The present invention relates to a spring-based contact system for the switching function of a relay operated by electrical current. This contact system is characterised by high performance and efficient producibility.

Spring-based contact systems for switching equipment, in particular for relays, are already known. Indeed, DE 10 2007 011 328 A1 describes a relay that has at least one contact spring for closing or interrupting the respective circuit between a first and a second relay contact. One end of the contact spring has a conducting connection to the first relay contact here. The circuit is closed in a first relay position of the contact spring or interrupted in a second relay position of the contact spring via the other, free end of the contact spring. The relay also has a solenoid actuator for moving the contact spring into the respective relay position, wherein the solenoid actuator has a pole-reversible magnetic coil and an armature with a permanent magnet that is held on the magnetic coil and can pivot between two switching positions. The at least one contact spring is held both from above and from below by the armature in its deflection direction. The contact spring can be constructed as a multilayer leaf spring here with a curve section that projects from its plane.

EP 2 394 284 B 1 describes an electromagnetic relay with a coil arrangement, a rotating armature arrangement and a switch arrangement. The switch arrangement encompasses a spring arrangement with three springs, wherein the spring arrangement encompasses three stacked spring elements and a longitudinal axis of the spring arrangement.

Contact carriers for movable contacts in relays and switches, which are typically constructed in the form of contact springs, need to meet a large number of requirements: low electrical resistance, which remains stable throughout the entire service life; low thermal resistance in order to minimise any temperature increase; facilitate movability of the contacts with minimal force requirements of the actuator; ensure secure absorption and transfer of the short-circuit forces and ensure absorption or transfer of the contact force.

In addition, there is a need for contact systems that take up less and less installation space, while still offering the same performance. Important functional elements therefore need to be consistently reduced in size.

The object of the invention lies in a contact system that caters to the aforementioned requirements, while at the same time delivering high performance and being inexpensive to produce.

The spring-based contact system according to the invention is generally suitable for the switching function of a switching device operated by electrical current. As such, the invention can be used for relays, switches, contactors, switching devices and circuit breakers. The spring-based contact system encompasses at least two pairs of contacts, each of which comprises one fixed contact piece that is attached to a first current-carrying component with a fixed location relative to the housing, and one contact piece that can be moved relative to the fixed contact piece for the switching function. Here, the contact pieces of each pair of contacts are positioned relative to one another in such a way that the movable contact piece can be pressed onto the fixed contact piece using a contact force. The at least two fixed contact pieces are arranged next to one another. In addition to this, the spring-based contact system encompasses a planar contact piece carrier for the movable contact pieces which, comprising no more than two current paths positioned above one another, is essentially constructed straight in its longitudinal section along its longitudinal axis from a first end up to a second end and is attached at the first end to a current-carrying component with a fixed location relative to the housing. Together with this current-carrying (live) component, the contact piece carrier forms a V-shape in its longitudinal section, wherein at the second, free end of the contact piece carrier the movable contact pieces are arranged and attached transversely to the longitudinal axis of the contact piece carrier. Here, the contact force is based at least partially on spring characteristics of the contact piece carrier and/or spring characteristics of additional spring elements that exert a spring force on the contact piece carrier. The spring-based contact system also encompasses a mechanical coupling element for transmuting a force generated by a magnetic actuator to the contact piece carrier in order to open or close the pairs of contacts. According to the invention, a geometric offset for delayed opening or closing of the at least two pairs of contacts is provided in the spring-based contact system.

With the characteristic of geometric offset within the spring-based contact system, a so-called lead-lag switching characteristic is introduced, with which the two or multiple pairs of contacts of a contact are switched with a time lag in order to keep the total contact resistance constant throughout the service life of the switching device. In addition to this, the essentially straight contact piece carrier facilitates the use of relatively short and thin current paths, also referred to as layers, for the movable contact pieces, wherein the contact piece carrier is ideally constructed of no more than two layers arranged above one another. This allows the total resistance to be kept low at minimum costs. At the same time, the requirements of short-circuit tests of met, in particular with regard to flexibility and spring constants.

The geometric offset according to the invention leads to the contact at one of the pairs of contacts opening first and closing last when the contact piece carrier moves for the movable contact pieces. This contact is referred to as the lag contact. The contact on the other pair of contacts, on the other hand, opens last and closes first. This contact is referred to as the lead contact. On each switching contact, the lead contact carries the full current for a brief period, as long as the lag contact is not closed. When closed, the current is then split between the two contacts. The switching arc only occurs at the lead contact, as the lag contact is open when switching on and off. As such, only the lead contact bums off. No switching arc occurs at the lag contact. The contact material does not wear and the contact resistance remains constant at a low level throughout the service life.

The mechanical coupling element is generally a slide, via which the contact piece carrier is held both from above and below in order to effect a movement for opening and closing the at least two pairs of contacts in the direction of motion. For example, a slide of this kind, which is connected to an armature, can be used to transmit a force generated by an exciter coil in a relay due to a magnetic field to the contact piece carrier with the attached movable contact pieces, so that the contact between the fixed contact piece and the movable contact piece can be switched by the exciter coil.

In a specific design, precisely two pairs of contacts are used, which can be openable and closable after one another with a time lag. According to a beneficial embodiment, the straight contact piece carrier that carries the movable contact pieces, itself a leaf spring according to a preferred embodiment is split into two spring legs. Here, each spring leg carries one movable contact piece.

Suitable measures for generating the geometric offset are as follows: a) a step in the slide, b) a step in one leg of the contact piece carrier for the movable contact pieces, c) offset fixed contact pieces, d) various heights of contact pieces.

The measure stated in version a) can be easily produced if the contact piece carrier is held from below by a lifting surface of the slide in order to lift the movable contact pieces. According to this embodiment, the geometric offset is constructed in the form of a step on the lifting surface of the slide in such a way that a partial lifting surface for a first movable contact piece and a partial lifting surface for a second movable contact piece are located on different planes in the direction of motion of the lifting movement. Version a) is particularly straightforward to implement, as the slide is generally produced from plastic, meaning that the contours can be accurately and precisely formed. In version b), the geometric offset is constructed in the form of a step on the contact piece carrier in such a way that the two different sections of the contact piece carrier carrying the movable contact pieces are positioned on different levels in the direction of motion. As per version c), the geometric offset is produced in the form of fixed contact pieces that are offset in the direction of motion of the movable contact pieces, for example positioned on different levels. However, as per version d), embodiments are also covered in which the fixed contact pieces positioned next to one another or the movable contact pieces positioned next to one another are set at different levels. In these examples, the geometric offset is then at least in part the result of different levels of the fixed contact pieces or different levels of the movable contact pieces, so that the contact heads are positioned at different levels. In the case of attaching the fixed contact pieces or movable contact pieces via rivet joint, the contact heads of the fixed contact pieces are also referred to as contact rivet heads. To keep the costs for the spring system low, the material usage must be minimised. This can be achieved by reducing the cross-section and the length of the contact piece carrier to a minimum. Good movability can be guaranteed by distributing the required cross-section over two current paths, also referred to as layers, that are positioned above one another. Most known contact systems have employed three or four current paths to date. The low number of current paths leads to a further cost reduction. However, smaller components also require tighter tolerances. This problem is resolved by dispensing with the curved U-shaped or V-shaped current paths typically used. Non-curved, straight stamped parts that guarantee extremely high precision can be used. The contact piece carrier preferably has a two-layer construction, comprising two straight current paths. The contact piece carrier can, for example, then be constructed in the form of a two-layer leaf spring. In a further embodiment, the contact piece carrier is constructed as a two-layer element, comprising a first, straight current path and a second current path, wherein the second current path is also constructed straight with the exception of one curve section that projects outward beyond its level and stretches transversely to the longitudinal axis across the entire width of the contact piece carrier. This curve section is preferably constructed on the outer current path, i.e. the current path that is located in the V-shape on the side facing away from the second current-carrying component.

Another advantage of contact piece carriers with straight current paths lies in the great electrodynamic force between the current-carrying component that is also referred to as the terminal and the contact piece carrier in the event of a short-circuit, wherein this force either occurs either in the form of an attraction force (blow-on force) or repellent force (blow-off force). In comparison with other designs of contact piece carriers with a U-shape or V-shape, the distance between the current-carrying component and the contact piece carrier is very small, while the forces are very high. In the case of parallel electrical conductors, the length of the parallel sections is directly proportional to the electrodynamic force generated between the conductors. Particularly in the case of contact piece carriers with very short current paths, the increased force is required due to the small distance. Firstly, this force is required in order to hold the contacts closed in the event of a short-circuit, and thereby provide a counterforce to the force which drive the contacts apart. Secondly, the increased force can generate a sufficient contact rolling motion to reduce the melting and fusing of the contacts. In addition to this, sufficient energy can be stored in the curved current paths of the contact piece carrier to be able to break open the unavoidable contact fusing when the short-circuit current subsides.

According to a particularly beneficial embodiment of the invention, at least one overtravel spring made of steel, as an additional spring element that applies a spring force to the contact piece carrier, is attached to the current-carrying component and applies a spring force on the contact piece carrier from there to the section on whose reverse side at least one of the movable contact piece is located. If an overtravel spring of this kind, preferably made of steel, is used to generate the contact pressure, the current paths of the contact piece carrier most not have any spring-based characteristics. The contact piece carrier can then be produced from a material with a copper content of > 99.9%. If a copper material of this kind is used, this leads to a further cost reduction, as well as improved conductivity.

Further details, features and benefits of embodiments of the invention result from the following description of specimen embodiments with reference to the accompanying drawings.

The invention shall be explained in detail in one exemplary embodiment by reference to Figures 1 to 6.

Fig. 1: The change in contact resistance of a contact system over the number of switching cycles without using a lead-lag function, state of the art, Fig. 2: The contact resistance of a contact system over the number of switching cycles when using a lead-lag function,

Fig. 3A: A slide with step as geometric offset for a contact system,

Fig. 3B: A schematic diagram of the contact system and the slide with two closed contacts,

Fig. 3C: A schematic diagram of the contact system and the slide with one open and one closed contact,

Fig. 3D: A schematic diagram of the contact system and the slide with two open contacts,

Fig. 4A: A U-shaped contact spring with three current paths positioned above one another, state of the art,

Fig. 4B: A V-shaped contact spring with three current paths positioned above one another, state of the art,

Fig. 5 A: A spring as a stamped part with two linear current paths,

Fig. 5B: A spring as a stamped part with one straight current path and one current path with curve section, and

Fig. 6: A planar contact piece carrier with a first end and a second end.

Fig. 1 contains a diagram that shows the contact resistance on a contact system according to the state of the art, without lead-lag function, as a function of the number of switching cycles throughout the service life of the contact system. It is clear to see in the diagram how the contact resistance goes up as the service life increases.

Fig. 2, on other hand, contains a diagram that shows the contact resistance on a contact system as a function of the number of switching cycles throughout the service life of a contact system according to an embodiment of the invention. This contact system has a lead-lag switching characteristic. This diagram shows that the contact resistance remains virtually identical and at a low level throughout the service life of the contact system.

Figs. 3 A to 3D schematically show how a lead-lag function as per an embodiment of the contact system according to the invention is implemented using a slide 1, which is shown in Fig. 3A. This slide 1 has a step 2 as geometric offset.

Fig. 3B schematically shows a part of the contact system 3 used in a relay. The contact system 3 include two pair of contacts 4, 5, each of which comprises one fixed contact piece 4.1; 5.1 that is attached to a first current-carrying component 6 with a fixed location relative to the housing of the switching device, and one contact piece 4.2; 5.2 that can be moved relative to the fixed contact piece for the switching function. Here, the contact pieces 4.1, 4.2; 5.1, 5.2 of each pair of contacts 4; 5 are positioned relative to one another in such a way that the movable contact piece 4.2; 5.2 can be pressed onto the fixed contact piece 4.1; 5.1 using a contact force. The at least two fixed contact pieces 4.1, 5.1 are arranged next to one another here. Fig. 3B shows the contact system in a condition in which the two contacts 4, 5 of the contact system 3 are closed. The movable contact pieces 4.2, 5.2 are attached to a planar contact piece carrier 7 which is essentially constructed straight and whose first end is attached to a second current-carrying component with a fixed location relative to the housing (not shown). As refer to Fig. 6, the planar contact piece carrier (7) extends in its longitudinal section along its longitudinal axis (7.3) from a first end (7.1) up to a second end (7.2). The movable contact pieces 4.2, 5.2 are arranged transversely to the longitudinal axis of the contact piece carrier 7 and attached to the second, free end of the contact piece carrier 7. In the embodiment shown, the contact piece carrier 7 is split into two spring legs 8, 9 arranged next to one another, to each of which one movable contact piece 4.2; 5.2 is attached. Fig. 3B also schematically shows the slide 1, which has a step 2. The slide 1 is a coupling element for transmuting a force generated by a magnetic actuator to the contact piece carrier 7 in order to open or close the pairs of contacts 4, 5. The contact piece carrier 7 is held both from above and below by the slide 1 in order to effect a movement for opening and closing the at least two pairs of contacts in the direction of motion. Here, the slide 1 presses the contacts 4, 5 by exerting a pressure with a pressure surface 10 in such a way that a flow of current occurs in parallel through both contacts 4, 5. The pressure surface 10 is the surface with which the slide 1 holds the top of the contact piece carrier 7. However, the pressure surface 10 preferably does not press directly on the contact piece carrier 7, but rather on a free end of a spring element arranged above the contact piece carrier 7, which is not shown in Figs. 3A to 3D, but is thereby pretensioned and generates a defined pressure on the contact piece carrier 7 or the contacts 4, 5, with simultaneous tolerance compensation, i.e. without a hard end stop. 50% of the current flow passes through each contact 4; 5, which is schematically shown through two parallel arrows pointing downwards. In contrast to the pressure surface 10, which is constructed as a flat surface (planar), the opposite lifting surface 11, with which the slide holds the bottom of the contact piece carrier 7, has a geometric offset in the form of a step 2 on the lifting surface 11 of the slide 1. As such, the lifting surface 11 of the slide is divided into partial lifting surfaces 12, 13 in such a way that one partial lifting surface 12 for a first movable contact piece 4.2 and one partial lifting surface 13 for a second movable contact piece 5.2 are at different levels (planes) in the direction of motion of the lifting movement.

Fig. 3C shows the contact system 3 in a condition in which a first contact 4, the lag contact 4, is opened first due to the pressure of the slide 1 on the spring leg 8 on the contact 4 after the movable contact piece 4.2 has been released from the fixed contact piece 4.1. On the other hand, the second contact 5, the lead contact 5, remains closed. Logically, 100% of the current flow goes through the lead contact 5 in this condition, which is shown schematically by an arrow pointing downwards. The step 2 in the slide 1 ensures that the lag contact 4 with the partial lifting surface 12 at a higher level is first pressed open by the slide 1, while the lead contact 5 remains closed, as the partial lifting surface 13 of the slide 1 at a lower level is not yet exerting any or sufficient pressure on the spring leg 9 of the contact 5.

Fig. 3D shows the contact system 3 in a condition in which both contacts 4, 5, i.e. both the lag contact 4 and the lead contact 5, are forced open by the slide 1 and are therefore open. This means that the movable contact pieces 4.2; 5.2 are each disconnected from their respective fixed contact piece 4.1; 5.1, which interrupts the current flow.

Fig. 4A and Fig. 4B show known solutions from the state of the art for construction of contact springs. Here, Fig. 4A shows a U-shaped spring with three current paths, while Fig. 4B shows a V-shaped spring, also with three current paths.

Fig. 5 A and Fig. 5B show embodiments for contact piece carriers 7 according to the invention.

Only one pair of contacts 4 is shown here, comprising one fixed contact piece 4.1, which is attached to a first current-carrying component 6 with a fixed location relative to the housing of the switching device, as well as one contact piece 4.2 that is movable relative to the fixed contact piece for the switching function. The contact pieces of each pair of contacts 4 are positioned relative to one another in such a way that the movable contact piece 4.2 can be pressed onto the fixed contact piece 4.1 using a contact force. To keep the costs for the spring-based contact system low, the material usage must be minimised. This objective is achieved by reducing the cross-section and the length of the contact piece carriers 7 for the movable contact pieces 4.2 to a minimum. Fig. 5A shows an I-shaped contact piece carrier 7, which is attached to a second current-carrying component 14 (preferably using a stamped connection) with a fixed location relative to the housing of the switching device that is constructed as an extended, fixed or non-flexible connection piece 14 and has two I-shaped, i.e. straight, current paths positioned above one another, referred to as layers 15, 16 in the following. Together with the connection piece, the I-shaped contact piece carrier forms a V-shape in its longitudinal section with a peaked crown section.

The good movability remains guaranteed by the required cross-section being spread over just two current paths 15, 16. As per the state of the art, as shown by the examples in Fig. 4A and Fig. 4B, three or four current paths are standard. Fig. 5B shows another embodiment of the invention, in which the contact piece carrier 7 also comprises two layers 15, 16, one of which is an inner layer 15 and is constructed straight in its longitudinal section along its longitudinal axis, while the other layer, the outer layer 16, is predominantly constructed straight in its longitudinal section along its longitudinal axis, although it has a curve section 17 that projects out of its plane in a neighbouring section to the crown of the V-shape that stretches transversely to the longitudinal axis across the entire width of the contact piece carrier. The low number of layers 15, 16 leads to a significant cost reduction.

However, smaller components also require tighter tolerances. This problem is resolved by dispensing with the curved U-shaped or V-shaped current paths typically used, as shown in Fig. 4A and Fig. 4B. Non-curved, straight stamped parts can be used, such as those shown in the contact piece carriers 7 shown in Fig. 5A and Fig. 5B, which guarantee extremely high precision.

Another advantage of straight current paths lies in the great electrodynamic force between the connection piece 14 and the contact piece carrier 7 in the event of a short-circuit. In comparison with other designs of contact piece carriers with a U-shape or V-shape and the spacings al and a2, the spacing a3 between the contact piece carrier 7 and the connection piece 14 with the I-shaped contact pieces is minimum, whereas the forces are maximum.

The increased force is necessary, particularly with very short current paths, due to the minimum spacing, so that in the event of a short-circuit

The contacts are held closed, wherein a counterforce to the force which naturally drives the contacts apart must be applied,

A sufficient contact rolling motion is generated in order to reduce the melting and fusing of the contacts 4, i.e. the fixed contact pieces 4.1 to the movable contact pieces 4.2 and

Sufficient energy is stored in the curved layers in order to break open the unavoidable contact fusing.

As shown in Fig. 5A and Fig. 5B, an additional spring element that applies a spring force to the contact piece carrier 7 in the form of an overtravel spring 18 is attached to the connection piece 14. From here, the overtravel spring 18 applies a spring force to the contact piece carrier 7 in the section on whose reverse side the movable contact piece 4.2 is located. If an overtravel spring of this kind 18, preferably made of steel, is used to generate the contact pressure, the layers 15, 16 of the contact piece carrier 7 must not have any spring-based characteristics themselves. In this case, pure copper (purity > 99.9%) can then be used, which leads to a further cost reduction and improved conductivity.

The spring element 18 encompasses an attachment section 19, with which the spring element 18 is preferably riveted to the connection piece 14. Starting from the attachment section 19, the spring element 18 has at least one spring arm 20, which runs from the attachment section 19 up to a free end 21 of the spring element 18. The at least one spring arm 20 can be split into two different spring arm sections 22, 23. A first spring arm section 22 runs from the attachment section 19 up to a Pressure region 24 with which the spring element 18 rests on the reverse side of the movable contact piece 4.2 or just on the reverse side of the section of the contact piece carrier 7 neighbouring the movable contact piece 4.2. Starting from the Pressure region 24, the second spring arm section 23 stretches up to the free end 21 of the spring arm 20. Here, the distance between the contact piece carrier 7 and the second spring arm section 23 increases, starting from the Pressure region 24 at which the spring element is still resting on the movable contact piece 5 or the contact piece carrier 7 gradually up to the end 21 of the spring arm 20. This means that the two different spring arm sections 22, 23 together form a V-shape.

As already mentioned, a pressure surface of the slide can pretension the overtravel spring 18 by applying pressure to the free end 21 of the second spring arm section 23 and also apply a defined pressure to the contact piece carrier 7 or to the movable contact piece 4.2 and thereby to the contact 4, while at the same time providing tolerance compensation.

Similar to that shown in Fig. 3A to Fig. 3D, a neighbouring movable contact piece 5.2 (not shown here) of a neighbouring contact 5 is pressed against a fixed contact piece 5.1 (also not shown here) via a second spring arm in the same way.

List of reference symbols

1 Slide

2 Step

3 Spring-based contact system

4 Contact, pair of contacts, lag contact

4.1 Fixed contact piece

4.2 Movable contact piece

5 Contact, pair of contacts, lead contact

5.1 Fixed contact piece

5.2 Movable contact piece

6 First current-carrying component with fixed position relative to the housing of the switching device

7 Contact piece carrier

7.1 First end

7.2 Second end

7.3 Longitudinal axis

8 Spring leg

9 Spring leg

10 Pressure surface of the slide

11 Lifting surface of the slide

12 Partial lifting surface of the slide

13 Partial lifting surface of the slide

14 Second current-carrying component with fixed position relative to the housing of the switching device, connection piece

15 Current path (layer), inner

16 Current path (layer), outer

17 Curve section

18 Overtravel spring Attachment section Spring arm

Free end of the spring arm First spring arm section Second spring arm section Pressure region