Title of Invention

A PASSIVE, HIGH-TEMPERATURE- RESISTANT RESISTANCE ELEMENT FOR TEMPERATURE DETECTION IN PASSENGER CARS AND UTILITY VEHICLES

Abstract

The invention proposes a passive, hightemperature-resistant resistance element for ection of temperature, which has a substantially internal insulation layer (9; 10) and two external conductive layers (8) comprising a ceramic composite structure, the aductive layers being connected to one another at the tip (11) of the resistance :ment, and the ceramic composite structure comprising trisilicon tetranitride, a metal icide and yttrium oxide, or trisilicon tetranitride, a metal silicide and a matrix phase mprising SixOyCzNw, where x = 1-2, Y = 0-2, z = 0-2 and w = 0-2. Furthermore, e invention proposes a combination element (3) comprising this resistance element ld, for example, a sheathed-element glow plug.

Full Text

The invention relates to a passive, high-temperature-resistant resistance element for temperature detection in passenger cars and utility vehicles. The invention also relate to a combination element comprising this resistance element and a functional element for use in thecombustion chamber of an internal-combustion engine. Prior art EP 0180 928 describes a refractory composition and products resulting therefrom and DE 19612 926 describes modified composite silicon nitride powders for thennal coating technologies and process for their production. The thermoresistive materials which are used to detect temperature in the application range up to 1400oC are mechanically unstable and therefore carmot generally be used as self-supporting temperature sensor elements. They are therefore usually fitted in protective tubes or onto or between substrates. These are generally ceramic substrates. Known temperature sensors which are suitable for exhaust gas are thermocouples, which generally comprise precious-metal wires comprising PtPtRh or Ni/CrNi, the connection lugs of which are insulated from one another in ceramic tubes and the contact of which is protected by a metal sheath or ceramic sheath or by being welded into the metal sheath of a sheathed-element glow plug. Temperature sensors which are constructed as thick-film or thin-film elements, in which the temperature-sensitive functional layer is vapour-deposited on or between the substrates or is sintered in, are also known. This entails a certain inertia of the thermocouples on account of the substrate material used in each case. The detection of the temperature during the combution sequences in the combustion chamber of internal-combustion engines is also very difficult. For access tc the combustion chamber, particularly in modem four-valve direct-injection engines, it is often impossible to provide an additional bore for a temperature sensor. Furthermore, the temperatures or temperature ranges of from -40 to 1400°C which are to be detected, in combination with an aggressive atmosphere in the form of hot gas, impose extremely high demands on corresponding temperature sensors. Object of the invention Therefore, the object of the present invention was to provide a self-supporting resistance pick-up which is mechanically stable, is thermally resistant to even very high temperatures of up to 1400°C and allows the exhaust-gas temperature in the exhaust system or the combustion-chamber temperature of passenger car and utility vehicle engines to be detected in the application range from -40 to I400°C. In the latter case, the temperature detection should be effected via one of the existing openings of the combustion chamber. According to the invention, the object is achieved by a passive, high-temperature-resistant resistance element for temperature detection, which is characterized in that it has a substantially internal insulation layer and two external conductive layers comprising a ceramic composite structure, the conductive layers being connected to one another at the tip of the resistance element, and in that the ceramic composite structure comprises trisilicon tetranitride, a metal silicide and yttrium oxide, or trisilicon tetranitride, a metal silicide and a matrix phase comprising SixOyC2Nw, where x = 1-2, y = 0-2, z = 0-2 and w = 0-2. In a preferreu embodiment of the invention, the internal insulation layer also has a ceramic composite structure. Since in this case the compositions of the insulation component and of the conductive component differ only slightly, co-sintering or co-pyrolysis of the composite materials is advantageously possible. With regard to the sintering, reference is made to EP 0 412 428 Al and DE 195 38695 Al, In a simplified variant, an airgap can remain for insulation purposes instead of the internal insulation layer comprising composite material. The ceramic composite structure of the resistant element according to the invention preferably comprises 30-70% by mass of SIJNA, 25-65% by mass of MSi2 where M is Mo, Nb, W or Ti, 0-5% by mass of Al2O3 and 2-9% by mass of Y2O3. It is also possible for the matrix phase comprising SixOyCzNw, in the ceramic composite structure to be the pyrolysis product of one or more organosilicon compounds. Suitable compounds are polysiloxane, such as NH2100 produced by Huls, and polysilozane, such as NCP200 produced by the Japanese company Nichimen Incorp. The composite materials based on trisihcon tetranitnde with fillers of a metal suicide MSi2 are both thermally and mechanically stable and, on account of the addition of a certain quantity of the corresponding filler component, have an electrical resistance which can be adjusted according to the added content, with a positive temperature coefficient. As stated in EP 0 412 428 Al and DE 195 38 695 A1, these combinations of properties enable sheathed elements which heat up particularly quickly, for example, to be produced therefrom. In a preferred embodiment of the invention, the tip of the resistance element is tapered. The tapering of the conductive area at the tip makes it possible to adjust the resistance of the sensor. The length of the tapered area also determines the location of the temperature measurement. The electrical resistance of the conductive composite material in the tip can, by changing the mixture compared to the material in the supply conductors, which is to be understood as meaning the main body of the resistance element, be changed by a plurality of orders of magnitude without, as a result, having a significant adverse effect on the thennal/mechanical properties. This is highly important in particular in the case of a cantilevered design. The high mechanical strength of the composite material makes it possible to form a self-supporting resistance element which, in cantilevered form or, like the ceramic sheathed-element glow plug, fitted in a suitable housing, can be installed directly in the exhaust system of a passenger car or utility vehicle. The unsupported introduction of the thermally sensitive material directly and, if appropriate, without a protective cap into the zone which is to be measured ensures a rapid change in resistance on the sensor and therefore advantageously ensures that the temperature is detected as far as possible without inertia. On account of the good resistance to oxidation of both the matrix material and the incorporated compounds used, the materials are stable at temperatures of up to 1400oC in both an oxidizing atmosphere and a reducing atmosphere. Since the materials have a virtually linear increase in the electrical resistance as the temperature rises in the range from -40 to 1400oC, temperature measurement throughout the entire range can be achieved. An application example which may be mentioned for the high-temperature-resistant resistance element according to the invention for temperature detection in the exhaust system of passenger cars and utility vehicles is the detection of the exhaust-gas temperature between the starting catalytic converter and the principal converter in lean-design engines, such as for example petrol direct-injection engines. The high mechanical strength of the composite ceramic, which allows a self-supporting design taking up extremely small amounts of space, advantageously allows particularly flexible positioning of the temperature sensor at a suitable location in the exhaust gas. In addition to being positioned upstream and downstream of the catalytic converter, it is also possible for the element to be mounted directly inside the catalytic converter for particular detection purposes. In a particularly preferred embodiment, the resistant element according to the invention is combined with a functional element which projects into the combustion chamber of an internal-combustion engine. This functional element may be a starting aid, an injection nozzle or a valve. The starting aid may be a sheathed-element glow pin. It is now possible, in this way, for the temperature to be detected via one of the existing openings of the combustion chamber of a passenger-car or utility-vehicle engine. A resistance element which is constructed from the above materials and is combined with a functional element has two functions, for example firstly, when subjected to voltage, that of a rapidly heating sheathed-element glow plug, and secondly the electrical resistance, which changes as a function of the temperature, can be evaluated for temperature detection as a measurement signal both during the active application of current, i.e. during the heating-up or glowing phase, and in passive, i.e. current-free at-rest phases. The high mechanical strength of the composite material makes it possible to form a self-supporting combination element which, fitted in cantilevered form in a suitable housing, can be installed instead of a conventional sheathed-element glow pin directly in the combustion chamber of passenger-car and utility-vehicle engines. The introduction of the thennosensitive material directly and without a protective cap into the zone which is to be measured advantageously ensures a rapid change in resistance at the sensor and therefore that the temperature is recorded as far as possible without inertia. The sensitivity of the sensor element can be adjusted by the ratio of supply-conductor resistance and sensor-tip resistance. An apphcation example which may be mentioned for the new type of combination element is the recording of the combustion-chamber temperature in diesel-injection engines. The particular advantage resides in the fact that the integration of the functions of temperature sensor and glowing means that no additional space is required. The combustion-chamber tenxperature can be used as a measure of the combustion operation. Drawing Figure 1 diagrammatically depicts, in section, the passive, high-temperature-resistant resistance element for temperature detection in the exhaust system of a passenger car or utility vehicle. Figure 2 diagrammatically depicts, in section, the passive, high-temperature-resistant combination element in the combustion chamber of a passenger-car or utility-vehicle engine. Figures 3 and 4 show the passive, high-temperature-resistant resistance element according to the invention, in each case in different embodiments. In Figure 1, a self-supporting PTC temperature sensor 4 made from composite ceramic projects into an exhaust system 6 including the catalytic converter. The direction of flow of the exhaust gas 7 is Indicated by an arrow. At the thickened end, the temperature sensor 4 is held by a housing 2 with screw-in thread. In this case, contact is with the engine control unit or with the measurement and evaluation electronics. The temperature-dependent resistance which is recorded on the pick-up can be matched to the characteristic of a standard Pt-200 or Pt-200 element using a resistance-measuring appliance or a plug with compensation electronics 1. In Figure 2, the combination element 3 comprising sheathed element and temperature sensor projects into the combustion chamber of the engine. In Figures 3 and 4, the conductive composite material 8 has a PTC resistance Ri. In Figure 3, the insulating composite material 9 has an electrical resistance R2 where R2 > 10 R1. This insulating composite material 9 may also be replaced by an airgap 10 of electrical resistance R2 (Figure 4). The conductive composite material with a PTC resistance R3, where R3 > 10 R1 forms the tip 11 of the resistant element according to the invention. The tapering of the conductive region at the tip 11 makes it possible to adjust the electrical resistance of the combination element. The length of the tapered region determines both the position of the hot zone during the application of current, when functioning as a sheathed clement, and the location of temperature measurement when functioning as a temperature sensor. WE CLAIM. 1. A passive, high-temperature-resistant resistance element for temperature detection, characterized in that it has an internal insulation layer (9; 10) and two external conductive layers (8) comprising a ceramic composite structure, the conductive layers being connected to one another at the tip (11) of the resistance element, and in that the ceramic composite structure comprises trisilicon tetranitride, a metal silicide and yttrium oxide, or trisilicon tetranitride, a metal silicide and a matrix phase comprising SixOyQNw, where x = 1 -2, y = 0-2, z = 0-2 and w = 0-2. 2. A resistance element as claimed in claim 1, wherein the internal insulation tayer (9) also has a ceramic composite structure, 3. A resistance element as claimed in claim 1 or 2, wherein the ceramic composite structure comprises 30-70 % by mass of Si3N4, 25-65% by mass of Msi2, where M is Mo, Nb, W or Ti, 0.5% by mass of A12O3 and 2-9% by mass of Y2O3. 4. A resistance element as claimed in claim 1 or 2, wherein the matrix phase comprising SixOyC2Nw in the ceramic composite structure is the pyrolysis product of one or more organosilicon compounds. 5. A resistance element as claimed in claim 4, wherein the organosilicon compound is a polysiloxane or a polysilozane. 6. A resistance element as claimed in any one of claims 1 and 3 to 5, wherein the internal insulation layer (10) is an airgap. 7. A resistance element as claimed in any one of claims 1 to 6, wherein its tip is tapered, 8. A resistance element as claimed in any one of claims 1 to 7, wherein it is fitted in a housing. 9. A resistance element as claimed in any one of claims 1 to 7, wherein it is combined with a functional element which projects into the combustion chamber (5) of an internal-combustion engine. 10. A resistance element as claimed in claim 9, wherein the functional element is a starting aid, an injection nozzle or a valve. 11. A resistance element as claimed in claim 10, wherein the starting aid is a sheath ed-element glow plug. 12. A resistance element as claimed in claim 1, wherein the resistance element is for an exhaust system of a passenger car or utility vehicle.

Documents:

in-pct-2001-1369-che others.pdf

in-pct-2001-1369-che abstract duplicate.pdf

in-pct-2001-1369-che abstract.pdf

in-pct-2001-1369-che claims duplicate.pdf

in-pct-2001-1369-che claims.pdf

in-pct-2001-1369-che correspondence others.pdf

in-pct-2001-1369-che correspondence po.pdf

in-pct-2001-1369-che description (complete) duplicate.pdf

in-pct-2001-1369-che description (complete).pdf

in-pct-2001-1369-che drawings.pdf

in-pct-2001-1369-che form-1.pdf

in-pct-2001-1369-che form-18.pdf

in-pct-2001-1369-che form-26.pdf

in-pct-2001-1369-che form-3.pdf

in-pct-2001-1369-che form-5.pdf

in-pct-2001-1369-che pct search report.pdf

in-pct-2001-1369-che pct.pdf

in-pct-2001-1369-che petition.pdf