Method for protecting an electronic safety switch and safety shutdown device with such a protected electronic safety switch

Abstract

In a method and a device for protecting an electronic safety switch (16), whose electrical conductivity can be controlled between an on-state and an off-state and which has a known thermal resistance, from thermal influences, the temperature of the safety switch (16) and the magnitude of the current flowing through the safety switch are measured. A safety threshold is determined based on the temperature measurement and the known thermal resistance of the safety switch (16). The safety switch (16), which is in the on-state, is activated to reduce its conductivity when the magnitude of the current flowing through the safety switch (16) lies within the range between the safety threshold and the off-state.Starting from its reduced conductivity in the on state, the safety switch (16) returns to its maximum conductivity by means of an increase in conductivity signal when the current is equal to or below the safety threshold.

Description

[0001] The invention relates to a method for protecting an electronic safety switch with a known thermal resistance, whose electrical conductivity can be controlled between an on-state and an off-state, from thermal influences due to current peaks in a line of a vehicle's on-board network. The safety switch is arranged in the line to protect the on-board network and / or to protect loads connected to the on-board network from damage that may be caused by excessive currents by switching off the safety switch at a current that exceeds a switch-off threshold. Furthermore, the invention relates to a safety switch-off device for arrangement in a vehicle's on-board network for supplying electrical energy to electrical loads of the vehicle.

[0002] In recent years, the automotive industry has continued to use electronic switches instead of fuses, which perform the safety shutdown function of fuses. One advantage of electronic safety switches is that they can continue to be used after a shutdown. Such electronic switches, installed in a vehicle's electrical system, can also be used to reconfigure and reconfigure the electrical system.

[0003] Electronic safety switches are therefore designed to automatically switch off when the current flowing through them exceeds a certain threshold. This is achieved by controlling the safety switches accordingly.

[0004] However, an electronic safety switch can become excessively hot due to brief, high currents, which are typically below the shutdown threshold. This poses the risk of thermal damage to such a safety switch if it is subjected to excessive currents below the shutdown threshold over a longer period of time or repeatedly at short intervals.

[0005] DE 20 2018 006 383 U1 discloses a protective device having an overall current path between a voltage input and a load connection, wherein the overall current path has a number of partial current paths connected in parallel. Each partial current path contains an electronic circuit breaker with a switching element and a control unit for actively limiting a partial current flowing in the respective partial current path, as well as for switching on and off a load output of the electronic circuit breaker. Each electronic circuit breaker has a communication device for receiving and outputting a control signal. The communication devices are coupled to one another in such a way that the control signal output by one of the communication devices is output in parallel to the other communication devices.

[0006] DE 10 2016 216 508 A1 discloses a method for controlling a semiconductor switch in a switching mode. A switching path (conduction path) of the semiconductor switch is controlled by an electrical switching potential at a control electrode of the semiconductor switch such that the switching path assumes an off or on state depending on the electrical switching potential. During a switching operation of the switching path from the on state to the off state, the electrical switching path voltage at the switching path is detected, and an electrical limiting potential is applied to the control electrode when a maximum voltage is reached.This limiting potential puts the switching gap into an electrically conductive state in order to limit the switching gap voltage to the maximum voltage, whereby a temperature of the switching gap is detected by means of a temperature sensor thermally coupled to the switching gap and the maximum voltage is determined depending on the detected temperature.

[0007] Finally, EP 1 186 086 B1 discloses a power distribution system with circuits supplied by a switch-mode power supply, in which an electronic circuit breaker is arranged in each circuit. This circuit breaker essentially serves to limit the current within a circuit potentially affected by a short circuit and / or overload. The current limit is adjustable.

[0008] The object of the invention is to provide a method for protecting an electronic safety switch from thermal destruction and to provide a safety shutdown device with a safety switch protected in this way.

[0009] To achieve this object, the invention relates, inter alia, to a method for protecting an electronic safety switch with a known thermal resistance, which can be controlled with respect to its electrical conductivity between a switched-on state and a switched-off state, from thermal influences due to current peaks in a line of a vehicle's on-board network, in which the safety switch is arranged to protect the on-board network and / or to protect loads connected to the on-board network from damage that is to be feared as a result of excessive currents by switching off the safety switch at a current that is greater than a switch-off threshold value, wherein in the method - the temperature of the safety switch is recorded and a temperature measurement signal representative of the temperature of the safety switch is generated, - the magnitude of the current flowing through the safety switch is recorded and a current measurement signal representative of this magnitude is generated and - based on the temperature measurement and the known thermal resistance of the safety switch, a safety threshold is determined which is below the switch-off threshold, - wherein the safety switch in its switched-on state has a controllable conductivity which lies between a maximum value and a value of reduced conductivity which is greater than the value of the conductivity in the switched-off state of the safety switch, - wherein the safety switch in the switched-on state is controlled to reduce its conductivity when the magnitude of the current flowing through the safety switch is in the range between the safety threshold value and the switch-off threshold value, and - whereby the safety switch, starting from its reduced conductivity in the switched-on state, returns to its maximum conductivity by being triggered to increase its conductivity when the magnitude of the current is again equal to the safety threshold or is again below the safety threshold.

[0010] Furthermore, to achieve this object, according to the invention, a safety shutdown device for arrangement in a vehicle on-board network for supplying electrical loads of the vehicle with electrical energy, with - an electronic safety switch which can be switched on and off and has a known thermal resistance and a conduction path whose conductivity can be controlled between a maximum value associated with its switched-on state and a minimum value associated with its switched-off state, which is ideally also zero, - a temperature sensor providing a temperature measurement signal to detect the temperature of the safety switch, - a current measuring device providing a current measuring signal to detect the current flowing through the safety switch and - an evaluation and control unit (22) which receives the current measurement signal from the current measuring means and controls the safety switch in its switched-on state to assume its switched-off state when the current flowing through the safety switch is equal to or greater than a switch-off threshold value, - wherein the evaluation and control unit (22) additionally receives the temperature measurement signal from the temperature sensor and, based on the temperature measurement signal and the thermal resistance of the safety switch, determines a safety threshold value which is below the switch-off threshold value and controls the safety switch in its switched-on state to reduce the conductivity of its current path from the maximum value to a lower value which is above the minimum value when the current flowing through the safety switch exceeds the safety threshold value, and controls the safety switch to increase the conductivity of its current path up to the maximum value when the current flowing through the safety switch is again below the safety threshold value or is equal to it.

[0011] According to the invention, the temperature of the safety switch is recorded continuously or discontinuously, i.e., at regular or irregular intervals. The temperature measurement signal representing this temperature is fed to an evaluation and control unit, as is a current measurement signal representing the magnitude of the current flowing through the safety switch. The evaluation and control unit serves, among other things, to switch off the safety switch when the magnitude of the current flowing through the safety switch is equal to or greater than the switch-off threshold. Depending on the application, it can be provided that this emergency switch-off occurs immediately or with a certain time delay, whereby this time delay must not lead to an impairment of the function of the consumers or loads protected by the safety switch. The temperature measurement value, i.e.According to the invention, the magnitude of the temperature measurement signal is used, together with the known thermal resistance of the safety switch, to determine an optimal safe operating area (SOA) operating point range for the safety switch with regard to thermal loads. In other words, a safety threshold is determined to protect the safety switch from thermal destruction, which is typically below the shutdown threshold.

[0012] If, during operation, i.e., when the safety switch is in the switched-on state, a current flowing through the safety switch is detected that is greater than the safety threshold, the invention counteracts thermal overload of the safety switch by reducing the magnitude of the current flowing through it. This is achieved by influencing the conductivity of the safety switch's conduction path in its switched-on state. Thus, while in the switched-off state of the safety switch its conductivity assumes the minimum possible value (minimum value), which is ideally zero, the safety switch used according to the invention exhibits a controllable conductivity in its switched-on state that lies between the maximum value, which should be virtually infinite, and a comparatively reduced conductivity value.The electronic safety switch remains switched on in this area; however, its conductivity may be lower than the maximum conductivity value.

[0013] This measure reduces the current flowing through the safety switch if it is above the safety threshold. This state is maintained until the current measurement signal detects that the current flowing through the safety switch is again below the safety threshold. The safety switch can now be operated at maximum conductivity again, so that the safety switch is controlled from its reduced conductivity in the switched-on state to increase it. The safety switch is thus fully functional again without any risk of thermal destruction.

[0014] The conceivable scenarios in which the inventive approach unfolds its advantages include, for example, the ramp-up of the supply voltage when switching on the vehicle or one of its consumers, or a transient event. When the supply voltage is ramped up, quite high currents can occur, meaning that the safety switch could leave its SOA operating point range. The reasons for the high starting currents can be found in the parasitic capacitances of the lines and possibly also of the consumer. However, a transient event can also occur during operation in which the consumer draws a quite high current for whatever reason. Reasons for this include, for example, short circuits in the supply tree structures of the on-board network following the electronic safety switch. In such a case, the electronic safety switch is then switched off and may already be excessively hot.Depending on the configuration or application, a retry function is triggered, during which the electronic safety switch is switched on again as planned. This situation then corresponds to the power-up of the supply voltage described above, in this case after a transient event. This means that the electronic safety switch becomes even hotter. Without the inventive protection against thermal destruction, the electronic safety switch's functionality may be permanently and irreversibly impaired.

[0015] When determining the SOA operating point range, i.e., among other things, when determining the size of the safety threshold, it is assumed that the temperature of the electronic safety switch is constant over time, since it can typically only cool down very slowly. The thermal (leakage) resistance of the electronic safety switch is also assumed to be constant. The housing temperature is also assumed to be constant, which should also apply to the ambient temperature according to the assumption. Based on all of these parameters, i.e., the temperature of the safety switch and its thermal leakage resistance, the junction temperature of the safety switch can now be determined. This makes it possible to find the optimal SOA operating point range, and the electronic safety switch can be protected from thermal destruction by regulating / controlling its electrical conductivity.

[0016] It is advisable to measure the temperature of the safety switch using a temperature sensor that detects the temperature of the safety switch housing. The magnitude of the current flowing through the safety switch can be conveniently measured using a shunt resistor or by measuring the voltage drop across the safety switch, particularly the voltage drop across its conduction path.

[0017] The invention is explained below with reference to the drawing ( Fig. 1), which shows an embodiment of the invention at block diagram level and schematically.

[0018] In a vehicle's on-board network 10, an electronic safety switch 16 is located in a line 14 leading directly or indirectly to a load 12 to be protected. The switch is designed, for example, as a CMOS transistor or, more generally, as a field-effect transistor. Alternatively, the electronic safety switch 16 can also be designed as a bipolar transistor.

[0019] The electronic safety switch 16 has a conduction path 18, the conductivity of which is set by a driver circuit 20 between a minimum value, which represents the switched-off state of the safety switch 16, and a maximum value, which is given when the safety switch 16 is switched on. The driver circuit 20, in turn, is controlled by an evaluation and control unit 22, which is, for example, a microcontroller with corresponding peripherals such as I / O interfaces and A / D and D / A converters. The size of the electrical current in the line 14 is recorded via a current measuring device 23, for example in the form of a shunt resistor 24. The current measuring device 23 can also be the conduction path 18 of the electronic safety switch 16. A temperature sensor 26, which is close to or near to theThe temperature of the safety switch 16 is measured by a sensor arranged on or even in the housing 28 of the electronic safety switch 16. The aforementioned measurement signals for the current and temperature are fed to the evaluation and control unit 22.

[0020] The evaluation and control unit 22 typically implements the main function of the safety switch 16, which is switched from the on state to the off state as quickly as possible when the current value exceeds a preset switch-off threshold.

[0021] Typically, the electronic safety switch 16 is already in the switched-on state before the load 12 is switched on, or at least simultaneously with its switching on. For this purpose, the safety switch 16 is switched on by a higher-level system (not shown) that enables coupling for switching on the vehicle or for switching on the load. At the beginning of the switching-on process, quite high starting currents sometimes flow, which are caused by the parasitic capacitances of cables or the vehicle's on-board network. High currents, even if they only occur briefly, cause thermal stress in the safety switch 16. Based on its temperature and its known leakage resistance, an SOA operating point range is determined for the safety switch 16, within which the operating point of the safety switch 16 should ideally lie. If the supply voltage V SUPswitched on, the current flowing through the safety switch 16 may be greater than the safety threshold, which typically limits the SOA operating point range. The potential exceedance of the SOA operating point range is detected in the evaluation and control unit 22, whereupon the safety switch 16, which is in the switched-on state, is reduced in terms of its conductivity. Once the starting current is reduced again due to the saturation of the parasitic capacitances, the conductivity of the electronic safety switch 16 can be increased again up to the maximum value.

[0022] The above scenario may not (yet) occur when the supply voltage for a load is first applied or when the vehicle is switched on. During normal operation, in which the safety switch 16 may have a certain operating temperature due to its function, situations can arise in which, for example, due to the re-try function, the safety switch 16 is switched on again after a brief failure or short circuit. The already heated safety switch 16 then continues to heat up and can ultimately be thermally damaged. To prevent this, the SOA operating point range is continuously determined and examined to determine whether the current SOA operating point range still allows a current of the measured magnitude to flow through the safety switch 16.As soon as this can no longer be guaranteed due to the thermal effects on the electronic switch 16, the reduction in conductivity provided for by the invention occurs in the switched-on state of the safety switch 16, which can then be increased again either in a time-controlled manner or controlled by the size of the current. LIST OF REFERENCE SYMBOLS 10 Vehicle on-board network 12 Last 14 Line 16 safety switches 18 Conductor path 20 driver circuit 22 Evaluation and control unit 23 current measuring instruments 24 Shunt resistance 26 temperature sensors 28 housings

Claims

[1] Method for protecting an electronic safety switch (16) with a known thermal resistance, which can be controlled with respect to its electrical conductivity between a switched-on state and a switched-off state, from thermal influences due to current peaks in a line (14) of a vehicle on-board network (10), in which the safety switch (16) is arranged to protect the on-board network (10) and / or to protect loads connected to the on-board network (10) from damages to be feared as a result of excessive currents by switching off the safety switch (16) at a current which is greater than a switch-off threshold value, wherein in the method - the temperature of the safety switch (16) is detected and a temperature measurement signal representative of the temperature of the safety switch (16) is generated, - the magnitude of the current flowing through the safety switch (16) is detected and a current measurement signal representative of this magnitude is generated and - based on the temperature measurement value and the known thermal resistance of the safety switch (16), a safety threshold value is determined which is below the switch-off threshold value, - wherein the safety switch (16) in its switched-on state has a controllable conductivity which lies between a maximum value and a value of reduced conductivity which is greater than the value of the conductivity in the switched-off state of the safety switch (16), - wherein the safety switch (16) in the switched-on state is controlled to reduce its conductivity when the magnitude of the current flowing through the safety switch (16) is in the range between the safety threshold value and the switch-off threshold value, and - wherein the safety switch (16), starting from its reduced conductivity in the switched-on state, again assumes its maximum conductivity by means of control to increase its conductivity when the magnitude of the current is again equal to the safety threshold value or is again below the safety threshold value. [2] Method according to claim 1, characterized by that the temperature of the safety switch (16) is detected by means of a temperature sensor (26) which detects the temperature of the housing (28) of the safety switch (16). [3] Method according to claim 1 or 2, characterized by that the magnitude of the current flowing through the safety switch (16) is detected by means of the voltage drop across a shunt resistor (24) connected in series with the safety switch (16) or by means of the voltage drop across the safety switch (16). [4] Safety shutdown device for arrangement in a vehicle on-board network (10) for supplying electrical loads of the vehicle with electrical energy, with - an electronic safety switch (16) which can be switched on and off and has a known thermal resistance and a conduction path (18) whose conductivity can be controlled between a maximum value associated with its switched-on state and a minimum value associated with its switched-off state, - a temperature sensor (26) providing a temperature measurement signal for detecting the temperature of the safety switch (16), - a current measuring means (23) providing a current measuring signal for detecting the current flowing through the safety switch (16) and - an evaluation and control unit (22) which receives the current measurement signal from the current measuring means (23) and controls the safety switch (16) in its switched-on state to assume its switched-off state when the current flowing through the safety switch (16) is equal to or greater than a switch-off threshold value, - wherein the evaluation and control unit (22) additionally receives the temperature measurement signal from the temperature sensor (26) and, based on the temperature measurement signal and the thermal resistance of the safety switch (16), determines a safety threshold value which is below the switch-off threshold value and controls the safety switch (16) in its switched-on state to reduce the conductivity of its current path from the maximum value to a lower value which is above the minimum value when the current flowing through the safety switch (16) exceeds the safety threshold value, and controls the safety switch (16) to increase the conductivity of its current path up to the maximum value when the current flowing through the safety switch (16) is again below the safety threshold value or is equal to it. [5] Device according to claim 4, characterized bythat the minimum value of the conductivity of its conduction path (18) associated with the switch-off state of the electronic safety switch (16) is zero. [6] Device according to claim 4 or 5, characterized by that the temperature of the safety switch (16) is detected by means of a temperature sensor (26) which detects the temperature of the housing (28) of the safety switch (16). [7] Device according to one of claims 4 to 6, characterized by that the magnitude of the current flowing through the safety switch (16) can be detected by means of the voltage drop across a shunt resistor (24) connected in series with the safety switch (16) or by means of the voltage drop across the safety switch (16).

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