The invention relates to a connecting lead for a sensor, in particular for a sensor for determining a physical property of a measured gas, in particular for determining the oxygen content or temperature in the exhaust gas of internal combustion engines.
In sensors that are used as exhaust gas lambda probes in the exhaust gas fittings of internal combustion engines in motor vehicles, upon installation the sheathing tube is bent largely at a right angle in order to make contact with the connecting lead, i.e. to allow connection to the electrical system of the motor vehicle. In order reliably to rule out a short-circuit of the electrical conductors, the electrical conductors are electrically insulated from one another and from the sheathing tube.
In a known connecting lead for a sensor of this kind (German Patent No. 195 23 911), the electrical conductors are sheathed in a high-strength electrical insulation, e.g. glass filament, and four or five sheathed electrical conductors are received, with the highest possible packing density, in a sheathing tube made of a temperature-resistant metal, e.g. CrNi or NiCr alloys. At the connection end, the electrical conductors are welded onto crimp sleeves in which the ends of connecting cables leading to a connector plug are caulked. The crimp sleeves are encapsulated, together with one end of the sheathing tube and the end region of the connecting cable, in a sealing element made, for example, of PTFE. To allow the sheathing tube to be bent without damage, care must be taken that the sheathed electrical conductors have sufficient looseness within the sheathing tube to compensate for the changes, during bending of the metal tube, in the lengths of the electrical conductors inside the sheathing tube.
In a heat-resistant connecting lead for an exhaust gas lambda probe that is also known (European Published Patent Application No. 0 843 321), a pair of bare electrical conductors made of nickel wire, and a pair of aeration tubes made of stainless steel, extend inside the stainless-steel sheathing tube. The electrical insulation is made up of a magnesium powder that is introduced into the metal tube in such a way that the two pairs of electrical conductors and aeration tubes are disposed, diametrically opposite one another, at the four corners of a square, and are completely insulated by the magnesium powder from one another and from the sheathing tube. A connecting lead of this kind cannot be bent upon installation.
The connecting lead according to the present invention has the advantage that the electrical conductors are guided by the insulating disks at a defined spacing from one another and from the sheathing tube, and bare wires can therefore be used as electrical conductors, without the sheathing (made of high-temperature-resistant material) that is very expensive to manufacture. The process of manufacturing the connecting lead can be configured in very simple and inexpensive fashion, since the insulating elements merely need to be threaded onto the conductors, and the threaded-on unit can then easily be pulled into the sheathing tube.
According to a preferred embodiment of the invention, the insulating elements are braced directly against one another in one element subregion and have, in the other element subregion remaining in the bracing plane, a clearance from one another that increases toward the element periphery. This spacing can be achieved by beveling or rounding the insulating elements. This geometry of the insulating elements guarantees the bendability of the connecting lead, since as the sheathing tube is bent, the insulating elements can assume an acute-angle incidence to one another because of the space present in the subregion, and thus allow curved guidance of the sheathing tube. As the sheathing tube is bent, the distances between the electrical conductors on the one hand, and between the electrical conductors and the sheathing tube on the other hand, are kept constant, and a short-circuit due to contact between the bare wires is avoided.
According to a preferred embodiment of the invention, the insulating elements are embodied as disks whose at least one disk surface are beveled toward the disk center in one subregion, and rest against one another with their flat disk surface region. The partial beveling of the insulating disks can be performed on each disk surface, or on one of the two disk surfaces. Instead of a bevel, a rounding can also be performed in such a way that a rounding radius joins the one disk surface to the other.
According to an advantageous embodiment of the invention, the through holes in each insulating disk are disposed in such a way that their hole axes lie next to one another on one diameter line. As a result, all the electrical conductors extend in a neutral zone of the sheathing tube, so that their lengths, clamped in place at the tube ends, are not modified upon bending.
According to an advantageous embodiment of the invention, the insulating disks each have a through opening, the through openings in the insulating disks resting against one another being mutually aligned. Guided through the through holes is a preferably round spring rod that is retained in axially nondisplaceable fashion in the sheathing tube. Retention is accomplished by axial bracing of the spring rod in the region of the tube ends. The spring rod places the insulating disks under stress after the sheathing tube has been bent, so that vibrations of the insulating disks during vehicle operation, which might cause breakage of the insulating disks, are prevented.
According to a preferred embodiment of the invention, the two outer ones of the insulating disks lying against one another are braced axially in the sheathing tube. The bracing is accomplished at the connection end of the sheathing tube by a seal element made of electrically insulating material and pressed into the sheathing tube, and bracing at the sensor end of the sheathing tube is accomplished by an insulating element that braces against the sheathing tube. The insulating element is in turn braced against at least one end disk, made of electrically insulating material, that closes off the sensor end of the sheathing tube. The insulating element and the at least one end disk are located in that part of the sheathing tube that is not bent but remains straight. The at least one end disk defines the desired connection pattern of the electrical conductors for the sensor element; and the insulating element creates, with its through orifices, the transition from the disposition, which deviates spatially from the connection pattern, of the through holes for the electrical conductors in the insulating disks.
The connecting lead depicted in
As is evident from
Disposed at sensor end 11 of measurement tube 13, specifically in the portion of sheathing tube 13 that is not bent during installation but remains straight, are an insulating element 21 and two end disks 22, resting against one another, that constitute the sensor-end bracing for the series of insulating disks 15. Sheathing tube 13 is crimped over at the end onto the outer end disk 22.
Insulating element 21, made of high-temperature-resistant electrical insulating material, is depicted in
Near connection end 12 of sheathing tube 13, electrical conductors 14 are each joined to an electrical connecting cable 29 by ultrasonic welding. Connecting cables 29, of which only one is visible in
Upon assembly of the connecting lead, the individual electrical conductors 14 are threaded through the mutually aligned through holes 16 in insulating disks 15, through the through orifices 26 in insulating element 21, and through the through holes 23 in the two end disks 22, and protrude at sensor end 11 of sheathing tube 13 so that contact can be appropriately made to them from the sensor element. A protective cap 32, indicated with dashed lines in
Upon installation of the sensor, the connecting lead is bent at a right angle in the direction of arrow 33 in
The configuration of the insulating elements is not limited to the geometric conformation of insulating disks 15. For example, insulating disks 15 can also, in the subregion of their disk surfaces, be beveled on only one of the sides facing away from one another or can be rounded on one or both sides. All that is important for the subsequent bending of sheathing tube 13 is that the insulating elements, braced against one another in one subregion, not touch one another in the other subregion within the bracing plane but rather have a clearance from one another that increases toward the outer periphery of the insulating elements. This clearance can be brought about by beveling or rounding on one or both sides. The insulating elements can, however, also be embodied as spheres that rest against one another at a single point, or as spherical caps that are serially arranged in the same direction, so that the one spherical shell is always braced in single-point fashion against the plane of the next spherical cap.
Number | Date | Country | Kind |
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102 40 238.8 | Aug 2002 | DE | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/DE03/02360 | 7/14/2003 | WO | 12/12/2005 |