Short circuit in a vehicle electric motor during an accident

Abstract

The invention relates to a device for generating an electrical short circuit on an electric motor (1) of a vehicle, comprising an electrical connection with electrical conductors (7) in order to connect the electric motor (1) of the vehicle to an electrical energy source (3) of the vehicle, wherein the device has a predetermined breaking point (5) which breaks open when a predefined mechanical limit force is exceeded, wherein at least one of the electrical conductors (7) is mechanically coupled to the predetermined breaking point (5) in such a way that when the predetermined breaking point (5) breaks open, the electrical conductors (7) are connected on the electric motor side in order to electrically short-circuit the electric motor (1). The electrical conductors (7) are routed through a common connector (11), wherein the connector (11), in its closed state, serves to electrically connect the vehicle's electric motor (1) and the energy source (3). When the connector (11) is open, the electrical conductors (7) are interrupted at the respective separation points and connected to one another at the electric motor-side ends of the separation points. For this purpose, the connector (11) has at least one prestressed force element (9) which relaxes when the connector (11) is moved from the closed to the open state and thereby electrically connects the electric motor-side ends of the separation points to one another. According to the invention, the respective force element (9) is an elastic volume element.

Description

The invention relates to a device for generating an electrical short circuit at an electric motor of a vehicle.A traffic accident with an electric vehicle can lead to an electrical connection, such as a line, being broken between an electric motor, for example a three-phase motor, and the power supplier, for example a battery (or the power electronics present thereon). In this case, an electrical voltage can be induced at the disconnected connections by further rotation of the electric motor. The contacts or power lines to the electric motor could then be under a (possibly high) electrical voltage. If the electric motor is a wheel hub motor, the electrical voltage can arise in the torn lines regardless of whether the wheel can still rotate or not, wherein a further rotation of the wheel introduces additional kinetic energy, which can likewise be converted into electrical energy in the electric motor. In all these cases, a risk due to electrical voltage can occur.In the prior art, it is known to be able to avoid high induced voltages in the environment of an electric machine with the aid of a intentionally caused electrical short circuit. In such fault cases, in the prior art an active short circuit is brought about at / in the vicinity of the electric motor between the lines, so that no electrical voltage occurs outside.DE 10 2014 019 119 A1 relates in this context to a drive device for a motor vehicle having a high-voltage system, a power converter and a three-phase machine, wherein the high-voltage system is electrically coupled to the three-phase machine via the power converter and can be supplied with electrical energy of the three-phase machine via the power converter in a generator mode of the three-phase machine, wherein the drive device has a sensor device which is designed to detect a total current provided by the three-phase machine, and has a control device which is designed to provide an active short circuit for the three-phase machine in the event of a deviation of the detected total current from a predefined current value.DE 10 2013 016 960 A1 further relates to an inverter unit for an electric machine having a DC / DC converter including a bridge having two bridge branches which each have a bridge switch, a current intermediate circuit at the output of the bridge, an inverter connected to the current intermediate circuit having a plurality of inverter branches which each have two inverter switches, and a control device for controlling the bridge switches and the inverter switches, wherein the control device is designed to cause an active short circuit in a first step in dependence on an error signal by closing all inverter switches and closing a bridge switch, and to cause free running in a second step by closing the inverter switches of one of the bridge legs and opening the remaining inverter switches.In addition, EP 3 479 391 A1 relates to a short-circuiting device for use in low-voltage and medium-voltage systems for protection of the object and persons, comprising a switching element, which can be actuated by the triggering signal of a fault detection device, two mutually opposite contact electrodes with means for supplying current, wherein these can be contacted to a circuit with terminals of different potentials, and furthermore, in at least one of the contact electrodes, a movable contact part, which is under mechanical prestressing and, in the event of a short circuit, carries out a movement towards the further contact electrode with spring force assistance, a sacrificial element as a spacer between the contact electrodes and with an electrical connection between the sacrificial element and the switching element on the one hand and one of the contact electrodes on the other hand, in order to specifically bring about a current-induced, thermal deformation or destruction of the sacrificial element, wherein the movable contact part is formed as a hollow cylinder closed on one side and a spring for generating prestress is inserted in the hollow cylinder, the hollow cylinder is guided movably in a complementary cutout in the first contact electrode, forming a sliding contact, and in the region of the base of the closed hollow cylinder, the cylinder wall of which merges on the outer circumference into a cone, furthermore a first pin-shaped extension extends in the interior of the hollow cylinder, starting from the base, said first pin-shaped extension being opposite a second pin-shaped extension insulated from the contact electrodes, wherein the sacrificial element, formed as a bolt or screw, is arranged between the first and second pin-shaped extensions, and a cutout with an inner cone adapted to the outer cone of the movable contact is provided in the second contact electrode, wherein the outer and inner cones form a bounce-free short-circuit contact region with force fit and form fit on account of plastic deformation occurring.DE 10 2014 115 396 A1 additionally relates to a switch, in particular a circuit breaker for high direct and alternating currents at high voltages, which can be transferred from a conducting position into a separating position and which has a housing, a first contact, a second contact, a switching piston guided by the housing and a connecting element which, in the conducting position of the switch, produces an electrical connection between the first contact and the second contact, wherein the housing has an interior space surrounding the connecting element, characterized in that the connecting element runs at least in sections in the interior space, in that the interior space is filled with an insulator medium, and in that the switch is designed such that a mechanical movement of the switching piston can transfer the switch from the conducting position into the separating position, wherein the switching piston acts mechanically on the connecting element in such a way, interrupting the electrical connection between the first contact and the second contact at at least one separating point.DE 10 2016 222 339 A1 relates to a pyrotechnic switch for switching off and producing electrical circuits, comprising a first electrical conductor, a second electrical conductor and an ignition element, wherein in a first state of the pyrotechnic switch the first electrical conductor and the second electrical conductor are electrically connected to one another, wherein a predetermined disconnection point is provided between the first electrical conductor and the second electrical conductor, wherein the predetermined disconnection point is disconnected as soon as the ignition element is triggered, wherein the pyrotechnic switch has a third electrical conductor, wherein in the first state of the pyrotechnic switch the third electrical conductor is electrically disconnected from the first electrical conductor and from the second electrical conductor and in a second state of the pyrotechnic switch the third electrical conductor is electrically connected to the second electrical conductor.In particular, DE 10 2007 035 987 A1, US 2009 / 0 186 504 A1, U.S. Pat. No. 3,512,043 A and JP S53-28 290 A show various designs of plug contacts in this regard, in which the conductors on an element of the plug contact are connected to one another in the unplugged state via a spring, in particular a helical spring, or another flat spring element, and thus form an electrical short circuit. In general, the plug contact in the plug element has two contacts each with a connected conductor, which can be connected via a short-circuiting arm, which is prestressed by a spring. For this purpose, the prestress is usually designed in the direction of the plug contact connection direction, so that when the plug elements are plugged against this prestress, the short-circuiting arm is pressed in the opposite direction and, therefore, in the plugged state of the plug elements, there is no longer any contact of the short-circuiting arm with the conductors or the contacts in the plug element and thus also no short circuit is produced between the conductors.It is the object of the invention to prevent a possible risk arising from an electrical voltage, caused by a continuing rotating electric motor after an accident of an electric vehicle with the electric motor, and in the process to provide alternatives to the prior art if appropriate.The invention results from the features of the independent claim. Advantageous refinements and refinements are the subject matter of the dependent claims.A first aspect of the invention relates to a device for generating an electrical short circuit at an electric motor of a vehicle, having an electrical connection with electrical conductors in order to connect the electric motor of the vehicle to an electrical energy source of the vehicle, wherein the device has a predetermined breaking point which breaks when a predefined mechanical limit force is exceeded, wherein the electrical conductors are mechanically coupled to the predetermined breaking point in such a way that, when the predetermined breaking point breaks, the electrical conductors are cut through in their course between the electric motor and the energy source, but are connected to one another on the electric motor side in order to electrically short-circuit the electric motor.The electric motor serves as a drive component for the vehicle, for example a battery-electric vehicle. For this purpose, the energy is provided from an energy source of the vehicle and then supplied to the electric motor by means of electrical conductors. The number of electrical conductors depends on the selected architecture of the current source and the electric motor. Whereas two electrical conductors are sufficient in a direct current power source, a plurality of conductors are to be provided for polyphase alternating current technology.If a traffic accident or another mechanical, correspondingly high load occurs on the predetermined breaking point provided in the device, this mechanical load leads to the predetermined breaking point breaking open. The predetermined breaking point is coupled to at least one of the electrical conductors or an auxiliary element in such a way that an electrical short circuit of the phases of the electric motor occurs. A possible risk due to an electrical voltage present at the electrical conductors, which does not originate from the electrical energy source but is induced by the continuing-rotating electric motor itself for a time after the traffic accident, can thus be advantageously avoided. Preferably, the breaking open of the predetermined breaking point is irreversible. At least, the predetermined breaking point preferably cannot return to its initial state by itself, but rather requires a manual repair process or an exchange of the predetermined breaking point.In particular, a wheel hub drive in which the electric motor is arranged on the wheel itself is susceptible to such a fault, since wheel tear typically always leads to the electric motor tearing and the electric motor is normally connected to the vehicle in a current-conducting manner via electrical lines / cables. A wheel torn off in this way can continue to rotate and the relative rotation between the stator and the rotor then still induces a high voltage in the electric motor, which can be applied to the lines.If, on the other hand, an electrical short circuit is generated at the electric motor, the electric motor is brought to a standstill and an electrical voltage can no longer be generated. The position of the predetermined breaking point in the vehicle is preferably selected such that it is ensured that in the event of an accident the electrical connection between the electric motor and the electrical energy source is also disconnected in the region of the predetermined breaking point.In contrast to DE 10 2016 222 339 A1, in which a pyrotechnic separation is used to produce an electrical short circuit, the procedure is reversed according to the invention in order to ensure a short circuit when a line is separated by external mechanical action by means of corresponding passive coupling.By breaking the predetermined breaking point by an external force and mechanically coupling the predetermined breaking point to at least one of the electrical conductors, no signal path has to be designed and implemented. Rather, an action chain acting by itself is provided structurally, which, when acted appropriately from the outside, leads by a mechanical causal chain not only to the disconnection of the electric motor from the energy source, but also to the short-circuiting of the electric motor. The predetermined breaking point can be realized, for example, by thin-walled material or a notch in a material section, so that a break occurs at this point if an externally induced load exceeds the durability of the predetermined breaking point.When the electrical conductors are severed, they may break at a zone intended for this purpose, but may also be designed such that contact of conductor sections is ended by moving them apart.An alternative technical implementation of the goal of short-circuiting the electric motor would be a pyrotechnic impulse triggering for actively reconfiguring electric lines, in particular in order to create an electric conduction path which leads to the connection points of the electric motor in a short-circuiting manner.A further solution for achieving a short circuit of the electric motor consists in providing an electric circuit arranged as close as possible to the electric motor. This circuit is designed to short-circuit the individual lines, for example for the individual phases of the electric motor, if a control cable of the circuit is not subjected to an electrical voltage. The circuit is mounted in such a way that, in the event of the mechanical disconnection of the electrical conductors between the electric motor and the energy source, it can short-circuit the conductors on the electric motor side. This means, for example, that the connection between the circuit and the conductors for the phases of a three-phase current remains when the electrical energy source is disconnected. This control cable of the circuit is arranged in such a way that, in the case of the mechanical disconnection of the electrical conductors between the electric motor and the energy source, it is likewise disconnected and the short circuit of the electric motor is thus triggered. The disconnection of the electrical conductors can be triggered in an uncontrolled or targeted manner at a specific position, for example by weakening a cable for realizing the electrical conductor or the like. In other words, the circuit serves to short-circuit the lines between the energy source and the electric motor without current being supplied by the control cable. For this purpose, the control cable is likewise cut through when the electrical conductors for supplying the electric motor are broken off.Alternatively, a prestressed force element of the device can also be mechanically coupled to the predetermined breaking point and to at least one of the mechanical conductors in each case and can be designed such that, after the predetermined breaking point has broken open, the force element relaxes and in the process connects the electrical conductors to one another electrically.This mechanical coupling results in the electrical conductors being separated from one another during normal operation of the vehicle and providing a respective continuous line between the electric motor and the energy source. The breaking open of the predetermined breaking point, however, leads to a prestressed force element, such as a prestressed spring, being able to expand, and this force element is in turn mechanically coupled to one or more conductors in such a way that they are brought into connection with one another and the electric motor is short-circuited.According to the invention, the electrical conductors are guided through a common plug connector, wherein the plug connector in its closed state serves to electrically connect the electric motor of the vehicle and the energy source, and wherein in the open state the electrical conductors are interrupted at respective separating points and are connected to one another at ends of the separating points on the electric motor side after the transfer of the plug connector into the open state, wherein the predetermined breaking point is designed to transfer the plug connector from the closed into the open state upon breaking thereof.For this purpose, the predetermined breaking point is in particular designed such that it fundamentally holds two elements of the plug connector together. Only when a sufficiently high mechanical load acts on the predetermined breaking point does it break open and separate the two elements of the plug connector from one another. By separating the two elements of the plug connector from one another, not only is the electrical lines disconnected, as a result of which the electrical connection between the electric motor and the energy source is interrupted, but the electrical conductors are also connected to one another on the electric motor side and are thus short-circuited.According to the invention, the plug connector has at least one prestressed force element which is arranged in each case such that, when the plug connector is moved from the closed into the open state, the respective force element relaxes and in the process connects the ends of the separation points on the electric motor side electrically to one another.According to the invention, the respective force element is an elastic volume element.The elastic volume element is preferably made of elastomer, which in particular forms a continuous material volume via the volume element. For example, the volume element is made of rubber or polymer foam.According to a further advantageous embodiment, the plug connector has at least two prestressed force elements which are arranged such that, when they are relaxed, triggered by the breaking open of the predetermined breaking point, they move respective ends of the disconnection points of the electrical conductors on the electric motor side towards one another and then hold them lying against one another.According to a further advantageous embodiment, the at least one prestressed force element is connected to a short-circuit plate which is arranged and designed such that, when the force element is relaxed, the short-circuit plate is moved and, at the end of the movement of the short-circuit plate, said short-circuit plate establishes an electrical contact between at least two electrical conductors.The short-circuit plate is not necessarily planar or plate-shaped; the geometry is to be selected inter alia depending on the spatial relationships of the electrical conductors to one another. The respective short-circuit plate is preferably made of a metal with a low electrical resistance, for example copper. If the force element, for example a prestressed spring, relaxes, the short-circuit plate(s) is / are moved in such a way that they connect the electrical conductors to one another. If more than two electrical conductors are provided, a plurality of short-circuit plates are advantageously used, so that each of the short-circuit plates connects at least one pair of electrical conductors to one another.In the prior art, the respective force element is often designed as a mechanical spring.According to a further advantageous embodiment, the predefined mechanical limit force is defined by a tensile stress. In this case, the predetermined breaking point tears apart due to tensile stress if a corresponding external force acts on the predetermined breaking point and causes a tensile stress. Alternatively or in combination therewith, the predetermined breaking point could break open in a manner designed for a limit shear stress; there are design degrees of freedom here in order to expediently adapt the predetermined breaking point to the configuration of the vehicle.In a vehicle, a device as described above and below with an electric motor designed as a wheel hub drive motor can be used.Advantages and preferred refinements of the proposed vehicle result from an analogous and analogous transfer of the explanations given above in connection with the proposed device.Further advantages, features and details are evident from the following description, in which--possibly with reference to the drawing--at least one exemplary embodiment is described in detail. Identical, similar and / or functionally identical parts are provided with the same reference numerals.The following are shown: FIG. 1 : shows an energetic structure of a vehicle in which a device for generating an electrical short circuit can be applied. FIG. 2 : A device for generating an electrical short circuit at an electric motor of a vehicle according to an exemplary embodiment of the invention. FIG. 3 : The device of FIG. 2 in the broken-open state of the predetermined breaking point. FIG. 4 : shows an alternative device for generating an electrical short circuit at an electric motor of a vehicle according to an exemplary embodiment of the invention. FIG. 5 : The device of FIG. 4 in the broken-open state of the predetermined breaking point.The representations in the figures are schematic and not to scale.FIG. 1 shows an exemplary architecture of an electric vehicle to which the device described below for generating an electrical short circuit can be applied. An electric motor 1 is designed as an electric machine and is capable of generating a torque by supplying electrical energy in order to accelerate the vehicle, and of recuperation, for which the electric motor 1 can be operated as a generator. The electric motor 1 is powered by a power source 3, in particular a rechargeable battery of the vehicle, which can be recharged by external electricity or by recuperation. The energy source 3 and the electric motor 1 are connected to one another by means of electrical conductors 7.FIG. 2 shows an exemplary device for generating an electrical short circuit at the electric motor 1 of the vehicle, as schematically outlined in FIG. 1. In this case, three electrical conductors 7 are provided, which each run between the energy source 3 and the electric motor 1. The exemplary device is integrated as close as possible to the electric motor 1. The electrical conductors 7 all pass through a common plug connector 11 in this case. the state of the plug connector 11 in FIG. 2 is closed, i.e. the vehicle can maintain its regular operation and the plug connector 11 permits an electrical connection without limitation between the electric motor 1 and the energy source 3. A predetermined breaking point 5 holds a left and a right part of the plug connector 11 together until, for example, an external force acts on the predetermined breaking point 5 so strongly as to separate into two halves due to an accident of the vehicle in which the electric motor 1 together with the hub and wheel releases. This predetermined breaking point 5 can be realized in a continuous material embodiment, but also by a frictional connection of two components. Before the breaking-up takes place, two springs 9 are present as prestressed force elements as energy stores, but are held in their tensioned position by a corresponding bolt of one half of the plug connector 11. During this, the electrical conductors 7 are not connected to one another but rather insulated from one another, and have a respective continuous electrical connection between the electric motor 1 and the energy source 3.FIG. 3 shows the device of FIG. 2, but in a state after the accident of the vehicle has taken place and the predetermined breaking point 5 has been broken open and thus the cohesion of the plug connector 11 is no longer ensured. Rather, the springs 9 no longer experience any counterforce by the other half of the plug connector 11, as a result of which they expand and guide a short-circuit plate 13 arranged in each case at their end to contact points of the electrical conductors 7 in the electric motor-side half of the broken-open plug connector 11, and thus short-circuit the electric conductors 7 on the electric motor side. The predetermined breaking point 5 is completely broken open in this case, so that the disconnection of the electrical conductors 7 and the simultaneously occurring short-circuiting connection of the electrical conductors 7 to the electric motor 1 thus take place permanently and irreversibly. Accordingly, the plug connector 11 has two separable halves, wherein the springs 9 with the short-circuit plates 13 are arranged in the electric motor-side half.FIG. 4 shows an alternative embodiment of a device which leads in principle to the same result as that of FIG. 2, and three electrical conductors 7 are again shown by way of example, which are led between an electric motor 1 and an energy source 3 of the vehicle. All the electrical conductors 7 lead insulated from one another through a plug connector 11 which in turn has two halves which are separated when a predetermined breaking point 5 breaks open. FIG. 4 shows the unseparated state of the device, the plug connector 11 is intact and all the electrical conductors 7 are separated from one another in an insulated manner and each has an electrical connection between the electric motor 1 and the energy source 3 by itself. However, a respective spring 9 is arranged on a first and on a second of the electrical conductors 7 and is under prestress, while the device is intact. As long as the two halves of the plug connector 11 are held together, the upper and lower electrical conductors 7 are separated from one another and electrically insulated. If the two halves are separated, the spring force of the springs 9, because of the wedge-shaped contour of the halves, not only causes the electrical conductors 7 to be pressed against one another, but also causes the two halves of the plug connector 11 to be separated.FIG. 5 shows the state of the plug connector 11 of FIG. 4 after the predetermined breaking point 5 is broken open by the action of an external force. Again, the two halves of the plug connector 11 no longer hold together and each of the electrical conductors 7 is separated, so that there is no longer any electrical connection between the electric motor 1 and the energy source 3. By separating the two halves of the plug connector 11, however, the two springs 9 can be relaxed and thereby press all the electrical conductors 7 against one another, as a result of which these are short-circuited. This in turn leads to a short circuit at the electric motor 1.Although the invention has been illustrated and explained in more detail by preferred exemplary embodiments, the invention is not restricted by the disclosed examples and other variations can be derived therefrom by the person skilled in the art without departing from the scope of protection of the invention. It is therefore clear that a large number of possible variations exist. It is also clear that embodiments mentioned by way of example represent only examples which are not to be understood in any way as limiting, for example, the scope of protection, the possible applications or the configuration of the invention. Rather, the preceding description and the description of the figures enable the person skilled in the art to implement the exemplary embodiments in concrete terms, wherein the person skilled in the art, knowing the disclosed inventive concept, can make various changes, for example with regard to the function or the arrangement of individual elements mentioned in an exemplary embodiment, without departing from the scope of protection defined by the claims and their legal equivalents, such as further explanations in the description.List of reference characters1 Electric motor 3 Energy source 5 Predetermined breaking point 7 Conductor 9 Force element 11 Plug connector 13 Short-circuit plate

Claims

Device for generating an electrical short circuit at an electric motor (1) of a vehicle, having an electrical connection with electrical conductors (7) in order to connect the electric motor (1) of the vehicle to an electrical energy source (3) of the vehicle, wherein the device has a predetermined breaking point (5) which breaks when a predefined mechanical limit force is exceeded, wherein the electrical conductors (7) are mechanically coupled to the predetermined breaking point (5) in such a way that, when the predetermined breaking point (5) breaks, the electrical conductors (7) are cut through in their course between the electric motor (1) and the energy source (3) but are connected to one another on the electric motor side in order to electrically short-circuit the electric motor (1), wherein the electrical conductors (7) are guided through a common plug connector (11), wherein the plug connector (11), in its closed state, serves to electrically connect the electric motor (1) of the vehicle and the energy source (3), and wherein, in the open state, the electrical conductors (7) are interrupted at respective separating points and are connected to one another at ends of the separating points on the electric motor side when the plug connector (11) is transferred into the open state, wherein the predetermined breaking point (5) is designed to transfer the plug connector (11) from the closed into the open state when it breaks open, wherein the plug connector (11) has at least one prestressed force element (9) which is arranged in each case such that, when the plug connector (11) is transferred from the closed into the open state, the respective force element (9) relaxes and in the process connects the ends of the separating points on the electric motor side electrically to one another, characterized in that the respective force element (9) is an elastic volume element.Device according to claim 1, characterised in that the plug connector (11) has at least two prestressed force elements (9) which are arranged such that, when they are relaxed, triggered by the breaking open of the predetermined breaking point (5), they move respective ends of the cut-off points of the electrical conductors (7) on the side of the electric motor towards one another and then hold them against one another.Device according to claim 1, characterised in that the at least one prestressed force element (9) is connected to a short-circuit plate (13) which is arranged and designed such that, when the force element (9) is relaxed, the short-circuit plate (13) is moved and, at the end of the movement of the short-circuit plate (13), said short-circuit plate makes electrical contact between at least two electrical conductors (7).Device according to one of the preceding claims, characterized in that the predefined mechanical limit force is defined by a tensile stress.

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