Method for manufacturing a sensor for determining at least one property of a measuring gas
Patent Information
- Authority / Receiving Office
- DE · DE
- Patent Type
- Patents
- Current Assignee / Owner
- ROBERT BOSCH GMBH
- Filing Date
- 2012-08-20
- Publication Date
- 2026-06-11
Smart Images
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Abstract
Description
State of the art
[0001] Numerous sensors and methods for determining at least one property of a sample gas in a sample gas chamber are known in the prior art. These properties can be any physical and / or chemical properties of the sample gas, and one or more properties can be measured. The invention is described below, in particular with reference to the qualitative and / or quantitative measurement of a gas component of the sample gas, specifically with reference to the measurement of the oxygen content in the sample gas. The oxygen content can be measured, for example, as a partial pressure and / or as a percentage. Alternatively or additionally, other properties of the sample gas, such as its temperature, can also be measured.
[0002] For example, such sensors can be designed as so-called lambda sensors, as described, for instance, in "REIF, Konrad (ed.): Sensor Design. In: Sensors in Motor Vehicles. 1st Edition. Wiesbaden: Vieweg + Teubner Verlag, 2010 (Bosch Automotive Technical Information), Chapter 3, pp. 160-165. ISBN 978-3-8348-1315-2. https: / / doi.org / 10.1007 / 978-3-8348-9718-3_3". Wideband lambda sensors, especially planar wideband lambda sensors, can be used to determine the oxygen concentration in the exhaust gas over a broad range, thus allowing conclusions to be drawn about the air-fuel ratio in the combustion chamber. Alternatively, a finger-type sensor design is also possible. The air-fuel ratio λ describes this air-fuel ratio.
[0003] In this type of sensor, a sensor element generally protrudes from the sensor housing along its longitudinal axis. This longitudinal axis can also serve as the sensor's axis of symmetry, as many conventional sensors have a rotationally symmetrical design and are oriented along this longitudinal axis. To protect the sensor element from damage, it is typically enclosed in at least one protective tube. Furthermore, it is usually crucial that the sensor element can be brought into direct contact with the gas being measured. Therefore, the protective tube of such sensors always has suitable openings to allow the flow of the gas through it.
[0004] Typically, the sensor element inside the sensor housing is connected to a contact element, such as a crimp contact. The contact element, in turn, is connected to a connecting cable. The connecting cable extends from the sensor housing. The connections between the sensor element and the contact element, as well as between the contact element and the connecting cable, are electrical connections. This allows a signal from the sensor element to be transmitted from the sensor housing. The connection between the contact element and the connecting cable is usually a positive-locking connection in the form of a crimp connection.
[0005] From US patent 2008 / 0149483A1, a method for manufacturing an exhaust gas sensor is known, comprising: positioning at least one part of a subassembly of the exhaust gas sensor in a molding device, overmolding at least one part of the subassembly with a ceramic material, and removing the overmolded subassembly from the molding device.
[0006] From JP H09-82376A, a cable joining method is known that improves the protection and joint strength of the conductor sections of the cables to be joined. The method comprises two opposing clamping devices and opposing welding electrodes positioned between the two clamping devices. These clamping devices and welding electrodes form an insertion chamber for the material to be joined. The conductor sections of the cables are inserted into the inner space of a cylindrical metal body. The cylindrical body and the conductor sections are placed in the insertion chamber for the material to be joined. Subsequently, the conductor sections are joined together by resistance welding while under the pressure of the two welding electrodes.
[0007] Despite the numerous advantages of the sensors and manufacturing processes known from the prior art, there is still room for improvement. Typically, the contact element is made of steel and the connecting cable is nickel-plated copper, meaning it has a copper core surrounded by a nickel layer. A robust and reliable electrical connection between the nickel-plated copper and the steel contact element is difficult to achieve due to hard oxide layers on the surface of both the connecting cable and the steel contact element. Therefore, attempts have been made to seal the crimp connection using laser welding to improve the positive fit and thus ensure reliable electrical contact.However, due to the materials of the contact element and the connecting cable, welding processes that create a melt cannot be used, or such material weakening would occur that the sensor would no longer withstand the requirements during operation. Disclosure of the invention
[0008] Therefore, a method for manufacturing a sensor for determining at least one physical property of a measuring gas in a measuring gas chamber is proposed, which largely avoids the disadvantages of known manufacturing methods.
[0009] The inventive method for manufacturing a measuring sensor, in particular a sensor for detecting at least one property of a measuring gas in a measuring gas space, in particular for detecting a gas component in the measuring gas or a temperature of the measuring gas, comprises the following steps: - Arranging at least one sensor element in a sensor housing, - Connecting the sensor element to at least one contact element, - Providing at least one connection cable, - positive locking and / or force-locking connection of the connecting cable to the contact element, and - material-bonded connection of the connecting cable to the contact element.
[0010] The contact element can at least partially surround the connecting cable. The contact element can have a crimp sleeve in which the connecting cable is arranged, with the contact element and the connecting cable being positively and / or force-fit connected by a crimp connection. The contact element can be made at least partially of stainless steel. The connecting cable can be made at least partially of copper with a nickel plating. The contact element and the connecting cable can be joined by a weld. To create the weld, the contact element and the connecting cable can be inserted into a first electrode, with a second electrode positioned on the contact element and the connecting cable such that a welding current flows from the second electrode through the contact element and the connecting cable to the first electrode.The contact element and the connecting cable can be positioned between the first and second electrodes. During welding, the first and second electrodes can be moved relative to each other with a predetermined force to deform the contact element and the connecting cable. Upon reaching a predetermined deformation of the contact element and the connecting cable, the welding current can flow from the second electrode through the contact element, bypassing the connecting cable, to the first electrode. The first and second electrodes can move relative to each other parallel to a plane perpendicular to the direction of extension of the contact element and the connecting cable.To create the weld connection, at least one third electrode can be provided, the contact element and the connecting cable can be deformed by the predetermined force so that the contact element touches the third electrode, whereby when there is contact between the contact element and the third electrode, the welding current flows from the second electrode through the contact element and via the third electrode to the first electrode.
[0011] A measuring sensor, in particular a sensor for detecting at least one property of a measuring gas in a measuring gas space, in particular for detecting a gas component in the measuring gas or a temperature of the measuring gas, comprises a measuring sensor housing and at least one sensor element in the measuring sensor housing, wherein the sensor element is connected to at least one contact element, wherein the contact element is positively and / or force-fit connected to at least one connecting cable, wherein the contact element is materially bonded to the connecting cable, in particular by means of a welded connection.
[0012] In the context of the present invention, a positive-locking connection is understood to be a connection in which one of the connecting partners obstructs the movement of another, thus preventing relative movement of the connecting partners in at least the direction in which one partner obstructs the other. Under operating load, compressive forces act normally, i.e., perpendicular to the surfaces of the connecting partners, and thus prevent movement. Such "locks" occur in at least one direction. Examples of positive-locking connections include dovetail joints, gear couplings, tongue-and-groove joints, parallel keys, connecting fittings, zippers, clinching, and hot riveting.
[0013] In the context of the present invention, a friction-fit connection is understood to be a connection that requires a normal force to be exerted on the surfaces of the connecting partners to be joined. Mutual displacement of the connecting partners is prevented as long as the opposing force caused by static friction is not exceeded. Examples of friction-fit connections are connections using clamps or screws.
[0014] In the context of this discussion, a metallurgical bond is understood to be a bond in which the bonding partners are held together by atomic or molecular forces. These are also inseparable bonds that can only be separated by destroying the bonding agents. Examples of metallurgical bonds include soldering, welding, gluing, and vulcanizing.
[0015] Within the scope of the present invention, stainless steel means alloyed or unalloyed steels with a special degree of purity, for example steels whose sulfur and phosphorus content, so-called iron impurities, does not exceed 0.025%. Examples of stainless steels are steels with the material numbers 1.4003 (X2CrNi12), 1.4006 (X12Cr13), 1.4016 (X6Cr17), 1.4021 (X20Cr13), 1.4104 (X14CrMoS17, formerly X12CrMoS17), 1.4301 (X5CrNi18-10), 1.4303 (X4CrNi18-12), 1.4305 (X8CrNiS18-9), 1.4306 (X2CrNi19-11), 1.4307 (X2CrNi18-9), 1.4310 (X10CrNi18-8), 1.4316 (X1CrNi19-9), 1.4401 (X5CrNiMo17-12-2), 1.4404 (X2CrNiMo17-12-2), 1.4440 (X2CrNiMo19-12), 1.4435 (X2CrNiMo18-14-3), 1.4452 (X13CrMnMoN18-14-3), 1.4462 (X2CrNiMoN22-5-3), 1.4541 (X6CrNiTi18-10), 1.4571 (X6CrNiMoTi17-12-2), 1.4581 (GX5CrNiMoNb19-11-2), 1.4841 (X15CrNiSi25-21) and 1.7218 (25CrMo4).
[0016] Crimping, also known as flanging, is understood within the scope of the present invention to be a joining process in which two components are joined together by plastic deformation. It is therefore a specific form of flanging. A crimped joint is only partially detachable and usually irreparable.
[0017] The sensor can be used to detect the physical and / or chemical properties of a gas, whereby one or more properties can be measured. The invention is described below, in particular with reference to the qualitative and / or quantitative measurement of a gas component, specifically the measurement of the oxygen content in the gas. The oxygen content can be measured, for example, as a partial pressure and / or as a percentage. However, other types of gas components can also be measured, such as nitrogen oxides, hydrocarbons, and / or hydrogen. Alternatively or additionally, other properties of the gas can also be measured. The invention is particularly applicable in the field of automotive engineering, so that the measuring gas chamber can be, in particular, the exhaust system of an internal combustion engine, and the gas can be, in particular, exhaust gas.
[0018] The core of the conductor is made of copper with a melting point of 1083 °C. The core is encased in a nickel layer with a melting point of 1455 °C. This nickel layer must be metallurgically bonded to the steel of the contact element, such as 1.4310, which has a melting point of approximately 1500 °C. The manufacturing process is carried out such that, through heating combined with an increase in internal pressure, a diffusion process occurs between the nickel plating and the steel (diffusion welding), without melting the copper. Avoiding the melting of the copper is advantageous, as otherwise the microstructure would be altered and weakened.
[0019] The process flow can be roughly described as follows: 1. The crimp is inserted into the electrodes. 2. Electrodes move together. 3. Electrodes press together with a precisely defined force. 4. A defined current is applied for a defined time, causing the material to heat up. The softer, heated material deforms and fills the lower electrode. This results in a more uniform pressure distribution inside, and the combination of pressure and temperature initiates a diffusion process between the interfaces, bonding the conductors to each other and to the crimp material. The design of the lower electrode can be such that the process is self-limiting once the lower electrode is filled. Upon contact of the crimp with the side electrodes, the current then flows through them, and no further heating occurs inside. 5. Power is switched off; the force with which the electrodes are pressed is maintained until the crimp has cooled sufficiently. 6. Open the electrodes. 7. The crimp is removed.
[0020] The inventive method for manufacturing a sensor involves breaking through the oxide layers of the contact element and the connecting cable, and directly bonding the metals together. This significantly improves the robustness of the component with regard to electrical contact. The invention aims to bond the contact partners together, thereby ensuring reliable electrical conductivity. Brief description of the drawings
[0021] Further optional details and features of the invention will become apparent from the following description of preferred embodiments, which are schematically illustrated in the figures. These show: Fig. 1 a schematic cross-sectional representation of a measuring sensor, Fig. 2 a side view of a contact element, Fig. 3 a top view of the contact element, Fig. 4 A top view of a crimp connection between the contact element and the connecting cable before a process step to create a material-bonded connection, Fig. 5 A top view of a crimp connection between the contact element and the connecting cable after a process step to create a material-bonded connection, Fig. 6 a sectional view along line AA of the Fig. 5, Fig. 7 a schematic representation of process steps for producing a materially bonded connection, Fig. 8 a perspective view of a “U”-shaped first electrode, and Fig. 9 a perspective view of a second electrode. Embodiments of the invention
[0022] Fig. Figure 1 shows a schematic cross-sectional view of a sensor 10. The sensor 10 is exemplified as a lambda probe. The lambda probe is used to control the air-fuel mixture of an internal combustion engine by measuring the oxygen concentration in the exhaust gas to achieve a mixture that is as stoichiometric as possible, thus minimizing pollutant emissions through optimal combustion. Therefore, the measuring gas chamber within the scope of the present invention can be the exhaust system of an internal combustion engine. The basic structure and function are described, for example, in Konrad Reif (ed.): Sensors in Motor Vehicles, 1st edition 2010, pages 160-165. With wideband lambda probes, especially planar wideband lambda probes, the oxygen concentration in the exhaust gas can be determined over a large range, allowing conclusions to be drawn about the air-fuel ratio in the combustion chamber.Alternatively, training as a finger probe is also possible. The air-fuel ratio λ describes this air-fuel ratio.
[0023] This lambda probe is described below as an embodiment of a measuring sensor 10 for determining at least one physical and / or chemical property of a measuring gas, in particular the temperature or the concentration of a gas component, especially in the exhaust gas of an internal combustion engine.
[0024] The sensor 10 has a sensor element 12 which protrudes from a sensor housing 16 with a gas-side sensor section 14 exposed to the measuring gas. This gas-side sensor section 14 of the sensor element 12 is initially surrounded, from the outside in, by a double protective tube 18. This double protective tube 18 comprises an outer protective tube 20 and an inner protective tube 22. The sensor element 12 is connected to at least one contact element 24. For example, four contact elements 24 are provided in a lambda sensor. For example, the contact element 24 is designed as a crimp contact 26, as described in the Fig. 2 and Fig. 3 is shown.
[0025] Fig. Figure 2 shows a side view of the crimp contact 26 and Fig. Figure 3 shows a top view of the crimp contact 26. In particular, the crimp contact 26 has a sensor-element end 28 and a connection-side end 30. The sensor element 12 is connected to the crimp contact 26, in particular electrically. The connection can be realized by a contact clip 32 at the sensor-side end 28, in which the contact clip 32 contacts the sensor element 12. For example, the contact clip 32 is elastically deformable and pre-tensioned so that it presses against the sensor element 12. At the connection-side end 30, the crimp contact 26 has a crimp sleeve 34. The crimp contact 26 is made of an electrically conductive material, such as stainless steel with material number 1.4310. In particular, the crimp sleeve 34 is made of stainless steel, such as stainless steel with material number 1.4310.
[0026] As the Fig. As shown in Figure 1, the contact element 24 is connected to at least one connecting cable 36, in particular electrically connected. For example, four connecting cables 36 are provided, each of which is connected to a contact element 24. The connection between the contact element 24 and the connecting cable 36 is positive-locking and / or friction-locking. For example, the contact element 24 is connected to the connecting cable 36 by means of a crimp connection.
[0027] Fig. Figure 4 shows, for example, a top view of a crimp connection between a contact element 24 and a connecting cable 36. The connecting cable 36 is, for example, designed as a conductor with a copper core 38 and an outer nickel plating 40. Accordingly, the copper core 38 is encased in the circumferential direction around its extent by the nickel plating 40 ( Fig. 6). The crimp sleeve 34 encloses the connecting cable 36. Fig. Figure 4 shows a top view of the crimp connection before the contact element 24 is joined to the connecting cable 36 in a material-bonded manner according to the invention.
[0028] Fig. Figure 5 shows, for example, a top view of a crimp connection between a contact element 24 and a connecting cable 36 after they have been joined by a material bond. In this embodiment, the material bond between the contact element 24 and the connecting cable 36 is made by means of a weld connection 42. How Fig. Figure 5 shows that the weld joint extends parallel to a plane perpendicular to an extension direction of the connecting cable 36 and the contact element 24.
[0029] Fig. Figure 6 shows a sectional view along line AA of the Fig. 5. From Fig. Figure 6 clearly shows the copper core 38 and the nickel plating 40 of the connecting cable 36. Furthermore, it is evident from Fig. Figure 6 clearly shows how the crimp sleeve 34 of the contact element 24 encloses the connecting cable 36. In particular, the metallurgical bond exists between the stainless steel of the crimp sleeve 34 and the nickel plating 40 of the contact element, but not with the copper core 38. This means that the copper core 38 is not melted by the weld. This is essential, as otherwise the microstructure would be altered and weakened, leading to component failure.
[0030] The inventive method for manufacturing the measuring sensor 10 will now be described. In particular, the following will be described with reference to the Fig. 7, Fig. 8 to Fig. 9 describes how the material-bonded connection between the contact element 24 and the connecting cable 36 is established.
[0031] First, the connecting cable 36 is provided. In particular, the connecting cable 36 is inserted into the crimp sleeve 34 at the connection-side end 30 of the contact element 24 and connected in a form-fit and / or force-fit manner using a crimping tool (not shown) in a manner known per se. Subsequently, the contact element 24 and the connecting cable 36 are inserted into a first electrode 44 in the area where they are connected. Such an electrode is, for example, in Fig. Figure 8 illustrates this. The first electrode 44 has a recess 46 for inserting the contact element 24 and the connecting cable 36 into the crimp connection area. For example, the first electrode 44 is formed in one piece, essentially in a "U" shape. The recess 46 can therefore be defined by two lateral legs and the base of the "U" shape of the first electrode 44. A second electrode 48 is then placed or attached to the crimp connection on the contact element 24 and the connecting cable 36. Such a second electrode 48 is, for example, Fig. Figure 9 shows the second electrode 48 having a tip 50. This tip 50 is, for example, designed as an approximately cuboid-shaped projection. The contact element 24 and the connecting cable 36 are located between the first electrode 44 and the second electrode 48, as shown in the left area of the figure. Fig. Figure 7 shows that, alternatively, the first electrode 44 can be a lower electrode 44 and can be joined by two third electrodes 52 to form an essentially "U" shape. In other words, these three joined electrodes 44 and 52 form a cross-section with the shape essentially of a "U". In particular, the two third electrodes 52 form the lateral arms of the "U" and the lower electrode 44 forms the base of the "U". Therefore, the third electrodes 52 can also be considered as side sections or side parts of the first electrode 44. In particular, the third electrodes 52 are suitable for allowing a current flow from the first electrode 44 to the second electrode 48 and vice versa.
[0032] The second electrode 48 is applied to the contact element 24 and the connecting cable 36 with a force of, for example, 130 N at the tip 50, such that the tip 50 is arranged essentially perpendicular to a direction of extension of the contact element 24 and the connecting cable 36.
[0033] A welding current is applied to the second electrode 48 and the first electrode 44. The welding current flows from the second electrode 48 to the first electrode 44. This welding current is applied, for example, with a rise time of 10 ms to, say, 1600 A. During this rise of the welding current, the second electrode 48 is moved towards the first electrode 44 with a force of, say, 360 N relative to it, as shown by arrows 54 in the figure. Fig. 7 is indicated. In particular, the second electrode 48 is moved parallel to a plane perpendicular to one direction of extension of the contact element 24 and the connecting cable 36. The welding current flows in particular from the second electrode 48 through the crimp sleeve 34, the nickel plating 40, the copper core 38 to the first electrode 44, as indicated by arrows 56 in the left area of the Fig. Figure 7 indicates that the welding current heats the crimp sleeve 34 and the connecting cable 36, particularly the nickel plating 40. This heating softens the materials of the crimp sleeve 34 and the connecting cable 36, allowing them to be deformed by pressing the second electrode 48 against them. The welding current is then held at 1600 A for, for example, 60 ms. During this holding time, the second electrode 48 presses against the crimp sleeve 34 and the connecting cable 36 with a force of, for example, 360 N. This further deforms the crimp sleeve 34 and the connecting cable 36. The deformation occurs laterally towards the third electrodes 52, as indicated, for example, by arrows 58 in the right-hand area of the figure. Fig. 7 is indicated. This results in a more uniform pressure distribution inside the crimp connection. The process is carried out such that, through heating combined with an increase in pressure inside the crimp connection, a diffusion process takes place between the nickel plating 40 and the steel of the crimp sleeve 34. Diffusion welding therefore occurs. The deformation is carried out until a predetermined deformation of the contact element 24 and the connecting cable 36 is achieved, at which point the crimp sleeve 34 contacts the third electrodes 52. Since current generally seeks the shortest electrically conductive path, the welding current flows at this point from the second electrode 48 through the crimp sleeve 34 to the third electrodes 52, as indicated by arrows 60 in the right-hand section of the Fig. 7 is shown, and from the third electrodes 52 to the first electrode 44, as indicated by arrows 62 in the right area of the Fig. As indicated in Figure 7, in an embodiment where the first electrode 44 is integrally formed in the shape of a "U", the current flows from the second electrode 48 via the lateral legs to the base of the "U" shape of the first electrode 44. The welding current bypasses the connecting cable 36 and therefore no longer flows through it, and in particular no longer through the copper core 38 and the nickel coating 40. Consequently, the connecting cable 36, and especially the copper core 38, is not heated further, preventing the copper core 38 from melting. The distance 64 traveled by the second electrode 48 to the first electrode 44 can be, for example, 130 µm to 200 µm. Finally, the welding current is switched off, which occurs with a drop-off time of, for example, 2 ms. The force with which the second electrode 48 is pressed is maintained for, for example, 50 ms, until the crimp connection has cooled sufficiently.It is understood that the first electrode 44 can also be moved to the second electrode 48. The current can also flow from the first electrode 44 to the second electrode 48.
[0034] After cooling, the first electrode 44 and the second electrode 48 are opened and the crimp connection can be removed. The sensor element 12 is placed in the sensor housing 16. The contact element 24, connected to the connecting cable 36, is then connected to the sensor element 12 at its sensor element-side end 28 in a manner known per se, as is done, for example, in Fig.Figure 1 illustrates this. It is understood that a functional test of the electrical connection between the connecting cable 36 and the contact element 24 can be performed. For example, if a current is applied to this connection, a good electrical connection is indicated by a measured voltage of, for example, a maximum of 1500 mV to 2200 mV. The qualitative target values for the voltage could be, for example, 900 mV to 1200 mV. The measured voltage indicates the electrical resistance and thus the conductivity of the electrical connection between the contact element 24 and the connecting cable 36. This functional test can also be performed at specific intervals to check the sensor 10.The material-bonded connection provided according to the invention between the contact element 24 and the connecting cable 36 is recognizable and verifiable by means of the visible imprint of the welded connection 42 on the crimp connection and the adhesion of the connecting cables 36 inside.
Claims
[1] Method for manufacturing a sensor (10), comprising the steps: - Arranging at least one sensor element (12) in a sensor housing (16), - Connecting the sensor element (12) to at least one contact element (24), - Provide at least one connection cable (36), - positive locking and / or force-locking connection of the connecting cable (36) to the contact element (24), and - materially bonded connection of the connecting cable (36) to the contact element (24), wherein the contact element (24) and the connecting cable (36) are materially bonded by a weld connection (42), wherein to create the weld connection (42) the contact element (24) and the connecting cable (36) are inserted into a first electrode (44), wherein a second electrode (48) is arranged on the contact element (24) and the connecting cable (36) such that a welding current flows from the second electrode (48) through the contact element (24) and the connecting cable (36) to the first electrode (44),wherein during welding the first electrode (44) and the second electrode (48) are moved relative to each other with a predetermined force to deform the contact element (24) and the connecting cable (36) and wherein, upon reaching a predetermined deformation of the contact element (24) and the connecting cable (36), the welding current flows from the second electrode (48) through the contact element (24) bypassing the connecting cable (36) to the first electrode (44). [2] Method for manufacturing a sensor (10), comprising the steps: - Arranging at least one sensor element (12) in a sensor housing (16), - Connecting the sensor element (12) to at least one contact element (24), - Provide at least one connection cable (36), - positive locking and / or force-locking connection of the connecting cable (36) to the contact element (24), and - material-bonded connection of the connecting cable (36) to the contact element (24), wherein the contact element (24) and the connecting cable (36) are material-bonded by a weld connection (42), wherein to produce the weld connection (42) the contact element (24) and the connecting cable (36) are inserted into a first electrode (44), wherein a second electrode (48) is arranged on the contact element (24) and the connecting cable (36) such that a welding current flows from the second electrode (48) through the contact element (24) and the connecting cable (36) to the first electrode (44), wherein during welding the first electrode (44) and the second electrode (48) are moved relative to each other with a predetermined force to deform the contact element (24) and the connecting cable (36), and wherein at least a third electrode (52) is provided to produce the weld connection (42),The contact element (24) and the connecting cable (36) are deformed by the predetermined force such that the contact element (24) touches the third electrode (52), whereby, upon contact between the contact element (24) and the third electrode (52), the welding current flows from the second electrode (48) through the contact element (24) and via the third electrode (52) to the first electrode (44). [3] Method according to one of the preceding claims, wherein the contact element (24) at least partially surrounds the connecting cable (36). [4] Method according to one of the preceding claims, wherein the contact element (24) has a crimp sleeve (34) in which the connecting cable (36) is arranged, wherein the contact element (24) and the connecting cable (36) are connected by a crimp connection in a form-fitting and / or force-fitting manner. [5] Method according to any of the preceding claims, wherein the contact element (24) is at least partially made of stainless steel. [6] Method according to one of the preceding claims, wherein the connecting cable (36) is at least partially made of a copper core (38) with a nickel coating (40). [7] Method according to one of the preceding claims, wherein the first electrode (44) and the second electrode (48) move relative to each other parallel to a plane perpendicular to an extension direction of the contact element (24) and the connecting cable (36).