Power relay for a vehicle

Abstract

A power relay for a vehicle is disclosed. The power relay has a housing formed by a connector base and a housing can set thereon, two connection bolts being inserted into the connector base for contacting a load circuit. The power relay further has a coil subassembly arranged in the housing and containing a solenoid coil and an armature. The armature is coupled by a force-transmission member to a contact bridge and can shift in the housing, under the effect of a magnetic field generated by the solenoid coil, in such a way that the contact bridge can be reversibly moved between a closing position, in which the contact bridge bridges the connection bolts in an electro conducting manner, and an opening position, in which the contact bridge is not in contact with the connection bolts. The housing can is configured as an injection-molded component made of plastic.

Claims

1. A power relay for a vehicle, comprising: a housing having a connector base and a housing can mounted on said connector base, said housing can being an injection molded component made of plastic; two terminal studs for contacting a load circuit and inserted into said connector base; a coil subassembly disposed in said housing and containing a solenoid coil, an armature, a force-transmission member and a contact bridge, said armature is coupled by said force-transmission member to said contact bridge and can be moved in said housing, under an action of a magnetic field generated by said solenoid coil, such that said contact bridge can be moved reversibly between a closed position, in which said contact bridge bridges said terminal studs in an electrically conducting manner, and an open position, in which said contact bridge is not in contact with said terminal studs; and said coil subassembly further having a magnet yoke, which has a torsionally stable structure, which is accommodated nonrotatably in said housing can over an entire axial height of said housing can.

2. The power relay according to claim 1, wherein said magnet yoke has, as said torsionally stable structure, an integral hoop angled in a U shape with legs which fit around said solenoid coil, parallel to a coil axis of said solenoid coil.

3. The power relay according to claim 1, wherein said connector base is coupled to said magnet yoke in a manner secure against rotation.

4. A power relay for a vehicle, comprising: a housing having a connector base and a housing can mounted on said connector base, said housing can being an infection molded component made of plastic; two terminal studs for contacting a load circuit and inserted into said connector base; a coil subassembly disposed in said housing and containing a solenoid coil, an armature, a force-transmission member and a contact bridge, said armature is coupled by said force-transmission member to said contact bridge and can be moved in said housing, under an action of a magnetic field generated by said solenoid coil, such that said contact bridge can be moved reversibly between a closed position, in which said contact bridge bridges said terminal studs in an electrically conducting manner, and an open position, in which said contact bridge is not in contact with said terminal studs; a potting compound, said connector base is connected fluid tightly to said housing can by means of said potting compound; and said housing can has, on an opening side, an encircling shoulder, on which said connector base rests by means of an encircling radial web, said housing can surrounding said encircling radial web on an outside by means of a collar and projects axially beyond said radial web, with a result that a trough-type receptacle for said potting compound is formed by said collar of said housing can and said connector base.

5. The power relay according to claim 4, wherein: said collar has at least one radial contour formed therein in a form of a radial recess or of a radial projection in a region of said trough-type receptacle; said connector base has at least one mating contour in said region of said trough-type receptacle; and said housing can and said connector base are locked relative to one another in a circumferential direction by a formation of a form-locking joint by said potting compound with said radial contour and said mating contour.

6. The power relay according to claim 5, wherein said radial contour and said mating contour each have at least one undercut formed therein, with a result that said housing can and said connector base are locked relative to one another in a radial direction by a formation of a form-locking joint by said potting compound with said radial contour and said mating contour.

7. A power relay for a vehicle, comprising: a housing having a connector base and a housing can mounted on said connector base, said housing can being an infection molded component made of plastic; two terminal studs for contacting a load circuit and inserted into said connector base; a coil subassembly disposed in said housing and containing a solenoid coil, an armature, a force-transmission member and a contact bridge, said armature is coupled by said force-transmission member to said contact bridge and can be moved in said housing, under an action of a magnetic field generated by said solenoid coil, such that said contact bridge can be moved reversibly between a closed position, in which said contact bridge bridges said terminal studs in an electrically conducting manner, and an open position, in which said contact bridge is not in contact with said terminal studs; and said housing having an excess pressure safeguard, which opens a gas expulsion opening in a case of a critical excess pressure in said housing.

8. The power relay according to claim 7, wherein said excess pressure safeguard is formed by a separately produced valve, which is inserted into said housing can or said connector base.

9. The power relay according to claim 7, wherein said excess pressure safeguard is formed by a predetermined breaking point molded into said housing.

10. The power relay according to claim 9, wherein said predetermined breaking point surrounds a tab-type section of said housing from three sides, and wherein a fourth side of said tab-type section is formed as a film hinge along a connecting line extending between ends of the predetermined breaking point.

11. The power relay according to claim 9, further comprising an electric safety line being coupled mechanically to said predetermined breaking point such that said electric safety line is severed or switched through electrically if said predetermined breaking point fails, wherein said electric safety line is in operative connection with said solenoid coil such that a severing or switching through of said electric safety line which takes place if said predetermined breaking point fails brings about permanent forced electric switching off of the power relay.

12. The power relay according to claim 1, wherein said coil subassembly has, as said force transmission member between said armature and said contact bridge, a coupling rod extending along a coil axis of said solenoid coil.

13. A power relay for a vehicle, comprising: a housing having a connector base and a housing can mounted on said connector base, said housing can being an injection molded component made of plastic; two terminal studs for contacting a load circuit and inserted into said connector base; a coil subassembly disposed in said housing and containing a solenoid coil, an armature, a force-transmission member and a contact bridge, said armature is coupled by said force-transmission member to said contact bridge and can be moved in said housing, under an action of a magnetic field generated by said solenoid coil, such that said contact bridge can be moved reversibly between a closed position, in which said contact bridge bridges said terminal studs in an electrically conducting manner, and an open position, in which said contact bridge is not in contact with said terminal studs; and said coil subassembly is configured as an inherently stable and coherent modular unit, and said coil subassembly having a support body, which is an integral injection molding made of plastic and onto which said solenoid coil is directly wound.

14. The power relay according to claim 13, further comprising a holder for a thermal cutoff for protecting the power relay from overheating is molded onto said support body.

15. The power relay according to claim 13, further comprising at least one holder for a fixed contact of a switching position contact for indicating a position of said contact bridge being molded onto said support body.

16. The power relay according to claim 1, further comprising control electronics, which are configured to activate said solenoid coil several times at short time intervals in a contact cleaning mode, with a result that said contact bridge strikes against said terminal studs several times.

17. A power relay for a vehicle, comprising: a housing having a connector base and a housing can mounted on said connector base, said housing can being an injection molded component made of plastic; two terminal studs for contacting a load circuit and inserted into said connector base; a coil subassembly disposed in said housing and containing a solenoid coil, an armature, a force-transmission member and a contact bridge, said armature is coupled by said force-transmission member to said contact bridge and can be moved in said housing, under an action of a magnetic field generated by said solenoid coil, such that said contact bridge can be moved reversibly between a closed position, in which said contact bridge bridges said terminal studs in an electrically conducting manner, and an open position, in which said contact bridge is not in contact with said terminal studs; and control electronics, being in contact with said terminal studs, said control electronics configured to determine an electric voltage drop across said terminal studs.

18. The power relay according to claim 8, wherein said excess pressure safeguard is a spring-loaded ball valve or a diaphragm.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) FIG. 1 is a diagrammatic, perspective view of a power relay for a heavy goods vehicle from above;

(2) FIG. 2 is a perspective view of the power relay from below;

(3) FIG. 3 is an exploded perspective view of four component subassemblies of the power relay, namely a connector base, a housing can, a coil subassembly and a circuit board carrying control electronics;

(4) FIG. 4 is a top, perspective view of the coil subassembly of the power relay;

(5) FIG. 5 is a bottom, perspective view of the coil subassembly according to FIG. 4;

(6) FIG. 6 is a top, perspective view of a magnetic circuit of the power relay with a magnet yoke and an armature and with a coupling rod, via which the armature acts on a contact bridge (not shown here);

(7) FIG. 7 is a top, perspective view of a support body of the coil subassembly;

(8) FIG. 8 is a bottom perspective view of the support body according to FIG. 7;

(9) FIG. 9 is a cross-sectional view of the support body taken along the cross section line IX-IX shown in FIG. 7;

(10) FIG. 10 is a top, perspective view of the power relay in an unencapsulated preassembly state;

(11) FIG. 11 is a perspective view of the housing of the power relay being an enlarged detail XI from FIG. 10;

(12) FIG. 12 is a longitudinal sectional view of the power relay taken along the longitudinal sectional line XII-XII shown in FIGS. 1 and 2;

(13) FIG. 13 is a longitudinal sectional view of the power relay according to taken along the longitudinal section line XIII-XIII shown in FIGS. 1 and 2;

(14) FIG. 14 is a cross-section view of the power relay taken along the cross section line XIV-XIV shown in FIGS. 1 and 2; and

(15) FIG. 15 is a top, perspective view of the housing can of the power relay.

DETAILED DESCRIPTION OF THE INVENTION

(16) Corresponding parts are always provided with the same reference signs in all the figures.

(17) Referring now to the figures of the drawings in detail and first, particularly to FIGS. 1 and 2 thereof, there is shown a power relay 1 shown as a whole in the figures and contains a housing 2, which is formed by two parts, namely a connector base 3 and a housing can 4. Both the connector base 3 and the housing can 4 are here formed as injection molded components made of plastics.

(18) The connector base 3 delimits the housing 2 in the direction of a connection side, on which the power relay 1 can be brought into contact with an external load circuit and with external control lines. The connection side is also referred to below as the upper side 5irrespective of the actual orientation of the power relay 1 in the surrounding space. With four side walls 6 and a housing bottom 7, the housing can 4 surrounds the remaining sides of an approximately cuboidal housing interior 8 (see FIGS. 12 to 14). In this arrangement, the housing bottom 7 closes off the housing 2 on an underside 9 remote from the upper side 5 (wherein the term underside is also used irrespective of the actual orientation of the power relay 1 in the surrounding space).

(19) To connect two connecting leads to the load circuit to be connected, two solid terminal studs 10, each of which projects outward with a threaded stem 11 from the housing 2, are fixed in the connector base 3. The terminal studs 10 are solid turned parts made of metal, which have a diameter of 0.8 cm in the region of the threaded stem 11, for example. To connect the respective connecting lead of the load circuit, a cable lug on the end of this connecting lead is placed on the associated threaded stem 11 and screwed into contact by a screw nut (contact nut). As an alternative, however, the terminal studs 10 can be formed by sleeves, each having a threaded hole. In this case, contact nuts are replaced by contact screws for bringing the connecting leads into contact, the contact nuts being screwed into threaded holes. As is apparent especially from FIG. 13, the terminal studs 10 are fixed in the connector base 3 by overmolding with the plastics material of the connector base 11.

(20) In order to exclude an electric arc or some other short circuit between the terminal studs 10 and the load-circuit connecting leads that may be secured thereon, a partition wall 12, which projects into the interspace formed between the terminal studs 10, is molded onto the outside of the connector base 3.

(21) To activate the power relay 1, i.e. to trigger switching processes, by which the power relay 1 is switched onby establishing an electrically conductive connection within the housing between the terminal studs 10or switched offby breaking this electrically conducting connectiona plurality of signal terminals 13 (in this case three, by way of example), via which three corresponding external control lines can each be screwed into contact with the power relay 1 by means of respective cable lugs at the ends thereof, are furthermore formed on the connector base 3. Each signal terminal 13 is electrically connected to the housing interior 8 by a connecting conductor 14 in the form of a bent sheet metal stamping. In this arrangement, the connecting conductors 14 are inserted between the connector base 3 and the housing can 4 or are likewise held in the connector base 3 by over molding. Toward the upper side 5, the signal terminals 13 are protected from being touched by a separate plastic cover 15 that can be latched on.

(22) FIG. 3 shows the power relay 1 in a partially disassembled state. From this illustration, it is apparent that the power relay 1 is formed by four subassemblies, each being self-contained. Apart from the housing parts already described, namely the connector base 3 with the terminal studs 10 and signal terminals 13 secured thereon and apart from the housing can 4, the power relay 1 accordingly has a coil subassembly 20 and a conductor support, referred to below as a circuit board 21.

(23) The coil subassembly 20, which is shown on an enlarged scale in FIG. 4, contains a contact bridge 22, which is coupled mechanically by a coupling rod 23 to an armature 24 of a magnetic circuit, which is shown separately in FIG. 6. As can be seen especially from this illustration, the magnetic circuit contains, in addition to the armature 24, a magnet yoke 25, wherein the magnet yoke 25 is formed by a central hollow-cylindrical core 26 concentrically surrounding the coupling rod 23, a hoop 27 bent into a U shape, and two pole shoes 28 extending toward one another from the ends of the legs of the hoop. In this arrangement, the pole shoes 28 enclose the armature 24 between them. The armature 24 and the component parts of the magnet yoke 15 are formed from ferromagnetic material.

(24) In the illustrative embodiment shown, the power relay 1 is a bistable relay. In this case, two plate-shaped permanent magnets 29 are arranged between the pole shoes 28 and each of the ends of the legs of the hoop 27. However, depending on the design of the power relay 1, one or two of the permanent magnets 29 associated with a pole shoe 28 can also be replaced here by ferromagnetic plates of the same size. In the case of a monostable variant (not shown specifically) of the power relay 1, the permanent magnets 29 are completely replaced by ferromagnetic material.

(25) As the component part which gives its name to the device, the coil subassembly 20 contains a solenoid coil 30 (FIG. 4), which lies in the volume framed by the magnet yoke 25. In this arrangement, the solenoid coil 30 surrounds the core 26 of the magnet yoke 25 concentrically and, for its part, is framed by the hoop 27 and the pole shoes 28.

(26) As is apparent especially from FIG. 5, the coil subassembly 20 furthermore contains a number of electric functional elements, namely a switching position contact 31 having two fixed contacts 32 and a moving contact 33 coupled to the coupling rod 23, two freewheeling diodes 34, which are used to provide protection against inductive voltage surges during switching, and a thermal cutoff 35, which brings about forced switching off of the power relay 1 in the event of overheating.

(27) The coil subassembly 20 furthermore contains two auxiliary conductors 36, which are each formed by a bent sheet metal stamping, a damping element 37 and two compression springs surrounding the coupling rod 23, namely a return spring 38 and a contact pressure spring 39 (see FIGS. 12 and 13).

(28) Here, the above-listed component parts of the coil subassembly 20 are held together mechanically by a support body 40, which is shown in isolation in FIGS. 7 to 9. The support body 40 is an integral, multifunctional injection-molded component made of plastics.

(29) On the one hand, the support body 40 supports the solenoid coil 30, which, for this purpose, is wound directly onto a central column 41 of the support body 40. On the other hand, the support body 40 holds the magnet yoke 25 and the armature 24. For this purpose, the armature 24 and the core 26 of the magnet yoke 25 are accommodated in the interior of the hollow column 41 of the support body 40 (see FIGS. 12 to 14). In this arrangement, the armature 24 is provided with sliding support directly on the support body 40. The hoop 27 of the magnet yoke 25 is placed on an upper platform 42 of the support body 40, with the result that its legs project downward laterally outside the solenoid coil 30. The pole shoes 28 and the permanent magnets 29 of the magnet yoke 25 lie in two pockets 44 formed at the opposite end in a lower platform 43 of the support body 40. As is apparent especially from FIG. 9, each of the two pockets 44 is delimited on the insideand thus toward the hollow interior of the column 41by a thin wall 45 of the support body 40, which has a defined wall thickness of 0.3 mm, which is constant at all points. In this arrangement, the walls 45 establish a defined gap width between the magnet yoke 25 and the armature 24.

(30) As can be seen especially from FIG. 8, the support body 40 furthermore has: a) holders 46 for the fixed contacts 32 of the switching position contact 31; b) installation space 47 for the freewheeling diodes 34 (in the illustrative embodiment shown, the freewheeling diodes 34 are held only indirectly on the support body 40 by coil connecting conductors); c) holders 48 for the thermal cutoff 35; d) holders 49 for the auxiliary conductors 36; and e) holders 50 for the damping element 37.

(31) In accordance with the intended purpose, identical support bodies 40 are used here for different designs of the power relay 1. The support body 40 thus has the respectively molded-on holders 46 to 50 even if not all the functional components described above (i.e. the switching position contact 31, the freewheeling diodes 34, the thermal cutoff 35, the auxiliary conductors 36 or the damping element 37) are present in a particular design of the power relay 1.

(32) The circuit board 21 shown in FIG. 3 is formed by the two sections 60 and 61, which are connected to one another in an articulated manner by a film hinge 62 and can therefore be bent out of a planar original state into the L-shaped arrangement shown in FIG. 3. In the electronic design shown of the power relay 1, section 60 carries control electronics 63. Section 61 primarily contains contact points for electrically contacting the fixed contacts 32 of the switching position contact 31, the coil connections with the freewheeling diodes 34, the thermal cutoff 35, the auxiliary conductors 36 and the solenoid coil 30.

(33) In the case of purely electromechanical designs of the power relay 1, the circuit board 21 is optionally likewise present. In this case, however, it does not carry any control electronics 63 but only conductor tracks for bringing the solenoid coil 30 and the electric functional elements that may be present into contact with the signal terminals 13. As an alternative, the circuit board 21 is replaced by wire conductors in purely electromechanical designs of the power relay 1.

(34) In the course of assembling the power relay 1, the support body 40 is first of all fitted with the solenoid coil 30, the magnet yoke 25, the armature 24 connected to the coupling rod 23, and the compression springs 38, 39, the contact bridge 22 and the electric functional components (i.e. the switching position contact 31, the freewheeling diodes 34, the thermal cutoff 35 and/or the auxiliary conductors 36) that may be present, and the damping element 37. The coil subassembly 20 is thus prepared as an inherently stable (self-supporting) modular unit.

(35) In this form, the coil subassembly 20 is clipped from below onto the connector base 3, which has been produced in advance in an injection molding process. For this purpose, the connector base 3 is provided on the underside thereof with integrally molded snap hooks 64 (FIG. 3), which engage on both sides under the upper platform 42 of the support body 40. In the state of the coil subassembly 20 in which it is secured on the connector base 3, the hoop 27 of the magnet yoke 25 furthermore engages positively by two molded projections 65 (FIGS. 3 and 4) in depressions of complementary shape on the underside of the connector base 3. In the clipped-on state, the hoop 27 of the magnet yoke 25 is thus connected nonrotatably to the connector base 3 in respect of a rotation about the axis of the solenoid coil or the respective axis of the terminal studs 10.

(36) After, before or simultaneously with the clipping on of the coil subassembly 20, the circuit board 21 is installed. For this purpose, connection points in the region of section 60 are, on the one hand, soldered to the connecting conductors 14 of the signal terminals 13. On the other hand, connection points in the region of section 61 are soldered to terminals of the solenoid coil 30 and of the electric functional elements present (that is to say optionally the fixed contacts 32 of the switching position contact 31, the freewheeling diodes 34, the thermal cutoff 35 and/or the auxiliary conductors 36). In the installation position thereof, section 60 of the circuit board 21 extends parallel to one leg of the hoop 27, wherein section 60 is arranged outside the hoop 27. Section 61 of the circuit board 21 extends perpendicularly to the coil axis, wherein it reaches under the magnet yoke 25 and the armature 24.

(37) The auxiliary conductors 36 are furthermore soldered to (voltage pickoff) terminals 66 (FIGS. 3 and 13). In this arrangement, the terminals 66 are associated in pairs with the terminal studs 10. One of the terminals 66 is thus brought into contact with one of the terminal studs 10, while the other terminal 66 is brought into contact with the other terminal stud 10. For this purpose, the terminals 66 are pre-welded to the respectively associated terminal studs 10 and are overmolded together with the latter by the plastics material of the connector base 3.

(38) After the installation of the coil subassembly 20 and of the circuit board 21 on the connector base 3, the housing can 4 is placed over the coil subassembly 20 and the circuit board 21 and latched and screwed to the connector base 3, thereby closing the housing 2. Here, the hoop 27 of the magnet yoke 25 lies in the housing can 4 in such a way that the legs thereof extend in the manner of cross members between two opposite side walls 6 of the housing can 4 and parallel to the remaining side walls 6 over the entire width of the housing interior 8. The hoop 27 is thus accommodated nonrotatably in the housing can 4 over the entire height of the latteras measured in the direction of the coil axis and of the axis of the housing can 4. By virtue of its torsionally stable structure, the hoop 27 thus stiffens the housing can 4 in relation to axial torques of the kind which are exerted particularly when tightening the contact nuts on the terminal studs 10.

(39) In the closed state of the housing 2, the connector base 3 rests by means of an encircling radial web 70 (see FIGS. 3, 12 and 13) on an encircling shoulder 71 (FIGS. 3, 12 and 13) in the wall of the housing can 4. In this arrangement, the housing can 4 fits around the outside of the radial web 70 of the connector base 3 by means of an encircling collar 72 delimiting its opening (FIGS. 3, 12 and 13) and projects beyond the radial web. Thus, the collar 72 surrounds the upper side of the radial web 70 like a balustrade and, together with the connector base 3, forms a trough-shaped structurevisible in FIGS. 12 and 13which is referred to below as trough 73. For liquid and gastight sealing of the joint between the connector base 3 and the housing can 4, this trough 73 is filled with a potting compound 74, which is initially liquid and hardens in the course of a hardening phase. Here, a two component system containing an epoxy resin and an added hardener, in particular, is used as potting compound 74.

(40) The potting compound 74 is furthermore also used to seal the leadthroughs of the connecting conductors 14. For this purpose, the connecting conductors 14 pass through the connector base 3 in the region of the trough 73. The leadthroughs of the terminal studs 10 through the connector base 3 are sealed off separately from the trough 73 by potting compound.

(41) In order to additionally secure the joint between the connector base 3 and the housing can 4, a number of radial projections 80 (see FIGS. 3, 10 and 11) is provided along the inside of the collar 72and here, in particular, in the straight sections of the collar 72the projections projecting inward from the inner wall of the collar 72. The radial projections 80 act, on the one hand, as latching noses, which fit around the radial web 70 of the connector base 3 and thus latch it in the installed position thereof. Moreover, each radial projection 80 is provided on each side with a respective undercut 81, with the result that each radial projection (80) has a dovetail contour when viewed from above. By virtue of the undercuts 81, the radial projections 80 interlock with the potting compound 74, thereby preventing both twisting of the housing can 4 relative to the connector base 3 and radial bulging of the side walls 6 of the housing can 4.

(42) To prevent the potting compound 47 being taken along with the housing can 4 under the action of forces acting on the side walls 6 of the housing can 4 and, in the process, coming away from the outside of the connector base 3, a number of mating contours in the form of projections 82 are formed on the upper side of the connector base 3. In this arrangement, the respective internal edges of these projections in turn form an undercut 83, which interlocks with the potting compound 74.

(43) In alternative designs (not shown), the power relay 1 is multipoled, in particular two-poled or three-poled. In this case, a number of coil subassemblies 20 corresponding to the number of poles is connected to a common connector base 3, wherein in each case 2 terminal studs 10 for each coil subassembly 20 are in this case fixed in the connector base 3. In this arrangement, depending on the design, a separate circuit board 21 can be provided for each coil subassembly 20 or a common circuit board can be provided for all the coil subassemblies 20. In the case of multipole designs of the power relay 1, a housing can 4expediently subdivided by transverse wallsis preferably provided to jointly accommodate all the coil subassemblies 20.

(44) FIGS. 12 to 14 show the power relay 1 in the fully assembled state. It can be seen from these illustrations that the terminal studs 10 each also form fixed contacts of the main switching device of the power relay 1, the switching device being provided to switch the load circuit. For this purpose, the ends of the terminal studs 10, which project from the underside of the connector base 3 into the housing interior 8, are each provided with a contact element 90. The corresponding moving contact of the main switching device is formed by the contact bridge 22, which, for this purpose, contains a respective mating contact element 91 situated opposite each of the contact elements 90. The mating contact elements 91 are electrically short circuited within the contact bridge 22.

(45) FIGS. 12 and 13 show the power relay 1 in an open position, in which the mating contact elements 91 have been raised from the contact elements 90 (moved out of contact), with the result that there is no electrically conducting connection between the terminal studs 10. To switch on the power relay 1, the solenoid coil 30 is energized. This produces a magnetic flux in the magnet yoke 25, thereby pulling the armature 24 against the core 26 of the magnet yoke 25. By means of the armature 24, the contact bridge 22 is deflected upward during this process via the coupling rod 23, with the result that the mating contact elements 91 strike against the corresponding contact elements 90. In the closed position of the power relay 1 produced in this way, a conducting connection is formed between the terminal studs 10 via the contact bridge 22.

(46) To switch off the power relay 1, the solenoid coil 30 is energized with a reverse polarity. Under the action of the magnetic flux produced during this process in the magnet yoke 25, the holding force produced by the permanent magnets 29 is compensated, with the result that the armature 24 is pulled away from the core 26 by the return spring 38 and thus pressed into the open position shown in FIGS. 12 and 13. In this case, the armature 24 once again takes along the contact bridge 22 via the coupling rod 23, as a result of which the mating contact elements 91 are moved out of contact with the corresponding contact elements 90, breaking the electric connection between the terminal studs 10. The damping element 37 mounted on the lower end of the support body 40 absorbs this movement and thus prevents the unit formed by the armature 24, the coupling rod 23 and the contact bridge 22 from springing back in the direction of the closed position. In addition, the damping element 37 reduces the play of the components of the coil subassembly 20.

(47) In the illustrated bistable design of the power relay 1, each of the two switching positions of the power relay 1 is stable, even in the deenergized state of the solenoid coil 30. Here, the solenoid coil 30 need only be energized temporarily.

(48) In a design variant (not shown explicitly) of the power relay 1, a bearing section of the coupling rod 23 projects upwards, i.e. beyond the side of the contact bridge 22 remote from the armature. Here, the bearing section enters a bearing opening 92 in the connector base 3, the bearing opening being arranged in alignment, thus ensuring that the coupling rod 23 is also provided with sliding support in the connector base 3. Particularly stable and precise positioning of the contact bridge 22 is thereby ensured.

(49) As is apparent especially from FIG. 12, section 60 of the circuit board 21 is arranged between one leg of the group 27 and the adjacent side wall 6 of the housing can 4 in the assembled state of the power relay 1. The control electronics 63 arranged on section 60 are thus shielded thermally by the hoop 27 from the heat arising when the solenoid coil 30 is energized. Consequently, the control electronics 36 are situated in a cold region of the housing 2, thereby preventing premature aging of the control electronics 63.

(50) The activation of the solenoid coil 30 is accomplished either directly via the signal terminals 14 or via the control electronics 63, which, for their part, are supplied with power via the terminals 66 and the auxiliary conductors 36 in the illustrative embodiment shown. The control electronics 63 activate the solenoid coil 30 in accordance with external or internal control commands, which are supplied to the control electronics 63 via the signal terminals 13. Via terminals 66, the control electronics 63 furthermore determine the voltage drop across the terminal studs 10 in the switched-on state of the power relay 1 as a measure of the load current flowing through the power relay 1 or to detect the relay position. In this case, the control electronics 63 optionally effect overload switch-off and short circuit switch-off by moving the power relay 1 automatically into the open position if the load current detected exceeds predetermined threshold values. In the case of multipole designs of the power relay 1, the control electronics 63 optionally also evaluate, by comparison, the respective voltage drops across the terminal studs 10 of the individual poles in order to switch off the power relay 1depending on the designwhen a fault current or an asymmetrical current distribution is detected.

(51) Finally, the control electronics 63 optionally have a contact cleaning function. In a corresponding contact cleaning mode, the control electronics 63 successively activate the solenoid coil 30 several times at regular short time intervals, producing an artificial contact bounce. In this process, the contact bridge 22 strikes several times against the terminal studs 10, as a result of which contaminants possibly adhering to the contact elements 90 and the mating contact elements 91 are rubbed off. During this process, the control electronics 63 first of all check the electric voltage applied across the terminal studs 10 and switch to the contact cleaning mode only if this voltage is negligible and the power relay 1 can thus be switched under no load.

(52) Particularly when the power relay 1 is switched off in the case of an overload or short circuit, the heating of the current-carrying parts and a switching arc which forms generally lead to a high excess pressure in the housing interior 8. Under unfavorable circumstances, this excess pressure can assume a value which jeopardizes the stability of the housing 2, in particular of the housing can 4 or of the joint between the connector base 3 and the housing can 4. In order to prevent explosion or uncontrolled bursting of the housing 2 under these circumstances, the housing can 4 is therefore provided with an excess pressure safeguard 100.

(53) As can be seen from FIG. 15, this excess pressure safeguard 100 is formed by a curved groove, which locally reduces the thickness of the material of the housing bottom 7 and thereby acts as a predetermined breaking point 101. The predetermined breaking point 101 delimits an approximately keyhole-shaped tab 102 from the housing bottom 7 on three sides. Extending between the ends of the predetermined breaking point 100 and thus at the narrow end of the keyhole-shaped tab 102 is a further groove, which has a shallower groove depth than the predetermined breaking point 101 and therefore acts as a film hinge 103. The predetermined breaking point 101 is dimensioned in such a way that it bursts open if the pressure in the housing interior 8 exceeds a critical limit value of, for example, about 2 to 3 bar. In this case, the tab 102 is bent open upward around the film hinge 103 and thus exposes a gas expulsion opening, via which a pressure equalization with the environment takes place.

(54) In a preferred embodiment of the power relay 1, an electric signal line (not shown explicitly) in the form of a vapor deposited or adhesively bonded conductor track, the electric volume resistivity of which is interrogated by the control electronics 36, is placed on the inner wall of the housing bottom 7, transversely across the predetermined breaking point 101 and the tab 102. In this arrangement, the signal line is automatically severed when the predetermined breaking point 100 bursts, this being detected by the control electronics 63 on the basis of the sudden increase in volume resistivity. In this case, the control electronics 63 transfer the power relay 1 to a safe state. In a design variant which is expedient for many applications, the control electronics 63 trigger a permanent forced switch off of the power relay 1 in order to enforce replacement of the power relay 1.

(55) As is apparent from FIG. 2, two alternative assembly possibilities are predetermined for the power relay 1. Thus, the housing can 4 bears a respective mounting surface 110 on the outside both on one side wall 6 and on the housing bottom 7. Four screw openings 111 are made in each mounting surface 110, in which openings the power relay 1 can be mounted by corresponding fastening screws, either directly or via an interposed adapter plate, depending on the intended purpose. The screw openings 101 are preferably formed by threaded sleeves made of metal, which are press-fitted or screwed into associated depressions (blind holes) in the plastics material of the housing can 4 or which are over molded with the plastics material.

(56) The invention will be particularly clear from the illustrative embodiments described above but is nevertheless not restricted to these illustrative embodiments. On the contrary, numerous further embodiments of the invention can be derived from the claims and the above description.

(57) The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention: 1 power relay 2 housing 3 connector base 4 housing can 5 upper side 6 side wall 7 housing bottom 8 housing interior 9 underside 10 terminal stud 11 threaded stem 12 partition wall 13 signal terminal 14 connecting conductor 15 cover 20 coil subassembly 21 circuit board 22 contact bridge 23 coupling rod 24 armature 25 magnet yoke 26 core 27 hoop 28 pole shoes 29 permanent magnet 30 solenoid coil 31 switching position contact 32 fixed contact 33 moving contact 34 freewheeling diode 35 thermal cutoff 36 auxiliary conductor 37 damping element 38 return spring 39 contact pressure spring 40 support body 41 column 42 (upper) platform 43 (lower) platform 44 pocket 45 wall 46 holder 47 holder 48 holder 49 holder 50 holder 60 section 61 section 62 film hinge 63 control electronics 64 snap hook 65 projection 66 (voltage pickoff) terminal 70 radial web 71 shoulder 72 collar 73 trough 74 potting compound 80 radial projection 81 undercut 82 projection 83 undercut 90 contact element 91 mating contact element 92 bearing opening 100 excess pressure safeguard 101 predetermined breaking point 102 tab 103 film hinge 110 mounting surface