Title of Invention

A PENCIL-TYPE GLOW PLUG

Abstract

Abstract •A PENCIL TYPE GLOW PLUG1 The invention relates to a pencil-type glow plug, in particular for starting a compression-ignition internal combustion engine, with a glow pencil, which reaches into a combustion chamber containing an ignitable fuel/air mixture and comprises an electrically conductive ceramic and can be heated to an ignition temperature by connection to a voltage source. Provision is made for the pencil-type glow plug (10) to comprise an integrated temperature sensor (30). (Figure 1)

Full Text

Pencil-type glow plug The invention relates to a pencil-type glow plug, in particular for starting a compression-ignition internal combustion engine Prior art Pencil-type glow plugs of the generic type are known. To start a compression-ignition internal combustion engine, initial ignition of a fuel/air mixture is required. For this purpose, use is made of pencil-type glow plugs, which are arranged in a wall of a combustion chamber. The pencil-type glow plugs comprise a glow pencil, which can be brought into contact with the fuel/air mixture to be ignited. Production of the glow pencil from an electrically conductive ceramic is known. In this case, the glow pencil has a defined electrical resistance, with the result that, when the glow pencil is connected to a voltage source, a heating current flows, resulting in heating of the glow pencil to a defined temperature. This temperature is sufficient to ignite the fuel/air mixture. To monitor and control the operation of the compression-ignition internal combustion engine, it is desirable to know a glow-pencil temperature. One known method of achieving this is to measure the heating , current flowing via the glow pencil in order to derive from it a temperature of the glow pencil. As is known, the electrically conductive ceramics from which the glow pencils are manufactured are composed of a material with a positive temperature coefficient. This means that the resistance rises as the temperature rises, with the result that, given a constant supply voltage, the heating current decreases. From this, it is possible to infer the instantaneous temperature of the glow pencil using the variation of the heating current with time. However, the disadvantage with this known arrangement is that temperature distribution over the length of the glow pencil can vary greatly with the same heating current. Temperature distribution is dependent on a speed, a load condition and/or cooling of the internal combustion engine, for example. Experimental studies have shown that temperature differences of up to 200°C can occur here. Advantages of the invention The pencil-type glow plug according to the invention with the features stated in Claim 1 offers the advantage that direct measurement of the temperature at a tip of the glow pencil can be performed without impairing the actual heating function of the pencil-type glow plug. By virtue of the fact that the pencil-type glow plug comprises an integrated temperature sensor, it is possible to determine a current temperature of the glow pencil both in the active mode of the pencil-type glow plug and in the case of passive arrangement of the pencil-type glow plug. In particular, accuracy of temperature determination is independent of an operating condition of the compression-ignition internal combustion engine. In a preferred refinement of the invention, provision is made for the temperature sensor to be integrated directly into the glow pencil and, in particular, for the glow pencil to have a hole extending essentially axially to accommodate the temperature sensor. This ensures that the temperature sensor can be integrated into the pencil-type glow plug in a particularly simple manner. An additional installation space for the temperature sensor is not required since it is integrated virtually internally into the glow pencil. In a preferred refinement of the invention, provision is furthermore made for the hole accommodating the temperature sensor to be arranged within an insulating core of the glow pencil. As a result, the temperature sensor is arranged without in any way impairing the actual heating function of the glow pencil. In a preferred refinement of the invention, provision is furthermore made for the hole in the glow pencil accommodating the temperature sensor to be a groove open at the edge in the glow pencil, at least over a certain area. This advantageously makes it possible to take the temperature sensor as far as an outer circumferential wall of the glow pencil, allowing particularly exact temperature measurement, since arrangement in the aperture open at the edge makes it unnecessary to take into account a thermal transition resistance of the ceramic material of the glow pencil. Further preferred refinements of the invention will emerge from the remaining features stated in the subclaims. Drawings The invention is explained in greater detail below in exemplary embodiments with reference to the associated drawings, in which: Figure 1 shows a sectional view through a pencil-type glow plug in a first embodiment; Figure 2 shows a schematic view of a temperature sensor; Figure 3 shows a schematic sectional view through a glow pencil; Figure 4 shows a sectional view through a pencil-type glow plug in a second embodiment; Figures 5 and 6 show schematic views of a glow pencil in accordance with the second embodiment, and Figures 7 and 8 show schematic views of a glow pencil in another embodiment. Description of the exemplary embodiments Figure 1 shows a pencil-type glow plug 10, which can be used to start a compression-ignition internal combustion engine. The pencil-type glow plug 10 comprises a plug housing 12, which is of essentially hollow-cylindrical design. The plug housing 12 accommodates a glow pencil 14. The plug housing 12 can be arranged in a sealing manner in a wall of a cylinder housing (not shown), with the result that the glow pencil 14 projects into the combustion chamber. The glow pencil 14 is connected in an electrically conducting manner to a contact stud 18 via a contact spring 16. The contact stud 18 can be connected in a manner not shown specifically to a voltage source, the motor-vehicle battery in a motor vehicle, allowing the glow pencil 14 to be supplied with a voltage via the contact stud 18 and a contact element, e.g. a contact spring 16. The glow pencil 14 itself is composed of a ceramic, electrically conductive material. The pencil-type glow plug 10 comprises further components, of which seals 20 and 22, a ceramic sleeve 24, a metal ring 26 and a clamping element 28 are indicated here. The pencil-type glow plug 10 furthermore comprises an integrated temperature sensor 30, which extends essentially over the entire length of the pencil-type glow plug 10, along a longitudinal axis 32. The construction and operation of pencil-type glow plugs 10 of this kind are well known, and no further specific details of them will therefore be given in the context of this description. During the use of the pencil-type glow plug 10 as intended, the glow pencil 14 is supplied with the voltage U, causing a heating current I to flow. The level of the heating current I depends on the electrical resistance R of the glow pencil 14. This is designed in such a way as to act as a heating element (glow element). At the same time, provision can be made for the distribution of the electrical resistance R to vary over the length of the glow pencil 14. In particular, a higher electrical resistance R is concentrated in the region of a tip 34 of the glow pencil, giving rise there to a higher drop in the voltage U and greater heating within the tip 34 of the glow pencil than in the remainder of the glow pencil 14. By means of the temperature sensor 30 integrated into the pencil-type glow plug 10, an instantaneous temperature can now be determined immediately in the region of the tip 34 of the glow pencil. The temperature sensor 30 is illustrated schematically in isolation in Figure 2. The temperature sensor 30 is composed of a combination of two electrically conductive materials, for example, producing a voltage proportional to the temperature acting. A platinum-platinum/rhodium thermocouple known per se is used as temperature sensor 30, for example. This electrical conductor 36 is routed as a conductor loop within the temperature sensor 30 and can be connected to an evaluation circuit by means of external connections 38. The temperature sensor 30 is composed of an electrically nonconductive, temperature-stable ceramic and, to accommodate the conductor loops, comprises a double capillary (not shown specifically) . The temperature sensor 30 is passed in an insulating manner through the terminal stud 18. For this purpose, the terminal stud 18 has a hole 40 extending in the longitudinal direction of the pencil-type glow plug. Since the temperature sensor 30 is composed of electrically insulating ceramic over its outer circumference, there is no possibility of a short circuit with the terminal stud 24. Within the glow pencil 14, the temperature sensor 30 is taken right into the tip 34 of the glow pencil. The glow pencil 14 itself is generally composed of the electrically conductive ceramic, which surrounds an insulating core 42. The U-shaped conductor loop composed of the electrically conductive ceramic material of the glow pencil 14 is thereby formed. The temperature sensor 30 is now arranged within the insulating core 30 or itself forms the insulating core 42 by virtue of its external electrically insulating properties. A spacing between the temperature sensor 30 and the electrically conductive region of the glow pencil 14 is 0.2 mm, for example. Figure 3 shows the glow pencil 14 in isolation. From this, it is apparent that the glow pencil 14 has a receptacle 44 that extends along the (longitudinal axis , (32) and into which the temperature sensor 30 can be 0" introduced. The receptacle 44 extends right into the tip 34 of the glow pencil. The receptacle 44 is formed by a pocket hole 45, for example. The receptacle 44 is preferably introduced in the green condition of the ceramic. Spalling or the like of the material during the introduction of the receptacle 44 is thereby avoided. Figure 4 shows another embodiment of a pencil-type glow plug 10, parts identical to those in Figure 1 being provided with identical reference numerals and not being explained again. To this extent, only the differences that exist are explained. Otherwise, its construction and operation are identical. From the view in Figure 4, it is already clear that the temperature sensor 30 is here arranged along a line that deviates from the longitudinal axis 32 within the glow pencil 14. Here, the arrangement of the temperature sensor 30 is chosen so that the radial distance from the longitudinal axis 32 increases as it approaches the tip 34 of the glow pencil, until the temperature sensor 30 intersects the circumferential surface 46 of the glow pencil 14. In Figures 5 to 8, the glow pencil 14 is shown in two different embodiments to achieve this. Figure 5 shows a plan view of the glow pencil 14 - seen from the right according to Figure 4 - and Figure 6 shows a sectional representation rotated through 90° relative to Figure 5. It is apparent that the receptacle 44 for accommodating the temperature sensor 30 is initially formed by a hole 47, which, starting in the region of the longitudinal axis 32, initially extends at an angle a to the longitudinal axis 32. The angle a is chosen so that the hole 47 emerges in the circumferential surface 46 about half way along the overall length 1 of the glow pencil 14 and merges into an aperture 48 open at the edge. A depth of the aperture 48 open at the edge is here matched to a diameter of the temperature sensor 30, with the result that the latter does not project radially beyond the circumferential surface 46 of the glow pencil 14. Figures 7 and 8 show another embodiment, in which the receptacle 44 is formed by a radial slot 50, which initially has a decreasing depth up to half way along the length 1 of the glow pencil 14 and then merges into the aperture 48 open at the edge already shown in Figure 6. The formation of the slot 50 makes it possible to place the temperature sensor 30 radially in the glow pencil 14 while, in the exemplary embodiment in Figures 5 and 6, it must first of all be introduced into the hole 47 to enable it then to be placed in the aperture 4 8 open at the edge. Both the hole 47 in the exemplary embodiment in Figures 5 and 6 and the groove 50 in the exemplary embodiment in Figures 7 and 8 and apertures 48 open at the edge, which are common to both exemplary embodiments, are arranged in a region of the glow pencil 14 which is composed of an insulating material. As is known, the glow pencil 14 has a laminar structure, an insulating ceramic being embedded in the U-shaped conductor loop composed of electrically conductive ceramic. Impairment of the electrically conductive ceramic, e.g. of the cross section of the electrically conductive layer, is thus avoided. The temperature sensor 30 can be secured in the hole 47 or groove 50 and the aperture 48 open at the edge by glassing it in with a glass ceramic. In this case, a thermal expansion behaviour of this glass ceramic, of the ceramic material of the temperature sensor 30 and of the insulating ceramic material of the glow pencil 14 are matched to one another, ensuring an essentially identical thermal expansion behaviour when the overall laminar composite heats up. WE CLAIM : 1. Pencil-type glow plug, in particular for starting a compression-ignition internal combustion engine, with a glow pencil, which reaches into a combustion chamber containing an ignitable fuel/air mixture and comprises an electrically conductive ceramic and can be heated to an ignition temperature by connection to a voltage source, characterized in that the pencil-type glow plug (10) comprises an integrated temperature sensor (30). 2. Pencil-type glow plug as claimed in claim 1, wherein the temperature sensor (30) is integrated into the glow pencil (14). 3. Pencil-type glow plug as claimed in one of the preceding claims, wherein the glow pencil (14) has a receptacle (44) for accommodating the temperature sensor (30). 4. Pencil-type glow plug as claimed in one of the preceding claims, wherein the receptacle (44) is a pocket hole (45), which extends on a longitudinal axis (32) of the glow pencil (14). 5. Pencil-type glow plug as claimed in one of Claims 1 to 3, wherein the receptacle (44) extends at an angle ^to the longitudinal axis (32). 6. Pencil-type glow plug as claimed in claim 5, wherein the receptacle (44) comprises a hole (47), which emerges at a , circumferential surface (46) of the glow pencil (14) and then merges into an aperture (48) open at the edge. 7. Pencil-type glow plug as claimed in one of the preceding claims, wherein the hole (47) reaches the shell surface (46) at about halfway the glow plug's (14) length. 8. Pencil-type glow plug as claimed in one of the preceding claims, characterized in that the aperture (48) open at the edge has a depth corresponding to a diameter of the temperature sensor (30). 9. Pencil-type glow plug as claimed in claim 5, wherein the receptacle (44) comprises a radial slot (50), which merges into the aperture (48) open at the edge.

Documents:

in-pct-2002-1039-che abstract-duplicate.pdf

in-pct-2002-1039-che abstract.pdf

in-pct-2002-1039-che claims-duplicate.pdf

in-pct-2002-1039-che claims.pdf

in-pct-2002-1039-che correspondence-others.pdf

in-pct-2002-1039-che correspondence-po.pdf

in-pct-2002-1039-che description (complete)-duplicate.pdf

in-pct-2002-1039-che description (complete).pdf

in-pct-2002-1039-che drawings.pdf

in-pct-2002-1039-che form-1.pdf

in-pct-2002-1039-che form-19.pdf

in-pct-2002-1039-che form-26.pdf

in-pct-2002-1039-che form-3.pdf

in-pct-2002-1039-che form-5.pdf

in-pct-2002-1039-che pct.pdf

in-pct-2002-1039-che petition.pdf