The control circuit (12') of the switching element (24) keeps the switching element (24) switched to conductive during normal operation of the control unit (12), and at least in the event that the corresponding voltage is greater than a predetermined threshold signaled by the corresponding measurement signal (32) of the at least one measurement circuit (27), the switching element (24) is switched to electrical cut-off, thereby interrupting the electrical coupling (23) to the ground potential (17).

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