Title of Invention

SHEATHED-ELEMENT GLOW PLUG AND A METHOD FOR PRODUCING THE SAME

Abstract

The invention provides a sheathed-element glow plug (1) having a ceramic sheathed element (14) and a connection element (5, 10) for supplying current, the connection element being electrically connected to the ceramic sheathed element (14) via a contacting element (12), characterized in that the contacting element (12) is formed as a tablet of electrically conductive powder. The invention also relates to a method for producing the same.

Full Text

The invention relates to a sheathed-element glow plug and a method for producing the same. The invention is based on a ceramic sheathed-element glow plug for diesel engines. Sheathed-element glow plugs with external ceramic heater have already been disclosed, for example by the patent application DE-A 40 28 859. Furthermore, metallic sheathed-element glow plugs in which the metallic glow plug filament is welded to a thermocouple are known, for example, from DE-A 29 37 884. In this case, the temperature in the corresponding cylinder can be measured while the sheathed-element glow plug is operating, by capturing the thermoelectric voltage. However a metallic glow plug filament is not present in a sheathed-element glow plug with ceramic heater element. Furthermore, DE 198 44 347 has disclosed a sheathed-element glow plug with a connection element which is electrically connected to the sheathed element via a contacting element. As can be seen from Figure 1, this contacting element is designed as a spring. Advantages of the invention The ceramic sheathed-element glow plug according to the invention has the advantage that the temperature of the sheathed element can be measured. It is for the first time possible, in a ceramic sheathed-element glow plug, to measure the temperature of the sheathed element directly in a selected region on the outer side of the sheathed element without additional outlay on equipment. The temperature is measured in a selected region, which is small compared to the volume of the overall sheathed element, so that the error which is caused by a temperature distribution over a large volume can be reduced during the temperature determination. Furthermore, it is advantageous that, in the sheathed-element glow plug according to the invention, it is possible to concentrate the heating capacity in a selected region of the sheathed element without changing the cross section of the conductive layer, so that the surface area in the region in which the concentration of the heating capacity is to take place remains constant, and therefore the interaction area is also kept constant. A further advantage is that a ceramic temperature-measurement sheathed-element glow plug of this type can be manufactured at low cost. The measures listed in the subclaims referring to the first independent claim allow advantageous refinements and improvements to the ceramic sheathed-element glow plug described in the main claim. In particular, it is ensured, by suitably selecting the ceramic materials used for the various regions of the sheathed-element glow plug, that the mechanical stability of the heater is not impaired. Processing of the measured temperature values by means of a control unit allows the temperature to be regulated in the selected region of the sheathed element. It is also advantageous for the sheathed-element glow plug according to the invention, in passive mode, after it has fulfilled the heating function, to be used as a temperature sensor. In this way, it is possible to establish whether the combustion in the corresponding cylinder is proceeding correctly. On the basis of this information, it is advantageously possible to influence parameters which are relevant to the combustion. The ceramic sheathed-element glow plug according to the invention having the features of the independent Claim 14 has the advantage over the prior art that, on account of the larger line cross section, higher currents can be transmitted without thermal destruction of the material of the contacting element. Furthermore, the large surface area of the contacting material is advantageous since it allows good thermal conductivity. The elastic spring component ensures that thermal displacements of the surrounding components resulting from different coefficients of thermal expansion can be compensated for. The measures listed in the dependent claims, referring to Claim 14 allow advantageous refinements and improvements to the ceramic sheathed element glow plug described in the main claim. In this context, it is advantageous for the contacting element to be formed as graphite or conductive ceramic powder, since these materials are resistant to corrosion* Furthermore, it is advantageous for only a majority of the material to be provided as graphite or conductive ceramic or metal powder, since it is possible to save on expensive materials while achieving approximately the same properties, Furthermore, it is advantageous for the sheathed-element glow plug having a contacting element according to the invention to be produced in the manner described below, since in this way the components located in the plug housing are arranged in such a way as to prevent short circuits. Moreover, it is ensured that the components are compressed in such a way that, on the one hand, there is no loosening of the components and, on the other hand, no springing open of components as a result of an excessive oppositely directed force from resilient elements (e.g. of the contacting element). Drawings The exemplary embodiments of the invention are illustrated in drawings and are explained in more detail in the description below, in which: Figure 1 shows a sheathed-element glow plug according to the invention in longitudinal section. Figure 2 shows the front part of the external ceramic heater, as a side view. Figure 3 shows a circuit arrangement of the sheathed-element g].ow plug according to the invention and the control units, Figure 4 shows the resistances which occur in the ceramic sheathed-element glow plug according to the invention and in the supply conductors, and Figure 5 shows a sheathed-element glow plug according to the invention in longitudinal section. Description of the exemplary embodiments Figure 1 diagrammatically depicts a longitudinal section through a ceramic sheathed-element glow plug 1 according to the invention. At that end of the sheathed-element glow plug 1 which is remote from the combustion chamber, electrical contact is made via a circular connector 2, which is separated from the plug housing 4 by a seal 3 and is connected to the cylindrical supply conductor 5, The cylindrical supply conductor 5 is fixed in the plug housing 4 by means of a metal ring 7 and an electrically insulating ceramic sleeve 8. The cylindrical supply conductor 5 is connected to the ceramic sheathed element 14 via a contact pin 10, it also being possible for the cylindrical supply conductor 5 to be combined with the contact pin 10 in a single component, and a suitable contacting element 12, which is preferably designed as a contact spring or as an electrically conductive powder packing or as an electrically conductive disk with an elastic spring component/ preferably made from graphite. The interior of the glow plug is sealed off from the combustion chamber by means of a seal packing 15. The seal packing 15 consists of an electrically conductive carbon compound. However, the seal packing 15 may also be formed by metals, a mixture of carbon and metal or a mixture of ceramic and metal. The sheathed element 14 comprises a ceramic heating layer 18 and ceramic supply conductor layers 2 0 and 21, the two supply conductor layers 20, 21 being connected by the heating layer 18 and, together with the heating layer 18, forming the conductor layer. The supply conductor layers 20, 21 are of any desired form, and the heating layer 18 may also be of any desired form. The conductor layer is preferably of U-shaped design * The supply conductor layers 20 and 21 are separated by an insulation layer 22, which likewise consists of ceramic material. In the exemplary embodiment illustrated in Figure 1, the sheathed element 14 is designed in such a manner that the supply conductor layers 20 and 21 and the heating layer 18 are arranged on the outside of the sheathed element 14. However, it is also possible for at least the supply conductor layers 20 and 21 to be arranged in such a way that they are situated inside the sheathed element and are also covered by an external, ceramic, insulating layer. Inside the plug housing, the ceramic sheathed element is insulated from the other components of the sheathed-element glow plug 4, 8, 12, 15 by a layer of glass (not shown). To produce the electrical contact between the contacting element 12 and the supply conductor layer 20, the layer of glass is interrupted at the location indicated by 24. The layer of glass is also interrupted so as to provide electrical contact between supply conductor layer 21 and plug housing 4 via the seal packing 15 at the location indicated by 26, In this exemplary embodiment, as a preferred design, the heating layer 18 has been positioned at the tip of the sheathed element. However, it is also conceivable for this heating layer to be positioned at a different location of the conductor layer. The heating layer 18 should be situated at the location at which the greatest heating action is to be produced. Figure 2 once again shows the ceramic heating element, in a view from the side. As in Figure 1, the embodiment in which the heating layer 18 is situated at the tip of the sheathed element is illustrated. The supply conductor layers 20, 21 and the insulation layer 22 can also be seen. This side view shows the embodiment in which the conductor layer, comprising the supply conductor layers 20, 21 and the heating layer 18, is of U-shaped form. The operating state in which the sheathed element is heated in order to assist combustion in the combustion chamber, this heating taking place when the internal-combustion engine is started up, during an afterglow phase, which preferably extends over a period of 3 minutes, and during an intermediate glow phase when the temperature of the combustion chamber, while the internal combustion engine is operating, falls excessively, is known as active operation. In the ceramic sheathed-element glow plug according to the invention, the material of the heating layer 18 is selected in such a way that the absolute electrical resistance of the heating layer 18 is greater than the absolute electrical resistance of the supply conductor layers 20, 21, (In the text which follows, the term resistance is to be understood as meaning the absolute electrical resistance, without these words being added.) To avoid crossover current between the conductor layer, the resistance of the insulation layer is selected in such a way that it is significantly greater than the resistance of the heating layer 18 and of the supply conductor layers 20, 21, Figure 3 diagrammatically illustrates which units are in communication with the sheathed element glow plug 1. The first of these units is the engine control unit 30, which includes a computer unit and a memory unit. The engine-dependent parameters of the sheathed-element glow plug are stored in the engine control unit 30, These parameters may, for example, be the resistance/temperature characteristic diagrams as a function of load and speed of the engine. The memory of the engine control unit also holds one or more temperature reference values for correct combustion. The engine control unit is able to control parameters which influence the combustion, for example the fuel injection duration, the fuel injection commencement and the end of fuel injection, The control unit 32 regulates a voltage which has been preset by the engine control unit. This voltage represents the overall voltage used for the sheathed-element glow plug. The control unit 32 also accommodates a current-measuring unit, which is used to measure the current intensity flowing across the sheathed element, Furthermore, the control unit 32 includes a memory unit and a computer unit. The engine control unit 30 and the control unit 32 can also be combined in a single unit * Figure 4 illustrates the resistances which occur across the sheathed-element glow plug. The resistor 41, with a resistance R20, represents the resistance of the ceramic supply conductor layer 20. The resistor 43, with a resistance Rl, incorporates the resistance of the heating layer. The resistor 45, with a resistance R21, incorporates the resistance of the ceramic supply conductor layer 21. In addition, there are also the resistances of the other supply and return conductor lines, but these are all low compared to the resistances R20 and R21 and are therefore not taken into account. They are not shown in Figure 4* The resistors 41, 4 3 and 45 are connected in series • Any crossover currents which occur should be disregarded for the considerations carried out on the basis of Figure 4. Therefore, the total resistance R results from the sum of the resistances R20, Rl and R21. The resistance Rl forms the largest summand. The engine control unit 30, on the basis of the characteristic diagrams contained therein and the desired temperature of the sheathed element, presets an effective voltage which is regulated by the control unit 32, On the basis of the temperature dependency of the resistors 41/ 43 and 4 5, a current I is established across the sheathed elament glow plug, i.e. across the resistance R, and this current is measured in the control unit 32. The temperature dependency of the total resistance R = R20 + Rl + R21 results predominantly from the temperature dependency of the resistance Rl, since this resistance has the highest value. The temperature dependency of the resistances R20, Rl and R21 is virtually constant over the entire operating range of the sheathed-element glow plug between room temperature and a temperature of approximately 1400 ,'C. The temperature of the combustion chamber lies within the operating range of the sheathed-element glow plug. The measured current intensity I is converted by the control unit 32, on the basis of a stored characteristic diagram, into a temperature which, since the resistance Rl is significantly higher than the resistances R2 0 and R21, results predominantly from the temperature of the heating layer 18, This temperature is fed back to the engine control unit 30, and the effective voltage for the sheathed-element glow plug is reset on the basis of the temperature determined. It is also possible for the temperature of the heating layer 18 of the sheathed element to be output in some other way, for example on a display. Furthermore, it is possible, on the basis of the temperature determined, for example taking into account one or more reference temperatures stored in the engine control unit 30, to draw conclusions as to the quality of the combustion on a cylinder-specific basis. In the event of incorrect combustion, cylinder-specific measures can be taken by the control unit, which influence the combustion process and are therefore able to ensure that correct combustion is reestablished. It would then be possible, to vary the fuel injection duration, the fuel injection commencement or the fuel injection pressure, In a further exemplary embodiment, it is possible to measure the temperature of the combustion chamber even in passive operation of the sheathed-element glow plug, i.e. after the afterglow time, when the sheathed-element glow plug is no longer in active operation. In this case, a correspondingly lower effective voltage is preset and, as with active operation, the current I which is established across the resistance R is measured, and in this way the temperature of the heating region is worked out, which then corresponds to the temperature of the combustion chamber. As in active operation, the temperature of the combustion chamber can be compared on a cylinder-specific basis with one or more reference values for correct combustion which are stored in the engine control unit. If the temperature of the combustion chamber does not correspond to correct combustion, it is possible, as described for active operation of the sheathed-element glow plug, to take measures which reestablish correct combustion, for example to vary the fuel injection duration, the fuel injection commencement and the fuel injection pressure. The resistances R20, Rl and R21 and their temperature dependency are set, on the basis of R - p * 1 / A, where 1 represents the length of the resistor and A represents the cross-sectional area, by the temperature dependency of the resistivity p. In this case, the temperature dependency results from P(T) - Po(To) , (1 ,' a(T) * (T-To) ) . In this equation, p(T) represents the resistivity as a function of the temperature T, po represents the resistivity at room temperature To and a(T) represents a temperature coefficient which is temperature-dependent. To achieve a different temperature dependency of the resistances of the supply conductors R20 and R21 compared to the resistance Rl, it is possible for the resistivity of the heating layer 18 to be selected in such a way that po of the heating layer is greater than po of the supply conductor layers. Alternatively, however, the temperature coefficient a of the heating layer 18 in the operating range of the sheathed,element glow plug may be greater than the temperature coefficient a of the supply conductor layers 20, 21. It is also possible for both po and a for the heating layer 18 for the operating range of the sheathed-element glow plug to be selected to be greater than for the supply conductor layers 20, 21. In one preferred exemplary embodiment, the composition of the heating layer 18 and of the supply conductor layers 20, 21 is selected in such a way that the po of the supply conductor layers 20, 21 is at least ten times lower than the po of the heating layer 18. The temperature coefficient a of the heating layer 18 and of the supply conductor layers 20, 21 is approximately equal - The result is an accuracy of the temperature measurement of 20 Kelvin throughout the entire operating range of the sheathed-element glow plug. In a preferred exemplary embodiment, the resistivity of the insulation layer 22 in the entire operating range of the sheathed-element glow plug is at least ten times greater than the resistivity of the heating layer 18. In a preferred exemplary embodiment, the heating layer, the supply conductor layers and the insulation layer consist of ceramic composite structures, which contains [sic] at least two of the compounds AI2O3, MoSi2f Sing and YsOs - These composite structures can be obtained using a single-stage or multistage sintering process, In this case, the resistivity of the layers may preferably be determined by the MoSi2 content and/or the grain size of MoSi2/ the Mosaic content of the supply conductor layers 20, 21 preferably being higher than the MoSi2 content of the heating layer 18, the heating layer 18 in turn having a higher MoSi2 content than the insulation layer 22. In a further exemplary embodiment, heating layer 18, supply conductor layer 20, 21 and the insulation layer 22 consist of a composite precursor ceramic with different amounts of fillers, The matrix of this material in this case consists of polysiloxanes, polysilsesquioxanes, polysilanes or polysilazanes, which may be doped with boron or aluminum and are produced by pyrolysis. At least one of the compounds AI2O3, MoSi2 and SiC form the filler for the individual layers. In a similar manner to the composite structure referred to above, it is preferably possible for the iyioSi2 content and/or the grain size of MoSi2 to determine the resistivity of the layers. Preferably the MoSi2 content of the supply conductor layers 20, 21 is set to be higher than the MoSi2 content of the heating layer 18, the heating layer 18 in turn having a higher MoSi2 content than the insulation layer 22. The compositions of the insulation layer, the supply conductor layers and the heating layer in the exemplary embodiments described above are selected in such a way that their coefficients of thermal expansion and the shrinkages of the individual supply conductor, heating and insulation layers which occur during the sintering or pyrolysis process are identical, so that no cracks are formed in the sheathed element. Figure 5 shows a further preferred exemplary embodiment of the invention on the basis of a diagrammatic longitudinal section through a sheathed-element glow plug 1 according to the invention. Identical reference symbols to those used in the previous figures denote identical components which are not explained again in connection with the present figure, In a similar manner to Figure 1, the sheathed-element glow plug illustrated in Figure 5 has a circular connector 2 which is in electrical contact with the cylindrical supply conductor 5. The cylindrical supply conductor 5 is electrically connected to the ceramic sheathed element 14 via the contact pin 10 and the contacting element 12. The cylindrical supply conductor 5, the contact pin 10, the contacting element 12 and the ceramic sheathed element 14 are arranged one behind the other, in this order, as illustrated in Figure 5, in the direction of the combustion chamber. In the preferred exemplary embodiment illustrated in Figure 5, the ceramic sheathed element 14 has a stud 11 at the end which is remote from the combustion chamber. An extension of the sheathed element 14 in the direction of the end which is remote from the combustion chamber forms the stud 11, as a result of the ceramic supply conductor layers 20, 21 and the insulation layer 22 being led out in the form of a cylinder, the stud 11 having a smaller external diameter than that part of the sheathed element 14 which adjoins it in the direction of the combustion chamber, namely the collar 13, Furthermore, it is not necessary for the sheathed element 14 to have a heating layer 18 at the combustion,chamber end. In a preferred exemplary embodiment, the two supply conductor layers 20 and 21 may simply be connected at the combustion-chamber end of the sheathed element, in the same way as that performed by means of the heating element 18, The cylindrical supply conductor 5 and the contact pin 10 together form the connection element, which may also be of single-part design. At the combustion-chamber end of the connection element, there is a flange which, together with the stud 11 delimits the contacting element 12 in the direction of the axis of the sheathed-element glow plug. The contacting element 12, which consists of a tablet of electrically conductive powder, is preferably formed as graphite or a metal powder or an electrically conductive ceramic powder. In a further preferred embodiment, the tablet of electrically conductive powder may also at least predominantly comprise graphite or the metal powder or the electrically conductive ceramic powder. On account of the contacting element 12 being formed as electrically conductive powder, the contacting element 12 ensures that resilient contact is made, making it possible to carry high currents without thermal destruction, The large surface area of the powder ensures good thermal conductivity. For the same reason, it is also possible to achieve a low contact resistance with good conductivity. Moreover, graphite and ceramic conductive materials are corrosion-resistant. The elastic spring component of the tablet of electrically conductive powder ensures that the tablet compensates for thermal movements of the components caused by different coefficients of thermal expansion. The tablet of electrically conductive powder is laterally delimited by a cylindrical clamping sleeve 9, which in this case is present as an independent component instead of the ceramic sleeve 8 illustrated in Figure 1. In a similar manner to the ceramic sleeve 8, the clamping sleeve 9 is provided as an insulating component; in a preferred exemplary embodiment, it consists of ceramic material, During production of the sheathed-element glow plug, the tablet of electrically conductive powder is pressed securely between the flange of the connection element on the end side which is remote from the combustion chamber, the stud 11 of the sheathed element 14 on the combustion-chamber end side and the clamping sleeve 9, The fact that it is clamped between these fixed components, in particular the fixed contact between the clamping sleeve 9 and the ceramic sleeve 8, i.e. the limited compression height, prevents the surrounding clamping sleeve 9 from being torn by an excessive build-up of internal pressure as a result of the pressing of the contacting element 12. The axial prestressing of the elastic spring component which is achieved by the clamping of the tablet of electrically conducting powder makes it possible to compensate for thermal expansion, settling and vibration loads when the sheathed-element glow plug is subject to shaking. A sheathed-element glow plug according to Figure 5, with a tablet of electrically conductive powder as contacting element 12, is produced in the following way- First of all, the seal packing 15 is guided over the ceramic sheathed element 14 from the tip of the ceramic sheathed element 14 which is on the combustion chamber side, and is introduced as an assembly into the plug housing 4 from the end which is remote from the combustion chamber. Then, the contacting element 12, the clamping sleeve 9, the connection element 5, 10, the ceramic sleeve 8 and the metal ring 7 are arranged in a holding element and are then likewise introduced into the plug housing 4 from the end which is remote from the combustion chamber. Next, an axial force which is applied to that end of the metal ring 7 which is remote from the combustion chamber is used to compress the components located in the plug housing, and in particular the contacting element 12, which comprises a tablet of electrically conductive powder, and the seal packing 15 are compressed. A force is only applied to the contacting element 12 until the contact pin of the connection element 5, 10 has pressed fully into the clamping sleeve 9 and the end side of the ceramic sleeve 8 rests on the end side of the clamping sleeve 9. Moreover, the compression of the tablet of electrically conductive powder ensures that the elastic spring component of the tablet is prostheses. Then, the metal ring 7 is jammed in place by means of a force which is applied radially from the outside to the plug housing 4, Next, the seal 3 and the circular connector 2 are fitted and likewise jammed in place by means of a force applied radially from the outside to the plug housing 4. WE CLAIM: 1. Sheathed-element glow plug (1) having a ceramic sheathed element (14) and a connection element (5, 10) for supplying current, the connection element being electrically connected to the ceramic sheathed element (14) via a contacting element (12), characterized in that the contacting element (12) is formed as a tablet of electrically conductive powder. 2. Sheathed-element glow plug as claimed in claim 1, wherein the tablet of electrically conductive powder has an axially prestressed elastic spring component, 3. Sheathed-element glow plug as claimed in claim 1, wherein the electrically conductive powder consists of graphite or of metal powder or of electrically conductive ceramic powder or at least predominantly comprises these materials. 4. Method for producing a sheathed-element glow plug as claimed in claim 1, comprising the steps of: a) introducing a seal packing (15) over the ceramic sheathed element (14) from the tip of the ceramic sheathed element (14) which is on the combustion chamber side and forming an assembly, this assembly being introduced into a plug housing (4), b) arranging the tablet of electrically conductive powder, a clamping sleeve (9), the connection element (5, 10), a ceramic sleeve (8) and a metal ring (7) in a holding element and introducing it into the plug housing (4), c) compressing the components located in the plug housing (4) by means of an axial force which is exerted on that end of the metal ring (7) which is remote from the combustion chamber, d) jamming the metal ring (7) in place by means of a force which is applied radially from the outside to the plug housing (4) 5. Method as claimed in claim 4, wherein an axial presses is applied to an elastic spring component of the tablet of electrically conductive powder by means of an axial force by compression of the components located in the plug housing (4).

Documents:

in-pct-2001-729-che-abstract.pdf

in-pct-2001-729-che-claims filed.pdf

in-pct-2001-729-che-claims granted.pdf

in-pct-2001-729-che-correspondnece-others.pdf

in-pct-2001-729-che-correspondnece-po.pdf

in-pct-2001-729-che-description(complete)filed.pdf

in-pct-2001-729-che-description(complete)granted.pdf

in-pct-2001-729-che-drawings.pdf

in-pct-2001-729-che-form 1.pdf

in-pct-2001-729-che-form 26.pdf

in-pct-2001-729-che-form 3.pdf

in-pct-2001-729-che-form 5.pdf

in-pct-2001-729-che-other documents.pdf

in-pct-2001-729-che-pct.pdf