RELAY HAVING TWO ELECTRICALLY PARALLEL CONTACT SPRINGS

Abstract

A relay with two current paths thermally connected in parallel is particularly fail-safe. In case of a failure of one main contact, the additional load current is led via the remaining functioning main contact. The failed main contact as well as the thermal connection between the two main contacts then serve as heat sinks, whereby the relay can continue to operate.

Claims

1. A method for switching a load current with a relay having at least two main contacts electrically connected in parallel to divide a total load current between said at least two main contacts, wherein a first main contact of the at least two main contacts has a first contact finger carrying a first contact piece of said first main contact, the first contact finger of said first main contact configured to be repositionable to contact a second contact piece of the first main contact to close the first main contact, and to be separated from the second contact piece of the first main contact to open the first main contact, wherein a second main contact of the at least two main contacts has a second contact finger carrying a first contact piece of said second main contact, the second contact finger of said second main contact configured to be repositionable to contact a second contact piece of the second main contact to close the second main contact, and to be separated from the second contact of the second main contact piece to open the second main contact, the method comprising: repositioning said first and second contact fingers to bring at least one of (i) the first contact piece of the first contact finger and (ii) the first contact piece of the second contact finger in contact with a respectively-corresponding second contact piece, to close the respectively-corresponding main contact from the at least two main contact; and in case of failure of a main contact from the at least two main contact, thermally dissipating at least a part of heat, caused by the total load current, by using the failed main contact as a heat sink for the at least one remaining-operational main contact, wherein the thermally dissipating comprises conducting heat from the at least one remaining-operational main contact from the at least two main contacts to the failed main contact via a heat sink that is thermally connected to both the at least one remaining-operational main contact and the failed main contact.

2. The method according to claim 1, comprising transferring said at least a part of heat from the remaining-operational main contact to the failed main contact through a thermally-conductive bridge that connects said remaining-operational and failed main contacts.

3. The method according to claim 1, further comprising at least one of (i) reducing the total load current and (ii) generating output indicia of fault in response to a temperature difference between the at least two main contacts being greater than a first threshold value.

4. The method according to claim 1, further comprising at least one of (i) reducing the total load current and (ii) generating output indicial of fault in response to a temperature of the at least one of the two main contacts exceeding a second threshold value.

5. The method according to claim 1, further comprising at least one of (i) reducing the total load current and (ii) generating output indicial of fault in response to having a voltage drop at one of contact fingers of the at least two main contacts rising above a third threshold value.

6. The method according to claim 1, further comprising at least one of (i) reducing the total load current and (ii) generating output indicial of fault in response to a difference between the values of currents, flowing through contact fingers of the at least two main contacts, exceeding a fourth threshold value.

7. A relay configured to switch a load circuit, the relay comprising: at least two main contacts configured to be operated and electrically connected in parallel, each main contact having a corresponding first movable contact finger that carries a first contact piece, said first contact piece arranged opposite to a complementary second contact piece of said main contact, and at least one actuator in operable connection with first contact pieces, of said at least two main contacts, and configured to bring said first contact pieces into contact with complementary second contact pieces of said at least two main contacts to electrically close the load circuit, wherein the main contacts are configured such that in case of failure of a main contact a total load current is passed via at least one main contact that remains operational, wherein at least two of first contact fingers, of the at least two main contacts, are connected to one another with a thermally-conductive member, wherein said thermally-conductive member configured to conduct at least a portion of heat, that is generated by the at least one main contact that remains operational, to a failed main contact to dissipate said at least a portion of heat at said failed contact.

8. The relay according to claim 7, wherein the thermally-conductive member is configured as a heat sink of said relay.

9. The relay according to claim 7, wherein the thermally-conductive member is disposed to connect first contact pieces, of the at least two main contacts, to one another.

10. The relay according to claim 7, wherein the thermally-conductive member is disposed to directly mechanically connect first contact pieces of the at least two main contacts.

11. The relay according to claim 7, wherein the thermally-conductive member is disposed to directly connect said first contact fingers to one another at a level of t first contact pieces.

12. The relay according to one claim 7, wherein each first contact finger from said first contact fingers has at least one metal strip with first and second ends, the first end being fixed to a carrier and the second end configured to be movable relative to the first end and to carry thereon at least one of said first contact pieces.

13. The relay according to claim 7, wherein a cross-section A of the thermally conductive member satisfies a condition of $A\ge \frac{P_v.Math.I}{\Delta .Math..Math.T.Math..Math.\lambda },$ wherein P.sub.V is a value of power loss at a main contact, from the at least two main contacts, at a nominal current; I is a length of the thermally conductive member between the at least two main contacts; λ is a value of specific thermal conductivity of the thermally-conductive member; and ΔT is a maximum value of permissible temperature difference between first and second ends of the thermally conductive member.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In the following, the invention will be described by way of example, without limitation of the general inventive concept, on examples of embodiment and with reference to the drawings.

[0033] FIG. 1 shows a view of an embodiment of a relay.

[0034] FIG. 2 shows a view of a partially assembled relay with two contact fingers and the corresponding contact pieces according to the prior art.

[0035] FIG. 3 shows a detail of an embodiment of a relay with thermal bridge.

[0036] FIG. 3a shows a detail of an embodiment of a relay with thermal bridge.

[0037] FIG. 4 shows a further view corresponding to FIG. 1 of an embodiment of a relay.

[0038] FIG. 5 shows a further view corresponding to FIG. 1 of an embodiment of a relay.

[0039] FIG. 6 shows a further view corresponding to FIG. 1 of an embodiment of a relay.

[0040] While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.

DETAILED DESCRIPTION

[0041] FIG. 1 shows a relay 10 in an oblique view. The relay 10 has a first main contact 19 and a second main contact 20 which can be electrically connected in parallel via a mounting base 41 or via a circuit board. Each of the main contacts 19, 20, respectively, is electrically connected to a first soldering lug 21, 23 as well as a second soldering lug 22, 24. The soldering lugs 21, 22, 23, 24 are arranged in the mounting base or carrier 41. The main contacts can be electrically contacted from the outside via the soldering lugs 21, 22, 23, 24. The first soldering lugs 21, 23 are each guided on a first contact finger 29, 30 and are electrically contacted with these. The first contact pieces 25, 27 of the first and second main contacts 19, 20 are attached to the upper end of the first contact fingers 29, 30. Lying opposite thereto, a respective second contact piece 26, 28 is attached at a first and a second conductive support rail 33, 34, as a counter contact to the corresponding first contact pieces 25, 27. With the main contact 19, 20 closed, the first contact pieces 25, 27 and the second contact pieces 26, 28 are pressed against each other and provide the electrical contact.

[0042] An actuator with a coil 40 and a movable armature (not shown) is on the carrier, which is in operative connection with the first contact fingers 29, 30 or with the first contact pieces 25, 27, in order to enable simultaneous movement of the contact fingers 29, 30 and the contact pieces 25, 27. The coil 40 is electrically contacted via a pair of coil connections 11, 12. When the coil 40 is energized, the contact springs 29, 30 are displaced in the direction of the support rails 33, 34 via a bracket (not shown) of the coil, which bracket is connected to the movable armature of the coil. The contact springs 29, 30 are thus brought into abutment with the second contact pieces 26, 28. By this, the load circuit is closed via the contact pieces 25, 26, 27, 28. A cooling plate 50 is arranged at the first contact finger 29 and the second contact finger 30, for the purpose of dissipating the additionally generated waste heat in the event of failure of one of the two main contacts 19, 20.

[0043] FIG. 2 shows a partially assembled relay with a carrier 41, on the bottom side of which connections (which are also called soldering lugs 21) for the relay are arranged. The two soldering lugs 21, 23 are respectively connected electrically conductive to one spring-elastic metal strip 25, 27 serving as a contact finger and can be connected in parallel on the connection side 21, 23.

[0044] A respective first contact piece 25, 27 of a pair of contacts is attached to the end regions of the contact fingers 29, 30 that face away from the connection (the end(s), for short). An actuator (not shown) acts on the contact fingers 29, 30 to move the contact fingers 29, 30, respectively, in the direction of a complementary second contact (not shown) of the corresponding pair of contacts and/or to open the pairs of contacts.

[0045] The second contacts (not shown) of the contact pairs can also be connected in parallel, that is e.g. on a common metallic carrier (not shown).

[0046] If the transition resistance of the two contacts 25, 26, 27, 28, 29, 30 is different, or one of the two parallel current paths is interfered in another way, a major part or the entire load current flows over the remaining, better conducting or still functioning current path, and the corresponding contact finger 29, 30 as well as the contact pieces 25, 26, 27, 28 are additionally heated.

[0047] According to the invention, the two contact fingers 29, 30 are connected to one another preferably in a thermally conductive manner, e.g. by a thermal bridge 31 (cf. FIGS. 3-6) made of a material that is as thermally conductive as best as possible, e.g. copper or aluminum. By means of the thermally conductive bridge 31, the contact finger 29, 30 of the defective current path acts as a heat sink 50 for the elements of the intact current path, whereby the heat can be dissipated in a controlled manner. This is indicated in FIGS. 3 to 5:

[0048] FIG. 3 shows a first contact finger 29 with a contact piece 25 which is connected to a second contact finger 30 via a heat sink, which serves as a thermal bridge 31. The thermal bridge 31 has a cross-sectional area A and a length I, measured here between the first contact pieces 25, 27. The cross in the cross-sectional area A symbolizes the rear side of an arrow, and shows the heat flow direction in the event of a failure from the warmer contact finger 29 to the colder contact finger 30. This means that, in the event of failure of the second main contact 20, the entire current flows via the contact pieces pair 25, 26. Due to this fact, the first main contact 19, in particular the first contact piece 25, 26 warms up additionally, and the heat dissipates in the direction of the first contact piece pair 27, 28 via the heat sink 50 or the thermally conductive bridge 31. The second contact spring 30 of the second main contact 20 acts as a heat sink due to the thermally conductive bridge. For improving heat dissipation, the thermally conductive bridge can optionally be provided with cooling ribs, as exemplarily shown.

[0049] FIG. 3a shows an alternative embodiment with the features of FIG. 3. In contrast to the embodiment shown in FIG. 3, the thermal bridge 31 is attached on the side of the first contact pieces 25, 27. This embodiment leads to an additional reduction in the thermal transition resistance between the two first contact fingers 29, 30 and thus to a faster heat dissipation in the event of a failure of one of the main contacts 19, 20. The cooling ribs 50 are optional.

[0050] In FIG. 4, the thermal bridge 31 is a metallic braid which thermally connects the two contact fingers 29, 30. The thermal bridge 31 can e.g. be soldered and/or riveted with the contact fingers 29, 30 and/or the contact pieces 25, 27. In contrast to the illustration, the braid is preferably attached at the level of the contact pieces 25, 27 to the contact fingers 29, 30 or directly to the contact pieces 25, 27.

[0051] As exemplarily shown in FIG. 5, the thermal bridge 31 has a plurality of thermally conductive connections between the contact fingers 29, 30 which are formed from thermally conductive strips 31, e.g. from a sheet metal. Preferably, the thermally conductive strips 31 are soldered, welded or riveted to the contact fingers 29, 30. Likewise, the strips 31 and the contact fingers 29, 30 can be made in one piece, e.g. punched from a sheet metal. In addition, passage openings 35 can be punched into the upper part of the contact fingers 29, 30 in order to improve the cooling.

[0052] In the embodiment of FIG. 6, the two contact fingers 29, 30 are made in one piece with the thermal bridge 31, e.g. cut or punched from a sheet metal. Also in this example, the thermal bridge 31 is arranged at the level of the contact pieces 25, 27 between the contact fingers 29, 30.

[0053] If the defect of one of the two parallel current paths is due to e.g. a defective connection, it is advantageous if the thermal bridge 31 is also electrically conductive, because the current can then again be split by the thermal bridge 31 onto the two contact fingers 29, 30, whereby the overall heat development is reduced (applies for all embodiments). In principle, however, a purely thermal connection of the contact fingers 29, 30 would suffice, i.e. the connection could be electrically insulating (applies for all embodiments).

[0054] In the above, the term metal strip has been used as a synonym for “electrical conductors”. In the examples shown, the metal strips, which are also called contact fingers 29, 30, have both a mechanical function and an electrical function. These functions can also be separated. In general, the invention can be summarized as at least thermally conductive connection between at least two parallel current paths, for example in a relay, whereby in the event of failure of one of the current paths, the heat generated in the still functioning current path is dissipated via the failed current path. The components of the failed current path act as or are then the heat sink of the still intact current path. The thermal bridge also acts as a heat sink.

[0055] It will be appreciated to those skilled in the art having the benefit of this disclosure that this invention is believed to provide a relay and a method for operating the relay. Further modifications and alternative embodiments of various aspects of the invention will be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the general manner of carrying out the invention. It is to be understood that the forms of the invention shown and described herein are to be taken as the presently preferred embodiments. Elements and materials may be substituted for those illustrated and described herein, parts and processes may be reversed, and certain features of the invention may be utilized independently, all as would be apparent to one skilled in the art after having the benefit of this description of the invention. Changes may be made in the elements described herein without departing from the spirit and scope of the invention as described in the following claims.

LIST OF REFERENCE NUMERALS

[0056] 10 Relay [0057] 11 A1, first coil connection [0058] 12 A2, second coil connection [0059] 19 first main contact [0060] 20 second main contact [0061] 21 first soldering lug of the first main contact [0062] 22 second soldering lug of the first main contact [0063] 23 first soldering lug of the second main contact [0064] 24 second soldering lug of the second main contact [0065] 25 first contact piece of the first main contact [0066] 26 second contact piece of the first main contact [0067] 27 first contact piece of the second main contact [0068] 28 second contact piece of the second main contact [0069] 29 first contact finger of the first main contact [0070] 30 first contact finger of the second main contact [0071] 31 thermal bridge [0072] 32 heat flow direction [0073] 33 first support rail, second contact finger of the first main contact [0074] 34 second stop rail, second contact finger of the second main contact [0075] 35 passage openings [0076] 40 coil with armature [0077] 41 carrier [0078] 50 heat sink/cooling plate [0079] I length of the heat sink [0080] A cross-sectional area of thermal bridge