The present invention relates to the field of electrical cables. It relates to a high temperature cable in accordance with the precharacterizing clause of claim 1 and to a use for such a high temperature cable.
In order to control and regulate internal combustion engines, lambda probes have long been used on the exhaust side, with which lambda probes the oxygen content in the exhaust gases is measured and monitored. For this purpose, in a known manner the lambda probes are screwed into an exhaust pipe from the outside at a suitable point of the exhaust section, in particular upstream of the catalytic converter, with the result that they protrude with the measurement-sensitive sensor part into the exhaust gas flow and can be electrically connected to the motor controller from the outside. The radial installation of the lambda probe and a comparatively long probe length in the radial direction make it possible to reduce the thermal load on the connection line for the lambda probe despite the high temperatures in the vicinity of the exhaust, with the result that plastic insulation and sheathing can be used in the construction of the multi-strand connection cable (see DE-A1-196 11 572, for example). However, this presupposes that there is sufficient space available around the exhaust pipe in order to produce enough distance from the exhaust pipe in the radial direction.
Recently, increasingly less space has been available in the exhaust region owing to the installation of additional assemblies and units. It is therefore desirable to use lambda probes with a relatively short physical length and to bend the connection cable back shortly after it emerges from the lambda probe and then to guide it further, parallel to the exhaust. As a result, the connection cable is guided closer to the exhaust pipe and is subjected to correspondingly higher temperatures.
It has already been proposed in DE-A1-198 33 863 to provide, in the case of a connection cable for a lambda probe, a metallic corrugated tube as the supporting sheathing instead of a corrugated PTFE flexible tube in order to achieve improved protection against kinking and a higher capacity for thermal loading. The individually insulated conductors which are guided within the corrugated tube are in this case surrounded by a flexible filling material, which completely fills the intermediate space between the conductors and the corrugated tube. Completely filling the corrugated tube with a filling material is complex and reduces the flexibility of the connection cable.
EP-A2-0 843 321 has disclosed a connection cable for a lambda probe in which bare connection wires and ventilation pipes are arranged in a common tubular sleeve consisting of stainless steel such that they are fixed and separated from one another by means of an insulating powder filling. In this case, too, manufacture is complex and flexibility is low. In addition, owing to the powder filling, contact between the wires and the tubular sleeve in the case of severe vibrations occurring during operation cannot permanently be ruled out.
Finally, DE-A1-102 40 238 has proposed a connection line for a sensor probe, in particular a lambda probe, in which a plurality of bare conductors in a metallic tubular sheath are insulated from one another and from the tubular sheath by insulating means, which comprise a large number of insulating bodies, which are arranged in series, are supported against one another and each have a plurality of through-holes for the conductors. The ceramic insulating bodies act in the same way as the individual vertebrae of a spinal column and are shaped specially in order to achieve the desired flexibility of the connection line. Mechanical stabilization of the series of insulating bodies is achieved by an additional spring rod passing through all of the insulating bodies, which spring rod is guided through special through-holes in the insulating bodies. This type of cable construction is extremely complex both in terms of production and in terms of assembly owing to the special and precise shaping of the insulating bodies, owing to the fact that all of the conductors are guided through the same insulating bodies, and owing to the additional stabilization measures. Furthermore, only restricted flexibility is achieved. It is also known (U.S. Pat. No. 2,931,852) to provide such interengaging insulating bodies with very complex shaping in individual conductors.
The object of the invention is therefore to provide a high temperature cable, in particular for use as a connection cable for a lambda probe, which avoids the disadvantages of known cables and is characterized in particular by a simple and functionally reliable construction, is easy to produce, withstands very high temperatures of up to 600° C. and is characterized by a high degree of flexibility and a high resistance to mechanical, primarily vibration loads.
The object is achieved by the entirety of the features of claim 1. The essence of the invention consists in separate insulating bodies being assigned to at least two conductors, which insulating bodies form, together with the conductors, at least two separate, electrically insulated strands, and in twisting or braiding these at least two separate, electrically insulated strands with one another within the sleeve. Owing to the twisting or braiding, on the one hand mutual fixing of the conductors is achieved which results in a lack of sensitivity to vibrations. On the other hand, the twisted or braided bundle of strands retains a high degree of flexibility. The fixing and movability are in this case largely independent of the external shape of the insulating bodies, with the result that few requirements are placed on the precision of the insulating bodies. Since the insulating bodies only need to be threaded in each case onto one conductor, considerable simplification in the production of the cable results.
Particularly favorable conditions result with respect to the movability and fixing if the insulating bodies are in the form of rings or beads with a central through-opening and are threaded onto in each case one of the at least two conductors, if the insulating bodies have a rounded portion on their outer circumferential surface, and if the insulating bodies have a rounded portion at the ends of the through-opening, in each case on the inner circumferential surface.
A long life even in the case of severe mechanical and thermal loads can be achieved by virtue of the fact that the insulating bodies comprise a material which is resistant to high temperatures and have a smooth surface, in order to reduce the friction of the insulating bodies with respect to one another and/or with respect to the conductors. It has proven particularly successful if the insulating bodies comprise glass or a glazed material, such as porcelain or glazed ceramic, for example, or another low-friction and sufficiently temperature-resistant material. In this case, the insulating bodies may have different colors in the sense of a color coding of the strands.
The conductors are preferably in the form of Cu wires or braided wires, and the sleeve is in the form of a tubular sheath, preferably in the form of a metallic corrugated tube. Owing to the corrugated tube, good flexibility of the cable with, at the same time, a high level of protection on the outside is achieved.
It may furthermore be advantageous if the high temperature cable merges with a second cable at a transition point, the conductors being designed to be continuous at the transition point, the insulating bodies in the strands being detached in each case by means of a continuous insulating sheath, and the sleeve being detached by means of a cable sheath.
According to the invention, the high temperature cable is used as a connection cable for a measuring probe which is subjected to high temperatures, in particular a lambda probe.
The invention will be explained in more detail below with reference to exemplary embodiments in connection with the drawing, in which:
An exemplary embodiment of such a connection cable 14 in the form of a high temperature cable is reproduced photographically in
The construction of the strands or of the bundle of strands 19 will be explained in more detail below with reference to
Preferably, an annular or bead-shaped body is used as the insulating body 15, as is illustrated by way of example in
If a plurality of strands 17a, . . . , d of the type illustrated in
Once, as shown in
A further possibility consists in guiding the connection cable 14 further, outside of the high temperature region around the lambda probe 10 as a normal cable 24, as is indicated in
It is furthermore conceivable to use insulating bodies 15 of different colors for each of the strands 17a, . . . , d in order to produce strands of different colors which, in the form of a color coding, make it possible to quickly identify the respective conductor.
In the context of the invention, it is also conceivable, for braiding or twisting purposes, to combine strands which contain individual conductors with strands in which a plurality of conductors are threaded, spaced apart from one another, through the same insulating body, if corresponding insulating bodies with a plurality of through-openings are used. In this way, a different number of conductors can be accommodated in the cable given the same number of strands.
It is naturally possible also to use the high temperature cable according to the invention in another application apart from in automobiles where it is necessary to withstand high temperatures and other more difficult environmental conditions. Examples of these applications are heaters, furnaces, gas turbines or the like.
Number | Date | Country | Kind |
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212/05 | Feb 2005 | CH | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/CH2006/000027 | 1/12/2006 | WO | 00 | 8/7/2007 |