Miniature safety switch

Abstract

A miniature safety switch is used in motor vehicle electronics. The miniature safety switch has a housing base, from which a fixed contact arm and a bimetallic contact arm, which has a moving contact and a bimetallic snap disk attached thereto, are led out. A PTC resistor is brought into direct contact with the bimetallic snap disk by a compression spring and is electrically integrated in such a way that, as a result of the heat generated by the PTC resistor, the bimetallic snap disk remains in the open position thereof in the event of triggering.

Claims

1. A miniature safety switch for use in motor vehicle electronics, comprising: a housing having a housing base made of an insulating material and a housing cover that can be fitted, or is fitted, on said housing base; first and second elongate and flat contact arms disposed parallel to one another in terms of a longitudinal direction, disposed in said housing base and being led at a base side from said housing base, said second contact arm having an second contact arm inner end in said housing opposite said base side; a fixed contact disposed in said housing and attached to said first contact arm; a moving contact for contacting said fixed contact; a bimetallic snap disk affixed to said second contact arm at said second contact arm inner end, said bimetallic snap disk spanning from said second contact arm inner end to said fixed contact and carrying said moving contact thereon in a position for contacting said fixed contact and connecting said first contact arm to said second contact arm; a separate compression spring supported on said first contact arm beneath said fixed contact in the longitudinal direction; and a PTC resistor being electrically incorporated such that, as a result of heat generated by said PTC resistor, said bimetallic snap disk remains in an open position thereof in an event of triggering, said PTC resistor being brought into direct contact with said bimetallic snap disk by means of said separate compression spring.

2. The miniature safety switch according to claim 1, wherein said compression spring is a conical spring having a base-side spring end contacting said first contact arm and an apex-side spring end contacting said PTC resistor.

3. The miniature safety switch according to claim 2, wherein said compression spring having a diameter of approximately 2 mm at said apex-side spring end thereof and is approximately 4 mm at said base-side spring end thereof.

4. The miniature safety switch according to claim 3, wherein said PTC resistor is a disk-shaped PTC resistor having a disk diameter corresponding to said diameter of said compression spring at said base-side spring end thereof.

5. The miniature safety switch according to claim 4, wherein: said disk diameter of said PTC resistor is 4.20.1 mm; and said PTC resistor has a disk thickness of is 1.050.06 mm.

6. The miniature safety switch according to claim 4, wherein said apex-side spring end of said compression spring contacts said disk-shaped PTC resistor centrally.

7. The miniature safety switch according to claim 1, wherein: said housing base has a housing crosspiece with a pocket-shaped base contour running in a transverse direction relative to said first contact arm; said first contact arm carrying said fixed contact is guided through said pocket-shaped base contour of said housing crosspiece; and said compression spring having a spring end remote from said PTC resistor and said spring end being inserted into said pocket-shaped base contour, where it is supported at least laterally.

8. The miniature safety switch according to claim 1, wherein said bimetallic snap disk is attached to said second contact arm at a fixing point, said PTC resistor being disposed between said fixing point and said moving contact or said fixed contact in the longitudinal direction.

9. The miniature safety switch according to claim 1, wherein said PTC resistor contacts said bimetallic snap disk approximately centrally.

10. The miniature safety switch according to claim 1, wherein said PTC resistor is electrically contacted with said first contact arm via said compression spring and with said second contact arm via said bimetallic snap disk, such that a current flows across said PTC resistor in an event of triggering and heats said PTC resistor.

11. The miniature safety switch according to claim 1, wherein said PTC resistor and said compression spring are connected in series with one another and in parallel with said moving contact and said fixed contact to maintain current flow via said compression spring and said PTC resistor when said bimetallic snap disk is in the open position.

12. The miniature safety switch according to claim 11, wherein in a closed position of said bimetallic snap disk with the moving contact and the fixed contact electrically contacted, current flow remains via said compression spring and said PTC resistor.

13. The miniature safety switch according to claim 11, wherein said PTC resistor limits current flow to 100 mA.

14. The miniature safety switch according to claim 1, wherein said PTC resistor is ceramic based.

15. The miniature safety switch according to claim 14, wherein said PTC resistor is a non-linear PTC resistor.

16. The miniature safety switch according to claim 1, wherein said PTC resistor is planar and is in full-area direct contact with said bi-metallic snap disk.

17. A miniature safety switch for use in motor vehicle electronics, comprising: a housing having a housing base made of an insulating material and a housing cover that can be fitted, or is fitted, on said housing base; first and second elongate and flat contact arms disposed parallel to one another in terms of a longitudinal direction, disposed in said housing base and being led at a base side from said housing base, said second contact arm having an second contact arm inner end in said housing opposite said base side; a fixed contact disposed in said housing and attached to said first contact arm; a moving contact for contacting said fixed contact; a bimetallic snap disk affixed to said second contact arm at said second contact arm inner end, said bimetallic snap disk spanning from said second contact arm inner end to said fixed contact and carrying said moving contact thereon in a position for contacting said fixed contact and connecting said first contact arm to said second contact arm; a separate compression spring supported on said first contact arm beneath said fixed contact in the longitudinal direction; and a PTC resistor being electrically incorporated such that, as a result of heat generated by said PTC resistor, said bimetallic snap disk remains in an open position thereof in an event of triggering, said PTC resistor being brought into direct contact with said bimetallic snap disk by means of said separate compression spring, said PTC resistor and said compression spring being connected in series with one another and in parallel with said moving contact and said fixed contact for maintaining current flow via said compression spring and said PTC resistor when said bimetallic snap disk is in the open position, said PTC resistor being a ceramic based non-linear PTC resistor, said PTC resistor limiting current flow to 100 mA, said PTC resistor being planar and in full-area direct contact with said bi-metallic snap disk, and even in a closed position of said bimetallic snap disk with the moving contact and the fixed contact electrically contacted, current flow remains via said compression spring and said PTC resistor.

18. The miniature safety switch according to claim 1, wherein said PTC resistor is disposed inwardly of said second contact arm inner end between said second contact arm inner end and said fixed contact.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) FIG. 1 is a diagrammatic, exploded perspective view of a safety switch having a housing formed from a housing base and a housing cover, two contact arms partially embedded in the housing base, a bimetallic snap disk, a heating resistor (PTC resistor) and a volute spring according to the invention;

(2) FIG. 2 is a perspective view of the safety switch according to FIG. 1 in the assembled state with a closed housing;

(3) FIG. 3 is a perspective view of the safety switch according to FIG. 1 in a partly assembled state with the volute spring inserted in the housing base, without the PTC resistor and the bimetallic snap disk;

(4) FIG. 4 is a perspective view of the safety switch according to FIG. 1 in the partly assembled state according to FIG. 3, but with the PTC resistor;

(5) FIG. 5 is a perspective view of the safety switch according to FIG. 1 in the partly assembled state according to FIG. 4, but with an assembled bimetallic snap disk;

(6) FIG. 6 is a side view of the safety switch according to FIG. 1 in the assembled state without a housing cover in an (electrically conductive) normal state;

(7) FIG. 7 is a side view according to FIG. 6 of the safety switch according to FIG. 1 in a triggered state; and

(8) FIG. 8 is a perspective view of the volute spring.

DETAILED DESCRIPTION OF THE INVENTION

(9) Corresponding parts are always denoted in all figures by like reference signs. Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, there is shown a safety switch 1 that contains a housing 2, which is formed from a housing base 3 and a housing cover 4. The safety switch 1 further contains a fixed contact arm 5, a bimetallic contact arm 6 and a bimetallic snap disk 7. The safety switch 1 also contains a fixed contact 8 in the form of a weld plate, a moving contact 9 in the form of a further weld plate, and, to fix the bimetallic snap disk 7, a further rivet 10 and a further weld plate 11.

(10) The housing base 3 and the housing cover 4 are fabricated from an electrically insulating material, namely a thermoplastic. The one-piece housing cover 4 is pot-shaped or cap-like and thus surrounds a volume, which defines an interior 12 of the safety switch 1, with five closed walls. The housing cover 4 can be snapped onto the housing base 3 via its open side. FIG. 2 shows the safety switch 1 with a closed housing 2, that is to say with the housing cover 4 fitted onto the housing base 3.

(11) The contact arms 5 and 6 are bent, stamped parts made of sheet metal, in particular tin-plated brass, with a flat, rectangular cross section. The fixed contact arm 5 and the bimetallic contact arm 6 are embedded with an interlocking fit in the housing base 3 since, when the safety switch 1 is produced, the contact arms 5 and 6 are insert-molded with the material of the housing base 3. In this case, the contact arms 5 and 6 each protrude out from the housing base 3 via a plug-in contact 14 at an underside 13 of the housing base 3. The housing 2 and in particular the housing cover 4 are shaped for example in the manner of a flat cuboid with a (housing) narrow side 15 and a (housing) broad side 16. The contact arms 5 and 6 are embedded in the housing base 3 in such a way that the plug-in contacts 14 are arranged parallel to one another, approximately centrally with respect to the housing narrow side 15 and at a distance from one another.

(12) The safety switch 1 is based on standard ISO 8820 Type F (miniature) in terms of its outer geometric dimensions. The miniature safety switch 1 therefore corresponds externally to a Type F blade-type fuse according to this standard, and therefore the safety switch 1 is compatible with a socket for such a blade-type fuse, that is to say can be plugged into such a socket, which is conventional in the automotive industry.

(13) With regard to the housing broad side 16, the plug-in contacts 14 of the contact arms 5 and 6 are each arranged at the edge, whereas they are guided, in each case, inwardly in the housing interior 12 toward the center of the housing so that an inner end 17 of the fixed contact arm 5 is arranged above an inner end 18 of the bimetallic contact arm 6. In this case, above, means the side of the safety switch 1 remote from the housing base 3 and the plug-in contacts 14, irrespective of the actual orientation of the safety switch 1 in space. As can be seen in particular from FIGS. 3 and 4, the inner ends 17 and 18 of the contact arms 5 and 6 are centered with regard to a central longitudinal axis 19 (FIG. 3) of the housing 2, as viewed from the housing broad side 16.

(14) As is relatively clear from FIGS. 3, 6 and 7, the inner ends 17 and 18 of the contact arms 5 and 6 are bent out from the central plane of the safety switch 1, defined by the plug-in contacts 14, by offset portions of the stamped, bent parts, as viewed from the housing narrow side 15, and extend in a slightly offset manner parallel to the central plane or central longitudinal axis 19. In this case, the inner end 17 of the fixed contact arm 5 is set back relative to the central plane (central longitudinal axis 19), whereas the inner end 18 of the bimetallic contact arm 6 is forward of the central plane (central longitudinal axis 19). The longitudinal extension of the contact arms 5 and 6, and in particular of the plug-in contacts 14 of these contact arms 5 and 6, defines a longitudinal direction 20, while a transverse direction 21 runs perpendicular thereto within the central plane.

(15) The housing base 3 has a base 22 running in the transverse direction 21 and two mutually spaced base struts 23, 24 extending in the longitudinal direction 20 as well as another base crossmember 25 extending in the transverse direction 21 and connecting the base struts at the upper ends thereof. The base struts 23, 24, in which the fixed contact arm 5 and the bimetallic contact arm 6 are embedded, and the base 22 as well as the base crossmember 25, also referred to hereinafter as a base crosspiece, define there between a window-like base cavity 26. The rivet 10, on which the bimetallic snap disk 7 is welded by the weld plate 11, is fixed in this region to the inner end 18 of the contact arm 6 at a distance from the housing base 3. The fixed contact 8 is welded onto the fixed contact arm 5 above this fixing point 10, 11 formed by the rivet and weld plate in the longitudinal direction 20 and therefore in alignment with the fixing point in the longitudinal direction 20.

(16) A base contour 27 referred to hereinafter as a receiving pocket is molded into the base crosspiece 25, is located in the assembled state between the fixing point 10, 11 and the fixed contact 8 in the longitudinal direction 20, and is penetrated by the fixed contact arm 5 in the longitudinal direction 20 (FIG. 3). Two semi-circular base shells 27a and 27b are thus formed, wherein the distance there between, or the clear width there between, is determined by the width of the fixed contact arm 5.

(17) In the assembled state, a compression spring 28 in the form of a volute spring referred to hereinafter as a conical spring for short lies in the receiving pocket 27 via its base-side spring end 28a. The cross-sectional free area of the receiving pocket 27, which is laterally defined by the base shells 27a and 27b in the transverse direction 21, is adapted to the relatively large spring diameter of the base-side spring end 28a of the conical spring 28. The conical spring 28 is thus horizontally positioned in the housing base 3 and sufficiently held at least in a simplified and reliable manner. An apex-side spring end 28b of the conical spring 28 opposite the base-side spring end 28a protrudes into the interior 12 of the safety switch 1 in the subassembly step shown in FIG. 3. FIG. 3 shows the relaxed state of the conical spring 28.

(18) FIG. 4, in a further subassembly step, shows the use of a PTC resistor 29 (referred to hereinafter simply as a resistor) within the safety switch 1 in the housing base 3. The resistor 29 is embodied as a circular plate (resistor plate or resistor disk). The diameter of the plate-shaped or disk-shaped resistor 29 is again suitably adapted to the inner diameter (clear width) of the receiving pocket and is thus held in the housing base 3 in an accurately positioned manner, again by the base pockets 27a, 27b as a result of the lateral delimitation when the conical spring 28 is pressed together. In accordance with FIGS. 3 and 4, it can be seen that the conical spring 28 and the resistor 29 are arranged on the contact arm 6 aligned in the longitudinal direction 20 and preferably centered with the central axis 19 between the fixed contact 8 and the rivet 10 used in the assembled state as a fixing point.

(19) FIGS. 5 to 7 show the assembled state with the bimetallic disk 7 arranged between the rivet 10 and the weld plate 11. In the assembled state, the oval bimetallic disk 7 is centered in terms of its longitudinal extension with the central axis 19 (FIG. 5) and is thus aligned in the longitudinal direction 20 of the safety switch 1 and the contact arms 5 and 6 thereof. The end of the bimetallic snap disk 7 held on the contact arm 6 by the rivet 10 and the weld plate 11 forms its fixing point 10, 11 at the corresponding contact arm 6, while the opposite free end of the bimetallic snap disk 7 carries the moving contact 9 (FIGS. 6 and 7). As can be seen from FIGS. 6 and 7, the conical spring 28 and the PTC resistor 29 are located between the fixing point 10, 11 of the bimetallic snap disk 7 and the contacts 8, 9. As can be seen, the PTC resistor 29 directly contacts the bimetallic snap disk 7 in a planar manner. The base-side spring end 28a of the conical spring 28 contacts the contact arm 5 of the fixed contact 8 and, in doing so, lies in the receiving pocket 27 of the housing base 3. With its opposite, apex-side spring end 28b, the conical spring contacts the PTC resistor 29 as centrally as possible, where it forms a central tilt point 30.

(20) In its normal position according to FIG. 6 with the bimetallic snap disk 7 running at an incline in the longitudinal direction 20, the moving contact 9 contacts the fixed contact 8 at an incline and under bias. An electrically conductive connection between the plug-in contacts 14 is thus produced via the contact arms 5 and 6, the fixed contact 8, the moving contact 9 and the rivet 10. The safety switch 1 is thus electrically conductive in the normal state. The bimetallic snap disk 7 is formed in such a way that it suddenly changes its shape when its temperature exceeds a trigger temperature, for example of 1700 C., predefined by the design. As a result of this change in shape, the moving contact 9 lifts from the fixed contact 8 so that the electrical connection existing between the fixed contact arm 5 and the bimetallic contact arm 6 is disconnected. FIG. 7 shows the safety switch 1 in the triggered position. The change in shape to the bimetallic snap disk 7 is reversible according to the temperature thereof, such that it springs back into the normal position (FIG. 6) when its temperature falls below a return temperature predefined by the design.

(21) In the event of triggering, when the electrical connection between the fixed contact arm 5 and the bimetallic contact arm 6 is interrupted due to the deflection of the bimetallic snap disk 7, a high-resistance electrical connection between the contact arms 5 and 6 is maintained via the PTC resistor 29 and the conical spring 28. Provided the overload condition once the safety switch 1 has been triggered and thus a flow of current between the fixed contact arms 5 and 6 is maintained, the bimetallic snap disk 7 is heated due to the thermal loss that is generated in the PTC resistor 29 directly contacting the bimetallic snap disk 7, and the bimetallic snap disk 7 is prevented from cooling below the return temperature. Once triggered for the first time, the safety switch 1 thus remains in the triggered state as long as the overload condition continues to exist.

(22) A ceramic-based non-linear thermistor is used for the PTC resistor 29. This heats up as a result of the current flow and limits the current to approximately 100 mA. This corresponds merely approximately to between one third and one quarter of the amperage that is required in the known solutions. In addition, a relatively loose correlation between the applied voltage and the output power is produced due to the non-linearity of the resistor 29. For the primary application in an on-board power supply system of a motor vehicle, the supplied temperature and therefore the power remain relatively constant over the total conventional voltage range from approximately 11 V to 14.5 V. This is a particular preference, accompanied by the advantage of a reduced power output. This in turn enables the use of a housing cover (housing cap) 4, which consists of plastics material, is therefore electrically insulating, and is snapped onto the housing base 3 in the subsequent assembly step. In contrast to this electrically insulating housing cover 4 or a housing cap, metal caps or the like, which may have to be insulated by an additional coating, are always necessary in known solutions due to construction and in particular for temperature reasons.

(23) On the whole, a PTC resistor 29 having a surface temperature of 275 C. is thus preferably selected, which deviates from the standard and appears to be the upper limit for this type of PTC resistor. The surface temperature of PTC resistors of this type used for heating is normally 250 C. at most. Since the PTC resistor 29 contacts the bimetallic snap disk 7 directly and in a planar manner and to this end is pressed against the bimetallic snap disk 7 with a specific bias to ensure effective thermal transfer, a particularly effective thermal transfer as well as a sufficient flow of current through the PTC resistor 29 are thus enabled.

(24) So as to adapt the movement of the bimetallic snap disk 7 during the opening process in the event of triggering, the PTC resistor 29 remains movable, since the conical spring 28 does not contact the resistor 29 over a large area, but in the region of the tilt point 30 and therefore instead in the central region over the small contact area produced thereby. The contact force of the conical spring 28 is dimensioned in such a way that the preferably disk-shaped PTC resistor 29 contacts the bimetallic snap disk 7 effectively and also does not negatively influence the snap behavior thereof.

(25) The compression spring 28 is formed in such a way that it can be pressed together as fully as possible. It is thus taken into account that only a very small amount of space is available in order to position and accommodate the compression spring 28 in the safety switch 1, more specifically between the fixed contact arm 5 and the bimetallic snap disk 7, and that the space is additionally already required in part by the PTC resistor 29. A compression spring 28 with a conical spring body and therefore, in turn, the use of a volute spring (conical spring) is thus particularly advantageous. The conical spring body is produced by continuously changing the coil diameter as the spring wire is wound.

(26) Such a preferred conical spring 28 is shown in FIG. 8. The coils or windings of the conical spring 28 are changed in this case from coil to coil in the longitudinal or axial direction of the spring in such a way that the coils can slide one inside the other as the conical spring 28 is pressed together. To this end, the spring free end 28c is suitably curved inwardly at the base-side spring end 28a in such a way that the spring height (block length) of the conical spring 28 corresponds practically merely to twice the spring wire thickness when the conical spring is pressed together. The greatest diameter D.sub.b of the conical spring 28 at the base-side spring end 28a thereof is approximately 4 mm and corresponds at least approximately to the diameter of the PTC resistor 29 with (4.20.1) mm. The conical spring 28 contacts the fixed contact arm 8 at this large coil diameter D.sub.b, whereas the smallest coil diameter D.sub.s contacts the PTC resistor 29 at the apex-side spring end 28b of the conical spring 28. The PTC resistor remains movable as a result of the merely central contact with formation of the tilt point 30, in such a way that the resistor 29 can advantageously adapt to the movement of the bimetallic snap disk 7.

(27) So as to also train the conical spring 28 so that the feed can be automated, the spring free end 28c of the base-side spring end is wound inwardly, preferably in the plane of the last coil of the greatest coil diameter D.sub.b. In the event of an automated feed, the conical springs 28 are thus prevented from engaging with their small spring diameter D.sub.s in the large coil diameter D.sub.b of another conical spring 28 and from becoming hooked thereon. In addition, if the conical spring 28 is pressed together completely, only two spring coils thus lie one on top of the other, which is advantageous for spatial reasons.

(28) The disk thickness of the PTC resistor 29 is dimensioned in such a way that it contacts the bimetallic snap disk 7 both when the safety switch 1 is in the switched-on position (FIG. 6) and when the bimetallic snap disk is in the triggered or switched-off position (FIG. 7), without sliding out from the lateral mounting of the receiving pocket 27: it is taken into account as a result of this constructional feature of the provision of the laterally supporting base shells 27a, 27b that different tolerances are to be expected with different amperages as a result of differently shaped bimetallic snap disks 7. The constructional embodiment of the conical spring 28 also ensures that it does not become rigid, even when pressed together (FIG. 6), and the PTC resistor 29 thus remains movable and does not hinder the snap behavior of the bimetallic snap disk 7. To this end, a disk thickness of the PTC resistor 29 of (1.050.06) mm has proven to be optimum. The disk diameter of the PTC resistor 29 is preferably (4.20.1) mm in this case.

(29) When the contacts 8, 9 are closed (FIG. 6), the current flows from the contact terminal 14 of the fixed contact arm 5 and the fixed contact 8 to the bimetallic contact 9 and via the bimetallic snap disk 7 and the fixing point 10, 11 to the bimetallic contact arm 6, and from there via the corresponding terminal 14. If the bimetallic snap disk 7 opens the circuit with a sudden movement in the event of an overcurrent, the operating voltage is then applied to the PTC resistor 29 and the current flows from the fixed contact arm 5 via the conical spring 28 to the PTC resistor 29, and from there via the bimetallic snap disk 7 and the fixing point (weld rivet) 10, 11 to the bimetallic contact arm 6. Due to the embodiment and arrangement of the resistor 29 and the compression spring 28 and also in particular the direct contact between the resistor 29 and the bimetallic snap disk 7, a sufficiently large thermal input into the bimetallic snap disk 7 is ensured as a result of the current flow, and therefore the bimetallic snap disk remains above the snapback temperature. This state is maintained until the voltage falls below a specific value (normal case) or falls completely to zero. The current (approximately 100 mA) determined while the snapback temperature is maintained by the resistance of the PTC resistor 29 is relatively low.

(30) The invention therefore relates to a miniature safety switch 1, preferably for use in motor vehicle electronics, containing the housing base 3, from which a fixed contact arm 5 and a bimetallic contact arm 6, which has a moving contact 9 and a bimetallic snap disk 7 attached thereto, are led out, wherein a PTC resistor 29 is brought into direct contact with the bimetallic snap disk 7 by a compression spring 28 and is electrically integrated in such a way that, as a result of the heat generated by the PTC resistor, the bimetallic snap disk 7 remains in the open position thereof in the event of triggering.

LIST OF REFERENCE NUMERALS AND SIGNS

(31) 1 safety switch 2 housing 3 housing base 4 housing cover/cap 5 fixed contact arm 6 bimetallic contact arm 7 bimetallic snap disk 8 fixed contact 9 moving contact 10 rivet 11 weld plate 12 interior 13 underside 14 plug-in contact 15 housing narrow side 16 housing broad side 17 inner end of the fixed contact arm 18 inner end of the bimetallic contact arm 19 central longitudinal axis 20 longitudinal direction 21 transverse direction 22 base 23, 24 base strut 25 base crossmember 26 base cavity 27 receiving pocket 27a, 27b base shell 28 conical/volute spring 28a base-side spring end/coil 28b apex-side spring end/coil 28c spring free end 29 PTC resistor 30 tilt point D.sub.b base-side spring/coil diameter D.sub.s apex-side spring/coil diameter