CERAMIC HEATING PLATE AS HEATING ELEMENT

Abstract

A device for aftertreatment of exhaust gases, having a flow section which is able to be flowed through by exhaust gas and has at least one honeycomb body, acting as a catalytic converter, and has at least one heating element. The heating element is formed from a ceramic material which is able to be flowed through along a plurality of flow channels from an inflow side to an outflow side. The heating element is electrically conductive along the walls delimiting the flow channels and, by an electrical contact, is connectable to a voltage source, wherein the heating element runs in a meandering manner over a through-flowable cross section of the flow section.

Claims

1.-7. (canceled)

8. A device for aftertreatment of exhaust gas, comprising: a flow section which is able to be flowed through by the exhaust gas; at least one honeycomb body configured as a catalytic converter; and at least one heating element formed from a ceramic material which is able to be flowed through along a plurality of flow channels from an inflow side to an outflow side, wherein the at least one heating element runs in a meandering manner over a through-flowable cross section of the flow section wherein the at least one heating element is electrically conductive along walls delimiting the flow channels; and an electrical contact configured for connection to a voltage source.

9. The device as claimed in claim 8, wherein the at least one heating element has multiple deflections within a plane.

10. The device as claimed in claim 8, wherein the at least one heating element is formed from a ceramic honeycomb body.

11. The device as claimed in claim 9, wherein, at the deflections, the at least one heating element has a cross-sectional thickening of an electrically conductive structure in comparison with remaining regions of the at least one heating element.

12. The device as claimed in claim 9, wherein, in regions of the deflections, the at least one heating element has a thermal conductivity which is different over a cross section of at least one heating element than at portions before and after the deflections.

13. The device as claimed in claim 9, wherein, in regions of the deflections, the at least one heating element has a heat capacity which is different over a cross section of the at least one heating element than at portions before and after the deflections.

14. The device as claimed in claim 9, wherein, in regions of the deflections, the at least one heating element has an electrical resistance which is different over a cross section of the at least one heating element.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The invention will be discussed in detail below on the basis of exemplary embodiments with reference to the drawings. In the drawings:

[0028] FIG. 1 is a plan view of a heating element which is arranged on one of the end faces of a heating disk formed by a honeycomb body;

[0029] FIG. 2 is a plan view of a deflection region of the heating element, wherein the cell density in the region of the deflection is higher than in the rest of the heating element;

[0030] FIG. 3 is a plan view of a deflection region of the heating element, wherein the walls delimiting the flow channels are of thicker configuration in the region of the deflection than in the rest of the heating element; and

[0031] FIG. 4 is a plan view of a deflection region of the heating element, wherein the walls delimiting the flow channels are sectionally formed from a material with different material properties.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

[0032] FIG. 1 shows, in a schematically indicated manner, a flow cross section 1 of the device for exhaust-gas aftertreatment. Within said flow cross section 1, there is arranged a heating element 2 which has a multiplicity of through-flowable flow channels which can be flowed through along a main throughflow direction, which is parallel to a surface normal to the plane of the drawing. The individual flow channels are delimited by walls in a direction transverse to the main throughflow direction. Since the heating element 2 is manufactured from a ceramic material, either it is provided with an electrically conductive surface coating or it comprises a certain proportion of electrically conductive material. The ceramic may for example have metallic particles added to it in order to produce sufficient electrical conductivity.

[0033] The heating element 2 is heated through electrical energization of the heating element 2. For this purpose, the heating element 2 can be connected at an end side to a voltage source via electrical contact 3. Using the ohmic resistance, heating of the heating element 2 thus takes place if current flows through the heating element 2.

[0034] The heating element 2 running in a meandering manner in the exemplary embodiment in FIG. 1 may be created, for example by a machining process, from a honeycomb body which is in the form of a disk.

[0035] In the exemplary embodiment in FIG. 1, the heating element 2 is arranged in a meandering manner over the cross section 1 of the catalytic converter, which is arranged upstream or downstream in the flow direction (not shown in FIG. 1). Arrangements differing therefrom may also be provided in order to optimally utilize the cross-sectional area of the catalytic converter and to ensure heat transmission that is as good as possible and heat generation that is as homogeneous as possible.

[0036] In contrast to the exemplary embodiment in FIG. 1, the heating element may also run in a direction which follows a surface normal to the plane of the drawing. This is applicable in particular in the case of a heating element situated in multiple planes one behind the other.

[0037] The heating element 2 has multiple deflection regions 4 in which it changes its direction. Preferably, said deflection regions 4 are formed in such a way that generation of local hot spots is avoided or at least significantly reduced. For this purpose, the deflection region 4 may for example be of thickened design, have reduced porosity in comparison with the rest of the heating element 2, have relatively low thermal conductivity or have increased heat capacity. Also, the material used or the wall thickness may vary over the cross section of the deflection region 4.

[0038] FIG. 2 shows a detail view of a deflection region 4, wherein provision is made in the curved region 6 of the deflection 4 of a cell density which is higher in comparison with the rest of the structure 5 of the heating element 2. The region 6 has more flow channels per unit of area than the rest of the heating element 2. This results in the properties as electrical conductor in the deflection region 4 being changed in comparison with the rest of the structure 5 of the heating element 2.

[0039] FIG. 3 shows an alternative configuration of the deflection region 7, wherein, in the curved region 8 of the deflection 7, the walls present, which delimit the flow channels, have a larger wall thickness than in the rest of the structure 5 of the heating element 2. As a result of the increased wall thickness, the electrical conductivity is likewise influenced.

[0040] FIG. 4 shows a further alternative configuration of a deflection region 9, wherein, in the curved region 10 of the deflection 9, the walls delimiting the flow channels are formed from different materials. The walls arranged in the region 11 of the smaller inner radius are formed from a first material, while the walls arranged in the region 12 of the larger outer radius are formed from a second material.

[0041] The materials may differ from one another in particular through the electrical resistivity, the metal proportion, the porosity, the surface coating or a combination of the aforementioned properties.

[0042] All the embodiments shown in the exemplary embodiments in FIGS. 1 to 4 may be combined with one another in any desired manner. In particular, it may be provided that individual variations are restricted only to limited regions within the deflection. For example, that the inner region at the smaller bending radii is of different construction than the outer region at the larger bending radii.

[0043] The aim in particular is to produce suitable influencing of the current flow within the heating element 2 in order to avoid the occurrence of local hot spots. For this purpose, it is possible, in particular regionally, for the resistivity to be adapted in order to locally restrict or locally promote the current flow. It is in principle advantageous if an intensified current flow takes place in the outer regions of the deflection, in order, in this way, to avoid hot spots forming at the inner radius. Since the current follows the principle of least resistance, suitable current steering is ensured by the targeted influencing of the resistance.

[0044] The increase in the number of walls, the thickening of the walls, as well as the reduction in the porosity all result overall in an increase in the cross-sectional area able to be flowed through by the current, which changes the electrical resistance of the respective region, which in turn changes the current conduction, in particular the current distribution, over the cross section of the heating element.

[0045] Beside the influencing of the resistance for influencing the flow conduction, it is possible, by way of the above-described changes, for the thermal conductivity of the heating conductor to be influenced directly too, which allows heat to be dissipated and distributed more effectively, which likewise allows the formation of hot spots to be avoided.

[0046] The exemplary embodiments in FIGS. 1 to 4 have in particular no limiting character and serve to illustrate the concept of the invention.

[0047] Thus, while there have shown and described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.