EXHAUST GAS HEATER

Abstract

An exhaust gas heater for an exhaust gas system of an internal combustion engine includes a carrier arrangement, a heating-conductor arrangement, carried on the carrier arrangement and having at least one heating conductor through which a current flows with at least one heating conductor being carried in an electrically insulated manner with respect to the carrier arrangement by at least one carrier-arrangement supporting unit and/or with at least one heating conductor being carried in an electrically insulated manner with respect to a further heating conductor by at least one heating-conductor supporting unit. A connecting arrangement securely connects the heating-conductor arrangement to the carrier arrangement and also a length-compensating arrangement for compensating for different thermal expansions of components of the exhaust gas heater.

Claims

1. An exhaust gas heater for an exhaust gas system of an internal combustion engine, the exhaust gas heater comprising: a carrier arrangement; a heating-conductor arrangement carried on said carrier arrangement and having first and second heating conductors through which current flows; at least one carrier arrangement supporting unit for carrying said first heating conductor in an electrically insulating manner with respect to said carrier arrangement; at least one heating-conductor supporting unit for carrying said first heating conductor in an electrically insulated manner with respect to said second heating conductor; a connecting arrangement for securely connecting said heating-conductor arrangement to said carrier arrangement; and, a length-compensating arrangement for compensating for different thermal expansions of components of said exhaust gas heater.

2. The exhaust gas heater of claim 1, wherein said connecting arrangement includes at least one connecting element; and, said length-compensating arrangement includes at least one length-compensating element in a connecting-force transmission path between said at least one connecting element and at least one of the following: i) said carrier arrangement; and, ii) said heating conductor arrangement.

3. The exhaust gas heater of claim 2, wherein: said exhaust gas heater defines a longitudinal axis (L); said carrier arrangement includes two carrier elements following one another in the direction of said longitudinal axis (L) for accommodating said heating conductor arrangement therebetween; and, said length-compensating arrangement includes at least one length-compensating element assigned to said at least one connecting element arranged in accordance with at least one of the following: i) in a supporting path between at least one of said carrier elements and said heating conductor arrangement; ii) in a supporting path between said first and second heating conductors of said heating conductor arrangement; and, iii) in a supporting path between at least one of said two carrier elements and said at least one connecting element.

4. The exhaust gas heater of claim 3, wherein at least one of the following applies: i) said at least one length-compensating element is arranged between one of said two carrier elements and said carrier element supporting unit; ii) said at least one length-compensating element is arranged between said first and second heating conductors; and, iii) said at least one length-compensating element is arranged between one of said two carrier elements and a connecting-element supporting region of said at least one connecting element supporting itself on the carrier element.

5. The exhaust gas heater of claim 2, wherein said at least one connecting element passes through said at least one length-compensating element and passes through at least one of the following: i) said at least one carrier-element supporting unit; and, ii) said at least one heating-conductor supporting unit.

6. The exhaust gas heater of claim 2, wherein said at least one length-compensating element is made from a material having a greater coefficient of thermal expansion than the material of said at least one connecting element.

7. The exhaust gas heater of claim 6, wherein said at least one connecting element is made from a nickel-chromium alloy material and said at least one length-compensating element is made from a steel material.

8. The exhaust gas heater of claim 7, wherein said steel material is 1.4980 steel.

9. The exhaust gas heater of claim 2, wherein said at least one length-compensating element includes an elastically deformable prestressing element.

10. The exhaust gas heater of claim 9, wherein said at least one length-compensating element is formed as a plate spring or corrugated spring.

11. The exhaust gas heater of claim 1, wherein at least one of the following applies: i) said carrier arrangement is made from a metal material; and, ii) said heating-conductor arrangement is made from a metal material.

12. The exhaust gas heater of claim 2, wherein said at least one connecting element is configured as a bolt.

13. An exhaust gas system for an internal combustion engine, the exhaust gas system comprising: an exhaust gas heater including: a carrier arrangement; a heating-conductor arrangement carried on said carrier arrangement and having first and second heating conductors through which current flows; at least one carrier arrangement supporting unit for carrying said first heating conductor in an electrically insulating manner with respect to said carrier arrangement; at least one heating-conductor supporting unit for carrying said first heating conductor in an electrically insulated manner with respect to said second heating conductor; a connecting arrangement for securely connecting said heating-conductor arrangement to said carrier arrangement; and, a length-compensating arrangement for compensating for different thermal expansions of components of said exhaust gas heater.

14. An exhaust gas heater for an exhaust gas system of an internal combustion engine, the exhaust gas heater comprising: a carrier arrangement; a heating-conductor arrangement carried on said carrier arrangement and having at least one heating conductor through which current flows; at least one carrier-arrangement supporting unit for carrying at least one heating conductor in an electrically insulating manner with respect to said carrier arrangement; a connecting arrangement for securely connecting said heating-conductor arrangement to said carrier arrangement; and, a length-compensating arrangement for compensating for different thermal expansions of components of said exhaust gas heater.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The invention will now be described with reference to the drawings wherein:

[0022] FIG. 1 shows a perspective view of an exhaust gas heater;

[0023] FIG. 2 shows a longitudinal sectional view of the exhaust gas heater from FIG. 1;

[0024] FIG. 3 shows a longitudinal section of an exhaust gas heater with carrier-arrangement supporting units and a length-compensating element of a length-compensating arrangement, arranged in assignment to a connecting element, in a schematic representation;

[0025] FIG. 4 shows a representation corresponding to FIG. 3 of an alternative type of configuration; and,

[0026] FIG. 5 shows a further representation corresponding to FIG. 3 of an alternative type of configuration.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] In FIGS. 1 and 2, an exhaust gas heater 10 for an exhaust gas system 12 of an internal combustion engine, for example on a motor vehicle, is shown. In the exhaust gas system 12, the exhaust gas heater 10 can be flowed through by exhaust gas in a main direction H of exhaust gas flow and has two heating conductors 14, 16 of a heating-conductor arrangement, denoted generally by 18, which are arranged following one another in the direction of a longitudinal axis L of the exhaust gas heater and consequently can be flowed around one after the other by exhaust gas flowing substantially in the main direction H of exhaust gas flow. The heating conductors 14, 16 are constructed as substantially plate-like or from flat material and can be produced with their structure that is provided with a plurality of portions running in a meandering structure by cutting out from a blank of flat material, in particular a metal blank.

[0028] On the sides of the two heating conductors 14, 16 that are lying facing away from one another in the direction of the longitudinal axis L of the exhaust gas heater, carrier elements 20, 22 of a carrier arrangement denoted generally by 24 that are of a substantially plate-like configuration are provided. On their outer circumferential region, the plate-like carrier elements 20, 22 are fixed on a substantially cylindrical carrier housing 26.

[0029] The two heating conductors 14, 16 may be arranged in series or parallel to one another. Provided for electrical connection to a voltage source are two connecting units 28, 30, which pass through the carrier housing 26 and are connected in an electrically conducting manner to the heating conductors 14, 16 in the interior space surrounded by the carrier housing 26.

[0030] To obtain a stable assembly, the two carrier elements 20, 22 and the heating conductors 14, 16 arranged between them, lying directly adjacent to one another, are securely connected to one another by a connecting arrangement 31 with a plurality of connecting elements 32 of a bolt-like form. The connecting elements 32 may for example be formed as screw bolts with a shank 34 and a head 36. A nut element 37 may be screwed onto the shank 34, for example, in order to clamp the layered construction including the carrier elements 20, 22 and heating conductors 14, 16 between the head 36 and the nut element 37.

[0031] To achieve electrical insulation of the heating conductors 14, 16 with respect to the carrier elements 20, 22 of the carrier arrangement 24, which are generally constructed from a metal material, provided between the heating conductor element 14 and the carrier element 20, for example in assignment to each connecting element 32, is a carrier-arrangement supporting unit 38, which is constructed from an electrically insulating material, for example a ceramic material, is of a substantially plate-like form and is passed through by the assigned connecting element 32 in the region of an opening provided in it. Also provided, for example in assignment to each connecting element 32, is a carrier-element supporting unit 40, arranged between the heating conductor 16 and the carrier element 22. The carrier-element supporting units 38, 40 may for example be substantially structurally the same as one another.

[0032] In order to support the two heating conductors 14, 16 lying next to one another with respect to one another in an electrically insulating manner, provided for example in assignment to each connecting element 32 is a heating-conductor supporting unit 42. Also each heating-conductor supporting unit 42 is of a substantially plate-like form, including one or more disks, and is constructed from a ceramic material. Where the heating conductors 14, 16 are passed through by the connecting element 32, sleeve-like insulating elements 43 may be inserted into the openings formed in the heating conductors 14, 16, in order to achieve defined positioning of the connecting element 32 in the openings provided in the heating conductors 14, 16.

[0033] FIG. 3 shows in conjunction with a connecting element 32 the construction of an exhaust gas heater 10 in which different thermal expansions of the various components of the exhaust gas heater 10 are compensated for by providing a length-compensating arrangement denoted generally by 44. It should be taken into consideration that, in the layered construction including the two carrier elements 20, 22 and the heating conductors 14, 16 as well as the carrier-element supporting units 38, 40 or the heating-conductor supporting units 42 arranged between them, these various components have different construction materials from one another, in particular different construction materials than the or each connecting element 32. Such different construction materials generally have different coefficients of thermal expansion, which may have the consequence that different thermally induced expansions when they undergo heating by the exhaust gas flowing through the exhaust gas heater 10 may lead to a loss of the bracing built up in the cold state by the connecting elements 32. The components of the exhaust gas heater 10 which are held between the head 36 and the nut element 37 and each provide a supporting region of a connecting element 32, may then get into a state in which they have an amount of play in terms of movement in the direction of the longitudinal axis L of the exhaust gas heater.

[0034] Such different thermal expansions are compensated for by the length-compensating arrangement 44 such that, even when the exhaust gas heater 10 is heated, the components of the exhaust gas heater 10 that are held together by the connecting elements 32 are stably held against one another by being braced. In order to achieve this, the length-compensating arrangement 44 includes, for example in assignment to each connecting element 32, a length-compensating element 46 of a disk-like or annular disk-like form. Like the various supporting units 38, 40, 42, it may be passed through by the assigned connecting element 32, or its shank 34, so that a stack including the supporting units 38, 40, 42 and a length-compensating element 46 that is also stably held together transversely to the longitudinal axis L of the exhaust gas heater is produced.

[0035] In the example of a configuration that is shown, the length-compensating element 46 assigned to the connecting element 32 shown is arranged between the carrier element 22 that is acted upon by the head 36 of the connecting element 32, and therefore supports it, and the carrier-element supporting unit 40 adjacent to this element. The length-compensating element 46 is constructed from a material which has a greater coefficient of thermal expansion than the construction material of the connecting element 32. If the connecting element 32 expands when it undergoes heating in the direction of the longitudinal axis L of the exhaust gas heater, the length-compensating element 46 also expands in this direction, and does so to a greater extent than the connecting element 32. It should also be taken into consideration here that the connecting element 32 has a much greater length of extent in the direction of the longitudinal axis L of the exhaust gas heater than the length-compensating element 46. Since, because of its comparatively great length of extent in the longitudinal direction L of the exhaust gas heater, the thermally induced relative change in length of the connecting element 32 leads to a comparatively great absolute change in length, the length-compensating element 46 is constructed from a material of which the relative change in length when it undergoes heating is so great that, in spite of the shorter length of extent of the length-compensating element 46 in the direction of the longitudinal axis L of the exhaust gas heater, the absolute change in length of the length-compensating element 46 compensates at least for the absolute change in length of the connecting element 32. It should also be taken into consideration here that the other components of the exhaust gas heater 10 that are arranged between the two carrier elements 20, 22, that is, the various supporting units 38, 40, 42 as well as the heating conductors 14, 16 and also the carrier elements 20, 22, also themselves experience an at least slight increase in their length of extent in the direction of the longitudinal axis L of the exhaust gas heater as a result of the heating they undergo, and therefore this already compensates for part of the change in length of the connecting element 32. Only the part of the absolute change in length of the connecting element 32 that is not compensated for by the change in length of these components must be compensated for by the change in length of the length-compensating element 46.

[0036] If, for example, in the case of the construction shown in FIG. 3, the two carrier elements 20, 22 are constructed from a steel sheet-metal material, the heating conductors 14, 16 are constructed from a metal material which, because of its electrical resistance, can be heated when a voltage is applied, the various supporting units 38, 40, 42 are constructed from a ceramic material and the connecting element 32 is constructed from a metal material, such as for example a nickel-chromium alloy material, the length-compensating element 46 may be constructed from a steel material, for example 1.4980 steel, in order to achieve the desired compensation for the change in length of the connecting element 32.

[0037] It should be pointed out that, preferably in assignment to each of the connecting elements 32 of the exhaust gas heater 10, the length-compensating arrangement 44 has such a length-compensating element 46. It should also be pointed out that such a length-compensating element 46 could also be arranged at a different location. For example, it could also be arranged between the carrier element 20 and the carrier-element supporting unit 38 or between one of the carrier-element supporting units 38, 40 and the heating conductor 14 or 16 that is respectively directly adjacent to it. A length-compensating element 46 could also be positioned between the two heating conductors 14, 16, for example between the heating-conductor supporting unit 42 and one of the heating conductors 14, 16, or between two disk-like parts of the heating-conductor supporting unit 42.

[0038] Depending on the extent to which a thermally induced change in length, in particular of the connecting element 32, has to be compensated for, it is also possible to provide a number of length-compensating elements 46 in the stacked assembly, for example at the previously stated positions.

[0039] An alternative type of configuration is shown in FIG. 4. This differs from the previously described construction substantially in that the connecting element 32 of a bolt-like construction is connected in a material-bonding and consequently secure manner to the two carrier elements 20, 22 at the axial end regions thereof in each case by a welding 48, 50. In the case of this construction, the stack including the carrier elements 20, 22, heating conductors 14, 16 and supporting units 38, 40, 42 can be held such that they are braced against one another during assembly and, in this state, the connecting element 32 can be securely connected at both its axial end regions to the supporting elements 20, 22 by the weldings 48, 50. Also in this case, is a length-compensating arrangement 44 with at least one length-compensating element 46 is provided in assignment to preferably each connecting element 32.

[0040] A further alternative type of configuration is shown in FIG. 5. In the case of this construction, the length-compensating element 46 provided in assignment to the connecting element 32, formed for example as a screw bolt, is formed as an elastically deformable prestressing element, in particular as a plate spring. As a result of its axial prestressing, the length-compensating element 46 holds the components of the exhaust gas heater 10 that are stacked one on top of the other, that is, the two carrier elements 20, 22, the heating conductors 14, 16 and the supporting units 38, 40, 42 arranged in between, against one another with prestressing even when there is a thermally induced change in length of the connecting element 32. In particular in the case of the configuration as a plate spring or corrugated spring constructed from a metal material, such a length-compensating element 46 ensures that the prestressing force generated by it is reliably maintained in the temperature range in which an exhaust gas heater 10 experiences temperature changes.

[0041] It should finally be pointed out that the previously described configurations of a length-compensating arrangement can be varied in a wide variety of aspects. As already mentioned, a number of length-compensating elements may also be arranged at different axial positions in assignment to one or more connecting elements. As an alternative or in addition, a length-compensating element could also be arranged on the outer side of one or both carrier elements 20 that is facing away from the heating conductors, so that it is arranged between a respective carrier element 20, 22 and a supporting region of the connecting element, that is, for example, the head 36 or the nut element 37. Also in the case of such a configuration, the length-compensating element 46 may may either be formed as an elastically deformable prestressing element producing a prestressing force, that is, for example, as a plate spring or corrugated spring, or be constructed from a material which, because of its greater coefficient of thermal expansion, compensates for the comparatively great absolute change in length of the connecting element 32.

[0042] It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.