COST EFFECTIVE CONTACT SPRING WITH HIGH DURABILITY

Abstract

 The invention relates to a contact spring (1) for a relay (16) comprising a main body (2), a make/break pad (12) and a contact pad (14), the make/break pad (12) and the contact pad (14), both being arranged on the main body (2), the make/break pad (12) being made from a first material and the contact pad (14) being made from a second material different from the first material, wherein at least one substrate layer (27) is provided between the make/break pad (12) and the contact pad (14) on one side and the main body (2) on the other side. By using different materials the make/break pad (14) can be optimised for the arc generated upon contacting and separating corresponding contact springs. Furthermore, costly material can be saved by replacing the intermediate layer of the contact pad (14) and the make/break pad (12) by the substrate layer (27).

Description

[0001] This invention relates to a contact spring for a relay with increased durability and a relay comprising at least one of said contact spring and a complementary contact spring.

[0002] A conventional relay includes a first and a second contact spring, with one of the contact springs being held movably relative to the other. The first and the second contact spring each comprise a single contact pad. The pair of contact pads is configured to provide low transition resistance, when said contact pads are in contact with one another and thereby close the electric circuit. In order to obtain a low transition resistance, the contact pads usually comprise or consist of silver. A contact pad made out of silver is not only expensive, raising the overall costs of the relay, it also is subject to high wear due to thermal and mechanical stress. For example an electric arc that extends from the contact pad of the first contact spring to the contact pad of the second contact spring before making the first contact or after breaking the last contact can lead to melting of the contact pads. Furthermore, the impact upon making the first contact causes high mechanical stress to the contact pads.

[0003] Accordingly, there is need for a more durable and cost effective contact spring for a relay.

[0004] In accordance with the present invention, the above stated problem is solved by providing a contact spring for a relay, comprising a main body, a make/break pad and a contact pad, the make/break pad and the contact pad both being arranged on the main body, the make/break pad being made from a first material and the contact pad being made from a second material different from the first material, wherein a substrate layer is provided between the make/break pad and the contact pad on one side and the main body on the other side.

[0005] With the inventive contact spring a single contact pad of a conventional contact spring is split into a make/break pad and a contact pad. The contact pad is smaller than the contact pad of the conventional contact spring. By having the contact pad split into the make/break pad and a smaller contact pad, it is possible to optimise said make/break pad and contact pad for their respective function. The make/break pad is adapted to catching an electric arc that occurs upon making or breaking a contact and to sustain the impact when making the contact, while the contact pad is adapted to close an electric circuit with low transition resistance. By providing a substrate layer between the make/break pad and the contact pad on one side and the main body on the other side, the material thickness of the make/break pad and the contact pad can be reduced while said make/break pad and said contact pad are still projected outwards from the main body far enough in order to be able to close the electric circuit without putting to much strain onto the main body.

[0006] Further, the problem is solved by a relay having at least one contact spring according to the invention as described above and below and at least one complementary contact spring according to the invention as described above and below, wherein the pair of make/break pads of the at least one contact spring and at least one complementary contact spring are spaced apart from one another when the contact is closed. Therefore, the contacting time of the make/break pads is reduced, leading to a lower possibility of the corresponding make/break pads melting together due to the heat generated by the high currents and the arc. Furthermore, as only the make/break pad is objected to thermal and mechanical wear due to the arc and impact, respectively, leading to a change in transition resistance, a stable transition resistance is achieved by only having the contact pads, which are protected from said thermal stress and said mechanical stress, contact each other when the contact is closed.

[0007] The overall material cost of the relay can be dramatically reduced by reducing the amount of expensive contact material in the contact spring and the complementary contact spring. Furthermore, the durability of the relay is increased by the make/break pad and the complementary make/break pad. The pair of make/break pads, which contact each other first when making the contact and are separated last when breaking the contact can be optimised for the impact of the contact springs and for the arc occurring upon making and breaking the contacts.

[0008] The contact spring and relay according to the invention can be further improved by the following features, which are independent of one another with respect to their respective technical effects and which can be combined arbitrarily.

[0009] According to a first aspect of the invention, the contact pad and/or make/break pad can be connected to the substrate layer by brazing, welding, soldering or any other method known in the art.

[0010] In order to increase the durability of the contact spring, the make/break pad can contain or consist of a material with high temperature resistance. With the high temperature resistance the make/break pad is not prone to melting due to an arc. Therefore, the material shift between the pair of complementary contact springs is avoided increasing the overall contact durability. With the high mechanical hardness the make/break pad is capable of withstanding the impact when making the contact. Preferably, the make/break pad can contain or consist of tungsten or a tungsten alloy. Tungsten exhibits high temperature durability as well as high hardness. Therefore, arc generated debris can be avoided.

[0011] The contact pad can contain or consist of a material with low transition resistance, for example gold or silver or a silver alloy. Due to the low transition resistance the voltage drop is minimised. Therefore, the contact spring can be used in higher power applications. The contact pad can preferably comprise or consist of a fine grain silver alloy.

[0012] According to another aspect of the invention, the substrate layer can comprise or consist of copper or a copper alloy. Since copper is relatively inexpensive compared to other conductors the raw material costs of the contact spring can be reduced.

[0013] The volume of the substrate layer can be larger than the volume of the make/break pad and/or contact pad. The contact pad and/or make/break contact can be realised as a thin strip that is attached to the substrate layer. Therefore, only a small fraction of expensive material with low transition resistance is necessary reducing the overall raw material costs since a large fraction of the contact pad's and/or make/break pad's material is substituted by an inexpensive substrate layer.

[0014] The contact pad and the make/break pad can be of the same size. In another embodiment, the make/break pad can be larger than the contact pad. The heat generated by the arc can therefore be spread on the larger surface minimising the risk of hotspots, causing the make/break pad to melt on said hotspot.

[0015] The contact pad and/or make/break pad can have a planar shape so that when the contact is established, the contact surface is fully utilised. However, the contact pad and/or make/break pad can also exhibit a different shape for example a spherical shape.

[0016] According to another embodiment, the contact pad and the make/break pad can be arranged adjoining to each other, resulting in a single contact shape.

[0017] In another embodiment, the contact pad and the make/break pad can be arranged spaced apart from one another in the longitudinal direction of the main body, resulting in a double contact shape. In the double contact shape it is ensured that the contact pad is distant from the make/break pad and, therefore, is not affected by the arc.

[0018] The make/break pad and contact pad can be arranged on a common substrate layer with a constant material thickness. Especially in the double contact shape, the substrate layer may comprise two areas which are separated from each other in the longitudinal direction, wherein one area is provided between the contact pad on one side and the main body on the other side and the other area is provided between the make/break pad on one side and the main body on the other side. Material of the substrate layer can be saved when the contact pad and make/break pad are spaced apart from one another and are attached to separate substrate layers resulting in further cost savings.

[0019] According to another embodiment, the make/break pad can be located in a longitudinal direction between a distal end of the main body and the contact pad. When the contact spring is moved towards a complementary contact spring by an axis of rotation that is essentially perpendicular to the longitudinal direction of the main body, it is ensured that the make/break pad will make the first contact since it is moved faster in the axial direction towards the complementary contact spring.

[0020] In order to ensure that the make/break pad contacts the complementary contact spring first, the main body of the contact spring may be angled so that the make/break pad is inclined towards the complementary contact spring.

[0021] The main body of the contact spring can exhibit a deformation zone with increased flexibility between the axis of rotation of the main body and the contact pad. The deformation zone can lead to a flexion of the main body, leading to a shift in the contacting zone from the make/break pad to the contact pad.

[0022] According to another embodiment, the make/break pad can be further projected from the main body in moving direction when transitioning from the open to the closed position than the contact pad. This ensures that the make/break contact is arranged closer to a complementary contact so that the make/break pad is in contact with the complementary contact in the make position and is spaced apart from the complementary contact last when the contact is broken.

[0023] At least one contact spring of the relay can be held movably relative to the complementary contact spring. Therefore, the contact spring can be moved towards the complementary contact spring by for example magnetic force induced by an electric coil.

[0024] At least one contact spring of the relay can be held stationary so that when the complementary contact spring is moved for example by magnetic force, the stationary contact spring is not affected.

[0025] One contact spring can comprise an angled portion, wherein at least the make/break contact is arranged on said angled portion, the angled portion is inclined towards the complementary contact spring. This ensures that only the make/break pads are in contact in the make and in the break position.

[0026] In the following the contact spring and the relay according to the invention are explained in greater detail with reference to the accompanying drawings, in which exemplary embodiments are shown.

[0027] In the figures, the same reference numerals are used for elements, which correspond to each other in their function and/or structure.

[0028] According to the description of the various aspects and embodiments, elements shown in the drawings can be omitted if the technical effect of these elements are not needed for a particular application. Vice versa, elements that are not shown or described with reference to the figures, but are described above, can be added if the technical effect of that particular element is advantageous in a specific application.

[0029] In the Figures:

Fig. 1 shows a schematic profile of a contact spring according to the invention with a double contact shape;

Fig. 2 shows a schematic profile of a relay according to the invention, when the contact is closed.

[0030] In Fig. 1 a contact spring 1 according to the invention is shown with a double contact shape.

[0031] The contact spring 1 comprises a main body 2 that is mounted on an armature 4, wherein the main body 2 is pressed against said armature 4 in the mounting point 5. The main body 2 consists of a conductive material and extends in a longitudinal direction y further than the armature 4, so that a free end 6 of said main body 2 is not located opposite to the armature 4.

[0032] Due to a spring force, the main body 2 is tilted away from the armature 4 with the mounting point 5 working as a hinge 8. Therefore, the main body 2 can be pivoted around an axis of rotation that is essentially perpendicular to the longitudinal direction y located at the hinge 8.

[0033] At the free end 6 on a face side 10 of the main body 2 facing towards the armature 4 said main body 2 exhibits a make/break pad 12 and a contact pad 14 that projects from the face side 10 in an axial direction x away from said main body 2.

[0034] The make/break pad 12 is located in the longitudinal direction y adjacent to the contact pad 14, wherein the contact pad 14 is arranged between the hinge 8 and the make/break pad 12. In order to realise the double contact shape, the contact pad 14 and the make/break pad 12 are not sharing a common border and are spaced apart in the longitudinal direction y. When pivoting the main body 12 towards the armature 4, the make/break pad 12 is moved faster in the axial direction x than the contact pad 14. The make/break pad 12 comprises or consists of a material that has a high thermal durability and a high durability against wear, for example a tungsten alloy. The contact pad 14, which is the main contact of the electric circuit of a relay 16, consists of or comprises a material with low transition resistance, for example a fine grain silver alloy.

[0035] Since the materials of the make/break pad 12 and especially the contact pad 14 are expensive a substrate layer 27 with two areas 18, 18' that are separated from one another in the longitudinal direction is provided. Wherein the area 18 is positioned between the make/break pad 12 on one side and the main body 2 on the other side and the second area 18' is positioned between the contact pad 14 on one side and the main body 2 on the other side. In an different embodiment the areas 18, 18' can also be connected resulting in a substrate layer 27 with a constant material thickness.

[0036] The substrate layer 27 replaces the material of the make/break pad between a contact surface 20 of the make/break pad 12 on one side and the main body 2 on the other side and the material between a contact surface 22 of the contact pad 14 on one side and the main body 2 on the other side. Therefore, only a thin layer of contact pad 14 material and make/break pad 12 material is necessary. Due to the reduced material thickness of the make/break pad 12 and the contact pad 14 the material costs for the contact spring are lowered.

[0037] Fig. 2 shows a sectional view of relay 16 according to the invention, when the contact is closed.

[0038] The relay 16 comprises at least one contact spring 1 and at least one complementary contact spring 26 which are arranged opposite to each other, wherein the contact surfaces 20, 22 of the make/break pad 12 and contact pad 14 are facing the complementary contact surfaces 20', 22' of the complementary contact spring's 26 make/break pad 12' and contact pad 14', respectively.

[0039] In the embodiment of the contact spring 1 and complementary contact spring shown in Fig. 2 the contact spring 1 and complementary contact spring 26 exhibit a single contact shape, meaning that the make/break pad 12 is arranged adjoining to the contact pad 14 and the make/break pad 12' is arranged adjoining to the contact pad 14'. The contact surfaces 20, 20' of the make/break pad 12, 12' are more than double the size of the contact surfaces 22, 22' of the contact pads 14, 14'.

[0040] The make/break pad 12 and the contact pad 14 are arranged on a substrate layer 27, so that said substrate layer 27 is provided between the make/break pad 12 and contact pad 14 on one side and the main body 2 on the other side. Analogous to the contact spring 1 a substrate layer 27' is provided between the make/break pad 12' and the contact pad 14' on one side and a main body 2' of the complementary contact spring 26 on the other side.

[0041] The complementary contact spring 26 is stationary and exhibits a tilted end portion 28 on which the common substrate layer 27' is located. The make/break pad 12' and the contact pad 14' are arranged on a face side of the substrate layer 27', facing the contact spring 1. The end portion 28 is tilted towards the contact spring 1, so that in the open position 30 indicated by the dashed line in Fig. 2 the distance between the pair of make/break pads 12, 12' is shorter than the distance between the pair of contact pads 14, 14'.

[0042] In the open position 30 the main body 2 of the contact spring 1 is arranged essentially perpendicular to the axial direction x, and the make/break pad 12 and the contact pad 14 are spaced apart from the corresponding make/break pad 12' and contact pad 14', respectively.

[0043] The contact spring 1 can be moved towards the stationary complementary contact spring 26 by for example a powered coil 32 which creates a magnetic field, whereby the complementary contact spring 26 is arranged in the axial direction x between the contact spring 1 and the coil 32. The magnetic field can create a pull that causes the main body 2 to pivot towards the complementary contact spring 26. Since the pair of make/break pads 12, 12' are positioned closer to one another, the arc extends between said make/break pads 12, 12' before making the first contact and after breaking the last contact. Furthermore, the impact upon first contact is caught by the make/break pads 12, 12' since the first contact between the contact springs 1, 26 is established by said make/break pads 12, 12' cushioning the impact of the following contacting of the pair of contact pads 14, 14'.

[0044] The main body 2 comprises a deformation zone 34 located between the hinge 8 and an end portion 36 of said main body 2 where the contact pad 14 and the make/break pad 14 are located. The deformation zone 34 is a zone with increased flexibility with respect to its immediate surrounding and can act as a second hinge 37. Upon first contact an axial force is exerted by the complementary contact spring 26 on the end portion 36 causing an elastic deformation at the deformation zone, with the end portion 36 being bent to the direction pointing away from the complementary contact spring 26. Therefore, the contact force gradually shifts from the pair of make/break contacts 12, 12' to the pair of contact pads 14, 14'.

[0045] In the transition position (not shown) the end portion 36 is arranged parallel to the end portion 28 of the complementary contact spring 26, with both the contact pad 14 and the make/break pad 12 contacting their respective counterparts.

[0046] In the closed position 38, as shown in Fig. 2 the make/break pad 12 is at least partially spaced apart from the make/break pad 12' of the complementary contact spring 26 and the contact force is completely shifted to the pair of contact pads 14, 14', closing the electric circuit.

[0047] The contact pads 14, 14' are secured against mechanical wear and high thermal stress by the make/break pads 12, 12'. By having the make/break pads 12, 12' at least partially spaced apart from one another in the contact established position, the contact is not affected by particle generation due to arcing or other wear related effects. Therefore, a stable contact resistance is achieved by the relay according to the invention. Furthermore, the durability of the spring contact is raised, resulting in an extended lifetime. The savings on expensive raw materials for the contact pads 14, 14' and the make/break pads 12, 12' lead to an overall decrease of the relay costs.

[0048] When transitioning from the contact established position into the break position 30, the make/break pad 12 is separated from the make break pad 12' after the contact pads 14, 14' are already spaced apart. Therefore, the arc that can occur before making the first contact and after breaking the last contact extends between the make/break pads 12, 12'.

[0049] Furthermore, the substrate layer 27 reduces the distance that needs to be overcome for closing the electric circuit. When only applying a thin layer of the contact pad 14 and make/break pad 12 directly onto the main body 2 of the contact spring 1, the distance for contacting the corresponding contact pad 14' and make/break pad 12' of the complementary contact spring 26 will be larger causing a higher strain on the main body 2.

Reference numerals

[0050] 

1

contact spring

2, 2'

main body

4

armature

5

mounting point

6

free end

8

hinge

10

face side

12, 12'

make/break pad

14, 14'

contact pad

16

relay

18, 18'

area of the substrate layer

20, 20'

contact surface

22, 22'

contact surface

26

complementary contact spring

27, 27'

substrate layer

28

end portion

30

break position

32

coil

34

deformation zone

36

end portion

37

hinge

38

closed position

x

axial direction

y

longitudinal direction

Claims

1. Contact spring (1) for a relay (16), comprising a main body (2), a make/break pad (12) and a contact pad (14), the make/break pad (12) and the contact pad (14), both being arranged on the main body (2), the make/break pad (12) being made from a first material and the contact pad (14) being made from a second material different from the first material, wherein at least one substrate layer (27) is provided between the make/break pad (12) and the contact pad (14) on one side and the main body (2) on the other side.

2. Contact spring (1) according to claim 1, wherein the at least one substrate layer (27) contains or consists of copper.

3. Contact spring (1) according to claim 1 or 2, wherein the volume of the at least one substrate layer (27) is larger then the volume of the make/break pad (12) and/or contact pad (14).

4. Contact spring (1) according to any one of claims 1 to 3, wherein the make/break pad (12) is larger than the contact pad (14).

5. Contact spring (1) according to any one of claims 1 to 4, wherein the make/break pad (12) comprises or consists of tungsten or a tungsten alloy.

6. Contact spring (1) according to any one of claims 1 to 5, wherein the contact pad (14) comprises or consists of silver or a silver alloy.

7. Contact spring (1) according to any one of claims 1 to 6, wherein the contact pad (14) and the make/break pad (12) are arranged adjoining one another.

8. Contact spring (1) according to any one of claims 1 to 6, wherein in the contact pad (14) and the make/break pad (12) are spaced apart from one another.

9. Contact spring (1) according to any one of claims 1 to 8, wherein the main body (2) exhibits a deformation zone (34) with increased flexibility.

10. Relay (16) having at least one contact spring (1) according to any one of claims 1 to 9 and at least one complementary contact spring (26) according to any one of claims 1 to 9, wherein, in the closed position, the make/break pad (12) of the contact spring (1) and the make/break pad (12') of the complementary contact spring (26) are spaced apart from one another.

Drawing