Patent Description:
The electrical connection (or electrical connector arrangement) may be installed in a jacket or casing of an exhaust-gas system of an internal combustion engine and electrically connected to an electrical component to be disposed in the jacket. The electrical component is preferably an electrically heatable grid or honeycomb body of a catalytic converter which is intended to be supplied with electric current through the electrical conductor after installation of the electrical component. The electrical connection is inserted into a mounting flange or an opening of the jacket and the bushing is fixed in the opening, e.g. by welding to the jacket. An end of the electrical conductor opposite to the electrical component may be connected to an electrical cable. An end of the cable opposite to the electrical connection may be connected to an electric power source, for example a battery or a control unit of a motor vehicle. Electrical connections of the above-mentioned kind are well-known in the art. For example, <CIT> describes an electrical connection which can draw currents of <NUM> amperes or more, up to several hundred amperes. The insulating layer is formed of compressed ceramic powder and is virtually incompressible. An outer cross section of the electrical connection has a non-circular form, e.g. a polygonal cross section, in order to avoid rotation of the electrical connection in the jacket or the like even in case of very high torques.

<CIT> describes an electrical connection having a sacrificial electrode, a protective layer or other kinds of protective configurations in contact with the bushing outside of the jacket or the like to which the bushing is welded. The bushing is made of metal and the insulating layer is made of aluminium oxide. The sacrificial electrode is a zinc block. This makes the sacrificial electrode corrode in case an electrolyte, e.g. salt water, accumulates above the bushing and prevents corrosion of the bushing or the electrical conductor.

<CIT> describes an electrical connection of the above-mentioned kind. Different types of connections between an end of the electrical conductor opposite to the electrical component (e.g. an electrically heatable grid or honeycomb body of a catalytic converter) and an electrical cable are suggested. Thus, a reliable electric connection can be achieved in a fast and easy manner.

Other electrical connections are disclosed in the documents <CIT> or <CIT>.

The known electrical connections have a number of drawbacks:.

Therefore, it is an object of the present invention to provide for an electrical connection which overcomes at least some of the above-mentioned drawbacks. In particular, it is an object to provide for an electrical connection with the following properties:.

This object is solved by an electrical connection comprising the features of claim <NUM>. In particular, starting from the electrical connection of the above-identified kind, it is suggested that the bushing, the insulating layer and the electric conductor are pressed together in order to achieve a mechanical cold transformation. The bushing, the insulating layer and the electric conductor are arranged coaxially in respect to the geometric central axis of the bushing and then pressed together in order to achieve the mechanical cold transformation. The bushing, the insulating layer and the electric conductor are preferably pressed together during a rotary forging process. The pressure acts on the external circumferential surface of the bushing of the electrical connection. The pressure is preferably directed in a radial direction inwards towards the geometric central axis.

Due to the mechanical cold transformation the interconnection between the bushing and the insulating layer and between the insulating layer and the electric conductor is significantly increased. The electrical connection can absorb much higher force and torque values without damage. In particular, the mechanical interconnection between the electric conductor and the insulating layer and/or between the insulating layer and the bushing does not loosen and break up, even if high force and torque values are applied to the electrical connection.

The bushing, the insulating layer and the electrical conductor are preferably rotationally symmetric in respect to the geometric central axis. In particular, in a cross sectional view the bushing, the insulating layer and the electrical conductor all have a circular or a circular ring form.

The electrical conductor is dimensioned such that it can withstand a minimum voltage of <NUM> V DC and a current of up to <NUM> A. To this end, it is suggested that the diameter of the conductor is between <NUM> and <NUM>, preferably between <NUM> and <NUM>. The external diameter of the bushing of the electrical connection is dictated by the dimensions of a mounting flange or opening, into which the bushing is fixed, and/or the intended use of the electrical connection. In particular, the bushing should neatly fit into the opening in the jacket or casing. Typical examples for the external diameter of the bushing are between <NUM> and <NUM>, preferably around <NUM>. In a cross section, the bushing preferably has a thickness between the internal circumferential surface and the external circumferential surface of between <NUM> to <NUM>, preferably of about <NUM>. The thickness of the insulating layer depends of the given diameters of the electrical conductor and of the bushing, as well as of the electrical properties to be achieved by the electrical connection. For example, the insulating layer should achieve an insulation resistance of more than <NUM> MΩ (preferably up to a couple of GΩ) under ambient environmental conditions (e.g. temperature <NUM> +/-<NUM>, pressure around <NUM>,<NUM> hPa and relative humidity <NUM>% - <NUM>%) and at <NUM> V DC-voltage. In order to achieve these insulating characteristics, depending on the material used for the insulating layer, it has a thickness of at least <NUM>, preferably around <NUM>.

According to a preferred embodiment of the present invention, it is suggested that the electrical conductor has an external circumferential surface with an arithmetic average roughness of at least Ra = <NUM> (or higher), on at least part of an external circumferential surface of the electrical conductor, which is covered by the insulating layer. The desired roughness may be achieved during manufacturing, i.e. by machine turning, of the electrical conductor, e.g. by reducing the rotational speed with which the external circumferential surface is machined, e.g. by means of a cutting or milling tool. In particular, if the rotational speed, with which the external circumferential surface is machined is reduced, the roughness of the circumferential surface may increase. Alternatively, a desired roughness value could also be achieved by an additional process step after the manufacturing of the electrical conductor.

During the mechanical cold transformation pressure acts in a radial direction onto the external circumferential surface of the bushing. The bushing transfers at least part of the radial pressure onto the insulating layer which is pressed onto the external circumferential surface of the electrical conductor. Some of the insulating material is pressed into the recesses provided on the external circumferential surface of the electrical conductor and/or the protrusions provided on the external circumferential surface of the electrical conductor are pressed into the insulating material. Thus, an interlocking connection is established between the electrical conductor and the insulating layer. This can further increase the force and torque values which the electrical connection can absorb without damage. In particular, the mechanical interconnection between the electric conductor and the insulating layer does not loosen and break up, even if high force and torque values are applied to the electrical connection.

Preferably, the protrusions have a cross section with a base on the external circumferential surface of the electrical conductor and side walls extending from the ends of the base and converging towards the top of the protrusion. Similarly, the grooves may have a cross section with an opening on the external circumferential surface and side walls extending from the ends of the opening and converging towards the bottom of the groove. A preferred cross section for the grooves is a U-shape, so the material of the insulating layer may enter and spread in the groove more easily. Of course, the grooves could also have any other cross section, e.g. a V-shaped cross section or a combination of a U- and a V-shape. A preferred cross section for the protrusions is a V-shape, so the protrusions enter more easily into the material of the insulating layer. Of course, the protrusions could also have any other cross section, e.g. a U-shaped cross section or a combination of a V- and a U-shape. A preferred depth of the recesses and a preferred height of the protrusions, respectively, may be between <NUM> and <NUM>, preferably about <NUM>, in respect to the rest of the external circumferential surface of the electrical conductor.

Further, it is suggested that the protrusions and/or the recesses provided on the external circumferential surface of the electrical conductor have a circumferential longitudinal extension and/or an axial longitudinal extension. For example, the protrusions or the recesses may have a longitudinal extension running in an essentially circumferential direction, i.e. around the geometric central axis of the bushing. Alternatively, the protrusions or the recesses may have a longitudinal extension running in an essentially axial direction, i.e. parallel to the geometric central axis of the bushing. Further, it is possible that the protrusions and/or the grooves have a longitudinal extension running in a circumferential as well as an axial direction. In that case, the protrusions and/or the grooves extend in a slanted or helical (i.e. spiral) manner on the external circumferential surface of the electrical conductor. Such protrusions and/or grooves may be achieved during manufacturing of the electrical conductor, e.g. by a certain feeding speed in respect to a rotational speed and a certain cutting depth of a cutting or milling tool with which the external circumferential surface is machined. Alternatively, the protrusions and/or grooves could also be achieved by an additional process step after the manufacturing of the electrical conductor. Of course, it is also possible that a first group of protrusions and/or grooves has a longitudinal extension in a first direction and a second group of protrusions and/or grooves has a longitudinal extension in a second direction and that the protrusions and/or the grooves of the first group intersect with the protrusions and/or the grooves of the second group.

It is preferred that the protrusions or recesses are part of a ribbed external circumferential surface of the electrical conductor. The ribbed surface preferably comprises a plurality of grooves. The grooves of a first group of grooves extend parallel to each other, preferably equidistant, and the grooves of a second group of grooves extend parallel to each other, preferably equidistant. The grooves of the first group of grooves run in an angle in respect to the grooves of the second group, the angle being larger than <NUM>° and smaller than <NUM>°. Preferably the angle between the first and second grooves is <NUM>° resulting in a ribbed surface with rectangles or squares between the grooves. Alternatively, the angle may be between <NUM>° and <NUM>° resulting in a ribbed surface with rhombi between the grooves. Of course, instead of or additionally to the grooves, the ribbed surface could also comprise protrusions.

In order to facilitate the material of the insulating layer entering and spreading in the grooves and/or the protrusions entering into the material of the insulating layer, it is suggested that the insulating layer is made of a material having a lower hardness than the material of which the electrical conductor is made. In particular, it is preferred that the material of the insulating layer has a hardness lower than <NUM> on the Mohs scale, preferably a lower hardness than magnesium oxide (MgO). Preferably, the material of the insulating layer has a hardness on the Mohs scale of approximately <NUM> to <NUM>, in particular of <NUM> to <NUM>. For comparison, , gold has a hardness on the Mohs scale of appr. <NUM> to <NUM>, a copper coin of appr. <NUM> and steel of appr. <NUM> to <NUM>. The material of the electrical conductor has a larger hardness than the insulating material.

According to another preferred embodiment of the invention, it is suggested that the bushing has an internal circumferential surface with at least one of an arithmetic average roughness of at least Ra = <NUM> (or higher), protrusions and recesses on at least part of an internal circumferential surface of the bushing, which covers the insulating layer. Hence, the bushing has the form of a hollow cylinder and the internal circumferential surface of the bushing, where the insulating layer is located, comprises the desired roughness, protrusions and/or recesses. The roughness of the circumferential surface is such that it provides protrusions (i.e. positive peaks) and/or recesses (i.e. negative peaks or troughs) in an irregular distribution in respect to a mean surface extension. The desired roughness may be achieved during manufacturing, i.e. by machine turning, of the bushing, e.g. by reducing the rotational speed with which the internal circumferential surface is machined, e.g. by means of a cutting or milling tool. In particular, if the rotational speed, with which the internal circumferential surface is machined is reduced, the roughness of the circumferential surface may increase. Alternatively, a desired roughness value could also be achieved by an additional process step after the manufacturing of the bushing.

During the mechanical cold transformation pressure acts in a radial direction onto the external circumferential surface of the bushing. The internal circumferential surface of the bushing is pressed in a radial direction onto the insulating layer. Some of the insulating material is pressed into the recesses provided on the internal circumferential surface of the bushing and/or the protrusions provided on the internal circumferential surface of the bushing are pressed into the insulating material. Thus, an interlocking connection is established between the bushing and the insulating layer. This can further increase the force and torque values which the electrical connection can absorb without damage. In particular, the mechanical interconnection between the bushing and the insulating layer does not loosen and break up, even if high force and torque values are applied to the electrical connection.

Preferably, the protrusions have a cross section with a base on the internal circumferential surface of the bushing and side walls extending from the ends of the base and converging towards the top of the protrusion. Similarly, the grooves may have a cross section with an opening on the internal circumferential surface and side walls extending from the ends of the opening and converging towards the bottom of the groove. A preferred cross section for the grooves is a U-shape, so the material of the insulating layer may enter and spread in the groove more easily. Of course, the grooves could also have any other cross section, e.g. a V-shaped cross section or a combination of a U- and a V-shape. A preferred cross section for the protrusions is a V-shape, so the protrusions enter more easily into the material of the insulating layer. Of course, the protrusions could also have any other cross section, e.g. a U-shaped cross section or a combination of a V- and a U-shape. A preferred depth of the recesses and a preferred height of the protrusions, respectively, may be between <NUM> and <NUM>, preferably about <NUM>, in respect to the rest of the internal circumferential surface of the bushing.

Further, it is suggested that the protrusions and/or the recesses provided on the internal circumferential surface of the bushing have at least one of a circumferential extension and an axial extension. For example, the protrusions or the recesses may have a longitudinal extension running in an essentially circumferential direction, i.e. around the geometric central axis of the bushing. Alternatively, the protrusions or the recesses may have a longitudinal extension running in an essentially axial direction, i.e. parallel to the geometric central axis of the bushing. Further, it is possible that the protrusions and/or the grooves have a longitudinal extension running in a circumferential as well as an axial direction. Hence, the protrusions and/or the grooves extend in a slanted or helical (i.e. spiral) manner on the internal circumferential surface of the bushing. Such protrusions and/or grooves may be achieved during manufacturing of the bushing, e.g. by a certain feeding speed in respect to a rotational speed and a certain cutting depth of a cutting or milling tool with which the internal circumferential surface is machined. Alternatively, the protrusions and/or grooves could also be achieved by an additional process step after the manufacturing of the bushing. Of course, it is also possible that a first group of protrusions and/or grooves has a longitudinal extension in a first direction and a second group of protrusions and/or grooves has a longitudinal extension in a second direction and that the protrusions and/or the grooves of the first group intersect with the protrusions and/or the grooves of the second group.

According to a preferred embodiment, the bushing has recesses in the form of axial grooves provided on the internal circumferential surface of the bushing and spaced apart from each other in a circumferential direction. The grooves have a longitudinal extension extending in an axial direction, i.e. parallel to the geometric central axis of the bushing. Preferably, the grooves are equally spaced apart from each other in the circumferential direction, i.e. each separated from neighbouring grooves by a given angle. If the angle is <NUM>°, there are three grooves equally spaced to each other on the internal circumferential surface of the bushing. Of course, a different number of grooves and different angles between the grooves, equally spaced apart from each other or not, could be provided, too.

Preferably, the axial grooves do not extend along the entire axial extension of the internal circumferential surface of the bushing. Rather, it is suggested that the grooves extend only along a part of the internal surface of the bushing, starting at one end surface of the bushing and ending in a distance to an opposite end surface of the bushing. Hence, the grooves do not reach the opposite end surface of the bushing. This can further increase the force and torque values which the electrical connection can absorb without damage. In particular, an electrode displacement force acting on the electrical conductor in a direction towards the opposite end surface of the bushing will prevent the electrical conductor to be pressed or pulled out of the bushing together with the insulating layer. The electrode displacement force is preferably above <NUM>,<NUM> N, in particular between <NUM>,<NUM> N and <NUM>,<NUM> N.

In order to facilitate the material of the insulating layer entering and spreading in the grooves and/or the protrusions entering into the material of the insulating layer, it is suggested that the insulating layer is made of a material having a lower hardness than the material of which the bushing is made. Preferably, the material of the insulating layer has a hardness on the Mohs scale of approximately <NUM> to <NUM>, in particular of <NUM> to <NUM>,<NUM>. The material of the bushing has a larger hardness than the insulating material.

According to a preferred embodiment of the invention, it is suggested that the bushing and/or the electrical conductor is made of a stainless steel, in particular of a nickel-chromium-iron alloy. In principle, the bushing and/or the electrical conductor could be made of any suitable material provided that it has the necessary physical, mechanical, electrical and thermal properties of the bushing and/or the electrical conductor required for the electrical connection.

According to another preferred embodiment of the invention, it is suggested that the insulating layer is made of a material comprising at least <NUM>% of a phyllosilicate mineral. Preferably, the insulating material comprises more than <NUM>%, in particular around <NUM>% of a phyllosilicate mineral. The rest of the material may be a laminate or bonding material. Preferably, the material of the insulting layer is less hygroscopic than magnesium oxide (MgO). In principle any material may be used for the insulating layer provided that it has the necessary physical, mechanical, electrical and thermal properties of the insulating material required for the electrical connection. In particular, the material should be elastic enough to compensate for the thermal expansion of the different materials used in the electrical connection due to the large range of thermal variation during the intended use of the electrical connection, without breaking or cracking. Hence, a high degree and long lasting air tightness of the electrical connection can be guaranteed.

Further advantages of the present invention are described hereinafter with reference to the accompanying drawings.

An electrical connection according to a preferred embodiment of the present invention is designated in its entirety with reference sign <NUM>. The connection <NUM> comprises a bushing <NUM> having a geometric central axis <NUM>. The bushing <NUM> has the form of a hollow cylinder. Further, the connection <NUM> comprises an electrical conductor <NUM> passing through said bushing <NUM> along the geometric central axis <NUM> and an insulating layer <NUM> electrically insulating said bushing <NUM> from said conductor <NUM>. <FIG> shows a fully assembled and ready to use electrical connection <NUM>. <FIG> shows an exploded view of the electrical connection <NUM>.

The bushing <NUM>, the insulating layer <NUM> and the electrical conductor <NUM> are preferably rotationally symmetric in respect to the geometric central axis <NUM>. In particular, in a cross sectional view the bushing <NUM>, the insulating layer <NUM> and the electrical conductor <NUM> all have a circular or a circular ring form.

As schematically shown in <FIG>, the electrical connection <NUM> may be installed in a jacket or casing <NUM> of an exhaust-gas system of an internal combustion engine and electrically connected to an electrical component <NUM> disposed in the jacket <NUM>. The embodiment of <FIG> shows a specific type of electrical connection <NUM>. Further embodiments will be described in further detail hereinafter. The electrical component <NUM> is preferably an electrically heatable grid or honeycomb body of a catalytic converter <NUM> which is intended to be supplied with electric current through the electrical conductors <NUM> of electrical connections <NUM> after installation of the electrical component <NUM>. In <FIG>, the catalytic converter <NUM> or its jacket <NUM>, respectively, is shown in a sectional view, in order to allow insight into the internal part of the jacket <NUM>. When in use, the catalytic converter <NUM> or its jacket <NUM>, respectively, will be closed in an airtight manner in order to prevent exhaust gases from escaping from the internal part of the jacket <NUM>.

The electrical connection <NUM> is inserted into a mounting flange or opening <NUM> of the jacket <NUM>, and the bushing <NUM> is fixed in the mounting flange or opening <NUM>, e.g. by welding to the jacket <NUM>. Alternatively, the bushing <NUM> could also be fixed in the mounting flange or opening <NUM> to the jacket <NUM> in any other way, e.g. by means of a threading or the like.

An internal (inside the jacket <NUM>) end of the electrical conductor <NUM> of the electrical connection <NUM> is connected to the electrical component <NUM>. An external end (outside the jacket <NUM>) of the electrical conductor <NUM> opposite to the electrical component <NUM> may be connected to an electrical cable (not shown) or the like. Preferably, the electrical conductor <NUM> of the electrical connection <NUM> is provided with a positive electric charge (+). An end of the cable opposite to the electrical connection <NUM> may be connected to an electric power source (not shown), for example a battery or a control unit of a motor vehicle, preferably to the positive pole of the battery or the control unit.

Similarly, an internal end of the electrical conductor of another electrical connection (not shown) is connected to the electrical component <NUM>. The connection may be achieved directly or indirectly via an internal casing of the electrical component <NUM>. An external end of the electrical conductor of the other electrical connection opposite to the electrical component <NUM> may be connected to an electrical cable (not shown) or the like. Preferably, the electrical conductor <NUM> of the other electrical connection is provided with a negative electric charge (-), e.g. connected to a ground or earth terminal (e.g. a vehicle body or a vehicle chassis). An end of the cable opposite to the other electrical connection may be connected to an electric power source (not shown), for example a battery or a control unit of a motor vehicle, preferably to the negative pole of the battery or the control unit or to the ground or earth terminal. In the latter case, the negative pole of the battery would be connected to the ground or earth terminal at some other point.

Finally, the electrical conductor of a further electrical connection (not shown) merely fulfils the function of an electrically isolated holding pin adapted for holding an internal casing of the electrical component <NUM> or the electrical component <NUM> itself inside the jacket <NUM>. To this end, it is suggested that an internal end of the electrical conductor of the further electrical connection is connected to the internal casing of the electrical component <NUM> or to the electrical component <NUM> itself. The connection is preferably electrically conductive and may be realized e.g. by welding, screwing, or in any other manner. The electrical conductor of the further electrical connection is electrically isolated in respect to the bushing by means of the insulating layer. Hence, the further electrical connection isolates the internal casing in respect to the jacket <NUM>.

Of course, the electrical connections <NUM> according to the present invention are not limited to the different uses described here by way of example. The electrical connection <NUM> may be used in many other applications, too.

According to the present invention the bushing <NUM>, the insulating layer <NUM> and the electric conductor <NUM> are pressed together in order to achieve a mechanical cold transformation. First, the bushing <NUM>, the insulating layer <NUM> and the electric conductor <NUM> are arranged coaxially in respect to the geometric central axis <NUM> of the bushing <NUM> (see <FIG>). To this end, before the mechanical cold transformation, an internal diameter of an internal circumferential surface 12a of the bushing <NUM> is slightly larger than an external diameter of the insulating layer <NUM>. For example, the internal diameter of the bushing <NUM> may be larger by approximately <NUM> than the external diameter of the insulating layer <NUM>, in order to be able to slip the bushing <NUM> over the insulating layer <NUM>. Similarly, an external diameter of an external circumferential surface 16b of the electrical conductor <NUM> is slightly smaller than an internal diameter of the insulating layer <NUM>, e.g. smaller by approximately <NUM>. After arranging the bushing <NUM>, the insulating layer <NUM> and the electric conductor <NUM> coaxially in respect to the geometric central axis <NUM> of the bushing <NUM>, these components <NUM>, <NUM>, <NUM> are pressed together in order to achieve a mechanical cold transformation (see <FIG>).

The bushing <NUM>, the insulating layer <NUM> and the electric conductor <NUM> are preferably pressed together during a rotary forging process thereby achieving the mechanical cold transformation. The pressure acts on the external circumferential surface of the bushing <NUM> of the electrical connection <NUM>. The pressure is preferably directed in a radial direction inwards towards the geometric central axis <NUM>. Due to the pressure and the mechanical cold transformation, the original dimensions (diameter A and length B) of the electrical connection <NUM> change (diameter A1 and length B1). In particular, the diameter will decrease and the length will increase (A1 < A; B1 > B), as could be depicted from <FIG>. Preferably, the change of dimensions refers to the bushing <NUM> and to the insulating layer <NUM>, whereas the electrical conductor <NUM> will essentially maintain its original dimensions.

The pressure acting on the electrical connection <NUM> may also modify the structure of the materials used for the bushing <NUM>, the insulating layer <NUM> and the electrical conductor <NUM>. In particular, the material of the insulating layer <NUM> and/or the bushing <NUM> may be hardened and/or the flexural fatigue strength may be increased due to the pressure applied to the electrical connection <NUM>.

Due to the mechanical cold transformation, the interconnection between the bushing <NUM> and the insulating layer <NUM> and between the insulating layer <NUM> and the electric conductor <NUM> is significantly increased. The electrical connection <NUM> can absorb much higher force and torque values without damage. In particular, the mechanical interconnection between the electric conductor <NUM> and the insulating layer <NUM> and/or between the insulating layer <NUM> and the bushing <NUM> does not loosen and break up, even if high force and torque values are applied to the electrical connection <NUM> during its intended use.

The electrical conductor <NUM> and its components (bushing <NUM>, insulating layer <NUM> and electrical connector <NUM>), respectively, could be dimensioned such and/or manufactured from special material that the electrical connector <NUM> can withstand up to <NUM> V DC and transmit up to <NUM> A. To this end, it is suggested that the diameter of the conductor <NUM> is between <NUM> and <NUM>, preferably between <NUM> and <NUM>. The external diameter A1 of the bushing <NUM> is dictated by the client and/or the intended use of the electrical connection <NUM>.

In particular, the bushing <NUM> should neatly fit into the opening <NUM> in the jacket or casing <NUM>. Typical examples for the external diameter A1 of the bushing <NUM> lie between <NUM> and <NUM>, preferably around <NUM>. In a cross section, the bushing <NUM> preferably has a thickness between the internal circumferential surface 12a and the external circumferential surface 12b (see <FIG>) of between <NUM> to <NUM>, preferably of about <NUM>. The thickness of the insulating layer <NUM> depends of the given diameters of the electrical conductor <NUM> and of the bushing <NUM>, as well as of the electrical or isolating properties to be achieved by the electrical connection <NUM>. For example, the insulating layer <NUM> should achieve an insulation resistance of at least <NUM> MΩ at <NUM> V DC-voltage, preferably of up to a couple of GΩ under ambient environmental conditions. Depending on the material used for the insulating layer <NUM>, it has a thickness of at least <NUM>, preferably around <NUM>. Of course, these are mere exemplary values, adapted in particular for the use shown in <FIG>. When using the electrical connection <NUM> in other applications one or more of the physical, mechanical, electrical and thermal values and properties may vary even significantly.

It is suggested that the electrical conductor <NUM> has an external circumferential surface 16b with an arithmetic average roughness of at least Ra = <NUM> (or higher) and/or protrusions and/or recesses <NUM> on at least part 16a of the external circumferential surface 16b, which is covered by the insulating layer <NUM> when assembled (see <FIG>). The roughness of the circumferential surface 16b is such that it provides protrusions (i.e. positive peaks) and/or recesses (i.e. negative peaks or troughs) <NUM> in an irregular distribution in respect to a mean surface extension. The desired roughness may be achieved during manufacturing, i.e. by machine turning, of the electrical conductor <NUM>, e.g. by reducing the rotational speed with which the external circumferential surface 16b is machined, e.g. by means of a cutting or milling tool. In particular, if the rotational speed, with which the external circumferential surface 16b is machined is reduced, the roughness of the circumferential surface 16b of the electrical conductor <NUM> may increase. Alternatively, a desired roughness value could also be achieved by an additional process step after the manufacturing of the electrical conductor <NUM>.

During the mechanical cold transformation, pressure acts in a radial direction onto the external circumferential surface 12b of the bushing <NUM>. The bushing <NUM> transfers at least part of the radial pressure onto the insulating layer <NUM> which is pressed onto the external circumferential surface 16b of the electrical conductor <NUM>. Some of the insulating material is pressed into the recesses <NUM> provided on the electrical conductor <NUM> and/or the protrusions <NUM> provided on the electrical conductor <NUM> are pressed into the insulating material of this insulating layer <NUM>. Thus, an interlocking connection is established between the electrical conductor <NUM> and the insulating layer <NUM>. This can further increase the force and torque values which the electrical conductor <NUM> can absorb without damage. In particular, the mechanical interconnection between the electric conductor <NUM> and the insulating layer <NUM> does not loosen and break up, even if high force and torque values are applied to the electrical connection <NUM>.

As shown in <FIG>, the protrusions <NUM> preferably have a cross section with a base 22a on the external circumferential surface 16b of the electrical conductor <NUM> and side walls 22b extending from the ends of the base 22a and preferably converging towards the top of the protrusion <NUM>. Similarly, as shown in <FIG>, the grooves <NUM> may have a cross section with an opening 24a on the external circumferential surface 16b and side walls 24b extending from the ends of the opening 24a and preferably converging towards the bottom of the groove <NUM>.

A preferred cross section for the grooves <NUM> is a U-shape, so the material of the insulating layer <NUM> may enter and spread in the groove <NUM> more easily (see <FIG>). Of course, the grooves <NUM> could also have any other cross section, e.g. a V-shaped cross section or a combination of a U- and a V-shape. In the case of a roughness on the external circumferential surface 16b of the electrical conductor <NUM>, the grooves could have any irregular form and position and could differentiate from each other.

A preferred cross section for the protrusions <NUM> is a V-shape, so the protrusions <NUM> enter more easily into the material of the insulating layer <NUM> (see <FIG>). Of course, the protrusions <NUM> could also have any other cross section, e.g. a U-shaped cross section or a combination of a V- and a U-shape. In the case of a roughness on the external circumferential surface 16b of the electrical conductor <NUM>, the protrusions could have any irregular form and position and could differentiate from each other.

A preferred depth of the recesses <NUM> and a preferred height of the protrusions <NUM>, respectively, may be between <NUM> and <NUM>, preferably about <NUM>, in respect to the rest of the external circumferential surface 16b of the electrical conductor <NUM>. Of course, these are just exemplary values and may vary in practice considerably.

Further, it is suggested that the protrusions <NUM> and/or the recesses <NUM> provided on the external circumferential surface 16b of the electrical conductor <NUM> have a circumferential longitudinal extension and/or an axial longitudinal extension. For example, as shown in <FIG>, the protrusions or the recesses 20a may have a longitudinal extension extending in an essentially circumferential direction, i.e. around the geometric central axis <NUM> of the bushing <NUM>. Alternatively, the protrusions or the recesses 20b may have a longitudinal extension extending in an essentially axial direction, i.e. parallel to the geometric central axis <NUM> of the bushing <NUM>. Further, it is possible that the protrusions and/or the grooves <NUM> have a longitudinal extension extending in a circumferential as well as in an axial direction. Hence, the protrusions and/or the grooves <NUM> extend in a slanted or helical (i.e. spiral) manner on the external circumferential surface 16b of the electrical conductor <NUM> (not shown). Such protrusions and/or grooves <NUM> may be achieved during manufacturing of the electrical conductor <NUM>, e.g. by a certain feeding speed in respect to a rotational speed and a certain cutting depth of a cutting or milling tool with which the external circumferential surface 16b is machined. Alternatively, the protrusions and/or grooves <NUM> could also be achieved by an additional process step after the manufacturing of the electrical conductor <NUM>. Of course, it is also possible that a first group of protrusions and/or grooves 20a has a longitudinal extension in a first direction and a second group of protrusions and/or grooves 20b has a longitudinal extension in a second direction and that the protrusions and/or the grooves 20a of the first group intersect with the protrusions and/or the grooves 20b of the second group (see <FIG>).

It is preferred that the protrusions or recesses <NUM> are part of a ribbed external circumferential surface 16a of the electrical conductor <NUM> like the one shown in <FIG>. The ribbed surface 16a preferably comprises a plurality of grooves 20a, 20b. The grooves 20a of a first group extend parallel to each other, preferably equidistant, and the grooves 20b of a second group extend parallel to each other, preferably equidistant. The grooves 20a of the first group runs in an angle in respect to the grooves 20b of the second group, the angle being larger than <NUM>° and smaller than <NUM>°. Preferably, the angle between the first and second grooves 20a, 20b is <NUM>° resulting in a ribbed surface 16a with rectangles or squares between the grooves 20a, 20b (see <FIG>). Alternatively, the angle may be between <NUM>° and <NUM>°, preferably around <NUM>°, resulting in a ribbed surface 16a with rhombi between the grooves 20a, 20b (see <FIG>). Of course, instead of or additionally to the grooves 20a, 20b, the ribbed surface 16a could also comprise protrusions.

In order to facilitate the material of the insulating layer <NUM> entering and spreading in the grooves <NUM> and/or to facilitate the protrusions <NUM> entering into the material of the insulating layer <NUM>, when the external pressure is applied to the electrical connection <NUM> during the mechanical cold transformation, it is suggested that the insulating layer <NUM> is made of a material having a lower hardness than the material of which the electrical conductor <NUM> is made. Preferably, the material of the insulating layer <NUM> has a hardness on the Mohs scale of approximately <NUM> to <NUM>, in particular of <NUM> to <NUM>. For comparison, gold has a hardness on the Mohs scale of appr. <NUM> to <NUM>, a copper coin of appr. <NUM> and steel of appr. <NUM> to <NUM>. The material of the electrical conductor <NUM> has a larger hardness than the insulating material.

Further, it is suggested that the bushing <NUM> has an internal circumferential surface 12a with at least one of an arithmetic average roughness of at least Ra = <NUM> (or higher), protrusions and recesses <NUM> on at least part of the internal circumferential surface 12a, which covers the insulating layer <NUM> when assembled. Hence, the bushing <NUM> may have the form of a hollow cylinder and the internal circumferential surface 12a of the bushing <NUM>, where the insulating layer <NUM> is located, comprises the desired roughness, protrusions and/or recesses <NUM>. The roughness of the circumferential surface 12a is such that it provides protrusions (i.e. positive peaks) and/or recesses (i.e. negative peaks or troughs) in an irregular distribution in respect to a mean surface extension. The desired roughness may be achieved during manufacturing, i.e. by machine turning, of the bushing <NUM>, e.g. by reducing the rotational speed with which the internal circumferential surface 12a is machined, e.g. by means of a cutting or milling tool. In particular, if the rotational speed, with which the internal circumferential surface 12a is machined, is reduced, the roughness of the circumferential surface 12a may increase. Alternatively, a desired roughness value could also be achieved by an additional process step after the manufacturing of the bushing <NUM>.

During the mechanical cold transformation pressure acts in a radial direction onto the external circumferential surface 12b of the bushing <NUM>. The internal circumferential surface 12a of the bushing <NUM> is pressed in a radial direction onto the insulating layer <NUM>. Some of the insulating material of the insulating layer <NUM> is pressed into the recesses <NUM> provided on the internal circumferential surface 12a of the bushing <NUM> and/or the protrusions <NUM> provided on the internal circumferential surface 12a of the bushing <NUM> are pressed into the insulating material of the insulating layer <NUM>. Thus, an interlocking connection is established between the bushing <NUM> and the insulating layer <NUM>. This can further increase the force and torque values which the electrical conductor <NUM> can absorb without damage. In particular, the mechanical interconnection between the bushing <NUM> and the insulating layer <NUM> does not loosen and break up, even if high force and torque values are applied to the electrical connection <NUM>.

Preferably, similar to what is shown in <FIG> and described above regarding the protrusions and grooves <NUM> of the electrical conductor <NUM>, the protrusions <NUM> of the internal circumferential surface 12a of the bushing <NUM> have a cross section with a base on the internal circumferential surface 12a of the bushing <NUM> and side walls extending from the ends of the base and preferably converging towards the top of the protrusions <NUM>. Similarly, the grooves <NUM> may have a cross section with an opening on the internal circumferential surface 12a and side walls extending from the ends of the opening and preferably converging towards the bottom of the groove.

A preferred cross section for the grooves <NUM> is a U-shape, so the material of the insulating layer <NUM> may enter and spread in the grooves <NUM> more easily. Of course, the grooves <NUM> could also have any other cross section, e.g. a V-shaped cross section or a combination of a U- and a V-shape. In the case of a roughness on the internal circumferential surface 12a of the bushing <NUM>, the grooves could have any irregular form and position and could differentiate from each other.

A preferred cross section for the protrusions <NUM> is a V-shape, so the protrusions <NUM> may enter more easily into the material of the insulating layer <NUM>. Of course, the protrusions <NUM> could also have any other cross section, e.g. a U-shaped cross section or a combination of a V- and a U-shape. In the case of a roughness on the internal circumferential surface 12a of the bushing <NUM>, the protrusions could have any irregular form and position and could differentiate from each other.

A preferred depth of the recesses <NUM> and a preferred height of the protrusions <NUM>, respectively, may be between <NUM> and <NUM>, preferably about <NUM>, in respect to the rest of the internal circumferential surface 12a of the bushing <NUM>. Of course, these are just exemplary values and may vary in practice considerably.

Further, it is suggested that the protrusions and/or the recesses <NUM> provided on the internal circumferential surface 12a of the bushing <NUM> have at least one of a circumferential extension and an axial extension. For example, the protrusions or the recesses <NUM> may have a longitudinal extension running in an essentially circumferential direction (not shown), i.e. around the geometric central axis <NUM> of the bushing <NUM>. Alternatively, the protrusions or the recesses <NUM> may have a longitudinal extension running in an essentially axial direction (see <FIG>, <FIG>, <FIG> and <FIG>), i.e. parallel to the geometric central axis <NUM> of the bushing <NUM>. Further, it is possible that the protrusions and/or the grooves <NUM> have a longitudinal extension running in a circumferential as well as in an axial direction. Hence, the protrusions and/or the grooves <NUM> extend in a slanted or helical (i.e. spiral) manner on the internal circumferential surface 12a of the bushing <NUM> (not shown). Such protrusions and/or grooves <NUM> may be achieved during manufacturing of the bushing <NUM>, e.g. by a certain feeding speed in respect to a rotational speed and a certain cutting depth of a cutting or milling tool with which the internal circumferential surface 12a is machined. Alternatively, the protrusions and/or grooves <NUM> could also be achieved by an additional process step after the manufacturing of the bushing <NUM>. Of course, it is also possible that a first group of protrusions and/or grooves <NUM> has a longitudinal extension in a first direction and a second group of protrusions and/or grooves <NUM> has a longitudinal extension in a second direction and that the protrusions and/or the grooves <NUM> of the first group intersect with the protrusions and/or the grooves <NUM> of the second group.

According to a preferred embodiment shown in <FIG>, <FIG>, <FIG> and <FIG>, the bushing <NUM> has recesses in the form of axial grooves <NUM> provided on the internal circumferential surface 12a of the bushing <NUM> and spaced apart from each other in a circumferential direction. The grooves <NUM> have a longitudinal extension extending in an axial direction, i.e. parallel to the geometric central axis <NUM> of the bushing <NUM>. Preferably, the grooves <NUM> are equally spaced apart from each other in the circumferential direction, i.e. each separated from neighbouring grooves by a given angle. If the angle is <NUM>°, there are six grooves <NUM> equally spaced to each other on the internal circumferential surface 12a of the bushing <NUM>. Of course, a different number of grooves <NUM> and different angles between the grooves <NUM>, equally spaced apart from each other or not, could be provided, too.

Preferably, the axial grooves <NUM> do not extend along the entire axial extension of the internal circumferential surface 12a of the bushing <NUM>. Rather, it is suggested that the grooves <NUM> extend only along a part of the internal surface 12a of the bushing <NUM>, starting at one end surface 12c of the bushing <NUM> and ending in a distance to an opposite end surface 12d of the bushing <NUM>. This can be seen in <FIG> and <FIG>. Hence, the grooves <NUM> do not reach the opposite end surface 12d of the bushing <NUM>. This can further increase the force and torque values which the electrical connection <NUM> can absorb without damage. In particular, a force F (see <FIG> and <FIG>) acting on the electrical conductor <NUM> in a direction towards the opposite end surface 12d of the bushing <NUM> will prevent the electrical conductor <NUM> from being pressed or pulled out of the bushing <NUM> together with the insulating layer <NUM>. The force F is also called an electrode displacement force. The electrode displacement force F is preferably above <NUM>,<NUM> N, in particular <NUM>,<NUM> N to <NUM>,<NUM> N.

<FIG> show another preferred embodiment of the electrical connection <NUM> according to the present invention. In particular, in this embodiment, the grooves 20a of the first group run in an angle in respect to the grooves 20b of the second group, the angle between <NUM>° and <NUM>°, preferably around <NUM>°, resulting in a ribbed surface 16a with rhombi between the grooves 20a, 20b (see <FIG>). Of course, instead of or additionally to the grooves 20a, 20b, the ribbed surface 16a could also comprise protrusions.

Of course, the external circumferential ribbed surface 16a may have any other design, too, provided that it permits a mechanical form fit interaction between the insulating layer <NUM> and the electrical conductor <NUM>, thereby achieving an interlocking connection between the two and enhancing the fixation of the insulating material <NUM> on the external circumferential surface 16b of the electrical conductor <NUM>.

It can be seen in <FIG> that the ribbed surface 16a has a larger axial extension than the insulating layer <NUM> and the bushing <NUM>. This allows an exact position of the electrical conductor <NUM> in respect to the busing <NUM> during the manufacturing process before the bushing <NUM>, the insulating layer <NUM> and the electric conductor <NUM> are pressed together in order to achieve the mechanical cold transformation.

<FIG> show the electrical connection <NUM> of <FIG> fixed in an opening <NUM> of a jacket or casing <NUM>, for example of an exhaust-gas system of an internal combustion engine. The electrical connection <NUM> may be fixed in the opening <NUM> by welding, screwing or similar connection techniques. In the <FIG> a welding bead <NUM> is visible. Alternatively or additionally, the electrical connection <NUM> could also be provided with a radially protruding collar (not shown) which rests on an outside surface of the jacket <NUM> when the electrical connection <NUM> is introduced into the opening <NUM>. The collar may additionally support an airtight fixation of the electrical connection <NUM> in the opening <NUM> of the jacket <NUM>.

<FIG> show another embodiment of an electrical connection <NUM> fixed in an opening <NUM> of a jacket or casing <NUM>, for example of an exhaust-gas system of an internal combustion engine. The ribbed external circumferential surface <NUM> may comprise grooves <NUM> which extend around the entire or part of the circumference of the external surface 16b of the electrical conductor <NUM>. The grooves <NUM> may have an annular or a helical form. The electrical connection <NUM> may be fixed in the opening <NUM> by welding, screwing or similar connection techniques. In the <FIG> the electrical connection is fixed into the opening by screwing. To this end, the external surface 12b of the bushing <NUM> or at least part of it is provided with an external thread. A corresponding internal thread may be provided in the opening <NUM>. Alternatively or additionally, the electrical connection <NUM> could also be provided with a radially protruding collar (not shown) which rests on an outside surface of the jacket <NUM> when the electrical connection <NUM> is introduced into the opening <NUM>. The collar may additionally support an airtight fixation of the electrical connection <NUM> in the opening <NUM> of the jacket <NUM>.

In order to facilitate the material of the insulating layer <NUM> entering and spreading in the grooves <NUM> and/or the protrusions <NUM> entering into the material of the insulating layer <NUM>, it is suggested that the insulating layer <NUM> is made of a material having a lower hardness than the material of which the bushing <NUM> is made. Preferably, the material of the insulating layer <NUM> has a hardness on the Mohs scale of approximately <NUM> to <NUM>, in particular of <NUM> to <NUM>,<NUM>. The material of the bushing <NUM> has a larger hardness than the insulating material.

It is suggested that the bushing <NUM> and/or the electrical conductor <NUM> is made of a stainless steel, in particular of a nickel-chromium-iron alloy. The material of the bushing <NUM> and/or the electrical conductor <NUM> may comprise a minimum of <NUM>% nickel (plus cobalt), <NUM>-<NUM>% chromium, and <NUM>-<NUM>% iron. Besides these components, the material can further comprise small amounts (< <NUM>%) of carbon, manganese, sulphur, silicon and/or copper. Preferably, the material of the bushing <NUM> and/or the electrical conductor <NUM> comprises a minimum of <NUM>% nickel (plus cobalt), <NUM>-<NUM>% chromium and <NUM>-<NUM>% iron. It may be advantageous if both the bushing <NUM> and the electrical conductor <NUM> are made of the same material. In principle, all materials may be used for the bushing <NUM> and the electrical conductor <NUM> which are adapted for providing the necessary physical, mechanical, electrical and thermal properties required for the electrical connection <NUM>.

It is further suggested that the insulating layer <NUM> is made of a material comprising at least <NUM>% of a phyllosilicate mineral. Preferably, the insulating material comprises more than <NUM>%, in particular around <NUM>% of a phyllosilicate mineral. The rest of the material of the insulating layer <NUM> may be a laminate or bonding material. Preferably, the material of the insulting layer <NUM> is less hygroscopic than magnesium oxide (MgO). In principle, all materials may be used for the insulating layer <NUM> which are adapted for providing the necessary physical, mechanical, electrical and thermal properties required for the electrical connection <NUM>. In particular, the material should be elastic enough to compensate for the thermal expansion of the different materials used in the electrical connection <NUM> due to the large range of thermal variation (more than <NUM>,<NUM>°K) during the intended use of the electrical connection <NUM>, without breaking or cracking. Hence, a high degree and long lasting air tightness of the electrical connection <NUM> can be guaranteed.

Claim 1:
An electrical connection (<NUM>) of an exhaust gas system of an internal combustion engine, comprising
- a bushing (<NUM>) having a geometric central axis (<NUM>),
- an electrical conductor (<NUM>) passing through said bushing (<NUM>) along the geometric central axis (<NUM>), and
- an insulating layer (<NUM>) electrically insulating said bushing (<NUM>) from said conductor (<NUM>),
characterized in that
the bushing (<NUM>), the insulating layer (<NUM>) and the electric conductor (<NUM>) are pressed together in order to achieve a mechanical cold transformation,
in that the insulating layer (<NUM>) is made of a material having a lower hardness than the material of which the electrical conductor (<NUM>) is made,
and in that the electrical conductor (<NUM>) has an external circumferential surface (16b) with protrusions and/or recesses (<NUM>; 20a, 20b) on at least part (16a) of the external circumferential surface (16b) of the electrical conductor (<NUM>), which is covered by the insulating layer (<NUM>).