DC overcurrent protection apparatus

A DC overcurrent protection apparatus includes an ignition current-controlled irreversible high-current switch-off element, an overcurrent detection unit which is electrically connected in a high-current path in series with the ignition current-controlled irreversible high-current switch-off element, and control contacts configured to control the ignition current-controlled irreversible high-current switch-off element. The control contacts are arranged such that they are electrically connectable to one another. The overcurrent detection unit is configured such that, when an overcurrent with a value equal to or greater than a predetermined current value flows in the high-current path, the control contacts, on account of an electromagnetic force generated by the overcurrent, are electrically connected to each other such that an ignition current is transmitted to the ignition current-controlled irreversible high-current switch-off element and the ignition current-controlled irreversible high-current switch-off element is switched by control to a switched-off state.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to a DC overcurrent protection apparatus, which comprises an ignition current-controlled irreversible high-current switch-off element, an overcurrent detection unit and control contacts for controlling the ignition current-controlled irreversible high-current switch-off element.

Many applications exist in which a direct current, also described as a DC current, must be restricted to a maximum value, in order to protect components against an overcurrent in the event of an overload or a short-circuit. One example is the high-voltage on-board network of an electric or hybrid vehicle. In this example, two contactors and a fuse are customarily incorporated in a high-voltage battery. The contactors isolate the high-voltage battery from other components in the vehicle in normal duty, and in the event of smaller overload currents. The fuse assumes the isolating function in the event of high overload and short-circuit currents. A conventional fuse has a disadvantage, in that it operates by the thermal principle, and thus requires a long current-dependent time interval for the interruption of the current flow. Accordingly, in the event of not too high currents, it may not be sufficiently rapid to protect the vehicle components against an overload.

In consequence, concepts already exist in which a pyrotechnic switch-off element is employed, in addition to conventional switching elements (contactors, fuses). An ignition element (also described as a detonator) of the pyrotechnic switch-off element is tripped by means of a current signal, and executes the interruption of the high-current path. The ignition signal is generated by an electronic control circuit, which measures the high current to be monitored and generates the ignition signal immediately the current in the high-voltage network exceeds a maximum permissible value.

This type of actuation of the pyrotechnic switch-off element has the following disadvantages: the current measurement circuit can be disturbed, and this disturbance can result in spurious tripping or, conversely, in non-tripping in response to an overcurrent. The current measurement circuit incorporating ignition electronics can be of a complex design, with a high failure rate. For its operation, the current measurement circuit requires energy at all times, and thus increases current consumption, if it is not completely deactivated.

The object of the present invention is the alleviation or elimination of the above-mentioned disadvantages of the prior art. Specifically, a DC overcurrent protection apparatus is disclosed which, for the prevention of spurious tripping, is insensitive to disturbances, specifically electromagnetic disturbances, is not associated with continuous current consumption, has a low failure rate, and responds rapidly to an overcurrent.

According to the invention, the above-mentioned object is fulfilled by the characteristics of the independent claim. Advantageous embodiments are the subject matter of sub-claims.

The DC overcurrent protection apparatus according to the invention comprises an ignition current-controlled irreversible high-current switch-off element, an overcurrent detection unit which is electrically connected in a high-current path in series with the ignition current-controlled irreversible high-current switch-off element, and control contacts for controlling the ignition current-controlled irreversible high-current switch-off element, which are arranged such that they can be electrically connected to one another. The overcurrent detection unit is designed such that, when an overcurrent with a value equal to or greater than a predetermined current value flows in the high-current path, the control contacts, on account of an electromagnetic force which is generated by the overcurrent, are electrically connected to each other in such a way that an ignition current is transmitted to the ignition current-controlled irreversible high-current switch-off element, so that the ignition current-controlled irreversible high-current switch-off element is switched by control to a switched-off state.

In one form of embodiment of the invention, the ignition current-controlled irreversible high-current switch-off element is a pyrotechnic switch-off element. Hereinafter, a normal current is understood as a current having a value in the range of approximately 1,000 amperes (abbreviated hereinafter to “A”) to approximately 1,500 A. Currents equal to or greater than approximately 1,500 A and smaller than approximately 3,000 A can be reversibly switched by means of a contactor. The high-current path is understood as an electrical path which conducts high currents equal to or greater than approximately 1,500 A up to a value of less than approximately 3,000 A. In one form of embodiment, currents of this type can be present in a high-voltage on-board network, which carries voltages between approximately 400 V and approximately 800 V, in a vehicle, specifically an electric, hybrid or fuel cell vehicle. Beyond approximately 3,000 A, an overcurrent may be present such that, in one form of embodiment, the predefined current value in the high-current path is approximately 3,000 A, and specifically is 3,000 A.

The electromagnetic force generated by the overcurrent can be, for example, a Lorentz force. The electromagnetic force is also understood as the force which, upon the flow of an electric current in any contact arrangement in the high-current path, is such that at least partially opposing and mutually touching high-current contact elements in said contact arrangement are mutually repulsed by the flow of current. This repulsive force occurs if the current in one of the two contact elements flows in one direction, transversely to a contact surface of said contact element and, in the other of the two contact elements, flows in another direction, transversely to a contact surface of the other contact element. The partially or totally mutually opposing, but at least directionally differing partial currents of the current flowing in the contact arrangement generate a repulsive force on the contact surfaces of the high-current contact elements of said contact arrangement. This effect in DC contacts is also described as electromagnetic levitation.

The apparatus according to the invention is insensitive to disturbances, specifically to electromagnetic disturbances which can impair a current measurement, but do not have sufficient energy to generate an electromagnetic force of sufficient magnitude and duration to cause the mutual electrical bonding of the control contacts. Spurious tripping of the irreversible high-current switch-off element by electromagnetic disturbances of this type is prevented accordingly.

In response to an electromagnetic force generated by the overcurrent, the control contacts which, at a high current which lies below the overcurrent value, are mutually separated, i.e. open, are mutually bonded, i.e. short-circuited, or are connected to an energy source for the generation of the ignition current, in order to transmit the ignition current to the ignition current-controlled irreversible high-current switch-off element. Accordingly, the electrical energy required to initiate the transmission of the ignition current is only tapped from the high-current path if an overcurrent is present. The apparatus according to the invention thus features no continuous current consumption. Forms of embodiment, described with reference to the figures hereinafter, for the generation of the electromagnetic force, associated with the overcurrent, for the mutual electrical connection of the control contacts can be realized without the use of electronic components, such that the failure rate of the apparatus is very low, and is reduced in comparison with conventional apparatuses. As a result of the simple design of the apparatus according to the invention, which employs the overcurrent for the transmission of the ignition current to the irreversible high-current switch-off element, the apparatus responds very rapidly, and more rapidly than conventional apparatuses.

In one form of embodiment of the invention, the overcurrent detection unit incorporates a retaining element, which is arranged between a wall section of the overcurrent detection unit and a permanent magnet which is moveable in relation to said wall section and held in the direction of the wall section by a retaining force of the retaining element, and to which a first control contact is attached. The high-current path is configured as a winding around the permanent magnet, and the overcurrent detection unit is configured such that, if the overcurrent flows in the high-current path, the permanent magnet moves against the retaining force of the retaining element, such that the first control contact engages with a second stationary control contact, which is arranged opposite said wall section. As a result, the first control contact is short-circuited with the second control contact, such that an energy source which is connected to the second control contact transmits the ignition current to the ignition current-controlled irreversible high-current switch-off element.

The arrangement for the short-circuiting of the control contacts is of simple conception, and comprises only a high-current path winding, the permanent magnet and a retaining element. Consequently, this DC overcurrent protection apparatus according to the invention is exceptionally fail-safe and reliable, and trips rapidly in the event of an overcurrent. Energy is only tapped from the high-current path in the event of an overcurrent, as a result of which the apparatus consumes little current. In this form of embodiment, the overcurrent detection unit is completely reversible, i.e. it can be reused, with no modification, further to the occurrence of an overcurrent, and is therefore reliable and of a low-maintenance design.

Only the spontaneous discharging of the energy source for the generation of the ignition current will require compensation on an occasional basis. A capacitor, a double-layer capacitor, a battery, a high-voltage battery supplying the on-board network which is to be protected against an overcurrent itself, or similar, can be employed as an energy source. Where applicable, a charging circuit can be implemented which recharges the energy source periodically, or in the event of a decline to a minimum energy value which is required for the maintenance of the operation of the energy source, in order to offset spontaneous discharging.

In this form of embodiment, the control contacts are incorporated in the overcurrent detection unit. However, forms of embodiment are also conceivable in which the permanent magnet is brought out of a housing of the overcurrent detection unit, and the first and/or second control contact are/is arranged outside the overcurrent detection unit.

The winding can be configured such that the high-current path incorporates an inductance, which comprises at least one loop.

In a further form of embodiment of the invention, the overcurrent detection unit incorporates a retaining element, which is arranged between a wall section of the overcurrent detection unit and a high-current-conducting bracket, which is moveable in relation to said wall section, to which a first control contact is attached. The bracket is held in the direction of the wall section by a retaining force of the retaining element, such that a flow of current in the high-current path is routed through the bracket, and the bracket constitutes an element of the high-current path. The overcurrent detection unit is configured such that, if the overcurrent flows in the high-current path, the bracket moves against the retaining force of the retaining element, such that the first control contact engages with a second stationary control contact, which is arranged opposite said wall section, as a result of which the first control contact is short-circuited with the second control contact. By means of this short-circuit, an energy source which is connected to the second control contact transmits the ignition current to the ignition current-controlled irreversible high-current switch-off element.

The first control contact can be separated from the bracket by an insulating element in the form of an insulating layer. The insulating element can be formed of plastic, or of another non-conductive material. The first control contact can be fitted to one side of the bracket, which is arranged opposite a side of the bracket to which the retaining element is attached.

As the bracket constitutes an element of the high-current path, the design of the short-circuiting arrangement for the control contacts can be even simpler than in the preceding forms of embodiment, and require only the incorporation of two contact points in the high-current path for the constitution of the bracket, and the fitting of a retaining element to the bracket. In this form of embodiment, the control contacts are incorporated in the overcurrent detection unit. In other forms of embodiment, the first and/or the second control contact can be arranged outside the overcurrent detection unit.

In a particular form of embodiment of the invention, the overcurrent detection unit incorporates a retaining element, which is arranged between a wall section of the overcurrent detection unit and a high-current-conducting bracket, which is moveable in relation to said wall section. The bracket is retained by a retaining force of the retaining element in the direction of the wall section, such that a current flow in the high-current path is routed through the bracket, and the bracket constitutes an element of the high-current path. In one direction of the current flow in the high-current path, a first control contact, up-circuit of the element of the high-current path constituted by the bracket, and a second control contact, down-circuit of the element of the high-current path constituted by the bracket, are respectively connected to the high-current path. The overcurrent detection unit is configured such that, if the overcurrent flows in the high-current path, the bracket, against the retaining force of the retaining element, moves away from the element of the high-current path which is not constituted by the bracket such that, on at least one high-current contact point between the bracket and the element of the high-current path which is not constituted by the bracket, an arc is generated, the resistance of which results in a voltage drop across the first and second control contacts. In response to the voltage and the resistance, the ignition current is transmitted to the ignition current-controlled irreversible high-current switch-off element.

In this form of embodiment, the arc which is generated when the bracket, in the event of an overcurrent, is separated from that element of the high-current path which is not constituted by the bracket, is employed as an energy source for the generation of the ignition current. An arc can occur at either end of the bracket. Alternatively, one end of the bracket can be rotatable, and connected to that element of the high-current path which is not constituted by the bracket in an electrically conductive manner. Conversely to the forms of embodiment described above, the control contacts are therefore not short-circuited, but are electrically interconnected via a resistance, which is constituted by the arc. The control contacts which are connected to that element of the high-current path which is not constituted by the bracket can be arranged such that the bracket is connected in-circuit between the control contacts. Accordingly, an arrangement of the control contacts, or of one of the two control contacts, either within or outside the overcurrent detection unit is possible.

In the forms of embodiment of the invention with the bracket described, the retaining element can be configured as a solid retainer, which fails if the electromagnetic force generated by the overcurrent exceeds a predefined value. The retaining element can thus be constituted in a simple and cost-effective manner.

In a further form of embodiment of the DC overcurrent protection apparatus according to the invention, the overcurrent detection unit incorporates a retaining element, which is arranged between a wall section of the overcurrent detection unit and a high-current-conducting bracket, which is moveable in relation to said wall section. The bracket is retained by a retaining force of the retaining element in the direction of the wall section, and a permanent magnet is attached to the bracket and is carried in a winding such that, if no control voltage from a voltage source is present on the winding, a flow of current in the high-current path through the bracket is prevented, and the bracket does not constitute an element of the high-current path. If the control voltage from the voltage source is present on the winding, and a current which is smaller than the predefined current is flowing in the high-current path, the bracket moves against the retaining force of the retaining element, such that the flow of current in the high-current path is routed through the bracket, and the bracket constitutes an element of the high-current path. In one direction of the current flow in the high-current path, a first control contact, up-circuit of the element of the high-current path constituted by the bracket, and a second control contact, down-circuit of the element of the high-current path constituted by the bracket, are respectively connected to the high-current path. Between at least one of the first and second control contacts and the ignition current-controlled irreversible high-current switch-off element, a contactor, which is connected to the voltage source, is connected in-circuit such that, if no control voltage from the voltage source is present on the winding and on the contactor, and the bracket does not constitute an element of the high-current path, a no-load voltage which is present across the first and second control contacts does not result in the transmission of the ignition current to the ignition current-controlled irreversible high-current switch-off element. The overcurrent detection unit is configured such that, if the overcurrent flows in the high-current path, the bracket, notwithstanding the control voltage from the voltage source which is present on the winding and on the contactor, moves away from that element of the high-current path which is not constituted by the bracket, in the direction of the retaining force of the retaining element, such that, on at least one high-current contact point between the bracket and the element of the high-current path which is not constituted by the bracket, an arc is generated. The arc has a resistance, which results in a voltage drop across the first and second control contacts. In response to the voltage and the resistance, the ignition current is transmitted to the ignition current-controlled irreversible high-current switch-off element.

In this form of embodiment, the overcurrent detection unit constitutes a high-voltage contactor, wherein, by means of the contactor, it is prevented that any no-load voltage which is present across the bracket when the high-voltage contactor is open results in the transmission of the ignition current to the irreversible high-current switch-off element. Consequently, this switch-off element is only tripped if the high-voltage contactor is closed to permit a flow of current in the high-current path, and an overcurrent occurs such that an arc is generated between the bracket and the element of the high-current path which is not constituted by the bracket which is sufficient to trip the interruption by the irreversible high-current switch-off element of the current flow in the high-current path. At currents below the overcurrent, or in the event of a residual current flow, the overcurrent detection unit can reversibly interrupt or close the high-current path.

Advantageously, in all the DC overcurrent protection apparatuses according to the invention described above, the retaining element can be configured as a spring.

The DC overcurrent protection apparatus according to the invention, in an advantageous form of embodiment, can be incorporated in a housing and/or in the form of a subassembly.

The DC overcurrent protection apparatus according to the invention can additionally be incorporated in a high-voltage on-board network of a vehicle, preferably of an electric or hybrid vehicle.

Exemplary embodiments of the invention are described in greater detail hereinafter with reference to figures. In the interests of clarity, any true-to-scale or proportionally accurate representation has been omitted from the figures. In the figures, unless indicated otherwise, the same reference symbols identify identical components, having the same significance.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1shows a schematic arrangement of the DC overcurrent protection apparatus100according to the invention, with an ignition current-controlled irreversible high-current switch-off element2, which is electrically connected in series to an overcurrent detection unit1in a high-current path4. The ignition current-controlled irreversible high-current switch-off element2is configured as a pyrotechnic switch-off element, and is electrically connected to a first ignition current transmission line13. An energy source3, for example a capacitor, a double-layer capacitor, a battery, or a high-voltage battery of a high-voltage on-board network which is to be protected against an overcurrent, is connected via the ignition current transmission line13to the pyrotechnic switch-off element. By the short-circuiting of control contacts11, which are incorporated in the overcurrent detection unit1, upon the occurrence of an overcurrent in the high-current path4, the energy source3can be connected to the pyrotechnic switch-off element2, such that an ignition current is transmitted from the energy source3to the pyrotechnic switch-off element, in order to switch the pyrotechnic switch-off element2to a switched-off state. Immediately the switched-off state is achieved, a flow of current in the high-current path4is prevented by the pyrotechnic switch-off element2.

The switching of the pyrotechnic switch-off element2to the switched-off state is irreversible such that, after the switch-off thereof, the pyrotechnic switch-off element2must be replaced in order to permit the further operation of the DC overcurrent protection apparatus. The function of the DC overcurrent protection apparatus is to permit the conduction of a normal high current, between approximately 1,500 A and a value of less than approximately 3,000 A, in the high-current path4and, in the event of an overcurrent of approximately 3,000 A or greater, to prevent a flow of current in the high-current path4. The overcurrent detection unit1according to the invention is configured such that, if an overcurrent flows in the high-current path4, the control contacts11, as a result of an electromagnetic force generated by the overcurrent, are short-circuited such that an ignition current is transmitted from the energy source3to the ignition current-controlled irreversible high-current switch-off element2, thereby switching said switch-off element2to the switched-off state.

FIG. 2shows the layout of the DC overcurrent protection apparatus100according to the invention in a further form of embodiment, with a fully-reversible overcurrent detection unit1which, further to the occurrence of the overcurrent in the high-current path4, can be re-used with no modification. The overcurrent detection unit1comprises a winding in the form of an inductance which, in the simplest case, as represented inFIG. 2, is configured as a conductor loop12in the high-current path4. The conductor loop12is routed around a permanent magnet8which, at one end, by means of a retaining element5in the form of a retaining spring, is connected to a wall section of a housing of the overcurrent detection unit1. The permanent magnet8is retained by means of a retaining force of the retaining element5in the direction of the wall section (see arrow Ff inFIG. 2) and, at another end, which lies opposite the first end, incorporates a first control contact11A which, in the event of a normal high current below the overcurrent in the high-current path4, is arranged opposite a stationary second control contact11B on the wall section, and is electrically connected to the pyrotechnic switch-off element2by means of a first control conductor13A.

A magnetic field generated by the conductor loop12in the event of a flow of current in the high-current path4acts on the permanent magnet8, and can result in the movement of the permanent magnet8. Immediately a current in the high-current path4achieves or exceeds the overcurrent value, i.e. becomes an overcurrent rather than a normal high current, an overcurrent is present, resulting in the generation by the conductor loop12of a magnetic field which is sufficiently strong to move the permanent magnet8against the retaining force of the retaining element5(see arrow Fi inFIG. 2), such that the moveable first control contact11A engages with the second stationary control contact11B, thereby resulting in the short-circuiting of the first and second control contacts11A,11B. As a result of the short-circuit on the first and second control contacts11A,11B, the energy source3, which is connected by means of a second control conductor13B to the second contact11B, is bonded to the pyrotechnic switch-off element2via a second ignition current transmission line13C, such that an ignition current is transmitted to the pyrotechnic switch-off element2for the switch-off of said pyrotechnic switch-off element2, thereby resulting in the interruption of a flow of current in the high-current path4.

FIG. 3Ashows the layout of the DC overcurrent protection apparatus100according to the invention, with an irreversible overcurrent detection unit1, at a normal high current below the overcurrent, in a further form of embodiment according to the schematic arrangement represented inFIG. 1. The overcurrent detection unit1incorporates a retaining element5A, which is arranged between a wall section of a housing of the overcurrent detection unit1and a high-current-conducting bracket6, arranged opposite the wall section in a moveable manner, to which the first control contact11A is attached. The first control contact11A is separated from the bracket6in an electrically-insulated manner by an insulating layer7. The bracket6is retained by a retaining force of the retaining element5A in the direction of the wall section (see arrow Ff inFIG. 3A), such that a current flow in the high-current path4, in the event of a normal high current below the overcurrent, is routed through the bracket6, such that the bracket6constitutes an element of the high-current path4.

Ends of the bracket6constitute high-current contacts with sections4A,4B of the element of the high-current path4which is not constituted by the bracket6. The bracket6is compressed against the high-current contacts by the retaining element5A, in the form of a retaining spring, such that, in the event of a current, the value of which is lower than the overcurrent value, in the high-current path4, this current is routed through the bracket6as an element of the high-current path4. In accordance with the DC overcurrent protection apparatus represented inFIG. 2, in the DC overcurrent protection apparatus according toFIG. 3A, the first control contact11A, at a normal high current in the high-current path4, is also arranged with a clearance to a second control contact11B, in a stationary manner with respect to the wall section, such that the first control contact11A is electrically connected to the pyrotechnic switch-off element2by means of a first control conductor13A. The energy source3, which is connected to the second contact11B via a second control conductor13B, is connected to the pyrotechnic switch-off element2via the second ignition current transmission line13C. In the presence of a current, an electromagnetic force is generated on each high-current contact in the high-current path4, which endeavors to separate the high-current contacts (see arrow Fi inFIG. 3A).

FIG. 3Bshows the layout of the DC overcurrent protection apparatus100according to the invention, as represented inFIG. 3A, in the event of an overcurrent. If an overcurrent flows in the high-current path4, the bracket6is moved against the retaining force of the retaining element (see arrow Fi inFIG. 3B), such that the first control contact11A engages with the second stationary control contact11B, as a result of which the first control contact11A and the second control contact11B are short-circuited, such that the energy source3transmits the requisite ignition current15to the pyrotechnic switch-off element2for the switch-off of said pyrotechnic switch-off element2, thereby resulting in an interruption16in the high-current path4.

If the current in the high-current path4exceeds a predefined overcurrent value, the high-current contacts on sections4A,4B of the high-current path4are mutually separated, and the bracket6moves against the retaining force of the retaining element5A, thereby short-circuiting the first and second control contacts11A,11B. Upon the separation of the high-current contacts, an arc14is generated on each of said high-current contacts. Advantageously, the arc14has a high resistance, thereby reducing the flow of current in the high-current path4. As a result, the interruption/suppression by the pyrotechnic switch-off element2of the current/current flow in the high-current path4is simplified. The employment of the arc14as a resistance in the interests of an easier switch-off by the pyrotechnic switch-off element2is particularly advantageous in the event of very high short-circuit currents in the high-current path4. However, the arc14, potentially associated with sparking, results in permanent damage to the overcurrent detection unit1such that, further to the occurrence of an overcurrent, the overcurrent detection unit1cannot be restored to regulation duty without the replacement of the damaged sections4A,4B of the high-current path4and the bracket6.

In the DC overcurrent protection apparatus100represented inFIGS. 3A and 3B, in place of the retaining element5A in the form of the retaining spring, a solid retainer can be employed, which fails if the electromagnetic force exceeds the predefined value for an overcurrent.

FIG. 4shows the layout of the DC overcurrent protection apparatus100according to the invention in a further form of embodiment, with a bracket6connected in-circuit between control contacts11C,11D, in the event of an overcurrent. High-current contacts are constituted by ends of the bracket6and sections4A,4B of the high-current path4. The overcurrent detection unit1incorporates a retaining element5B, which is arranged between a wall section of a housing of the overcurrent detection unit1and the high-current-conducting bracket6, which is moveable in relation to said wall section. The bracket6is retained by a retaining force of the retaining element5B (see arrow Ff inFIG. 4) in the direction of the wall section, such that a current flow in the high-current path4, at a current below the overcurrent, is routed through the bracket6, and the bracket6constitutes an element of the high-current path4. In this respect, the layout of the overcurrent detection unit1represented inFIG. 4corresponds to the layout of the overcurrent detection unit1which is represented inFIGS. 3A, 3B.

In a distinction from the overcurrent detection unit1represented inFIGS. 3A, 3B, in one direction of the current flow in the high-current path4(see arrows in the high-current path4, which indicate the flow from the overcurrent detection unit1to the pyrotechnic switch-off element2), the first control contact11C is connected, up-circuit of the element of the high-current path4constituted by the bracket, to section4A of the high-current path4. In the direction of the current flow in the high-current path4, the second control contact11D is connected, down-circuit of the element of the high-current path4constituted by the bracket6, to section4B of the high-current path4.

If the overcurrent flows in the high-current path4, the bracket6moves against the retaining force of the retaining element5B, away from the element of the high-current path4, including the sections4A,4B, which is not constituted by the bracket (see arrow Fi inFIG. 4), such that an arc14is generated respectively on the high-current contact points between the bracket6and the sections4A,4B of the high-current path4, the resistance of which results in a voltage drop across the first and second control contacts11C,11D. This voltage, and the resistance of the arc14, generate the ignition current15, which is transmitted to the pyrotechnic switch-off element2for the execution of an interruption16in the high-current path4.

In the DC overcurrent protection apparatus100represented inFIG. 4, conversely to the DC overcurrent protection apparatus100represented inFIGS. 3A, 3B, there is no energy source3which is connected to the second control conductor13B and the second ignition current transmission line13C. Instead, the bracket6is connected in-circuit between the first and second control contacts11C,11D such that, in the event of an overcurrent, arcs14generated at the ends of the bracket6and sections4A,4B of the high-current path4have a voltage and a resistance which are sufficient for the generation of the requisite ignition current15for the interruption of the high-current path4, and for the transmission thereof to the pyrotechnic switch-off element2. Conversely to the DC overcurrent protection apparatus represented inFIGS. 3A, 3B, in the form of embodiment represented inFIG. 4there are no mutually moveable control contacts, which are short-circuited in the event of an overcurrent in order to permit the delivery by the energy source3of the ignition current to the pyrotechnic switch-off element2. Instead, the first and second control contacts11C,11D are directly electrically connected to the pyrotechnic switch-off element2in a mutually stationary arrangement on the high-current path4by means of third and fourth control conductors13D,13E, wherein, in a further alternative form of embodiment, indirect connection is possible, such that the arc14or the voltage generated by the arc14on the high-current contacts at the ends of the bracket6constitutes the energy source for the ignition of the pyrotechnic switch-off element2.

In normal duty, at currents below the overcurrent, the high-current contacts are closed, and the voltage drop across these high-current contacts is small, and is not sufficient for the ignition of the pyrotechnic switch-off element2. If, however, in the event of an overcurrent, an arc14is generated on at least one end of the bracket6, a large voltage drop occurs across said bracket6, as the arc has a high resistance. This voltage is sufficient to ignite the pyrotechnic switch-off element2, and to trip the interruption16of the high-current path.

FIG. 5shows the layout of a further form of embodiment of the DC overcurrent protection apparatus100according to the invention, with a bracket6connected in-circuit between first and second control contacts11E,11F and, below the overcurrent, a reversibly-isolating overcurrent detection unit1, in the event of an overcurrent. The overcurrent detection unit1incorporates a retaining element5C, which is arranged between a wall section of a housing of the overcurrent detection unit1and a high-current-conducting bracket6, which is moveable in relation to said wall section. The bracket is retained by a retaining force of the retaining element5C in the direction of the wall section, and a permanent magnet18is attached to the bracket6and is carried in a winding22such that, if no control voltage from a voltage source20is present on the winding22, a flow of current in the high-current path4through the bracket6is prevented, and the bracket6does not constitute an element of the high-current path4. If the control voltage from the voltage source20is present on the winding22, and a current which is smaller than the overcurrent flows in the high-current path4, the bracket6moves against the retaining force of the retaining element5C, such that the flow of current in the high-current path4is routed through the bracket6, and the bracket6constitutes an element of the high-current path4.

High-current contacts are constituted by ends of the bracket6and sections4A,4B of the high-current path4. In accordance with the overcurrent detection unit1represented inFIG. 4, in one direction of the current flow in the high-current path4, the first control contact11E, up-circuit of the element of the high-current path4constituted by the bracket, is connected to section4A of the high-current path4. In the direction of the current flow in the high-current path4, the second control contact11F, down-circuit of the element of the high-current path4constituted by the bracket6, is connected to section4B of the high-current path4. In a distinction from the DC overcurrent protection apparatus represented inFIG. 4, in the apparatus according to the invention represented inFIG. 5, the first and second control contacts11E,11F are not incorporated in the overcurrent detection unit1, but are connected outside the overcurrent detection unit1to the sections4A,4B of the high-current path4.

The first control contact11E is connected via the third control conductor13D to the pyrotechnic switch-off element2. Between the second control contact11F and the pyrotechnic switch-off element2, via a fifth control conductor13F and a sixth control conductor13G, a contactor21is connected which, in turn, is connected to the voltage source20. Energy for the voltage source20and/or the overcurrent detection unit1can be tapped, for example, from an on-board network at a voltage of 12V or 48V in a vehicle, specifically an electric, hybrid or fuel cell vehicle. If no control voltage from the voltage source20is present on the winding22and on the contactor21, and the bracket6does not constitute an element of the high-current path4, the contactor21ensures that a voltage dropped across the first and second control contacts11E,11F, also described as the no-load voltage, does not result in the transmission of an ignition current15to the pyrotechnic switch-off element2.

If an overcurrent flows in the high-current path4, the bracket6, notwithstanding the control voltage from the voltage source20which is present on the winding22and on the contactor21, moves away from that element of the high-current path which is not constituted by the bracket, in the direction of the retaining force of the retaining element5C, such that, on the high-current contact points between the ends of the bracket6and the sections4A,4B of the element of the high-current path4which is not constituted by the bracket6, an arc14is generated in each case, having a resistance, which results in a voltage drop across the first and second control contacts11E,11F. In response to the voltage and the resistance of the arcs14, the ignition current15is transmitted to the pyrotechnic switch-off element2, thereby resulting in the interruption of the high-current path4by the pyrotechnic switch-off element2.

In the form of embodiment represented inFIG. 5, the bracket6, the sections4A,4B of the high-current path4, the retaining element5C, the permanent magnet18and the winding22of the overcurrent detection unit1constitute a high-current contactor. In the absence of a control voltage from the voltage source20, the high-current contactor is open, such that a current flow in the high-current path4is interrupted. This state can occur in a parked vehicle with the ignition switched off. In the open state of the high-current contactor, said high-current contactor shows a high resistance, and it must be ensured accordingly that a voltage across this resistance or present on the high-current contactor does not result in the ignition of the pyrotechnic switch-off element2. To this end, the contactor21, which is required to be able to switch a lower current than the high-current contactor, is arranged in the ignition circuit which comprises the third, fifth and sixth control conductors13D,13F,13G. Advantageously, the contactor21is supplied with a control voltage from the same voltage source20as the high-current contactor. In this arrangement, an ignition current only flows in the ignition circuit if, firstly, the control voltage is present on the high-current contactor, and the high-current contactor is therefore genuinely in a closed state, such that current can flow in the high-current path4, and secondly the current flowing through the high-current contactor in the high-current path4is sufficiently high to separate the high-current contacts at the ends of the bracket6, such that an arc14is generated, resulting in a voltage which delivers the requisite ignition current to the pyrotechnic switch-off element2for the interruption of the high-current path4.

The form of embodiment of the DC overcurrent protection apparatus100according to the invention represented inFIG. 5can thus effect both the controlled interruption of the high-current path4by the high-current contactor of the overcurrent detection unit1, at currents below the overcurrent, and the interruption of the high-current path4in the event of an overcurrent, by means of the ignition of the pyrotechnic switch-off element2.

All the forms of embodiment described permit the integration of the DC overcurrent protection apparatus according to the invention in a housing or in a component. All the forms of embodiment of the DC overcurrent protection apparatus according to the invention moreover employ an electromagnetic force for the ignition/tripping/switch-off of the pyrotechnic switch-off element2.

The present invention provides the following advantages over the switch-off of the pyrotechnic switch-off element using a switch-off apparatus based upon a current measurement: the DC overcurrent protection apparatus according to the invention is not sensitive to disturbances, specifically to electromagnetic disturbances which can corrupt a current measurement, but which do not have sufficient energy to generate an electromagnetic force, the magnitude and duration of which are sufficient to execute a movement against a retaining element such as a spring. In this manner, any spurious tripping of the pyrotechnic switch-off element in response to such electromagnetic disturbances is prevented. The DC overcurrent protection apparatus according to the invention requires no continuous current for its operation, and is thus associated with no continuous current consumption. Only the spontaneous discharging of any energy source3present, according to the forms of embodiment of the invention represented inFIGS. 1, 2, 3A and 3Bwill require compensation at occasional time intervals. A capacitor, a double-layer capacitor, a battery, a high-voltage battery supplying a high-voltage on-board network which is to be protected, or similar, can be employed as an energy source3. Where applicable, a charging circuit can be implemented in the DC overcurrent protection apparatus according to the invention which recharges the voltage source20periodically, or in the event of a decline to a minimum energy value which is required for the maintenance of the operation of the energy source, in order to offset spontaneous discharging. As the employment of the electromagnetic force for the mutual electrical connection of the control contacts11,11A-11F does not involve any electronic components, the failure rate of the apparatus according to the invention is very low. Moreover, the apparatus according to the invention responds to an overcurrent very rapidly, specifically in the forms of embodiment described with reference toFIGS. 4 and 5.

The characteristics of the invention described with reference to the forms of embodiment represented, including, for example, the arrangement of the first control contact11E outside the overcurrent detection unit1, as represented inFIG. 5, can also be present in other forms of embodiment of the invention, including, for example, the arrangement of the second control contact11D within the overcurrent detection unit1, as represented inFIG. 4, unless indicated otherwise or precluded per se on technical grounds.